One document matched: draft-josefsson-pppext-eap-tls-eap-06.txt
Differences from draft-josefsson-pppext-eap-tls-eap-05.txt
PPPEXT Working Group Ashwin Palekar
INTERNET-DRAFT Dan Simon
Category: Standards Track Microsoft
<draft-josefsson-pppext-eap-tls-eap-06.txt> Glen Zorn
22 March 2003 Cisco
S. Josefsson
Extundo
Protected EAP Protocol (PEAP)
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
The Extensible Authentication Protocol (EAP), defined in RFC 2284,
provides for support of multiple authentication methods. While EAP
was originally created for use with PPP, it has since been adopted
for use with IEEE 802.1X "Network Port Authentication".
Since its deployment, a number of weaknesses in EAP or some EAP
protocols have become apparent. These include no per packet
confidentiality and integrity protection; which results in lack of
protection to user identity, notification messages or EAP
negotiation; and sequencing of EAP methods. In addition, there is no
standardized mechanism for key exchange; no built-in support for
fragmentation and reassembly; no support for acknowledged
success/failure indications; and no support for fast reconnect.
In addition, some EAP protocols (e.g. like EAP-MD5) are susceptible
to dictionary and brute force attacks; do not provide
confidentiality; do not support server authentication required to
prevent spoofing by rogue servers (gateways), and do not support the
generation of key strength required for 802.11i.
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By wrapping the EAP protocol within TLS, Protected EAP (PEAP)
addresses these deficiencies in EAP or EAP protocols. EAP method(s)
running within PEAP are provided with built-in support for
Privacy of user identity.
Protection to individual EAP methods. For example, protection can
provide dictionary attack resistance to protocols susceptible to
that attack.
Protected EAP notification.
Protected sequencing of EAP methods.
Protected negotiation.
Protected EAP header.
Protected exchange of parameters (TLVs) between client and server.
Standardized mechanism for key exchange.
Proven key derivation and management.
Session resumption.
Server authentication.
Protected Acknowledged and result exchange.
Fragmentation and reassembly.
Table of Contents
Protected EAP Protocol (PEAP)......................................1
1. Introduction.................................................3
1.1. Requirements language.......................................5
1.2. Terminology.................................................5
1.3. Operational model...........................................6
2. Protocol overview............................................7
2.1. PEAP Part 1.................................................8
2.2. PEAP Part 2................................................11
2.3. Version negotiation........................................12
2.4. Termination................................................12
2.5. Error handling.............................................14
2.6. Retry behavior.............................................15
2.7. Session resumption.........................................15
2.8. Fragmentation..............................................16
2.9. Key derivation.............................................17
2.10. Ciphersuite negotiation....................................18
3. Detailed description of the PEAP protocol...................18
3.1. PEAP Packet Format.........................................18
3.2. PEAP Request Packet........................................20
4. EAP TLV method..............................................23
4.1. Protected success/failure..................................23
4.2. EAP-TLV Request Packet.....................................25
4.3. EAP-TLV Response Packet....................................25
4.4. EAP-TLV TLV format.........................................26
4.5. Result TLV.................................................27
4.6. NAK TLV....................................................28
5. Security Considerations.....................................28
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5.1. Authentication and integrity protection....................28
5.2. Method negotiation.........................................29
5.3. TLS session cache handling.................................29
5.4. Certificate revocation.....................................30
5.5. Separation of the EAP server and the authenticator.........31
5.6. Separation of PEAP Part 1 and Part 2 Servers...............31
5.7. Identity verification......................................32
5.8. Man-in-the-middle protection...............................34
6. IANA Considerations.........................................35
6.1. Definition of Terms........................................35
6.2. Recommended Registration Policies..........................35
7. Normative references........................................35
8. Informative references......................................36
9. Appendix A - Examples.......................................37
10. and Contributions..........................................49
11. Intellectual Property Statement.............................50
12. Full Copyright Statement....................................51
1. Introduction
The Extensible Authentication Protocol (EAP), described in
[RFC2284], provides a standard mechanism for support of multiple
authentication methods. Through the use of EAP, support for a
number of authentication schemes may be added, including smart
cards, Kerberos, Public Key, One Time Passwords, and others.
EAP was developed or use on wired networks, where physical security
was presumed. EAP over PPP, defined in [RFC2284], is typically
deployed with leased lines or modem connections, requiring an
attacker to gain access to the telephone network in order to snoop
on the conversation or inject packets. [IEEE8021X] defines EAP over
IEEE 802 local area networks(EAPOL), presuming the existence of
switched media; in order to snoop or inject packets, an attacker
would need to gain administrative access to
the switch. Due to the presumption of physical security, facilities
for protection of the EAP conversation were not provided.
Where an attacker can easily gain access to the medium (such as on a
wireless network or where EAP is run over IP), the presumption of
physical security is no longer valid. Since the EAP method
negotiation is unprotected, an attacker can inject packets in order
to cause the negotiation of a method with lesser security. Denial of
service attacks are also possible. Since the initial EAP Identity
Request/Response exchange is sent in the clear, an attacker snooping
on the conversation can collect user identities for use in
subsequent attacks.
By initially negotiating a TLS channel, and then conducting the EAP
conversation within it, PEAP provides for per-packet encryption,
authentication, integrity and replay protection of the EAP
conversation.
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Benefits include:
Identity protection
By encrypting the identity exchange, and allowing client
credentials to be provided after negotiation of the TLS channel,
PEAP provides for identity protection.
Dictionary attack resistance
By conducting the EAP conversation within a TLS channel, PEAP
protects EAP methods that might be subject to an offline
dictionary attack were they to be conducted in the clear.
Protected negotiation
Since within PEAP, the EAP conversation is authenticated,
integrity and replay protected on a per-packet basis, the EAP
method negotiation that occurs within PEAP is protected, as are
error messages sent within the TLS channel (TLS alerts or EAP
Notification packets).
Header protection
Within PEAP, the EAP conversation is conducted within a TLS
channel. As a result, the EAP header is protected against
modification.
Protected termination
By sending success/failure indications within the TLS channel,
PEAP provides support for protected termination of the EAP
conversation. This prevents an attacker from carrying out denial
of service attacks by spoofing EAP Failure messages, or fooling
the EAP peer into accepting a rogue NAS, by spoofing EAP Success
messages.
Fragmentation and Reassembly
Since EAP does not include support for fragmentation and
reassembly, individual methods need to include this capability.
By including support for fragmentation and reassembly within
PEAP,methods leveraging PEAP do not need to support this on their
own.
Fast reconnect
Where EAP is used for authentication in wireless networks, the
authentication latency is a concern. As a result, it is valuable
to be able to do a quick re-authentication on roaming between
access points. PEAP supports this capability by leveraging the
TLS session resumption facility, and any EAP method running under
PEAP can take advantage of it.
Proven and Method independent key management
In order to provide keying material for a wide range of link
layer ciphersuites, EAP methods need to provide a key hierarchy
generating authentication and encryption keys, as well as
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initialization vectors. Development of a secure key hierarchy is
complex, and not easy to generalize for all EAP methods. By
relying on the well-reviewed TLS [RFC2246] key derivation method,
PEAP provides the required keying material for any EAP method
running within it. This frees EAP method developments from
creating keying material with key strength required for 802.11i
wireless LAN. If EAP methods will also be deployed without the
protection of PEAP or IPSEC, then the EAP methods should derive
key material of sufficient strength to prevent a Man-in-the-
middle attack described in the compound binding draft
[CompoundBinding].
1.1. Requirements language
In this document, the key words "MAY", "MUST, "MUST NOT",
"OPTIONAL", "RECOMMENDED", "SHOULD", and "SHOULD NOT", are to
be interpreted as described in [RFC2119].
1.2. Terminology
This document frequently uses the following terms:
Access Point
A Network Access Server implementing 802.11.
Authenticator
The end of the link requiring the authentication.
Backend Authentication Server
An Authentication Server is an entity that provides an
Authentication Service to an NAS. This service verifies from
the credentials provided by the peer, the claim of identity
made by the peer.
EAP server
The EAP server is the entity that terminates the EAP
conversation with the peer. The EAP server may reside on the
NAS, or alternatively within a backend authentication server.
Link layer ciphersuite
The ciphersuite negotiated for use at the link layer.
Master key
The key derived between the EAP client and EAP server during
the EAP authentication process.
Master session key
The keys derived from the master key are subsequently
used in generation of the transient session keys for
authentication, encryption, binding exchange, and
IV-generation.
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NAS Short for "Network Access Server".
Peer
The other end of the point-to-point link (PPP),
point-to-point LAN segment (IEEE 802.1X) or 802.11
wireless link, which is being authenticated by the NAS.
In IEEE 802.1X, this end is known as the Supplicant.
TLS Ciphersuite
The ciphersuite negotiated for protection of the PEAP Part 2
conversation.
Transient session keys
The transient session keys are derived from the master session
keys, and are of the appropriate size and type for use with
the chosen link layer ciphersuite.
1.3. Operational model
In EAP, the EAP server may be implemented either within a Network
Access Server (NAS) or on a backend authentication server. Where the
EAP server resides on a NAS, the NAS is required to implement the
desired EAP methods, and therefore needs to be upgraded to support
each new EAP method.
One of the goals of EAP is to enable development of new
authentication methods without requiring deployment of new code on
the Network Access Server (NAS). Where a backend authentication
server is deployed, the NAS acts as a "passthrough" and need not
understand specific EAP methods.
This allows new EAP methods to be deployed on the EAP peer and
backend authentication server, without the need to upgrade code
residing on the NAS.
Figure 1 describes the relationship between the EAP peer, NAS and
EAP server. As described in the figure, the EAP conversation occurs
between the EAP peer and EAP server, "passing through" the NAS. In
order for the conversation to proceed in the case where the NAS and
EAP server reside on separate machines, the NAS and EAP server need
to establish trust beforehand.
In PEAP, the conversation between the EAP peer and the EAP server is
encrypted, authenticated, integrity and replay protected within a
TLS channel, and mutual authentication is required between the EAP
peer and the EAP server.
As a result, where the NAS acts as a "passthrough" it does not have
knowledge of the TLS master secret derived between the EAP Peer and
the EAP server. In order to provide keying material for link-layer
ciphersuites, the NAS obtains the master session keys, which are
derived from the TLS master secret via a one-way function. This
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enables the NAS and EAP peer to derive keys suitable for encrypting,
authenticating and integrity protecting session data. However, the
NAS cannot decrypt the PEAP conversation or spoof session
resumption, since this requires knowledge of the TLS master secret.
+-+-+-+-+-+ +-+-+-+-+-+
| | | |
| Link | | Link |
| Layer | | Layer |
| Cipher- | | Cipher- |
| Suite | | Suite |
| | | |
+-+-+-+-+-+ +-+-+-+-+-+
^ ^
| |
| |
| |
V V
+-+-+-+-+-+ +-+-+-+-+-+ Trust +-+-+-+-+-+
| | EAP | |<======>| |
| | Conversation | | | |
| EAP |<================================>| EAP |
| Peer | (over PPP, | NAS | | Server |
| | 802.11,etc.) | |<=======| |
| | | | Keys | |
| | | | | |
+-+-+-+-+-+ +-+-+-+-+-+ +-+-+-+-+-+
^ ^
| |
| EAP API | EAP API
| |
V V
+-+-+-+-+-+ +-+-+-+-+-+
| | | |
| | | |
| EAP | | EAP |
| Method | | Method |
| | | |
+-+-+-+-+-+ +-+-+-+-+-+
Figure 1 - Relationship between EAP client, backend authentication
server and NAS.
2. Protocol overview
Protected EAP (PEAP) is comprised of a two-part conversation:
[1] In Part 1, a TLS session is negotiated, with server
authenticating to the client and optionally the client to the
server. The negotiated key is then used to encrypt the rest of
the conversation.
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[2] In Part 2, within the TLS session, a complete EAP conversation
is carried out, unless part 1 provided client authentication.
In the next two sections, we provide an overview of each of the
parts of the PEAP conversation.
2.1. PEAP Part 1
The PEAP conversation typically begins with an optional identity
exchange. The authenticator will typically send an EAP-
Request/Identity packet to the peer, and the peer will respond with
an EAP-Response/Identity packet to the authenticator, containing the
peer's EAP-ID. Since the initial identity exchange is used
primarily to route the EAP conversation to the EAP server, if the
EAP server is known in advance (such as when all users authenticate
against the same backend server infrastructure and roaming is not
supported), or if the identity is otherwise determined (such as from
the dialing phone number or client MAC address), then the identity
exchange MAY be omitted.
Once the optional initial Identity Request/Response exchange is
completed, while nominally the EAP conversation occurs between the
authenticator and the peer, the authenticator MAY act as a
passthrough device, with the EAP packets received from the peer
being encapsulated for transmission to a backend authentication
server. However, PEAP does not require a backend authentication
server; if the authenticator implements PEAP and is provisioned with
the appropriate certificates, then it can authenticate local users.
In the discussion that follows, we will use the term "EAP server" to
denote the ultimate endpoint conversing with the peer.
Once having received the peer's Identity, and determined that PEAP
authentication is to occur, the EAP server MUST respond with a
PEAP/Start packet, which is an EAP-Request packet with EAP-
Type=PEAP,the Start (S) bit set, and no data. Assuming that the
peer supports PEAP, the PEAP conversation will then begin, with the
peer sending an EAP-Response packet with EAP-Type=PEAP.
The data field of the EAP-Response packet will encapsulate one or
more TLS records in TLS record layer format, containing a TLS
client_hello handshake message. The current cipher spec for the TLS
records will be TLS_NULL_WITH_NULL_NULL and null compression. This
current cipher spec remains the same until the change_cipher_spec
message signals that subsequent records will have the negotiated
attributes for the remainder of the handshake.
The client_hello message contains the client's TLS version number, a
sessionId, a random number, and a set of TLS ciphersuites supported
by the client. The version offered by the client MUST correspond to
TLS v1.0 or later.
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The EAP server will then respond with an EAP-Request packet with
EAP-Type=PEAP. The data field of this packet will encapsulate one or
more TLS records. These will contain a TLS server_hello handshake
message, possibly followed by TLS certificate, server_key_exchange,
certificate_request, server_hello_done and/or finished handshake
messages, and/or a TLS change_cipher_spec message.
Since after the TLS session is established, another complete EAP
negotiation will occur and the peer will authenticate using a
secondary mechanism, with PEAP the client need not authenticate as
part of TLS session establishment. As a result, although the EAP-
Request packet sent by the EAP Server MAY contain a
certificate_request message, this is not required.
The certificate_request message indicates that the server desires
the client to authenticate itself via public key. Typically when the
EAP server sends a certificate_request message, the intent is to
complete the PEAP authentication without requiring negotiation of an
additional EAP method. However, it is valid for the server to
request a certificate in the server_hello and for the client refuse
to provide one. In this case, the EAP server MUST require that PEAP
Part 2 be completed.
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 PEAP part 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 PEAP part 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.
The server_hello handshake message contains a TLS version number,
another random number, a sessionId, and a TLS ciphersuite. The
version offered by the server MUST correspond to TLS v1.0 or later.
In order to provide confidentiality, integrity and replay
protection, and authentication, the negotiated TLS ciphersuite MUST
provide all of these security services.
If the client's sessionId is null or unrecognized by the server, the
server MUST choose the sessionId to establish a new session;
otherwise, the sessionId will match that offered by the client,
indicating a resumption of the previously established session with
that sessionId. The server will also choose a TLS ciphersuite from
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those offered by the client; if the session matches the client's,
then the TLS ciphersuite MUST match the one negotiated during the
handshake protocol execution that established the session.
PEAP implementations need not necessarily support all TLS
ciphersuites listed in [RFC2246]. Not all TLS ciphersuites are
supported by available TLS tool kits and licenses may be required to
support some TLS ciphersuites (e.g. TLS ciphersuites utilizing the
IDEA encryption algorithm). To ensure interoperability, PEAP peers
and Authenticators MUST support and be able to negotiate the
following TLS ciphersuites:
TLS_RSA_WITH_RC4_128_MD5
TLS_RSA_WITH_RC4_128_SHA
TLS_RSA_WITH_3DES_EDE_CBC_SHA (FIPS compliant)
TLS as described in [RFC2246] supports compression as well as
ciphersuite negotiation. Therefore during the PEAP Part 1
conversation the EAP endpoints MAY request or negotiate TLS
compression.
If the EAP server is not resuming a previously established session,
then it MUST include a TLS server_certificate handshake message, and
a server_hello_done handshake message MUST be the last handshake
message encapsulated in this EAP-Request packet.
The certificate message contains a public key certificate chain for
either a key exchange public key (such as an RSA or Diffie-Hellman
key exchange public key) or a signature public key (such as an RSA
or DSS signature public key). In the latter case, a TLS
server_key_exchange handshake message MUST also be included to allow
the key exchange to take place.
The peer MUST respond to the EAP-Request with an EAP-Response packet
of EAP-Type=PEAP. The data field of this packet will encapsulate
one or more TLS records containing a TLS change_cipher_spec message
and finished handshake message, and possibly certificate,
certificate_verify and/or client_key_exchange handshake messages.
If the preceding server_hello message sent by the EAP server in the
preceding EAP-Request packet indicated the resumption of a previous
session, then the peer MUST send only the change_cipher_spec and
finished handshake messages.
The finished message contains the peer's authentication response to
the EAP server.
If the preceding server_hello message sent by the EAP server in the
preceding EAP-Request packet did not indicate the resumption of a
previous session, then the peer MUST send, in addition to the
change_cipher_spec and finished messages, a client_key_exchange
message, which completes the exchange of a shared master secret
between the peer and the EAP server.
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The EAP server MUST then respond with an EAP-Request packet with
EAP-Type=PEAP, which includes, in the case of a new TLS session, one
or more TLS records containing TLS change_cipher_spec and finished
handshake messages. The latter contains the EAP server's
authentication response to the peer. The peer will then verify the
hash in order to authenticate the EAP server.
If the EAP server authenticates unsuccessfully, the peer MAY send an
EAP-Response packet of EAP-Type=PEAP containing a TLS Alert message
identifying the reason for the failed authentication. The peer MAY
send a TLS alert message rather than immediately terminating the
conversation so as to allow the EAP server to log the cause of the
error for examination by the system administrator.
To ensure that the EAP Server receives the TLS alert message, the
peer MUST wait for the EAP-Server to reply before terminating the
conversation. The EAP Server MUST reply with an EAP-Failure packet
since server authentication failure is a terminal condition.
If the EAP server authenticates successfully, the peer MUST send an
EAP-Response packet of EAP-Type=PEAP, and no data. The EAP-Server
then continues with Part 2 of the PEAP conversation.
2.2. PEAP Part 2
The second portion of the PEAP conversation consists of another
complete EAP conversation occurring within the TLS session
negotiated in PEAP Part 1. It will therefore occur only if
establishment of a new TLS session in Part 1 is successful or a TLS
session is successfully resumed in Part 1.
It MUST NOT occur if the EAP Server authenticates unsuccessfully or
if an EAP-Failure has been sent by the EAP Server to the peer,
terminating the conversation. Since all packets sent within the
PEAP Part 2 conversation occur after TLS session establishment, they
are protected using the negotiated TLS ciphersuite. All EAP packets
of the EAP conversation in part 2 including the EAP header are
protected using the negotiated TLS ciphersuite.
Part 2 of the PEAP conversation typically begins with the
Authenticator sending an EAP-Request/Identity packet to the peer,
protected by the TLS ciphersuite negotiated in PEAP Part 1. The peer
responds with an EAP-Response/Identity packet to the authenticator,
containing the peer's userId. Since this Identity Request/Response
exchange is protected by
the ciphersuite negotiated in TLS, it is protected against snooping
or packet modification attacks.
After the TLS session-protected Identity exchange, the EAP server
will then select authentication method(s) for the peer, and will
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send an EAP-Request with the EAP-Type set to the initial method. As
described in [RFC2284], the peer can NAK the suggested EAP method,
suggesting an alternative. Since the NAK will be sent within the TLS
channel, it is protected from snooping or packet modification. As a
result, an attacker snooping on the exchange will be unable to
inject NAKs in order to "negotiate down" the authentication method.
An attacker will also not be able to determine which EAP method was
negotiated.
2.3. Version negotiation
PEAP packets contain a three bit version field, which enables PEAP
implementations to be backward compatible with previous versions of
the protocol. Implementations of this specification MUST use a
version field set to 2. This specification documents the protocol
for version 2.
Version negotiation proceeds as follows:
[1] In the first EAP-Request sent with EAP type=PEAP, the EAP
server MUST set the version field to the highest supported version
number.
[2] If the EAP client supports this version of the protocol, it
MUST respond with an EAP-Response of EAP type=PEAP, and the version
number proposed by the EAP server.
[3] If the EAP client does not support this version, it responds
with an EAP-Response of EAP type=PEAP and the highest supported
version number.
[4] If the EAP server supports the version proposed by the client,
then all future EAP-Request packets of EAP type=PEAP MUST include
the version field set to the agreed upon version number. Similarly,
the EAP client MUST include the agreed upon version number in all
EAP-Response packets of EAP type=PEAP.
[5] If the PEAP server does not support the version number proposed
by the PEAP client, it terminates the conversation, as described in
Section 2.4.
This version negotiation procedure guarantees that the EAP client
and server will agree to the latest version supported by both
parties. If version negotiation fails, then use of PEAP will not be
possible, and another mutually acceptable EAP method will need to be
negotiated if authentication is to proceed. In order to protect
against a downgrade version attack between PEAP versions support by
the peers, the peers MUST exchange information on the highest
version number supported during the binding exchange.
2.4. Termination
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As described in [RFC2284], EAP Success and Failure packets are not
authenticated, so that they may be forged by an attacker without
fear of detection. Forged EAP Failure packets can be used to
convince an EAP peer to disconnect. Forged EAP Success packets may
be used by a rogue NAS to convince a peer to let itself access the
network, even though the NAS has not authenticated itself.
By requiring mutual authentication and by supporting encrypted,
authenticated and integrity protected success/failure indications,
(described below as "protected" indications) PEAP provides
protection against these attacks. Within PEAP, protected
success/failure indications are supported by sending these
indications within the TLS channel.
PEAP support for protected success/failure indications is
constrained by the [RFC2284] and [IEEE8021X] specifications. In
[IEEE8021X], the authenticator "manufactures" cleartext EAP Success
and Failure packets based on the result indicated by the backend
authentication server. As a result, were a PEAP server to send a
protected EAP Success or EAP Failure packet as the final packet
within the EAP exchange, authenticators compliant with [IEEE8021X]
would silently discard the packet, and replace it with a cleartext
EAP Success or Failure. Since the client will discard these
unprotected indications, where an authenticator compliant with
[IEEE8021X] is present, it is not be possible to conclude a
successful authentication. As a result, this approach does not
provide reliable authenticated success/failure indications on all
media.
In addition, [RFC2284] states that an EAP Success or EAP Failure
packet terminates the EAP conversation, so that no response is
possible. Since EAP Success and EAP Failure packets are not
retransmitted, if the final packet is lost, then authentication will
fail. As a result, where packet loss is expected to be non-
negligible, unacknowledged success/failure indications lack
robustness.
As a result, a PEAP server SHOULD NOT send a protected EAP Success
or EAP Failure packet as the final packet within a PEAP
conversation. However, in the spirit of being "conservative in what
you send, liberal in what you receive", a PEAP client SHOULD accept
and process such a packet if it is received. This behavior makes it
possible for implementations to save a round-trip (improving the
performance of fast reconnect), assuming that the authentication
occurs within a low packet loss environment in which "manufacture"
of packets is guaranteed not to occur.
Instead, EAP servers MUST utilize the acknowledged and protected
success/failure indications defined in Section 4. In this approach,
the PEAP server sends the success/failure indication as an EAP-
Request with type=33 (EAP TLV), protected within the TLS channel.
The PEAP client then replies with a protected success/failure
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indication as an EAP-Response with type=33 (EAP TLV). The
conversation concludes with the PEAP server sending a cleartext
success/failure indication.
Since both sides have already concluded a protected termination
conversation, this final packet is ceremonial.
Use of a protected and acknowledged success/failure indication
provides the PEAP protocol immunity against the "manufacture" of
cleartext success/failure indications mandated by [IEEE8021X]. It
also enables both sides of the conversation to communicate the
outcome of PEAP mutual authentication, although the TLS alert
mechanism already provides this capability to some extent. On the
other hand, this approach requires an extra round-trip, which
affects the performance of fast reconnect.
Once PEAP has been selected as the authentication method, compliant
PEAP implementations MUST silently discard unprotected success
indications (e.g. cleartext EAP Success) unless both the PEAP peer
and server have indicated a successful authentication exchange via
the mechanism described in Section 4.
Similarly, once the TLS channel has been set up, compliant PEAP
implementations MUST silently discard unprotected failure
indications (e.g. cleartext EAP Failure) unless they are proceeded
by a protected failure indication. Protected failure indications
include the TLS alert mechanism, as well the indication mechanism
described in Section 4. For example, if a PEAP peer has previously
received a protected EAP-Request of Type=33 (EAP TLV) with
Result=Failure, or if it has received a protected EAP-Request of
Type=33 (EAP-TLV) with Result=Success, and responded with a
protected EAP-Response of Type=33 (EAP-TLV) with Result=Failure,
then it will accept and process a cleartext EAP Failure.
However, if a PEAP peer has previously received a protected EAP-
Request of Type=33 (EAP-TLV) with Result=Success, and has responded
with a protected EAP-Request of Type=33 (EAP-TLV) with
Result=Success, then an unprotected failure indication MUST be
silently discarded.
Prior to establishment of the TLS channel, no keying material
exists, so that protected success/failure indications are not
possible. However, within PEAP a failure to establish the TLS
channel (e.g. failure to verify the server certificate) is
considered an unrecoverable error, so that where this failure has
occurred, an unprotected failure indication can be safely accepted.
2.5. Error handling
Other than supporting TLS alert messages, PEAP does not have its own
error message capabilities. This is unnecessary since errors in the
PEAP Part 1 conversation are communicated via TLS alert messages,
and errors in the PEAP Part 2 conversation are expected to be
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handled by individual EAP methods.
If an error occurs at any point in the PEAP conversation, the EAP
server SHOULD send an EAP-Request packet with EAP-Type=PEAP,
encapsulating a TLS record containing the appropriate TLS alert
message. The EAP server SHOULD send a 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. To ensure that the peer receives the
TLS alert message, the EAP server MUST wait for the peer to reply
with an EAP-Response packet.
2.6. Retry behavior
As with other EAP protocols, the EAP server is responsible for retry
behavior. This means that if the EAP server does not receive a reply
from the peer, it MUST resend the EAP-Request for which it has not
yet received an EAP-Response. However, the peer MUST NOT resend EAP-
Response packets without first being prompted by the EAP server.
For example, if the initial PEAP start packet sent by the EAP server
were to be lost, then the peer would not receive this packet, and
would not respond to it. As a result, the PEAP start packet would be
resent by the EAP server. Once the peer received the PEAP start
packet, it would send an EAP-Response encapsulating the client_hello
message. If the EAP-Response were to be lost, then the EAP server
would resend the initial PEAP start, and the peer would resend the
EAP-Response.
As a result, it is possible that a peer will receive duplicate EAP-
Request messages, and may send duplicate EAP-Responses. Both the
peer and the EAP Server should be engineered to handle this
possibility.
2.7. Session resumption
The purpose of the sessionId within the TLS protocol is to allow for
improved efficiency in the case where a client repeatedly attempts
to authenticate to an EAP server within a short period of time. This
capability is particularly useful for support of wireless roaming.
It is left up to the peer whether to attempt to continue a previous
session, thus shortening the PEAP Part 1 conversation. Typically the
peer's decision will be made based on the time elapsed since the
previous authentication attempt to that EAP server.
Based on the sessionId chosen by the peer, and the time elapsed
since the previous authentication, the EAP server will decide
whether to allow the continuation, or whether to choose a new
session.
In the case where the EAP server and the authenticator reside on the
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same device, then the client will only be able to continue sessions
when connecting to the same NAS or channel server. Should these
devices be set up in a rotary or round-robin then it may not be
possible for the peer to know in advance the authenticator it will
be connecting to, and therefore which sessionId to attempt to reuse.
As a result, it is likely that the continuation attempt will fail.
In the case where the EAP authentication is remoted then
continuation is much more likely to be successful, since multiple
NAS devices and channel servers will remote their EAP
authentications to the same backend authentication server.
If the EAP server is resuming a previously established session, then
it MUST include only a TLS change_cipher_spec message and a TLS
finished handshake message after the server_hello message. The
finished message contains the EAP server's authentication response
to the peer.
After a session is successfully resumed, the EAP-Server starts with
Part 2 of the PEAP conversation. The peer may have roamed to a
different network and successfully resumed with same EAP server. The
peer and the EAP server MUST not assume that a session resume
implies either of them will skip inner EAP methods.
2.8. 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 16MB. The group of PEAP messages sent
in a single round may thus be larger than the PPP MTU size, the
maximum RADIUS packet size of 4096 octets, or even the Multilink
Maximum Received Reconstructed Unit (MRRU). As described in [2],
the multilink MRRU is negotiated via the Multilink MRRU LCP option,
which includes an MRRU length field of two octets, and thus can
support MRRUs as large as 64 KB.
However, 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 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.
If this value is chosen, then fragmentation can be handled via the
multilink PPP fragmentation mechanisms described in [RFC1990]. While
this is desirable, EAP methods are used in other applications such
as [IEEE80211] and there may be cases in which multilink or the MRRU
LCP option cannot be negotiated. As a result, a PEAP implementation
MUST provide its own support for fragmentation and reassembly.
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Since EAP is an ACK-NAK 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 as is provided in IPv4.
PEAP fragmentation support is provided through 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 PEAP 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 PEAP 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 a PEAP peer receives an EAP-Request packet with the M bit set,
it MUST respond with an EAP-Response with EAP-Type=PEAP 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 server receives an EAP-Response with the M
bit set, it MUST respond with an EAP-Request with EAP-Type=PEAP 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.
2.9. Key derivation
Since the normal TLS keys are used in the handshake, and therefore
should not be used in a different context, new keys must be derived
from the TLS master secret for use with the selected link layer
ciphersuites.
In the most general case, keying material must be provided for
authentication, encryption and initialization vectors (IVs) in each
direction.
Since EAP methods may not know the link layer ciphersuite that has
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been negotiated, it may not be possible for them to provide link
layer ciphersuite-specific keys. In addition, attempting to provide
such keys is undesirable, since it would require the EAP method to
be revised each time a new link layer ciphersuite is developed. As a
result, PEAP derives master session keys which can subsequently be
truncated for use with a particular link layer ciphersuite. Since
the truncation algorithms are ciphersuite-specific, they are not
discussed here; examples of such algorithms are provided in
[RFC3079]. This draft also does not discuss the format of the
attributes used to communicate the master session keys from the
backend authentication server to the NAS; examples of such
attributes are provided in [RFC2548].
Both the peer and EAP server MUST derive master session keys as
described in the compound Session Key derivation section (section
4.2) of the draft Compound Authentication Binding Problem
[compoundbinding].
Algorithms for the truncation of these encryption and authentication
master session keys are specific to each link layer ciphersuite.
Link layer ciphersuites in use with PPP include DESEbis [RFC2419],
3DES [RFC2420] and MPPE [RFC3078]. IEEE 802.11 ciphersuites are
described in [IEEE80211]. An example of how encryption keys for use
with MPPE [RFC3078] are derived from the TLS master session keys is
given in [RFC3079].
2.10. Ciphersuite negotiation
Since TLS supports TLS ciphersuite negotiation, peers completing the
TLS negotiation will also have selected a TLS ciphersuite, which
includes key strength, encryption and hashing methods. However,
unlike in [RFC2716], within PEAP, the negotiated TLS ciphersuite
relates only to the mechanism by which the PEAP Part 2 conversation
will be protected, and has no relationship to link layer security
mechanisms negotiated within the PPP Encryption Control Protocol
(ECP) [RFC1968] or within IEEE 802.11 [IEEE80211].
As a result, this specification currently does not support secure
negotiation of link layer ciphersuites, although this capability may
be added in future by addition of TLVs to the EAP TLV method defined
in Section 4.
3. Detailed description of the PEAP protocol
3.1. PEAP Packet Format
A summary of the PEAP Request/Response packet format is shown 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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Flags | Ver | Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code
1 - Request
2 - Response
Identifier
The Identifier field is one octet and aids in matching responses
with requests.
Length
The Length field is two octets and indicates the length of the
EAP packet including the Code, Identifier, Length, Type, 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
25 - PEAP
Flags
0 1 2 3 4
+-+-+-+-+-+
|L M S R R|
+-+-+-+-+-+
L = Length included
M = More fragments
S = PEAP start
R = Reserved (must be zero)
The L bit (length included) 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
bit(more fragments) is set on all but the last fragment. The S bit
(PEAP start) is set in a PEAP Start message. This differentiates the
PEAP Start message from a fragment acknowledgment.
Version
0 1 2
+-+-+-+
|R|1|0|
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+-+-+-+
R = Reserved (must be zero)
Data
The format of the Data field is determined by the Code field.
3.2. PEAP Request Packet
A summary of the PEAP Request packet format is shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Flags | Ver | TLS Message Length
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLS Message Length | TLS Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code
1
Identifier
The Identifier field is one octet and aids in matching responses
with requests. The Identifier field MUST be changed on each Request
packet.
Length
The Length field is two octets and indicates the length of the
EAP packet including the Code, Identifier, Length, Type, and TLS
Response fields.
Type
25 - PEAP
Flags
0 1 2 3 4
+-+-+-+-+-+
|L M S R R|
+-+-+-+-+-+
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L = Length included
M = More fragments
S = PEAP start
R = Reserved (must be zero)
The L bit (length included) 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
bit(more fragments) is set on all but the last fragment. The S bit
(PEAP start) is set in a PEAP Start message. This differentiates the
PEAP Start message from a fragment acknowledgment.
Version
0 1 2
+-+-+-+
|R|1|0|
+-+-+-+
R = Reserved (must be zero)
TLS Message Length
The TLS Message Length field is four octets, and is present only
if the L bit is set. This field provides the total length of the
TLS message or set of messages that is being fragmented.
TLS data
The TLS data consists of the encapsulated packet in TLS record
format.
3.3. PEAP Response Packet
A summary of the PEAP Response packet format is shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Flags |Ver| TLS Message Length
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLS Message Length | TLS Data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code
2
Identifier
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The Identifier field is one octet and 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, and TLS
data fields.
Type
25 - PEAP
Flags
0 1 2 3 4
+-+-+-+-+-+
|L M S R R|
+-+-+-+-+-+
L = Length included
M = More fragments
S = PEAP start
R = Reserved (must be zero)
The L bit (length included) 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
bit (more fragments) is set on all but the last fragment. The S bit
(PEAP start) is set in a PEAP Start message. This differentiates the
PEAP Start message from a fragment acknowledgment.
Version
0 1 2
+-+-+-+
|R|1|0|
+-+-+-+
R = Reserved (must be zero)
TLS Message Length
The TLS Message Length field is four octets, and is present only
if the L bit is set. This field provides the total length of the TLS
message or set of messages that is being fragmented.
TLS data
The TLS data consists of the encapsulated TLS packet in TLS record
format.
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4. EAP TLV method
The EAP-TLV method is a payload with standard Type-Length-Value
(TLV) objects. The TLV objects could be used to carry arbitrary
parameters between EAP peer and EAP server. Possible uses for TLV
objects include: language and character set for Notification
messages; cryptographic binding; IPv6 Binding Update.
The EAP peer may not necessarily implement all the TLVs supported by
the EAP server; and hence to allow for interoperability, the TLV
method allows a EAP server to discover if a TLV is supported by the
EAP peer, using the NAK TLV.
The mandatory bit in a TLV indicates that the peer MUST understand
the TLV. A peer can determine that a TLV is unknown when it does not
support the TLV; or when the TLV is corrupted. The mandatory bit
does not indicate that the peer successfully applied the value of
the TLV. The specification of a TLV could define additional
conditions under which the TLV can be determined to be unknown.
If an EAP peer finds an unknown TLV which is marked as mandatory; it
MUST indicate a failure to the EAP server using the NAK TLV; and all
the other TLVs in the message MUST be ignored.
If an EAP peer finds an unknown TLV which is marked as optional;
then it MUST ignore the TLV. The EAP peer is not required to inform
the EAP server of unknown TLVs which are marked as optional. If the
EAP peer finds that the packet has no TLVs, then it MUST send a
response with EAP-TLV Response Packet. The Response packet may
contain no TLVs.
If an EAP server finds an unknown TLV which is marked as mandatory;
the other TLVs in the message MUST be ignored. The EAP server can
drop the connection or send a EAP-TLV request packet with NAK-TLV to
the EAP client.
Compliant PEAP implementations MUST support the EAP TLV method,
processing of mandatory/optional settings on the TLV, the NAK TLV.
TLVs can be contained/nested in other TLVs. A EAP-TLV Request packet
is a EAP method; and it can be sequenced before or after any other
EAP method. The packet does not have to contain any TLVs or does not
have to contain any mandatory TLVs.
4.1. Protected success/failure
Compliant PEAP implementations MUST support acknowledged protected
success/failure together with the Binding exchange.
The Result TLV is used to indicate success or failure of the PEAP
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tunnel. The PEAP tunnel success/failure packet MUST contain a Result
TLV along with the Cryto-Binding TLV. Crypto-Binding TLV may be used
in other EAP-TLV packets. Result TLV MUST NOT be sent in packets
other than the protected success/failure indication.
If a CRYPTO BINDING TLV does not exist in a packet that contains
Result TLV, then the EAP peer must disconnect the connection.
If a CRYPTO BINDING TLV fails validation, then peer must disconnect
the connection. Implementations that can delete the TLS handle MUST
delete the TLS handle. Implementations that keep track of session
state MUST ensure that the session handle cannot be used to skip
stage2 authentication.
When using the Result-TLV, the only outcome which should be
considered as successful authentication is when an EAP Request of
Type=EAP-TLVs with Result TLV of Status=Success is answered by an
EAP Response of Type=EAP-TLVs with Result TLV of Status=Success.
If the EAP server has set Result-TLV with Status=Success; and the
response from the EAP peer is Status=Failure, then the server MUST
either continue EAP conversation or return Result=TLV with
Status=Failure. This allows EAP peer to indicate that it refuses to
accept the authentication without negotiating certain auth methods
as per its policy.
All other combinations (EAP-TLVs Failure, EAP-TLVs Success), (EAP-
TLVs Failure, EAP-TLVs Failure), (no EAP-TLVs exchange or no
protected EAP Success or Failure, no Crypto-Binding TLVs, crypto-
binding TLV validation is not successful) should be considered
failed authentications, both by the PEAP peer and authenticator.
Once the PEAP peer and authenticator considers them as failed
authentications, they are the last packets inside the protected
tunnel. These are considered failed authentications regardless of
whether a cleartext EAP Success or EAP Failure packet is
subsequently sent. Because the EAP-TLVs method is protected within
the TLS channel, these packets cannot be spoofed, whereas cleartext
EAP Success and EAP Failure messages can be sent by an attacker.
In order for the validation of crypto-binding TLV to be successful,
the EAP server and EAP peer should be in-sync on which EAP methods
inside the tunnel have been successful. If any or all EAP methods
inside the tunnels have failed as per EAP server or EAP peer, then
that does not mean the Result will always be set to failure.
In a successful authentication for a tunnel, the last packet
exchange (both request and response) inside the tunnel MUST always
contain a valid Crypto-Binding TLV and Result-TLV=Success.
Compliant PEAP implementations MUST support the EAP TLV method,
processing of mandatory/optional settings on the TLV, the NAK TLV,
Result-TLV, Method-Identity-TLV, Crypto-Binding-TLV.
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4.2. EAP-TLV Request Packet
A summary of the EAP EAP-TLVs Request packet format is shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Data....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Code
1
Identifier
The Identifier field is one octet and aids in matching responses
with requests. The Identifier field MUST be changed on each Request
packet.
Length
The Length field is two octets and indicates the length of the
EAP packet including the Code, Identifier, Length, Type, and Data
fields.
Type
33 - EAP-TLV
Data
The Data field is of variable length, and contains EAP-TLV TLVs.
4.3. EAP-TLV Response Packet
A summary of the EAP-TLV Response packet format is shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code | Identifier | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Data....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Code
2
Identifier
The Identifier field is one octet and aids in matching responses
with requests. The Identifier field MUST be changed on each Request
packet.
Length
The Length field is two octets and indicates the length of the
EAP packet including the Code, Identifier, Length, Type, and Data
fields.
Type
33 - EAP EAP-TLV
Data
The Data field is of variable length, and contains Attribute-
Value Pairs (TLVs).
4.4. EAP-TLV TLV format
EAP-TLV TLVs are 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
0 - Non-mandatory TLV
1 - Mandatory TLV
R
Reserved, set to 0.
TLV Type
A 14-bit field, denoting the attribute type. Allocated TLV Types
include:
0 - Reserved
1 - Reserved
2 - Reserved
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3 - - RESULT_TLV - Acknowledged Result
4 - NAK_TLV
5 - CRYPTO_BINDING TLV
6 - METHOD_IDENTITY TLV
Length
The length of the Value field in octets.
Value
The value of the attribute.
CRYPTO_BINDING_TLV and METHOD_IDENTITY_TLV are defined in the draft
Compound Authentication Binding Problem[CompoundBinding].
4.5. Result TLV
The Result TLV provides support for acknowledged Success and Failure
messages within PEAP. It 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
1 - Mandatory TLV
R
Reserved, set to zero (0)
TLV Type
3 - Success/Failure
Length
2
Status
The status field is two octets. Values include:
1 - Success
2 - - Failure
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4.6. NAK TLV
The NAK TLV allows a peer to detect when TLVs that are not supported
by the other peer. It 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type number | TLVsą |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M
1 - Mandatory TLV
R
Reserved, set to zero (0)
TLV Type
4 -
Length
<tbd>
TLV Type number.
The field contains TLV type that is not supported.
TLVs..
The field contains a list of optional TLVs. These could be used
in future to send information on why the field was determined to
be unknown.
5. Security Considerations
5.1. Authentication and integrity protection
The EAP-TLV method is presumed to run before or after an EAP
method that supports mutual authentication and establishes a
protected channel. PEAP is such a method, and as a result the
acknowledged Success and Failure messages are always protected.
Note however, that [IEEE8021X] manufactures cleartext EAP Success
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and EAP Failure messages, so that even though the Result TLV will be
protected, this will be followed by a cleartext EAP Success or EAP
Failure packet.
5.2. Method negotiation
If the peer does not support PEAP, or does not wish to utilize PEAP
authentication, it MUST respond to the initial EAP-Request/PEAP-
Start with a NAK, suggesting an alternate authentication method.
Since the NAK is sent in cleartext with no integrity protection or
authentication, it is subject to spoofing. Unauthentic NAK packets
can be used to trick the peer and Authenticator into "negotiating
down" to a weaker form of authentication, such as EAP-MD5 (which
only provides one way authentication and does not derive a key).
Since a subsequent protected EAP conversation can take place within
the TLS session, selection of PEAP as an authentication method does
not limit the potential secondary authentication methods. As a
result, the only legitimate reason for a peer to NAK PEAP as an
authentication method is that it does not support it. Where the
additional security of PEAP is required, server implementations
SHOULD respond to a NAK with an EAP-Failure, terminating the
authentication conversation.
5.3. TLS session cache handling
In cases where a TLS session has been successfully resumed, in some
circumstances, it is possible for the EAP server to skip the PEAP
Part 2 conversation, and successfully conclude the conversation as
described in Section 2.4.
PEAP "fast reconnect" is desirable in applications such as wireless
roaming, since it minimizes interruptions in connectivity. It is
also desirable when the "inner" EAP mechanism used is such that it
requires user interaction. The user should not be required to re-
authenticate herself, using biometrics, token cards or similar,
every time the radio connectivity is handed over between access
points in wireless environments.
However, there are issues that need to be understood in order to
avoid introducing security vulnerabilities.
Since PEAP Part 1 may not provide client authentication,
establishment of a TLS session (and an entry in the TLS session
cache) does not by itself provide an indication of the peer's
authenticity. The peer's authenticity is only proven after
successful completion of the protected acknowledge exchange in PEAP
part 2.
Some PEAP implementations may not be capable of removing TLS session
cache entries established in PEAP Part 1 after an unsuccessful PEAP
Part 2 authentication. In such implementations, the existence of a
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TLS session cache entry provides no indication that the peer has
previously been authenticated. As a result, implementations that do
not remove TLS session cache entries after a failed PEAP Part 2
authentication or failed protected ack MUST use other means than
successful TLS resumption as the indicator of whether the client is
authenticated or not. The implementation MUST determine that the
client is authenticated only after the protected acknowledge has
been successfully exchanged. Failing to do this would enable a
peer to gain access by completing PEAP Part 1, tearing down the
connection, re-connecting and resuming PEAP Part 1, thereby proving
herself authenticated. Thus, TLS resumption MUST only be enabled if
the implementation supports TLS session cache removal.
If an EAP server implementing PEAP removes TLS session cache entries
of peers failing PEAP Part 2 authentication, then it MAY skip the
PEAP Part 2 conversation entirely after a successful session
resumption, successfully terminating the PEAP conversation as
described in Section 2.4.
5.4. Certificate revocation
Since the EAP server is on the Internet during the EAP conversation,
the server is capable of following a certificate chain or verifying
whether the peer's certificate has been revoked. In contrast, the
peer may or may not have Internet connectivity, and thus while it
can validate the EAP server's certificate based on a pre-configured
set of CAs, it may not be able to follow a certificate chain or
verify whether the EAP server's certificate has been revoked.
In the case where the peer is initiating a voluntary Layer 2 channel
using PPTP or L2TP, the peer will typically already have Internet
connectivity established at the time of channel initiation. As a
result, during the EAP conversation it is capable of checking for
certificate revocation.
As part of the TLS negotiation, the server presents a certificate to
the peer. The peer SHOULD 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 remoted, 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 destination and whether the EAP server exists within a
target sub-domain.
In the case where the peer is attempting to obtain network access,
it will not have Internet connectivity. The TLS Extensions [TLSEXT]
support piggybacking of an Online Certificate Status Protocol (OCSP)
response within TLS, therefore can be utilized by the peer in order
to verify the validity of server certificate. However, since all TLS
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implementations do not implement the TLS extensions, it may be
necessary for the peer to wait to check for certificate revocation
until after Internet access has been obtained. In this case, the
peer SHOULD conduct the certificate status check immediately upon
going online and SHOULD NOT send data until it has received a
positive response to the status request. If the server certificate
is found to be invalid, then the peer SHOULD disconnect.
5.5. Separation of the EAP server and the authenticator
As a result of a complete PEAP Part 1 and Part 2 conversation, the
EAP endpoints will mutually authenticate, and derive a session key
for subsequent use in link layer security. Since the peer and EAP
client reside on the same machine, it is necessary for the EAP
client module to pass the session key to the link layer encryption
module.
The situation may be more complex on the Authenticator, which may or
may not reside on the same machine as the EAP server. In the case
where the EAP server and the Authenticator reside on different
machines, there are several implications for security. Firstly, the
mutual authentication defined in PEAP will occur between the peer
and the EAP server, not between the peer and the authenticator. This
means that as a result of the PEAP conversation, it is not possible
for the peer to validate the identity of the NAS or channel server
that it is speaking to.
The second issue is that the session key negotiated between the peer
and EAP server will need to be transmitted to the authenticator.
Therefore a mechanism needs to be provided to transmit the session
key from the EAP server to the authenticator or channel server that
needs to use the key. The specification of this transit mechanism is
outside the scope of this document.
5.6. Separation of PEAP Part 1 and Part 2 Servers
The EAP server involved in PEAP Part 2 need not necessarily be the
same as the EAP server involved in PEAP Part 1. For example, a local
authentication server or proxy might serve as the endpoint for the
Part 1 conversation, establishing the TLS channel. Subsequently,
once the EAP-Response/Identity has been received within the TLS
channel, it can be decrypted and forwarded in cleartext to the
destination realm EAP server. The rest of the conversation will
therefore occur between the destination realm EAP server and the
peer, with the local authentication server or proxy acting as an
encrypting/decrypting gateway. This permits a non-TLS capable EAP
server to participate in the PEAP conversation.
Note however that such an approach introduces security
vulnerabilities. Since the EAP Response/Identity is sent in the
clear between the proxy and the EAP server, this enables an attacker
to snoop the user's identity. It also enables a remote
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environments, which may be public hot spots or Internet coffee
shops, to gain knowledge of the identity of their users. Since one
of the potential benefits of PEAP is identity protection, this is
undesirable.
If the EAP method negotiated during PEAP Part 2 does not support
mutual authentication, then if the Part 2 conversation is proxied to
another destination, the PEAP peer will not have the opportunity to
verify the secondary EAP server's identity. Only the initial EAP
server's identity will have been verified as Part of TLS session
establishment.
Similarly, if the EAP method negotiated during PEAP Part 2 is
vulnerable to dictionary attack, then an attacker capturing the
cleartext exchange will be able to mount an offline dictionary
attack on the password.
Finally, when a Part 2 conversation is terminated at a different
location than the Part 1 conversation, the Part 2 destination is
unaware that the EAP client has negotiated PEAP. As a result, it is
unable to enforce policies requiring PEAP. Since some EAP methods
require PEAP in order to generate keys or lessen security
vulnerabilities, where such methods are in use, such a configuration
may be unacceptable.
In summary, PEAP encrypting/decrypting gateway configurations are
vulnerable to attack and SHOULD NOT be used. Instead, the entire
PEAP connection SHOULD be proxied to the final destination, and the
subsequently derived master session keys need to be transmitted
back. This provides end to end protection of PEAP. The
specification of this transit mechanism is outside the scope of this
document, but mechanisms similar to [RFC2548] can be used. These
steps protects the client from revealing her identity to the remote
environment.
In order to find the proper PEAP destination, the EAP client SHOULD
place a Network Access Identifier (NAI) conforming to [RFC2486] in
the Identity Response.
There may be cases where a natural trust relationship exists between
the (foreign) authentication server and final EAP server, such as on
a campus or between two offices within the same company, where there
is no danger in revealing the identity of the station to the
authentication server. In these cases, using a proxy solution
without end to end protection of PEAP MAY be used. The PEAP
encrypting/decrypting gateway SHOULD provide support for IPsec
protection of RADIUS in order to provide confidentiality for the
portion of the conversation between the gateway and the EAP server,
as described in [RFC3162].
5.7. Identity verification
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Since the TLS session has not yet been negotiated, the initial
Identity request/response occurs in the clear without integrity
protection or authentication. It is therefore subject to snooping
and packet modification.
In configurations where all users are required to authenticate with
PEAP and the first portion of the PEAP conversation is terminated at
a local backend authentication server, without routing by proxies,
the initial cleartext Identity Request/Response exchange is not
needed in order to determine the required authentication method(s)
or route the authentication conversation to its destination. As a
result, the initial Identity and Request/Response exchange MAY NOT
be present, and a subsequent Identity Request/Response exchange MAY
occur after the TLS session is established.
If the initial cleartext Identity Request/Response has been tampered
with, after the TLS session is established, it is conceivable that
the EAP Server will discover that it cannot verify the peer's claim
of identity. For example, the peer's userID may not be valid or may
not be within a realm handled by the EAP server. Rather than
attempting to proxy the authentication to the server within the
correct realm, the EAP server SHOULD terminate the conversation.
The PEAP peer can present the server with multiple identities. This
includes the claim of identity within the initial EAP-
Response/Identity(MyID) packet, which is typically used to route the
EAP conversation to the appropriate home backend authentication
server. There may also be subsequent EAP-Response/Identity packets
sent by the peer once the TLS channel has been established.
Note that since the PEAP peer may not present a certificate, it is
not always possible to check the initial EAP-Response/Identity
against the identity presented in the certificate, as is done in
[RFC2716].
Moreover, it cannot be assumed that the peer identities presented
within multiple EAP-Response/Identity packets will be the same. For
example, the initial EAP-Response/Identity might correspond to a
machine identity, while subsequent identities might be those of the
user. Thus, PEAP implementations SHOULD NOT abort the authentication
just because the identities do not match. However, since the
initial EAP-Response/Identity will determine the EAP server handling
the authentication, if this or any other identity is inappropriate
for use with the destination EAP server, there is no alternative but
to terminate the PEAP conversation.
The protected identity or identities presented by the peer within
PEAP Part 2 may not be identical to the cleartext identity presented
in PEAP Part 1, for legitimate reasons. In order to shield the
userID from snooping, the cleartext Identity may only provide enough
information to enable routing of the authentication request to the
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correct realm. For example, the peer may initially claim the
identity of "nouser@bigco.com" in order to route the authentication
request to the bigco.com EAP server. Subsequently, once the TLS
session has been negotiated, in PEAP Part 2, the peer may claim the
identity of "fred@bigco.com". Thus, PEAP can provide protection for
the user's identity, though not necessarily the destination realm,
unless the PEAP Part 1 conversation terminates at the local
authentication server.
As a result, PEAP implementations SHOULD NOT attempt to compare the
Identities claimed with Parts 1 and 2 of the PEAP conversation.
Similarly, if multiple Identities are claimed within PEAP Part 2,
these SHOULD NOT be compared. An EAP conversation may involve more
than one EAP authentication method, and the identities claimed for
each of these authentications could be different (e.g. a machine
authentication, followed by a user authentication).
5.8. Man-in-the-middle protection
If an EAP method protected by PEAP is also deployed without
protection (from PEAP or IPSEC), and if the same credential is
allowed in both cases, then a man-in-the-middle attack is possible.
A man-in-the-middle can spoof the client to authenticate to it
instead of the real EAP server; and forward the authentication to
the real server over a protected tunnel. Since the attacker has
access to the keys derived from the tunnel, it can gain access to
the network.
The compound binding draft [CompoundBinding] identifies a number of
solutions to this attack.
The preferred solution is to deploy the authentication method with
protection from PEAP or IPSEC. Protection can address the man-in-
the-middle attack; and in addition can address EAP method and EAP
protocol weaknesses listed in the abstract and introduction sections
in this document.
Another solution is to use knowledge known only to the real peers to
verify that there is no man-in-the-middle. A number of protocols
derive keys for encryption, and these keys are not known to the man-
in-the-middle. These keys can be used in the binding phase exchange
described in compound binding [compoundbinding] draft to detect man-
in-the-middle. PEAP implementations MUST support the binding phase
exchange using compound MACs as described in the section 4.2 of the
compound binding draft[CompoundBinding].
Another solution is for EAP methods to securely signal to peers that
they are inside the protected channel. This may require changes to
the EAP protocol. In order to allow EAP methods to implement secure
signaling, PEAP implementations SHOULD inform the EAP methods that
they are being protected by PEAP.
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6. IANA Considerations
This section provides guidance to the Internet Assigned Numbers
Authority (IANA) regarding registration of values related to the EAP
protocol, in accordance with BCP 26, [RFC2434].
There is one name space in EAP-TLV that require registration: TLV-
Types.
6.1. Definition of Terms
The following terms are used here with the meanings defined in BCP
26:
"name space", "assigned value", "registration".
The following policies are used here with the meanings defined in
BCP
26: "Private Use", "First Come First Served", "Expert Review",
"Specification Required", "IETF Consensus", "Standards Action".
6.2. Recommended Registration Policies
For registration requests where a Designated Expert should be
consulted, the responsible IESG area director should appoint the
Designated Expert. For Designated Expert with Specification
Required, the request is posted to the EAP WG mailing list (or, if
it has been disbanded, a successor designated by the Area Director)
for comment and review, and MUST include a pointer to a public
specification. Before a period of 30 days has passed, the Designated
Expert will either approve or deny the registration request and
publish a notice of the decision to the EAP WG mailing list or its
successor. A denial notice must be justified by an explanation and,
in the cases where it is possible, concrete suggestions
on how the request can be modified so as to become acceptable.
For registration requests requiring Expert Review, the EAP mailing
list should be consulted. If the EAP mailing list is no longer
operational, an alternative mailing list may be designated by the
responsible IESG Area Director.
EAP-TLVs have a 14-bit field, of which 1-6 have been allocated.
7. Normative references
[RFC1321] Rivest, R., Dusse, S., "The MD5 Message-Digest Algorithm",
RFC
1321, April 1992.
[RFC1570] Simpson, W., Editor, "PPP LCP Extensions", RFC 1570,
January
1994.
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[RFC1661] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)",
STD
51, RFC 1661, July 1994.
[RFC1962] D. Rand. "The PPP Compression Control Protocol", RFC
1962,
Novell, June 1996.
[RFC1968] Meyer, G., "The PPP Encryption Protocol (ECP)", RFC 1968,
June
1996.
[RFC1990] Sklower, K., Lloyd, B., McGregor, G., Carr, D., and T.
Coradetti, "The PPP Multilink Protocol (MP)", RFC 1990,
August
1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T., Allen, C., "The TLS Protocol Version 1.0", RFC
2246, November 1998.
[RFC2284] Blunk, L., Vollbrecht, J., "PPP Extensible Authentication
Protocol (EAP)", RFC 2284, March 1998.
[RFC2486] Aboba, B., Beadles, M., "The Network Access Identifier",
RFC 2486, January 1999.
[TLSEXT] Blake-Wilson, S., et al. "TLS Extensions", Internet draft
(work in progress), draft-ietf-tls-extensions-06.txt, Feb
2003.
[IEEE8021X]
IEEE Standards for Local and Metropolitan Area Networks:
Port
based Network Access Control, IEEE Std 802.1X-2001, June
2001.
[CompoundBinding]
Puthenkulam, J., Lortz, V., Palekar, A., Simon, D.,
"The Compound Authentication Binding Problem", March 2003;
draft-puthenkulam-eap-binding-02.txt.
8. Informative references
[RFC2419] Sklower, K., Meyer, G., "The PPP DES Encryption Protocol,
Version 2 (DESE-bis)", RFC 2419, September 1998.
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[RFC2420] Hummert, K., "The PPP Triple-DES Encryption Protocol
(3DESE)",
RFC 2420, September 1998.
[RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes",
RFC2548, March 1999.
[RFC2716] Aboba, B., Simon, D., "PPP EAP TLS Authentication
Protocol",
RFC 2716, October 1999.
[RFC3078] Pall, G., Zorn, G., "Microsoft Point-to-Point Encryption
(MPPE) Protocol", RFC 3078, March 2001.
[RFC3079] Zorn, G., "Deriving Keys for use with Microsoft Point-to-
Point
Encryption (MPPE)", RFC 3079, March 2001.
[FIPSDES] National Bureau of Standards, "Data Encryption Standard",
FIPS
PUB 46 (January 1977).
[IEEE80211]
Information technology - Telecommunications and
information
exchange between systems - Local and metropolitan area
networks - Specific Requirements Part 11: Wireless LAN
Medium
Access Control (MAC) and Physical Layer (PHY)
Specifications,
IEEE Std. 802.11-1999, 1999.
[MODES] National Bureau of Standards, "DES Modes of Operation",
FIPS
PUB 81 (December 1980).
[PEAP version 0]
Kamath, V., Palekar, A., Wodrich, M.,
"Microsoft's PEAP version 0 (Implementation in Windows XP
SP1)",
draft-kamath-pppext-peapv0-00.txt.
9. Appendix A - Examples
In the case where an identity exchange occurs within PEAP Part 1,
the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
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Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(PEAP Start, S bit set)
EAP-Response/
EAP-Type=PEAP, V=1
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
EAP-Response/
EAP-Type=PEAP, V=2
([TLS certificate,]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP ->
TLS channel established
(messages sent within the TLS channel)
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID2) ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X or NAK ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X ->
<- EAP-Request/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
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methods=1, Result TLV (Success), Method_Identity_TLV (EAP-Type=X,
EAP-Type-Version=0, keylengthusedforderivation,
ClientIdentityLength= sizeof(MyID2), MyID2, ServerIdentityLength=0,
Media-type=19), Method_Identity_TLV (EAP-Type=PEAP, EAP-Type-
Version=2, keylengthusedforderivation, ClientIdentityLength=
sizeof(MyID1), MyID1, ServerIdentityLength=0, Media-type=19),
CompoundMAC (over entire EAP TLV inside the tunnel including EAP-
header))
EAP-Response/
EAP-Type=EAP-TLV
Result=Success
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=1, Result TLV (Success), Method_Identity_TLV (EAP-Type=X,
EAP-Type-Version=0, keylengthusedforderivation,
ClientIdentityLength= sizeof(MyID2), MyID2, ServerIdentityLength=0,
Media-type=19), Method_Identity_TLV (EAP-Type=PEAP, EAP-Type-
Version=2, keylengthusedforderivation, ClientIdentityLength=
sizeof(MyID1), MyID1, ServerIdentityLength=0, Media-type=19),
CompoundMAC (over entire EAP TLV inside the tunnel including EAP-
header))
->
TLS channel torn down
(messages sent in cleartext)
<- EAP-Success
Where all peers are known to support PEAP, a non-certificate
authentication is desired for the client and the PEAP Part 1
conversation is carried out between the peer and a local EAP server,
the cleartext identity exchange may be omitted and the conversation
appears as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
EAP-Type=PEAP, V=1
(PEAP Start, S bit set)
EAP-Response/
EAP-Type=PEAP, V=1
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
EAP-Response/
EAP-Type=PEAP, V=2
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([TLS certificate,]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2 ->
TLS channel established
(messages sent within the TLS channel)
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X or NAK ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X ->
<- EAP-Request/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, Result TLV (Success), Method_Identity_TLV (for
each EAP-Type inside PEAP), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header))
EAP-Response/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, Result TLV (Success), Method_Identity_TLV (for
each EAP-Type inside PEAP), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header))
TLS channel torn down
(messages sent in cleartext)
<- EAP-Success
Where all peers are known to support PEAP, where client certificate
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authentication is desired and the PEAP Part 1 conversation is
carried out between the peer and a local EAP server, the cleartext
identity exchange may be omitted and the conversation appears as
follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
EAP-Type=PEAP, V=2
(PEAP Start, S bit set)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
TLS server_hello_done)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_key_exchange,
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2 ->
TLS channel established
(messages sent within the TLS channel)
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS hello_request)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
EAP-Response/
EAP-Type=PEAP, V=2
([TLS certificate,]
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TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2 ->
<- EAP-Request/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, Result TLV (Success), Method_Identity_TLV (for
each EAP-Type inside PEAP), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header))
EAP-Response/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, Result TLV (Success), Method_Identity_TLV (for
each successful EAP-Type inside PEAP), Method_Identity_TLV (for
PEAP), CompoundMAC (over entire EAP TLV packet inside the tunnel
including EAP-header))
TLS channel torn down
(messages sent in cleartext)
<- EAP-Success
In the case where the PEAP fragmentation is required, the
conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(PEAP Start, S bit set)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS certificate,
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[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
(Fragment 1: L, M bits set)
EAP-Response/
EAP-Type=PEAP, V=2 ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(Fragment 2: M bit set)
EAP-Response/
EAP-Type=PEAP, V=2 ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(Fragment 3)
EAP-Response/
EAP-Type=PEAP, V=2
([TLS certificate,]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished)
(Fragment 1: L, M bits set)->
<- EAP-Request/
EAP-Type=PEAP, V=2
EAP-Response/
EAP-Type=PEAP, V=2
(Fragment 2)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2 ->
TLS channel established
(messages sent within the TLS channel)
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X or NAK ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X ->
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<- EAP-Request/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, Result TLV (Success), Method_Identity_TLV (for
each EAP-Type inside PEAP), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header))
EAP-Response/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, Result TLV (Success), Method_Identity_TLV (for
each EAP-Type inside PEAP), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header))
TLS channel torn down
(messages sent in cleartext)
<- EAP-Success
In the case where the server authenticates to the client
successfully in PEAP Part 1, but the client fails to authenticate to
the server in PEAP Part 2, the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(PEAP Start, S bit set)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
[TLS certificate_request,]
TLS server_hello_done)
EAP-Response/
EAP-Type=PEAP, V=2
([TLS certificate,]
TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
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(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2 ->
TLS channel established
(messages sent within the TLS channel)
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X or NAK ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X ->
<- EAP-Request/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, Result TLV (Failure), Method_Identity_TLV (for
each EAP-Type inside PEAP), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header))
// Compound MAC calculated using TLS key material only.
EAP-Response/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, Result TLV (Failure), Method_Identity_TLV (for
each EAP-Type inside PEAP), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header))
Result=Failure ->
(TLS session cache entry flushed)
TLS channel torn down
(messages sent in cleartext)
<- EAP-Failure
In the case where server authentication is unsuccessful in PEAP Part
1, the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
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<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(PEAP Start)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS certificate,
[TLS server_key_exchange,]
TLS server_hello_done)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_key_exchange,
[TLS certificate_verify,]
TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished)
<- EAP-Request/
EAP-Type=PEAP, V=2
EAP-Response/
EAP-Type=PEAP, V=2
(TLS Alert message) ->
<- EAP-Failure
(TLS session cache entry flushed)
In the case where a previously established session is being resumed,
the EAP server supports TLS session cache flushing for unsuccessful
PEAP Part 2 authentications and both sides authenticate
successfully, the conversation will appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Type=PEAP,V=2
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INTERNET-DRAFT PEAP March 24, 2003
(PEAP Start)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS change_cipher_spec
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=0, Result TLV (Success), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header))
// Compound MAC calculated using TLS keys since there were no inner
EAP methods.
EAP-Response/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=0, Result TLV (Success), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header)) .
->
TLS channel torn down
(messages sent in cleartext)
<- EAP-Success
In the case where a previously established session is being resumed,
and the server authenticates to the client successfully but the
client fails to authenticate to the server, the conversation will
appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Request/
EAP-Type=PEAP, V=2
(TLS Start)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_hello) ->
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<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished) ->
<- EAP-Request
EAP-Type=PEAP, V=2
(TLS Alert message)
EAP-Response
EAP-Type=PEAP, V=2 ->
<- EAP-Failure
(TLS session cache entry flushed)
In the case where a previously established session is being resumed,
and the server authentication is unsuccessful, the conversation will
appear as follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Request/
EAP-Type=PEAP, V=2
(TLS Start)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=2
(TLS server_hello,
TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2
(TLS change_cipher_spec,
TLS finished)
<- EAP-Request/
EAP-Type=PEAP, V=2
EAP-Response/
EAP-Type=PEAP, V=2
(TLS Alert message) ->
(TLS session cache entry flushed)
<- EAP-Failure
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In the case where the peer and authenticator have mismatched PEAP
versions (e.g. the peer has a pre-standard implementation with
version 0, and the authenticator has an implementation compliant
with this specification), the session is being resumed, but the
authentication is unsuccessful, the conversation will occur as
follows:
Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID) ->
<- EAP-Request/
EAP-Request/
EAP-Type=PEAP, V=2
(TLS Start)
EAP-Response/
EAP-Type=PEAP, V=0
(TLS client_hello)->
<- EAP-Request/
EAP-Type=PEAP, V=0
(TLS server_hello,
TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=0
(TLS change_cipher_spec,
TLS finished)
<- EAP-Request/
EAP-Type=PEAP, V=0
EAP-Response/
EAP-Type=PEAP, V=0
(TLS Alert message) ->
(TLS session cache entry flushed)
<- EAP-Failure
10. Acknowledgments and Contributions
Thanks to Jan-Ove Larsson, Magnus Nystrom of RSA Security; Bernard
Aboba, Vivek Kamath, Stephen Bensley, Narendra Gidwani of Microsoft;
Joe Salowey, Hao Zhou, Ilan Frenkel, Nancy Cam-Winget of Cisco;
Hakan Andersson of RSA; Jose Puthenkulam of Intel for their
contributions and critiques.
The compound binding exchange to address man-in-the-middle attack is
based on the draft "The Compound Authentication Binding
Problem"[CompoundBinding].
The vast majority of the work by Simon Josefsson and Hakan Andersson
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INTERNET-DRAFT PEAP March 24, 2003
was done while he was employed at RSA Laboratories.
Author Addresses
Ashwin Palekar
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: +1 425 882 8080
EMail: ashwinp@microsoft.com
Dan Simon
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Phone: +1 425 706 6711
EMail: dansimon@microsoft.com
Glen Zorn
Cisco Systems
500 108th Avenue N.E.
Suite 500
Bellevue, Washington 98004
USA
Phone: + 1 425 438 8210
Fax: + 1 425 438 1848
EMail: gwz@cisco.com
Simon Josefsson
Drottningholmsvgen 70
112 42 Stockholm
Sweden
Phone: +46 8 619 04 22
EMail: jas@extundo.com
11. Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
intellectual property 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; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards-related documentation can be found in BCP-11. Copies of
Palekar, et all. Expires in Six Months [Page 50]
INTERNET-DRAFT PEAP March 24, 2003
claims of rights made available for publication 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 implementors or users of this specification
can be obtained from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
12. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English. The limited permissions granted above are perpetual and
will not be revoked by the Internet Society or its successors or
assigns. This document and the information contained herein is
provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
Expiration Date
This memo is filed as <draft-josefsson-pppext-eap-tls-eap-06.txt>,
and expires after six months.
Palekar, et all. Expires in Six Months [Page 51]
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