WDIFF

draft-ietf-eap-keying-01.txt --> draft-ietf-eap-keying-02.txt

EAP Working Group B. Bernard Aboba
Internet-Draft D.
INTERNET-DRAFT Dan Simon
Expires: April 26, 2004
Category: Informational Microsoft
<draft-ietf-eap-keying-02.txt> J. Arkko
26 June 2004 Ericsson
P. Eronen
Nokia
H. Levkowetz, Ed.
ipUnplugged
October 27, 2003

EAP

Extensible Authentication Protocol (EAP) Key Management Framework
<draft-ietf-eap-keying-01.txt>

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. RFC 2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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This Internet-Draft will expire on April 26, 2004.
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Abstract

The Extensible Authentication Protocol (EAP), defined in [RFC3748],
enables extensible network access authentication. This document
provides a framework for EAP key management, including
a statement of applicability and guidelines for the generation, transport and usage of EAP
keying material. Algorithms for key derivation or
mechanisms for key transport are not specified in this document.
Rather, this document provides a framework within which algorithms
and transport mechanisms can be discussed and evaluated. material generated by EAP authentication algorithms, known as
"methods".

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . .......................................... 4
1.1 Requirements Language . . . . . . . . . . . . . . . . ........................... 4
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . ..................................... 4
1.3 Conversation Overview . . . . . . . . . . . . . . . . 6
1.3.1 Discovery Phase . . . . . . . . . . . . . . . . 7
1.3.2 Authentication Phase . . . . . . . . . . . . . . 8
1.3.3 Secure Association Phase . . . . . . . . . . . . 9 ........................................ 5
1.4 Authorization issues . . . . . . . . . . . . . . . . . 9
1.4.1 Correctness in fast handoff . . . . . . . . . . EAP Invariants .................................. 11
2. EAP Key Hierarchy . . . . . . . . . . . . . . . . . . . . . ..................................... 13
2.1 EAP Invariants . . . . . . . . . . . . . . . . . . . . 14
2.1.1 Media Independence . . . . . . . . . . . . . . . 14
2.1.2 Method Independence . . . . . . . . . . . . . . 14
2.1.3 Ciphersuite Independence . . . . . . . . . . . . 14 Key Terminology ................................. 13
2.2 Key Hierarchy . . . . . . . . . . . . . . . . . . . . ................................... 15
2.3 Exchanges . . . . . . . . . . . . . . . . . . . . . . 19 Key Lifetimes ................................... 17
2.4 AAA-Key Scope ................................... 24
2.5 Fast Handoff Support ............................ 26
3. Security Associations . . . . . . . . . . . . . . . . . . . 22 associations ................................. 30
3.1 EAP Method SA (peer - EAP server) . . . . . . . . . . . . . . 23 ................................... 31
3.2 EAP method EAP-Key SA (peer - EAP server) . . . . . . . . . . 23
3.2.1 Example: EAP-TLS . . . . . . . . . . . . . . . . 24
3.2.2 Example: EAP-AKA . . . . . . . . . . . . . . . . 24 ...................................... 33
3.3 EAP-key SA . . . . . . . . . . . . . . . . . . . . . . 25
3.4 AAA SA(s) (authenticator - backend auth. server) . . . 25
3.4.1 Example: RADIUS . . . . . . . . . . . . . . . . 25
3.4.2 Example: Diameter with TLS . . . . . . . . . . . 25 ....................................... 33
3.4 Service SA(s) ................................... 34
3.5 Unicast Secure Association SA . . . . . . . . . . . . 26
3.6 Multicast Secure Association SA . . . . . . . . . . . 27
3.7 Key Naming . . . . . . . . . . . . . . . . . . . . . . 28 ....................................... 37
4. Threat Model . . . . . . . . . . . . . . . . . . . . . . . . 29 Security Considerations .............................. 39
4.1 Security Assumptions . . . . . . . . . . . . . . . . . 29 Terminology ............................ 39
4.2 Threat Model .................................... 39
4.3 Security Requirements . . . . . . . . . . . . . . . . 32
4.2.1 EAP method requirements . . . . . . . . . . . . 32
4.2.2 AAA Protocol Requirements . . . . . . . . . . . 34
4.2.3 Secure Association Protocol Requirements . . . . 36
4.2.4 Ciphersuite Requirements . . . . . . . . . . . . 37
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . 38
6. Security Considerations . . . . . . . . . . . . . . . . . . 38
6.1 Key Strength . . . . . . . . . . . . . . . . . . . . . 38
6.2 Key Wrap . . . . . . . . . . . . . . . . . . . . . . . 38
6.3 Analysis ............................... 41
4.4 Man-in-the-middle Attacks . . . . . . . . . . . . . . 39
6.4 Impersonation . . . . . . . . . . . . . . . . . . . . 39
6.5 ....................... 45
4.5 Denial of Service Attacks . . . . . . . . . . . . . . 40
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41
Normative References . . . . . . . . . . . . . . . . . . . . 41
Informative References . . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . ....................... 45
4.6 Impersonation ................................... 46
4.7 Channel Binding ................................. 47
4.8 Key Strength .................................... 48
4.9 Key Wrap ........................................ 48

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5. Security Requirements ................................. 49
5.1 EAP Method Requirements ......................... 49
5.2 AAA Protocol Requirements ....................... 52
5.3 Secure Association Protocol Requirements ........ 54
5.4 Ciphersuite Requirements ........................ 55
6. IANA Considerations ................................... 56
7. References ............................................ 56
7.1 Normative References ............................ 56
7.2 Informative References .......................... 57
Acknowledgments .............................................. 60
Author's Addresses ........................................... 61
Appendix A - Ciphersuite Keying Requirements . . . . . . . . . . . . . . 46
B. ................. 62
Appendix B - Transient EAP Key (TEK) Hierarchy . . . . . . . . . . . . . 47
C. MSK and EMSK ............... 63
Appendix C - EAP Key Hierarchy . . . . . . . . . . . . . . . . . . . 48
D. ............................... 64
Appendix D - Transient Session Key (TSK) Derivation . . . . . . . . . . . 51
E. .......... 66
Appendix E - AAA-Key Derivation . . . . . . . . . . . . . . . . . . . . . 52
F. Open issues . . . . . . . . . . . . . . . . . . . . . . . . 53 .............................. 67
Intellectual Property and Statement .............................. 68
Full Copyright Statements . . . . . . . 54 Statement ..................................... 68

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1. Introduction

The Extensible Authentication Protocol (EAP), defined in
[I-D.ietf-eap-rfc2284bis], [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 EAP keying material is generated by EAP
methods, transported by AAA protocols, transformed into session keys
by secure association protocols Secure Association Protocols and used by lower layer ciphersuites,
it is necessary to describe each of these elements and provide a
system-level security analysis.

1.1

1.1. Requirements Language

In this document, several words are used to signify the requirements
of the specification. These words are often capitalized.

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

1.2. Terminology

This document frequently uses the following terms:

authenticator
The end of the link initiating EAP authentication. Where no
backend authentication server is present, the authenticator acts
as the EAP server, terminating the EAP conversation with the peer.
Where a backend authentication server is present, the
authenticator may act as a pass-through for one or more
authentication methods and for non-local users. This terminology The term
Authenticator is also used in [IEEE8021X], [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 methods for the authenticator. This
terminology is also used in [IEEE8021X].

AAA-Token
The package within which keying material [IEEE-802.1X].

AAA Authentication, Authorization and one or more
attributes is transported between Accounting. AAA protocols with
EAP support include RADIUS [RFC3579] and Diameter [I-D.ietf-aaa-
eap]. In this document, the backend authentication terms "AAA server" and "backend

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authentication server" are used interchangeably.

EAP server and the authenticator.
The attributes provide entity that terminates the
authenticator EAP authentication method with usage context and key names suitable to bind the key to
peer. In the appropriate context. The format and wrapping case where no backend authentication server is used,
the EAP server is part of the
AAA-Token, which authenticator. In the case where the
authenticator operates in pass-through mode, the EAP server is intended to be accessible only to
located on the backend authentication server server.

security association
A set of policies and authenticator, key(s) used to protect information. This
information in the security association is defined stored by each party of
the AAA
protocol. Examples include RADIUS [RFC2548], security association and Diameter
[I-D.ietf-aaa-eap].

Cryptographic binding
The demonstration of must be consistent among the parties.
Elements of a security association include cryptographic keys,
negotiated ciphersuites and other parameters, counters, sequence
spaces, authorization attributes, etc.

1.3. Overview

EAP peer is typically deployed in order to the EAP server that support extensible network
access authentication in situations where a single
entity has acted as peer desires network
access via one or more authenticators. The situation is illustrated
in Figure 1.

Since both the EAP peer for all methods executed within a
sequence and authenticator may have more than one physical
or tunnel. Binding MAY also imply that logical port, a given peer may simultaneously access the EAP server
demonstrates 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 in one
location. Alternatively, the peer that may be mobile, changing its point
of attachment from one authenticator to another, or moving between
points of attachment on a single entity has acted as authenticator.

Where authenticators are deployed standalone, the EAP
server for all methods executed within a sequence or tunnel. 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 conversation
occurs between the protocol cannot
compute x from y or y from x without "breaking" some cryptographic
assumption. In particular, this definition allows that peer and authenticator, and the
adversary has authenticator must
locally implement an EAP method acceptable to the knowledge peer.

However, one 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 advantages of a
cryptographic pseudo-random number generator EAP is that it enables deployment
of new authentication methods without knowledge requiring development of new
code on the secret state. In other words, if authenticator. While the keys are
cryptographically separate, there is no shortcut to compute x from
y or y from x.

EAP server
The entity which terminates authenticator may implement
some EAP authentication with methods locally and use those methods to authenticate local
users, it may at the peer is
known same time act as the EAP server. Where a pass-through is supported, for other users
and methods, forwarding EAP packets back and forth between the
backend authentication server functions as the EAP server; where
authentication occurs locally, the EAP server is the
authenticator.

AAA-Key
A key derived by the EAP peer and EAP server and transported to
the authenticator. In 802.11 terminology, the first 32 octets of
the AAA-Key is known as the Pairwise Master Key (PMK).

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

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Mutual authentication 26 June 2004

+-+-+-+-+
| |
| 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

This refers to an is accomplished by encapsulating EAP method in which, packets within an interlocked
exchange, the authenticator authenticates the peer
Authentication, Authorization and Accounting (AAA) protocol, spoken
between the peer
authenticates the authenticator. Two one-way conversations,
running in opposite directions do not provide mutual authenticator and backend authentication as defined here.

peer
The end of the link that responds to the authenticator. In
[IEEE8021X], this end is known as the Supplicant.

1.3 Conversation Overview server. AAA
protocols supporting EAP include RADIUS [RFC3579] and Diameter [I-
D.ietf-aaa-eap].

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Where EAP key derivation is supported, EAP authentication is the conversation between the
peer and the authenticator typically a component of a takes place in three phase exchange: phases:

Phase 0: Discovery phase (phase 0)
Phase 1: Authentication
1a: EAP authentication, key derivation and transport (phase 1) authentication
1b: AAA-Key Transport (optional)
Phase 2: Secure Association Establishment
2a: Unicast and multicast secure association establishment (phase 2) Secure Association
2b: Multicast Secure Association (optional)

In the discovery phase (phase 0), the EAP peers locate each other authenticators and
discover their capabilities. This can include an EAP For example, a peer
locating may locate an
authenticator suitable for providing access to a particular network, or it could involve an EAP a peer locating may
locate an authenticator behind a bridge with which it desires to
establish a secure
association. Typically the discovery Secure Association.

The authentication phase takes place between the
EAP peer and authenticator.

Once (phase 1) may begin once the EAP peer and
authenticator discover each other, other. This phase always includes EAP
authentication may begin (phase 1a). EAP 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 Where the same time act as a pass-through for other users and
methods, forwarding chosen EAP packets back and forth between method supports key
derivation, in phase 1a keying material is derived on both the backend
authentication server peer
and the peer.

As described in Section 2, in addition to supporting authentication, EAP methods may also support derivation of server. This keying material may be used for
purposes multiple
purposes, including protection of the EAP conversation and subsequent
data exchanges. EAP key derivation takes place between the EAP peer
and EAP server, and methods supporting key derivation MUST also
support mutual authentication. Where an authenticator server

An additional step (phase 1b) is
present, it acts as the EAP server and transports derived 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 authenticator.

A Secure Association exchange (phase 1b).

EAP methods may mutually authenticate 2) then occurs between the peer
and derive keys. However a

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distinct secure association exchange is required authenticator in order to manage the creation and deletion of
unicast (phase 2a) and multicast (phase 2b) security associations
between the EAP peer and authenticator.

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

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Figure 1: 2: Conversation Overview

1.3.1

1.3.1. Discovery Phase

In the peer discovery exchange phase (phase 0), the EAP peer and authenticator
locate each other and discover each other's capabilities. For example, PPPoE [RFC2516] includes support for a Discovery Stage to allow a peer to identify the Ethernet MAC address
of one
can occur manually or more authenticators and establish a PPPoE SESSION_ID. In
IEEE 802.11 [IEEE80211], automatically, depending on the lower layer
over which EAP peer (also known as the Station or
STA) discovers the authenticator (Access Point or AP) and determines
its capabilities using Beacon or Probe Request/Response frames. runs. Since device discovery is handled outside of EAP,
there is no need to provide this functionality within EAP.

Device discovery can occur manually or automatically. In

For example, where EAP
implementations running 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.

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Since device discovery can occur prior to authentication and key
derivation, it may not be possible

In contrast, PPPoE [RFC2516] provides support for the discovery phase a Discovery Stage
to be
protected using keying material derived during an authentication
exchange. As allow a result, device 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 protocols may be insecure,
leaving them vulnerable support
utilizing Beacon and/or Probe Request/Response frames, allowing the
peer (known as the station or STA) to spoofing unless determine the discovered parameters
can subsequently be securely verified.

1.3.2 MAC address and
capabilities of one or more authenticators (known as Access Point or
APs).

1.3.2. Authentication Phase

Once the EAP 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 are Network Access Servers (NASes)
providing 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 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 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.

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Successful completion of EAP authentication and key derivation by an
EAP 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
Secure Association Protocol (phase 2). As a result, EAP may be used
for "pre-authentication" in situations where it is necessary to
pre-establish pre-
establish EAP security associations in order to decrease handoff or
roaming latency.

1.3.3

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1.3.3. Secure Association Phase

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

[1] The Entity Naming. A basic feature of a Secure Association Protocol is
the naming of the parties engaged in the exchange. As illustrated
in Figure 1, it is possible for both the peer and NAS to have more
than one physical or virtual port. For the purposes of
identification, it is therefore not possible to identify either
peers or NAS devices using port identifiers. Proper identification
of the parties is critical to the Secure Association phase, 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] Secure capabilities negotiation. This provides for the secure
negotiation of capabilities. This includes usage modes, session parameters and (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 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.

[2]

[3] Generation of fresh transient session keys. This is keys (TSKs). The Secure
Association Protocol typically
accomplished via guarantees the exchange freshness of session
keys by exchanging nonces within the secure
association protocol, and includes generation of 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 AAA-
Key directly to protect data, the secure association
protocol Association Protocol
protects against compromise of the AAA-Key, and by guaranteeing the
freshness of transient session key, keys, assures that
session keys they are not
reused.

[3]

[4] Key activation and deletion.

[4] Mutual proof of possession of the AAA-Key. This demonstrates
that both In order for the EAP peer and
authenticator have been authenticated
and authorized by the AAA server. Since mutual proof of
possession to communicate securely, it is not necessary for both
sides to derive the same as mutual authentication, the EAP peer
cannot verify authenticator assertions (including session keys, and remain in sync with
respect to key state going forward. One of the
authenticator identity) functions of the
Secure Association Protocol is to synchronize the activation and
deletion of keys so as a result to enable seamless rekey, or recovery from
partial or complete loss of this exchange.

1.4 Authorization issues

In a typical network access scenario (dial-in, wireless LAN, etc.)
access control mechanisms are typically applied. These mechanisms
include user 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 well as authorization for mutual authentication, the offered

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service.

As 26 June 2004

peer cannot verify authenticator assertions (including the
authenticator identity) as a part result of the authentication process, the AAA network determines
the user's authorization profile. The user authorizations are
transmitted by the AAA server to this exchange.

1.4. EAP Invariants

By utilizing a three phase exchange, the EAP authenticator (also key management framework
guarantees that certain basic characteristics, known as the Network Access Server or NAS) included with the AAA-Token, which
also contains the AAA-Key, in Phase 1b "EAP
Invariants" hold true for all implementations of EAP. These include:

Media independence
Method independence
Ciphersuite independence

1.4.1. Media Independence

One of the goals of EAP conversation.
Typically, the profile is determined based to allow EAP methods to function on any
lower layer meeting the user identity, but
a certificate presented by the user may also provide authorization
information.

The AAA server is responsible for making a user authorization
decision, answering 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 following questions:

o Is this lower layer over which
they are transported, and cannot utilize identifiers associated with
a legitimate user for this particular network?

o Is this user allowed usage environment (e.g. MAC addresses).

The need for media independence has also motivated the type development of access he or she is requesting?

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

o Is three phase exchange. Since discovery is typically media-
specific, this user function is handled outside of EAP, rather than being
incorporated within it. Similarly, the subscription rules regarding time Secure Association Protocol
often contains media dependencies such as negotiation of day?

o Is media-
specific ciphersuites or session parameters, and as a result this user
functionality also cannot be incorporated within his limits for concurrent sessions?

o Are there any fraud, credit limit, or other concerns that indicate EAP.

Note that access should media independence may 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 retained within EAP methods that
support channel binding or proxies are involved, all method-specific identification. An EAP
method need not be aware of the AAA
devices content of an identifier in the chain from the NAS 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 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 form of day or limits on the number an opaque blob, and receive
confirmation of
concurrent sessions). In addition to the Accept/Reject decision made
by the AAA chain, parameters or constraints can be communicated to
the NAS.

The criteria for Accept/Reject decisions or the reasons for choosing
particular authorizations are typically not communicated to the NAS,
only the final result. As a result, the NAS has no way to know what whether the decision was based on. Was a set of authorization parameters
sent because this service is always provided to the user, or was the match, without requiring
media-specific knowledge.

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1.4.2. Method Independence

By enabling pass-through, authenticators can support any method
implemented on the time/day peer and server, not just locally implemented
methods. This allows the capabilities of the requesting
NAS device?

Within EAP, "fast handoff" is defined as a conversation in which the authenticator to avoid implementing code
for each EAP exchange (phase 1a) and associated AAA passthrough method required by peers. In fact, since a pass-through
authenticator is bypassed,
so as not required to reduce latency. Depending on the fast handoff mechanism,
AAA-Key transport (phase 1b) may also be bypassed in favor a context
transfer (see [IEEE80211f] and [I-D.aboba-802-context]) or implement any EAP methods at all, it may
cannot be
provided in assumed to support any EAP method-specific code.

As a pre-emptive manner result, as noted in [IEEE-03-084] [RFC3748], authenticators must by default be
capable of supporting any EAP method. Since the Discovery and
[I-D.irtf-aaaarch-handoff].

As we will discuss, Secure
Association exchanges are also method independent, an authenticator
can carry out the introduction of fast handoff creates a new
class of 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 vulnerabilities as well as requirements for the
secure handling of authorization context.

1.4.1 Correctness media
in fast handoff

Bypassing all or portions of use. For example, the AAA conversation creates challenges
in ensuring that authorization [RFC3748] mandatory-to-implement EAP method
(MD5-Challenge) does not provide dictionary attack resistance, mutual
authentication or key derivation, and as a result is properly handled. These include:

o Consistent application of session time limits. A fast handoff
should not automatically increase appropriate
for use in wireless LAN authentication [WLANREQ]. However, despite
this it is possible for the available session time,
allowing a user peer and authenticator to endlessly extend their network access by
changing interoperate as
long as a suitable EAP method is supported on the point EAP server.

1.4.3. Ciphersuite Independence

While EAP methods may negotiate the ciphersuite used in protection of attachment.

o Avoidance
the EAP conversation, the ciphersuite used for the protection of privilege elevation. A fast handoff should data
is negotiated within the Secure Association Protocol, out-of-band of
EAP.

The backend authentication server is not
result in a user being granted access party to services which they are
not entitled to.

o Consideration of dynamic state. In situations in which dynamic
state this negotiation
nor is involved it an intermediary 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 data flow between the AAA server.

o Encoding of restrictions. Since a NAS 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
criteria considered by a AAA server when allowing access, ciphersuite negotiated between
them, and therefore does not implement ciphersuite-specific code.

Since ciphersuite negotiation occurs in order
to ensure consistent authorization during a fast handoff it may be
necessary to explicitly encode the restrictions Secure Association
protocol, not in EAP, ciphersuite-specific key generation, if
implemented within an EAP method, would potentially conflict with the
authorizations provided
transient session key derivation occurring in the AAA-Token.

o 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 Secure Association
protocol. As a result, EAP methods generate keying material that is said
ciphersuite-independent. Additional advantages of ciphersuite-
independence include:

Update requirements
If EAP methods were to be "correct". One condition for correctness is as follows: specify how to derive transient session keys

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device the same context as 26 June 2004

for each ciphersuite, they would have been created had the new device
completed need to be updated each time a AAA conversation new
ciphersuite is developed. In addition, backend authentication
servers might not be usable with all EAP-capable authenticators,
since the backend authentication server.

A properly designed fast handoff scheme will only succeed if it is
"correct" in this way. If a successful fast handoff server would establish
"incorrect" state, it is preferable also need to be
updated each time support for it a new ciphersuite is added to fail, in order the
authenticator.

EAP method complexity
Requiring each EAP method to avoid
creation of incorrect context.

Some AAA server include ciphersuite-specific code for
transient session key derivation would increase method complexity
and NAS configurations are incapable result in duplicated effort.

Knowledge of meeting this
definition capabilities
In practice, an EAP method may not have knowledge of "correctness". the
ciphersuite that has been negotiated between the peer and
authenticator, since this negotiation typically occurs within the
Secure Association Protocol.

For example, if PPP ciphersuite negotiation occurs in the old Encryption
Control Protocol (ECP) [RFC1968]. Since ECP negotiation occurs
after authentication, unless an EAP method is utilized that
supports ciphersuite negotiation, the peer, authenticator and new device
differ in their capabilities, it
backend authentication server may not be difficult able to meet this
definition of correctness in a fast handoff mechanism that bypasses
AAA. AAA servers often perform conditional evaluation, in which anticipate the
authorizations returned in an Access-Accept message are contingent on
negotiated ciphersuite and therefore this information cannot be
provided to the NAS or on dynamic state such as EAP method. Since ciphersuite negotiation is
assumed to occur out-of-band, there is no need for ciphersuite
negotiation within EAP.

2. EAP Key Hierarchy

2.1. Key Terminology

The EAP Key Hierarchy makes use of the time following types of day or number keys:

Long Term Credential
EAP methods frequently make use of
simultaneous sessions. For example, long term secrets in a heterogeneous deployment, order to
enable authentication between the AAA server might return different authorizations depending peer and server. In the case of
a method based on pre-shared key authentication, the
NAS making long term
credential is the request, in order to make sure that pre-shared key. In the requested
service case of a public-key
based method, the long term credential is consistent with the NAS capabilities.

If differences corresponding private
key.

Master Session Key (MSK)
Keying material that is derived between the new EAP peer and old device would result 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 AAA peer and server sending that
is exported by the EAP method. The EMSK is at least 64 octets in
length, and is never shared with a different set third party.

AAA-Key
A key derived by the peer and EAP server, used by the peer and
authenticator in the derivation of messages to Transient Session Keys (TSKs).
Where a backend authentication server is present, the new device than
were sent AAA-Key is
transported from the backend authentication server to the old device, then if
authenticator, wrapped within the fast handoff mechanism
bypasses AAA, then AAA-Token; it is therefore known
by the fast handoff cannot be carried out correctly.

For example, if some NAS devices within peer, authenticator and backend authentication server.
However, despite the name, the AAA-Key is computed regardless of
whether a deployment support dynamic
VLANs while others do not, then attributes present backend authentication server is present. AAA-Key
derivation is discussed in Appendix E; in existing implementations
the
Access-Request (such MSK is used as the NAS-IP-Address, NAS-Identifier,
Vendor-Identifier, etc.) could be examined to determine when VLAN
attributes will AAA-Key.

Application-specific Master Session Keys (AMSKs)
Keys derived from the EMSK which are cryptographically separate
from each other and may be returned, as described subsequently used in [RFC3580]. VLAN
support the derivation of
Transient Session Keys (TSKs) for extended uses. AMSK derivation
is defined discussed in [IEEE8021Q]. If Appendix E.

AAA-Token
Where a fast handoff bypassing the
AAA backend server were to occur is present, the AAA-Key and one or more
attributes is transported between the backend authentication server
and the authenticator within a NAS supporting dynamic VLANs package known as the AAA-Token. The
format and
another NAS wrapping of the AAA-Token, which does not, then a guest user with access restricted is intended to a guest VLAN could be given unrestricted access
accessible only to the network.

Similarly, in a network where access backend authentication server and
authenticator, is restricted based on defined by the day AAA protocol. Examples include
RADIUS [RFC2548] and time, SSID, Calling-Station-Id or other factors, unless 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
restrictions are encoded within peer and
EAP server. Since the authorizations, or a partial AAA
conversation IV is included, then a fast handoff could result known value in the
user bypassing the restrictions.

In practice, these considerations limit the situations in which fast
handoff mechanisms bypassing AAA can methods such as EAP-
TLS [RFC2716], it cannot be expected 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 successful.
Where unpredictable.

Pairwise Master Key (PMK)
The AAA-Key is divided into two halves, the deployed devices implement "Peer to Authenticator
Encryption Key" (Enc-RECV-Key) and "Authenticator to Peer
Encryption Key" (Enc-SEND-Key) (reception is defined from the same set point
of view of services, it may
be possible to do successful fast handoffs within such mechanisms.
However, where the supported services differ between devices, authenticator). Within [IEEE80211i] Octets 0-31 of
the
fast handoff may not succeed. For example, [RFC2865], section 1.1 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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"A NAS that does not implement a given service MUST NOT implement 26 June 2004

their Transient Session Keys (TSKs) solely from the RADIUS attributes for that service. For example, a NAS that
is unable to offer ARAP service MUST NOT implement PMK, whereas
the RADIUS
attributes for ARAP. A NAS MUST treat a RADIUS access-accept
authorizing an unavailable service WEP ciphersuite as an access-reject instead."

Note that this behavior only applies to attributes that are known,
but not implemented. For attributes that are unknown, section noted in [RFC3580], derives its TSKs from
both halves of 5
of [RFC2865] states:

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

In order the AAA-Key.

Transient EAP Keys (TEKs)
Session keys which are used to perform a correct fast handoff, if a new device is
provided with RADIUS context for establish a known but unavailable service,
then it MUST process this context protected channel
between the same way it would handle a
RADIUS Access-Accept requesting an unavailable service. This MUST
cause EAP peer and server during the fast handoff to fail. However, if a new device is provided EAP authentication
exchange. The TEKs are appropriate for use 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 AAA ciphersuite
negotiated between EAP peer and server would not
request that a device carry out a service that it does not implement.
This implies that if for use in protecting the new device were to complete a AAA
conversation
EAP conversation. Note 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 ciphersuite used to set up the AAA
protected channel between the EAP peer and server in order during EAP
authentication is unrelated to receive the appropriate service definition.

In practice, this implies that fast handoff mechanisms which bypass
AAA are most likely ciphersuite used 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 subsequently
protect data sent between a NAS providing confidentiality the EAP peer and another NAS that does not
support this service. The correct result of such a fast handoff
would be a failure, since if authenticator. An
example TEK key hierarchy is described in Appendix C.

Transient Session Keys (TSKs)
Session keys used to protect data which are appropriate for the handoff were blindly carried out,
then
ciphersuite negotiated between the user would be moved from a secure to an insecure channel
without permission EAP peer and authenticator. The
TSKs are derived from AAA-Key during the AAA server. Thus Secure Association
Protocol. In the definition case 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 [IEEE80211i] the Secure Association
Protocol consists of the 4-way handshake and group key derivation.
An example TSK derivation is provided in
[RFC2548]."

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2. EAP Appendix D.

2.2. Key Hierarchy

2.1 EAP Invariants

The EAP key management framework assumes that certain basic
characteristics, known as the "EAP Invariants" hold true for all
implementations of EAP. These include:

Media independence
Method independence
Ciphersuite independence

2.1.1 Media Independence

As described Key Hierarchy, illustrated in [I-D.ietf-eap-rfc2284bis], Figure 3, has at the root the
long term credential utilized by the selected EAP method. If
authentication can run
over multiple lower layers, including PPP [RFC1661] and IEEE 802
wired networks [IEEE8021X]. Use with IEEE 802.11 wireless LANs is
also contemplated [IEEE80211i]. Since EAP methods cannot be assumed
to have knowledge of the lower layer over which they are transported,
EAP methods can function based on any lower layer meeting the criteria
outlined in [I-D.ietf-eap-rfc2284bis], Section 3.1. As a result, pre-shared key, the parties store the
EAP
methods should not utilize identifiers associated with a particular
usage environment (e.g. MAC addresses).

2.1.2 Method Independence

Supporting pass-through of authentication method to be used and the backend
authentication pre-shared key. The EAP server enables also
stores the authenticator peer's identity and/or other information necessary to support any
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 method implemented is based on proof of possession of the backend authentication
server and peer, not just locally implemented methods.

This implies that private key
corresponding to the public key contained within a certificate, the
parties store the authenticator need not implement code for each EAP method required by authenticating peers. In fact, to be used and the
authenticator is not required trust anchors used to implement any
validate the certificates. The EAP methods at all,
nor can it server also stores the peer's
identity and/or other information necessary to decide whether access
to some service should be assumed granted. The peer stores information
necessary to implement code specific choose which certificate to any EAP method.

This is useful where there is no single EAP method that is both
mandatory-to-implement and offers acceptable security use for which service.

Based on the media
in use. For example, long term credential established between the peer and
the server, EAP derives four types of keys:

[1] Keys calculated locally by the [I-D.ietf-eap-rfc2284bis]
mandatory-to-implement EAP method (MD5-Challenge) does but not provide
dictionary attack resistance, mutual authentication or key
derivation, and as a result is not appropriate for use in wireless
authentication.

2.1.3 Ciphersuite Independence

While exported
by the EAP methods may negotiate method, such as the ciphersuite used in protection of TEKs.
[2] Keys exported by the EAP method: MSK, EMSK, IV

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

In order to protect the EAP conversation, the methods supporting key
derivation typically negotiate a ciphersuite used and derive Transient EAP
Keys (TEKs) for use with that ciphersuite. The TEKs are stored
locally by the protection 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 data the IV is negotiated within deprecated.

On both the secure association protocol, out-of-band of
EAP. The peer and EAP server, the exported MSK and EMSK are
utilized in order to calculate the AAA-Key, as described in Appendix
E.

Where a backend authentication server is not a party to this
negotiation nor is it an intermediary in present, the data flow between AAA-Key is
transported from the
EAP peer and authenticator. The backend authentication server may
not even have knowledge of to the ciphersuites implemented by
authenticator within the AAA-Token, using the AAA protocol.

Once EAP authentication completes and is successful, the peer and authenticator, or be aware of
authenticator obtain the ciphersuite negotiated between
them, AAA-Key and therefore does not implement ciphersuite-specific code.

Since ciphersuite negotiation occurs in the secure association
protocol, not in EAP, ciphersuite-specific key generation, if
implemented within an EAP method, would potentially conflict with Secure Association Protocol
is run between the
transient session key derivation occurring peer and authenticator 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 EAP methods were to specify how order to derive transient session
keys for each securely
negotiate the ciphersuite, they would need derive fresh TSKs used 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 protect data,
and provide mutual proof of possession of the backend authentication server would also
need to be updated each time support for a new ciphersuite is
added to AAA-Key.

When the authenticator acts as an endpoint of the authenticator. EAP method complexity
Requiring each conversation
rather than a pass-through, EAP method to include ciphersuite-specific code for
transient session key derivation would increase methods are implemented on the
authenticator as well as the peer. If the complexity of
each EAP method and would result in duplicated effort.

Knowledge of capabilities
In practice, an EAP method may not have knowledge of the
ciphersuite that has been negotiated
between the EAP peer and
authenticator. In PPP, ciphersuite negotiation occurs in the
Encryption Control Protocol (ECP) [RFC1968]. Since ECP
negotiation occurs after authentication, unless an EAP method is
utilized that supports ciphersuite negotiation, the peer, authenticator and backend supports mutual authentication server may not be able to
anticipate the negotiated ciphersuite
and therefore this
information cannot be provided to key derivation, the EAP method. Since
ciphersuite negotiation is assumed to occur out-of-band, there is
no need for ciphersuite negotiation within EAP.

2.2 Key Hierarchy

The EAP keying hierarchy, illustrated in Figure 2, makes use of the

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following types of keys:

EAP Master key (MK)
A key derived between the EAP client and server during the EAP
authentication process, and that is kept local to the EAP method Session Key (MSK) and not exported or made available to a third party. Extended
Master Session Key (MSK)
Keying material (at least 64 octets) that is (EMSK) are derived between on the EAP client peer and server
authenticator and exported by the EAP method.

AAA-Key
Where a backend authentication server is present, acting as an EAP
server, keying material known as the AAA-Key is transported from In this case, the authentication server MSK
and EMSK are known only to the authenticator wrapped within the
AAA-Token. The AAA-Key is used by the EAP peer and authenticator
in the derivation of Transient Session Keys (TSKs) for the
ciphersuite negotiated between and no other
parties. The TEKs and TSKs also reside solely on the EAP peer and
authenticator. As
a result, the AAA-Key This is typically known by all parties illustrated in the EAP
exchange: the peer, authenticator and the authentication server
(if present). AAA-Key derivation is discussed Figure 4. As demonstrated in Appendix E.

Extended Master Session Key (EMSK)
Additional keying material (64 octets) derived
[I-D.ietf-roamops-cert], in this case it is still possible to support
roaming between the EAP
client and providers, using certificate-based authentication.

Where a backend authentication server that is exported by utilized, the EAP method. The EMSK situation is
known only to
illustrated in Figure 5. Here the authenticator acts as a pass-
through between the EAP peer and server and is not provided to a
third party.

Initialization Vector (IV)
A quantity of at least 64 octets, suitable for use in an
initialization vector field, that is derived between the EAP
client and backend authentication server. Since In
this model, 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.

Pairwise Master Key (PMK)
The AAA-Key is divided into two halves, authenticator delegates the "Peer to Authenticator
Encryption Key" (Enc-RECV-Key) and "Authenticator access control decision
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 backend authentication server, which acts as the Pairwise
Master a Key (PMK). IEEE 802.11i ciphersuites [IEEE80211i] derive
their Transient Session Keys (TSKs) solely from the PMK, whereas
Distribution Center (KDC). In this case, the WEP ciphersuite, when used authenticator
encapsulates EAP packet with [IEEE8021X], a AAA protocol such as noted in
[RFC3580], derives its TSKs from both halves of the AAA-Key, the
Enc-RECV-Key RADIUS [RFC3579]
or Diameter [I-D.ietf-aaa-eap], and forwards packets to and from the Enc-SEND-Key.

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Transient EAP Keys (TEKs)
Session keys 26 June 2004

backend authentication server, which are used to establish a protected channel
between acts as the EAP peer and server during server. Since
the authenticator acts as a pass-through, EAP authentication
exchange. The TEKs are appropriate for use with methods reside only on
the ciphersuite
negotiated between EAP peer and EAP server for use in protecting the
EAP conversation. Note that the ciphersuite used to set up As a result, the
protected channel between 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 during 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 is unrelated server
sends an Access-Accept to the ciphersuite 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
subsequently protect data sent between
the EAP peer and authenticator. An example TEK

2.3. Key Lifetimes

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

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

Key lifetime issues associated with each type of key hierarchy is described are discussed in
Appendix C.
the sections that follow. Challenges include:

[a] Security. Where key lifetimes cannot be assumed, it may be
necessary to negotiate them. While key lifetimes may be announced
or negotiated in the clear, a protected lifetime negotiation is
RECOMMENDED.

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

Figure 2: 3: EAP Key Hierarchy

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Transient Session Keys 26 June 2004

Figure 4: Relationship between an EAP peer and an 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 |
| | | | | |
| | Secure Assoc. | | AAA-Key| |
| peer |<------------->|Authenti-|<-------| auth |
| |===============| cator |========| server |
| | Link Layer | | AAA | (EAP |
| | (PPP,IEEE 802)| |Protocol| server) |
|MSK,EMSK | | | | |
| AAA-Key | | AAA-Key | |MSK,EMSK,|
| (TSKs) | | (TSKs) | | AAA-Key |
| | | | | |
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
^ ^
| |
| MSK, EMSK | MSK, EMSK
| |
| |
+-+-+-+-+-+ +-+-+-+-+-+
| | | |
| EAP | | EAP |
| Method | | Method |
| | | |
| (TEKs) | | (TEKs) |
| | | |
+-+-+-+-+-+ +-+-+-+-+-+

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

[b] Resource reclaimation. While key lifetimes may be securely
negotiated, it is possible for the NAS or peer to reboot or reclaim
resources, and therefore not be able to cache keys for their full

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lifetime. As a result, lifetime negotiation does not guarantee
that the key cache will remain sychronized. 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 in this situation one or more of the parties
initially do not possess a key with which to protect the
resynchronization exchange.

2.3.1. 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. They remain valid only for the duration of the EAP
conversation, and are lost once the EAP conversation completes.

EAP methods may also implement a cache for other local keying
material which may persist for multiple EAP conversations. For
example, EAP methods based on TLS (such as EAP-TLS [RFC2716]) derive
and cache the TLS Master Secret, typically for substantial time
periods. The lifetime of other local 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 reauthentication, the lifetime of
exported keys is conceptually distinct from the reauthentication
time, since while reauthentication causes new exported keys to be
derived, exported keys may be cached on the peer and server after a
session completes and therefore their lifetime may be greater than
the reauthentication 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 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 may be cached on the EAP server as well as
on the peer. On the EAP server, it is RECOMMENDED that the lifetime
of exported keys be managed as a system parameter. Where the EAP
method does not support the negotiation of the exported key lifetime,
and where a negotiation mechanism is not provided by the lower lower,
it is RECOMMENDED that the peer assume a default value of the
exported key lifetime. A value of 8 hours is suggested.

Managing the lifetime of exported keys using a AAA attribute is NOT

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RECOMMENDED. This is problematic because although this would ensure
transport of the exported key lifetime between the AAA server and the
authenticator, the goal is to synchronize the exported key lifetime
between the peer and EAP server. Providing the the exported key
lifetime on an per-session basis to the authenticator results in
requiring the authenticator to maintain EAP-Key SA state. As a
described in Section 3, EAP-Key SA state is typically only maintained
on the peer and server, so that this represents a substantial
additional burden.

2.3.3. Calculated Key Lifetimes

When keying material exported by EAP methods is replaced, new
calculated keys are also put in place. Similarly, when the keying
material exported by EAP methods expires, so do the calculated keys.
As a result, the lifetime of keys calculated from material exported
by EAP methods can be no larger than the lifetime of the keying
material they are calculated from. Since the lifetime of calculated
keys can be less than that of the exported keys they are derived
from, calculated key lifetimes are conceptually distinct from
exported key lifetimes and reauthentication times, and need to be
managed as a separate parameter.

Note that just as the reauthentication time and the exported key
lifetime are conceptually distinct parameters, so too are calculated
key lifetimes conceptually distinct from the reauthentication time.

Today AAA protocols such as RADIUS [RFC2865] support the Session-
Timeout attribute. As described in [RFC3580], this may be used to
determine the maximum session time prior to reauthentication. Since
reauthentication results in the derivation of new exported keys and
the transport of a new AAA-Key, while a session is in progress the
maximum session time prior to reauthentication places an upper bound
on the AAA-Key lifetime.

However, after the session has terminated, it is possible for the
AAA-Key to be cached on the authenticator. Therefore the AAA-Key
lifetime may be larger than the reauthentication time. As a result,
the AAA-Key lifetime needs to be managed as a separate parameter.

Since the lifetime of the AAA-Key within the authenticator key cache
is in part determined by authenticator resources, the AAA-Key
lifetime is typically managed as a system parameter on the
authenticator. Since the authenticator may have considerably fewer
resources than either the EAP peer or server, it is possible that
AAA-Key lifetime on the authenticator may be less than exported key
lifetime maintained by the server, or that the authenticator may need
to reclaim AAA-Key resources prior to expiration of the AAA-Key

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lifetime.

As a result, the primary issue with managing the AAA-Key lifetime is
the determination by the peer whether a particular AAA-Key exists
within the key cache of a given authenticator. Transmitting the AAA-
Key lifetime from the AAA server to the authenticator is not helpful
in solving this problem in several important scenarios.

Where the AAA-key lifetime is negotiated between the authenticator
and the peer within the Secure Association Protocol, this may be used
by the peer to manage the lifetime of the AAA-Key once the Secure
Association Protocol has completed.

However, should a time gap may exist between the time of completion
of the EAP method and the initiation of the Secure Association
Protocol, the lifetime of the AAA-Key cannot be determined by the
peer during this period. As a result, unless the Secure Association
Protocol always follos the completion of the EAP method exchange
without a gap in time, it may not be possible for the peer and
authenticator to negotiate session-specific value of the AAA-Key
lifetime. For example, where EAP pre-authentication is used, the
AAA-Key may be derived and remain resident on the peer and
authenticator prior to initiation of the Secure Association Protocol.

However, if the AAA-Key lifetime is managed as an authenticator
system parameter, it may be possible for lower layer solutions to
bridge the gap. For example, the lower layer may utilize Discovery
mechanisms to ensure AAA-Key cache synchronization between the peer
and authenticator.

If 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
implies replacement of the TSKs. However, replacement of the TSKs
only implies replacement of the AAA-Key when the TSKs are taken from
a portion of the AAA-Key.

Therefore while the lifetime of the TSKs may be shorter than or equal
to the AAA-Key lifetime, the TSK lifetime cannot exceed the AAA-Key
lifetime. Where a Secure Association Protocol exists, it is possible
for TSKs to be refreshed prior to reauthentication, and so the TSK

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Key Lifetime may also be shorter than or equal to the
reauthentication timeout. It is therefore RECOMMENDED that the TSK
Key lifetime be managed parameter distinct from the reauthentication
timeout and the AAA-Key lifetime (except where the TSK is taken from
the AAA-Key).

Where TSKs are established as the result of a Secure Association
Protocol 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.

As described in Section 3, TSKs are part of Service SAs which reside
on the peer and authenticator and as with the AAA-Key lifetime, the
TSK lifetime is often determined by authenticator resources. As a
result, the AAA server has no insight into the TSK derivation
process, and by the principle of ciphersuite independence, it is not
appropriate for the AAA server to manage any aspect of the TSK
derivation process, including the TSK lifetime.

2.4. AAA-Key Scope

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

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 is present). However, in practice
difficulties arise in ensuring that the AAA-Key is used only within
the defined scope.

A wide variety of authenticator and peer designs need to be
accomodated within the EAP key management framework. An
authenticator may contain multiple physical ports; a single physical
authenticator may, for the purpose of peer discovery, advertise
itself as multiple "virtual authenticators"; authenticators may be
compromised of multiple CPUs; authenticators may utilize clustering
in order to provide load balancing or failover. Similarly, a peer
may support multiple ports; may support multiple CPUs; or may support
clustering.

As illustrated in Figure 1, an EAP peer with multiple ports may be

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attached to one or more authenticators, each with multiple ports.
Where an authenticator identifies itself to the peer only via use of
a port identifer (such as a link layer address), it may not be
obvious to the peer which authenticator ports are associated with
which authenticators.

Similarly, where an EAP peer identifies itself using a port
identifier (such as a link layer address), it may not be obvious to
the authenticator which peer ports are associated with which peers.
In such situations, the peer and authenticator may not be able to
determine the appropriate AAA-Key scope.

Additional issues arise when a single physical authenticator
advertises itself as multiple "virtual authenticators". In such a
situation, the EAP peer may act as though each "virtual
authenticator" represented a distinct physical authenticator, thereby
restricting the AAA-Key to use with the "virtual authenticator" that
it interacts with. However, depending on the architecture of the
physical AP, it may or may not share AAA-Keys between "virtual
authenticators". Once again, the peer and authenticator may not be
in agreement on the AAA-key scope.

This lack of synchronization may create security vulnerabilities.
For example, where the AAA-Key is shared between "virtual
authenticators" an EAP peer could authenticate with the "Guest"
"virtual authenticator" and derive a AAA-Key. The peer could then
use that AAA-Key within the Secure Association Protocol in order to
connect to the "Corporate Intranet" "virtual authenticator" within
the same physical authenticator. If the "virtual authenticators"
share a AAA-Key cache, then the attempt will be successful.

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 Secure Association Protocols utilize peer
and authenticator identities that are unambiguous and do not
incorporate implicit assumptions about peer and authenticator
architectures.

For example, using port-specific MAC addresses as identifiers is a
particularly poor choice, given that peers and authenticators may
have multiple ports.

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

[d] Where a "virtual authenticator" is implemented, the AAA client MAY
also be virtualized. Where a "virtual AAA client" is implemented,
each "virtual authenticator" identifies itself distinctly to the
AAA server. Where the AAA client and server communicate directly,
this enables the AAA server to authenticate each "virtual AAA
client" distinctly.

[e] The AAA server and authenticator MAY implement additional
attributes in order to further restrict the AAA-Key scope. When
this is done, it is RECOMMENDED that the Secure Association
Protocol be extended to enable the restrictions to be communicated
between the authenticator and the peer. For example, in 802.11,
the AAA server may provide the authenticator with a list of
authorized Called-Station-Ids and/or SSIDs for which the AAA-Key
is valid, restricting the use of the AAA-Key by the peer.
Similarly, the authenticator may provide the peer with a list of
Calling-Station-Ids for which the AAA-Key is valid.

2.5. Fast Handoff Support

Within EAP, "fast handoff" is defined as a conversation in which the
EAP exchange (phase 1a) and associated AAA passthrough is bypassed,
so as to reduce latency. Depending on the fast handoff mechanism,
AAA-Key transport (phase 1b) may also be bypassed or it may be
provided in a pre-emptive manner as in [IEEE-03-084] and [I-D.irtf-
aaaarch-handoff].

The introduction of fast handoff creates a new class of security
vulnerabilities as well as requirements for the secure handling of
authorization context.

2.5.1. Authorization Issues

In a typical network access scenario (dial-in, wireless LAN, etc.)
access control mechanisms are typically applied. These mechanisms
include user authentication as well as authorization for the offered
service.

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

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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
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?

2.5.2. Correctness in Fast Handoff

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

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[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
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 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

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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 well 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 three party exchange fast handoff bypassing the backend authentication server were
to occur between an EAP peer,
an a authenticator supporting dynamic VLANs and an EAP server.

Figure 3 illustrates
another authenticator which does not, then a guest user with access
restricted to a guest VLAN could be given unrestricted access to
the two party exchange. Here EAP network.

Similarly, in a network where access is spoken
between restricted based on the peer day
and authenticator, encapsulated time, Service Set Identifier (SSID), Calling-Station-Id or
other factors, unless the restrictions are encoded within the
authorizations, or a lower layer
protocol, such as PPP, defined partial AAA conversation is included, then a
fast handoff could result in [RFC1661] or IEEE 802, defined the user bypassing the restrictions.

In practice, these considerations limit the situations in
[IEEE802].

Since 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 authenticator acts as an endpoint of supported services differ
between devices, the EAP conversation
rather than fast handoff may not succeed. For example,
[RFC2865], section 1.1 states:

"A authenticator that does not implement a pass-through, EAP methods are implemented on given service MUST
NOT implement the RADIUS attributes for that service. For
example, a authenticator as well as the peer. If the EAP method negotiated
between that is unable to offer ARAP service
MUST NOT implement the EAP peer and RADIUS attributes for ARAP. A
authenticator supports mutual authentication
and key derivation, the MUST treat a RADIUS access-accept authorizing an
unavailable service as an access-reject instead."

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

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

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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 EAP peer and
authenticator and exported by same way it would handle a
RADIUS Access-Accept requesting an unavailable service. This MUST
cause the EAP method.

Where no 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 is present, would not request that a device carry out a service that it
does not implement. This implies that if the MSK and EMSK
are known only 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 peer and authenticator and neither
fast handoff is
transported the desired result. This will cause the new device
to a third party. As demonstrated go back to the AAA server in
[I-D.ietf-roamops-cert], despite order to receive the absence of appropriate
service definition.

In practice, this implies that fast handoff mechanisms which bypass
AAA are most likely to be successful within a backend
authentication server, such exchanges can support roaming between
providers; homogeneous device
deployment within a single administrative domain. For example, it is even possible
would not be advisable to support carry out a fast handoff without
re-authentication. However, this is typically only possible where
both the EAP peer bypassing AAA
between a authenticator providing confidentiality and another
authenticator that does not support certificate-based
authentication, or where 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 base is sufficiently small that EAP
authentication can occur locally.

In order would be moved from
a secure to protect an insecure channel without permission from the EAP conversation, backend
authentication server. Thus the EAP method may
negotiate definition of a ciphersuite and derive Transient EAP Keys (TEKs) "known but
unsupported service" MUST encompass requests for unavailable
security services. This includes vendor-specific attributes
related to
provide keys for that ciphersuite security, such as those described in order to protect some or all of
the EAP exchange. The TEKs are stored locally within the [RFC2548].

3. Security Associations

During EAP method authentication and subsequent exchanges, four types of
security associations (SAs) are not exported.

Once created:

[1] EAP mutual authentication completes and is successful, the
secure association protocol method SA. This SA is run between the peer and

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authenticator. This derives fresh transient session keys (TSKs),
provides for the secure negotiation of the ciphersuite server. It
stores state that can be used to
protect data, and supports mutual proof of possession of the AAA-Key.

Figure 3: Relationship between methods. Not all EAP methods create such
an SA.

[2] EAP-Key SA. This is an SA between the peer and authenticator (acting as
an EAP server), where no backend authentication server server, which
is present. used to store the keying material exported by the EAP method.
Current EAP server implementations do not retain this SA after the

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+-+-+-+-+-+ +-+-+-+-+-+
| | | |
| | | |
| Cipher- | | Cipher- |
| Suite | | Suite |
| | | |
+-+-+-+-+-+ +-+-+-+-+-+
^ ^
| |
| |
| |
V V
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
| |===============| |========| |
| |EAP, TEK Deriv.| | | |
| |<-------------------------------->| backend |
| | | | | |
| | Secure Assoc. | | AAA-Key| |
| peer |<------------->|Authenti-|<-------| auth |
| |===============| cator |========| server |
| | Link Layer | | AAA | (EAP |
| | (PPP,IEEE 802)| |Protocol| server) |
| | | | | |
|MSK,EMSK | | MSK | |MSK,EMSK |
| (TSKs) | | (TSKs) | | |
| | | | | |
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
^ ^
| |
| MSK, EMSK | MSK, EMSK
| |
| |
+-+-+-+-+-+ +-+-+-+-+-+
| | | |
| EAP | | 26 June 2004

Figure 4: Pass-through relationship conversation completes, but future implementations could use
this SA for purposes such as pre-emptive key distribution.

[3] AAA SA(s). These SAs are between EAP peer, the authenticator and the backend
authentication server.

Where these conditions cannot be met, 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 backend authentication 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 typically required. used for "fast resume": the peer and EAP server
can confirm that they are still talking to the same party, perhaps
using fewer roundtrips or less computational power. In this exchange, 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 support pseudonym-based
identity protection. This is typically a cache as described 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 and is most useful when the peer accesses many
different authenticators.

An EAP method is responsible for specifying how the parties select if
an existing EAP method SA should be used, and if so, which one.
Where multiple backend authentication 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 resume" assumes that the information
required (primarily the keys in [RFC3579], the authenticator acts as EAP method SA) hasn't been
compromised. In case the original authentication was carried out
using, for instance, a pass-through between smart card, it may be easier to compromise the
EAP peer and a
backend authentication server. In this model, method SA (stored on the authenticator PC, for instance), so typically the EAP
method SAs have a limited lifetime.

Contents:

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delegates the access control decision to 26 June 2004

o Implicitly, the backend authentication
server, which acts as a Key Distribution Center (KDC), supplying
keying material EAP method this SA refers to both the
o One or more internal (non-exported) keys
o EAP peer and authenticator.

Figure 4 illustrates the case where method SA name
o SA lifetime

3.1.1. Example: EAP-TLS

In EAP-TLS [RFC2716], after the authenticator acts as a
pass-through. Here EAP is spoken between authentication the peer and authenticator
as before. The authenticator then encapsulates EAP packets within a
AAA protocol such as RADIUS [RFC3579] or Diameter [I-D.ietf-aaa-eap],
and forwards packets to client (peer)
and from server can store the backend authentication server,
which acts as following information:

o Implicitly, the EAP server. Since method this SA refers to (EAP-TLS)
o Session identifier (a value selected by the authenticator acts as a
pass-through, EAP methods (as well as server)
o Certificate of the derived EAP Master Key, and
TEKs) reside only on other party (server stores the peer clients's
certificate and backend authentication server.

On completion of a successful authentication, EAP methods on the EAP
peer vice versa)
o Ciphersuite and EAP server export compression method
o TLS Master secret (known as the EAP-TLS Master Session Key (MSK) and Extended
Master Session Key (EMSK). The backend authentication server then
sends a message to the authenticator indicating or MK)
o SA lifetime (ensuring that authentication
has been successful, providing the AAA-Key within SA is not stored forever)
o If the client has multiple different credentials (certificates
and corresponding private keys), a protected package
known as pointer to those credentials

When the AAA-Token. Along with server initiates EAP-TLS, the keying material, client can look up the
AAA-Token contains attributes naming EAP-TLS
SA based on the enclosed keys credentials it was going to use (certificate and providing
context.

The MSK
private key), and EMSK are used to derive the AAA-Key and key name which
are enclosed within expected credentials (certificate or name) of
the AAA-Token, transported to server. If an EAP-TLS SA exists, and it is not too old, the NAS by
client informs the AAA
server, and used within server about the secure association protocol for
derivation existence of Transient Session Keys (TSKs) required for this SA by including
its Session-Id in the
negotiated ciphersuite. TLS ClientHello message. The TSKs are known only to server then looks
up the peer 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
authenticator.

3. Security Associations server can store the following information:

o Implicitly, the EAP method this SA refers to (EAP-AKA)
o A re-authentication pseudonym
o The client's permanent identity (IMSI) (server)
o Replay protection counter
o Authentication key management involves four types of security associations
(SAs):

[1] EAP SA. This (K_aut)
o Encryption key (K_encr)
o Original Master Key (MK)
o SA lifetime (ensuring that the SA is an not stored forever)

When the server initiates EAP-AKA, the client can look up the EAP-AKA
SA between based on the peer and EAP server, which
allows them credentials it was going to authenticate each other.

[2] EAP method SA. This use (permanent identity).
If an EAP-AKA SA exists, and it is also between not too old, the peer and EAP server.
It stores state that can be used for "fast resume" or other
functionality client informs
the server about the existence of this SA by sending its re-
authentication pseudonym as its identity in some EAP methods. Not all Identity Response

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[3] EAP-Key SA. Key Management Framework 26 June 2004

message, instead of its permanent identity. The server then looks up
the correct SA based on this identity.

3.2. 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 future implementations could use this SA for pre-emptive pre-
emptive key distribution.

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[4]

Contents:

o Name/identifier for this SA
o Identities of the parties
o MSK and EMSK
o SA lifetime

3.3. AAA SA(s). These SAs are between SA(s) (authenticator - backend authentication server)

In order for the authenticator and the backend authentication server. They permit the parties server to
mutually
authenticate each other and protect other, they need to store some information.

In case the communications
between them.

3.1 EAP authenticator and backend authentication server are
colocated, and they communicate using local procedure calls or shared
memory, this SA (peer - EAP server) need not necessarily contain any information.

3.3.1. Example: RADIUS

In order for RADIUS, where shared secret authentication is used, the peer client and
server store each other's IP address and EAP server the shared secret, which is
used to authenticate each other, they
need calculate the Response Authenticator [RFC2865] and Message-
Authenticator [RFC3579] values, and to store encrypt some information.

The authentication can be based on different mechanisms, such attributes (such
as
shared secrets or certificates. If the authentication AAA-Key [RFC2548]).

Where IPsec is based on a
shared secret key, used to protect RADIUS [RFC3579] and IKE is used for
key management, the parties store the EAP method information necessary to be used
authenticate and authorize the key. other party (e.g. certificates, trust
anchors and names). The EAP server also stores IKE exchange results in IKE Phase 1 and
Phase 2 SAs containing information used to protect the peer's identity and/or other conversation
(session keys, selected ciphersuite, etc.)

3.3.2. Example: Diameter with TLS

When using Diameter protected by TLS, the parties store information
necessary to decide whether access to some service should
be granted. authenticate and authorize the other party (e.g.
certificates, trust anchors and names). The peer stores TLS handshake results in
a short-term TLS SA that contains information necessary to choose which
secret used to use for which service.

3.2 protect the

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

3.4. Service SA(s) (peer - EAP server)

An EAP method may store some state on authenticator)

The service SA stores information about the peer and EAP server even
after phase 1a has completed.

Typically, this is used for "fast resume": service being provided.
This includes:

o Service parameters (or at least those parameters
that are still needed)
o On the peer and EAP authenticator, service authorization
information received from the backend authentication
server
can confirm that they are still talking (or necessary parts of it)
o On the peer, usually locally configured service
authorization information.
o Transient Session Keys used to protect the same party, perhaps
using fewer roundtrips communication
o The AAA-Key, if it can be needed again (to refresh
and/or resynchronize other keys or less computational power. In this case,
the EAP method SA is essentially a cache for performance
optimization, and either party may remove another reason)
o AAA-Key lifetime

The information in the service SA from its cache at
any point.

An EAP method may also keep state in order to support pseudonym-based
identity protection. This is typically a cache as well (the
information can be recreated if grouped into several
different SAs. This would make sense if, for instance, the original EAP method service
provided is naturally divided into several different subconversations
with different parameters.

How exactly the relevant service SA is lost),
but may chosen at each point depends
on the protocol; see below for examples.

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 stored
consulted for longer periods of time. details.

o Pairwise Master Key Security Association (PMKSA)

The EAP method SA PMKSA is not restricted to a particular service or
authenticator bi-directional SA, used by both parties for sending
and receiving. It is most useful when created on the peer accesses many
different authenticators.

An EAP method is responsible for specifying how the parties select if
an existing when EAP method SA should be used, and if so, which one.
Where multiple backend authentication servers are used, EAP method
SAs are not typically synchronized between them.

EAP method implementations should consider
completes successfully or a pre-shared key is configured. The
PMKSA is created on the appropriate lifetime
for authenticator when the EAP method SA. "Fast resume" assumes that PMK is received or
created on the information
required (primarily authenticator or a pre-shared key is configured.
The PMKSA is used to create the keys in PTKSA. PMKSAs are cached for
their lifetimes. The PMKSA consists of the EAP method SA) hasn't been following elements:

- PMKID (security association identifier)
- Authenticator MAC address
- PMK
- Lifetime
- Authenticated Key Management Protocol (AKMP)

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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 26 June 2004

- Authorization parameters specified the PC, for instance), so typically AAA server or
by local configuration. This can include
parameters such as the EAP
method SAs have a limited lifetime.

Contents:
o Implicitly, peer's authorized SSID.
On the EAP method peer, this SA refers information can be locally
configured.
- Key replay counters (for EAPOL-Key messages)
- Reference to PTKSA (if any), needed to:
o One or more internal (non-exported) keys delete it (e.g. AAA server initiated disconnect)
o EAP method SA name replace it when a new four-way handshake is done
- Reference to accounting context (the details of which depend
on the accounting protocol used, and various implementation
and administrative details. In RADIUS, this 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 lifetime

3.2.1 Example: EAP-TLS

In EAP-TLS [RFC2716], after the EAP authentication created as the client (peer) result of a
successful four-way handshake. There may only be one PTKSA
between a pair of peer and server can store authenticator MAC addresses. PTKSAs
are cached for the following information:

o Implicitly, lifetime of the EAP method this SA refers PMKSA. Since the PTKSA is tied
to (EAP-TLS)
o Session identifier (a value selected by the server)
o Certificate PMKSA, it only has the addititional information from the
4-way handshake. The PTKSA consists of the other party (server stores following:

- Key (PTK)
- Selected ciphersuite
- MAC addresses of the clients's
certificate parties
- Replay counters, and vice versa) ciphersuite specific state
- Reference to PMKSA: This is needed when:
o Ciphersuite A new four-way handshake is needed (lifetime, TKIP
countermeasures), and compression method we need to know which PMKSA to use

o TLS Master secret (known as Group Transient Key Security Association (GTKSA)

The GTKSA is a uni-directional SA created based on the EAP-TLS Master four-way
handshake or the group key handshake. A GTKSA consists of the
following:

- Direction vector (whether the GTK is used for transmit or receive)
- Group cipher suite selector
- Key (GTK)
- Authenticator MAC addres
- Via reference to PMKSA, or MK) copied here:
o SA lifetime (ensuring Authorization parameters
o Reference to accounting context

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3.4.2. Example: IKEv2/IPsec

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

o If IKEv2 SA

- Protocol version
- Identitities of the client has multiple different credentials (certificates and
corresponding private keys), a pointer to those credentials

When 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 server initiates EAP-TLS, authenticator, service authorization information
received from the client can look backend authentication server.

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

o IPsec SAs/SPD

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

The 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.

3.4.3. Sharing service SAs

A single service may be provided by multiple logical or physical
service elements. Each service is responsible for specifying how
changing service elements is handled. Some approaches include:

Transparent sharing
If the credentials it was going service parameters visible to use (certificate and
private key), and the expected credentials (certificate other party (either peer
or name) of
the server. If an EAP-TLS SA exists, and it is authenticator) do not too old, the
client informs change, the server about service can be moved without
requiring cooperation from the existence other party.

Whether such a move should be supported or used depends on
implementation and administrative considerations. For instance, an

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administrator may decide to configure a group of this SA by including
its Session-Id IKEv2/IPsec
gateways in a cluster for high-availability purposes, if the TLS ClientHello message.
implementation used supports this. The server then looks
up peer does not necessarily
have any way of knowing when the correct SA based on change occurs.

No sharing
If the Session-Id (or detects that service parameters require changing, some changes may
require terminating the old service, and starting a new
conversation from phase 0. This approach is used by all services
for at least some parameters, and it doesn't
yet have one).

3.2.2 Example: EAP-AKA

In EAP-AKA [I-D.arkko-pppext-eap-aka], after EAP authentication require any protocol
for transferring the
client and server can store service SA between the following information:

o Implicitly, service elements.

The service may support keeping the EAP method this SA refers old service element active
while the new conversation takes phase, to (EAP-AKA)
o A re-authentication pseudonym
o The client's permanent identity (IMSI) (server)
o Replay protection counter
o Authentication key (K_aut)
o Encryption key (K_encr)
o Original Master Key (MK)

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o SA lifetime (ensuring that decrease the SA time the
service is not stored forever)

When the server initiates EAP-AKA, available.

Some sharing
The service may allow changing some parameters by simply agreeing
about the client can look up new values. This may involve a similar exchange as in
phase 2, or perhaps a shorter conversation.

This option usually requires some protocol for transferring the EAP-AKA
service SA based on between the credentials it was going elements. An administrator may decide not to use (permanent identity).
If an EAP-AKA SA exists,
enable this feature at all, and it typically the sharing is restricted
to some particular service elements (defined either by a service
parameter, or simple administrative decision). If the old and new
service element do not too old, support such "context transfer", this
approach falls back to the client informs previous option (no transfer).

Services supporting this feature should also consider what changes
require new authorization from the backend authentication server about
(see Section 1.7).

Note that these considerations are not limited to service
parameters related to the existence of this SA by sending its
re-authentication pseudonym authenticator--they apply to peer's
parameters as its identity in EAP Identity Response
message, instead well.

3.5. SA Naming

In order to support the correct processing of its permanent identity. The server then looks up phase 2 security
associations, the Secure Association (phase 2) protocol supports the
naming of phase 2 security associations and associated transient
session keys, so that the correct SA based on this identity.

3.3 EAP-key SA

This is an SA set of transient session keys can
be identified for processing a given packet. Explicit creation and
deletion operations are also typically supported so that
establishment and re-establishment of transient session keys can be
synchronized between the peer and parties.

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In order to store
the keying material exported by securely bind the EAP method. Current EAP server
implementations do not retain this AAA SA after (phase 1b) to its child phase 2
security associations, the phase 2 Secure Association Protocol allows
the EAP conversation
completes, but future implementations could use this SA for
pre-emptive key distribution.

Contents:
o Name/identifier for this SA
o Identities peer and authenticator to mutually prove possession of the parties
o MSK and EMSK

3.4 AAA SA(s) (authenticator - backend auth. server)
AAA-Key. In order for the authenticator and backend authentication server to
authenticate each other, they need to store some information.

In case avoid confusion in the authenticator and backend authentication server are
colocated, and they communicate using local procedure calls or shared
memory, this SA need not necessarily contain any information.

3.4.1 Example: RADIUS

In RADIUS, case where shared secret authentication an EAP peer
has more than one AAA-Key (phase 1b) applicable to establishment of a
phase 2 security association, it is used, the client and
server store each other's IP address and necessary for the shared secret, which is
used secure
Association Protocol (phase 2) to calculate support key selection, so that the Response Authenticator [RFC2865] and
Message-Authenticator [RFC3579] values, and
appropriate phase 1b keying material can be utilized by both parties
in the Secure Association Protocol exchange.

For example, a peer might be pre-configured with policy indicating
the ciphersuite to encrypt some
attributes (such as be used in communicating with a given
authenticator. Within PPP, the AAA-Key [RFC2548]).

Where IPsec ciphersuite is used to protect RADIUS [RFC3579] and IKE negotiated within the
Encryption Control Protocol (ECP), after EAP authentication is used for
key management,
completed. Within [IEEE80211i], the AP ciphersuites are advertised
in the parties store information necessary to
authenticate Beacon and authorize the other party (e.g. certificates, trust
anchors Probe Responses, and names). The IKE are securely verified during a
4-way exchange results in IKE Phase 1 and
Phase 2 SAs containing information used to protect the conversation
(session keys, selected ciphersuite, etc.)

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3.4.2 Example: Diameter with TLS

When using Diameter protected by TLS, authentication has completed.

As part of the parties store information Secure Association Protocol (phase 2), it is necessary
to authenticate and authorize bind the other party (e.g.
certificates, trust anchors and names). The TLS handshake results Transient Session Keys (TSKs) to the keying material
provided in
a short-term TLS SA the AAA-Token. This ensures that contains information used the EAP peer and
authenticator are both clear about what key to protect use to provide mutual
proof of possession.

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

3.5 Unicast Secure Association EAP key hierarchy are named as follows:

EAP SA name
The unicast secure EAP security association SA exists is negotiated between the EAP peer and
authenticator. It includes:

the
EAP server, and is uniquely named as follows <EAP peer port identifier (Calling-Station-Id)
the NAS port identifier (Called-Station-Id)
the unicast Transient Session Keys (TSKs)
the unicast secure association name, EAP
server name, EAP Method Type, EAP peer nonce
the unicast secure association authenticator nonce nonce, EAP server nonce>.
Here the negotiated unicast capabilities EAP peer name and unicast ciphersuite.

During EAP server name are the phase 2a exchange, identifiers
securely exchanged within the EAP method. Since multiple EAP SAs
may exist between an EAP peer and EAP server, the EAP peer nonce
and authenticator
demonstrate mutual possession EAP server nonce allow EAP SAs to be differentiated. The
inclusion of the AAA-Key derived and transported Method Type in phase 1; securely negotiate the session capabilities (including
unicast ciphersuites), and derive fresh unicast transient session
keys. EAP SA name ensures that each
EAP method has a distinct EAP SA space.

AAA-Key Name
The AAA-Key SA (phase 1b) is therefore used to create named by the
unicast secure association concatenation of the EAP SA (phase 2a), name, "AAA-
Key" and in the process authenticator name, since the
phase 2a unicast secure association SA AAA-Key is bound to ports a
particular authenticator. For the purpose of identification, the
NAS-Identifier attribute is recommended. In order to ensure that
all parties can agree on the NAS name this requires the NAS to
advertise its name (typically using a media-specific mechanism,
such as the 802.11 Beacon/Probe Response)."

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4. Security considerations

4.1. Security Terminology

Cryptographic binding
The demonstration of the EAP peer to the EAP server that a single
entity has acted as the EAP peer and authenticator. However in order for all methods executed within a phase 2a security
association
tunnel method. Binding MAY also imply that the EAP server
demonstrates to be established, it is not necessary 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 phase 1a
exchange to be rerun each time. This enables
adversary has the EAP exchange to be
bypassed when fast handoff support is desired.

Since both peer and authenticator knowledge of all nonces are sent in cleartext as well
as all predictable counter values used in the creation 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 unicast secure association SA, secret state. In
other words, if the transient session keys (TSKs) are guaranteed to be fresh, even if the AAA-Key cryptographically separate, there is not. As a result
one
no shortcut to compute x from y or more unicast secure association SAs (phase 2a) may be derived y from a single AAA-Key SA (phase 1b). The phase 2a security
associations may utilize x, but the same security parameters (e.g. mode,
ciphersuite, etc.) or they may utilize different parameters.

A unicast secure association SA (phase 2a) may not persist longer
than work an
adversary must do to perform this computation is equivalent to
performing exhaustive search for the maximum lifetime of its parent AAA-Key SA (if known).
However, secret state value.

Key strength
If the deletion 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 parent
typical block cipher.

Mutual authentication
This refers to an EAP or AAA-Key SA does not
necessarily imply deletion of method in which, within an interlocked
exchange, the corresponding unicast secure
association SA. Similarly, authenticator authenticates the deletion of a unicast secure
association protocol SA does not imply peer and the deletion of peer
authenticates the parent
AAA-key SA or authenticator. Two independent one-way methods,
running in opposite directions do not provide mutual authentication
as defined here.

4.2. Threat Model

The EAP SA. Failure threat model is described in [RFC3748], Section 7.1. In
order to mutually prove possession of the
AAA-Key during address these threats, EAP relies on the unicast secure association protocol exchange 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].

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(phase 2a) need not be grounds 26 June 2004

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 removal RADIUS/EAP.

Given the existing documentation of a AAA-Key SA by both
parties; rate-limiting unicast secure association exchanges should
suffice EAP and AAA threat models and
responses, there is no need to prevent a brute force attack. 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 EAP peer attacker may be able try to negotiate multiple phase 2a SAs with a
single 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 be able attempt to maintain multiple phase
2a SAs with multiple authenticators, based perform downgrading attacks on a single EAP SA derived the
ciphersuite negotiation within the Secure Association Protocol in phase 1a. For example, during
order to ensure that a re-key of the secure association
protocol SA, it weaker ciphersuite is possible for two phase 2a SAs used to exist during the
period between when protect data.

Depending on the new phase 2a SA parameters (such as lower layer, these attacks may be carried out
without requiring physical proximity.

In order to address these threats, [Housley56] describes the TSKs)
are calculated and when they
mandatory system security properties:

Algorithm independence
Wherever cryptographic algorithms are installed. Except where explicitly
specified by chosen, the semantics of the unicast secure association
protocol, it should not algorithms must
be assumed that the installation negotiable, in order to provide resilient against compromise of
a new
phase 2a SA necessarily implies deletion particular algorithm. Algorithm independence must be
demonstrated within all aspects of the old phase 2a SA.

On some media (e.g. 802.11) a port on an EAP peer may only establish
phase 2a and 2b SAs with a single port of an authenticator system, including within a
given Local Area Network (LAN). This implies that the successful
negotiation of phase 2a and/or 2b SAs between an EAP peer port
EAP, AAA and a
new authentiator port within a given LAN implies the deletion Secure Association Protocol. However, for
interoperability, at least one suite of
existing phase 2a and 2b SAs with authenticators offering access algorithms MUST be
implemented.

Strong, fresh session keys
Session keys must be demonstrated to
that Local Area Network (LAN). However, since a given IEEE 802.11
SSID may be comprised of multiple LANs, this does not imply an
implicit binding of phase 2a strong and 2b SAs to an SSID.

3.6 Multicast fresh in all
circumstances, while at the same time retaining algorithm
independence.

Replay protection
All protocol exchanges must be replay protected. This includes

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exchanges within EAP, AAA, and the Secure Association SA Protocol.

Authentication
All parties need to be authenticated. The multicast secure association SA includes: confidentiality of the multicast Transient
authenticator must be maintained. No plaintext passwords are
allowed.

Authorization
EAP peer and authenticator authorization must be performed.

Session Keys
the direction vector (for a uni-directional SA) keys
Confidentiality of session keys must be maintained.

Ciphersuite negotiation
The selection of the negotiated multicast capabilities and multicast "best" ciphersuite

It is possible for more than one multicast secure association SA to must be derived from securely confirmed.

Unique naming
Session keys must be uniquely named.

Domino effect
Compromise of a single unicast secure association SA. However, a
multicast secure association SA is authenticator cannot compromise any other
part of the system, including session keys and long-term secrets.

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

4.3. Security Analysis

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

EAP SA 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 a
single AAA-Key SA.

During a re-key auth. server

The peer and EAP server communicate using EAP [RFC3748]. The

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security properties of this communication are largely determined by
the multicast secure association protocol SA, it
is possible 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
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 two phase 2b SAs to exist during the period mutual authentication
between
when the new phase 2b SA parameters (such as the multicast TSKs) are
calculated EAP peer and when they are installed. Except where explicitly
specified by the semantics of the multicast secure association
protocol, it should not EAP Server.

Ciphersuite independence is also required:

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

In terms of a new
phase 2b SA necessarily implies deletion key strength and freshness, [RFC3748] Section 10 says:

EAP methods SHOULD ensure the freshness of the old phase 2b SA.

A multicast secure association SA (phase 2b) MSK and EMSK even
in cases where one party may not persist longer
than have a high quality random number
generator.... In order to preserve algorithm independence, EAP
methods deriving keys SHOULD support (and document) the maximum lifetime protected
negotiation of its parent AAA-Key or unicast secure

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association SA. However,
conversation between the deletion 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 parent EAP, AAA-Key AAA protocol such as RADIUS [RFC3579] or
unicast secure association SA does not necessarily imply deletion of
the corresponding multicast secure association SA. Diameter [I-D.ietf-aaa-
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 example, a
unicast secure association SA may RADIUS, [RFC3579] Section 4.2
recommends that RADIUS be rekeyed without implying a rekey
of the multicast secure association SA.

Similarly, the deletion of protected by IPsec ESP with a multicast secure association protocol SA
does not imply the deletion of non-null
transform, and where IPsec is implemented replay protection must be
supported.

The peer and authenticator communicate using the parent EAP, AAA-Key or unicast
secure association SA. Failure to mutually prove possession of Secure Association
Protocol.

As noted in the
AAA-Key during figure, each party in the unicast secure association protocol exchange
(phase 2a) need not be grounds for removal mutually
authenticates with each of the AAA-Key, unicast
secure association other parties, and multicast secure association SAs;
rate-limiting unicast secure association exchanges should suffice to
prevent derives a brute force attack.

3.7 Key Naming

In order to support unique
key. All parties in the correct processing of phase 2 security
associations, diagram have access to the secure association (phase 2) protocol supports AAA-Key.

The EAP peer and backend authentication server mutually authenticate

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via the
naming of phase 2 security associations EAP method, and associated transient
session keys, so that derive the correct set of transient session keys can
be identified for processing a given packet. Explicit creation TEKs and
deletion operations EMSK which are also typically supported so that
establishment and re-establishment known only
to them. The TEKs are used to protect some or all of transient session keys can be
synchronized the EAP
conversation between the parties.

In order peer and authenticator, so as to securely bind guard
against modification or insertion of EAP packets by an attacker. The
degree of protection afforded by the AAA SA (phase 1b) to its child phase 2
security associations, TEKs is determined by the phase 2 secure association protocol allows EAP
method; some methods may protect the entire EAP peer and authenticator to mutually prove possession packet, including the
EAP header, while other methods may only protect the contents of the
AAA-Key. In order to avoid confusion
Type-Data field, defined in [RFC3748].

Since EAP is spoken only between the case where an EAP peer
has more than one AAA-Key (phase 1b) applicable to establishment of and server, if a
phase 2 security association, it
backend authentication server is necessary for present then the secure
association protocol (phase 2) to support key selection, so that EAP conversation
does not provide mutual authentication between the
appropriate phase 1b keying material can be utilized by both parties
in peer and
authenticator, only between the secure association protocol exchange.

For example, EAP peer and EAP server (backend
authentication server). As a result, mutual authentication between
the peer might be pre-configured with policy indicating and authenticator only occurs where a Secure Association
protocol is used, such the ciphersuite to be used unicast and group key derivation handshake
supported in communicating with [IEEE80211i]. This means that absent use of a given
authenticator. Within PPP, secure
Association Protocol, from the ciphersuite is negotiated within point of view of the
Encryption Control Protocol (ECP), after peer, EAP mutual
authentication only proves that the authenticator is
completed. Within [IEEE80211i], trusted by the AP ciphersuites are advertised
in
backend authentication server; the Beacon 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 Probe Responses, replay
protection, authentication and are securely verified during a
4-way exchange after EAP confidentiality. The AAA-Key is
distributed by the backend authentication has completed.

As server to the authenticator
over this channel, bound to attributes constraining its usage, as
part of the secure association protocol (phase 2), it is necessary AAA-Token. The binding of attributes to bind the Transient Session Keys (TSKs) to 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
provided has not been replayed, or
mis-directed in the AAA-Token. This ensures that some way.

The security properties of the EAP peer and
authenticator exchange are both clear about what key to use to provide mutual

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proof dependent on each leg
of possession. Keys within the EAP key hierarchy are named as
follows:

EAP SA name
The EAP security association is negotiated between triangle: the selected EAP peer method, AAA protocol and EAP server, 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 uniquely named
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 follows <EAP peer name,
EAP server name, EAP Method Type, EAP peer nonce, EAP server
nonce>. Here to avoid compromise of the
AAA-Token. This can be avoided by use of re-direct as defined in
[RFC3588].

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When EAP server name are is used for authentication on PPP or wired IEEE 802
networks, it is typically assumed that the
identifiers securely exchanged within link is physically secure,
so that an attacker cannot gain access to the link, or insert a rogue
device. EAP method. Since
multiple EAP SAs may exist between an methods defined in [RFC3748] reflect this usage model.
These include EAP peer MD5, as well as One-Time Password (OTP) and EAP server, the Generic
Token Card. These methods support one-way authentication (from EAP
peer nonce and EAP server nonce allow EAP SAs to be
differentiated. The inclusion of authenticator) but not mutual authentication or key
derivation. As a result, these methods do not bind the Method Type in initial
authentication and subsequent data traffic, even when the EAP SA
name ensures that each EAP method has the
ciphersuite used to protect data supports per-packet authentication
and integrity protection. As a distinct EAP SA space.

MK Name
The result, EAP Master Key, if supported 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 EAP method, is named 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
concatenation threat of rogue devices,
and provide keying material to bind the initial authentication to
subsequent data traffic.

If the selected EAP SA name and a method-specific session-id.

AAA-Key Name
The AAA-Key is named by method does not support mutual authentication,
then the concatenation of peer will be vulnerable to attack by rogue authenticators
and backend authentication servers. If the EAP SA name,
"AAA-Key" 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 authenticator name, since initial EAP
authentication and subsequent data traffic, leaving the AAA-Key is bound session
vulnerable to a particular authenticator. For hijack.

If the purpose backend authentication server does not protect against
authenticator masquerade, or provide the proper binding of identification, the NAS-Identifier attribute is recommended. In order AAA-
Key to ensure
that all parties can agree on the NAS name this requires session within the NAS 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 advertise its name (typically using a media-specific mechanism,
such as the 802.11 Beacon/Probe Response)."

4. Threat Model

4.1 Security Assumptions

Figure 5 illustrates the relationship between network. If the peer, authenticator
and backend authentication server. As noted in AAA-Token is provided to an
untrusted AAA intermediary, then that intermediary may be able to
modify the figure, each party
in AAA-Key, or the exchange mutually authenticates attributes associated with each of the other
parties, and derives a unique key. All parties it, as
described in [RFC2607].

If the Secure Association Protocol does not provide mutual proof of
possession of the diagram AAA-Key material, then the peer will not have
access
assurance that it is connected to the AAA-Key. 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

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

Figure 5: Three-party EAP key distribution

The EAP peer and 26 June 2004

authenticators receive AAA-Keys from the backend authentication server mutually authenticate
via the EAP method, and derive
server, such as where fast handoff is supported. If the MK, TEKs TSK
derivation does not provide for protected ciphersuite and EMSK which
capabilities negotiation, then downgrade attacks are known
only possible.

4.4. Man-in-the-middle Attacks

As described in [I-D.puthenkulam-eap-binding], EAP method sequences
and compound authentication mechanisms may be subject to them. The TEKs man-in-the-
middle attacks. When such attacks are used to protect some or all of successfully carried out, the EAP
conversation
attacker acts as an intermediary between the peer a victim and a legitimate
authenticator. This allows the attacker to authenticate successfully
to the authenticator, so as well 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 obtain access to the contents network.

In order to prevent these attacks, [I-D.puthenkulam-eap-binding]
recommends derivation of the
Type-Data field, defined in [I-D.ietf-eap-rfc2284bis].

Since EAP is spoken only between a compound key by which the EAP peer and server, if a
backend authentication
server is present then can prove that they have participated in the entire EAP conversation
does not provide mutual authentication between
exchange. Since the peer and compound key must not be known to an attacker
posing as an authenticator, only between the EAP peer and yet must be derived from quantities
that are exported by EAP server (backend
authentication server). As a result, mutual authentication between methods, it may be desirable to derive the peer and authenticator only occurs where
compound key from a secure association
protocol is used, such portion of the unicast and group EMSK. In order to provide proper
key derivation handshake
supported in [IEEE80211i]. This means hygiene, it is recommended that absent use of a secure
association protocol, the compound key used for man-in-
the-middle protection be cryptographically separate from other keys
derived from the point EMSK, such as fast handoff keys, discussed in
Appendix E.

4.5. Denial of view Service Attacks

The caching of the peer, security associations may result in vulnerability to
denial of service attacks. Since an EAP mutual
authentication only proves that the authenticator is trusted by the
backend authentication server; the identity peer may derive multiple EAP
SAs with a given EAP server, and creation of the authenticator is a new EAP SA does not confirmed.

Utilizing the AAA protocol,
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 authenticator and backend
authentication number of cached EAP SAs (Phase 1a) corresponding to an EAP peer.
For example, an EAP server mutually authenticate and derive session keys
known may choose to only retain a few EAP SAs
for each peer. This prevents a rogue peer from denying access to them, used
other peers.

Similarly, an authenticator may have multiple AAA-Key SAs
corresponding to provide per-packet integrity and replay
protection, authentication and confidentiality. The MSK is
distributed by the backend authentication server a given EAP peer; to the conserve resources an
authenticator
over this channel, bound may choose to attributes constraining its usage, as
part of limit the AAA-Token. The binding number of attributes to cached AAA-Key (Phase
1 b) SAs for each peer.

Depending on the MSK within media, creation of 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, new unicast Secure Association
SA may or mis-directed in some may not imply deletion of a previous unicast secure

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way.

The security properties of 26 June 2004

association SA. Where there is no implied deletion, the EAP exchange are dependent on
authenticator may choose to limit Phase 2 (unicast and multicast)
Secure Association SAs for each leg
of peer.

4.6. Impersonation

Both the triangle: 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 selected EAP method,
AAA protocol client) and the secure
association protocol.

Assuming that backend authentication server (known as the AAA protocol provides protection against rogue
authenticators forging their identity, then
server), the AAA-Token can be
assumed to be sent security mechanisms vary according 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, protocol.

In RADIUS, the AAA-Token must
not be provided to shared secret used for authentication is determined by
the intermediary so as to avoid compromise source address of the
AAA-Token. This can be avoided by use of re-direct as defined RADIUS packet. As noted in
[RFC3588].

When EAP is used for authentication on PPP or wired IEEE 802
networks, [RFC3579]
Section 4.3.7, it is typically assumed highly desirable that the link is physically secure, source address be
checked against one or more NAS identification attributes so that an attacker cannot gain access as to
detect and prevent impersonation attacks.

When RADIUS requests are forwarded by a proxy, the link, NAS-IP-Address or insert a rogue
device. EAP methods defined in [I-D.ietf-eap-rfc2284bis] 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 peer
NAS-IPv6-Address attributes may not correspond to authenticator) but the source address.
Since the NAS-Identifier attribute need not mutual
authentication or key derivation. As a result, these methods do contain an FQDN, it also
may not
bind correspond to the initial authentication and subsequent data traffic, source address, even
when indirectly. [RFC2865]
Section 3 states:

A RADIUS server MUST use the source IP address of the ciphersuite used RADIUS
UDP packet to decide which shared secret to protect data supports per-packet
authentication and integrity protection. As use, so that
RADIUS requests can be proxied.

This implies that it is possible for 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 authenticator to mount, since any attacker forge
NAS-IP-Address, NAS-IPv6-Address or NAS-Identifier attributes within range
a RADIUS Access-Request in order to impersonate another
authenticator. Among other things, this can access result in messages (and
MSKs) being sent to the
wireless medium, wrong authenticator. Since the rogue
authenticator is authenticated by the RADIUS proxy 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. server purely
based on the source address, other mechanisms are required to detect
the forgery. In addition, mutual authentication and key
derivation, provided by methods it is possible for attributes such as EAP-TLS [RFC2716] are
required [IEEE80211i], so as to address the threat of rogue devices,
Called-Station-Id and provide keying material to bind the initial authentication Calling-Station-Id to
subsequent data traffic.

If the selected EAP method does not support mutual authentication,
then the peer will be vulnerable to attack forged as well.

As recommended in [RFC3579], this vulnerability can be mitigated by rogue authenticators
and backend authentication servers. If
having RADIUS proxies check authenticator identification attributes
against the EAP method does not derive
keys, then TSKs will not be available for use with a negotiated
ciphersuite, source address.

To allow verification of session parameters such as the Called-
Station- Id and there will Calling-Station-Id, these can be no binding between sent by the initial EAP
authentication and subsequent data traffic, leaving peer
to the session server, protected by the TEKs. The RADIUS server can then
check the parameters sent by the EAP peer against those claimed by

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the authenticator. If a discrepancy is found, an error can be
logged.

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

If this attack as RADIUS, if not more so. To address
this vulnerability, it is necessary to allow the backend
authentication server does not protect against
authenticator masquerade, or provide the proper binding of the
AAA-Key to communicate with the session within authenticator directly,
such as via the AAA-Token, then one redirect functionality supported in [RFC3588].

4.7. Channel binding

It is possible for a compromised or more
AAA-Keys may be sent to an unauthorized party, and an attacker may be
able poorly implemented EAP
authenticator to gain access communicate incorrect information to the network. If the AAA-Token is provided to
an untrusted AAA intermediary, then that intermediary EAP peer
and/or server. This may be able enable an authenticator to
modify the AAA-Key, impersonate
another authenticator or the attributes associated with it, communicate incorrect information via out-
of-band mechanisms (such as
described via a AAA or lower layer protocol).

Where EAP is used in [RFC2607].

If the secure association protocol does not provide mutual proof of
possession of the AAA-Key material, then pass-through mode, the EAP peer will typically does
not have
assurance that it is connected to verify the correct identity of the pass-through authenticator, it only
verifies that the pass-through 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 trusted by the TSK
derivation does not provide for protected ciphersuite and
capabilities negotiation, then downgrade attacks are possible.

4.2 Security Requirements EAP
server. This section describes the creates a potential security requirements for vulnerability, described in
Section 7.15 of [RFC2284bis].

Section 4.3.7 of [RFC3579] describes how an EAP methods, pass-through
authenticator acting as a AAA
protocols, secure association protocols and Ciphersuites. These
requirements MUST client can be met detected if it attempts
to impersonate another authenticator (such by specifications requesting publication as
an RFC. Based on these requirements, sending incorrect NAS-
Identifier [RFC2865], NAS-IP-Address [RFC2865] or NAS-IPv6-Address
[RFC3162] attributes via the security properties of EAP
exchanges are analyzed.

4.2.1 EAP method requirements

It AAA protocol). However, 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
subsequently negotiated ciphersuite, an EAP method supporting key
derivation MUST export pass-through authenticator acting as 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 AAA client to provide for mutual
authentication between
correct information to the EAP peer and AAA server while communicating misleading
information to 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 peer via a lower layer protocol.

For example, it is possible for a AAA-Key
subsequently used compromised authenticator to derive Transient Session Keys (TSKs) for use
utilize another authenticator's Called-Station-Id or NAS-Identifier
in communicating with the selected ciphersuite. Each ciphersuite is responsible EAP peer via a lower layer protocol, or for
specifying how
a pass-through authenticator acting as a AAA client to provide an
incorrect peer Calling-Station-Id [RFC2865][RFC3580] to derive the TSKs from the AAA-Key.

The AAA-Key is derived from AAA
server via the keying material exported AAA protocol.

As noted in Section 7.15 of [RFC3748] this vulnerability can be
addressed by the use of EAP
method (MSK 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 EMSK). This derivation occurs on the AAA server. In NAS-IPv6-Address [RFC3162].

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many existing protocols that use EAP, the AAA-Key and MSK are
equivalent, but more complicated mechanisms are possible (see
Appendix E for details).

EAP methods SHOULD ensure the freshness of the MSK and EMSK even in
cases where one party may not have 26 June 2004

Using such a high quality random number
generator. A RECOMMENDED method protected exchange, it is for each party possible to provide a nonce
of at least 128 bits, used in match the derivation of channel
properties provided by the MSK and EMSK.

EAP methods export authenticator via out-of-band mechanisms
against those exchanged within the MSK and EMSK and not Transient Session Keys so
as to allow EAP methods method.

4.8. Key Strength

In order to be ciphersuite and media independent.
Keying material exported by guard against brute force attacks, EAP methods MUST deriving
keys need to be independent capable of the
ciphersuite negotiated generating keys with an appropriate
effective symmetric key strength. In order to protect data.

Depending on the lower layer, EAP methods may run before or after
ciphersuite negotiation, so ensure that the selected ciphersuite may key
generation is not be
known to the EAP method. By providing keying material usable with
any ciphersuite, weakest link, it is necessary for EAP methods can used with
utilizing public key cryptography to choose a wide range of
ciphersuites and media.

It is RECOMMENDED public key that methods providing integrity protection of EAP
packets include coverage of all has a
cryptographic strength meeting the EAP header fields, including symmetric key strength
requirement.

As noted in Section 5 of [RFC3766], this results in the
Code, Identifier, Length, Type following
required RSA or DH module and Type-Data fields.

In order to preserve algorithm independence, EAP methods deriving
keys SHOULD support (and document) the protected negotiation 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

4.9. Key Wrap

As described in [RFC3579], Section 4.3, known problems exist in the
ciphersuite used to protect
key wrap specified in [RFC2548]. Where the same RADIUS shared secret
is used by a PAP authenticator and an EAP conversation between authenticator, there is a
vulnerability to known plaintext attack. Since RADIUS uses the peer and
server. This
shared secret for multiple purposes, including per-packet
authentication, attribute hiding, considerable information is distinct from exposed
about the ciphersuite negotiated between shared secret with each packet. This exposes the
peer and authenticator, used shared
secret to protect data.

The strength of Transient Session Keys (TSKs) dictionary attacks. MD5 is used both 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 compute the TSKs may be subject to brute force
attack. In order to enable deployments requiring strong keys, EAP
methods supporting key derivation SHOULD be capable of generating an
MSK RADIUS
Response Authenticator and EMSK, each with an effective key strength of at least 128
bits.

Methods supporting key derivation MUST demonstrate cryptographic
separation between the MSK Message-Authenticator attribute, and EMSK branches of the EAP key
hierarchy. Without violating a fundamental cryptographic assumption
(such as
some concerns exist relating to the non-invertibility security of a one-way function) an attacker
recovering the MSK or EMSK MUST NOT be able to recover this hash
[MD5Attack].

As discussed in [RFC3579], Section 4.3, the other
quantity with a level security vulnerabilities
of effort less than brute force.

Non-overlapping substrings RADIUS are extensive, and therefore development of an alternative
key wrap technique based on the MSK MUST be cryptographically
separate from each other. That is, knowledge of one substring MUST RADIUS shared secret would not
substantially improve security. As a result, [RFC3759], Section 4.2

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NOT help in recovering some other substring without breaking some
hard cryptographic assumption. This 26 June 2004

recommends running RADIUS over IPsec. The same approach is required because some
existing ciphersuites form TSKs taken in
Diameter EAP [I-D.ietf-aaa-eap], which defines cleartext key
attributes, to be protected by simply splitting IPsec or TLS.

Where an untrusted AAA intermediary is present (such as a RADIUS
proxy or a Diameter agent), and data object security is not used, the
AAA-Key to
pieces of appropriate length. Likewise, non-overlapping substrings may be recovered by an attacker in control of the EMSK MUST be cryptographically separate from each other, and
from substrings untrusted
intermediary. Possession of the MSK.

The EMSK MUST remain on AAA-Key enables decryption of data
traffic sent between the EAP peer and EAP server a specific authenticator; however
where it key separation is
derived; it MUST NOT be transported to, or shared with, additional
parties, or used to derive any other keys.

Since EAP implemented, compromise of the AAA-Key does
not provide for explicit key lifetime negotiation, EAP
peers, authenticators and authentication servers MUST be prepared for
situations in which one enable an attacker to impersonate the peer to another
authenticator, since that requires possession of the parties discards key state MK or EMSK,
which
remains valid on another party.

The development and validation are not transported by the AAA protocol. This vulnerability
may be mitigated by implementation of key derivation algorithms is
difficult, and as a result EAP methods SHOULD reuse well established
and analyzed mechanisms for key derivation (such redirect functionality, as those specified
provided 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.

4.2.2 AAA Protocol [RFC3588].

5. Security Requirements

AAA protocols suitable for use in transporting EAP MUST provide

This section summarizes the
following facilities:

Security services
AAA protocols used for transport of security requirements that must be met by
EAP keying material MUST
implement and SHOULD use per-packet integrity and authentication,
replay protection methods, AAA protocols, Secure Association Protocols and confidentiality.
Ciphersuites in order to address the security threats described in
this document. These requirements are MUST be met by Diameter EAP [I-D.ietf-aaa-eap], as well specifications
requesting publication as RADIUS over IPsec
[RFC3579].

Session Keys
AAA protocols used for transport an RFC. Each requirement provides a
pointer to the sections of this document describing the threat that
it mitigates.

5.1. EAP keying material MUST
implement Method Requirements

It is possible for the peer and SHOULD use dynamic key management in order EAP server to mutually authenticate
and derive
fresh session keys, as keys. In order to provide keying material for use in Diameter a
subsequently negotiated ciphersuite, an EAP [I-D.ietf-aaa-eap] and
RADIUS over IPsec [RFC3579], rather than using method supporting key
derivation MUST export a static key, as
originally defined in RADIUS [RFC2865].

Mutual authentication
AAA protocols used for transport Master Session Key (MSK) of at least 64
octets, and an Extended Master Session Key (EMSK) of at least 64
octets. EAP keying material Methods deriving keys MUST provide for mutual
authentication between the authenticator 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
backend authentication server. These requirements MSK are met by
Diameter EAP [I-D.ietf-aaa-eap] as well as by RADIUS EAP
[RFC3579].
equivalent, but more complicated mechanisms are possible (see
Appendix E for details).

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AAA protocols used for transport of 26 June 2004

EAP keying material methods SHOULD
provide protection against rogue authenticators masquerading as
other authenticators. This can be accomplished, for example, by
requiring that AAA agents check ensure the source address freshness of packets
against the origin attributes (Origin-Host AVP MSK and EMSK even in Diameter,
NAS-IP-Address, NAS-IPv6-Address, NAS-Identifier
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 RADIUS). For
details, see Section 4.3.7 the derivation of [RFC3579].

Key transport
Since the MSK and EMSK.

EAP methods do not export the MSK and EMSK and not Transient Session Keys (TSKs) in
order so
as to maintain media allow EAP methods to be ciphersuite and media independent.
Keying material exported by EAP methods MUST be independent of the
ciphersuite independence, negotiated to protect data.

Depending on the AAA
server MUST NOT transport TSKs from lower layer, EAP methods may run before or after
ciphersuite negotiation, so that the backend authentication
server selected ciphersuite may not be
known to authenticator.

Key transport specification 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 enable backend authentication servers to provide
keying material to the authenticator in a well defined format, AAA
protocols suitable for use with preserve algorithm independence, EAP MUST define methods deriving
keys SHOULD support (and document) the format and
wrapping protected negotiation of the AAA-Token.

EMSK transport
Since the EMSK is a secret known only
ciphersuite used to protect the backend
authentication server and peer, the AAA-Token MUST NOT transport EAP conversation between the EMSK peer and
server. This is distinct from the backend authentication server to the
authenticator.

AAA-Token protection
To ensure against compromise, ciphersuite negotiated between the AAA-Token MUST be integrity
protected, authenticated, replay protected
peer and encrypted in
transit, using well-established cryptographic algorithms. authenticator, used to protect data.

The strength of Transient 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 (TSKs) used to ensure against confusion between protect data is
ultimately dependent on the appropriate strength of keys generated by the EAP
method. If an EAP method cannot produce keying material to be used in a given secure association protocol
exchange, of
sufficient strength, then the AAA-Token TSKs may be subject to brute force
attack. In order to enable deployments requiring strong keys, EAP
methods supporting key derivation SHOULD include explicit be capable of generating an
MSK and EMSK, each with an effective key names strength of at least 128
bits.

Methods supporting key derivation MUST demonstrate cryptographic
separation between the MSK and
context appropriate for informing EMSK branches of the authenticator how EAP key
hierarchy. Without violating a fundamental cryptographic assumption
(such as the keying
material is to be used.

Key Compromise
Where untrusted intermediaries are present, non-invertibility of a one-way function) an attacker
recovering the AAA-Token SHOULD MSK or EMSK MUST NOT be provided able to recover the intermediaries. In Diameter, handling other
quantity with a level of
keys by intermediaries can effort less than brute force.

Non-overlapping substrings of the MSK MUST be avoided using Redirect functionality cryptographically
separate from each other. That is, knowledge of one substring MUST
NOT help in recovering some other 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

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[RFC3588].

4.2.3 Secure Association Protocol Requirements

The Secure Association Protocol supports the following:

Mutual proof of possession
The peer and authenticator MUST each demonstrate possession 26 June 2004

of the
keying material transported between the AAA server and
authenticator (AAA-Key).

Key Naming
The Secure Association Protocol EMSK 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 cryptographically separate from each other, and Deletion
In order to support the correct processing
from substrings of phase 2 security
associations, the secure association (phase 2) protocol MSK.

The EMSK MUST
support remain on the naming of phase 2 security associations EAP peer and associated
transient session keys, so that the correct set of transient
session keys can EAP server where it is
derived; it MUST NOT be identified transported to, or shared with, additional
parties, or used to derive any other keys.

Since EAP does not provide for processing a given packet. The
phase 2 secure association protocol also MUST support transient
session explicit key activation and SHOULD support deletion, so that
establishment lifetime negotiation, EAP
peers, authenticators and re-establishment of transient session keys can authentication servers MUST be synchronized between prepared for
situations in which one of the parties.

Integrity and Replay Protection parties discards key state which
remains valid on another party.

The Secure Association Protocol MUST support integrity development and replay
protection validation of all messages.

Direct operation
Since the phase 2 secure association protocol key derivation algorithms is concerned with
the establishment of security associations between the
difficult, and as a result EAP peer methods SHOULD reuse well established
and authenticator, including the analyzed mechanisms for key derivation of transient session
keys, only (such as those parties have "a need 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.

5.1.1. Requirements for EAP methods

In order for an EAP method to know" meet the transient
session keys. guidelines for EMSK usage it
must meet the following requirements:

o It must specify how to derive the EMSK

o The secure association protocol key material used for the EMSK MUST operate
directly between be
computationally independent of the peer and authenticator, MSK and TEKs.

o The EMSK MUST NOT be
passed-through used for any other purpose than the key
derivation described in this document.

o The EMSK MUST be secret and not known to someone observing
the backend authentication server, or include
additional parties.

Derivation of transient session keys
The secure association mechanism protocol negotiation exchange.

o The EMSK MUST support
derivation of unicast and multicast transient session be maintained within the EAP server.
Only keys
suitable (AMSKs) derived according to this specification
may be exported from the EAP server.

o The EMSK MUST be unique for use with each session.

o The EAP mechanism SHOULD provide a way of naming the negotiated ciphersuite. 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.

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TSK freshness 26 June 2004

5.1.2. Requirements for EAP applications

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

o The secure association (phase 2) protocol application MAY use the MSK transmitted to the NAS in any
way it chooses. This is required for backward compatibility. New
applications following this specification SHOULD NOT use the
MSK. If more than one application uses the MSK, then the
cryptographic separation is not achieved. Implementations SHOULD
prevent such combinations.

o The application MUST support NOT use the EMSK in any other way except to
derive Application Master Session Keys (AMSK) using the key
derivation specified in this document. It MUST NOT
use the EMSK directly for cryptographic protection of fresh unicast and multicast transient session keys,
even when data.

o Applications MUST define distinct key labels, application
specific data, length of derived key material used in the key
derivation described in section 2.4.3.

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

5.2. 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 provided MUST
implement and SHOULD use per-packet integrity and authentication,
replay protection and confidentiality. These requirements are met
by the Diameter EAP [I-D.ietf-aaa-eap], as well as RADIUS over IPsec
[RFC3579].

Session Keys
AAA 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 protocols used for the derivation transport of unicast EAP keying material MUST
implement and multicast keys in each
direction, so as not to require two separate phase 2 exchanges SHOULD use dynamic key management 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 derive
fresh session keys, as the
security association identifier (SAID) in Diameter EAP [I-D.ietf-aaa-eap] and ciphersuites. It also
includes confirmation
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 capabilities discovered during the
discovery phase (phase 0), so authenticator and
backend authentication server. These requirements are met by
Diameter EAP [I-D.ietf-aaa-eap] as to ensure that the announced
capabilities have not been forged.

4.2.4 Ciphersuite Requirements

Ciphersuites suitable well as by RADIUS EAP [RFC3579].

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

Key transport
Since EAP methods do not export Transient Session Keys (TSKs) in
order to maintain media and ciphersuite independence, the AAA
server MUST provide NOT transport TSKs from the
following facilities:

TSK derivation backend authentication
server to authenticator.

Key transport specification
In order to allow a ciphersuite enable backend authentication servers to be usable within the EAP provide keying
framework,
material to the authenticator in a specification MUST be provided describing how
transient session keys well defined format, AAA
protocols 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 define the EAP method. However, algorithms for
deriving TEKs MAY be specific format and
wrapping of the AAA-Token.

EMSK transport
Since the EMSK is a secret known only to the EAP method.

Cryptographic separation
The TSKs derived from backend authentication
server and peer, the AAA-Key MUST be cryptographically
separate from each other. Similarly, TEKs AAA-Token MUST be
cryptographically separate from each other. In addition, NOT transport the TSKs
MUST be cryptographically separate EMSK from the TEKs.

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5. IANA Considerations

This specification does not create any new registries, or define any
new EAP codes or types.

6. Security Considerations

6.1 Key Strength

In order the
backend authentication server to guard the authenticator.

AAA-Token protection
To ensure against brute force attacks, EAP methods deriving
keys need to compromise, the AAA-Token MUST be capable of generating keys integrity
protected, authenticated, replay protected and encrypted in
transit, using well-established cryptographic algorithms.

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

Key naming
In order to ensure that key
generation is not against confusion between the weakest link, it is necessary for EAP methods
utilizing public key cryptography appropriate keying
material to choose a public key that has a
cryptographic strength meeting the symmetric key strength
requirement.

As noted in Section 5 of [I-D.orman-public-key-lengths], this results
in the following required RSA or DH module and DSA subgroup size be used in
bits, for a given level of attack resistance in bits:

6.2 Key Wrap

As described in [RFC3579], Section 4.3, known problems exist in Secure Association Protocol
exchange, the AAA-Token SHOULD include explicit key wrap specified in [RFC2548]. Where the same RADIUS shared secret
is used by a PAP authenticator names 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
context appropriate for informing the shared
secret to dictionary attacks. MD5 authenticator how the keying
material is used both to compute the RADIUS
Response Authenticator and be used.

Key Compromise
Where untrusted intermediaries are present, the Message-Authenticator attribute, and
some concerns exist relating AAA-Token SHOULD
NOT be provided to the security intermediaries. In Diameter, handling of this hash
[MD5Attack]. As discussed in [RFC3579], Section 4.2, these and other
RADIUS vulnerabilities may be addressed
keys by running RADIUS over IPsec. intermediaries can be avoided using Redirect functionality
[RFC3588].

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Where an untrusted AAA intermediary is present (such as a RADIUS
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 26 June 2004

5.3. Secure Association Protocol Requirements

The Secure Association Protocol supports the following:

Entity Naming
The peer and authenticator SHOULD identify themselves in a specific authenticator; however
where key separation manner
that is implemented, compromise independent of the AAA-Key does
not enable an attacker to impersonate the their attached ports.

Mutual proof of possession
The peer to another
authenticator, since that requires and authenticator MUST each demonstrate possession of the MK or EMSK,
which are not
keying material transported by between the AAA protocol. This vulnerability
may be mitigated by implementation of redirect functionality, as
provided in[RFC3588].

6.3 Man-in-the-middle Attacks

As described in [I-D.puthenkulam-eap-binding], EAP method sequences
and compound backend 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
server and a legitimate authenticator. This allows authenticator (AAA-Key).

Key Naming
The Secure Association Protocol MUST explicitly name the attacker to
authenticate successfully to keys used
in the authenticator, as well proof of possession exchange, so as to obtain
access to the network.

In order to prevent these attacks, [I-D.puthenkulam-eap-binding]
recommends derivation confusion
when more than one set of a compound key by which keying material could potentially be used
as the EAP peer and
server can prove that they have participated in basis for the entire EAP exchange. Since the compound key must not be known to an attacker
posing as an authenticator,

Creation and yet must be derived from quantities
that are exported by EAP methods, it may be desirable Deletion
In order to derive support the
compound key from a portion correct processing of phase 2 security
associations, the EMSK. In order to provide proper
key hygiene, it is recommended Secure Association (phase 2) protocol MUST
support the naming of phase 2 security associations and associated
transient session keys, so that the compound key used for
man-in-the-middle protection correct set of transient
session keys can be cryptographically separate from other 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 derived from the EMSK, such as fast handoff keys, discussed in
Appendix E.

6.4 Impersonation

Both can be
synchronized between the RADIUS parties.

Integrity and Diameter protocols are potentially vulnerable to
impersonation by a rogue authenticator.

When RADIUS requests are forwarded by a proxy, Replay Protection
The Secure Association Protocol MUST support integrity and replay
protection of all messages.

Direct operation
Since the NAS-IP-Address or
NAS-IPv6-Address attributes may not correspond to phase 2 Secure Association Protocol is concerned with the source address.
Since
establishment of security associations between the NAS-Identifier attribute EAP peer and
authenticator, including the derivation of transient session keys,
only those parties have "a need not contain an FQDN, it also
may not correspond to know" the source address, even indirectly. [RFC2865]
Section 3 states:

A RADIUS server transient session
keys. The Secure Association Protocol MUST use operate directly between
the source IP address 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 RADIUS
UDP packet to decide which shared secret to use, so that
RADIUS requests can be proxied. negotiated ciphersuite.

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

Bi-directional operation
While some ciphersuites only require a rogue authenticator single set of transient
session keys to forge
NAS-IP-Address, NAS-IPv6-Address or NAS-Identifier attributes within protect traffic in both directions, other
ciphersuites require a RADIUS Access-Request unique set of transient session keys in order 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 impersonate another
authenticator. Among other things, this can result require two separate phase 2 exchanges in messages (and
MSKs) being sent 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 wrong authenticator. Since
security association identifier (SAID) and ciphersuites, as well as
negotiation of the rogue
authenticator is authenticated by lifetime of the RADIUS proxy or server purely
based on TSKs, AAA-Key and exported EAP
keys. Secure capabilities negotiation also includes confirmation
of the source address, other mechanisms are required to detect capabilities discovered during the forgery. In addition, it is possible for attributes such discovery phase (phase
0), so 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 ensure that the source address.

To allow verification announced capabilities have not been
forged.

Key Scoping
The Secure Association Protocol MUST ensure the synchronization of session parameters such as
key scope between the
Called-Station- Id peer and Calling-Station-Id, these can be sent authenticator. This includes
negotiation of restrictions on key usage.

5.4. Ciphersuite Requirements

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

TSK derivation
In order to allow a ciphersuite to be usable within the server, protected by EAP keying
framework, a specification MUST be provided describing how
transient session keys suitable for use with the TEKs. The RADIUS server can
then check 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 parameters sent by EAP method. However, algorithms for
deriving TEKs MAY be specific to the EAP peer against those claimed
by method.

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Cryptographic separation
The TSKs derived from the authenticator. If a discrepancy is found, an error can AAA-Key MUST be
logged.

While [RFC3588] requires use of cryptographically
separate from each other. Similarly, TEKs MUST be
cryptographically separate from each other. In addition, the Route-Record AVP, this utilizes
FQDNs, so that impersonation detection requires DNS A/AAAA and PTR
RRs to TSKs
MUST 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 cryptographically separate from the TEKs.

6. IANA Considerations

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

The following terms are used here with the authenticator directly,
such as via the redirect functionality supported meanings defined in [RFC3588].

6.5 Denial of Service Attacks BCP
26: "name space", "assigned value", "registration".

The caching of security associations may result in vulnerability to
denial of service attacks. Since an EAP peer may derive multiple EAP
SAs following policies are used here with a given EAP server, and creation of a new EAP SA does not
implicitly delete a previous EAP SA, EAP methods that result the meanings defined in
creation of persistant state may be vulnerable to denial of service
attacks by a rogue EAP peer.

As BCP
26: "Private Use", "First Come First Served", "Expert Review",
"Specification Required", "IETF Consensus", "Standards Action".

For registration requests where a result, EAP methods creating persistent state may wish 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 limit allow for the number
allocation of cached EAP SAs (Phase 1a) corresponding to an EAP peer.
For example, an EAP server may choose values prior to only retain a few EAP SAs the RFC being approved for each peer. This prevents a rogue peer from denying access to
other peers.

Similarly, publication,
the Designated Expert can approve allocations once it seems clear
that an authenticator may have multiple AAA-Key SAs
corresponding to RFC will be published. The Designated expert will post a given EAP peer; to conserve resources an
authenticator may choose
request to limit the number of cached AAA-Key (Phase
1 b) SAs for each peer.

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Depending on WG mailing list (or a successor designated by the media, creation of
Area Director) for comment and review, including an Internet-Draft.
Before a new unicast secure association
SA may or may not imply deletion period of 30 days has passed, the Designated Expert will
either approve or deny the registration request and publish a previous unicast secure
association SA. Where there notice
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 no implied deletion, possible, concrete
suggestions on how the
authenticator may choose request can be modified so as to limit Phase 2 (unicast and multicast)
secure association SAs for each peer. become
acceptable.

7. Acknowledgements

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. References

7.1. Normative References

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

[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.

[I-D.ietf-eap-rfc2284bis]

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[RFC3748]
Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. Lefkowetz,
"Extensible Authentication Protocol (EAP)",
draft-ietf-eap-rfc2284bis-06 (work in progress), September
2003.

[IEEE802] Institute of Electrical and Electronics Engineers, "IEEE
Standards for Local and Metropolitan Area Networks:
Overview and Architecture", ANSI/IEEE Standard 802, 1990. RFC 3748, June 2004.

7.2. Informative References

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

[RFC1321] Rivest, R.,

[RFC1661] Simpson, W., "The MD5 Message-Digest Algorithm", Point-to-Point Protocol (PPP)", STD 51, RFC 1321,
April 1992.
1661, July 1994.

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

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

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[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.

[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.

[RFC2855] Fujisawa, K., "DHCP for IEEE 1394", RFC 2855,

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INTERNET-DRAFT EAP Key Management Framework 26 June 2000. 2004

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

[RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
Zhang, L. and V. Paxson, "Stream Control Transmission
Protocol", RFC 2960, October 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.

[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, September 2002.

[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote Authentication Dial
In User Service) Support For Extensible

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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
(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>.

[FIPS197] National

[IEEE802] Institute of Standards Electrical and Technology, "Advanced
Encryption Standard (AES)", FIPS PUB 197, November 2001.

[FIPS.180-1.1995]
National Institute of Electronics Engineers, "IEEE
Standards for Local and Technology, "Secure
Hash Standard", FIPS PUB 180-1, April 1995, <http://
www.itl.nist.gov/fipspubs/fip180-1.htm>. Metropolitan Area Networks: Overview
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
802.11-1997, 1997. 802.11-1999, 1999.

[IEEE8021X]
Institute of Electrical and Electronics Engineers, "Local and
Metropolitan Area Networks: Port-Based Network Access

Aboba, et al. Informational [Page 58]

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Control", IEEE Standard 802.1X-2001, June 2002. 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]

[IEEE80211F]
Institute of Electrical and Electronics Engineers,
"Recommended Practice for Multi-Vendor Access Point

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Internet-Draft EAP Key Management Framework October 2003
Interoperability via an Inter-Access Point Protocol Across
Distribution Systems Supporting IEEE 802.11 Operation", IEEE
802.11F, July 2003.

[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/
D6.1, August 2003. 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.

[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.

[EAPAPI] Microsoft Developer Network, "Windows 2000 EAP API",
http://msdn.microsoft.com/library/default.asp?url=/
library/en-us/eap/eapport_0fj9.asp, August 2000.

[I-D.ietf-roamops-cert]
Aboba, B., "Certificate-Based Roaming",
draft-ietf-roamops-cert-02 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-02 (work in progress), July 2003.

[I-D.irtf-aaaarch-handoff]
Arbaugh, W. and B. Aboba, "Experimental Handoff Extension
to RADIUS", draft-irtf-aaaarch-handoff-03 (work in
progress), October 2003. draft-ietf-aaa-

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INTERNET-DRAFT EAP Key Management Framework October 2003

[I-D.orman-public-key-lengths]
Orman, H. 26 June 2004

eap-08 (work in progress), June 2004.

[I-D.irtf-aaaarch-handoff]
Arbaugh, W. and P. Hoffman, "Determining Strengths For
Public Keys Used For Exchanging Symmetric Keys",
draft-orman-public-key-lengths-05 B. Aboba, "Handoff Extension to RADIUS",
draft-irtf-aaaarch-handoff-04 (work in progress),
January 2002. October
2003.

[I-D.puthenkulam-eap-binding]
Puthenkulam, J., "The Compound Authentication Binding
Problem", draft-puthenkulam-eap-binding-03 draft-puthenkulam-eap-binding-04 (work in progress), July
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
2003.

[I-D.arkko-pppext-eap-aka]
Arkko, J. and H. Haverinen, "EAP AKA Authentication",
draft-arkko-pppext-eap-aka-10 draft-
arkko-pppext-eap-aka-11 (work in progress), June October 2003.

[IKEv2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", draft-
ietf-ipsec-ikev2-12 (work in progress), March 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.

Authors'

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

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Housley of Vigil Security for useful feedback.

Author Addresses

Bernard Aboba
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA

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

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Dan Simon
Microsoft Research
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
USA

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

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

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. 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 [ECP]
negotiation phase [RFC1968]." 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

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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
authentication key (used in both directions); 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).

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. 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:

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TLS-PRF-X = TLS pseudo-random function defined in [RFC2246],
computed to X octets.
master_secret = TLS term for the MK.

| | |
| | pre_master_secret |
server| | | client
Random| V | Random
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | | |
| | | |
+---->| master_secret |<------+
| | (MK) | |
| | | |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| | |
| | |
V V V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| |
| Key Block |
| (TEKs) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | | | |
| client | server | client | server | client | server
| MAC | MAC | write | write | IV | IV
| | | | | |
V V V V V V

Figure B-1 - TLS [RFC2246] Key Hierarchy

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Appendix C. MSK and EMSK C - EAP Key Hierarchy

In EAP-TLS [RFC2716], the MSK is divided into two halves,
corresponding to the "Peer to Authenticator Encryption Key"
(Enc-RECV-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 MS-MPPE-Send-
Key attribute.

The EMSK is also divided into two halves, corresponding to the "Peer

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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 via a
one-way one-
way function. This ensures that the MK 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, if the MK 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, "client EAP encryption",
client.random || server.random)
EMSK = second 64 octets of:
TLS-PRF-128(MK, "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) =
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:

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IV(32,63) = Authenticator to Peer Initialization vector (SEND-IV)

Where:

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

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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 = TLS master_secret
TLS-PRF-X = TLS PRF function [RFC2246], 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 Master Secret".

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

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

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Appendix D. D - 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:

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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. 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], and [8021XHandoff], keying material may be required
for use in fast handoff between IEEE 802.11 authenticators. Where the backend
authentication server provides keying material to multiple
authenticators in order to fascilitate facilitate fast handoff, it is highly
desirable for the keying material used on different authenticators to
be cryptographically separate, so that if one authenticator is
compromised, it does not lead to the compromise of other
authenticators. Where keying material is provided by the backend
authentication server, a key hierarchy derived from the EMSK, as
suggested in [IEEE-03-155] can be
used to provide cryptographically separate keying material for use in
fast handoff:

AAA-Key-A = MSK(0,63)

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AAA-Key-B = PRF(EMSK(0,63),AAA-Key-A,
B-Called-Station-Id,Calling-Station-Id) 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),AAA-Key-A,
E-Called-Station-Id,Calling-Station-Id) 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
length = length of derived key material

Here AAA-Key-A is the AAA-Key derived during the initial EAP
authentication between the peer and authenticator A. Based on this
initial EAP authentication, the EMSK is also derived, which can be
used to derive AAA-Keys for fast authentication between the EAP peer
and authenticators B and E. Since the EMSK is cryptographically
separate from the MSK, each of these AAA-Keys is cryptographically
separate from each other, and are guaranteed to be unique between the
EAP peer (also known as the STA) and the authenticator (also known as
the AP).

Appendix F. Open issues

(This section should be removed by the RFC editor before publication)

Open issues relating to this specification are tracked on the
following web site:

http://www.drizzle.com/~aboba/EAP/eapissues.html

The current working documents for this draft are available at this
web site:

http://www.levkowetz.com/pub/ietf/drafts/eap/keying/

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WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgment

Funding for PURPOSE."

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Open Issues

Open issues relating to this specification are tracked on the RFC Editor function
following web site:

http://www.drizzle.com/~aboba/EAP/eapissues.html

Expiration Date

This memo is currently provided by the
Internet Society. filed as <draft-ietf-eap-keying-02.txt>, and expires
December 22, 2004.

Aboba, et al. Expires April 26, 2004 Informational [Page 55] 69]

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