The Tunneled Extensible Authentication Protocol Method (TEAM)
draft-zorn-emu-team-00

Abstract

The Extensible Authentication Protocol (EAP) provides support for multiple authentication methods. This document defines the Tunneled Extensible Authentication Method (TEAM), which provides an encrypted and authenticated tunnel based on transport layer security (TLS) that encapsulates EAP authentication mechanisms. TEAM uses TLS to protect against rogue authenticators, protect against various attacks on the confidentiality and integrity of the inner EAP method exchange and provide EAP peer identity privacy. TEAM also provides support for chaining multiple EAP mechanisms, cryptographic binding between authentications performed by inner EAP mechanisms and the tunnel, exchange of arbitrary parameters (TLVs), and fragmentation and reassembly.

Status of This Memo

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This Internet-Draft will expire on April 21, 2011.

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Table of Contents

1.  Introduction
2.  Requirements Language
3.  Terminology
4.  Protocol Overview
    4.1.  Operational Model
    4.2.  Sequences
    4.3.  TEAM Phase 1
        4.3.1.  Initial identity exchange
        4.3.2.  TLS Session Establishment
        4.3.3.  Session Resumption
        4.3.4.  Version Negotiation
    4.4.  TEAM Phase 2
        4.4.1.  Protected Conversation
        4.4.2.  Protected Termination
        4.4.3.  Provisioning of Credentials
    4.5.  Error Handling
    4.6.  Fragmentation and Reassembly
    4.7.  Key Derivation
        4.7.1.  Compound Session Key Derivation
    4.8.  Ciphersuite Negotiation
5.  TEAM Protocol Description
    5.1.  TEAM Protocol Layers
    5.2.  TEAM Packet Format
6.  Type-Length-Value Tuples
    6.1.  TLV Format
    6.2.  Result TLV
    6.3.  NAK TLV
    6.4.  Error-Code TLV
    6.5.  Crypto-Binding TLV
    6.6.  Connection-Binding TLV
    6.7.  Vendor-Specific TLV
    6.8.  URI TLV
    6.9.  EAP-Payload TLV
    6.10.  Intermediate-Result TLV
    6.11.  Calling-Station-Id TLV
    6.12.  Called-Station-Id TLV
    6.13.  NAS-Port-Type TLV
    6.14.  Server-Identifier TLV
    6.15.  Identity-Type TLV
    6.16.  Server-Trusted-Root TLV
    6.17.  PKCS#7 TLV
    6.18.  Request-Action-TLV
7.  Security Considerations
8.  IANA Considerations
9.  References
    9.1.  Normative References
    9.2.  Informative References

1.  Introduction

The Extensible Authentication Protocol (EAP), defined in [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.), provides support for multiple authentication methods. EAP over PPP [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.) is typically deployed with leased lines or modem connections. [IEEE.802‑1X.2004] (IEEE Computer Society, “IEEE Standard for Local and metropolitan area networks: Port-Based Network Access Control,” December 2004.) defines EAP over IEEE 802 local area networks (EAPOL).

Since its initial development, a number of weaknesses in the EAP framework have become apparent. These include lack of support for:

Identity protection

Protected method negotiation

Protected notification messages

Protected termination messages

Sequences of EAP methods

Fragmentation and reassembly

Exchange of arbitrary parameters in a secure channel

Optimized re-authentication

In addition, some EAP methods lack the following features:

Mutual authentication

Resistance to dictionary attacks

Adequate key generation

By wrapping the EAP protocol within TLS, TEAM addresses deficiencies in EAP or EAP methods. Benefits of TEAM include:

Identity protection

By encrypting the identity exchange, and allowing client identity to be provided after negotiation of the TLS channel, TEAM provides for identity protection.

Dictionary attack resistance

By conducting the EAP conversation within a TLS channel, TEAM protects EAP methods that might be subject to an offline dictionary attack were they to be conducted in the clear.

Protected negotiation

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

Header protection

Within TEAM, TLS provides per-packet encryption, authentication, integrity and replay protection for the EAP conversation. As a result, the Type-Data field within TEAM (including the EAP header of the EAP method within TEAM) is protected against modification. However, the EAP header of TEAM itself is not protected against modification, including the Code, Identifier and Type fields.

Protected termination

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

Standard key establishment

In order to provide keying material for a wide range of link layer ciphersuites, EAP methods need to provide keying material. Key derivation is complex. TEAM provides for key establishment by relying on the widely implemented and well-reviewed TLS [RFC4346] (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.1,” April 2006.) key derivation mechanism. TEAM provides keying material for any EAP method running within it.

Sequencing of multiple EAP methods

In order to enhance security, TEAM 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). TEAM provides a standard way to chain different types of authentication mechanisms supporting different types of credentials.

Protected exchange of arbitrary parameters

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 the EAP protocol, provisioning parameters, media specific and environment specific data, and authorization parameters. The advantage of using TEAM TLVs is that every EAP method does not have to be modified.

Credential provisioning

TEAM supports provisioning of certificate trust anchors by the server using TLVs and can be extended to support provisioning of other peer credentials.

Optimized for light weight devices

In order to support peers that may not support certificate ciphersuites, and may not support provisioning of certificate trust anchors, TEAM enables negotiation of other TLS ciphersuites.

Server unauthenticated tunnel provisioning mode

In some cases, the peer may only support password credentials and may not be provisioned with a certificate trust anchor.

In server unauthenticated tunnel provisioning mode, a TEAM peer can authenticate using a password, in order to be provisioned with a pre-shared key and other credentials that can be used for subsequent authentication. In server unauthenticated tunnel provisioning mode the TEAM peer only confirms possession of the private key corresponding to the public key contained within the server certificate, but does not otherwise validate the server certificate. As a result, it is possible for an attacker to act as a man-in-the-middle during the initial exchange in order to perform an offline dictionary attack, based on capture of the password- based authentication exchange.

In TEAM, implementation of server unauthenticated tunnel provisioning mode is optional and due to the security vulnerabilities introduced by this mode, it is not recommended for use with peers that support certificate validation and provisioning of certificate trust anchors.

2.  Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

3.  Terminology

This document frequently uses the following terms:

Access Point

A Network Access Server implementing 802.11.

Authenticator

The end of the link initiating EAP authentication. This term is also used in [IEEE.802‑1X.2004] (IEEE Computer Society, “IEEE Standard for Local and metropolitan area networks: Port-Based Network Access Control,” December 2004.). and has the same meaning in this document.

Backend Authentication Server

A backend authentication server is an entity that provides an authentication service to an Authenticator. When used, this server typically executes EAP methods for the Authenticator. This terminology is also used in [IEEE.802‑1X.2004] (IEEE Computer Society, “IEEE Standard for Local and metropolitan area networks: Port-Based Network Access Control,” December 2004.).

EAP server

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

Link layer ciphersuite

The ciphersuite negotiated for use at the link layer.

NAS

Short for "Network Access Server".

Peer

The end of the link that responds to the authenticator. In [IEEE.802‑1X.2004] (IEEE Computer Society, “IEEE Standard for Local and metropolitan area networks: Port-Based Network Access Control,” December 2004.), this end is known as the Supplicant.

TLS Ciphersuite

The ciphersuite negotiated for protection of Phase 2 of the TEAM conversation Section 4.4 (TEAM Phase 2).

EAP Master key (MK)

A key derived between the TEAM client and server during the authentication conversation, and that is kept local to TEAM and not exported or made available to a third party.

Master Session Key (MSK)

Keying material that is derived between the EAP peer and server and exported by the EAP method. The MSK is at least 64 octets in length. In existing implementations, a AAA server acting as an EAP server transports the MSK to the authenticator.

Extended Master Session Key (EMSK)

Additional keying material derived between the EAP client and server that is exported by the EAP method. The EMSK is at least 64 octets in length. The EMSK is not shared with the authenticator or any other third party. The EMSK is reserved for future uses that are not defined yet.

Type Length Value (TLV)

The TEAM protocol utilizes objects in Type Length Value (TLV) format. The TLV format is defined in Section 6.1 (TLV Format) of this document.

4.  Protocol Overview

TEAM is comprised of a two-part conversation:

1. In Phase 1 a TLS session is negotiated, with the server authenticating to the client and (optionally) the client to the server. The negotiated key is then used to protect Phase 2 of the conversation.
   
   
2. In Phase 2, within the TLS session, zero or more EAP methods are carried out. Phase 2 completes with a success/failure indication protected by the TLS session or a protected error (TLS alert).

In the following sections, we discuss the TEAM operational model, its support for EAP method sequencing and provide an overview of each of the parts of the TEAM conversation.

4.1.  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 (Relationship between EAP client, backend authentication server and NAS) illustrates the relationship between the EAP peer, NAS and EAP server. As shown 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.

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

4.2.  Sequences

EAP [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.) prohibits use of multiple authentication methods within a single EAP conversation, except when tunneled methods such as TEAM 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 TEAM these concerns are addressed since TEAM includes support for cryptographic binding to address man-in-the-middle attacks, as well as version negotiation so as to enable backward compatibility with future versions of the protocol.

Within this document, the term "sequence" refers to a series of EAP authentication methods run in sequence or TLV exchanges before or after EAP methods. 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.

TEAM supports initiating additional EAP method(s) after a successful or a failed EAP method. The result of failure of a EAP method does not always imply a failure of the overall authentication. The overall result of authentication depends on the policy at EAP server and the peer. For example, successful authentication might require a successful machine authentication followed by a successful user authentication. Alternatively, if machine authentication fails, then user authentication can be attempted. TEAM does not support initiating multiple EAP methods simultaneously.

4.3.  TEAM Phase 1

4.3.1.  Initial identity exchange

The TEAM 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.

The initial identity exchange is used primarily to route the EAP conversation to the EAP 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, during Phase 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 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, TEAM does not require a backend authentication server; if the authenticator implements TEAM, 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.

4.3.2.  TLS Session Establishment

In this section, the protocol is described. While this section will often describe negotiation of a certificate-based ciphersuite within TLS, TEAM supports negotiation of other ciphersuites (for example, ciphersuites that do not use certificates) or extensions. However, the conversation may slightly differ if other TLS ciphersuites or extensions are used.

Once having received the peer's Identity, and determined that TEAM authentication is to occur, the EAP server MUST respond with a TEAM/Start packet, which is an EAP-Request packet with EAP-Type=TEAM, the Start (S) bit set, the TEAM version as specified in Section 4.3.4 (Version Negotiation), and optionally, the Server-Identifier TLV (Section 6.14 (Server-Identifier TLV)).

Assuming that the peer supports TEAM, the TEAM conversation will then begin, with the peer sending an EAP-Response packet with EAP- Type=TEAM. The Type-Data field of the EAP-Response Packet will encapsulate one or more TLS records containing the TLS handshake messages. As defined in [RFC4346] (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.1,” April 2006.), the TLS handshake is used to negotiate parameters and cryptographic keys and may take several roundtrips between the TLS client and server.

The version offered by the TLS client and server MUST be TLS v1.0 or later. TEAM implementations need not necessarily support all TLS ciphersuites listed in [RFC4346] (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.1,” April 2006.). Not all TLS ciphersuites are supported by available TLS tool kits and licenses may be required in some cases.

To ensure interoperability, TEAMv2 peers and servers MUST support the TLS v1.1 [RFC4346] (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.1,” April 2006.) mandatory-to-implement ciphersuite:

TLS_DHE_DSS_WITH_3DES_EDE_CBC_SHA

In addition, TEAM servers SHOULD support and be able to negotiate all of the following TLS ciphersuites:

TLS_RSA_WITH_3DES_EDE_CBC_SHA

TLS_RSA_WITH_RC4_128_MD5

TLS_RSA_WITH_RC4_128_SHA

TLS_RSA_WITH_AES_128_CBC_SHA

In addition, TEAM peers SHOULD support at least one of the following TLS ciphersuites:

TLS_RSA_WITH_3DES_EDE_CBC_SHA

TLS_RSA_WITH_RC4_128_MD5

TLS_RSA_WITH_RC4_128_SHA

TLS_RSA_WITH_AES_128_CBC_SHA

TLS as described in [RFC4346] (Dierks, T. and E. Rescorla, “The Transport Layer Security (TLS) Protocol Version 1.1,” April 2006.) supports compression as well as ciphersuite negotiation. Therefore during the TEAM Phase 1 conversation the TEAM endpoints MAY request or negotiate TLS compression.

If the full TLS handshake is performed, then the first payload of TEAM Phase 2 MAY be sent along with finished handshake message to reduce number of round trips.

Since after the TLS session is established, another complete EAP negotiation will occur and the peer will authenticate using a secondary mechanism, with TEAM the client need not authenticate as part of TLS session establishment.

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. Alternatively, if identity protection is required, then it is possible to perform certificate authentication using a EAP method (for example: EAP-TLS [RFC5216] (Simon, D., Aboba, B., and R. Hurst, “The EAP-TLS Authentication Protocol,” March 2008.)) within the TLS session during TEAM Phase 2.

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 TEAM Phase 2 begins, 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 TEAM Phase 2 instead. Assuming that the client permits renegotiation by sending a client_hello, then the server will respond with server_hello, a certificate and certificate_request messages. The client replies with certificate, client_key_exchange and certificate_verify messages. Since this re-negotiation occurs within the encrypted TLS channel, it does not reveal client certificate details.

4.3.3.  Session Resumption

The purpose of the sessionId within the TLS protocol and the Server- Identifier TLV in TEAM 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.

In order to help the peer choose a sessionID that belongs to the specific server, the EAP server MAY send an identifier (Server- Identifier TLV) that the peer can use as a hint. The Server- Identifier TLV MAY be sent in the first TEAM packet from the EAP server to the peer. In order to detect modification of the Server- Identifier TLV, the Server-Identifier TLV is included in calculation of the compound MAC.

It is left up to the peer whether to attempt to continue a previous session, thus shortening the TEAM Phase 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.

If the EAP server is resuming a previously established session, then it MUST include only a TLS change_cipher_spec message and a TLS finished handshake message after the server_hello message. The finished message contains the EAP server's authentication response to the peer.

If the preceding server_hello message sent by the EAP server in the preceding EAP-Request packet indicated the resumption of a previous session, then the peer MUST send only the change_cipher_spec and finished handshake messages. The finished message contains the peer's authentication response to the EAP server. The latter contains the EAP server's authentication response to the peer. The peer will verify the hash in order to authenticate the EAP server.

If authentication fails, then the peer and EAP-server MUST follow the error handling behavior specified in Section 4.5 (Error Handling)

Even if the session is successfully resumed with the same EAP server, the peer and EAP server MUST NOT assume that either will skip inner EAP methods. The peer may have roamed to a network which may use the same EAP server, but may require conformance with a different authentication policy, and therefore may require inner EAP authentication methods.

4.3.4.  Version Negotiation

TEAM packets contain a three bit version field, which enables TEAM implementations to be backward compatible with previous versions of the protocol. This specification documents version1 of the TEAM protocol; implementations of this specification MUST use a version field set to 1. Version negotiation proceeds as follows:

1. In the first EAP-Request sent with EAP-Type=TEAM, the EAP server MUST set the version field to the highest supported version number.
   
   
2. If the EAP peer supports that version of the protocol, it MUST respond with an EAP-Response of EAP-Type=TEAM, and the version number proposed by the EAP server.
   
   
3. If the EAP peer does not support that version, it responds with an EAP-Response of EAP-Type=TEAM and the highest supported version number.
   
   
4. If the TEAM server does not support the version number proposed by the TEAM peer, it either starts a different EAP type or terminates the conversation by sending an EAP-Failure, depending on the server policy.
   
   

The 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 use of TEAM will not be possible, and another mutually acceptable EAP method will need to be negotiated if authentication is to proceed.

The TEAM version field is not protected by TLS and therefore can be modified in transit. In order to detect modification of the TEAM version which could occur as part of a "downgrade" attack, the peer and EAP server check if the version it sent during negotiation is same as the version claimed to be received by the other party. Each party uses the Crypto-Binding TLV (Section 6.5 (Crypto-Binding TLV)) to inform the other party of the version number it received during the TEAM version negotiation. The receiver of the Crypto-Binding TLV must verify that the version in the Crypto-Binding TLV matches the version it sent during TEAM version negotiation.

4.4.  TEAM Phase 2

The second part of the TEAMv2 conversation typically consists of a complete EAP conversation occurring within the TLS session negotiated in TEAM Phase 1, ending with protected termination using the Result TLV. TEAM Phase 2 will occur only if establishment of a new TLS session in Phase 1 is successful or a TLS session is successfully resumed in Phase 1. In cases where a new TLS session is established in TEAMv2 Phase 1, the first payload of the Phase 2 conversation MAY be sent by the EAP server along with the finished message to save a round-trip.

Phase 2 SHOULD NOT occur if the EAP Server authenticates unsuccessfully, and MUST NOT occur if establishment of the TLS session in Phase 1 was not successful or a TLS fatal error has been sent terminating the conversation.

Since all packets sent within the TEAM Phase 2 conversation occur after TLS session establishment, they are protected using the negotiated TLS ciphersuite. All EAP packets of the EAP conversation in Phase 2 including the EAP header of the inner EAP method are protected using the negotiated TLS ciphersuite.

Phase 2 may not always include a EAP conversation within the TLS session, referred to in this document as inner EAP methods. However, Phase 2 MUST always end with either protected termination or protected error termination (e.g. TLS alert).

Within Phase 2, protected EAP conversation and protected termination packets are always carried within TLVs. There are TLVs defined for specific purposes such as carrying EAP-authentication messages and carrying cryptographic binding information. New TLVs may be developed for other purposes.

4.4.1.  Protected Conversation

Phase 2 of the TEAM conversation typically begins with the EAP server sending an optional EAP-Request/Identity packet to the peer, protected by the TLS ciphersuite negotiated in Phase 1 of TEAM. The peer responds with an EAP-Response/Identity packet to the EAP server, containing the peer's userId. Since this Identity Request/Response exchange is protected by the ciphersuite negotiated in TLS, it is 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 Type field set to the initial method. As described in [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.), 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.

The EAP conversation within the TLS protected session may involve a sequence of zero or more EAP authentication methods; it completes with the protected termination described in Section 4.4.2 (Protected Termination) Several TLVs may be included in each Request and Response. EAP packets are always encapsulated within EAP Payload TLVs.

In a typical EAP conversation, the result of the conversation is communicated by sending EAP Success or EAP Failure packets after the EAP method is complete. The EAP Success or Failure packet is considered the last packet of the EAP 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 server MUST use the Intermediate-Result TLV (Section 6.10 (Intermediate-Result TLV)) to communicate the result.

In a typical EAP conversation, the EAP Success or EAP Failure is considered the last packet of the EAP conversation. Within TEAM, the EAP server can start another EAP method after success or failure of the previous EAP method inside the protected session.

In a sequence of more than one EAP authentication method, to make sure the same parties are involved in tunnel establishment and successful completion of previous inner EAP methods, before completing negotiation of the next EAP method, both peer and EAP server MUST use crypto binding (Crypto-Binding TLV).

The Intermediate-Result TLV is used to indicate the result of a individual successful EAP method, and the Result TLV (Section 6.2 (Result TLV)) is used to indicate result of the entire TEAM conversation.

The Intermediate-Result and Crypto-Binding TLVs MUST be sent after each EAP method that was successful. If the EAP method failed, or if the EAP method negotiation did not complete, then an Intermediate- Result TLV MAY be included, and the Crypto-Binding TLV MUST NOT be included. An exception is that the Crypto-Binding TLV MUST be sent along with a protected success/failure indication (see Section 4.4.2 (Protected Termination)).

If these TLVs are not sent after a successful EAP method, it should be considered a tunnel compromise error by peer and EAP server, resulting in the termination of the conversation (as described in Section 4.5 (Error Handling)).

A subsequent EAP conversation can be started after both TLVs are exchanged in a TLV packet. Alternatively, if a subsequent EAP conversation is being attempted, then in order to reduce round trips, both TLVs SHOULD be sent with the EAP-Payload of the first EAP packet of the next EAP conversation (for example, EAP- Identity or EAP packet of the EAP method). Alternatively, if the next packet is the protected success/failure packet, then in order to reduce round trips, both TLVs MUST be sent with the protected success/failure packet.

If the EAP server sends a valid Crypto-Binding TLV to the peer, the peer MUST respond with a Crypto-Binding TLV. If the Crypto-Binding TLV is invalid, it should be considered a tunnel compromise error by the peer. If the peer does not respond with a TLV packet containing the Crypto-Binding TLV, it MUST be considered a tunnel compromise error by the EAP server.

Within a TEAM part 2 conversation, a peer MAY request the trusted root of a server certificate using a Server-Trusted-Root TLV (Section 6.16 (Server-Trusted-Root TLV)), and the EAP server MAY respond with a Server-Trusted-Root TLV to the peer. The Server-Trusted-Root TLV can be exchanged in regular authentication mode or server unauthenticated tunnel provisioning mode.

After the peer has determined that it has successfully authenticated the EAP server and determined that the tunnel and inner EAP methods were between the same peer and EAP server by validating the Crypto-Binding TLV, it MAY send one or more Server-Trusted-Root TLVs (marked as optional) to request the trusted root of server certificate from the EAP server. The peer may receive a response, but is not required to use the trusted root received from the EAP server.

If the EAP server has determined that it has successfully authenticated the peer and determined that the tunnel and inner EAP methods were between the same peer and EAP server by validating the Crypto-Binding TLV, then it MAY respond with the the server-trusted- root containing the PCKS#7 TLV (Section 6.17 (PKCS#7 TLV)).

4.4.2.  Protected Termination

Phase 2 of the TEAM conversation is completed by the exchange of success/failure indications (Result TLV) within a TLV packet protected by the TLS session.

Even if Crypto-Binding TLVs have been exchanged in previous conversations, the Crypto-Binding TLV MUST be included in both protected success/failure (Result TLV) indications. If the TLVs are not included, or if the TLVs are invalid, it should be considered a tunnel compromise error, and the peer and EAP server MUST follow the rules described in Section 4.5 (Error Handling) to abort the conversation.

The Result TLV is sent within the TLS channel. The TEAM client then replies with a Result TLV. The conversation concludes with the TEAM server sending a cleartext success/failure indication.

The only outcome which should be considered as successful authentication is when a Result TLV of Status=Success is answered by the peer with a Result TLV of Status=Success.

The combinations (Result TLV=Failure, Result TLV=Success), (Result TLV=Failure, Result TLV=Failure), (no TLVs exchange or no protected success or failure) should be considered an authentication failure by both the peer and EAP server. Once the peer and EAP server consider that authentiation has failed, these are the last packets inside the protected tunnel. These combinations are considered an authentication failure regardless of whether a cleartext EAP Success or EAP Failure packet is subsequently sent.

If the EAP server wants authentication to fail, it sends the TLV response with Result TLV=Failure. If the EAP server sends a failure, the peer MUST respond with Result TLV=Failure and the Crypto-Binding TLV, without any other mandatory TLVs. The Crypto-Binding TLV is calculated using the key derivation formula in Section 2.5; if for some reason one or more inner EAP method MSKs were not derived, then these MSKs are assumed to be null.

If the EAP server has sent the success indication (Result TLV=Success), the peer is allowed to refuse to accept a Success message from the EAP server since the client's policy may require completion of certain EAP methods or the client may require credentials.

If the EAP server has sent a success indication (Result TLV=success), and the peer wants authentication to fail, it sends the TLV response with Result TLV=Failure and Crypto-Binding TLV.

After the EAP-server returns success, if the peer wants to request the EAP server to continue conversation, it sends a Result TLV=Success along with a Request-Action TLV with the appropriate action (e.g. Negotiate-EAP, or Process-TLV). If the Request-Action TLV is set to mandatory, then the EAP server MUST process the action, or return status=failure, closing the conversation inside the tunnel. If the Request-Action TLV is set to optional, then the EAP server can ignore the TLV and return Result TLV=Success again, closing the conversation inside the tunnel.

4.4.3.  Provisioning of Credentials

TEAM supports built-in provisioning of certificate trust anchors and can be extended to provisioning of other types of credentials. The following two provisioning modes are suported:

1. Provisioning inside a server authenticated TLS tunnel
2. Provisioning inside a server unauthenticated TLS tunnel

4.4.3.1.  Provisioning Inside a Server Authenticated TLS Tunnel

After regular authentication in TEAM Phase 2, the peer and EAP server can use the Server-Trusted-Root TLV to request and provision peer credentials. The provisioning payload is exchanged after the peer and EAP server have determined that both have successfully authenticated each other (either thru TLS handshake and/or inner EAP method), and the tunnel and inner EAP methods are between the same peers.

After the peer has determined that it has successfully authenticated the EAP server and determined that the tunnel and inner EAP methods were between the same peer and EAP server by validating the Crypto-Binding TLV, it MAY send one or more Server- Trusted-Root TLVs (marked as optional) to request credentials from the EAP server. The EAP server will send corresponding credentials in the Server-Trusted-Root TLVs if its internal policy has been satisfied. It may ignore the credential provisioning request or request additional authentication methods if its policy so dictates. The peer may receive a credential, but is not required to use the credentials received from the EAP server.

4.4.3.2.  Provisioning Inside a Server Unauthenticated TLS Tunnel

In some cases, the peer may lack the credentials necessary to authenticate the server in the TLS handshake. At the same time, bootstrapping the information to the peer out of band may be prohibitive from a deployment cost perspective. It can rely on the inner EAP method using existing credentials to authenticate the server. This provisioning mode provides ease of deployment at the cost of introducing man-in-the-middle vulnerabilities. As a result, implementation of the server unauthenticated tunnel provisioning mode is OPTIONAL.

In this provisioning mode, as part of TEAM Phase 1, if the peer does not authenticate, or does not successfully authenticate the EAP server during TLS negotiation, it can decide to go into server unauthenticated tunnel provisioning mode. While this section describes negotiation of a certificate-based ciphersuite within TLS, TEAM supports negotiation of other ciphersuites (for example, ciphersuites that do not use certificates such as anonymous DH) or extensions. However, the conversation may slightly differ if other TLS ciphersuites or extensions are used. For example, in a certificate based TLS handshake, the peer verifies that the EAP server possesses the private key corresponding to the public key contained in the certificate presented by the EAP server. However, the peer does not verify whether the certificate presented by the server chains to a provisioned trust anchor, as the peer may not be configured with a certificate trust anchor required to validate the server certificate. If the peer cannot verify that the server possesses the corresponding private key, or if the certificate presented by the server is unacceptable for any reason other than the lack of an appropriate trust anchor, the peer MUST NOT use this provisioning mode. Assuming that the server demonstrates possession of the private key, the peer continues with establishment of the tunnel (TEAM Phase 2). As a result, it is possible that the TLS channel (TEAM Phase 2) may be terminated by an attacker.

The TEAM Phase 2 conversation is unchanged in this mode, except that the peer will only accept an EAP method supporting mutual authentication and key derivation that is compatible with its initial credentials (such as a password-based EAP method). The peer then uses the Crypto-Binding TLV to validate that the same server terminates both the TLS channel and the successfully completed EAP method, thereby verifying that the exchange was not subject to a man-in-the-middle attack. Assuming that the Crypto- Binding TLV exchange is successful, the peer will request and the server will subsequently provide a trusted root, using the Server- Trusted-Root TLV.

Once the initial provisioning exchange completes, the peer is expected to use the provisioned credentials in subsequent TEAM authentications, and SHOULD NOT use this provisioning mode.

TEAM servers implementing this provisioning mode MUST support the following additional ciphersuites, beyond those specified in Section 4.3.2 (TLS Session Establishment):

TLS_DH_anon_WITH_AES_128_CBC_SHA

TEAM peers implementing this provisioning mode MAY support the following additional ciphersuites, beyond those specified in Section 4.3.2 (TLS Session Establishment):

TLS_DH_anon_WITH_AES_128_CBC_SHA

4.5.  Error Handling

TEAM does not have its own error message capabilities since:

1. TLS errors are communicated via TLS alert messages.
2. Errors within the EAP conversation in TEAM Phase 2 are expected to be handled by individual EAP methods.
3. Violation of the TLV rules for inner-TLVs are handled using Result-TLVs together with the Error-Code TLV.

If an error occurs at any point in the 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=TEAM, 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.

The EAP-Response packet sent by the peer MAY encapsulate a TLS client_hello handshake message, in which case the EAP server MAY allow the TEAM conversation to be restarted, or it MAY contain an EAP-Response packet with EAP-Type=TEAM and no data, in which case the TEAM server MUST send an EAP-Failure packet, and terminate the conversation.

It is up to the EAP server whether to allow restarts, and if so, how many times the conversation can be restarted. An EAP server implementing restart capability SHOULD impose a limit on the number of restarts, so as to protect against denial of service attacks.

If an error occurs at any point in the TLS layer, the peer SHOULD send a TLS alert message instead of the next EAP-response packet to the EAP server. The peer SHOULD send an EAP-Response packet with EAP-Type=TEAM, encapsulating a TLS record containing the appropriate TLS alert message. The EAP server may restart the conversation by sending a EAP-Request packet encapsulating the TLS hello_request_handshake message, in which case the peer MAY allow the TEAM conversation to be restarted; or the EAP server can response with EAP Failure.

Any time the peer or the EAP server finds an error when processing the sequence of exchanges, such as a violation of TLV rules, it should send a Result TLV of failure and Error-Code TLV=Unexpected_TLVs_Exchanged (a Fatal error), and terminate the tunnel. This is usually due to an implementation problem and is considered an fatal error. The party that receives the Error-Code TLV=Unexpected_TLVs_Exchanged should terminate the tunnel.

If a tunnel compromise error (see (TEAM Phase 2)) is detected by the Peer or EAP server, the party SHOULD send a Result TLV of failure without a Crypto-Binding TLV, and Error-Code TLV=Tunnel-compromise- error (a Fatal error), and terminate the tunnel. The party that receives the Error-Code TLV=Tunnel-compromise error should terminate the tunnel.

4.6.  Fragmentation and Reassembly

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 TEAM 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 [RFC1990] (Sklower, K., Lloyd, B., McGregor, G., Carr, D., and T. Coradetti, “The PPP Multilink Protocol (MP),” August 1996.), 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] (Sklower, K., Lloyd, B., McGregor, G., Carr, D., and T. Coradetti, “The PPP Multilink Protocol (MP),” August 1996.). this is desirable, EAP methods are used in other applications such as [IEEE.802‑11.2007] (IEEE Computer Society, “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,” June 2007.) and there may be cases in which multilink or the MRRU LCP option cannot be negotiated. As a result, a TEAM 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.

TEAM fragmentation support is provided through addition of flag bits within the EAP-Response and EAP-Request packets, as well as a TLV Message Length field of four octets. Flags include the Length included (L), More fragments (M), and TEAM Start (S) bits. The L flag is set to indicate the presence of the four octet TLV Message Length field, and MUST be set only for the first fragment of a fragmented TLV message or set of messages.

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

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 a single group of Outer-TLV 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 for all the Outer-TLVs in a group of messages might be 64 KB.

The M flag is set on all but the last fragment. The S flag is set only within the TEAM start message sent from the EAP server to the peer. The TLV Message Length field is four octets, and provides the total length of the TLV message or set of messages that is being fragmented; this simplifies buffer allocation.

When a peer receives an EAP-Request packet with the M bit set, it MUST respond with an EAP-Response with EAP-Type=TEAM 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=TEAM and no TLS 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.

4.7.  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 to protect the conversation within the TEAM tunnel.

Instead of deriving keys specific to link layer ciphersuites, EAP methods provide a Master Session Key (MSK) used to derive keys in a link layer specific manner. The method used to extract ciphering keys from the MSK is beyond the scope of this document.

TEAM also derives an Extended Master Session Key (EMSK) which is reserved for use in 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] (Zorn, G., “Microsoft Vendor-specific RADIUS Attributes,” March 1999.).

TEAM 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 compound MAC and compound session keys using the procedure described below.

The input for the cryptographic binding includes the following:

1. The TEAM tunnel key (TK) is calculated using the first 40 octets of the (secret) key material generated as described in the EAP-TLS algorithm (see Section 2.3 of (Simon, D., Aboba, B., and R. Hurst, “The EAP-TLS Authentication Protocol,” March 2008.) [RFC5216]) More explicitly, the TK is the first 40 octets of the PRF as defined in RFC 5216:
   
   

   Key_Material = TLS-PRF-128(

   master_secret, "client EAP encryption", client.random || server.random )

   
   
   
2. The first 32 octets of the MSK provided by each successful inner EAP method for each successful EAP method completed within the tunnel.
   
   ISK1..ISKn are the MSK portion of the EAP keying material obtained from methods 1 to n. The ISKj SHALL be the first 32 octets of the generated MSK of the jth EAP method. If the MSK length is less than 32 octets, it SHALL be padded with 0x00's to ensure the MSK is 32 octets. Similarly, if no keying material is provided for the EAP method, then ISKj SHALL be set to zero (e.g. 32 octets of 0x00).

The PRF algorithm is based on PRF+ from IKEv2 [RFC5996] (Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, “Internet Key Exchange Protocol Version 2 (IKEv2),” September 2010.) shown below ("|" denotes concatenation).

PRF (K,S,LEN) = T1 | T2 | T3 | T4 | ...

Where:

K = Key

S = Seed

LEN = output length, represented as binary in a single octet

and

T1 = HMAC-SHA1(K, S | LEN | 0x01)

T2 = HMAC-SHA1 (K, T1 | S | LEN | 0x02)

T3 = HMAC-SHA1 (K, T2 | S | LEN | 0x03)

T4 = HMAC-SHA1 (K, T3 | S | LEN | 0x04)

...

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

S-IPMK0 = TK

for j = 1 to k do

IPMKj = PRF+(

S-IPMK(j-1),"Inner Methods Compound Keys " | ISKj, 60 )

Where

S-IPMKj are the first 40 octets of IPMKj and CMKj are the last 20 octets of IPMKj used to generate the intermediate Compound MACs

and

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

Each IPMKj output is 60 octets. The first 40 octets are used as the key input to the succeeding IPMK(j+1) derivation and the latter 20 octets are used as the key, CMKj, used to generate the intermediate Crypto-Binding Compound MAC value at the jth EAP method.

4.7.1.  Compound Session Key Derivation

The compound session key (CSK) is derived on both the peer and EAP server:

CSK = PRF+(S-IPMKn, "Session Key Generating Function", OutputLength)

The output length of the CSK must be at least 128 bytes. The first 64 octets are taken as the MSK and the second 64 octets are taken as the EMSK. The MSK and EMSK are described in [RFC3748] (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.).

4.8.  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 [RFC5216] (Simon, D., Aboba, B., and R. Hurst, “The EAP-TLS Authentication Protocol,” March 2008.), within TEAM, the negotiated TLS ciphersuite relates only to the mechanism by which the TEAM Phase 2 conversation will be protected, and has no relationship to link layer security mechanisms negotiated within the PPP Encryption Control Protocol (ECP) [RFC1968] (Meyer, G. and K. Fox, “The PPP Encryption Control Protocol (ECP),” June 1996.) or within IEEE 802.11 [IEEE.802‑11.2007] (IEEE Computer Society, “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,” June 2007.).

As a result, this specification currently does not support secure negotiation of link layer ciphersuites.

5.  TEAM Protocol Description

5.1.  TEAM Protocol Layers

TEAM packets may include TLVs both inside and outside the TLS tunnel. The term "Outer TLVs" is used to refer to optional TLVs outside the TLS tunnel, which are only allowed in the first two messages in the TEAM protocol. That is the first EAP server to peer message and first peer to EAP server message. If the message is fragmented, the whole set of messages is counted as one message. The term "Inner TLVs" is used to refer to TLVs sent within the TLS tunnel.

In TEAM Phase 1, Outer TLVs are used to help establishing the TLS tunnel, but no Inner TLVs are used. Therefore the layering of TEAM Phase 1 is as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            TLS        |  Optional Outer TLVs    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    TEAM                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     EAP                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

In Phase 2 of the TEAM conversation, TLS records may encapsulate zero or more Inner TLVs, but no Outer TLVs. EAP packets (including EAP header fields) used within tunneled EAP authentication methods are carried within Inner TLVs. Therefore the layering of TEAM Part 2 is as follows:

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     EAP                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Inner-TLVs (EAP-Payload TLV)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     TLS                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    TEAM                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                     EAP                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2.  TEAM Packet Format

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

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Code      |   Identifier  |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |   Flags | Ver |    Fragment Message Length
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Fragment Message Length     |    TLS Message Length
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     TLS Message Length        |      TLS Data...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |             Outer TLVs...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Code

1 -

Request

2 -

Response

Identifier

The Identifier field is one octet and aids in matching responses with requests. The Identifier field MUST be changed on each Request packet. The Identifier field in a Response packet MUST match the Identifier field from the corresponding Request.

Length

The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, Flags, Version, Fragmented Length, TLS Message Length, TLS Data, and Outer-TLV fields. Octets outside the range of the Length field should be treated as Data Link Layer padding and should be ignored on reception.

Type

<TBD1> - TEAM

Flags

    0 1 2 3 4
   +-+-+-+-+-+
   |L M S T R|
   +-+-+-+-+-+

L =

Length included

M =

More fragments

S =

TEAM start

T =

TLS length included

R =

Reserved (must be zero)

The L bit (Fragmented Message Length included) is set to indicate the presence of the four octet Fragmented Message Length field, and MUST be set for the first fragment of a fragmented TEAM message or set of messages. The M bit (more fragments) is set on all but the last fragment. The S bit (TEAM start) is set in a TEAM Start message. This differentiates the TEAM Start message from a fragment acknowledgment. The T bit (TLS Message Length included) is set to indicate the presence of the four octet TLS Message Length field, and MUST only be set for packet that contains Outer-TLVs. It can be used to calculate the start of the Outer-TLVs.

Version

    0 1 2
   +-+-+-+
   |R|0|1|
   +-+-+-+

R = Reserved (must be zero)

Fragmented Message Length

The Fragmented Message Length field is four octets, and is present only if the L bit is set. This field provides the total length of the data after the Fragmented Message Length field in the TEAM message or set of messages that is being fragmented.

TLS Message Length

The TLS Message Length field is four octets, and is present only if the T bit is set. This field provides the total length of the TLS Data in the TEAM message. Data after this length of TLS data are the Outer TLVs.

TLS Data

The TLS data consists of the encapsulated packet in TLS record format.

Outer TLVs

The Outer-TLVs consists of the optional data used to help establishing the TLS tunnel in TLV format. The start of the Outer-TLV can be derived from the EAP Length field and TLS Length field.

6.  Type-Length-Value Tuples

The TLVs used within TEAM are 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 and cryptographic binding.

The EAP peer may not necessarily implement all the TLVs supported by the EAP server; and hence to allow for interoperability, TLVs allow an EAP server to discover if a TLV is supported by the EAP peer, using the NAK TLV. The TEAM packet does not have to contain any TLVs, nor need it contain any mandatory TLVs.

The mandatory bit in a TLV indicates whether support of the TLV is required. If the peer or server does not support the TLV, it MUST send a NAK TLV in response, and all the other TLVs in the message MUST be ignored. If an EAP peer or server finds an unsupported TLV which is marked as optional, it can ignore the unsupported TLV. It MUST NOT send an NAK TLV.

Note that a peer or server may support a TLV with the mandatory bit set, but may not understand the contents. The appropriate response to a supported TLV with content that is not understood is defined by the TLV specification.

Outer-TLVs SHOULD NOT be included in messages after the first two Outer-TLV messages sent by the peer and EAP server respectively. A single Outer-TLV message may be fragmented in multiple TEAM packets.

All Outer-TLVs MUST NOT have the mandatory bit set. If an Outer-TLV has the mandatory bit set, then the packet MUST be ignored.

TEAM implementations MUST support TLVs, as well as processing of mandatory/optional settings on the TLV.

6.1.  TLV Format

TLVs are defined as described below. The fields are transmitted from left to right.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |M|R|            TLV Type       |            Length             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                              Value...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

0 -

Optional TLV

1 -

Mandatory TLV

R

Reserved, set to zero (0)

TLV Type

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

1 -

Result

2 -

NAK

3 -

Error-Code

4 -

Connection-Binding

5 -

Vendor-Specific

6 -

URI

7 -

EAP-Payload

8 -

Intermediate-Result

9 -

Crypto-Binding

10 -

Calling-Station-Id

11 -

Called-Station-Id

12 -

NAS-Port-Type

13 -

Server-Identifier

14 -

Identity-Type

15 -

Server-Trusted-Root

16 -

Request-Action

17 -

PKCS#7

Length

The length of the Value field in octets

Value

The value of the TLV

6.2.  Result TLV

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

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R|         TLV Type          |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             Status            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

1 (Mandatory)

R

0

TLV Type

1 for Result

Length

2

Status

The Status field is two octets. Values include:

1 -

Success

2 -

Failure

6.3.  NAK TLV

The NAK TLV allows a peer to detect TLVs that are not supported by the other peer. A TLV packet can contain 0 or more NAK TLVs. TEAM implementations MUST support the NAK TLV, which 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....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

1 (Mandatory)

R

0

TLV Type

2 for NAK

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.

6.4.  Error-Code TLV

The Error-Code TLV allows a TEAM peer or server to indicate errors to the other party. A TLV packet can contain 0 or more Error TLVs. Error-Code TLVs MUST be marked as Mandatory. TEAM implementations MUST support the Error-Code TLV, which cannot be responded to with a NAK TLV. The Error-Code TLV is defined as follows:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R|         TLV Type          |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Error-Code                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

1 (Mandatory)

R

0

TLV Type

3 for Error-Code

Length

4

Error-Code

The Error-Code field is four octets. Error Codes 1-999 represent successful outcomes (informative messages), 1000-1999 represent warnings, and codes 2000-2999 represent fatal errors. If an Error- Code TLV with a fatal error has been sent, then the conversation must be terminated.

Currently defined values for Error-Code include:

2001 -

Tunnel_Compromise_Error

2002 -

Unexpected_TLVs_Exchanged

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

The Crypto-Binding TLV MUST be used to perform Cryptographic Binding after each successful EAP method in a sequence of EAP methods is complete in TEAM Phase 2. The Crypto-Binding TLV can also be used during Protected Termination.

The Crypto-Binding TLV must have the version number received during the TEAM version negotiation. The receiver of the Crypto-Binding TLV must verify that the version in the Crypto-Binding TLV matches the version it sent during the TEAM version negotiation. If this check fails then the TLV is invalid.

The receiver of the Crypto-Binding TLV must verify that the subtype is not set to any value other than the ones allowed. If this check fails then the TLV is invalid.

This message format is used for the Binding Request (B1) and also the Binding Response. This uses TLV type CRYPTO_BINDING_TLV. TEAM implementations MUST support this TLV and this TLV cannot be responded to with a NAK TLV. The Crypto-Binding TLV is defined as follows:

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

M

1 (Mandatory)

R

0

TLV Type

9 for Crypto-Binding

Length

56

Reserved

Reserved, set to zero (0)

Version

The Version field is a single octet, which is set to the version of Crypto-Binding TLV. For the Crypto-Binding TLV defined in this specification, it is set to one (1).

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 S_NONCE for the B1 message and a C_NONCE for the B2 message.

Compound MAC

The Compound MAC field is 20 octets. This can be the Server MAC (B1_MAC) or the Client MAC (B2_MAC). It is computed using the HMAC-SHA1-160 keyed MAC that provides 160 bits of output using the CMK key. The MAC is computed over the buffer created after concatenating these fields in the following order:

1. The entire Crypto-Binding TLV attribute with the MAC field zeroed out
2. The EAP Type sent by the other party in the first TEAM message
3. All the Outer-TLVs from the first TEAM message sent by EAP-server to peer. If a single TEAM message is fragmented into multiple TEAM packets; then the Outer-TLVs in all the fragments of that message MUST be included.
4. All the Outer-TLVs from the first TEAM message sent by the peer to the EAP server. If a single TEAM message is fragmented into multiple TEAM packets, then the Outer-TLVs in all the fragments of that message MUST be included.

6.6.  Connection-Binding TLV

The Connection-Binding TLV allows for connection specific information to be sent by the peer to the AAA server. This TLV should be logged by the EAP or AAA server. The AAA or EAP server should not deny access if there is a mismatch between the value sent through the AAA protocol and this TLV.

The format of this TLV is defined for the layer that defines the parameters. The format of the value sent by the peer to the EAP server may be different from the format of the corresponding value sent through the AAA protocol. For example, the connection binding TLV may contain the 802.11 MAC Address or SSID [IEEE.802‑11.2007] (IEEE Computer Society, “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,” June 2007.).

TEAM implementations MAY support this TLV and this TLV MUST NOT be responded to with a NAK TLV. The Connection-Binding TLV is defined as follows:

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

M

0 (Optional)

R

0

TLV Type

4 for Connection-Binding

Length

>= 0

TLVs

The field contains a list of TLVs, each in the same format defined in Section 6.1 (TLV Format), with the Mandatory flag bit cleared (0). These TLVs contain information on the identity of the peer and authenticator (layer 2 or IP addresses); the media used to connect the peer and authenticator (NAS-Port-Type); and/or the service the client is trying to access on the gateway (SSID). The format of these TLVs will be defined in a separate draft.

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

TEAM implementations MUST support the Vendor-Specific TLV, and this TLV MUST NOT be responded to with a NAK TLV. TEAM implementations may not support the Vendor TLVs inside in the Vendor-Specific TLV, and can respond to the Vendor TLVs with a NAK TLV containing the appropriate Vendor-ID and Vendor-TLV type.

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.

The Vendor-Specific TLV is defined as follows:

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

M

1 (Mandatory)

R

0

TLV Type

5 for Vendor-Specific

Length

>= 4

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.

Vendor TLVs

This field is of indefinite length. It contains vendor-specificTLVs, in a format defined by the vendor.

6.8.  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 RFC 3986 [RFC3986] (Berners-Lee, T., Fielding, R., and L. Masinter, “Uniform Resource Identifier (URI): Generic Syntax,” January 2005.) with UTF-8 encoding. Interpretation of the value of the URI is outside the scope of this document.

If a packet contains multiple URI TLVs, then the client SHOULD select the first TLV it can implement, and ignore the others. If the client is unable to implement any of the URI TLVs, then it MAY ignore the error. TEAM implementations MAY support this TLV; and this TLV cannot be responded to with a NAK TLV. The URI 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              URI
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

0 (Optional)

R

0

TLV Type

6 for URI

Length

>= 0

URI

This field is of indefinite length, and conforms to the format specified in RFC 3986.

6.9.  EAP-Payload TLV

To allow piggybacking EAP request and response with other TLVs, the EAP Payload TLV is defined, which includes an encapsulated EAP packet and 0 or more TLVs. TEAM implementations MUST support this TLV, which cannot be responded to with a NAK TLV. The EAP-Payload 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          EAP-Packet...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

1 (Mandatory)

R

0

TLV Type

7 for EAP-Payload

Length

>= 0

EAP-Packet

This field contains a complete EAP packet, including the EAP header (Code, Identifier, Length, Type) fields. The length of this field is determined by the Length field of the encapsulated EAP packet.

TLVs

This (optional) field contains a list of TLVs associated with the EAP-Packet field. The TLVs utilize the same format described Section 6.1 (TLV Format), 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.

6.10.  Intermediate-Result TLV

The Intermediate-Result TLV provides support for acknowledged intermediate Success and Failure messages within EAP. TEAM implementations MUST support this TLV, which cannot be responded to with a NAK TLV. The Intermediate-Result TLV is defined as follows:

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

M

1 (Mandatory)

R

0

TLV Type

8 for Intermediate-Result

Length

>= 2

Status

The Status field is two octets. Values include:

1 - Success

2 - Failure

TLVs

This (optional) field contains a list of TLVs associated with the Intermediate-Result TLV. The TLVs utilize the same format described Section 6.1 (TLV Format), and MUST NOT have the mandatory bit set.

6.11.  Calling-Station-Id TLV

This TLV allows a peer to send information to EAP server about the call originator. This TLV MAY be included in the Connection-Binding- TLV.

For dial-up, the Called-Station-ID TLV contains the phone number of the peer. For use with IEEE 802.1X, the MAC address of the peer is included [RFC3580] (Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese, “IEEE 802.1X Remote Authentication Dial In User Service (RADIUS) Usage Guidelines,” September 2003.).

For VPN, this attribute is used to send the IPv4 or IPV6 address of the interface of the peer used to initiate the VPN in ASCII format. Where the Fully Qualified Domain Name (FQDN) of the VPN client is known, it SHOULD be appended, separated from the address with a " " (space). Example: "12.20.2.3 vpnserver.company.com".

As described in Section 7.15 of (Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J., and H. Levkowetz, “Extensible Authentication Protocol (EAP),” June 2004.) [RFC3748], this TLV SHOULD be logged by the EAP or AAA server, and MAY be used for comparison with information gathered by other means.

However, since the format of this TLV may not match the format of the information gathered by other means, if an EAP server or AAA server supports the capability to deny access based on a mismatch, spurious authentication failures may occur. As a result, implementations SHOULD allow the administrator to disable this check.

TEAM implementations MAY support this TLV and this TLV MUST NOT be responded to with a NAK TLV. The Calling-Station-ID 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

0 (Optional)

R

0

TLV Type

10 for Calling-Station-Id

Length

>= 0

String

The field should be the same as the value of the Calling-Station-ID attribute in [RFC2865] (Rigney, C., Willens, S., Rubens, A., and W. Simpson, “Remote Authentication Dial In User Service (RADIUS),” June 2000.).

6.12.  Called-Station-Id TLV

This TLV allows a peer to send information to EAP server about the NAS it called. This TLV MAY be included in the Connection-Binding TLV.

For dial-up, the Calling-Station-ID TLV contains the phone number called by the peer. For use with IEEE 802.1X, the MAC address of the NAS is included, as specified in [RFC3580] (Congdon, P., Aboba, B., Smith, A., Zorn, G., and J. Roese, “IEEE 802.1X Remote Authentication Dial In User Service (RADIUS) Usage Guidelines,” September 2003.).

For VPN, this attribute is used to send the IPv4 or IPv6 address of VPN server in ASCII format. Where the Fully Qualified Domain Name (FQDN) of the VPN server is known, it SHOULD be appended, separated from the address with a " " (space). Example: "12.20.2.3 vpnserver.company.com".

This TLV SHOULD be logged by the EAP or AAA server, and MAY be used for comparison with information gathered by other means. However, since the format of this TLV may not match the format of the information gathered by other means, if an EAP server or AAA server supports the capability to deny access based on a mismatch, spurious authentication failures may occur. As a result, implementations SHOULD allow the administrator to disable this check.

TEAM implementations MAY support this TLV, and this TLV MUST NOT be responded to with a NAK TLV. The Called-Station-ID 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

0 (Optional)

R

0

TLV Type

11 for Called-Station-Id

Length

>= 0

String

The field should be the same as the value of the Called-Station-ID attribute in [RFC2865] (Rigney, C., Willens, S., Rubens, A., and W. Simpson, “Remote Authentication Dial In User Service (RADIUS),” June 2000.).

6.13.  NAS-Port-Type TLV

This TLV allows a peer to send information to EAP server about the type of physical connection used by the peer to connect to NAS. This TLV MAY be included in the Connection-Binding-TLV.

The value of this field is the same as the value of NAS-Port-Type attribute in [RFC2865] (Rigney, C., Willens, S., Rubens, A., and W. Simpson, “Remote Authentication Dial In User Service (RADIUS),” June 2000.).

This TLV SHOULD be logged by the EAP or AAA server and MAY be used for comparison with information gathered by other means. However, since the format of this TLV may not match the format of the information gathered by other means, if an EAP server or AAA server supports the capability to deny access based on a mismatch, spurious authentication failures may occur. As a result, implementations SHOULD allow the administrator to disable this check.

TEAM implementations MAY support this TLV; and this TLV MUST NOT be responded to with a NAK TLV. The NAS-Port-Type 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            Value                              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

0 (Optional)

R

0

TLV Type

12 for NAS-Port-Type

Length

4

String

The String field is four octets. Values are the same as for the NAS-Port-Type attribute defined in [RFC2865] (Rigney, C., Willens, S., Rubens, A., and W. Simpson, “Remote Authentication Dial In User Service (RADIUS),” June 2000.).

6.14.  Server-Identifier TLV

This TLV allows a EAP server to send a hint to the EAP peer to help the EAP peer select the appropriate sessionID for session resumption. The field is a string sent by the EAP server, and the field should be treated as a opaque string by the peer. During a full-tls-handshake, the EAP peer MAY keep track of this field and the corresponding sessionID, and use it as a hint to select the appropriate sessionID during session resumption.

TEAM implementations MAY support this TLV and this TLV MUST NOT be responded to with a NAK TLV. The Server-Identifier 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                            String...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

0 (Optional)

R

0

TLV Type

13 for Server-Identifier

Length

≥ 0

String

Contains an identifier sent by the EAP server.

6.15.  Identity-Type TLV

The Identity-Type TLV allows an EAP-server to send a hint to help the EAP-peer select the right type of identity; for example; user or machine.

TEAM implementations MAY support this TLV, which cannot be responded to with a NAK TLV.

If the Identity-type field does not contain one of the known values or if the EAP peer does not have an identity corresponding to the identity-type, then the peer MUST ignore the value. The Identity- Type 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             Identity-Type     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

0 (Optional)

R

0

TLV Type

14 for Identity-Type

Length

2

Identity-Type

The Identity-Type field is two octets. Values include:

1 - Human

2 - Machine

6.16.  Server-Trusted-Root TLV

The Server-Trusted-Root TLV allows the peer to send a request to the EAP server for a trusted root in PKCS #7 format.

The Server-Trusted-Root TLV is always marked as optional, and cannot be responded to with a NAK TLV. TEAM server implementations that claim to support provisioning MUST support Server-Trusted-Root TLV, PKCS#7 TLV, and the PKCS#7-Server-Certificate-Root credential format defined in this TLV. TEAM peer implementations may not support this TLV.

The Server-Trusted-Root TLV can only be sent as an inner TLV (inside the TEAM Phase 2 conversation), in both server unauthenticated tunnel provisioning mode, and the regular authentication process.

The peer MUST NOT request, or accept the trusted root sent inside the Server-Root credential TLV by the EAP-server until it has completed authentication of the EAP server, and validated the Crypto-Binding TLV. The peer may receive a trusted root, but is not required to use the trusted root received from the EAP server.

If the EAP server sets credential-format to PKCS#7-Server- Certificate-Root, then the Server-Trusted-Root TLV MUST contain the root of the certificate chain of the certificate issued to the EAP server packages in a PKCS#7 TLV. If the Server certificate is a self-signed certificate, then the root is the self-signed certificate. In this case, the EAP server does not have to sign the certificate inside the PCKS#7 TLV since it does not necessarily have access to the private key for it.

If the Server-Trusted-Root TLV credential format does not contain one of the known values, then the EAP-server MUST ignore the value.

The Server-Trusted-Root 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Credential Format   |     TLVs...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-

M

0 (Optional)

R

0

TLV Type

15 for Server-Trusted-Root

Length

≥ 2

Credential Format

The Credential Format field is two octets. Values include:

1 - PKCS#7-Server-Certificate-Root

TLVs

This (optional) field contains a list of TLVs associated with the Server-Trusted-Root TLV. The TLVs utilize the same format described Section 6.1 (TLV Format), and MUST NOT have the mandatory bit set.

6.17.  PKCS#7 TLV

This TLV contains a certificate or certificate chain requested by the peer in PKCS#7 format [RFC2315] (Kaliski, B., “PKCS #7: Cryptographic Message Syntax Version 1.5,” March 1998.).

The PKCS#7 TLV is always marked as optional, and cannot be responded to with a NAK TLV. PEAPv2 server implementations that claim to support provisioning MUST support this TLV. PEAPv2 peer implementations may not support this TLV.

If the PKCS#7 TLV contains a certificate or certificate chain that is not acceptable to the peer, then peer MUST ignore the value.

The PKCS#7 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             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           PKCS#7 data...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

0 (Optional)

R

0

TLV Type

17 for PKCS#7

Length

≥ 0

PKCS#7 Data

This field contains a certificate or certificate chain in PKCS#7 format.

6.18.  Request-Action-TLV

The Request-Action TLV MAY be sent by the peer along with acknowledged failure. It allows the peer to request the EAP server to negotiate EAP methods or process TLVs specified in the failure packet. The server MAY ignore this TLV.

PEAPv2 implementations MUST support this TLV, which cannot be responded to with a NAK TLV.

The Request-Action TLV is defined as follows:

 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|M|R|         TLV Type          |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|             Action            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

M

1 (Mandatory)

R

0

TLV Type

16 for Request-Action

Length

2

Action

The Action field is two octets. Values include:

1 - Process-TLV

2 - Negotiate-EAP

7.  Security Considerations

TBC.

8.  IANA Considerations

TBC.

9.  References

9.1. Normative References

9.2. Informative References

Authors' Addresses