Internet Engineering Task Force M. Badra INTERNET DRAFT P. Urien ENST Paris Expires: December 2006 June 15, 2006 EAP-Double-TLS Authentication Protocol Status 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 15, 2006. Copyright Notice Copyright (C) The Internet Society (2006). All Rights Reserved. 1 Abstract EAP-Double-TLS is an EAP protocol that extends EAP-TLS. In EAP-TLS, a full TLS handshake is used to mutually authenticate a peer and server and to share a secret key. EAP-Double-TLS extends this authentication negotiation by establishing a secure connection based on the use of Pre Shared Keys (PSK). The secure connection may then be used to allow the server and the peer to securely exchange their identity and to update security attributes for next sessions. EAP-Double-TLS allows the peer and the server to establish keying material for use in the data connection between the peer and the authenticator. The keying material is established implicitly between peer and server based on the TLS Pre-Shared-Key handshake. Badra & Urien Expires December 2006 [Page 1] Internet-Draft EAP-Double-TLS June 2006 It provides additional security services such as anonymous exchanges and identity protection against eavesdropping and the PFS (Perfect Forward Secrecy). Table of Contents 1 Abstract.........................................................1 2 Introduction.....................................................3 2.1 Requirements language.......................................4 3 Protocol design considerations and overview......................4 3.1 EAP identity protection.....................................4 3.2 Structure of the session identifier.........................4 3.3 Overview of the EAP-Double-TLS conversation.................5 3.3.1 Phase 1: Handshake....................................7 3.3.2 Phase 2...............................................8 3.3.2.1 Case 1: TLS Handshake...............................9 3.3.2.2 Case 2: AVP Exchanges...............................9 3.4. Retry behavior............................................10 3.5. Fragmentation.............................................10 3.6. Key derivation............................................10 3.7. CCP and CCP negotiation...................................11 3.8. Inner method encapsulation................................11 3.7. Examples.....................................................12 4 Detailed description of the EAP-Double-TLS protocol.............15 4.1 EAP-Double-TLS Packet Format...............................15 4.2 EAP-Double-TLS Request Packet..............................16 4.3 EAP-Double-TLS Response Packet.............................17 5 Security Considerations.........................................18 5.1 Security claims............................................18 5.1.1 Authentication, confidentiality, and Integrity. Replay, man in-the-middle and dictionary attack protection.18 5.1.2 Session independence or perfect forward secrecy....19 5.1.4 Key strength.......................................20 5.1.5 Channel binding....................................20 5.1.6 Fast reconnect.....................................20 7 IANA Considerations.............................................20 Acknowledgements..................................................20 References........................................................20 Author's Addresses................................................21 Appendix A. EAP-Double-TLS protocol within EAP Smartcards.........21 A.1 Fragmentation issues.......................................22 Badra & Urien Expires December 2006 [Page 2] Internet-Draft EAP-Double-TLS June 2006 2 Introduction The Extensible Authentication Protocol (EAP) [EAP] defines a mechanism that may be extended with additional authentication protocols within PPP [PPP] such as MD5 [MD5], TLS [TLS] and PEAP [PEAP]. The EAP-TLS authentication method, described in [EAPTLS], provides a standard method for mutual authentication and key generation. However, this method requires the use of certificates and Public Key Infrastructures (PKI) that MUST be well maintained. On the other hand, this protocol can not provide some security services, such as the supplicant's identity protection. TLS itself allows the peer and the server to resume secure sessions [TLS]. A secure connection may be terminated and resumed later. Secure sessions can be resumed if the peer and the server agree. During a resume Handshake, both the peer and the serve will use the old master_secret and the new random numbers to calculate new cryptographic keys. This will generate fewer cryptographic computations and less processing time than a full TLS handshake. In addition, it will save the bandwidth which is the bottleneck in the wireless networks. Shared-key handshake runs as a resume session using pre-installed secret key. A detailed description may be found in [SKTLS]. However, it may be an advantageous to use shared-key authentication handshake instead of PKI based certificates. Further, shared-key TLS does not require any asymmetric cryptographic operation (e.g. asymmetric encrypt/decrypt or certificates verification). EAP-Double-TLS is an EAP protocol that extends EAP-TLS. In EAP-TLS, a TLS handshake is used to mutually authenticate a peer and a server. EAP-Double-TLS extends this authentication negotiation; using the PSK authentication. EAP-Double-TLS is composed of two phases. The first phase is based on the use of PSKs to mutually authenticate the peer and the server and to generate cryptographic keys, as it is defined in [SKTLS]. The second phase is used to allow additional security services, such as identity protection. It allows also the peer and the server to update their security attributes for next sessions and then to ensure the PFS (Perfect Forward Secrecy). EAP-Double-TLS provides a mechanism for session key establishment for encryption protocols within PPP such as PPP-DES [PPPDES] and PPP-3DES [PPP3DES] protocols. Badra & Urien Expires December 2006 [Page 3] Internet-Draft EAP-Double-TLS June 2006 2.1 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 RFC-2119. 3 Protocol design considerations and overview 3.1 EAP identity protection At the beginning of an EAP session, EAP identity (EAP-ID) is transmitted in clear text, in the identity response message. This parameter is used by the authenticator to forward EAP packets to the authentication server which in turn uses it as an index for users' database management. In EAP-Double-TLS, EAP-ID SHOULD be replaced either by the TLS session_id value (see 3.2) or by the session_id concatenated to the authentication server address (session_id@server.com). This process will protect the user's privacy against surveillance and make the subscriber's EAP exchanges untraceable to eavesdroppers. In fact, the current session_id will be replaced by a new one computing or generating during phase 2 (see 3.2). 3.2 Structure of the session identifier According to TLS, the peer hello message includes a variable length session identifier. If not empty, the identifier identifies a TLS session already established between the peer and the authentication server. EAP-Double-TLS defines a new structure of the session identifier, used during the first phase. The structure is defined as follows: struct { opaque random_bytes<0..24>; SecondPhaseExchange second_phase_exchange<1..8>; } SessionID; SecondPhaseExchange None = { 0x00 }; SecondPhaseExchange TLS = { 0x01 }; SecondPhaseExchange TLS_RSA_anon = { 0x02 }; SecondPhaseExchange TLS_DH_anon = { 0x03 }; SecondPhaseExchange AVP = { 0x04 }; This new structure allows to the peer and to the server to negotiate the key exchange method during the second phase. These methods are sent by the peer, ordered according to its preference. There MUST be Badra & Urien Expires December 2006 [Page 4] Internet-Draft EAP-Double-TLS June 2006 at least one method acceptable to the server. This document defines five methods: None, TLS, TLS_RSA_anon, TLS_DH_anon and AVP. None refers to the option that means that the peer is satisfied by running TLS resumed handshake (phase 2 will then not be executed). TLS refers to the RFC2246 authentication based-certificate, TLS_RSA_anon and TLS_DH_anon refers respectively to unauthenticated (or ephemeral) RSA key exchange and Diffie_Hellman anonymous key exchange. These last three types allow both the peer and the server to generate new session_id and new master_secret. Concerning the attribute-value pairs (AVPs), it is used to allow the server to send back to the peer, a new master_secret and a new session_id. More details are given through the document. Note that TLS generates a variable length session identifier, which MAY be at maximum 32 bytes. EAP-Double-TLS implementation MUST then generate a variable length session identifier smaller than 24 bytes. 3.3 Overview of the EAP-Double-TLS conversation In order to apply the use of shared key TLS, this document suggests sharing a TLS session between the peer and the server. The session is identified by a 24-byte session_id. It corresponds to, among others, the value of the master_secret and the cipher_suite. The cipher_suite represents the cryptographic option supported by both the server and the peer and it is initialized by them to a particular option. In general, EAP-Double-TLS negotiation consists in two phases: During the first phase, Shared-key handshake is used for mutual authentication and key generation. This phase uses a cipher suite allowing phase 2 to securely exchange TLS records or AVP. peer Server ---- ------ ClientHello --------> (session_id) ServerHello ChangeCipherSpec <-------- Finished ChangeCipherSpec Finished --------> Figure 1: Phase 1, the Shared-key handshake The second phase MAY be a full TLS handshake with mutual authentication, only server-side authentication, or with anonymous key exchange. Nevertheless, it MAY be an exchange of AVPs. In this latter case, the server MUST generate a new (session_id, Badra & Urien Expires December 2006 [Page 5] Internet-Draft EAP-Double-TLS June 2006 master_secret) and send them to the peer, over a link encrypted with the cryptographic keys generated during the first phase (examples of exchanges are given in the section 3.7). peer server ---- ------ Tunnel TLS ................................... . +----------+ +----------+ . . | Handshake| | Handshake| . . | phase 2 | | phase 2 | . . +-----^----+ +----^-----+ . . | | . +---------+ . | | . +---------+ |Handshake| . | | . |Handshake| | phase 1 | . | | . | phase 1 | +----^----+ . | | . +----^----+ | . | | . | | . | | . | | . +----v----+ +----v----+ . | | . | Record | | Record | . | | . | phase 2 |<----->| phase 2 | . | | . +--^------+ +------^--+ . | | ......|.....................|...... | | | | | | +----+ +----+ | | | | | +-v-------v-+ +-v-------v-+ | Record | | Record | | phase 1 |<------------------------->| phase 1 | +-----^-----+ +-----^-----+ | | <=======================================> Carrier Protocol (PPP, EAPOL, RADIUS, etc) Figure 2- Relationship between the EAP-Double-TLS peer and the EAP- Double-TLS server, in the case of the use of TLS during the second phase. Badra & Urien Expires December 2006 [Page 6] Internet-Draft EAP-Double-TLS June 2006 peer server ---- ------ AVP exchange ................................ . +--------+ +--- ----+ . . | AVP | | AVP | . . |Phase 2 | |Phase 2 | . . +---^----+ +---^----+ . ......|................|........ +---------+ | | +---------+ |Handshake| | | |Handshake| | phase 1 | | | | phase 1 | +----^----+ | | +----^----+ | | | | | | | | | | | | +-v------------v---+ +-v-----------v---+ | Record (Phase 1)|<-------->| Record(Phase 1)| +-----^------------+ +-----^-----------+ | | <=============================> Carrier Protocol (PPP, EAPOL, RADIUS, etc) Figure 3- Relationship between the EAP-Double-TLS peer and the EAP- Double-TLS server, in the case of AVP exchange during the second phase. 3.3.1 Phase 1: Handshake In the first phase, the EAP-Double-TLS begins with the authenticator sending an EAP-Request/Identity packet to the peer. The peer will respond with an EAP-Response/Identity packet to the authenticator, containing the peer's UserId (User Identifier). Once this is established, the authenticator MAY act as a pass-through device, with the EAP packets received from the peer being encapsulated for transmission to a RADIUS server or back-end security server. When the server receives the peer's Identity, it MUST respond with an EAP-Double-TLS/Start packet. This is an EAP-Request packet with EAP-Type= EAP-Double-TLS, the Start (S) bit set and no data. When receiving this message, the peer will answer by EAP-Response packet with EAP-Type= EAP-Double-TLS. The data field encapsulates the TLS client_hello resumed handshake message. This message contains, among others parameters, a random number and the session_id corresponds to the TLS shared session the peer wishes to use. The session_id contains both the SessionID.random_bytes and SessionID.SecondPhaseExchange. Badra & Urien Expires December 2006 [Page 7] Internet-Draft EAP-Double-TLS June 2006 The server then checks its sessions' database for a match. If a match is found and that the server is able to negotiate one of the second_phase_exchange methods supported by the peer, the server replays with EAP-Request with an EAP-Type= EAP-Double-TLS. This packet will encapsulate the TLS server_hello handshake message. This message transports, among others, the same value of SessionID.random_bytes and another random number. The session_id includes the second_phase_exchange method selected by the server (SessionID.SecondPhaseExchange). After the hello messages, the server will send its TLS change cipher spec message and proceed directly to finished message. The finished message will serve to authenticate the server to the peer since it is encrypted and MACed using keys derived from the shared key. If the EAP server authenticates unsuccessfully, the peer MAY send an EAP-Response packet of EAP-Type= EAP-Double-TLS containing a TLS Alert message identifying the reason for the failed authentication. A fatal error message results in the immediate termination of the connection. In order to make sure that the server receives the TLS alert message, the peer MUST wait for the server to reply before terminating the conversation. Like in [EAPTLS], the server MUST reply with an EAP-Failure packet since server authentication failure is a terminal condition. If the EAP server authenticates successfully (the peer decrypts the finished message and verify the MAC), the peer MUST send an EAP- Response packet of EAP-Type= EAP-Double-TLS, that transports the change cipher spec and the finished messages. Once this establishment is complete, the peer and the server MAY start the second phase. Otherwise, the server will send data connection keying information and other authorization information to the authenticator. If the peer authenticates unsuccessfully, the server MAY send an EAP-Response packet of EAP-Type= EAP-Double-TLS containing a TLS Alert message identifying the reason for the failed authentication. Alert messages with a level of fatal result in the immediate termination of the connection. In order to make sure that the peer receives the TLS alert message, the server MUST wait for the peer to reply before terminating the conversation. 3.3.2 Phase 2 EAP-Double-TLS Phase 2 will occur if the establishment of its first phase is successfully terminated. Phase 2 is used to ensure Badra & Urien Expires December 2006 [Page 8] Internet-Draft EAP-Double-TLS June 2006 additional services such as peer identity protection and PFS. This phase MAY be established by executing a TLS session or by exchanging AVPs between the peer and the server. 3.3.2.1 Case 1: TLS Handshake During the second phase, the TLS Record layer is used to securely tunnel data related to the second phase. TLS session data will be encapsulated in sequences of TLS attributes, whose use and format are described in [TLS]. The peer starts the second phase by sending its hello. The ClientHello follows the Finished message sent by the peer during the first phase Next, the peer and the server continue to exchange EAP packets until either the TLS session is successfully established or an error occurs. If the session is successfully established, the peer MUST send an EAP-Response packet of EAP-Type= EAP-Double-TLS, and no data. The EAP-Server must then respond with an EAP-Success message. At this point, the server distributes data connection keying information and other authorization data to the authenticator, which are derived from the shared key that was used during the first phase. Next, the server and the peer replace the security parameters (e.g. the shared key and its identity) with the security parameters that are generated by TLS during the second phase. These new TLS security parameters will be then used during the next EAP-Double-TLS sessions. 3.3.2.2 Case 2: AVP Exchanges The second phase MAY be established using AVP exchanges, if the peer and the server agree. The AVP is securely tunneled between the client and server by TLS Record. This document defines the AVP Session-Id-Master-Secret (AVP Code TBS). The Data field is 48 or more octets and contains a new (session_id, master_secret) generated by the server. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Code (TBS) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AVP Length | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data = master_secret#session_id (# means concatenation) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Badra & Urien Expires December 2006 [Page 9] Internet-Draft EAP-Double-TLS June 2006 In this case of AVPs exchange, the server encodes a new 24-byte session_id (e.g. SessionID.random_bytes) and a new 48-byte master_secret, encapsulates them in the AVP Session-Id-Master- Secret, passes the result to the TLS record layer, and sends the resulting data to the peer. The peer recovers the AVP in clear text from the TLS record layer. If this is successfully established, the peer MUST send an EAP-Response packet of EAP-Type= EAP-Double-TLS, and no data. The EAP-Server must then respond with an EAP-Success message. At this point, the peer and the server update their shared master_secret and session_id with the new ones generated by the server and delivered to the peer. Next, the server distributes data connection keying information and other authorization data to the authenticator. 3.4. Retry behavior See section 3.2 of RFC 2716. 3.5. Fragmentation See section 3.3 of RFC 2716. 3.6. Key derivation EAP-Double-TLS derives keying material after each successful negotiation in each phase. The first phase allows the peer and the server to generate a 48-byte master_secret (MS1) by applying the TLS-PRF (Pseudo Random Function) [TLS] on the shared key (SK), ClientHello.random and ServerHello.random: MS1 = PRF(SK, "master_secret", ClientHello.random + ServerHello.random)[0..48] This key is used to derive keying material used to encrypt and to calculate the MAC of each message. Keys derived from MS1 are then delivered to the authenticator for additional keys computation. When TLS is selected as second_key_exchange, the peer and the server will exchange new random values. The peer is also able to randomly generate a secret key (the pre_master_secret in TLS terminology). This key is sent securely to the server using the server public key and it is used to generate a new and fresh master_secret key (FMS) by applying the PRF on, among others, the pre_master_secret (PMS). The generated key will be then used during the future EAP-Double-TLS session. FMS = PRF(PMS, "master_secret", ClientHello.random + ServerHello.random) [0..48] Badra & Urien Expires December 2006 [Page 10] Internet-Draft EAP-Double-TLS June 2006 When AVP is selected as second_key_exchange, both the peer and the server will replace the old master_secret and the old session_id with the new ones that are generated by the server and delivered to the peer. Note: the client and the server can derive and compute the required keys (e.g. MSK, EMSK, etc.) by applying the TLS-PRF on the MS1 and the random values of the first phase. PRF's P_hash can be iterated as many times as is necessary to produce the required key length (e.g., OutputKey = PRF(MS1, "output_key", ClientHello.random + ServerHello.random) [OutputLength]) 3.7. CCP and CCP negotiation See section 3.6 and 3.7 of RFC 2716. 3.8. Inner method encapsulation As stated before, EAP-Double-TLS uses the TLS record layer to tunnel information between the peer and the server to, among others operations perform additional authentication. In this optic, EAP- Double-TLS reuses the attribute-value pairs (AVPs) defined in [EAPTTLS]. Badra & Urien Expires December 2006 [Page 11] Internet-Draft EAP-Double-TLS June 2006 3.7. Examples The following exchanges show where TLS is selected as second_key_exchange: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/Identity EAP-Response/Identity -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (EAP-Double-TLS Start) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS server_hello, TLS change_cipher_spec, TLS finished) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS change_cipher_spec, TLS finished TLS client_hello) -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS server_hello, [TLS certificate], [TLS server_key_exchange], [TLS certificate_request], TLS server_hello_done) EAP-Response/ EAP-Type= EAP-Double-TLS ([TLS certificate], TLS client_key_exchange, [TLS certificate_verify], TLS change_cipher_spec, TLS finished) -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS change_cipher_spec, TLS finished) EAP-Response/ EAP-Type= EAP-Double-TLS -> <- EAP-Success Badra & Urien Expires December 2006 [Page 12] Internet-Draft EAP-Double-TLS June 2006 The following exchanges show where AVP is selected as second_key_exchange: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/Identity EAP-Response/Identity -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (EAP-Double-TLS Start) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS server_hello, TLS change_cipher_spec, TLS finished) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS change_cipher_spec, TLS finished) -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (AVP [session_id, master_secret]) EAP-Response/ EAP-Type= EAP-Double-TLS -> <- EAP-Success The following exchanges show where TLS is selected as second_key_exchange and fragmentation is required (during the phase 1, no fragmentation is required), the conversation (during the phase 2) will be as follows: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS Hello Request, S bit set) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS server_hello, TLS change_cipher_spec, TLS finished) (Fragment 1: L, M bits set) Badra & Urien Expires December 2006 [Page 13] Internet-Draft EAP-Double-TLS June 2006 EAP-Response/ EAP-Type= EAP-Double-TLS -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (Fragment 2: M bits set) EAP-Response/ EAP-Type= EAP-Double-TLS -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (Fragment 3) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS change_cipher_spec, TLS finished)(Fragment 1: L, M bits set)-> <- EAP-Success During the phase 1 and in the case where the server authenticates to the peer successfully, but the peer fails to authenticate to the server, the conversation will be as follows: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/Identity EAP-Response/Identity -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS Start) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS client_hello)-> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS server_hello, TLS change_cipher_spec TLS finished) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS change_cipher_spec, TLS finished) -> <- EAP-Request EAP-Type= EAP-Double-TLS (TLS Alert message) EAP-Response/ EAP-Type= EAP-Double-TLS -> <- EAP-Failure (User Disconnected) Badra & Urien Expires December 2006 [Page 14] Internet-Draft EAP-Double-TLS June 2006 During the phase 1 and in the case where server authentication is unsuccessful, the conversation will be as follows: Authenticating Peer Authenticator ------------------- ------------- <- EAP-Request/Identity EAP-Response/Identity -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS Start) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS client_hello) -> <- EAP-Request/ EAP-Type= EAP-Double-TLS (TLS server_hello, TLS change_cipher_spec, TLS finished) EAP-Response/ EAP-Type= EAP-Double-TLS (TLS Alert message) -> <- EAP-Failure (User Disconnected) 4 Detailed description of the EAP-Double-TLS protocol This section shows the conversation between the peer and the authenticator using EAP-Double-TLS protocol. It takes the same notifications introduced in the section 4 of RFC2716 [EAPTLS]. 4.1 EAP-Double-TLS Packet Format A summary of the EAP-Double-TLS Request/Response packet format is shown below. The fields are transmitted from left to right. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Request | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Data... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The description of the EAP/Response/identity is detailed according to the IETF RFC 2284. Badra & Urien Expires December 2006 [Page 15] Internet-Draft EAP-Double-TLS June 2006 4.2 EAP-Double-TLS Request Packet A summary of the EAP-Double-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=01 | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Flag | EAP-Double-TLS Message Length +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | EAP-Double-TLS Message Length | EAP-Double-TLS Data... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Code 1 Identifier The Identifier field is one octet and aids in matching responses with requests. The Identifier field MUST be changed on each Request packet. Length The Length field is two octets and indicates the length of the EAP packet including the Code, Identifier, Length, Type, and Double-TLS Response fields. Type TBD - EAP Double TLS Flags 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L M S R R R R R| +-+-+-+-+-+-+-+-+ L = Length included M = More fragments S = EAP-Double-TLS start R = Reserved The L bit (length included) is set to indicate the presence of the four octet Double-TLS Message Length field, and MUST be set for the first fragment of a fragmented EAP-Double-TLS message or set of Badra & Urien Expires December 2006 [Page 16] Internet-Draft EAP-Double-TLS June 2006 messages. The M bit (more fragments) is set on all but the last fragment. The S Bit (EAP-Double-TLS start) is set in an EAP-Double- TLS Start message. This differentiates the EAP-Double-TLS Start message from a fragment acknowledgement. Double-TLS Message Length The Double-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 Double-TLS message or set of messages that is being fragmented. Double-TLS data The Double-TLS data consists of the encapsulated Double-TLS packet in TLS record format. 4.3 EAP-Double-TLS Response Packet A summary of the EAP-Double-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=01 | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Flag | EAP-Double-TLS Message Length +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | EAP-Double-TLS Message Length | EAP-Double-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 Double-TLS Response fields. Type TBD - EAP Double TLS Badra & Urien Expires December 2006 [Page 17] Internet-Draft EAP-Double-TLS June 2006 Flags 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L M S R R R R R| +-+-+-+-+-+-+-+-+ L = Length included M = More fragments S = EAP-Double-TLS start R = Reserved The L bit (length included) is set to indicate the presence of the four octet Double-TLS Message Length field, and MUST be set for the first fragment of a fragmented EAP-Double-TLS message or set of messages. The M bit (more fragments) is set on all but the last fragment. The S Bit (EAP-Double-TLS start) is set in an EAP-Double- TLS Start message. This differentiates the EAP-Double-TLS Start message from a fragment acknowledgement. Double-TLS Message Length The Double-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 Double-TLS message or set of messages that is being fragmented. Double-TLS data The Double-TLS data consists of the encapsulated Double-TLS packet in TLS record format. 5 Security Considerations The EAP-Double-TLS server MUST stock the TLS session in a secure and protected manner in order to prevent attackers from retrieving the master_secret values and session' parameters. 5.1 Security claims This section describes EAP-Double-TLS in terms of specific security terminology as required by [EAP]. 5.1.1 Authentication, confidentiality, and Integrity. Replay, man in-the-middle and dictionary attack protection EAP-Double-TLS provides mutual authentication using the shared key during the first phase. EAP-Double-TLS mitigates man-in-the-middle vulnerabilities because of the mutual authentication established during the first phase. The confidentiality and integrity are provided using the negotiated cryptographic algorithms as well as Badra & Urien Expires December 2006 [Page 18] Internet-Draft EAP-Double-TLS June 2006 encryption and authentication keys derived from the shared key. Furthermore and during the second phase, messages notification (failure or success) are also protected against man-in-the-middle and eavesdropping attacks. This is because they are encrypted with the tunnel established during the first phase. On the other hand and like TLS, EAP-Double-TLS natively protects against replay protection attacks using sequence numbers. The use of sequence numbers and of strong cryptographic algorithms (e.g., AES) defends the protocol against dictionary attacks. 5.1.2 Session independence or perfect forward secrecy EAP-Double-TLS protocol independently generates keys per session and it MAY uses ephemeral public/private keys during its second phase. As a result, it provides Perfect Forward Secrecy (i.e. ephemeral Deffie-Hellman and RSA public keys are both supported by EAP-Double- TLS as key exchange methods in the case where TLS is selected as second_phase_exchange). Added to that, passive attacks (such as capture of the EAP conversation) or active attacks (including the recovery of the shared key) do not entail the compromising of prior shared keys and are thus incapable of decrypting previous sessions. In the case of AVP, the PFS is provided, by generating new secret key which is independent to any old secret. 5.1.3 Protected cipher suite negotiation and user identity protection EAP-Double-TLS ensures cipher suite negotiation in a protected manner. In fact, it uses the same TLS principle that offers an integrated mechanism to protect cipher suite negotiation. This is because at the end of the first phase, the peer and server exchange the finished messages. These messages are always sent immediately after a change cipher spec message to verify that the key exchange and authentication processes were successful. They are the first messages protected with the just-negotiated algorithms and the secret key, and it is computed in function of, among others, all handshake messages data, including the negotiated cipher suite. Concerning the identity protection and as we cited above, the shared key and its identity are replaced with new values if the second phase of EAP-Double-TLS is successfully terminated. This process will protect the user's privacy and identity against surveillance and make the subscriber's EAP exchanges untraceable to eavesdroppers. In fact, the EAP-ID value used at the beginning and the session_id used during the first phase will be replaced by a new session_id securely computing and generating during the EAP-Double- TLS second phase. Badra & Urien Expires December 2006 [Page 19] Internet-Draft EAP-Double-TLS June 2006 5.1.4 Key strength EAP-Double-TLS reuses the TLS-PRF for keys generation (See [TLS]). 5.1.5 Channel binding EAP-Double-TLS does not explicitly include any channel binding. 5.1.6 Fast reconnect Due to the nature of wireless connections, the peer MAY be disconnected at any time. Fortunately, the EAP-Double-TLS peer and the server don't have to go through the entire process every time they want to communicate. While EAP-Double-TLS is based on TLS, fast reconnection option is implicitly included; executing TLS resumed Handshake (as described in phase 1). 7 IANA Considerations This document requires IANA to allocate a new EAP Type for EAP- Double-TLS, new AVP Code for Session-Id-Master-Secret AVP and for values related to the SecondPhaseExchange. Acknowledgements This EAP method has been inspired by [EAPTLS] and [TLS]. Thus, it reused extracts of these documents. References [TLS] Dierks, T., et. al, "The TLS Protocol Version 1.0", RFC 2246, November 1998. [SKTLS] Gutmann, P., "Use of Shared Keys in the TLS Protocol", draft-ietf-tls-sharedkeys-02 (expired), October 2003. [PPP] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, July 1994. [EAPTLS] Aboba, B., and D., Simon, "PPP EAP TLS Authentication Protocol", RFC 2716, October 1999. [MD5] Rivest, R., and S., Dusse, "The MD5 Message-Digest Algorithm", RFC 1321, April 1992. [EAP] Aboba, B., et. al., "PPP Extensible Authentication Protocol EAP)", RFC 3748, June 2004. [PPPDES] Sklower, K., and G., Meyer, "The PPP DES Encryption Protocol, Version 2 (DESE-bis)", RFC 2419, September Badra & Urien Expires December 2006 [Page 20] Internet-Draft EAP-Double-TLS June 2006 1998. [PPP3DES] Hummert, K., "The PPP Triple-DES Encryption Protocol (3DESE)", RFC 2420, September 1998. [EAPTTLS] Funk, P., et. al., "EAP Tunneled TLS Authentication Protocol (EAP-TTLS)" draft-ietf-pppext-eap-ttls-05.txt, Internet draft (work in progress), August 2004. [PEAP] TBC [EAPSC] Urien, P., et. al., "EAP support in smartcards", draft-urien-eap-smartcard-08.txt, Internet draft (work in progress), July 2005. [GSM] GSM Technical Specification GSM 11.11. Digital cellular telecommunications system (Phase 2+); Specification of the Subscriber Identity Module - Mobile Equipment (SIM – ME) interface, Version 5.0.0, December 1995. [802.11] IEEE Std. 802.11, IEEE Standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications, 1997. [ISOAPDU] ISO 7816-4 SmartCard Standard: Part 4: Inter industry Commands for Interchange, 1995. Author's Addresses Mohamad Badra ENST 46 rue Barrault 75634 Paris Phone: NA France Email: Mohamad.Badra@enst.fr Pascal Urien ENST 46 rue Barrault 75634 Paris Phone: NA France Email: Pascal.Urien@enst.fr Appendix A. EAP-Double-TLS protocol within EAP Smartcards EAP-support in smartcards is described and detailed by an Internet draft [EAPSC]. It is an opened, ISO 7816 microcontroller supporting most authentication protocols. An EAP smartcard implements an EAP method (EAP-TLS, etc) and works in cooperation with a smartcard Badra & Urien Expires December 2006 [Page 21] Internet-Draft EAP-Double-TLS June 2006 interface entity, which transparently sends and receives EAP messages to and from this component. Smartcard is one of the news technologies added to the world of information technology. In fact, they can make significant impact on current computer systems and network environments because of their inherent security and mobility. Further, they are an effective means of adding enhanced protection to wireless networks; namely 802.11 wireless LAN. Added to that, they are widely used in the Global System for Mobile Communication (GSM) [GSM] in the form of a SIM (Subscriber Identity Module) card for secure access to the mobile network, for storing basic network information and for accounting/billing procedures. Smartcards have a bear particular attraction, as they generally considered as the most secure computing platform. In fact, they offer good tamper resistance. This means that certain physical hardware and software protections are used, which makes it difficult to extract or modify private and secret information in the module. So it seems a good idea to store the (strong) master_secret keys on a smartcard. Further, smartcard deployment in a typical network such as WLAN 802.11 [802.11] offers the enhanced functionality of tighter authentication. A.1 Fragmentation issues Data is exchanged between the terminal and the smartcard through a card acceptance device (CAD) in the form of messages exchanged from the terminal to the card and vice versa. Data transport is established by using Data Pocket called Application Protocol Data Unit (APDU). Each APDU consists of two fields: 5 bytes header and 0- 255 bytes of data. The ISO [ISOAPDU] standard defines these command/response packets that are used for reading, writing and exchanging data between the host and the smartcard. These packets transferred from the CAD to the module (command APDU) are followed by a response APDU from the module back to the CAD. The TLS Record Layer fragments information blocks into TLS records carrying data in chunks of 16384 bytes or less [TLS]. Furthermore, TLS message may carry multiple TLS records. Since the IEEE 802.3 MAC may not send frames greater than 1518 bytes in length and because fragmentation support is not provided by EAP, it is the responsibility of EAP methods to provide the fragmentation required. For that, EAP-Double-TLS extends the EAP-TLS segmentation method, which defines a segmentation process that splits TLS messages in smaller blocks, acknowledged by the recipient. In this context, the RADIUS server generates acknowledged requests and the supplicant answers by acknowledged responses. Badra & Urien Expires December 2006 [Page 22] Internet-Draft EAP-Double-TLS June 2006 EAP-TLS defines the fragmentation mechanism for data exchanged between the server and the terminal. It will not define the data segmentation between the terminal and the smartcard because the latter is not readable to the EAP-TLS server. For that and in order to allow smartcards use, a double segmentation mechanism was introduces by EAP-Double-TLS to forward TLS packets to the smartcard. We defined this mechanism as following. First, TLS server messages are divided in smaller segments (E1, E2), whose size is typically 1400 bytes or less (figure 3). Next, the segments are encapsulated in EAP-Double-TLS packets that are split in a collection of APDUs (A11 .. A1p .. An1 .. Anq) in the form of ISO7816 commands. Afterwards, the APDUs (each APDUs size is around 240 bytes) are forwarded to the EAP-Double-TLS smartcard. Note that for each APDU received by the smartcard, an APDU response, with 2 bytes of data, is generated to inform the supplicant of the APDUs status (if the APDU was arrived and correctly processed or no). EAP-Double-TLS Supplicant Authentication Smartcard Smartcard interface server +---------------------+ +-------------+ +--------------+ | | | | | | TLS EAP-Double-TLS EAP-Double-TLS TLS ----- --------- --------- ----- Send: TLS message M1 = E1 .. En EAP-Double-TLS: E1 <= 1400 octets <-- Frag E1 = A11 .. A1p <-- APDU : Frag A11 (<= 240 octets) APDU --> Ack A11 . . . . <-- APDU : Frag A1p (<= 240 octets) APDU --> Ack A1p Ack E1 --> . . . . EAP-Double-TLS: En <= 1400 octets <-- Frag En = An1 .. Alq <-- APDU : Frag An1 (<= 240 octets) APDU --> Ack Ap1 . . . Badra & Urien Expires December 2006 [Page 23] Internet-Draft EAP-Double-TLS June 2006 . <-- APDU : Frag Anq (<= 240 octets) <---- Receive: TLS message M1 Send: TLS message M2= F1 .. Fk = A1 .. Ak EAP-Double-TLS: F1 (<= 240 octets) --> <-- EAP-TLS . Ack F1 . . . . reassembly M2 fragments and send the result using packets of 1400 octets or less --> . <-- EAP-TLS . Ack EAP-Double-TLS: Fi (<= 240 octets) --> <-- EAP-TLS . Ack Fi . EAP-Double-TLS: Fk . (<= 240 octets) --> . . <-- EAP-TLS . Ack Fk --> Receive: TLS message M2 Figure 3 - Smartcard double segmentation using EAP-Double-TLS Authentication Protocol However, for the smartcard part and in order to prevent multiple segmentation and re-assembly operations, the maximum EAP message length of a no fragmented packet SHALL be set to 240 bytes. For a fragmented EAP message, the maximum length value shall be 240 bytes. As defined in EAP-TLS, when the EAP-Double-TLS smartcard 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. Badra & Urien Expires December 2006 [Page 24] Internet-Draft EAP-Double-TLS June 2006 Intellectual Property Statement 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 IETF's procedures with respect to rights in IETF 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. Disclaimer of Validity 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 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. Copyright Statement Copyright (C) The Internet Society (2006). 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Badra & Urien Expires December 2006 [Page 25]