WDIFF

draft-ietf-msec-gdoi-03.txt --> draft-ietf-msec-gdoi-04.txt

Internet Engineering Task Force Mark Baugher(Cisco)
INTERNET-DRAFT Thomas Hardjono (Verisign)
Document: draft-ietf-msec-gdoi-03.txt draft-ietf-msec-gdoi-04.txt Hugh Harney (Sparta)
Expires: July, August, 2002 Brian Weis (Cisco)

January 16,

February 26, 2002

The Group Domain of Interpretation
<draft-ietf-msec-gdoi-03.txt>
<draft-ietf-msec-gdoi-04.txt>

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

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Abstract

This document presents an ISAMKP Domain of Interpretation (DOI) for
group key management to support secure group communications. The
"GDOI" incorporates the definition of a Phase 1 SA of the Internet
DOI, and proposes new payloads and exchanges according to the ISAKMP
standard. The GDOI manages group security associations, which are
used by IPSEC and potentially other data security protocols running
at the IP or application layers. These security associations protect
one or more key-encrypting keys, traffic-encrypting keys, or data
shared by group members.

Comments on this document should be sent to msec@securemulticast.org.

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Table of Contents

1.0 Introduction......................................................3
1.1 GDOI Applications...............................................4 Applications..............................................4
1.2 Extending GDOI..................................................5 GDOI.................................................5
2.0 ISAKMP Phase 1 protocol...........................................5
2.1 DOI value.....................................................5
2. 2 UDP port.....................................................5
3.0 GROUPKEY-PULL Exchange............................................5
3.1 Authorization...................................................5
3.2 Messages........................................................5 Messages........................................................6
3.2.1 Perfect Forward Secrecy.....................................7
3.2.2 ISAKMP Header Initialization................................8
3.3 Initiator Operations............................................8
3.4 Receiver Operations.............................................9
4.0 GROUPKEY-PUSH Message.............................................9
4.1 Perfect Forward Secrecy (PFS)..................................10
4.2 Forward and Backward Access Control............................10
4.3 Delegation of Key Management...................................10 Management...................................11
4.4 Use of signature keys..........................................10 keys..........................................11
4.5 ISAKMP Header Initialization...................................11
4.6 Deletion of SAs................................................11
4.7 Initiator Operations...........................................11 GCKS Operations................................................12
4.8 Receiver Operations............................................12 Group Member Operations........................................12
5.0 Payloads and Defined Values......................................12 Values......................................13
5.1 Identification Payload.........................................13
5.1.1 Identification Type Values.................................13 Values.................................14
5.2 Security Association Payload...................................14
5.2.1 Payloads following the SA payload..........................14 payload..........................15
5.3 SA KEK payload.................................................15 payload.................................................16
5.3.1 KEK Attributes.............................................17
5.3.2 KEK_MANAGEMENT_ALGORITHM...................................17 KEK_MANAGEMENT_ALGORITHM...................................18
5.3.3 KEK_ALGORITHM..............................................17 KEK_ALGORITHM..............................................18
5.3.4 KEK_KEY_LENGTH.............................................18 KEK_KEY_LENGTH.............................................19
5.3.5 KEK_KEY_LIFETIME...........................................18 KEK_KEY_LIFETIME...........................................19
5.3.6 SIG_HASH_ALGORITHM.........................................18 SIG_HASH_ALGORITHM.........................................19
5.3.7 SIG_ALGORITHM..............................................19
5.3.8 SIG_KEY_LENGTH.............................................19 SIG_KEY_LENGTH.............................................20
5.3.9 KE_OAKLEY_GROUP............................................19 KE_OAKLEY_GROUP............................................20
5.4 SA TEK Payload.................................................19 Payload.................................................20
5.4.1 PROTO_IPSEC_ESP............................................20 PROTO_IPSEC_ESP............................................21
5.4.2 Other Security Protocols...................................22
5.5 Key Download Payload...........................................22 Payload...........................................23
5.5.1 TEK Download Type..........................................23 Type..........................................24
5.5.2 KEK Download Type..........................................24 Type..........................................25
5.5.3 LKH Download Type..........................................25 Type..........................................26
5.6 Sequence Number Payload........................................27 Payload........................................28

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5.7 Proof of Possession............................................27 Possession............................................28
5.8 Nonce..........................................................28 Nonce..........................................................29
7.0 Security Considerations..........................................28 Considerations..........................................29
8.0 IANA Considerations..............................................28 Considerations..............................................29
8.1 ISAKMP DOI.....................................................28 DOI.....................................................29
8.2 Payload Types..................................................28 Types..................................................29
8.3 New Namespaces.................................................29 Namespaces.................................................30
8.3 UDP Port.......................................................29 Port.......................................................30
9.0 Acknowledgements.................................................29 Acknowledgements.................................................30
10.0 References......................................................29 References......................................................30
10.1 Normative References..........................................30
10.2 Informative References........................................31
Authors Addresses....................................................30 Addresses....................................................32

1.0 Introduction

This document presents an ISAMKP Domain of Interpretation (DOI) for
group key management called the ?Group Domain of Interpretation?
(GDOI). In this group key management model, the GDOI protocol is run
between a group member and a ?group controller/key server? (GCKS),
which establishes security associations [Section 4.6.2 RFC2401] among
authorized group members. ISAKMP defines two "phases" of negotiation
[p.16 RFC2408]. The GDOI incorporates the Phase 1 security
association (SA) definition from the Internet DOI [RFC2407, RFC2409].
The Phase 2 exchange is defined in this document, and proposes new
payloads and exchanges according to the ISAKMP standard [p. 14
RFC2408].

There are six new payloads:
1) GDOI SA
2) SA KEK (SAK) which follows the SA payload
3) SA TEK (SAT) which follows the SA payload
4) Key Download Array (KD)
5) Sequence number (SEQ)
6) Proof of Possession (POP)

There are two new exchanges.

1) A Phase 2 exchange creates Re-key and Data-Security Protocol SAs.

The new Phase 2 exchange, called "GROUPKEY-PULL," downloads keys for
a group?s ?Re-key? SA and/or ?Data-security? SA. The Re-key SA
includes a key encrypting key, or KEK, common to the group; a Data-
security SA includes a data encryption key, or TEK, used by a data-
security protocol to encrypt or decrypt data traffic [Section 2.1
RFC2407]. The SA for the KEK or TEK includes authentication keys,
encryption keys, cryptographic policy, and attributes. The GROUPKEY-
PULL exchange uses "pull" behavior since the member initiates the
retrieval of these SAs from a GCKS.

2) A datagram subsequently establishes additional Rekey and/or Data-
Security Protocol SAs.

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2) A datagram subsequently establishes additional Rekey and/or Data-
Security Protocol SAs.

The GROUPKEY-PUSH datagram is "pushed" from the GCKS to the members
to create or update a Re-key or Data-security SA. A Re-key SA
protects GROUPKEY-PUSH messages. Thus, a GROUPKEY-PULL is necessary
to establish at least one Re-key SA in order to protect subsequent
GROUPKEY-PUSH messages. The GDOI sender GCKS encrypts the GROUPKEY-PUSH message
using the KEK Re-key SA. GDOI accommodates the use of arrays of KEKs
for group key management algorithms using the Logical Key Hierarchy
(LKH) algorithm to efficiently add and remove group members
[RFC2627]. Implementation of the LKH algorithm is OPTIONAL.

Although the GROUPKEY-PUSH specified by this document can be used to
refresh a Re-key SA, the most common use of GROUPKEY-PUSH is to
establish a Data-security SA for a data security protocol. GDOI can
accommodate future extensions to support a variety of data security
protocols. This document only specifies data-security SAs for one
security protocol, IPsec ESP. A separate RFC will specify support for
other data security protocols such as a future secure Real-time
Transport Protocol. A security protocol uses the TEK and "owns" the
data-security SA in the same way that IPsec ESP uses the IKE Phase 2
keys and owns the Phase 2 SA; for GDOI, IPsec ESP uses the TEK.

GDOI uses the Phase 1 exchanges defined in [RFC2409] and definitions
and an ISAKMP-compliant header from [RFC2408]. "GDOI" is the
declared domain of interpretation in the header used in the Phase 1
and subsequent GDOI Phase 2 (GROUPKEY-PULL) exchanges.

Thus, GDOI is a group security association management protocol: All
GDOI messages are used to create, maintain, or delete security
associations for a group. As described above, these security
associations protect one or more key-encrypting keys, traffic-
encrypting keys, or data shared by group members for multicast and
groups-security applications.

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in RFC 2119 [RFC2119].

1.1 GDOI Applications

Secure multicast applications include video broadcast and multicast
file transfer. In a business environment, many of these applications
require network security and may use IPsec ESP to secure their data
traffic. Section 5.4.1 specifies how GDOI carries the needed SA
parameters for ESP. In this way, GDOI supports multicast ESP with
group authentication of ESP packets using the shared, group key
(authentication of unique sources of ESP packets is not possible).

GDOI can also secure group applications that do not use multicast
transport such as video-on-demand. For example, the GROUPKEY-PUSH

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message may establish a pair-wise IPsec ESP SA for a member of a
subscription group without the need for key management exchanges and
costly asymmetric cryptography.

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1.2 Extending GDOI

Not all secure multicast or multimedia applications can use IPsec
ESP. Many Real Time Transport Protocol applications, for example,
require security above the IP layer to preserve RTP header
compression efficiencies and transport-independence [RFC1889]. A
future RTP security protocol may benefit from using GDOI to establish
group SAs for multicast and unicast security services. In order to
add a new data security protocol, a new RFC MUST specify the data-
security SA parameters conveyed by GDOI for that security protocol;
these parameters are listed in section 5.4.2 of this document.

2.0 ISAKMP Phase 1 protocol

The GDOI uses ISAKMP phase 1 exchanges as defined in [RFC2409]. The
following sections define characteristics which are unique for these
exchanges when used for GDOI.

2.1 DOI value

The Phase 1 SA payload has a DOI value. That value MUST be the GDOI
DOI value as defined later in this document.

2. 2 UDP port.

GDOI MUST NOT run on port 500 (the port commonly used for IKE). A new
port number MUST be defined by IANA for GDOI.

3.0 GROUPKEY-PULL Exchange

The goal of the GROUPKEY-PULL exchange is to establish a Re-key
and/or Data-security SAs at the member for a particular group. A
Phase 1 SA (as defined in [RFC2407]) protects the GROUPKEY-PULL;
there may MAY be multiple GROUPKEY-PULL exchanges for a given Phase 1 SA.
The GROUPKEY-PULL exchange downloads the data security keys (TEKs)
and/or group key encrypting key (KEK) or KEK array under the
protection of the Phase 1 SA.

3.1 Authorization

There are two alternative means for authorizing the GROUPKEY-PULL
message. First, the Phase 1 identity can be used to authorize the
Phase 2 (GROUPKEY-PULL) request for a group key. Second, a new
identity can be passed in the GROUPKEY-PULL request. The new
identity could be specific to the group and use a certificate that is
signed by the group owner to identify the holder as an authorized
group member. The Proof-of-Possession payload validates that the
holder possesses the secret key associated with the Phase 2 identity.

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3.2 Messages

The GROUPKEY-PULL is an a Phase 2 exchange. Phase 1 computes SKEYID_a
from the DH keying material exchanged in Phase 1. SKEYID_a is the

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"key" in the keyed hash used in the GROUPKEY-PULL HASH payloads. As
with the IKE HASH payload generation [RFC 2409 section 5.5], each
GROUPKEY-PULL message hashes a uniquely defined set of values.
Nonces permute the HASH and provide some protection against replay
attacks. Replay protection is important to protect the GCKS from
attacks that a key management server will attract.

The GROUPKEY-PULL uses nonces to guarantee "liveliness", or against
replay of a recent GROUPKEY-PULL message. The replay attack is only
useful in the context of the current Phase 1. If a GROUPKEY-PULL
message is replayed based on a previous Phase 1, the HASH calculation
will fail due to a wrong SKEYID_a. The message will fail processing
before the nonce is ever evaluated. In order for either peer to get
the benefit of the replay protection it must postpone as much
processing as possible until it receives the message in the protocol
that proves the peer is live. For example, the Responder MUST NOT
compute the shared Diffie-Hellman number (if KE payloads were
included) or install the new SAs until it receives a message with Nr
included properly in the HASH payload.

Nonces require an additional message in the protocol exchange to
ensure that the GCKS does not add a group member until it proves
liveliness. The GROUPKEY-PULL member-initiator expects to find its
nonce, Ni, in the HASH of a returned message. And the GROUPKEY-PULL
GKCS responder expects to see its nonce, Nr, in the HASH of a
returned message before providing group-keying material as in the
following exchange.

Initiator (Member) Responder (GCKS)
------------------ ----------------
HDR*, HASH(1), Ni, ID -->
<-- HDR*, HASH(2), Nr, SA
HDR*, HASH(3) [,KE_I] -->
[,CERT] [,POP_I]
<-- HDR*, HASH(4),[KE_R,][SEQ,]
KD [,CERT] [,POP_R]

Hashes are computed as follows:
HASH(1) = prf(SKEYID_a, M-ID | Ni | ID)
HASH(2) = prf(SKEYID_a, M-ID | Ni_b | Nr | SA)
HASH(3) = prf(SKEYID_a, M-ID | Ni_b | Nr_b [ | KE_I ][ | POP_I ])
HASH(4) = prf(SKEYID_a, M-ID | Ni_b | Nr_b [ | KE_R ] [ | SEQ | ]
KD [ | POP_R])

POP payload is constructed as described in Section 5.7.
* Protected by the Phase 1 SA, encryption occurs after HDR

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HDR is an ISAKMP header payload that uses the Phase 1 cookies and a
message identifier (M-ID) as in IKE [RFC2409]. Note that nonces are
included in the first two exchanges, with the GCKS returning only the
SA policy payload before liveliness is proven. The HASH payloads
[RFC2409] prove that the peer has the Phase 1 secret (SKEYID_a) and
the nonce for the exchange identified by message id, M-ID. Once

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liveliness is established, the last message completes the real
processing of downloading the KD payload.

In addition to the Nonce and HASH payloads, the member-initiator
identifies the group it wishes to join through the ISAKMP ID payload.
The GCKS responder informs the member of the current value of the
sequence number in the SEQ payload; the sequence number orders the
GROUPKEY-PUSH datagrams (section 4); the member MUST check to see
that the sequence number is greater than in the previous SEQ payload
the member holds for the group (if it holds any) before installing
any new SAs . The SEQ payload MUST be present if the SA payload
contains an SA KEK attribute. The GCKS responder informs the member
of the cryptographic policies of the group in the SA payload, which
describes the DOI, KEK and/or TEK keying material, and authentication
transforms. The SPIs are also determined by the GCKS and downloaded
in the SA payload chain (see section 5.2). The SA KEK attribute
contains the ISAKMP cookie pair for the Re-key SA, which is not
negotiated but downloaded. The SA TEK attribute contains an SPI as
defined in section 5.4 of this document. The second message
downloads this SA payload. If a Re-key SA is defined in the SA
payload, then KD will contain the KEK; if one or more Data-security
SAs are defined in the SA payload, KD will contain the TEKs. This is
useful if there is an initial set of TEKs for the particular group
and can obviate the need for future TEK GROUPKEY-PUSH messages
(described in section 4).

As described above, the member may establish an identity in the
GROUPKEY-PULL exchange in an optional CERT payload that is separate
from the Phase 1 identity. When the member passes a new CERT, a
proof of possession (POP) payload accompanies it. The POP payload
demonstrates that the member or GCKS has used the very secret that
authenticates it. POP_I is an ISAKMP SIG payload containing a hash
including the nonces Ni and Nr signed by the member, when the member
passes a CERT, signed by the Group Owner to prove its authorization.
POP_R contains the hash including the concatenated nonces Ni and Nr
signed by the GCKS, when the GCKS passes a CERT, signed by the group
owner, to prove its authority to provide keys for a particular group.
The use of the nonce pair for the POP payload, transformed through a
pseudo-random function (prf) and encrypted, is designed to withstand
compromise of the Phase 1 key. Implementation of the CERT and POP
payloads is OPTIONAL.

3.2.1 Perfect Forward Secrecy

If PFS is desired and the optional KE payload is used in the
exchange, then both sides compute a DH secret and use it to protect
the new keying material contained in KD. The GCKS responder will xor

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the DH secret with the KD payload and send it to the member
Initiator, which recovers the KD by repeating this operation as in
the Oakley IEXTKEY procedure [RFC2412]. Implementation of the KE
payload is OPTIONAL.

3.2.2 ISAKMP Header Initialization

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Cookies are used in the ISAKMP header as a weak form of denial of
service protection. The GDOI GROUPKEY-PULL exchange uses cookies
according to ISAKMP [RFC2408].

Next Payload identifies an ISAKMP or GDOI payload (see Section 5.0).

Major Version is 1 and Minor Version is 0 according to ISAKMP
[RFC2408, Section 3.1].

The Exchange Type has value 240 for the GDOI GROUPKEY-PULL exchange.

Flags, Message ID, and Length are according to ISAKMP [RFC2408,
Section 3.1]

3.3 Initiator Operations

Before a group member (GDOI initiator) contacts the GCKS, it must
determine the group identifier and acceptable Phase 1 policy via an
out-of-band method such as SDP. Phase 1 is initiated using the GDOI
DOI in the SA payload. Once Phase 1 is complete the initiator state
machine moves to the GDOI protocol.

To construct the first GDOI message the initiator chooses Ni and
creates a nonce payload, builds an identity payload including the
group identifier, and generates HASH(1).

Upon receipt of the second GDOI message, the initiator validates
HASH(2), extracts the nonce Nr, and interprets the SA payload. If the
policy in the SA payload is acceptable (e.g., the security protocol
and cryptographic protocols can be supported by the initiator), the
initiator continues the protocol.

If the group policy uses certificates for authorization, the
initiator generates a hash including Ni and Nr and signs it. This
becomes the contents of the POP payload. If necessary, a CERT payload
is constructed which holds the public key corresponding to the
private key used to sign the POP payload.

The initiator constructs the third GDOI message by including the CERT
and POP payloads (if needed) and creating HASH(3).

Upon receipt of the fourth GDOI messages, the initiator validates
HASH(4). If the responder sent CERT and POP_R payloads, the POP
signature is validated.

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If a SEQ payload is present, the sequence number in the SEQ payload
must be checked against any previously received sequence number for
this group. If it is less than the previously received number, it
should be considered stale and ignored. This could happen if two
GROUPKEY-PULL messages happened in parallel, and the sequence number
changed between the times the results of two GROUPKEY-PULL messages
were returned from the GCKS.

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The initiator interprets the KD key packets, matching the SPIs in the
key packets to SPIs previously sent in the SA payloads identifying
particular policy. For TEKs, once the keys and policy are matched,
the initiator is ready to send or receive packets matching the TEK
policy. (If policy and keys had been previously received for this
TEK policy, the initiator may decide instead to ignore this TEK
policy in case it is stale.) If this group has a KEK, the KEK policy
and keys are marked as ready for use.

3.4 Receiver Operations

The GCKS (responder) passively listens for incoming requests from
group members. The Phase 1 authenticates the group member and sets up
the secure session with them.

Upon receipt of the first GDOI message the GCKS validates HASH(1),
extracts the Nr and group identifier in the ID payload. It verifies
that its database contains the group information for the group
identifier.

The GCKS constructs the second GDOI message, including a nonce Nr,
and the policy for the group in an SA payload, followed by SA TEK
payloads for traffic SAs, and SA KEK policy (if the group controller
will be sending Re-key messages to the group).

Upon receipt of the third GDOI message the GCKS validates HASH(3). If
the initiator sent CERT and POP_I payloads, the POP signature is
validated.

The GCKS constructs the fourth GDOI message, including the SEQ
payload (if the GCKS sends rekey messages), the KD payload containing
keys corresponding to policy previously sent in the SA TEK and SA KEK
payloads, and the CERT and POP payloads (if needed).

4.0 GROUPKEY-PUSH Message

GDOI sends control information securely using group communications.
Typically this will be using IP multicast distribution of a GROUPKEY-
PUSH message but it can also be "pushed" using unicast delivery if IP
multicast is not possible. The GROUPKEY-PUSH message replaces a Re-
key SA KEK or KEK array, and/or creates a new Data-security SA (see
section 1.3).

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Member GCKS or Delegate
------ ----------------

<---- HDR*, SEQ, SA, KD, [CERT,] SIG

* Protected by the Re-key SA KEK; encryption occurs after HDR

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HDR is defined below. The SEQ payload is defined in the Payloads
section. The SA defines the policy (e.g. protection suite) and
attributes (e.g. SPI) for a Re-key and/or Data-security SAs. The
GCKS or delegate optionally provides a CERT payload for verification
of the SIG. KD is the key download payload as described in the
Payloads section.

The SIG payload is a signature of a hash of the entire message before
encryption (including the header and excluding the SIG payload
itself), prefixed with the string "rekey". The prefixed string
ensures that the signature of the Rekey datagram cannot be used for
any other purpose in the GDOI protocol.

If the SA defines an LKH-style LKH KEK array or single KEK, KD contains a KEK
or KEK array for a new Re-key SA, which has a new cookie pair. When
the KD payload carries a new SA KEK attribute (section 5.3), a Re-key
SA is replaced with a new SA having the same group identifier (ID
specified in message 1 of section 3.1) and incrementing the same
sequence counter, which is initialized in message 4 of section 3.1.
If the SA defines an SA TEK payload, this informs the member that a
new Data-security SA has been created, with keying material carried
in KD (Section 5.5).

4.1

If the SA defines a large LKH KEK array (e.g., during group
initialization and batched rekeying), parts of the array MAY be sent
in different unique GROUPKEY-PUSH datagrams. However, each of the
GROUPKEY-PUSH datagrams MUST be a fully formed GROUPKEY-PUSH
datagram. This results in each datagram containing a sequence number
and the policy in the SA payload which corresponds to the KEK array
portion sent in the KD payload.

4.1 Perfect Forward Secrecy (PFS)

The GROUPKEY-PUSH message is protected by the group KEK though in all
cases, the GROUPKEY-PUSH message carries new key downloads, among
other information. A freshly generated secret must protect the key
download for the GROUPKEY-PUSH message to have PFS. This issue is
for further study.

4.2 Forward and Backward Access Control

Through GROUPKEY-PUSH, the GDOI supports algorithms such as LKH that
have the property of denying access to a new group key by a member
removed from the group (forward access control) and to an old group
key by a member added to the group (backward access control). An
unrelated notion to PFS, "forward access control" and "backward

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access control" have been called "perfect forward security" and
"perfect backward security" in the literature [RFC2627].

Group management algorithms providing forward and backward access
control other than LKH have been proposed in the literature,
including [OTF]and [NNL]. These algorithms could be used with GDOI,
but are not specified as a part of this document.

4.3 Delegation of Key Management

GDOI supports delegation of GROUPKEY-PUSH datagrams through the
delegation capabilities of the PKI. However, GDOI does not explicitly
specify how the GCKS identifies delegates, but leaves this to the PKI
that is used by a particular GDOI implementation.

4.4 Use of signature keys

The GCKS SHOULD NOT use the same key to sign the SIG payload in the
GROUPKEY-PUSH message as was used for authorization in the GROUPKEY-
PULL POP payload. If the same key must be used, a different hash

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function SHOULD be used as a base for the POP payload than is used as
a base for the SIG payload.

4.5 ISAKMP Header Initialization

Unlike ISAKMP or IKE, the cookie pair is completely determined by the
GCKS. The cookie pair in the GDOI ISAKMP header identifies the Re-key
SA to differentiate the secure groups managed by a GCKS. Thus, GDOI
uses the cookie fields as an SPI

Next Payload identifies an ISAKMP or GDOI payload (see Section 5.0).

Major Version is 1 and Minor Version is 0 according to ISAKMP
[RFC2408, Section 3.1].

The Exchange Type has value 241 for the GDOI GROUPKEY-PUSH message.

Flags,

Flags MUST have the Encryption bit set according to [RFC2008, Section
3.1]. All other bits MUST be set to zero.

Message ID, and ID MUST be set to zero.

Length are is according to ISAKMP [RFC2408, Section 3.1]

4.6 Deletion of SAs

There are times the GCKS may want to signal to receivers to delete
SAs, for example at the end of a broadcast. Deletion of keys may be
accomplished by sending an ISAKMP Delete payload [RFC2408, Section
3.15] as part of a GDOI GROUPKEY-PUSH message.

One or more Delete payloads MAY be placed following the SEQ payload
in a GROUPKEY-PUSH message. If a GCKS has no further SAs to send to

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group members, the SA and KD payloads MUST be omitted from the
message.

The following fields of the Delete Payload are further defined as
follows:

o The Domain of Interpretation field contains the GDOI DOI.

o The Protocol-Id field contains TEK protocol id values defined in
Section 5.4 of this document. To delete a KEK SA, the value of zero
MUST be used as the protocol id. Note that only one protocol id value
can be defined in a Delete payload. If a TEK SA and a KEK SA must be
deleted, they must be sent in different Delete payloads.

4.7 Initiator GCKS Operations

An initiator (GCKS

GCKS or delegate) its delegate may initate a Rekey message for one of several
reasons, e.g. the group membership has changed or keys are due to
expire.

To begin the rekey datagram the GCKS builds an ISAKMP HDR with the
correct cookie pair, and a SEQ payload that includes a sequence
number which is one greater than the previous rekey datagram.

An SA payload is then added. This is identical in structure and
meaning to a SA payload sent in a GROUPKEY-PULL exchange. If there
are changes to the KEK (in the case of a static KEK) or in group
membership (in the case of LKH) an SA_KEK attribute is added to the
SA. If there are one or more new TEKs then SA_TEK attributes are
added to describe that policy.

A KD payload is then added. This is identical in structure and
meaning to a KD payload sent in a GROUPKEY-PULL exchange. If an
SA_KEK attribute was included in the SA payload then corresponding
KEK keys (or a KEK array) is included. TEK keys are sent for each
SA_TEK attribute included in the SA payload.
The payloads following the HDR are then encrypted using the current
KEK encryption key.

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A CERT payload is added if the initiator needs to provide its
certificate.

Finally, the initiator hashes the string "rekey" followed by the key
management message already formed. The hash is signed, placed in a
SIG payload and added to the datagram. The datagram can now be sent.

4.8 Receiver Group Member Operations

A group member receiving the GROUPKEY-PUSH datagram matches the
cookie pair in the ISAKMP HDR to an existing SA. The message is
decrypted, and the form of the datagram is validated. This weeds out
obvious ill-formed messages (which may be sent as part of a Denial of
Service attack on the group).

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The signature of the decrypted message is then validated, possibly
using the CERT payload if it is included.

The sequence number in the SEQ payload is validated to ensure that it
is greater than the previously received sequence number, and that it
fits within a window of acceptable values.

The SA and KD payloads are processed which results in a new GDOI
Rekey SA (if the SA payload included an SA_KEK attribute) and/or new
IPsec SAs being added to the system.

5.0 Payloads and Defined Values

This document specifies use of several ISAKMP payloads, which are
defined in accordance with RFC2408. The following payloads are
extended or further specified.

Next Payload Type Value
----------------- -----
Security Association (SA) 1
Identification (ID) 5
Nonce (N) 10

Several new payload formats are required in the group security
exchanges. The Payload types for the new headers are defined in the
ISAKMP "Private USE" range.

Next Payload Type Value
----------------- -----
RESERVED 128 - 129
SA KEK Payload (SAK) 130
SA TEK Payload (SAT) 131
Key Download (KD) 132
Sequence Number (SEQ) 133
Proof of Possession (POP) 134
RESERVED 135 - 200
GDOI Private Use 201 - 255

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5.1 Identification Payload

The Identification Payload is used to identify a group identity that
will later be associated with Security Associations for the group. A
group identity may map to a specific IP multicast group, or may
specify a more general identifier, such as one that represents a set
of related multicast streams.

The Identification Payload is defined as follows:

0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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! Next Payload ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! ID Type ! RESERVE2 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Identification Payload 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, this field will be zero (0).

o RESERVED (1 octet) - Unused, must be zero (0).

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

o Identification Type (1 octet) - Value describing the identity
information found in the Identification Data field.

o RESERVED2 (2 octets) - Unused, must be zero (0).

O Identification Data (variable length) - Value, as indicated by
the Identification Type.

5.1.1 Identification Type Values

The following table lists the assigned values for the Identification
Type field found in the Identification Payload.

ID Type Value
------- -----
RESERVED 0 - 10
ID_KEY_ID 11
RESERVED 12 - 127
Private Use 128 - 255

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5.1.1.1 ID_KEY_ID
In the context of a GDOI ID payload, ID_KEY_ID specifies a four (4)-
octet group identifier.

5.2 Security Association Payload

The Security Association payload is defined in RFC 2408. For the
GDOI, it is used by the GCKS to assert security attributes for both
Re-key and Data-security SAs
0 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 ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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! DOI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Situation !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

! SA Attribute Next Payload ! RESERVED2 !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

The Security Association Payload fields are defined as follows:

o Next Payload (1 octet) - Identifies the next payload for the
GROUPKEY-PULL or the GROUPKEY-PUSH message as defined above. The next
payload MUST NOT be a SAK Payload or SAT Payload type, but the next
non-Security Association type payload.

o RESERVED (1 octet) - Must be zero.

o Payload Length (2 octets) is the octet length of the current
payload including the generic header and all TEK and KEK payloads.

o DOI (4 octets) - Is the GDOI, which is value 196 pending
assignment by the IANA.

o Situation (4 octets) - Must be zero.

o SA Attribute Next Payload (1 octet) - Must be either a SAK
Payload or a SAT Payload. See section 5.3.2 for a description of
which circumstances are required for each payload type to be present.

o RESERVED (2 octets) - Must be zero.

5.2.1 Payloads following the SA payload

Payloads that define specific security association attributes for the
KEK and/or TEKs used by the group MUST follow the SA payload. How
many of each payload is dependant upon the group policy. There may be
zero or one SAK Payloads, and zero or more SAT Payloads, where either
one SAK or SAT payload MUST be present.

This latitude allows for various group policies to be accommodated.
For example if the group policy does not require the use of a Re-key
SA, the GCKS would not need to send an SA KEK attribute to the group
member since all SA updates would be performed using the Registration

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SA. Alternatively, group policy might use a Re-key SA but choose to
download a KEK to the group member only as part of the Registration
SA. Therefore, the KEK policy (in the SA KEK attribute) would not be
necessary as part of the Re-key SA message SA payload.

Specifying multiple SATs allows multiple sessions to be part of the
same group and multiple streams to be associated with a session
(e.g., video, audio, and text) but each with individual security
association policy.

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5.3 SA KEK payload

The SA KEK (SAK) payload contains security attributes for the KEK
method for a group and parameters specific to the GROUPKEY-PULL
operation. The source and destination identities describe the
identities used for the GROUPKEY-PULL datagram.

0 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 ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Protocol ! SRC ID Type ! SRC ID Port !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
!SRC ID Data Len! SRC Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! DST ID Type ! DST ID Port !DST ID Data Len!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! DST Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! !
~ SPI ~
! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! POP Algorithm ! POP Key Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
~ KEK Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

The SAK Payload fields are defined as follows:

o Next Payload (1 octet) - Identifies the next payload for the
GROUPKEY-PULL or the GROUPKEY-PUSH message. The only valid next
payload types for this message are a SAT Payload or zero to indicate
there is no SA TEK payload.

o RESERVED (1 octet) - Must be zero.

o Payload Length (2 octets) - Length of this payload, including
the KEK attributes.

o Protocol (1 octet) - Value describing an IP protocol ID (e.g.,
UDP/TCP) for the rekey datagram.

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o SRC ID Type (1 octet) - Value describing the identity
information found in the SRC Identification Data field. Defined
values are specified by the IPSEC Identification Type section in the
IANA isakmpd-registry [ISAKMP-REG].

o SRC ID Port (2 octets) - Value specifying a port associated
with the source Id. A value of zero means that the SRC ID Port field
should be ignored.

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o SRC ID Data Len (1 octet) - Value specifying the length of the
SRC Identification Data field.

o SRC Identification Data (variable length) - Value, as indicated
by the SRC ID Type.

o DST ID Type (1 octet) - Value describing the identity
information found in the DST Identification Data field. Defined
values are specified by the IPSEC Identification Type section in the
IANA isakmpd-registry [ISAKMP-REG].

o DST ID Prot (1 octet) - Value describing an IP protocol ID
(e.g., UDP/TCP).

o DST ID Port (2 octets) - Value specifying a port associated
with the source Id.

o DST ID Data Len (1 octet) - Value specifying the length of the
DST Identification Data field.

o DST Identification Data (variable length) - Value, as indicated
by the DST ID Type.

o SPI (16 octets) - Security Parameter Index for the KEK. The SPI
must be the ISAKMP Header cookie pair where the first 8 octets become
the "Initiator Cookie" field of the GROUPKEY-PUSH message ISAKMP HDR,
and the second 8 octets become the "Responder Cookie" in the same
HDR. As described above, these cookies are assigned by the GCKS.

o POP Algorithm (2 octets) - The POP payload algorithm. Defined
values are specified in the following table. If no POP algorithm is
defined by the KEK policy this field must be zero.

Algorithm Type Value
-------------- -----
RESERVED 0
POP_ALG_RSA 1
POP_ALG_DSS 2
POP_ALG_ECDSS 3
RESERVED 4-127
Private Use 128-255

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o POP Key Length (2 octets) - Length of the POP payload key. If
no POP algorithm is defined in the KEK policy this field must be
zero.

o KEK Attributes - Contains KEK policy attributes associated with
the group. The following sections describe the possible attributes.
Any or all attributes may be optional, depending on the group policy.

5.3.1 KEK Attributes

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The following attributes may be present in a SAK Payload. The
attributes must follow the format defined in ISAKMP [RFC2408] section
3.3. In the table, attributes that are defined as TV are marked as
Basic (B); attributes that are defined as TLV are marked as Variable
(V).

ID Class Value Type
-------- ----- ----
RESERVED 0
KEK_MANAGEMENT_ALGORITHM 1 B
KEK_ALGORITHM 2 B
KEK_KEY_LENGTH 3 B
KEK_KEY_LIFETIME 4 V
SIG_HASH_ALGORITHM 5 B
SIG_ALGORITHM 6 B
SIG_KEY_LENGTH 7 B
KE_OAKLEY_GROUP 10 B

The following attributes may only be included in a GROUPKEY-PULL
message: KEK_MANAGEMENT_ALGORITHM, KE_OAKLEY_GROUP.

5.3.2 KEK_MANAGEMENT_ALGORITHM

The KEK_MANAGEMENT_ALGORITHM class specifies the group KEK management
algorithm used to provide forward or backward access control (i.e.,
used to exclude group members). Defined values are specified in the
following table.

KEK Management Type Value
------------------- -----
RESERVED 0
LKH 1
RESERVED 2-127
Private Use 128-255

5.3.3 KEK_ALGORITHM

The KEK_ALGORITHM class specifies the encryption algorithm using with
the KEK. Defined values are specified in the following table.

Algorithm Type Value
-------------- -----
RESERVED 0
KEK_ALG_DES 1
KEK_ALG_3DES 2
KEK_ALG_AES 3
RESERVED 4-127
Private Use 128-255

]. A GDOI implementation MUST support the following algorithm attribute
KEK_ALG_3DES.

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KEK_ALG_DES 1
KEK_ALG_3DES 2
KEK_ALG_AES 3
RESERVED 4-127
Private Use 128-255

5.3.3.1 KEK_ALG_DES

This algorithm specifies DES using the Cipher Block Chaining (CBC) mode
as described in [FIPS81].

5.3.3.2 KEK_ALG_3DES

This algorithm specifies 3DES using three independent keys as described
in "Keying Option 1" in [FIPS46-3].

5.3.3.3 KEK_ALG_AES

This algorithm specifies AES as described in [FIPS197]. The mode of
operation for AES is Cipher Block Chaining (CBC) as recommended in [AES-
MODES].

5.3.4 KEK_KEY_LENGTH

The KEK_KEY_LENGTH class specifies the KEK Algorithm key length (in
bits).

5.3.5 KEK_KEY_LIFETIME

The KEK_KEY_LIFETIME class specifies the maximum time for which the
KEK is valid. The GCKS may refresh the KEK at any time before the end
of the valid period. The value is a four (4) octet number defining a
valid time period in seconds.

5.3.6 SIG_HASH_ALGORITHM

SIG_HASH_ALGORITHM specifies the SIG payload hash algorithm. The
following tables define the algorithms for SIG_HASH_ALGORITHM.

Algorithm Type Value
-------------- -----
RESERVED 0
SIG_HASH_MD5 1
SIG_HASH_SHA1 2
RESERVED 3-127
PRIVATE USE 128-255

SIG_HASH_ALGORITHM is not required if the SIG_ALGORITHM is
SIG_ALG_DSS or SIG_ALG_ECDSS, which imply SIG_HASH_SHA1.

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5.3.7 SIG_ALGORITHM

The SIG_ALGORITHM class specifies the SIG payload signature
algorithm.
Defined values are specified in the following table.
Algorithm Type Value
-------------- -----

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RESERVED 0
SIG_ALG_RSA 1
SIG_ALG_DSS 2
SIG_ALG_ECDSS 3
RESERVED 4-127
Private Use 128-255

]. A GDOI implementation MUST support the following algorithm attribute:
SIG_ALG_RSA.

5.3.7.1 SIG_ALG_RSA

This algorithm specifies the RSA digital signature algorithm as
described in [RSA].

5.3.7.2 SIG_ALG_DSS

This algorithm specifies the DSS digital signature algorithm as
described in [FIPS186-2].

5.3.7.3 SIG_ALG_ECDSS

This algorithm specifies the Eliptic Elliptic Curve digital signature algorithm
as described in [FIPS186-2].

5.3.8 SIG_KEY_LENGTH

The SIG_KEY_LENGTH class specifies the length of the SIG payload key.

5.3.9 KE_OAKLEY_GROUP

The KE_OAKLEY_GROUP class defines the OAKLEY Group used to compute
the PFS secret in the optional KE payload of the GDOI GROUPKEY-PULL
exchange. This attribute uses the values assigned to Group
Definitions in the IANA IPsec-registry [IPSEC-REG].

5.4 SA TEK Payload

The SA TEK (SAT) payload contains security attributes for a single
TEK associated with a group.

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! Protocol-ID ! TEK Protocol-Specific Payload ~
+-+-+-+-+-+-+-+-+ ~
~ ~

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

The SAT Payload fields are defined as follows:

o Next Payload (1 octet) - Identifies the next payload for the
GROUPKEY-PULL or the GROUPKEY-PUSH message. The only valid next
payload types for this message are another SAT Payload or zero to
indicate there are no more security association attributes.

o RESERVED (1 octet) - Must be zero.

o Payload Length (2 octets) - Length of this payload, including
the TEK Protocol-Specific Payload.

o Protocol-ID (1 octet) - Value specifying the Security Protocol.
The following table defines values for the Security Protocol

Protocol ID Value
----------- -----
RESERVED 0
GDOI_PROTO_IPSEC_ESP 1
RESERVED 2-127
PRIVATE USE 128-255

o TEK Protocol-Specific Payload (variable) - Payload which
describes the attributes specific for the Protocol-ID.

5.4.1 PROTO_IPSEC_ESP

The TEK Protocol-Specific payload for ESP is as follows:

0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Protocol ! SRC ID Type ! SRC ID Port !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
!SRC ID Data Len! SRC Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! DST ID Type ! DST ID Port !DST ID Data Len!
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! DST Identification Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! Transform ID ! SPI !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! SPI ! RFC 2407 SA Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

The SAT Payload fields are defined as follows:

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o Protocol (1 octet) - Value describing an IP protocol ID (e.g.,
UDP/TCP). A value of zero means that the SRC Id Prot that the Protocol field should be
ignored.

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o SRC ID Port (2 octets) - Value specifying a port associated
with the source Id. A value of zero means that the SRC ID Port field
should be ignored.

o SRC ID Data Len (1 octet) - Value specifying the length of the
SRC Identification Data field.

o SRC Identification Data (variable length) - Value, as indicated
by the SRC ID Type. Set to three bytes of zero for multiple-source
multicast groups that use a common TEK for all senders.

o DST ID Prot (1 octet) - Value describing an IP protocol ID
(e.g., UDP/TCP). A value of zero means that the DST Id Prot field
should be ignored.

o DST ID Port (2 octets) - Value specifying a port associated
with the source Id. A value of zero means that the DST ID Port field
should be ignored.

o DST ID Data Len (1 octet) - Value specifying the length of the
DST Identification Data field.

o DST Identification Data (variable length) - Value, as indicated
by the DST ID Type.

o Transform ID (1 octet) - Value specifying which ESP transform
is to be used. The list of valid values are defined in the IPSEC ESP
Transform Identifiers section of the IANA isakmpd-registry [ISAKMP-
REG].

o SPI (4 octets) - Security Parameter Index for ESP.

o RFC 2407 Attributes - ESP Attributes from RFC 2407 Section 4.5.
The GDOI supports all IPSEC DOI SA Attributes for PROTO_IPSEC_ESP
excluding the Group Description [RFC2407, section 4.5], which MUST
NOT be sent by a GDOI implementation and is ignored by a GDOI
implementation if received. All mandatory IPSEC DOI attributes are
mandatory in GDOI PROTO_IPSEC_ESP. The Authentication Algorithm
attribute of the IPSEC DOI is group authentication in GDOI.

5.4.2 Other Security Protocols

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5.4.2 Other Security Protocols

Besides ESP, GDOI should serve to establish SAs for secure groups
needed by other Security Protocols that operate at the transport,
application, and internetwork layers. These other Security
Protocols, however, are in the process of being developed or do not
yet exist.

The following information needs to be provided for a Security
Protocol to the GDOI.

o The Protocol-ID for the particular Security Protocol
o The SPI Size
o The method of SPI generation
o The transforms, attributes and keys needed by the Security
Protocol

All Security Protocols must provide the information in the bulleted
list above to guide the GDOI implementation for that protocoland
will be specified in separate documents.
5.5 Key Download Payload

The Key Download Payload contains group keys for the group specified
in the SA Payload. These key download payloads can have several
security attributes applied to them based upon the security policy of
the group as defined by the associated SA Payload.

When included as part of the Re-key SA with an optional KE payload,
The Key Download Payload will be xor'ed with the new Diffie-Hellman
shared secret. The xor operation will begin at the "Number of Key
Packets" field.

The Key Download Payload 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 zero.

o RESERVED (1 octet) - Unused, set to zero.

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

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o Number of Key Packets (2 octets) -- Contains the total number
of both TEK and Rekey arrays being passed in this data block.

o Key Packets
Several types of key packets are defined. Each Key Packet has
the following format.

0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! KD Type ! RESERVED ! KD Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
! SPI Size ! SPI (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!
~ Key Packet Attributes ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-!

o Key Download (KD) Type (1 octet) -- Identifier for the Key
Data field of this Key Packet.

Key Download Type Value
----------------- -----
RESERVED 0
TEK 1
KEK 2
LKH 3
RESERVED 4-127
Private Use 128-255

"KEK" is a single key whereas LKH is an array of key-encrypting
keys
keys.

o RESERVED (1 octet) - Unused, set to zero.

o Key Download Length (2 octets) -- Length in octets of the Key
Packet data following this field.

o SPI Size (1 octet) - Value specifying the length in octets of
the SPI as defined by the Protocol-Id.

o SPI (variable length) - Security Parameter Index which matches
a SPI previously sent in an SAK or SAT Payload.

o Key Packet Attributes (variable length) -- Contains Key
information. The format of this field is specific to the value of the
KD Type field. The following sections describe the format of each KD
Type.

5.5.1 TEK Download Type

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The following attributes may be present in a SAT Payload. Exactly one
attribute matching each type sent in the SAT payload MUST be present.
The attributes must follow the format defined in ISAKMP [RFC2408]

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section 3.3. In the table, attributes which are defined as TV are
marked as Basic (B); attributes which are defined as TLV are marked
as Variable (V).

TEK Class Value Type
--------- ----- ----
RESERVED 0
TEK_ALGORITHM_KEY 1 V
TEK_INTEGRITY_KEY 2 V
TEK_SOURCE_AUTH_KEY 3 V

If no TEK key packets are included in a Registration KD payload, the
group member can expect to receive the TEK as part of a Re-key SA. At
least one TEK must be included in each Re-key KD payload. Multiple TEKs
may be included if multiple streams associated with the SA are to be
rekeyed.

5.5.1.1 TEK_ALGORITHM_KEY

The TEK_ALGORITHM_KEY class declares that the encryption key for this
SPI is contained as the Key Packet Attribute. The encryption
algorithm that will use this key was specified in the SAT payload.

In the case that the algorithm requires multiple keys (e.g., 3DES),
all keys will be included in one attribute.

DES keys will consist of 64 bits (the 56 key bits with parity bit).
Triple DES keys will be be specified as 64 bits a single 192 bit attribute
(including parity bits) in the order that they the keys are to be used for
encryption (e.g., DES_KEY1, DES_KEY2, DES_KEY3).

5.5.1.2 TEK_INTEGRITY_KEY

The TEK_INTEGRITY_KEY class declares that the integrity key for this
SPI is contained as the Key Packet Attribute. The integrity algorithm
that will use this key was specified in the SAT payload. Thus GDOI
assumes that both the symmetric encryption and integrity keys are
pushed to the member. SHA keys will consist of 160 bits, and MD5 keys
will consist of 128 bits.

5.5.1.3 TEK_SOURCE_AUTH_KEY

The TEK_SOURCE_AUTH_KEY class declares that the source authentication
key for this SPI is contained in the Key Packet Attribute. The source
authentication algorithm that will use this key was specified in the
SAT payload.

5.5.2 KEK Download Type

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The following attributes may be present in a SAK Payload. Exactly one
attribute matching each type sent in the SAK payload MUST be present.
The attributes must follow the format defined in ISAKMP [RFC2408]
section 3.3. In the table, attributes which are defined as TV are
marked as Basic (B); attributes which are defined as TLV are marked
as Variable (V).

KEK Class Value Type
--------- ----- ----
RESERVED 0
KEK_ALGORITHM_KEY 1 V
SIG_ALGORITHM_KEY 2 V

If the KEK key packet is included, there MUST be only one present in
the KD payload.

5.5.2.1 KEK_ALGORITHM_KEY

The KEK_ALGORITHM_KEY class declares the encryption key for this SPI
is contained in the Key Packet Attribute. The encryption algorithm
that will use this key was specified in the SAK payload.

If the mode of operation for the algorithm requires an Initialization
Vector (IV), an explicit IV MUST be included in the KEK_ALGORITHM_KEY
before the actual key.

5.5.2.2 SIG_ALGORITHM_KEY

The SIG_ALGORITHM_KEY class declares that the public key for this SPI
is contained in the Key Packet Attribute, which may be useful when no
public key infrastructure is available. The signature algorithm that
will use this key was specified in the SAK payload.

5.5.3 LKH Download Type

The LKH key packet is comprised of attributes representing different
leaves in the LKH key tree.

The following attributes are used to pass an LKH KEK array in the KD
payload. The attributes must follow the format defined in ISAKMP
[RFC2408] section 3.3. In the table, attributes which are defined as
TV are marked as Basic (B); attributes which are defined as TLV are
marked as Variable (V).

KEK Class Value Type
--------- ----- ----
RESERVED 0
KEK_LKH 1 V
RESERVED 2-127
PRIVATE USE 128-255

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If an LKH key packet is included in the KD payload, there must be
only one present.

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5.5.3.1 KEK_LKH

This attribute consists of a header block, followed by one or more
LKH keys.

0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! LKH Version ! Leaf ID ! Number of ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ LKH Keys ! !
+-+-+-+-+-+-+-+-+ LKH Keys !
~ ~
+---------------------------------------------------------------+

The KEK_LKH attribute fields are defined as follows:

o LKH version (1 octet) - Contains the version of the LKH
protocol which the data is formatted in. Must be one.

o Leaf ID (2 octets) -- This is the Leaf Node ID of the LKH
sequence contained in this Key Packet Data block.

o Number of LKH Keys (2 octets) -- This value is the number of
distinct LKH keys in this sequence.

Each LKH Key is defined as follows:
0 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! LKH ID ! Key Type ! ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Key Creation Date ! ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Key expiration Date ! ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Key Handle ! !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- !
! !
~ Key Data ~
+---------------------------------------------------------------+

o LKH ID (2 octets) -- This is the position of this key in the
binary tree structure used by LKH.

o Key Type (1 octet) -- This is the encryption algorithm for
which this key data is to be used. This value is specified in the
Policy Token.
Section 5.3.3.

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o Key Creation Date (4 octets) -- This is the time value of when
this key data was originally generated.

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o Key Expiration Date (4 octets) -- This is the time value of
when this key is no longer valid for use.

o Key Handle (4 octets) -- This is the randomly generated value
to uniquely identify a key.

o Key Data (variable length) -- This is the actual encryption
key data, which is dependent on the Key Type algorithm for its
format.

5.6 Sequence Number Payload

The Sequence Number Payload (SEQ) provides an anti-replay protection
for GROUPKEY-PUSH messages. Its use is similar to the Sequence Number
field defined in the IPsec ESP protocol [RFC2406].

0 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 ! RESERVED ! Payload Length !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
! Sequence Number !
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Sequence Number Payload 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 zero.

o RESERVED (1 octet) - Unused, set to zero.

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

o Sequence Number (4 octets) - This field contains a
monotonically increasing counter value for the group. It is
initialized to zero by the GCKS, and incremented in each
subsequently-transmitted message. Thus the first packet sent for a
given Rekey SA will have a Sequence Number of 1. The GDOI
implementation keeps a sequence counter as an attribute for the Rekey
SA and increments the counter upon receipt of a GROUPKEY-PUSH
message. The current value of the sequence number must be transmitted
to group members as a part of the Registration SA SA payload. A
group member must keep a sliding receive window. The window must be
treated as in the ESP protocol [RFC2406] Section 3.4.3.

5.7 Proof of Possession

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The Proof of Possession Payload is used as part of group membership
authorization during a GDOI exchange. The Proof of Possession Payload

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is identical to an ISAKMP SIG payload. However, the usage is entirely
different.

The GCKS, GCKS delegate or member signs a prf (i.e., RFC 2409 keyed
MAC) hash of the following
values:
POP_HASH = prf("pop" hash("pop" | Ni | Nr)
Where hash() is the hash function used with the signature.

The "pop" prefix ensures that the signature of the POP payload
cannot be used for any other purpose in the GDOI protocol.

5.8 Nonce

The data portion of the Nonce payload (i.e., Ni_b and Nr_b included
in the HASHs) MUST be a value between 8 and 128 bytes.

7.0 Security Considerations

GDOI is a security association (SA) protocol for groups of senders
and receivers. This protocol uses best-known practices for defense
against man-in-middle, connection hijacking, replay, reflection, and
denial-of-service (DOS) attacks.

GDOI may inherit the problems of its ancestors, ISAKMP [RFC2408] and
Internet Key Exchange [RFC2409]. Some problems remain to be
addressed in ISAKMP and IKE [FS00]. GDOI should benefit, however,
from improvements to its ancestor protocols just as it benefits from
years of experience and work embodied in those protocols

Of course, GDOI supports secure groups and differs from ISAKMP and
IKE in authorization, policy, SA structure, and exchanges. The SA
structure is more complex than ISAKMP and IKE. Complexity is bad for
a Security Protocol because it makes correctness analysis more
difficult than in a simpler protocol and may lead to implementation
problems. The distribution of keying material using multicast
techniques, moreover, is novel. Novelty is bad for a key management
protocol because it can contain unexpected results and problems.

8.0 IANA Considerations

8.1 ISAKMP DOI

A new ISAKMP DOI number needs to be assigned to GDOI. RFC 2407
indicates that the namespace for DOI values is in STD-2, although
that does not yet exist such as section there. The present document
is in accordance with the "Supported Security Protocols" section in
[RFC2408].

8.2 Payload Types

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New ISAKMP Next Payload types need to be allocated for GDOI payload
types. No ISAKMP registry for payload types currently exists, but the
Private Use payload type namespace can be further partitioned for the
GDOI DOI. See Section 5.0 for the payloads defined in this document.

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8.3 New Namespaces

The present document describes many new namespaces for use in the
GDOI payloads. Those may be found in subsections under Section 5.0. A
new GDOI registry should be created for these namespaces.

8.3 UDP Port
A new UDP port is required for GDOI.

9.0 Acknowledgements

The authors thank Ran Canetti, Cathy Meadows and Meadows, Andrea Colegrove. Colegrove, and
Lakshminath Dondeti. Ran has advised the authors on secure group
cryptography, which has led to changes in the exchanges and payload
definitions. Cathy identified several problems in previous versions
of this document, including a replay attack against the proof of
possession exchange, as well as several man-in-the-middle. man-in-the-middle attacks.
Andrea has contributed to the group policy section of this draft.
Lakshminath identified several protocol issues which needed further
specification and helped to resolve them.

10.0 References

10.1 Normative References

[AES-MODES] "Recommendation for Block Cipher Modes of Operation",
United States of American, National Institute of Science and
Technology, NIST Special Publication 800-38A 2001 Edition, December
2001.

[FIPS46-3] "Data Encryption Standard (DES)", United States of
American, National Institute of Science and Technology, Federal
Information Processing Standard (FIPS) 46-3, October 1999.

[FIPS81] "DES Modes of Operation", United States of American,
National Institute of Science and Technology, Federal Information
Processing Standard (FIPS) 81, December 1980.

[FIPS186-2] "Digital Signature Standard (DSS)", United States of
American, National Institute of Science and Technology, Federal
Information Processing Standard (FIPS) 186-2, January 2000.

[FIPS197] "Advanced Encryption Standard (AES)", United States of
American, National Institute of Science and Technology, Federal
Information Processing Standard (FIPS) 197, November 2001.

[FS00] N. Ferguson and B. Schneier, A Cryptographic Evaluation of
IPsec, CounterPane, http://www.counterpane.com/ipsec.html.

[IPSEC-REG] http://www.iana.org/assignments/ipsec-registry

[ISAKMP-REG] http://www.iana.org/assignments/isakmp-registry

[NAI] http://www.nai.com/media/pdf/products/tns/6_PGP_VPN_001.pdf

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[RFC1889] H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson, RTP:
A Transport Protocol for Real-Time Applications, January 1996.

[RFC2093] Harney, H., and Muckenhirn, C., "Group Key Management
Protocol (GKMP) Specification," RFC 2093, July 1997.

[RFC2094] Harney, H., and Muckenhirn, C., "Group Key Management
Protocol (GKMP) Architecture," RFC 2094, July 1997.

[ISAKMP-REG] http://www.iana.org/assignments/isakmp-registry

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Level", BCP 14, RFC 2119, March 1997.

[RFC2327] M. Handley, V. Jacobson, SDP: Session Description Protocol,
April 1998.

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

[RFC2401] S. Kent, R. Atkinson, Security Architecture for the
Internet Protocol, November 1998

[RFC2406] S. Kent, R. Atkinson, IP Encapsulating Security Payload
(ESP), November 1998.

[RFC2407] D. Piper, The Internet IP Domain of Interpretation for
ISAKMP, November 1998.

[RFC2408] D. Maughan, M. Shertler, M. Schneider, J. Turner, Internet
Security Association and Key Management Protocol, November 1998.

[RFC2409] D. Harkins, D. Carrel, The Internet Key Exchange (IKE),
November, 1998.

[RFC2412] H. Orman, The OAKLEY Key Determination Protocol, November
1998.

[RFC2627] D. M. Wallner, E. Harder, R. C. Agee, Key Management for
Multicast: Issues and Architectures, September 1998.

[RSA] RSA Laboratories, "PKCS #1 v2.0: RSA Encryption Standard",
October 1998.

10.2 Informative References

[FS00] N. Ferguson and B. Schneier, A Cryptographic Evaluation of
IPsec, CounterPane, http://www.counterpane.com/ipsec.html.

[NNL] D. Naor, M. Naor and J. Lotspiech, Revocation and Tracing
Schemes for Stateless Receivers, Advances in Cryptology, Crypto ?01,
Springer-Verlag LNCS 2139, 2001, pp. 41-62. A full version of the
paper appears in http://www.wisdom.weizmann.ac.il/~naor/.

[OFT] D. Mcgrew and A. Sherman, Key Establishment in Large Dynamic
Groups Using One-Way Function Trees, Manuscript submitted to IEEE
Transactions on Software Engineering. A full version of the paper
appears in
http://download.nai.com/products/media/pgp/misc/oft052098.ps, 1998

[RFC1889] H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson, RTP:
A Transport Protocol for Real-Time Applications, January 1996.

[RFC2093] Harney, H., and Muckenhirn, C., "Group Key Management
Protocol (GKMP) Specification," RFC 2093, July 1997.

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[RFC2094] Harney, H., and Muckenhirn, C., "Group Key Management
Protocol (GKMP) Architecture," RFC 2094, July 1997.

[RFC2367] D. McDonald, C. Metz, B. Phan, PF_KEY Key Management API,
Version 2, July 1998.
[STS] Diffie, P. van Oorschot, M. J. Wiener, Authentication and
Authenticated Key Exchanges, Designs, Codes and Cryptography, 2, 107-
125 (1992), Kluwer Academic Publishers.

Authors Addresses

Mark Baugher
Cisco Systems
5510 SW Orchid Street
Portland, OR 97219, USA

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(503) 245-4543
mbaugher@cisco.com

Thomas Hardjono
VeriSign
401 Edgewater Place, Suite 280
Wakefield, MA 01880
Tel: 781-245-6996
Email: thardjono@verisign.com

Hugh Harney
Sparta
9861 Broken Land Parkway
Columbia, MD 21046
(410) 381-9400 x203
hh@sparta.com

Brian Weis
Cisco Systems
170 W. Tasman Drive,
San Jose, CA 95134-1706, USA
(408) 526-4796
bew@cisco.com

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