Network Working Group Li Zhiming (editor) Internet Draft Huawei Nora Dabbous Gemplus JunHyuk Song Samsung Electronics Jian Wang DMT Expires: 15 October, 2004 15 April, 2004 EAP CAVE Authentication draft-lizhiming-pppext-eap-cave-00.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 10 of RFC2026. 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. Comments should be submitted to the eap@frascone.com mailing list. Distribution of this memo is unlimited. Abstract This document specifies an Extensible Authentication Protocol (EAP) mechanism for authentication and session key distribution using the cdma Universal Identity Module (UIM). The mechanism includes network authentication, user anonymity support and a re-authentication procedure. Lizhiming [Page 1] Internet Draft EAP CAVE Authentication 15 April, 2004 Table of Contents Status of this Memo.........................................1 Abstract....................................................1 Table of Contents...........................................2 1. Introduction.............................................3 2. Terms....................................................4 3. Overview.................................................6 4. Operation................................................8 4.1. Version Negotiation....................................8 4.2. Identity Management....................................9 4.3. Re-Authentication.....................................26 4.4. EAP/CAVE SSD Update...................................30 4.5. EAP/CAVE Notifications................................32 4.6. Error Cases...........................................33 4.7. Key Generation........................................35 5. Message Format and Protocol Extensibility...............38 5.1. Message Format........................................38 5.2. Protocol Extensibility................................39 6. Messages................................................39 6.1. EAP-Request/UIM/Start.................................40 6.2. EAP-Response/UIM/Start................................40 6.3. EAP-Request/UIM/Challenge.............................41 6.4. EAP-Response/UIM/Challenge............................41 6.5. EAP-Request/UIM/Re-authentication.....................42 6.6. EAP-Response/UIM/Re-authentication....................42 6.7. EAP-Request/UIM/Update................................42 6.8. EAP-Response/UIM/Update-server-challenge..............42 6.9. EAP-Request/UIM/Update-server-challenge...............43 6.10. EAP-Response/UIM/Update-client-success...............43 6.11. EAP-Request/UIM/Update-challenge.....................43 6.12. EAP-Response/UIM/Update-challenge....................43 6.13. EAP-Response/UIM/Client-Error........................44 6.14. EAP-Request/UIM/Notification.........................44 6.15. EAP-Response/UIM/Notification........................44 7. Attributes..............................................44 7.1. Table of Attributes...................................45 7.2. AT_MAC................................................46 7.3. AT_IV, AT_ENCR_DATA and AT_PADDING....................47 7.4. AT_VERSION_LIST.......................................49 7.5. AT_SELECTED_VERSION...................................50 7.6. AT_NONCE_MT...........................................50 7.7. AT_PERMANENT_ID_REQ...................................51 7.8. AT_ANY_ID_REQ.........................................51 7.9. AT_FULLAUTH_ID_REQ....................................51 7.10. AT_IDENTITY..........................................52 7.11. AT_RAND..............................................52 7.12. AT_NEXT_REAUTH_ID....................................53 7.13. AT_RANDU.............................................53 7.14. AT_RANDBS............................................54 Lizhiming [Page 2] Internet Draft EAP CAVE Authentication 15 April, 2004 7.15. AT_RANDSSD...........................................54 7.16. AT_NOTIFICATION......................................54 7.17. AT_CLIENT_ERROR_CODE.................................55 7.18. AT_SSD_UPDATE_SUCCESS................................55 7.19. AT_ESN...............................................56 7.20. AT_AUTHR.............................................56 8. IANA Considerations.....................................56 9. Security Considerations.................................58 9.1. Identity Protection...................................58 9.2. Mutual Authentication.................................58 9.3. Key Derivation........................................59 9.4. Dictionary Attacks....................................59 9.5. Credentials Reuse.....................................59 9.6. Integrity and Replay Protection, and Confidentiality..60 9.7. Negotiation Attacks...................................60 9.8. Fast Reconnect........................................61 9.9. Acknowledged Result Indications.......................61 9.10. Man-in-the-middle Attacks............................61 9.11. Generating Random Numbers............................62 10. Security Claims........................................62 11. Acknowledgements and Contributions.....................63 11.1. Contributors.........................................63 11.2. Acknowledgements.....................................63 Normative References.......................................63 Informative References.....................................64 Editors' and Contributors' Contact Information.............64 Annex A. Pseudo-Random Number Generator....................65 1. Introduction This document specifies an Extensible Authentication Protocol (EAP) [EAP] mechanism for authentication and session key distribution using the cdma Universal Identity Module (UIM). CDMA uses the standardized CAVE (Cellular Authentication and Voice Encryption) algorithm to generate a 128-bits sub-key called the "Shared Secret Data" (SSD). The A-Key, the ESN(Electronic Serial Number) and the network-supplied RANDSSD are the inputs to the CAVE that generates SSD. The SSD has two parts: SSD_A (64 bits), for creating authentication signatures and SSD_B (64 bits), for generating keys to encrypt voice and signaling messages.In cdma, authentication is based on a challenge-response mechanism. The UIM runs CAVE algorithm, which takes the RANDU(24bits) or RAND(32bits), the ESN(32bits) ,MIN(34bits) and SSD-A as input, and produces a response AUTHU(24bits) or AUTHR(24bits).The UIM uses the SSD_B and the CAVE algorithm to generate a Cellular Message Encryption Algorithm (CMEA) key (64 bits). The CMEA key is used to encrypt of signaling messages sent over the air and to decrypt the information received. In this protocol, CMEA key is used for deriving keying material and not directly used. Please find more information about cdma authentication in [3GPP2 S.S0053]. Lizhiming [Page 3] Internet Draft EAP CAVE Authentication 15 April, 2004 The lack of mutual authentication is a weakness in cdma authentication. In EAP/CAVE the client issues a random number NONCE_MT to the network, in order to contribute to key derivation, and to prevent replays of EAP/CAVE requests from previous exchanges. The NONCE_MT can be conceived as the client's challenge to the network. EAP/CAVE also extends the RAND or RANDU challenges and other messages with a message authentication code in order to provide message integrity protection along with mutual authentication. EAP/CAVE specifies optional support for protecting the privacy of subscriber identity using the same concept as cdma, which is using pseudonyms/temporary identifiers. The security of EAP/CAVE builds on underlying cdma mechanisms. The security properties of EAP/CAVE are documented in Section 9 of this document.Implementers and users of EAP/CAVE are advised to carefully study the security considerations in Section 9 in order to determine whether the security properties are sufficient for the environment in question, especially as the secrecy of CEMA keys is key to the security of EAP/CAVE. In brief, EAP/CAVE is in no sense weaker than the cdma mechanisms. In some cases EAP/CAVE provides better security properties than the underlying cdma mechanisms, particularly if the UIM credentials are only used for EAP/CAVE and not re-used from cdma. Many of the security features of EAP_CAVE rely upon the secrecy of the CMEA values, so protecting this values is key to the security of the EAP-CAVE protocol. In any case, if the cdma authentication mechanisms are considered to be sufficient for use on the cellular networks, then EAP/CAVE is expected to be sufficiently secure for other networks. 2. Terms 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]. The terms and abbreviations "authenticator", "backend authentication server", "EAP server", "Silently Discard", "Master Session Key (MSK)", and "Extended Master Session Key (EMSK)" in this document are to be interpreted as described in [EAP]. This document frequently uses the following terms and abbreviations: AAA protocol Authentication, Authorization and Accounting protocol AC Authentication Centre. The cdma network element that manages the authentication information related to the subscriber. Lizhiming [Page 4] Internet Draft EAP CAVE Authentication 15 April, 2004 A-Key A 64-bit cryptographic key stored in the mobile station and AC, it is used to generate or update the mobiel station's SSD. AUTHBS Authentication response of the RANDBS challenge from the AC,which together with the RANDSSD authenticates the network to the peer, 24bits. AUTHR Authentication response of the global challenge from the peer, which together with the RANDU authenticates the peer to the server, 24bits. AUTHU Authentication response of the unique challenge from the peer, which together with the RAND authenticates the peer to the server, 24bits. cdma Code Division Multiple Access. CAVE Cellular Message Encryption Algorithm used in the cdma system. EAP Extensible Authentication Protocol. ESN A 32-bit number assigned by the mobile station manufacturer, uniquely identifying the mobile station equipment. IMSI International Mobile Subscriber Identifier, used in cdma to identify subscribers. MAC Message Authentication Code NAI Network Access Identifier Permanent Identity The permanent identity of the peer,including an NAI realm portion in environments where a realm is used. The permanent identity is usually based on the IMSI. Used on full authentication only. Lizhiming [Page 5] Internet Draft EAP CAVE Authentication 15 April, 2004 Permanent Username The username portion of permanent identity, ie. not including any realm portions. Pseudonym Identity A pseudonym identity of the peer, including an NAI realm portion in environments where a real is used. Used on full authentication only. Pseudonym Username The username portion of pseudonym identity, ie. not including any realm portions. RAND Random number generated by the AC or EAP server, 32 bits. RANDBS Random number generated by the peer for network authentication in SSD update procedure, 32 bits. RANDSSD Random number generated by the AC for updating SSD currently stored at the peer and the AC, 56 bits. RANDU Random number generated by the EAP server for unique challenge, 24 bits. SSD Shared Secret Data consists of SSD_A and SSD_B,128bits. SSD_A Shared Secret Data_A used for authentication response calculation, 64bits. SSD_B Shared Secret Data_B used for encryption information derivation, 64bits. UIM Universal Identity Module. The UIM is an application traditionally resident on smart cards distributed by cdma operators. 3. Overview Figure 1 shows an overview of the EAP/CAVE full authentication procedure. The authenticator typically communicates with an EAP server that is located on a backend authentication server using an Lizhiming [Page 6] Internet Draft EAP CAVE Authentication 15 April, 2004 AAA protocol. The AAA communications is not shown in the figure. The first EAP Request issued by the network is EAP-Request/Identity. On full authentication, the peer's response includes either the user's International Mobile Subscriber Identity (IMSI) or a temporary identity (pseudonym) if identity privacy is in effect, as specified in Section 4.2. Following the peer's EAP-Response/Identity packet, the peer receives EAP Requests of type xx (UIM) from the EAP server and sends the corresponding EAP Responses. The EAP packets that are of the Type UIM also have a Subtype field. On full authentication, the first EAP-Request/UIM packet is of the Subtype xx(Start). EAP CAVE packets encapsulate parameters in attributes, encoded in a Type, Length, Value format. The packet format and the use of attributes are specified in Section 5. The EAP-Request/UIM/Start packet contains the list of EAP/UIM version supported by the EAP server in the AT_VERSION_LIST attribute. This packet may also include attributes for requesting the subscriber identity, as specified in Section 4.2. The peer responds to EAP-Request/UIM/Start with the EAP- Response/UIM/Start packet, which includes the AT_NONCE_MT attribute that contains a random number NONCE_MT, chosen by the peer, the AT_SELECTED_VERSION attribute that contains the version number selected by the peer, and the AT_ESN attribute that contains the ESN of the peer. The version negotiation is protected by including the version list and the selected version in the calculation of keying material (Section 4.7). After receiving the EAP Response/UIM/Start, the EAP server stores the ESN value and determins which kind of challenge will be used for full authentication. If global chanllenge is slected, the EAP server generates a fresh random number RAND. If unique challenge is selected, the EAP server interacts with AC to get authentication vector including RANDU and AUTHU. The next EAP Request the EAP Server issues is of the type UIM and subtype Challenge (11). It contains the RAND or RANDU challenges and a message authentication code attribute AT_MAC to cover the challenges. On receipt of the EAP-Request/UIM/Challenge message, the peer runs the cave algorithm and calculates a copy of the message authentication code. The peer then verifies that the calculated MAC equals the received MAC. If the MAC's do not match, then the peer sends the EAP-Response/UIM/Client-Error packet and the authentication exchange terminates. Since the RAND or RANDU given to a peer are accompanied with the message authentication code AT_MAC, and since the peer's NONCE_MT value contributes to AT_MAC, the peer is able to verify that the Lizhiming [Page 7] Internet Draft EAP CAVE Authentication 15 April, 2004 EAP CAVE message is fresh (not a replay). If all checks out, the peer responds with the EAP- Response/UIM/Challenge. If the peer receives the AT_RAND attribute, the EAP-Response/UIM/Challenge contains the AT_MAC attribute and AT_AUTHR attribute. If the peer receive the AT_RANDU attribute, the EAP-Response/UIM/Challenge contains the AT_MAC attribute that covers the peer's AUTHU response values (Section 6.4). On receipt of the EAP-Response/UIM/Challenge message,The EAP server verifies the MAC. If unique challenge is used, the EAP server can get authentication result directly through check the MAC. If global challenge is used, the EAP server gets AUTHR value from the EAP- Response/UIM/Challenge message. The EAP server sends random number RAND and response AUTHR to the AC for verification of the subscriber, and obtain authentication result and encryption informaiton(including CMEA key) and SSD information from the AC. From the encryption information and SSD information, the EAP server derives the keying material, as specified in Section 4.7. If authenticatin is successful, the EAP server sends the EAP-Success packet, indicating that the authentication was successful.If authentication fails, the EAP server may notify the AC the failure of authentication, the AC may initates a SSD update procedure when the AC determins to execute SSD update procedure. If authentication successes, the EAP server may notify the AC the authentication result and get SSD information from the AC. Lizhiming [Page 8] Internet Draft EAP CAVE Authentication 15 April, 2004 Peer Authenticator | | | EAP-Request/Identity | |<---------------------------------------------------------| | EAP-Response/Identity | |--------------------------------------------------------->| | EAP-Request/UIM/Start | | (AT_VERSION_LIST) | |<---------------------------------------------------------| | EAP-Response/UIM/Start | | (AT_NONCE_MT, AT_SELECTED_VERSION, AT_ESN) | |--------------------------------------------------------->| | EAP-Request/UIM/Challenge | | (AT_RAND or AT_RANDU, AT_MAC) | |<---------------------------------------------------------| | | +-------------------------------------+ | | Peer runs CAVE algorithms, | | | verifies AT_MAC, derives | | | AUTHR or AUTHU and session keys | | +-------------------------------------+ | | | | EAP-Response/UIM/Challenge | | (AT_MAC, AUTHR) | |--------------------------------------------------------->| | +-------------------------------------+ | | Server checks the response | | | and MAC, if success, derives | | | session keys | | +-------------------------------------+ | EAP-Success | |<---------------------------------------------------------| | | Figure 1 EAP/CAVE full authentication procedure EAP CAVE also includes a separate re-authentication procedure. which use the Shared Secret Data shared in the server. Re-authentication is based on keys derived on full authentication. If the peer has maintained state information for re-authentication and wants to use re-authentication, then the peer indicates this by using a specific re-authentication identity instead of the permanent identity or a pseudonym identity. The re-authentication procedure is described in Section 4.3. EAP CAVE also includes a separate update procedure, which handle the asynchronous SSD between the peer and the AC. When the AC determins that the SSD currently stored at the peer should be update,the EAP server executes SSD update procedure as described in section 4.4. Lizhiming [Page 9] Internet Draft EAP CAVE Authentication 15 April, 2004 4. Operation 4.1. Version Negotiation EAP/CAVE includes version negotiation so as to allow future developments in the protocol. The version negotiation is performed on full authentication and it uses two attributes, AT_VERSION_LIST, which the server always includes in EAP-Request/UIM/Start, and AT_SELECTED_VERSION, which the peer includes in EAP- Response/UIM/Start on full authentication. AT_VERSION_LIST includes the EAP/UIM versions supported by the server. If AT_VERSION_LIST does not include a version that is implemented by the peer and allowed in the peer's security policy, then the peer MUST send the EAP-Response/UIM/Client-Error packet (Section 6.13) to the server with the error code "unsupported version". If a suitable version is included, then the peer includes the AT_SELECTED_VERSION attribute, containing the selected version, in the EAP-Response/UIM/Start packet. The peer MUST only indicate a version that is included in AT_VERSION_LIST. If several versions are acceptable, then the peer SHOULD choose the version that occurs first in the version list. The version number list of AT_VERSION_LIST and the selected version of AT_SELECTED_VERSION are included in the key derivation procedure (Section 4.7). If an attacker modifies either one of these attributes, then the peer and the server derive different keying material. Because K_aut keys are different, the server and peer calculate different AT_MAC values. Hence, the peer detects that AT_MAC included in EAP-Request/UIM/Challenge is incorrect and sends the EAP-Response/UIM/Client-Error packet. The authentication procedure terminates. 4.2. Identity Management 4.2.1 Format, Generation and Usage of Peer Identities General In the beginning of EAP authentication, the Authenticator or the EAP server usually issues the EAP-Request/Identity packet to the peer. The peer responds with EAP-Response/Identity, which contains the user's identity. The formats of these packets are specified in [EAP]. cdma subscribers are identified with the International Mobile Subscriber Identity (IMSI) [3GPP2 N.S0009]. The IMSI is composed of a three digit Mobile Country Code (MCC),a two or three digit Mobile Network Code (MNC) and a not more than 10 digit Mobile Subscriber Identification Number (MSIN). In other words, the IMSI is a string of not more than 15 digits. MCC and MNC uniquely identify the cdma operator and help identify the AC from which the authentication result need to be obtained for this subscriber. Lizhiming [Page 10] Internet Draft EAP CAVE Authentication 15 April, 2004 Internet AAA protocols identify users with the Network Access Identifier (NAI) [RFC 2486]. When used in a roaming environment, the NAI is composed of a username and a realm, separated with "@" (username@realm). The username portion identifies the subscriber within the realm. This section specifies the peer identity format used in EAP/CAVE.In this document, the term identity or peer identity refers to the whole identity string that is used to identify the peer. The peer identity may include a realm portion. "Username" refers to the portion of the peer identity that identifies the user, i.e. the username does not include the realm portion. Identity Privacy Support EAP/CAVE includes optional identity privacy (anonymity) support that can be used to hide the cleartext permanent identity and thereby to make the subscriber's EAP exchanges untraceable to eavesdroppers. Because the permanent identity never changes, revealing it would help observers to track the user. The permanent identity is usually based on the IMSI, which may further help the tracking, because the same identifier may used in other contexts as well. Identity privacy is based on temporary identities, or pseudonyms, which are equivalent to but separate from the Temporary Mobile Subscriber Identities (TMSI) that are used on cellular networks. Please see Section 9.1 for security considerations regarding identity privacy. Username Types in EAP/CAVE identities There are three types of usernames in EAP/CAVE peer identities: (1) Permanent usernames. For example, 1123456789098765@myoperator.com might be a valid permanent identity. In this example, 1123456789098765 is the permanent username. (2) Pseudonym usernames. For example, 3s7ah6n9q@myoperator.com might be a valid pseudonym identity. In this example, 3s7ah6n9q is the pseudonym username. (3) Re-authentication usernames. For example, 53953754a@myoperator.com might be a valid re-authentication identity. In this case, 53953754 is the re-authentication username. The first two types of identities are only used on full authentication and the last one only on re-authentication. When the optional identity privacy support is not used, the non-pseudonym permanent identity is used on full authentication. The re- authentication exchange is specified in Section 4.3. Lizhiming [Page 11] Internet Draft EAP CAVE Authentication 15 April, 2004 Username Decoration In some environments, the peer may need to decorate the identity by prepending or appending the username with a string, in order to indicate supplementary AAA routing information in addition to the NAI realm. (The usage of a NAI realm portion is not considered to be decoration.) Username decoration is out of the scope of this document. However, it should be noted that username decoration might prevent the server from recognizing a valid username. Hence, although the peer MAY use username decoration in the identities the peer includes in EAP-Response/Identity, and the EAP server MAY accept a decorated peer username in this message, the peer or the EAP server MUST NOT decorate any other peer identities that are used in various EAP/CAVE attributes. Only the identity used in EAP- Response/Identity may be decorated. NAI Realm Portion The peer MAY include a realm portion in the peer identity, as per the NAI format. The use of a realm portion is not mandatory. If a realm is used, the realm MAY be chosen by the operator and it MAY a configurable parameter in the EAP/CAVE peer implementation.In this case, the peer is typically configured with the NAI realm of the home operator. Operators MAY reserve a specific realm name for EAP/CAVE users. This convention makes it easy to recognize that the NAI identifies a cdma subscriber. Such reserved NAI realm may be useful as a hint as to the first authentication method to use during method negotiation. When the peer is using a pseudonym username instead of the permanent username, the peer selects the realm name portion similarly as it select the realm portion when using the permanent username. If no configured realm name is available, the peer MAY derive the realm name from the MCC and MNC portions of the IMSI. A recommended way to derive the realm from the IMSI using the realm 3gpp2network.org will be specified in 3GPP2. Alternatively, the realm name may be obtained by concatenating "mnc", the MNC digits of IMSI, ".mcc", the MCC digits of IMSI and ".owlan.org". For example, if the IMSI is 123456789098765, and the MNC is three digits long, then the derived realm name is "mnc456.mcc123.owlan.org". The IMSI is a string of digits without any explicit structure, so the peer may not be able to determine the length of the MNC portion. If the peer is not able to determine whether the MNC is two or three digits long, the peer MAY use a 3-digit MNC. If the correct length of the MNC is two, then the MNC used in the realm name includes the first digit of MSIN. Hence, when configuring AAA networks for operators that have 2-digit MNC's, the network SHOULD also be prepared for realm names with incorrect 3-digit MNC's. Lizhiming [Page 12] Internet Draft EAP CAVE Authentication 15 April, 2004 Format of the Permanent Username The non-pseudonym permanent username SHOULD be derived from the IMSI. In this case, the permanent username MUST be of the format "1" | IMSI, where the character "|" denotes concatenation. In other words, the first character of the username is the digit one (ASCII value 0x31), followed by the IMSI. The IMSI is an ASCII string that consists of not more than 15 decimal digits (ASCII values between 0x30 and 0x39) as specified in [3GPP2 N.S0009]. The EAP server MAY use the leading "1" as a hint to try EAP/CAVE as the first authentication method during method negotiation, rather than for example EAP/AKA. The EAP/CAVE server MAY propose EAP/CAVE even if the leading character was not "1". Alternatively, an implementation MAY choose a permanent username that is not based on the IMSI. In this case the selection of the username, its format, and its processing is out of the scope of this document. In this case, the peer implementation MUST NOT prepend any leading characters to the username. Generating Pseudonyms and Re-authentication Identities by the Server Pseudonym usernames and re-authentication identities are generated by the EAP server. The EAP server produces pseudonym usernames and re-authentication identities in an implementation-dependent manner. Only the EAP server needs to be able to map the pseudonym username to the permanent identity, or to recognize a re-authentication identity. Regardless of construction method, the pseudonym username MUST conform to the grammar specified for the username portion of an NAI. The re-authentication identity also MUST conform to the NAI grammar. The EAP servers that the subscribers of an operator can use MUST ensure that the pseudonym usernames and the username portions used in re-authentication identities they generate are unique. In any case, it is necessary that permanent usernames, pseudonym usernames and re-authentication usernames are separate and recognizable from each other. In general, it is the task of the EAP server and the policies of its administrator to ensure sufficient separation in the usernames. Pseudonym usernames and re-authentication usernames are both produced and used by the EAP server. The EAP server MUST compose pseudonym usernames and re-authentication usernames so that it can recognize if a NAI username is an EAP CAVE pseudonym username or an EAP CAVE re-authentication username. For instance, when the usernames have been derived from the IMSI, the server could use different leading characters in the pseudonym usernames and re-authentication usernames (e.g. the pseudonym could begin with a leading "3" character). When mapping a re-authentication identity to a permanent identity, the server SHOULD only examine the username portion of the re-authentication identity and ignore the realm portion of the identity. Lizhiming [Page 13] Internet Draft EAP CAVE Authentication 15 April, 2004 Because the peer may fail to save a pseudonym username sent to in an EAP-Request/UIM/Challenge, for example due to malfunction, the EAP server SHOULD maintain at least one old pseudonym username in addition to the most recent pseudonym username. Transmitting Pseudonyms and Re-authentication Identities to the Peer The server transmits pseudonym usernames and re-authentication identities to the peer in cipher, using the AT_ENCR_DATA attribute. The EAP-Request/UIM/Challenge message MAY include an encrypted pseudonym username and/or an encrypted re-authentication identity in the value field of the AT_ENCR_DATA attribute. Because identity privacy support and re-authentication are optional to implement, the peer MAY ignore the AT_ENCR_DATA attribute and always use the permanent identity. On re-authentication (discussed in Section 4.3), the server MAY include a new encrypted re-authentication identity in the EAP-Request/SIM/Re-authentication message. On receipt of the EAP-Request/UIM/Challenge, the peer MAY decrypt the encrypted data in AT_ENCR_DATA and if a pseudonym username is included, the peer may use the obtained pseudonym username on the next full authentication. If a re-authentication identity is included, then the peer MAY save it and other re-authentication state information, as discussed in Section 4.3, for the next re- authentication. If the peer does not receive a new pseudonym username in the EAP- Request/UIM/Challenge message, the peer MAY use an old pseudonym username instead of the permanent username on next full authentication. The username portions of re-authentication identities are one-time usernames, which the peer MUST NOT re-use. Lizhiming [Page 14] Internet Draft EAP CAVE Authentication 15 April, 2004 Usage of the Re-authentication Identity by the Peer On re-authentication, the peer uses the re-authentication identity, received as part of the previous authentication sequence. A new re- authentication identity may be delivered as part of both full authentication and re-authentication. The peer MUST NOT modify the username part of the re-authentication identity received in AT_NEXT_REAUTH_ID, except in cases when username decoration is required. Even in these cases, the "root" re-authentication username must not be modified, but it may be appended or prepended with another string. 4.2.2 Communicating the Peer Identity to the Server General The peer identity MAY be communicated to the server with the EAP- Response/Identity message. This message MAY contain the permanent identity, a pseudonym identity, or a re-authentication identity. If the peer uses the permanent identity or a pseudonym identity, which the server is able to map to the permanent identity, then the authentication proceeds as discussed in the overview of Section 3. If the peer uses a re-authentication identity, and the server recognized the identity and agrees on using re-authentication, then a re-authentication exchange is performed, as described in 4.3. The peer identity can also be transmitted from the peer to the server using EAP/CAVE messages instead of EAP-Response/Identity. In this case, the server includes an identity requesting attribute (AT_ANY_ID_REQ, AT_FULLAUTH_ID_REQ or AT_PERMANENT_ID_REQ) in the EAP-Request/UIM/Start message, and the peer includes the AT_IDENTITY attribute, which contains the peer's identity, in the EAP- Response/UIM/Start message. The AT_ANY_ID_REQ attribute is a general identity requesting attribute, which the server uses if it does not specify which kind of an identity the peer should return in AT_IDENTITY. The server uses the AT_FULLAUTH_ID_REQ attribute to request either the permanent identity or a pseudonym identity. The server uses the AT_PERMANENT_ID_REQ attribute to request the peer to send its permanent identity. The identity format in the AT_IDENTITY attribute is the same as in the EAP-Response/Identity packet (except that identity decoration is not allowed). The AT_IDENTITY attribute contains a permanent identity, a pseudonym identity or a re-authentication identity. Obtaining the subscriber identity via EAP/CAVE messages is useful if the server does not have any EAP/CAVE peer identity at the beginning of the EAP/CAVE exchange or does not recognize the identity the peer used in EAP-Response/Identity. This may happen if, for example, the EAP-Response/Identity has been issued by some EAP method other than EAP/CAVE or if intermediate entities or software layers in the peer have modified the identity string in the EAP-Response/Identity packet. Also, some EAP layer implementations may cache the identity Lizhiming [Page 15] Internet Draft EAP CAVE Authentication 15 April, 2004 string from the first EAP authentication and do not obtain a new identity string from the EAP method implementation on subsequent authentication exchanges. As the identity string is used in key derivation, any of these cases will result in failed authentication unless the EAP server uses EAP/CAVE attributes to obtain an unmodified copy of the identity string. Therefore, unless the EAP server can be certain that no intermediate element or software layer has modified the EAP- Response/Identity packet, the EAP server SHOULD always use the EAP/CAVE attributes to obtain the identity, even if the identity received in EAP-Response/Identity was valid. Please note that the EAP/CAVE peer and the EAP/CAVE server only process the AT_IDENTITY attribute and entities that only pass through EAP packets do not process this attribute. Hence, if the EAP server is not co-located in the authenticator, then the authenticator and other intermediate AAA elements (such as possible AAA proxy servers) will continue to refer to the peer with the original identity from the EAP-Response/Identity packet regardless of whether the AT_IDENTITY attribute is used in EAP/CAVE to transmit another identity. Choice of Identity for the EAP-Response/Identity If EAP/CAVE peer is started upon receiving an EAP-Request/Identity message, then the peer performs the following steps. If the peer has maintained re-authentication state information and if the peer wants to use re-authentication, then the peer transmits the re-authentication identity in EAP-Response/Identity. Else, if the peer has a pseudonym username available, then the peer transmits the pseudonym identity in EAP-Response/Identity. In other cases, the peer transmits the permanent identity in EAP- Response/Identity. Server Operation in the Beginning of EAP/CAVE Exchange If the EAP server has not received any identity (permanent identity, pseudonym identity or re-authentication identity) from the peer when sending the first EAP/CAVE request, or if the EAP server has received an EAP-Response/Identity packet but the contents do not appear to be a valid permanent identity, pseudonym identity or a re- authentication identity, then the server MUST request an identity from the peer using one of the methods below. The server sends the EAP-Request/UIM/Start message with the AT_PERMANENT_ID_REQ message to indicate that the server wants the peer to include the permanent identity in the AT_IDENTITY attribute of the EAP-Response/SIM/Start message. This is done in the following cases: Lizhiming [Page 16] Internet Draft EAP CAVE Authentication 15 April, 2004 - The server does not support re-authentication or identity privacy. - The server received an identity that it recognizes as a pseudonym identity but the server is not able to map the pseudonym identity to a permanent identity. The server issues the EAP-Request/UIM/Start packet with the AT_FULLAUTH_ID_REQ attribute to indicate that the server wants the peer to include a full authentication identity (pseudonym identity or permanent identity) in the AT_IDENTITY attribute of the EAP- Response/UIM/Start message. This is done in the following cases: - The server does not support re-authentication and the server supports identity privacy - The server received an identity that it recognizes as a re- authentication identity but the server is not able to map the re- authentication identity to a permanent identity The server issues the EAP-Request/UIM/Start packet with the AT_ANY_ID_REQ attribute to indicate that the server wants the peer to include an identity in the AT_IDENTITY attribute of the EAP- Response/UIM/Start message, and the server does not indicate any preferred type for the identity. This is done in other cases, such as when the server does not have any identity, or the server does not recognize the format of a received identity. Processing of EAP-Request/SIM/Start by the Peer Upon receipt of an EAP-Request/UIM/Start message, the peer MUST perform the following steps. If the EAP-Request/UIM/Start does not include any identity request attribute, then the peer responds with EAP-Response/UIM/Start without AT_IDENTITY. The peer includes the AT_SELECTED_VERSION, AT_NONCE_MT attributes and AT_ESN attribute, because the exchange is a full authentication exchange. If the EAP-Request/UIM/Start includes AT_PERMANENT_ID_REQ the peer MUST either respond with EAP-Response/UIM/Start and include the permanent identity in AT_IDENTITY and AT_ESN attribute or respond with EAP-Response/UIM/Client-Error packet with code "unable to process packet". If the EAP-Request/UIM/Start includes AT_FULL_AUTH_ID_REQ, and if the peer has a pseudonym available, then the peer SHOULD respond with EAP-Response/UIM/Start and includes the pseudonym identity in AT_IDENTITY. If the peer does not have a pseudonym when it receives this message, then the peer MUST either respond with EAP- Response/UIM/Start and include the permanent identity in AT_IDENTITY and AT_ESN attribute or respond with EAP-Response/UIM/Client-Error packet with code "unable to process packet." The Peer MUST NOT use a re-authentication identity in the AT_IDENTITY attribute. Lizhiming [Page 17] Internet Draft EAP CAVE Authentication 15 April, 2004 If the EAP-Request/UIM/Start includes AT_ANY_ID_REQ, and if the peer has maintained re-authentication state information and the peer wants to use re-authentication, then the peer responds with EAP- Response/UIM/Start and includes the re-authentication identity in AT_IDENTITY. Else, if the peer has a pseudonym identity available, then the peer responds with EAP-Response/UIM/Start and includes the pseudonym identity in AT_IDENTITY. Else, the peer responds with EAP- Response/UIM/Start and includes the permanent identity in AT_IDENTITY and AT_ESN attribute. An EAP/CAVE exchange may include several EAP/UIM/Start rounds. The server may issue a second EAP-Request/UIM/Start, if it was not able to recognize the identity the peer used in the previous AT_IDENTITY attribute. At most three EAP/UIM/Start rounds can be used. AT_ANY_ID_REQ can only be used in the first EAP-Request/UIM/Start, in other words AT_ANY_ID_REQ MUST NOT be used in the second or third EAP-Request/SIM/Start. AT_FULLAUTH_ID_REQ MUST NOT be used if the previous EAP-Request/UIM/Start included AT_PERMANENT_ID_REQ. The peer operation in cases when it receives an unexpected attribute is specified in Section 4.6.1. AT_ESN attribute must not be included if a pseudonym identity or a re-authentication identity is contained in the EAP-Response/UIM/Start message. Attacks against Identity Privacy The section above specifies two possible ways the peer can operate upon receipt of AT_PERMANENT_ID_REQ. This is because a received AT_PERMANENT_ID_REQ does not necessarily originate from the valid network, but an active attacker may transmit an EAP- Request/UIM/Start packet with an AT_PERMANENT_ID_REQ attribute to the peer, in an effort to find out the true identity of the user. If the peer does not want to reveal its permanent identity, then the peer sends the EAP-Response/UIM/Client-Error packet with the error code "unable to process packet", and the authentication exchange terminates. Basically, there are two different policies that the peer can employ with regard to AT_PERMANENT_ID_REQ. A "conservative" peer assumes that the network is able to maintain pseudonyms robustly. Therefore, if a conservative peer has a pseudonym username, the peer responds with EAP-Response/UIM/Client-Error to the EAP packet with AT_PERMANENT_ID_REQ, because the peer believes that the valid network is able to map the pseudonym identity to the peer's permanent identity. (Alternatively, the conservative peer may accept AT_PERMANENT_ID_REQ in certain circumstances, for example if the pseudonym was received a long time ago.) The benefit of this policy is that it protects the peer against active attacks on anonymity. On the other hand, a "liberal" peer always accepts the AT_PERMANENT_ID_REQ and responds with the permanent identity. The benefit of this policy is that it works even if the valid network Lizhiming [Page 18] Internet Draft EAP CAVE Authentication 15 April, 2004 sometimes loses pseudonyms and is not able to map them to the permanent identity. Processing of AT_IDENTITY by the Server When the server receives an EAP-Response/UIM/Start message with the AT_IDENTITY (in response to the server's identity requesting attribute), the server MUST operate as follows. If the server used AT_PERMANENT_ID_REQ, and if the AT_IDENTITY does not contain a valid permanent identity, then the server sends EAP Failure and the EAP exchange terminates. If the server recognizes the permanent identity and is able to continue, then the server proceeds with full authentication by sending EAP- Request/UIM/Challenge. If the server used AT_FULLAUTH_ID_REQ, and if AT_IDENTITY contains a valid permanent identity or a pseudonym identity that the server can map to a valid permanent identity, then the server proceeds with full authentication by sending EAP-Request/UIM/Challenge. If AT_IDENTITY contains a pseudonym identity that the server is not able to map to a valid permanent identity, or an identity that the server is not able to recognize or classify, then the server sends EAP-Request/UIM/Start with AT_PERMANENT_ID_REQ. If the server used AT_ANY_ID_REQ, and if the AT_IDENTITY contains a valid permanent identity or a pseudonym identity that the server can map to a valid permanent identity, then the server proceeds with full authentication by sending EAP-Request/UIM/Challenge. If the server used AT_ANY_ID_REQ, and if AT_IDENTITY contains a valid re-authentication identity and the server agrees on using re- authentication, then the server proceeds with re-authentication by sending EAP-Request/UIM/Re-authentication (Section 4.3). If the server used AT_ANY_ID_REQ, and if the peer sent an EAP- Response/UIM/Start with only AT_IDENTITY (indicating re- authentication), but the server is not able to map the identity to a permanent identity, then the server sends EAP-Request/UIM/Start with AT_FULLAUTH_ID_REQ. If the server used AT_ANY_ID_REQ, and if AT_IDENTITY contains a valid re-authentication identity, which the server is able to map to a permanent identity, and if the server does not want to use re- authentication, then the server sends EAP-Request/UIM/Start without any identity requesting attributes. If the server used AT_ANY_ID_REQ, and AT_IDENTITY contains an identity that the server recognizes as a pseudonym identity but the server is not able to map the pseudonym identity to a permanent identity, then the server sends EAP-Request/UIM/Start with AT_PERMANENT_ID_REQ. Lizhiming [Page 19] Internet Draft EAP CAVE Authentication 15 April, 2004 If the server used AT_ANY_ID_REQ, and AT_IDENTITY contains an identity that the server is not able to recognize or classify, then the server sends EAP-Request/UIM/Start with AT_FULLAUTH_ID_REQ. 4.2.3 Message Sequence Examples (Informative) This section contains non-normative message sequence examples to illustrate how the peer identity can be communicated to the server. Full Authentication This case for full authentication is illustrated in the figure below. In this case, AT_IDENTITY contains either the permanent identity or a pseudonym identity. The same sequence is also used in case the server uses the AT_FULLAUTH_ID_REQ in EAP- Request/UIM/Start. Peer Authenticator | | | +------------------------------+ | | Server does not have any | | | Subscriber identity available| | | When starting EAP/CAVE | | +------------------------------+ | | | EAP-Request/UIM/Start | | (AT_ANY_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/UIM/Start | | (AT_IDENTITY, AT_NONCE_MT, | | AT_SELECTED_VERSION, AT_ESN) | |------------------------------------------------------>| | | If the peer uses its full authentication identity and the AT_IDENTITY attribute contains a valid permanent identity or a valid pseudonym identity that the EAP server is able to map to the permanent identity, then the full authentication sequence proceeds as usual with the EAP Server issuing the EAP-Request/UIM/Challenge message. AT_ESN attribute must not be included if a pseudomnym identity is contained in the EAP-Response/UIM/Start message. Lizhiming [Page 20] Internet Draft EAP CAVE Authentication 15 April, 2004 Re-authentication The case when the server uses the AT_ANY_ID_REQ and the peer wants to perform re-authentication is illustrated below. Peer Authenticator | | | +------------------------------+ | | Server does not have any | | | Subscriber identity available| | | When starting EAP/CAVE | | +------------------------------+ | | | EAP-Request/UIM/Start | | (AT_ANY_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/UIM/Start | | (AT_IDENTITY containing a re-authentication identity) | |------------------------------------------------------>| | | On re-authentication, if the AT_IDENTITY attribute contains a valid re-authentication identity and the server agrees on using re- authentication, then the server proceeds with the re-authentication sequence and issues the EAP-Request/SIM/Re-authentication packet, as specified in Section 4.3. Lizhiming [Page 21] Internet Draft EAP CAVE Authentication 15 April, 2004 Fall Back to Full Authentication The case when the server does not recognize the re-authentication identity the peer used in AT_IDENTITY, and issues a second EAP- Request/UIM/Start message is illustrated below. Peer Authenticator | | | +------------------------------+ | | Server does not have any | | | Subscriber identity available| | | When starting EAP/CAVE | | +------------------------------+ | | | EAP-Request/UIM/Start | | (AT_ANY_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/UIM/Start | | (AT_IDENTITY containing a re-authentication identity) | |------------------------------------------------------>| | | | +------------------------------+ | | Server does not recognize | | | The re-authentication | | | Identity | | +------------------------------+ | | | EAP-Request/UIM/Start | | (AT_FULLAUTH_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/UIM/Start | | (AT_IDENTITY with a full-auth. identity, AT_NONCE_MT, | | AT_SELECTED_VERSION, AT_ESN) | |------------------------------------------------------>| | | Lizhiming [Page 22] Internet Draft EAP CAVE Authentication 15 April, 2004 Requesting the Permanent Identity 1 The figure below illustrates the case when the EAP server fails to map the pseudonym identity included in the EAP-Response/Identity packet to a valid permanent identity. Peer Authenticator | | | EAP-Request/Identity | |<------------------------------------------------------| | | | EAP-Response/Identity | | (Includes a pseudonym) | |------------------------------------------------------>| | | | +------------------------------+ | | Server fails to map the | | | Pseudonym to a permanent id. | | +------------------------------+ | | | EAP-Request/UIM/Start | | (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/UIM/Start | | (AT_IDENTITY with permanent identity, AT_NONCE_MT, | | AT_SELECTED_VERSION, AT_ESN) | |------------------------------------------------------>| | | If the server recognizes the permanent identity, then the authentication sequence proceeds as usual with the EAP Server issuing the EAP-Request/UIM/Challenge message. Lizhiming [Page 23] Internet Draft EAP CAVE Authentication 15 April, 2004 Requesting the Permanent Identity 2 The figure below illustrates the case when the EAP server fails to map the pseudonym included in the AT_IDENTITY attribute to a valid permanent identity. Peer Authenticator | | | +------------------------------+ | | Server does not have any | | | Subscriber identity available| | | When starting EAP/CAVE | | +------------------------------+ | | | EAP-Request/UIM/Start | | (AT_ANY_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | |EAP-Response/UIM/Start | |(AT_IDENTITY with a pseudonym identity, AT_NONCE_MT, | | AT_SELECTED_VERSION) | |------------------------------------------------------>| | | | | | +-------------------------------+ | | Server fails to map the | | | Pseudonym in AT_IDENTITY | | | to a valid permanent identity | | +-------------------------------+ | | | EAP-Request/UIM/Start | | (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/UIM/Start | | (AT_IDENTITY with permanent identity, | | AT_NONCE_MT, AT_SELECTED_VERSION, AT_ESN) | |------------------------------------------------------>| | | Lizhiming [Page 24] Internet Draft EAP CAVE Authentication 15 April, 2004 Three EAP/UIM/Start Roundtrips In the worst case, there are three EAP/UIM/Start round trips before the server has obtained an acceptable identity. This case is illustrated below. Peer Authenticator | | | +------------------------------+ | | Server does not have any | | | Subscriber identity available| | | When starting EAP/CAVE | | +------------------------------+ | | | EAP-Request/UIM/Start | | (Includes AT_ANY_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | EAP-Response/UIM/Start | | (AT_IDENTITY with re-authentication identity) | |------------------------------------------------------>| | | | +------------------------------+ | | Server does not accept | | | The re-authentication | | | Identity | | +------------------------------+ | | | EAP-Request/UIM/Start | | (AT_FULLAUTH_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | |EAP-Response/UIM/Start | |(AT_IDENTITY with a pseudonym identity, AT_NONCE_MT, | | AT_SELECTED_VERSION) | |------------------------------------------------------>| | | | +-------------------------------+ | | Server fails to map the | | | Pseudonym in AT_IDENTITY | | | to a valid permanent identity | | +-------------------------------+ | | | EAP-Request/UIM/Start | | (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/UIM/Start | | (AT_IDENTITY with permanent identity, AT_NONCE_MT, | | AT_SELECTED_VERSION,AT_ESN) | |------------------------------------------------------>| | | Lizhiming [Page 25] Internet Draft EAP CAVE Authentication 15 April, 2004 After the last EAP-Response/UIM/Start message, the full authentication sequence proceeds as usual. If the EAP Server recognizes the permanent identity and is able to proceed, the server issues the EAP-Request/UIM/Challenge message. 4.3. Re-Authentication 4.3.1 General In some environments, EAP authentication may be performed frequently. Because the EAP CAVE full authentication procedure requires the authentication informatin from the Authentication Centre, the full authentication procedure is not very well suitable for frequent use. Therefore, EAP CAVE includes a re-authentication procedure that does not need new authenticaiton and encryption information from the Authentication Centre. Re- authentication can be performed in fewer roundtrips than the full authentication. After a succesful full authentication, the Authentication Center should share the Shared Secret Data with the Server. In following re-authentication procedure, the server can locally perform global challenge or unique challenge without interaction with the Authentication Center. Re-authentication is optional to implement for both the EAP CAVE server and peer. On each EAP authentication, either one of the entities may also fall back on full authentication if they do not want to use re-authentication. Re-authentication is based on the keys derived on the preceding full authentication. The same K_aut and K_encr keys as in full authentication are used to protect EAP CAVE packets and attributes, and the original Master Key from full authentication is used to generate a fresh Master Session Key, as specified in Section 4.7. In order to use re-authentication, the peer and the EAP server need to store the following values: Master Key and the next re-authentication identity. K_aut, K_encr may either be stored or derived again from MK. The server may also need to store the permanent identity of the user. 4.3.2 Re-authentication Identity The re-authentication procedure makes use of separate re- authentication user identities. Pseudonyms and the permanent identity are reserved for full authentication only. If a re- authentication identity is lost and the network does not recognize it, the EAP server can fall back on full authentication. Lizhiming [Page 26] Internet Draft EAP CAVE Authentication 15 April, 2004 If the EAP server supports re-authentication, it MAY include the skippable AT_NEXT_REAUTH_ID attribute in the encrypted data of EAP- Request/UIM/Challenge message (Section 6.3). This attribute contains a new re-authentication identity for the next re-authentication. The peer MAY ignore this attribute, in which case it MUST use full authentication next time. If the peer wants to use re- authentication, it uses this re-authentication identity on next authentication. Even if the peer has a re-authentication identity, the peer MAY discard the re-authentication identity and use a pseudonym or the permanent identity instead, in which case full authentication MUST be performed. In environments where a realm portion is needed in the peer identity, the re-authentication identity received in AT_NEXT_REAUTH_ID MUST contain both a username portion and a realm portion, as per the NAI format. The EAP Server can choose an appropriate realm part in order to have the AAA infrastructure route subsequent re-authentication related requests to the same AAA server. For example, the realm part MAY include a portion that is specific to the AAA server. Hence, it is sufficient to store the context required for re-authentication in the AAA server that performed the full authentication. The peer MAY use the re-authentication identity in the EAP- Response/Identity packet or, in response to server's AT_ANY_ID_REQ attribute, the peer MAY use the re-authentication identity in the AT_IDENTITY attribute of the EAP-Response/SIM/Start packet. The peer MUST NOT modify the username portion of the re-authentication identity, but the peer MAY modify the realm portion or replace it with another realm portion. Even if the peer uses a re-authentication identity, the server may want to fall back on full authentication, for example because the server does not recognize the re-authentication identity or does not want to use re-authentication. In this case, the server starts the full authentication procedure by issuing an EAP-Request/UIM/Start packet. This packet always starts a full authentication sequence if it does not include the AT_ANY_ID_REQ attribute. If the server was not able to recover the peer's identity from the re-authentication identity, the server includes either the AT_FULLAUTH_ID_REQ or the AT_PERMANENT_ID_REQ attribute in this EAP request. Lizhiming [Page 27] Internet Draft EAP CAVE Authentication 15 April, 2004 4.3.3 Re-authentication Procedure The following figure illustrates the re-authentication procedure. Encrypted attributes are denoted with '*'. The peer uses its re- authentication identity in the EAP-Response/Identity packet. As discussed above, an alternative way to communicate the re- authentication identity to the server is for the peer to use the AT_IDENTITY attribute in the EAP-Response/UIM/Start message. This latter case is not illustrated in the figure below, and it is only possible when the server requests the peer to send its identity by including the AT_ANY_ID_REQ attribute in the EAP-Request/UIM/Start packet. If the server recognizes the re-authentication identity and agrees on using re-authentication, then the server firstly determins which way of challenge, e.g. global challenge or unique challenge, will be used, generates a corresponding fresh random number RAND or RANDU as challenge, then sends the EAP-Request/UIM/Re-authentication packet to the peer. The EAP server also runs CAVE algorithm to produce coresponding response AUTHR or AUTHU. This packet MUST include the encrypted AT_RAND or AT_RANDU attribute that contains a random number chosen by the server, the AT_ENCR_DATA and the AT_IV attributes used for encryption, and the AT_MAC attribute that contains a message authentication code over the packet. The packet MAY also include an encrypted AT_NEXT_REAUTH_ID attribute that contains the next re-authentication identity. Re-authentication identities are one-time identities. If the peer does not receive a new re-authentication identity, it MUST use either the permanent identity or a pseudonym identity on the next authentication to initiate full authentication. The peer verifies that AT_MAC is correct. The peer MAY save the next re-authentication identity from the encrypted AT_NEXT_REAUTH_ID for next time. The peer takes RAND or RANDU value as input of CAVE algorithm to produce response AUTHR or AUTHU. The peer also calculates a new MAC covering the packet concatenated to the AUTHR or AUTHU. The peer responds with the EAP-Response/UIM/Re- authentication packet. The server verifies the AT_MAC attribute. If the checks is successful, the re-authentication has succeeded and the server sends the EAP-Success packet to the peer. Lizhiming [Page 28] Internet Draft EAP CAVE Authentication 15 April, 2004 Peer Authenticator | | | EAP-Request/Identity | |<------------------------------------------------------| | | | EAP-Response/Identity | | (Includes a re-authentication identity) | |------------------------------------------------------>| | | | +--------------------------------+ | | Server recognizes the identity | | | and agrees on using fast | | | re-authentication. Server | | | determins global challenge or | | | unique challenge is used, then | | | generates random number RAND | | | (global challenge)or RANDU | | | (unique challenge) | | +--------------------------------+ | | | EAP-Request/UIM/Re-authentication | | (AT_IV, AT_ENCR_DATA, *AT_RAND or *AT_RANDU, | | *AT_NEXT_REAUTH_ID, AT_MAC) | |<------------------------------------------------------| | | | | +-----------------------------------------------+ | | Peer verifies AT_MAC and runs CAVE algorithm | | | to calculate response AUTH or AUTHU. Peer MAY | | | store the new re-authentication identity | | | for next re-auth. | | +-----------------------------------------------+ | | | | EAP-Response/UIM/Re-authentication | | (AT_IV, AT_ENCR_DATA, AT_MAC) | |------------------------------------------------------>| | | | +--------------------------------+ | | Server verifies AT_MAC | | +--------------------------------+ | | | EAP-Success | |<------------------------------------------------------| | | Lizhiming [Page 29] Internet Draft EAP CAVE Authentication 15 April, 2004 4.4. EAP/CAVE SSD Update In full authentication, the Authentication Center may determins that the SSD stored at the peer must be updated if the full- authenticaiton failed. The following figure illustrates the SSD update procedure. On SSD Update, the server obtains the RANDSSD challenge and a pair of parameter RANDU and AUTHU from the AC. The server sends this challenge in AT_RANDSSD attribute of the EAP-Request/UIM/Update packet containing the AT_MAC attribute to the peer. When the peer receive this challenge, the peer check the AT_MAC. If check is successful and the the peer agrees to start SSD update procedure,the peer runs CAVE algorithm to generate a new pending SSD, then generates a new random number RANDBS as a challenge for network. The peer runs CAVE algorithm again to calculate the corresponding response AUTHBS. The peer responds the server with a EAP-response/UIM/Update-Server- challenge packet containing the AT_RANDBS and AT_MAC attribute. The server verifies the AT_MAC attribute, then forwards the RANDBS value to the AC and obtains the response AUTHB from the AC. The server responds with the EAP-request/UIM/Update-Server-challenge, containing the AT_MAC attribute covering the packet concatenated to the AUTHBS values. The peer checks the AT_MAC attribute.If check is successful, the peer updates the SSD of UIM with the pending SSD, and responds to the server with EAP-response/UIM/Update-Client-success packet containing AT_MAC attribute and AT_Update_Success_indication attribute indicating the ssd update success of the peer. The server verifies the AT_MAC attribute and checks the peer's AT_ SSD_Update_Success attibute. If these check are succesful, the server sends EAP-request/UIM/Update-challenge packet to the peer, which contains AT_RANDU attribute as a challenge to the peer and AT_MAC attribute. The peer checks the AT_MAC attribute and runs CAVE algorithm to calculate the response AUTHU, then the peers responds with EAP- response/UIM/Update-challenge packet containing AT_MAC attribute that cover the AUTHU value. The server verifies the AT_MAC attribute. If the checks are successful, the server notifies the AC that the SSD update procedure has been successfully completed and obtains the new SSD value from the AC, then the server sends the EAP-Success packet to the peer. Lizhiming [Page 30] Internet Draft EAP CAVE Authentication 15 April, 2004 Peer Authenticator | | | | | +----------------------------------------+ | | Based on the SSD update information | | | received from the AC, the server | | | agrees to start SSD update procedure | | | and gets the corresponding parameter | | | including RANDSSD,RAND,AUTHU from the | | | Authencation Center. | | +----------------------------------------+ | | | EAP-Request/UIM/Update | | (AT_RANDSSD,AT_MAC) | |<------------------------------------------------------| | | | | +-----------------------------------------------+ | | Peer verifies AT_MAC and runs CAVE algorithm | | | to calculate the new SSD, then the peer | | | generates a fresh random number RANDBS, runs | | | CAVE algorithm again to calculate AUTHBS. | | | Peer must keep the old SSD if SSD update | | | fail. | | +-----------------------------------------------+ | | | | EAP-Response/UIM/Update-Server-challenge | | (AT_RANDBS, AT_MAC) | |------------------------------------------------------>| | +--------------------------------+ | | Server verifies AT_MAC , | | | forwards RANDBS value to the | | | AC, and obtain response AUTHBS | | | from the AC | | +--------------------------------+ | | | | | EAP-Request/UIM/Update-Server-challenge | | (AT_MAC) | |<------------------------------------------------------| +-----------------------------------------------+ | | Peer verifies AT_MAC, if success, | | | Peer update SSD, then send success message | | +-----------------------------------------------+ | | | | EAP-Response/UIM/Update-Client-success | | (AT_SSD_Update_Success, AT_MAC) | |------------------------------------------------------>| | | | | Lizhiming [Page 31] Internet Draft EAP CAVE Authentication 15 April, 2004 | | | | | +--------------------------------+ | | Server verifies AT_MAC and | | | SSD Update Success indication. | | +--------------------------------+ | EAP-Request/UIM/Update-challenge | | (AT_RANDU, AT_MAC) | |<------------------------------------------------------| +-----------------------------------------------+ | | Peer verifies AT_MAC and runs CAVE algorithm | | | to calculate AUTHU | | +-----------------------------------------------+ | | EAP-Response/UIM/Update-challenge | | (AT_MAC) | |------------------------------------------------------>| | +--------------------------------+ | | Server verifies AT_MAC. | | | Server notifies the AC | | | the success of SSD Updating, | | | and gets new SSD from the AC | | +--------------------------------+ | | | EAP-Success | |<------------------------------------------------------| | | 4.5. EAP/CAVE Notifications The EAP-Request/Notification, specified in [EAP], can be used to convey a displayable message from the EAP server to the peer. Because these messages are textual messages, it may be hard for the peer to present them in the user's preferred language. Therefore, EAP/CAVE uses a separate EAP/CAVE message subtype to transmit localizable notification codes instead of the EAP- Request/Notification packet. The EAP server MAY issue an EAP-Request/UIM/Notification packet to the peer. The peer MAY show a notification message to the user and the peer MUST respond to the EAP server with an EAP- Response/UIM/Notification packet, even if the peer did not recognize the notification code. The notification code is a 16-bit number. The most significant bit is called the Failure bit (F bit). The F bit specifies whether the notification implies failure. The code values with the F bit set to zero (code values 0...32767) are used on unsuccessful cases. The receipt of a notification code from this range implies failed authentication, so the peer can use the notification as a failure indication. After receiving the EAP-Response/UIM/Notification for these notification codes, the server MUST send the EAP-Failure packet. Lizhiming [Page 32] Internet Draft EAP CAVE Authentication 15 April, 2004 The receipt of a notification code with the F bit set to one (values 32768...65536) does not imply failure, so the peer MUST NOT change its state when it receives such a notification. (This version of the protocol does not specify any notification codes with the F bit set to one.) The second most significant bit of the notification code is called the Phase bit (P bit). It specifies at which phase of the EAP/CAVE exchange the notification can be used. If the P bit is set to zero, the notification can only be used after the EAP/CAVE/Challenge round in full authentication or the EAP/CAVE/Re-authentication round in reautentication. For these notifications, the AT_MAC attribute MUST be included in both EAP-Request/UIM/Notification and EAP- Response/UIM/Notification. If the P bit is set to one, the notification can only by used before the EAP/CAVE/Challenge round in full authentication or the EAP/CAVE/Re-authentication round in reauthentication. For these notifications, the AT_MAC attribute MUST NOT be included in either EAP-Request/UIM/Notification or EAP-Response/UIM/Notification. (This version of the protocol does not specify any notification codes with the P bit set to one.) Some of the notification codes are authorization related and hence not usually considered as part of the responsibility of an EAP method. However, they are included as part of EAP/CAVE because there are currently no other ways to convey this information to the user in a localizable way, and the information is potentially useful for the user. An EAP/CAVE server implementation may decide never to send these EAP/CAVE notifications. 4.6. Error Cases This section specifies the operation of the peer and the server in error cases. The subsections below require the EAP/CAVE peer and server to send an error packet (EAP-Response/UIM/Client-Error or EAP Failure) in error cases. However, implementations SHOULD NOT rely upon the correct error reporting behavior of the peer, authenticator, or the server. It is possible for error and other messages to be lost in transit or for a malicious participant to attempt to consume resources by not issuing error messages. Both the peer and the EAP server SHOULD have a mechanism to clean up state even if an error message or EAP Success is not received after a timeout period. 4.6.1 Peer Operation In general, if an EAP/CAVE peer detects an error in a received EAP/CAVE packet, the EAP/CAVE implementation responds with the EAP- Response/UIM/Client-Error packet. In response to the EAP- Response/UIM/Client-Error, the EAP server MUST issue the EAP Failure packet and the authentication exchange terminates. Lizhiming [Page 33] Internet Draft EAP CAVE Authentication 15 April, 2004 By default, the peer uses the client error code 0, "unable to process packet". This error code is used in the following cases: - the peer is not able to parse the EAP request, i.e. the EAP request is malformed - the peer encountered a malformed attribute - wrong attribute types or duplicate attributes have been included in the EAP request - a mandatory attribute is missing - unrecognized non-skippable attribute - unrecognized or unexpected EAP/CAVE Subtype in the EAP request - A RAND challenge repeated in AT_RAND - invalid AT_MAC - invalid pad bytes in AT_PADDING - the peer does not want to process AT_PERMANENT_ID_REQ Separate error codes have been defined for the following error cases in Section 7.18. As specified in Section 4.1, when processing the AT_VERSION_LIST attribute, which lists the EAP/CAVE versions supported by the server, if the attribute does not include a version that is implemented by the peer and allowed in the peer's security policy, then the peer MUST send the EAP-Response/UIM/Client-Error packet with the error code "unsupported version". If the peer believes that the RAND challenges included in AT_RAND are not fresh e.g. because it is capable of remembering some previously used RANDs, the peer MUST send the EAP- Response/UIM/Client-Error packet with the error code "RAND are not fresh". 4.6.2 Server Operation If an EAP/CAVE server detects an error in a received EAP/CAVE response, the server MUST issue the EAP Failure packet and the authentication exchange terminates. The errors cases when the server issues an EAP Failure include the following: - the server is not able to parse the peer's EAP response - the server encounters a malformed attribute, a non-recognized non- skippable attribute, or a duplicate attribute Lizhiming [Page 34] Internet Draft EAP CAVE Authentication 15 April, 2004 - a mandatory attribute is missing or an invalid attribute was included - unrecognized or unexpected EAP/CAVE Subtype in the EAP Response - invalid AT_MAC 4.6.3 EAP Failure As normally in EAP, the EAP server sends the EAP-Failure packet to the peer when the authentication procedure fails on the EAP Server. In EAP/CAVE, this may occur for example if the EAP server does not recognize the peer identity, or if the EAP server is not able to obtain the cdma authentication informatin for the subscriber or the authentication exchange times out. The server may also send EAP Failure if there is an error in the received EAP/CAVE response, as discussed in Section 4.6.2. The server can send EAP-Failure at any time in the EAP exchange. The peer MUST process EAP-Failure. 4.6.4 EAP Success On full authentication, the server can only send EAP-Success after the EAP/CAVE/Challenge round. The peer MUST silently discard any EAP- Success packets if they are received before the peer has successfully authenticated the server and sent the EAP- Response/UIM/Challenge packet. On re-authentication, EAP-Success can only be sent after the EAP/CAVE/Re-authentication round. The peer MUST silently discard any EAP-Success packets if they are received before the peer has successfully authenticated the server and sent the EAP- Response/UIM/Re-authentication packet. On SSD Update, EAP-Success can only be sent after the EAP/CAVE/Update round. The peer MUST silently discard any EAP-Success packets if they are received before the peer has successfully authenticated the server and sent the EAP- Response/UIM/Update-Challenge packet. If the peer receives an EAP/CAVE notification (section 4.5) that indicates failure, then the peer MUST no longer accept the EAP- Success packet even if the server authentication was successfully completed. 4.7. Key Generation This section specifies how keying material is generated. Lizhiming [Page 35] Internet Draft EAP CAVE Authentication 15 April, 2004 On EAP CAVE full authentication and SSD Update procedure, a Master Key (MK) is derived from the underlying cdma encryption information (CMEA keys), the NONCE_MT and other relevant context as follows. MK = SHA1(Identity|CMEA | NONCE_MT| Version List| Selected Version) In the formula above, the "|" character denotes concatenation. Identity denotes the peer identity string without any terminating null characters. It is the identity from the AT_IDENTITY attribute from the last EAP-Response/UIM/Start packet, or, if AT_IDENTITY was not used, the identity from the EAP-Response/Identity packet. The identity string is included as-is, without any changes and including the possible identity decoration. The notation CMEA denotes the CMEA key value, which is derived from SSD_B based on CAVE algorithm [3GPP2 N.S0005]. NONCE_MT denotes the NONCE_MT value (not the AT_NONCE_MT attribute but just the nonce value). The Version List includes the 2-byte supported version numbers from AT_VERSION_LIST, in the same order as in the attribute. The Selected Version is the 2-byte selected version from AT_SELECTED_VERSION. Network byte order is used, just as in the attributes. The hash function SHA-1 is specified in [SHA-1]. If several EAP/UIM/Start roundtrips are used in an EAP/CAVE exchange, then the NONCE_MT, Version List and Selected version from the last EAP/UIM/Start round are used, and the previous EAP/UIM/Start rounds are ignored. The Master Key is fed into a Pseudo-Random number Function (PRF) which generates separate Transient EAP Keys (TEKs) for protecting EAP CAVE packets, as well as a Master Session Key (MSK) for link layer security and an Extended Master Session Key (EMSK) for other purposes. On re-authentication, the same TEKs MUST be used for protecting EAP packets, but a new MSK and a new EMSK MUST be derived from the original MK and new values exchanged in the re- authentication. EAP CAVE requires two TEKs for its own purposes, the authentication key K_aut to be used with the AT_MAC attribute, and the encryption key K_encr, to be used with the AT_ENCR_DATA attribute. The same K_aut and K_encr keys are used in full authentication and subsequent re-authentications. Key derivation is based on the random number generation specified in NIST Federal Information Processing Standards (FIPS) Publication 186-2 [PRF]. The pseudo-random number generator is specified in the change notice 1 (2001 October 5) of [PRF] (Algorithm 1). As specified in the change notice (page 74), when Algorithm 1 is used as a general-purpose pseudo-random number generator, the "mod q" term in step 3.3 is omitted. The function G used in the algorithm is constructed via Secure Hash Standard as specified in Appendix 3.3 of the standard. It should be noted that the function G is very similar to SHA-1, but the message padding is different. Please refer to [PRF] for full details. For convenience, the random number algorithm with the correct modification is cited in Annex B. Lizhiming [Page 36] Internet Draft EAP CAVE Authentication 15 April, 2004 160-bit XKEY and XVAL values are used, so b = 160. On each full authentication, the Master Key is used as the initial secret seed- key XKEY. The optional user input values (XSEED_j) in step 3.1 are set to zero. The resulting 320-bit random numbers x_0, x_1, ..., x_m-1 are concatenated and partitioned into suitable-sized chunks and used as keys in the following order: K_encr (128 bits), K_aut (128 bits), Master Session Key (64 bytes), Extended Master Session Key (64 bytes). On re-authentication, the same pseudo-random number generator can be used to generate a new Master Session Key and new Initialization Vectors. The seed value XKEY' is calculated as follows: XKEY' = SHA1(Identity|RAND| MK) (1) or XKEY' = SHA1(Identity|RANDU| MK) (2) In the formula above, the formula selection is based on the type of cdma challenge. The formula (1) is slected when the server determins that global challenge is used, the formula (2) is slected when the server determins that unique challenge is used. The Identity denotes the re-authentication identity, without any terminating null characters, from the AT_IDENTITY attribute of the EAP-Response/UIM/Start packet, or, if EAP-Response/UIM/Start was not used on re-authentication, the identity string from the EAP-Response/Identity packet. The RAND denotes the 32bits RAND value from the AT_RAND attribute used in the EAP-Request/UIM/Re-authentication packet.The RANDU denotes the 24bits RANDU value from the AT_RANDU attribute used in the EAP-Request/UIM/Re-authentication packet. The MK is the Master Key derived on the preceding full authentication. The pseudo-random number generator is run with the new seed value XKEY', and the resulting 320-bit random numbers x_0, x_1, ..., x_m-1 are concatenated and partitioned into 64-byte chunks and used as the new 64-byte Master Session Key and the new 64-byte Extended Master Session Key. The first 32 bytes of the MSK can be used as the Pairwise Master Key (PMK) for IEEE 802.11i. When the RADIUS attributes specified in [RFC 2548] are used to transport keying material, then the first 32 bytes of the MSK correspond to MS-MPPE-RECV-KEY and the second 32 bytes to MS-MPPE- SEND-KEY. In this case, only 64 bytes of keying material (the MSK) are used. Lizhiming [Page 37] Internet Draft EAP CAVE Authentication 15 April, 2004 5. Message Format and Protocol Extensibility 5.1. Message Format As specified in [EAP], EAP packets begin with the Code, Identifiers, Length, and Type fields, which are followed by EAP method specific Type-Data. The Code field in the EAP header is set to 1 for EAP requests, and to 2 for EAP Responses. The usage of the Length and Identifier fields in the EAP header are also specified in [EAP]. In EAP/CAVE, the Type field is set to xx. In EAP/CAVE, the Type-Data begins with an EAP/CAVE header that consists of a 1-octet Subtype field and a 2-octet reserved field. The Subtype values used in EAP/CAVE are defined in Section 8. The formats of the EAP header and the EAP/CAVE header are shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Code | Identifier | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Subtype | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The rest of the Type-Data, immediately following the EAP/CAVE header, consists of attributes that are encoded in Type, Length, Value format. The figure below shows the generic format of an attribute. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Value... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Attribute Type Indicates the particular type of attribute. The attribute type values are listed in Section 8. Length Indicates the length of this attribute in multiples of four bytes. The maximum length of an attribute is 1024 bytes. The length includes the Attribute Type and Length bytes. Value The particular data associated with this attribute. This field is always included and it may be two or more bytes in length. The type and length fields determine the format and length of the value field. Lizhiming [Page 38] Internet Draft EAP CAVE Authentication 15 April, 2004 Attributes numbered within the range 0 through 127 are called non- skippable attributes. When an EAP/CAVE peer encounters a non- skippable attribute that the peer does not recognize, the peer MUST send the EAP-Response/UIM/Client-Error packet which terminates the authentication exchange. If an EAP/CAVE server encounters a non- skippable attribute that the server does not recognize, then the server sends the EAP Failure packet which terminates the authentication exchange. Attributes within the range of 128 through 255 are called skippable attributes. When a skippable attribute is encountered that is not recognized it is ignored. The rest of the attributes and message data MUST still be processed. The Length field of the attribute is used to skip the attribute value in searching for the next attribute. Unless otherwise specified, the order of the attributes in an EAP/CAVE message is insignificant and an EAP/CAVE implementation should not assume a certain order to be used. Attributes can be encapsulated within other attributes. In other words, the value field of an attribute type can be specified to contain other attributes. 5.2. Protocol Extensibility EAP/CAVE can be extended by specifying new attribute types. If skippable attributes are used, it is possible to extend the protocol without breaking old implementations. However, any new attributes added to the EAP-Request/UIM/Start or EAP-Response/UIM/Start packets would not be integrity protected. Therefore, these messages MUST NOT be extended in the current version of EAP/CAVE. When specifying new attributes, it should be noted that EAP/CAVE does not support message fragmentation. Hence, the sizes of the new extensions MUST be limited so that the maximum transfer unit (MTU) of the underlying lower layer is not exceeded. According to [EAP], lower layers must provide an EAP MTU of 1020 bytes or greater, so any extensions to EAP/CAVE SHOULD NOT exceed the EAP MTU of 1020 bytes. Because EAP/CAVE supports version negotiation, new versions of the protocol can also be specified by using a new version number. 6. Messages This section specifies the messages used in EAP/CAVE. It specifies when a message may be transmitted or accepted, which attributes are allowed in a message, which attributes are required in a message, and other message specific details. The general message format is specified in Section 5.1. Lizhiming [Page 39] Internet Draft EAP CAVE Authentication 15 April, 2004 6.1. EAP-Request/UIM/Start In full authentication the first CAVE specific EAP Request is EAP- Request/UIM/Start. The EAP/UIM/Start roundtrip is used for two purposes. In full authentication this packet is used to request the peer to send the AT_NONCE_MT attribute to the server. In addition, as specified in Section 4.2, the Start round trip may be used by the server for obtaining the peer identity and ESN value of the peer. As discussed in Section 4.2, several Start rounds may be required in order to obtain a valid peer identity. The server MUST always include the AT_VERSION_LIST attribute. The server MAY include one of the following identity requesting attributes: AT_PERMANENT_ID_REQ, AT_FULLAUTH_ID_REQ, and AT_ANY_ID_REQ. These three attributes are mutually exclusive, so the server MUST NOT include more than one of the attributes. If the server has received a response from the peer, it MUST NOT issue a new EAP-Request/UIM/Start packet if it has either previously issued an EAP-Request/UIM/Start message without any identity requesting attributes or with the AT_PERMANENT_ID_REQ attribute. If the server has received a response from the peer, it MUST NOT issue a new EAP-Request/UIM/Start packet with the AT_ANY_ID_REQ or AT_FULLAUTH_ID_REQ attributes if it has previously issued an EAP- Request/UIM/Start message with the AT_FULLAUTH_ID_REQ attribute If the server has received a response from the peer, it MUST NOT issue a new EAP-Request/UIM/Start packet with the AT_ANY_ID_REQ attribute if the server has previously issued an EAP- Request/UIM/Start message with the AT_ANY_ID_REQ attribute. This message MUST NOT include AT_MAC, AT_IV, or AT_ENCR_DATA. 6.2. EAP-Response/UIM/Start The peer sends EAP-Response/SIM/Start in response to a valid EAP- Request/SIM/Start from the server. If and only if the server's EAP-Request/UIM/Start includes one of the identity requesting attributes, then the peer MUST include the AT_IDENTITY attribute. The usage of AT_IDENITY is defined in Section 4.2. The AT_NONCE_MT attribute MUST NOT be included if the AT_IDENTITY with a re-authentication identity is present for re-authentication. AT_NONCE_MT MUST be included in all other cases (full authentication). Lizhiming [Page 40] Internet Draft EAP CAVE Authentication 15 April, 2004 The AT_ESN attribute must be including if the server's EAP- Request/UIM/Start do not include the identity requesting attribute or the permanent identity of the peer is included in the EAP- Response/UIM/Start packet. The AT_SELECTED_VERSION attribute MUST NOT be included if the AT_IDENTITY attribute with a re-authentication identity is present for re-authentication. In all other cases, AT_SELECTED_VERSION MUST be included (full authentication). This attribute is used in version negotiation, as specified in Section 4.1. This message MUST NOT include AT_MAC, AT_IV, or AT_ENCR_DATA. 6.3. EAP-Request/UIM/Challenge The server sends the EAP-Request/UIM/Challenge after receiving a valid EAP-Response/UIM/Start, containing AT_NONCE_MT, AT_ESN and AT_SELECTED_VERSION, and after successfully obtaining the subscriber identity. The AT_RAND or AT_RANDU attribute MUST be included. The selection of the AT_RAND or AT_RANDU attribute is based on the way of challenge, i.e., global challenge or unique challenge is selected. The AT_MAC attribute MUST be included. For EAP- Request/UIM/Challenge, the MAC code is calculated over the following data: EAP packet| NONCE_MT The EAP packet is represented as specified in Section 5.1. It is followed by the 16-byte NONCE_MT value from the peer's AT_NONCE_MT attribute. 6.4. EAP-Response/UIM/Challenge The peer sends EAP-Response/UIM/Challenge in response to a valid EAP-Request/UIM/Challenge. The AT_MAC attribute MUST be included. For EAP- Response/UIM/Challenge, when the AT_RANDU attribute is included in the EAP_Request/UIM/Challenge, the MAC code is calculated over the following data: EAP packet| AUTHU The EAP packet is represented as specified in Section 5.1. The EAP packet bytes are immediately followed by one AUTHU values concatenated. The AUTHU is the response of AT_RANDU. For EAP-Response/UIM/Challenge, when the AT_RAND attribute is included in the EAP_Request/UIM/Challenge,the MAC code is calculated over the EAP packet and AT_AUTHR attribute must be included. Lizhiming [Page 41] Internet Draft EAP CAVE Authentication 15 April, 2004 6.5. EAP-Request/UIM/Re-authentication The server sends the EAP-Request/UIM/Re-authentication message if it wants to use re-authentication, and if it has received a valid re- authentication identity in EAP-Response/Identity or EAP- Response/UIM/Start. AT_MAC MUST be included. No message-specific data is included in the MAC calculation. See Section 7.2. The AT_IV and AT_ENCR_DATA attributes MUST be included. The plaintext consists of the following nested encrypted attributes, which MUST be included: AT_RANDU or AT_RAND. The selection of the AT_RAND or AT_RANDU attribute is based on the way of challenge, i.e., global challenge or unique challenge is selected.In addition, the nested encrypted attributes MAY include the following attributes: AT_NEXT_REAUTH_ID and AT_PADDING. 6.6. EAP-Response/UIM/Re-authentication The client sends the EAP-Response/UIM/Re-authentication packet in response to a valid EAP-Request/UIM/Re-authentication. The AT_MAC attribute MUST be included. For EAP-Response/UIM/Re- authentication, the MAC code is calculated over the following data: EAP packet| AUTHR or AUTHU The EAP packet is represented as specified in Section 5.1. It is followed by the 3-byte AUTHR or AUTHU value, which is the response to the RAND or RANDU value. The AT_IV and AT_ENCR_DATA attributes may be included. The AT_PADDING attribute MAY be included. 6.7. EAP-Request/UIM/Update The server sends the EAP-Request/UIM/Update if the server agree to executes SSD update procedure based on the received information from the Authentication Center. AT_MAC MUST be included. No message-specific data is included in the MAC calculation. See Section 7.2. The AT_RANDSSD must be included. 6.8. EAP-Response/UIM/Update-server-challenge The peer sends the EAP-Response/UIM/Update-server-challenge packet in response to a valid EAP-Request/UIM/Update. AT_MAC MUST be included. No message-specific data is included in the MAC calculation. See Section 7.2. Lizhiming [Page 42] Internet Draft EAP CAVE Authentication 15 April, 2004 AT_RANDBS MUST be included. 6.9. EAP-Request/UIM/Update-server-challenge The server sends the EAP-Request/UIM/Update-server-challenge packet in response to a valid EAP-Response/UIM/Update-server-challenge. The AT_MAC attribute MUST be included. For EAP- request/UIM/Update-server-challenge, the MAC code is calculated over the following data: EAP packet| AUTHBS The EAP packet is represented as specified in Section 5.1. The EAP packet bytes are immediately followed by one AUTHBS which is obtained from the Authentication Center. 6.10. EAP-Response/UIM/Update-Client-Success The peer sends the EAP-Response/UIM/Update-Client-Success packet in response to a valid EAP-Request/UIM/Update-server-challenge. AT_MAC MUST be included. No message-specific data is included in the MAC calculation. See Section 7.2. AT_SSD_UPDATE_SUCCESS MUST be included. 6.11. EAP-Request/UIM/Update-challenge The Server sends the EAP-Request/UIM/Update-challenge packet in response to a valid EAP-Response/UIM/Update-client-success. AT_MAC MUST be included. No message-specific data is included in the MAC calculation. See Section 7.2. AT_RANDU MUST be included. 6.12. EAP-Response/UIM/Update-challenge The peer sends the EAP-Response/UIM/Update-challenge packet in response to a valid EAP-Request/UIM/Update-challenge. The AT_MAC attribute MUST be included. For EAP- response/UIM/Update-challenge, the MAC code is calculated over the following data: EAP packet| AUTHU The EAP packet is represented as specified in Section 5.1. The EAP packet bytes are immediately followed by one AUTHU values concatenated. Lizhiming [Page 43] Internet Draft EAP CAVE Authentication 15 April, 2004 6.13. EAP-Response/UIM/Client-Error The peer sends EAP-Response/UIM/Client-Error in error cases, as specified in Section 4.6.1. The AT_CLIENT_ERROR_CODE attribute MUST be included. The AT_MAC, AT_IV, or AT_ENCR_DATA attributes MUST NOT be used with this packet. 6.14. EAP-Request/UIM/Notification The usage of this message is specified in Section 4.5. The AT_NOTIFICATION attribute MUST be included. The AT_MAC attribute is included in cases discussed in Section 4.5. No message-specific data is included in the MAC calculation. See Section 7.2. Later versions of this protocol MAY make use of the AT_ENCR_DATA and AT_IV attributes in this message to include encrypted (skippable) attributes. These attributes MAY be included only if the P bit of the notification code in AT_NOTIFICATION is set to zero. 6.15. EAP-Response/UIM/Notification The usage of this message is specified in Section 4.5. Because this packet is only an acknowledgement of EAP-Request/UIM/Notification, it does not contain any mandatory attributes. The AT_MAC attribute is included in cases described in Section 4.5. No message-specific data is included in the MAC calculation, see Section 7.2. Later versions of this protocol MAY make use of the AT_ENCR_DATA and AT_IV attributes in this message to include encrypted (skippable) attributes. These attributes MAY be included only if the P bit of the notification code in the AT_NOTIFICATION attribute of the server's EAP-Request/UIM/Notification packet is set to zero. 7. Attributes This section specifies the format of message attributes. The attribute type numbers are specified in Section 8. Lizhiming [Page 44] Internet Draft EAP CAVE Authentication 15 April, 2004 7.1. Table of Attributes The following table provides a guide to which attributes may be found in which kinds of messages, and in what quantity. Messages are denoted with numbers in parentheses as follows: (1) EAP- Request/UIM/Start, (2) EAP-Response/UIM/Start, (3) EAP- Request/UIM/Challenge, (4) EAP-Response/UIM/Challenge, (5) EAP- Request/UIM/Notification, (6) EAP-Response/UIM/Notification, (7) EAP-Response/UIM/Client-Error,(8) EAP-Request/UIM/Re-authentication, (9) EAP-Response/UIM/Re-authentication, (10) EAP-Request/UIM/Update, (11) EAP-Response/UIM/Update-Server-challenge, (12) EAP-Request/UIM/ Update-Server-Challenge, (13) EAP-Response/UIM/Update-Client-Success , (14) EAP-Request/UIM/Update-Challenge and (15) EAP-Response/UIM/ Update-Challenge. The column denoted with "Encr" indicates whether the attribute is a nested attribute that MUST be included within AT_ENCR_DATA, and the column denoted with "Skip" indicates whether the attribute is a skippable attribute. "0" indicates that the attribute MUST NOT be included in the message, "1" indicates that the attribute MUST be included in the message, "0-1" indicates that the attribute is sometimes included in the message, and "0*" indicates that the attribute is not included in the message in cases specified in this document, but MAY be included in the future versions of the protocol. Attribute (1) (2) (3) (4) (5) (6) (7) (8) (9) Encr Skip AT_MAC 0 0 1 1 0-1 0-1 0 1 1 N N AT_IV 0 0 0 0 0* 0* 0 1 1 N Y AT_ENCR_DATA 0 0 0 0 0* 0* 0 1 1 N Y AT_PADDING 0 0 0 0 0* 0* 0 0-1 0-1 Y N AT_VERSION_LIST 1 0 0 0 0 0 0 0 0 N N AT_SELECTED_VERSION 0 0-1 0 0 0 0 0 0 0 N N AT_NONCE_MT 0 0-1 0 0 0 0 0 0 0 N N AT_PERMANENT_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N AT_ANY_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N AT_FULLAUTH_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N AT_IDENTITY 0 0-1 0 0 0 0 0 0 0 N N AT_RAND 0 0 0-1 0 0 0 0 0-1 0 N N AT_RANDU 0 0 0 0 0 0 0 0-1 0 N N AT_RANDSSD 0 0 0 0 0 0 0 0 0 N N AT_RANDBS 0 0 0 0 0 0 0 0 0 N N AT_ESN 0 0-1 0 0 0 0 0 0 0 N N AT_AUTHR 0 0 0 0-1 0 0 0 0 0 N N AT_NEXT_PSEUDONYM 0 0 0 0 0 0 0 0 0 N N AT_NEXT_REAUTH_ID 0 0 0 0 0 0 0 0-1 0 Y Y AT_NOTIFICATION 0 0 0 0 1 0 0 0 0 N N AT_CLIENT_ERROR_CODE 0 0 0 0 0 0 1 0 0 N N AT_SSD_UPDATE_SUCCESS 0 0 0 0 0 0 0 0 0 N N Lizhiming [Page 45] Internet Draft EAP CAVE Authentication 15 April, 2004 Attribute (10)(11)(12)(13)(14)(15) Encr Skip AT_MAC 1 1 1 1 1 1 N N AT_IV 0 0 0 0 0 0 N N AT_ENCR_DATA 0 0 0 0 0 0 N N AT_PADDING 0 0 0 0 0 0 N N AT_VERSION_LIST 0 0 0 0 0 0 N N AT_SELECTED_VERSION 0 0 0 0 0 0 N N AT_NONCE_MT 0 0 0 0 0 0 N N AT_PERMANENT_ID_REQ 0 0 0 0 0 0 N N AT_ANY_ID_REQ 0 0 0 0 0 0 N N AT_FULLAUTH_ID_REQ 0 0 0 0 0 0 N N AT_IDENTITY 0 0 0 0 0 0 N N AT_RAND 0 0 0 0 0 0 N N AT_RANDU 0 0 0 0 1 0 N N AT_RANDSSD 1 0 0 0 0 0 N N AT_RANDBS 0 1 0 0 0 0 N N AT_ESN 0 0 0 0 0 0 N N AT_AUTHR 0 0 0 0 0 0 N N AT_SSD_UPDATE_SUCCESS 0 0 0 1 0 0 N N AT_NEXT_PSEUDONYM 0 0 0 0 0 0 N N AT_NEXT_REAUTH_ID 0 0 0 0 0 0 N N AT_NOTIFICATION 0 0 0 0 0 0 N N AT_CLIENT_ERROR_CODE 0 0 0 0 0 0 N N It should be noted that attributes AT_PERMANENT_ID_REQ, AT_ANY_ID_REQ and AT_FULLAUTH_ID_REQ are mutually exclusive, so that only one of them can be included at the same time. In re-authentication and full authentication, the attributes AT_RAND and AT_RANDU are mutually exclusive, only one of them can be included at the same time. If one of the attributes AT_IV and AT_ENCR_DATA is included, then both of the attributes MUST be included. 7.2. AT_MAC The AT_MAC attribute is used for EAP/CAVE message authentication. Section 6 specifies which messages AT_MAC MUST be included. The value field of the AT_MAC attribute contains two reserved bytes followed by a keyed message authentication code (MAC). The MAC is calculated over the whole EAP packet concatenated with optional message-specific data, with the exception that the value field of the MAC attribute is set to zero when calculating the MAC. The EAP packet includes the EAP header that begins with the Code field, the EAP/CAVE header that begins with the Subtype field, and all the attributes, as specified in Section 5.1. The reserved bytes in AT_MAC are set to zero when sending and ignored on reception. The contents of the message-specific data that may be included in the MAC calculation are specified separately for each EAP/CAVE message in Section 6. Lizhiming [Page 46] Internet Draft EAP CAVE Authentication 15 April, 2004 The format of the AT_MAC attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_MAC | Length = 5 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | MAC | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The MAC algorithm is HMAC-SHA1-128 [RFC 2104] keyed hash value. (The HMAC-SHA1-128 value is obtained from the 20-byte HMAC-SHA1 value by truncating the output to 16 bytes. Hence, the length of the MAC is 16 bytes.) The derivation of the authentication key (K_aut) used in the calculation of the MAC is specified in Section 4.7. When the AT_MAC attribute is included in an EAP/CAVE message, the recipient MUST process the AT_MAC attribute before looking at any other attributes. If the message authentication code is invalid, then the recipient MUST ignore all other attributes in the message and operate as specified in Section 4.6. 7.3. AT_IV, AT_ENCR_DATA and AT_PADDING AT_IV and AT_ENCR_DATA attributes can be used to transmit encrypted information between the EAP/CAVE peer and server. The value field of AT_IV contains two reserved bytes followed by a 16-byte initialization vector required by the AT_ENCR_DATA attribute. The reserved bytes are set to zero when sending and ignored on reception. The AT_IV attribute MUST be included if and only if the AT_ENCR_DATA is included. Section 4.6 specifies the operation if a packet that does not meet this condition is encountered. The sender of the AT_IV attribute chooses the initialization vector by random. The sender MUST NOT reuse the initialization vector value from previous EAP CAVE packets and the sender MUST choose it freshly for each AT_IV attribute. The sender SHOULD use a good source of randomness to generate the initialization vector. Please see [RFC 1750] for more information about generating random numbers for security applications. The format of AT_IV is shown below. Lizhiming [Page 47] Internet Draft EAP CAVE Authentication 15 April, 2004 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_IV | Length = 5 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | Initialization Vector | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of the AT_ENCR_DATA attribute consists of two reserved bytes followed by cipher text bytes encrypted using the Advanced Encryption Standard (AES) [AES] in the Cipher Block Chaining (CBC) mode of operation using the initialization vector from the AT_IV attribute. The reserved bytes are set to zero when sending and ignored on reception. Please see [CBC] for a description of the CBC mode. The format of the AT_ENCR_DATA attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_ENCR_DATA | Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Encrypted Data . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The derivation of the encryption key (K_encr) is specified in Section 4.7. The plaintext consists of nested EAP/CAVE attributes. The encryption algorithm requires the length of the plaintext to be a multiple of 16 bytes. The sender may need to include the AT_PADDING attribute as the last attribute within AT_ENCR_DATA. The AT_PADDING attribute is not included if the total length of other nested attributes within the AT_ENCR_DATA attribute is a multiple of 16 bytes. As usual, the Length of the Padding attribute includes the Attribute Type and Attribute Length fields. The length of the Padding attribute is 4, 8 or 12 bytes. It is chosen so that the length of the value field of the AT_ENCR_DATA attribute becomes a multiple of 16 bytes. The actual pad bytes in the value field are set to zero (0x00) on sending. The recipient of the message MUST verify that the pad bytes are set to zero. If this verification fails on the peer, then it MUST send the EAP-Response/UIM/Client- Error packet with the error code "unable to process packet" to Lizhiming [Page 48] Internet Draft EAP CAVE Authentication 15 April, 2004 terminate the authentication exchange. If this verification fails on the server, then the server sends EAP Failure to terminate the authentication exchange. The format of the AT_PADDING attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_PADDING | Length | Padding... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 7.4. AT_VERSION_LIST The format of the AT_VERSION_LIST attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_VERSION_L..| Length | Actual Version List Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Supported Version 1 | Supported Version 2 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Supported Version N | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This attribute is used in version negotiation, as specified in Section 4.1. The attribute contains the version numbers supported by the EAP/CAVE server. The server MUST only include versions that it implements and that are allowed in its security policy. The server SHOULD list the versions in the order of preference, most preferred versions first. At least one version number MUST be included. The version number for the protocol described in this document is one (0x0001). The value field of this attribute begins with 2-byte Actual Version List Length, which specifies the length of the Version List in bytes, not including the Actual Version List Length attribute length. This field is followed by the list of the versions supported by the server, which each have a length of 2 bytes. For example, if there is only one supported version, then the Actual Version List Length is 2. Because the length of the attribute must be a multiple of 4 bytes, the sender pads the value field with zero bytes when necessary. Lizhiming [Page 49] Internet Draft EAP CAVE Authentication 15 April, 2004 7.5. AT_SELECTED_VERSION The format of the AT_SELECTED_VERSION attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_SELECTED...| Length = 1 | Selected Version | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ This attribute is used in version negotiation, as specified in Section 4.1. The value field of this attribute contains a two-byte version number, which indicates the EAP/CAVE version that the peer wants to use. 7.6. AT_NONCE_MT The format of the AT_NONCE_MT attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |AT_NONCE_MT | Length = 5 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | NONCE_MT | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of the NONCE_MT attribute contains two reserved bytes followed by a random number generated by the peer (16 bytes long) freshly for this EAP/CAVE authentication exchange. The random number is used as a seed value for the new keying material. The reserved bytes are set to zero upon sending and ignored upon reception. The peer MUST choose the NONCE_MT value freshly for each EAP/CAVE authentication exchange. If an EAP/CAVE exchange includes several EAP/UIM/Start rounds, then the peer MAY use the same NONCE_MT value in all EAP-Response/UIM/Start packets. The peer SHOULD use a good source of randomness to generate NONCE_MT. Please see [RFC 1750] for more information about generating random numbers for security applications. Lizhiming [Page 50] Internet Draft EAP CAVE Authentication 15 April, 2004 7.7. AT_PERMANENT_ID_REQ The format of the AT_PERMANENT_ID_REQ attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |AT_PERM..._REQ | Length = 1 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The use of the AT_PERMANENT_ID_REQ is defined in Section 4.2. The value field only contains two reserved bytes, which are set to zero on sending and ignored on reception. 7.8. AT_ANY_ID_REQ The format of the AT_ANY_ID_REQ attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |AT_ANY_ID_REQ | Length = 1 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The use of the AT_ANY_ID_REQ is defined in Section 4.2. The value field only contains two reserved bytes, which are set to zero on sending and ignored on reception. 7.9. AT_FULLAUTH_ID_REQ The format of the AT_FULLAUTH_ID_REQ attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |AT_ANY_ID_REQ | Length = 1 | Reserved | +---------------+---------------+-------------------------------+ The use of the AT_FULLAUTH_ID_REQ is defined in Section 4.2. The value field only contains two reserved bytes, which are set to zero on sending and ignored on reception. Lizhiming [Page 51] Internet Draft EAP CAVE Authentication 15 April, 2004 7.10. AT_IDENTITY The format of the AT_IDENTITY attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_IDENTITY | Length | Actual Identity Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Identity (optional) . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The use of the AT_IDENTITY is defined in Section 4.2. The value field of this attribute begins with 2-byte actual identity length, which specifies the length of the identity in bytes. This field is followed by the subscriber identity of the indicated actual length. The identity is the permanent identity, a pseudonym identity or a re-authentication identity. The identity format is specified in Section 4.2.1. The same identity format is used in the AT_IDENTITY attribute and the EAP-Response/Identity packet, with the exception that the peer MUST NOT decorate the identity it includes in AT_IDENTITY. The identity does not include any terminating null characters. Because the length of the attribute must be a multiple of 4 bytes, the sender pads the identity with zero bytes when necessary. 7.11. AT_RAND The format of the AT_RAND attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_RAND | Length =2 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RAND | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of this attribute contains two reserved bytes followed by the RAND (4 bytes). The reserved bytes are set to zero upon sending and ignored upon reception. Lizhiming [Page 52] Internet Draft EAP CAVE Authentication 15 April, 2004 7.12. AT_NEXT_REAUTH_ID The format of the AT_NEXT_REAUTH_ID attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_NEXT_REAU..| Length | Actual Re-Auth Identity Length| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Next Re-authentication Username . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of this attribute begins with 2-byte actual re- authentication identity length which specifies the length of the following re-authentication identity in bytes. This field is followed by a re-authentication identity that the peer can use in the next re-authentication, as described in Section 4.3. In environments where a realm portion is required, the re- authentication identity includes both a username portion and a realm name portion. The re-authentication identity does not include any terminating null characters. Because the length of the attribute must be a multiple of 4 bytes, the sender pads the re-authentication identity with zero bytes when necessary. The identity encoding MUST follow the UTF-8 transformation format [RFC2279]. 7.13. AT_RANDU The format of the AT_RANDU attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_RANDU | Length=2 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | RANDU | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of this attribute contains three reserved bytes followed by the RANDU (3 bytes). The reserved bytes are set to zero upon sending and ignored upon reception. Lizhiming [Page 53] Internet Draft EAP CAVE Authentication 15 April, 2004 7.14. AT_RANDBS The format of the AT_RANDBS attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_RANDBS | Length=2 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | RANDBS | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of this attribute contains three reserved bytes followed by the RANDBS (4 bytes). The reserved bytes are set to zero upon sending and ignored upon reception. 7.15. AT_RANDSSD The format of the AT_RANDSSD attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_RANDSSD | Length = 3 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | | +-+-+-+-+-+-+-+-+ | | RANDSSD | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of the AT_RANDSSD attribute contains three reserved bytes followed by a random number generated by the AC (7 bytes) freshly for this EAP/CAVE SSD Update. The random number is used as a seed for the new SSD. The reserved bytes are set to zero upon sending and ignored upon reception. 7.16. AT_NOTIFICATION The format of the AT_NOTIFICATION attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |AT_NOTIFICATION| Length = 1 |F|P| Notification Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of this attribute contains a two-byte notification code. The first and second bit (F and P) of the notification code are interpreted as described in Section 4.5. The notification code values listed below have been reserved. The descriptions below illustrate the semantics of the notifications. Lizhiming [Page 54] Internet Draft EAP CAVE Authentication 15 April, 2004 The peer implementation MAY use different wordings when presenting the notifications to the user. The "requested service" depends on the environment where EAP/CAVE is applied. 1026 - User has been temporarily denied access to the requested service. (Implies failure, used after the challenge round) 1031 - User has not subscribed to the requested service (implies failure, used after the challenge round) 7.17. AT_CLIENT_ERROR_CODE The format of the AT_CLIENT_ERROR_CODE attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |AT_CLIENT_ERR..| Length = 1 | Client Error Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of this attribute contains a two-byte client error code. The following error code values have been reserved. 0 "unable to process packet": a general error code 1 "unsupported version": the peer does not support any of the versions listed in AT_VERSION_LIST 2 "insufficient number of challenges": the peer's policy requires more triplets than the server included in AT_RAND 3 "RAND are not fresh": the peer believes that the RAND challenges included in AT_RAND were not fresh 7.18. AT_SSD_UPDATE_SUCCESS The format of the AT_SSD_UPDATE_SUCCESS attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |AT_SSD_UP_SUC | Length = 1 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The use of the AT_SSD_UPDATE_SUCCESS is defined in Section 4.4. The value field only contains two reserved bytes, which are set to zero on sending and ignored on reception. Lizhiming [Page 55] Internet Draft EAP CAVE Authentication 15 April, 2004 7.19. AT_ESN The format of the AT_ESN attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_ESN | Length=2 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ESN | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of this attribute contains two reserved bytes followed by the ESN (4 bytes). The reserved bytes are set to zero upon sending and ignored upon reception. 7.20. AT_AUTHR The format of the AT_AUTHR attribute is shown below. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AT_AUTHR | Length=2 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reserved | AUTHR | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The value field of this attribute contains three reserved bytes followed by the AUTHR (3 bytes). The reserved bytes are set to zero upon sending and ignored upon reception. 8. IANA Considerations The realm name "owlan.org" has been reserved for NAI realm names generated from the IMSI. EAP/CAVE messages include a Subtype field. The following Subtypes are temporarily specified: Lizhiming [Page 56] Internet Draft EAP CAVE Authentication 15 April, 2004 Start..........................................10 Challenge......................................11 Notification...................................12 Re-authentication..............................13 Client-Error...................................14 Update.........................................15 Update_server_challenge........................16 Update_Client_success..........................17 Update_Challenge...............................18 The Subtype-specific data is composed of attributes, which have attribute type numbers. The following attribute types are temporarily specified: AT_RAND.........................................1 AT_PADDING......................................6 AT_NONCE_MT.....................................7 AT_PERMANENT_ID_REQ............................10 AT_MAC.........................................11 AT_NOTIFICATION................................12 AT_ANY_ID_REQ..................................13 AT_IDENTITY....................................14 AT_VERSION_LIST................................15 AT_SELECTED_VERSION............................16 AT_FULLAUTH_ID_REQ.............................17 AT_RANDU.......................................19 AT_RANDSSD.....................................20 AT_RANDBS......................................22 AT_ESN.........................................24 AT_AUTHR.......................................26 AT_CLIENT_ERROR_CODE...........................28 AT_IV.........................................129 AT_ENCR_DATA..................................130 AT_NEXT_REAUTH_ID.............................133 The AT_NOTIFICATION attribute contains a notification code value. Values 1024, 1026 and 1031 have been specified in Section 7.16 of this document. The AT_VERSION_LIST and AT_SELECTED_VERSION attributes contain version numbers. Version 1 has been specified in Section 7.4 of this document. The AT_CLIENT_ERROR_CODE attribute contains a client error code. Values 0, 1, 2 and 3 have been specified in Section 7.17 of this document. Lizhiming [Page 57] Internet Draft EAP CAVE Authentication 15 April, 2004 All requests for value assignment from the various number spaces described in this document require proper documentation, according to the "Specification Required" policy described in [RFC 2434]. Requests must be specified in sufficient detail so that interoperability between independent implementations is possible. Possible forms of documentation include, but are not limited to, RFCs, the products of another standards body (e.g. 3GPP2), or permanently and readily available vendor design notes. 9. Security Considerations The EAP base protocol [EAP] highlights several attacks that are possible against the EAP protocol as there is no inherent security mechanisms provided. This section discusses the claimed security properties of EAP CAVE as well as vulnerabilities and security recommendations. 9.1. Identity Protection EAP/CAVE includes optional identity privacy support that protects the privacy of the subscriber identity against passive eavesdropping. The mechanism cannot be used on the first EAP exchange with a given server, because the permanent identity will have to be sent in the clear. The terminal SHOULD store the pseudonym in a non-volatile memory so that it can be maintained across reboots. An active attacker that impersonates the network may use the AT_PERMANENT_ID_REQ attribute to attempt to learn the subscriber's permanent identity. However, as discussed in Section 4.2.2, the terminal can refuse to send the cleartext permanent identity if it believes that the network should be able to recognize the pseudonym. If the peer and server cannot guarantee that the pseudonym will be maintained reliably and identity privacy is required then additional protection from an external security mechanism such as Protected Extensible Authentication Protocol (PEAP) [PEAP] may be used. If an external security mechanism is in use the identity privacy features of EAP-CAVE may not be useful. The security considerations of using an external security mechanism with EAP-CAVE are beyond the scope of this document. 9.2. Mutual Authentication EAP/CAVE provides mutual authentication. The peer believes that the network is authentic because the network can calculate a correct AT_MAC value in the EAP-Request/UIM/Challenge packet. Since the security of EAP/CAVE is based on the secrecy of CMEA key. care should be taken not to expose these values to attackers when they are transmitted between entities, stored or handled. Steps should be taken to limit the transport, storage and handling of this values outside a protected environment. These considerations are important at both the peer and EAP server implementations. Lizhiming [Page 58] Internet Draft EAP CAVE Authentication 15 April, 2004 9.3. Key Derivation EAP/CAVE supports key derivation. The key hierarchy is specified in Section 4.7. The actual strength of the resulting keys depends, among other things, on some operator specific parameters including authentication algorithms, the strength of the A-key, and the quality of the RAND or RANDU challenges. Because the strength of the CMEA key is 64 bits, the ultimate strength of any derived secret key material is never more than 64 bits. The EAP Transient Keys used to protect EAP CAVE packets (K_encr, K_aut) and the Master Session Key are cryptographically separate. An attacker cannot derive any non- trivial information from K_encr or K_aut based on the Master Session Key or vice versa. An attacker also cannot calculate the pre-shared secret from the cdma CMEA key used, EAP CAVE K_encr, EAP CAVE K_aut, or from the Master Session Key. Each EAP/CAVE exchange generates fresh keying material. The EAP CAVE peer contributes to the keying material with the NONCE_MT parameter, which must be chosen freshly for each exchange. 9.4. Dictionary Attacks Because EAP/CAVE is not a password protocol, it is not vulnerable to dictionary attacks. (The pre-shared symmetric secret stored on the UIM card shall not be a weak password.) 9.5. Credentials Reuse Lizhiming [Page 59] Internet Draft EAP CAVE Authentication 15 April, 2004 9.6. Integrity and Replay Protection, and Confidentiality AT_MAC, AT_IV and AT_ENCR_DATA attributes are used to provide integrity, replay and confidentiality protection for EAP/CAVE requests and responses. Integrity protection includes the EAP header. These attributes cannot be used during the EAP/UIM/Start roundtrip. However, the protocol values (identity, NONCE_MT and version negotiation parameters) are protected by later EAP/CAVE messages. Integrity protection (AT_MAC) is based on a keyed message authentication code. Confidentiality (AT_ENCR_DATA and AT_IV) is based on a block cipher. On full authentication, replay protection is provided by the RAND or RANDU values from the underlying cdma authentication scheme and the use of the NONCE_MT value. On re-authentication, a similar way is used to provide replay protection. Contents of the EAP-Response/Identity packet are implicitly integrity protected by including them in key derivation. Because EAP/CAVE is not a tunneling method, EAP Notification, EAP Success or EAP Failure packets are not confidential, integrity protected or replay protected in EAP/CAVE. On physically insecure networks, this may enable an attacker to send false notifications to the peer and to mount denial of service attacks by spoofing these packets. An eavesdropper will see the EAP Notification, EAP Success and EAP Failure packets sent in the clear. With EAP CAVE, confidential information MUST NOT be transmitted in EAP Notification packets. 9.7. Negotiation Attacks EAP/CAVE does not protect the EAP-Response/Nak packet. Because EAP/CAVE does not protect the EAP method negotiation, EAP method downgrading attacks may be possible, especially if the user uses the same identity with EAP/CAVE and other EAP methods. EAP/CAVE includes a version negotiation procedure. In EAP/CAVE the keying material derivation includes the version list and selected version to ensure that the protocol cannot be downgraded and that the peer and server use the same version of EAP/CAVE. As described in Section 5, EAP/CAVE allows the protocol to be extended by defining new attribute types. When defining such attributes, it should noted that any extra attributes included in EAP-Request/UIM/Start or EAP-Response/UIM/Start packets are not included in the MACs later on, and thus some other precautions must be taken to avoid modifications to them. Lizhiming [Page 60] Internet Draft EAP CAVE Authentication 15 April, 2004 EAP/CAVE does not support ciphersuite negotiation. 9.8. Fast Reconnect EAP/CAVE includes an optional re-authentication ("fast reconnect") procedure, as recommended in [EAP] for EAP types that are intended for physically insecure networks. 9.9. Acknowledged Result Indications EAP/CAVE does not provide acknowledged or integrity protected Success or Failure indications. If an EAP Success or EAP Failure packet is lost when using EAP/CAVE over an unreliable medium and if the protocol over which EAP/CAVE is transported does not address the possible loss of Success or Failure, then the peer and EAP server may end up having a different interpretation of the state of the authentication conversation. On physically insecure networks, an attacker may mount denial of service attacks by sending false EAP Success or EAP Failure indications. However, the attacker cannot force the peer or the EAP server to believe successful authentication has occurred when mutual authentication failed or has not happened yet. 9.10. Man-in-the-middle Attacks In order to avoid man-in-the-middle attacks and session hijacking, user data SHOULD be integrity protected on physically insecure networks. The EAP/CAVE Master Session Key or keys derived from it MAY be used as the integrity protection keys, or, if an external security mechanism such as PEAP is used, then the link integrity protection keys MAY be derived by the external security mechanism. There are man-in-the-middle attacks associated with the use of any EAP method within a tunneled protocol such as PEAP, or within a sequence of EAP methods followed by each other. This specification does not address these attacks. If EAP/CAVE is used with a tunneling protocol or as part of a sequence of methods, there should be cryptographic binding provided between the protocols and EAP/CAVE to prevent man-in-the-middle attacks through rogue authenticators being able to setup one-way authenticated tunnels. The EAP/CAVE Master Session Key MAY be used to provide the cryptographic binding. However the mechanism how the binding is provided depends on the tunneling or sequencing protocol and is beyond the scope of this document. Lizhiming [Page 61] Internet Draft EAP CAVE Authentication 15 April, 2004 9.11. Generating Random Numbers An EAP/CAVE implementation SHOULD use a good source of randomness to generate the random numbers required in the protocol. Please see [RFC 1750] for more information on generating random numbers for security applications. 10. Security Claims This section provides the security claims required by [EAP]. [a] Intended use. EAP CAVE is intended for use over both physically insecure networks and physically or otherwise secure networks. Applicable media include but are not limited to PPP, IEEE 802 wired networks and IEEE 802.11. [b] Mechanism. EAP CAVE is based on the cama CAVE mechanism, which is a challenge/response authentication and key agreement mechanism based on a symmetric 64-bit pre-shared secret. EAP CAVE also makes use of a peer challenge to provide mutual authentication. [c] Security claims. The security properties of the method are discussed in Section 9. [d] Key strength. EAP CAVE supports key derivation with 64-bit effective key strength. However, as discussed in Section 9, if the same credentials are used in cdma and in EAP/CAVE, then the key strength may be reduced considerably, basically to the same level as in cdma, by mounting attacks over cdma. For example an active attack using a false cdma base station reduces the effective key strength to almost zero. [e] Description of key hierarchy. Please see Section 4.7. [f] Indication of vulnerabilities. Vulnerabilities are discussed in Section 9. Lizhiming [Page 62] Internet Draft EAP CAVE Authentication 15 April, 2004 11. Acknowledgements and Contributions 11.1. Contributors In addition to the editors, Nora Dabbous, JunHyuk Song, and Jian Wang were significant contributors to this document. 11.2. Acknowledgements This protocol has been partly developed based on the EAP SIM [EAP SIM], and hence this specification incorporates many ideas from Jari Arkko. Normative References [3GPP2 S.S0053] 3GPP2 Technical Specification 3GPP2 S.S0053 V1.0: "Common Cryptographic Algorithms", 3rd Generation Partnership Project 2, Jan 2002. [3GPP2 N.S0005] 3GPP2 Technical Specification 3GPP2 N.S0005 V1.0: "Cellular Radiotelecommunications Intersystem Operations", 3rd Generation Partnership Project 2, June 2001. [RFC 2119] S. Bradner, "Key words for use in RFCs to indicate Requirement Levels", RFC 2119, March 1997. [3GPP2 N.S0009] 3GPP2 Technical Specification 3GPP2 N.S0009 V1.0: "IMSI", 3rd Generation Partnership Project 2, June 2001. [RFC 2486] Aboba, B. and M. Beadles, "The Network Access Identifier", RFC 2486, January 1999. [RFC 2104] H. Krawczyk, M. Bellare, R. Canetti, "HMAC: Keyed-Hashing for Message Authentication", RFC 2104, February 1997. [AES] Federal Information Processing Standards (FIPS) Publication 197, "Advanced Encryption Standard (AES)", National Institute of Standards and Technology, November 26, 2001. http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf [CBC] NIST Special Publication 800-38A, "Recommendation for Block Cipher Modes of Operation - Methods and Techniques", National Institute of Standards and Technology, December 2001. http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf [SHA-1] Federal Information Processing Standard (FIPS) Publication 180-1, "Secure Hash Standard," National Institute of Standards and Technology, U.S. Department of Commerce, October 17, 1995. Lizhiming [Page 63] Internet Draft EAP CAVE Authentication 15 April, 2004 [PRF] Federal Information Processing Standards (FIPS) Publication 186-2 (with change notice), "Digital Signature Standard (DSS)", National Institute of Standards and Technology, January 27, 2000. Available on-line at: http://csrc.nist.gov/publications/fips/fips186-2/fips186-2- change1.pdf [RFC 2434] T. Narten, H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, October 1998. [RFC2279] F. Yergeau, "UTF-8, a transformation format of ISO 10646", RFC 2279, January 1998. [EAP] L. Blunk et al., "Extensible Authentication Protocol (EAP)", draft-ietf-eap-rfc2284bis-05.txt, work-in-progress, September 2003. Informative References [PEAP] H. Andersson, S. Josefsson, G. Zorn, D. Simon, A. Palekar, "Protected EAP Protocol (PEAP)", draft-josefsson-pppext-eap-tls-eap- 05.txt, work-in-progress, September 2002. [RFC 1750] D. Eastlake, 3rd, S. Crocker, J. Schiller, "Randomness Recommendations for Security", RFC 1750 (Informational), December 1994. [RFC 3344] C. Perkins (editor), "IP Mobility Support", RFC 3344, August 2002. [EAP SIM] H. Haverinen, J. Salowey, "EAP SIM Authentication", draft- arkko-pppext-eap-sim-12.txt, Oct 2003 (work in progress). [RFC 2548] G. Zorn, "Microsoft Vendor-specific RADIUS Attributes", RFC 2548, March 1999 Lizhiming [Page 64] Internet Draft EAP CAVE Authentication 15 April, 2004 Editors' and Contributors' Contact Information Zhiming Li Huawei Technologies Co., LTD Pudong Lujiazui Software Park No 98, Lane 91, Eshan Road, Pudong, Shanghai,China, 200127 E-mail: lizhiming@huawei.com Phone: +86 21 68644808-24039 Nora Dabbous Gemplus 34 rue Guynemer 92447 Issy les Moulineaux France E-mail: nora.dabbous@gemplus.com Phone: +33 1 4648 2000 JunHyuk Song Samsung Electronics NTP Lab1 Email: junhyuk.song@samsung.com Phone: +82 31 279-3639 Jian Wang Datang Mirco elctronics Technology No 40, Xueyuan Road, Haidian District, Beijing, China,100083 E-mail:wangj@dmt.com.cn Phoneś¦+86-10-62302680 Annex A. Pseudo-Random Number Generator The "|" character denotes concatenation, and "^" denotes involution. Step 1: Choose a new, secret value for the seed-key, XKEY Step 2: In hexadecimal notation let t = 67452301 EFCDAB89 98BADCFE 10325476 C3D2E1F0 This is the initial value for H0|H1|H2|H3|H4 in the FIPS SHS [SHA-1] Step 3: For j = 0 to m - 1 do 3.1 XSEED_j = 0 /* no optional user input */ 3.2 For i = 0 to 1 do a. XVAL = (XKEY + XSEED_j) mod 2^b b. w_i = G(t, XVAL) c. XKEY = (1 + XKEY + w_i) mod 2^b 3.3 x_j = w_0|w_1 Lizhiming [Page 65] Internet Draft EAP CAVE Authentication 15 April, 2004