WDIFF

draft-ietf-ipsec-ikev2-03.txt --> draft-ietf-ipsec-ikev2-04.txt

IPSEC Working Group Charlie Kaufman
INTERNET-DRAFT editor
draft-ietf-ipsec-ikev2-03.txt October 2002
draft-ietf-ipsec-ikev2-04.txt January 2003

Internet Key Exchange (IKEv2) Protocol
<draft-ietf-ipsec-ikev2-03.txt>
<draft-ietf-ipsec-ikev2-04.txt>

Status of this Memo

This document is a submission by the IPSEC Working Group of the
Internet Engineering Task Force (IETF). Comments should be submitted
to the ipsec@lists.tislabs.com mailing list.

Distribution of this memo is unlimited.

This document is an Internet Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [Bra96]. Internet Drafts are
working documents of the Internet Engineering Task Force (IETF), its
areas, and working groups. Note that other groups may also distribute
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Internet Drafts are draft documents valid for a maximum of six months
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ftp.isi.edu (US West Coast).

Abstract

This document describes version 2 of the IKE (Internet Key Exchange)
protocol. IKE performs mutual authentication and establishes an IKE
security association that can be used to efficiently establish SAs
for ESP, AH ESP and/or IPcomp. AH. This version greatly simplifies IKE by replacing
the 8 possible phase 1 exchanges with a single exchange based on
either public signature keys or shared secret keys. The single
exchange provides identity hiding, yet works in 2 round trips (all
the identity hiding exchanges in IKE v1 required 3 round trips).
Latency of setup of an IPsec SA is further reduced from IKEv1 by
allowing setup of an SA for ESP, AH, ESP and/or IPcomp AH to be piggybacked on the
initial IKE exchange. It also improves security by allowing the

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Responder to be stateless until it can be assured that the Initiator
can receive at the claimed IP source address. This version also
presents the entire protocol in a single self-contained document, in
contrast to IKEv1, in which the protocol was described in ISAKMP (RFC
2408), IKE (RFC 2409), and the DOI (RFC 2407) documents.

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Table of Contents

Abstract.....................................................1
1 Summary of Changes from IKEv1..............................3
2 Requirements Terminology...................................4
3 IKE Protocol Overview......................................4 Overview......................................5
3.1 Usage Scenarios..........................................6
3.1.1 Gateway to Gateway Tunnel..............................6
3.1.2 Endpoint to Endpoint Transport.........................6
3.1.3 Endpoint to Gateway Transport..........................7
3.1.4 Other Scenarios........................................8
3.2 The Initial (Phase 1) Exchange...........................6
3.2 Exchange.....................................8
3.3 The CREATE_CHILD_SA (Phase 2) Exchange...................7
3.3 Exchange.............................9
3.4 The Informational (Phase 2) Exchange.........................9 Exchange..............................11
3.5 Informational Messages outside of an IKE-SA.............12
4 IKE Protocol Details and Variations.......................10 Variations.......................13
4.1 Use of Retransmission Timers............................10 Timers............................13
4.2 Use of Sequence Numbers for Message ID..................11 ID..................13
4.3 Window Size for overlapping requests....................12 requests....................14
4.4 State Synchronization and Connection Timeouts...........12 Timeouts...........15
4.5 Version Numbers and Forward Compatibility...............14 Compatibility...............16
4.6 Cookies.................................................15 Cookies.................................................18
4.7 Cryptographic Algorithm Negotiation.....................18 Negotiation.....................20
4.8 Rekeying................................................19 Rekeying................................................20
4.9 Traffic Selector Negotiation............................20 Negotiation............................21
4.10 Nonces.................................................21 Nonces.................................................23
4.11 Address and Port Agility...............................22 Agility...............................24
4.12 Reuse of Diffie-Hellman Exponentials...................22 Exponentials...................24
4.13 Generating Keying Material.............................23 Material.............................25
4.14 Generating Keying Material for the IKE-SA..............23 IKE-SA..............25
4.15 Authentication of the IKE-SA...........................24 IKE-SA...........................26
4.16 Generating Keying Material for Child-SAs...............25 CHILD-SAs...............27
4.17 Rekaying IKE-SAs using a CREATE_CHILD_SA exchange......26 exchange......28
4.18 Requesting an internal address on a remote network.....28
4.19 Requesting a Peer's Version............................30
4.20 Error Handling.........................................26 Handling.........................................30
4.21 IPcomp.................................................31
5 Header and Payload Formats................................27 Formats................................32
5.1 The IKE Header..........................................27 Header..........................................32
5.2 Generic Payload Header..................................30 Header..................................34
5.3 Security Association Payload............................31 Payload............................35

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5.3.1 Proposal Substructure.................................32 Substructure.................................36
5.4 Key Exchange Payload....................................33 Payload....................................38
5.5 Identification Payload..................................34 Payload..................................38
5.6 Certificate Payload.....................................36 Payload.....................................40
5.7 Certificate Request Payload.............................37 Payload.............................41
5.8 Authentication Payload..................................38 Payload..................................42
5.9 Nonce Payload...........................................39 Payload...........................................44
5.10 Notify Payload.........................................40 Payload.........................................44
5.10.1 Notify Message Types.................................41 Types.................................45
5.11 Delete Payload.........................................43 Payload.........................................50
5.12 Vendor ID Payload......................................45 Payload......................................51
5.13 Traffic Selector Payload...............................46 Payload...............................53
5.13.1 Traffic Selector.....................................46 Selector.....................................53
5.14 Encrypted Payload......................................48 Payload......................................55
5.15 Configuration Payload..................................57
5.15.1 Configuration Attributes.............................59
5.16 Other Payload types....................................49

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6 Conformance Requirements..................................50 Requirements..................................62
7 Security Considerations...................................50 Considerations...................................62
8 IANA Considerations.......................................51 Considerations.......................................63
8.1 Transform Types and Attribute Values....................64
8.2 Exchange Types..........................................64
8.3 Payload Types...........................................64
9 Acknowledgements..........................................52 Acknowledgements..........................................64
10 References...............................................64
10 References...............................................52 Normative References.....................................64
10 Non-normative References.................................64
Appendix A: NAT Traversal...................................67
Appendix B: Diffie-Hellman Groups...........................55 Groups...........................69
Change History..............................................58 History..............................................71
Author's Address............................................59 Address............................................73
Full Copyright Statement....................................74

1 Summary of changes from IKEv1

The goals of this revision to IKE are:

1) To define the entire IKE protocol in a single document, rather
than three that cross reference one another;

2) To simplify IKE by replacing the eight different initial phase 1
exchanges with a single four message exchange (with changes in
authentication mechanisms affecting only a single AUTH payload rather
than restructuring the entire exchange);

3) To remove the Domain of Interpretation (DOI), Situation (SIT), and
Labeled Domain Identifier fields, and the Commit and Authentication

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only bits;

4) To decrease IKE's latency in the common case by making the initial
exchange be 2 round trips (4 messages), and allowing the ability to
piggyback setup of a Child-SA CHILD-SA on that exchange;

5) To replace the cryptographic syntax for protecting the IKE
messages themselves with one based closely on ESP to simplify
implementation and security analysis;

6) To reduce the number of possible error states by making the
protocol reliable (all messages are acknowledged) and sequenced. This
allows shortening Phase 2 exchanges from 3 messages to 2;

7) To increase robustness by allowing the responder to not do
significant processing until it receives a message proving that the
initiator can receive messages at its claimed IP address, and not
commit any state to an exchange until the initiator can be
cryptographically authenticated;

8) To fix bugs such as the hash problem documented in [draft-ietf-
ipsec-ike-hash-revised-02.txt];

9) To specify Traffic Selectors in their own payloads type rather

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than overloading ID payloads, and making more flexible the Traffic
Selectors that may be specified;

10) To replace the complex mix and match negotiation of cryptographic
algorithms with proposals based on suites of algorithms. algorithms;

11) To specify required behavior under certain error conditions or
when data that is not understood is received in order to make it
easier to make future revisions in a way that does not break
backwards compatibility;

12) To incorporate ideas from draft-ietf-ipsec-nat-reqts-02.txt to
allow IKE to negotiate through NAT gateways;

12) To simplify and clarify how shared state is maintained in the
presence of network failures and Denial of Service attacks; and

13) To maintain existing syntax and magic numbers to the extent
possible to make it likely that implementations of IKEv1 can be
enhanced to support IKEv2 with minimum effort.

2 Requirements Terminology

Keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT" and

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"MAY" that appear in this document are to be interpreted as described
in [Bra97].

3 IKE Protocol Overview

IP Security (IPsec) provides confidentiality, data integrity, access
control, and data source authentication to IP datagrams. These
services are provided by maintaining shared state between the source
and the sink of an IP datagram. This state defines, among other
things, the specific services provided to the datagram, which
cryptographic algorithms will be used to provide the services, and
the keys used as input to the cryptographic algorithms.

Establishing this shared state in a manual fashion does not scale
well. Therefore a protocol to establish this state dynamically is
needed. This memo describes such a protocol-- the Internet Key
Exchange (IKE). This is version 2 of IKE. Version 1 of IKE was
defined in RFCs 2407, 2408, and 2409. This single document is
intended to replace all three of those RFCs.

IKE performs mutual authentication between two parties and
establishes an IKE security association that includes shared secret
information that can be used to efficiently establish SAs for ESP
(RFC 2406), 2406) and/or AH (RFC 2402) and/or 2402). It also negotiates use of IPcomp
(RFC 2393). 2393) in connection with an ESP and/or AH SA. We call the IKE
SA an "IKE-SA". The SAs for ESP, AH, ESP and/or IPcomp AH that get set up through
that IKE-SA we call "child-SA"s.

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We call the first four messages establishing an IKE-SA a "phase 1"
exchange and subsequent IKE exchanges "phase 2", inheriting this
terminology from IKEv1. The phase 1 exchange establishes the IKE-SA
and the first child-SA. CHILD-SA. In some scenarios, only a single child-SA CHILD-SA is
needed between the IPsec endpoints and therefore there would be no
phase 2 exchanges. Phase 2 exchanges MAY be used to establish
additional child-SAs CHILD-SAs between the same authenticated pair of endpoints
as well as other housekeeping.
and to perform housekeeping functions. The phase 1 exchange consists
of two request/response pairs. A phase 2 exchange is one
request/response pair, and can be used to create or delete a child-SA, CHILD-
SA, rekey or delete the IKE-SA, or report information such as error
conditions.

IKE message flow always consists of a request followed by a response.
It is the responsibility of the requester to ensure reliability. If
the response is not received within a timeout interval, the requester
MUST retransmit the request (or abandon the connection).

The first request/response of a phase 1 exchange negotiates security
parameters for the IKE-SA, sends nonces, and sends Diffie-Hellman

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values. We call the request message IKE_SA_init initial exchange IKE_SA_INIT (request and the response
IKE_SA_init_response.
response).

The second request/response, which we'll call IKE_auth and
IKE_auth_response IKE_AUTH transmits
identities, proves knowledge of the secrets corresponding to the two
identities, and sets up an SA for the first (and often only) AH
and/or ESP and/or IPcomp child-SA. In
order to allow Bob to be stateless until receiving message 3, message
3 must repeat all of message 1 and Bob must be able to reconstruct
(bit for bit) what he sent in message 2. CHILD-SA.

Phase 2 exchanges each consist of a single request/response pair. The
types of exchanges are CREATE_CHILD_SA (which creates a child-SA), CHILD-SA), or
an Informational exchange which deletes a child-SA or the IKE-SA an SA, reports error
conditions, or
informs the does other side of some error condition. housekeeping. All these messages require a
response. An informational message with no payloads is commonly used
as a check for liveness.

In the description that follow, follows, we assume that no errors occur.
Modifications to the flow should errors occur are described in
section 4.

3.1 The Initial (Phase 1) Exchange

The base Phase 1 exchange Usage Scenarios

IKE is expected to be used to negotiate ESP and/or AH SAs in a four message exchange (two
request/response pairs). The first pair number
of messages (IKE_SA_init)
negotiate cryptographic algorithms, exchange nonces, and do a
Diffie-Hellman exchange.

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The second pair different scenarios, each with their own special requirements.

3.1.1 Gateway to Gateway Tunnel

+-+-+-+-+-+ +-+-+-+-+-+
! ! IPsec ! !
Protected !Tunnel ! Tunnel !Tunnel ! Protected
Subnet <-->!Endpoint !<---------->!Endpoint !<--> Subnet
! ! ! !
+-+-+-+-+-+ +-+-+-+-+-+

Figure 1: Firewall to Firewall Tunnel

In this scenario, neither endpoint of messages (IKE_AUTH) authenticate the previous
messages, exchange identities and certificates, and establish the
first child_SA. Parts IP connection implements
IPsec, but network nodes between them protect traffic for part of these messages are encrypted the
way. Protection is transparent to the endpoints, and integrity
protected with keys established depends on
ordinary routing sending packets through the IKE_SA_init exchange, so tunnel endpoints for
processing. Each endpoint would announce the identities are hidden from eavesdroppers set of addresses
"behind" it, and all fields packets would be sent in all Tunnel Mode where the messages are authenticated. inner
IP header would contain the IP addresses of the actual endpoints.

3.1.2 Endpoint to Endpoint Transport

+-+-+-+-+-+ +-+-+-+-+-+
! ! IPsec ! !
!Protected! Tunnel !Protected!

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!Endpoint !<---------------------------------------->!Endpoint !
! ! ! !
+-+-+-+-+-+ +-+-+-+-+-+

Figure 2: Endpoint to Endpoint

In this scenario, both endpoints of the following description, IP connection implement
IPsec. These endpoints may implement application layer access
controls based on the payloads contained in authenticated identities of the message
are indicated by names such participants.
Transport mode will commonly be used with no inner IP header. If
there is an inner IP header, the inner addresses will be the same as SA. The details of
the contents outher addresses. A single pair of
each payload are described later. Payloads which may optionally
appear addresses will be shown negotiated
for packets to be sent over this SA.

It is possible in brackets, such as [CERTREQ], would indicate this scenario that optionally a certificate request payload can one of the protected endpoints
will be included.

The Phase 1 exchange is as follows:

Initiator Responder
----------- -----------
HDR, SAi1, KEi, Ni -->

HDR contains the SPIs (formerly called cookies), version numbers, and
flags of various sorts. The SAi1 payload states the cryptographic
algorithms the Initiator supports for the IKE SA. The KE payload
sends the Initiator's Diffie-Hellman value. Ni is the Initiator's
nonce.

<-- HDR, SAr1, KEr, Nr, [CERTREQ]

The Responder chooses behind a cryptographic suite from network address translation (NAT) node, in which
case the Initiator's
offered choices and expresses tunnelled packets will have to be UDP encapsulated so that choice
port numbers in the SAr1 payload,
completes UDP headers can be used to identify individual
endpoints "behind" the Diffie-Hellman exchange with NAT.

3.1.3 Endpoint to Gateway Transport

+-+-+-+-+-+ +-+-+-+-+-+
! ! IPsec ! ! Protected
!Protected! Tunnel !Tunnel ! Subnet
!Endpoint !<------------------------>!Endpoint !<--- and/or
! ! ! ! Internet
+-+-+-+-+-+ +-+-+-+-+-+

Figure 3: Endpoint to Gateway

In this scenario, a protected endpoint (typically a portable roaming
computer) connects back to its corporate network through an IPsec
protected tunnel. It might use this tunnel only to access information
on the KEr payload, and sends corporate network or it might tunnel all of its nonce in traffic back
through the Nr payload.

At this point corporate network in time each party can generate SKEYSEED from which all
keys are derived for that IKE SA. Parts order to take advantage of
protection provided by a corporate firewall against Internet based
attacks. In either case, the following two
messages, protected endpoint will want an IP
address associated with the IKE_AUTH and IKE_AUTH_response, are encrypted gateway so that packets returned to it
will go to the gateway and
integrity protected. The keys used be tunnelled back. This IP address may be
static or may be dynamically allocated by the gateway. In support of
the latter case, IKEv2 includes a mechanism for the encryption and integrity
protection are derived from SKEYSEED and are known as SK_e
(encryption) and SK_a (authentication, a.k.a. integrity protection).
A separate SK_e and SK_a is computed initiator to
request an IP address owned by the gateway for use for the duration
of its SA.

In this scenario, packets will use tunnel mode. On each direction. The
notation SK { ... } indicates that these payloads are encrypted and
integrity packet from
the protected using that direction's SK_e and SK_a.

HDR, SAi1, KEi, Ni, Nr,
SK {IDi, [CERT,] [CERTREQ,] [IDr,]
AUTH, SAi2, TSi, TSr} -->

The initial payloads in message three are identical to endpoint, the payloads
in message 1. If message 1 included any optional payloads (e.g. outer IP header will contain the source
IP address associated with its current location (i.e. the address

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Vendor ID), they must be repeated in message 3 in the same order.
Then she includes Nr (Bob's nonce) copied from message 2. The
Initiator identifies herself with January 2003

that will get traffic routed to the IDi payload, proves knowledge
of endpoint directly) while the secret corresponding to IDi and integrity protects
inner IP header will contain the
contents of source IP address assigned by the first two messages using
gateway (i.e. the AUTH payload. She might
also send her certificate(s) in CERT payload(s) and a list of her
trust anchors in CERTREQ payload(s). The optional payload IDr
enables Alice address that will get traffic routed to specify which of Bob's identities she wants the gateway
for forwarding to talk
to. This is useful when Bob is hosting multiple identities at the
same IP address. She begins negotiation endpoint). The outer destination address will
always be that of a child-SA using the SAi2
payload. The fields starting with SAi2 are described in the
description of Phase 2.

There are optional fields where the Initiator can provide
certificates [CERT] gateway, while the Responder might find useful in validating
AUTH, her list of preferred root certifiers [CERTREQ], and inner destination address
will be the name
of ultimate destination for the entity with which she packet.

In this scenario, it is trying to open a connection [IDr]
(for possible that the case where multiple named entities exist at protected endpoint will be
behind a single NAT. In that case, the IP
address).

<-- HDR, SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr}

The Responder identifies himself with address as seen by the IDr payload, optionally
sends one or more certificates, authenticates himself with gateway
will not be the AUTH
payload, and completes negotiation of a child-SA with same as the additional
fields described below in IP address sent by the phase 2 exchange.

The recipients of messages 3 and 4 MUST verify that all signatures
and MACs are computed correctly protected
endpoint, and that the names in the ID payloads
correspond to the keys used packets will have to generate the AUTH payload.

3.2 The CREATE_CHILD_SA (Phase 2) Exchange

A phase 2 exchange is one request/response pair, and can be used UDP encapsulated in order to
create or delete a child-SA, delete or rekey the IKE-SA, check the
liveness be
routed properly.

3.1.4 Other Scenarios

Other scenarios are possible, as are nested combinations of the IKE-SA, or deliver information such as error
conditions. It is encrypted
above. One noteable example combines aspects of 3.1.1 and integrity protected 3.1.3. A
subnet may make all external accesses through a remote gateway using
an IPsec tunnel, where the keys
negotiated during the creation of addresses on the IKE-SA.

Messages subnet are cryptographically protected using routed to the cryptographic
algorithms and keys negotiated in
gateway by the first two messages rest of the IKE
exchange using a syntax described in section 5.14. Encryption uses
keys derived from SK_e, one in each direction; Integrity uses keys
derived from SK_a, one in each direction.

Either endpoint may initiate a CREATE_CHILD_SA exchange, so in this
section Internet. An example would be someones
home network being virtually on the term Initiator refers to Internet with static IP addresses
even though connectivity is provided by an ISP that assigns a single
dynamically assigned IP address (where the endpoint initiating this

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exchange.

A child-SA static IP addresses and an
IPsec relay is created provided by sending a CREATE_CHILD_SA request. third party located elsewhere).

3.2 The
CREATE_CHILD_SA request MAY optionally contain a KE payload for Initial Exchange

Communication using IKE always begins with an
additional Diffie-Hellman initial exchange to enable stronger guarantees (known
in IKEv1 as Phase 1). This initial exchange normally consists of
forward secrecy for four
messages, though in some scenarios that number can grow. All
communications using IKE consist of request/response pairs. We'll
describe the child-SA. base exchange first, followed by variations. The keying material for the child-
SA is a function first
pair of SK_d established during the establishment messages (IKE_SA_INIT) negotiate cryptographic algorithms,
exchange nonces, and do a Diffie-Hellman exchange.

The second pair of messages (IKE_AUTH) authenticate the
IKE-SA, previous
messages, exchange identities and certificates, and establish the nonces exchanged during
first CHILD-SA. Parts of these messages are encrypted and integrity
protected with keys established through the CREATE_CHILD_SA IKE_SA_INIT exchange, and so
the Diffie-Hellman value (if KE payloads identities are included hidden from eavesdroppers and all fields in all
the
CREATE_CHILD_SA exchange). messages are authenticated.

In the child-SA created following description, the payloads contained in the message
are indicated by names such as part SA. The details of the phase 1 exchange, a second KE contents of
each payload MUST NOT be used, and the Nonces are not transmitted but are
assumed to described later. Payloads which may optionally
appear will be the same shown in brackets, such as the phase 1 nonces.

The CREATE_CHILD_SA [CERTREQ], would indicate
that optionally a certificate request contains: payload can be included.

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The initial exchange is as follows:

Initiator Responder
----------- -----------
HDR, SK {SA, Ni, [KEi],
[TSi, TSr]} SAi1, KEi, Ni -->

HDR contains the SPIs, version numbers, and flags of various sorts.
The SAi1 payload states the cryptographic algorithms the Initiator
supports for the IKE-SA. The KE payload sends SA offer(s) in the SA payload, Initiator's
Diffie-Hellman value. Ni is the Initiator's nonce.

<-- HDR, SAr1, KEr, Nr, [CERTREQ]

The Responder chooses a nonce cryptographic suite from the Initiator's
offered choices and expresses that choice in the Ni SAr1 payload, optionally a
completes the Diffie-Hellman value in exchange with the KEi KEr payload, and sends
its nonce in the proposed traffic selectors Nr payload.

At this point in the TSi and TSr payloads. If negotiation each party can generate SKEYSEED,
from which all keys are derived for that IKE-SA. All but the SA
offers include different Diffie-Hellman groups, KEi must be an
element headers
of all the first group offered. messages that follow are encrypted and integrity
protected. The message past keys used for the header encryption and integrity protection
are derived from SKEYSEED and are known as SK_e (encryption) and SK_a
(authentication, a.k.a. integrity protection). A separate SK_e and
SK_a is computed for each direction. The notation SK { ... }
indicates that these payloads are encrypted and the message including
the header is integrity protected
using the cryptographic algorithms
negotiated in Phase 1.

The CREATE_CHILD_SA response contains:

<-- HDR, that direction's SK_e and SK_a.

HDR, SK {SA, Nr, [KEr],
[TSi, TSr]} {IDi, [CERT,] [CERTREQ,] [IDr,]
AUTH, SAi2, TSi, TSr} -->

The Responder replies (using the same Message ID to respond) Initiator asserts her identity with the
accepted offer in an SA IDi payload, a Diffie-Hellman value in the KEr
payload if KEi was included in proves
knowledge of the request secret corresponding to IDi and integrity protects
the selected
cryptographic suite includes that group. If contents of the responder chooses a
cryptographic suite with first two messages using the AUTH payload. She
might also send her certificate(s) in CERT payload(s) and a different group, it list of
her trust anchors in CERTREQ payload(s). If any CERT payloads are
included, the first certificate provided must reject contain the
request and have public key
used to verify the initiator make another one. AUTH field. The traffic selectors for traffic optional payload IDr enables
Alice to be sent on that SA are specified
in the TS payloads, specify which may be a subset of what Bob's identities she wants to talk to. This
is useful when Bob is hosting multiple identities at the Initiator same IP
address. She begins negotiation of a CHILD-SA using the child-SA proposed. Traffic selectors SAi2
payload. The final fields (starting with SAi2) are omitted if this
CREATE_CHILD_SA request is being used to change described in the key
description of the IKE- CREATE_CHILD_SA exchange.

<-- HDR, SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr}

The Responder asserts his identity with the IDr payload, optionally

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SA.

3.3 Informational (Phase 2) Exchange

At various points during an IKE-SA, peers may desire to convey
control messages to each other regarding errors January 2003

sends one or notifications more certificates (again with the certificate containing
the public key used to verify AUTH listed first), authenticates his
identity with the AUTH payload, and completes negotiation of
certain events. To accomplish this IKE defines a (reliable)
Informational exchange. Usually Informational exchanges happen
during phase 2 and are cryptographically protected
CHILD-SA with the IKE additional fields described below in the
CREATE_CHILD_SA exchange.

Control

The recipients of messages that pertain to an IKE-SA 3 and 4 MUST be sent under verify that
IKE-SA. Control messages all signatures
and MACs are computed correctly and that pertain to Child-SAs MUST be sent under the protection of names in the IKE-SA which generated them (or its successor
if ID payloads
correspond to the IKE-SA is replaced for keys used to generate the purpose AUTH payload.

3.3 The CREATE_CHILD_SA Exchange

This exchange consists of rekeying).

There a single request/response pair, and was
referred to as a phase 2 exchange in IKEv1.

All messages following the initial exchange are two cases cryptographically
protected using the cryptographic algorithms and keys negotiated in which there is no IKE-SA to protect
the
information. One is first two messages of the IKE exchange using a syntax described
in section 5.14.

Either endpoint may initiate a CREATE_CHILD_SA exchange, so in this
section the response to an IKE_SA_init_request term Initiator refers to
refuse the SA proposal. This would be conveyed in endpoint initiating this
exchange.

A CHILD-SA is created by sending a Notify CREATE_CHILD_SA request. The
CREATE_CHILD_SA request MAY optionally contain a KE payload for an
additional Diffie-Hellman exchange to enable stronger guarantees of
forward secrecy for the IKE_SA_init_response. CHILD-SA. The other case in which there is no IKE-SA to protect keying material for the information CHILD-
SA is when a packet is received with an unknown SPI. function of SK_d established during the establishment of the
IKE-SA, the nonces exchanged during the CREATE_CHILD_SA exchange, and
the Diffie-Hellman value (if KE payloads are included in the
CREATE_CHILD_SA exchange).

In that case the
notification CHILD-SA created as part of this condition will the initial exchange, a second KE
payload and nonce MUST NOT be sent in an informational sent. The nonces from the initial
exchange that is not cryptographically protected.

Messages are used in an Informational Exchange contain zero or more
Notification or Delete payloads. computing the keys for the CHILD-SA.

The Recipient of an Informational
Exchange CREATE_CHILD_SA request MUST send some response (else contains:

Initiator Responder
----------- -----------
HDR, SK {SA, Ni, [KEi],
[TSi, TSr]} -->

The Initiator sends SA offer(s) in the Sender will assume SA payload, a nonce in the message was lost Ni
payload, optionally a Diffie-Hellman value in the network KEi payload, and will retransmit it). That
response can be a message with no payloads. Actually,
the request
message proposed traffic selectors in an Informational Exchange can also contain no payloads.
This is the expected way an endpoint can ask the other endpoint to
verify that it is alive.

ESP, AH, TSi and IPcomp SAs always exist in pairs, with one TSr payloads. If the SA in each
direction. When
offers include different Diffie-Hellman groups, KEi must be an SA is closed, both members

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element of the pair MUST be
closed. When SAs are nested, as when data is encapsulated first with
IPcomp, then with ESP, and finally with AH between group the same pair of
endpoints, all of Initiator expects the SAs (up responder to six) must be deleted together. To
delete an SA, an Informational Exchange with one or more delete
payloads is sent listing the SPIs (as known to the recipient) of accept.
If she guesses wrong, the
SAs CREATE_CHILD_SA exchange will fail and she
will have to be deleted. retry with a different KEi.

The recipient MUST close message past the designated SAs.
Normally, header is encrypted and the reply in message including
the Informational Exchange will contain delete
payloads for header is integrity protected using the paired SAs going cryptographic algorithms
negotiated in Phase 1.

The CREATE_CHILD_SA response contains:

<-- HDR, SK {SA, Nr, [KEr],
[TSi, TSr]}

The Responder replies (using the other direction. There is
one exception. If by chance both ends of a set of SAs independently
decide same Message ID to close them, each may send respond) with the
accepted offer in an SA payload, a delete payload and Diffie-Hellman value in the two
requests may cross KEr
payload if KEi was included in the network. request and the selected
cryptographic suite includes that group. If the responder chooses a node receives
cryptographic suite with a delete

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request and have the initiator make another one.

The traffic selectors for SAs traffic to be sent on that it has already issued SA are specified
in the TS payloads, which may be a delete request for, it
MUST delete subset of what the incoming SAs while processing Initiator of
the CHILD-SA proposed. Traffic selectors are omitted if this
CREATE_CHILD_SA request and is being used to change the
outgoing SAs while processing key of the response. In that case, IKE-
SA.

3.4 The Informational Exchange

At various points during the
responses MUST NOT include delete payloads for the deleted SAs, since
that would result in duplicate deletion operation of an IKE-SA, peers may desire
to convey control messages to each other regarding errors or
notifications of certain events. To accomplish this IKE defines an
Informational exchange. Informational exchanges MUST occur after an
initial exchange and could in theory delete are cryptographically protected with the wrong SA.

A node SHOULD regard half open connections as anomalous and audit
their existence should they persist. Note
negotiated keys.

Control messages that this specification
nowhere specifies time periods, so it is up to individual endpoints
to decide how long pertain to wait. A node MAY refuse an IKE-SA MUST be sent under that
IKE-SA. Control messages that pertain to accept incoming data
on half open connections but CHILD-SAs MUST NOT unilaterally close them and
reuse be sent under
the SPIs. If connection state becomes sufficiently messed up, a
node MAY close protection of the IKE-SA which will implicitly close all SAs
negotiated under it. It can then rebuild generated them (or its successor
if the SA's it needs on a clean
base under a new IKE-SA.

The IKE-SA was replaced for the purpose of rekeying).

Messages in an Informational Exchange is defined as:

Initiator Responder
----------- -----------
HDR, SK {N, ..., D, ...} -->
<-- HDR, SK {N, ..., D, ...} contain zero or more
Notification or Delete payloads. The processing Recipient of an Informational
Exchange is determined by its
component payloads.

4 IKE Protocol Details request MUST send some response (else the Sender will assume
the message was lost in the network and Variations

IKE runs over UDP port 500. Since UDP is will retransmit it). That
response MAY be a datagram (unreliable)
protocol, IKE includes message with no payloads. The request message in its definition recovery from transmission
errors, including packet loss, packet replay, and packet forgery. IKE an
Informational Exchange MAY also contain no payloads. This is designed the
expected way an endpoint can ask the other endpoint to function so long as at least verify that it
is alive.

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ESP and AH SAs always exist in pairs, with one SA in each direction.
When an SA is closed, both members of a series of
retransmitted packets reaches its destination before timing out the pair MUST be closed. When
SAs are nested, as when data (and IP headers if in tunnel mode) are
encapsulated first with IPcomp, then with ESP, and finally with AH
between the channel is not so full same pair of forged endpoints, all of the SAs MUST be deleted
together. Each endpoint MUST close the SAs it sends on and replayed packets so as allow the
other endpoint to
exhaust close the network other SA in each pair. To delete an SA,
an Informational Exchange with one or CPU capacities of either endpoint. Even more delete payloads is sent
listing the SPIs (as they would be placed in the
absence headers of those minimum performance requirements, IKE is designed outbound
packets) of the SAs to
fail cleanly (as though be deleted. The recipient MUST close the network were broken).

4.1 Use of Retransmission Timers

All messages
designated SAs. Normally, the reply in IKE exist the Informational Exchange
will contain delete payloads for the paired SAs going in pairs: a request and a response. The
setup of an IKE SA normally consists of two request/response pairs.
Once the IKE SA other
direction. There is set up, either end one exception. If by chance both ends of a security association may
initiate requests at any time, and there can be many requests and
responses "in flight" at any given moment. But set
of SAs independently decide to close them, each message is
labelled as either a request or may send a response and for each
request/response pair one end of the security association is the

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Initiator delete
payload and the other is the Responder.

For every pair of messages, the Initiator is responsible for
retransmission two requests may cross in the event of a timeout. The Responder will never
retransmit network. If a response unless it node
receives a retransmission of the
request. In that event, the Responder MUST either ignore the
retransmitted delete request except insofar as for SAs for which it triggers has already issued a retransmission
of
delete request, it MUST delete the response OR if incoming SAs while processing the
request a second time has no
adverse effects, the Responder may choose to process the request
again and send a semantically equivalent reply.

IKE is a reliable protocol, in the sense outgoing SAs while processing the response. In that
case, the Initiator responses MUST
retransmit a request until either it receives a corresponding reply
OR it deems NOT include delete payloads for the IKE security association to have failed deleted
SAs, since that would result in duplicate deletion and it
discards all state associated with could in
theory delete the IKE-SA and any Child-SAs
negotiated using that IKE-SA.

4.2 Use of Sequence Numbers for Message ID

Every IKE message contains a Message ID wrong SA.

A node SHOULD regard half open connections as part of its fixed header.
This Message ID anomalous and audit
their existence should they persist. Note that this specification
nowhere specifies time periods, so it is used to match up requests and responses, and to
identify retransmissions of messages.

The Message ID is individual endpoints
to decide how long to wait. A node MAY refuse to accept incoming data
on half open connections but MUST NOT unilaterally close them and
reuse the SPIs. If connection state becomes sufficiently messed up, a 32 bit quantity, which is zero for
node MAY close the first IKE
request in each direction. The IKE SA initial setup messages IKE-SA which will
always be numbered 0 and 1. Each endpoint in the IKE Security
Association maintains two "current" Message IDs: implicitly close all SAs
negotiated under it. It can then rebuild the next one to be
used for SAs it needs on a request clean
base under a new IKE-SA.

The Informational Exchange is defined as:

Initiator Responder
----------- -----------
HDR, SK {N, ..., D, ...} -->
<-- HDR, SK {N, ..., D, ...}

The processing of an Informational Exchange is determined by its
component payloads.

3.5 Informational Messages outside of an IKE-SA

If a packet arrives with an unrecognised SPI, it initiates could be because the
receiving node has recently crashed and lost state or because of some
other system malfunction or attack. If the next one it expects receiving node has an
active IKE-SA to see the IP address from whence the other end. These counters increment as requests are
generated and received. Responses always contain the same message ID
as packet came, it MAY

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send a notification of the corresponding request. That means wayward packet over that after the initial
exchange, each integer n may appear as the IKE-SA. If it
does not, it MAY send an Informational message ID in four
distinct messages: The nth request from without cryptographic
protection to the original source IP address to alert it to a possible
problem.

4 IKE Initiator,
the corresponding response, the nth request Protocol Details and Variations

IKE normally listens on UDP port 500, though IKE messages may also be
received on UDP port 4500 with a slightly different format. Since
UDP is a datagram (unreliable) protocol, IKE includes in its
definition recovery from the original transmission errors, including packet loss,
packet replay, and packet forgery. IKE
Responder, is designed to function so
long as (1) at least one of a series of retransmitted packets reaches
its destination before timing out; and (2) the corresponding response. If the two ends make very
different numbers channel is not so full
of requests, forged and replayed packets so as to exhaust the Message IDs network or CPU
capacities of either endpoint. Even in the two directions
can be very different. There absence of those minimum
performance requirements, IKE is no ambiguity in the messages,
however, because each packet contains enough information designed to determine
which of fail cleanly (as though
the four network were broken).

4.1 Use of Retransmission Timers

All messages in IKE exist in pairs: a particular one is.

Note that Message IDs are cryptographically protected request and provide
protection against message replays.

4.3 Window Size for overlapping requests

In order to maximize IKE throughput, an IKE endpoint MAY issue
multiple requests before getting a response to any response. The
setup of them. For

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simplicity, an IKE implementation MAY choose to process requests
strictly in order and/or wait for a response to one request before
issuing another. Certain rules must be followed to assure
interoperability between implementations using different strategies.

After an IKE-SA normally consists of two request/response pairs.
Once the IKE-SA is set up, either end can of the security association may
initiate one or more
requests. These requests may pass one another over the network. An
IKE endpoint MUST be prepared to accept at any time, and process a request while
it has a request outstanding in order to avoid a deadlock in this
situation. An IKE endpoint SHOULD there can be prepared to accept and process
multiple many requests while it has and
responses "in flight" at any given moment. But each message is
labelled as either a request outstanding.

An IKE endpoint MUST wait for or a response to and for each
request/response pair one end of the security association is the
Initiator and the other is the Responder.

For every pair of messages, the Initiator is responsible for
retransmission in the event of its messages
before sending a subsequent message timeout. The Responder MUST never
retransmit a response unless it has received receives a Notify
message from its peer informing it retransmission of the
request. In that event, the peer is prepared to
maintain state for multiple outstanding messages in order to allow
greater throughput.

An IKE endpoint Responder MUST NOT exceed ignore the peer's stated window size (see
section 5.3.2) for transmitted IKE requests. In other words, if Bob
stated his window size is N, then when Alice needs to make a request
X, she MUST wait until she has received responses to all requests up
through retransmitted
request X-N. An IKE endpoint MUST keep except insofar as it triggers a copy retransmission of (or be able
to regenerate exactly) the
response. The Initiator MUST remember each request it has sent until it receives
the corresponding response. An IKE endpoint The Responder MUST keep remember each response
until it receives a copy of (or be
able to regenerate with semantic equivalence) request whose sequence number is larger than the
sequence number of previous
responses equal to its contracted in the response plus his window size (see section
4.3).

IKE is a reliable protocol, in case its response
was lost and the sense that the Initiator requests its retransmission by
retransmitting MUST
retransmit a request until either it receives a corresponding reply
OR it deems the request.

An IKE endpoint SHOULD be capable of processing incoming requests out
of order security association to maximize performance in the event of network failures or
packet reordering.

4.4 State Synchronization have failed and Connection Timeouts

An IKE endpoint is allowed to forget it
discards all of its state associated with
an the IKE-SA and the collection of corresponding child-SAs at any time. CHILD-SAs
negotiated using that IKE-SA.

4.2 Use of Sequence Numbers for Message ID

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Every IKE message contains a Message ID as part of its fixed header.
This Message ID is the anticipated behavior in the event of an endpoint crash used to match up requests and restart. It is important when an endpoint either fails or
reinitializes its state that the other endpoint detect those
conditions responses, and not continue to waste network bandwidth by sending
packets over those SAs and having them fall into
identify retransmissions of messages.

The Message ID is a black hole.

Since IKE 32 bit quantity, which is designed to operate in spite of Denial of Service (DoS)
attacks from the network, an endpoint MUST NOT conclude that zero for the
other endpoint has failed based on any routing information (e.g. ICMP
messages) or first IKE
request in each direction. The IKE-SA initial setup messages that arrive without cryptographic

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protection (e.g., notify messages complaining about unknown SPIs). An will
always be numbered 0 and 1. Each endpoint MUST conclude that in the other endpoint has failed only when
repeated attempts IKE Security
Association maintains two "current" Message IDs: the next one to contact it have gone unanswered be
used for a timeout
period. An endpoint SHOULD suspect that the other endpoint has failed
based on routing information and initiate a request it initiates and the next one it expects to see whether
from the other endpoint is alive. To check whether end. These counters increment as requests are
generated and received. Responses always contain the other side is
alive, IKE specifies an empty Informational same message ID
as the corresponding request. That means that (like all
IKE requests) requires an acknowledgment. If a cryptographically
protected after the initial
exchange, each integer n may appear as the message has been received ID in four
distinct messages: The nth request from the other side recently,
unprotected notifications MAY be ignored. Implementations MUST limit original IKE Initiator,
the rate at which they take actions based on unprotected messages.

Numbers of retries corresponding response, the nth request from the original IKE
Responder, and lengths the corresponding response. If the two ends make very
different numbers of timeouts are not covered requests, the Message IDs in this
specification because they do not affect interoperability. It is
suggested that messages the two directions
can be retransmitted at least a dozen times over
a period of at least several minutes before giving up on an SA, but
different environments may require different rules. If there is
outgoing traffic on an SA, it very different. There is essential no ambiguity in the messages,
however, because each packet contains enough information to confirm liveness determine
which of the four messages a particular one is.

Note that SA to avoid black holes. If no Message IDs are cryptographically protected
messages have been received on and provide
protection against message replays.

4.3 Window Size for overlapping requests

In order to maximize IKE throughput, an IKE-SA or IKE endpoint MAY issue
multiple requests before getting a response to any of its child-SAs
recently, them. For
simplicity, an IKE implementation MAY choose to process requests
strictly in order and/or wait for a liveness check MUST response to one request before
issuing another. Certain rules must be performed. Receipt of a fresh
cryptographically protected message on followed to assure
interoperability between implementations using different strategies.

After an IKE-SA is set up, either end can initiate one or any of its
child-SAs assures liveness of more
requests. These requests may pass one another over the IKE-SA network. An
IKE endpoint MUST be prepared to accept and all of its child-SAs.

There is process a Denial of Service attack on the Initiator of an IKE-SA
that can be avoided if the Initiator takes the proper care. Since the
first two messages of an SA setup are not cryptographically
protected, an attacker could respond request while
it has a request outstanding in order to the Initiator's message
before the genuine Responder and poison the connection setup attempt.
To prevent this, the Initiator avoid a deadlock in this
situation. An IKE endpoint SHOULD be willing prepared to accept multiple
responses to its first message, treat each as potentially legitimate,
respond to it, and then discard all the invalid half open connections
when she receives process
multiple requests while it has a request outstanding.

An IKE endpoint MUST wait for a valid cryptographically protected response to any
one each of her requests. Once its messages
before sending a cryptographically valid response is
received, all subsequent responses should be ignorred whether or not
they are cryptographically valid.

Note message unless it has received a Notify
message from its peer informing it that with these rules, there is no reason to negotiate and agree
upon an SA lifetime. If IKE presumes the partner peer is dead, based on
repeated lack of acknowledgment to an IKE message, then the IKE SA
and all child-SAs set up through that IKE-SA are deleted.

An IKE endpoint MAY delete inactive Child-SAs prepared to recover resources
used
maintain state for multiple outstanding messages in order to hold their state. If an allow
greater throughput.

An IKE endpoint chooses to do so, it MUST send Delete payloads to NOT exceed the peer's stated window size for
transmitted IKE requests. In other end notifying it of the
deletion. It MAY similarly time out the IKE-SA. Closing the IKE-SA
implicitly closes words, if Bob stated his window

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size is N, then when Alice needs to make a request X, she MUST wait
until she has received responses to all associated Child-SAs. requests up through request
X-N. An IKE endpoint SHOULD
send MUST keep a Delete payload indicating that copy of (or be able to regenerate
exactly) each request it has closed sent until it receives the IKE-SA.

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4.5 Version Numbers and Forward Compatibility

This document describes version 2.0 corresponding
response. An IKE endpoint MUST keep a copy of IKE, meaning the major version
number is 2 and (or be able to
regenerate exactly) the minor version number is zero. It is likely that
some implementations will want of previous responses equal to support both version 1.0 and
version 2.0, and its
declared window size in case its response was lost and the future, other versions.

The major version number should only Initiator
requests its retransmission by retransmitting the request.

An IKE endpoint supporting a window size greater than one SHOULD be incremented if
capable of processing incoming requests out of order to maximize
performance in the packet
formats event of network failures or required actions have changed so dramatically that an
older version node would not be able packet reordering.

4.4 State Synchronization and Connection Timeouts

An IKE endpoint is allowed to interoperate forget all of its state associated with a newer
version node if it simply ignored the fields it did not understand
an IKE-SA and took the actions specified in the older specification. The minor
version number indicates new capabilities, collection of corresponding CHILD-SAs at any time.
This is the anticipated behavior in the event of an endpoint crash
and MUST be ignored restart. It is important when an endpoint either fails or
reinitializes its state that the other endpoint detect those
conditions and not continue to waste network bandwidth by sending
packets over those SAs and having them fall into a
node with a smaller minor version number, but used for informational
purposes by black hole.

Since IKE is designed to operate in spite of Denial of Service (DoS)
attacks from the node with network, an endpoint MUST NOT conclude that the larger minor version number. For
example, it might indicate
other endpoint has failed based on any routing information (e.g. ICMP
messages) or IKE messages that arrive without cryptographic
protection (e.g., notify messages complaining about unknown SPIs). An
endpoint MUST conclude that the ability other endpoint has failed only when
repeated attempts to process contact it have gone unanswered for a newly defined timeout
period or when a cryptographically protected INITIAL-CONTACT
notification message. The node with is received on a different IKE-SA to the larger minor version number
would simply note same
authenticated identity. An endpoint SHOULD suspect that its correspondent would not be able the other
endpoint has failed based on routing information and initiate a
request to
understand that see whether the other endpoint is alive. To check whether
the other side is alive, IKE specifies an empty Informational message and therefore would not send it.
that (like all IKE requests) requires an acknowledgment. If you receive a
cryptographically protected message with a higher major version number, you has been received from the other
side recently, unprotected notifications MAY be ignored.
Implementations MUST
drop limit the message rate at which they take actions based
on unprotected messages.

Numbers of retries and SHOULD send lengths of timeouts are not covered in this
specification because they do not affect interoperability. It is
suggested that messages be retransmitted at least a dozen times over
a period of at least several minutes before giving up on an unauthenticated notification
message containing the highest version number you support. SA, but
different environments may require different rules. If you
support major version n, and major version m, you MUST support there has only
been outgoing traffic on all
versions between n and m. If you receive a message with a major
version that you support, you MUST respond of the SAs associated with that version number.
In order an IKE-SA, it

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is essential to prevent two nodes from being tricked into corresponding
with a lower major version number than confirm liveness of the maximum that they both
support, IKE has other endpoint to avoid black
holes. If no cryptographically protected messages have been received
on an IKE-SA or any of its CHILD-SAs recently, a flag that indicates that the node is capable liveness check MUST
be performed. Receipt of
speaking a higher major version number.

Thus fresh cryptographically protected message
on an IKE-SA or any of its CHILD-SAs assures liveness of the major version number in IKE-SA
and all of its CHILD-SAs. Note that this places requirements on the
failure modes of an IKE header indicates the version
number endpoint. An implementation MUST NOT continue
sending on any SA if some failure prevents it from receiving on all
of the message, not the highest version number that the
transmitter supports. associated SAs. If A is capable of speaking versions n, n+1,
and n+2, and B is capable of speaking versions n and n+1, then they
will negotiate speaking n+1, where A will set CHILD-SAs can fail independently from one
another without the flag indicating
ability associated IKE-SA being able to speak send a higher version. If delete
message, then they mistakenly (perhaps
through MUST be negotiated by separate IKE-SAs.

There is a Denial of Service attack on the Initiator of an IKE-SA
that can be avoided if the Initiator takes the proper care. Since the
first two messages of an SA setup are not cryptographically
protected, an active attacker sending error messages) negotiate could respond to
version n, then both will notice that the other side can support a
higher version number, Initiator's message
before the genuine Responder and they MUST break poison the connection setup attempt.
To prevent this, the Initiator MAY be willing to accept multiple
responses to its first message, treat each as potentially legitimate,
respond to it, and
reconnect using version n+1. then discard all the invalid half open connections
when she receives a valid cryptographically protected response to any
one of her requests. Once a cryptographically valid response is
received, all subsequent responses should be ignored whether or not
they are cryptographically valid.

Note that IKEv1 does not follow with these rules, because there is no way
in v1 of noting that you are capable of speaking a higher version
number. So reason to negotiate and agree
upon an active attacker can trick two v2-capable nodes into
speaking v1. When a v2-capable node negotiates down SA lifetime. If IKE presumes the partner is dead, based on
repeated lack of acknowledgment to v1, it SHOULD
note that fact in its logs.

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Also for forward compatibility, an IKE message, then the IKE SA
and all fields marked RESERVED MUST be CHILD-SAs set up through that IKE-SA are deleted.

An IKE endpoint may at any time delete inactive CHILD-SAs to zero by a version 2.0 implementation and recover
resources used to hold their content state. If an IKE endpoint chooses to do
so, it MUST be
ignored by a version 2.0 implementation ("Be conservative in what you send and liberal in what you receive"). In this way, future versions Delete payloads to the other end notifying it of the protocol can use those fields in
deletion. It MAY similarly time out the IKE-SA. Closing the IKE-SA
implicitly closes all associated CHILD-SAs. In this case, an IKE
endpoint SHOULD send a way that is guaranteed to
be ignored by implementations that do not understand them.
Similarly, Delete payload types indicating that are not defined are reserved for future
use it has closed
the IKE-SA.

4.5 Version Numbers and implementations of Forward Compatibility

This document describes version 2.0 MUST skip over those payloads
and ignore their contents.

IKEv2 adds a "critical" flag to each payload header for further
flexibility for forward compatibility. If of IKE, meaning the critical flag major version
number is set 2 and the payload type minor version number is unsupported, the message MUST be rejected zero. It is likely that
some implementations will want to support both version 1.0 and
version 2.0, and in the response to future, other versions.

The major version number should only be incremented if the IKE request containing packet
formats or required actions have changed so dramatically that payload MUST include
a notify payload UNSUPPORTED-CRITICAL-PAYLOAD, indicating an
unsupported critical payload was included. If
older version node would not be able to interoperate with a newer

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version node if it simply ignored the critical flag is fields it did not set understand
and took the payload type is unsupported, that payload is simply
skipped. While new payload types may be added actions specified in the future older specification. The minor
version number indicates new capabilities, and may
appear interleaved MUST be ignored by a
node with a smaller minor version number, but used for informational
purposes by the fields defined in this specification,
implementations MUST send node with the payloads defined in this specification
in larger minor version number. For
example, it might indicate the stated order and implementations SHOULD reject as invalid ability to process a
message with payloads in an unexpected order.

4.6 Cookies newly defined
notification message. The term "cookies" originates node with Karn the larger minor version number
would simply note that its correspondent would not be able to
understand that message and Simpson [RFC 2522] in
Photuris, therefore would not send it.

If an early proposal for key management endpoint receives a message with IPsec. It has
persisted because the IETF has never rejected a proposal involving
cookies. The ISAKMP fixed higher major version number,
it MUST drop the message header includes two eight octet
fields titled "cookies", and that syntax is used by both IKEv1 and
IKEv2. Those eight octet fields are used as SHOULD send an SPI or connection
identifier at unauthenticated
notification message containing the beginning of IKE packets. They were also intended
to be used as Karn/Simpson "anti-clogging" tokens in IKEv1, but
certain aspects of highest version number it
supports. If an endpoint supports major version n, and major version
m, it MUST support all versions between n and m. If it receives a
message with a major version that design prevented them it supports, it MUST respond with
that version number. In order to prevent two nodes from being used as
such. IKEv2 was carefully constructed to allow an implementation to
implement these anti-clogging tokens, either using tricked
into corresponding with a lower major version number than the fields titled
"cookies" or by creative choices of nonces.

While maximum
that they both support, IKE implementations SHOULD implement anti-clogging tokens to
protect themselves from denial of service attacks, has a flag that indicates that the algorithms and
syntax they use in cookies and/or nonces does not affect
interoperability and hence node
is not specified here. The following
should be interpreted as an explanation capable of why speaking a higher major version number.

Thus the protocol has major version number in the
fields it does and as an example IKE header indicates the version
number of how an implementation could
implementing anti-clogging tokens.

In IKEv2, the cookies are used as IKE-SA identifiers in message, not the headers
of IKE messages. As with ESP and AH, in IKEv2 highest version number that the recipient
transmitter supports. If A is capable of a

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message chooses speaking versions n, n+1,
and n+2, and B is capable of speaking versions n and n+1, then they
will negotiate speaking n+1, where A will set the flag indicating
ability to speak a higher version. If they mistakenly (perhaps
through an IKE-SA identifier active attacker sending error messages) negotiate to
version n, then both will notice that uniquely defines the other side can support a
higher version number, and they MUST break the connection and
reconnect using version n+1.

Note that SA to IKEv1 does not follow these rules, because there is no way
in v1 of noting that recipient. For this purpose (IKE-SA identifiers), you are capable of speaking a higher version
number. So an active attacker can trick two v2-capable nodes into
speaking v1. When a v2-capable node negotiates down to v1, it might be
convenient SHOULD
note that fact in its logs.

Also for the cookie value to forward compatibility, all fields marked RESERVED MUST be chosen so as
set to be zero by a table
index for fast lookups of SAs. But this conflicts with the second use
of the cookies.

Unlike ESP version 2.0 implementation and AH where only the recipient's SA identifier appears in
the message, their content MUST be
ignored by a version 2.0 implementation ("Be conservative in IKE the sender's IKE SA identifier is also sent what you
send and liberal in
every message. what you receive"). In IKEv1 the IKE-SA identifier consisted this way, future versions
of the pair
(Initiator cookie, Responder cookie), whereas protocol can use those fields in IKEv2, the SA a way that is
uniquely defined guaranteed to
be ignored by the recipient's SA identifier even though both
are included in the implementations that do not understand them.
Similarly, payload types that are not defined are reserved for future
use and implementations of version 2.0 MUST skip over those payloads
and ignore their contents.

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IKEv2 adds a "critical" flag to each payload header for further
flexibility for forward compatibility. If the critical flag is state set
and CPU exhaustion, where the
target payload type is flooded with session initiation requests from forged IP
addresses. This attack can be made less effective if an
implementation of a responder uses minimal CPU and commits no state
to a connection until it has received unrecognised, the third message of MUST be rejected
and the
protocol. That third message repeats information from response to the second
message, and hence proves IKE request containing that payload MUST
include a notify payload UNSUPPORTED-CRITICAL-PAYLOAD, indicating an
unsupported critical payload was included. If the initiator can receive packets at
the address it claims to be sending from.

Since all of critical flag is
not set and the information from message 1 payload type is repeated unsupported, that payload MUST be
ignored.

While new payload types may be added in message 3, the responder need not store any of that information. What future and may appear
interleaved with the
responder must be able to do is: (1) assure itself that fields defined in this specification,
implementations MUST send the Nr
returned payloads defined in message this specification
in order shown in section 3 is fresh and (2) assure that message 3 came
from the same IP address implementations SHOULD reject as
invalid a message 1. If the responder uses multiple
KEr's during the period of message 1 & 3, it must encode with payloads in message 2
some way to figure out which KEr applies to this exchange.

A good way to do this is to set any other order.

4.6 Cookies

The term "cookies" originates with Karn and Simpson [RFC 2522] in
Photuris, an early proposal for key management with IPsec. It has
persisted because the IKE-SA identifier to be:

SPIr = Hash(KEr | Nr | IPi | <secret>)

where <secret> is IETF has never rejected a randomly generated secret known only to the
responder and periodically changed. This value can be recomputed when proposal involving
cookies. The ISAKMP fixed message 3 arrives header includes two eight octet
fields titled "cookies", and compared to the SPIr in message 3. If it
matches, the responder knows that Nr was generated since the last
change to <secret> syntax is used by both IKEv1 and that IPi must be the same
IKEv2 though in IKEv2 they are referred to as the source
address it saw IKE SPI and there
is a new separate field in message 1.

To prevent replays of message 3 without remembering all a NOTIFY payload holding the Nr's that
were used, cookie. The
initial two eight octet fields in the responder must keep header are used as a list connection
identifier at the beginning of all IKE packets. Each endpoint chooses one
of the Nr's that
have been returned in a message 3 since <secret> was last changed.
If this list becomes long enough two SPIs and SHOULD choose them so as to be cumbersome, the responder can
change <secret> and forget all unique identifiers
of the used values.

If a new an IKE-SA. An SPI value for <secret> is chosen while there are connections in

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the process of being initialized, a message 3 might be returned where zero is special and indicates that the responder does
remote SPI value is not know which of its values for <secret> were
used in generating message 2. Using the formula above, yet known by the responder
could compute SPIr with each candidate <secret> sender.

Unlike ESP and accept message 3
if any of AH where only the values match. A similar situation occurs if recipient's SPI appears in the
responder uses multiple values
header of KEr. An alternative implementation
would be to take a few bits of SPIr as indices of <secret>s and KEr's
(where message, in IKE the rest of SPIr sender's SPI is computed as also sent in every
message. Since the above hash).

If SPI chosen by the responder wants to keep other forms original initiator of state without tying up
its memory, it can encode that state in the nonce. The nonce can be
up IKE-SA
is always sent first, an endpoint with multiple IKE-SAs open that
wants to 256 octets long, and find the protocol is secure so long as values
are not reused, so appropriate IKE-SA using the responder can put state there (possibly
encrypted) and be guaranteed that SPI it will come back with message 3.
For subtle cryptographic reasons, the nonce SHOULD contain some
random bits - assigned must
look at least as many random bits as the size of I(nitiator) Flag bit in the
strongest key be generated by header to determine whether
it assigned the exchange.

It may be convenient for first or the IKE-SA identifier to be an index into a
table. It is not difficult for second eight octets.

In the Initiator to choose first message of an IKE-SA
identifier that is convenient as a table identifier, since initial IKE exchange, the
Initiator does initiator will
not need to use it as an anti-clogging token, know the responder's SPI value and will therefore set that field
to zero.

An expected attack against IKE is
keeping state. IKEv2 allows state and CPU exhaustion, where the Responder to initially choose a
stateless anti-clogging type cookie by responding to an IKE_SA_init
target is flooded with session initiation requests from forged IP
addresses. This attack can be made less effective if an
implementation of a cookie request, responder uses minimal CPU and then upon receipt of commits no state
to an IKE_SA_init with a
valid cookie, change his cookie value from SA until it knows the computed anti-clogging
token initiator can receive packets at the
address from which he claims to a more convenient value, by be sending them. To accomplish this,

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a different value for
his responder SHOULD - when it detects a large number of half-open
IKE-SAs - reject initial IKE messages unless they contain a notify
payload of type "cookie". It SHOULD instead send an unprotected IKE
message as a response and include its cookie in the IKE_SA_auth_response. This will not confuse the
Initiator (Alice), because she will have chosen a unique cookie value
A, so if her SA state for notify payload.
Initiators who receive such responses MUST retry the partially set up IKE-SA says that Bob's
cookie for IKE_SA_INIT with
the SA that Alice knows responder supplied cookie as "A" is B, and she receives a
response from Bob with cookies (A,C), that means that Bob wants to
change his value from B to C for the SA that Alice knows uniquely first payload. The initial
exchange will then be as
"A".

Another reason why Bob might want to change his cookie value is that
it is possible (though unlikely) that Bob will choose the same cookie
for multiple SAs if the hash of the follows:

Initiator IP address, Responder
----------- -----------
HDR(A,0), SAi1, KEi, Ni -->

<-- HDR(A,0), N(COOKIE-REQUIRED),
N(COOKIE)

HDR(A,0), N(COOKIE), SAi1, KEi, Ni -->

<-- HDR(A,B), SAr1, KEr, Nr, and
whatever other information might be included happens to hash to [CERTREQ]

HDR(A,B), SK {IDi, [CERT,] [CERTREQ,] [IDr,]
AUTH, SAi2, TSi, TSr} -->

<-- HDR(A,B), SK {IDr, [CERT,] AUTH,
SAr2, TSi, TSr}

The first two messages do not affect any initiator or responder state
except for communicating the
same value. cookie. In IKEv2, like IKEv1, both 8-octet cookies appear in particular, the message, but message
sequence numbers in IKEv2 (unlike v1), the value chosen by first four messages will all be zero and the
message recipient
always appears first sequence numbers in the message. last two messages will be one.

An IKE implementation SHOULD implement its responder cookie
generation is such a way as to not require any saved state to
recognise its valid cookie when the second IKE_SA_INIT message
arrives. The exact algorithms and syntax they use to generate
cookies are one does not affect interoperability and hence is not specified
here. The following is an example of the inputs into the function that computes the
keying material. If how an endpoint could use
cookies to implement limited DOS protection.

A good way to do this is to set the responder changes its cookie to be:

Cookie = <SecretVersionNumber> | Hash(IPi | SPIi | <secret>)

where <secret> is a different randomly generated secret known only to the
responder and periodically changed. <SecretVersionNumber> should be
changed whenever <secret> is regenerated. This value can be
recomputed when it sends its IKE_AUTH_response, it is the IKE_SA_INIT arrives the second time and compared
to the cookie value in

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knows that SPIr was generated since the last change to <secret> and
that IPi must be the same as the source address it saw the first
time. Incorporating SPIi into the calculation assures that if
multiple IKE-SAs are being set up in parallel they will all get
different cookies (assuming the initiator chooses unique SPIi's).

If a new value for <secret> is chosen while there are connections in
the input process of being initialized, an IKE_SA_INIT might be returned
with other than the current <SecretVersionNumber>. The responder in
that case MAY reject the message by sending another response with a
new cookie or it MAY keep the old value of <secret> around for generating a
short time and accept cookies computed from either one. The
responder SHOULD NOT accept cookies indefinitely after <secret> is
changed, since that would defeat part of the keying
material. denial of service
protection.

4.7 Cryptographic Algorithm Negotiation

The payload type known as "SA" indicates a proposal for a set of
choices of protocols (IKE, ESP, AH, and/or IPcomp) AH) for the SA as well as
cryptographic algorithms associated with each protocol. In IKEv1
it was extremely complex, and was one of the motivations for revising
the spec.

An SA consists of one or more proposals. Each proposal includes a
Suite-ID, which implies one or more protocols and the associated
cryptographic algorithms.

In IKEv2, since the Initiator

Since Alice sends her Diffie-Hellman value in the
IKE_SA_init, IKE_SA_INIT, she
must guess at the Diffie-Hellman group that Bob will select from her
list of supported groups. Her guess MUST be the first
in the list to allow cryptographic suites. If she guesses wrong, Bob to unambiguously identify which group the
accompanying KE
will respond with a NOTIFY payload is from. If her guess is incorrect then Bob's
response informs her of type INVALID-KE-PAYLOAD
indicating the group he chose, and includes his KE from
his chosen group. selected cryptographic suite. In this case, Alice
MUST choose a KE from Bob's
chosen group, compute keys based on her and Bob's values and send retry the
new KE in message 3.

You might wonder why IKE_SA_INIT with the corrected Diffie-Hellman group.
Alice includes KE in MUST again propose her full set of acceptable cryptographic
suites because the first rejection message given
that Bob doesn't need it until message 3 was unauthenticated and it could change in
message 3. The reason is to allow
otherwise an optional optimization in Bob.
Bob MAY start his Diffie-Hellman computation as soon as he receives
message 1 and likely complete it by the time he receives message 3.
This will minimize latency of connection setup in the common case
where Alice correctly guesses the Diffie-Hellman group that Bob will
choose. If Bob accepts Alice's first choice of Diffie-Hellman group, active attacker could trick Alice MUST send the same value for KE in message 3 as she sent in
message 1.

Note that an implementation cannot simultaneously exploit this
optimization and protect itself from a denial of service attack using
cookies. But an implementation could alternate between the two based
on load.

If none of Alice's options are acceptable, then Bob notifies her
accordingly. into
negotiating a weaker suite than a stronger one that they both prefer.

4.8 Rekeying

Security associations negotiated in both phase 1

IKE, ESP, and phase 2 contain

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only be used for a limited amount of time and to protect a limited
amount of data. This determines limits the lifetime of the entire security
association. When the lifetime of a security association expires the
security association MUST NOT be used. If there is demand, new
security associations can MAY be established. Reestablishment of
security associations to take the place of ones which expire is
referred to as "rekeying".

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To rekey a child-SA, CHILD-SA, create a new, equivalent SA (see section 4.17
below), and when the new one is established, delete the old one. To
rekey an IKE-SA, establish a new equivalent IKE-SA (see section 4.18 4.20
below) with the peer to whom the old IKE-SA is shared using a Phase 2
negotiation within the existing IKE-SA. An IKE-SA so created inherits
all of the original IKE-SA's child SAs. CHILD-SAs. Use the new IKE-SA for all
control messages needed to maintain the child-SAs CHILD-SAs created by the old
IKE-SA, and delete the old IKE-SA. The Delete payload to delete
itself MUST be the last request sent over an IKE-SA.

SAs SHOULD be rekeyed proactively, i.e., the new SA should be
established before the old one expires and becomes unusable. Enough
time should elapse between the time the new SA is established and the
old one becomes unusable so that traffic can be switched over to the
new SA.

A difference between IKEv1 and IKEv2 is that in IKEv1 SA lifetimes
were negotiated. In IKEv2, each end of the SA is responsible for
enforcing its own lifetime policy on the SA and rekeying the SA when
necessary. If the two ends have different lifetime policies, the end
with the shorter lifetime will end up always being the one to request
the rekeying. If an SA bundle has been inactive for a long time and
if an endpoint would not initiate the SA in the absense of traffic,
the endpoint MAY choose to close the SA instead of rekeying it when
its lifetime expires. It SHOULD do so if there has been no traffic
since the last time the SA was rekeyed.

If the two ends have the same lifetime policies, it is possible that
both will initiate a rekeying at the same time (which will result in
redundant SAs). To reduce the probability of this happening, the
timing of rekeying requests should SHOULD be jittered (delayed by a random
amount of time). time after the need for rekeying is noticed).

This form of rekeying will may temporarily result in multiple similar SAs
between the same pairs of nodes. When there are two SAs eligible to
receive packets, a node MUST accept incoming packets through either
SA. The node that initiated the rekeying An endpoint SHOULD delete the older SA
after wait a random amount of time before closing a
redundant SA to prevent cycling.

The node that initiated the rekeyed SA SHOULD delete the replaced SA
after the new one is established.

4.9 Traffic Selector Negotiation

When an IP packet is received by an RFC2401 compliant IPsec subsystem
and matches a "protect" selector in its SPD, the subsystem MUST
protect that packet with IPsec. When no SA exists yet it is the task

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of IKE to create it. Information about the traffic that needs
protection is transmitted to the IKE subsystem in Maintenance of of a manner system's SPD is outside the

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scope of this document IKE (see [PFKEY] for an example). This
information is negotiated between example protocol), though some
implementations might update their SPD in connection with the two running
of IKE (for an example scenario, see section 3.1.3).

Traffic Selector (TS) payloads allow endpoints using to communicate some of
the information from their SPD to their peers. TS
(Traffic Selector) payloads. payloads specify
the selection criteria for packets that will be forwarded over the
newly set up SA. This can serve as a consistency check in some
scenarios to assure that the SPDs are consistent. In others, it
guides the dynamic update of the SPD.

Two TS payloads appear in each of the messages in the exchange that
creates a child-SA CHILD-SA pair. Each TS payload contains one or more Traffic
Selectors. Each Traffic Selector consists of an address range (IPv4
or IPv6), a port range, and a protocol ID.

IKEv2 is more flexible than IKEv1. IKEv2 allows sets of ranges In support of
both addresses and ports, the scenario
described in section 3.1.3, an initiator may request that the
responder assign an IP address and tell the initiator what it is.

IKEv2 allows the responder to choose a subset of the requested traffic rather than simply responding "not
acceptable". proposed
by the initiator. This could happen when the configuration of the
two endpoints are being updated but only one end has received the new
information. Since the two endpoints may be configured by different
people, the incompatibility may persist for an extended period even
in the absense of errors. It also allows for intentionally different
configurations, as when one end is configured to tunnel all addresses
and depends on the other end to have the up to date list.

The first of the two TS payloads is known as TSi (Traffic Selector-
initiator). The second is known as TSr (Traffic Selector-responder).
TSi specifies the source address of traffic forwarded from (or the
destination address of traffic forwarded to) the initiator of the
child-SA
CHILD-SA pair. TSr specifies the destination address of the traffic
forwarded from (or the source address of the traffic forwarded to)
the responder of the child-SA CHILD-SA pair. For example, if Alice initiates
the creation of the child-SA CHILD-SA pair from Alice to Bob, and wishes to
tunnel all traffic from subnet 10.2.16.* on Alice's side to subnet
18.16.*.* on Bob's side, Alice would include a single traffic
selector in each TS payload. TSi would specify the address range
(10.2.16.0 - 10.2.16.255) and TSr would specify the address range
(18.16.0.0 - 18.16.255.255). Assuming that proposal was acceptable to
Bob, he would send identical TS payloads back.

The Responder is allowed to narrow the choices by selecting a subset
of the traffic, for instance by eliminating or narrowing the range of
one or more members of the set of traffic selectors, provided the set
does not become the NULL set.

It is possible for the Responder's policy to contain multiple smaller

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ranges, all encompassed by the Initiator's traffic selector, and with
the Responder's policy being that each of those ranges should be sent
over a different SA. Continuing the example above, Bob might have a
policy of being willing to tunnel those addresses to and from Alice,
but might require that each address pair be on a separately

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negotiated child-SA. CHILD-SA. If Alice generated her request in response to an
incoming packet from 10.2.16.43 to 18.16.2.123, there would be no way
for Bob to determine which pair of addresses it is most urgent to should be included in
this tunnel, and he would have to make his best guess or reject the
request with a status of SINGLE-PAIR-REQUIRED.

To enable Bob to choose the appropriate range in this case, if Alice
has initiated the SA due to a data packet, Alice MAY include as the
first traffic selector in each of TSi and TSr a very specific traffic
selector including the addresses in the packet triggering the
request. In the example, Alice would include in TSi two traffic
selectors: the first containing the address range (10.2.16.43 -
10.2.16.43) and the source port and protocol from the packet and the
second containing (10.2.16.0 - 10.2.16.255) with all ports and
protocols. She would similarly include two traffic selectors in TSr.

If Bob's policy does not allow him to accept the entire set of
traffic selectors in Alice's request, but does allow him to accept
the first selector of TSi and TSr, then Bob MUST narrow the traffic
selectors to a subset that includes Alice's first choices. In this
example, Bob might respond with TSi being (10.2.16.43 - 10.2.16.43)
with all ports and protocols.

If Alice creates the child-SA CHILD-SA pair not in response to an arriving
packet, but rather - say - upon startup, then there may be no
specific data packet to describe. addresses Alice prefers for the initial tunnel over any
other. In that case, the first values in TSi and TSr are MAY be ranges
rather than specific values, and Bob chooses a subset of Alice's TSi
and TSr that are acceptable to him. If more than one subset is
acceptable but their union is not, Bob MUST accept some subset and
MAY include a NOTIFY payload of type ADDITIONAL-TS-
POSSIBLE ADDITIONAL-TS-POSSIBLE to
indicate that Alice might want to try again. This case will only
occur when Alice and Bob are configured differently from one another.
If Alice and Bob agree on the granularity of tunnels, she will never
request a tunnel wider than Bob will accept.

4.10 Nonces

The IKE_SA_init and the IKE_SA_init_response IKE_SA_INIT messages each contain a nonce. These nonces are used
as inputs to cryptographic functions. The CREATE_CHILD_SA request
and the CREATE_CHILD_SA response also contain nonces. These nonces
are used to add freshness to the key derivation technique used to
obtain keys for child SAs. CHILD-SAs. Nonces used in IKEv2 MUST therefore be unique (either deterministically by use of
timestamps

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randomly chosen and sequence numbers or probabilistically by use of a
strong pseudo-random number generator). size at least equal to the key size of the
strongest cryptographic algorithm used.

4.11 Address and Port Agility

IKE runs over UDP port 500, ports 500 and 4500, and implicitly sets up ESP, AH, ESP and
IPcomp
AH associations for the same IP addresses it runs over. The IP
addresses and ports in the outer header are, however, not themselves

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cryptographically protected, and IKE is designed to work even through
Network Address Translation (NAT) boxes. An implementation MUST
accept incoming connection requests even if not received from UDP
port 500, 500 or 4500, and should MUST respond to the address and port from which
the request was received. An implementation MUST, however, accept
incoming requests only on UDP port 500 and send all responses from
UDP port 500. IKE functions identically over IPv4 or
IPv6.

4.12 Reuse of Diffie-Hellman Exponentials

IKE generates keying material using an ephemeral Diffie-Hellman
exchange in order to gain the property of "perfect forward secrecy".
This means that once a connection is closed and its corresponding
keys are forgotten, even someone who has recorded all of the data
from the connection and gets access to all of the long term keys of
the two endpoints cannot reconstruct the keys used to protect the
conversation.

Achieving perfect forward secrecy requires that when a connection is
closed, each endpoint must forget not only the keys used by the
connection but any information that could be used to recompute those
keys. In particular, it must forget the secrets used in the Diffie-
Hellman calculation and any state that may persist in the state of a
pseudo-random number generater that could be used to recompute the
Diffie-Hellman secrets.

Since the computing of Diffie-Hellman exponentials is computationally
expensive, an endpoint may find it advantageous to reuse those
exponentials for multiple connection setups. There are several
reasonable strategies for doing this. An endpoint could choose a new
exponential only periodically though this could result in less-than-
perfect forward secrecy if some connection lasts for less than the
lifetime of the exponential. Or it could keep track of which
exponential was used for each connection and delete the information
associated with the exponential only when some corresponding
connection was closed. This would allow the exponential to be reused
without losing perfect forward secrecy at the cost of maintaining
more state.

Decisions as to whether and when to reuse Diffie-Hellman exponentials
is a private decision in the sense that it will not affect

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interoperability. An implementation that reuses exponentials may
choose to remember the exponential used by the other endpoint on past
exchanges and if one is reused to avoid the second half of the
calculation.

4.13 Generating Keying Material

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In the context of the IKE SA, IKE-SA, three cryptographic algorithms are
negotiated: an encryption algorithm, a Diffie-Hellman group, and a
pseudo-random function (prf). The pseudo-random function is used both
for integrity protection of the IKE payloads and for the construction
of keying material for all of the cryptographic algorithms used in
both the IKE SA IKE-SA and the Child-SAs. CHILD-SAs.

We assume that each cryptographic algorithm accepts a fixed size key,
and that any randomly chosen value of that fixed size can serve as an
appropriate key. For functions that accept a variable length key, a
fixed key size MUST be specified as part of the cryptographic suite
negotiated. For prf functions based on HMAC, the fixed key size is
the size of the output of the HMAC.

Keying material will always be derived as the output of the
negotiated prf algorithm. If Since the amount of keying material is needed
may be greater than the size of the output of the prf algorithm, we
will use the prf iteratively. We will use the terminology prf+ to
describe the function that outputs a pseudo-random stream based on
the inputs to a prf as follows: (where | indicates concatenation)

prf+ (K,S) = T1 | T2 | T3 | T4 | ...

where:
T1 = prf (K, S | 0x01)
T2 = prf (K, T1 | S | 0x02)
T3 = prf (K, T2 | S | 0x03)
T4 = prf (K, T3 | S | 0x04)

as needed to compute all required keys. The keys are taken from the
output string without regard to boundaries (e.g. if the required keys
are a 256 bit AES key and a 160 bit HMAC key, and the prf function
generates 160 bits, the AES key will come from T1 and the beginning
of T2, while the HMAC key will come from the rest of T2 and the
beginning of T3).

The constant concatenated to the end of each string feeding the prf
is a single octet. prf+ in this document is not defined beyond 255
times the size of the prf output.

4.14 Generating Keying Material for the IKE-SA

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The shared keys are computed as follows. A quantity called SKEYSEED
is calculated from the nonces exchanged during the IKE_SA_init IKE_SA_INIT
exchange and the Diffie-Hellman shared secret established during that
exchange. SKEYSEED is used to calculate three five other secrets: SK_d
used for deriving new keys for the child-SAs CHILD-SAs established with this
IKE-SA; SK_a SK_ai and SK_ar used as a key to the prf algorithm for
authenticating

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SK_ei and SK_er used for encrypting (and of course decrypting) all
subsequent exchanges. SKEYSEED and its derivatives are computed as
follows:

SKEYSEED = prf(Ni | Nr, g^ir)

{SK_d, SK_ai, SK_ar, SK_ei, SK_er}
= prf+ (SKEYSEED, g^ir | Ni | Nr | CKY-I | CKY-R)

(indicating that the quantities SK_d, SK_ai, SK_ar, SK_ei, and SK_er
are taken in order from the generated bits of the prf+). g^ir is the
shared secret from the ephemeral Diffie-Hellman exchange. Ni and Nr
are the nonces, stripped of any headers.

The two directions of flow use different keys. The keys used to
protect messages from the original initiator are SK_ai and SK_ei. The
keys used to protect messages in the other direction are SK_ar and
SK_er. Each algorithm takes a fixed number of bits of keying
material, which is specified as part of the algorithm. For integrity
algorithms based on HMAC, the key size is always equal to the length
of the underlying hash function.

4.15 Authentication of the IKE-SA

The peers are authenticated by having each sign (or MAC using a
shared secret as the key) a block of data. For the responder, the
octets to be signed start with the first octet of the first SPI in
the header of the second message and end with the last octet of the
last payload in the second message. Appended to this (for purposes
of computing the signature) is the initiator's nonce Ni (just the
value, not the payload containing it). The Similarly, the initiator
signs the unencrypted part of
message 3, first message, starting with the first octet of the IKE first
SPI in the header and ending with the last octet of the last unencrypted payload. Note that
message 3 includes Nr, so it does not need to be appended in order
Appended to
be included under this (for purposes of computing the signature) is the signature.
responder's nonce Nr. It is critical to the security of the exchange
that each side sign the other side's nonce.

Note that all of the payloads are included under the signature,
including any payload types not defined in this document. If the
first message of the exchange is sent twice (the second time with a
responder cookie and/or a different Diffie-Hellman group), it is the

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second version of the message that is signed.

Optionally, messages 3 and 4 MAY include a certificate, or
certificate chain providing evidence that the key used to compute a
digital signature belongs to the name in the ID payload. The
signature or MAC will be computed using algorithms dictated by the
type of key used by the signer, an RSA-signed PKCS1-padded-hash for
an RSA digital signature, a DSS-signed SHA1-hash for a DSA digital
signature, or the negotiated PRF function for a pre-shared key.
There is no requirement that the Initiator and Responder sign with
the same cryptographic algorithms. The choice of cryptographic
algorithms depends on the type of key each has. This type is either
indicated in the certificate supplied or, if the keys were exchanged

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out of band, the key types must have been similarly learned. In
particular, the initiator may be using a shared key while the
responder may have a public signature key and certificate. It will
commonly be the case (but it is not required) that if a shared secret
is used for authentication that the same key is used in both
directions. In particular, the initiator may be using a shared key
while the responder may have a public signature key and certificate. Note that it is a common but insecure practice to have a
shared key derived from a user chosen password. This is insecure
because user chosen passwords are unlikely to have sufficient
randomness to resist dictionary attacks. The pre-shared key SHOULD
contain as much randomness as the strongest key being negotiated. In
the case of a pre-shared key, the AUTH value is computed as:

AUTH = prf(Shared Secret | "Key Pad for IKEv2", <message bytes>)

where the string "Key Pad for IKEv2" is ASCII encoded and not null
terminated. The shared secret can be variable length. The pad string
is added so that if the shared secret is derived from a password,
this exchange will not compromise use of the same password in other
protocols.

Note that the requirement that the responder sign the content of
message 2 in message 4 introduces some special challenges when As noted above, deriving the
responder shared secret from a
password is not maintaining state between messages 2 and 4 (see
Section 4.6). Either the responder must be able to regenerate message
2 octet for octet from the information in message 3, or secure. This construction is used because it must
encode in its nonce enough information to be able to construct the
signature on message 2 after message 3 is returned.
anticipated that people will do it anyway.

4.16 Generating Keying Material for CHILD-SAs

Child-SAs

CHILD-SAs are created either by being piggybacked on the phase 1
exchange, or in a phase 2 CREATE_CHILD_SA exchange. Keying material
for them is generated as follows:

KEYMAT = prf+(SK_d, Ni | Nr)

Where Ni and Nr are the Nonces from the IKE_init IKE_SA_INIT exchange if this
request is the first CHILD-SA created or the fresh Ni and Nr from the
CREATE_CHILD_SA exchange if this is a subsequent creation.

For phase 2 exchanges with PFS the keying material is defined as:

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KEYMAT = prf+(SK_d, g^ir (ph2) | Ni | Nr )

where g^ir (ph2) is the shared secret from the ephemeral Diffie-
Hellman exchange of this phase 2 exchange,

A single child-SA CHILD-SA negotiation may result in multiple security
associations. ESP, AH, ESP and IPcomp AH SAs exist in pairs (one in each

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and six four SAs could be created in a single child-SA CHILD-SA negotiation if a
combination of ESP, AH, ESP and IPcomp AH is being negotiated. KEYMAT is generated
as described in section 4.13.

Keying material is taken from the expanded KEYMAT in the following
order:

All keys for SAs carrying data from the initiator to the responder
are taken before SAs going in the reverse direction.

If multiple protocols are negotiated, keying material is taken in
the order in which the protocol headers will appear in the
encapsulated packet.

If a single protocol has both encryption and authentication keys,
the encryption key is taken from the first octets of KEYMAT and
the authentication key is taken from the next octets.

Each cryptographic algorithm takes a fixed number of bits of keying
material specified as part of the algorithm.

4.17 Rekeying IKE-SAs using a CREATE_CHILD_SA exchange

The CREATE_CHILD_SA exchange can be used to re-key an existing IKE-SA
(see section 4.8). New Initiator and Responder cookies SPIs are supplied in
the SPI fields. The TS payloads are omitted when rekeying an IKE-
SA. IKE-SA.
SKEYSEED for the new IKE-SA is computed using SK_d from the existing
IKE-SA as follows:

SKEYSEED = prf(SK_d (old), [g^ir (ph2)] | Ni | Nr)

where g^ir (ph2) is the shared secret from the ephemeral Diffie-
Hellman exchange of this phase 2 exchange and Ni and Nr are the two
nonces stripped of any headers.

The new IKE SA IKE-SA MUST reset its message counters to 0.

SK_d, SK_ai, SK_ar, and SK_ei, and SK_er are computed from SKEYSEED
as specified in section 4.14.

4.18 Error Handling

There are many kinds of errors that can occur during IKE processing.
If a request is received that is badly formatted or unacceptable for
reasons of policy (e.g. no matching cryptographic algorithms), the
response MUST contain a Notify payload indicating the error. If an
error occurs outside the context of Requesting an IKE request (e.g. the node is
getting ESP messages internal address on a non-existent SPI), the node SHOULD initiate remote network

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Most commonly in the endpoint to gateway scenario, an Informational Exchange with a Notify payload describing endpoint may
need an IP address on the
problem.

Errors gateway's internal network, and may need to
have that occur before address dynamically assigned. A request for such a cryptographically protected IKE-SA is
established must be handled very carefully. There is a trade-off
between wanting to
temporary address can be helpful included in diagnosing a problem and responding
to it and wanting any request to avoid being create a dupe CHILD-SA
(including the implicit request in message 3) by including a denial of service attack
based on forged messages.

If a node receives CP
payload.

This function provides address allocation to an IRAC trying to tunnel
into a message on UDP port 500 outside network protected by an IRAS. Since the context of IKE_SA_AUTH exchange
creates an IKE-SA (and not and a CHILD-SA the IRAC MUST request to start one), it the internal
address, and optionally other information concerning the internal
network, in the IKE_SA_AUTH exchange. The may be IRAS procure an
internal address for the result IRAC from any number of a
recent crash. If the message is marked sources such as a response, the node
DHCP/BOOTP server or its own address pool.

Initiator Responder
----------------------------- ---------------------------
HDR, SAi1, KEi, Ni, Nr,
SK {IDi, [CERT,] [CERTREQ,]
[IDr,] AUTH, CP(CFG_REQUEST),
SAi2, TSi, TSr} -->

<-- HDR, SK {IDr, [CERT,] AUTH,
CP(CFG_REPLY), SAr2,
TSi, TSr}

CP(CFG_REQUEST) MUST contain at least an INTERNAL_ADDRESS attribute
(either IPv4 or IPv6) but MAY
audit contain any number of additional
attributes the suspicious event but MUST NOT respond. If initiator wants returned in the response.

For example, message is
marked as from Initiator to Responder:
CP(CFG_REQUEST)=
INTERNAL_ADDRESS(0.0.0.0)
INTERNAL_NETMASK(0.0.0.0)
INTERNAL_DNS(0.0.0.0)
TSi = (0, 0-65536,0.0.0.0-255.255.255.255)
TSr = (0, 0-65536,0.0.0.0-255.255.255.255)

NOTE: Traffic Selectors are a request, (protocol, port range, address range)

Message from Responder to Initiator:

CP(CFG_REPLY)=
INTERNAL_ADDRESS(192.168.219.202)
INTERNAL_NETMASK(255.255.255.0)
INTERNAL_SUBNET(192.168.219.0/255.255.255.0)
TSi = (0, 0-65536,192.168.219.202-192.168.219.202)
TSr = (0, 0-65536,192.168.219.0-192.168.219.255)

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All returned values will be implementation dependent. As can be seen
in the node MAY audit above example, the suspicious event and IRAS MAY also send a response. If a response is sent, other attributes that
were not included in CP(CFG_REQUEST) and MAY ignore the response MUST be sent to
the IP address and port from whence non-
mandatory attributes that it came with does not support.

4.19 Requesting the Peer's Version

An IKE cookies
reversed in peer wishing to inquire about the header other peer's version
information MUST use the method below. This is an example of a
configuration request within an Informational Exchange, after the
IKE-SA and first CHILD-SA have been created.

An IKE implementation MAY decline to give out version information
prior to authentication or even after authentication to prevent
trolling in case some implementation is known to have some security
weakness. In that case, it MUST return an empty string.

Initiator Responder
----------------------------- --------------------------
HDR, SK{CP(CFG_REQUEST)} -->
<-- HDR, SK{CP(CFG_REPLY)}

CP(CFG_REQUEST)=
APPLICATION_VERSION("")

CP(CFG_REPLY)
APPLICATION_VERSION("foobar v1.3beta, (c) Foo Bar Inc.")

4.20 Error Handling

There are many kinds of errors that can occur during IKE processing.
If a request is received that is badly formatted or unacceptable for
reasons of policy (e.g. no matching cryptographic algorithms), the Message ID copied. The
response MUST
NOT be cryptographically protected and MUST contain a notify Notify payload indicating INVALID-COOKIE.

A node receiving such a message MUST NOT respond and MUST NOT change the state error. If an
error occurs outside the context of any existing SAs. The message might be a forgery or
might be an IKE request (e.g. the node is
getting ESP messages on a response non-existent SPI), the genuine correspondent was tricked into
sending. A node SHOULD treat such initiate
an Informational Exchange with a message (and also Notify payload describing the
problem.

Errors that occur before a network
message like ICMP destination unreachable) as cryptographically protected IKE-SA is
established must be handled very carefully. There is a hint that there might trade-off
between wanting to be problems with SAs helpful in diagnosing a problem and responding
to that IP address it and SHOULD wanting to avoid being a dupe in a denial of service attack
based on forged messages.

If a node receives a message on UDP port 500 outside the context of
an IKE-SA known to it (and not a request to start one), it may be the
result of a recent crash of the node. If the message is marked as a

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response, the node MAY audit the suspicious event but MUST NOT
respond. If the message is marked as a request, the node MAY audit
the suspicious event and MAY send a response. If a response is sent,
the response MUST be sent to the IP address and port from whence it
came with the same IKE SPIs and the Message ID copied. The response
MUST NOT be cryptographically protected and MUST contain a notify
payload indicating INVALID-SPI.

A node receiving such an unprotected NOTIFY payload MUST NOT respond
and MUST NOT change the state of any existing SAs. The message might
be a forgery or might be a response the genuine correspondent was
tricked into sending. A node SHOULD treat such a message (and also a
network message like ICMP destination unreachable) as a hint that
there might be problems with SAs to that IP address and SHOULD
initiate a liveness test for any such IKE-SA. An implementation
SHOULD limit the frequency of such tests to avoid being tricked into
participating in a denial of service attack.

A node receiving a suspicious message from an IP address with which
it has an IKE-SA MAY send an IKE notify payload in an IKE
Informational exchange over that SA. The recipient MUST NOT change
the state of any SA's as a result but SHOULD audit the event to aid
in diagnosing malfunctions. A node MUST limit the rate at which it
will send messages in response to unprotected messages.

5 Header and Payload Formats

5.1 The IKE Header

IKE messages use UDP port 500, with one IKE message per UDP datagram.
Information from

4.21 IPcomp

Use of IP compression [IPCOMP] can be negotiated as part of the UDP setup
of a CHILD-SA. While IP compression involves an extra header is largely ignored except in each
packet and a CPI (compression parameter index), the virtual
"compression association" has no life outside the ESP or AH SA that
contains it. Compression associations disappear when the IP
addresses
corresponding ESP or AH SA goes away, and UDP ports is not explicitly mentioned
in any DELETE payload.

Negotiation of IP compression is separate from the headers are reversed and used for
return packets. Each IKE message begins negotiation of
cryptographic parameters associated with the IKE header, denoted
HDR in this memo. Following the header are a CHILD-SA. A node
requesting a CHILD-SA MAY advertise its support for one or more IKE
compression algorithms though one or more NOTIFY payloads
each identified by of type
IPCOMP_SUPPORTED. The response MAY indicate acceptance of a "Next Payload" field single
compression algorithm with a NOTIFY payload of type IPCOMP_SUPPORTED.
These payloads MAY ONLY occur in the preceding payload.
Payloads are processed in same messages that contain SA
payloads.

While there has been discussion of allowing multiple compression
algorithms to be accepted and to have different compression
algorithms available for the order in which they appear in two directions of a CHILD-SA,
implementations of this specification MUST NOT accept an IKE IPcomp

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message by invoking the appropriate processing routine according to
the "Next Payload" field in the IKE header January 2003

algorithm that was not proposed, MUST NOT accept more than one, and subsequently according
to the "Next Payload" field
MUST NOT compress using an algorithm other than one proposed and
accepted in the IKE payload itself until a "Next
Payload" field setup of zero indicates that no payloads follow. If a
payload the CHILD-SA.

A side effect of type "Encrypted" separating the negotiation of IPcomp from
cryptographic parameters is found, that payload it is decrypted not possible to propose
multiple cryptographic suites and
its contents parsed as additional payloads. An propose IP compression with some of
them but not others.

5 Header and Payload Formats

5.1 The IKE Header

IKE messages use UDP ports 500 and/or 4500, with one IKE message per
UDP datagram. Information from the UDP header is largely ignored
except that the IP addresses and UDP ports from the headers are
reversed and used for return packets. When sent of UDP port 500, IKE
messages begin immediately following the UDP header. When sent on UDP
port 4500, IKE messages have prepended for octets of zero. These
four octets of zero are not part of the IKE message and are not
included in any of the length fields or checksums defined by IKE.
Each IKE message begins with the IKE header, denoted HDR in this
memo. Following the header are one or more IKE payloads each
identified by a "Next Payload" field in the preceding payload.
Payloads are processed in the order in which they appear in an IKE
message by invoking the appropriate processing routine according to
the "Next Payload" field in the IKE header and subsequently according
to the "Next Payload" field in the IKE payload itself until a "Next
Payload" field of zero indicates that no payloads follow. If a
payload of type "Encrypted" is found, that payload is decrypted and
its contents parsed as additional payloads. An Encrypted payload must MUST
be the last payload in a packet and an encrypted payload may not MUST NOT
contain another encrypted payload.

The Recipient SPI in the header identifies an instance of an IKE
security association. It is therefore possible for a single instance
of IKE to multiplex distinct sessions with multiple peers.

The format of the IKE header is shown in Figure 1.
1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Recipient IKE-SA Initiator's SPI !
! SPI (aka Cookie) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Sender IKE-SA Responder's SPI !
! SPI (aka Cookie) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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! Next Payload ! MjVer ! MnVer ! Exchange Type ! Flags !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Message ID !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: IKE Header Format

o Recipient Initiator's SPI (aka Cookie) (8 octets) - A value chosen by the
recipient
initiator to identify a unique IKE security association. For
the first packet of an IKE_SA_init, this This
value MUST be zero.
It MUST NOT be zero for any other packet.
[NOTE: this is a deviation from ISAKMP and IKEv1, where the
cookies were always sent with the Initiator of the IKE-SA's
cookie first and the Responder's second. See section 3.6.] zero.

o Sender Responder's SPI (aka Cookie) (8 octets) - A value chosen by the
sender
responder to identify a unique IKE security association. This
value MUST be zero in the first message of an IKE Initial
Exchange and MUST NOT be zero. zero in any other message.

o Next Payload (1 octet) - Indicates the type of payload that
immediately follows the header. The format and value of each
payload is defined below.

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o Major Version (4 bits) - indicates the major version of the IKE
protocol in use. Implementations based on this version of IKE
MUST set the Major Version to 2. Implementations based on
previous versions of IKE and ISAKMP MUST set the Major Version
to 1. Implementations based on this version of IKE MUST reject
(or ignore) messages containing a version number greater than
2.

o Minor Version (4 bits) - indicates the minor version of the
IKE protocol in use. Implementations based on this version of
IKE MUST set the Minor Version to 0. They MUST ignore the minor
version number of received messages.

o Exchange Type (1 octet) - indicates the type of exchange being
used. This dictates the payloads sent in each message and
message orderings in the exchanges.

Exchange Type Value

RESERVED 0
Reserved for ISAKMP 1 - 31 1-31
Reserved for IKEv1 32 - 33
IKE_SA_init 32-33
IKE_SA_INIT 34
IKE_SA_AUTH 35
CREATE_CHILD_SA 36
Informational 37

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Reserved for IKEv2+ 38-239
Reserved for private use 240-255

o Flags (1 octet) - indicates specific options that are set
for the message. Presence of options are indicated by the
appropriate bit in the flags field being set. The bits are
defined LSB first, so bit 0 would be the least significant
bit of the Flags octet. In the description below, a bit
being 'set' means its value is '1', while 'cleared' means
its value is '0'.

-- R(eserved) (bits 0-2) - These bits MUST be cleared
when sending and MUST be ignored on receipt.

-- I(nitiator) (bit 3 of Flags) - This bit MUST be set in
messages sent by the original Initiator of the IKE SA IKE-SA
and MUST be cleared in messages sent by the original
Responder. It is used by the recipient to determine
whether the message ID should be interpreted
in the context of its initiating state is a request or its responding
state.

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-- V(ersion) (bit 4 of Flags) - This bit indicates that
the transmitter is capable of speaking a higher major
version number of the protocol than the one indicated
in the major version number field. Implementations of
IKEv2 must clear this bit when sending and MUST ignore
it in incoming messages.

-- R(eserved) (bits 5-7 of Flags) - These bits MUST be
cleared when sending and MUST be ignored on receipt.

o Message ID (4 octets) - Message identifier used to control
retransmission of lost packets and matching of requests and
responses. See section 4.2. In the first message of a Phase 1
negotiation, the value MUST be set to 0. The response to that
message MUST also have a Message ID of 0.

o Length (4 octets) - Length of total message (header + payloads)
in octets. Session encryption can expand the size of an IKE
message and that is reflected in the total length of the
message.

5.2 Generic Payload Header

Each IKE payload defined in sections 5.3 through 5.14 begins with a
generic header, shown in Figure 2. Figures for each payload below
will include the generic payload header but for brevity the
description of each field will be omitted. The construction and
processing of the generic payload header is identical for each

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payload and will similarly be omitted.

Figure 2: Generic Payload Header

The Generic Payload Header fields are defined as follows:

o Next Payload (1 octet) - Identifier for the payload type of the
next payload in the message. If the current payload is the last
in the message, then this field will be 0. This field provides
a "chaining" capability whereby additional payloads can be
added to a message by appending it to the end of the message
and setting the "Next Payload" field of the preceding payload
to indicate the new payload's type. For an Encrypted payload,
which must always be the last payload of a message, the Next

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Payload field is set to the payload type of the first contained
payload.

o Critical (1 bit) - MUST be set to zero if the sender wants
the recipient to skip this payload if he does not
understand the payload type code. code in the Next Payload field
of the previous payload. MUST be set to one if the
sender wants the recipient to reject this entire message
if he does not understand this the payload type. MUST be ignored
by the recipient if the recipient understands the payload type
code. SHOULD be set to zero for payload types defined in this
document. Note that the critical bit applies to the current
payload rather than the "next" payload whose type code
appears in the first octet. The reasoning behind not setting
the critical bit for payloads defined in this document is
that all implementations MUST understand all payload types
defined in this document and therefore must ignore the
Critical bit's value. Skipped payloads are expected to
have valid Next Payload and Payload Length fields.

o RESERVED (7 bits) - MUST be sent as zero; MUST be ignored.

o Payload Length (2 octets) - Length in octets of the current
payload, including the generic payload header.

5.3 Security Association Payload

The Security Association Payload, denoted SA in this memo, is used to

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negotiate attributes of a security association. An SA may contain
multiple proposals. Each proposal may propose multiple protocols
(where a protocol is IKE, ESP, AH, or IPcomp), AH), along with a suite of
cryptographic algorithms to be used by the protocols. The
protocol(s), cryptographic algorithms, and any associated parameters
are determined by the suite number. An SA payload MAY contain
proposals for different protocols. For example, one suite might
contain AH, ESP, AH and IPcomp, ESP, while another might contain only ESP and a third ESP and IPcomp.
only AH.

The Proposal structure contains within it a Proposal # and a Suite-
ID. The first proposal MUST have Proposal # = 1, the second MUST
have Proposal # = 2, etc. If the proposals are misnumbered, the
responder MUST reject all of them. Unrecognised Suite-IDs MUST be
ignored.

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! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: Security Association Payload

o Proposals (variable) - one or more proposal substructures.

The payload type for the Security Association Payload is one (1).

5.3.1 Proposal Substructure

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! 0 (last) or 2 ! RESERVED ! Proposal Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Proposal # ! RESERVED-MBZ ! Suite-ID !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ SPI(S) (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: Proposal Substructure

o 0 (last) or 2 (more) (1 octet) - Specifies whether this is the
last Proposal Substructure in the SA. This syntax is inherited

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from ISAKMP, but is unnecessary because the last Proposal
could be identified from the length of the SA. The value (2)
corresponds to a Payload Type of Proposal, and the first
four octets of the Proposal structure are designed to look
somewhat like the header of a Payload.

o RESERVED (1 octet) - MUST be sent as zero; MUST be ignored.

o Proposal Length (2 octets) - Length of this proposal,
including the SPI

o Proposal # (1 octet) - When In an SA payload requesting a proposal new
SA is made, the sent, it may contain multiple proposals. The first
proposal in an SA MUST be #1, and subsequent proposals
MUST be one greater than the previous proposal. When a
proposal an
SA is accepted, the SA payload sent back MUST contain a
single proposal and the proposal number MUST match the accepted proposal
from
number in the Initiator. accepted proposal.

o RESERVED-MBZ (1 octet) - This field is reserved for
possible use in specifying different kinds of proposals.
This field MUST be sent as zero and a proposal containing
a non-zero value MUST NOT be accepted.

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MAY still succeed if there is another acceptable
proposal in the SA payload.

o Suite-ID (2 octets) - This field specifies a suite of
protocols and cryptographic algorithms. See table below.

o SPI(S) (variable) - The sending entity's SPI(s). If the
suite proposed includes more than one protocol, the SPIs
are concatenated together in the order in which they would
appear in a packet sent using the suite (i.e. AH followed
by ESP followed by IPcomp. ESP). When an initial IKE SA IKE-SA is being
proposed, SPIs are implicit from the IKE header and are not
repeated here. Even if the SPI
Size is not a multiple of 4 octets, there is Note that no padding
applied to the payload. When the SPI Size field is zero,
this field is not present in the Security Association
payload. applied.

For Suite-ID, the following values are defined:

Name Number Algorithms
IKE_CLASSIC 0 DH-Group #5 (1536 bits)
3DES encryption
HMAC-SHA1 integrity and prf

ESP_CLASSIC 1 3DES encryption
HMAC-SHA1 integrity

<some AES

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<some AES variants, ESP+IPcomp, AH (?))

values 2-65000 are reserved to IANA. Values 65501-65533 65001-65533 are
for private use among mutually consenting parties.

5.4 Key Exchange Payload

The Key Exchange Payload, denoted KE in this memo, is used to
exchange Diffie-Hellman public numbers as part of a Diffie-Hellman
key exchange. The Key Exchange Payload consists of the IKE generic
header followed by the Diffie-Hellman public value itself.

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Suite-ID ! RESERVED (MBZ) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Key Exchange Data ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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Figure 7: Key Exchange Payload Format

A key exchange payload is constructed by copying one's ones Diffie-Hellman
public value into the "Key Exchange Data" portion of the payload.
The length of the Diffie-Hellman public value MUST be equal to the
length of the prime modulus over which the exponentiation was
performed, prepending zero bits to the value if necessary.

A key exchange payload is processed by first checking whether the
length of the key exchange data (the "Payload Length" from the
generic header minus the size of the generic header) is equal to the
length of the prime modulus over which the exponentiation was
performed. The message should be treated as invalid if the payload is
not the expected size.

The Suite-ID is the identifier of the cryptographic suite from which
the Diffie-Hellman group was taken. If the selected proposal uses a
different Diffie-Hellman group, the message MUST be rejected with a
Notify payload of type INVALID-KE-PAYLOAD.

The payload type for the Key Exchange payload is four (4).

5.5 Identification Payload

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The Identification Payload, denoted ID in this memo, allows peers to
assert an identify themselves to each other. In Phase 1, the one another. The ID Payload names the identity
to be authenticated with the signature. In Phase 2, the
ID Payload is optional and if present names an identity asserted to
be responsible for this SA. An example use would be a shared computer
opening an IKE-SA to a server and asserting the name of its logged in
user for the Phase 2 SA. If missing, this defaults to the Phase 1
identity. AUTH payload.

NOTE: In IKEv1, two ID payloads were used in each direction in Phase
2 to hold Traffic Selector information for data passing over the SA.
In IKEv2, this information is carried in Traffic Selector (TS)
payloads (see section 5.13).

The Identification Payload consists of the IKE generic header
followed by identification fields as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! ID Type ! RESERVED |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Identification Data ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 8: Identification Payload Format

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o ID Type (1 octet) - Specifies the type of Identification being
used.

o RESERVED - MUST be sent as zero; MUST be ignored.

o Identification Data (variable length) - Value, as indicated by
the Identification Type. The length of the Identification Data
is computed from the size in the ID payload header.

The payload type for the Identification Payload is five (5).

The following table lists the assigned values for the Identification
Type field, followed by a description of the Identification Data
which follows:

ID Type Value
------- -----
RESERVED 0

ID_IPV4_ADDR 1

A single four (4) octet IPv4 address.

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ID_FQDN 2

A fully-qualified domain name string. An example of a
ID_FQDN is, "lounge.org". The string MUST not contain any
terminators (e.g. NULL, CR, etc.).

ID_RFC822_ADDR 3

A fully-qualified RFC822 email address string, An example of
a ID_RFC822_ADDR is, "lizard@lounge.org". The string MUST
not contain any terminators.

ID_IPV6_ADDR 5

A single sixteen (16) octet IPv6 address.

ID_DER_ASN1_DN 9

The binary DER encoding of an ASN.1 X.500 Distinguished Name
[X.501].

ID_DER_ASN1_GN 10

The binary DER encoding of an ASN.1 X.500 GeneralName
[X.509].

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ID_KEY_ID 11

An opaque octet stream which may be used to pass vendor-
specific information necessary to do certain proprietary
forms of identification.

5.6 Certificate Payload

The Certificate Payload, denoted CERT in this memo, provides a means
to transport certificates or other certificate-related information
via IKE. Certificate payloads SHOULD be included in an exchange if
certificates are available to the sender.

The Certificate Payload is defined as follows:

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! Cert Encoding ! !
+-+-+-+-+-+-+-+-+ !
~ Certificate Data ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 9: Certificate Payload Format

o Certificate Encoding (1 octet) - This field indicates the type
of certificate or certificate-related information contained
in the Certificate Data field.

Certificate Encoding Value
-------------------- -----
NONE 0
PKCS #7 wrapped X.509 certificate 1
PGP Certificate 2
DNS Signed Key 3
X.509 Certificate - Signature 4
Kerberos Token 6
Certificate Revocation List (CRL) 7
Authority Revocation List (ARL) 8
SPKI Certificate 9
X.509 Certificate - Attribute 10
RESERVED 11 - 255

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o Certificate Data (variable length) - Actual encoding of
certificate data. The type of certificate is indicated
by the Certificate Encoding field.

The payload type for the Certificate Payload is six (6).

5.7 Certificate Request Payload

The Certificate Request Payload, denoted CERTREQ in this memo,
provides a means to request preferred certificates via IKE and can
appear in the first, second, or third message of Phase 1.
Certificate Request payloads SHOULD be included in an exchange
whenever the peer may have multiple certificates, some of which might
be trusted while others are not. If multiple root CA's are trusted,
then multiple Certificate Request payloads SHOULD be transmitted.

Empty (zero length) CA names MUST NOT be generated and SHOULD be
ignored.

The Certificate Request Payload is defined as follows:

1 2 3

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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Cert Encoding ! !
+-+-+-+-+-+-+-+-+ !
~ Certification Authority ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 10: Certificate Request Payload Format

o Certificate Encoding (1 octet) - Contains an encoding of the type
of certificate requested. Acceptable values are listed in
section 5.6.

o Certification Authority (variable length) - Contains an encoding
of an acceptable certification authority for the type of
certificate requested.

The payload type for the Certificate Request Payload is seven (7).

The Certificate Request Payload is constructed by setting the "Cert
Encoding" field to be the type of certificate being desired and the
"Certification Authority" field to a proper encoding of a
certification authority for the specified certificate. For example,

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for an X.509 certificate this field would contain the Distinguished
Name encoding of the Issuer Name of an X.509 certification authority
acceptable to the sender of this payload.

The Certificate Request Payload is processed by inspecting the "Cert
Encoding" field to determine whether the processor has any
certificates of this type. If so the "Certification Authority" field
is inspected to determine if the processor has any certificates which
can be validated up to the specified certification authority. This
can be a chain of certificates. If a certificate exists which
satisfies the criteria specified in the Certificate Request Payload
it MUST be sent back to the certificate requestor; if a certificate
chain exists which goes back to the certification authority specified
in the request the entire chain SHOULD be sent back to the
certificate requestor. If no certificates exist then no further
processing is performed-- this is not an error condition of the
protocol. There may be cases where there is a preferred CA, but an
alternate might be acceptable (perhaps after prompting a human
operator).

5.8 Authentication Payload

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The Authentication Payload, denoted AUTH in this memo, contains data
used for authentication purposes. The only authentication method
defined in this memo is digital signatures and therefore the contents
of this payload when used with this memo will be the output generated
by a digital signature function.

The Authentication Payload is defined as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Auth Method ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Authentication Data ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 11: Authentication Payload Format

o Authentication Data (variable length) Auth Method (1 octet) - Data that results from
applying the digital signature function to Specifies the IKE state
(see method of authentication
used. Values defined are:

Digital Signature (1) - Computed as specified in section 3).

The 4.15
using the public key in the first CERT payload type for or known the Authentication Payload is nine (9).

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recipient by some out of band means.

Shared Key Message Integrity Code (2) - Computed as specified in
section 4.15 using the shared key associated with the identity
in the ID payload.

o Authentication Data (variable length) - Data that results from
applying the digital signature function to the IKE state
(see section 3).

The payload type for the Authentication Payload is nine (9).

The Authentication Payload is constructed by computing a digital
signature (or secret key MAC) over part of one of the sender's
messages (see section 4.15). The result is placed in the
"Authentication Data" portion of the payload. The encoding depends
on the type of key being used to authenticate (see section 4.2). 4.15).
The payload length is the size of the generic header plus the size of
the "Authentication Data" portion of the payload which depends on the
specific authentication method being used.

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The Authentication Payload is processed by extracting the
"Authentication Data" from the payload and verifying it according to
the specific authentication method being used. If the specified
authentication method is not supported or validation fails a NOTIFY
Error message of AUTHENTICATION-FAILED MUST be sent back to the peer
and the connection closed. (An exception to this case is that a peer
MAY treat unsupported, invalid, or missing authentication data as a
request to open an unauthenticated SA.

5.9 Nonce Payload

The Nonce Payload, denoted Ni and Nr in this memo for the Initiator's
and Responder's nonce respectively, contains random data used to
guarantee liveness during an exchange and protect against replay
attacks.

The Nonce Payload is defined as follows:

Figure 12: Nonce Payload Format

o Nonce Data (variable length) - Contains the random data generated
by the transmitting entity.

The payload type for the Nonce Payload is ten (10).

The Nonce Payload is constructed by computing a pseudo-random value
and copying it into the "Nonce Data" field. The size of a Nonce MUST
be between 8 and 256 octets inclusive. Nonce values MUST NOT be
reused. They MAY be as long as 256 octets to support there use in
carrying state when defending against certain denial of service
attacks (see Section 4.6).

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5.10 Notify Payload

The Notify Payload, denoted N in this document, is used to transmit
informational data, such as error conditions and state transitions to
an IKE peer. A Notify Payload may appear in a response message
(usually specifying why a request was rejected), or in an
Informational Exchange (to report an error not in an IKE request).

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The Notify Payload is defined as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Protocol-ID ! SPI Size ! Notify Message Type !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Security Parameter Index (SPI) ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Notification Data ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 13: Notification Payload Format

o Protocol-Id (1 octet) - Specifies the protocol about which
this notification is being sent. For phase 1 notifications,
this field MUST be zero (0). For phase 2 notifications
concerning IPsec SAs this field will contain an IPsec
protocol (either ESP, AH, or IPcomp). AH). For notifications
for which no protocol ID is relevant, this field MUST be
sent as zero and MUST be ignored.

o SPI Size (1 octet) - Length in octets of the SPI as defined by
the Protocol-Id or zero if no SPI is applicable. For phase 1
notification concerning the IKE-SA, the SPI Size MUST be zero.

o Notify Message Type (2 octets) - Specifies the type of
notification message.

o SPI (variable length) - Security Parameter Index.

o Notification Data (variable length) - Informational or error data
transmitted in addition to the Notify Message Type. Values for
this field are message specific, see below.

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The payload type for the Notification Payload is eleven (11).

5.10.1 Notify Message Types

Notification information can be error messages specifying why an SA
could not be established. It can also be status data that a process
managing an SA database wishes to communicate with a peer process.

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For example, a secure front end or security gateway may use the
Notify message to synchronize SA communication. The table below
lists the Notification messages and their corresponding values. The
number of different error statuses was greatly reduced from IKE V1
both for simplication and to avoid giving configuration information
to probers.

Types in the range 0 - 16383 are intended for reporting errors. An
implementation receiving a Notify payload with one of these types
that it does not recognise in a response MUST assume that the
corresponding request has failed entirely. Unrecognised error types
in a request and status types in a request or response MUST be
ignored except that they SHOULD be logged.

Notify payloads with status types MAY be added to any message and
MUST be ignored if not recognised. They are intended to indicate
capabilities, and as part of SA negotiation are used to negotiate
non-cryptographic parameters.

NOTIFY MESSAGES - ERROR TYPES Value
----------------------------- -----
UNSUPPORTED-CRITICAL-PAYLOAD 1

Sent if the payload has the "critical" bit set and the
payload type is not recognised. Notification Data contains
the one octet payload type.

INVALID-COOKIE

INVALID-SPI 4

Indicates an IKE message was received with an unrecognized
destination cookie. SPI. This usually indicates that the recipient
has rebooted and forgotten the existence of an IKE-SA.

INVALID-MAJOR-VERSION 5

Indicates the recipient cannot handle the version of IKE
specified in the header. The closest version number that the
recipient can support will be in the reply header.

INVALID-SYNTAX 7

Indicates the IKE message was received was invalid because
some type, length, or value was out of range or because the
request was rejected for policy reasons. To avoid a denial
of service attack using forged messages, this status may
only be returned for and in an encrypted packet if the
MESSAGE-ID and cryptographic checksum were valid. To avoid
leaking information to someone probing a node, this status

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MUST be sent in response to any error not covered by one of
the other status codes. To aid debugging, more detailed
error information SHOULD be written to a console or log.

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INVALID-MESSAGE-ID 9

Sent when an IKE MESSAGE-ID outside the negotiated supported window is
received. This Notify MUST NOT be sent in a response; the
invalid request MUST NOT be acknowledged. Instead, inform
the other side by initiating an Informational exchange with
Notification data containing the four octet invalid
MESSAGE-ID.

INVALID-SPI 11

MAY Sending this notification is optional, MUST be
rate limited, and MUST NOT be sent unless an IKE-SA exists
to the sending address and port.

INVALID-SPI 11

MAY be sent in an IKE Informational Exchange when a node
receives an ESP or AH packet with an invalid SPI. The
Notification Data contains the SPI of the invalid packet.
This usually indicates a node has rebooted and forgotten an
SA. If this Informational Message is sent outside the
context of an IKE-SA, it should only be used by the
recipient as a "hint" that something might be wrong (because
it could easily be forged).

NO-PROPOSAL-CHOSEN 14

None of the proposed crypto suites was acceptable.

AUTHENTICATION-FAILED 24

Sent in the response to an IKE_AUTH message when for some
reason the authentication failed. There is no associated
data.

SINGLE-PAIR-REQUIRED 34

This error indicates that a Phase 2 SA request is
unacceptable because the Responder is willing to accept
traffic selectors specifying a single pair of addresses.
The Initiator is expected to respond by requesting an SA for
only the specific traffic he is trying to forward.

NO-ADDITIONAL-SAS 35

This error indicates that a Phase 2 SA request is
unacceptable because the Responder is unwilling to accept

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any more Child-SAs CHILD-SAs on this IKE-SA. Some minimal
implementations may only accept a single Child-SA CHILD-SA setup in
the context of an initial IKE exchange and reject any
subsequent attempts to add more.

INTERNAL-ADDRESS-FAILURE 36
Indicates an error assigning an internal address (i.e.,
INTERNAL_IP4_ADDRESS or INTERNAL_IP6_ADDRESS) during the
processing of a Configuration Payload by a Responder. If
this error is generated within an IKE_AUTH exchange no
CHILD-SA will be created.

RESERVED TO IANA - Errors 36 37 - 8191

Private Use - Errors 8192 - 16383

NOTIFY MESSAGES - STATUS TYPES Value

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------------------------------ -----

RESERVED TO IANA - STATUS 16384 - 24577

INITIAL-CONTACT 24578

This notification asserts that this IKE-SA is the only IKE-
SA currently active between the authenticated identities. It
MAY be sent when an IKE-SA is established after a crash, and
the recipient MAY use this information to delete any other
IKE-SAs it has to the same authenticated identity without
waiting for a timeout if those IKE-SAs reside at the IP
address from which this notification arrived. This
notification MUST NOT be sent by an entity that may be
replicated (e.g. a roaming user's credentials where the user
is allowed to connect to the corporate firewall from two
remote systems at the same time).

SET-WINDOW-SIZE 24579

This notification asserts that the sending endpoint is
capable of keeping state for multiple outstanding Phase 2
exchanges, permitting the recipient to send multiple Phase 2
requests before getting a response to the first. The data
associated with a SET-WINDOW-SIZE notification MUST be 4
octets long an contain the big endian represention of the
number of messages the sender promises to keep.

ADDITIONAL-TS-POSSIBLE 24580

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This notification asserts that the sending endpoint narrowed
the proposed traffic selectors but that other traffic
selectors would also have been acceptable, though only in a
separate SA. There is no data associated with this notify
type. It may only be sent as an additional payload in a
message including accepted TSs.

RESERVED

IPCOMP-SUPPORTED 24581 - 40959

Private Use - STATUS 40960 - 65535

5.11 Delete Payload

The Delete Payload, denoted D

This notification may only be included in this memo, contains a protocol-
specific security association identifier that the sender has removed
from message
containing an SA payload negotiating a CHILD-SA and
indicates a willingness by its security association database sender to use IPcomp on this
SA. The data associated with this notification includes a
two byte IPcomp CPI followed by a one octet transform ID
optionally followed by attributes whose length and is, therefore, no longer
valid. Figure 14 shows the format of the Delete Payload. It is

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possible to send
defined by that transform ID. A message proposing an SA may
contain multiple SPIs in a Delete payload, however, each SPI
MUST be for the same protocol. Mixing of Protocol Identifiers MUST
NOT be performed with the Delete payload. It is permitted, however, IPCOMP-SUPPORTED notifications to include indicate
multiple Delete payloads in a single Informational
Exchange where each Delete payload lists SPIs supported algorithms. A message accepting an SA may
contain at most one.

The transform IDs currently defined are:

NAME NUMBER DEFINED IN
----------- ------ -----------
RESERVED 0
IPCOMP_OUI 1
IPCOMP_DEFLATE 2 RFC 2394
IPCOMP_LZS 3 RFC 2395

values 4-240 are reserved to IANA. Values 241-255 are
for a different
protocol.

Deletion of the IKE-SA private use among mutually consenting parties.

NAT-DETECTION-SOURCE-IP 24582

This notification is indicated used to by its recipient to determine
whether the source is behind a Protocol-Id NAT box. The data associated
with this notification is a digest of 0 (IKE) but
no SPIs. Deletion the SPIs, IP address
and port on which this packet was sent. There MAY be
multiple notify payloads of this type in a Child-SA, such as ESP or AH, message if the
sender does not know which of several network attachments
will contain be used to send the
Protocol-Id packet. The recipient of that protocol (e.g. ESP, AH) and this
notification MAY compare the SPI supplied value to a hash of the
source IP address and port and if they don't match it MAY
invoke NAT specific handling (like using UDP encapsulation
of ESP packets and subsequent IKE packets). The digest is
computed using the
receiving entity's SPI(s).

NOTE: What's negotiated digest algorithm for the deal with IPcomp SAs. IKE-
SA.

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NAT-DETECTION-DESTINATION-IP 24583

This mechanism notification is probably not
appropriate for deleting them!! used to by its recipient to determine
whether the it is behind a NAT box. The Delete Payload data associated with
this notification is defined as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Protocol-Id ! SPI Size ! # of SPIs !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Security Parameter Index(es) (SPI) ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 14: Delete Payload Format

o Protocol-Id (1 octet) - Must be zero for an IKE-SA, 50 for
ESP, 51 for AH, and 108 for IPcomp.

o SPI Size (1 octet) - Length in octets a digest of the SPI as defined by
the Protocol-Id. Zero for IKE (SPI is in message header),
four for AH SPIs, IP address and ESP, two for IPcomp.

o # of SPIs (2 octets) - The number of SPIs contained in the Delete
payload.
port to which this packet was sent. The size recipient of each SPI is defined by the SPI Size field.

o Security Parameter Index(es) (variable length) - Identifies this
notification MAY compare the
specific security association(s) supplied value to delete.
The length a hash of this field is
determined by the SPI Size
destination IP address and # port and if they don't match it
MAY invoke NAT specific handling (like using UDP
encapsulation of SPIs fields. ESP packets and subsequent IKE packets).
The payload type digest is computed using the negotiated digest algorithm
for the Delete Payload is twelve (12).

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5.12 Vendor ID Payload

The Vendor ID Payload contains a vendor defined constant. The
constant is used by vendors to identify and recognize remote
instances of their implementations. IKE-SA.

COOKIE 24584

This mechanism allows a vendor
to experiment with new features while maintaining backwards
compatibility.

The Vendor ID payload is not notification MAY be included in an announcement from IKE_SA_INIT request
or response. In the sender that response, it
will send private payload types but rather an announcement of indicates that the
sort of private payloads it is willing to accept. The implementation
sending request
should be retried with the Vendor ID COOKIE included in the request.
That data associated with this notification MUST not make any assumptions about private
payloads that it may send unless a Vendor ID of like stature is
received as well. Multiple Vendor ID payloads MAY be sent. An
implementation is NOT REQUIRED to send any Vendor ID payload at all.

A Vendor ID payload may between
1 and 64 octets in length (inclusive).

USE-TRANSPORT-MODE 24585

This notification MAY be sent as part of any message. Reception of included in a familiar Vendor ID payload allows request message that
also includes an implementation to make SA requesting a CHILD-SA. It requests that
the CHILD-SA use of
Private USE numbers described throughout this memo-- private
payloads, private exchanges, private notifications, etc. Unfamiliar
Vendor IDs transport mode rather than tunnel mode for
the SA created. If the request is accepted, the response
MUST be ignored.

Writers also include a notification of Internet-Drafts who wish to extend type USE-TRANSPORT-MODE.
If the responder declines the request, the CHILD-SA can
still be established, but will use tunnel mode. If this protocol MUST
define a Vendor ID payload is
unacceptable to announce the ability to implement initiator, the
extension initiator MUST delete the
SA.

RESERVED TO IANA - STATUS 24586 - 40959

Private Use - STATUS 40960 - 65535

5.11 Delete Payload

The Delete Payload, denoted D in this memo, contains a protocol-
specific security association identifier that the Internet-Draft. sender has removed
from its security association database and is, therefore, no longer
valid. Figure 14 shows the format of the Delete Payload. It is expected that Internet-Drafts
which gain acceptance and are standardized will
possible to send multiple SPIs in a Delete payload, however, each SPI
MUST be given "magic
numbers" out of for the Future Use range by IANA and same protocol. Mixing of Protocol Identifiers MUST
NOT be performed with the requirement Delete payload. It is permitted, however,
to
use include multiple Delete payloads in a Vendor ID single Informational

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Exchange where each Delete payload lists SPIs for a different
protocol.

Deletion of the IKE-SA is indicated by a Protocol-Id of 0 (IKE) but
no SPIs. Deletion of a CHILD-SA, such as ESP or AH, will go away. contain the
Protocol-Id of that protocol (e.g. ESP, AH) and the SPI is the
receiving entity's SPI(s).

The Vendor ID Delete Payload fields are is defined as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Protocol-Id ! SPI Size ! # of SPIs !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Vendor ID (VID) Security Parameter Index(es) (SPI) ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 15: Vendor ID 14: Delete Payload Format

o Vendor ID (variable length) Protocol-Id (1 octet) - It is the responsibility Must be zero for an IKE-SA, 50 for
ESP, or 51 for AH.

o SPI Size (1 octet) - Length in octets of the person choosing SPI as defined by
the Vendor ID to assure its uniqueness Protocol-Id. Zero for IKE (SPI is in spite message header)
or four for AH and ESP.

o # of SPIs (2 octets) - The number of SPIs contained in the absence Delete
payload. The size of any central registry for IDs.
Good practice each SPI is defined by the SPI Size field.

o Security Parameter Index(es) (variable length) - Identifies the
specific security association(s) to include a company name, a person name
or some such. If you want to show off, you might include

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the latitude and longitude and time where you were when
you chose the ID and some random input. A message digest delete. The length of a long unique string this
field is preferable to determined by the long unique
string itself. SPI Size and # of SPIs fields.

The payload type for the Delete Payload is twelve (12).

5.12 Vendor ID Payload is thirteen (13).

5.13 Traffic Selector

The Vendor ID Payload contains a vendor defined constant. The Traffic Selector Payload, denoted TS in this memo,
constant is used by vendors to identify and recognize remote
instances of their implementations. This mechanism allows peers a vendor
to experiment with new features while maintaining backwards
compatibility.

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A Vendor ID payload MAY announce that the sender is capable to
accepting certain extensions to the protocol, or it MAY simply
identify packet flows the implementation as an aid in debugging. If parameter
values "reserved for processing use by IPsec security services.
The Traffic Selector Payload consists of the IKE generic header
followed consenting parties" are used, they must
be preceded by individual traffic selectors as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Number a Vendor ID payload that disambiguates them. A Vendor
ID payload MUST NOT change the interpretation of TSs ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ <Traffic Selectors> ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 16: Traffic Selectors Payload Format

o Number of TSs (1 octet) - Number of traffic selectors
being provided.

o RESERVED - This field any information
defined in this specification (i.e. it MUST be non-critical).
Multiple Vendor ID payloads MAY be sent. An implementation is NOT
REQUIRED to send any Vendor ID payload at all.

A Vendor ID payload may be sent as zero and part of any message. Reception of
a familiar Vendor ID payload allows an implementation to make use of
Private USE numbers described throughout this memo-- private
payloads, private exchanges, private notifications, etc. Unfamiliar
Vendor IDs MUST be ignored.

o Traffic Selectors (variable length) - one or more individual
traffic
selectors.

The length

Writers of the Traffic Selector Internet-Drafts who wish to extend this protocol MUST
define a Vendor ID payload includes to announce the TS header and
all ability to implement the traffic selectors.
The payload type for
extension in the Traffic Selector payload Internet-Draft. It is fourteen (14).

5.13.1 Traffic Selector expected that Internet-Drafts
which gain acceptance and are standardized will be given "magic
numbers" out of the Future Use range by IANA and the requirement to
use a Vendor ID will go away.

The Vendor ID Payload fields are defined as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! TS Type Next Payload !C! RESERVED ! Protocol ID | Selector Payload Length |

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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start-Port | End-Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Starting Address ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Ending Address Vendor ID (VID) ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 17: Traffic Selector 15: Vendor ID Payload Format

o TS Type (one octet) Vendor ID (variable length) - Specifies It is the type responsibility of traffic selector.

o Protocol ID (1 octet) - Value specifying an associated IP
protocol
the person choosing the Vendor ID (e.g. UDP/TCP). A value to assure its uniqueness
in spite of zero means that the
Protocol ID absence of any central registry for IDs.
Good practice is not relevant to this traffic selector-- include a company name, a person name
or some such. If you want to show off, you might include
the SA can carry all protocols.

o Selector Length - Specifies latitude and longitude and time where you were when
you chose the length ID and some random input. A message digest
of this Traffic
Selector Substructure including the header.

o Start-Port (2 octets) - Value specifying the smallest port
number allowed by this Traffic Selector. For protocols for
which port a long unique string is undefined, or if all ports are allowed by
this Traffic Selector, this field MUST be zero.

o End-Port (2 octets) - Value specifying preferable to the largest port
number allowed by this Traffic Selector. For protocols long unique
string itself.

The payload type for
which port the Vendor ID Payload is undefined, or it all ports are allowed by
this thirteen (13).

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5.13 Traffic Selector, this field MUST be 65535.

o Starting Address - Selector Payload

The smallest address included in this Traffic Selector (length determined by Payload, denoted TS type).

o Ending Address - The largest address included in this
Traffic Selector (length determined memo, allows peers
to identify packet flows for processing by TS type). IPsec security services.
The following table lists the assigned values for the Traffic Selector Type field and the corresponding Address Payload consists of the IKE generic header
followed by individual traffic selectors as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Number of TSs ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ <Traffic Selectors> ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 16: Traffic Selectors Payload Format

o Number of TSs (1 octet) - Number of traffic selectors
being provided.

o RESERVED - This field MUST be sent as zero and MUST be ignored.

o Traffic Selectors (variable length) - one or more individual
traffic selectors.

The length of the Traffic Selector Data. payload includes the TS Type Value
------- -----
RESERVED header and
all the traffic selectors.

The payload type for the Traffic Selector payload is fourteen (14).

5.13.1 Traffic Selector

1 2 3
0

TS_IPV4_ADDR_RANGE 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! TS Type ! Protocol ID | Selector Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start-Port | End-Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Starting Address ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !

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A range January 2003

~ Ending Address ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 17: Traffic Selector

o TS Type (one octet) - Specifies the type of IPv4 addresses, represented by two four (4) octet
values. traffic selector.

o Protocol ID (1 octet) - Value specifying an associated IP
protocol ID (e.g. UDP/TCP). A value of zero means that the
Protocol ID is not relevant to this traffic selector--
the SA can carry all protocols.

o Selector Length - Specifies the length of this Traffic
Selector Substructure including the header.

o Start-Port (2 octets) - Value specifying the smallest port
number allowed by this Traffic Selector. For protocols for
which port is undefined, or if all ports are allowed by
this Traffic Selector, this field MUST be zero.

o End-Port (2 octets) - Value specifying the largest port
number allowed by this Traffic Selector. For protocols for
which port is undefined, or it all ports are allowed by
this Traffic Selector, this field MUST be 65535.

o Starting Address - The smallest address included in this
Traffic Selector (length determined by TS type).

o Ending Address - The largest address included in this
Traffic Selector (length determined by TS type).

The following table lists the assigned values for the Traffic
Selector Type field and the corresponding Address Selector Data.

TS Type Value
------- -----
RESERVED 0

TS_IPV4_ADDR_RANGE 7

A range of IPv4 addresses, represented by two four (4) octet
values. The first value is the beginning IPv4 address
(inclusive) and the second value is second value is the ending IPv4 address
(inclusive). All addresses falling between the two specified
addresses are considered to be within the list.

TS_IPV6_ADDR_RANGE 8

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A range of IPv6 addresses, represented by two sixteen (16)
octet values. The first value is the beginning IPv6 address
(inclusive) and the second value is the ending IPv6 address
(inclusive). All addresses falling between the two specified
addresses are considered to be within the list.

TS_IPV4_ADDR_REQUEST 9

This TS type requests that the responder assign an IPv4
address for use with this SA. The length of the addresses
field is zero.

TS_IPV6_ADDR_REQUEST 10

This TS type requests that the responder assign an IPv6
address for use with this SA. The length of the addresses
field is zero.

5.14 Encrypted Payload

The Encrypted Payload, denoted SK{...} in this memo, contains other
payloads in encrypted form. The Encrpted Payload, if present in a
message, must be the last payload in the message. Often, it is the
only payload in the message.

The algorithms for encryption and integrity protection are negotiated
during IKE-SA setup, and the keys are computed as specified in
sections 4.14 and 4.17.

The encryption and integrity protection algorithms are modelled after
the ESP algorithms described in RFCs 2104, 2406, 2451. This document
completely specifies the cryptographic processing of IKE data, but
those documents should be consulted for design rationale. We assume a
block cipher with a fixed block size and an integrity check algorithm
that computes a fixed length checksum over a variable size message.
The mandatory to implement algorithms are AES-128-CBC and HMAC-SHA1.

The Payload Type for an Encrypted payload is fifteen (15). The
Encrypted Payload consists of the IKE generic header followed by
individual fields as follows:

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! (length is block size for encryption algorithm) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Encrypted IKE Payloads !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! ! Padding (0-255 octets) !
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
! ! Pad Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Integrity Checksum Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 18: Encrypted Payload Format

o Next Payload - The payload type of the first embedded payload.
Since the Encrypted payload must be last in a message, there
is no need to specify a payload type for a payload beyond it.

o Payload Length - Includes the lengths of the IV, Padding, and
Authentication data.

o Initialization Vector - A randomly chosen value whose length
is equal to the block length of the underlying encryption
algorithm. Recipients MUST accept any value. Senders SHOULD
either pick this value pseudo-randomly and independently for
each message or use the final ciphertext block of the previous
message sent. Senders MUST NOT use the same value for each
message, use a sequence of values with low hamming distance
(e.g. a sequence number), or use ciphertext from a received
message.

o IKE Payloads are as specified earlier in this section. This
field is encrypted with the negotiated cipher.

o Padding may contain any value chosen by the sender, and must
have a length that makes the combination of the Payloads, the
Padding, and the Pad Length to be a multiple of the encryption
block size. This field is encrypted with the negotiated
cipher.

o Pad Length is the length of the Padding field. The sender
SHOULD set the Pad Length to the minimum value that makes
the combination of the Payloads, the Padding, and the Pad
Length a multiple of the block size, but the recipient MUST
accept any length that results in proper alignment. This
field is encrypted with the negotiated cipher.

o Integrity Checksum Data is the cryptographic checksum of
the entire message starting with the Fixed IKE Header

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through the Pad Length. The checksum MUST be computed over
the encrypted message.

5.15 Configuration Payload

The Configuration payload, denoted CP in this document, is used to
exchange configuration information between IKE peers. Currently, the
only defined uses for this exchange is for an IRAC to request an
internal IP address from an IRAS or for either party to request
version information from the other, but this payload is intended as a
likely place for future extensions.

Configuration payloads are of type CFG_REQUEST/CFG_REPLY or
CFG_SET/CFG_ACK (see CFG Type in the payload description below).
CFG_REQUEST and CFG_SET payloads may optionally be added to any IKE
request. The IKE response MUST include either a corresponding
CFG_REPLY or CFG_ACK or a Notify payload with an error code
indicating why the request could not be honored.

"CFG_REQUEST/CFG_REPLY" allows an IKE endpoint to request information
from its peer. If an attribute in the CFG_REQUEST Configuration
Payload is not zero length it is taken as a suggestion for that
attribute. The CFG_REPLY Configuration Payload MAY return that
value, or a new one. It MAY also add new attributes and not include
some requested ones. Requestors MUST ignore returned attributes that
they do not recognise.

Some attributes MAY be multi-valued, in which case multiple attribute
values of the same type are sent and/or returned. Generally, all
values of an attribute are returned when the attribute is requested.
For some attributes (in this version of the specification only
internal addresses), multiple requests indicates a request that
multiple values be assigned. For these attributes, the number of
values returned SHOULD NOT exceed the number requested.

If the data type requested in a CFG_REQUEST is not recognised or not
supported, the responder MUST NOT return an error code but rather
MUST send a CFG_REPLY which MAY be empty. Error returns are reserved
for cases where the request is recognised but cannot be performed as
requested or the request is badly formatted.

"CFG_SET/CFG_ACK" allows an IKE endpoint to push configuration data
to its peer. In this case the CFG_SET Configuration Payload contains
attributes the initiator wants its peer to alter. The responder MUST
return a Configuration Payload and it MUST contain the zero length
attributes that the ending IPv4 address
(inclusive). All addresses falling between responder accepted. Those attributes that it did
not accept MUST NOT be in the two specified
addresses CFG_ACK Configuration Payload. There
are considered to be within currently no defined uses for the list.

TS_IPV6_ADDR_RANGE 8

A range CFG_SET/CFG_ACK exchange,

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though they may be used in connection with extensions based on Vendor
IDs. An implementation of IPv6 addresses, represented by two sixteen (16)
octet values. The first value is this specification without extensions MUST
recognise the beginning IPv6 address
(inclusive) and CFG_SET payload but MUST always respond with an empty
CFG_ACK.

Extensions via the second value CP payload SHOULD NOT be used for general purpose
management. Its main intent is the ending IPv6 address
(inclusive). All addresses falling between the two specified
addresses are considered to be provide a bootstrap mechanism to
exchange information within the list.

5.14 Encrypted Payload IPSec from IRAS to IRAC. While it MAY be
useful to use such a method to exchange information between some
Security Gateways (SGW) or small networks, existing management
protocols such as DHCP [DHCP], RADIUS [RADIUS], SNMP or LDAP [LDAP]
should be preferred for enterprise management as well as subsequent
information exchanges.

The Encrypted Payload, denoted SK{...} in this memo, contains other
payloads in encrypted form. Configuration Payload is defined as follows:

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! CFG Type ! RESERVED !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! !
~ Configuration Attributes ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 19: Configuration Payload Format

The Encrpted Payload, if present in a
message, must be the last payload in type for the message. Often, it Configuration Payload is the
only payload in the message. 16.

o CFG Type (1 octet) - The algorithms for encryption and integrity protection are negotiated
during IKE-SA setup, and type of exchange represented by the keys
Configuration Attributes.

CFG Type Value
=========== =====
RESERVED 0
CFG_REQUEST 1
CFG_REPLY 2
CFG_SET 3
CFG_ACK 4

values 5-127 are computed reserved to IANA. Values 128-255 are for private
use among mutually consenting parties.

o RESERVED (3 octets) - MUST be sent as specified in
sections 4.14 and 4.17.

The encryption and integrity protection algorithms zero; MUST be ignored.

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o Configuration Attribute (variable length) - These are modelled after type length
values specific to the ESP algorithms described Configuration Payload and are defined
below. There may be zero or more Configuration Attributes in RFCs 2104, 2406, 2451. this
payload.

5.15.1 Configuration Attributes

1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
!R| Attribute Type ! Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Value ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 20: Configuration Attribute Format

o Reserved (1 bit) - This document
completely specifies the cryptographic processing of IKE data, but
those documents should bit MUST be consulted for design rationale. We assume a
block cipher with a fixed block size and an integrity check algorithm
that computes a fixed length checksum over a variable size message.
The mandatory set to implement algorithms are AES-128-CBC zero and HMAC-SHA1.

The Payload MUST be
ignored.

o Attribute Type (7 bits) - A unique identifier for an Encrypted payload is fifteen (15). The
Encrypted Payload consists each of the IKE generic header followed by
individual fields as follows:

1 2 3
Configuration Attribute Types.

o Length (2 octets) - Length in octets of Value.

o Value (0 or more octets) - The variable length value of this
Configuration Attribute.

The following attribute types have been defined:

MUST Multi-
Attribute Type Value Support Valued Length
======================= ===== ======= ====== ==================
RESERVED 0
INTERNAL_IP4_ADDRESS 1 YES YES* 0 or 4 octets
INTERNAL_IP4_NETMASK 2 NO NO 0 or 4 octets
INTERNAL_IP4_DNS 3 NO YES 0 or 4 5 6 7 8 9 octets
INTERNAL_IP4_NBNS 4 NO YES 0 1 2 3 or 4 octets
INTERNAL_ADDRESS_EXPIRY 5 6 7 8 9 YES NO 0 1 2 3 or 4 5 octets
INTERNAL_IP4_DHCP 6 NO YES 0 or 4 octets
APPLICATION_VERSION 7 YES NO 0 or more
INTERNAL_IP6_ADDRESS 8 YES YES* 0 or 16 octets
INTERNAL_IP6_NETMASK 9 NO NO 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Next Payload !C! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Initialization Vector !
! (length is block size for encryption algorithm) !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Encrypted IKE Payloads !
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! ! Padding (0-255 octets) ! or 16 octets
INTERNAL_IP6_DNS 10 NO YES 0 or 16 octets
INTERNAL_IP6_NBNS 11 NO YES 0 or 16 octets
INTERNAL_IP6_DHCP 12 NO YES 0 or 16 octets

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+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
! ! Pad Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Integrity Checksum Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 9: Encrypted Payload Format January 2003

INTERNAL_IP4_SUBNET 13 YES NO 0 or 8 octets
SUPPORTED_ATTRIBUTES 14 YES NO Multiple of 2
INTERNAL_IP6_SUBNET 15 YES NO 17 octets

* These attributes may be multi-valued on return only if
multiple values were requested.

Types 16-16383 are reserved to IANA. Values 16384-32767 are for
private use among mutually consenting parties.

o Next Payload INTERNAL_IP4_ADDRESS, INTERNAL_IP6_ADDRESS - An address on the
internal network, sometimes called a red node address or
private
address and MAY be a private address on the Internet. Multiple
internal addresses MAY be requested by requesting multiple
internal address attributes. The payload type responder MAY only send up to
the number of addresses requested.

The requested address is valid until the first embedded payload.
Since expiry time defined
with
the Encrypted payload must be last in a message, INTERNAL_ADDRESS EXPIRY attribute or there
is are no need to specify a payload type for a payload beyond it. IKE-SAs
between the peers.

o Payload Length INTERNAL_IP4_NETMASK, INTERNAL_IP6_NETMASK - Includes the lengths of The internal
network's netmask. Only one netmask is allowed in the IV, Padding, request
and
Authentication data.
reply messages (e.g. 255.255.255.0) and it MUST be used only
with
an INTERNAL_ADDRESS attribute.

o Initialization Vector INTERNAL_IP4_DNS, INTERNAL_IP6_DNS - A randomly chosen value whose length
is equal to the block length Specifies an address of a
DNS server within the underlying encryption
algorithm. Recipients MUST accept any value. Senders SHOULD
either pick this value pseudo-randomly and independently for
each message network. Multiple DNS servers MAY be
requested. The responder MAY respond with zero or use the final ciphertext block more DNS
server
attributes.

o INTERNAL_IP4_NBNS, INTERNAL_IP6_NBNS - Specifies an address of the previous
message sent. Senders MUST NOT use the same value for each
message, use
a sequence of values
NetBios Name Server (WINS) within the network. Multiple NBNS
servers MAY be requested. The responder MAY respond with low hamming distance
(e.g. a sequence number), zero
or use ciphertext from a received
message.

o IKE Payloads are as specified earlier in this section. This
field is encrypted with the negotiated cipher.
more NBNS server attributes.

o Padding may contain any value chosen by INTERNAL_ADDRESS_EXPIRY - Specifies the sender, and must
have a length number of seconds that makes
the combination of host can use the Payloads, internal IP address. The host MUST renew
the
Padding, and
IP address before this expiry time. Only one of these
attributes

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MAY be present in the Pad Length reply.

o INTERNAL_IP4_DHCP, INTERNAL_IP6_DHCP - Instructs the host to
send any internal DHCP requests to the address contained within
the attribute. Multiple DHCP servers MAY be a multiple requested. The
responder MAY respond with zero or more DHCP server attributes.

o APPLICATION_VERSION - The version or application information of
the encryption
block size. IPSec host. This field is encrypted with the negotiated
cipher. a string of printable ASCII characters
that is NOT null terminated.

o Pad Length INTERNAL_IP4_SUBNET - The protected sub-networks that this
edge-
device protects. This attribute is the length made up of two fields; the Padding field. The sender
SHOULD set
first being an IP address and the Pad Length second being a netmask.
Multiple sub-networks MAY be requested. The responder MAY
respond
with zero or more sub-network attributes.

o SUPPORTED_ATTRIBUTES - When used within a Request, this
attribute must be zero length and specifies a query to the minimum value that makes
the combination
responder to reply back with all of the Payloads, the Padding, and the Pad
Length attributes that it
supports. The response contains an attribute that contains a multiple
set
of the block size, but the recipient MUST
accept any attribute identifiers each in 2 octets. The length that results divided
by
2 (bytes) would state the number of supported attributes
contained
in proper alignment. This
field is encrypted with the negotiated cipher. response.

o Integrity Checksum Data INTERNAL_IP6_SUBNET - The protected sub-networks that this
edge-
device protects. This attribute is the cryptographic checksum made up of two fields; the entire message starting with the Fixed IKE Header
through
first being a 16 octet IPv6 address the Pad Length. The checksum MUST second being a one
octet
prefix-mask as defined in [ADDRIPV6]. Multiple sub-networks
MAY
be computed over
the encrypted message.

5.15 requested. The responder MAY respond with zero or more sub-
network attributes.

Note that no recommendations are made in this document how an
implementation actually figures out what information to send in a
reply. i.e. we do not recommend any specific method of an IRAS
determining which DNS server should be returned to a requesting
IRAC.

5.16 Other Payload Types

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Payload type values 16-127 17-127 are reserved to IANA for future assignment
in IKE. IKEv2 (see section 10). Payload type values 128-255 are for
private use among mutually consenting parties.

6 Conformance Requirements

In order to assure that all implementations of IKEv2 can
interoperate, there are MUST support requirements in addition to
those listed elsewhere. Of course, IKEv2 is a security protocol, and
one of its major functions is preventing the bad guys from
interoperating with one's systems. So a particular implementation may
be configured with any of a number of restrictions concerning
algorithms and trusted authorities that will prevent universal
interoperability. For an implementation to be called conforming to
this specification, it MUST be possible to configure it to accept the
following:

X.509 certificates containing and signed by RSA keys of size 512,
768, 1024, and 2048 bits. (It SHOULD accept RSA keys of any multiple
of 8 bits in size from 512 bits to 4092 bits, and MAY accept RSA keys
of any size). If there is a limit on the size of an X.509
certificate, it MUST be at least 8K. If there is a limit on the
length of a certificate chain, it MUST be at least 10.

X.509 certificates containing and signed by DSS keys of size 512,
768, 1024, and 2048 bits. (It MAY accept DSS keys of any size).

An implementation MUST be capable of accepting a shared key for
authentication of any size from 1 - 255 bytes.

An implementation MUST be capable of accepting IKE messages with
sizes up to 16K bytes and SHOULD be capable of accepting IKE messages
up to 64K bytes.

An implementation MUST be capable of establishing an IKE-SA and a
single CHILD-SA in the initial four message exchange. An
implementation MAY reject subsequent requests to establish a CHILD-
SA. An implementation MUST respond to valid phase 2 messages, but MAY
otherwise ignore all such messages other than DELETE. There is no
requirement that an implementation be capable of initiating phase 2
exchanges.

The above paragraph allows for a minimal implementation to only do
the initial 4 message IKE exchange and respond to phase 2 pings and
still interoperate with any compliant implementation. In support of
this, and an implementation that tries to rekey the IKE-SA by means of a
CREATE_CHILD_SA exchange be called conforming to
this specification, it MUST be prepared possible to tear down configure it to accept the IKE-SA
following:

RSA keys: 1024 and
establish a new one 2048 bits

Cert types/lengths/algs

Symmetric key (pwd authentication)

setup 1 CHILD-SA in first 4 messages; may reject subsequent. Must
respond to "pings". Must accept "deletes". Must respond to all
messages; may ignore all but delete (what if the rekeying operation fails.

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....

7 Security Considerations

Repeated re-keying using Phase 2 without PFS can consume the entropy
of the Diffie-Hellman shared secret. Implementers should take note of
this fact and set a limit on Phase 2 Exchanges between
exponentiations. This memo does not prescribe such a limit.

The strength of a key derived from a Diffie-Hellman exchange using
any of the groups defined here depends on the inherent strength of
the group, the size of the exponent used, and the entropy provided by
the random number generator used. Due to these inputs it is difficult
to determine the strength of a key for any of the defined groups.
Diffie-Hellman group number two when used with a strong random number
generator and an exponent no less than 160 bits is sufficient to use
for 3DES. Groups three through five provide greater security. Group
one is for historic purposes only and does not provide sufficient
strength to the required cipher (although it is sufficient for use
with DES, which is also for historic use only). Implementations
should make note of these conservative estimates when establishing

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policy and negotiating security parameters.

Note that these limitations are on the Diffie-Hellman groups
themselves. There is nothing in IKE which prohibits using stronger
groups nor is there anything which will dilute the strength obtained
from stronger groups. In fact, the extensible framework of IKE
encourages the definition of more groups; use of elliptical curve
groups may greatly increase strength using much smaller numbers.

It is assumed that the Diffie-Hellman exponents in this exchange are
erased from memory after use. In particular, these exponents MUST NOT
be derived from long-lived secrets like the seed to a pseudo-random
generator that is not erased after use.

The security of this protocol is critically dependent on the
randomness of the Diffie-Hellman exponents, which should be generated
by a strong random or properly seeded pseudo-random source (see
RFC1715). While the protocol was designed to be secure even if the
Nonces and other values specified as random are not strongly random,
they should similarly be generated from a strong random source as
part of a conservative design.

8 IANA Considerations

This document contains many "magic numbers" to be maintained by the
IANA. This section explains the criteria to be used by the IANA to
assign additional numbers in each of these lists.

8.1.2 Encryption Algorithm

Cryptographic Suite-IDs
Error Codes
Status Codes
IPcomp Transform Type

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Configuration request types
Configuration attribute types
Payload Types
IKE Exchange Types

Values of the Encryption Algorithm Cryptographic Suite-ID define an encryption algorithm a set of cryptographic
algorithms to
use when called for be used in this document. an IKE, ESP, or AH SA. Requests for
assignment of new
encryption algorithm values must be accompanied by a reference to an RFC
that describes how to use this algorithm with ESP.

8.1.4 Authentication Method Transform Type

The only Authentication method defined in the memo is for digital
signatures. Other methods of authentication are possible and MUST be
accompanied by an RFC which defines the following:

- the cryptographic method of authentication.
- content of the Authentication Data in the Authentication
Payload.
- new payloads, their construction and processing, if needed.
- additions of payloads to any messages, if needed.

8.1.5 Diffie-Hellman Groups

Values of the Diffie-Hellman Group Transform types define a group in
which a Diffie-Hellman key exchange can be completed. Requests for
assignment of a new Diffie-Hellman group type MUST be accompanied by
a reference to an RFC which fully defines the group.

8.2 Exchange Types these algorithms.

This memo defines three exchange types for use with IKEv2. Requests
for assignment of new exchange types MUST be accompanied by an RFC
which defines the following:

- the purpose of and need for the new exchange.
- the payloads (mandatory and optional) that accompany

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messages in the exchange.
- the phase of the exchange.
- requirements the new exchange has on existing
exchanges which have assigned numbers.

8.3 Payload Types

Payloads are defined in this memo to convey information between
peers. New payloads may be required when defining a new
authentication method or exchange. Requests for new payload types
MUST be accompanied by an RFC which defines the physical layout of
the payload and the fields it contains. All payloads MUST use the
same generic header defined in Figure 2.

9 Acknowledgements

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9 Acknowledgements

This document is a collaborative effort of the entire IPsec WG. If
there were no limit to the number of authors that could appear on an
RFC, the following, in alphabetical order, would have been listed:
Bill Aiello, Stephane Beaulieu, Steve Bellovin, Sara Bitan, Matt
Blaze, Ran Canetti, Darren Dukes, Dan Harkins, Paul Hoffman, J.
Ioannidis, Steve Kent, Angelos Keromytis, Tero Kivinen, Hugo
Krawczyk, Andrew Krywaniuk, Radia Perlman, O. Reingold. Many other
people contributed to the design. It is an evolution of IKEv1,
ISAKMP, and the IPSec DOI, each of which has its own list of authors.
Hugh Daniel suggested the feature of having the initiator, in message
3, specify a name for the responder, and gave the feature the cute
name "You Tarzan, Me Jane". David Faucher and Valery Smyzlov helped
refine the design of the traffic selector negotiation.

10 References

10.1 Normative References

[Bra96] Bradner, S., "The Internet Standards Process -- Revision 3",
BCP 9, RFC 2026, October 1996.

[Bra97] Bradner, S., "Key Words for use in RFCs to indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

10.2 Non-normative References

[Ble98] Bleichenbacher, D., "Chosen Ciphertext Attacks against
Protocols Based on RSA Encryption Standard PKCS#1", Advances
in Cryptology Eurocrypt '98, Springer-Verlag, 1998.

[BR94] Bellare, M., and Rogaway P., "Optimal Asymmetric
Encryption", Advances in Cryptology Eurocrypt '94,
Springer-Verlag, 1994.

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[DES] ANSI X3.106, "American National Standard for Information
Systems-Data Link Encryption", American National Standards
Institute, 1983.

[DH] Diffie, W., and Hellman M., "New Directions in
Cryptography", IEEE Transactions on Information Theory, V.
IT-22, n. 6, June 1977.

[DSS] 6, June 1977.

[DHCP] R. Droms, "Dynamic Host Configuration Protocol",
RFC2131

[DSS] NIST, "Digital Signature Standard", FIPS 186, National
Institute of Standards and Technology, U.S. Department of
Commerce, May, 1994.

[HC98] Harkins, D., Carrel, D., "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.

[IDEA] Lai, X., "On the Design and Security of Block Ciphers," ETH
Series in Information Processing, v. 1, Konstanz: Hartung-
Gorre Verlag, 1992

[Ker01] Keronytis, A., Sommerfeld, B., "The 'Suggested ID' Extension
for IKE", draft-keronytis-ike-id-00.txt, 2001

[KBC96] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.

[LDAP] M. Wahl, T. Howes, S. Kille., "Lightweight Directory
Access Protocol (v3)", RFC2251

[MD5] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321,
April 1992.

[MSST98] Maughhan, D., Schertler, M., Schneider, M., and Turner, J.
"Internet Security Association and Key Management Protocol
(ISAKMP)", RFC 2408, November 1998.

[Orm96] Orman, H., "The Oakley Key Determination Protocol", RFC
2412, November 1998.

[PFKEY] McDonald, D., Metz, C., and Phan, B., "PFKEY Key Management
API, Version 2", RFC2367, July 1998.

[PKCS1] Kaliski, B., and J. Staddon, "PKCS #1: RSA Cryptography
Specifications Version 2", September 1998.

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[PK01] Perlman, R., and Kaufman, C., "Analysis of the IPsec key
exchange Standard", WET-ICE Security Conference, MIT, 2001,
http://sec.femto.org/wetice-2001/papers/radia-paper.pdf.

[Pip98] Piper, D., "The Internet IP Security Domain Of
Interpretation for ISAKMP", RFC 2407, November 1998.

[RADIUS] C. Rigney, A. Rubens, W. Simpson, S. Willens, "Remote
Authentication Dial In User Service (RADIUS)", RFC2138

[RSA] Rivest, R., Shamir, A., and Adleman, L., "A Method for
Obtaining Digital Signatures and Public-Key Cryptosystems",
Communications of the ACM, v. 21, n. 2, February 1978.

[SHA] NIST, "Digital Signature "Secure Hash Standard", FIPS 186, 180-1, National Institute
of Standards and Technology, U.S. Department of Commerce, May,
May 1994.

[HC98] Harkins, D., Carrel, D., "The Internet

[SKEME] Krawczyk, H., "SKEME: A Versatile Secure Key Exchange (IKE)",
RFC 2409, November 1998.

[IDEA] Lai, X., "On
Mechanism for Internet", from IEEE Proceedings of the 1996
Symposium on Network and Distributed Systems Security.

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Appendix A: NAT Traversal

NAT (Network Address Translation) gateways are a controversial
subject. This appendix briefly describes what they are and how they
are likely to act on IKE traffic. Many people believe that NATs are
evil and that we should not design our protocols so as to make them
work better. IKEv2 does specify some unintuitive processing rules in
order that NATs are more likely to work.

NATs exist primarily because of the shortage of IPv4 addresses,
though there are other rationales. IP nodes that are "behind" a NAT
have IP addresses that are not globally unique, but rather are
assigned from some space that is unique within the network behind the
NAT but which are likely to be reused by nodes behind other NATs.
Generally, nodes behind NATs can communicate with other nodes behind
the same NAT and with nodes with globally unique addresses, but not
with nodes behind other NATs. There are exceptions to that rule.
When those nodes make connections to nodes on the real Internet, the
NAT gateway "translates" the IP source address to an address that
will be routed back to the gateway. Messages to the gateway from the
Internet have their destination addresses "translated" to the
internal address that will route the packet to the correct endnode.

NATs are designed to be "transparent" to endnodes. Neither software
on the node behind the NAT nor the node on the Internet require
modification to communicate through the NAT. Achieving this
transparency is more difficult with some protocols than with others.
Protocols that include IP addresses of the Design and Security endpoints within the
payloads of Block Ciphers," ETH
Series the packet will fail unless the NAT gateway understands
the protocol and modifies the internal references as well as those in Information Processing, v. 1, Konstanz: Hartung-
Gorre Verlag, 1992

[Ker01] Keronytis, A., Sommerfeld, B., "The 'Suggested ID' Extension

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for IKE", draft-keronytis-ike-id-00.txt, 2001

[KBC96] Krawczyk, H., Bellare, M.,
the headers. Such knowledge is inherently unreliable, is a network
layer violation, and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104, February
1997.

[SKEME] Krawczyk, H., "SKEME: A Versatile Secure Key Exchange
Mechanism for Internet", from IEEE Proceedings of often results in subtle problems.

Opening an IPsec connection through a NAT introduces special
problems. If the 1996
Symposium connection runs in transport mode, changing the IP
addresses on Network packets will cause the checksums to fail and Distributed Systems Security.

[MD5] Rivest, R., "The MD5 Message Digest Algorithm", RFC 1321,
April 1992.

[MSST98] Maughhan, D., Schertler, M., Schneider, M., the NAT
cannot correct the checksums because they are cryptographically
protected. Even in tunnel mode, there are routing problems because
transparently translating the addresses of AH and Turner, J.
"Internet Security Association ESP packets
requires special logic in the NAT and Key Management Protocol
(ISAKMP)", RFC 2408, November 1998.

[Orm96] Orman, H., "The Oakley Key Determination Protocol", RFC
2412, November 1998.

[PFKEY] McDonald, D., Metz, C., that logic is heuristic and Phan, B., "PFKEY Key Management
API, Version 2", RFC2367, July 1998.

[PKCS1] Kaliski, B.,
unreliable in nature. For that reason, IKEv2 can negotiate UDP
encapsulation of ESP and AH packets. This encoding is slightly less
efficient but is easier for NATs to process. In addition, firewalls
may be configured to pass IPsec traffic over UDP but not ESP/AH or
vice versa.

It is a common practice of NATs to translate TCP and J. Staddon, "PKCS #1: RSA Cryptography
Specifications Version 2", September 1998.

[PK01] Perlman, R., UDP port numbers
as well as addresses and Kaufman, C., "Analysis use the port numbers of inbound packets to

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decide which internal node should get a given packet. For this
reason, even though IKE packets MUST be sent from and to UDP port
500, they SHOULD be accepted coming from any port and responses
SHOULD be sent to the IPsec key
exchange Standard", WET-ICE Security Conference, MIT, 2001,
http://sec.femto.org/wetice-2001/papers/radia-paper.pdf.

[Pip98] Piper, D., "The Internet port from whence they came. This is because the
ports may be modified as the packets pass through NATs. Similarly, IP Security Domain Of
Interpretation for ISAKMP", RFC 2407, November 1998.

[RSA] Rivest, R., Shamir, A.,
addresses of the IKE endpoints are generally not included in the IKE
payloads because the payloads are cryptographically protected and Adleman, L., "A Method
could not be transparently modified by NATs.

Port 4500 is reserved for
Obtaining Digital Signatures UDP encapsulated ESP, AH, and Public-Key Cryptosystems",
Communications of IKE. When
working through a NAT, it is generally better to pass IKE packets
over port 4500 because some older NATs modify IKE traffic on port 500
in an attempt to transparently establish IPsec connections. Such NATs
may interfere with the ACM, v. 21, n. 2, February 1978.

[SHA] NIST, "Secure Hash Standard", FIPS 180-1, National Institute
of Standards straightforward NAT traversal envisioned by
this document, so an IPsec endpoint that discovers a NAT between it
and Technology, U.S. Department of Commerce,
May 1994. its correspondent SHOULD send all subsequent traffic to and from
port 4500, which all NATs should know run the NAT-friendly protocol.

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Appendix B: Diffie-Hellman Groups

There are 5 groups different Diffie-Hellman groups defined for use in
IKE. These groups were generated by Richard Schroeppel at the
University of Arizona. Properties of these primes are described in
[Orm96].

The strength supplied by group one may not be sufficient for the
mandatory-to-implement encryption algorithm and is here for historic
reasons.

B.1 Group 1 - 768 Bit MODP

IKE implementations MAY support a MODP group with the following prime
and generator. This group is assigned id 1 (one).

The prime is: 2^768 - 2 ^704 - 1 + 2^64 * { [2^638 pi] + 149686 }
Its hexadecimal value is:

The generator is 2.

B.2 Group 2 - 1024 Bit MODP

IKE implementations SHOULD support a MODP group with the following
prime and generator. This group is assigned id 2 (two).

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The prime is 2^1024 - 2^960 - 1 + 2^64 * { [2^894 pi] + 129093 }.
Its hexadecimal value is:

The generator is 2.

B.3 Group 3 - 155 Bit EC2N

IKE implementations MAY support a EC2N group with the following
characteristics. This group is assigned id 3 (three). The curve is
based on the Galois Field GF[2^155]. The field size is 155. The
irreducible polynomial for the field is:
u^155 + u^62 + 1.
The equation for the elliptic curve is:
y^2 + xy = x^3 + ax^2 + b.

Field Size: 155
Group Prime/Irreducible Polynomial:
0x0800000000000000000000004000000000000001
Group Generator One: 0x7b
Group Curve A: 0x0
Group Curve B: 0x07338f
Group Order: 0x0800000000000000000057db5698537193aef944

The data in the KE payload when using this group is the value x from
the solution (x,y), the point on the curve chosen by taking the
randomly chosen secret Ka and computing Ka*P, where * is the
repetition of the group addition and double operations, P is the
curve point with x coordinate equal to generator 1 and the y
coordinate determined from the defining equation. The equation of
curve is implicitly known by the Group Type and the A and B
coefficients. There are two possible values for the y coordinate;
either one can be used successfully (the two parties need not agree
on the selection).

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B.4 Group 4 - 185 Bit EC2N

IKE implementations MAY support a EC2N group with the following
characteristics. This group is assigned id 4 (four). The curve is
based on the Galois Field GF[2^185]. The field size is 185. The
irreducible polynomial for the field is:
u^185 + u^69 + 1.

The equation for the elliptic curve is:
y^2 + xy = x^3 + ax^2 + b.

Field Size: 185
Group Prime/Irreducible Polynomial:
0x020000000000000000000000000000200000000000000001
Group Generator One: 0x18
Group Curve A: 0x0
Group Curve B: 0x1ee9
Group Order: 0x01ffffffffffffffffffffffdbf2f889b73e484175f94ebc

The data in the KE payload when using this group will be identical to
that as when using Oakley Group 3 (three).

B.5 Group 5 - 1536 Bit MODP

IKE implementations MUST support a MODP group with the following
prime and generator. This group is assigned id 5 (five).

The prime is 2^1536 - 2^1472 - 1 + 2^64 * {[2^1406 pi] + 741804}.
Its hexadecimal value is

FFFFFFFF FFFFFFFF C90FDAA2 2168C234 C4C6628B 80DC1CD1 29024E08
8A67CC74 020BBEA6 3B139B22 514A0879 8E3404DD EF9519B3 CD3A431B
302B0A6D F25F1437 4FE1356D 6D51C245 E485B576 625E7EC6 F44C42E9
A637ED6B 0BFF5CB6 F406B7ED EE386BFB 5A899FA5 AE9F2411 7C4B1FE6
49286651 ECE45B3D C2007CB8 A163BF05 98DA4836 1C55D39A 69163FA8
FD24CF5F 83655D23 DCA3AD96 1C62F356 208552BB 9ED52907 7096966D
670C354E 4ABC9804 F1746C08 CA237327 FFFFFFFF FFFFFFFF

The generator is 2.

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Change History

H.1 Changes from IKEv2-00 to IKEv2-01 February 2002

1) Changed Appendix B to specify the encryption and authentication
processing for IKE rather than referencing ESP. Simplified the format

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by removing idiosyncracies not needed for IKE.

2) Added option for authentication via a shared secret key.

3) Specified different keys in the two directions of IKE messages.
Removed requirement of different cookies in the two directions since
now no longer required.

4) Change the quantities signed by the two ends in AUTH fields to
assure the two parties sign different quantities.

5) Changed reference to AES to AES_128.

6) Removed requirement that Diffie-Hellman be repeated when rekeying
IKE SA.
IKE-SA.

7) Fixed typos.

8) Clarified requirements around use of port 500 at the remote end in
support of NAT.

9) Clarified required ordering for payloads.

10) Suggested mechanisms for avoiding DoS attacks.

11) Removed claims in some places that the first phase 2 piggybacked
on phase 1 was optional.

H.2 Changes from IKEv2-01 to IKEv2-02 April 2002

1) Moved the Initiator CERTREQ payload from message 1 to message 3.

2) Added a second optional ID payload in message 3 for the Initiator
to name a desired Responder to support the case where multiple named
identities are served by a single IP address.

3) Deleted the optimization whereby the Diffie-Hellman group did not
need to be specified in phase 2 if it was the same as in phase 1 (it
complicated the design with no meaningful benefit).

4) Added a section on the implications of reusing Diffie-Hellman
expontentials

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5) Changed the specification of sequence numbers to being at 0 in
both directions.

6) Many editorial changes and corrections, the most significant being
a global replace of "byte" with "octet".

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H.3 Changes from IKEv2-02 to IKEv2-03 October 2002

1) Reorganized the document moving introductory material to the
front.

2) Simplified the specification of Traffic Selectors to allow only
IPv4 and IPv6 address ranges, as was done in the JFK spec.

3) Fixed the problem brought up by David Faucher with the fix
suggested by Valery Smyslov. If Bob needs to narrow the selector
range, but has more than one matching narrower range, then if Alice's
first selector is a single address pair, Bob chooses the range that
encompasses that.

4) To harmonize with the JFK spec, changed the exchange so that the
initial exchange can be completed in four messages even if the
responder must invoke an anti-clogging defense and the initiator
incorrectly anticipates the responder's choice of Diffie-Hellman
group. This required changing the syntax of encrypted messages to
allow messages that are partially encrypted.

5) Replaced the hierarchical SA payload with a simplified version
that only negotiates suites of cryptographic algorithms. Separated
out negotiation of window size. Removed specifications of large
numbers

H.4 Changes from IKEv2-03 to IKEv2-04 January 2003

1) Integrated NAT traversal changes (including Appendix A).

2) Moved the anti-clogging token (cookie) from the SPI to a NOTIFY
payload; changed negotation back to 6 messages when a cookie is
needed.

3) Made capitalization of rarely used algorithms.

6) IKE-SA and CHILD-SA consistent.

4) Changed the formulas how IPcomp was negotiated.

5) Added usage scenarios.

6) Added configuration payload for key derivation as proposed by Hugo
Krawczyk. acquiring internal addresses on
remote networks.

7) Added Comformance Requirements section. negotiation of tunnel vs transport mode.

Author's Address

Charlie Kaufman charlie_kaufman@notesdev.ibm.com IBM

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Full Copyright Statement

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
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followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."

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