📄 draft-haverinen-pppext-eap-sim-11.txt
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Haverinen and Salowey Expires in six months [Page 9] Internet Draft EAP SIM Authentication June 2003 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". If the client is not able to determine whether the MNC is two or three digits long, the client MAY use a 3-digit MNC. If the correct length of the MNC is two, then the MNC used in the realm name will include 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. 5.2. Obtaining Subscriber Identity via EAP/SIM Messages It may be useful to obtain the identity of the subscriber through means other than EAP Request/Identity. This can eliminate the need for an identity request when using EAP method negotiation. If this was not possible then it might not be possible to negotiate EAP/SIM as the second method since it is not specified how to deal with a new EAP Request/Identity. If the EAP server has not received any identity (permanent identity, pseudonym or re-authentication identity) from the client when sending the first EAP/SIM request, then the EAP server SHOULD issue the EAP-Request/SIM/Start packet and includes the AT_ANY_ID_REQ attribute (specified in Section 9). This attribute does not contain any data. If the EAP server has received an EAP-Response/Identity packet but the contents do not appear to be a valid permanent identity, pseudonym or a re-authentication identity, the EAP server SHOULD issue an EAP-Request/SIM/Start packet with the AT_ANY_ID_REQ attribute. In some environments the intermediate entities or software layers in the client may modify the identity string in the EAP- Response/Identity packet. For example, some EAP layer implementations may cache the identity string from the first authentication and do not obtain a new identity string from the EAP method implementation on subsequent authentication exchanges. Because the identity string is used in key derivation, such modifications will result in failed authentication unless the EAP server uses the AT_ANY_ID_REQ attribute to obtain an unmodified copy of the identity string. Therefore, in cases when there is a possibility that an intermediate element or software layer may modify the EAP-Response/Identity packet, the EAP server SHOULD always use the AT_ANY_ID_REQ attribute, even if the identity received in EAP-Response/Identity was valid. The AT_ANY_ID_REQ attribute requests the client to include the AT_IDENTITY attribute (specified in Section 10) in the EAP- Response/SIM/Start packet. The identity format in the AT_IDENTITY Haverinen and Salowey Expires in six months [Page 10] Internet Draft EAP SIM Authentication June 2003 attribute is the same as in the EAP-Response/Identity packet. The AT_IDENTITY attribute contains a permanent identity, a pseudonym identity or a re-authentication identity. If the server does not support re-authentication, it uses the AT_FULLAUTH_ID_REQ attribute instead of the AT_ANY_ID_REQ attribute to directly request for a full authentication identity (either the permanent identity or a pseudonym identity). If the server uses the AT_FULLAUTH_ID_REQ attribute, the client MUST NOT use a re-authentication identity in the AT_IDENTITY attribute. The use of pseudonyms for anonymity is specified in Section 5.3. The use of re-authentication identities is specified in Section 6. 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/SIM/Start. Client Authenticator | | | +------------------------------+ | | Server does not have any | | | Subscriber identity available| | | When starting EAP/SIM | | +------------------------------+ | | | EAP-Request/SIM/Start | | (AT_ANY_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/SIM/Start | | (AT_IDENTITY, AT_NONCE_MT, | | AT_SELECTED_VERSION) | |------------------------------------------------------>| | | If the client wants to perform full authentication, it includes the permanent identity or a pseudonym identity in the AT_IDENTITY attribute. The client may use these identities in response to either AT_ANY_ID_REQ or AT_FULLAUTH_ID_REQ. In this case, the client MUST include AT_NONCE_MT and AT_SELECTED_VERSION attributes in EAP- Response/SIM/Start message, as required on full authentication. If the server uses the AT_ANY_ID_REQ and the client wants to perform re-authentication, then the client includes a re-authentication identity in the AT_IDENTITY attribute. On re-authentication, the client MUST NOT include AT_NONCE_MT or AT_SELECTED_VERSION attributes. This case is illustrated below. Haverinen and Salowey Expires in six months [Page 11] Internet Draft EAP SIM Authentication June 2003 Client Authenticator | | | +------------------------------+ | | Server does not have any | | | Subscriber identity available| | | When starting EAP/SIM | | +------------------------------+ | | | EAP-Request/SIM/Start | | (AT_ANY_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/SIM/Start | | (AT_IDENTITY containing a re-authentication identity) | |------------------------------------------------------>| | | If the client 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 decode to the permanent identity, then the full authentication sequence proceeds as usual with the EAP Server issuing the EAP-Request/SIM/Challenge message. 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 6. If the server does not recognize the re- authentication identity, then the server issues a second EAP- Request/SIM/Start message and includes the AT_FULLAUTH_ID_REQ attribute. In this case, a second EAP/SIM/Start round trip is required. The messages used on the first roundtrip are ignored. (However, all EAP/SIM/Start messages are taken into account when calculating the checkcode for AT_CHECKCODE. AT_CHECKCODE is specified in Section 8.2.) This is illustrated below. Haverinen and Salowey Expires in six months [Page 12] Internet Draft EAP SIM Authentication June 2003 Client Authenticator | | | +------------------------------+ | | Server does not have any | | | Subscriber identity available| | | When starting EAP/SIM | | +------------------------------+ | | | EAP-Request/SIM/Start | | (AT_ANY_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/SIM/Start | | (AT_IDENTITY containing a re-authentication identity) | |------------------------------------------------------>| | | | +------------------------------+ | | Server does not recognize | | | The re-authentication | | | Identity | | +------------------------------+ | | | EAP-Request/SIM/Start | | (AT_FULLAUTH_ID_REQ, AT_VERSION_LIST) | |<------------------------------------------------------| | | | | | EAP-Response/SIM/Start | | (AT_IDENTITY with a full-auth. identity, AT_NONCE_MT, | | AT_SELECTED_VERSION) | |------------------------------------------------------>| | | If the server recognizes the re-authentication identity, but still wants to fall back on full authentication, the server may issue the EAP-Request/SIM/Start packet without any identity request attributes (AT_FULLAUTH_ID_REQ or AT_PERMANENT_ID_REQ). In this case, the server only includes the AT_VERSION_LIST attribute, and full authentication proceeds as usual. The client does not include any identity attributes in the EAP-Response/SIM/Start packet. An extra EAP/SIM/Start round trip is also required in cases when the AT_IDENTITY attribute contains a pseudonym identity that the EAP server fails to decode. The operation in this case is specified in Section 5.3. 5.3. Identity Privacy Support EAP/SIM includes optional identity privacy (anonymity) support that can be used to hide the cleartext permanent identity and to make the subscriber's connections unlinkable to eavesdroppers. Identity Haverinen and Salowey Expires in six months [Page 13] Internet Draft EAP SIM Authentication June 2003 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 19.1 for security considerations regarding identity privacy. If identity privacy is not used or if the client does not have any pseudonyms or re-authentication identities are available, the client transmits the permanent identity in the EAP-Response/Identity packet or in the AT_IDENTITY attribute. The EAP-Request/SIM/Challenge message MAY include an encrypted pseudonym in the value field of the AT_ENCR_DATA attribute. The AT_IV and AT_MAC attributes are also used to transport the pseudonym to the client, as described in Section 11. Because the identity privacy support is optional to implement, the client MAY ignore the AT_IV and AT_ENCR_DATA attributes and always transmit the permanent identity in the EAP-Response/Identity packet and in the AT_IDENTITY attribute. On receipt of the EAP-Request/SIM/Challenge, the client verifies the AT_MAC attribute before looking at the AT_ENCR_DATA attribute. If ⌨️ 快捷键说明
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