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draft-ietf-eap-keying-03.txt --> draft-ietf-eap-keying-04.txt-178480.txt

INTERNET-DRAFT Dan Simon
Category: Informational Microsoft
<draft-ietf-eap-keying-03.txt>
<draft-ietf-eap-keying-04.txt> J. Arkko
18 July
14 November 2004 Ericsson
P. Eronen
Nokia
H. Levkowetz, Ed.
ipUnplugged

Extensible Authentication Protocol (EAP) Key Management Framework

Status of

By submitting this Memo

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and is any of which I become aware will be disclosed, in full conformance accordance with
all provisions of Section 10 of
RFC 2026. 3668.

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This Internet-Draft will expire on May 22, 2005.

Abstract

The Extensible Authentication Protocol (EAP), defined in [RFC3748],
enables extensible network access authentication. This document
provides a framework for the generation, transport and usage of
keying material generated by EAP authentication algorithms, known as
"methods". It also specifies the EAP key hierarchy.

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Table of Contents

1. Introduction .......................................... 4
1.1 Requirements Language ........................... 4
1.2 Terminology ..................................... 4
1.3 Overview ........................................ 5
1.4 EAP Invariants .................................. 11
2. EAP Key Hierarchy ..................................... 13
2.1 Key Terminology ................................. 13
2.2 Key Hierarchy ................................... 15
2.3 Key Lifetimes ................................... 17
2.4 Key Naming ...................................... Names and Scopes ............................ 24
2.5 AAA-Key Derivation .............................. 27
2.6 AMSK Key Derivation ............................. 28
2.7 Key Scope Issues ................................ 29
3. Security associations ................................. 26 30
3.1 EAP Method SA ................................... 26 31
3.2 EAP-Key SA ...................................... 28 33
3.3 AAA SA(s) ....................................... 28 33
3.4 Service SA(s) ................................... 29 34
4. Handoff Support ....................................... 34 39
4.1 Key Scope Issues ................................ 35
4.2 Authorization Issues ............................ 36
4.3 39
4.2 Correctness Issues .............................. 38 41
5. Security Considerations .............................. 40 44
5.1 Security Terminology ............................ 40 44
5.2 Threat Model .................................... 41 44
5.3 Security Analysis ............................... 43 45
5.4 Man-in-the-middle Attacks ....................... 47 49
5.5 Denial of Service Attacks ....................... 47 49
5.6 Impersonation ................................... 48 50
5.7 Channel Binding ................................. 49 51
5.8 Key Strength .................................... 50 52
5.9 Key Wrap ........................................ 50 53

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6. Security Requirements ................................. 51 53
6.1 EAP Method Requirements ......................... 51 53
6.2 AAA Protocol Requirements ....................... 54 56
6.3 Secure Association Protocol Requirements ........ 55 58
6.4 Ciphersuite Requirements ........................ 57 60
7. IANA Considerations ................................... 58 60
8. References ............................................ 59 61
8.1 Normative References ............................ 59 61
8.2 Informative References .......................... 59 61
Acknowledgments .............................................. 63 65
Author's Addresses ........................................... 63 65
Appendix A - Ciphersuite Keying Requirements ................. 65 67
Appendix B - Example Transient EAP Key (TEK) Hierarchy ............... 66 ....... 68
Appendix C - EAP EAP-TLS Key Hierarchy ............................... 67 ........................... 69
Appendix D - Example Transient Session Key (TSK) Derivation .......... 69 .. 71
Appendix E - AAA-Key Derivation .............................. 70
Appendix F - AMSK Derivation ................................. 71 Key Names and Scope in Existing Methods ......... 72
Intellectual Property Statement .............................. 72
Full 73
Disclaimer of Validity ....................................... 73
Copyright Statement ..................................... 72 .......................................... 73

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1. Introduction

The Extensible Authentication Protocol (EAP), defined in [RFC3748],
was designed to enable extensible authentication for network access
in situations in which the IP protocol is not available. Originally
developed for use with PPP [RFC1661], it has subsequently also been
applied to IEEE 802 wired networks [IEEE8021X].

This document provides a framework for the generation, transport and
usage of keying material generated by EAP authentication algorithms,
known as "methods". Since in In EAP keying material is generated by EAP
methods,
methods. Part of this keying material may be used by EAP methods
themselves and part of this material may be exported. The exported
keying material may be transported by AAA protocols, protocols or transformed into session keys by
Secure Association Protocols and into session keys which are used by
lower layer ciphersuites,
it is necessary to describe ciphersuites. This document describes each of these
elements and provide provides a system-level security analysis. It also
specifies the EAP key hierarchy.

1.1. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 [RFC2119].

1.2. Terminology

This document frequently uses the following terms:

authenticator
The end of the link initiating EAP authentication. The term
Authenticator is used in [IEEE-802.1X], and authenticator has the
same meaning in this document.

peer The end of the link that responds to the authenticator. In
[IEEE-802.1X], this end is known as the Supplicant.

Supplicant
The end of the link that responds to the authenticator in
[IEEE-802.1X]. In this document, this end of the link is called
the peer.

backend authentication server
A backend authentication server is an entity that provides an
authentication service to an authenticator. When used, this server
typically executes EAP methods for the authenticator. This
terminology is also used in [IEEE-802.1X].

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AAA Authentication, Authorization and Accounting. AAA protocols with
EAP support include RADIUS [RFC3579] and Diameter [I-D.ietf-aaa-
eap]. In this document, the terms "AAA server" and "backend

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authentication server" are used interchangeably.

EAP server
The entity that terminates the EAP authentication method with the
peer. In the case where no backend authentication server is used,
the EAP server is part of the authenticator. In the case where the
authenticator operates in pass-through mode, the EAP server is
located on the backend authentication server.

security association
A set of policies and key(s) cryptographic state used to protect
information. This
information in the security association is stored by each party of
the security association and must be consistent among the parties. Elements of a security association may include
cryptographic keys, negotiated ciphersuites and other parameters,
counters, sequence spaces, authorization attributes, etc.

1.3. Overview

EAP is typically deployed in order to support extensible network
access authentication in situations where a peer desires network
access via one or more authenticators. The situation is illustrated
in Figure 1. Since both the peer and
authenticator may have more than one physical or logical port, a
given peer may simultaneously access the network via multiple
authenticators, or via multiple physical or logical ports on a given
authenticator. Similarly, an authenticator may offer network access
to multiple peers, each via a separate physical or logical port. The peer may be stationary, in which case it may establish
communications with one or more authenticators while remaining
situation is illustrated in one
location. Alternatively, the peer may be mobile, changing its point
of attachment from one authenticator to another, or moving between
points of attachment on a single authenticator. Figure 1.

Where authenticators are deployed standalone, the EAP conversation
occurs between the peer and authenticator, and the authenticator must
locally implement an EAP method acceptable to the peer. However, one
of the advantages of EAP is that it enables deployment of new
authentication methods without requiring development of new code on
the authenticator. While the authenticator may implement some EAP
methods locally and use those methods to authenticate local users, it
may at the same time act as a pass-through for other users and
methods, forwarding EAP packets back and forth between the backend
authentication server and the peer.

This is accomplished by encapsulating EAP packets within the
Authentication, Authorization and Accounting (AAA) protocol, spoken
between the authenticator and backend authentication server. AAA
protocols supporting EAP include RADIUS [RFC3579] and Diameter [I-
D.ietf-aaa-eap].

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+-+-+-+-+
| |
| EAP |
| Peer |
| |
+-+-+-+-+
| | | Peer Ports
/ | \
/ | \
Phase 0: Discovery
/ | \
Phase 1: Authentication
/ | \
Phase 2: Secure
/ | \
Association
/ | \
/ | \
/ | \
| | | | | | | | | Authenticator Ports
+-+-+-+-+ +-+-+-+-+ +-+-+-+-+
| | | | | |
| Auth. | | Auth. | | Auth. |
| | | | | |
+-+-+-+-+ +-+-+-+-+ +-+-+-+-+
\ | /
\ | /
\ | /
EAP over AAA \ | /
(optional) \ | /
\ | /
\ | /
\ | /
+-+-+-+-+
| |
| AAA |
|Server |
| |
+-+-+-+-+

Figure 1: Relationship between peer, authenticator and backend server

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Where EAP key derivation is supported, the conversation between the
peer and the authenticator typically takes place in three phases:

Phase 0: Discovery
Phase 1: Authentication
1a: EAP authentication
1b: AAA-Key Transport (optional)
Phase 2: Secure Association Establishment
2a: Unicast Secure Association
2b: Multicast Secure Association (optional)

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In the discovery phase (phase 0), peers locate authenticators and
discover their capabilities. For example, a peer may locate an
authenticator providing access to a particular network, or a peer may
locate an authenticator behind a bridge with which it desires to
establish a Secure Association.

The authentication phase (phase 1) may begin once the peer and
authenticator discover each other. This phase always includes EAP
authentication (phase 1a). Where the chosen EAP method supports key
derivation, in phase 1a keying material is derived on both the peer
and the EAP server. This keying material may be used for multiple
purposes, including protection of the EAP conversation and subsequent
data exchanges.

An additional step (phase 1b) is required in deployments which
include a backend authentication server, in order to transport keying
material (known as the AAA-Key) from the backend authentication
server to the authenticator.

A Secure Association exchange (phase 2) then occurs between the peer
and authenticator in order to manage the creation and deletion of
unicast (phase 2a) and multicast (phase 2b) security associations
between the peer and authenticator.

The conversation phases and relationship between

EAP may be used in the parties following scenarios:

[a] Stationary peer. Where the peer is shown stationary it will establish
communications with one or more authenticators while remaining in Figure 2.

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one location. In this scenario, EAP Key Management Framework 18 July 2004 authentication typically
represents only a small fraction of the total session time, so that
it is acceptable for EAP authentication to occur each time the peer Authenticator Auth. Server
-------- ------------- ------------
|<----------------------------->| |
| Discovery (phase 0) | |
|<----------------------------->|<----------------------------->|
| EAP auth (phase 1a) | AAA pass-through (optional) |
| | |
| |<----------------------------->|
| | AAA-Key transport |
|
wishes to access the network. In this scenario, the Secure
Association Protocol (Phase 2) MAY be ommitted.

[b] Mobile peer. Where the peer is mobile, it may move its point of
attachment from one authenticator to another, or between points of
attachment on a single authenticator. In this scenario, it is
often desirable to minimize the handoff latency, so that it is
desirable to avoid EAP authentication each time the peer changes
its point of attachment. In this scenario, the Secure Association
Protocol (Phase 2) is REQUIRED.

The conversation phases and relationship between the parties is
shown in Figure 2.

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Figure 2: Conversation Overview

1.3.1. Discovery Phase

In the discovery phase (phase 0), the EAP peer and authenticator
locate each other and discover each other's capabilities. Discovery
can occur manually or automatically, depending on the lower layer
over which EAP runs. Since authenticator discovery is handled
outside of EAP, there is no need to provide this functionality within
EAP.

For example, where EAP runs over PPP, the EAP peer might be
configured with a phone book providing phone numbers of
authenticators and associated capabilities such as supported rates,
authentication protocols or ciphersuites.

In contrast, PPPoE [RFC2516] provides support for a Discovery Stage
to allow a peer to identify the Ethernet MAC address of one or more
authenticators and establish a PPPoE SESSION_ID.

IEEE 802.11 [IEEE80211] also provides integrated discovery support
utilizing Beacon and/or Probe Request/Response frames, allowing the
peer (known as the station or STA) to determine the MAC address and
capabilities of one or more authenticators (known as Access Point or
APs).

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1.3.2. Authentication Phase

Once the peer and authenticator discover each other, they exchange
EAP packets. Typically, the peer desires access to the network, and

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the authenticators provide that access. In such a situation, access
to the network can be provided by any authenticator attaching to the
desired network, and the EAP peer is typically willing to send data
traffic through any authenticator that can demonstrate that it is
authorized to provide access to the desired network.

An EAP authenticator may handle the authentication locally, or it may
act as a pass-through to a backend authentication server. In the
latter case the EAP exchange occurs between the EAP peer and a
backend authenticator server, with the authenticator forwarding EAP
packets between the two. The entity which terminates EAP
authentication with the peer is known as the EAP server. Where pass-
through is supported, the backend authentication server functions as
the EAP server; where authentication occurs locally, the EAP server
is the authenticator. Where a backend authentication server is
present, at the successful completion of an authentication exchange,
the AAA-Key is transported to the authenticator (phase 1b).

EAP may also be used when it is desired for two network devices (e.g.
two switches or routers) to authenticate each other, or where two
peers desire to authenticate each other and set up a secure
association suitable for protecting data traffic.

Some EAP methods exist which only support one-way authentication;
however, EAP methods deriving keys are required to support mutual
authentication. In either case, it can be assumed that the parties
do not utilize the link to exchange data traffic unless their
authentication requirements have been met. For example, a peer
completing mutual authentication with an EAP server will not send
data traffic over the link until the EAP server has authenticated
successfully to the peer, and a Secure Association has been
negotiated.

Since EAP is a peer-to-peer protocol, an independent and simultaneous
authentication may take place in the reverse direction. Both peers
may act as authenticators and authenticatees at the same time.

Successful completion of EAP authentication and key derivation by a
peer and EAP server does not necessarily imply that the peer is
committed to joining the network associated with an EAP server.
Rather, this commitment is implied by the creation of a security
association between the EAP peer and authenticator, as part of the
Secure Association Protocol (phase 2). As a result, EAP may be used
for "pre-authentication" in situations where it is necessary to pre-
establish EAP security associations in order to decrease handoff or
roaming latency.

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establish EAP security associations in order to decrease handoff or
roaming latency.

1.3.3. Secure Association Phase

The Secure Association phase (phase 2) always occurs 2), if it occurs, begins after
the completion of EAP authentication (phase 1a) and key transport
(phase 1b), and typically supports the following features:

[1] Entity Naming. A basic feature Generation of a Secure Association Protocol fresh transient session keys (TSKs). Where AAA-Key
caching is supported, the naming EAP peer may initiate a new session using
a AAA-Key that was used in a previous session. Were the TSKs to be
derived from a portion of the parties engaged AAA-Key, this would result in reuse
of the exchange. session keys which could expose the underlying ciphersuite
to attack.

As illustrated
in Figure 1, it a result, where AAA-Key caching is possible for both supported, freshness of TSKs
MUST be provided by mechanisms outside of EAP. This is typically
handled within the peer Secure Association protocol via the exchange of
nonces or counters, which are then mixed with the AAA-Key in order
to generate fresh unicast (phase 2a) and NAS possibly multicast (phase
2b) session keys. By not using the AAA-Key directly to have more
than one physical or virtual port. For protect
data, the purposes secure Association Protocol protects against compromise
of
identification, it the AAA-Key.

[2] Entity Naming. A basic feature of a Secure Association Protocol is therefore not possible to identify either
peers or NAS devices using port identifiers. Proper
the explicit naming of the parties engaged in the exchange.
Explicit identification of the parties is critical to the Secure Association phase, critical, since without
this the parties engaged in the exchange are not identified and the
scope of the transient session keys (TSKs) generated during the
exchange is undefined.

[2] As illustrated in Figure 1, both the peer
and NAS may have more than one physical or virtual port, so that
port identifiers are typically inappropriate as a naming mechanism.

[3] Secure capabilities negotiation. This provides for the secure
negotiation of usage modes, session parameters (such as key
lifetimes), ciphersuites, and required filters, including
confirmation of the capabilities discovered during phase 0. By
securely negotiating session parameters, the secure Association
Protocol protects against spoofing during the discovery phase and
ensures that the peer and authenticator are in agreement about how
data is to be secured.

[3] Generation of fresh transient session keys (TSKs). The Secure
Association Protocol typically guarantees the freshness of session
keys by exchanging nonces between both parties and then mixing the
nonces with the AAA-Key in order to generate fresh unicast (phase
2a) and multicast (phase 2b) session keys. By not using the AAA-
Key directly to protect data, the secure Association Protocol
protects against compromise of the AAA-Key, and by guaranteeing the
freshness of transient session keys, assures that they are not
reused.

[4] Key activation and deletion. In order for the peer and
authenticator to communicate securely, it is necessary for both
sides to derive the same session keys, and remain in sync with
respect to key state going forward. One of the functions of the
Secure Association Protocol is to synchronize the activation and
deletion of keys so as to enable seamless rekey, or recovery

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deletion of keys so as to enable seamless rekey, or recovery from
partial or complete loss of key state by the peer or authenticator.

[5] Mutual proof of possession of the AAA-Key. This demonstrates that
both the peer and authenticator have been authenticated and
authorized by the backend authentication server. Since mutual
proof of possession is not the same as mutual authentication, the

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peer cannot verify authenticator assertions (including the
authenticator identity) as a result of this exchange.

1.4. EAP Invariants

By utilizing a three phase exchange, the EAP key management framework
guarantees that certain

Certain basic characteristics, known as the "EAP Invariants" hold
true for all EAP implementations of EAP. These include: on all media:

Media independence
Method independence
Ciphersuite independence

1.4.1. Media Independence

One of the goals of EAP is to allow EAP methods to function on any
lower layer meeting the criteria outlined in [RFC3748], Section 3.1.
For example, as described in [RFC3748], EAP authentication can be run
over PPP [RFC1661], IEEE 802 wired networks [IEEE8021X], and IEEE
802.11 wireless LANs [IEEE80211i].

In order to maintain media independence, it is necessary for EAP to
avoid inclusion of media-specific elements. For example, EAP methods
cannot be assumed to have knowledge of the lower layer over which
they are transported, and cannot utilize identifiers associated with
a particular usage environment (e.g. MAC addresses).

The need for media independence has also motivated the development of
the three phase exchange. Since discovery is typically media-
specific, this function is handled outside of EAP, rather than being
incorporated within it. Similarly, the Secure Association Protocol
often contains media dependencies such as negotiation of media-
specific ciphersuites or session parameters, and as a result this
functionality also cannot be incorporated within EAP.

Note that media independence may be retained within EAP methods that
support channel binding or method-specific identification. An EAP
method need not be aware of the content of an identifier in order to
use it. This enables an EAP method to use media-specific identifiers
such as MAC addresses without compromising media independence. To
support channel binding, an EAP method can pass binding parameters to
the AAA server in the form of an opaque blob, and receive
confirmation of whether the parameters match, without requiring
media-specific knowledge.

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confirmation of whether the parameters match, without requiring
media-specific knowledge.

1.4.2. Method Independence

By enabling pass-through, authenticators can support any method
implemented on the peer and server, not just locally implemented
methods. This allows the authenticator to avoid implementing code
for each EAP method required by peers. In fact, since a pass-through
authenticator is not required to implement any EAP methods at all, it
cannot be assumed to support any EAP method-specific code.

As a result, as noted in [RFC3748], authenticators must by default be
capable of supporting any EAP method. Since the Discovery and Secure
Association exchanges are also method independent, an authenticator
can carry out the three phase exchange without having an EAP method
in common with the peer.

This is useful where there is no single EAP method that is both
mandatory-to-implement and offers acceptable security for the media
in use. For example, the [RFC3748] mandatory-to-implement EAP method
(MD5-Challenge) does not provide dictionary attack resistance, mutual
authentication or key derivation, and as a result is not appropriate
for use in wireless LAN authentication [WLANREQ]. However, despite
this it is possible for the peer and authenticator to interoperate as
long as a suitable EAP method is supported on the EAP server.

1.4.3. Ciphersuite Independence

While EAP methods may negotiate the ciphersuite used in protection of
the EAP conversation, the ciphersuite used for the protection of the
data exchanged after EAP authentication has completed is negotiated within
between the Secure Association Protocol, peer and authenticator out-of-band of EAP.

The backend authentication server Since
ciphersuite negotiation is not a party assumed to this negotiation
nor occur out-of-band, there is it an intermediary in the data flow between the EAP peer and
authenticator. The backend authentication server may not even have
knowledge of the ciphersuites implemented by the peer and
authenticator, or be aware of the no
need for ciphersuite negotiated between
them, and therefore does not implement ciphersuite-specific code. negotiation within EAP. Since ciphersuite
negotiation occurs in the Secure Association
protocol, not in outside of EAP, ciphersuite-specific key generation, if
implemented within an EAP method, would potentially conflict with the
transient session key derivation occurring in the Secure Association
protocol. As a result, EAP methods generate keying
material that is ciphersuite-independent. Additional advantages of ciphersuite-
independence include:

Update requirements
If

For example, within PPP, the ciphersuite is negotiated within the
Encryption Control Protocol (ECP) defined in [RFC1968], after EAP methods were to specify how
authentication is completed. Within [IEEE80211i], the AP
ciphersuites are advertised in the Beacon and Probe Responses prior
to derive transient session keys

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handshake exchange after EAP authentication has completed.

Advantages of ciphersuite-independence include:

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Reduced update requirements
If EAP methods were to specify how to derive transient session keys
for each ciphersuite, they would need to be updated each time a new
ciphersuite is developed. In addition, backend authentication
servers might not be usable with all EAP-capable authenticators,
since the backend authentication server would also need to be
updated each time support for a new ciphersuite is added to the
authenticator.

Reduced EAP method complexity
Requiring each EAP method to include ciphersuite-specific code for
transient session key derivation would increase method complexity
and result in duplicated effort.

Knowledge

Simplified configuration
The ciphersuite is negotiated between the peer and authenticator
out-of-band of capabilities
In practice, EAP. The backend authentication server is neither a
party to this negotiation, nor is it an intermediary in the data
flow between the EAP method peer and authenticator. The backend
authentication server may not have knowledge of the
ciphersuite that has been negotiated between ciphersuites
and negotiation policies implemented by the peer and authenticator, since this negotiation typically occurs within
or be aware of the
Secure Association Protocol.

For example, PPP ciphersuite negotiation occurs in negotiated between them. This
simplifies the Encryption
Control Protocol (ECP) [RFC1968]. Since configuration of the backend authentication server.

For example, since ECP negotiation occurs after authentication, unless an EAP method is utilized that
supports ciphersuite negotiation,
when run over PPP, the EAP peer, authenticator and backend
authentication server may not be able to anticipate the negotiated ciphersuite
and therefore this information cannot be provided to the EAP
method. Since ciphersuite negotiation is
assumed to occur out-of-band, there is no need for ciphersuite
negotiation within EAP.

For example, a peer might be pre-configured with policy indicating
the ciphersuite to be used in communicating with a given
authenticator. Within PPP, the ciphersuite is negotiated within
the Encryption Control Protocol (ECP), after EAP authentication is
completed. Within [IEEE80211i], the AP ciphersuites are advertised
in the Beacon and Probe Responses, and are securely verified during
a 4-way handshake exchange after EAP authentication has completed.

2. EAP Key Hierarchy

2.1. Key Terminology

The EAP Key Hierarchy makes use of the following types of keys:

Long Term Credential
EAP methods frequently make use of long term secrets in order to
enable authentication between the peer and server. In the case of
a method based on pre-shared key authentication, the long term
credential is the pre-shared key. In the case of a public-key
based method, the long term credential is the corresponding private

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key.

Master Session Key (MSK)
Keying material that is derived between the EAP peer and server and
exported by the EAP method. The MSK is at least 64 octets in
length.

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Extended Master Session Key (EMSK)
Additional keying material derived between the peer and server that
is exported by the EAP method. The EMSK is at least 64 octets in
length, and is never shared with a third party.

AAA-Key
A key derived by the peer and EAP server, used by the peer and
authenticator in the derivation of Transient Session Keys (TSKs).
Where a backend authentication server is present, the AAA-Key is
transported from the backend authentication server to the
authenticator, wrapped within the AAA-Token; it is therefore known
by the peer, authenticator and backend authentication server.
Despite the name, the AAA-Key is computed regardless of whether a
backend authentication server is present. AAA-Key derivation is
discussed in Appendix E; Section 2.5; in existing implementations the MSK is
used as the AAA-Key.

Application-specific Master Session Keys (AMSKs)
Keys derived from the EMSK which are cryptographically separate
from each other and may be subsequently used in the derivation of
Transient Session Keys (TSKs) for extended uses. AMSK derivation
is discussed in Appendix F. Section 2.6.

AAA-Token
Where a backend server is present, the AAA-Key and one or more
attributes is transported between the backend authentication server
and the authenticator within a package known as the AAA-Token. The
format and wrapping of the AAA-Token, which is intended to be
accessible only to the backend authentication server and
authenticator, is defined by the AAA protocol. Examples include
RADIUS [RFC2548] and Diameter [I-D.ietf-aaa-eap].

Initialization Vector (IV)
A quantity of at least 64 octets, suitable for use in an
initialization vector field, that is derived between the peer and
EAP server. Since the IV is a known value in methods such as EAP-
TLS [RFC2716], it cannot be used by itself for computation of any
quantity that needs to remain secret. As a result, its use has
been deprecated and EAP methods are not required to generate it.
However, when it is generated it MUST be unpredictable.

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Pairwise Master Key (PMK)
The AAA-Key is divided into two halves, the "Peer to Authenticator
Encryption Key" (Enc-RECV-Key) and "Authenticator to Peer
Encryption Key" (Enc-SEND-Key) (reception is defined from the point
of view of the authenticator). Within [IEEE80211i] Octets 0-31 of
the AAA-Key (Enc-RECV-Key) are known as the Pairwise Master Key
(PMK). In [IEEE80211i] the TKIP and AES CCMP ciphersuites derive

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their Transient Session Keys (TSKs) solely from the PMK, whereas
the WEP ciphersuite as noted in [RFC3580], derives its TSKs from
both halves of the AAA-Key.

Transient EAP Keys (TEKs)
Session keys which are used to establish a protected channel
between the EAP peer and server during the EAP authentication
exchange. The TEKs are appropriate for use with the ciphersuite
negotiated between EAP peer and server for use in protecting the
EAP conversation. Note that the ciphersuite used to set up the
protected channel between the EAP peer and server during EAP
authentication is unrelated to the ciphersuite used to subsequently
protect data sent between the EAP peer and authenticator. An
example TEK key hierarchy is described in Appendix C.

Transient Session Keys (TSKs)
Session keys used to protect data which exchanged between the peer and
the authenticator after the EAP authentication has successfully
completed. TSKs are appropriate for the lower layer ciphersuite
negotiated between the EAP peer and authenticator. The
TSKs are derived from AAA-Key during the Secure Association
Protocol. In the case of [IEEE80211i] the Secure Association
Protocol consists Examples of the 4-way handshake and group key derivation.
An example TSK
derivation is are provided in Appendix D.

2.2. Key Hierarchy

The EAP Key Hierarchy, illustrated in Figure 3, has at the root the
long term credential utilized by the selected EAP method. If
authentication is based on a pre-shared key, the parties store the
EAP method to be used and the pre-shared key. The EAP server also
stores the peer's identity and/or other information necessary to
decide whether access to some service should be granted. The peer
stores information necessary to choose which secret to use for which
service.

If authentication is based on proof of possession of the private key
corresponding to the public key contained within a certificate, the
parties store the EAP method to be used and the trust anchors used to
validate the certificates. The EAP server also stores the peer's
identity and/or other information necessary to decide whether access
to some service should be granted. The peer stores information
necessary to choose which certificate to use for which service.

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Based on the long term credential established between the peer and
the server, EAP derives four two types of keys:

[1] Keys calculated locally by the EAP method but not exported
by the EAP method, such as the TEKs.
[2] Keys exported by the EAP method: MSK, EMSK, IV

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From the keys exported by the EAP method, two other types of keys may
be derived:

[3] Keys calculated from exported quantities: AAA-Key, AMSKs.
[4] Keys calculated by the Secure Association Protocol: Protocol from the
AAA-Key or AMSKs: TSKs.

In order to protect the EAP conversation, methods supporting key
derivation typically negotiate a ciphersuite and derive Transient EAP
Keys (TEKs) for use with that ciphersuite. The TEKs are stored
locally by the EAP method and are not exported.

As noted in [RFC3748] Section 7.10, EAP methods generating keys are
required to calculate and export the MSK and EMSK, which must be at
least 64 octets in length. EAP methods also may export the IV;
however, the use of the IV is deprecated.

On both the peer and EAP server, the exported MSK and EMSK keys derived
from the AMSK are utilized in order to calculate the AAA-Key, as
described in Appendix
E. Section 2.5.

Where a backend authentication server is present, the AAA-Key is
transported from the backend authentication server to the
authenticator within the AAA-Token, using the AAA protocol.

Once EAP authentication completes and is successful, the peer and
authenticator obtain the AAA-Key and the Secure Association Protocol
is run between the peer and authenticator in order to securely
negotiate the ciphersuite, derive fresh TSKs used to protect data,
and provide mutual proof of possession of the AAA-Key.

When the authenticator acts as an endpoint of the EAP conversation
rather than a pass-through, EAP methods are implemented on the
authenticator as well as the peer. If the EAP method negotiated
between the EAP peer and authenticator supports mutual authentication
and key derivation, the EAP Master Session Key (MSK) and Extended
Master Session Key (EMSK) are derived on the EAP peer and
authenticator and exported by the EAP method. In this case, the MSK
and EMSK are known only to the peer and authenticator and no other
parties. The TEKs and TSKs also reside solely on the peer and
authenticator. This is illustrated in Figure 4. As demonstrated in
[I-D.ietf-roamops-cert], in this case it is still possible to support
roaming between providers, using certificate-based authentication.

Where a backend authentication server is utilized, the situation is
illustrated in Figure 5. Here the authenticator acts as a pass-

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through between the EAP peer and a backend authentication server. In
this model, the authenticator delegates the access control decision

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to the backend authentication server, which acts as a Key
Distribution Center (KDC). In this case, the authenticator
encapsulates EAP packet with a AAA protocol such as RADIUS [RFC3579]
or Diameter [I-D.ietf-aaa-eap], and forwards packets to and from the
backend authentication server, which acts as the EAP server. Since
the authenticator acts as a pass-through, EAP methods reside only on
the peer and EAP server As a result, the TEKs, MSK and EMSK are
derived on the peer and EAP server.

On completion of EAP authentication, EAP methods on the peer and EAP
server export the Master Session Key (MSK) and Extended Master
Session Key (EMSK). The peer and EAP server then calculate the AAA-
Key from the MSK and EMSK, and the backend authentication server
sends an Access-Accept to the authenticator, providing the AAA-Key
within a protected package known as the AAA-Token.

The AAA-Key is then used by the peer and authenticator within the
Secure Association Protocol to derive Transient Session Keys (TSKs)
required for the negotiated ciphersuite. The TSKs are known only to
the peer and authenticator.

2.3. Key Lifetimes

As noted earlier, the EAP Key Management framework includes several
types of keys.

Key lifetime issues associated with each type of key are discussed in the sections that follow. Challenges
Issues include:

[a] Security. Key lifetime negotiation. Where key lifetimes cannot be assumed,
it may be necessary to negotiate them. While Where negotiation is
supported, it is RECOMMENDED that the negotiation be secured. Note
that key lifetimes lifetime negotiation may not always be announced
or negotiated required. A
difference between IKEv1 and IKEv2 is that in IKEv1 SA lifetimes
were negotiated. In IKEv2, each end of the clear, a protected lifetime negotiation SA is
RECOMMENDED. responsible for
enforcing its own lifetime policy on the SA and rekeying the SA
when necessary.

[b] Resource reclamation. While key lifetimes may be securely
negotiated, it Key resynchronization. It is possible for the NAS or peer or
authenticator to reboot or reclaim resources, and therefore not be able to cache keys for their full
lifetime. As a result, clearing portions or
all of the key cache. Therefore, key lifetime negotiation does not cannot
guarantee that the key cache will remain synchronized. synchronized, and the peer
may not be able to determine before attempting to use it whether a
particular key exists within the authenticator cache. It is
therefore RECOMMENDED for the lower layer to provide a mechanism
for key state resynchronization. Note that securing this mechanism may be
difficult since Since in this situation one or
more of the parties initially do not possess a key with which to
protect the resynchronization exchange. exchange, securing this mechanism may
be difficult.

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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+
| | ^
| EAP Method | |
| | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ | |
| | | | | | |
| | EAP Method Key |<->| Long-Term | | |
| | Derivation | | Credential | | |
| | | | | | |
| | | +-+-+-+-+-+-+-+ | Local to |
| | | | EAP |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Method |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
| V | | | |
| +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+ | |
| | TEK | | MSK | |EMSK | |IV | | |
| |Derivation | |Derivation | |Derivation | |Derivation | | |
| +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+ +-+-+-+-+-+-+ | |
| | | | | |
| | | | | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+
| | | ^
| | | |
| MSK (64B) | EMSK (64B) | IV (64B) |
| | | Exported|
| | | by |
V V V EAP |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ Method|
| AAA Key Derivation, | | Known | |
| Naming & Binding | |(Not Secret) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+ V
| ---+
| AAA-Key/ Transported |
| AAA-Key Name by AAA |
| Protocol |
V V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+
| | ^
| TSK Derivation | Ciphersuite Lower layer |
| Derivation [AAA-Key Cache] | Specific |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+

Figure 3: EAP Key Hierarchy

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Figure 4: Relationship between EAP peer and authenticator
(acting as an EAP server), where no backend authentication
server is present.

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+-+-+-+-+-+ +-+-+-+-+-+
| | | |
| | | |
| Cipher- | | Cipher- |
| Suite | | Suite |
| | | |
+-+-+-+-+-+ +-+-+-+-+-+
^ ^
| |
| |
| |
V V
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
| |===============| |========| |
| |EAP, TEK Deriv.| | | |
| |<-------------------------------->| backend |
| | | | | |AAA-Key/| |
| | Secure Assoc. | | AAA-Key| Name | |
| peer |<------------->|Authenti-|<-------| auth |
| |===============| cator |========| server |
| | Link Layer | | AAA | (EAP |
| | (PPP,IEEE 802)| |Protocol| server) |
|MSK,EMSK | | | | |
| AAA-Key | | AAA-Key AAA-Key/| | AAA-Key/| |MSK,EMSK,|
| (TSKs) | Name | (TSKs) | Name | AAA-Key | AAA-Key/|
| (TSKs) | | (TSKs) | | Name |
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
^ ^
| |
| MSK, EMSK | MSK, EMSK
| |
| |
+-+-+-+-+-+ +-+-+-+-+-+
| | | |
| EAP | | EAP |
| Method | | Method |
| | | |
| (TEKs) | | (TEKs) |
| | | |
+-+-+-+-+-+ +-+-+-+-+-+

Figure 5: Pass-through relationship between EAP peer,
authenticator and backend authentication server.

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2.3.1. Local Key Lifetimes

The Transient Parent-child relationships

When keying material exported by EAP Keys (TEKs) are session keys used to protect methods expires, all keying
material derived from the
EAP conversation. The TEKs are internal to exported keying material, (including the
AAA-Key, AMSKs and TSKs) also expires.

Similarly, when an EAP method reauthentication takes place, new keying
material is derived and are
not exported. They remain valid only for exported by the duration EAP method, which eventually
results in replacement of calculated keys, including the EAP
conversation, AAA-Key,
AMSKs, and are lost once the EAP conversation completes.

EAP methods may also implement TSKs.

As a cache for other local result, the lifetime of keys calculated from the exported keying
material which may persist for multiple EAP conversations. For
example, EAP methods based on TLS (such as EAP-TLS [RFC2716]) derive
and cache can be no longer than the TLS Master Secret, typically for substantial time
periods. The lifetime of other local the exported keying
material calculated
within the EAP method is defined by the method.

2.3.2. Exported Key Lifetimes

All EAP methods generating keys are required to generate the MSK and
EMSK, and may optionally generate the IV. However, although new
exported keys are generated during re-authentication, itself. However, the lifetime of
exported keys is conceptually distinct from the re-authentication
time, since while re-authentication causes new exported keys to be
derived, exported calculated keys may be cached on the peer and server after a
session completes and therefore their lifetime may can be greater
less than
the re-authentication time.

Although exported keys are generated by the EAP method, most existing
EAP methods do not negotiate the lifetime of the exported keys. EAP,
defined in [RFC3748], also does not support the negotiation that of
lifetimes for exported keying material such as the MSK, EMSK and IV.

Several mechanisms exist for managing the lifetime of exported EAP keys. Exported EAP keys For example, TSK rekey may be cached on the EAP server as well as
on the peer. On the
occur prior to EAP server, it is RECOMMENDED reauthentication.

Note that the lifetime deletion of exported keys be managed as a system parameter. Where the EAP
method AAA-Key does not support the negotiation necessarily imply deletion
of the exported key lifetime,
and where a negotiation mechanism is not provided by corresponding TSKs. Replacement or deletion of TSKs only
implies replacement of the lower lower,
it is RECOMMENDED that AAA-Key when the peer assume TSKs are taken from a default value
portion of the
exported key lifetime. A value of 8 hours is suggested.

Attempting AAA-Key.

Failure to manage the lifetime mutually prove possession of the EAP-Key SA using AAA
attributes is NOT RECOMMENDED, since this requires AAA-Key during the authenticator
to maintain EAP-Key SA state. As described in Section 3, EAP-Key SA
state is Secure
Association Protocol exchange need not be grounds for deletion of the
AAA-Key by both parties; rate-limiting Secure Association Protocol
exchanges could be used to prevent a brute force attack.

2.3.2. Local Key Lifetimes

The Transient EAP Keys (TEKs) are session keys used to protect the
EAP conversation. The TEKs are internal to the EAP method and are
not exported. TEKs are typically only maintained on created during an EAP conversation,
used until the peer end of the conversation and server, so
requiring EAP-Key SA state then discarded. However,
methods may rekey TEKs during a conversation.

When using TEKs within an EAP conversation or across conversations,
it is necessary to be maintained ensure that replay protection and key separation
requirements are fulfilled. For instance, if a replay counter is
used, TEK rekey MUST occur prior to wrapping of the counter.
Similarly, TSKs MUST remain cryptographically separate from TEKs
despite TEK rekeying or caching. This prevents TEK compromise from
leading directly to compromise of the TSKs and vice versa.

EAP methods may cache local keying material which may persist for
multiple EAP conversations when fast reconnect is used [RFC 3748].
For example, EAP methods based on TLS (such as EAP-TLS [RFC2716])
derive and cache the authenticator
represents an unnecessary additional burden. TLS Master Secret, typically for substantial
time periods. The lifetime of other local keying material calculated

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2.3.3. Calculated Key Lifetimes

When keying material exported by

within the EAP methods method is replaced, new
calculated keys are also put defined by the method. Note that in place. Similarly,
general, when using fast reconnect, there is no guarantee to that the keying
material exported by EAP methods expires, so do
original long-term credentials are still in the calculated keys.
As possession of the
peer. For instance, a result, card hold holding the lifetime of keys calculated from private key material
exported for EAP-TLS
may have been removed. EAP servers should verify that the long-term
credentials are still valid, such as by checking that certificate
used in the original authentication has not yet expired.

2.3.3. Exported and Calculated Key Lifetimes

All EAP methods can be no larger than generating keys are required to generate the lifetime of MSK and
EMSK, and may optionally generate the
exported keying material.

However, since IV. Existing EAP methods do
not negotiate the lifetime of calculated keys can be less than that
of the exported keys they are derived from, calculated key keys. EAP, defined in
[RFC3748], also does not support the negotiation of lifetimes
are conceptually distinct from for
exported key lifetimes and re-
authentication times, and need to be managed as a separate parameter.

Note that just keying material such as the re-authentication time MSK, EMSK and the exported key
lifetime are conceptually distinct parameters, so too are calculated IV.

Several mechanisms exist for managing key lifetimes conceptually distinct from the re-authentication time. lifetimes:

[a] AAA attributes. AAA protocols such as RADIUS [RFC2865] and
Diameter [DiamEAP] support the Session-Timeout attribute. As described in [RFC3580], this may be used to determine The
Session-Timeout value represents the maximum session time prior to re-authentication. Since re-
authentication results in the derivation lifetime of new the
exported keys keys, and the
transport of a new AAA-Key, while a session is all keys calculated from it, in progress all
circumstances. The AAA server MUST expire the
maximum session time exported keys, and
all keys calculated from them, prior to re-authentication places an upper bound
on the AAA-Key lifetime.

However, after future time indicated
by Session-Timeout. On the session has terminated, it authenticator, where EAP is possible used for
authentication, the
AAA-Key to be cached on the authenticator. Therefore the AAA-Key
lifetime may be larger than the re-authentication time. As a result, Session-Timeout value represents the AAA-Key lifetime needs maximum
session time prior to be managed re-authentication, as a separate parameter.

Since described in [RFC3580].
Where EAP is used for pre-authentication, the lifetime of session may not start
until some future time, or may never occur. Nevertheless, the AAA-Key within
Session-Timeout value represents the authenticator key cache
is in part determined by authenticator resources, time after which the AAA-Key
lifetime is often managed as a system parameter AAA-Key,
and all keys calculated from it, will have expired on the
authenticator.
Since If the authenticator may have fewer resources than either session subsequently starts, re-
authentication will be initiated once the EAP
peer Session-Time has expired.
If the session never started, or server, it is possible that AAA-Key lifetime on started and ended, the
authenticator may AAA-Key and
all keys calculated from it will be less than exported key lifetime maintained expired by the server, or that the authenticator may need to reclaim AAA-Key
resources
prior to expiration of the AAA-Key lifetime. As a result,
knowledge of future time indicated by Session-Timeout.

Since the AAA-Key TSK lifetime may is often determined by authenticator
resources, the AAA server has no insight into the TSK derivation
process, and by the principle of ciphersuite independence, it is
not be sufficient appropriate for the peer AAA server to determine whether a particular AAA-Key exists within manage any aspect of the TSK
derivation process, including the TSK lifetime.

[b] Lower layer mechanisms. While AAA attributes can communicate the
maximum exported key cache
of a given authenticator.

Issues arise when attempting lifetime, this only serves to manage synchronization of calculated synchronize the
key lifetimes lifetime between the AAA backend authentication server and the authenticator using AAA
attributes.

Failure
authenticator. Lower layer mechanisms can then be used to mutually prove possession of the AAA-Key during enable
the Secure lifetime of exported and calculated keys to be negotiated

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between the peer and authenticator.

Where TSKs are established as the result of a Secure Association
Protocol exchange exchange, it is RECOMMENDED that the Secure Association
Protocol include secure negotiation of the TSK lifetime between the
peer and authenticator. Where the TSK is taken from the AAA-Key,
there is no need to manage the TSK lifetime as a separate
parameter, since the TSK lifetime and AAA-Key lifetime are
identical.

[c] System defaults. Where the EAP method does not be grounds for deletion support the
negotiation of the
AAA-Key exported key lifetime, and a negotiation
mechanism is not provided by both parties; rate-limiting Secure Association Protocol
exchanges could the lower lower, there may be used no way
for the peer to prevent learn knowledge of the exported key liftime. In
this case it is RECOMMENDED that the peer assume a brute force attack. default value of
the exported key lifetime; 8 hours is suggested. Similarly, the
lifetime of calculated keys can also be managed as a system
parameter on the authenticator.

2.3.4. Key cache synchronization

Issues arise when attempting to synchronize the key cache on the peer
and authenticator. Lifetime negotiation alone cannot guarantee key
cache synchronization.

One problem is that the AAA protocol cannot guarantee synchronization
of key lifetimes between the peer and authenticator with respect to calculated key
lifetimes. While this synchronization could be provided by authenticator. Where the
Secure Association Protocol, in situations in which this protocol Protocol is not run immediately after EAP
authentication, the exported and calculated key
lifetime lifetimes will not be undefined during
known by the hiatus between peer during the two
protocols. This hiatus. Where EAP pre-authentication
occurs, this can lead to problems with respect to key cache
management.

For example, where the AAA-key lifetime is negotiated between the
authenticator and the peer within the Secure Association Protocol,
this may be used by leave the peer uncertain whether a subsequent
attempt to manage the lifetime of the AAA-Key
once use the Secure Association Protocol has completed. exported keys will prove successful.

However, even where
EAP pre-authentication is used, a hiatus may exist between the
completion of the EAP method and the initiation of the Secure Association Protocol, during which peer cannot determine the lifetime
of the AAA-Key.

As a result, unless the AAA-Key lifetime Protocol is negotiated within the EAP
method or the lower layer, the peer will not be able to determine a
session-specific AAA-Key lifetime until run
immediately after EAP, it attempts to negotiate the
Secure Association Protocol, which could fail due to AAA-Key lifetime
expiration.

One solution is to simplify management of the AAA-Key lifetime by
treating it as a system parameter of still possible for the peer, authenticator and
server. This enables a wider range of solutions. For example, to
reclaim resources if the created key state is not immediately
utilized.

The lower layer may utilize Discovery mechanisms to ensure AAA-Key cache
synchronization between the peer and authenticator.

If assist in this.
For example, the authenticator manages the AAA-Key cache by deleting
the oldest AAA-Key first (LIFO), the relative creation time of the
last AAA-Key to be deleted could be advertised with the Discovery
phase, enabling the peer to determine whether a given AAA-Key had
been expired from the authenticator key cache.

2.3.4. TSK Key Lifetimes

Since the TSKs depend on the AAA-Key, replacement of the AAA-Key
typically results in replacement of the TSKs. However, deletion of
the AAA-Key does not necessarily imply deletion of the corresponding
TSKs. Replacement or deletion of TSKs only implies replacement of
the AAA-Key when the TSKs are taken from a portion of the AAA-Key. cache prematurely.

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While the lifetime of

2.4. Key Names and Scopes

Each key created within the TSKs may be shorter than or equal to the
AAA-Key lifetime, the TSK lifetime cannot exceed the AAA-Key
lifetime. Where EAP key management framework has a Secure Association Protocol exists, it is possible
for TSKs to be refreshed prior to re-authentication, and so name
(the identifier by which the TSK
Key Lifetime may also key can be shorter than or equal identified), as well as a
scope (the parties to whom the re-
authentication timeout. It key is RECOMMENDED that available). This section
describes how keys are named, and the TSK Key lifetime
be managed as scope within which that name
applies.

Session-Id

EAP methods supporting key naming MUST specify a parameter distinct temporally unique
method identifier known as the EAP Method-Id, which is typically
constructed from nonces or counters used within the re-authentication timeout exchange. Since
multiple EAP sessions may exist between an EAP peer and EAP server,
the AAA-Key lifetime (except where Method-Id allows MSKs to be differentiated.

The combination of the TSK is taken from EAP Type and the AAA-
Key).

Where TSKs are established Method-Id is known as the result EAP
Session-Id. The inclusion of a Secure Association
Protocol exchange, it is RECOMMENDED the Type in the EAP Session-Id ensures
that each EAP method has a distinct name space.

The EAP Session-Id uniquely identifies the Secure Association
Protocol include secure negotiation of EAP session to the TSK lifetime between EAP
peer and server terminating the EAP conversation. However, suitable
EAP peer and authenticator. Where server names may not always be available. As described
in [RFC3748] Section 7.3, the TSK is taken identity provided in the EAP-
Response/Identity, may be different from the AAA-Key,
there is no need to manage identity authenticated
by the TSK lifetime EAP method, and as a separate parameter,
since result the TSK lifetime and AAA-Key lifetime are identical.

As described in Section 3, TSKs are part EAP-Response/Identity is
unsuitable for determination of Service SAs which reside the peer identity. As a result, the
Session-Id scope is defined by the EAP peer name (if securely
exchanged within the method) concatenated with the EAP server name
(also only if securely exchanged). Where a peer or server name is
missing the null string is used. Since an EAP session is not bound
to a particular authentication or specific ports on the peer and
authenticator, the authenticator and as with port or identity are not included in
the AAA-Key lifetime, Session-Id scope.

The EAP Session-Id is exported by the
TSK lifetime EAP method along with the
Session-Id scope, if available, and is often determined used to construct names for
other EAP keys. Note that the EAP Session-Id and scope are only
known by authenticator resources. the EAP method. As a result, the AAA server has no insight into format of the TSK derivation
process, EAP Session-
Id and by the principle definition of ciphersuite independence, it is not
appropriate for the AAA server Session-Id scope needs to manage any aspect of be specified
within the TSK
derivation process, including method. Appendix E defines the TSK lifetime.

2.4. Key Naming EAP Session-Id and scope
provided by existing methods.

MSK Name

This key is created between the EAP peer and EAP server, and is
uniquely named by the concatenation of can be
referred to using the string "MSK", EAP
Method Type, EAP peer name, EAP server name, EAP peer nonce, "MSK" and the EAP server nonce. Here Session-Id. As with
the EAP Session-Id, the MSK scope is defined by the EAP peer name and (if

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are the identifiers Key Management Framework 14 November 2004

securely exchanged within the EAP method.
Since multiple MSKs may exist between an EAP peer method) and EAP server, the EAP server name (also
only if securely exchanged). Where a peer nonce and EAP or server nonce allow MSKs to be
differentiated; at least one of these nonces is necessary. The
inclusion of the Method Type in the name ensures that each EAP
method has a distinct name space.

Note that the components of the MSK Name are only known by the EAP
method. As a result, the MSK Name is exported from the method, and
no detailed format of missing
the MSK Name can be specified without a
reference to a particular method. null string is used.

EMSK Name

The EMSK is named similarly can be referred to the above. Its name is the

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concatenation of using the string "EMSK", "EMSK" and the EAP Method Type, EAP peer
name, EAP server name, EAP peer nonce, and
Session-Id.

As with the EAP server nonce.

Note that neither Session-Id, the MSK nor EMSK names include the authenticator
identity or the peer or authenticator port over which scope is defined by the EAP
conversation took place. This is because peer
name (if securely exchanged within the MSK method) and EMSK are not
bound to an authenticator, or to specific ports on the EAP server
name (also only if securely exchanged). Where a peer or
authenticator. server name
is missing the null string is used.

AMSK Name

AMSKs, if any, may can be named by the concatenation of referred to using the string "AMSK", the key
label, application data (see Appendix F), Section 2.6) and EMSK
Name.

AAA-Key Name

The AAA-Key is named by the concatenation of EAP Session-Id.

As with the string "AAA-Key", EAP Session-Id, the authenticator AMSK scope is defined by the EAP peer
name (since (if securely exchanged within the AAA-Key is bound to a particular
authenticator), method) and the EAP server
name of the key from which (also only if securely exchanged). Where a peer or server name
is missing the null string is used.

AAA-Key Name

The AAA-Key is derived (MSK from either the MSK or AMSK Name). For and so can be
referred to using the purpose MSK or AMSK names.

The AAA-Key scope is provided by the concatenation of the EAP peer
name (if securely provided to the authenticator), and the
authenticator name (if securely provided to the peer).

For the purpose of identifying the
authenticator, authenticator to the contents peer, the
value of the NAS-Identifier attribute is recommended. In order The
authenticator may include the NAS-Identifier attribute to ensure that all parties can agree on the
authenticator name this requires AAA
server in an Access-Request, and the authenticator may provide the
NAS-Identifier (unsecured) to advertise
its name (typically using the EAP peer in the EAP-
Request/Identity or via a lower layer mechanism, such mechanism (such as the 802.11
Beacon/Probe Response).

Note Where the NAS-Identifier is provided by the
authenticator to the peer a secure mechanism is RECOMMENDED.

For the purpose of identifying the peer to the authenticator, the EAP
peer identifier provided within the EAP method is recommended. It
cannot be assumed that the AAA-Key authenticator is aware of the EAP peer
name does not used within the method. Therefore alternatives mechanisms need
to be used to provide the EAP peer name to the authenticator. For
example, the AAA server may include the EAP peer name in the User-

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Name attribute of the Access-Accept or the peer may provide the
authenticator port over which with its name via a lower layer mechanism.

Absent an explicit binding step within the EAP conversation took place.
This is because Secure Association
Protocol, the AAA-Key is not bound to a specific peer or
authenticator port. As a result, the peer or authenticator port over
which the EAP conversation takes place is not included in the AAA-Key
scope.

PMK Name

This document does not specify a naming scheme for the PMK. The PMK has no name of its own, and
is only identified by the AAA-
Key AAA-Key from which it is derived.
Similarly, the PMK scope is the same as the AAA-Key scope.

Note: IEEE 802.11i names the PMKID for the purposes of being able to
refer to it in the Secure Association protocol; this naming is based
on a hash of the PMK itself as well as some other parameters (see
Section 8.5.1.2 [IEEE80211i]).

TEKs

The TEKs may or may not be named. Their naming is specified in the
EAP method. Since the TEKs are only known by the EAP peer and
server, the TEK scope is the same as the Session-Id scope.

TSKs

The TSKs are typically named. Their naming is specified in the Secure
Association (phase 2) protocol, so that the correct set of transient
session keys can be identified for processing a given

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scope of the TSKs is negotiated within the Secure Association
Protocol.

TSK creation and deletion operations are also typically supported so that
establishment and re-establishment of
transient session keys TSKs can be synchronized
between the parties.

In order to avoid confusion in the case where an EAP peer has more
than one AAA-Key (phase 1b) applicable to establishment of a phase 2
security association, the secure Association protocol needs to
name
utilize the AAA-Key name so that the appropriate phase 1b keying
material can be identified for use in the Secure Association Protocol
exchange.

3. Security Associations

During

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2.5. AAA-Key Derivation

Where a AAA-Key is generated as the result of
security associations (SAs) are created:

[1] a successful EAP method SA. This SA
authentication with the authenticator A, the AAA-Key is between based on the peer
MSK: AAA-Key = MSK(0,63).

As discussed in [I-D.irtf-aaaarch-handoff], [IEEE-02-758],
[IEEE-03-084], and EAP server. It
stores state that can [8021XHandoff], keying material may be used required
for "fast resume" or other
functionality use in some EAP methods. Not all EAP methods create such
an SA.

[2] EAP-Key SA. This is an SA fast handoff between authenticators. Where the peer and EAP server, which
is used backend
authentication server provides keying material to store additional
authenticators in order to facilitate fast handoff, it is highly
desirable for the keying material exported by the EAP method.
Current EAP server implementations do not retain this SA after the
EAP conversation completes, but proposals such as [IEEE-03-084] and
[I-D.irtf-aaaarch-handoff] use this SA for purposes such as pre-
emptive key distribution.

[3] AAA SA(s). These SAs are between the used on different authenticators B,
C to be cryptographically separate, so that if one authenticator and is
compromised, it does not lead to the compromise of other
authenticators. Where keying material is provided by the backend
authentication server. They permit server, a key hierarchy derived from the parties AMSK can be
used to mutually
authenticate each other and protect the communications between
them.

[4] Service SA(s). These SAs are between provide cryptographically separate keying material for use in
fast handoff. Instead of using the peer and authenticator,
and they are created EMSK directly an application
specific key (AMSK) is derived as a result of phases 1-2 described in Section 2.6:

AAA-Key = MSK(0,63)

AMSK = KDF(EMSK, "EAP AAA-Key derivation for multiple attachments",
length)

AAA-Key-B = prf(AMSK(0,63),"EAP AAA-Key derivation for
multiple attachments", AAA-Key, B-Called-Station-Id,
Calling-Station-Id,length)

AAA-Key-C = prf(AMSK(0,63),"EAP AAA-Key derivation for
multiple attachments",AAA-Key, C-Called-Station-Id,
Calling-Station-Id, length)

Where:
Calling-Station-Id = STA MAC address
B-Called-Station-Id = AP B MAC address
C-Called-Station-Id = AP C MAC address
prf = HMAC-SHA1
KDF = defined in Section 2.6
length = length of derived key material

Here AAA-Key is derived during the conversation
(see Section 1.3).

3.1. EAP Method SA (peer - EAP server)

An initial EAP method may store some state on authentication between
the peer and EAP server even
after phase 1a has completed.

Typically, authenticator A. Based on this initial EAP
authentication, an AMSK is also derived, which can be used to derive
AAA-Keys for "fast resume": fast authentication between the EAP peer and EAP server
can confirm that they are still talking to
authenticators B and C. Since the same party, perhaps
using fewer round-trips or less computational power. In this case, AMSK is cryptographically separate
from the EAP method SA MSK, each of these AAA-Keys is essentially a cache for performance
optimization, cryptographically separate
from each other, and either party may remove are guaranteed to be unique between the SA from its cache at
any point. EAP peer

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An EAP method may also keep state in order to support pseudonym-based
identity protection. This is typically a cache

(also known as well (the
information can be recreated if the original EAP method SA is lost),
but may be stored for longer periods of time.

The EAP method SA is not restricted to a particular service or
authenticator STA) and is most useful when the peer accesses many
different authenticators. An authenticator (also known as the AP).

2.6. AMSK Key Derivation

The EAP method is responsible for
specifying how AMSK key derivation function (KDF) derives an AMSK from the parties select if
Extended Master Session Key (EMSK), an existing EAP method SA should
be used, application key label,
optional application data, and if so, which one. Where multiple backend authentication
servers are used, EAP method SAs output length.

AMSK = KDF(EMSK, key label, optional application data, length)

The key labels are not typically synchronized
between them.

EAP method implementations should consider the appropriate lifetime printable ASCII strings unique for the EAP method SA. "Fast resume" assumes that the information
required (primarily the each
application (see Section 7 for IANA Considerations).

Additional ciphering keys in the EAP method SA) hasn't been
compromised. In case (TSKs) can be derived from the original authentication was carried out
using, for instance, a smart card, AMSK using
an application specific key derivation mechanism. In many cases,
this AMSK->TSK derivation can simply split the AMSK to pieces of
correct length. In particular, it may be easier is not necessary to compromise the
EAP method SA (stored on the PC, for instance), so typically the EAP
method SAs have use a limited lifetime.

Contents:

o Implicitly,
cryptographic one-way function. The length of the EAP method this SA refers to
o One or more internal (non-exported) keys
o EAP method SA name
o SA lifetime

3.1.1. Example: EAP-TLS

In EAP-TLS [RFC2716], after AMSK MUST be
specified by the EAP authentication application.

The AMSK key derivation function is taken from the client (peer) PRF+ key expansion
PRF from [IKEv2]. This KDF takes 4 parameters as input: secret,
label, application data, and server can store the following information:

o Implicitly, the EAP method this SA refers output length. It is only defined for
255 iterations so it may produce up to (EAP-TLS)
o Session identifier (a value selected by the server)
o Certificate 5100 bytes of key material.

For the other party (server stores purposes of this specification the client's
certificate and vice versa)
o Ciphersuite and compression method
o TLS Master secret (known is taken as the EAP-TLS Master Key or MK)
o SA lifetime (ensuring that
EMSK, the SA label is not stored forever)
o If the client has multiple different credentials (certificates
and corresponding private keys), key label described above concatenated with a pointer to those credentials

When
NUL byte, the server initiates EAP-TLS, application data is also described above and the client can look up the EAP-TLS
SA output
length is two bytes. Application data MAY be an empty string. The
KDF is based on the credentials it HMAC-SHA1 [RFC2104] [SHA1]. For this specification we
have:

KDF (K,L,D,O) = 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)

prf = HMAC-SHA1
K = EMSK
L = key label
D = application data
O = OutputLength (2 bytes)
S = L | " " | D | O

The prf+ construction was going to use (certificate and
private key), and the expected credentials (certificate or name) chosen because of
the server. If an EAP-TLS SA exists, its simplicity and it is not too old, the
client informs the server about the existence of this SA by including

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its Session-Id

efficiency over other PRFs such as those used in the TLS ClientHello message. [TLS]. The server then looks
up the correct SA based on the Session-Id (or detects that it doesn't
yet have one).

3.1.2. Example: EAP-AKA

In EAP-AKA [I-D.arkko-pppext-eap-aka], after EAP authentication the
client and server can store the following information:

o Implicitly,
motivation for the EAP method design of this SA refers to (EAP-AKA)
o A re-authentication pseudonym
o PRF is described in [SIGMA].

The client's permanent identity (IMSI)
o Replay protection counter
o Authentication NUL byte after the key (K_aut)
o Encryption label is used to avoid collisions if one
key (K_encr)
o Original Master Key (MK)
o SA lifetime (ensuring that the SA label is not stored forever)

When a prefix of another label (e.g. "foobar" and
"foobarExtendedV2"). This is considered a simpler solution than
requiring a key label assignment policy that prevents prefixes from
occurring.

Where another prf needs to be negotiated, this can be handled within
the server initiates EAP-AKA, EAP method.

2.7. Key Scope Issues

As described in Section 2.5, the client can look up AAA-Key is calculated from the EAP-AKA
SA based on EMSK
and MSK by the credentials it was going to use (permanent identity).
If an EAP-AKA SA exists, EAP peer and server, and it is not too old, used as the client informs root of the
ciphersuite-specific key hierarchy. Where a backend authentication
server about is present, the AAA-Key is transported from the existence of this SA by sending its re-
authentication pseudonym as its identity in EAP Identity Response
message, instead of its permanent identity. The server then looks up to
the correct SA based on this identity.

3.2. EAP-Key SA

This authenticator; where it is an SA between not present, the peer and EAP server, which AAA-Key is used to store calculated
on the keying material exported by authenticator.

Regardless of how many sessions are initiated using it, the EAP method. Current EAP server
implementations do not retain this SA after AAA-Key
scope is between the EAP conversation
completes, but future implementations could use this SA for pre-
emptive key distribution.

Contents:

o MSK and EMSK names
o MSK peer that calculates it, and EMSK
o SA lifetime

3.3. AAA SA(s) (authenticator - backend authentication server)

In order for the
authenticator and backend authentication that either calculates it (where no backend
authenticator is present) or receives it from the server (where a
backend authenticator server is present).

It should be understood that an authenticator or peer:

[a] may contain multiple physical ports;
[b] may advertise itself as multiple "virtual" authenticators
or peers;
[c] may utilize multiple CPUs;
[d] may support clustering services for load balancing or failover.

As illustrated in Figure 1, an EAP peer with multiple ports may be
attached to
authenticate one or more authenticators, each other, they need with multiple ports.
Where the peer and authenticator identify themselves using a port
identifier such as a link layer address, it may not be obvious to store some information.

In case the
peer which authenticator and backend authentication server ports are
colocated, associated with which
authenticators. Similarly, it may not be obvious to the
authenticator which peer ports are associated with which peers. As a
result, the peer and they communicate using local procedure calls or shared
memory, this SA need authenticator may not necessarily contain any information. be able to determine the
scope of the AAA-Key.

When a single physical authenticator advertises itself as multiple
"virtual authenticators", the EAP peer and authenticator also may not
be able to agree on the scope of the AAA-Key, creating a security

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3.3.1. Example: RADIUS

In RADIUS, where shared secret authentication is used, the client and
server store each other's IP address and

vulnerability. For example, the shared secret, which is
used to calculate peer may assume that the Response Authenticator [RFC2865] "virtual
authenticators" are distinct and Message-
Authenticator [RFC3579] values, do not share a key cache, whereas,
depending on the architecture of the physical AP, a shared key cache
may or may not be implemented.

Where the AAA-Key is shared between "virtual authenticators" an
attacker acting as a peer could authenticate with the "Guest"
"virtual authenticator" and derive a AAA-Key. If the virtual
authenticators share a key cache, then the peer can utilize the AAA-
Key derived for the "Guest" network to obtain access to the
"Corporate Intranet" virtual authenticator.

Several measures are recommended to address these issues:

[a] Authenticators are REQUIRED to cache associated authorizations
along with the AAA-Key and apply authorizations consistently. This
ensures that an attacker cannot obtain elevated privileges even
where the AAA-Key cache is shared between "virtual authenticators".

[b] It is RECOMMENDED that physical authenticators maintain separate
AAA-Key caches for each "virtual authenticator".

[c] It is RECOMMENDED that each "virtual authenticator" identify itself
distinctly to the AAA server, such as by utilizing a distinct NAS-
identifier attribute. This enables the AAA server to utilize a
separate credential to authenticate each "virtual authenticator".

[d] It is RECOMMENDED that Secure Association Protocols identify peers
and authenticators unambiguously, without incorporating implicit
assumptions about peer and authenticator architectures. Using
port-specific MAC addresses as identifiers is NOT RECOMMENDED where
peers and authenticators may support multiple ports.

[e] The AAA server and authenticator MAY implement additional
attributes in order to further restrict the AAA-Key scope. For
example, in 802.11, the AAA server may provide the authenticator
with a list of authorized Called or Calling-Station-Ids and/or
SSIDs for which the AAA-Key is valid.

[f] Where the AAA server provides attributes restricting the key scope,
it is RECOMMENDED that restrictions be securely communicated by the
authenticator to the peer. This is typically accomplished using
the Secure Association Protocol, but also can be accomplished via
the EAP method or the lower layer.

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3. Security Associations

During EAP authentication and subsequent exchanges, four types of
security associations (SAs) are created:

[1] EAP method SA. This SA is between the peer and EAP server. It
stores state that can be used for "fast reconnect" or other
functionality in some EAP methods. Not all EAP methods create such
an SA.

[2] EAP-Key SA. This is an SA between the peer and EAP server, which
is used to store the keying material exported by the EAP method.
Current EAP server implementations do not retain this SA after the
EAP conversation completes, but proposals such as [IEEE-03-084] and
[I-D.irtf-aaaarch-handoff] use this SA for purposes such as pre-
emptive key distribution.

[3] AAA SA(s). These SAs are between the authenticator and the backend
authentication server. They permit the parties to mutually
authenticate each other and protect the communications between
them.

[4] Service SA(s). These SAs are between the peer and authenticator,
and they are created as a result of phases 1-2 of the conversation
(see Section 1.3).

3.1. EAP Method SA (peer - EAP server)

An EAP method may store some state on the peer and EAP server even
after phase 1a has completed.

Typically, this is used for "fast reconnect": the peer and EAP server
can confirm that they are still talking to the same party, perhaps
using fewer round-trips or less computational power. In this case,
the EAP method SA is essentially a cache for performance
optimization, and either party may remove the SA from its cache at
any point.

An EAP method may also keep state in order to encrypt some attributes (such support pseudonym-based
identity protection. This is typically a cache as well (the
information can be recreated if the AAA-Key [RFC2548]).

Where IPsec original EAP method SA is used lost),
but may be stored for longer periods of time.

The EAP method SA is not restricted to protect RADIUS [RFC3579] a particular service or
authenticator and IKE is used most useful when the peer accesses many
different authenticators. An EAP method is responsible for
key management,
specifying how the parties select if an existing EAP method SA should
be used, and if so, which one. Where multiple backend authentication

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servers are used, EAP method SAs are not typically synchronized
between them.

EAP method implementations should consider the appropriate lifetime
for the EAP method SA. "Fast reconnect" assumes that the information
required (primarily the keys in the EAP method SA) hasn't been
compromised. In case the original authentication was carried out
using, for instance, a smart card, it may be easier to compromise the
EAP method SA (stored on the PC, for instance), so typically the EAP
method SAs have a limited lifetime.

Contents:

o Implicitly, the EAP method this SA refers to
o Internal (non-exported) cryptographic state
o EAP method SA name
o SA lifetime

3.1.1. Example: EAP-TLS

In EAP-TLS [RFC2716], after the EAP authentication the parties store information necessary to
authenticate client (peer)
and authorize server can store the other party (e.g. certificates, trust
anchors and names). The IKE exchange results in IKE Phase 1 and Phase
2 SAs containing information used to protect following information:

o Implicitly, the conversation
(session keys, EAP method this SA refers to (EAP-TLS)
o Session identifier (a value selected ciphersuite, etc.)

3.3.2. Example: Diameter with TLS

When using Diameter protected by TLS, the parties store information
necessary to authenticate and authorize server)
o Certificate of the other party (e.g.
certificates, trust anchors (server stores the client's
certificate and names). The TLS handshake results in
a short-term vice versa)
o Ciphersuite and compression method
o TLS Master secret (known as the EAP-TLS Master Key)
o SA lifetime (ensuring that contains information used the SA is not stored forever)
o If the client has multiple different credentials (certificates
and corresponding private keys), a pointer to protect those credentials

When the
actual communications (session keys, selected TLS ciphersuite, etc.).

3.4. Service SA(s) (peer - authenticator)

The service SAs store information about server initiates EAP-TLS, the service being provided.
These include client can look up the Root service EAP-TLS
SA based on the credentials it was going to use (certificate and derived unicast
private key), and multicast
service SAs.

The Root service SA is established as the result expected credentials (certificate or name) of
the completion of
EAP authentication (phase 1a) server. If an EAP-TLS SA exists, and AAA-Key derivation or transport
(phase 1b). It includes:

o Service parameters (or at least those parameters
that are still needed)
o On it is not too old, the authenticator, service authorization
information received from
client informs the backend authentication server (or necessary parts about the existence of it)
o On this SA by including
its Session-Id in the peer, usually locally configured service
authorization information.
o TLS ClientHello message. The AAA-Key, if it can be needed again (to refresh
and/or resynchronize other keys or for another reason)
o AAA-Key lifetime

Unicast and (optionally) multicast service SAs are derived from server then looks
up the
Root service SA, via correct SA based on the Secure Association Protocol. In order for
unicast and multicast service SAs and associated TSKs to be
established, Session-Id (or detects that it is not necessary for doesn't
yet have one).

3.1.2. Example: EAP-AKA

In EAP-AKA [I-D.arkko-pppext-eap-aka], after EAP authentication (phase 1a) the
client and server can store the following information:

o Implicitly, the EAP method this SA refers to (EAP-AKA)

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be rerun each time. Instead, the Secure Association Protocol can be
used to mutually prove possession of the AAA-Key and create
associated unicast (phase 2a) and multicast (phase 2b) service SAs
and TSKs, enabling the EAP exchange to be bypassed. Unicast and
multicast service SAs include:

o Service parameters negotiated by the Secure Association Protocol. A re-authentication pseudonym
o Endpoint identifiers. The client's permanent identity (IMSI)
o Transient Session Keys used to protect the communication. Replay protection counter
o Transient Session Authentication key (K_aut)
o Encryption key (K_encr)
o Original Master Key lifetime.

One function of (MK)
o SA lifetime (ensuring that the Secure Association Protocol SA is not stored forever)

When the server initiates EAP-AKA, the client can look up the EAP-AKA
SA based on the credentials it was going to bind the the
unicast and multicast service SAs use (permanent identity).
If an EAP-AKA SA exists, and TSKs to endpoint identifiers.
For example, within [IEEE802.11i], it is not too old, the 4-way handshake binds client informs
the TSKs
to server about the MAC addresses existence of the endpoints; this SA by sending its re-
authentication pseudonym as its identity in IKE [RFC2409], the TSKs are
bound to the IP addresses EAP Identity Response
message, instead of its permanent identity. The server then looks up
the endpoints and the negotiated SPI.

It is possible for more than one unicast or multicast service correct SA to
be derived from a single Root service SA. However, a unicast or
multicast service based on this identity.

3.2. EAP-Key SA

This is always descended from only one Root service
SA. Unicast or multicast service SAs descended from the same Root
service an SA may utilize between the same security parameters (e.g. mode,
ciphersuite, etc.) or they may utilize different parameters.

An EAP peer may be able to negotiate multiple service SAs with a
given authenticator, or may be able and EAP server, which is used to maintain one or more service
SAs with multiple authenticators, depending on the properties of store
the
media.

Except where explicitly specified keying material exported by the Secure Association Protocol,
it should EAP method. Current EAP server
implementations do not be assumed that the installation of new service SAs
implies deletion of old service SAs. It is possible for multicast
Root service SAs to between retain this SA after the same EAP peer conversation
completes, but future implementations could use this SA for pre-
emptive key distribution.

Contents:

o MSK and authenticator;
during a re-key of a unicast or multicast service EMSK names
o MSK and EMSK
o SA it is possible lifetime

3.3. AAA SA(s) (authenticator - backend authentication server)

In order for two service SAs to exist during the period between when authenticator and backend authentication server to
authenticate each other, they need to store some information.

In case the new
service SA authenticator and corresponding TSKs backend authentication server are calculated
colocated, and when they are
installed.

Similarly, deletion or creation of a unicast or multicast service SA
does not necessarily imply deletion or creation of related unicast communicate using local procedure calls or
multicast service SAs, unless specified by the Secure Association
protocol. For example, a unicast service SA may be rekeyed without
implying a rekey of the multicast service SA.

The deletion of the Root service shared
memory, this SA does need not necessarily imply the
deletion of contain any information.

3.3.1. Example: RADIUS

In RADIUS, where shared secret authentication is used, the derived unicast client and multicast service SAs
server store each other's IP address and
associated TSKs. Failure to mutually prove possession of the AAA-Key
during the Secure Association Protocol exchange need not be grounds

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for deletion of the AAA-Key by both parties; the action to be taken shared secret, which is defined by the Secure Association Protocol.

3.4.1. Example: 802.11i

[IEEE802.11i] Section 8.4.1.1 defines the security associations
used
within IEEE 802.11. A summary follows; to calculate the Response Authenticator [RFC2865] and Message-
Authenticator [RFC3579] values, and to encrypt some attributes (such
as the standard should be
consulted for details.

o Pairwise Master Key Security Association (PMKSA)

The PMKSA AAA-Key, see [RFC3580] Section 3.16).

Where IPsec is a bi-directional SA, used by both parties for sending to protect RADIUS [RFC3579] and receiving. It IKE is created on the peer when used for

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completes successfully or a pre-shared Key Management Framework 14 November 2004

key is configured. The
PMKSA is created on the authenticator when management, the PMK is received or
created on parties store information necessary to
authenticate and authorize the authenticator or a pre-shared key is configured. other party (e.g. certificates, trust
anchors and names). The PMKSA is IKE exchange results in IKE Phase 1 and Phase
2 SAs containing information used to create the PTKSA. PMKSAs are cached for
their lifetimes. The PMKSA consists of the following elements:

- PMKID (security association identifier)
- Authenticator MAC address
- PMK
- Lifetime
- Authenticated Key Management Protocol (AKMP)
- Authorization parameters specified by protect the AAA server or conversation
(session keys, selected ciphersuite, etc.)

3.3.2. Example: Diameter with TLS

When using Diameter protected by local configuration. This can include
parameters such as the peer's authorized SSID.
On TLS, the peer, this parties store information can be locally
configured.
- Key replay counters (for EAPOL-Key messages)
- Reference
necessary to PTKSA (if any), needed to:
o delete it authenticate and authorize the other party (e.g. AAA server-initiated disconnect)
o replace it when a new four-way
certificates, trust anchors and names). The TLS handshake is done
- Reference to accounting context, the details of which depend
on results in
a short-term TLS SA that contains information used to protect the accounting protocol used,
actual communications (session keys, selected TLS ciphersuite, etc.).

3.4. Service SA(s) (peer - authenticator)

The service SAs store information about the implementation
and administrative details. In RADIUS, this could service being provided.
These include
(e.g. packet the Root service SA and octet counters, derived unicast and Acct-Multi-Session-Id).

o Pairwise Transient Key Security Association (PTKSA) multicast
service SAs.

The PTKSA is a bi-directional Root service SA created is established as the result of a
successful four-way handshake. There may only be one PTKSA
between a pair the completion of peer
EAP authentication (phase 1a) and authenticator MAC addresses. PTKSAs AAA-Key derivation or transport
(phase 1b). It includes:

o Service parameters (or at least those parameters
that are cached for still needed)
o On the lifetime authenticator, service authorization
information received from the backend authentication
server (or necessary parts of it)
o On the PMKSA. Since peer, usually locally configured service
authorization information.
o The AAA-Key, if it can be needed again (to refresh
and/or resynchronize other keys or for another reason)
o AAA-Key lifetime

Unicast and (optionally) multicast service SAs are derived from the PTKSA
Root service SA, via the Secure Association Protocol. In order for
unicast and multicast service SAs and associated TSKs to be
established, it is tied not necessary for EAP authentication (phase 1a) to
be rerun each time. Instead, the PMKSA, it only has Secure Association Protocol can be
used to mutually prove possession of the additional information from AAA-Key and create
associated unicast (phase 2a) and multicast (phase 2b) service SAs
and TSKs, enabling the EAP exchange to be bypassed. Unicast and
multicast service SAs include:

o Service parameters negotiated by the
4-way handshake. The PTKSA consists of Secure Association Protocol.
o Endpoint identifiers.
o Transient Session Keys used to protect the following:

- Key (PTK) communication.

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- Selected ciphersuite
- MAC addresses of the parties
- Replay counters, and ciphersuite specific state
- Reference to PMKSA: This is needed when:
o A new four-way handshake is needed (lifetime, TKIP
countermeasures), and we need to know which PMKSA to use

o Group Transient Session Key Security lifetime.

One function of the Secure Association (GTKSA)

The GTKSA Protocol is a uni-directional SA created based on to bind the four-way
handshake or the group key handshake. A GTKSA consists of
unicast and multicast service SAs and TSKs to endpoint identifiers.
For example, within [IEEE802.11i], the
following:

- Direction vector (whether 4-way handshake binds the GTK is used for transmit or receive)
- Group cipher suite selector
- Key (GTK)
- Authenticator MAC address
- Via reference to PMKSA, or copied here:
o Authorization parameters
o Reference to accounting context

3.4.2. Example: IKEv2/IPsec

Note that this example is intended TSKs
to be informative, and it does not
necessarily include all information stored.

o IKEv2 SA

- Protocol version
- Identities the MAC addresses of the parties
- IKEv2 SPIs
- Selected ciphersuite
- Replay protection counters (Message ID)
- Keys for protecting IKEv2 messages (SK_ai/SK_ar/SK_ei/SK_er)
- Key for deriving keys for IPsec SAs (SK_d)
- Lifetime information
- On endpoints; in [IKEv2], the authenticator, service authorization information
received from TSKs are bound
to the backend authentication server.

When processing an incoming message, IP addresses of the correct SA is looked up based
on endpoints and the SPIs.

o IPsec SAs/SPD

- Traffic selectors
- Replay protection counters
- Selected ciphersuite
- IPsec SPI

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- Keys
- Lifetime information
- Protocol mode (tunnel or transport)

The correct SA negotiated SPI.

It is looked up based on SPI (for inbound packets), or
SPD traffic selectors (for outbound traffic). A separate IPsec SA
exists possible for each direction.

3.4.3. Sharing more than one unicast or multicast service SAs

A SA to
be derived from a single Root service may be provided by multiple logical SA. However, a unicast or physical
service elements. Each
multicast service SA is responsible for specifying how
changing always descended from only one Root service elements is handled. Some approaches include:

Transparent sharing
If
SA. Unicast or multicast service SAs descended from the same Root
service parameters visible to SA may utilize the other party (either peer same security parameters (e.g. mode,
ciphersuite, etc.) or authenticator) do not change, the service can they may utilize different parameters.

An EAP peer may be moved without
requiring cooperation from the other party.

Whether such able to negotiate multiple service SAs with a move should be supported
given authenticator, or used depends on
implementation and administrative considerations. For instance, an
administrator may decide be able to configure a group of IKEv2/IPsec
gateways in a cluster for high-availability purposes, if maintain one or more service
SAs with multiple authenticators, depending on the
implementation used supports this. The peer does not necessarily
have any way properties of knowing when the change occurs.

No sharing
If
media.

Except where explicitly specified by the Secure Association Protocol,
it should not be assumed that the installation of new service parameters require changing, some changes may
require terminating the SAs
implies deletion of old service, and starting a new
conversation from phase 0. This approach service SAs. It is used by all services
for at least some parameters, and it doesn't require any protocol possible for transferring the multicast
Root service SA SAs to between the same EAP peer and authenticator;
during a re-key of a unicast or multicast service elements.

The service may support keeping the old SA it is possible
for two service element active
while the new conversation takes phase, SAs to decrease exist during the time period between when the new
service is SA and corresponding TSKs are calculated and when they are
installed.

Similarly, deletion or creation of a unicast or multicast service SA
does not available.

Some sharing
The necessarily imply deletion or creation of related unicast or
multicast service may allow changing some parameters SAs, unless specified by simply agreeing
about the new values. This may involve Secure Association
protocol. For example, a similar exchange as in
phase 2, or perhaps unicast service SA may be rekeyed without
implying a shorter conversation.

This option usually requires some protocol for transferring rekey of the multicast service SA between SA.

The deletion of the elements. An administrator may decide Root service SA does not to
enable this feature at all, necessarily imply the
deletion of the derived unicast and typically multicast service SAs and
associated TSKs. Failure to mutually prove possession of the AAA-Key
during the Secure Association Protocol exchange need not be grounds
for deletion of the sharing is restricted AAA-Key by both parties; the action to some particular service elements (defined either be taken
is defined by a service
parameter, or simple administrative decision). If the old and new
service element do not support such "context transfer", this Secure Association Protocol.

3.4.1. Example: 802.11i

[IEEE802.11i] Section 8.4.1.1 defines the security associations used
within IEEE 802.11. A summary follows; the standard should be
consulted for details.

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approach falls back to

o Pairwise Master Key Security Association (PMKSA)

The PMKSA is a bi-directional SA, used by both parties for sending
and receiving. The PMKSA is the previous option (no transfer).

Services supporting this feature should also consider what changes
require new authorization from Root Service SA. It is created
on the backend peer when EAP authentication server
(see Section 4.2).

Note that these considerations are not limited completes successfully or a
pre-shared key is configured. The PMKSA is created on the
authenticator when the PMK is received or created on the
authenticator or a pre-shared key is configured. The PMKSA is
used to service create the PTKSA. PMKSAs are cached for their lifetimes.
The PMKSA consists of the following elements:

- PMKID (security association identifier)
- Authenticator MAC address
- PMK
- Lifetime
- Authenticated Key Management Protocol (AKMP)
- Authorization parameters related to specified by the authenticator--they apply to peer's AAA server or
by local configuration. This can include
parameters such as well.

4. Handoff Support

Within EAP, the peer's authorized SSID.
On the peer, this information can be locally
configured.
- Key replay counters (for EAPOL-Key messages)
- Reference to PTKSA (if any), needed to:
o delete it (e.g. AAA server-initiated disconnect)
o replace it when a number of mechanisms may be utilized in order new four-way handshake is done
- Reference to reduce accounting context, the latency details of handoff between authenticators. One such mechanism is
EAP pre-authentication, in which EAP is utilized to pre-establish a
AAA-Key depend
on an authenticator prior to arrival of the peer.

"Fast Handoff" is defined as a conversation in which EAP exchange
(phase 1a) accounting protocol used, the implementation
and associated AAA pass-through is bypassed, so as to
reduce latency. Unlike EAP pre-authentication, "Fast Handoff"
mechanisms do not result in additional AAA server load. Fast handoff
mechanisms include:

[a] Pre-emptive handoff. administrative details. In RADIUS, this technique, the AAA server pre-
establishes key state on could include
(e.g. packet and octet counters, and Acct-Multi-Session-Id).

o Pairwise Transient Key Security Association (PTKSA)

The PTKSA is a bi-directional SA created as the authenticator prior to arrival result of the
peer, without completion a
successful four-way handshake. The PTKSA is a unicast service SA.
There may only be one PTKSA between a pair of EAP authentication. As described in
[IEEE-03-084] peer and [I.D.irtf-aaaarch-handoff], this technique
includes conventional AAA-Key transport, but without an EAP
authentication.

[b] Context transfer. In this technique, the old
authenticator
transfers MAC addresses. PTKSAs are cached for the session text lifetime
of the PMKSA. Since the PTKSA is tied to the new authenticator, either prior
to, or after PMKSA, it only has
the arrival additional information from the 4-way handshake. The PTKSA
consists of the following:

- Key (PTK)
- Selected ciphersuite
- MAC addresses of the peer. As a result, AAA-Key
transport (phase 1b) parties
- Replay counters, and ciphersuite specific state
- Reference to PMKSA: This is bypassed.

Regardless of how the AAA-Key needed when:
o A new four-way handshake is provisioned on a given
authenticator, AAA-Key caching may be utilized in order needed (lifetime, TKIP
countermeasures), and we need to enable a
peer know which PMKSA to quickly re-establish use

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o Group Transient Key Security Association (GTKSA)

The GTKSA is a session with an authenticator.

Where uni-directional SA created based on the four-way
handshake or the group key caching handshake. The GTKSA is supported, once a multicast
service SA. A GTKSA consists of the AAA-Key following:

- Direction vector (whether the GTK is derived and/or
transported used for transmit or receive)
- Group cipher suite selector
- Key (GTK)
- Authenticator MAC address
- Via reference to the authenticator, it may remain cached on the peer PMKSA, or copied here:
o Authorization parameters
o Reference to accounting context

3.4.2. Example: IKEv2/IPsec

Note that this example is intended to be informative, and authenticator, even after a subsequent session terminates. To
initiate a subsequent session with the same authenticator, the peer
may utilize the Secure Association it does not
necessarily include all information stored.

o IKEv2 SA

- Protocol to confirm mutual
possession version
- Identities of the AAA-Key by parties
- IKEv2 SPIs
- Selected ciphersuite
- Replay protection counters (Message ID)
- Keys for protecting IKEv2 messages (SK_ai/SK_ar/SK_ei/SK_er)
- Key for deriving keys for IPsec SAs (SK_d)
- Lifetime information
- On the peer and authenticator, thereby re-
activating service authorization information
received from the AAA-Key for use in a subsequent session. backend authentication server.

When processing an incoming message, the correct SA is looked up based
on the SPIs.

o IPsec SAs/SPD

- Traffic selectors
- Replay protection counters
- Selected ciphersuite
- IPsec SPI
- Keys
- Lifetime information
- Protocol mode (tunnel or transport)

The introduction of handoff support introduces new security correct SA is looked up based on SPI (for inbound packets), or
SPD traffic selectors (for outbound traffic). A separate IPsec SA
exists for each direction.

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vulnerabilities as well as requirements for the secure handling of
authorization context. These issues are discussed in the sections
that follow.

4.1. Key Scope Issues

As described in Appendix E, the AAA-Key is calculated from the EMSK
and MSK

3.4.3. Sharing service SAs

A single service may be provided by the EAP peer and server, and is used as the root of the
ciphersuite-specific key hierarchy. Where a backend authentication
server is present, the AAA-Key is transported from the EAP server to
the authenticator; where it is not present, the AAA-Key multiple logical or physical
service elements. Each service is calculated
on the authenticator.

Regardless of responsible for specifying how many sessions are initiated using it, the AAA-Key
is restricted to use between the EAP peer that calculates it, and the
authenticator that either calculates it (where no backend
authenticator is present) or receives it from the server (where a
backend authenticator server
changing service elements is present). In handled. Some approaches include:

Transparent sharing
If the process of defining service parameters visible to the scope of other party (either peer
or authenticator) do not change, the AAA-Key, it service can be moved without
requiring cooperation from the other party.

Whether such a move should be understood that an
authenticator or peer:

[a] may contain multiple physical ports;

[b] may advertise itself as multiple "virtual" authenticators or peers;

[c] may utilize multiple CPUs;

[d] may support clustering services for load balancing supported or failover.

As illustrated in Figure 1, used depends on
implementation and administrative considerations. For instance, an EAP peer with multiple ports
administrator may be
attached decide to one or more authenticators, each with multiple ports.
Where the peer and authenticator identify themselves using configure a port
identifier such as group of IKEv2/IPsec
gateways in a link layer address, it may not be obvious to cluster for high-availability purposes, if the
implementation used supports this. The peer which authenticator ports are associated with which
authenticators. Similarly, it may does not be obvious to necessarily
have any way of knowing when the
authenticator which peer ports are associated with which peers. As a
result, change occurs.

No sharing
If the peer service parameters require changing, some changes may
require terminating the old service, and authenticator starting a new
conversation from phase 0. This approach is used by all services
for at least some parameters, and it doesn't require any protocol
for transferring the service SA between the service elements.

The service may not be able support keeping the old service element active
while the new conversation takes phase, to determine decrease the
scope of time the AAA-Key.

When
service is not available.

Some sharing
The service may allow changing some parameters by simply agreeing
about the new values. This may involve a single physical authenticator advertises itself similar exchange as multiple
"virtual authenticators", in
phase 2, or perhaps a shorter conversation.

This option usually requires some protocol for transferring the EAP peer and authenticator also
service SA between the elements. An administrator may decide not
be able to agree on the scope of
enable this feature at all, and typically the AAA-Key, creating sharing is restricted
to some particular service elements (defined either by a security
vulnerability. For example, the peer may assume that service
parameter, or simple administrative decision). If the "virtual
authenticators" are distinct old and new
service element do not share a key cache, whereas,
depending on support such "context transfer", this
approach falls back to the architecture of previous option (no transfer).

Services supporting this feature should also consider what changes
require new authorization from the physical AP, a shared key cache
may or may backend authentication server
(see Section 4.2).

Note that these considerations are not be implemented.

Where limited to service
parameters related to the AAA-Key is shared between "virtual authenticators" an authenticator--they apply to peer's

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attacker acting as a peer could authenticate with the "Guest"
"virtual authenticator" and derive a AAA-Key. If the virtual
authenticators share a key cache, then the peer can utilize the AAA-
Key derived for the "Guest" network to obtain access to the
"Corporate Intranet" virtual authenticator.

Several measures are recommended to address these issues: peers and
authenticators 14 November 2004

parameters as well.

4. Handoff Support

With EAP, a number of mechanisms may have multiple ports.

[a] Authenticators are REQUIRED be utilized in order to cache associated authorizations
along with the AAA-Key and apply authorizations consistently. This
ensures that an attacker cannot obtain elevated privileges even
where reduce
the AAA-Key cache is shared latency of handoff between "virtual authenticators".

[b] It authenticators. One such mechanism is RECOMMENDED that physical authenticators maintain separate
AAA-Key caches for each "virtual authenticator".

[c] It
EAP pre-authentication, in which EAP is RECOMMENDED that each "virtual authenticator" identify itself
distinctly utilized to pre-establish a
AAA-Key on an authenticator prior to arrival of the AAA server, such peer.

"Fast Handoff" is defined as by utilizing a distinct NAS-
identifier attribute. This enables the conversation in which EAP exchange
(phase 1a) and associated AAA server to utilize a
separate credential to authenticate each "virtual authenticator".

[d] It pass-through is RECOMMENDED that Secure Association Protocols identify peers
and authenticators unambiguously, without incorporating implicit
assumptions about peer and authenticator architectures. Using
port-specific MAC addresses bypassed, so as identifiers is NOT RECOMMENDED where
peers and authenticators may support multiple ports.

[e] The to
reduce latency. Unlike EAP pre-authentication, "Fast Handoff"
mechanisms do not result in additional AAA server and load. Fast handoff
mechanisms include:

[a] Pre-emptive handoff. In this technique, the AAA server pre-
establishes key state on the authenticator MAY implement additional
attributes prior to arrival of the
peer, without completion of EAP authentication. As described in order
[IEEE-03-084] and [I.D.irtf-aaaarch-handoff], this technique
includes conventional AAA-Key transport, but without an EAP
authentication.

[b] Context transfer. In this technique, the old authenticator
transfers the session text to further restrict the AAA-Key scope. For
example, in 802.11, new authenticator, either prior
to, or after the AAA server may provide arrival of the authenticator
with peer. As a list result, AAA-Key
transport (phase 1b) is bypassed.

Regardless of authorized Called or Calling-Station-Ids and/or
SSIDs for which how the AAA-Key is valid.

[f] provisioned on a given
authenticator, AAA-Key caching may be utilized in order to enable a
peer to quickly re-establish a session with an authenticator.

Where the AAA server provides attributes restricting the key scope,
it caching is RECOMMENDED that restrictions be securely communicated by supported, once the
authenticator AAA-Key is derived and/or
transported to the peer. This is typically accomplished using authenticator, it may remain cached on the peer
and authenticator, even after a subsequent session terminates. To
initiate a subsequent session with the same authenticator, the peer
may utilize the Secure Association Protocol, but also can be accomplished via Protocol to confirm mutual
possession of the EAP method or AAA-Key by the lower layer.

4.2. peer and authenticator, thereby re-
activating the AAA-Key for use in a subsequent session.

The introduction of handoff support introduces new security
vulnerabilities as well as requirements for the secure handling of
authorization context. These issues are discussed in the sections
that follow.

4.1. Authorization Issues

In a typical network access scenario (dial-in, wireless LAN, etc.)
access control mechanisms are typically applied. These mechanisms

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include user authentication as well as authorization for the offered
service.

As a part of the authentication process, the AAA network determines

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the user's authorization profile. The user authorizations are
transmitted by the backend authentication server to the EAP
authenticator (also known as the Network Access Server or
authenticator) included with the AAA-Token, which also contains the
AAA-Key, in Phase 1b of the EAP conversation. Typically, the profile
is determined based on the user identity, but a certificate presented
by the user may also provide authorization information.

The backend authentication server is responsible for making a user
authorization decision, answering the following questions:

[a] Is this a legitimate user for this particular network?

[b] Is this user allowed the type of access he or she is requesting?

[c] Are there any specific parameters (mandatory tunneling, bandwidth,
filters, and so on) that the access network should be aware of for
this user?

[d] Is this user within the subscription rules regarding time of day?

[e] Is this user within his limits for concurrent sessions?

[f] Are there any fraud, credit limit, or other concerns that indicate
that access should be denied?

While the authorization decision is in principle simple, the process
is complicated by the distributed nature of AAA decision making.
Where brokering entities or proxies are involved, all of the AAA
devices in the chain from the authenticator to the home AAA server
are involved in the decision. For instance, a broker can disallow
access even if the home AAA server would allow it, or a proxy can add
authorizations (e.g., bandwidth limits).

Decisions can be based on static policy definitions and profiles as
well as dynamic state (e.g. time of day or limits on the number of
concurrent sessions). In addition to the Accept/Reject decision made
by the AAA chain, parameters or constraints can be communicated to
the authenticator.

The criteria for Accept/Reject decisions or the reasons for choosing
particular authorizations are typically not communicated to the
authenticator, only the final result. As a result, the authenticator
has no way to know what the decision was based on. Was a set of

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authorization parameters sent because this service is always provided
to the user, or was the decision based on the time/day and the
capabilities of the requesting authenticator device?

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4.3.

4.2. Correctness Issues

Bypassing all or portions of the AAA conversation creates challenges
in ensuring that authorization is properly handled. These include:

[a] Consistent application of session time limits. A fast handoff
should not automatically increase the available session time,
allowing a user to endlessly extend their network access by
changing the point of attachment.

[b] Avoidance of privilege elevation. A fast handoff should not result
in a user being granted access to services which they are not
entitled to.

[c] Consideration of dynamic state. In situations in which dynamic
state is involved in the access decision (day/time, simultaneous
session limit) it should be possible to take this state into
account either before or after access is granted. Note that
consideration of network-wide state such as simultaneous session
limits can typically only be taken into account by the backend
authentication server.

[d] Encoding of restrictions. Since a authenticator may not be aware
of the criteria considered by a backend authentication server when
allowing access, in order to ensure consistent authorization during
a fast handoff it may be necessary to explicitly encode the
restrictions within the authorizations provided in the AAA-Token.

[e] State validity. The introduction of fast handoff should not render
the authentication server incapable of keeping track of network-
wide state.

A fast handoff mechanism capable of addressing these concerns is said
to be "correct". One condition for correctness is as follows: For a
fast handoff to be "correct" it MUST establish on the new device the
same context as would have been created had the new device completed
a AAA conversation with the authentication server.

A properly designed fast handoff scheme will only succeed if it is
"correct" in this way. If a successful fast handoff would establish
"incorrect" state, it is preferable for it to fail, in order to avoid
creation of incorrect context.

Some backend authentication server and authenticator configurations

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are incapable of meeting this definition of "correctness". For
example, if the old and new device differ in their capabilities, it
may be difficult to meet this definition of correctness in a fast
handoff mechanism that bypasses AAA. Backend authentication servers

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often perform conditional evaluation, in which the authorizations
returned in an Access-Accept message are contingent on the
authenticator or on dynamic state such as the time of day or number
of simultaneous sessions. For example, in a heterogeneous
deployment, the backend authentication server might return different
authorizations depending on the authenticator making the request, in
order to make sure that the requested service is consistent with the
authenticator capabilities.

If differences between the new and old device would result in the
backend authentication server sending a different set of messages to
the new device than were sent to the old device, then if the fast
handoff mechanism bypasses AAA, then the fast handoff cannot be
carried out correctly.

For example, if some authenticator devices within a deployment
support dynamic VLANs while others do not, then attributes present in
the Access-Request (such as the authenticator-IP-Address,
authenticator-Identifier, Vendor-Identifier, etc.) could be examined
to determine when VLAN attributes will be returned, as described in
[RFC3580]. VLAN support is defined in [IEEE8021Q]. If a fast
handoff bypassing the backend authentication server were to occur
between a authenticator supporting dynamic VLANs and another
authenticator which does not, then a guest user with access
restricted to a guest VLAN could be given unrestricted access to the
network.

Similarly, in a network where access is restricted based on the day
and time, Service Set Identifier (SSID), Calling-Station-Id or other
factors, unless the restrictions are encoded within the
authorizations, or a partial AAA conversation is included, then a
fast handoff could result in the user bypassing the restrictions.

In practice, these considerations limit the situations in which fast
handoff mechanisms bypassing AAA can be expected to be successful.
Where the deployed devices implement the same set of services, it may
be possible to do successful fast handoffs within such mechanisms.
However, where the supported services differ between devices, the
fast handoff may not succeed. For example, [RFC2865] section 1.1
states:

"A authenticator that does not implement a given service MUST NOT
implement the RADIUS attributes for that service. For example, a
authenticator that is unable to offer ARAP service MUST NOT

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implement the RADIUS attributes for ARAP. A authenticator MUST
treat a RADIUS access-accept authorizing an unavailable service as
an access-reject instead."

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Note that this behavior only applies to attributes that are known,
but not implemented. For attributes that are unknown, [RFC2865]
Section 5 states:

"A RADIUS server MAY ignore Attributes with an unknown Type. A
RADIUS client MAY ignore Attributes with an unknown Type."

In order to perform a correct fast handoff, if a new device is
provided with RADIUS context for a known but unavailable service,
then it MUST process this context the same way it would handle a
RADIUS Access-Accept requesting an unavailable service. This MUST
cause the fast handoff to fail. However, if a new device is provided
with RADIUS context that indicates an unknown attribute, then this
attribute MAY be ignored.

Although it may seem somewhat counter-intuitive, failure is indeed
the "correct" result where a known but unsupported service is
requested. Presumably a correctly configured backend authentication
server would not request that a device carry out a service that it
does not implement. This implies that if the new device were to
complete a AAA conversation that it would be likely to receive
different service instructions. In such a case, failure of the fast
handoff is the desired result. This will cause the new device to go
back to the AAA server in order to receive the appropriate service
definition.

In practice, this implies that fast handoff mechanisms which bypass
AAA are most likely to be successful within a homogeneous device
deployment within a single administrative domain. For example, it
would not be advisable to carry out a fast handoff bypassing AAA
between a authenticator providing confidentiality and another
authenticator that does not support this service. The correct result
of such a fast handoff would be a failure, since if the handoff were
blindly carried out, then the user would be moved from a secure to an
insecure channel without permission from the backend authentication
server. Thus the definition of a "known but unsupported service"
MUST encompass requests for unavailable security services. This
includes vendor-specific attributes related to security, such as
those described in [RFC2548].

5. Security Considerations

5.1. Security Terminology

Cryptographic binding
The demonstration of the EAP peer to the EAP server that a single
entity has acted as the EAP peer for all methods executed within a
tunnel method. Binding MAY also imply that the EAP server

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demonstrates to the peer that a single entity has acted as the EAP
server for all methods executed within a tunnel method. If
executed correctly, binding serves to mitigate man-in-the-middle
vulnerabilities.

Cryptographic separation
Two keys (x and y) are "cryptographically separate" if an adversary
that knows all messages exchanged in the protocol cannot compute x
from y or y from x without "breaking" some cryptographic
assumption. In particular, this definition allows that the
adversary has the knowledge of all nonces sent in cleartext as well
as all predictable counter values used in the protocol. Breaking a
cryptographic assumption would typically require inverting a one-
way function or predicting the outcome of a cryptographic pseudo-
random number generator without knowledge of the secret state. In
other words, if the keys are cryptographically separate, there is
no shortcut to compute x from y or y from x, but the work an
adversary must do to perform this computation is equivalent to
performing exhaustive search for the secret state value.

Key strength
If the effective key strength is N bits, the best currently known
methods to recover the key (with non-negligible probability)
require on average an effort comparable to 2^(N-1) operations of a
typical block cipher.

Mutual authentication
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5. Security Considerations

5.1. Security Terminology

"Cryptographic binding", "Cryptographic separation", "Key strength"
and "Mutual authentication" are defined in which, within an interlocked
exchange, the authenticator authenticates the peer [RFC3748] and are used
with the peer
authenticates the authenticator. Two independent one-way methods,
running in opposite directions do not provide mutual authentication
as defined same meaning here.

5.2. Threat Model

The EAP threat model is described in [RFC3748] Section 7.1. In order
to address these threats, EAP relies on the security properties of
EAP methods (known as "security claims", described in [RFC3784]
Section 7.2.1). EAP method requirements for application such as
Wireless LAN authentication are described in [WLANREQ].

The RADIUS threat model is described in [RFC3579] Section 4.1, and
responses to these threats are described in [RFC3579] Sections 4.2
and 4.3. Among other things, [RFC3579] Section 4.2 recommends the
use of IPsec ESP with non-null transform to provide per-packet
authentication and confidentiality, integrity and replay protection
for RADIUS/EAP.

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Given the existing documentation of EAP and AAA threat models and
responses, there is no need to duplicate that material here.
However, there are many other system-level threats no covered in
these document which have not been described or analyzed elsewhere.
These include:

[1] An attacker may try to modify or spoof Secure Association Protocol
packets.

[2] An attacker compromising an authenticator may provide incorrect
information to the EAP peer and/or server via out-of-band
mechanisms (such as via a AAA or lower layer protocol). This
includes impersonating another authenticator, or providing
inconsistent information to the peer and EAP server.

[3] An attacker may attempt to perform downgrading attacks on the
ciphersuite negotiation within the Secure Association Protocol in
order to ensure that a weaker ciphersuite is used to protect data.

Depending on the lower layer, these attacks may be carried out
without requiring physical proximity.

In order to address these threats, [Housley56] describes the
mandatory system security properties:

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Algorithm independence
Wherever cryptographic algorithms are chosen, the algorithms must
be negotiable, in order to provide resilient against compromise of
a particular algorithm. Algorithm independence must be
demonstrated within all aspects of the system, including within
EAP, AAA and the Secure Association Protocol. However, for
interoperability, at least one suite of algorithms MUST be
implemented.

Strong, fresh session keys
Session keys must be demonstrated to be strong and fresh in all
circumstances, while at the same time retaining algorithm
independence.

Replay protection
All protocol exchanges must be replay protected. This includes
exchanges within EAP, AAA, and the Secure Association Protocol.

Authentication
All parties need to be authenticated. The confidentiality of the
authenticator must be maintained. No plaintext passwords are
allowed.

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Authorization
EAP peer and authenticator authorization must be performed.

Session keys
Confidentiality of session keys must be maintained.

Ciphersuite negotiation
The selection of the "best" ciphersuite must be securely confirmed.

Unique naming
Session keys must be uniquely named.

Domino effect
Compromise of a single authenticator cannot compromise any other
part of the system, including session keys and long-term secrets.

Key binding
The key must be bound to the appropriate context.

5.3. Security Analysis

Figure 6 illustrates the relationship between the peer, authenticator
and backend authentication server.

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EAP peer
/\
/ \
Protocol: EAP / \ Protocol: Secure Association
Auth: Mutual / \ Auth: Mutual
Unique keys: / \ Unique keys: TSKs
TEKs,EMSK / \
/ \
EAP server +--------------+ Authenticator
Protocol: AAA
Auth: Mutual
Unique key: AAA session key

Figure 6: Relationship between peer, authenticator and auth. server

The peer and EAP server communicate using EAP [RFC3748]. The
security properties of this communication are largely determined by
the chosen EAP method. Method security claims are described in
[RFC3748] Section 7.2. These include the key strength, protected
ciphersuite negotiation, mutual authentication, integrity protection,
replay protection, confidentiality, key derivation, key strength,
dictionary attack resistance, fast reconnect, cryptographic binding,
session independence, fragmentation and channel binding claims. At a

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minimum, methods claiming to support key derivation must also support
mutual authentication. As noted in [RFC3748] Section 7.10:

EAP Methods deriving keys MUST provide for mutual authentication
between the EAP peer and the EAP Server.

Ciphersuite independence is also required:

Keying material exported by EAP methods MUST be independent of the
ciphersuite negotiated to protect data.

In terms of key strength and freshness, [RFC3748] Section 10 says:

EAP methods SHOULD ensure the freshness of the MSK and EMSK even
in cases where one party may not have a high quality random number
generator.... In order to preserve algorithm independence, EAP
methods deriving keys SHOULD support (and document) the protected
negotiation of the ciphersuite used to protect the EAP
conversation between the peer and server... In order to enable
deployments requiring strong keys, EAP methods supporting key
derivation SHOULD be capable of generating an MSK and EMSK, each
with an effective key strength of at least 128 bits.

The authenticator and backend authentication server communicate using
a AAA protocol such as RADIUS [RFC3579] or Diameter [I-D.ietf-aaa-

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eap]. As noted in [RFC3588] Section 13, Diameter must be protected
by either IPsec ESP with non-null transform or TLS. As a result,
Diameter requires per-packet integrity and confidentiality. Replay
protection must be supported. For RADIUS, [RFC3579] Section 4.2
recommends that RADIUS be protected by IPsec ESP with a non-null
transform, and where IPsec is implemented replay protection must be
supported.

The peer and authenticator communicate using the Secure Association
Protocol.

As noted in the figure, each party in the exchange mutually
authenticates with each of the other parties, and derives a unique
key. All parties in the diagram have access to the AAA-Key.

The EAP peer and backend authentication server mutually authenticate
via the EAP method, and derive the TEKs and EMSK which are known only
to them. The TEKs are used to protect some or all of the EAP
conversation between the peer and authenticator, so as to guard
against modification or insertion of EAP packets by an attacker. The
degree of protection afforded by the TEKs is determined by the EAP
method; some methods may protect the entire EAP packet, including the
EAP header, while other methods may only protect the contents of the

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Type-Data field, defined in [RFC3748].

Since EAP is spoken only between the EAP peer and server, if a
backend authentication server is present then the EAP conversation
does not provide mutual authentication between the peer and
authenticator, only between the EAP peer and EAP server (backend
authentication server). As a result, mutual authentication between
the peer and authenticator only occurs where a Secure Association
protocol is used, such the unicast and group key derivation handshake
supported in [IEEE80211i]. This means that absent use of a secure
Association Protocol, from the point of view of the peer, EAP mutual
authentication only proves that the authenticator is trusted by the
backend authentication server; the identity of the authenticator is
not confirmed.

Utilizing the AAA protocol, the authenticator and backend
authentication server mutually authenticate and derive session keys
known only to them, used to provide per-packet integrity and replay
protection, authentication and confidentiality. The AAA-Key is
distributed by the backend authentication server to the authenticator
over this channel, bound to attributes constraining its usage, as
part of the AAA-Token. The binding of attributes to the AAA-Key
within a protected package is important so the authenticator
receiving the AAA-Token can determine that it has not been
compromised, and that the keying material has not been replayed, or

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mis-directed in some way.

The security properties of the EAP exchange are dependent on each leg
of the triangle: the selected EAP method, AAA protocol and the Secure
Association Protocol.

Assuming that the AAA protocol provides protection against rogue
authenticators forging their identity, then the AAA-Token can be
assumed to be sent to the correct authenticator, and where it is
wrapped appropriately, it can be assumed to be immune to compromise
by a snooping attacker.

Where an untrusted AAA intermediary is present, the AAA-Token must
not be provided to the intermediary so as to avoid compromise of the
AAA-Token. This can be avoided by use of re-direct as defined in
[RFC3588].

When EAP is used for authentication on PPP or wired IEEE 802
networks, it is typically assumed that the link is physically secure,
so that an attacker cannot gain access to the link, or insert a rogue
device. EAP methods defined in [RFC3748] reflect this usage model.
These include EAP MD5, as well as One-Time Password (OTP) and Generic
Token Card. These methods support one-way authentication (from EAP

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peer to authenticator) but not mutual authentication or key
derivation. As a result, these methods do not bind the initial
authentication and subsequent data traffic, even when the the
ciphersuite used to protect data supports per-packet authentication
and integrity protection. As a result, EAP methods not supporting
mutual authentication are vulnerable to session hijacking as well as
attacks by rogue devices.

On wireless networks such as IEEE 802.11 [IEEE80211], these attacks
become easy to mount, since any attacker within range can access the
wireless medium, or act as an access point. As a result, new
ciphersuites have been proposed for use with wireless LANs
[IEEE80211i] which provide per-packet authentication, integrity and
replay protection. In addition, mutual authentication and key
derivation, provided by methods such as EAP-TLS [RFC2716] are
required [IEEE80211i], so as to address the threat of rogue devices,
and provide keying material to bind the initial authentication to
subsequent data traffic.

If the selected EAP method does not support mutual authentication,
then the peer will be vulnerable to attack by rogue authenticators
and backend authentication servers. If the EAP method does not derive
keys, then TSKs will not be available for use with a negotiated
ciphersuite, and there will be no binding between the initial EAP
authentication and subsequent data traffic, leaving the session

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vulnerable to hijack.

If the backend authentication server does not protect against
authenticator masquerade, or provide the proper binding of the AAA-
Key to the session within the AAA-Token, then one or more AAA-Keys
may be sent to an unauthorized party, and an attacker may be able to
gain access to the network. If the AAA-Token is provided to an
untrusted AAA intermediary, then that intermediary may be able to
modify the AAA-Key, or the attributes associated with it, as
described in [RFC2607].

If the Secure Association Protocol does not provide mutual proof of
possession of the AAA-Key material, then the peer will not have
assurance that it is connected to the correct authenticator, only
that the authenticator and backend authentication server share a
trust relationship (since AAA protocols support mutual
authentication). This distinction can become important when multiple
authenticators receive AAA-Keys from the backend authentication
server, such as where fast handoff is supported. If the TSK
derivation does not provide for protected ciphersuite and
capabilities negotiation, then downgrade attacks are possible.

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5.4. Man-in-the-middle Attacks

As described in [I-D.puthenkulam-eap-binding], EAP method sequences
and compound authentication mechanisms may be subject to man-in-the-
middle attacks. When such attacks are successfully carried out, the
attacker acts as an intermediary between a victim and a legitimate
authenticator. This allows the attacker to authenticate successfully
to the authenticator, as well as to obtain access to the network.

In order to prevent these attacks, [I-D.puthenkulam-eap-binding]
recommends derivation of a compound key by which the EAP peer and
server can prove that they have participated in the entire EAP
exchange. Since the compound key must not be known to an attacker
posing as an authenticator, and yet must be derived from quantities
that are exported by EAP methods, it may be desirable to derive the
compound key from a portion of the EMSK. In order to provide proper
key hygiene, it is recommended that the compound key used for man-in-
the-middle protection be cryptographically separate from other keys
derived from the EMSK, such as fast handoff keys, discussed in
Appendix E.
Section 2.5.

5.5. Denial of Service Attacks

The caching of security associations may result in vulnerability to
denial of service attacks. Since an EAP peer may derive multiple EAP
SAs with a given EAP server, and creation of a new EAP SA does not

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implicitly delete a previous EAP SA, EAP methods that result in
creation of persistent state may be vulnerable to denial of service
attacks by a rogue EAP peer.

As a result, EAP methods creating persistent state may wish to limit
the number of cached EAP SAs (Phase 1a) corresponding to an EAP peer.
For example, an EAP server may choose to only retain a few EAP SAs
for each peer. This prevents a rogue peer from denying access to
other peers.

Similarly, an authenticator may have multiple AAA-Key SAs
corresponding to a given EAP peer; to conserve resources an
authenticator may choose to limit the number of cached AAA-Key (Phase
1 b) SAs for each peer.

Depending on the media, creation of a new unicast Secure Association
SA may or may not imply deletion of a previous unicast secure
association SA. Where there is no implied deletion, the
authenticator may choose to limit Phase 2 (unicast and multicast)
Secure Association SAs for each peer.

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5.6. Impersonation

Both the RADIUS and Diameter protocols are potentially vulnerable to
impersonation by a rogue authenticator.

While AAA protocols such as RADIUS [RFC2865] or Diameter [RFC3588]
support mutual authentication between the authenticator (known as the
AAA client) and the backend authentication server (known as the AAA
server), the security mechanisms vary according to the AAA protocol.

In RADIUS, the shared secret used for authentication is determined by
the source address of the RADIUS packet. As noted in [RFC3579]
Section 4.3.7, it is highly desirable that the source address be
checked against one or more NAS identification attributes so as to
detect and prevent impersonation attacks.

When RADIUS requests are forwarded by a proxy, the NAS-IP-Address or
NAS-IPv6-Address attributes may not correspond to the source address.
Since the NAS-Identifier attribute need not contain an FQDN, it also
may not correspond to the source address, even indirectly. [RFC2865]
Section 3 states:

A RADIUS server MUST use the source IP address of the RADIUS
UDP packet to decide which shared secret to use, so that
RADIUS requests can be proxied.

This implies that it is possible for a rogue authenticator to forge

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NAS-IP-Address, NAS-IPv6-Address or NAS-Identifier attributes within
a RADIUS Access-Request in order to impersonate another
authenticator. Among other things, this can result in messages (and
MSKs) being sent to the wrong authenticator. Since the rogue
authenticator is authenticated by the RADIUS proxy or server purely
based on the source address, other mechanisms are required to detect
the forgery. In addition, it is possible for attributes such as the
Called-Station-Id and Calling-Station-Id to be forged as well.

As recommended in [RFC3579], this vulnerability can be mitigated by
having RADIUS proxies check authenticator identification attributes
against the source address.

To allow verification of session parameters such as the Called-
Station- Id and Calling-Station-Id, these can be sent by the EAP peer
to the server, protected by the TEKs. The RADIUS server can then
check the parameters sent by the EAP peer against those claimed by
the authenticator. If a discrepancy is found, an error can be
logged.

While [RFC3588] requires use of the Route-Record AVP, this utilizes

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FQDNs, so that impersonation detection requires DNS A/AAAA and PTR
RRs to be properly configured. As a result, it appears that Diameter
is as vulnerable to this attack as RADIUS, if not more so. To address
this vulnerability, it is necessary to allow the backend
authentication server to communicate with the authenticator directly,
such as via the redirect functionality supported in [RFC3588].

5.7. Channel binding

It is possible for a compromised or poorly implemented EAP
authenticator to communicate incorrect information to the EAP peer
and/or server. This may enable an authenticator to impersonate
another authenticator or communicate incorrect information via out-
of-band mechanisms (such as via a AAA or the lower layer protocol).

Where EAP is used in pass-through mode, the EAP peer typically does
not verify the identity of the pass-through authenticator, it only
verifies that the pass-through authenticator is trusted by the EAP
server. This creates a potential security vulnerability, described in
[RFC3748] Section 7.15.

[RFC3579] Section 4.3.7 describes how an EAP pass-through
authenticator acting as a AAA client can be detected if it attempts
to impersonate another authenticator (such by sending incorrect NAS-
Identifier [RFC2865], NAS-IP-Address [RFC2865] or NAS-IPv6-Address
[RFC3162] attributes via the AAA protocol). However, it is possible
for a pass-through authenticator acting as a AAA client to provide

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correct information to the AAA server while communicating misleading
information to the EAP peer via a lower layer protocol.

For example, it is possible for a compromised authenticator to
utilize another authenticator's Called-Station-Id or NAS-Identifier
in communicating with the EAP peer via a lower layer protocol, or for
a pass-through authenticator acting as a AAA client to provide an
incorrect peer Calling-Station-Id [RFC2865][RFC3580] to the AAA
server via the AAA protocol.

As noted in [RFC3748] Section 7.15, this vulnerability can be
addressed by use of EAP methods that support a protected exchange of
channel properties such as endpoint identifiers, including (but not
limited to): Called-Station-Id [RFC2865][RFC3580], Calling-Station-Id
[RFC2865][RFC3580], NAS-Identifier [RFC2865], NAS-IP-Address
[RFC2865], and NAS-IPv6-Address [RFC3162].

Using such a protected exchange, it is possible to match the channel
properties provided by the authenticator via out-of-band mechanisms
against those exchanged within the EAP method.

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[ServiceIdent].

5.8. Key Strength

In order to guard against brute force attacks, EAP methods deriving
keys need to be capable of generating keys with an appropriate
effective symmetric key strength. In order to ensure that key
generation is not the weakest link, it is necessary for EAP methods
utilizing public key cryptography to choose a public key that has a
cryptographic strength meeting the symmetric key strength
requirement.

As noted in [RFC3766] Section 5, this results in the following
required RSA or DH module and DSA subgroup size in bits, for a given
level of attack resistance in bits:

Attack Resistance RSA or DH Modulus DSA subgroup
(bits) size (bits) size (bits)
----------------- ----------------- ------------
70 947 128
80 1228 145
90 1553 153
100 1926 184
150 4575 279
200 8719 373
250 14596 475

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5.9. Key Wrap

As described in [RFC3579] Section 4.3, known problems exist in the
key wrap specified in [RFC2548]. Where the same RADIUS shared secret
is used by a PAP authenticator and an EAP authenticator, there is a
vulnerability to known plaintext attack. Since RADIUS uses the
shared secret for multiple purposes, including per-packet
authentication, attribute hiding, considerable information is exposed
about the shared secret with each packet. This exposes the shared
secret to dictionary attacks. MD5 is used both to compute the RADIUS
Response Authenticator and the Message-Authenticator attribute, and
some concerns exist relating to the security of this hash
[MD5Attack].

As discussed in [RFC3579] Section 4.3, the security vulnerabilities
of RADIUS are extensive, and therefore development of an alternative
key wrap technique based on the RADIUS shared secret would not
substantially improve security. As a result, [RFC3759] Section 4.2
recommends running RADIUS over IPsec. The same approach is taken in
Diameter EAP [I-D.ietf-aaa-eap], which defines cleartext key
attributes, to be protected by IPsec or TLS.

Where an untrusted AAA intermediary is present (such as a RADIUS

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proxy or a Diameter agent), and data object security is not used, the
AAA-Key may be recovered by an attacker in control of the untrusted
intermediary. Possession of the AAA-Key enables decryption of data
traffic sent between the peer and a specific authenticator; however
where key separation is implemented, compromise of the AAA-Key does
not enable an attacker to impersonate the peer to another
authenticator, since that requires possession of the MK or EMSK, which are is
not transported by the AAA protocol. This vulnerability may be
mitigated by implementation of redirect functionality, as provided in
[RFC3588].

6. Security Requirements

This section summarizes the security requirements that must be met by
EAP methods, AAA protocols, Secure Association Protocols and
Ciphersuites in order to address the security threats described in
this document. These requirements MUST be met by specifications
requesting publication as an RFC. Each requirement provides a
pointer to the sections of this document describing the threat that
it mitigates.

6.1. EAP Method Requirements

It is possible for the peer and EAP server to mutually authenticate
and derive keys. In order to provide keying material for use in a

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subsequently negotiated ciphersuite, an EAP method supporting key
derivation MUST export a Master Session Key (MSK) of at least 64
octets, and an Extended Master Session Key (EMSK) of at least 64
octets. EAP Methods deriving keys MUST provide for mutual
authentication between the EAP peer and the EAP Server.

The MSK and EMSK MUST NOT be used directly to protect data; however,
they are of sufficient size to enable derivation of a AAA-Key
subsequently used to derive Transient Session Keys (TSKs) for use
with the selected ciphersuite. Each ciphersuite is responsible for
specifying how to derive the TSKs from the AAA-Key.

The AAA-Key is derived from the keying material exported by the EAP
method (MSK and EMSK). This derivation occurs on the AAA server. In
many existing protocols that use EAP, the AAA-Key and MSK are
equivalent, but more complicated mechanisms are possible (see
Appendix E Section
2.5 for details).

EAP methods SHOULD ensure the freshness of the MSK and EMSK even in
cases where one party may not have a high quality random number
generator. A RECOMMENDED method is for each party to provide a nonce
of at least 128 bits, used in the derivation of the MSK and EMSK.

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EAP methods export the MSK and EMSK and not Transient Session Keys so
as to allow EAP methods to be ciphersuite and media independent.
Keying material exported by EAP methods MUST be independent of the
ciphersuite negotiated to protect data.

Depending on the lower layer, EAP methods may run before or after
ciphersuite negotiation, so that the selected ciphersuite may not be
known to the EAP method. By providing keying material usable with
any ciphersuite, EAP methods can used with a wide range of
ciphersuites and media.

It is RECOMMENDED that methods providing integrity protection of EAP
packets include coverage of all the EAP header fields, including the
Code, Identifier, Length, Type and Type-Data fields.

In order to preserve algorithm independence, EAP methods deriving
keys SHOULD support (and document) the protected negotiation of the
ciphersuite used to protect the EAP conversation between the peer and
server. This is distinct from the ciphersuite negotiated between the
peer and authenticator, used to protect data.

The strength of Transient Session Keys (TSKs) used to protect data is
ultimately dependent on the strength of keys generated by the EAP
method. If an EAP method cannot produce keying material of
sufficient strength, then the TSKs may be subject to brute force

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attack. In order to enable deployments requiring strong keys, EAP
methods supporting key derivation SHOULD be capable of generating an
MSK and EMSK, each with an effective key strength of at least 128
bits.

Methods supporting key derivation MUST demonstrate cryptographic
separation between the MSK and EMSK branches of the EAP key
hierarchy. Without violating a fundamental cryptographic assumption
(such as the non-invertibility of a one-way function) an attacker
recovering the MSK or EMSK MUST NOT be able to recover the other
quantity with a level of effort less than brute force.

Non-overlapping substrings of the MSK MUST be cryptographically
separate from each other. That is, knowledge of one substring MUST
NOT help in recovering some other non-overlapping substring without
breaking some hard cryptographic assumption. This is required
because some existing ciphersuites form TSKs by simply splitting the
AAA-Key to pieces of appropriate length. Likewise, non-overlapping
substrings of the EMSK MUST be cryptographically separate from each
other, and from substrings of the MSK.

The EMSK MUST remain on the EAP peer and EAP server where it is
derived; it MUST NOT be transported to, or shared with, additional

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parties, or used to derive any for purposes other keys. than AMSK derivation (see Section
2.6).

Since EAP does not provide for explicit key lifetime negotiation, EAP
peers, authenticators and authentication servers MUST be prepared for
situations in which one of the parties discards key state which
remains valid on another party.

The development and validation of key derivation algorithms is
difficult, and as a result EAP methods SHOULD reuse well established
and analyzed mechanisms for MSK and EMSK key derivation (such as
those specified in IKE [RFC2409] or TLS [RFC2246]), rather than
inventing new ones.
EAP methods SHOULD also utilize well established and analyzed
mechanisms for MSK and EMSK derivation.

6.1.1. Requirements for EAP methods

In order for an EAP method to meet the guidelines for EMSK usage it
must meet the following requirements:

o It must MUST specify how to derive the EMSK

o The key material used for the EMSK MUST be
computationally independent of the MSK and TEKs.

o The EMSK MUST NOT be used for any other purpose than the key

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derivation described in this document.

o The EMSK MUST be secret and not known to someone observing
the authentication mechanism protocol exchange.

o The EMSK MUST NOT be maintained within exported from the EAP server.
Only keys (AMSKs) derived according to this specification
may be exported from the EAP server.

o The EMSK MUST be unique for each session.

o The EAP mechanism SHOULD provide a way of unique identifier suitable for naming the EMSK.

Implementations of EAP frameworks on the EAP-Peer and EAP-Server
SHOULD provide an interface to obtain AMSKs. The implementation MAY
restrict which callers can obtain which keys.

6.1.2. Requirements for EAP applications

In order for an application to meet the guidelines for EMSK usage it
must meet the following requirements:

o New applications following this specification SHOULD NOT use the

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MSK. If more than one application uses the MSK, then the
cryptographic separation is not achieved. Implementations SHOULD
prevent such combinations.

o A peer MUST NOT use the EMSK in any other way except to
derive Application Master Session Keys (AMSKs) using the
key derivation specified in Appendix F. Section 2.6. It MUST NOT
use the EMSK directly for cryptographic protection of data,
and SHOULD provide only the AMSKs to applications.

o Applications MUST define distinct key labels, application
specific data, and the length of derived key material used in the key
derivation described in Appendix F. Section 2.6.

o Applications MUST define how they use their AMSK to derive TSKs
for their use.

6.2. AAA Protocol Requirements

AAA protocols suitable for use in transporting EAP MUST provide the
following facilities:

Security services
AAA protocols used for transport of EAP keying material MUST
implement and SHOULD use per-packet integrity and authentication,

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replay protection and confidentiality. These requirements are met
by Diameter EAP [I-D.ietf-aaa-eap], as well as RADIUS over IPsec
[RFC3579].

Session Keys
AAA protocols used for transport of EAP keying material MUST
implement and SHOULD use dynamic key management in order to derive
fresh session keys, as in Diameter EAP [I-D.ietf-aaa-eap] and
RADIUS over IPsec [RFC3579], rather than using a static key, as
originally defined in RADIUS [RFC2865].

Mutual authentication
AAA protocols used for transport of EAP keying material MUST
provide for mutual authentication between the authenticator and
backend authentication server. These requirements are met by
Diameter EAP [I-D.ietf-aaa-eap] as well as by RADIUS EAP [RFC3579].

Authorization
AAA protocols used for transport of EAP keying material SHOULD
provide protection against rogue authenticators masquerading as
other authenticators. This can be accomplished, for example, by
requiring that AAA agents check the source address of packets
against the origin attributes (Origin-Host AVP in Diameter, NAS-IP-

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Address, NAS-IPv6-Address, NAS-Identifier in RADIUS). For details,
see [RFC3579] Section 4.3.7.

Key transport
Since EAP methods do not export Transient Session Keys (TSKs) in
order to maintain media and ciphersuite independence, the AAA
server MUST NOT transport TSKs from the backend authentication
server to authenticator.

Key transport specification
In order to enable backend authentication servers to provide keying
material to the authenticator in a well defined format, AAA
protocols suitable for use with EAP MUST define the format and
wrapping of the AAA-Token.

EMSK transport
Since the EMSK is a secret known only to the backend authentication
server and peer, the AAA-Token MUST NOT transport the EMSK from the
backend authentication server to the authenticator.

AAA-Token protection
To ensure against compromise, the AAA-Token MUST be integrity
protected, authenticated, replay protected and encrypted in
transit, using well-established cryptographic algorithms.

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Session Keys
The AAA-Token SHOULD be protected with session keys as in Diameter
[RFC3588] or RADIUS over IPsec [RFC3579] rather than static keys,
as in [RFC2548].

Key naming
In order to ensure against confusion between the appropriate keying
material to be used in a given Secure Association Protocol
exchange, the AAA-Token SHOULD include explicit key names and
context appropriate for informing the authenticator how the keying
material is to be used.

Key Compromise
Where untrusted intermediaries are present, the AAA-Token SHOULD
NOT be provided to the intermediaries. In Diameter, handling of
keys by intermediaries can be avoided using Redirect functionality
[RFC3588].

6.3. Secure Association Protocol Requirements

The Secure Association Protocol supports the following:

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The Secure Association Protocol supports the following:

Entity Naming
The peer and authenticator SHOULD identify themselves in a manner
that is independent of their attached ports.

Mutual proof of possession
The peer and authenticator MUST each demonstrate possession of the
keying material transported between the backend authentication
server and authenticator (AAA-Key).

Key Naming
The Secure Association Protocol MUST explicitly name the keys used
in the proof of possession exchange, so as to prevent confusion
when more than one set of keying material could potentially be used
as the basis for the exchange.

Creation and Deletion
In order to support the correct processing of phase 2 security
associations, the Secure Association (phase 2) protocol MUST
support the naming of phase 2 security associations and associated
transient session keys, so that the correct set of transient
session keys can be identified for processing a given packet. The
phase 2 Secure Association Protocol also MUST support transient
session key activation and SHOULD support deletion, so that
establishment and re-establishment of transient session keys can be
synchronized between the parties.

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Integrity and Replay Protection
The Secure Association Protocol MUST support integrity and replay
protection of all messages.

Direct operation
Since the phase 2 Secure Association Protocol is concerned with the
establishment of security associations between the EAP peer and
authenticator, including the derivation of transient session keys,
only those parties have "a need to know" the transient session
keys. The Secure Association Protocol MUST operate directly between
the peer and authenticator, and MUST NOT be passed-through to the
backend authentication server, or include additional parties.

Derivation of transient session keys
The Secure Association Protocol negotiation MUST support derivation
of unicast and multicast transient session keys suitable for use
with the negotiated ciphersuite.

TSK freshness
The Secure Association (phase 2) Protocol MUST support the
derivation of fresh unicast and multicast transient session keys,
even when the keying material provided by the backend

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authentication server is not fresh. This is typically supported by
including an exchange of nonces within the Secure Association
Protocol.

Bi-directional operation
While some ciphersuites only require a single set of transient
session keys to protect traffic in both directions, other
ciphersuites require a unique set of transient session keys in each
direction. The phase 2 Secure Association Protocol SHOULD provide
for the derivation of unicast and multicast keys in each direction,
so as not to require two separate phase 2 exchanges in order to
create a bi-directional phase 2 security association.

Secure capabilities negotiation
The Secure Association Protocol MUST support secure capabilities
negotiation. This includes security parameters such as the
security association identifier (SAID) and ciphersuites, as well as
negotiation of the lifetime of the TSKs, AAA-Key and exported EAP
keys. Secure capabilities negotiation also includes confirmation
of the capabilities discovered during the discovery phase (phase
0), so as to ensure that the announced capabilities have not been
forged.

Key Scoping
The Secure Association Protocol MUST ensure the synchronization of
key scope between the peer and authenticator. This includes

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negotiation of restrictions on key usage.

6.4. Ciphersuite Requirements

Ciphersuites suitable for keying by EAP methods MUST provide the
following facilities:

TSK derivation
In order to allow a ciphersuite to be usable within the EAP keying
framework, a specification MUST be provided describing how
transient session keys suitable for use with the ciphersuite are
derived from the AAA-Key.

EAP method independence
Algorithms for deriving transient session keys from the AAA-Key
MUST NOT depend on the EAP method. However, algorithms for
deriving TEKs MAY be specific to the EAP method.

Cryptographic separation
The TSKs derived from the AAA-Key MUST be cryptographically
separate from each other. Similarly, TEKs MUST be
cryptographically separate from each other. In addition, the TSKs

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MUST be cryptographically separate from the TEKs.

7. IANA Considerations

This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to EAP key
management, in accordance with BCP 26, [RFC2434].

The following terms are used here with the meanings defined in BCP
26: "name space", "assigned value", "registration".

The following policies are used here with the meanings defined in BCP
26: "Private Use", "First Come First Served", "Expert Review",
"Specification Required", "IETF Consensus", "Standards Action".

For registration requests where a Designated Expert should be
consulted, the responsible IESG area director should appoint the
Designated Expert. The intention is that any allocation will be
accompanied by a published RFC. But in order to allow for the
allocation of values prior to the RFC being approved for publication,
the Designated Expert can approve allocations once it seems clear
that an RFC will be published. The Designated expert will post a
request to the EAP WG mailing list (or a successor designated by the
Area Director) for comment and review, including an Internet-Draft.
Before a period of 30 days has passed, the Designated Expert will
either approve or deny the registration request and publish a notice

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of the decision to the EAP WG mailing list or its successor, as well
as informing IANA. A denial notice must be justified by an
explanation and, in the cases where it is possible, concrete
suggestions on how the request can be modified so as to become
acceptable.

This document introduces a new name space for "key labels". Key
labels are ASCII strings and are assigned via IETF Consensus. It is
expected that key label specifications will include the following
information:

o A description of the application
o The key label to be used
o How TSKs will be derived from the AMSK and how they will be used
o If application specific data is used, what it is and how it is
maintained
o Where the AMSKs or TSKs will be used and how they are
communicated if necessary.

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8. References

8.1. Normative References

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

[RFC2434]
Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

[RFC3748]
Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. Lefkowetz,
"Extensible Authentication Protocol (EAP)", RFC 3748, June 2004.

8.2. Informative References

[RFC0793]
Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
September 1981.

[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC
1661, July 1994.

[RFC1968] Meyer, G. and K. Fox, "The PPP Encryption Control Protocol
(ECP)", RFC 1968, June 1996.

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[RFC2104] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.

[RFC2246] Dierks, T., Allen, C., Treese, W., Karlton, P., Freier, A.
and P. Kocher, "The TLS Protocol Version 1.0", RFC 2246,
January 1999.

[RFC2401] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.

[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.

[RFC2419] Sklower, K. and G. Meyer, "The PPP DES Encryption Protocol,
Version 2 (DESE-bis)", RFC 2419, September 1998.

[RFC2420] Kummert, H., "The PPP Triple-DES Encryption Protocol (3DESE)",
RFC 2420, September 1998.

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[RFC2516] Mamakos, L., Lidl, K., Evarts, J., Carrel, D., Simone, D. and
R. Wheeler, "A Method for Transmitting PPP Over Ethernet
(PPPoE)", RFC 2516, February 1999.

[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes", RFC
2548, March 1999.

[RFC2607] Aboba, B. and J. Vollbrecht, "Proxy Chaining and Policy
Implementation in Roaming", RFC 2607, June 1999.

[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication Protocol",
RFC 2716, October 1999.

[RFC2865] Rigney, C., Willens, S., Rubens, A. and W. Simpson, "Remote
Authentication Dial In User Service (RADIUS)", RFC 2865, June
2000.

[RFC3078] Pall, G. and G. Zorn, "Microsoft Point-To-Point Encryption
(MPPE) Protocol", RFC 3078, March 2001.

[RFC3079] Zorn, G., "Deriving Keys for use with Microsoft Point-to-Point
Encryption (MPPE)", RFC 3079, March 2001.

[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial
In User Service) Support For Extensible Authentication
Protocol (EAP)", RFC 3579, September 2003.

[RFC3580] Congdon, P., Aboba, B., Smith, A., Zorn, G. and J. Roese,
"IEEE 802.1X Remote Authentication Dial In User Service

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(RADIUS) Usage Guidelines", RFC 3580, September 2003.

[RFC3588] Calhoun, P., Loughney, J., Guttman, E., Zorn, G. and J.
Arkko, "Diameter Base Protocol", RFC 3588, September 2003.

[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths For Public
Keys Used For Exchanging Symmetric Keys", RFC 3766, April
2004.

[FIPSDES] National Institute of Standards and Technology, "Data
Encryption Standard", FIPS PUB 46, January 1977.

[DESMODES]
National Institute of Standards and Technology, "DES Modes of
Operation", FIPS PUB 81, December 1980, <http://
www.itl.nist.gov/fipspubs/fip81.htm>.

[IEEE802] Institute of Electrical and Electronics Engineers, "IEEE
Standards for Local and Metropolitan Area Networks: Overview

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and Architecture", ANSI/IEEE Standard 802, 1990.

[IEEE80211]
Institute of Electrical and Electronics Engineers,
"Information technology - Telecommunications and information
exchange between systems - Local and metropolitan area
networks - Specific Requirements Part 11: Wireless LAN Medium
Access Control (MAC) and Physical Layer (PHY) Specifications",
IEEE IEEE Standard 802.11-1999, 1999.

[IEEE8021X]
Institute of Electrical and Electronics Engineers, "Local and
Metropolitan Area Networks: Port-Based Network Access
Control", IEEE Standard 802.1X-2004, September 2004.

[IEEE8021Q]
Institute of Electrical and Electronics Engineers, "IEEE
Standards for Local and Metropolitan Area Networks: Draft
Standard for Virtual Bridged Local Area Networks", IEEE
Standard 802.1Q/D8, January 1998.

[IEEE80211F]
Institute of Electrical and Electronics Engineers,
"Recommended Practice for Multi-Vendor Access Point
Interoperability via an Inter-Access Point Protocol Across
Distribution Systems Supporting IEEE 802.11 Operation", IEEE
802.11F, July 2003.

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[IEEE80211i]
Institute of Electrical and Electronics Engineers, "Draft
Supplement to STANDARD FOR Telecommunications and Information
Exchange between Systems - LAN/MAN Specific Requirements -
Part 11: Wireless Medium Access Control (MAC) and physical
layer (PHY) specifications: Specification for Enhanced
Security", IEEE Draft 802.11I/ D8, February 2004.

[IEEE-02-758]
Mishra, A., Shin, M., Arbaugh, W., Lee, I. and K. Jang,
"Proactive Caching Strategies for IAPP Latency Improvement
during 802.11 Handoff", IEEE 802.11 Working Group,
IEEE-02-758r1-F Draft 802.11I/D5.0, November 2002.

[IEEE-03-084]
Mishra, A., Shin, M., Arbaugh, W., Lee, I. and K. Jang,
"Proactive Key Distribution to support fast and secure
roaming", IEEE 802.11 Working Group, IEEE-03-084r1-I,
http://www.ieee802.org/11/Documents/DocumentHolder/ 3-084.zip,
January 2003.

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[IEEE-03-155]
Aboba, B., "Fast Handoff Issues", IEEE 802.11 Working Group,
IEEE-03-155r0-I, http://www.ieee802.org/11/
Documents/DocumentHolder/3-155.zip, March 2003.

[I-D.ietf-roamops-cert]
Aboba, B., "Certificate-Based Roaming", draft-ietf-roamops-
cert-02 (work in progress), April 1999.

[I-D.ietf-aaa-eap]
Eronen, P., Hiller, T. and G. Zorn, "Diameter Extensible
Authentication Protocol (EAP) Application", draft-ietf-aaa-
eap-08 (work in progress), June 2004.

[I-D.irtf-aaaarch-handoff]
Arbaugh, W. and B. Aboba, "Handoff Extension to RADIUS",
draft-irtf-aaaarch-handoff-04 (work in progress), October
2003.

[I-D.puthenkulam-eap-binding]
Puthenkulam, J., "The Compound Authentication Binding
Problem", draft-puthenkulam-eap-binding-04 (work in progress),
October 2003.

[I-D.aboba-802-context]
Aboba, B. and T. Moore, "A Model for Context Transfer in IEEE
802", draft-aboba-802-context-03 (work in progress), October

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2003.

[I-D.arkko-pppext-eap-aka]
Arkko, J. and H. Haverinen, "EAP AKA Authentication", draft-
arkko-pppext-eap-aka-11 (work in progress), October 2003.

[IKEv2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", draft-
ietf-ipsec-ikev2-14 (work in progress), June 2004.

[8021XHandoff]
Pack, S. and Y. Choi, "Pre-Authenticated Fast Handoff in a
Public Wireless LAN Based on IEEE 802.1X Model", School of
Computer Science and Engineering, Seoul National University,
Seoul, Korea, 2002.

[MD5Attack]
Dobbertin, H., "The Status of MD5 After a Recent Attack",
CryptoBytes, Vol.2 No.2, 1996.

[WLANREQ] Stanley, D., Walker, J. and B. Aboba, "EAP Method Requirements
for Wireless LANs", draft-walker-ieee802-req-02.txt (work in

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progress), July 2004.

[Housley56]
Housley, R., "Key Management in AAA", Presentation to the AAA
WG at IETF 56,
http://www.ietf.org/proceedings/03mar/slides/aaa-5/index.html,
March 2003.

Acknowledgments

Thanks to Arun Ayyagari, Ashwin Palekar, and Tim Moore of Microsoft,
Dorothy Stanley of Agere, Bob Moskowitz of TruSecure, and Russ
Housley of Vigil Security for useful feedback.

Author Addresses

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

EMail: bernarda@microsoft.com
Phone: +1 425 706 6605
Fax: +1 425 936 7329

Dan Simon
Microsoft Research

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Microsoft Corporation
One Microsoft Way
Redmond, WA 98052

EMail: dansimon@microsoft.com
Phone: +1 425 706 6711
Fax: +1 425 936 7329

Jari Arkko
Ericsson
Jorvas 02420
Finland

Phone:
EMail: jari.arkko@ericsson.com

Pasi Eronen
Nokia Research Center
P.O. Box 407
FIN-00045 Nokia Group
Finland

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EMail: pasi.eronen@nokia.com

Henrik Levkowetz (editor)
ipUnplugged AB
Arenavagen 27
Stockholm S-121 28
SWEDEN

Phone: +46 708 32 16 08
EMail: henrik@levkowetz.com

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Appendix A - Ciphersuite Keying Requirements

To date, PPP and IEEE 802.11 ciphersuites are suitable for keying by
EAP. This Appendix describes the keying requirements of common PPP
and 802.11 ciphersuites.

PPP ciphersuites include DESEbis [RFC2419], 3DES [RFC2420], and MPPE
[RFC3078]. The DES algorithm is described in [FIPSDES], and DES
modes (such as CBC, used in [RFC2419] and DES-EDE3-CBC, used in
[RFC2420]) are described in [DESMODES]. For PPP DESEbis, a single
56-bit encryption key is required, used in both directions. For PPP
3DES, a 168-bit encryption key is needed, used in both directions. As
described in [RFC2419] for DESEbis and [RFC2420] for 3DES, the IV,
which is different in each direction, is "deduced from an explicit
64-bit nonce, which is exchanged in the clear during the [ECP]
negotiation phase." There is therefore no need for the IV to be
provided by EAP.

For MPPE, 40-bit, 56-bit or 128-bit encryption keys are required in
each direction, as described in [RFC3078]. No initialization vector
is required.

While these PPP ciphersuites provide encryption, they do not provide
per-packet authentication or integrity protection, so an
authentication key is not required in either direction.

Within [IEEE80211], Transient Session Keys (TSKs) are required both
for unicast traffic as well as for multicast traffic, and therefore
separate key hierarchies are required for unicast keys and multicast
keys. IEEE 802.11 ciphersuites include WEP-40, described in
[IEEE80211], which requires a 40-bit encryption key, the same in
either direction; and WEP-128, which requires a 104-bit encryption
key, the same in either direction. These ciphersuites also do not
support per-packet authentication and integrity protection. In
addition to these unicast keys, authentication and encryption keys
are required to wrap the multicast encryption key.

Recently, new ciphersuites have been proposed for use with IEEE
802.11 that provide per-packet authentication and integrity
protection as well as encryption [IEEE80211i]. These include TKIP,
which requires a single 128-bit encryption key and a 128-bit two 64-bit
authentication key (used in both directions); keys (one for each direction); and AES CCMP, which
requires a single 128-bit key (used in both directions) in order to
authenticate and encrypt data; and WRAP, which requires a single
128-bit key (used in both directions). data.

As with WEP, authentication and encryption keys are also required to
wrap the multicast encryption (and possibly, authentication) keys.

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Appendix B - Transient EAP Key (TEK) Hierarchy

Figure B-1 illustrates the TEK key hierarchy for EAP-TLS [RFC2716],
which is based on the TLS key hierarchy described in [RFC2246]. The
TLS-negotiated ciphersuite is used to set up a protected channel for
use in protecting the EAP conversation, keyed by the derived TEKs.
The TEK derivation proceeds as follows:

master_secret = TLS-PRF-48(pre_master_secret, "master secret",
client.random || server.random)
TEK = TLS-PRF-X(master_secret, "key expansion",
server.random || client.random)
Where:
TLS-PRF-X = TLS pseudo-random function defined in [RFC2246],
computed to X octets.
master_secret = TLS term for the MK.

Figure B-1 - TLS [RFC2246] Key Hierarchy

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Appendix C - EAP EAP-TLS Key Hierarchy

In EAP-TLS [RFC2716], the MSK is divided into two halves,
corresponding to the "Peer to Authenticator Encryption Key" (Enc-
RECV-Key, 32 octets, also known as the PMK) and "Authenticator to
Peer Encryption Key" (Enc-SEND-Key, 32 octets). In [RFC2548], the
Enc-RECV-Key (the PMK) is transported in the MS-MPPE-Recv-Key
attribute, and the Enc-SEND-Key is transported in the MS-MPPE-Send-
Key attribute.

The EMSK is also divided into two halves, corresponding to the "Peer
to Authenticator Authentication Key" (Auth-RECV-Key, 32 octets) and
"Authenticator to Peer Authentication Key" (Auth-SEND-Key, 32
octets). The IV is a 64 octet quantity that is a known value; octets
0-31 are known as the "Peer to Authenticator IV" or RECV-IV, and
Octets 32-63 are known as the "Authenticator to Peer IV", or SEND-IV.

In EAP-TLS, the MSK, EMSK and IV are derived from the MK TLS master
secret via a one-
way one-way function. This ensures that the MK TLS master
secret cannot be derived from the MSK, EMSK or IV unless the one-way
function (TLS PRF) is broken. Since the MSK is derived from the MK, the
TLS master secret, if the MK TLS master secret is compromised then the
MSK is also compromised.

As described in [RFC2716], the formula for the derivation of the MSK,
EMSK and IV from the MK is as follows:

MSK = TLS-PRF-64(MK, TLS-PRF-64(TMS, "client EAP encryption",
client.random || server.random)
EMSK = second 64 octets of:
TLS-PRF-128(MK,
TLS-PRF-128(TMS, "client EAP encryption",
client.random || server.random)
IV = TLS-PRF-64("", "client EAP encryption",
client.random || server.random)

AAA-Key(0,31) = Peer to Authenticator Encryption Key (Enc-RECV-Key)
(MS-MPPE-Recv-Key in [RFC2548]). Also known as the
PMK.
AAA-Key(32,63)= Authenticator to Peer Encryption Key (Enc-SEND-Key)
(MS-MPPE-Send-Key in [RFC2548])
EMSK(0,31) = Peer to Authenticator Authentication Key (Auth-RECV-Key)
EMSK(32,63) = Authenticator to Peer Authentication Key (Auth-Send-Key)
IV(0,31) = Peer to Authenticator Initialization Vector (RECV-IV)
IV(32,63) = Authenticator to Peer Initialization vector (SEND-IV)

Where:

AAA-Key(W,Z) = Octets W through Z includes of the AAA-Key.

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AAA-Key(W,Z) = Octets W through Z includes of the AAA-Key.
IV(W,Z) = Octets W through Z inclusive of the IV.
MSK(W,Z) = Octets W through Z inclusive of the MSK.
EMSK(W,Z) = Octets W through Z inclusive of the EMSK.
MK
TMS = TLS master_secret
TLS-PRF-X = TLS PRF function defined in [RFC2246] computed to X octets
client.random = Nonce generated by the TLS client.
server.random = Nonce generated by the TLS server.

Figure C-1 describes the process by which the MSK,EMSK,IV and
ultimately the TSKs, are derived from the MK. Note that in [RFC2716],
the MK is referred to as the "TLS TLS Master Secret". Secret.

---+
| ^
| TLS Master Secret (MK) (TMS) |
| |
V |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | EAP |
| Master Session Key (MSK) | Method |
| Derivation | |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ EAP ---+
| | | API ^
| MSK | EMSK | IV |
| | | |
V V V v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+
| | |
| | |
| backend authentication server | |
| | |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+
| | ^
| AAA-Key(0,31) | AAA-Key(32,63) |
| (PMK) | Transported |
| | via AAA |
| | |
V V V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+
| | ^
| Ciphersuite-Specific Transient Session | Auth.|
| Key Derivation | |
| | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---+

Figure C-1 - EAP TLS [RFC2716] Key hierarchy

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Appendix D - Example Transient Session Key (TSK) Derivation

Within IEEE 802.11 RSN, the Pairwise Transient Key (PTK), a transient
session key used to protect unicast traffic, is derived from the PMK
(octets 0-31 of the MSK), known in [RFC2716] as the Peer to
Authenticator Encryption Key. In [IEEE80211i], the PTK is derived
from the PMK via the following formula:

PTK = EAPOL-PRF-X(PMK, "Pairwise key expansion", Min(AA,SA) ||
Max(AA, SA) || Min(ANonce,SNonce) || Max(ANonce,SNonce))

Where:

PMK = AAA-Key(0,31)
SA = Station MAC address (Calling-Station-Id)
AA = Access Point MAC address (Called-Station-Id)
ANonce = Access Point Nonce
SNonce = Station Nonce
EAPOL-PRF-X = Pseudo-Random Function based on HMAC-SHA1, generating
a PTK of size X octets.

TKIP uses X = 64, while CCMP, WRAP, and WEP use X = 48.

The EAPOL-Key Confirmation Key (KCK) is used to provide data origin
authenticity in the TSK derivation. It utilizes the first 128 bits
(bits 0-127) of the PTK. The EAPOL-Key Encryption Key (KEK) provides
confidentiality in the TSK derivation. It utilizes bits 128-255 of
the PTK. Bits 256-383 of the PTK are used by Temporal Key 1, and Bits
384-511 are used by Temporal Key 2. Usage of TK1 and TK2 is
ciphersuite specific. Details are available in [IEEE80211i].

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Appendix E - AAA-Key Derivation

Where a AAA-Key is generated as the result of a successful EAP
authentication, the AAA-Key is set to MSK(0,63).

As discussed in [I-D.irtf-aaaarch-handoff], [IEEE-02-758],
[IEEE-03-084], Key Names and [8021XHandoff], keying material may be required
for use Scope in fast handoff between authenticators. Where Existing Methods

This appendix specifies the backend
authentication server provides keying material to multiple
authenticators key names and scope in order to facilitate fast handoff, it is highly
desirable for the keying material used on different authenticators to
be cryptographically separate, so methods that if one authenticator is
compromised, it does not lead have
been published prior to the compromise publication of other
authenticators. Where keying material this RFC. What is provided by the backend
authentication server, a key hierarchy derived from the EMSK, can be
used to provide cryptographically separate keying material for use needed
in
fast handoff:

AAA-Key-A = MSK(0,63)
AAA-Key-B = PRF(EMSK(0,63),"EAP AAA-Key derivation for
multiple attachments", AAA-Key-A,B-Called-Station-Id,
Calling-Station-Id,length)

AAA-Key-E = PRF(EMSK(0,63),"EAP AAA-Key derivation for
multiple attachments",AAA-Key-A,E-Called-Station-Id,
Calling-Station-Id, length)

Where:
Calling-Station-Id = STA MAC address
B-Called-Station-Id = AP B MAC address
E-Called-Station-Id = AP E MAC address
PRF = Some suitable pseudo-random function
length = length of derived key material

Here AAA-Key-A addition to the rules in Section 2.4 is the AAA-Key derived during the initial definition of what EAP
authentication between
peer and server names are used, what Method-Id is used, and how these
are encoded.

EAP-TLS

The EAP-TLS Method-Id is provided by the concatenation of the peer
and authenticator A. Based on this
initial EAP authentication, server nonces.

Where certificates are used, the EMSK Session-Id scope is also derived, which can be
used to derive AAA-Keys for fast authentication between determined via
the EAP peer and authenticators B and E. Since the EMSK is cryptographically
separate server names, deduced from the MSK, each of these AAA-Keys is cryptographically
separate from each other, altSubjectName in the
peer and server certificates.

Issue: What happens if a pre-shaked key ciphersuite is negotiated?
How are guaranteed to be unique between the EAP peer (also known as the STA) and server names determined?

EAP-AKA

The EAP-AKA Method-Id is the authenticator (also known as contents of the AP).

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Appendix F - AMSK Key Derivation

The EAP AMSK key derivation function (KDF) derives an AMSK RAND field from the
Extended Master Session Key (EMSK), an application key label,
optional application data, and output length.

AMSK = KDF(EMSK, key label, optional application data, length)
AT_RAND attribute, followed by the contents of the AUTN field in the
AT_AUTN attribute.

The key labels are printable ASCII strings unique for each
application (see Section 7 for IANA Considerations).

Additional ciphering keys (TSKs) can be derived EAP peer name is the contents of the Identity field from the AMSK
AT_IDENTITY attribute, using
an application specific key derivation mechanism. In many cases, this
AMSK->TSK derivation can simply split only the AMSK to pieces of correct
length. In particular, it is not necessary to use a cryptographic
one-way function. Actual Identity Length octets
from the beginning, however. Note that the length of the AMSK must be specified
by contents are used as they
are transmitted, regardless of whether the application.

F.1 transmitted identity was a
permanent, pseudonym, or fast reauthentication identity. The EAP AMSK Key Derivation Function
server name is an empty string.

EAP-SIM

The EAP key derivation function Method-Id is taken from the PRF+ key expansion
PRF from [IKEv2]. This KDF takes 4 parameters as input: secret,
label, application data, and output length. It is only defined for
255 iterations so it may produce up to 5100 bytes contents of key material.

For the purposes RAND field from the AT_RAND
attribute, followed by the contents of this specification the secret NONCE_MT field in the
AT_NONCE_MT attribute.

The EAP peer name is taken as the
EMSK, contents of the label is Identity field from the key label described above concatenated with a
NUL byte,
AT_IDENTITY attribute, using only the application data is also described above and Actual Identity Length octets
from the output
length is two bytes. The application data is optional and may not be beginning, however. Note that the contents are used by some applications. The KDF is based on HMAC-SHA1 [RFC2104]
[SHA1]. For this specification we have:

KDF (K,L,D,O) = 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)

prf = HMAC-SHA1
K = EMSK
L = key label
D = application data
O = OutputLength (2 bytes)
S = L | " " | D | O

The prf+ construction was chosen because as they
are transmitted, regardless of its simplicity and whether the transmitted identity was a
permanent, pseudonym, or fast reauthentication identity. The EAP
server name is an empty string.

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efficiency over other PRFs such as those used in [TLS]. The
motivation for the design of this PRF is described in [SIGMA].

The NUL byte after the key label is used to avoid collisions if one
key label is a prefix of another label (e.g. "foobar" and
"foobarExtendedV2"). This is considered a simpler solution than
requiring a key label assignment policy that prevents prefixes from
occurring.

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Expiration Date

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