wdiff draft-josefsson-pppext-eap-tls-eap-06.txt draft-josefsson-pppext-eap-tls-eap-07.txt

PPPEXT Working Group Ashwin Palekar
INTERNET-DRAFT Dan Simon
Category: Standards Track Microsoft
<draft-josefsson-pppext-eap-tls-eap-06.txt> Corporation
<draft-josefsson-pppext-eap-tls-eap-07.txt> Glen Zorn
22 March
26 October 2003 Joe Salowey
Hao Zhou
Cisco Systems
S. Josefsson
Extundo
Exundo

Protected EAP Protocol (PEAP) Version 2

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
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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.

Abstract

The Extensible Authentication Protocol (EAP), defined in RFC 2284, (EAP) 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; This document defines the Protected
Extensible Authentication Protocol (PEAP) Version 2, 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; provides
an encrypted and no support for fast reconnect.

In addition, some authenticated tunnel based on transport layer
security (TLS) that encapsulates 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 mechanisms.
PEAPv2 uses TLS to
prevent spoofing by protect against rogue servers (gateways), and do not support authenticators, protect
against various attacks on the
generation confidentiality and integrity of key strength required for 802.11i.

By wrapping the
inner EAP protocol within TLS, Protected EAP (PEAP)
addresses these deficiencies in EAP or EAP protocols. method exchange and provide EAP method(s)
running within PEAP are provided with built-in peer identity privacy.
PEAPv2 also provides 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 chaining multiple EAP methods.
Protected negotiation.
Protected mechanisms,
cryptographic binding between authentications performed by inner EAP header.
Protected
mechanisms and the tunnel, exchange of arbitrary parameters (TLVs) between client and server.
Standardized mechanism for key exchange.
Proven key derivation and management.
Session resumption.
Server authentication.
Protected Acknowledged (TLVs),
optimized session resumption, and result exchange.
Fragmentation fragmentation and reassembly.

Table of Contents

Protected EAP Protocol (PEAP)......................................1

1. Introduction.................................................3
1.1. Introduction .......................................... 4
1.1 Requirements language.......................................5
1.2. Terminology.................................................5
1.3. language ........................... 6
1.2 Terminology ..................................... 6
1.3 Operational model...........................................6 model ............................... 8
2. Protocol overview............................................7
2.1. PEAP overview ..................................... 11
2.1 PEAPv2 Part 1.................................................8
2.2. PEAP 1 .................................. 11
2.2 PEAPv2 Part 2................................................11
2.3. Version negotiation........................................12
2.4. Termination................................................12
2.5. 2 .................................. 16
2.3 Error handling.............................................14
2.6. Retry behavior.............................................15
2.7. Session resumption.........................................15
2.8. Fragmentation..............................................16
2.9. handling ................................. 19
2.4 Fragmentation .................................. 21
2.5 Key derivation.............................................17
2.10. derivation ................................. 22
2.6 Ciphersuite negotiation....................................18 negotiation ........................ 24
3. Detailed description of the PEAP protocol...................18
3.1. PEAP PEAPv2 protocol .......... 25
3.1 PEAPv2 Packet Format.........................................18
3.2. PEAP Format ........................... 25
3.2 PEAPv2 Request Packet........................................20 Packet .......................... 26
3.3 PEAPv2 Response Packet ......................... 28
3.4 PEAPv2 Part 2 Packet Format ................... 29
4. EAP TLV method..............................................23
4.1. Protected success/failure..................................23
4.2. method ....................................... 30
4.1 EAP-TLV Request Packet.....................................25
4.3. packet ......................... 30
4.2 EAP-TLV Response Packet....................................25
4.4. EAP-TLV packet ......,,................ 31
4.3 TLV format.........................................26
4.5. format ..................................... 32
4.4 Result TLV.................................................27
4.6. TLV ..................................... 33
4.5 NAK TLV....................................................28 TLV ........................................ 34
4.6 Crypto-Binding TLV ............................. 35
4.7 Connection-Binding TLV ......................... 37
4.8 Vendor-Specific TLV ............................ 38
4.9 URI TLV ........................................ 39
4.10 EAP Payload TLV ................................ 40
4.11 Intermediate Result TLV ........................ 41
4.12 TLV Rules ...................................... 42
5. Security Considerations.....................................28
5.1. considerations .............................. 43
5.1 Authentication and integrity protection....................28
5.2. protection ........ 43
5.2 Method negotiation.........................................29
5.3. negotiation ............................. 44
5.3 TLS session cache handling.................................29
5.4. handling ..................... 44
5.4 Certificate revocation.....................................30
5.5. revocation ......................... 45
5.5 Separation of the EAP server and the authenticator.........31
5.6. authenticator ..... 46
5.6 Separation of PEAP PEAPv2 Part 1 and Part 2 Servers...............31
5.7. Servers . 47
5.7 Identity verification......................................32
5.8. verification .......................... 48
5.8 Man-in-the-middle protection...............................34 attack protection ............ 50
5.9 Cleartext forgeries ............................ 50
5.10 TLS Ciphersuites ............................... 51
5.11 Denial of service attacks ...................... 51
5.12 Security Claims ................................ 52

6. IANA Considerations.........................................35
6.1. Considerations ................................. 53
6.1 Definition of Terms........................................35
6.2. Terms ............................ 53
6.2 Recommended Registration Policies..........................35 Policies .............. 53
7. References .......................................... 53
7.1 Normative references........................................35
8. references ........................... 53
7.2 Informative references......................................36
9. references ......................... 54
Appendix A - Examples.......................................37
10. and Contributions..........................................49
11. Examples ........................................ 56
Acknowledgments .............................................. 70
Author's Addresses ........................................... 70
Intellectual Property Statement.............................50
12. Statement .............................. 71
Full Copyright Statement....................................51 Statement ..................................... 72
1. Introduction

The Extensible Authentication Protocol (EAP), described defined in
[RFC2284],
[RFC2284bis], 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 for use on wired networks, where physical
security was presumed. EAP over PPP, defined in [RFC2284], [RFC2284bis], 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 its deployment, a number of weaknesses in EAP framework have
become apparent. These include lack of:

identity protection
protected method negotiation is unprotected, an attacker can inject packets in order
to cause the negotiation of a method with lesser security. Denial
protected notification messages
protected termination messages
support for sequences of
service attacks are also possible. Since the initial EAP Identity
Request/Response methods
support for fragmentation and reassembly
support for a generic way to exchange is sent arbitrary
parameters in the clear, an attacker snooping
on the conversation can collect user identities a secure channel
support for use in
subsequent attacks. generic optimized re-authentication

In addition many EAP methods lack the following features:

mutual authentication
resistance to dictionary attacks
adequate key generation

By initially negotiating a TLS channel, and then conducting wrapping the EAP
conversation protocol within it, PEAP TLS, Protected EAP (PEAP) Version
2 addresses these deficiencies in EAP or EAP methods. TLS provides for
per-packet encryption, authentication, integrity and replay
protection of the EAP conversation. Benefits of PEAP Version 2
include:

Identity protection
By encrypting the identity exchange, and allowing client
credentials
certificates to be provided after negotiation of the TLS channel,
PEAP
PEAPv2 provides for identity protection.

Dictionary attack resistance
By conducting the EAP conversation within a TLS channel, PEAP PEAPv2
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, PEAPv2, the EAP conversation is authenticated,
integrity and replay protected on a per-packet basis, the EAP
method negotiation that occurs within PEAP PEAPv2 is protected, as are
error messages sent within the TLS channel (TLS alerts or EAP
Notification packets). EAP negotiation outside of PEAPv2 is not
protected.

Header protection
Within PEAP, PEAPv2, the EAP conversation is conducted within a TLS
channel. As a result, the Type-Data field within PEAPv2 (including
the EAP header of the EAP method within PEAPv2) is protected
against modification. However, the EAP header of PEAPv2 itself is
not protected against modification, including the Code, Identifier
and Type fields.

Protected termination
By sending success/failure indications within the TLS channel,
PEAP
PEAPv2 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 PEAPv2,
methods leveraging PEAP PEAPv2 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 PEAPv2 supports this capability by leveraging the
TLS session resumption facility, and any EAP method running under
PEAP
PEAPv2 can take advantage of it.

Proven and Method independent

Standard key management establishment
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
initialization vectors. Development of a secure key hierarchy keying material. Key
derivation is
complex, and not easy to generalize complex. PEAPv2 provides for all EAP methods. By key establishment by
relying on the widely implemented and well-reviewed TLS [RFC2246]
key derivation method,
PEAP mechanism. PEAPv2 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 external protection of PEAP (e.g PEAPv2 or IPSEC, IPSec), then the EAP
methods should derive
key material of sufficient strength follow the guidelines in section 6.8 to prevent a Man-in-the-
middle attack described in the compound binding draft
[CompoundBinding].
man-in-the-middle attacks.

Sequencing of multiple EAP methods
In order to enhance security, PEAPv2 implementations may choose to
provide multi-factor authentication that validates different
identities (for example user and machine identities) and/or uses
different credentials of the same or different identities of the
peer (e.g. user password and machine cert). PEAPv2 provides a
standard way to chain different types of authentication mechanisms
supporting different types of credentials.

Protected exchange of arbitrary parameters (TLVs)
Type-Length-Value (TLV) tuples provide a way to exchange arbitrary
information between peer and EAP server within a secure channel.
This information can include signaling parameters for EAP protocol,
provisioning parameters, media specific and environment specific
data, and authorization parameters. The advantage of using PEAP
TLVs is that every EAP method does not have to be modified.

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 initiating EAP authentication. This term is
also used in [IEEE8021X] and has the same meaning in this document.

Backend Authentication Server
An Authentication Server
A backend authentication server is an entity that provides an
Authentication Service
authentication service to an NAS. This service verifies from
the credentials provided by the peer, the claim of identity
made by Authenticator. When used, this server
typically executes EAP methods for the peer. Authenticator. This
terminology is also used in [IEEE8021X].

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

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 that responds to the NAS. authenticator. In IEEE 802.1X,
[IEEE8021X], this end is known as the Supplicant.

TLS Ciphersuite
The ciphersuite negotiated for protection of the PEAP PEAPv2 Part 2
conversation.

EAP Master key (MK)
A key derived between the PEAPv2 client and server during the
authentication conversation, and that is kept local to PEAPv2 and
not exported or made available to a third party.

Master Session Key (MSK)
Keying material (64 octets) that is derived between the PEAPv2
client and server and exported by the PEAPv2 implementation.

AAA-Key
Where a backend authentication server is present, acting as an EAP
server, keying material known as the AAA-Key is transported from
the authentication server to the authenticator. The AAA-Key is
used by the EAP peer and authenticator in the derivation of
Transient session keys Session Keys (TSKs) for the ciphersuite negotiated
between the EAP peer and authenticator. As a result, the AAA-Key
is typically known by all parties in the EAP exchange: the peer,
authenticator and the authentication server (if present).

Extended Master Session Key (EMSK)
Additional keying material (64 octets) derived between the EAP
client and server that is exported by the EAP method. The transient session keys are EMSK is
known only to the EAP peer and server and is not provided to a
third party.

Initialization Vector (IV)
A 64 octet quantity, suitable for use in an initialization vector
field, that is derived from between the master session
keys, EAP client and server. Since
the IV is a known value in PEAPv2, it cannot be used by itself for
computation of any quantity that needs to remain secret. As a
result, PEAPv2 implementations are not required to generate it.

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

Transient EAP Keys (TEKs)
Session keys which are used to establish a protected channel
between the EAP peer and type server during the EAP authentication
exchange. The TEKs are appropriate for use with the chosen link layer ciphersuite. ciphersuite
negotiated between EAP peer and server for use in protecting the
EAP conversation. Note that the ciphersuite used to set up the
protected channel between the EAP peer and server during EAP
authentication is unrelated to the ciphersuite used to subsequently
protect data sent between the EAP peer and Authenticator.

TLV TLV standards for objects of format Type-Length-Value. The TLV
format is defined in Section 4 of this document.

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
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.

In PEAPv2, the conversation between the EAP peer and the EAP server
is encrypted, authenticated, integrity and replay protected within a
TLS channel.

As a result, where the NAS acts as a "passthrough" it does not have
knowledge of the TLS master secret derived between the peer and the
EAP server. In order to provide keying material for link-layer
ciphersuites, the NAS obtains the master session key, which is
derived from a one-way function of the TLS master secret as well as
keying material provided by EAP methods protected within a TLS
channel. This enables the NAS and EAP peer to subsequently derive
transient session keys suitable for encrypting, authenticating and
integrity protecting session data. However, the NAS cannot decrypt
the PEAPv2 conversation or spoof session resumption, since this
requires knowledge of the TLS master secret.

1.3.1. Sequences

EAP [RFC2284bis] prohibits use of multiple authentication methods
within a single EAP conversation, except when tunneled methods such
as PEAPv2 are used. This restriction was imposed in order to limit
vulnerabilities to man-in-the-middle attacks as well as to ensure
compatibility with existing EAP implementations.

Within PEAP these concerns are addressed since PEAPv2 includes
support for cryptographic binding to address man-in-the-middle
attacks, as well as version negotiation so as to enable backward
compatibility with prior versions of PEAP.

Within this document, the term "sequence" refers to a series of EAP
authentication methods run in sequence. The methods need not be
distinct - for example, EAP-TLS could be run initially with machine
credentials followed by the same protocol authenticating with user
credentials.

PEAPv2 supports two types of sequences:

[1] Serial authentication. Initiating additional EAP method(s) after a
first successful authentication. In this case the sequence is
successful if each of the EAP authentication methods completes
successfully. For example, successful authentication might require
a successful machine authentication followed by a successful user
authentication.

[2] Parallel authentication. Initiating an alternative EAP method after
failure of one or more initial methods. In this case the overall
authentication is successful if any of the methods is successful.
For example, if machine authentication fails, then user
authentication can be attempted.

2. Protocol overview

Protected EAP (PEAP) Version 2 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.

[2] In Part 2, within the TLS session, a complete zero or more EAP conversation
is methods are
carried out, unless part 1 provided client authentication. out. Part 2 completes with a success/failure indication
protected by the TLS session or a protected error (TLS alert).

In the next two sections, we provide an overview of each of the parts
of the PEAP PEAPv2 conversation.

2.1. PEAP PEAPv2 Part 1

2.1.1. Initial identity exchange

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 authenticator.

The initial identity exchange is used primarily to route the EAP
conversation to the EAP server, if server. Since the initial identity exchange
is in the clear, the peer MAY decide to place a routing realm instead
of its real name in the EAP-Response/Identity. The real identity of
the peer can be established later in PEAPv2 part 2.

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 EAP-Request/Response-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, PEAP, 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.

2.1.2. TLS Session Establishment

In this section, the protocol is described assuming a certificate
based ciphersuite is negotiated in TLS. The conversation may
slightly differ if other TLS ciphersuites are used.

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 EAP-Type=PEAP,
the Start (S) bit set, the PEAP version as specified in Section
2.1.5, 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.

The EAP server will then respond with an EAP-Request packet with
EAP-Type=PEAP. 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 PEAPv2 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 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 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
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 EAP servers MUST support
and be able to negotiate the following TLS ciphersuites:

TLS_RSA_WITH_3DES_EDE_CBC_SHA

In addition, PEAP peers and EAP servers SHOULD support and be able to
negotiate the following TLS ciphersuites.

TLS_RSA_WITH_AES_128_CBC_SHA
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 PEAPv2 Part 1
conversation the EAP endpoints MAY request or negotiate TLS
compression.

2.1.3. Full handshake

If the EAP server is not resuming a previously established session,
and if a ciphersuite based on certificates is used, 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

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 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

The EAP server in the
preceding MUST then respond with an EAP-Request packet indicated with EAP-
Type=PEAP, which includes, in the case of a new TLS session, one or
more TLS records containing TLS change_cipher_spec, finished
handshake messages; and the first payload of PEAPv2 part 2. The
first payload of PEAPv2 part 2 is sent along with finished handshake
message to reduce number of round trips.

2.1.4. 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
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 send include only the a TLS change_cipher_spec message and a TLS
finished handshake messages. message after the server_hello message. The
finished message contains the peer's EAP server's authentication response to
the EAP server. peer.

If the preceding server_hello message sent by the EAP server in the
preceding EAP-Request packet did not indicate indicated the resumption of a previous
session, then the peer MUST send, in addition to send only the change_cipher_spec and
finished messages, a client_key_exchange
message, which completes the exchange of a shared master secret
between handshake messages. The finished message contains the peer and
peer's authentication response to the EAP server. 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, authentication fails, then the peer MAY send an
EAP-Response packet of EAP-Type=PEAP containing a TLS Alert message
identifying and EAP-server MUST follow the reason for
error handling behavior specified in section 2.3.

Even if the failed authentication. The peer MAY
send a TLS alert message rather than immediately terminating session is successfully resumed with the
conversation so as to allow same EAP server,
the peer and EAP server MUST not assume that either will skip inner
EAP methods. The peer may have roamed to log a network which may use the cause
same EAP server, but may require conformance with a different
authentication policy.

2.1.5. Version negotiation

PEAP packets contain a three bit version field, which enables PEAP
implementations to be backward compatible with previous versions of
the
error for examination by protocol. This specification documents the system administrator.

To ensure that PEAP version 2
protocol; implementations of this specification MUST use a version
field set to 2. Version negotiation proceeds as follows:

[1] In the first EAP-Request sent with EAP Server receives the TLS alert message, type=PEAP, the
peer EAP server
MUST wait for set the EAP-Server version field to reply before terminating the
conversation. The highest supported version number.

[2] If the EAP Server peer supports this version of the protocol, it MUST reply
respond with an EAP-Failure packet
since server authentication failure is a terminal condition.

If EAP-Response of EAP type=PEAP, and the version
number proposed by the EAP server authenticates successfully, server.

[3] If the EAP peer MUST send does not support this version, it responds with an
EAP-Response packet of EAP-Type=PEAP, EAP type=PEAP and no data. the highest supported version
number.

[4] If the PEAP server does not support the version number proposed by
the PEAP peer, it terminates the conversation, as described in
Section 2.2.2.

The EAP-Server version negotiation procedure guarantees that the EAP peer and
server will agree to the latest version supported by both parties.
If version negotiation fails, then continues with Part 2 use of PEAP will not be possible,
and another mutually acceptable EAP method will need to be negotiated
if authentication is to proceed.

The PEAP version field is not protected by TLS and therefore can be
modified in transit. In order to detect modification of the PEAP conversation.
version which could occur as part of a "downgrade" attack, the
PEAPv2 peer and server MUST exchange information on the highest
supported versions proposed by the peers using the crypto-binding-
TLV.

2.2. PEAP PEAPv2 Part 2

The second portion of the PEAP PEAPv2 conversation typically consists of another a
complete EAP conversation occurring within the TLS session negotiated
in PEAP PEAPv2 Part 1. It 1; ending with protected termination using the Result-
TLV. PEAPv2 part 2 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 In cases where a new TLS session is established
in PEAPv2 part 1, the first payload of the part 2 conversation is
sent by the EAP server along with the finished message to save a
round-trip.

Part 2 MUST NOT occur if the EAP Server authenticates unsuccessfully
or if an EAP-Failure has been sent by the EAP Server server to the peer,
terminating the conversation. Since all packets sent within the
PEAP
PEAPv2 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 of
the inner EAP method are protected using the negotiated TLS
ciphersuite.

Part 2 MAY NOT always include a EAP conversation within the TLS
session, referred to in this document as inner EAP methods. However,
Part 2 MUST always end with either protected termination or protected
error termination.

Within Part 2, protected EAP conversation and protected termination
packets are always carried within an EAP-TLV packet. The EAP-TLV
packet does not include an EAP header. There are TLVs defined for
specific purposes such as carrying EAP-authentication messages and
carrying cryptographic binding. New TLVs may be developed for other
purposes.

2.2.1. Protected conversation

Part 2 of the PEAP conversation typically begins with the
Authenticator EAP server
sending an optional 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, EAP server,
containing the peer's userId. Since this Identity Request/Response
exchange is protected by the ciphersuite negotiated in TLS, it is protected against not
vulnerable to 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 send
an EAP-Request with the EAP-Type Type field set to the initial method. As
described in [RFC2284], [RFC2284BIS], 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

The EAP type=PEAP, conversation within the TLS protected session may involve a
sequence of zero or more EAP
server MUST set the version field to authentication methods; it completes
with the highest supported version
number.

[2] If protected termination described in section 2.2.2. Several
EAP-TLVs may be included in each Request and Response. EAP-methods
(except if the type is EAP-TLV) are always encapsulated within EAP client supports this version of
Payload-TLV.

In a typical EAP conversation, the protocol, it
MUST respond with an EAP-Response result of EAP type=PEAP, and the version
number proposed conversation is
communicated by the sending EAP server.

[3] If Success or EAP Failure packets after the
EAP client does not support this version, it responds
with an EAP-Response of method is complete. The EAP type=PEAP and Success or Failure packet is
considered the highest supported
version number.

[4] If last packet of the EAP server supports the version proposed by the client,
then all future EAP-Request packets conversation; and therefore
cannot be used when sequences need to be supported. Hence, instead
of using the EAP-success or EAP-failure packet, both peer and EAP type=PEAP
server MUST include use the version field set Intermediate Result TLV to communicate the agreed upon version number. Similarly,
result.

In a typical EAP conversation, the EAP client MUST include Success or EAP Failure is
considered the agreed upon version number in all
EAP-Response packets last packet of the EAP type=PEAP.

[5] If conversation. Within PEAP, the PEAP
EAP server does not support can start another EAP method after success or failure of
the version number proposed
by previous EAP method inside the PEAP client, it terminates protected session.

In a sequence of more than one EAP authentication method, to make
sure the conversation, as described same parties are involved in
Section 2.4.

This version tunnel establishment and
successful completion of previous inner EAP methods, before
completing negotiation procedure guarantees that of the next EAP client method, both peer and EAP
server will agree to the latest version supported by both
parties. If version negotiation fails, then MUST use of PEAP will not be
possible, and another mutually acceptable crypto binding (Crypto-Binding TLV). If no EAP method will need to be
methods have been negotiated if authentication is to proceed. In order to protect
against a downgrade version attack between PEAP versions support by inside the peers, tunnel or no EAP methods have
been successfully completed inside the peers MUST exchange information on tunnel, the highest
version number supported during crypto-binding TLV
MUST NOT be used.

The Crypto-Binding TLV and the binding exchange.

2.4. Termination
As described in [RFC2284], Intermediate-Result TLV MUST be sent
after each successful EAP Success and Failure packets method (except for type EAP-TLV). If these
TLVs are not
authenticated, so that they may sent, it should be forged considered as tunnel compromise error
by an attacker without
fear of detection. Forged peer and EAP Failure packets server.

Both TLVs can be used to
convince sent in an EAP-TLV packet. Alternatively, if a
subsequent EAP peer conversation is being attempted, then in order to disconnect. Forged EAP Success packets may
reduce round trips, both TLVs SHOULD be used by a rogue NAS to convince a peer to let itself access the
network, even though sent in 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 EAP-Payload of
the TLS channel.

PEAP support for protected success/failure indications is
constrained by first EAP packet of the [RFC2284] and [IEEE8021X] specifications. In
[IEEE8021X], next EAP conversation (for example, EAP-
Identity or EAP-packet of the authenticator "manufactures" cleartext EAP Success
and Failure packets based on method). Alternatively, if the result indicated by
next packet is the backend
authentication server. As a result, were a PEAP server termination packet, then in order to send a
protected EAP Success or EAP Failure packet as reduce
round trips, both TLVs SHOULD be sent with the final packet
within termination packet.

If the EAP exchange, authenticators compliant with [IEEE8021X]
would silently discard server sends a valid Crypto-Binding-TLV to the packet, and replace it peer, the
peer MUST respond with a cleartext
EAP Success or Failure. Since Crypto-Binding TLV. If the client will discard these
unprotected indications, where an authenticator compliant with
[IEEE8021X] Crypto-Binding-
TLV is present, invalid, it is not should be possible to conclude a
successful authentication. As considered a result, this approach tunnel compromise error by
the peer. If the peer does not
provide reliable authenticated success/failure indications on all
media.

In addition, [RFC2284] states that an EAP Success or EAP Failure respond with a EAP-TLV packet terminates the EAP conversation, so that no response is
possible. Since EAP Success and EAP Failure packets are not
retransmitted, if
containing the final packet is lost, then authentication will
fail. As crypto-binding TLV, it should be considered a result, where packet loss tunnel
compromise error by the EAP server.

2.2.2. Protected Termination

The PEAPv2 part 2 conversation is expected to be non-
negligible, unacknowledged completed by an exchange of
success/failure indications lack
robustness.

As a result, a PEAP server SHOULD NOT send (Result-TLV) within a protected EAP Success
or EAP Failure EAP-TLV packet as
protected by the final packet within a PEAP
conversation. However, in TLS session.

If the spirit of being "conservative in what
you send, liberal in what you receive", a PEAP client SHOULD accept Crypto-Binding TLV 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 Intermediate-Result TLV have NOT
been exchanged in which "manufacture"
of packets is guaranteed not to occur.

Instead, EAP servers MUST utilize the acknowledged and protected
success/failure indications defined previous conversation, then they MUST be
present in Section 4. In this approach, the PEAP server sends the success/failure indication as an EAP-
Request with type=33 (EAP TLV), protected indication packet. Otherwise, it should be
considered a tunnel compromise error by the peer and EAP server.

The Result TLV is sent within the TLS channel. The PEAP client then
replies with a protected success/failure
indication as an EAP-Response with type=33 (EAP TLV). Result-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

The only outcome which should be considered as successful
authentication is ceremonial.

Use when an EAP Request of a 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.

All other combinations (EAP-TLVs Failure, EAP-TLVs Success), (EAP-
TLVs Failure, EAP-TLVs Failure), (no EAP-TLVs exchange or no
protected and acknowledged success/failure indication
provides EAP Success or Failure) should be considered failed
authentications, both by the PEAP protocol immunity against peer and EAP server. Once the
PEAPv2 peer and PEAPv2 server considers them as failed
authentications, they are the last packets inside the "manufacture" protected
tunnel. These are considered failed authentications regardless of
whether a cleartext success/failure indications mandated by [IEEE8021X]. It
also enables both sides of EAP Success or EAP Failure packet is subsequently
sent.

After the conversation to communicate PEAPv2 server has sent the
outcome of PEAP mutual authentication, although success indication, the TLS alert
mechanism already provides this capability peer is
allowed to some extent. On refuse to accept a Success message from the
other hand, this approach requires an extra round-trip, which
affects PEAPv2 server
since the performance client's policy may require completion of fast reconnect.

Once PEAP has been selected as certain EAP
methods. If the authentication method, compliant
PEAP implementations peer wants the server to negotiate EAP methods, it
MUST silently discard unprotected send the EAP-TLV packet with Result-TLV with Status=Failure. If
the success
indications (e.g. cleartext EAP Success) unless both indication from the PEAP peer
and EAP server have indicated a successful authentication exchange via contains the mechanism described in Section 4.

Similarly, once crypto-
binding TLV, then the TLS channel has been set up, compliant PEAP
implementations peer MUST silently discard unprotected failure
indications (e.g. cleartext EAP Failure) unless they are proceeded
by a protected failure indication. Protected failure indications include a crypto-binding TLV in the TLS alert mechanism, as well
EAP-TLV response. If 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) does not respond with
Result=Failure, a EAP-TLV packet
containing the crypto-binding TLV or if the crypto-binding TLV is
invalid, it has received should be considered as a protected EAP-Request of
Type=33 (EAP-TLV) tunnel compromise error by the
EAP server.

If the EAP server has set Result-TLV with Result=Success, Status=Success; and responded with a the
response from the peer is Status=Failure, then the EAP server MUST
either start another EAP conversation inside the protected EAP-Response of Type=33 (EAP-TLV) channel or
return Result=TLV with Result=Failure,
then it will accept Status=Failure without a crypto-binding TLV
and process Intermediate Result TLV.

A PEAPv2 tunnel may be nested inside another tunnel, for example,
PEAPv2 may be negotiated as a cleartext EAP Failure.
However, if a PEAP peer has previously received method inside a PEAPv2 tunnel. In
this case, each tunnel MUST use protected EAP-
Request of Type=33 (EAP-TLV) termination.

2.3. Error handling

Once the peer responds with Result=Success, the first PEAP packet and has responded
with the EAP server
receives the first PEAP packet from the peer, both MUST silently
discard all clear text EAP messages unless both the PEAP peer and
server have indicated success or failure or an error using a
protected EAP-Request of Type=33 (EAP-TLV) with
Result=Success, error or protected termination mechanism. If the PEAPv2
tunnel is nested inside another tunnel, then an unprotected failure indication MUST the clear text EAP
messages should be
silently discarded.

Prior to establishment accepted after protected termination of all the TLS channel, no keying material
exists, so that protected success/failure indications are not
possible. However, within PEAP
tunnels. After a failure to establish the TLS
channel (e.g. failure to verify Fatal alert is received or after protected
termination is complete, the peer or EAP 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 should accept clear
text EAP messages.

Other than supporting TLS alert messages, PEAP PEAPv2 does not have its
own error message capabilities. This is unnecessary since errors in
the
PEAP PEAPv2 Part 1 conversation are communicated via TLS alert
messages, and errors in the PEAP PEAPv2 Part 2 conversation are expected
to be handled by individual EAP methods.

If an error occurs at any point in the PEAP conversation, TLS layer, the EAP server
SHOULD send a TLS alert message instead of the next EAP-request
packet to the peer. 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-Response packet sent by the EAP server is responsible for retry
behavior. This means that if peer MAY encapsulate a TLS
client_hello handshake message, in which case the EAP server does not receive a reply
from the peer, it MUST resend MAY
allow the EAP-Request for which PEAPv2 conversation to be restarted, or it has not
yet received MAY contain an EAP-Response. However,
EAP-Response packet with EAP-Type=PEAP and no data, in which case the peer
PEAPv2 server MUST NOT resend EAP-
Response packets without first being prompted by send an EAP-Failure packet, and terminate the
conversation.

It is up to the EAP server.

For example, server whether to allow restarts, and if so, how
many times the initial PEAP start packet sent by the conversation can be restarted. An EAP server
were
implementing restart capability SHOULD impose a limit on the number
of restarts, so as to be lost, then protect against denial of service attacks.

If an error occurs at any point in the TLS layer, the peer would not receive this packet, and
would not respond to it. As SHOULD
send a result, TLS alert message instead of the PEAP start next EAP-response packet would be
resent by to
the EAP server. Once the The peer received the PEAP start
packet, it would SHOULD send an EAP-Response packet with
EAP-Type=PEAP, encapsulating a TLS record containing the client_hello appropriate
TLS alert message. If the EAP-Response were to be lost, then the 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 restart the sessionId within conversation by
sending a EAP-Request packet encapsulating the TLS protocol is to allow for
improved efficiency
hello_request_handshake message, in the which 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 MAY allow the
previous authentication attempt
PEAPv2 conversation to that EAP server.

Based on the sessionId chosen by the peer, and the time elapsed
since the previous authentication, be restarted; or the EAP server will decide
whether to allow can response
with EAP Failure.

Any time the continuation, peer or whether to choose a new
session.

In the case where the EAP server and the authenticator reside on the
same device, then the client will only be able to continue sessions finds an error when connecting to processing
the same NAS or channel server. Should these
devices be set up in sequence of exchanges, such a rotary or round-robin then it may not be
possible for the peer to know in advance the authenticator violation of TLV rules, it will
be connecting to, and therefore which sessionId to attempt to reuse.
As should
send a result, it is likely that the continuation attempt will fail.

In the case where Result TLV of failure and terminate the EAP authentication is remoted then
continuation tunnel. This is much more likely
usually due to be successful, since multiple
NAS devices an implementation problem 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 considered an fatal
error.

If a TLS change_cipher_spec message and tunnel compromise error (see Section 2.2) is detected by the
peer, the peer SHOULD send a TLS
finished handshake message after the server_hello message. The
finished Internal Error alert (a Fatal error)
message contains instead of the EAP server's authentication response next EAP-response packet to the peer.

After EAP server.
Similarly, if a session tunnel compromise error is successfully resumed, the EAP-Server starts with
Part 2 of detected by the PEAP conversation. The peer may have roamed to a
different network and successfully resumed with same EAP server. The
peer and
server, the EAP server MUST not assume that SHOULD send a session resume
implies either TLS Internal error alert (a
Fatal error) message instead of them will skip inner EAP methods.

2.8. the next EAP-response packet to the
peer.

2.4. 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],
[RFC1990], 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 PEAPv2 implementation
MUST provide its own support for fragmentation and reassembly.

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

PEAPv2 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 only for the first fragment of a
fragmented TLS message or set of messages.

The TLS Message Length field in the PEAPv2 header is not protected;
and hence can be modified by a attacker. The TLS record length in
the TLS data is protected. Hence, if TLS Message length received in
the first packet (with L bit set) is greater or less than the total
size of TLS data received including multiple fragments, then the TLS
message length should be ignored.

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. 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.

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 PEAPv2 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.

2.5. 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
been negotiated, it may not be possible for them

Instead of deriving keys specific to provide link layer ciphersuite-specific keys. In addition, attempting to provide
such keys is undesirable, since it would require the ciphersuites EAP method
methods provides a Master Session Key (MSK) used to
be revised each time derive keys in a new
link layer ciphersuite specific manner. The method used to extract ciphering
keys from the MSK is developed. As a
result, PEAP beyond the scope of this document.

PEAPv2 also derives master session keys an Extended Master Session Key (EMSK) which can subsequently be
truncated is
reserved 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]. deriving keys in other ciphering applications.
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].

PEAPv2 combines key material from the TLS exchange with key material
from inner key generating EAP methods to provide stronger keys and to
bind inner authentication mechanisms to the TLS tunnel. Both the
peer and EAP server MUST derive master compound MAC and compound session
keys using the procedure described below.

The input for the cryptographic binding includes the following:

[a] The PEAPv2 tunnel key (TK) is calculated using the first 64 octets
of the (secret) key material generated as described in the compound Session Key derivation EAP-TLS
algorithm (RFC2716 section (section
4.2) of 3.5)

[b] The MSK provided by each successful inner EAP method (should not
include the draft Compound Authentication Binding Problem
[compoundbinding].

Algorithms 64 octets of EMSK); for each successful EAP method
completed within the truncation of these encryption and authentication
master session keys tunnel.

ISK1..ISKn are specific the MSK portion of the EAP keying material obtained
from methods 1 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 n. In some cases (except in [IEEE80211]. An example the case of how encryption keys the EAP-
TLV method), where the inner EAP method does not provide keys: ISKi,
for use
with MPPE [RFC3078] are derived from some i, may be the null string ("").

The algorithm uses P_SHA-1 PRF specified in the TLS master specification
[RFC2246] ("|" denotes concatenation).

The intermediate combined key is generated after each successful EAP
method inside the tunnel.

Generating the intermediate combined key:

Take the second 32 octets of TK

IPMK0 = TK

for j = 1 to k do
IPMKj = P_SHA1(IPMK(j-1),"Intermediate PEAP MAC key" | ISKj);

k = the last successful EAP method inside the tunnel at the point
where the combined MAC key is derived.

Each IPMKj output is 32 octets. IPMKn is the intermediate combined
key used to derive combined session and combined MAC keys.

Compound MAC Key derivation:

The Compound MAC Key for the server (the B1_MAC) is derived CMK_B1

CMK_B1 = P_SHA1(IPMKn,"PEAP Server B1 MAC key" | S_NONCE)

The Compound MAC Key for the client (the B2_MAC) is derived from MAC
key called CMK B2.

CMK_B2 = P_SHA1(IPMKn,"PEAP Client B2 MAC key" | C_NONCE | S_NONCE)

The compound MAC keys (CMK_B1 and CMK_B2) are each 20 octets long.

Compound Session Key derivation:

The compound session key (CSK) is
given derived on both the peer and EAP
server after successful completion of protected termination.

CSK = P_SHA1 (IPMKn, "PEAP compound session key" | C_NONCE | S_NONCE
| OutputLength)

The output length of the CSK must be at least 128 bytes. The first
64 octets are taken and the MSK and the second 64 octets are taken as
the EMSK. The MSK and EMSK are described in [RFC3079].

2.10. [RFC2284bis].

2.6. 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, PEAPv2, the negotiated TLS ciphersuite
relates only to the mechanism by which the PEAP PEAPv2 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 PEAPv2 protocol

3.1. PEAP PEAPv2 Packet Format

A summary of the PEAP PEAPv2 Request/Response packet format is shown
below. The fields are transmitted from left to right.

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 L
bit MUST NOT be set for other fragments of the same 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)

Data

The format of the Data field is determined by the Code field.

3.2. PEAP PEAPv2 Request Packet

A summary of the PEAP PEAPv2 Request packet format is shown below. The
fields are transmitted from left to right.

Code

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, Flags, TLS
message length and TLS
Response 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 packet in TLS record
format.

3.3. PEAP PEAPv2 Response Packet

A summary of the PEAP PEAPv2 Response packet format is shown below. The
fields are transmitted from left to right.

Code

Identifier

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, Flags, Ver,
TLS message length, 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.

3.4. PEAPv2 Part 2 Packet Format

The PEAPv2 Part 2 packet format is the same as the PEAPv2 Request and
Response packet formats described in Sections 3.1 and 3.2, except
that the TLS Data field encapsulates TLS packets in TLS record
format, representing encrypted EAP-TLVs.

Although the EAP-TLV method has been allocated an EAP Type, use of
this method is prohibited outside of a tunnel by [RFC2284bis]. Since
EAP-TLVs are self-describing, when transmitted within PEAPv2, the EAP
header portion of the EAP-TLV packet is absent (including the Code,
Identifier, Length and Type fields), leaving only a list of TLVs as
the payload.

Within PEAPv2, all inner EAP method packets are encapsulated in EAP-
TLV format. The EAP-Payload is an (optional) TLV which encapsulates
EAP packets (including all EAP header fields) and in addition carries
TLVs associated with them.

PEAP Part 2 packet format = EAP-TLV [EAP-Payload TLV [[EAP packet],
TLVs, ...], TLVs, ...] OR TLS Alert
The EAP-TLV packet is included without the EAP header fields (Code,
Identifier, Length, Type)

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 MIPv6 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 if 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; TLV, it MUST indicate send a failure to the EAP server using the NAK TLV; TLV in response; and all the
other TLVs in the message MUST be ignored. If an EAP peer finds an unknown
unsupported TLV which is marked as optional;
then optional, it MUST ignore the NOT send an NAK
TLV.

The EAP mandatory bit does not imply that the peer is not required to inform
understand the EAP server contents of unknown TLVs which are marked as optional. the TLV. The appropriate response to a
supported TLV with content that is not understood is defined by the
TLV specification.

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. mandatory bit in a TLV indicates that if the EAP server does not
support the TLV, it MUST send a NAK TLV in response; otherwise it
MUST send a protected termination message. If an EAP server finds an unknown
unsupported TLV which is marked as mandatory; the other TLVs in the
message MUST be ignored. The

An EAP-TLV packet is a EAP server method and within a PEAPv2 tunnel, it can
drop the connection
be sequenced before or send a after any other EAP method. An EAP-TLV request packet with NAK-TLV
does not have to
the EAP client.

Compliant PEAP contain any TLVs nor need it contain any mandatory
TLVs.

PEAPv2 implementations MUST support the EAP TLV method, as well as
processing of mandatory/optional settings on the TLV, the NAK TLV.

TLVs can be contained/nested in other TLVs.

4.1. EAP-TLV Request Packet

A summary of the EAP-TLV Request packet format is a EAP method; 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

Identifier

The Identifier field is one octet and it can aids in matching responses
with requests. The Identifier field MUST be sequenced before or after any other changed on each
Request packet.

Length

The Length field is two octets and indicates the length of the EAP method.
packet including the Code, Identifier, Length, Type, and Data
fields.

Type

33 - EAP-TLV

Data

The Data field is of variable length, and contains Type-Length-
Value tuples (TLVs).

4.2. EAP-TLV Response Packet

A summary of the Extension Response packet does not have format is shown below.
The fields are transmitted from left to contain any 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
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-TLV

Data

The Data field is of variable length, and contains Type-Length-
Value tuples (TLVs).

4.3. TLV format

EAP-TLV TLVs or are defined as follows:

0 - Non-mandatory TLV
1 - Mandatory TLV

Reserved, set to zero (0)

TLV Type

A 14-bit field, denoting the TLV type. Allocated Types include:

0 - Reserved
1 - Reserved
2 - Reserved
3 - RESULT_TLV - Acknowledged Result
4 - NAK_TLV
5 - Crypto-Binding TLV
6 - Connection-Binding TLV
7 - Vendor-Specific TLV
8 - URI TLV
9 - EAP Payload TLV
10 - Intermediate Result TLV

Length

The length of the Value field in octets.

Value

The value of the TLV.

4.4. Result TLV

The Result TLV provides support for acknowledged success and failure
messages within PEAPv2. PEAPv2 implementations MUST support this
TLV, which cannot be responded to with a NAK TLV. If the Status
field does not
have contain one of the known values, then the peer or EAP
server MUST drop the connection. The Result TLV is defined as
follows:

1 - Mandatory TLV

Reserved, set to zero (0)

TLV Type

Length

Status

The Status field is two octets. Values include:

1 - Success
2 - Failure

4.5. NAK TLV

The NAK TLV allows a peer to detect TLVs that are not supported by
the other peer. An EAP-TLV packet can contain any mandatory 0 or more NAK TLVs.

4.1. Protected success/failure

Compliant PEAP
PEAPv2 implementations MUST support acknowledged protected
success/failure together this TLV and this TLV cannot be
responded to with a NAK TLV. The NAK TLV is defined as follows:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vendor-Id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| NAK-Type | TLVs....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

1 - Mandatory TLV

Reserved, set to zero (0)

TLV Type

Length

>=6

Vendor-Id

The Vendor-Id field is four octets, and contains the Vendor-Id of
the TLV that was not supported. The high-order octet is 0 and the
low-order 3 octets are the SMI Network Management Private
Enterprise Code of the Vendor in network byte order. The Vendor-
Id field MUST be zero for TLVs that are not Vendor-Specific TLVs.
For Vendor-Specific TLVs, the Vendor-ID MUST be set to the SMI
code.

NAK-Type

The NAK-Type field is two octets. The field contains the Type of
the TLV that was not supported. A TLV of this Type MUST have been
included in the previous packet.

TLVs

This field contains a list of TLVs, each of which MUST NOT have
the mandatory bit set. These optional TLVs can be used in the
future to communicate why the offending TLV was determined to be
unsupported.

4.6. Crypto-binding TLV

The Crypto-Binding TLV is used prove that both peers participated in
the sequence of authentications (specifically the TLS session and
inner EAP methods that generate keys).

Both the Binding exchange. Request (B1) and Binding Response (B2) use the same
packet format. However the Sub-Type indicates whether it is B1 or
B2.

The Result Crypto-Binding TLV is MUST be used to indicate success or failure perform Cryptographic Binding
after each successful EAP method (except EAP-TLV) in a sequence of the PEAP
tunnel.
EAP methods is complete in PEAPv2 part 2. The PEAP tunnel success/failure packet MUST contain a Result
TLV along with the Cryto-Binding TLV. Crypto-Binding TLV may can
also be used during Protected Termination.

The crypto-binding TLV must have the version number received during
the PEAP version negotiation. The receiver of the crypto binding TLV
must verify that the version in other EAP-TLV packets. Result the crypto binding TLV MUST NOT be matches the
version it sent in packets
other than during the protected success/failure indication. PEAP version negotiation. If a CRYPTO BINDING TLV does not exist in a packet that contains
Result TLV, this check
fails then the EAP peer TLV is invalid.

The receiver of the crypto binding TLV must disconnect verify that the connection. subtype
is not set to any value other than the ones allowed. If a CRYPTO BINDING TLV this check
fails validation, then peer must disconnect the connection. Implementations that can delete TLV is invalid.

This message format is used for the TLS handle MUST
delete Binding Request (B1) and also the TLS handle. Implementations that keep track of session
state
Binding Response. This uses TLV type CRYPTO_BINDING_TLV. PEAPv2
implementations MUST ensure that the session handle support this TLV and this TLV cannot be used
responded to skip
stage2 authentication.

When using the Result-TLV, the only outcome which should be
considered with a NAK TLV. The format is as successful authentication given below.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R| TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version |Received Ver. | Sub-Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Nonce ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Compound MAC ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

1 - Mandatory TLV

Reserved, set to zero (0)

TLV Type

Length

Version

The Version field is when an EAP Request a single octet, which is set to the version
of
Type=EAP-TLVs with Result crypto binding TLV. For the crypto-binding TLV of Status=Success defined in this
specification, It is answered by an
EAP Response set to zero (0).

Received Version

The Received Version field is a single octet and MUST be set to
the PEAP version number received during version negotiation. Note
that this field only provides protection against downgrade attacks
where a version of Type=EAP-TLVs with Result PEAP requiring support for this TLV of Status=Success.

If is required
on both sides (such as PEAPv2 or a more recent version).

Sub-Type
The Sub-Type field is two octets. Possible values include:

0 - Binding Request
1 - Binding Response

Nonce

The Nonce field is 32 octets. It contains a 256 bit nonce that is
temporally unique, used for compound MAC key derivation at each
end. This is the EAP server has set Result-TLV with Status=Success; S_NONCE for the B1 message and a C_NONCE for the
response from
B2 message.

Compound MAC

The Compound MAC field is 16 octets. This can be the EAP peer Server MAC
(B1_MAC) or the Client MAC (B2_MAC). It is Status=Failure, then computed over the server MUST
either continue EAP conversation
entire Crypto-Binding TLV attribute using the HMAC-SHA1-128 that
provides 128 bits of output using the CMK_B1 or return Result=TLV CMK_B2 with
Status=Failure. This the
MAC field zeroed out.

4.7. Connection-Binding TLV

The Connection-Binding TLV allows EAP peer for connection specific information
to indicate that it refuses be sent by the peer 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 AAA server. This TLV validation is not successful) should be considered
failed authentications, both logged
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 AAA server. The AAA or EAP Failure packet is
subsequently sent. Because server should not deny
access if there i s a mismatch between the EAP-TLVs method is protected within value sent through the TLS channel, these packets cannot be spoofed, whereas cleartext
EAP Success AAA
protocol and EAP Failure messages can be sent by an attacker.

In order this TLV.

The format of this TLV is defined for the validation layer that defines the
parameters. The format of crypto-binding TLV the value sent by the peer to be successful, the EAP
server and EAP peer should may be in-sync on which EAP methods
inside the tunnel have been successful. If any or all EAP methods
inside different from the tunnels have failed as per EAP server or EAP peer, then
that does not mean format of the Result will always be set to failure.

In a successful authentication for a tunnel, corresponding value
sent through the last packet
exchange (both request and response) inside AAA protocol. For example, the tunnel MUST always
contain a valid Crypto-Binding connection binding
TLV may contain 802.11 MAC Address and Result-TLV=Success.

Compliant SSID.

PEAP implementations MUST MAY support the EAP this TLV method,
processing of mandatory/optional settings on the TLV, the and this TLV MUST NOT be
responded to with a NAK TLV,
Result-TLV, Method-Identity-TLV, Crypto-Binding-TLV.

4.2. EAP-TLV Request Packet

A summary of the EAP EAP-TLVs Request packet format TLV. It is shown below.
The fields are transmitted from left to right. defined as follows:

Code

Identifier

0 - Optional TLV

Reserved, set to zero (0)

TLV Type

Length

>=0

TLVs...

The Identifier field is one octet and aids contains a list of TLVs, each in matching responses the same format defined
in Section 4.3, with requests. The Identifier field MUST be changed the optional bit set. These TLVs contain
information on each Request
packet.

Length

The Length field is two octets and indicates the length identity of the
EAP packet including peer and authenticator (layer 2
or IP addresses); the Code, Identifier, Length, Type, media used to connect the peer and Data
fields.

Type

33 - EAP-TLV

Data
authenticator (NAS-Port-Type); and/or the service the client is
trying to access on the gateway (SSID). The Data field format of these TLVs
will be defined in a separate draft.

4.8. Vendor-Specific TLV

The Vendor-Specific TLV is available to allow vendors to support
their own extended attributes not suitable for general usage.

A Vendor-Specific-TLV attribute can contain one or more TLVs,
referred to as Vendor-TLVs. The TLV-type of variable length, the Vendor-TLV will be
defined by the vendor. All the Vendor-TLVs inside a single Vendor-
Specific TLV belong to the same vendor.

PEAPv2 implementations MUST support the Vendor-Specific TLV; and contains EAP-TLV TLVs.

4.3. EAP-TLV Response Packet this
TLV cannot be responded to with a NAK TLV. PEAPv2 implementations
MAY NOT support the Vendor-TLVs included in the Vendor-Specific TLV
and can respond with a NAK TLV.

Vendor-TLVs may be optional or mandatory. Vendor-TLVs sent in the
protected success and failure packets MUST be marked as optional. If
Vendor-TLVs sent in protected success/failure packets are marked as
Mandatory, then the peer or EAP server MUST drop the connection.

A summary of the EAP-TLV Response packet Vendor-Specific Attribute format is shown below.
The fields are transmitted from left to right.

Identifier
| Vendor-TLVs....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

1 - Mandatory TLV

Reserved, set to zero (0)

TLV Type

Length

>=4

Vendor-Id

The Identifier Vendor-Id field is one four octets. The high-order octet is 0 and aids
the low-order 3 octets are the SMI Network Management Private
Enterprise Code of the Vendor in matching responses
with requests. network byte order. The Identifier field Vendor-
Id MUST be changed on each Request
packet.

Length

The Length zero for TLVs that are not Vendor-Specific TLVs. For
Vendor-Specific TLVs, the Vendor-ID MUST be set to the SMI code.

Vendor-TLVs

This field is two octets and indicates the length of indefinite length. It contains vendor-specific
TLVs, in a format defined by the
EAP vendor.

4.9. URI TLV

The URI TLV allows a server to send a URI to the client to refer it
to a resource. The TLV contains a URI in the format specified in
RFC2396 with UTF-8 encoding. If a packet including contains multiple URI TLVs,
then the Code, Identifier, Length, Type, client SHOULD select the first TLV it can implement, and Data
fields.

Type

33 - EAP EAP-TLV

Data

The Data field
ignore the others. If the client is unable to implement any of variable length, the
URI TLVs, then it MAY ignore the error. PEAP implementations MAY
support this TLV; and contains Attribute-
Value Pairs (TLVs).

4.4. EAP-TLV this TLV format

EAP-TLV TLVs are defined as follows: cannot be responded to with a NAK TLV.

A summary of this field is shown below:

0 - Non-mandatory TLV
1 - Mandatory Optional TLV

Reserved, set to 0. zero (0)

TLV Type

A 14-bit field, denoting the attribute type. Allocated TLV Types
include:
0 - Reserved
1 - Reserved
2 - Reserved
3 - - RESULT_TLV - Acknowledged Result
4 - NAK_TLV
5 - CRYPTO_BINDING TLV
6 - METHOD_IDENTITY TLV

Length

The length of the Value

>=0

URI

This field in octets.

Value

The value is of the attribute.

CRYPTO_BINDING_TLV indefinite length, and METHOD_IDENTITY_TLV are defined conforms to the format
specified in [RFC2396].

4.10. EAP-Payload TLV

To allow piggybacking EAP request and response with other TLVs, the draft
Compound Authentication Binding Problem[CompoundBinding].

4.5. Result
EAP Payload TLV is defined, which includes an encapsulated EAP packet
and 0 or more TLVs. PEAPv2 implementations MUST support this TLV,
which cannot be responded to with a NAK TLV. The Result EAP-Payload 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 EAP packet...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
M

1 - Mandatory TLV

Reserved, set to zero (0)

TLV Type

3 - Success/Failure

Length

Status

>=0

EAP packet

This field contains a complete EAP packet, including the EAP
header (Code, Identifier, Length, Type) fields. The status length of
this field is two octets. Values include:

1 - Success
2 - - Failure

4.6. NAK determined by the Length field of the encapsulated
EAP packet.

TLVs...

This (optional) field contains a list of TLVs associated with the
EAP packet field. The TLVs utilize the same format described
Section 4.3, and MUST NOT have the mandatory bit set. The total
length of this field is equal to the Length field of the EAP-
Payload-TLV, minus the Length field in the EAP header of the EAP
packet field.

4.11. Intermediate Result TLV

The NAK Intermediate Result TLV allows a peer provides support for acknowledged
intermediate Success and Failure messages within EAP. PEAPv2
implementations MUST support this TLV, which cannot be responded to detect when TLVs that are not supported
by the other peer. It
with a NAK TLV. This TLV is defined as follows:

M
1 - Mandatory TLV

Reserved, set to zero (0)

TLV Type

4 -

Length

<tbd>

TLV Type number.

>=2

Status

The Status field is two octets. Values include:

1 - Success
2 - Failure

TLVs

This (optional) field is of indeterminate length, and contains the
TLVs associated with the Intermediate Result TLV, in the same
format as described in Section 4.3. The TLVs in this field MUST
NOT have the mandatory bit set.

4.12. TLV type that Rules

To save round trips, multiple TLVs can be sent in the single PEAPv2
packet. However, multiple EAP Payload TLVs within one single PEAPv2
packet is not supported.

TLVs.. supported in this version and MUST NOT be sent. If the
peer or EAP server receives multiple EAP Payload TLVs, then it MUST
drop the connection.

The field contains following table provides a list guide to which TLVs may be found in
which kind of optional TLVs. These could packets, and in which quantity:

Request Response Success Failure TLV
0-1 0-1 0-1 0-1 Intermediate Result TLV
0-1 0-1 0 0 EAP Payload TLV
0-1 0-1 1 1 Result TLV
0-1 0-1 0-1 0-1 Crypto-Binding TLV
0+ 0+ 0 0 NAK TLV
0-1 0-1 0-1 0-1 Connection-Binding TLV
0+ 0+ 0+ 0+ Vendor-Specific TLV
0+ 0 0+ 0-1 URI TLV
The following table defines the meaning of the above table entries.

0 This TLV MUST NOT be used present in future to send information on why the field was determined packet.
0+ Zero or more instances of this TLV MAY be present in packet.
0-1 Zero or one instance of this TLV MAY be present in packet.
1 Exactly one instance of this TLV MUST be present in packet.

Packet type Description
----------------------------
Request - EAP-TLV request packet sent by EAP server to peer.
Response - EAP-TLV response packet sent by peer to EAP server.
Success - EAP-TLV packet sent by Peer or EAP server as
protected success
Failure - EAP-TLV packet sent by Peer or EAP server as
protected failure.

The EAP-Payload TLV can contain other TLVs. The table below
defines which TLVs can be contained inside the EAP-Payload TLV
and how many such TLVs can be unknown. included.

EAP-Payload-TLV TLV
0 Intermediate Result TLV
0 EAP Payload TLV
0 Result TLV
0 Crypto-Binding TLV
0+ NAK TLV
0 Connection-Binding TLV
0+ Vendor-Specific TLV
0 URI TLV

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

PEAPv2 provides a server authenticated, encrypted and integrity
protected channel. PEAP is tunnel. All data within the tunnel has these properties.
Data outside the tunnel such a method, and as a result the
acknowledged Success and Failure messages are always protected.

Note however, that [IEEE8021X] manufactures cleartext EAP Success and EAP Failure messages, so that even though Failure,
authentication methods negotiated outside of PEAPv2 and the Result TLV will be
protected, this will be followed PEAPv2
headers themselves are not protected by a cleartext EAP Success or EAP
Failure packet. this tunnel.

In addition, the crypto-binding TLV can reveal man-in-the-middle
attack described in section 6.8. Hence, the server should not reveal
any sensitive data to the client until after the Crypto-Binding TLV
has been properly verified.

5.2. Method negotiation

If the peer does not support PEAP, PEAPv2, or does not wish to utilize PEAP
PEAPv2 authentication, it MUST respond to the initial EAP-Request/PEAP-
Start 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 Inauthentic
NAK packets can be used to trick the peer and Authenticator authenticator into
"negotiating down" to a weaker form of authentication, such as EAP-MD5 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 PEAPv2 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 PEAPv2 as an
authentication method is that it does not support it. Where the
additional security of PEAP PEAPv2 is required, server implementations
SHOULD respond to a NAK with an EAP-Failure, terminating the
authentication conversation.

Since method negotiation outside of PEAP is not protected, if the
peer is configured to allow PEAP and other EAP methods at the same
time, the negotiation is subject to downgrade attacks. Since method
negotiation outside of PEAP is not protected, if the peer is
configured to allow PEAP version 2; and previous PEAP versions at the
same time, the negotiation is subject to negotiation downgrade
attacks. However, peers configured to allow PEAPv2 and later PEAP
versions may not be subject to downgrade negotiation attack since the
highest version supported by both peers is checked within the
protected tunnel.

If peer implementations select incorrect methods or credentials with
EAP servers, then attacks are possible on the credentials. Hence, a
PEAPv2 peer implementation should preferably be configured with a set
of credentials and methods that may be used with a specific PEAPv2
Server. The peer implementation may be configured to use different
methods and/or credentials based on the PEAPv2 server.

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 PEAPv2
Part 2 conversation, and successfully conclude the conversation as
described in Section 2.4.

PEAP with
a protected termination.

PEAPv2 "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 PEAPv2 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 PEAPv2 implementations may not be capable of removing TLS
session cache entries established in PEAP PEAPv2 Part 1 after an
unsuccessful PEAP PEAPv2 Part 2 authentication. In such implementations,
the existence of a 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 PEAPv2 Part 2 authentication or failed protected ack termination
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
completion of protected acknowledge has
been successfully exchanged. termination. Failing to do this would enable
a peer to gain access by completing PEAP PEAPv2 Part 1, tearing down the
connection, re-connecting and resuming PEAP PEAPv2 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 PEAPv2 removes TLS session cache entries of peers
failing PEAP PEAPv2 Part 2 authentication, then it MAY skip the
PEAP PEAPv2
Part 2 conversation entirely after a successful session resumption,
successfully terminating the PEAP PEAPv2 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] [RFC3546]
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 not all
TLS 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, invalid
as per client policy, then the peer SHOULD disconnect.

If the client has a policy to require checking certificate revocation
and it cannot obtain revocation information then it may need to
disallow the use of all or some of the inner methods since some
methods may reveal some sensitive information.

5.5. Separation of the EAP server and the authenticator

As a result of a complete PEAP PEAPv2 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 secure 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 PEAPv2 Part 1 and Part 2 Servers

The EAP server involved in PEAP PEAPv2 Part 2 need not necessarily be the
same as the EAP server involved in PEAP PEAPv2 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 PEAPv2 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 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 PEAPv2 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 part of TLS session
establishment.

Similarly, if the EAP method negotiated during PEAP PEAPv2 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. PEAPv2. As a result, it is
unable to enforce policies requiring PEAP. Since some EAP methods
require PEAP PEAPv2 in order to generate keys or lessen security
vulnerabilities, where such methods are in use, such a configuration
may be unacceptable.

In summary, PEAP PEAPv2 encrypting/decrypting gateway configurations are
vulnerable to attack and SHOULD NOT be used. Instead, the entire
PEAP
PEAPv2 connection SHOULD be proxied to the final destination, and the
subsequently derived master session keys need to be transmitted back. This
T his provides end to end protection of PEAP. PEAPv2. The specification of
this transit mechanism is outside the scope of this document, but
mechanisms similar to [RFC2548] can be used. These steps protects protect 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 PEAPv2 MAY be used. The PEAP If RADIUS is used to
communicate between gateway and EAP server, then the PEAPv2
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]. [RFC3579].

5.7. Identity verification

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
PEAPv2 and the first portion of the PEAP PEAPv2 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 PEAPv2 peer can present the server with multiple identities. This
includes the claim of identity within the initial EAP-
Response/Identity(MyID)
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 PEAPv2 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 PEAPv2 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 PEAPv2 conversation.

The protected identity or identities presented by the peer within
PEAP
PEAPv2 Part 2 may not be identical to the cleartext identity
presented in PEAP PEAPv2 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 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 PEAPv2 Part 2, the peer
may claim the identity of "fred@bigco.com". Thus, PEAP PEAPv2 can provide
protection for the user's identity, though not necessarily the
destination realm, unless the PEAP PEAPv2 Part 1 conversation terminates
at the local authentication server.

As a result, PEAP PEAPv2 implementations SHOULD NOT attempt to compare the
Identities claimed with Parts 1 and 2 of the PEAP PEAPv2 conversation.
Similarly, if multiple Identities are claimed within PEAP PEAPv2 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 attack protection

If an

TLS protection can address a number of weaknesses in the EAP method;
as well as EAP protocol weaknesses listed in the abstract and
introduction sections in this document.

Hence, the recommended solution is to always deploy authentication
methods with protection of PEAPv2.

if a deployment chooses to allow a EAP method protected by PEAP is also deployed
without protection (from of PEAP or IPSEC), and if IPsec at the same credential is
allowed in both cases, time, then this opens
up a possibility of a man-in-the-middle attack is possible. attack.

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

PEAP version 2 prevents this attack.

The preferred solution attack by using the keys generated by
the inner EAP method in the crypto-binding exchange described in
protected termination section. This attack is to deploy not prevented if the authentication
inner EAP method with
protection from PEAP does not generate keys or IPSEC. Protection if the keys generated by
the inner EAP method can address be compromised.

Alternatively, the man-in-
the-middle attack; and in addition attack can address also be thwarted if the inner EAP
method and EAP
protocol weaknesses listed in can signal to the abstract and introduction sections
in peer that the packets are being sent within
the tunnel. In most cases this document.

Another solution may require modification to the inner
EAP method. In order to allow for these implementations, PEAPv2
implementations should inform inner EAP methods that the EAP method
is being protected by a PEAPv2 tunnel.

Since all sequence negotiations and exchanges are protected by TLS
channel, they are immune to snooping and MITM attacks with the use knowledge known only of
Crypto-Binding TLV. To make sure the same parties are involved tunnel
establishment and previous inner method, before engaging the next
method to sent more sensitive information, both peer and server MUST
use the real peers Crypto-Binding TLV between methods to
verify check the tunnel
integrity. If the Crypto-Binding TLV failed validation, they SHOULD
stop the sequence and terminate the tunnel connection, to prevent
more sensitive information being sent in subsequent methods.

5.9. Cleartext forgeries

As described in [RFC2284bis], EAP Success and Failure packets are not
authenticated, so that there 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 and Failure packets may be
used to convince a peer to disconnect; or convince a peer to access
the network even before authentication is no man-in-the-middle. A number complete, resulting in
denial of protocols
derive keys service for encryption, the peer.

By supporting encrypted, authenticated and integrity protected
success/failure indications, PEAPv2 provides protection against these keys
attacks.

When the peer responds with the first PEAP packet; and the EAP server
receives the first PEAPv2 packet from the peer, both MUST silently
discard all clear text EAP messages unless both the PEAPv2 peer and
server have indicated success or failure or error using a protected
error or protected termination mechanism. The success/failure
decisions sent by a protected mechanism indicate the final decision
of the EAP authentication conversation. After success/failure has
been indicated by a protected mechanism, the PEAPv2 client can
process unprotected EAP success and EAP failure message; however MUST
ignore any unprotected EAP success or failure messages where the
decision does not match the decision of the protected mechanism.

[RFC2284bis] 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 known 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 EAP server SHOULD send a clear text EAP success or
EAP-failure packet after the man-
in-the-middle. These keys can protected success or failure packet or
TLS alert. The peer MUST NOT require the clear text EAP Success or
EAP Failure if it has received the protected success or failure or
TLS alert. For more details, refer to [RFC228bis], Section 4.2.

5.10. TLS Ciphersuites

Anonymous ciphersuites are vulnerable to man-in-the-middle attacks,
and SHOULD NOT be used with PEAPv2, unless the EAP methods inside
PEAPv2 can address the man-in-the-middle attack or unless the man-in-
the-middle attack can be addressed by mechanisms external to PEAPv2.

5.11. Denial of service attacks

Denial of service attacks are possible if the attacker can insert or
modify packets in the binding phase exchange
described authentication channel. The attacker can
modify unprotected fields in compound binding [compoundbinding] draft to detect man-
in-the-middle. PEAP implementations MUST support the binding phase
exchange using compound MACs PEAP packet such as described in the section 4.2 EAP protocol
or PEAP version number. This can result in a denial of the
compound binding draft[CompoundBinding].

Another solution service
attack. It is also possible for EAP methods the attacker to securely signal modify protected
fields in a packet to cause decode errors resulting in a denial of
service. In these ways the attacker can prevent access for peers that
they
connecting to the network.

Denial of service attacks with multiplier impacts are inside more
interesting than the protected channel. This may require changes ones above. It is possible to multiply the
impact by creating a large number of TLS sessions with the EAP protocol. In order to allow
server.

5.12. Security Claims

Intended use: Wireless or Wired networks, and over
the Internet, where physical security
cannot be assumed.
Auth. mechanism: Use arbitrary EAP methods to implement secure
signaling, PEAP implementations SHOULD inform and TLS authentication
mechanisms for authentication of the
client and server.
Ciphersuite negotiation: Yes.
Mutual authentication: Yes. Depends on the type of EAP methods method
used within the tunnel and the type of
authentication used within TLS.
Integrity protection: Yes
Replay protection: Yes
Confidentiality: Yes
Key derivation: Yes
Key strength: Variable
Dictionary attack prot: Not susceptible.
Fast reconnect: Yes
Crypt. binding: Yes.
Acknowledged S/F: Yes
Session independence: Yes.
Fragmentation: Yes

PEAPv2 derives keys by combining keys from TLS and the inner EAP
methods. It should be noted that the use of TLS ciphersuites with a
particular key lengths does not guarantee that the key strength of
the keys will be equivalent to the length. The key exchange
mechanisms (eg. RSA or Diffie-Hellman) used must provide sufficient
security or they are being protected by PEAP. will be the weakest link. For example RSA key sizes
with a modulus of 1024 bits provides less than 128 bits of security,
this may provide sufficient key strength for some applications and
not for others. See [PKLENGTH] for a detailed analysis of
determining the public key strengths used to exchange symmetric keys.

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 requires registration: TLV-
Types. PEAPv2
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 "Designated Expert with Specification
Required, 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 0-10 have been allocated.

Additional EAP-TLV type codes may be allocated following Designated
Expert with Specification Required [RFC2434].

7. References

7.1. Normative references

[RFC1321] Rivest, R., R. and S. Dusse, S., "The MD5 Message-Digest Algorithm",
RFC 1321, April 1992.

[RFC1570] Simpson, W., Editor, "PPP LCP Extensions", RFC 1570,
January
1994.

[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., T. and C. 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., B. and M. Beadles, M., "The Network Access Identifier", RFC
2486, January 1999.

[TLSEXT]

[RFC2396] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396, August
1998.

[RFC3546] Blake-Wilson, S., et al. "TLS Extensions", RFC 3546, June
2003.

[RFC2284bis]
Blunk, L. et al., "Extensible Authentication Protocol (EAP)",
draft-ietf-eap-rfc2284bis-06.txt, Internet draft (work in
progress), draft-ietf-tls-extensions-06.txt, Feb October 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.

7.2. Informative references

[RFC2419]

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

[RFC1990] Sklower, K., Meyer, Lloyd, B., McGregor, G., Carr, D. and T.
Coradetti, "The PPP Multilink Protocol (MP)", RFC 1990, August
1996.

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

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

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

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

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

[RFC3078] Pall, G., G. and 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 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]

[PEAPv0] Kamath, V., Palekar, A., A. and M. Wodrich, M., "Microsoft's PEAP
version 0 (Implementation in Windows XP SP1)",
draft-kamath-pppext-peapv0-00.txt.

9. draft-kamath-
pppext-peapv0-00.txt, Internet draft (work in progress), July
2002.

[PKLENGTH]
H. Orman and P. Hoffman, "Determining Strengths For Public
Keys Used For Exchanging Symmetric Keys", draft-orman-public-
key-lengths-05.txt, Internet Draft (work in progress),
December 2002.

[RFC3579] Aboba, B. and P. Calhoun, "RADIUS Support for EAP", RFC 3579,
September 2003.

[CompoundBinding]
Puthenkulam, J., Lortz, V., Palekar, A. and D. Simon, "The
Compound Authentication Binding Problem", draft-puthenkulam-
eap-binding-03.txt, Internet Draft (work in progress), May
2003.

[IEEE8021X]
IEEE Standards for Local and Metropolitan Area Networks: Port
based Network Access Control, IEEE Std 802.1X-2001, June 2001.

Appendix A - Examples

A.1 Cleartext Identity Exchange

In the case where an identity exchange occurs within PEAP PEAPv2 Part 1,
the conversation will appear as follows:

Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->

// Identity sent in the clear. May be a hint to help route the
authentication request to EAP server, instead of the full user
identity.

<- EAP-Request/
EAP-Type=PEAP, V=2
(PEAP Start, S bit set)
EAP-Response/
EAP-Type=PEAP, V=1 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
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP -> finished,
EAP-Request/EAP-Type=EAP-TLV
[EAP-Payload-TLV[EAP-Request/
Identity]])

// identity protected by TLS. EAP-TLV packet does not include an EAP-
header.

TLS channel established
(messages (EAP 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 -> channel
encapsulated in EAP-TLV packets without EAP header)

EAP-TLV [EAP-Payload-TLV
[EAP-Response/Identity (MyID2)]]]->

<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X EAP-TLV [EAP-Payload-TLV
[EAP-Request/EAP-Type=X]]

EAP-TLV [EAP-Payload-TLV
[EAP-Response/EAP-Type=X]] ->

// Protected termination

<- EAP-Request/
EAP-Type=EAP-TLV

Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=1, Result EAP-TLV [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
Crypto-Binding-TLV (Version=0,
received-version=2, Nonce, B1_MAC),
Intermediate-Result-TLV (Success)]

EAP-TLV [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))

->
Intermediate-Result-TLV (Success),
Crypto-Binding-TLV (Version=0,
received-version=2,Nonce, B2_MAC)]->

TLS channel torn down
(messages sent in cleartext)

<- EAP-Success

A.2 No cleartext Identity Exchange

Where all peers are known to support PEAP, PEAPv2, 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 V=2
(PEAP Start, S bit set)

EAP-Response/
EAP-Type=PEAP, V=1 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
(TLS change_cipher_spec,
TLS finished)
EAP-Response/
EAP-Type=PEAP, V=2 -> finished,
EAP-TLV [EAP-Payload-TLV
(EAP-Request/Identity)])

TLS channel established
(messages sent within the TLS channel)

<- EAP-Request/
Identity
EAP-Response/
Identity (MyID)

EAP-TLV [EAP-Payload-TLV
[EAP-Response/Identity (MyID)]] ->

<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X EAP-TLV [EAP-Payload-TLV
[EAP-Type=EAP-Request/
EAP-Type=X]]

EAP-TLV [EAP-Payload-TLV
[EAP-Response/EAP-Type=X
or NAK NAK] ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X EAP-TLV [EAP-Payload-TLV
[EAP-Request/EAP-Type=X]]

EAP-TLV [EAP-Payload-TLV [EAP-Response/
EAP-Type=X]] ->

// Protected success
<- EAP-Request/
EAP-Type=EAP-TLV

Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, EAP-TLV [Crypto-Binding-TLV=
(Version=0, Received-version=2,
Nonce, B1_MAC),
Intermediate-Result-TLV(Success),
Result TLV (Success)]

EAP-TLV [Crypto-Binding-TLV=
(Version=0,Received-version=2,
Nonce, B2_MAC),
Intermediate-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)) (Success)]->

TLS channel torn down
(messages sent in cleartext)

<- EAP-Success

A.3 Client certificate authentication with identity privacy

Where all peers are known to support PEAP, PEAPv2, where client certificate
authentication is desired and the PEAP PEAPv2 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) finished,TLS Hello-Request)
EAP-Response/
EAP-Type=PEAP, V=2 ->
(TLS client_hello)->

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,]
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 finished, EAP-TLV
[Crypto-binding-TLV (version=0,
Received-version=2, Nonce,
B1_MAC),
Result-TLV (Success)])

// packet inside format within the tunnel including
EAP-header))
EAP-Response/
EAP-Type=EAP-TLV TLS channel

EAP-TLV [
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>,
Received-version=2,
Nonce, B2_MAC),
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)) (Success)]

TLS channel torn down
(messages sent in cleartext)

<- EAP-Success

A.4 Fragmentation and Reassembly

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 ->

<- 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 -> finished, EAP-TLV
[EAP-Payload-TLV[
EAP-Request/Identity]])

TLS channel established
(messages sent within the TLS channel)

<- EAP-Request/
Identity
EAP-Response/
Identity (MyID)

EAP-TLV
[EAP-Payload-TLV
[EAP-Response/Identity(myID)]] ->

<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X EAP-TLV [ EAP-Payload-TLV
[EAP-Request/EAP-Type=X]]

EAP-TLV [EAP-Payload-TLV
[EAP-Response/EAP-Type=X or NAK -> NAK]]->

<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X EAP-TLV [ EAP-Payload-TLV
[EAP-Request/EAP-Type=X]]

EAP-TLV [EAP-Payload-TLV
[EAP-Response/EAP-Type=X] ->

<- EAP-Request/
EAP-Type=EAP-TLV
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>, EAP-TLV [Crypto-Binding-TLV
=(Version=0, Received-Version=2,
Nonce, B1_MAC),
Intermediate-Result-TLV(Success),
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 (Success)]

EAP-TLV [
Crypto-Binding-TLV=(Version=0, Nounce, Number of inner EAP
methods=<number>,
Received-Version=2,Nonce, B2_MAC),
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))
Intermediate-Result-TLV (Success)] ->

TLS channel torn down
(messages sent in cleartext)

<- EAP-Success

A.5 Server authentication fails in Part 2

In the case where the server authenticates to the client successfully
in PEAP PEAPv2 Part 1, but the client fails to authenticate to the server
in PEAP PEAPv2 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
(TLS change_cipher_spec,
TLS finished)

EAP-Response/
EAP-Type=PEAP, V=2 -> finished, EAP-TLV
[EAP-Payload-TLV
[EAP-Request/Identity]])

TLS channel established
(messages sent within the TLS channel)

<- EAP-Request/
Identity
EAP-Response/
Identity (MyID)

EAP-TLV [EAP-Payload-TLV
[EAP-Response/Identity (MyID)]] ->

<- EAP-Request/
EAP-Type=X
EAP-Response/

EAP-Type=X EAP-TLV [EAP-Payload-TLV
[EAP-Request/EAP-Type=X]]

EAP-TLV [EAP-Payload
[EAP-Response/EAP-Type=X
or NAK NAK]] ->
<- EAP-Request/
EAP-Type=X
EAP-Response/
EAP-Type=X EAP-TLV [EAP-Payload
[EAP-Request/EAP-Type=X]]

EAP-TLV [EAP-Payload
[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 EAP-TLV [Crypto-Binding-TLV
(Version=0, Received-Version=2,
Nonce, B1_MAC),
Intermediate-Result-TLV (Failure), Method_Identity_TLV (for
each EAP-Type inside PEAP), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP
Result 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>, (Failure)]

EAP-TLV [Crypto-Binding-TLV
(Version=0, Received-version=2,
Nonce, B2_MAC),
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 ->
Intermediate-Result-TLV (Failure)]

(TLS session cache entry flushed)
TLS channel torn down
(messages sent in cleartext)

<- EAP-Failure

A.6 Server authentication fails in Part 1

In the case where server authentication is unsuccessful in PEAP Part
1, 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)
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 finished, EAP-TLV
[EAP-Payload-TLV [
EAP-Request/Identity]])
EAP-Response/
EAP-Type=PEAP, V=2
(TLS Alert message) ->
<- EAP-Failure
(TLS session cache entry flushed)

A.7 Session resume success

In the case where a previously established session is being resumed,
the EAP server supports TLS session cache flushing for unsuccessful
PEAP
PEAPv2 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
(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)) (Success)

// 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, Nonce, B2_MAC),
Result TLV (Success), Method_Identity_TLV (for PEAP),
CompoundMAC (over entire EAP TLV packet inside the tunnel including
EAP-header)) .
-> (Success)->
TLS channel torn down
(messages sent in cleartext)

<- EAP-Success

A.8 Session resume failure

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
(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=PEAP, V=2
(TLS Alert message)
EAP-Response
EAP-Type=PEAP, V=2 ->
<- EAP-Failure
(TLS session cache entry flushed)

A.9 Session resume failure

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
(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=PEAP, V=2
EAP-Response/
EAP-Type=PEAP, V=2
(TLS Alert message) ->

(TLS session cache entry flushed)
<- EAP-Failure

A.10 PEAP version negotiation

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
(PEAP 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)

//conversation continued using pre-standard PEAP version 0

A.11 Sequences of EAP methods

Where PEAPv2 is negotiated, with a sequence of EAP method X followed
by method Y, the conversation will occur as follows:

Authenticating Peer Authenticator
------------------- -------------
<- EAP-Request/
Identity
EAP-Response/
Identity (MyID1) ->
<- EAP-Request/
EAP-Type=PEAP, V=0 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=0
EAP-Response/
EAP-Type=PEAP, V=0 V=2
(TLS Alert message) change_cipher_spec,
TLS finished, EAP-TLV

[EAP-Payload-TLV[
EAP-Request/Identity]])

TLS channel established
(messages sent within the TLS channel)

EAP-TLV [EAP-Payload-TLV
[EAP-Response/Identity]] ->
(TLS session cache entry flushed)

<- EAP-Failure

10. Acknowledgments EAP-TLV [EAP-Payload-TLV
[EAP-Request/EAP-Type=X]]]

EAP-TLV [EAP-Payload-TLV
[EAP-Response/EAP-Type=X]] ->

<- EAP-TLV [ EAP-Payload-TLV
[EAP-Request/EAP-Type=X]]

EAP-TLV [EAP-Payload-TLV
[EAP-Response/EAP-Type=X]]->

<- EAP-TLV [EAP Payload TLV [EAP-Type=Y],
(Intermediate Result TLV (Success),
Crypto-Binding-TLV
(Version=0, Received-version=2,
Nonce, B1_MAC))]

// Next EAP conversation started after successful completion of
previous method X. The intermediate-status and crypto-binding TLVs
are sent in next packet to minimize round-trips. In this example,
identity request is not sent before negotiating EAP-Type=Y.

EAP-TLV [EAP-Payload-TLV [EAP-Type=Y],
(Intermediate Result TLV (Success),
Crypto-Binding-TLV (Version=0,
Received-version=2, Nonce, B2_MAC))]->

// Compound MAC calculated using Keys generated from
EAP methods X and the TLS tunnel.

<- EAP-TLV [EAP Payload TLV [
EAP-Type=Y]]

EAP-TLV[EAP Payload TLV
[EAP-Type=Y]] ->
<- EAP-TLV [Result-TLV (Success),
Intermediate Result TLV (Success),
Crypto-Binding-TLV
(Version=0, Received-version=2,
Nonce, B1_MAC))]

EAP-TLV [(Result-TLV (Success),
Intermediate Result TLV (Success),
Crypto-Binding-TLV (Version=0,
Received-version=2, Nonce, B2_MAC))]->

// Compound MAC calculated using Keys generated from EAP methods X
and Y and the TLS tunnel. // Compound Keys generated using Keys
generated from EAP methods X and Contributions Y; and the TLS tunnel.

TLS channel torn down (messages sent in cleartext)

<- EAP-Success

Acknowledgments

Thanks to Hakan Andersson, Jan-Ove Larsson, Larsson and Magnus Nystrom of RSA
Security; Bernard Aboba, Vivek Kamath, Stephen Bensley, Bensley and Narendra
Gidwani of Microsoft;
Joe Salowey, Hao Zhou, Ilan Frenkel, Frenkel and 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
was done while he was they were 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
Drottningholmsv�gen
Drottningholmsvagen 70
112 42 Stockholm
Sweden

Phone: +46 8 619 04 22
EMail: jas@extundo.com

11.

Hao Zhou
Cisco Systems, Inc.
4125 Highlander Parkway
Richfield, OH 44286

Phone: +1 330 523 2132
Fax: +1 330 523 2239
EMail: hzhou@cisco.com

Joseph Salowey
Cisco Systems
2901 3rd Ave
Seattle, WA 98121

Phone: +1 206 256 3380
EMail: jsalowey@cisco.com

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