The Flexible Authentication via Secure Tunneling Extensible Authentication Protocol Method (EAP-FAST)
RFC 4851
| Document | Type |
RFC
- Informational
(May 2007)
Errata
IPR
Was
draft-cam-winget-eap-fast
(individual in sec area)
|
|
|---|---|---|---|
| Authors | Joseph A. Salowey , Hao Zhou , Nancy Cam-Winget , David McGrew | ||
| Last updated | 2020-01-21 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | (None) | ||
| IESG | IESG state | RFC 4851 (Informational) | |
| Action Holders |
(None)
|
||
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Russ Housley | ||
| Send notices to | (None) |
RFC 4851
Network Working Group N. Cam-Winget
Request for Comments: 4851 D. McGrew
Category: Informational J. Salowey
H. Zhou
Cisco Systems
May 2007
The Flexible Authentication via Secure Tunneling
Extensible Authentication Protocol Method (EAP-FAST)
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines the Extensible Authentication Protocol (EAP)
based Flexible Authentication via Secure Tunneling (EAP-FAST)
protocol. EAP-FAST is an EAP method that enables secure
communication between a peer and a server by using the Transport
Layer Security (TLS) to establish a mutually authenticated tunnel.
Within the tunnel, Type-Length-Value (TLV) objects are used to convey
authentication related data between the peer and the EAP server.
Cam-Winget, et al. Informational [Page 1]
RFC 4851 EAP-FAST May 2007
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Specification Requirements . . . . . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Architectural Model . . . . . . . . . . . . . . . . . . . 6
2.2. Protocol Layering Model . . . . . . . . . . . . . . . . . 7
3. EAP-FAST Protocol . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Version Negotiation . . . . . . . . . . . . . . . . . . . 8
3.2. EAP-FAST Authentication Phase 1: Tunnel Establishment . . 9
3.2.1. TLS Session Resume Using Server State . . . . . . . . 10
3.2.2. TLS Session Resume Using a PAC . . . . . . . . . . . . 10
3.2.3. Transition between Abbreviated and Full TLS
Handshake . . . . . . . . . . . . . . . . . . . . . . 12
3.3. EAP-FAST Authentication Phase 2: Tunneled
Authentication . . . . . . . . . . . . . . . . . . . . . . 12
3.3.1. EAP Sequences . . . . . . . . . . . . . . . . . . . . 13
3.3.2. Protected Termination and Acknowledged Result
Indication . . . . . . . . . . . . . . . . . . . . . . 13
3.4. Determining Peer-Id and Server-Id . . . . . . . . . . . . 14
3.5. EAP-FAST Session Identifier . . . . . . . . . . . . . . . 15
3.6. Error Handling . . . . . . . . . . . . . . . . . . . . . . 15
3.6.1. TLS Layer Errors . . . . . . . . . . . . . . . . . . . 15
3.6.2. Phase 2 Errors . . . . . . . . . . . . . . . . . . . . 16
3.7. Fragmentation . . . . . . . . . . . . . . . . . . . . . . 16
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 18
4.1. EAP-FAST Message Format . . . . . . . . . . . . . . . . . 18
4.1.1. Authority ID Data . . . . . . . . . . . . . . . . . . 20
4.2. EAP-FAST TLV Format and Support . . . . . . . . . . . . . 20
4.2.1. General TLV Format . . . . . . . . . . . . . . . . . . 21
4.2.2. Result TLV . . . . . . . . . . . . . . . . . . . . . . 22
4.2.3. NAK TLV . . . . . . . . . . . . . . . . . . . . . . . 23
4.2.4. Error TLV . . . . . . . . . . . . . . . . . . . . . . 24
4.2.5. Vendor-Specific TLV . . . . . . . . . . . . . . . . . 25
4.2.6. EAP-Payload TLV . . . . . . . . . . . . . . . . . . . 26
4.2.7. Intermediate-Result TLV . . . . . . . . . . . . . . . 28
4.2.8. Crypto-Binding TLV . . . . . . . . . . . . . . . . . . 29
4.2.9. Request-Action TLV . . . . . . . . . . . . . . . . . . 31
4.3. Table of TLVs . . . . . . . . . . . . . . . . . . . . . . 32
5. Cryptographic Calculations . . . . . . . . . . . . . . . . . . 32
5.1. EAP-FAST Authentication Phase 1: Key Derivations . . . . . 32
5.2. Intermediate Compound Key Derivations . . . . . . . . . . 33
5.3. Computing the Compound MAC . . . . . . . . . . . . . . . . 34
5.4. EAP Master Session Key Generation . . . . . . . . . . . . 35
5.5. T-PRF . . . . . . . . . . . . . . . . . . . . . . . . . . 35
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
Cam-Winget, et al. Informational [Page 2]
RFC 4851 EAP-FAST May 2007
7. Security Considerations . . . . . . . . . . . . . . . . . . . 37
7.1. Mutual Authentication and Integrity Protection . . . . . . 37
7.2. Method Negotiation . . . . . . . . . . . . . . . . . . . . 38
7.3. Separation of Phase 1 and Phase 2 Servers . . . . . . . . 38
7.4. Mitigation of Known Vulnerabilities and Protocol
Deficiencies . . . . . . . . . . . . . . . . . . . . . . . 39
7.4.1. User Identity Protection and Verification . . . . . . 39
7.4.2. Dictionary Attack Resistance . . . . . . . . . . . . . 40
7.4.3. Protection against Man-in-the-Middle Attacks . . . . . 40
7.4.4. PAC Binding to User Identity . . . . . . . . . . . . . 41
7.5. Protecting against Forged Clear Text EAP Packets . . . . . 41
7.6. Server Certificate Validation . . . . . . . . . . . . . . 42
7.7. Tunnel PAC Considerations . . . . . . . . . . . . . . . . 42
7.8. Security Claims . . . . . . . . . . . . . . . . . . . . . 43
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 44
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 44
9.1. Normative References . . . . . . . . . . . . . . . . . . . 44
9.2. Informative References . . . . . . . . . . . . . . . . . . 45
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 46
A.1. Successful Authentication . . . . . . . . . . . . . . . . 46
A.2. Failed Authentication . . . . . . . . . . . . . . . . . . 47
A.3. Full TLS Handshake using Certificate-based Ciphersuite . . 48
A.4. Client Authentication during Phase 1 with Identity
Privacy . . . . . . . . . . . . . . . . . . . . . . . . . 50
A.5. Fragmentation and Reassembly . . . . . . . . . . . . . . . 52
A.6. Sequence of EAP Methods . . . . . . . . . . . . . . . . . 53
A.7. Failed Crypto-Binding . . . . . . . . . . . . . . . . . . 56
A.8. Sequence of EAP Method with Vendor-Specific TLV
Exchange . . . . . . . . . . . . . . . . . . . . . . . . . 57
Appendix B. Test Vectors . . . . . . . . . . . . . . . . . . . . 60
B.1. Key Derivation . . . . . . . . . . . . . . . . . . . . . . 60
B.2. Crypto-Binding MIC . . . . . . . . . . . . . . . . . . . . 62
Cam-Winget, et al. Informational [Page 3]
RFC 4851 EAP-FAST May 2007
1. Introduction
Network access solutions requiring user friendly and easily
deployable secure authentication mechanisms highlight the need for
strong mutual authentication protocols that enable the use of weaker
user credentials. This document defines an Extensible Authentication
Protocol (EAP), which consists of establishing a Transport Layer
Security (TLS) tunnel using TLS 1.0 [RFC2246], TLS 1.1 [RFC4346], or
a successor version of TLS, using the latest version supported by
both parties. Once the tunnel is established, the protocol further
exchanges data in the form of type, length, and value objects (TLV)
to perform further authentication. EAP-FAST supports the TLS
extension defined in [RFC4507] to support fast re-establishment of
the secure tunnel without having to maintain per-session state on the
server. [EAP-PROV] defines EAP-FAST-based mechanisms to provision
the credential for this extension which is called a Protected Access
Credential (PAC).
EAP-FAST's design motivations included:
o Mutual authentication: an EAP server must be able to verify the
identity and authenticity of the peer, and the peer must be able
to verify the authenticity of the EAP server.
o Immunity to passive dictionary attacks: many authentication
protocols require a password to be explicitly provided (either as
cleartext or hashed) by the peer to the EAP server; at minimum,
the communication of the weak credential (e.g., password) must be
immune from eavesdropping.
o Immunity to man-in-the-middle (MitM) attacks: in establishing a
mutually authenticated protected tunnel, the protocol must prevent
adversaries from successfully interjecting information into the
conversation between the peer and the EAP server.
o Flexibility to enable support for most password authentication
interfaces: as many different password interfaces (e.g., Microsoft
Challenge Handshake Authentication Protocol (MS-CHAP), Lightweight
Directory Access Protocol (LDAP), One-Time Password (OTP), etc.)
exist to authenticate a peer, the protocol must provide this
support seamlessly.
o Efficiency: specifically when using wireless media, peers will be
limited in computational and power resources. The protocol must
enable the network access communication to be computationally
lightweight.
Cam-Winget, et al. Informational [Page 4]
RFC 4851 EAP-FAST May 2007
With these motivational goals defined, further secondary design
criteria are imposed:
o Flexibility to extend the communications inside the tunnel: with
the growing complexity in network infrastructures, the need to
gain authentication, authorization, and accounting is also
evolving. For instance, there may be instances in which multiple
existing authentication protocols are required to achieve mutual
authentication. Similarly, different protected conversations may
be required to achieve the proper authorization once a peer has
successfully authenticated.
o Minimize the authentication server's per user authentication state
requirements: with large deployments, it is typical to have many
servers acting as the authentication servers for many peers. It
is also highly desirable for a peer to use the same shared secret
to secure a tunnel much the same way it uses the username and
password to gain access to the network. The protocol must
facilitate the use of a single strong shared secret by the peer
while enabling the servers to minimize the per user and device
state it must cache and manage.
1.1. Specification Requirements
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 [RFC2119] .
1.2. Terminology
Much of the terminology in this document comes from [RFC3748].
Additional terms are defined below:
Protected Access Credential (PAC)
Credentials distributed to a peer for future optimized network
authentication. The PAC consists of, at most, three components: a
shared secret, an opaque element, and optionally other
information. The shared secret component contains the pre-shared
key between the peer and the authentication server. The opaque
part is provided to the peer and is presented to the
authentication server when the peer wishes to obtain access to
network resources. Finally, a PAC may optionally include other
information that may be useful to the peer. The opaque part of
the PAC is the same type of data as the ticket in [RFC4507] and
the shared secret is used to derive the TLS master secret.
Cam-Winget, et al. Informational [Page 5]
RFC 4851 EAP-FAST May 2007
2. Protocol Overview
EAP-FAST is an authentication protocol similar to EAP-TLS [RFC2716]
that enables mutual authentication and cryptographic context
establishment by using the TLS handshake protocol. EAP-FAST allows
for the established TLS tunnel to be used for further authentication
exchanges. EAP-FAST makes use of TLVs to carry out the inner
authentication exchanges. The tunnel is then used to protect weaker
inner authentication methods, which may be based on passwords, and to
communicate the results of the authentication.
EAP-FAST makes use of the TLS enhancements in [RFC4507] to enable an
optimized TLS tunnel session resume while minimizing server state.
The secret key used in EAP-FAST is referred to as the Protected
Access Credential key (or PAC-Key); the PAC-Key is used to mutually
authenticate the peer and the server when securing a tunnel. The
ticket is referred to as the Protected Access Credential opaque data
(or PAC-Opaque). The secret key and ticket used to establish the
tunnel may be provisioned through mechanisms that do not involve the
TLS handshake. It is RECOMMENDED that implementations support the
capability to distribute the ticket and secret key within the EAP-
FAST tunnel as specified in [EAP-PROV].
The EAP-FAST conversation is used to establish or resume an existing
session to typically establish network connectivity between a peer
and the network. Upon successful execution of EAP-FAST, both EAP
peer and EAP server derive strong session key material that can then
be communicated to the network access server (NAS) for use in
establishing a link layer security association.
2.1. Architectural Model
The network architectural model for EAP-FAST usage is shown below:
+----------+ +----------+ +----------+ +----------+
| | | | | | | Inner |
| Peer |<---->| Authen- |<---->| EAP-FAST |<---->| Method |
| | | ticator | | server | | server |
| | | | | | | |
+----------+ +----------+ +----------+ +----------+
EAP-FAST Architectural Model
The entities depicted above are logical entities and may or may not
correspond to separate network components. For example, the EAP-FAST
server and inner method server might be a single entity; the
authenticator and EAP-FAST server might be a single entity; or the
functions of the authenticator, EAP-FAST server, and inner method
Cam-Winget, et al. Informational [Page 6]
RFC 4851 EAP-FAST May 2007
server might be combined into a single physical device. For example,
typical 802.11 deployments place the Authenticator in an access point
(AP) while a Radius server may provide the EAP-FAST and inner method
server components. The above diagram illustrates the division of
labor among entities in a general manner and shows how a distributed
system might be constructed; however, actual systems might be
realized more simply. The security considerations Section 7.3
provides an additional discussion of the implications of separating
the EAP-FAST server from the inner method server.
2.2. Protocol Layering Model
EAP-FAST packets are encapsulated within EAP; EAP in turn requires a
carrier protocol for transport. EAP-FAST packets encapsulate TLS,
which is then used to encapsulate user authentication information.
Thus, EAP-FAST messaging can be described using a layered model,
where each layer encapsulates the layer above it. The following
diagram clarifies the relationship between protocols:
+---------------------------------------------------------------+
| Inner EAP Method | Other TLV information |
|---------------------------------------------------------------|
| TLV Encapsulation (TLVs) |
|---------------------------------------------------------------|
| TLS |
|---------------------------------------------------------------|
| EAP-FAST |
|---------------------------------------------------------------|
| EAP |
|---------------------------------------------------------------|
| Carrier Protocol (EAP over LAN, RADIUS, Diameter, etc.) |
+---------------------------------------------------------------+
Protocol Layering Model
The TLV layer is a payload with Type-Length-Value (TLV) Objects
defined in Section 4.2. The TLV objects are used to carry arbitrary
parameters between an EAP peer and an EAP server. All conversations
in the EAP-FAST protected tunnel must be encapsulated in a TLV layer.
Methods for encapsulating EAP within carrier protocols are already
defined. For example, IEEE 802.1X [IEEE.802-1X.2004] may be used to
transport EAP between the peer and the authenticator; RADIUS
[RFC3579] or Diameter [RFC4072] may be used to transport EAP between
the authenticator and the EAP-FAST server.
Cam-Winget, et al. Informational [Page 7]
RFC 4851 EAP-FAST May 2007
3. EAP-FAST Protocol
EAP-FAST authentication occurs in two phases. In the first phase,
EAP-FAST employs the TLS handshake to provide an authenticated key
exchange and to establish a protected tunnel. Once the tunnel is
established the second phase begins with the peer and server engaging
in further conversations to establish the required authentication and
authorization policies. The operation of the protocol, including
Phase 1 and Phase 2, are the topic of this section. The format of
EAP-FAST messages is given in Section 4 and the cryptographic
calculations are given in Section 5.
3.1. Version Negotiation
EAP-FAST packets contain a 3-bit version field, following the TLS
Flags field, which enables EAP-FAST implementations to be backward
compatible with previous versions of the protocol. This
specification documents the EAP-FAST version 1 protocol;
implementations of this specification MUST use a version field set to
1.
Version negotiation proceeds as follows:
In the first EAP-Request sent with EAP type=EAP-FAST, the EAP
server must set the version field to the highest supported version
number.
If the EAP peer supports this version of the protocol, it MUST
respond with an EAP-Response of EAP type=EAP-FAST, and the version
number proposed by the EAP-FAST server.
If the EAP-FAST peer does not support this version, it responds
with an EAP-Response of EAP type=EAP-FAST and the highest
supported version number.
If the EAP-FAST server does not support the version number
proposed by the EAP-FAST peer, it terminates the conversation.
Otherwise the EAP-FAST conversation continues.
The version negotiation procedure guarantees that the EAP-FAST peer
and server will agree to the latest version supported by both
parties. If version negotiation fails, then use of EAP-FAST will not
be possible, and another mutually acceptable EAP method will need to
be negotiated if authentication is to proceed.
The EAP-FAST version is not protected by TLS; and hence can be
modified in transit. In order to detect a modification of the EAP-
FAST version, the peers MUST exchange the EAP-FAST version number
Cam-Winget, et al. Informational [Page 8]
RFC 4851 EAP-FAST May 2007
received during version negotiation using the Crypto-Binding TLV
described in Section 4.2.8. The receiver of the Crypto-Binding TLV
MUST verify that the version received in the Crypto-Binding TLV
matches the version sent by the receiver in the EAP-FAST version
negotiation.
3.2. EAP-FAST Authentication Phase 1: Tunnel Establishment
EAP-FAST is based on the TLS handshake [RFC2246] to establish an
authenticated and protected tunnel. The TLS version offered by the
peer and server MUST be TLS v1.0 or later. This version of the EAP-
FAST implementation MUST support the following TLS ciphersuites:
TLS_RSA_WITH_RC4_128_SHA
TLS_RSA_WITH_AES_128_CBC_SHA [RFC3268]
TLS_DHE_RSA_WITH_AES_128_CBC_SHA [RFC3268]
Other ciphersuites MAY be supported. It is RECOMMENDED that
anonymous ciphersuites such as TLS_DH_anon_WITH_AES_128_CBC_SHA only
be used in the context of the provisioning described in [EAP-PROV].
Care must be taken to address potential man-in-the-middle attacks
when ciphersuites that do not provide authenticated tunnel
establishment are used. During the EAP-FAST Phase 1 conversation the
EAP-FAST endpoints MAY negotiate TLS compression.
The EAP server initiates the EAP-FAST conversation with an EAP
request containing an EAP-FAST/Start packet. This packet includes a
set Start (S) bit, the EAP-FAST version as specified in Section 3.1,
and an authority identity. The TLS payload in the initial packet is
empty. The authority identity (A-ID) is used to provide the peer a
hint of the server's identity that may be useful in helping the peer
select the appropriate credential to use. Assuming that the peer
supports EAP-FAST the conversation continues with the peer sending an
EAP-Response packet with EAP type of EAP-FAST with the Start (S) bit
clear and the version as specified in Section 3.1. This message
encapsulates one or more TLS records containing the TLS handshake
messages. If the EAP-FAST version negotiation is successful then the
EAP-FAST conversation continues until the EAP server and EAP peer are
ready to enter Phase 2. When the full TLS handshake is performed,
then the first payload of EAP-FAST Phase 2 MAY be sent along with
server-finished handshake message to reduce the number of round
trips.
After the TLS session is established, another EAP exchange MAY occur
within the tunnel to authenticate the EAP peer. EAP-FAST
implementations MUST support client authentication during tunnel
Cam-Winget, et al. Informational [Page 9]
RFC 4851 EAP-FAST May 2007
establishment using the TLS ciphersuites specified in Section 3.2.
EAP-FAST implementations SHOULD also support the immediate
renegotiation of a TLS session to initiate a new handshake message
exchange under the protection of the current ciphersuite. This
allows support for protection of the peer's identity. Note that the
EAP peer does not need to authenticate as part of the TLS exchange,
but can alternatively be authenticated through additional EAP
exchanges carried out in Phase 2.
The EAP-FAST tunnel protects peer identity information from
disclosure outside the tunnel. Implementations that wish to provide
identity privacy for the peer identity must carefully consider what
information is disclosed outside the tunnel.
The following sections describe resuming a TLS session based on
server-side or client-side state.
3.2.1. TLS Session Resume Using Server State
EAP-FAST session resumption is achieved in the same manner TLS
achieves session resume. To support session resumption, the server
and peer must minimally cache the SessionID, master secret, and
ciphersuite. The peer attempts to resume a session by including a
valid SessionID from a previous handshake in its ClientHello message.
If the server finds a match for the SessionID and is willing to
establish a new connection using the specified session state, the
server will respond with the same SessionID and proceed with the EAP-
FAST Authentication Phase 1 tunnel establishment based on a TLS
abbreviated handshake. After a successful conclusion of the EAP-FAST
Authentication Phase 1 conversation, the conversation then continues
on to Phase 2.
3.2.2. TLS Session Resume Using a PAC
EAP-FAST supports the resumption of sessions based on client-side
state using techniques described in [RFC4507]. This version of EAP-
FAST does not support the provisioning of a ticket through the use of
the SessionTicket handshake message. Instead it supports the
provisioning of a ticket called a Protected Access Credential (PAC)
as described in [EAP-PROV]. Implementations may provide additional
ways to provision the PAC, such as manual configuration. Since the
PAC mentioned here is used for establishing the TLS Tunnel, it is
more specifically referred to as the Tunnel PAC. The Tunnel PAC is a
security credential provided by the EAP server to a peer and
comprised of:
Cam-Winget, et al. Informational [Page 10]
RFC 4851 EAP-FAST May 2007
1. PAC-Key: this is a 32-octet key used by the peer to establish the
EAP-FAST Phase 1 tunnel. This key is used to derive the TLS
premaster secret as described in Section 5.1. The PAC-Key is
randomly generated by the EAP server to produce a strong entropy
32-octet key. The PAC-Key is a secret and MUST be treated
accordingly. For example, as the PAC-Key is a separate component
provisioned by the server to establish a secure tunnel, the
server may deliver this component protected by a secure channel,
and it must be stored securely by the peer.
2. PAC-Opaque: this is a variable length field that is sent to the
EAP server during the EAP-FAST Phase 1 tunnel establishment. The
PAC-Opaque can only be interpreted by the EAP server to recover
the required information for the server to validate the peer's
identity and authentication. For example, the PAC-Opaque
includes the PAC-Key and may contain the PAC's peer identity.
The PAC-Opaque format and contents are specific to the PAC
issuing server. The PAC-Opaque may be presented in the clear, so
an attacker MUST NOT be able to gain useful information from the
PAC-Opaque itself. The server issuing the PAC-Opaque must ensure
it is protected with strong cryptographic keys and algorithms.
3. PAC-Info: this is a variable length field used to provide, at a
minimum, the authority identity of the PAC issuer. Other useful
but not mandatory information, such as the PAC-Key lifetime, may
also be conveyed by the PAC issuing server to the peer during PAC
provisioning or refreshment.
The use of the PAC is based on the SessionTicket extension defined in
[RFC4507]. The EAP server initiates the EAP-FAST conversation as
normal. Upon receiving the A-ID from the server, the peer checks to
see if it has an existing valid PAC-Key and PAC-Opaque for the
server. If it does, then it obtains the PAC-Opaque and puts it in
the SessionTicket extension in the ClientHello. It is RECOMMENDED in
EAP-FAST that the peer include an empty Session ID in a ClientHello
containing a PAC-Opaque. EAP-FAST does not currently support the
SessionTicket Handshake message so an empty SessionTicket extension
MUST NOT be included in the ClientHello. If the PAC-Opaque included
in the SessionTicket extension is valid and the EAP server permits
the abbreviated TLS handshake, it will select the ciphersuite allowed
to be used from information within the PAC and finish with the
abbreviated TLS handshake. If the server receives a Session ID and a
PAC-Opaque in the SessionTicket extension in a ClientHello, it should
place the same Session ID in the ServerHello if it is resuming a
session based on the PAC-Opaque. The conversation then proceeds as
described in [RFC4507] until the handshake completes or a fatal error
occurs. After the abbreviated handshake completes, the peer and
server are ready to commence Phase 2. Note that when a PAC is used,
Cam-Winget, et al. Informational [Page 11]
RFC 4851 EAP-FAST May 2007
the TLS master secret is calculated from the PAC-Key, client random,
and server random as described in Section 5.1.
Specific details for the Tunnel PAC format, provisioning and security
considerations are best described in [EAP-PROV]
3.2.3. Transition between Abbreviated and Full TLS Handshake
If session resumption based on server-side or client-side state
fails, the server can gracefully fall back to a full TLS handshake.
If the ServerHello received by the peer contains a empty Session ID
or a Session ID that is different than in the ClientHello, the server
may be falling back to a full handshake. The peer can distinguish
the server's intent of negotiating full or abbreviated TLS handshake
by checking the next TLS handshake messages in the server response to
the ClientHello. If ChangeCipherSpec follows the ServerHello in
response to the ClientHello, then the server has accepted the session
resumption and intends to negotiate the abbreviated handshake.
Otherwise, the server intends to negotiate the full TLS handshake. A
peer can request for a new PAC to be provisioned after the full TLS
handshake and mutual authentication of the peer and the server. In
order to facilitate the fallback to a full handshake, the peer SHOULD
include ciphersuites that allow for a full handshake and possibly PAC
provisioning so the server can select one of these in case session
resumption fails. An example of the transition is shown in
Appendix A.
3.3. EAP-FAST Authentication Phase 2: Tunneled Authentication
The second portion of the EAP-FAST Authentication occurs immediately
after successful completion of Phase 1. Phase 2 occurs even if both
peer and authenticator are authenticated in the Phase 1 TLS
negotiation. Phase 2 MUST NOT occur if the Phase 1 TLS handshake
fails. Phase 2 consists of a series of requests and responses
encapsulated in TLV objects defined in Section 4.2. Phase 2 MUST
always end with a protected termination exchange described in
Section 3.3.2. The TLV exchange may include the execution of zero or
more EAP methods within the protected tunnel as described in
Section 3.3.1. A server MAY proceed directly to the protected
termination exchange if it does not wish to request further
authentication from the peer. However, the peer and server must not
assume that either will skip inner EAP methods or other TLV
exchanges. The peer may have roamed to a network that requires
conformance with a different authentication policy or the peer may
request the server take additional action through the use of the
Request-Action TLV.
Cam-Winget, et al. Informational [Page 12]
RFC 4851 EAP-FAST May 2007
3.3.1. EAP Sequences
EAP [RFC3748] prohibits use of multiple authentication methods within
a single EAP conversation in order to limit vulnerabilities to man-
in-the-middle attacks. EAP-FAST addresses man-in-the-middle attacks
through support for cryptographic protection of the inner EAP
exchange and cryptographic binding of the inner authentication
method(s) to the protected tunnel. EAP methods are executed serially
in a sequence. This version of EAP-FAST does not support initiating
multiple EAP methods simultaneously in parallel. The methods need
not be distinct. For example, EAP-TLS could be run twice as an inner
method, first using machine credentials followed by a second instance
using user credentials.
EAP method messages are carried within EAP-Payload TLVs defined in
Section 4.2.6. If more than one method is going to be executed in
the tunnel then, upon completion of a method, a server MUST send an
Intermediate-Result TLV indicating the result. The peer MUST respond
to the Intermediate-Result TLV indicating its result. If the result
indicates success, the Intermediate-Result TLV MUST be accompanied by
a Crypto-Binding TLV. The Crypto-Binding TLV is further discussed in
Section 4.2.8 and Section 5.3. The Intermediate-Result TLVs can be
included with other TLVs such as EAP-Payload TLVs starting a new EAP
conversation or with the Result TLV used in the protected termination
exchange. In the case where only one EAP method is executed in the
tunnel, the Intermediate-Result TLV MUST NOT be sent with the Result
TLV. In this case, the status of the inner EAP method is represented
by the final Result TLV, which also represents the result of the
whole EAP-FAST conversation. This is to maintain backward
compatibility with existing implementations.
If both peer and server indicate success, then the method is
considered complete. If either indicates failure. then the method is
considered failed. The result of failure of an EAP method does not
always imply a failure of the overall authentication. If one
authentication method fails, the server may attempt to authenticate
the peer with a different method.
3.3.2. Protected Termination and Acknowledged Result Indication
A successful EAP-FAST Phase 2 conversation MUST always end in a
successful Result TLV exchange. An EAP-FAST server may initiate the
Result TLV exchange without initiating any EAP conversation in EAP-
FAST Phase 2. After the final Result TLV exchange, the TLS tunnel is
terminated and a clear text EAP-Success or EAP-Failure is sent by the
server. The format of the Result TLV is described in Section 4.2.2.
Cam-Winget, et al. Informational [Page 13]
RFC 4851 EAP-FAST May 2007
A server initiates a successful protected termination exchange by
sending a Result TLV indicating success. The server may send the
Result TLV along with an Intermediate-Result TLV and a Crypto-Binding
TLV. If the peer requires nothing more from the server it will
respond with a Result TLV indicating success accompanied by an
Intermediate-Result TLV and Crypto-Binding TLV if necessary. The
server then tears down the tunnel and sends a clear text EAP-Success.
If the peer receives a Result TLV indicating success from the server,
but its authentication policies are not satisfied (for example it
requires a particular authentication mechanism be run or it wants to
request a PAC), it may request further action from the server using
the Request-Action TLV. The Request-Action TLV is sent along with
the Result TLV indicating what EAP Success/Failure result the peer
would expect if the requested action is not granted. The value of
the Request-Action TLV indicates what the peer would like to do next.
The format and values for the Request-Action TLV are defined in
Section 4.2.9.
Upon receiving the Request-Action TLV the server may process the
request or ignore it, based on its policy. If the server ignores the
request, it proceeds with termination of the tunnel and send the
clear text EAP Success or Failure message based on the value of the
peer's result TLV. If the server honors and processes the request,
it continues with the requested action. The conversation completes
with a Result TLV exchange. The Result TLV may be included with the
TLV that completes the requested action.
Error handling for Phase 2 is discussed in Section 3.6.2.
3.4. Determining Peer-Id and Server-Id
The Peer-Id and Server-Id may be determined based on the types of
credentials used during either the EAP-FAST tunnel creation or
authentication.
When X.509 certificates are used for peer authentication, the Peer-Id
is determined by the subject or subjectAltName fields in the peer
certificate. As noted in [RFC3280] (updated by [RFC4630]):
The subject field identifies the entity associated with the public
key stored in the subject public key field. The subject name MAY
be carried in the subject field and/or the subjectAltName
extension.... If subject naming information is present only in
the subjectAltName extension (e.g., a key bound only to an email
address or URI), then the subject name MUST be an empty sequence
and the subjectAltName extension MUST be critical.
Cam-Winget, et al. Informational [Page 14]
RFC 4851 EAP-FAST May 2007
Where it is non-empty, the subject field MUST contain an X.500
distinguished name (DN).
If an inner EAP method is run, then the Peer-Id is obtained from the
inner method.
When the server uses an X.509 certificate to establish the TLS
tunnel, the Server-Id is determined in a similar fashion as stated
above for the Peer-Id; e.g., the subject or subjectAltName field in
the server certificate defines the Server-Id.
3.5. EAP-FAST Session Identifier
The EAP session identifier is constructed using the random values
provided by the peer and server during the TLS tunnel establishment.
The Session-Id is defined as follows:
Session-Id = 0x2B || client_random || server_random)
client_random = 32 byte nonce generated by the peer
server_random = 32 byte nonce generated by the server
3.6. Error Handling
EAP-FAST uses the following error handling rules summarized below:
1. Errors in the TLS layer are communicated via TLS alert messages
in all phases of EAP-FAST.
2. The Intermediate-Result TLVs carry success or failure indications
of the individual EAP methods in EAP-FAST Phase 2. Errors within
the EAP conversation in Phase 2 are expected to be handled by
individual EAP methods.
3. Violations of the TLV rules are handled using Result TLVs
together with Error TLVs.
4. Tunnel compromised errors (errors caused by Crypto-Binding failed
or missing) are handled using Result TLVs and Error TLVs.
3.6.1. TLS Layer Errors
If the EAP-FAST server detects an error at any point in the TLS
Handshake or the TLS layer, the server SHOULD send an EAP-FAST
request encapsulating a TLS record containing the appropriate TLS
alert message rather than immediately terminating the conversation so
as to allow the peer to inform the user of the cause of the failure
and possibly allow for a restart of the conversation. The peer MUST
send an EAP-FAST response to an alert message. The EAP-Response
Cam-Winget, et al. Informational [Page 15]
RFC 4851 EAP-FAST May 2007
packet sent by the peer may encapsulate a TLS ClientHello handshake
message, in which case the EAP-FAST server MAY allow the EAP-FAST
conversation to be restarted, or it MAY contain an EAP-FAST response
with a zero-length message, in which case the server MUST terminate
the conversation with an EAP-Failure packet. It is up to the EAP-
FAST server whether to allow restarts, and if so, how many times the
conversation can be restarted. An EAP-FAST Server implementing
restart capability SHOULD impose a limit on the number of restarts,
so as to protect against denial-of-service attacks.
If the EAP-FAST peer detects an error at any point in the TLS layer,
the EAP-FAST peer should send an EAP-FAST response encapsulating a
TLS record containing the appropriate TLS alert message. The server
may restart the conversation by sending an EAP-FAST request packet
encapsulating the TLS HelloRequest handshake message. The peer may
allow the EAP-FAST conversation to be restarted or it may terminate
the conversation by sending an EAP-FAST response with an zero-length
message.
3.6.2. Phase 2 Errors
Any time the peer or the server finds a fatal error outside of the
TLS layer during Phase 2 TLV processing, it MUST send a Result TLV of
failure and an Error TLV with the appropriate error code. For errors
involving the processing of the sequence of exchanges, such as a
violation of TLV rules (e.g., multiple EAP-Payload TLVs), the error
code is Unexpected_TLVs_Exchanged. For errors involving a tunnel
compromise, the error-code is Tunnel_Compromise_Error. Upon sending
a Result TLV with a fatal Error TLV the sender terminates the TLS
tunnel. Note that a server will still wait for a message from the
peer after it sends a failure, however the server does not need to
process the contents of the response message.
If a server receives a Result TLV of failure with a fatal Error TLV,
it SHOULD send a clear text EAP-Failure. If a peer receives a Result
TLV of failure, it MUST respond with a Result TLV indicating failure.
If the server has sent a Result TLV of failure, it ignores the peer
response, and it SHOULD send a clear text EAP-Failure.
3.7. Fragmentation
A single TLS record may be up to 16384 octets in length, but a TLS
message may span multiple TLS records, and a TLS certificate message
may in principle be as long as 16 MB. This is larger than the
maximum size for a message on most media types, therefore it is
desirable to support fragmentation. Note that in order to protect
against reassembly lockup and denial-of-service attacks, it may be
desirable for an implementation to set a maximum size for one such
Cam-Winget, et al. Informational [Page 16]
RFC 4851 EAP-FAST May 2007
group of TLS messages. Since a typical certificate chain is rarely
longer than a few thousand octets, and no other field is likely to be
anywhere near as long, a reasonable choice of maximum acceptable
message length might be 64 KB. This is still a fairly large message
packet size so an EAP-FAST implementation MUST provide its own
support for fragmentation and reassembly.
Since EAP is an lock-step protocol, fragmentation support can be
added in a simple manner. In EAP, fragments that are lost or damaged
in transit will be retransmitted, and since sequencing information is
provided by the Identifier field in EAP, there is no need for a
fragment offset field.
EAP-FAST fragmentation support is provided through the addition of
flag bits within the EAP-Response and EAP-Request packets, as well as
a TLS Message Length field of four octets. Flags include the Length
included (L), More fragments (M), and EAP-FAST Start (S) bits. The L
flag is set to indicate the presence of the four-octet TLS Message
Length field, and MUST be set for the first fragment of a fragmented
TLS message or set of messages. The M flag is set on all but the
last fragment. The S flag is set only within the EAP-FAST start
message sent from the EAP server to the peer. The TLS Message Length
field is four octets, and provides the total length of the TLS
message or set of messages that is being fragmented; this simplifies
buffer allocation.
When an EAP-FAST peer receives an EAP-Request packet with the M bit
set, it MUST respond with an EAP-Response with EAP-Type of EAP-FAST
and no data. This serves as a fragment ACK. The EAP server must
wait until it receives the EAP-Response before sending another
fragment. In order to prevent errors in processing of fragments, the
EAP server MUST increment the Identifier field for each fragment
contained within an EAP-Request, and the peer must include this
Identifier value in the fragment ACK contained within the EAP-
Response. Retransmitted fragments will contain the same Identifier
value.
Similarly, when the EAP-FAST server receives an EAP-Response with the
M bit set, it must respond with an EAP-Request with EAP-Type of EAP-
FAST and no data. This serves as a fragment ACK. The EAP peer MUST
wait until it receives the EAP-Request before sending another
fragment. In order to prevent errors in the processing of fragments,
the EAP server MUST increment the Identifier value for each fragment
ACK contained within an EAP-Request, and the peer MUST include this
Identifier value in the subsequent fragment contained within an EAP-
Response.
Cam-Winget, et al. Informational [Page 17]
RFC 4851 EAP-FAST May 2007
4. Message Formats
The following sections describe the message formats used in EAP-FAST.
The fields are transmitted from left to right in network byte order.
4.1. EAP-FAST Message Format
A summary of the EAP-FAST Request/Response packet format is shown
below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Flags | Ver | Message Length :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Message Length | Data... +
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code
The code field is one octet in length defined as follows:
1 Request
2 Response
Identifier
The Identifier field is one octet and aids in matching
responses with requests. The Identifier field MUST be changed
on each Request packet. The Identifier field in the Response
packet MUST match the Identifier field from the corresponding
request.
Length
The Length field is two octets and indicates the length of the
EAP packet including the Code, Identifier, Length, Type, Flags,
Ver, Message Length, and Data fields. Octets outside the range
of the Length field should be treated as Data Link Layer
padding and should be ignored on reception.
Type
43 for EAP-FAST
Cam-Winget, et al. Informational [Page 18]
RFC 4851 EAP-FAST May 2007
Flags
0 1 2 3 4
+-+-+-+-+-+
|L M S R R|
+-+-+-+-+-+
L Length included; set to indicate the presence of the four-
octet Message Length field
M More fragments; set on all but the last fragment
S EAP-FAST start; set in an EAP-FAST Start message
R Reserved (must be zero)
Ver
This field contains the version of the protocol. This document
describes version 1 (001 in binary) of EAP-FAST.
Message Length
The Message Length field is four octets, and is present only if
the L bit is set. This field provides the total length of the
message that may be fragmented over the data fields of multiple
packets.
Data
In the case of an EAP-FAST Start request (i.e., when the S bit
is set) the Data field consists of the A-ID described in
Section 4.1.1. In other cases, when the Data field is present,
it consists of an encapsulated TLS packet in TLS record format.
An EAP-FAST packet with Flags and Version fields, but with zero
length data field, is used to indicate EAP-FAST acknowledgement
for either a fragmented message, a TLS Alert message or a TLS
Finished message.
Cam-Winget, et al. Informational [Page 19]
RFC 4851 EAP-FAST May 2007
4.1.1. Authority ID Data
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (0x04) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ID
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
The Type field is two octets. It is set to 0x0004 for
Authority ID
Length
The Length filed is two octets, which contains the length of
the ID field in octets.
ID
Hint of the identity of the server. It should be unique across
the deployment.
4.2. EAP-FAST TLV Format and Support
The TLVs defined here are standard Type-Length-Value (TLV) objects.
The TLV objects could be used to carry arbitrary parameters between
EAP peer and EAP server within the protected TLS tunnel.
The EAP peer may not necessarily implement all the TLVs supported by
the EAP server. To allow for interoperability, TLVs are designed to
allow an EAP server to discover if a TLV is supported by the EAP
peer, using the NAK TLV. The mandatory bit in a TLV indicates
whether support of the TLV is required. If the peer or server does
not support a TLV marked mandatory, then it MUST send a NAK TLV in
the response, and all the other TLVs in the message MUST be ignored.
If an EAP peer or server finds an unsupported TLV that is marked as
optional, it can ignore the unsupported TLV. It MUST NOT send an NAK
TLV for a TLV that is not marked mandatory.
Note that a peer or server may support a TLV with the mandatory bit
set, but may not understand the contents. The appropriate response
to a supported TLV with content that is not understood is defined by
the individual TLV specification.
Cam-Winget, et al. Informational [Page 20]
RFC 4851 EAP-FAST May 2007
EAP implementations compliant with this specification MUST support
TLV exchanges, as well as the processing of mandatory/optional
settings on the TLV. Implementations conforming to this
specification MUST support the following TLVs:
Result TLV
NAK TLV
Error TLV
EAP-Payload TLV
Intermediate-Result TLV
Crypto-Binding TLV
Request-Action TLV
4.2.1. General TLV Format
TLVs are defined as described below. The fields are transmitted from
left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
0 Optional TLV
1 Mandatory TLV
R
Reserved, set to zero (0)
TLV Type
A 14-bit field, denoting the TLV type. Allocated Types
include:
Cam-Winget, et al. Informational [Page 21]
RFC 4851 EAP-FAST May 2007
0 Reserved
1 Reserved
2 Reserved
3 Result TLV (Section 4.2.2)
4 NAK TLV (Section 4.2.3)
5 Error TLV (Section 4.2.4)
7 Vendor-Specific TLV (Section 4.2.5)
9 EAP-Payload TLV (Section 4.2.6)
10 Intermediate-Result TLV (Section 4.2.7)
11 PAC TLV [EAP-PROV]
12 Crypto-Binding TLV (Section 4.2.8)
18 Server-Trusted-Root TLV [EAP-PROV]
19 Request-Action TLV (Section 4.2.9)
20 PKCS#7 TLV [EAP-PROV]
Length
The length of the Value field in octets.
Value
The value of the TLV.
4.2.2. Result TLV
The Result TLV provides support for acknowledged success and failure
messages for protected termination within EAP-FAST. If the Status
field does not contain one of the known values, then the peer or EAP
server MUST treat this as a fatal error of Unexpected_TLVs_Exchanged.
The behavior of the Result TLV is further discussed in Section 3.3.2
and Section 3.6.2. A Result TLV indicating failure MUST NOT be
accompanied by the following TLVs: NAK, EAP-Payload TLV, or Crypto-
Binding TLV. The Result TLV is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
Mandatory, set to one (1)
Cam-Winget, et al. Informational [Page 22]
RFC 4851 EAP-FAST May 2007
R
Reserved, set to zero (0)
TLV Type
3 for Result TLV
Length
2
Status
The Status field is two octets. Values include:
1 Success
2 Failure
4.2.3. NAK TLV
The NAK TLV allows a peer to detect TLVs that are not supported by
the other peer. An EAP-FAST packet can contain 0 or more NAK TLVs.
A NAK TLV should not be accompanied by other TLVs. A NAK TLV MUST
NOT be sent in response to a message containing a Result TLV, instead
a Result TLV of failure should be sent indicating failure and an
Error TLV of Unexpected_TLVs_Exchanged. The NAK TLV is defined as
follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NAK-Type | TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
Mandatory, set to one (1)
R
Reserved, set to zero (0)
Cam-Winget, et al. Informational [Page 23]
RFC 4851 EAP-FAST May 2007
TLV Type
4 for NAK TLV
Length
>=6
Vendor-Id
The Vendor-Id field is four octets, and contains the Vendor-Id
of the TLV that was not supported. The high-order octet is 0
and the low-order three octets are the Structure of Management
Information (SMI) Network Management Private Enterprise Code of
the Vendor in network byte order. The Vendor-Id field MUST be
zero for TLVs that are not Vendor-Specific TLVs.
NAK-Type
The NAK-Type field is two octets. The field contains the Type
of the TLV that was not supported. A TLV of this Type MUST
have been included in the previous packet.
TLVs
This field contains a list of zero or more TLVs, each of which
MUST NOT have the mandatory bit set. These optional TLVs are
for future extensibility to communicate why the offending TLV
was determined to be unsupported.
4.2.4. Error TLV
The Error TLV allows an EAP peer or server to indicate errors to the
other party. An EAP-FAST packet can contain 0 or more Error TLVs.
The Error-Code field describes the type of error. Error Codes 1-999
represent successful outcomes (informative messages), 1000-1999
represent warnings, and codes 2000-2999 represent fatal errors. A
fatal Error TLV MUST be accompanied by a Result TLV indicating
failure and the conversation must be terminated as described in
Section 3.6.2. The Error TLV is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error-Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Cam-Winget, et al. Informational [Page 24]
RFC 4851 EAP-FAST May 2007
M
Mandatory, set to one (1)
R
Reserved, set to zero (0)
TLV Type
5 for Error TLV
Length
4
Error-Code
The Error-Code field is four octets. Currently defined values
for Error-Code include:
2001 Tunnel_Compromise_Error
2002 Unexpected_TLVs_Exchanged
4.2.5. Vendor-Specific TLV
The Vendor-Specific TLV is available to allow vendors to support
their own extended attributes not suitable for general usage. A
Vendor-Specific TLV attribute can contain one or more TLVs, referred
to as Vendor TLVs. The TLV-type of a Vendor-TLV is defined by the
vendor. All the Vendor TLVs inside a single Vendor-Specific TLV
belong to the same vendor. There can be multiple Vendor-Specific
TLVs from different vendors in the same message.
Vendor TLVs may be optional or mandatory. Vendor TLVs sent with
Result TLVs MUST be marked as optional.
Cam-Winget, et al. Informational [Page 25]
RFC 4851 EAP-FAST May 2007
The Vendor-Specific TLV is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
0 or 1
R
Reserved, set to zero (0)
TLV Type
7 for Vendor Specific TLV
Length
4 + cumulative length of all included Vendor TLVs
Vendor-Id
The Vendor-Id field is four octets, and contains the Vendor-Id
of the TLV. The high-order octet is 0 and the low-order 3
octets are the SMI Network Management Private Enterprise Code
of the Vendor in network byte order.
Vendor TLVs
This field is of indefinite length. It contains vendor-
specific TLVs, in a format defined by the vendor.
4.2.6. EAP-Payload TLV
To allow piggybacking an EAP request or response with other TLVs, the
EAP-Payload TLV is defined, which includes an encapsulated EAP packet
and a list of optional TLVs. The optional TLVs are provided for
future extensibility to provide hints about the current EAP
authentication. Only one EAP-Payload TLV is allowed in a message.
The EAP-Payload TLV is defined as follows:
Cam-Winget, et al. Informational [Page 26]
RFC 4851 EAP-FAST May 2007
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EAP packet...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
Mandatory, set to (1)
R
Reserved, set to zero (0)
TLV Type
9 for EAP-Payload TLV
Length
length of embedded EAP packet + cumulative length of additional
TLVs
EAP packet
This field contains a complete EAP packet, including the EAP
header (Code, Identifier, Length, Type) fields. The length of
this field is determined by the Length field of the
encapsulated EAP packet.
TLVs
This field contains a list of zero or more TLVs associated with
the EAP packet field. The TLVs MUST NOT have the mandatory bit
set. The total length of this field is equal to the Length
field of the EAP-Payload TLV, minus the Length field in the EAP
header of the EAP packet field.
Cam-Winget, et al. Informational [Page 27]
RFC 4851 EAP-FAST May 2007
4.2.7. Intermediate-Result TLV
The Intermediate-Result TLV provides support for acknowledged
intermediate Success and Failure messages between multiple inner EAP
methods within EAP. An Intermediate-Result TLV indicating success
MUST be accompanied by a Crypto-Binding TLV. The optional TLVs
associated with this TLV are provided for future extensibility to
provide hints about the current result. The Intermediate-Result TLV
is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status | TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
Mandatory, set to (1)
R
Reserved, set to zero (0)
TLV Type
10 for Intermediate-Result TLV
Length
2 + cumulative length of the embedded associated TLVs
Status
The Status field is two octets. Values include:
1 Success
2 Failure
TLVs
This field is of indeterminate length, and contains zero or
more of the TLVs associated with the Intermediate Result TLV.
The TLVs in this field MUST NOT have the mandatory bit set.
Cam-Winget, et al. Informational [Page 28]
RFC 4851 EAP-FAST May 2007
4.2.8. Crypto-Binding TLV
The Crypto-Binding TLV is used to prove that both the peer and server
participated in the tunnel establishment and sequence of
authentications. It also provides verification of the EAP-FAST
version negotiated before TLS tunnel establishment, see Section 3.1.
The Crypto-Binding TLV MUST be included with the Intermediate-Result
TLV to perform Cryptographic Binding after each successful EAP method
in a sequence of EAP methods. The Crypto-Binding TLV can be issued
at other times as well.
The Crypto-Binding TLV is valid only if the following checks pass:
o The Crypto-Binding TLV version is supported
o The MAC verifies correctly
o The received version in the Crypto-Binding TLV matches the version
sent by the receiver during the EAP version negotiation
o The subtype is set to the correct value
If any of the above checks fail, then the TLV is invalid. An invalid
Crypto-Binding TLV is a fatal error and is handled as described in
Section 3.6.2.
The Crypto-Binding TLV is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Version | Received Ver. | Sub-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Nonce ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Compound MAC ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
Mandatory, set to (1)
Cam-Winget, et al. Informational [Page 29]
RFC 4851 EAP-FAST May 2007
R
Reserved, set to zero (0)
TLV Type
12 for Crypto-Binding TLV
Length
56
Reserved
Reserved, set to zero (0)
Version
The Version field is a single octet, which is set to the
version of Crypto-Binding TLV the EAP method is using. For an
implementation compliant with this version of EAP-FAST, the
version number MUST be set to 1.
Received Version
The Received Version field is a single octet and MUST be set to
the EAP version number received during version negotiation.
Note that this field only provides protection against downgrade
attacks, where a version of EAP requiring support for this TLV
is required on both sides.
Sub-Type
The Sub-Type field is one octet. Defined values include:
0 Binding Request
1 Binding Response
Nonce
The Nonce field is 32 octets. It contains a 256-bit nonce that
is temporally unique, used for compound MAC key derivation at
each end. The nonce in a request MUST have its least
significant bit set to 0 and the nonce in a response MUST have
the same value as the request nonce except the least
significant bit MUST be set to 1.
Cam-Winget, et al. Informational [Page 30]
RFC 4851 EAP-FAST May 2007
Compound MAC
The Compound MAC field is 20 octets. This can be the Server
MAC (B1_MAC) or the Client MAC (B2_MAC). The computation of
the MAC is described in Section 5.3.
4.2.9. Request-Action TLV
The Request-Action TLV MAY be sent by the peer along with a Result
TLV in response to a server's successful Result TLV. It allows the
peer to request the EAP server to negotiate additional EAP methods or
process TLVs specified in the response packet. The server MAY ignore
this TLV.
The Request-Action TLV is defined as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Action |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
Mandatory set to one (1)
R
Reserved, set to zero (0)
TLV Type
19 for Request-Action TLV
Length
2
Action
The Action field is two octets. Values include:
Process-TLV
Negotiate-EAP
Cam-Winget, et al. Informational [Page 31]
RFC 4851 EAP-FAST May 2007
4.3. Table of TLVs
The following table provides a guide to which TLVs may be found in
which kinds of messages, and in what quantity. The messages are as
follows: Request is an EAP-FAST Request, Response is an EAP-FAST
Response, Success is a message containing a successful Result TLV,
and Failure is a message containing a failed Result TLV.
Request Response Success Failure TLVs
0-1 0-1 0-1 0-1 Intermediate-Result
0-1 0-1 0 0 EAP-Payload
0-1 0-1 1 1 Result
0-1 0-1 0-1 0-1 Crypto-Binding
0+ 0+ 0+ 0+ Error
0+ 0+ 0 0 NAK
0+ 0+ 0+ 0+ Vendor-Specific [NOTE1]
0 0-1 0-1 0-1 Request-Action
[NOTE1] Vendor TLVs (included in Vendor-Specific TLVs) sent with a
Result TLV MUST be marked as optional.
The following table defines the meaning of the table entries in the
sections below:
0 This TLV MUST NOT be present in the message.
0+ Zero or more instances of this TLV MAY be present in the message.
0-1 Zero or one instance of this TLV MAY be present in the message.
1 Exactly one instance of this TLV MUST be present in the message.
5. Cryptographic Calculations
5.1. EAP-FAST Authentication Phase 1: Key Derivations
The EAP-FAST Authentication tunnel key is calculated similarly to the
TLS key calculation with an additional 40 octets (referred to as the
session_key_seed) generated. The additional session_key_seed is used
in the Session Key calculation in the EAP-FAST Tunneled
Authentication conversation.
Cam-Winget, et al. Informational [Page 32]
RFC 4851 EAP-FAST May 2007
To generate the key material required for the EAP-FAST Authentication
tunnel, the following construction from [RFC4346] is used:
key_block = PRF(master_secret, "key expansion",
server_random + client_random)
where '+' denotes concatenation.
The PRF function used to generate keying material is defined by
[RFC4346].
For example, if the EAP-FAST Authentication employs 128-bit RC4 and
SHA1, the key_block is 112 octets long and is partitioned as follows:
client_write_MAC_secret[20]
server_write_MAC_secret[20]
client_write_key[16]
server_write_key[16]
client_write_IV[0]
server_write_IV[0]
session_key_seed[40]
The session_key_seed is used by the EAP-FAST Authentication Phase 2
conversation to both cryptographically bind the inner method(s) to
the tunnel as well as generate the resulting EAP-FAST session keys.
The other quantities are used as they are defined in [RFC4346].
The master_secret is generated as specified in TLS unless a PAC is
used to establish the TLS tunnel. When a PAC is used to establish
the TLS tunnel, the master_secret is calculated from the specified
client_random, server_random, and PAC-Key as follows:
master_secret = T-PRF(PAC-Key, "PAC to master secret label hash",
server_random + client_random, 48)
where T-PRF is described in Section 5.5.
5.2. Intermediate Compound Key Derivations
The session_key_seed derived as part of EAP-FAST Phase 2 is used in
EAP-FAST Phase 2 to generate an Intermediate Compound Key (IMCK) used
to verify the integrity of the TLS tunnel after each successful inner
authentication and in the generation of Master Session Key (MSK) and
Extended Master Session Key (EMSK) defined in [RFC3748]. Note that
the IMCK must be recalculated after each successful inner EAP method.
Cam-Winget, et al. Informational [Page 33]
RFC 4851 EAP-FAST May 2007
The first step in these calculations is the generation of the base
compound key, IMCK[n] from the session_key_seed and any session keys
derived from the successful execution of n inner EAP methods. The
inner EAP method(s) may provide Master Session Keys, MSK1..MSKn,
corresponding to inner methods 1 through n. The MSK is truncated at
32 octets if it is longer than 32 octets or padded to a length of 32
octets with zeros if it is less than 32 octets. If the ith inner
method does not generate an MSK, then MSKi is set to zero (e.g., MSKi
= 32 octets of 0x00s). If an inner method fails, then it is not
included in this calculation. The derivations of S-IMCK is as
follows:
S-IMCK[0] = session_key_seed
For j = 1 to n-1 do
IMCK[j] = T-PRF(S-IMCK[j-1], "Inner Methods Compound Keys",
MSK[j], 60)
S-IMCK[j] = first 40 octets of IMCK[j]
CMK[j] = last 20 octets of IMCK[j]
where T-PRF is described in Section 5.5.
5.3. Computing the Compound MAC
For authentication methods that generate keying material, further
protection against man-in-the-middle attacks is provided through
cryptographically binding keying material established by both EAP-
FAST Phase 1 and EAP-FAST Phase 2 conversations. After each
successful inner EAP authentication, EAP MSKs are cryptographically
combined with key material from EAP-FAST Phase 1 to generate a
compound session key, CMK. The CMK is used to calculate the Compound
MAC as part of the Crypto-Binding TLV described in Section 4.2.8,
which helps provide assurance that the same entities are involved in
all communications in EAP-FAST. During the calculation of the
Compound-MAC the MAC field is filled with zeros.
The Compound MAC computation is as follows:
CMK = CMK[j]
Compound-MAC = HMAC-SHA1( CMK, Crypto-Binding TLV )
where j is the number of the last successfully executed inner EAP
method.
Cam-Winget, et al. Informational [Page 34]
RFC 4851 EAP-FAST May 2007
5.4. EAP Master Session Key Generation
EAP-FAST Authentication assures the master session key (MSK) and
Extended Master Session Key (EMSK) output from the EAP method are the
result of all authentication conversations by generating an
Intermediate Compound Key (IMCK). The IMCK is mutually derived by
the peer and the server as described in Section 5.2 by combining the
MSKs from inner EAP methods with key material from EAP-FAST Phase 1.
The resulting MSK and EMSK are generated as part of the IMCKn key
hierarchy as follows:
MSK = T-PRF(S-IMCK[j], "Session Key Generating Function", 64)
EMSK = T-PRF(S-IMCK[j],
"Extended Session Key Generating Function", 64)
where j is the number of the last successfully executed inner EAP
method.
The EMSK is typically only known to the EAP-FAST peer and server and
is not provided to a third party. The derivation of additional keys
and transportation of these keys to a third party is outside the
scope of this document.
If no EAP methods have been negotiated inside the tunnel or no EAP
methods have been successfully completed inside the tunnel, the MSK
and EMSK will be generated directly from the session_key_seed meaning
S-IMCK = session_key_seed.
5.5. T-PRF
EAP-FAST employs the following PRF prototype and definition:
T-PRF = F(key, label, seed, outputlength)
Where label is intended to be a unique label for each different use
of the T-PRF. The outputlength parameter is a two-octet value that
is represented in big endian order. Also note that the seed value
may be optional and may be omitted as in the case of the MSK
derivation described in Section 5.4.
Cam-Winget, et al. Informational [Page 35]
RFC 4851 EAP-FAST May 2007
To generate the desired outputlength octets of key material, the
T-PRF is calculated as follows:
S = label + 0x00 + seed
T-PRF output = T1 + T2 + T3 + ... + Tn
T1 = HMAC-SHA1 (key, S + outputlength + 0x01)
T2 = HMAC-SHA1 (key, T1 + S + outputlength + 0x02)
T3 = HMAC-SHA1 (key, T2 + S + outputlength + 0x03)
Tn = HMAC-SHA1 (key, Tn-1 + S + outputlength + 0xnn)
where '+' indicates concatenation. Each Ti generates 20-octets of
keying material. The last Tn may be truncated to accommodate the
desired length specified by outputlength.
6. IANA Considerations
This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to the EAP-
FAST protocol, in accordance with BCP 26, [RFC2434].
EAP-FAST has already been assigned the EAP Method Type number 43.
The document defines a registry for EAP-FAST TLV types, which may be
assigned by Specification Required as defined in [RFC2434].
Section 4.2 defines the TLV types that initially populate the
registry. A summary of the EAP-FAST TLV types is given below:
0 Reserved
1 Reserved
2 Reserved
3 Result TLV
4 NAK TLV
5 Error TLV
7 Vendor-Specific TLV
9 EAP-Payload TLV
10 Intermediate-Result TLV
11 PAC TLV [EAP-PROV]
12 Crypto-Binding TLV
18 Server-Trusted-Root TLV [EAP-PROV]
19 Request-Action TLV
20 PKCS#7 TLV [EAP-PROV]
The Error-TLV defined in Section 4.2.4 requires an error-code. EAP-
FAST Error-TLV error-codes are assigned based on specifications
required as defined in [RFC2434]. The initial list of error codes is
as follows:
Cam-Winget, et al. Informational [Page 36]
RFC 4851 EAP-FAST May 2007
2001 Tunnel_Compromise_Error
2002 Unexpected_TLVs_Exchanged
The Request-Action TLV defined in Section 4.2.9 contains an action
code which is assigned on a specification required basis as defined
in [RFC2434]. The initial actions defined are:
1 Process-TLV
2 Negotiate-EAP
The various values under Vendor-Specific TLV are assigned by Private
Use and do not need to be assigned by IANA.
7. Security Considerations
EAP-FAST is designed with a focus on wireless media, where the medium
itself is inherent to eavesdropping. Whereas in wired media, an
attacker would have to gain physical access to the wired medium;
wireless media enables anyone to capture information as it is
transmitted over the air, enabling passive attacks. Thus, physical
security can not be assumed and security vulnerabilities are far
greater. The threat model used for the security evaluation of EAP-
FAST is defined in the EAP [RFC3748].
7.1. Mutual Authentication and Integrity Protection
EAP-FAST as a whole, provides message and integrity protection by
establishing a secure tunnel for protecting the authentication
method(s). The confidentiality and integrity protection is defined
by TLS and provides the same security strengths afforded by TLS
employing a strong entropy shared master secret. The integrity of
the key generating authentication methods executed within the EAP-
FAST tunnel is verified through the calculation of the Crypto-Binding
TLV. This ensures that the tunnel endpoints are the same as the
inner method endpoints.
The Result TLV is protected and conveys the true Success or Failure
of EAP-FAST, and should be used as the indicator of its success or
failure respectively. However, as EAP must terminate with a clear
text EAP Success or Failure, a peer will also receive a clear text
EAP Success or Failure. The received clear text EAP success or
failure must match that received in the Result TLV; the peer SHOULD
silently discard those clear text EAP Success or Failure messages
that do not coincide with the status sent in the protected Result
TLV.
Cam-Winget, et al. Informational [Page 37]
RFC 4851 EAP-FAST May 2007
7.2. Method Negotiation
As is true for any negotiated EAP protocol, NAK packets used to
suggest an alternate authentication method are sent unprotected and
as such, are subject to spoofing. During unprotected EAP method
negotiation, NAK packets may be interjected as active attacks to
negotiate down to a weaker form of authentication, such as EAP-MD5
(which only provides one-way authentication and does not derive a
key). Both the peer and server should have a method selection policy
that prevents them from negotiating down to weaker methods. Inner
method negotiation resists attacks because it is protected by the
mutually authenticated TLS tunnel established. Selection of EAP-FAST
as an authentication method does not limit the potential inner
authentication methods, so EAP-FAST should be selected when
available.
An attacker cannot readily determine the inner EAP method used,
except perhaps by traffic analysis. It is also important that peer
implementations limit the use of credentials with an unauthenticated
or unauthorized server.
7.3. Separation of Phase 1 and Phase 2 Servers
Separation of the EAP-FAST Phase 1 from the Phase 2 conversation is
not recommended. Allowing the Phase 1 conversation to be terminated
at a different server than the Phase 2 conversation can introduce
vulnerabilities if there is not a proper trust relationship and
protection for the protocol between the two servers. Some
vulnerabilities include:
o Loss of identity protection
o Offline dictionary attacks
o Lack of policy enforcement
There may be cases where a trust relationship exists between the
Phase 1 and Phase 2 servers, such as on a campus or between two
offices within the same company, where there is no danger in
revealing the inner identity and credentials of the peer to entities
between the two servers. In these cases, using a proxy solution
without end-to-end protection of EAP-FAST MAY be used. The EAP-FAST
encrypting/decrypting gateway SHOULD, at a minimum, provide support
for IPsec or similar protection in order to provide confidentiality
for the portion of the conversation between the gateway and the EAP
server.
Cam-Winget, et al. Informational [Page 38]
RFC 4851 EAP-FAST May 2007
7.4. Mitigation of Known Vulnerabilities and Protocol Deficiencies
EAP-FAST addresses the known deficiencies and weaknesses in the EAP
method. By employing a shared secret between the peer and server to
establish a secured tunnel, EAP-FAST enables:
o Per packet confidentiality and integrity protection
o User identity protection
o Better support for notification messages
o Protected EAP inner method negotiation
o Sequencing of EAP methods
o Strong mutually derived master session keys
o Acknowledged success/failure indication
o Faster re-authentications through session resumption
o Mitigation of dictionary attacks
o Mitigation of man-in-the-middle attacks
o Mitigation of some denial-of-service attacks
It should be noted that with EAP-FAST, as in many other
authentication protocols, a denial-of-service attack can be mounted
by adversaries sending erroneous traffic to disrupt the protocol.
This is a problem in many authentication or key agreement protocols
and is therefore noted for EAP-FAST as well.
EAP-FAST was designed with a focus on protected authentication
methods that typically rely on weak credentials, such as password-
based secrets. To that extent, the EAP-FAST Authentication mitigates
several vulnerabilities, such as dictionary attacks, by protecting
the weak credential-based authentication method. The protection is
based on strong cryptographic algorithms in TLS to provide message
confidentiality and integrity. The keys derived for the protection
relies on strong random challenges provided by both peer and server
as well as an established key with strong entropy. Implementations
should follow the recommendation in [RFC4086] when generating random
numbers.
7.4.1. User Identity Protection and Verification
The initial identity request response exchange is sent in cleartext
outside the protection of EAP-FAST. Typically the Network Access
Identifier (NAI) [RFC4282] in the identity response is useful only
for the realm information that is used to route the authentication
requests to the right EAP server. This means that the identity
response may contain an anonymous identity and just contain realm
information. In other cases, the identity exchange may be eliminated
altogether if there are other means for establishing the destination
realm of the request. In no case should an intermediary place any
trust in the identity information in the identity response since it
Cam-Winget, et al. Informational [Page 39]
RFC 4851 EAP-FAST May 2007
is unauthenticated an may not have any relevance to the authenticated
identity. EAP-FAST implementations should not attempt to compare any
identity disclosed in the initial cleartext EAP Identity response
packet with those Identities authenticated in Phase 2
Identity request-response exchanges sent after the EAP-FAST tunnel is
established are protected from modification and eavesdropping by
attackers.
Note that since TLS client certificates are sent in the clear, if
identity protection is required, then it is possible for the TLS
authentication to be re-negotiated after the first server
authentication. To accomplish this, the server will typically not
request a certificate in the server_hello, then after the
server_finished message is sent, and before EAP-FAST Phase 2, the
server MAY send a TLS hello_request. This allows the client to
perform client authentication by sending a client_hello if it wants
to, or send a no_renegotiation alert to the server indicating that it
wants to continue with EAP-FAST Phase 2 instead. Assuming that the
client permits renegotiation by sending a client_hello, then the
server will respond with server_hello, a certificate and
certificate_request messages. The client replies with certificate,
client_key_exchange and certificate_verify messages. Since this re-
negotiation occurs within the encrypted TLS channel, it does not
reveal client certificate details. It is possible to perform
certificate authentication using an EAP method (for example: EAP-TLS)
within the TLS session in EAP-FAST Phase 2 instead of using TLS
handshake renegotiation.
7.4.2. Dictionary Attack Resistance
EAP-FAST was designed with a focus on protected authentication
methods that typically rely on weak credentials, such as password-
based secrets. EAP-FAST mitigates dictionary attacks by allowing the
establishment of a mutually authenticated encrypted TLS tunnel
providing confidentiality and integrity to protect the weak
credential based authentication method.
7.4.3. Protection against Man-in-the-Middle Attacks
Allowing methods to be executed both with and without the protection
of a secure tunnel opens up a possibility of a man-in-the-middle
attack. To avoid man-in-the-middle attacks it is recommended to
always deploy authentication methods with protection of EAP-FAST.
EAP-FAST provides protection from man-in-the-middle attacks even if a
deployment chooses to execute inner EAP methods both with and without
EAP-FAST protection, EAP-FAST prevents this attack in two ways:
Cam-Winget, et al. Informational [Page 40]
RFC 4851 EAP-FAST May 2007
1. By using the PAC-Key to mutually authenticate the peer and server
during EAP-FAST Authentication Phase 1 establishment of a secure
tunnel.
2. By using the keys generated by the inner authentication method
(if the inner methods are key generating) in the crypto-binding
exchange and in the generation of the key material exported by
the EAP method described in Section 5.
7.4.4. PAC Binding to User Identity
A PAC may be bound to a user identity. A compliant implementation of
EAP-FAST MUST validate that an identity obtained in the PAC-Opaque
field matches at minimum one of the identities provided in the EAP-
FAST Phase 2 authentication method. This validation provides another
binding to ensure that the intended peer (based on identity) has
successfully completed the EAP-FAST Phase 1 and proved identity in
the Phase 2 conversations.
7.5. Protecting against Forged Clear Text EAP Packets
EAP Success and EAP Failure packets are, in general, sent in clear
text and may be forged by an attacker without detection. Forged EAP
Failure packets can be used to attempt to convince an EAP peer to
disconnect. Forged EAP Success packets may be used to attempt to
convince a peer that authentication has succeeded, even though the
authenticator has not authenticated itself to the peer.
By providing message confidentiality and integrity, EAP-FAST provides
protection against these attacks. Once the peer and AS initiate the
EAP-FAST Authentication Phase 2, compliant EAP-FAST implementations
must silently discard all clear text EAP messages, unless both the
EAP-FAST peer and server have indicated success or failure using a
protected mechanism. Protected mechanisms include TLS alert
mechanism and the protected termination mechanism described in
Section 3.3.2.
The success/failure decisions within the EAP-FAST tunnel indicate the
final decision of the EAP-FAST authentication conversation. After a
success/failure result has been indicated by a protected mechanism,
the EAP-FAST peer can process unprotected EAP success and EAP failure
messages; however the peer MUST ignore any unprotected EAP success or
failure messages where the result does not match the result of the
protected mechanism.
To abide by [RFC3748], the server must send a clear text EAP Success
or EAP Failure packet to terminate the EAP conversation. However,
since EAP Success and EAP Failure packets are not retransmitted, the
Cam-Winget, et al. Informational [Page 41]
RFC 4851 EAP-FAST May 2007
final packet may be lost. While an EAP-FAST protected EAP Success or
EAP Failure packet should not be a final packet in an EAP-FAST
conversation, it may occur based on the conditions stated above, so
an EAP peer should not rely upon the unprotected EAP success and
failure messages.
7.6. Server Certificate Validation
As part of the TLS negotiation, the server presents a certificate to
the peer. The peer MUST verify the validity of the EAP server
certificate, and SHOULD also examine the EAP server name presented in
the certificate, in order to determine whether the EAP server can be
trusted. Please note that in the case where the EAP authentication
is remote, the EAP server will not reside on the same machine as the
authenticator, and therefore the name in the EAP server's certificate
cannot be expected to match that of the intended destination. In
this case, a more appropriate test might be whether the EAP server's
certificate is signed by a CA controlling the intended domain and
whether the authenticator can be authorized by a server in that
domain.
7.7. Tunnel PAC Considerations
Since the Tunnel PAC is stored by the peer, special care should be
given to the overall security of the peer. The Tunnel PAC must be
securely stored by the peer to prevent theft or forgery of any of the
Tunnel PAC components.
In particular, the peer must securely store the PAC-Key and protect
it from disclosure or modification. Disclosure of the PAC-Key
enables an attacker to establish the EAP-FAST tunnel; however,
disclosure of the PAC-Key does not reveal the peer or server identity
or compromise any other peer's PAC credentials. Modification of the
PAC-Key or PAC-Opaque components of the Tunnel PAC may also lead to
denial of service as the tunnel establishment will fail.
The PAC-Opaque component is the effective TLS ticket extension used
to establish the tunnel using the techniques of [RFC4507]. Thus, the
security considerations defined by [RFC4507] also apply to the PAC-
Opaque.
The PAC-Info may contain information about the Tunnel PAC such as the
identity of the PAC issuer and the Tunnel PAC lifetime for use in the
management of the Tunnel PAC. The PAC-Info should be securely stored
by the peer to protect it from disclosure and modification.
Cam-Winget, et al. Informational [Page 42]
RFC 4851 EAP-FAST May 2007
7.8. Security Claims
This section provides the needed security claim requirement for EAP
[RFC3748].
Auth. mechanism: Certificate based, shared secret based and
various tunneled authentication mechanisms.
Ciphersuite negotiation: Yes
Mutual authentication: Yes
Integrity protection: Yes, Any method executed within the EAP-FAST
tunnel is integrity protected. The
cleartext EAP headers outside the tunnel are
not integrity protected.
Replay protection: Yes
Confidentiality: Yes
Key derivation: Yes
Key strength: See Note 1 below.
Dictionary attack prot.: Yes
Fast reconnect: Yes
Cryptographic binding: Yes
Session independence: Yes
Fragmentation: Yes
Key Hierarchy: Yes
Channel binding: No, but TLVs could be defined for this.
Notes
1. BCP 86 [RFC3766] offers advice on appropriate key sizes. The
National Institute for Standards and Technology (NIST) also
offers advice on appropriate key sizes in [NIST.SP800-57].
[RFC3766] Section 5 advises use of the following required RSA or
DH module and DSA subgroup size in bits, for a given level of
attack resistance in bits. Based on the table below, a 2048-bit
RSA key is required to provide 128-bit equivalent key strength:
Attack Resistance RSA or DH Modulus DSA subgroup
(bits) size (bits) size (bits)
----------------- ----------------- ------------
70 947 129
80 1228 148
90 1553 167
100 1926 186
150 4575 284
200 8719 383
250 14596 482
Cam-Winget, et al. Informational [Page 43]
RFC 4851 EAP-FAST May 2007
8. Acknowledgements
The EAP-FAST design and protocol specification is based on the ideas
and hard efforts of Pad Jakkahalli, Mark Krischer, Doug Smith, and
Glen Zorn of Cisco Systems, Inc.
The TLV processing was inspired from work on the Protected Extensible
Authentication Protocol version 2 (PEAPv2) with Ashwin Palekar, Dan
Smith, and Simon Josefsson. Helpful review comments were provided by
Russ Housley, Jari Arkko, Bernard Aboba, Ilan Frenkel, and Jeremy
Steiglitz.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol
Version 1.0", RFC 2246, January 1999.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in RFCs",
BCP 26, RFC 2434, October 1998.
[RFC3268] Chown, P., "Advanced Encryption Standard (AES)
Ciphersuites for Transport Layer Security (TLS)",
RFC 3268, June 2002.
[RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson,
J., and H. Levkowetz, "Extensible Authentication
Protocol (EAP)", RFC 3748, June 2004.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer
Security (TLS) Protocol Version 1.1", RFC 4346,
April 2006.
[RFC4507] Salowey, J., Zhou, H., Eronen, P., and H.
Tschofenig, "Transport Layer Security (TLS)
Session Resumption without Server-Side State",
RFC 4507, May 2006.
Cam-Winget, et al. Informational [Page 44]
RFC 4851 EAP-FAST May 2007
9.2. Informative References
[EAP-PROV] Cam-Winget, N., "Dynamic Provisioning using EAP-
FAST", Work in Progress, January 2007.
[IEEE.802-1X.2004] "Local and Metropolitan Area Networks: Port-Based
Network Access Control", IEEE Standard 802.1X,
December 2004.
[NIST.SP800-57] National Institute of Standards and Technology,
"Recommendation for Key Management", Special
Publication 800-57, May 2006.
[RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS
Authentication Protocol", RFC 2716, October 1999.
[RFC3280] Housley, R., Polk, W., Ford, W., and D. Solo,
"Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL)
Profile", RFC 3280, April 2002.
[RFC3579] Aboba, B. and P. Calhoun, "RADIUS (Remote
Authentication Dial In User Service) Support For
Extensible Authentication Protocol (EAP)",
RFC 3579, September 2003.
[RFC3766] Orman, H. and P. Hoffman, "Determining Strengths
For Public Keys Used For Exchanging Symmetric
Keys", BCP 86, RFC 3766, April 2004.
[RFC4072] Eronen, P., Hiller, T., and G. Zorn, "Diameter
Extensible Authentication Protocol (EAP)
Application", RFC 4072, August 2005.
[RFC4086] Eastlake, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106,
RFC 4086, June 2005.
[RFC4282] Aboba, B., Beadles, M., Arkko, J., and P. Eronen,
"The Network Access Identifier", RFC 4282,
December 2005.
[RFC4630] Housley, R. and S. Santesson, "Update to
DirectoryString Processing in the Internet X.509
Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile",
RFC 4630, August 2006.
Cam-Winget, et al. Informational [Page 45]
RFC 4851 EAP-FAST May 2007
Appendix A. Examples
In the following examples the version field in EAP Fast is always
assumed to be 1. The S, M, and L bits are assumed to be 0 unless
otherwise specified.
A.1. Successful Authentication
The following exchanges show a successful EAP-FAST authentication
with optional PAC refreshment; the conversation will appear as
follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/EAP-FAST
(S=1, A-ID)
EAP-Response/EAP-FAST
(TLS client_hello with
PAC-Opaque in SessionTicket extension)->
<- EAP-Request/EAP-FAST
(TLS server_hello,
TLS change_cipher_spec,
TLS finished)
EAP-Response/EAP-FAST
(TLS change_cipher_spec,
TLS finished) ->
TLS channel established
(Subsequent messages sent within the TLS channel,
encapsulated within EAP-FAST)
<- EAP Payload TLV
(EAP-Request/EAP-GTC(Challenge))
EAP Payload TLV (EAP-Response/
EAP-GTC(Response with both
user name and password)) ->
optional additional exchanges (new pin mode,
password change etc.) ...
Cam-Winget, et al. Informational [Page 46]
RFC 4851 EAP-FAST May 2007
<- Intermediate-Result TLV (Success)
Crypto-Binding TLV (Request)
Intermediate-Result TLV (Success)
Crypto-Binding TLV(Response) ->
<- Result TLV (Success)
[Optional PAC TLV]
Result TLV (Success)
[PAC TLV Acknowledgment] ->
TLS channel torn down
(messages sent in clear text)
<- EAP-Success
A.2. Failed Authentication
The following exchanges show a failed EAP-FAST authentication due to
wrong user credentials; the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/EAP-FAST
(S=1, A-ID)
EAP-Response/EAP-FAST
(TLS client_hello with
PAC-Opaque in SessionTicket extension)->
<- EAP-Request/EAP-FAST
(TLS server_hello,
TLS change_cipher_spec,
TLS finished)
EAP-Response/EAP-FAST
(TLS change_cipher_spec,
TLS finished) ->
Cam-Winget, et al. Informational [Page 47]
RFC 4851 EAP-FAST May 2007
TLS channel established
(Subsequent messages sent within the TLS channel,
encapsulated within EAP-FAST)
<- EAP Payload TLV (EAP-Request/
EAP-GTC (Challenge))
EAP Payload TLV (EAP-Response/
EAP-GTC (Response with both
user name and password)) ->
<- EAP Payload TLV (EAP-Request/
EAP-GTC (error message))
EAP Payload TLV (EAP-Response/
EAP-GTC (empty data packet to
acknowledge unrecoverable error)) ->
<- Result TLV (Failure)
Result TLV (Failure) ->
TLS channel torn down
(messages sent in clear text)
<- EAP-Failure
A.3. Full TLS Handshake using Certificate-based Ciphersuite
In the case where an abbreviated TLS handshake is tried and failed,
and a fallback to certificate-based full TLS handshake occurs within
EAP-FAST Phase 1, the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/Identity
EAP-Response/
Identity (MyID1) ->
// Identity sent in the clear. May be a hint to help route
the authentication request to EAP server, instead of the
full user identity.
<- EAP-Request/EAP-FAST
(S=1, A-ID)
Cam-Winget, et al. Informational [Page 48]
RFC 4851 EAP-FAST May 2007
EAP-Response/EAP-FAST
(TLS client_hello
with PAC-Opaque extension)->
// Peer sends PAC-Opaque of Tunnel PAC along with a list of
ciphersuites supported. If the server rejects the PAC-
Opaque, it falls through to the full TLS handshake
<- EAP-Request/EAP-FAST
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
EAP-Response/EAP-FAST
([TLS certificate,]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/EAP-FAST
(TLS change_cipher_spec,
TLS finished,
EAP-Payload-TLV
(EAP-Request/Identity))
// TLS channel established
(Subsequent messages sent within the TLS channel,
encapsulated within EAP-FAST)
// First EAP Payload TLV is piggybacked to the TLS Finished as
Application Data and protected by the TLS tunnel
EAP-Payload-TLV
(EAP-Response/Identity (MyID2))->
// identity protected by TLS.
<- EAP-Payload-TLV
(EAP-Request/Method X)
EAP-Payload-TLV
(EAP-Response/Method X) ->
Cam-Winget, et al. Informational [Page 49]
RFC 4851 EAP-FAST May 2007
// Method X exchanges followed by Protected Termination
<- Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
Result TLV (Success)
Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
Result-TLV (Success) ->
// TLS channel torn down
(messages sent in clear text)
<- EAP-Success
A.4. Client Authentication during Phase 1 with Identity Privacy
In the case where a certificate-based TLS handshake occurs within
EAP-FAST Phase 1, and client certificate authentication and identity
privacy is desired, the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/Identity
EAP-Response/
Identity (MyID1) ->
// Identity sent in the clear. May be a hint to help route
the authentication request to EAP server, instead of the
full user identity.
<- EAP-Request/EAP-FAST
(S=1, A-ID)
EAP-Response/EAP-FAST
(TLS client_hello)->
<- EAP-Request/EAP-FAST
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
EAP-Response/EAP-FAST
(TLS client_key_exchange,
TLS change_cipher_spec,
TLS finished) ->
Cam-Winget, et al. Informational [Page 50]
RFC 4851 EAP-FAST May 2007
<- EAP-Request/EAP-FAST
(TLS change_cipher_spec,
TLS finished,TLS Hello-Request)
// TLS channel established
(Subsequent messages sent within the TLS channel,
encapsulated within EAP-FAST)
// TLS Hello-Request is piggybacked to the TLS Finished as
Handshake Data and protected by the TLS tunnel
// Subsequent messages are protected by the TLS Tunnel
EAP-Response/EAP-FAST
(TLS client_hello) ->
<- EAP-Request/EAP-FAST
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
EAP-Response/EAP-FAST
([TLS certificate,]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/EAP-FAST
(TLS change_cipher_spec,
TLS finished,
Result TLV (Success))
EAP-Response/EAP-FAST
(Result-TLV (Success)) ->
//TLS channel torn down
(messages sent in clear text)
<- EAP-Success
Cam-Winget, et al. Informational [Page 51]
RFC 4851 EAP-FAST May 2007
A.5. Fragmentation and Reassembly
In the case where EAP-FAST fragmentation is required, the
conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/EAP-FAST
(S=1, A-ID)
EAP-Response/EAP-FAST
(TLS client_hello)->
<- EAP-Request/EAP-FAST
(L=1,M=1, TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,])
EAP-Response/EAP-FAST ->
<- EAP-Request/EAP-FAST
(M=1,
[TLS certificate_request(con't),])
EAP-Response/EAP-FAST ->
<- EAP-Request/EAP-FAST
([TLS certificate_request(con't),]
TLS server_hello_done)
EAP-Response/EAP-FAST,
(L=1,M=1,[TLS certificate,])->
<- EAP-Request/EAP-FAST
EAP-Response/EAP-FAST
([TLS certificate(con't),]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished))->
<- EAP-Request/EAP-FAST
( TLS change_cipher_spec,
TLS finished,
EAP-Payload-TLV
(EAP-Request/Identity))
Cam-Winget, et al. Informational [Page 52]
RFC 4851 EAP-FAST May 2007
// TLS channel established
(Subsequent messages sent within the TLS channel,
encapsulated within EAP-FAST)
// First EAP Payload TLV is piggybacked to the TLS Finished as
Application Data and protected by the TLS tunnel
EAP-Payload-TLV
(EAP-Response/Identity (MyID2))->
// identity protected by TLS.
<- EAP-Payload-TLV
(EAP-Request/Method X)
EAP-Payload-TLV
(EAP-Response/Method X) ->
// Method X exchanges followed by Protected Termination
<- Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
Result TLV (Success)
Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
Result-TLV (Success) ->
// TLS channel torn down
(messages sent in clear text)
<- EAP-Success
A.6. Sequence of EAP Methods
Where EAP-FAST is negotiated, with a sequence of EAP method X
followed by method Y, the conversation will occur as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/EAP-FAST
(S=1, A-ID)
Cam-Winget, et al. Informational [Page 53]
RFC 4851 EAP-FAST May 2007
EAP-Response/EAP-FAST
(TLS client_hello)->
<- EAP-Request/EAP-FAST
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
EAP-Response/EAP-FAST
([TLS certificate,]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/EAP-FAST
(TLS change_cipher_spec,
TLS finished,
EAP-Payload-TLV(
EAP-Request/Identity))
// TLS channel established
(Subsequent messages sent within the TLS channel,
encapsulated within EAP-FAST)
// First EAP Payload TLV is piggybacked to the TLS Finished as
Application Data and protected by the TLS tunnel
EAP-Payload-TLV
(EAP-Response/Identity) ->
<- EAP-Payload-TLV
(EAP-Request/Method X)
EAP-Payload-TLV
(EAP-Response/Method X) ->
// Optional additional X Method exchanges...
<- EAP-Payload-TLV
(EAP-Request/Method X)
EAP-Payload-TLV
(EAP-Response/EAP-Type X)->
Cam-Winget, et al. Informational [Page 54]
RFC 4851 EAP-FAST May 2007
<- Intermediate Result TLV (Success),
Crypto-Binding TLV (Version=1
EAP-FAST Version=1, Nonce,
CompoundMAC),
EAP Payload TLV (EAP-Request/Method Y)
// Next EAP conversation started after successful completion
of previous method X. The Intermediate-Result and Crypto-
Binding TLVs are sent in this packet to minimize round-
trips. In this example, identity request is not sent
before negotiating EAP-Type=Y.
// Compound MAC calculated using Keys generated from
EAP methods X and the TLS tunnel.
Intermediate Result TLV (Success),
Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
EAP-Payload-TLV (EAP-Response/Method Y) ->
// Optional additional Y Method exchanges...
<- EAP Payload TLV
(EAP-Request/Method Y)
EAP Payload TLV
(EAP-Response/Method Y) ->
<- Intermediate-Result-TLV (Success),
Crypto-Binding TLV (Version=1
EAP-FAST Version=1, Nonce,
CompoundMAC),
Result TLV (Success)
Intermediate-Result-TLV (Success),
Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
Result-TLV (Success) ->
// Compound MAC calculated using Keys generated from EAP
methods X and Y and the TLS tunnel. Compound Keys
generated using Keys generated from EAP methods X and Y;
and the TLS tunnel.
Cam-Winget, et al. Informational [Page 55]
RFC 4851 EAP-FAST May 2007
// TLS channel torn down (messages sent in clear text)
<- EAP-Success
A.7. Failed Crypto-Binding
The following exchanges show a failed crypto-binding validation. The
conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/EAP-FAST
(S=1, A-ID)
EAP-Response/EAP-FAST
(TLS client_hello without
PAC-Opaque extension)->
<- EAP-Request/EAP-FAST
(TLS Server Key Exchange,
TLS Server Hello Done)
EAP-Response/EAP-FAST
(TLS Client Key Exchange,
TLS change_cipher_spec,
TLS finished)->
<- EAP-Request/EAP-FAST
(TLS change_cipher_spec,
TLS finished)
EAP-Payload-TLV(
EAP-Request/Identity))
// TLS channel established
(messages sent within the TLS channel)
// First EAP Payload TLV is piggybacked to the TLS Finished as
Application Data and protected by the TLS tunnel
EAP-Payload TLV
(EAP-Response/Identity) ->
<- EAP Payload TLV (EAP-Request/
EAP-MSCHAPV2 (Challenge))
EAP Payload TLV (EAP-Response/
EAP-MSCHAPV2 (Response)) ->
Cam-Winget, et al. Informational [Page 56]
RFC 4851 EAP-FAST May 2007
<- EAP Payload TLV (EAP-Request/
EAP-MSCHAPV2 (Success Request))
EAP Payload TLV (EAP-Response/
EAP-MSCHAPV2 (Success Response)) ->
<- Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
Result TLV (Success)
Result TLV (Failure),
Error TLV (Error Code = 2001) ->
// TLS channel torn down
(messages sent in clear text)
<- EAP-Failure
A.8. Sequence of EAP Method with Vendor-Specific TLV Exchange
Where EAP-FAST is negotiated, with a sequence of EAP method followed
by Vendor-Specific TLV exchange, the conversation will occur as
follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/EAP-FAST
(S=1, A-ID)
EAP-Response/EAP-FAST
(TLS client_hello)->
<- EAP-Request/EAP-FAST
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
Cam-Winget, et al. Informational [Page 57]
RFC 4851 EAP-FAST May 2007
EAP-Response/EAP-FAST
([TLS certificate,]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/EAP-FAST
(TLS change_cipher_spec,
TLS finished,
EAP-Payload-TLV
(EAP-Request/Identity))
// TLS channel established
(Subsequent messages sent within the TLS channel,
encapsulated within EAP-FAST)
// First EAP Payload TLV is piggybacked to the TLS Finished as
Application Data and protected by the TLS tunnel
EAP-Payload-TLV
(EAP-Response/Identity) ->
<- EAP-Payload-TLV
(EAP-Request/Method X)
EAP-Payload-TLV
(EAP-Response/Method X) ->
<- EAP-Payload-TLV
(EAP-Request/Method X)
EAP-Payload-TLV
(EAP-Response/Method X)->
<- Intermediate Result TLV (Success),
Crypto-Binding TLV (Version=1
EAP-FAST Version=1, Nonce,
CompoundMAC),
Vendor-Specific TLV
// Vendor Specific TLV exchange started after successful
completion of previous method X. The Intermediate-Result
and Crypto-Binding TLVs are sent with Vendor Specific TLV
in this packet to minimize round-trips.
// Compound MAC calculated using Keys generated from
EAP methods X and the TLS tunnel.
Cam-Winget, et al. Informational [Page 58]
RFC 4851 EAP-FAST May 2007
Intermediate Result TLV (Success),
Crypto-Binding TLV (Version=1,
EAP-FAST Version=1, Nonce,
CompoundMAC),
Vendor-Specific TLV ->
// Optional additional Vendor-Specific TLV exchanges...
<- Vendor-Specific TLV
Vendor Specific TLV ->
<- Result TLV (Success)
Result-TLV (Success) ->
// TLS channel torn down (messages sent in clear text)
<- EAP-Success
Cam-Winget, et al. Informational [Page 59]
RFC 4851 EAP-FAST May 2007
Appendix B. Test Vectors
B.1. Key Derivation
PAC KEY:
0B 97 39 0F 37 51 78 09 81 1E FD 9C 6E 65 94 2B
63 2C E9 53 89 38 08 BA 36 0B 03 7C D1 85 E4 14
Server_hello Random
3F FB 11 C4 6C BF A5 7A 54 40 DA E8 22 D3 11 D3
F7 6D E4 1D D9 33 E5 93 70 97 EB A9 B3 66 F4 2A
Client_hello Random
00 00 00 02 6A 66 43 2A 8D 14 43 2C EC 58 2D 2F
C7 9C 33 64 BA 04 AD 3A 52 54 D6 A5 79 AD 1E 00
Master_secret = T-PRF(PAC-Key,
"PAC to master secret label hash",
server_random + Client_random,
48)
4A 1A 51 2C 01 60 BC 02 3C CF BC 83 3F 03 BC 64
88 C1 31 2F 0B A9 A2 77 16 A8 D8 E8 BD C9 D2 29
38 4B 7A 85 BE 16 4D 27 33 D5 24 79 87 B1 C5 A2
Key_block = PRF(Master_secret,
"key expansion",
server_random + Client_random)
59 59 BE 8E 41 3A 77 74 8B B2 E5 D3 60 AC 4D 35
DF FB C8 1E 9C 24 9C 8B 0E C3 1D 72 C8 84 9D 57
48 51 2E 45 97 6C 88 70 BE 5F 01 D3 64 E7 4C BB
11 24 E3 49 E2 3B CD EF 7A B3 05 39 5D 64 8A 44
11 B6 69 88 34 2E 8E 29 D6 4B 7D 72 17 59 28 05
AF F9 B7 FF 66 6D A1 96 8F 0B 5E 06 46 7A 44 84
64 C1 C8 0C 96 44 09 98 FF 92 A8 B4 C6 42 28 71
Session Key Seed
D6 4B 7D 72 17 59 28 05 AF F9 B7 FF 66 6D A1 96
8F 0B 5E 06 46 7A 44 84 64 C1 C8 0C 96 44 09 98
FF 92 A8 B4 C6 42 28 71
Cam-Winget, et al. Informational [Page 60]
RFC 4851 EAP-FAST May 2007
IMCK = T-PRF(SKS,
"Inner Methods Compound Keys",
ISK,
60)
Note: ISK is 32 octets 0's.
16 15 3C 3F 21 55 EF D9 7F 34 AE C8 1A 4E 66 80
4C C3 76 F2 8A A9 6F 96 C2 54 5F 8C AB 65 02 E1
18 40 7B 56 BE EA A7 C5 76 5D 8F 0B C5 07 C6 B9
04 D0 69 56 72 8B 6B B8 15 EC 57 7B
[SIMCK 1]
16 15 3C 3F 21 55 EF D9 7F 34 AE C8 1A 4E 66 80
4C C3 76 F2 8A A9 6F 96 C2 54 5F 8C AB 65 02 E1
18 40 7B 56 BE EA A7 C5
MSK = T-PRF(S-IMCKn,
"Session Key Generating Function",
64);
4D 83 A9 BE 6F 8A 74 ED 6A 02 66 0A 63 4D 2C 33
C2 DA 60 15 C6 37 04 51 90 38 63 DA 54 3E 14 B9
27 99 18 1E 07 BF 0F 5A 5E 3C 32 93 80 8C 6C 49
67 ED 24 FE 45 40 A0 59 5E 37 C2 E9 D0 5D 0A E3
EMSK = T-PRF(S-IMCKn,
"Extended Session Key Generating Function",
64);
3A D4 AB DB 76 B2 7F 3B EA 32 2C 2B 74 F4 28 55
EF 2D BA 78 C9 57 2F 0D 06 CD 51 7C 20 93 98 A9
76 EA 70 21 D7 0E 25 54 97 ED B2 8A F6 ED FD 0A
2A E7 A1 58 90 10 50 44 B3 82 85 DB 06 14 D2 F9
Cam-Winget, et al. Informational [Page 61]
RFC 4851 EAP-FAST May 2007
B.2. Crypto-Binding MIC
[Compound MAC Key 1]
76 5D 8F 0B C5 07 C6 B9 04 D0 69 56 72 8B 6B B8
15 EC 57 7B
[Crypto-Binding TLV]
80 0C 00 38 00 01 01 00 D8 6A 8C 68 3C 32 31 A8 56 63 B6 40 21 FE
21 14 4E E7 54 20 79 2D 42 62 C9 BF 53 7F 54 FD AC 58 43 24 6E 30
92 17 6D CF E6 E0 69 EB 33 61 6A CC 05 C5 5B B7
[Server Nonce]
D8 6A 8C 68 3C 32 31 A8 56 63 B6 40 21 FE 21 14
4E E7 54 20 79 2D 42 62 C9 BF 53 7F 54 FD AC 58
[Compound MAC]
43 24 6E 30 92 17 6D CF E6 E0 69 EB 33 61 6A CC
05 C5 5B B7
Cam-Winget, et al. Informational [Page 62]
RFC 4851 EAP-FAST May 2007
Authors' Addresses
Nancy Cam-Winget
Cisco Systems
3625 Cisco Way
San Jose, CA 95134
US
EMail: ncamwing@cisco.com
David McGrew
Cisco Systems
San Jose, CA 95134
US
EMail: mcgrew@cisco.com
Joseph Salowey
Cisco Systems
2901 3rd Ave
Seattle, WA 98121
US
EMail: jsalowey@cisco.com
Hao Zhou
Cisco Systems
4125 Highlander Parkway
Richfield, OH 44286
US
EMail: hzhou@cisco.com
Cam-Winget, et al. Informational [Page 63]
RFC 4851 EAP-FAST May 2007
Full Copyright Statement
Copyright (C) The IETF Trust (2007).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Cam-Winget, et al. Informational [Page 64]