EMU Working Group Dan Simon Internet-Draft Bernard Aboba Obsoletes: 2716 Ryan Hurst Category: Proposed Standard Microsoft Corporation Expires: December 25, 2007 1 July 2007 The EAP TLS Authentication Protocol draft-simon-emu-rfc2716bis-11.txt By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on December 25, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). All rights reserved. Abstract The Extensible Authentication Protocol (EAP), defined in RFC 3748, provides support for multiple authentication methods. Transport Level Security (TLS) provides for mutual authentication, integrity- protected ciphersuite negotiation and key exchange between two endpoints. This document defines EAP-TLS, which includes support for certificate-based mutual authentication and key derivation. This document obsoletes RFC 2716. A summary of the changes between this document and RFC 2716 is available in Appendix A. Simon, Aboba & Hurst Proposed Standard [Page 1]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 Table of Contents 1. Introduction.............................................. 3 1.1 Requirements Language ........................... 3 1.2 Terminology ..................................... 3 2. Protocol Overview ........................................ 4 2.1 Overview of the EAP-TLS Conversation ............ 4 2.2 Identity Verification ........................... 15 2.3 Key Hierarchy ................................... 16 2.4 Ciphersuite and Compression Negotiation ......... 18 3. Detailed Description of the EAP-TLS Protocol ............. 19 3.1 EAP TLS Request Packet ......................... 19 3.2 EAP TLS Response Packet ........................ 20 4. IANA Considerations ...................................... 22 5. Security Considerations .................................. 22 5.1 Security Claims ................................ 22 5.2 Peer and Server Identities ..................... 23 5.3 Certificate Validation ......................... 24 5.4 Certificate Revocation ......................... 25 5.5 Packet Modification Attacks .................... 26 6. References ............................................... 27 6.1 Normative references ....... .................... 27 6.2 Informative references .......................... 27 Acknowledgments .............................................. 29 Authors' Addresses ........................................... 29 Appendix A - Changes from RFC 2716 ........................... 30 Full Copyright Statement ..................................... 31 Intellectual Property ........................................ 31 Simon, Aboba & Hurst Proposed Standard [Page 2]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 1. Introduction The Extensible Authentication Protocol (EAP), described in [RFC3748], 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-TLS has been defined for use with a variety of lower layers, including Point-to-Point Protocol (PPP) [RFC1661], Layer 2 tunneling protocols such as PPTP [RFC2637] or L2TP [RFC2661], IEEE 802 wired networks [IEEE-802.1X] and wireless technologies such as IEEE 802.11 [IEEE-802.11] and IEEE 802.16 [IEEE-802.16e]. While the EAP methods defined in [RFC3748] did not support mutual authentication, the use of EAP with wireless technologies such as [IEEE-802.11] has resulted in development of a new set of requirements. As described in "EAP Method Requirements for Wireless LANs" [RFC4017], it is desirable for EAP methods used for wireless LAN authentication to support mutual authentication and key derivation. PPP Encryption Control Protocol (ECP) is defined in [RFC1968]. Since PPP encryption protocols such as DESE-bis [RFC2419], 3DESE [RFC2420], and MPPE [RFC3078] assume existence of a session key, it is useful to have a mechanism for session key establishment. Since design of secure key management protocols is non-trivial, it is desirable to avoid creating new mechanisms for this. The EAP protocol described in this document allows a EAP peer to take advantage of the protected ciphersuite negotiation, mutual authentication and key management capabilities of the TLS protocol, described in "The Transport Layer Security (TLS) Protocol Version 1.1" [RFC4346]. 1.1. Requirements The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 1.2. Terminology This document frequently uses the following terms: authenticator The entity initiating EAP authentication. peer The entity that responds to the authenticator. In [IEEE-802.1X], this entity is known as the Supplicant. Simon, Aboba & Hurst Proposed Standard [Page 3]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 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]. 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. 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. 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. 2. Protocol Overview 2.1. Overview of the EAP-TLS Conversation As described in [RFC3748], the EAP-TLS conversation will typically begin with the authenticator and the peer negotiating EAP. The authenticator will then 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 userId. From this point forward, while nominally the EAP conversation occurs between the EAP 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 security server. In the discussion that follows, we will use the term "EAP server" to denote the ultimate endpoint conversing with the peer. 2.1.1. Base Case Once having received the peer's Identity, the EAP server MUST respond with an EAP-TLS/Start packet, which is an EAP-Request packet with EAP-Type=EAP-TLS, the Start (S) bit set, and no data. The EAP-TLS conversation will then begin, with the peer sending an EAP-Response packet with EAP-Type=EAP-TLS. The data field of that packet will encapsulate one or more TLS records in TLS record layer format, Simon, Aboba & Hurst Proposed Standard [Page 4]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 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 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=EAP-TLS. 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. The server_hello handshake message contains a TLS version number, another random number, a sessionId, and a ciphersuite. The version offered by the server MUST correspond to TLS v1.0 or later. 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 ciphersuite from those offered by the client. If the session matches the client's, then the ciphersuite MUST match the one negotiated during the handshake protocol execution that established the session. If the EAP server is not resuming a previously established session, then it MUST include a TLS server_certificate handshake message, and a server_hello_done handshake message MUST be the last handshake message encapsulated in this EAP-Request packet. The certificate message contains a public key certificate chain for either a key exchange public key (such as an RSA or Diffie-Hellman key exchange public key) or a signature public key (such as an RSA or DSS signature public key). In the latter case, a TLS server_key_exchange handshake message MUST also be included to allow the key exchange to take place. The certificate_request message is included when the server desires the client to authenticate itself via public key. While the EAP server SHOULD require client authentication, this is not a requirement, since it may be possible that the server will require that the peer authenticate via some other means. Simon, Aboba & Hurst Proposed Standard [Page 5]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 If the peer supports EAP-TLS and is configured to use it, it MUST respond to the EAP-Request with an EAP-Response packet of EAP- Type=EAP-TLS. 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, the data field of this packet MUST encapsulate one or more TLS records containing a TLS client_key_exchange, change_cipher_spec and finished messages. If the EAP server sent a certificate_request message in the preceding EAP-Request packet, then unless the peer is configured for privacy (see Section 2.1.4) the peer MUST send, in addition, certificate and certificate_verify messages. The former contains a certificate for the peer's signature public key, while the latter contains the peer's signed authentication response to the EAP server. After receiving this packet, the EAP server will verify the peer's certificate and digital signature, if requested. 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. In the case where the EAP-TLS mutual authentication is successful, the conversation will appear as follows: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/ Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP-TLS (TLS Start) EAP-Response/ EAP-Type=EAP-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type=EAP-TLS (TLS server_hello, TLS certificate, [TLS server_key_exchange,] TLS certificate_request, TLS server_hello_done) EAP-Response/ EAP-Type=EAP-TLS (TLS certificate, TLS client_key_exchange, Simon, Aboba & Hurst Proposed Standard [Page 6]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 TLS certificate_verify, TLS change_cipher_spec, TLS finished) -> <- EAP-Request/ EAP-Type=EAP-TLS (TLS change_cipher_spec, TLS finished) EAP-Response/ EAP-Type=EAP-TLS -> <- EAP-Success 2.1.2. 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. While this model was developed for use with HTTP authentication, it also can be used to provide "fast reconnect" functionality as defined in [RFC3748] Section 7.2.1. It is left up to the peer whether to attempt to continue a previous session, thus shortening the TLS 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 authenticator reside on the same device, then client will only be able to continue sessions when connecting to the same NAS or tunnel 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 tunnel servers will remote their EAP authentications to the same backend authentication server. If the EAP server is resuming a previously established session, then it MUST include only a TLS change_cipher_spec message and a TLS finished handshake message after the server_hello message. The finished message contains the EAP server's authentication response to the peer. In the case where a previously established session is being resumed, and both sides authenticate successfully, the conversation will Simon, Aboba & Hurst Proposed Standard [Page 7]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 appear as follows: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/ Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Request/ EAP-Type=EAP-TLS (TLS Start) EAP-Response/ EAP-Type=EAP-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type=EAP-TLS (TLS server_hello, TLS change_cipher_spec TLS finished) EAP-Response/ EAP-Type=EAP-TLS (TLS change_cipher_spec, TLS finished) -> <- EAP-Success 2.1.3. Termination If the peer's authentication is unsuccessful, the EAP server SHOULD send an EAP-Request packet with EAP-Type=EAP-TLS, encapsulating a TLS record containing the appropriate TLS alert message. The EAP server SHOULD send a TLS alert message rather 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 EAP-TLS conversation to be restarted, or it MAY contain an EAP-Response packet with EAP-Type=EAP-TLS and no data, in which case the EAP-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. Simon, Aboba & Hurst Proposed Standard [Page 8]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 If the peers authenticates successfully, the EAP server MUST respond with an EAP-Request packet with EAP-Type=EAP-TLS, which includes, in the case of a new TLS session, one or more TLS records containing TLS change_cipher_spec and finished handshake messages. The latter contains the EAP server's authentication response to the peer. The peer will then verify the hash in order to authenticate the EAP server. If the EAP server authenticates unsuccessfully, the peer MAY send an EAP-Response packet of EAP-Type=EAP-TLS containing a TLS Alert message identifying the reason for the failed authentication. The peer MAY send a TLS alert message rather than immediately terminating the conversation so as to allow the EAP server to log the cause of the error for examination by the system administrator. To ensure that the EAP Server receives the TLS alert message, the peer MUST wait for the EAP-Server to reply before terminating the conversation. The EAP Server MUST reply with an EAP-Failure packet since server authentication failure is a terminal condition. If the EAP server authenticates successfully, the peer MUST send an EAP-Response packet of EAP-Type=EAP-TLS, and no data. The EAP-Server then MUST respond with an EAP-Success message. In the case where 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-Type=EAP-TLS (TLS Start) EAP-Response/ EAP-Type=EAP-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type=EAP-TLS (TLS server_hello, TLS certificate, [TLS server_key_exchange,] TLS certificate_request, TLS server_hello_done) EAP-Response/ Simon, Aboba & Hurst Proposed Standard [Page 9]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 EAP-Type=EAP-TLS (TLS certificate, TLS client_key_exchange, TLS certificate_verify, TLS change_cipher_spec, TLS finished) -> <- EAP-Request/ EAP-Type=EAP-TLS (TLS change_cipher_spec, TLS finished) EAP-Response/ EAP-Type=EAP-TLS -> <- EAP-Request EAP-Type=EAP-TLS (TLS Alert message) EAP-Response/ EAP-Type=EAP-TLS -> <- EAP-Failure (User Disconnected) In the case where server authentication is unsuccessful, the conversation will appear as follows: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/ Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP-TLS (TLS Start) EAP-Response/ EAP-Type=EAP-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type=EAP-TLS (TLS server_hello, TLS certificate, [TLS server_key_exchange,] TLS certificate_request, TLS server_hello_done) EAP-Response/ EAP-Type=EAP-TLS (TLS Alert message) -> <- EAP-Failure (User Disconnected) Simon, Aboba & Hurst Proposed Standard [Page 10]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 2.1.4. Privacy EAP-TLS peer and server implementations MAY support privacy. Disclosure of the username is avoided by utilizing a privacy Network Access Identifier (NAI) [RFC4282] in the EAP-Response/Identity, and transmitting the client certificate within a TLS session providing confidentiality. In order to avoid disclosing the peer username, an EAP-TLS peer configured for privacy MUST negotiate a TLS ciphersuite supporting confidentiality and MUST provide a client certificate list containing no entries in response to the initial certificate_request from the EAP-TLS server. An EAP-TLS server supporting privacy MUST NOT treat a certificate list containing no entries as a terminal condition; instead it MUST bring up the TLS session and then send a hello_request. The handshake then proceeds normally; the client sends a client_hello and the server replies with a server_hello, certificate, server_key_exchange, certificate_request, server_hello_done, etc. An EAP-TLS peer supporting privacy MUST provide a certificate list containing at least one entry in response to the subsequent certificate_request sent by the server. If the EAP-TLS server supporting privacy does not receive a client certificate in response to the subsequent certificate_request, then it MUST abort the session. EAP-TLS privacy support is designed to allow EAP-TLS peers that do not support privacy to interoperate with EAP-TLS servers supporting privacy. EAP-TLS servers supporting privacy MUST request a client certificate, and MUST accept a client certificate offered by the EAP- TLS peer, in order to preserve interoperability with EAP-TLS peers that do not support privacy. However, an EAP-TLS peer configured for privacy typically will not be able to successfully authenticate with an EAP-TLS server that does not support privacy, since such a server will typically treat the refusal to provide a client certificate as a terminal error. As a result, unless authentication failure is considered preferable to disclosure of the username, EAP-TLS peers should only be configured for privacy on networks known to support it. This is most easily achieved with EAP lower layers that support network advertisement, so that the network and appropriate privacy configuration can be determined. In order to determine the privacy configuration on link layers (such as IEEE 802 wired networks) which do not support network advertisement, it may be desirable to utilize Simon, Aboba & Hurst Proposed Standard [Page 11]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 information provided in the server certificate or within identity selection hints [RFC4284] to determine the appropriate configuration. In the case where the peer and server support privacy and mutual authentication, the conversation will appear as follows: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/ Identity EAP-Response/ Identity (AnonymousNAI) -> <- EAP-Request/ EAP-Type=EAP-TLS (TLS Start) EAP-Response/ EAP-Type=EAP-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type=EAP-TLS (TLS server_hello, TLS certificate, [TLS server_key_exchange,] TLS certificate_request, TLS server_hello_done) EAP-Response/ EAP-Type=EAP-TLS (TLS certificate (no cert), TLS client_key_exchange, TLS change_cipher_spec, TLS finished) -> <- EAP-Request/ EAP-Type=EAP-TLS (TLS change_cipher_spec, finished, hello_request) EAP-Response/ EAP-Type=EAP-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type=EAP-TLS (TLS server_hello, TLS certificate, TLS server_key_exchange, TLS certificate_request, TLS server_hello_done) EAP-Response/ EAP-Type=EAP-TLS Simon, Aboba & Hurst Proposed Standard [Page 12]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 (TLS certificate, TLS client_key_exchange, TLS certificate_verify, TLS change_cipher_spec, TLS finished) -> <- EAP-Request/ EAP-Type=EAP-TLS (TLS change_cipher_spec, TLS finished) EAP-Response/ EAP-Type=EAP-TLS -> <- EAP-Success 2.1.5. 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 EAP-TLS messages sent in a single round may thus be larger than the MTU size or the maximum RADIUS packet size of 4096 octets. As a result, an EAP-TLS implementation MUST provide its own support for fragmentation and reassembly. However, in order to ensure interoperability with existing implementations, TLS handshake messages SHOULD NOT be fragmented into multiple TLS records if they fit within a single TLS record. 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 single certificate 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. Since EAP is a simple 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. EAP-TLS fragmentation support is provided through addition of a flags octet within the EAP-Response and EAP-Request packets, as well as a TLS Message Length field of four octets. Flags include the Length included (L), More fragments (M), and EAP-TLS Start (S) bits. The L flag is set to indicate the presence of the four octet TLS Message Length field, and MUST be set for the first fragment of a fragmented TLS message or set of messages. The M flag is set on all but the last fragment. The S flag is set only within the EAP-TLS start message sent from the EAP server to the peer. The TLS Message Length field is Simon, Aboba & Hurst Proposed Standard [Page 13]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 four octets, and provides the total length of the TLS message or set of messages that is being fragmented; this simplifies buffer allocation. When an EAP-TLS peer receives an EAP-Request packet with the M bit set, it MUST respond with an EAP-Response with EAP-Type=EAP-TLS 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=EAP-TLS 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. In the case where the EAP-TLS mutual authentication is successful, and fragmentation is required, the conversation will appear as follows: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/ Identity EAP-Response/ Identity (MyID) -> <- EAP-Request/ EAP-Type=EAP-TLS (TLS Start, S bit set) EAP-Response/ EAP-Type=EAP-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type=EAP-TLS (TLS server_hello, TLS certificate, [TLS server_key_exchange,] TLS certificate_request, TLS server_hello_done) (Fragment 1: L, M bits set) Simon, Aboba & Hurst Proposed Standard [Page 14]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 EAP-Response/ EAP-Type=EAP-TLS -> <- EAP-Request/ EAP-Type=EAP-TLS (Fragment 2: M bit set) EAP-Response/ EAP-Type=EAP-TLS -> <- EAP-Request/ EAP-Type=EAP-TLS (Fragment 3) EAP-Response/ EAP-Type=EAP-TLS (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=EAP-TLS EAP-Response/ EAP-Type=EAP-TLS (Fragment 2)-> <- EAP-Request/ EAP-Type=EAP-TLS (TLS change_cipher_spec, TLS finished) EAP-Response/ EAP-Type=EAP-TLS -> <- EAP-Success 2.2. Identity Verification As noted in [RFC3748] Section 5.1: It is RECOMMENDED that the Identity Response be used primarily for routing purposes and selecting which EAP method to use. EAP Methods SHOULD include a method-specific mechanism for obtaining the identity, so that they do not have to rely on the Identity Response. As part of the TLS negotiation, the server presents a certificate to the peer, and if mutual authentication is requested, the peer presents a certificate to the server. EAP-TLS therefore provides a mechanism for determining both the peer identity (Peer-Id in [KEYFRAME]) and server identity (Server-Id in [KEYFRAME]). For details, see Section 5.2. Simon, Aboba & Hurst Proposed Standard [Page 15]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 Since the identity presented in the EAP-Response/Identity need not be related to the identity presented in the peer certificate, EAP-TLS implementations SHOULD NOT require that they be identical. However, if they are not identical, the identity presented in the EAP- Response/Identity is unauthenticated information, and SHOULD NOT be used for access control or accounting purposes. 2.3. Key Hierarchy Figure 1 illustrates the Transient EAP Key (TEK) hierarchy for EAP- TLS which is based on the TLS key hierarchy described in [RFC4346]. The TLS-negotiated ciphersuite is used to set up a protected channel for use in protecting the EAP conversation, keyed by the derived TEKs. The TEK derivation proceeds as follows: master_secret = TLS-PRF-48(pre_master_secret, "master secret", client.random || server.random) TEK = TLS-PRF-X(master_secret, "key expansion", server.random || client.random) Where: TLS-PRF-X = TLS pseudo-random function defined in [RFC4346], computed to X octets. In EAP-TLS, the MSK, EMSK and IV are derived from the TLS master secret via a one-way function. This ensures that the TLS master secret cannot be derived from the MSK, EMSK or IV unless the one-way function (TLS PRF) is broken. Since the MSK and EMSK are derived from the TLS master secret, if the TLS master secret is compromised then the MSK and EMSK are also compromised. The MSK is divided into two halves, corresponding to the "Peer to Authenticator Encryption Key" (Enc-RECV-Key, 32 octets) and "Authenticator to Peer Encryption Key" (Enc-SEND-Key, 32 octets). The IV is a 64 octet quantity that is a known value; octets 0-31 are known as the "Peer to Authenticator IV" or RECV-IV, and Octets 32-63 are known as the "Authenticator to Peer IV", or SEND-IV. Simon, Aboba & Hurst Proposed Standard [Page 16]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 | | pre_master_secret | server| | | client Random| V | Random | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | +---->| master_secret |<----+ | | (TMS) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | V V V +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Key Block (TEKs) | | label == "key expansion" | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | | | client | server | client | server | client | server | MAC | MAC | write | write | IV | IV | | | | | | V V V V V V Figure 1 - TLS [RFC4346] Key Hierarchy EAP-TLS derives exported keying material and parameters as follows: Key_Material = TLS-PRF-128(TMS, "client EAP encryption", client.random || server.random) MSK = Key_Material(0,63) EMSK = Key_Material(64,127) IV = TLS-PRF-64("", "client EAP encryption", client.random || server.random) Enc-RECV-Key = MSK(0,31) = Peer to Authenticator Encryption Key (MS-MPPE-Recv-Key in [RFC2548]). Also known as the PMK in [IEEE-802.11]. Enc-SEND-Key = MSK(32,63) = Authenticator to Peer Encryption Key (MS-MPPE-Send-Key in [RFC2548]) RECV-IV = IV(0,31) = Peer to Authenticator Initialization Vector SEND-IV = IV(32,63) = Authenticator to Peer Initialization Vector Session-Id = 0x0D || client.random || server.random Where: Key_Material(W,Z) = Octets W through Z inclusive of the key material. IV(W,Z) = Octets W through Z inclusive of the IV. MSK(W,Z) = Octets W through Z inclusive of the MSK. Simon, Aboba & Hurst Proposed Standard [Page 17]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 EMSK(W,Z) = Octets W through Z inclusive of the EMSK. TMS = TLS master_secret TLS-PRF-X = TLS PRF function computed to X octets client.random = Nonce generated by the TLS client. server.random = Nonce generated by the TLS server. | | pre_master_secret | server| | | client Random| V | Random | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | +---->| master_secret |<----+ | | (TMS) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | V V V +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | MSK, EMSK | | label == "client EAP encryption" | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | MSK(0,31) | MSK(32,63) | EMSK(0,63) | | | | | | V V V Figure 2 - EAP-TLS Key Hierarchy The use of these keys is specific to the lower layer, as described in [KEYFRAME] Section 2.1. 2.4. Ciphersuite and Compression Negotiation EAP-TLS implementations MUST support TLS v1.0. EAP-TLS implementations need not necessarily support all TLS ciphersuites listed in [RFC4346]. Not all TLS ciphersuites are supported by available TLS tool kits and licenses may be required in some cases. To ensure interoperability, EAP-TLS peers and servers MUST support the TLS [RFC4346] mandatory-to-implement ciphersuite: TLS_RSA_WITH_3DES_EDE_CBC_SHA. In addition, EAP-TLS servers SHOULD support and be able to negotiate Simon, Aboba & Hurst Proposed Standard [Page 18]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 all of the following TLS ciphersuites: TLS_RSA_WITH_RC4_128_MD5 TLS_RSA_WITH_RC4_128_SHA TLS_RSA_WITH_AES_128_CBC_SHA In addition, EAP-TLS peers SHOULD support the following TLS ciphersuites defined in [RFC3268]: TLS_RSA_WITH_AES_128_CBC_SHA TLS_RSA_WITH_RC4_128_SHA Since TLS supports ciphersuite negotiation, peers completing the TLS negotiation will also have selected a ciphersuite, which includes encryption and hashing methods. Since the ciphersuite negotiated within EAP-TLS applies only to the EAP conversation, TLS ciphersuite negotiation MUST NOT be used to negotiate the ciphersuites used to secure data. TLS also supports compression as well as ciphersuite negotiation. However, during the EAP-TLS conversation the EAP peer and server MUST NOT request or negotiate compression. 3. Detailed description of the EAP-TLS protocol 3.1. EAP TLS Request Packet A summary of the EAP TLS Request packet format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Flags | TLS Message Length +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLS Message Length | TLS Data... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 1 Identifier The Identifier field is one octet and aids in matching responses with requests. The Identifier field MUST be changed on each Simon, Aboba & Hurst Proposed Standard [Page 19]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 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. Octets outside the range of the Length field should be treated as Data Link Layer padding and MUST be ignored on reception. Type 13 - EAP TLS Flags 0 1 2 3 4 5 6 7 8 +-+-+-+-+-+-+-+-+ |L M S R R R R R| +-+-+-+-+-+-+-+-+ L = Length included M = More fragments S = EAP-TLS start R = Reserved 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 (EAP-TLS start) is set in an EAP-TLS Start message. This differentiates the EAP-TLS Start message from a fragment acknowledgment. Implementations of this specification MUST set the reserved bits to zero, and MUST ignore them on reception. 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. Simon, Aboba & Hurst Proposed Standard [Page 20]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 3.2. EAP TLS Response Packet A summary of the EAP TLS Response packet format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Flags | TLS Message Length +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLS Message Length | TLS Data... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 2 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, and Data fields. Octets outside the range of the Length field should be treated as Data Link Layer padding and MUST be ignored on reception. Type 13 - EAP TLS Flags 0 1 2 3 4 5 6 7 8 +-+-+-+-+-+-+-+-+ |L M R R R R R R| +-+-+-+-+-+-+-+-+ L = Length included M = More fragments R = Reserved The L bit (length included) is set to indicate the presence of the Simon, Aboba & Hurst Proposed Standard [Page 21]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 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. Implementations of this specification MUST set the reserved bits to zero, and MUST ignore them on reception. 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. 4. IANA Considerations IANA has allocated EAP Type 13 for EAP-TLS. The allocation should be updated to reference this document. There are no other IANA actions. 5. Security Considerations 5.1. Security Claims EAP security claims are defined in [RFC3748] Section 7.2.1. The security claims for EAP-TLS are as follows: Auth. mechanism: Certificates Ciphersuite negotiation: Yes [1] Mutual authentication: Yes [1] Integrity protection: Yes [1] Replay protection: Yes [1] Confidentiality: Yes [2] Key derivation: Yes Key strength: [3] Dictionary attack prot.: Yes Fast reconnect: Yes Crypt. binding: N/A Session independence: Yes [1] Fragmentation: Yes Channel binding: No Notes ----- [1] A formal proof of the security of EAP-TLS when used with Simon, Aboba & Hurst Proposed Standard [Page 22]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 [IEEE-802.11] is provided in [He]. This proof relies on the assumption that the private key pairs used by the EAP peer and server are not shared with other parties or applications. For example, a backend authentication server supporting EAP-TLS SHOULD NOT utilize the same certificate with https. [2] Privacy is an optional feature described in Section 2.1.4. [3] BCP 86 [RFC3766] Section 5 offers advice on the required RSA or DH module and DSA subgroup size in bits, for a given level of attack resistance in bits. For example, a 2048-bit RSA key is recommended to provide 128-bit equivalent key strength. The National Institute for Standards and Technology (NIST) also offers advice on appropriate key sizes in [SP800-57]. 5.2. Peer and Server Identities The EAP-TLS peer name (Peer-Id) represents the identity to be used for access control and accounting purposes. The Server-Id represents the identity of the EAP server. Together the Peer-Id and Server-Id name the entities involved in deriving the MSK/EMSK. In EAP-TLS, the Peer-Id and Server-Id are determined from the subject or subjectAltName fields in the peer and server certificates. For details, see [RFC3280] Section 4.1.2.6. Where the subjectAltName field is present in the peer or server certificate, the Peer-Id or Server-Id MUST be set to the contents of the subjectAltName. If subject naming information is present only in the subjectAltName extension of a peer or server certificate, then the subject field MUST be an empty sequence and the subjectAltName extension MUST be critical. Where the peer identity represents a host, a subjectAltName of type dnsName SHOULD be present in the peer certificate. Where the peer identity represents a user and not a resource, a subjectAltName of type rfc822Name SHOULD be used, conforming to the grammar for the Network Access Identifier (NAI) defined in [RFC4282] Section 2.1. If a dnsName or rfc822Name are not available other field types (for example a subjectAltName of type ipAddress or uniformResourceIdentifier) MAY be used. A server identity will typically represent a host, not a user or a resource. As a result, a subjectAltName of type dnsName SHOULD be present in the server certificate. If a dnsName is not available other field types (for example a subjectAltName of type ipAddress or uniformResourceIdentifier) MAY be used. Conforming implementations generating new certificates with Network Simon, Aboba & Hurst Proposed Standard [Page 23]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 Access Identifiers (NAIs) MUST use the rfc822Name in the subject alternative name field to describe such identities. The use of the subject name field to contain an emailAddress RDN is deprecated, and MUST NOT be used. The subject name field MAY contain other RDNs for representing the subject's identity. Where it is non-empty, the subject name field MUST contain an X.500 distinguished name (DN). If subject naming information is present only in the subject name field of a peer certificate and the peer identity represents a host or device the subject name field SHOULD contain a CN RDN or serialNumber RDN. If subject naming information is present only in the subject name field of a server certificate, then the subject name field SHOULD contain a CN RDN or serialNumber RDN. It is possible for more than one subjectAltName field to be present in a peer or server certificate in addition to an empty or non-empty subject distinguished name. EAP-TLS implementations supporting export of the Peer-Id and Server-Id SHOULD export all the subjectAltName fields within Peer-Ids or Server-Ids, and SHOULD also export a non-empty subject distinguished name field within the Peer- Ids or Server-Ids. All of the exported Peer-Ids and Server-Ids are considered valid. EAP-TLS implementations supporting export of the Peer-Id and Server- Id SHOULD export Peer-Ids and Server-Ids in the same order in which they appear within the certificate. Such canonical ordering would aid in comparison operations and would enable using those IDs for key derivation if that is deemed useful. However, the ordering of fields within the certificate SHOULD NOT be used for access control. 5.3. Certificate Validation Since the EAP-TLS server is typically connected to the Internet, it SHOULD support validating the peer certificate using RFC 3280 [RFC3280] conformant path validation, including the ability to retrieve intermediate certificates that may be necessary to validate the peer certificate. For details, see [RFC3280] Section 4.2.2.1. Where the EAP-TLS server is unable to retrieve intermediate certificates, it must be pre-configured with the necessary intermediate certificates to complete path validation or rely on the EAP-TLS peer to provide this information as part of the TLS Handshake (see [RFC4346] section 7.4.6). In contrast to the EAP-TLS server, the EAP-TLS peer may not have Internet connectivity. Therefore the EAP-TLS server SHOULD provide its entire certificate chain minus the root to facilitate certificate Simon, Aboba & Hurst Proposed Standard [Page 24]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 validation by the peer. The EAP-TLS peer SHOULD support validating the server certificate using RFC 3280 [RFC3280] conformant path validation. Once a TLS session is established EAP-TLS peer and server implementations MUST validate that the identities represented in the certificate are appropriate and authorized for use with EAP-TLS. The authorization process makes use of the contents of the certificates as well as other contextual information. While authorization requirements will vary from deployment to deployment it is RECOMMENDED that implementations be able to authorize based on the EAP-TLS Peer-Id and Server-Id determined as described in Section 5.2. In the case of the EAP-TLS peer this involves ensuring that the certificate presented by the EAP-TLS server was intended to be used as a server certificate. Implementations SHOULD use the Extended Key Usage (see [RFC3280] section 4.2.1.13) extension and ensure that at least one of the following is true: 1) The certificate issuer included no Extended Key Usage identifiers in the certificate. 2) The issuer included the anyExtendedKeyUsage identifier in the certificate (see [RFC3280] section 4.2.1.13). 3) The issuer included the id-kp-serverAuth identifier in the certificate (See [RFC3280] section 4.2.1.13). When performing this comparison implementations MUST follow the validation rules specified in [RFC2818] Section 3.1. In the case of the server this involves ensuring the certificate presented by the EAP-TLS peer was intended to be used as a client certificate. Implementations SHOULD use the Extended Key Usage (see [RFC3280] Section 4.2.1.13) extension and ensure that at least one of the following is true: 1) The certificate issuer included no Extended Key Usage identifiers in the certificate. 2) The issuer included the anyExtendedKeyUsage identifier in the certificate (see [RFC3280] section 4.2.1.13). 3) The issuer included the id-kp-clientAuth identifier in the certificate (see [RFC3280] section 4.2.1.13). 5.4. Certificate Revocation Certificates are long lived assertions of identity. Therefore it is important for EAP-TLS implementations to be capable of checking whether these assertions have been revoked. EAP-TLS peer and server implementations MUST support the use of Simon, Aboba & Hurst Proposed Standard [Page 25]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 Certificate Revocation Lists (CRLs); for details, see [RFC3280] section 3.3. EAP-TLS peer and server implementations SHOULD also support the Online Certificate Status Protocol (OCSP), described in "X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP" [RFC2560]. OCSP messages are typically much smaller than CRLs which can shorten connection times especially in bandwidth constrained environments. While EAP-TLS servers are typically connected to the Internet during the EAP conversation, an EAP-TLS peer may not have Internet connectivity until authentication completes. In the case where the peer is initiating a voluntary Layer 2 tunnel using PPTP [RFC2637] or L2TP [RFC2661], the peer will typically already have a PPP interface and Internet connectivity established at the time of tunnel initiation. However, in the case where the EAP-TLS peer is attempting to obtain network access, it will not have network connectivity and is therefore not capable of checking for certificate revocation until after authentication completes and network connectivity is available. For this reason EAP-TLS peers and servers SHOULD implement Certificate Status Request messages, as described in "Transport Layer Security (TLS) Extensions" [RFC4366] section 3.6. To enable revocation checking in situations where servers do not support Certificate Status Request messages and network connectivity is not available prior to authentication completion, peer implementations MUST also support checking for certificate revocation after authentication completes and network connectivity is available, and they SHOULD utilize this capability by default. 5.5. Packet Modification Attacks The integrity protection of EAP-TLS packets does not extend to the EAP header fields (Code, Identifier, Length) or the Type or Flags fields. As a result, these fields may be modified by an attacker. In most cases modification of the Code or Identifier fields will only result in a denial of service attack. However, it may be possible for an attacker to add additional data to an EAP-TLS packet so as to cause it to be longer than implied by the Length field. EAP peers, authenticators or servers that do not check for this could be vulnerable to a buffer overrun. It is also possible for an attacker to modify the Type or Flags fields. By modifying the Type field, an attacker could cause one TLS-based EAP method to be negotiated instead of another. For example, the EAP-TLS Type field (13) could be changed to indicate another TLS-based EAP method. Unless the alternative TLS-based EAP Simon, Aboba & Hurst Proposed Standard [Page 26]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 method utilizes a different key derivation formula, it is possible that an EAP method conversation altered by a man-in-the-middle could run all the way to completion without detection. Unless the ciphersuite selection policies are identical for all TLS-based EAP methods utilizing the same key derivation formula, it may be possible for an attacker to mount a successful downgrade attack, causing the peer to utilize an inferior ciphersuite or TLS-based EAP method. 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S. and C. Adams, "X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP", RFC 2560, June 1999. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC3268] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites for Transport Layer Security (TLS)", RFC 3268, June 2002. [RFC3280] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 3280, April 2002. [RFC3748] Aboba, B., Blunk, L., Vollbrecht, J., Carlson, J. and H. Levkowetz, "Extensible Authentication Protocol (EAP)", RFC 3748, June 2004. [RFC4282] Aboba, B., Beadles, M., Arkko, J. and P. Eronen, "The Network Access Identifier", RFC 4282, December 2005. [RFC4346] Dierks, T. and E. Rescorla, "The TLS Protocol Version 1.1", RFC 4346, April 2006. [RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J. and T. Wright, "Transport Layer Security (TLS) Extensions", RFC 4366, April 2006. 6.2. Informative References [IEEE-802.1X] Institute of Electrical and Electronics Engineers, "Local and Metropolitan Area Networks: Port-Based Network Access Simon, Aboba & Hurst Proposed Standard [Page 27]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 Control", IEEE Standard 802.1X-2004, December 2004. [IEEE-802.11] 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. 802.11-2007, 2007. [IEEE-802.16e] Institute of Electrical and Electronics Engineers, "IEEE Standard for Local and Metropolitan Area Networks: Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems: Amendment for Physical and Medium Access Control Layers for Combined Fixed and Mobile Operations in Licensed Bands" IEEE 802.16e, August 2005. [He] He, C., Sundararajan, M., Datta, A., Derek, A. and J. Mitchell, "A Modular Correctness Proof of IEEE 802.11i and TLS", CCS '05, November 7-11, 2005, Alexandria, Virginia, USA [KEYFRAME] Aboba, B., Simon, D. and P. Eronen, "Extensible Authentication Protocol (EAP) Key Management Framework", Internet Draft (work in progress), draft-ietf-eap- keying-19.txt, July 2007. [RFC1661] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, July 1994. [RFC1968] Meyer, G., "The PPP Encryption Protocol (ECP)", RFC 1968, June 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. [RFC2548] Zorn, G., "Microsoft Vendor-specific RADIUS Attributes", RFC 2548, March 1999. [RFC2637] Hamzeh, K., Pall, G., Verthein, W., Taarud, J., Little, W., and G. Zorn, "Point-to-Point Tunneling Protocol", RFC 2637, July 1999. [RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn, G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"", Simon, Aboba & Hurst Proposed Standard [Page 28]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 RFC 2661, August 1999. [RFC2716] Aboba, B. and D. Simon, "PPP EAP TLS Authentication Protocol", RFC 2716, October 1999. [RFC3078] Pall, G. and G. Zorn, "Microsoft Point-to-Point Encryption (MPPE) Protocol", RFC 3078, March 2001. [RFC3766] Orman. H. and P. Hoffman, "Determining Strengths for Public Keys Used for Exchanging Symmetric Keys", RFC 3766, April 2004. [RFC4017] Stanley, D., Walker, J. and B. Aboba, "Extensible Authentication Protocol (EAP) Method Requirements for Wireless LANs", RFC 4017, March 2005. [RFC4284] Adrangi, F., Lortz, V., Bari, F. and P. Eronen, "Identity Selection Hints for the Extensible Authentication Protocol (EAP)", RFC 4284, January 2006. [SP800-57] National Institute of Standards and Technology, "Recommendation for Key Management", Special Publication 800-57, May 2006. Acknowledgments Thanks to Terence Spies, Mudit Goel, Anthony Leibovitz and Narendra Gidwani of Microsoft, Glen Zorn and Joe Salowey of Cisco, and Pasi Eronen of Nokia for useful discussions of this problem space. Authors' Addresses Dan Simon Bernard Aboba Ryan Hurst Microsoft Corporation One Microsoft Way Redmond, WA 98052-6399 Phone: +1 425 882 8080 Fax: +1 425 936 7329 EMail: {dansimon,bernarda,rmh}@microsoft.com Simon, Aboba & Hurst Proposed Standard [Page 29]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 Appendix A - Changes from RFC 2716 This Appendix lists the major changes between [RFC2716] and this document. Minor changes, including style, grammar, spelling, and editorial changes are not mentioned here. o As EAP is now in use with a variety of lower layers, not just PPP for which it was first designed, mention of PPP is restricted to situations relating to PPP-specific behavior and reference is made to other lower layers such as IEEE 802.11, IEEE 802.16, etc. o The terminology section has been updated to reflect definitions from [RFC3748] (Section 1.2), and the EAP Key Management Framework [KEYFRAME] (Section 1.2). o Privacy is supported as an optional feature (Section 2.1.4). o It is no longer recommended that the identity presented in the EAP-Response/Identity be compared to the identity provided in the peer certificate (Section 2.2). o The EAP-TLS key hierarchy is defined, using terminology from [RFC3748]. This includes formulas for the computation of TEKs as well as the MSK, EMSK, IV and Session-Id (Section 2.3). o Mandatory and recommended TLS ciphersuites are provided. The use of TLS ciphersuite negotiation for determining the lower layer ciphersuite is prohibited (Section 2.4). o The Start bit is not set within an EAP-Response packet (Section 3.2). o A section on security claims has been added and advice on key strength is provided (Section 5.1). o The Peer-Id and Server-Id are defined (Section 5.2) and requirements for certificate validation (Section 5.3) and revocation (Section 5.4) are provided. o Packet modification attacks are described (Section 5.5). o The examples have been updated to reflect typical messages sent in the described scenarios. For example, where mutual authentication is performed, the EAP-TLS server is shown to request a client certificate and the client is shown to provide a certificate_verify message. A privacy example is provided, and two faulty examples of session resume failure were removed. Simon, Aboba & Hurst Proposed Standard [Page 30]
INTERNET-DRAFT EAP TLS Authentication Protocol 1 July 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Simon, Aboba & Hurst Proposed Standard [Page 31]
