7 Network Working Group H. Haverinen, Ed.
8 Request for Comments: 4186 Nokia
9 Category: Informational J. Salowey, Ed.
14 Extensible Authentication Protocol Method for
15 Global System for Mobile Communications (GSM)
16 Subscriber Identity Modules (EAP-SIM)
20 This memo provides information for the Internet community. It does
21 not specify an Internet standard of any kind. Distribution of this
26 Copyright (C) The Internet Society (2006).
30 The EAP-SIM protocol was developed by 3GPP. The documentation of
31 EAP-SIM is provided as information to the Internet community. While
32 the EAP WG has verified that EAP-SIM is compatible with EAP, as
33 defined in RFC 3748, no other review has been done, including
34 validation of the security claims. The IETF has also not reviewed
35 the security of the cryptographic algorithms.
39 This document specifies an Extensible Authentication Protocol (EAP)
40 mechanism for authentication and session key distribution using the
41 Global System for Mobile Communications (GSM) Subscriber Identity
42 Module (SIM). GSM is a second generation mobile network standard.
43 The EAP-SIM mechanism specifies enhancements to GSM authentication
44 and key agreement whereby multiple authentication triplets can be
45 combined to create authentication responses and session keys of
46 greater strength than the individual GSM triplets. The mechanism
47 also includes network authentication, user anonymity support, result
48 indications, and a fast re-authentication procedure.
58 Haverinen & Salowey Informational [Page 1]
60 RFC 4186 EAP-SIM Authentication January 2006
65 1. Introduction ....................................................4
66 2. Terms ...........................................................5
67 3. Overview ........................................................8
68 4. Operation ......................................................10
69 4.1. Version Negotiation .......................................10
70 4.2. Identity Management .......................................11
71 4.2.1. Format, Generation and Usage of Peer Identities ....11
72 4.2.2. Communicating the Peer Identity to the Server ......17
73 4.2.3. Choice of Identity for the EAP-Response/Identity ...19
74 4.2.4. Server Operation in the Beginning of
75 EAP-SIM Exchange ...................................19
76 4.2.5. Processing of EAP-Request/SIM/Start by the Peer ....20
77 4.2.6. Attacks Against Identity Privacy ...................21
78 4.2.7. Processing of AT_IDENTITY by the Server ............22
79 4.3. Message Sequence Examples (Informative) ...................23
80 4.3.1. Full Authentication ................................24
81 4.3.2. Fast Re-authentication .............................25
82 4.3.3. Fall Back to Full Authentication ...................26
83 4.3.4. Requesting the Permanent Identity 1 ................27
84 4.3.5. Requesting the Permanent Identity 2 ................28
85 4.3.6. Three EAP-SIM/Start Roundtrips .....................28
86 5. Fast Re-Authentication .........................................30
87 5.1. General ...................................................30
88 5.2. Comparison to UMTS AKA ....................................31
89 5.3. Fast Re-authentication Identity ...........................31
90 5.4. Fast Re-authentication Procedure ..........................33
91 5.5. Fast Re-authentication Procedure when Counter Is
92 Too Small .................................................36
93 6. EAP-SIM Notifications ..........................................37
94 6.1. General ...................................................37
95 6.2. Result Indications ........................................39
96 6.3. Error Cases ...............................................40
97 6.3.1. Peer Operation .....................................40
98 6.3.2. Server Operation ...................................41
99 6.3.3. EAP-Failure ........................................42
100 6.3.4. EAP-Success ........................................42
101 7. Key Generation .................................................43
102 8. Message Format and Protocol Extensibility ......................45
103 8.1. Message Format ............................................45
104 8.2. Protocol Extensibility ....................................47
105 9. Messages .......................................................48
106 9.1. EAP-Request/SIM/Start .....................................48
107 9.2. EAP-Response/SIM/Start ....................................49
108 9.3. EAP-Request/SIM/Challenge .................................49
109 9.4. EAP-Response/SIM/Challenge ................................50
110 9.5. EAP-Request/SIM/Re-authentication .........................51
114 Haverinen & Salowey Informational [Page 2]
116 RFC 4186 EAP-SIM Authentication January 2006
119 9.6. EAP-Response/SIM/Re-authentication ........................51
120 9.7. EAP-Response/SIM/Client-Error .............................52
121 9.8. EAP-Request/SIM/Notification ..............................52
122 9.9. EAP-Response/SIM/Notification .............................53
123 10. Attributes ....................................................53
124 10.1. Table of Attributes ......................................53
125 10.2. AT_VERSION_LIST ..........................................54
126 10.3. AT_SELECTED_VERSION ......................................55
127 10.4. AT_NONCE_MT ..............................................55
128 10.5. AT_PERMANENT_ID_REQ ......................................56
129 10.6. AT_ANY_ID_REQ ............................................56
130 10.7. AT_FULLAUTH_ID_REQ .......................................57
131 10.8. AT_IDENTITY ..............................................57
132 10.9. AT_RAND ..................................................58
133 10.10. AT_NEXT_PSEUDONYM .......................................59
134 10.11. AT_NEXT_REAUTH_ID .......................................59
135 10.12. AT_IV, AT_ENCR_DATA, and AT_PADDING .....................60
136 10.13. AT_RESULT_IND ...........................................62
137 10.14. AT_MAC ..................................................62
138 10.15. AT_COUNTER ..............................................63
139 10.16. AT_COUNTER_TOO_SMALL ....................................63
140 10.17. AT_NONCE_S ..............................................64
141 10.18. AT_NOTIFICATION .........................................64
142 10.19. AT_CLIENT_ERROR_CODE ....................................65
143 11. IANA Considerations ...........................................66
144 12. Security Considerations .......................................66
145 12.1. A3 and A8 Algorithms .....................................66
146 12.2. Identity Protection ......................................66
147 12.3. Mutual Authentication and Triplet Exposure ...............67
148 12.4. Flooding the Authentication Centre .......................69
149 12.5. Key Derivation ...........................................69
150 12.6. Cryptographic Separation of Keys and Session
151 Independence .............................................70
152 12.7. Dictionary Attacks .......................................71
153 12.8. Credentials Re-use .......................................71
154 12.9. Integrity and Replay Protection, and Confidentiality .....72
155 12.10. Negotiation Attacks .....................................73
156 12.11. Protected Result Indications ............................73
157 12.12. Man-in-the-Middle Attacks ...............................74
158 12.13. Generating Random Numbers ...............................74
159 13. Security Claims ...............................................74
160 14. Acknowledgements and Contributions ............................75
161 14.1. Contributors .............................................75
162 14.2. Acknowledgements .........................................75
163 14.2.1. Contributors' Addresses ...........................77
164 15. References ....................................................78
165 15.1. Normative References .....................................78
166 15.2. Informative References ...................................79
170 Haverinen & Salowey Informational [Page 3]
172 RFC 4186 EAP-SIM Authentication January 2006
175 Appendix A. Test Vectors .........................................81
176 A.1. EAP-Request/Identity .....................................81
177 A.2. EAP-Response/Identity ....................................81
178 A.3. EAP-Request/SIM/Start ....................................82
179 A.4. EAP-Response/SIM/Start ...................................82
180 A.5. EAP-Request/SIM/Challenge ................................83
181 A.6. EAP-Response/SIM/Challenge ...............................86
182 A.7. EAP-Success ..............................................86
183 A.8. Fast Re-authentication ...................................86
184 A.9. EAP-Request/SIM/Re-authentication ........................87
185 A.10. EAP-Response/SIM/Re-authentication ......................89
186 Appendix B. Pseudo-Random Number Generator .......................90
190 This document specifies an Extensible Authentication Protocol (EAP)
191 [RFC3748] mechanism for authentication and session key distribution
192 using the Global System for Mobile Communications (GSM) Subscriber
193 Identity Module (SIM).
195 GSM is a second generation mobile network standard. Second
196 generation mobile networks and third generation mobile networks use
197 different authentication and key agreement mechanisms. EAP-AKA
198 [EAP-AKA] specifies an EAP method that is based on the Authentication
199 and Key Agreement (AKA) mechanism used in 3rd generation mobile
202 GSM authentication is based on a challenge-response mechanism. The
203 A3/A8 authentication and key derivation algorithms that run on the
204 SIM can be given a 128-bit random number (RAND) as a challenge. The
205 SIM runs operator-specific algorithms, which take the RAND and a
206 secret key Ki (stored on the SIM) as input, and produce a 32-bit
207 response (SRES) and a 64-bit long key Kc as output. The Kc key is
208 originally intended to be used as an encryption key over the air
209 interface, but in this protocol, it is used for deriving keying
210 material and is not directly used. Hence, the secrecy of Kc is
211 critical to the security of this protocol. For more information
212 about GSM authentication, see [GSM-03.20]. See Section 12.1 for more
213 discussion about the GSM algorithms used in EAP-SIM.
215 The lack of mutual authentication is a weakness in GSM
216 authentication. The derived 64-bit cipher key (Kc) is not strong
217 enough for data networks in which stronger and longer keys are
218 required. Hence, in EAP-SIM, several RAND challenges are used for
219 generating several 64-bit Kc keys, which are combined to constitute
220 stronger keying material. In EAP-SIM, the client issues a random
221 number NONCE_MT to the network in order to contribute to key
222 derivation, and to prevent replays of EAP-SIM requests from previous
226 Haverinen & Salowey Informational [Page 4]
228 RFC 4186 EAP-SIM Authentication January 2006
231 exchanges. The NONCE_MT can be conceived as the client's challenge
232 to the network. EAP-SIM also extends the combined RAND challenges
233 and other messages with a message authentication code in order to
234 provide message integrity protection along with mutual
237 EAP-SIM specifies optional support for protecting the privacy of
238 subscriber identity using the same concept as the GSM, which uses
239 pseudonyms/temporary identifiers. It also specifies an optional fast
240 re-authentication procedure.
242 The security of EAP-SIM builds on underlying GSM mechanisms. The
243 security properties of EAP-SIM are documented in Section 11 of this
244 document. Implementers and users of EAP-SIM are advised to carefully
245 study the security considerations in Section 11 in order to determine
246 whether the security properties are sufficient for the environment in
247 question, especially as the secrecy of Kc keys is essential to the
248 security of EAP-SIM. In brief, EAP-SIM is in no sense weaker than
249 the GSM mechanisms. In some cases EAP-SIM provides better security
250 properties than the underlying GSM mechanisms, particularly if the
251 SIM credentials are only used for EAP-SIM and are not re-used from
252 GSM/GPRS. Many of the security features of EAP-SIM rely upon the
253 secrecy of the Kc values in the SIM triplets, so protecting these
254 values is key to the security of the EAP-SIM protocol.
256 The 3rd Generation Partnership Project (3GPP) has specified an
257 enhanced Authentication and Key Agreement (AKA) architecture for the
258 Universal Mobile Telecommunications System (UMTS). The 3rd
259 generation AKA mechanism includes mutual authentication, replay
260 protection, and derivation of longer session keys. EAP-AKA [EAP-AKA]
261 specifies an EAP method that is based on the 3rd generation AKA.
262 EAP-AKA, which is a more secure protocol, may be used instead of
263 EAP-SIM, if 3rd generation identity modules and 3G network
264 infrastructures are available.
268 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
269 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
270 document are to be interpreted as described in [RFC2119].
272 The terms and abbreviations "authenticator", "backend authentication
273 server", "EAP server", "peer", "Silently Discard", "Master Session
274 Key (MSK)", and "Extended Master Session Key (EMSK)" in this document
275 are to be interpreted as described in [RFC3748].
282 Haverinen & Salowey Informational [Page 5]
284 RFC 4186 EAP-SIM Authentication January 2006
287 This document frequently uses the following terms and abbreviations:
291 Authentication, Authorization, and Accounting protocol
295 Authentication Centre. The GSM network element that provides
296 the authentication triplets for authenticating
299 Authentication vector
301 GSM triplets can be alternatively called authentication
306 Extensible Authentication Protocol
308 Fast re-authentication
310 An EAP-SIM authentication exchange that is based on keys
311 derived upon a preceding full authentication exchange.
312 The GSM authentication and key exchange algorithms are not
313 used in the fast re-authentication procedure.
315 Fast Re-authentication Identity
317 A fast re-authentication identity of the peer, including an NAI
318 realm portion in environments where a realm is used. Used on
319 fast re-authentication only.
321 Fast Re-authentication Username
323 The username portion of fast re-authentication identity,
324 i.e., not including any realm portions.
328 An EAP-SIM authentication exchange based on the GSM
329 authentication and key agreement algorithms.
333 Global System for Mobile communications.
338 Haverinen & Salowey Informational [Page 6]
340 RFC 4186 EAP-SIM Authentication January 2006
345 The tuple formed by the three GSM authentication values RAND,
350 International Mobile Subscriber Identifier, used in GSM to
351 identify subscribers.
355 Message Authentication Code
359 Network Access Identifier
363 A value that is used at most once or that is never repeated
364 within the same cryptographic context. In general, a nonce can
365 be predictable (e.g., a counter) or unpredictable (e.g., a
366 random value). Since some cryptographic properties may depend
367 on the randomness of the nonce, attention should be paid to
368 whether a nonce is required to be random or not. In this
369 document, the term nonce is only used to denote random nonces,
370 and it is not used to denote counters.
374 The permanent identity of the peer, including an NAI realm
375 portion in environments where a realm is used. The permanent
376 identity is usually based on the IMSI. Used on full
381 The username portion of permanent identity, i.e., not including
386 A pseudonym identity of the peer, including an NAI realm
387 portion in environments where a realm is used. Used on
388 full authentication only.
394 Haverinen & Salowey Informational [Page 7]
396 RFC 4186 EAP-SIM Authentication January 2006
401 The username portion of pseudonym identity, i.e., not including
406 Subscriber Identity Module. The SIM is traditionally a smart
407 card distributed by a GSM operator.
411 Figure 1 shows an overview of the EAP-SIM full authentication
412 procedure, wherein optional protected success indications are not
413 used. The authenticator typically communicates with an EAP server
414 that is located on a backend authentication server using an AAA
415 protocol. The authenticator shown in the figure is often simply
416 relaying EAP messages to and from the EAP server, but these backend
417 AAA communications are not shown.
420 | EAP-Request/Identity |
421 |<---------------------------------------------------------|
423 | EAP-Response/Identity |
424 |--------------------------------------------------------->|
426 | EAP-Request/SIM/Start (AT_VERSION_LIST) |
427 |<---------------------------------------------------------|
429 | EAP-Response/SIM/Start (AT_NONCE_MT, AT_SELECTED_VERSION)|
430 |--------------------------------------------------------->|
432 | EAP-Request/SIM/Challenge (AT_RAND, AT_MAC) |
433 |<---------------------------------------------------------|
434 +-------------------------------------+ |
435 | Peer runs GSM algorithms, verifies | |
436 | AT_MAC and derives session keys | |
437 +-------------------------------------+ |
438 | EAP-Response/SIM/Challenge (AT_MAC) |
439 |--------------------------------------------------------->|
442 |<---------------------------------------------------------|
445 Figure 1: EAP-SIM full authentication procedure
450 Haverinen & Salowey Informational [Page 8]
452 RFC 4186 EAP-SIM Authentication January 2006
455 The first EAP Request issued by the authenticator is
456 EAP-Request/Identity. On full authentication, the peer's response
457 includes either the user's International Mobile Subscriber Identity
458 (IMSI) or a temporary identity (pseudonym) if identity privacy is in
459 effect, as specified in Section 4.2.
461 Following the peer's EAP-Response/Identity packet, the peer receives
462 EAP Requests of Type 18 (SIM) from the EAP server and sends the
463 corresponding EAP Responses. The EAP packets that are of the Type
464 SIM also have a Subtype field. On full authentication, the first
465 EAP-Request/SIM packet is of the Subtype 10 (Start). EAP-SIM packets
466 encapsulate parameters in attributes, encoded in a Type, Length,
467 Value format. The packet format and the use of attributes are
468 specified in Section 8.
470 The EAP-Request/SIM/Start packet contains the list of EAP-SIM
471 versions supported by the EAP server in the AT_VERSION_LIST
472 attribute. This packet may also include attributes for requesting
473 the subscriber identity, as specified in Section 4.2.
475 The peer responds to a EAP-Request/SIM/Start with the
476 EAP-Response/SIM/Start packet, which includes the AT_NONCE_MT
477 attribute that contains a random number NONCE_MT, chosen by the peer,
478 and the AT_SELECTED_VERSION attribute that contains the version
479 number selected by the peer. The version negotiation is protected by
480 including the version list and the selected version in the
481 calculation of keying material (Section 7).
483 After receiving the EAP Response/SIM/Start, the EAP server obtains n
484 GSM triplets for use in authenticating the subscriber, where n = 2 or
485 n = 3. From the triplets, the EAP server derives the keying
486 material, as specified in Section 7. The triplets may be obtained by
487 contacting an Authentication Centre (AuC) on the GSM network; per GSM
488 specifications, between 1 and 5 triplets may be obtained at a time.
489 Triplets may be stored in the EAP server for use at a later time, but
490 triplets MUST NOT be re-used, except in some error cases that are
491 specified in Section 10.9.
493 The next EAP Request the EAP Server issues is of the type SIM and
494 subtype Challenge (11). It contains the RAND challenges and a
495 message authentication code attribute AT_MAC to cover the challenges.
496 The AT_MAC attribute is a general message authentication code
497 attribute that is used in many EAP-SIM messages.
499 On receipt of the EAP-Request/SIM/Challenge message, the peer runs
500 the GSM authentication algorithm and calculates a copy of the message
501 authentication code. The peer then verifies that the calculated MAC
502 equals the received MAC. If the MAC's do not match, then the peer
506 Haverinen & Salowey Informational [Page 9]
508 RFC 4186 EAP-SIM Authentication January 2006
511 sends the EAP-Response/SIM/Client-Error packet and the authentication
514 Since the RANDs given to a peer are accompanied by the message
515 authentication code AT_MAC, and since the peer's NONCE_MT value
516 contributes to AT_MAC, the peer is able to verify that the EAP-SIM
517 message is fresh (i.e., not a replay) and that the sender possesses
518 valid GSM triplets for the subscriber.
520 If all checks out, the peer responds with the
521 EAP-Response/SIM/Challenge, containing the AT_MAC attribute that
522 covers the peer's SRES response values (Section 9.4). The EAP server
523 verifies that the MAC is correct. Because protected success
524 indications are not used in this example, the EAP server sends the
525 EAP-Success packet, indicating that the authentication was
526 successful. (Protected success indications are discussed in
527 Section 6.2.) The EAP server may also include derived keying
528 material in the message it sends to the authenticator. The peer has
529 derived the same keying material, so the authenticator does not
530 forward the keying material to the peer along with EAP-Success.
532 EAP-SIM also includes a separate fast re-authentication procedure
533 that does not make use of the A3/A8 algorithms or the GSM
534 infrastructure. Fast re-authentication is based on keys derived on
535 full authentication. If the peer has maintained state information
536 for fast re-authentication and wants to use fast re-authentication,
537 then the peer indicates this by using a specific fast
538 re-authentication identity instead of the permanent identity or a
539 pseudonym identity. The fast re-authentication procedure is
540 described in Section 5.
544 4.1. Version Negotiation
546 EAP-SIM includes version negotiation so as to allow future
547 developments in the protocol. The version negotiation is performed
548 on full authentication and it uses two attributes, AT_VERSION_LIST,
549 which the server always includes in EAP-Request/SIM/Start, and
550 AT_SELECTED_VERSION, which the peer includes in
551 EAP-Response/SIM/Start on full authentication.
553 AT_VERSION_LIST includes the EAP-SIM versions supported by the
554 server. If AT_VERSION_LIST does not include a version that is
555 implemented by the peer and allowed in the peer's security policy,
556 then the peer MUST send the EAP-Response/SIM/Client-Error packet
557 (Section 9.7) to the server with the error code "unsupported
558 version". If a suitable version is included, then the peer includes
562 Haverinen & Salowey Informational [Page 10]
564 RFC 4186 EAP-SIM Authentication January 2006
567 the AT_SELECTED_VERSION attribute, containing the selected version in
568 the EAP-Response/SIM/Start packet. The peer MUST only indicate a
569 version that is included in the AT_VERSION_LIST. If several versions
570 are acceptable, then the peer SHOULD choose the version that occurs
571 first in the version list.
573 The version number list of AT_VERSION_LIST and the selected version
574 of AT_SELECTED_VERSION are included in the key derivation procedure
575 (Section 7). If an attacker modifies either one of these attributes,
576 then the peer and the server derive different keying material.
577 Because K_aut keys are different, the server and peer calculate
578 different AT_MAC values. Hence, the peer detects that AT_MAC,
579 included in EAP-Request/SIM/Challenge, is incorrect and sends the
580 EAP-Response/SIM/Client-Error packet. The authentication procedure
583 4.2. Identity Management
585 4.2.1. Format, Generation and Usage of Peer Identities
589 In the beginning of EAP authentication, the Authenticator or the EAP
590 server usually issues the EAP-Request/Identity packet to the peer.
591 The peer responds with the EAP-Response/Identity, which contains the
592 user's identity. The formats of these packets are specified in
595 GSM subscribers are identified with the International Mobile
596 Subscriber Identity (IMSI) [GSM-03.03]. The IMSI is a string of not
597 more than 15 digits. It is composed of a three digit Mobile Country
598 Code (MCC), a two or three digit Mobile Network Code (MNC), and a
599 Mobile Subscriber Identification Number (MSIN) of no more than 10
600 digits. MCC and MNC uniquely identify the GSM operator and help
601 identify the AuC from which the authentication vectors need to be
602 retrieved for this subscriber.
604 Internet AAA protocols identify users with the Network Access
605 Identifier (NAI) [RFC4282]. When used in a roaming environment, the
606 NAI is composed of a username and a realm, separated with "@"
607 (username@realm). The username portion identifies the subscriber
610 This section specifies the peer identity format used in EAP-SIM. In
611 this document, the term "identity" or "peer identity" refers to the
612 whole identity string that is used to identify the peer. The peer
618 Haverinen & Salowey Informational [Page 11]
620 RFC 4186 EAP-SIM Authentication January 2006
623 identity may include a realm portion. "Username" refers to the
624 portion of the peer identity that identifies the user, i.e., the
625 username does not include the realm portion.
627 4.2.1.2. Identity Privacy Support
629 EAP-SIM includes optional identity privacy (anonymity) support that
630 can be used to hide the cleartext permanent identity and thereby make
631 the subscriber's EAP exchanges untraceable to eavesdroppers. Because
632 the permanent identity never changes, revealing it would help
633 observers to track the user. The permanent identity is usually based
634 on the IMSI, which may further help the tracking, because the same
635 identifier may be used in other contexts as well. Identity privacy
636 is based on temporary identities, or pseudonyms, which are equivalent
637 to but separate from the Temporary Mobile Subscriber Identities
638 (TMSI) that are used on cellular networks. Please see Section 12.2
639 for security considerations regarding identity privacy.
641 4.2.1.3. Username Types in EAP-SIM identities
643 There are three types of usernames in EAP-SIM peer identities:
645 (1) Permanent usernames. For example,
646 1123456789098765@myoperator.com might be a valid permanent identity.
647 In this example, 1123456789098765 is the permanent username.
649 (2) Pseudonym usernames. For example, 3s7ah6n9q@myoperator.com might
650 be a valid pseudonym identity. In this example, 3s7ah6n9q is the
653 (3) Fast re-authentication usernames. For example,
654 53953754@myoperator.com might be a valid fast re-authentication
655 identity. In this case, 53953754 is the fast re-authentication
656 username. Unlike permanent usernames and pseudonym usernames, fast
657 re-authentication usernames are one-time identifiers, which are not
658 re-used across EAP exchanges.
660 The first two types of identities are used only on full
661 authentication and the last one only on fast re-authentication. When
662 the optional identity privacy support is not used, the non-pseudonym
663 permanent identity is used on full authentication. The fast
664 re-authentication exchange is specified in Section 5.
666 4.2.1.4. Username Decoration
668 In some environments, the peer may need to decorate the identity by
669 prepending or appending the username with a string, in order to
670 indicate supplementary AAA routing information in addition to the NAI
674 Haverinen & Salowey Informational [Page 12]
676 RFC 4186 EAP-SIM Authentication January 2006
679 realm. (The usage of an NAI realm portion is not considered
680 decoration.) Username decoration is out of the scope of this
681 document. However, it should be noted that username decoration might
682 prevent the server from recognizing a valid username. Hence,
683 although the peer MAY use username decoration in the identities that
684 the peer includes in EAP-Response/Identity, and although the EAP
685 server MAY accept a decorated peer username in this message, the peer
686 or the EAP server MUST NOT decorate any other peer identities that
687 are used in various EAP-SIM attributes. Only the identity used in
688 the EAP-Response/Identity may be decorated.
690 4.2.1.5. NAI Realm Portion
692 The peer MAY include a realm portion in the peer identity, as per the
693 NAI format. The use of a realm portion is not mandatory.
695 If a realm is used, the realm MAY be chosen by the subscriber's home
696 operator and it MAY be a configurable parameter in the EAP-SIM peer
697 implementation. In this case, the peer is typically configured with
698 the NAI realm of the home operator. Operators MAY reserve a specific
699 realm name for EAP-SIM users. This convention makes it easy to
700 recognize that the NAI identifies a GSM subscriber. Such a reserved
701 NAI realm may be a useful hint as to the first authentication method
702 to use during method negotiation. When the peer is using a pseudonym
703 username instead of the permanent username, the peer selects the
704 realm name portion similarly as it select the realm portion when
705 using the permanent username.
707 If no configured realm name is available, the peer MAY derive the
708 realm name from the MCC and MNC portions of the IMSI. A RECOMMENDED
709 way to derive the realm from the IMSI using the realm 3gppnetwork.org
710 is specified in [3GPP-TS-23.003].
712 Some old implementations derive the realm name from the IMSI by
713 concatenating "mnc", the MNC digits of IMSI, ".mcc", the MCC digits
714 of IMSI, and ".owlan.org". For example, if the IMSI is
715 123456789098765, and the MNC is three digits long, then the derived
716 realm name is "mnc456.mcc123.owlan.org". As there are no DNS servers
717 running at owlan.org, these realm names can only be used with
718 manually configured AAA routing. New implementations SHOULD use the
719 mechanism specified in [3GPP-TS-23.003] instead of owlan.org.
721 The IMSI is a string of digits without any explicit structure, so the
722 peer may not be able to determine the length of the MNC portion. If
723 the peer is not able to determine whether the MNC is two or three
724 digits long, the peer MAY use a 3-digit MNC. If the correct length
725 of the MNC is two, then the MNC used in the realm name includes the
726 first digit of the MSIN. Hence, when configuring AAA networks for
730 Haverinen & Salowey Informational [Page 13]
732 RFC 4186 EAP-SIM Authentication January 2006
735 operators that have 2-digit MNCs, the network SHOULD also be prepared
736 for realm names with incorrect, 3-digit MNCs.
738 4.2.1.6. Format of the Permanent Username
740 The non-pseudonym permanent username SHOULD be derived from the IMSI.
741 In this case, the permanent username MUST be of the format "1" |
742 IMSI, where the character "|" denotes concatenation. In other words,
743 the first character of the username is the digit one (ASCII value 31
744 hexadecimal), followed by the IMSI. The IMSI is encoded as an ASCII
745 string that consists of not more than 15 decimal digits (ASCII values
746 between 30 and 39 hexadecimal), one character per IMSI digit, in the
747 order specified in [GSM-03.03]. For example, a permanent username
748 derived from the IMSI 295023820005424 would be encoded as the ASCII
749 string "1295023820005424" (byte values in hexadecimal notation: 31 32
750 39 35 30 32 33 38 32 30 30 30 35 34 32 34).
752 The EAP server MAY use the leading "1" as a hint to try EAP-SIM as
753 the first authentication method during method negotiation, rather
754 than, for example EAP/AKA. The EAP-SIM server MAY propose EAP-SIM,
755 even if the leading character was not "1".
757 Alternatively, an implementation MAY choose a permanent username that
758 is not based on the IMSI. In this case, the selection of the
759 username, its format, and its processing is out of the scope of this
760 document. In this case, the peer implementation MUST NOT prepend any
761 leading characters to the username.
763 4.2.1.7. Generating Pseudonyms and Fast Re-authentication Identities by
766 Pseudonym usernames and fast re-authentication identities are
767 generated by the EAP server. The EAP server produces pseudonym
768 usernames and fast re-authentication identities in an
769 implementation-dependent manner. Only the EAP server needs to be
770 able to map the pseudonym username to the permanent identity, or to
771 recognize a fast re-authentication identity.
773 EAP-SIM includes no provisions to ensure that the same EAP server
774 that generated a pseudonym username will be used on the
775 authentication exchange when the pseudonym username is used. It is
776 recommended that the EAP servers implement some centralized mechanism
777 to allow all EAP servers of the home operator to map pseudonyms
778 generated by other severs to the permanent identity. If no such
779 mechanism is available, then the EAP server failing to understand a
780 pseudonym issued by another server can request the that peer send the
786 Haverinen & Salowey Informational [Page 14]
788 RFC 4186 EAP-SIM Authentication January 2006
791 When issuing a fast re-authentication identity, the EAP server may
792 include a realm name in the identity to make the fast
793 re-authentication request be forwarded to the same EAP server.
795 When generating fast re-authentication identities, the server SHOULD
796 choose a fresh, new fast re-authentication identity that is different
797 from the previous ones that were used after the same full
798 authentication exchange. A full authentication exchange and the
799 associated fast re-authentication exchanges are referred to here as
800 the same "full authentication context". The fast re-authentication
801 identity SHOULD include a random component. This random component
802 works as a full authentication context identifier. A
803 context-specific fast re-authentication identity can help the server
804 to detect whether its fast re-authentication state information
805 matches that of its peer (in other words, whether the state
806 information is from the same full authentication exchange). The
807 random component also makes the fast re-authentication identities
808 unpredictable, so an attacker cannot initiate a fast
809 re-authentication exchange to get the server's EAP-Request/SIM/
810 Re-authentication packet.
812 Transmitting pseudonyms and fast re-authentication identities from
813 the server to the peer is discussed in Section 4.2.1.8. The
814 pseudonym is transmitted as a username, without an NAI realm, and the
815 fast re-authentication identity is transmitted as a complete NAI,
816 including a realm portion if a realm is required. The realm is
817 included in the fast re-authentication identity to allow the server
818 to include a server-specific realm.
820 Regardless of the construction method, the pseudonym username MUST
821 conform to the grammar specified for the username portion of an NAI.
822 The fast re-authentication identity also MUST conform to the NAI
823 grammar. The EAP servers that the subscribers of an operator can use
824 MUST ensure that the pseudonym usernames and the username portions
825 used in fast re-authentication identities they generate are unique.
827 In any case, it is necessary that permanent usernames, pseudonym
828 usernames, and fast re-authentication usernames are separate and
829 recognizable from each other. It is also desirable that EAP-SIM and
830 EAP-AKA [EAP-AKA] usernames be distinguishable from each other as an
831 aid for the server on which method to offer.
833 In general, it is the task of the EAP server and the policies of its
834 administrator to ensure sufficient separation of the usernames.
835 Pseudonym usernames and fast re-authentication usernames are both
836 produced and used by the EAP server. The EAP server MUST compose
837 pseudonym usernames and fast re-authentication usernames so that it
838 can determine if an NAI username is an EAP-SIM pseudonym username or
842 Haverinen & Salowey Informational [Page 15]
844 RFC 4186 EAP-SIM Authentication January 2006
847 an EAP-SIM fast re-authentication username. For instance, when the
848 usernames have been derived from the IMSI, the server could use
849 different leading characters in the pseudonym usernames and fast
850 re-authentication usernames (e.g., the pseudonym could begin with a
851 leading "3" character). When mapping a fast re-authentication
852 identity to a permanent identity, the server SHOULD only examine the
853 username portion of the fast re-authentication identity and ignore
854 the realm portion of the identity.
856 Because the peer may fail to save a pseudonym username sent in an
857 EAP-Request/SIM/Challenge, for example due to malfunction, the EAP
858 server SHOULD maintain at least the most recently used pseudonym
859 username in addition to the most recently issued pseudonym username.
860 If the authentication exchange is not completed successfully, then
861 the server SHOULD NOT overwrite the pseudonym username that was
862 issued during the most recent successful authentication exchange.
864 4.2.1.8. Transmitting Pseudonyms and Fast Re-authentication Identities
867 The server transmits pseudonym usernames and fast re-authentication
868 identities to the peer in cipher, using the AT_ENCR_DATA attribute.
870 The EAP-Request/SIM/Challenge message MAY include an encrypted
871 pseudonym username and/or an encrypted fast re-authentication
872 identity in the value field of the AT_ENCR_DATA attribute. Because
873 identity privacy support and fast re-authentication are optional
874 implementations, the peer MAY ignore the AT_ENCR_DATA attribute and
875 always use the permanent identity. On fast re-authentication
876 (discussed in Section 5), the server MAY include a new, encrypted
877 fast re-authentication identity in the
878 EAP-Request/SIM/Re-authentication message.
880 On receipt of the EAP-Request/SIM/Challenge, the peer MAY decrypt the
881 encrypted data in AT_ENCR_DATA. If the authentication exchange is
882 successful, and the encrypted data includes a pseudonym username,
883 then the peer may use the obtained pseudonym username on the next
884 full authentication. If a fast re-authentication identity is
885 included, then the peer MAY save it together with other fast
886 re-authentication state information, as discussed in Section 5, for
887 the next fast re-authentication. If the authentication exchange does
888 not complete successfully, the peer MUST ignore the received
889 pseudonym username and the fast re-authentication identity.
891 If the peer does not receive a new pseudonym username in the
892 EAP-Request/SIM/Challenge message, the peer MAY use an old pseudonym
893 username instead of the permanent username on the next full
894 authentication. The username portions of fast re-authentication
898 Haverinen & Salowey Informational [Page 16]
900 RFC 4186 EAP-SIM Authentication January 2006
903 identities are one-time usernames, which the peer MUST NOT re-use.
904 When the peer uses a fast re-authentication identity in an EAP
905 exchange, the peer MUST discard the fast re-authentication identity
906 and not re-use it in another EAP authentication exchange, even if the
907 authentication exchange was not completed.
909 4.2.1.9. Usage of the Pseudonym by the Peer
911 When the optional identity privacy support is used on full
912 authentication, the peer MAY use a pseudonym username received as
913 part of a previous full authentication sequence as the username
914 portion of the NAI. The peer MUST NOT modify the pseudonym username
915 received in AT_NEXT_PSEUDONYM. However, as discussed above, the peer
916 MAY need to decorate the username in some environments by appending
917 or prepending the username with a string that indicates supplementary
918 AAA routing information.
920 When using a pseudonym username in an environment where a realm
921 portion is used, the peer concatenates the received pseudonym
922 username with the "@" character and an NAI realm portion. The
923 selection of the NAI realm is discussed above. The peer can select
924 the realm portion similarly, regardless of whether it uses the
925 permanent username or a pseudonym username.
927 4.2.1.10. Usage of the Fast Re-authentication Identity by the Peer
929 On fast re-authentication, the peer uses the fast re-authentication
930 identity that was received as part of the previous authentication
931 sequence. A new re-authentication identity may be delivered as part
932 of both full authentication and fast re-authentication. The peer
933 MUST NOT modify the username part of the fast re-authentication
934 identity received in AT_NEXT_REAUTH_ID, except in cases when username
935 decoration is required. Even in these cases, the "root" fast
936 re-authentication username must not be modified, but it may be
937 appended or prepended with another string.
939 4.2.2. Communicating the Peer Identity to the Server
943 The peer identity MAY be communicated to the server with the
944 EAP-Response/Identity message. This message MAY contain the
945 permanent identity, a pseudonym identity, or a fast re-authentication
946 identity. If the peer uses the permanent identity or a pseudonym
947 identity, which the server is able to map to the permanent identity,
948 then the authentication proceeds as discussed in the overview of
949 Section 3. If the peer uses a fast re-authentication identity, and
950 if the fast re-authentication identity matches with a valid fast
954 Haverinen & Salowey Informational [Page 17]
956 RFC 4186 EAP-SIM Authentication January 2006
959 re-authentication identity maintained by the server, and if the
960 server agrees to use fast re-authentication, then a fast
961 re-authentication exchange is performed, as described in Section 5.
963 The peer identity can also be transmitted from the peer to the server
964 using EAP-SIM messages instead of the EAP-Response/Identity. In this
965 case, the server includes an identity-requesting attribute
966 (AT_ANY_ID_REQ, AT_FULLAUTH_ID_REQ or AT_PERMANENT_ID_REQ) in the
967 EAP-Request/SIM/Start message, and the peer includes the AT_IDENTITY
968 attribute, which contains the peer's identity, in the
969 EAP-Response/SIM/Start message. The AT_ANY_ID_REQ attribute is a
970 general identity-requesting attribute, which the server uses if it
971 does not specify which kind of an identity the peer should return in
972 AT_IDENTITY. The server uses the AT_FULLAUTH_ID_REQ attribute to
973 request either the permanent identity or a pseudonym identity. The
974 server uses the AT_PERMANENT_ID_REQ attribute to request that the
975 peer send its permanent identity.
977 The identity format in the AT_IDENTITY attribute is the same as in
978 the EAP-Response/Identity packet (except that identity decoration is
979 not allowed). The AT_IDENTITY attribute contains a permanent
980 identity, a pseudonym identity, or a fast re-authentication identity.
982 Please note that the EAP-SIM peer and the EAP-SIM server only process
983 the AT_IDENTITY attribute; entities that only pass through EAP
984 packets do not process this attribute. Hence, the authenticator and
985 other intermediate AAA elements (such as possible AAA proxy servers)
986 will continue to refer to the peer with the original identity from
987 the EAP-Response/Identity packet unless the identity authenticated in
988 the AT_IDENTITY attribute is communicated to them in another way
989 within the AAA protocol.
991 4.2.2.2. Relying on EAP-Response/Identity Discouraged
993 The EAP-Response/Identity packet is not method-specific, so in many
994 implementations it may be handled by an EAP Framework. This
995 introduces an additional layer of processing between the EAP peer and
996 EAP server. The extra layer of processing may cache identity
997 responses or add decorations to the identity. A modification of the
998 identity response will cause the EAP peer and EAP server to use
999 different identities in the key derivation, which will cause the
1002 For this reason, it is RECOMMENDED that the EAP peer and server use
1003 the method-specific identity attributes in EAP-SIM, and the server is
1004 strongly discouraged from relying upon the EAP-Response/Identity.
1010 Haverinen & Salowey Informational [Page 18]
1012 RFC 4186 EAP-SIM Authentication January 2006
1015 In particular, if the EAP server receives a decorated identity in
1016 EAP-Response/Identity, then the EAP server MUST use the
1017 identity-requesting attributes to request that the peer send an
1018 unmodified and undecorated copy of the identity in AT_IDENTITY.
1020 4.2.3. Choice of Identity for the EAP-Response/Identity
1022 If EAP-SIM peer is started upon receiving an EAP-Request/Identity
1023 message, then the peer MAY use an EAP-SIM identity in the EAP-
1024 Response/Identity packet. In this case, the peer performs the
1027 If the peer has maintained fast re-authentication state information
1028 and wants to use fast re-authentication, then the peer transmits the
1029 fast re-authentication identity in EAP-Response/Identity.
1031 Else, if the peer has a pseudonym username available, then the peer
1032 transmits the pseudonym identity in EAP-Response/Identity.
1034 In other cases, the peer transmits the permanent identity in
1035 EAP-Response/Identity.
1037 4.2.4. Server Operation in the Beginning of EAP-SIM Exchange
1039 As discussed in Section 4.2.2.2, the server SHOULD NOT rely on an
1040 identity string received in EAP-Response/Identity. Therefore, the
1041 RECOMMENDED way to start an EAP-SIM exchange is to ignore any
1042 received identity strings. The server SHOULD begin the EAP-SIM
1043 exchange by issuing the EAP-Request/SIM/Start packet with an
1044 identity-requesting attribute to indicate that the server wants the
1045 peer to include an identity in the AT_IDENTITY attribute of the EAP-
1046 Response/SIM/Start message. Three methods to request an identity
1047 from the peer are discussed below.
1049 If the server chooses not to ignore the contents of EAP-
1050 Response/Identity, then the server may have already received an EAP-
1051 SIM identity in this packet. However, if the EAP server has not
1052 received any EAP-SIM peer identity (permanent identity, pseudonym
1053 identity, or fast re-authentication identity) from the peer when
1054 sending the first EAP-SIM request, or if the EAP server has received
1055 an EAP-Response/Identity packet but the contents do not appear to be
1056 a valid permanent identity, pseudonym identity or a re-authentication
1057 identity, then the server MUST request an identity from the peer
1058 using one of the methods below.
1060 The server sends the EAP-Request/SIM/Start message with the
1061 AT_PERMANENT_ID_REQ attribute to indicate that the server wants the
1062 peer to include the permanent identity in the AT_IDENTITY attribute
1066 Haverinen & Salowey Informational [Page 19]
1068 RFC 4186 EAP-SIM Authentication January 2006
1071 of the EAP-Response/SIM/Start message. This is done in the following
1074 o The server does not support fast re-authentication or identity
1077 o The server decided to process a received identity, and the server
1078 recognizes the received identity as a pseudonym identity but the
1079 server is not able to map the pseudonym identity to a permanent
1082 The server issues the EAP-Request/SIM/Start packet with the
1083 AT_FULLAUTH_ID_REQ attribute to indicate that the server wants the
1084 peer to include a full authentication identity (pseudonym identity or
1085 permanent identity) in the AT_IDENTITY attribute of the
1086 EAP-Response/SIM/Start message. This is done in the following cases:
1088 o The server does not support fast re-authentication and the server
1089 supports identity privacy.
1091 o The server decided to process a received identity, and the server
1092 recognizes the received identity as a re-authentication identity
1093 but the server is not able to map the re-authentication identity
1094 to a permanent identity.
1096 The server issues the EAP-Request/SIM/Start packet with the
1097 AT_ANY_ID_REQ attribute to indicate that the server wants the peer to
1098 include an identity in the AT_IDENTITY attribute of the
1099 EAP-Response/SIM/Start message, and the server does not indicate any
1100 preferred type for the identity. This is done in other cases, such
1101 as when the server ignores a received EAP-Response/Identity, the
1102 server does not have any identity, or the server does not recognize
1103 the format of a received identity.
1105 4.2.5. Processing of EAP-Request/SIM/Start by the Peer
1107 Upon receipt of an EAP-Request/SIM/Start message, the peer MUST
1108 perform the following steps.
1110 If the EAP-Request/SIM/Start does not include an identity request
1111 attribute, then the peer responds with EAP-Response/SIM/Start without
1112 AT_IDENTITY. The peer includes the AT_SELECTED_VERSION and
1113 AT_NONCE_MT attributes, because the exchange is a full authentication
1116 If the EAP-Request/SIM/Start includes AT_PERMANENT_ID_REQ, and if the
1117 peer does not have a pseudonym available, then the peer MUST respond
1118 with EAP-Response/SIM/Start and include the permanent identity in
1122 Haverinen & Salowey Informational [Page 20]
1124 RFC 4186 EAP-SIM Authentication January 2006
1127 AT_IDENTITY. If the peer has a pseudonym available, then the peer
1128 MAY refuse to send the permanent identity; hence, in this case the
1129 peer MUST either respond with EAP-Response/SIM/Start and include the
1130 permanent identity in AT_IDENTITY or respond with EAP-Response/SIM/
1131 Client-Error packet with the code "unable to process packet".
1133 If the EAP-Request/SIM/Start includes AT_FULL_AUTH_ID_REQ, and if the
1134 peer has a pseudonym available, then the peer SHOULD respond with
1135 EAP-Response/SIM/Start and include the pseudonym identity in
1136 AT_IDENTITY. If the peer does not have a pseudonym when it receives
1137 this message, then the peer MUST respond with EAP-Response/SIM/Start
1138 and include the permanent identity in AT_IDENTITY. The Peer MUST NOT
1139 use a re-authentication identity in the AT_IDENTITY attribute.
1141 If the EAP-Request/SIM/Start includes AT_ANY_ID_REQ, and if the peer
1142 has maintained fast re-authentication state information and the peer
1143 wants to use fast re-authentication, then the peer responds with
1144 EAP-Response/SIM/Start and includes the fast re-authentication
1145 identity in AT_IDENTITY. Else, if the peer has a pseudonym identity
1146 available, then the peer responds with EAP-Response/SIM/Start and
1147 includes the pseudonym identity in AT_IDENTITY. Else, the peer
1148 responds with EAP-Response/SIM/Start and includes the permanent
1149 identity in AT_IDENTITY.
1151 An EAP-SIM exchange may include several EAP/SIM/Start rounds. The
1152 server may issue a second EAP-Request/SIM/Start if it was not able to
1153 recognize the identity that the peer used in the previous AT_IDENTITY
1154 attribute. At most, three EAP/SIM/Start rounds can be used, so the
1155 peer MUST NOT respond to more than three EAP-Request/SIM/Start
1156 messages within an EAP exchange. The peer MUST verify that the
1157 sequence of EAP-Request/SIM/Start packets that the peer receives
1158 comply with the sequencing rules defined in this document. That is,
1159 AT_ANY_ID_REQ can only be used in the first EAP-Request/SIM/Start; in
1160 other words, AT_ANY_ID_REQ MUST NOT be used in the second or third
1161 EAP-Request/SIM/Start. AT_FULLAUTH_ID_REQ MUST NOT be used if the
1162 previous EAP-Request/SIM/Start included AT_PERMANENT_ID_REQ. The
1163 peer operation, in cases when it receives an unexpected attribute or
1164 an unexpected message, is specified in Section 6.3.1.
1166 4.2.6. Attacks Against Identity Privacy
1168 The section above specifies two possible ways the peer can operate
1169 upon receipt of AT_PERMANENT_ID_REQ. This is because a received
1170 AT_PERMANENT_ID_REQ does not necessarily originate from the valid
1171 network, but an active attacker may transmit an EAP-Request/SIM/
1172 Start packet with an AT_PERMANENT_ID_REQ attribute to the peer, in an
1173 effort to find out the true identity of the user. If the peer does
1174 not want to reveal its permanent identity, then the peer sends the
1178 Haverinen & Salowey Informational [Page 21]
1180 RFC 4186 EAP-SIM Authentication January 2006
1183 EAP-Response/SIM/Client-Error packet with the error code "unable to
1184 process packet", and the authentication exchange terminates.
1186 Basically, there are two different policies that the peer can employ
1187 with regard to AT_PERMANENT_ID_REQ. A "conservative" peer assumes
1188 that the network is able to maintain pseudonyms robustly. Therefore,
1189 if a conservative peer has a pseudonym username, the peer responds
1190 with EAP-Response/SIM/Client-Error to the EAP packet with
1191 AT_PERMANENT_ID_REQ, because the peer believes that the valid network
1192 is able to map the pseudonym identity to the peer's permanent
1193 identity. (Alternatively, the conservative peer may accept
1194 AT_PERMANENT_ID_REQ in certain circumstances, for example, if the
1195 pseudonym was received a long time ago.) The benefit of this policy
1196 is that it protects the peer against active attacks on anonymity. On
1197 the other hand, a "liberal" peer always accepts the
1198 AT_PERMANENT_ID_REQ and responds with the permanent identity. The
1199 benefit of this policy is that it works even if the valid network
1200 sometimes loses pseudonyms and is not able to map them to the
1203 4.2.7. Processing of AT_IDENTITY by the Server
1205 When the server receives an EAP-Response/SIM/Start message with the
1206 AT_IDENTITY (in response to the server's identity requesting
1207 attribute), the server MUST operate as follows.
1209 If the server used AT_PERMANENT_ID_REQ, and if the AT_IDENTITY does
1210 not contain a valid permanent identity, then the server sends
1211 EAP-Request/SIM/Notification with AT_NOTIFICATION code "General
1212 failure" (16384), and the EAP exchange terminates. If the server
1213 recognizes the permanent identity and is able to continue, then the
1214 server proceeds with full authentication by sending EAP-Request/SIM/
1217 If the server used AT_FULLAUTH_ID_REQ, and if AT_IDENTITY contains a
1218 valid permanent identity or a pseudonym identity that the server can
1219 map to a valid permanent identity, then the server proceeds with full
1220 authentication by sending EAP-Request/SIM/Challenge. If AT_IDENTITY
1221 contains a pseudonym identity that the server is not able to map to a
1222 valid permanent identity, or an identity that the server is not able
1223 to recognize or classify, then the server sends EAP-Request/SIM/Start
1224 with AT_PERMANENT_ID_REQ.
1226 If the server used AT_ANY_ID_REQ, and if the AT_IDENTITY contains a
1227 valid permanent identity or a pseudonym identity that the server can
1228 map to a valid permanent identity, then the server proceeds with full
1229 authentication by sending EAP-Request/SIM/Challenge.
1234 Haverinen & Salowey Informational [Page 22]
1236 RFC 4186 EAP-SIM Authentication January 2006
1239 If the server used AT_ANY_ID_REQ, and if AT_IDENTITY contains a valid
1240 fast re-authentication identity and the server agrees on using
1241 re-authentication, then the server proceeds with fast
1242 re-authentication by sending EAP-Request/SIM/Re-authentication
1245 If the server used AT_ANY_ID_REQ, and if the peer sent an
1246 EAP-Response/SIM/Start with only AT_IDENTITY (indicating
1247 re-authentication), but the server is not able to map the identity to
1248 a permanent identity, then the server sends EAP-Request/SIM/Start
1249 with AT_FULLAUTH_ID_REQ.
1251 If the server used AT_ANY_ID_REQ, and if AT_IDENTITY contains a valid
1252 fast re-authentication identity that the server is able to map to a
1253 permanent identity, and if the server does not want to use fast
1254 re-authentication, then the server sends EAP-Request/SIM/Start
1255 without any identity requesting attributes.
1257 If the server used AT_ANY_ID_REQ, and AT_IDENTITY contains an
1258 identity that the server recognizes as a pseudonym identity but the
1259 server is not able to map the pseudonym identity to a permanent
1260 identity, then the server sends EAP-Request/SIM/Start with
1261 AT_PERMANENT_ID_REQ.
1263 If the server used AT_ANY_ID_REQ, and AT_IDENTITY contains an
1264 identity that the server is not able to recognize or classify, then
1265 the server sends EAP-Request/SIM/Start with AT_FULLAUTH_ID_REQ.
1267 4.3. Message Sequence Examples (Informative)
1269 This section contains non-normative message sequence examples to
1270 illustrate how the peer identity can be communicated to the server.
1290 Haverinen & Salowey Informational [Page 23]
1292 RFC 4186 EAP-SIM Authentication January 2006
1295 4.3.1. Full Authentication
1297 This case for full authentication is illustrated below in Figure 2.
1298 In this case, AT_IDENTITY contains either the permanent identity or a
1299 pseudonym identity. The same sequence is also used in case the
1300 server uses the AT_FULLAUTH_ID_REQ in EAP-Request/SIM/Start.
1304 | +------------------------------+
1305 | | Server does not have a |
1306 | | Subscriber identity available|
1307 | | When starting EAP-SIM |
1308 | +------------------------------+
1310 | EAP-Request/SIM/Start |
1311 | (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1312 |<------------------------------------------------------|
1315 | EAP-Response/SIM/Start |
1316 | (AT_IDENTITY, AT_NONCE_MT, |
1317 | AT_SELECTED_VERSION) |
1318 |------------------------------------------------------>|
1321 Figure 2: Requesting any identity, full authentication
1323 If the peer uses its full authentication identity and the AT_IDENTITY
1324 attribute contains a valid permanent identity or a valid pseudonym
1325 identity that the EAP server is able to map to the permanent
1326 identity, then the full authentication sequence proceeds as usual
1327 with the EAP Server issuing the EAP-Request/SIM/Challenge message.
1346 Haverinen & Salowey Informational [Page 24]
1348 RFC 4186 EAP-SIM Authentication January 2006
1351 4.3.2. Fast Re-authentication
1353 The case when the server uses the AT_ANY_ID_REQ and the peer wants to
1354 perform fast re-authentication is illustrated below in Figure 3.
1358 | +------------------------------+
1359 | | Server does not have a |
1360 | | Subscriber identity available|
1361 | | When starting EAP-SIM |
1362 | +------------------------------+
1364 | EAP-Request/SIM/Start |
1365 | (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1366 |<------------------------------------------------------|
1369 | EAP-Response/SIM/Start |
1370 | (AT_IDENTITY containing a fast re-auth. identity) |
1371 |------------------------------------------------------>|
1374 Figure 3: Requesting any identity, fast re-authentication
1376 On fast re-authentication, if the AT_IDENTITY attribute contains a
1377 valid fast re-authentication identity and the server agrees on using
1378 fast re-authentication, then the server proceeds with the fast
1379 re-authentication sequence and issues the EAP-Request/SIM/
1380 Re-authentication packet, as specified in Section 5.
1402 Haverinen & Salowey Informational [Page 25]
1404 RFC 4186 EAP-SIM Authentication January 2006
1407 4.3.3. Fall Back to Full Authentication
1409 Figure 4 illustrates cases in which the server does not recognize the
1410 fast re-authentication identity the peer used in AT_IDENTITY, and
1411 issues a second EAP-Request/SIM/Start message.
1415 | +------------------------------+
1416 | | Server does not have a |
1417 | | Subscriber identity available|
1418 | | When starting EAP-SIM |
1419 | +------------------------------+
1421 | EAP-Request/SIM/Start |
1422 | (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1423 |<------------------------------------------------------|
1426 | EAP-Response/SIM/Start |
1427 | (AT_IDENTITY containing a fast re-auth. identity) |
1428 |------------------------------------------------------>|
1430 | +------------------------------+
1431 | | Server does not recognize |
1432 | | The fast re-auth. |
1434 | +------------------------------+
1436 | EAP-Request/SIM/Start |
1437 | (AT_FULLAUTH_ID_REQ, AT_VERSION_LIST) |
1438 |<------------------------------------------------------|
1441 | EAP-Response/SIM/Start |
1442 | (AT_IDENTITY with a full-auth. identity, AT_NONCE_MT, |
1443 | AT_SELECTED_VERSION) |
1444 |------------------------------------------------------>|
1447 Figure 4: Fall back to full authentication
1458 Haverinen & Salowey Informational [Page 26]
1460 RFC 4186 EAP-SIM Authentication January 2006
1463 4.3.4. Requesting the Permanent Identity 1
1465 Figure 5 illustrates the case in which the EAP server fails to map
1466 the pseudonym identity included in the EAP-Response/Identity packet
1467 to a valid permanent identity.
1471 | EAP-Request/Identity |
1472 |<------------------------------------------------------|
1474 | EAP-Response/Identity |
1475 | (Includes a pseudonym) |
1476 |------------------------------------------------------>|
1478 | +------------------------------+
1479 | | Server fails to map the |
1480 | | Pseudonym to a permanent id. |
1481 | +------------------------------+
1482 | EAP-Request/SIM/Start |
1483 | (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) |
1484 |<------------------------------------------------------|
1486 | EAP-Response/SIM/Start |
1487 | (AT_IDENTITY with permanent identity, AT_NONCE_MT, |
1488 | AT_SELECTED_VERSION) |
1489 |------------------------------------------------------>|
1492 Figure 5: Requesting the permanent identity
1494 If the server recognizes the permanent identity, then the
1495 authentication sequence proceeds as usual with the EAP Server issuing
1496 the EAP-Request/SIM/Challenge message.
1514 Haverinen & Salowey Informational [Page 27]
1516 RFC 4186 EAP-SIM Authentication January 2006
1519 4.3.5. Requesting the Permanent Identity 2
1521 Figure 6 illustrates the case in which the EAP server fails to map
1522 the pseudonym included in the AT_IDENTITY attribute to a valid
1527 | +------------------------------+
1528 | | Server does not have a |
1529 | | Subscriber identity available|
1530 | | When starting EAP-SIM |
1531 | +------------------------------+
1532 | EAP-Request/SIM/Start |
1533 | (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1534 |<------------------------------------------------------|
1536 |EAP-Response/SIM/Start |
1537 |(AT_IDENTITY with a pseudonym identity, AT_NONCE_MT, |
1538 | AT_SELECTED_VERSION) |
1539 |------------------------------------------------------>|
1540 | +-------------------------------+
1541 | | Server fails to map the |
1542 | | Pseudonym in AT_IDENTITY |
1543 | | to a valid permanent identity |
1544 | +-------------------------------+
1546 | EAP-Request/SIM/Start |
1547 | (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) |
1548 |<------------------------------------------------------|
1550 | EAP-Response/SIM/Start |
1551 | (AT_IDENTITY with permanent identity, |
1552 | AT_NONCE_MT, AT_SELECTED_VERSION) |
1553 |------------------------------------------------------>|
1556 Figure 6: Requesting a permanent identity (two EAP-SIM Start rounds)
1558 4.3.6. Three EAP-SIM/Start Roundtrips
1560 In the worst case, there are three EAP/SIM/Start round trips before
1561 the server obtains an acceptable identity. This case is illustrated
1570 Haverinen & Salowey Informational [Page 28]
1572 RFC 4186 EAP-SIM Authentication January 2006
1577 | +------------------------------+
1578 | | Server does not have a |
1579 | | Subscriber identity available|
1580 | | When starting EAP-SIM |
1581 | +------------------------------+
1582 | EAP-Request/SIM/Start |
1583 | (Includes AT_ANY_ID_REQ, AT_VERSION_LIST) |
1584 |<------------------------------------------------------|
1586 | EAP-Response/SIM/Start |
1587 | (AT_IDENTITY with fast re-auth. identity) |
1588 |------------------------------------------------------>|
1590 | +------------------------------+
1591 | | Server does not accept |
1592 | | The fast re-auth. |
1594 | +------------------------------+
1595 | EAP-Request/SIM/Start |
1596 | (AT_FULLAUTH_ID_REQ, AT_VERSION_LIST) |
1597 |<------------------------------------------------------|
1603 |EAP-Response/SIM/Start |
1604 |(AT_IDENTITY with a pseudonym identity, AT_NONCE_MT, |
1605 | AT_SELECTED_VERSION) |
1606 |------------------------------------------------------>|
1608 | +-------------------------------+
1609 | | Server fails to map the |
1610 | | Pseudonym in AT_IDENTITY |
1611 | | to a valid permanent identity |
1612 | +-------------------------------+
1613 | EAP-Request/SIM/Start |
1614 | (AT_PERMANENT_ID_REQ, AT_VERSION_LIST) |
1615 |<------------------------------------------------------|
1617 | EAP-Response/SIM/Start |
1618 | (AT_IDENTITY with permanent identity, AT_NONCE_MT, |
1619 | AT_SELECTED_VERSION) |
1620 |------------------------------------------------------>|
1622 Figure 7: Three EAP-SIM Start rounds
1626 Haverinen & Salowey Informational [Page 29]
1628 RFC 4186 EAP-SIM Authentication January 2006
1631 After the last EAP-Response/SIM/Start message, the full
1632 authentication sequence proceeds as usual. If the EAP Server
1633 recognizes the permanent identity and is able to proceed, the server
1634 issues the EAP-Request/SIM/Challenge message.
1636 5. Fast Re-Authentication
1640 In some environments, EAP authentication may be performed frequently.
1641 Because the EAP-SIM full authentication procedure makes use of the
1642 GSM SIM A3/A8 algorithms, and therefore requires 2 or 3 fresh
1643 triplets from the Authentication Centre, the full authentication
1644 procedure is not very well suited for frequent use. Therefore,
1645 EAP-SIM includes a more inexpensive fast re-authentication procedure
1646 that does not make use of the SIM A3/A8 algorithms and does not need
1647 new triplets from the Authentication Centre. Re-authentication can
1648 be performed in fewer roundtrips than the full authentication.
1650 Fast re-authentication is optional to implement for both the EAP-SIM
1651 server and peer. On each EAP authentication, either one of the
1652 entities may also fall back on full authentication if it does not
1653 want to use fast re-authentication.
1655 Fast re-authentication is based on the keys derived on the preceding
1656 full authentication. The same K_aut and K_encr keys that were used
1657 in full authentication are used to protect EAP-SIM packets and
1658 attributes, and the original Master Key from full authentication is
1659 used to generate a fresh Master Session Key, as specified in Section
1662 The fast re-authentication exchange makes use of an unsigned 16-bit
1663 counter, included in the AT_COUNTER attribute. The counter has three
1664 goals: 1) it can be used to limit the number of successive
1665 reauthentication exchanges without full authentication 2) it
1666 contributes to the keying material, and 3) it protects the peer and
1667 the server from replays. On full authentication, both the server and
1668 the peer initialize the counter to one. The counter value of at
1669 least one is used on the first fast re-authentication. On subsequent
1670 fast re-authentications, the counter MUST be greater than on any of
1671 the previous re-authentications. For example, on the second fast
1672 re-authentication, the counter value is two or greater. The
1673 AT_COUNTER attribute is encrypted.
1675 Both the peer and the EAP server maintain a copy of the counter. The
1676 EAP server sends its counter value to the peer in the fast
1677 re-authentication request. The peer MUST verify that its counter
1678 value is less than or equal to the value sent by the EAP server.
1682 Haverinen & Salowey Informational [Page 30]
1684 RFC 4186 EAP-SIM Authentication January 2006
1687 The server includes an encrypted server random nonce (AT_NONCE_S) in
1688 the fast re-authentication request. The AT_MAC attribute in the
1689 peer's response is calculated over NONCE_S to provide a
1690 challenge/response authentication scheme. The NONCE_S also
1691 contributes to the new Master Session Key.
1693 Both the peer and the server SHOULD have an upper limit for the
1694 number of subsequent fast re-authentications allowed before a full
1695 authentication needs to be performed. Because a 16-bit counter is
1696 used in fast re-authentication, the theoretical maximum number of
1697 re-authentications is reached when the counter value reaches FFFF
1700 In order to use fast re-authentication, the peer and the EAP server
1701 need to store the following values: Master Key, latest counter value
1702 and the next fast re-authentication identity. K_aut, K_encr may
1703 either be stored or derived again from MK. The server may also need
1704 to store the permanent identity of the user.
1706 5.2. Comparison to UMTS AKA
1708 When analyzing the fast re-authentication exchange, it may be helpful
1709 to compare it with the UMTS Authentication and Key Agreement (AKA)
1710 exchange, which it resembles closely. The counter corresponds to the
1711 UMTS AKA sequence number, NONCE_S corresponds to RAND, AT_MAC in
1712 EAP-Request/SIM/Re-authentication corresponds to AUTN, the AT_MAC in
1713 EAP-Response/SIM/Re-authentication corresponds to RES,
1714 AT_COUNTER_TOO_SMALL corresponds to AUTS, and encrypting the counter
1715 corresponds to the usage of the Anonymity Key. Also, the key
1716 generation on fast re-authentication, with regard to random or fresh
1717 material, is similar to UMTS AKA -- the server generates the NONCE_S
1718 and counter values, and the peer only verifies that the counter value
1721 It should also be noted that encrypting the AT_NONCE_S, AT_COUNTER,
1722 or AT_COUNTER_TOO_SMALL attributes is not important to the security
1723 of the fast re-authentication exchange.
1725 5.3. Fast Re-authentication Identity
1727 The fast re-authentication procedure makes use of separate
1728 re-authentication user identities. Pseudonyms and the permanent
1729 identity are reserved for full authentication only. If a
1730 re-authentication identity is lost and the network does not recognize
1731 it, the EAP server can fall back on full authentication.
1738 Haverinen & Salowey Informational [Page 31]
1740 RFC 4186 EAP-SIM Authentication January 2006
1743 If the EAP server supports fast re-authentication, it MAY include the
1744 skippable AT_NEXT_REAUTH_ID attribute in the encrypted data of
1745 EAP-Request/SIM/Challenge message (Section 9.3). This attribute
1746 contains a new fast re-authentication identity for the next fast
1747 re-authentication. The attribute also works as a capability flag
1748 that, indicating that the server supports fast re-authentication, and
1749 that the server wants to continue using fast re-authentication within
1750 the current context. The peer MAY ignore this attribute, in which
1751 case it MUST use full authentication next time. If the peer wants to
1752 use re-authentication, it uses this fast re-authentication identity
1753 on next authentication. Even if the peer has a fast
1754 re-authentication identity, the peer MAY discard the fast
1755 re-authentication identity and use a pseudonym or the permanent
1756 identity instead, in which case full authentication MUST be
1757 performed. If the EAP server does not include the AT_NEXT_REAUTH_ID
1758 in the encrypted data of EAP-Request/SIM/Challenge or
1759 EAP-Request/SIM/ Re-authentication, then the peer MUST discard its
1760 current fast re-authentication state information and perform a full
1761 authentication next time.
1763 In environments where a realm portion is needed in the peer identity,
1764 the fast re-authentication identity received in AT_NEXT_REAUTH_ID
1765 MUST contain both a username portion and a realm portion, as per the
1766 NAI format. The EAP Server can choose an appropriate realm part in
1767 order to have the AAA infrastructure route subsequent fast
1768 re-authentication related requests to the same AAA server. For
1769 example, the realm part MAY include a portion that is specific to the
1770 AAA server. Hence, it is sufficient to store the context required
1771 for fast re-authentication in the AAA server that performed the full
1774 The peer MAY use the fast re-authentication identity in the
1775 EAP-Response/Identity packet or, in response to the server's
1776 AT_ANY_ID_REQ attribute, the peer MAY use the fast re-authentication
1777 identity in the AT_IDENTITY attribute of the EAP-Response/SIM/Start
1780 The peer MUST NOT modify the username portion of the fast
1781 re-authentication identity, but the peer MAY modify the realm portion
1782 or replace it with another realm portion. The peer might need to
1783 modify the realm in order to influence the AAA routing, for example,
1784 to make sure that the correct server is reached. It should be noted
1785 that sharing the same fast re-authentication key among several
1786 servers may have security risks, so changing the realm portion of the
1787 NAI in order to change the EAP server is not desirable.
1794 Haverinen & Salowey Informational [Page 32]
1796 RFC 4186 EAP-SIM Authentication January 2006
1799 Even if the peer uses a fast re-authentication identity, the server
1800 may want to fall back on full authentication, for example because the
1801 server does not recognize the fast re-authentication identity or does
1802 not want to use fast re-authentication. In this case, the server
1803 starts the full authentication procedure by issuing an
1804 EAP-Request/SIM/Start packet. This packet always starts a full
1805 authentication sequence if it does not include the AT_ANY_ID_REQ
1806 attribute. If the server was not able to recover the peer's identity
1807 from the fast re-authentication identity, the server includes either
1808 the AT_FULLAUTH_ID_REQ or the AT_PERMANENT_ID_REQ attribute in this
1811 5.4. Fast Re-authentication Procedure
1813 Figure 8 illustrates the fast re-authentication procedure. In this
1814 example, the optional protected success indication is not used.
1815 Encrypted attributes are denoted with '*'. The peer uses its
1816 re-authentication identity in the EAP-Response/Identity packet. As
1817 discussed above, an alternative way to communicate the
1818 re-authentication identity to the server is for the peer to use the
1819 AT_IDENTITY attribute in the EAP-Response/SIM/Start message. This
1820 latter case is not illustrated in the figure below, and it is only
1821 possible when the server requests that the peer send its identity by
1822 including the AT_ANY_ID_REQ attribute in the EAP-Request/SIM/Start
1825 If the server recognizes the identity as a valid fast
1826 re-authentication identity, and if the server agrees to use fast
1827 re-authentication, then the server sends the EAP-Request/SIM/
1828 Re-authentication packet to the peer. This packet MUST include the
1829 encrypted AT_COUNTER attribute, with a fresh counter value, the
1830 encrypted AT_NONCE_S attribute that contains a random number chosen
1831 by the server, the AT_ENCR_DATA and the AT_IV attributes used for
1832 encryption, and the AT_MAC attribute that contains a message
1833 authentication code over the packet. The packet MAY also include an
1834 encrypted AT_NEXT_REAUTH_ID attribute that contains the next fast
1835 re-authentication identity.
1837 Fast re-authentication identities are one-time identities. If the
1838 peer does not receive a new fast re-authentication identity, it MUST
1839 use either the permanent identity or a pseudonym identity on the next
1840 authentication to initiate full authentication.
1842 The peer verifies that AT_MAC is correct, and that the counter value
1843 is fresh (greater than any previously used value). The peer MAY save
1844 the next fast re-authentication identity from the encrypted
1845 AT_NEXT_REAUTH_ID for next time. If all checks are successful, the
1846 peer responds with the EAP-Response/SIM/Re-authentication packet,
1850 Haverinen & Salowey Informational [Page 33]
1852 RFC 4186 EAP-SIM Authentication January 2006
1855 including the AT_COUNTER attribute with the same counter value and
1858 The server verifies the AT_MAC attribute and also verifies that the
1859 counter value is the same that it used in the EAP-Request/SIM/
1860 Re-authentication packet. If these checks are successful, the
1861 re-authentication has succeeded and the server sends the EAP-Success
1864 If protected success indications (Section 6.2) were used, the
1865 EAP-Success packet would be preceded by an EAP-SIM notification
1906 Haverinen & Salowey Informational [Page 34]
1908 RFC 4186 EAP-SIM Authentication January 2006
1913 | EAP-Request/Identity |
1914 |<------------------------------------------------------|
1916 | EAP-Response/Identity |
1917 | (Includes a fast re-authentication identity) |
1918 |------------------------------------------------------>|
1920 | +--------------------------------+
1921 | | Server recognizes the identity |
1922 | | and agrees to use fast |
1923 | | re-authentication |
1924 | +--------------------------------+
1930 | EAP-Request/SIM/Re-authentication |
1931 | (AT_IV, AT_ENCR_DATA, *AT_COUNTER, |
1932 | *AT_NONCE_S, *AT_NEXT_REAUTH_ID, AT_MAC) |
1933 |<------------------------------------------------------|
1935 +-----------------------------------------------+ |
1936 | Peer verifies AT_MAC and the freshness of | |
1937 | the counter. Peer MAY store the new fast re- | |
1938 | authentication identity for next re-auth. | |
1939 +-----------------------------------------------+ |
1941 | EAP-Response/SIM/Re-authentication |
1942 | (AT_IV, AT_ENCR_DATA, *AT_COUNTER with same value, |
1944 |------------------------------------------------------>|
1945 | +--------------------------------+
1946 | | Server verifies AT_MAC and |
1948 | +--------------------------------+
1951 |<------------------------------------------------------|
1954 Figure 8: Fast Re-authentication
1962 Haverinen & Salowey Informational [Page 35]
1964 RFC 4186 EAP-SIM Authentication January 2006
1967 5.5. Fast Re-authentication Procedure when Counter Is Too Small
1969 If the peer does not accept the counter value of EAP-Request/SIM/
1970 Re-authentication, it indicates the counter synchronization problem
1971 by including the encrypted AT_COUNTER_TOO_SMALL in EAP-Response/SIM/
1972 Re-authentication. The server responds with EAP-Request/SIM/Start to
1973 initiate a normal full authentication procedure. This is illustrated
1974 in Figure 9. Encrypted attributes are denoted with '*'.
1977 | EAP-Request/SIM/Start |
1978 | (AT_ANY_ID_REQ, AT_VERSION_LIST) |
1979 |<------------------------------------------------------|
1981 | EAP-Response/SIM/Start |
1983 | (Includes a fast re-authentication identity) |
1984 |------------------------------------------------------>|
1986 | EAP-Request/SIM/Re-authentication |
1987 | (AT_IV, AT_ENCR_DATA, *AT_COUNTER, |
1988 | *AT_NONCE_S, *AT_NEXT_REAUTH_ID, AT_MAC) |
1989 |<------------------------------------------------------|
1990 +-----------------------------------------------+ |
1991 | AT_MAC is valid but the counter is not fresh. | |
1992 +-----------------------------------------------+ |
1994 | EAP-Response/SIM/Re-authentication |
1995 | (AT_IV, AT_ENCR_DATA, *AT_COUNTER_TOO_SMALL, |
1996 | *AT_COUNTER, AT_MAC) |
1997 |------------------------------------------------------>|
1998 | +----------------------------------------------+
1999 | | Server verifies AT_MAC but detects |
2000 | | That peer has included AT_COUNTER_TOO_SMALL |
2001 | +----------------------------------------------+
2003 | EAP-Request/SIM/Start |
2004 | (AT_VERSION_LIST) |
2005 |<------------------------------------------------------|
2006 +---------------------------------------------------------------+
2007 | Normal full authentication follows. |
2008 +---------------------------------------------------------------+
2011 Figure 9: Fast Re-authentication, counter is not fresh
2018 Haverinen & Salowey Informational [Page 36]
2020 RFC 4186 EAP-SIM Authentication January 2006
2023 In the figure above, the first three messages are similar to the
2024 basic fast re-authentication case. When the peer detects that the
2025 counter value is not fresh, it includes the AT_COUNTER_TOO_SMALL
2026 attribute in EAP-Response/SIM/Re-authentication. This attribute
2027 doesn't contain any data, but it is a request for the server to
2028 initiate full authentication. In this case, the peer MUST ignore the
2029 contents of the server's AT_NEXT_REAUTH_ID attribute.
2031 On receipt of AT_COUNTER_TOO_SMALL, the server verifies AT_MAC and
2032 verifies that AT_COUNTER contains the same counter value as in the
2033 EAP-Request/SIM/Re-authentication packet. If not, the server
2034 terminates the authentication exchange by sending the
2035 EAP-Request/SIM/Notification with AT_NOTIFICATION code "General
2036 failure" (16384). If all checks on the packet are successful, the
2037 server transmits a new EAP-Request/SIM/Start packet and the full
2038 authentication procedure is performed as usual. Since the server
2039 already knows the subscriber identity, it MUST NOT include
2040 AT_ANY_ID_REQ, AT_FULLAUTH_ID_REQ, or AT_PERMANENT_ID_REQ in the
2041 EAP-Request/SIM/Start.
2043 It should be noted that in this case, peer identity is only
2044 transmitted in the AT_IDENTITY attribute at the beginning of the
2045 whole EAP exchange. The fast re-authentication identity used in this
2046 AT_IDENTITY attribute will be used in key derivation (see Section 7).
2048 6. EAP-SIM Notifications
2052 EAP-SIM does not prohibit the use of the EAP Notifications as
2053 specified in [RFC3748]. EAP Notifications can be used at any time in
2054 the EAP-SIM exchange. It should be noted that EAP-SIM does not
2055 protect EAP Notifications. EAP-SIM also specifies method-specific
2056 EAP-SIM notifications that are protected in some cases.
2058 The EAP server can use EAP-SIM notifications to convey notifications
2059 and result indications (Section 6.2) to the peer.
2061 The server MUST use notifications in cases discussed in
2062 Section 6.3.2. When the EAP server issues an
2063 EAP-Request/SIM/Notification packet to the peer, the peer MUST
2064 process the notification packet. The peer MAY show a notification
2065 message to the user and the peer MUST respond to the EAP server with
2066 an EAP-Response/SIM/Notification packet, even if the peer did not
2067 recognize the notification code.
2074 Haverinen & Salowey Informational [Page 37]
2076 RFC 4186 EAP-SIM Authentication January 2006
2079 An EAP-SIM full authentication exchange or a fast re-authentication
2080 exchange MUST NOT include more than one EAP-SIM notification round.
2082 The notification code is a 16-bit number. The most significant bit
2083 is called the Success bit (S bit). The S bit specifies whether the
2084 notification implies failure. The code values with the S bit set to
2085 zero (code values 0...32767) are used on unsuccessful cases. The
2086 receipt of a notification code from this range implies a failed EAP
2087 exchange, so the peer can use the notification as a failure
2088 indication. After receiving the EAP-Response/SIM/Notification for
2089 these notification codes, the server MUST send the EAP-Failure
2092 The receipt of a notification code with the S bit set to one (values
2093 32768...65536) does not imply failure. Notification code "Success"
2094 (32768) has been reserved as a general notification code to indicate
2095 successful authentication.
2097 The second most significant bit of the notification code is called
2098 the Phase bit (P bit). It specifies at which phase of the EAP-SIM
2099 exchange the notification can be used. If the P bit is set to zero,
2100 the notification can only be used after a successful
2101 EAP/SIM/Challenge round in full authentication or a successful
2102 EAP/SIM/Re-authentication round in reauthentication. A
2103 re-authentication round is considered successful only if the peer has
2104 successfully verified AT_MAC and AT_COUNTER attributes, and does not
2105 include the AT_COUNTER_TOO_SMALL attribute in
2106 EAP-Response/SIM/Re-authentication.
2108 If the P bit is set to one, the notification can only by used before
2109 the EAP/SIM/Challenge round in full authentication, or before the
2110 EAP/SIM/Re-authentication round in reauthentication. These
2111 notifications can only be used to indicate various failure cases. In
2112 other words, if the P bit is set to one, then the S bit MUST be set
2115 Section 9.8 and Section 9.9 specify what other attributes must be
2116 included in the notification packets.
2118 Some of the notification codes are authorization related and, hence,
2119 are not usually considered part of the responsibility of an EAP
2120 method. However, they are included as part of EAP-SIM because there
2121 are currently no other ways to convey this information to the user in
2122 a localizable way, and the information is potentially useful for the
2123 user. An EAP-SIM server implementation may decide never to send
2124 these EAP-SIM notifications.
2130 Haverinen & Salowey Informational [Page 38]
2132 RFC 4186 EAP-SIM Authentication January 2006
2135 6.2. Result Indications
2137 As discussed in Section 6.3, the server and the peer use explicit
2138 error messages in all error cases. If the server detects an error
2139 after successful authentication, the server uses an EAP-SIM
2140 notification to indicate failure to the peer. In this case, the
2141 result indication is integrity and replay protected.
2143 By sending an EAP-Response/SIM/Challenge packet or an
2144 EAP-Response/SIM/Re-authentication packet (without
2145 AT_COUNTER_TOO_SMALL), the peer indicates that it has successfully
2146 authenticated the server and that the peer's local policy accepts the
2147 EAP exchange. In other words, these packets are implicit success
2148 indications from the peer to the server.
2150 EAP-SIM also supports optional protected success indications from the
2151 server to the peer. If the EAP server wants to use protected success
2152 indications, it includes the AT_RESULT_IND attribute in the
2153 EAP-Request/SIM/Challenge or the EAP-Request/SIM/Re-authentication
2154 packet. This attribute indicates that the EAP server would like to
2155 use result indications in both successful and unsuccessful cases. If
2156 the peer also wants this, the peer includes AT_RESULT_IND in
2157 EAP-Response/SIM/Challenge or EAP-Response/SIM/Re-authentication.
2158 The peer MUST NOT include AT_RESULT_IND if it did not receive
2159 AT_RESULT_IND from the server. If both the peer and the server used
2160 AT_RESULT_IND, then the EAP exchange is not complete yet, but an
2161 EAP-SIM notification round will follow. The following EAP-SIM
2162 notification may indicate either failure or success.
2164 Success indications with the AT_NOTIFICATION code "Success" (32768)
2165 can only be used if both the server and the peer indicate they want
2166 to use them with AT_RESULT_IND. If the server did not include
2167 AT_RESULT_IND in the EAP-Request/SIM/Challenge or
2168 EAP-Request/SIM/Re-authentication packet, or if the peer did not
2169 include AT_RESULT_IND in the corresponding response packet, then the
2170 server MUST NOT use protected success indications.
2172 Because the server uses the AT_NOTIFICATION code "Success" (32768) to
2173 indicate that the EAP exchange has completed successfully, the EAP
2174 exchange cannot fail when the server processes the EAP-SIM response
2175 to this notification. Hence, the server MUST ignore the contents of
2176 the EAP-SIM response it receives from the
2177 EAP-Request/SIM/Notification with this code. Regardless of the
2178 contents of the EAP-SIM response, the server MUST send EAP-Success as
2186 Haverinen & Salowey Informational [Page 39]
2188 RFC 4186 EAP-SIM Authentication January 2006
2193 This section specifies the operation of the peer and the server in
2194 error cases. The subsections below require the EAP-SIM peer and
2195 server to send an error packet (EAP-Response/SIM/Client-Error from
2196 the peer or EAP-Request/SIM/Notification from the server) in error
2197 cases. However, implementations SHOULD NOT rely upon the correct
2198 error reporting behavior of the peer, authenticator, or the server.
2199 It is possible for error and other messages to be lost in transit or
2200 for a malicious participant to attempt to consume resources by not
2201 issuing error messages. Both the peer and the EAP server SHOULD have
2202 a mechanism to clean up state, even if an error message or
2203 EAP-Success is not received after a timeout period.
2205 6.3.1. Peer Operation
2207 In general, if an EAP-SIM peer detects an error in a received EAP-SIM
2208 packet, the EAP-SIM implementation responds with the
2209 EAP-Response/SIM/Client-Error packet. In response to the
2210 EAP-Response/SIM/Client-Error, the EAP server MUST issue the
2211 EAP-Failure packet and the authentication exchange terminates.
2213 By default, the peer uses the client error code 0, "unable to process
2214 packet". This error code is used in the following cases:
2216 o EAP exchange is not acceptable according to the peer's local
2219 o the peer is not able to parse the EAP request, i.e., the EAP
2220 request is malformed.
2222 o the peer encountered a malformed attribute.
2224 o wrong attribute types or duplicate attributes have been included
2227 o a mandatory attribute is missing.
2229 o unrecognized, non-skippable attribute.
2231 o unrecognized or unexpected EAP-SIM Subtype in the EAP request.
2233 o A RAND challenge repeated in AT_RAND.
2235 o invalid AT_MAC. The peer SHOULD log this event.
2237 o invalid pad bytes in AT_PADDING.
2242 Haverinen & Salowey Informational [Page 40]
2244 RFC 4186 EAP-SIM Authentication January 2006
2247 o the peer does not want to process AT_PERMANENT_ID_REQ.
2249 Separate error codes have been defined for the following error cases
2252 As specified in Section 4.1, when processing the AT_VERSION_LIST
2253 attribute, which lists the EAP-SIM versions supported by the server,
2254 if the attribute does not include a version that is implemented by
2255 the peer and allowed in the peer's security policy, then the peer
2256 MUST send the EAP-Response/SIM/Client-Error packet with the error
2257 code "unsupported version".
2259 If the number of RAND challenges is smaller than what is required by
2260 peer's local policy when processing the AT_RAND attribute, the peer
2261 MUST send the EAP-Response/SIM/Client-Error packet with the error
2262 code "insufficient number of challenges".
2264 If the peer believes that the RAND challenges included in AT_RAND are
2265 not fresh e.g., because it is capable of remembering some previously
2266 used RANDs, the peer MUST send the EAP-Response/SIM/Client-Error
2267 packet with the error code "RANDs are not fresh".
2269 6.3.2. Server Operation
2271 If an EAP-SIM server detects an error in a received EAP-SIM response,
2272 the server MUST issue the EAP-Request/SIM/Notification packet with an
2273 AT_NOTIFICATION code that implies failure. By default, the server
2274 uses one of the general failure codes ("General failure after
2275 authentication" (0), or "General failure" (16384)). The choice
2276 between these two codes depends on the phase of the EAP-SIM exchange,
2277 see Section 6. When the server issues an EAP-
2278 Request/SIM/Notification that implies failure, the error cases
2279 include the following:
2281 o the server is not able to parse the peer's EAP response
2283 o the server encounters a malformed attribute, a non-recognized
2284 non-skippable attribute, or a duplicate attribute
2286 o a mandatory attribute is missing or an invalid attribute was
2289 o unrecognized or unexpected EAP-SIM Subtype in the EAP Response
2291 o invalid AT_MAC. The server SHOULD log this event.
2293 o invalid AT_COUNTER
2298 Haverinen & Salowey Informational [Page 41]
2300 RFC 4186 EAP-SIM Authentication January 2006
2305 The EAP-SIM server sends EAP-Failure in two cases:
2307 1) In response to an EAP-Response/SIM/Client-Error packet the server
2308 has received from the peer, or
2310 2) Following an EAP-SIM notification round, when the AT_NOTIFICATION
2311 code implies failure.
2313 The EAP-SIM server MUST NOT send EAP-Failure in cases other than
2314 these two. However, it should be noted that even though the EAP-SIM
2315 server would not send an EAP-Failure, an authorization decision that
2316 happens outside EAP-SIM, such as in the AAA server or in an
2317 intermediate AAA proxy, may result in a failed exchange.
2319 The peer MUST accept the EAP-Failure packet in case 1) and case 2),
2320 above. The peer SHOULD silently discard the EAP-Failure packet in
2325 On full authentication, the server can only send EAP-Success after
2326 the EAP/SIM/Challenge round. The peer MUST silently discard any
2327 EAP-Success packets if they are received before the peer has
2328 successfully authenticated the server and sent the
2329 EAP-Response/SIM/Challenge packet.
2331 If the peer did not indicate that it wants to use protected success
2332 indications with AT_RESULT_IND (as discussed in Section 6.2) on full
2333 authentication, then the peer MUST accept EAP-Success after a
2334 successful EAP/SIM/Challenge round.
2336 If the peer indicated that it wants to use protected success
2337 indications with AT_RESULT_IND (as discussed in Section 6.2), then
2338 the peer MUST NOT accept EAP-Success after a successful
2339 EAP/SIM/Challenge round. In this case, the peer MUST only accept
2340 EAP-Success after receiving an EAP-SIM Notification with the
2341 AT_NOTIFICATION code "Success" (32768).
2343 On fast re-authentication, EAP-Success can only be sent after the
2344 EAP/SIM/Re-authentication round. The peer MUST silently discard any
2345 EAP-Success packets if they are received before the peer has
2346 successfully authenticated the server and sent the
2347 EAP-Response/SIM/Re-authentication packet.
2349 If the peer did not indicate that it wants to use protected success
2350 indications with AT_RESULT_IND (as discussed in Section 6.2) on fast
2354 Haverinen & Salowey Informational [Page 42]
2356 RFC 4186 EAP-SIM Authentication January 2006
2359 re-authentication, then the peer MUST accept EAP-Success after a
2360 successful EAP/SIM/Re-authentication round.
2362 If the peer indicated that it wants to use protected success
2363 indications with AT_RESULT_IND (as discussed in Section 6.2), then
2364 the peer MUST NOT accept EAP-Success after a successful EAP/SIM/Re-
2365 authentication round. In this case, the peer MUST only accept
2366 EAP-Success after receiving an EAP-SIM Notification with the
2367 AT_NOTIFICATION code "Success" (32768).
2369 If the peer receives an EAP-SIM notification (Section 6) that
2370 indicates failure, then the peer MUST no longer accept the
2371 EAP-Success packet, even if the server authentication was
2372 successfully completed.
2376 This section specifies how keying material is generated.
2378 On EAP-SIM full authentication, a Master Key (MK) is derived from the
2379 underlying GSM authentication values (Kc keys), the NONCE_MT, and
2380 other relevant context as follows.
2382 MK = SHA1(Identity|n*Kc| NONCE_MT| Version List| Selected Version)
2384 In the formula above, the "|" character denotes concatenation.
2385 "Identity" denotes the peer identity string without any terminating
2386 null characters. It is the identity from the last AT_IDENTITY
2387 attribute sent by the peer in this exchange, or, if AT_IDENTITY was
2388 not used, it is the identity from the EAP-Response/Identity packet.
2389 The identity string is included as-is, without any changes. As
2390 discussed in Section 4.2.2.2, relying on EAP-Response/Identity for
2391 conveying the EAP-SIM peer identity is discouraged, and the server
2392 SHOULD use the EAP-SIM method-specific identity attributes.
2394 The notation n*Kc in the formula above denotes the n Kc values
2395 concatenated. The Kc keys are used in the same order as the RAND
2396 challenges in AT_RAND attribute. NONCE_MT denotes the NONCE_MT value
2397 (not the AT_NONCE_MT attribute, but only the nonce value). The
2398 Version List includes the 2-byte-supported version numbers from
2399 AT_VERSION_LIST, in the same order as in the attribute. The Selected
2400 Version is the 2-byte selected version from AT_SELECTED_VERSION.
2401 Network byte order is used, just as in the attributes. The hash
2402 function SHA-1 is specified in [SHA-1]. If several EAP/SIM/Start
2403 roundtrips are used in an EAP-SIM exchange, then the NONCE_MT,
2404 Version List and Selected version from the last EAP/SIM/Start round
2405 are used, and the previous EAP/SIM/Start rounds are ignored.
2410 Haverinen & Salowey Informational [Page 43]
2412 RFC 4186 EAP-SIM Authentication January 2006
2415 The Master Key is fed into a Pseudo-Random number Function (PRF)
2416 which generates separate Transient EAP Keys (TEKs) for protecting
2417 EAP-SIM packets, as well as a Master Session Key (MSK) for link layer
2418 security, and an Extended Master Session Key (EMSK) for other
2419 purposes. On fast re-authentication, the same TEKs MUST be used for
2420 protecting EAP packets, but a new MSK and a new EMSK MUST be derived
2421 from the original MK and from new values exchanged in the fast
2424 EAP-SIM requires two TEKs for its own purposes; the authentication
2425 key K_aut is to be used with the AT_MAC attribute, and the encryption
2426 key K_encr is to be used with the AT_ENCR_DATA attribute. The same
2427 K_aut and K_encr keys are used in full authentication and subsequent
2428 fast re-authentications.
2430 Key derivation is based on the random number generation specified in
2431 NIST Federal Information Processing Standards (FIPS) Publication
2432 186-2 [PRF]. The pseudo-random number generator is specified in the
2433 change notice 1 (2001 October 5) of [PRF] (Algorithm 1). As
2434 specified in the change notice (page 74), when Algorithm 1 is used as
2435 a general-purpose pseudo-random number generator, the "mod q" term in
2436 step 3.3 is omitted. The function G used in the algorithm is
2437 constructed via the Secure Hash Standard, as specified in Appendix
2438 3.3 of the standard. It should be noted that the function G is very
2439 similar to SHA-1, but the message padding is different. Please refer
2440 to [PRF] for full details. For convenience, the random number
2441 algorithm with the correct modification is cited in Appendix B.
2443 160-bit XKEY and XVAL values are used, so b = 160. On each full
2444 authentication, the Master Key is used as the initial secret seed-key
2445 XKEY. The optional user input values (XSEED_j) in step 3.1 are set
2448 On full authentication, the resulting 320-bit random numbers (x_0,
2449 x_1, ..., x_m-1) are concatenated and partitioned into suitable-sized
2450 chunks and used as keys in the following order: K_encr (128 bits),
2451 K_aut (128 bits), Master Session Key (64 bytes), Extended Master
2452 Session Key (64 bytes).
2454 On fast re-authentication, the same pseudo-random number generator
2455 can be used to generate a new Master Session Key and a new Extended
2456 Master Session Key. The seed value XKEY' is calculated as follows:
2458 XKEY' = SHA1(Identity|counter|NONCE_S| MK)
2460 In the formula above, the Identity denotes the fast re-authentication
2461 identity, without any terminating null characters, from the
2462 AT_IDENTITY attribute of the EAP-Response/SIM/Start packet, or, if
2466 Haverinen & Salowey Informational [Page 44]
2468 RFC 4186 EAP-SIM Authentication January 2006
2471 EAP-Response/SIM/Start was not used on fast re-authentication, it
2472 denotes the identity string from the EAP-Response/Identity packet.
2473 The counter denotes the counter value from the AT_COUNTER attribute
2474 used in the EAP-Response/SIM/Re-authentication packet. The counter
2475 is used in network byte order. NONCE_S denotes the 16-byte NONCE_S
2476 value from the AT_NONCE_S attribute used in the
2477 EAP-Request/SIM/Re-authentication packet. The MK is the Master Key
2478 derived on the preceding full authentication.
2480 On fast re-authentication, the pseudo-random number generator is run
2481 with the new seed value XKEY', and the resulting 320-bit random
2482 numbers (x_0, x_1, ..., x_m-1) are concatenated and partitioned into
2483 two 64-byte chunks and used as the new 64-byte Master Session Key and
2484 the new 64-byte Extended Master Session Key. Note that because
2485 K_encr and K_aut are not derived on fast re-authentication, the
2486 Master Session Key and the Extended Master Session key are obtained
2487 from the beginning of the key stream (x_0, x_1, ...).
2489 The first 32 bytes of the MSK can be used as the Pairwise Master Key
2490 (PMK) for IEEE 802.11i.
2492 When the RADIUS attributes specified in [RFC2548] are used to
2493 transport keying material, then the first 32 bytes of the MSK
2494 correspond to MS-MPPE-RECV-KEY and the second 32 bytes to
2495 MS-MPPE-SEND-KEY. In this case, only 64 bytes of keying material
2498 When generating the initial Master Key, the hash function is used as
2499 a mixing function to combine several session keys (Kc's) generated by
2500 the GSM authentication procedure and the random number NONCE_MT into
2501 a single session key. There are several reasons for this. The
2502 current GSM session keys are, at most, 64 bits, so two or more of
2503 them are needed to generate a longer key. By using a one-way
2504 function to combine the keys, we are assured that, even if an
2505 attacker managed to learn one of the EAP-SIM session keys, it
2506 wouldn't help him in learning the original GSM Kc's. In addition,
2507 since we include the random number NONCE_MT in the calculation, the
2508 peer is able to verify that the EAP-SIM packets it receives from the
2509 network are fresh and not replays (also see Section 11).
2511 8. Message Format and Protocol Extensibility
2515 As specified in [RFC3748], EAP packets begin with the Code,
2516 Identifiers, Length, and Type fields, which are followed by EAP-
2517 method-specific Type-Data. The Code field in the EAP header is set
2518 to 1 for EAP requests, and to 2 for EAP Responses. The usage of the
2522 Haverinen & Salowey Informational [Page 45]
2524 RFC 4186 EAP-SIM Authentication January 2006
2527 Length and Identifier fields in the EAP header are also specified in
2528 [RFC3748]. In EAP-SIM, the Type field is set to 18.
2530 In EAP-SIM, the Type-Data begins with an EAP-SIM header that consists
2531 of a 1-octet Subtype field and a 2-octet reserved field. The Subtype
2532 values used in EAP-SIM are defined in the IANA considerations section
2533 of the EAP-AKA specification [EAP-AKA]. The formats of the EAP
2534 header and the EAP-SIM header are shown below.
2537 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
2538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2539 | Code | Identifier | Length |
2540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2541 | Type | Subtype | Reserved |
2542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2544 The rest of the Type-Data that immediately follows the EAP-SIM header
2545 consists of attributes that are encoded in Type, Length, Value
2546 format. The figure below shows the generic format of an attribute.
2549 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
2550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2551 | Type | Length | Value...
2552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2557 Indicates the particular type of attribute. The attribute type
2558 values are listed in the IANA considerations section of the
2559 EAP-AKA specification [EAP-AKA].
2563 Indicates the length of this attribute in multiples of four
2564 bytes. The maximum length of an attribute is 1024 bytes. The
2565 length includes the Attribute Type and Length bytes.
2569 The particular data associated with this attribute. This field
2570 is always included and it may be two or more bytes in length.
2571 The type and length fields determine the format and length
2578 Haverinen & Salowey Informational [Page 46]
2580 RFC 4186 EAP-SIM Authentication January 2006
2583 Attributes numbered within the range 0 through 127 are called
2584 non-skippable attributes. When an EAP-SIM peer encounters a
2585 non-skippable attribute that the peer does not recognize, the peer
2586 MUST send the EAP-Response/SIM/Client-Error packet, which terminates
2587 the authentication exchange. If an EAP-SIM server encounters a
2588 non-skippable attribute that the server does not recognize, then the
2589 server sends the EAP-Request/SIM/Notification packet with an
2590 AT_NOTIFICATION code, which implies general failure ("General failure
2591 after authentication" (0), or "General failure" (16384), depending on
2592 the phase of the exchange), which terminates the authentication
2595 Attributes within the range of 128 through 255 are called skippable
2596 attributes. When a skippable attribute is encountered and is not
2597 recognized, it is ignored. The rest of the attributes and message
2598 data MUST still be processed. The Length field of the attribute is
2599 used to skip the attribute value in searching for the next attribute.
2601 Unless otherwise specified, the order of the attributes in an EAP-SIM
2602 message is insignificant and an EAP-SIM implementation should not
2603 assume a certain order to be used.
2605 Attributes can be encapsulated within other attributes. In other
2606 words, the value field of an attribute type can be specified to
2607 contain other attributes.
2609 8.2. Protocol Extensibility
2611 EAP-SIM can be extended by specifying new attribute types. If
2612 skippable attributes are used, it is possible to extend the protocol
2613 without breaking old implementations.
2615 However, any new attributes added to the EAP-Request/SIM/Start or
2616 EAP-Response/SIM/Start packets would not be integrity-protected.
2617 Therefore, these messages MUST NOT be extended in the current version
2618 of EAP-SIM. If the list of supported EAP-SIM versions in the
2619 AT_VERSION_LIST does not include versions other than 1, then the
2620 server MUST NOT include attributes other than those specified in this
2621 document in the EAP-Request/SIM/Start message. Note that future
2622 versions of this protocol might specify new attributes for
2623 EAP-Request/SIM/Start and still support version 1 of the protocol.
2624 In this case, the server might send an EAP-Request/SIM/Start message
2625 that includes new attributes and indicates support for protocol
2626 version 1 and other versions in the AT_VERSION_LIST attribute. If
2627 the peer selects version 1, then the peer MUST ignore any other
2628 attributes included in EAP-Request/SIM/Start, other than those
2629 specified in this document. If the selected EAP-SIM version in
2630 peer's AT_SELECTED_VERSION is 1, then the peer MUST NOT include other
2634 Haverinen & Salowey Informational [Page 47]
2636 RFC 4186 EAP-SIM Authentication January 2006
2639 attributes aside from those specified in this document in the
2640 EAP-Response/SIM/Start message.
2642 When specifying new attributes, it should be noted that EAP-SIM does
2643 not support message fragmentation. Hence, the sizes of the new
2644 extensions MUST be limited so that the maximum transfer unit (MTU) of
2645 the underlying lower layer is not exceeded. According to [RFC3748],
2646 lower layers must provide an EAP MTU of 1020 bytes or greater, so any
2647 extensions to EAP-SIM SHOULD NOT exceed the EAP MTU of 1020 bytes.
2649 Because EAP-SIM supports version negotiation, new versions of the
2650 protocol can also be specified by using a new version number.
2654 This section specifies the messages used in EAP-SIM. It specifies
2655 when a message may be transmitted or accepted, which attributes are
2656 allowed in a message, which attributes are required in a message, and
2657 other message-specific details. The general message format is
2658 specified in Section 8.1.
2660 9.1. EAP-Request/SIM/Start
2662 In full authentication the first SIM-specific EAP Request is
2663 EAP-Request/SIM/Start. The EAP/SIM/Start roundtrip is used for two
2664 purposes. In full authentication this packet is used to request the
2665 peer to send the AT_NONCE_MT attribute to the server. In addition,
2666 as specified in Section 4.2, the Start round trip may be used by the
2667 server for obtaining the peer identity. As discussed in Section 4.2,
2668 several Start rounds may be required to obtain a valid peer identity.
2670 The server MUST always include the AT_VERSION_LIST attribute.
2672 The server MAY include one of the following identity-requesting
2673 attributes: AT_PERMANENT_ID_REQ, AT_FULLAUTH_ID_REQ, or
2674 AT_ANY_ID_REQ. These three attributes are mutually exclusive, so the
2675 server MUST NOT include more than one of the attributes.
2677 If the server has received a response from the peer, it MUST NOT
2678 issue a new EAP-Request/SIM/Start packet if it has previously issued
2679 an EAP-Request/SIM/Start message either without any identity
2680 requesting attributes or with the AT_PERMANENT_ID_REQ attribute.
2682 If the server has received a response from the peer, it MUST NOT
2683 issue a new EAP-Request/SIM/Start packet with the AT_ANY_ID_REQ or
2684 AT_FULLAUTH_ID_REQ attributes if it has previously issued an
2685 EAP-Request/SIM/Start message with the AT_FULLAUTH_ID_REQ attribute.
2690 Haverinen & Salowey Informational [Page 48]
2692 RFC 4186 EAP-SIM Authentication January 2006
2695 If the server has received a response from the peer, it MUST NOT
2696 issue a new EAP-Request/SIM/Start packet with the AT_ANY_ID_REQ
2697 attribute if the server has previously issued an
2698 EAP-Request/SIM/Start message with the AT_ANY_ID_REQ attribute.
2700 This message MUST NOT include AT_MAC, AT_IV, or AT_ENCR_DATA.
2702 9.2. EAP-Response/SIM/Start
2704 The peer sends EAP-Response/SIM/Start in response to a valid
2705 EAP-Request/SIM/Start from the server.
2707 If and only if the server's EAP-Request/SIM/Start includes one of the
2708 identity-requesting attributes, then the peer MUST include the
2709 AT_IDENTITY attribute. The usage of AT_IDENTITY is defined in
2712 The AT_NONCE_MT attribute MUST NOT be included if the AT_IDENTITY
2713 with a fast re-authentication identity is present for fast
2714 re-authentication. AT_NONCE_MT MUST be included in all other cases
2715 (full authentication).
2717 The AT_SELECTED_VERSION attribute MUST NOT be included if the
2718 AT_IDENTITY attribute with a fast re-authentication identity is
2719 present for fast re-authentication. In all other cases,
2720 AT_SELECTED_VERSION MUST be included (full authentication). This
2721 attribute is used in version negotiation, as specified in
2724 This message MUST NOT include AT_MAC, AT_IV, or AT_ENCR_DATA.
2726 9.3. EAP-Request/SIM/Challenge
2728 The server sends the EAP-Request/SIM/Challenge after receiving a
2729 valid EAP-Response/SIM/Start that contains AT_NONCE_MT and
2730 AT_SELECTED_VERSION, and after successfully obtaining the subscriber
2733 The AT_RAND attribute MUST be included.
2735 The AT_RESULT_IND attribute MAY be included. The usage of this
2736 attribute is discussed in Section 6.2.
2738 The AT_MAC attribute MUST be included. For
2739 EAP-Request/SIM/Challenge, the MAC code is calculated over the
2742 EAP packet| NONCE_MT
2746 Haverinen & Salowey Informational [Page 49]
2748 RFC 4186 EAP-SIM Authentication January 2006
2751 The EAP packet is represented as specified in Section 8.1. It is
2752 followed by the 16-byte NONCE_MT value from the peer's AT_NONCE_MT
2755 The EAP-Request/SIM/Challenge packet MAY include encrypted attributes
2756 for identity privacy and for communicating the next fast
2757 re-authentication identity. In this case, the AT_IV and AT_ENCR_DATA
2758 attributes are included (Section 10.12).
2760 The plaintext of the AT_ENCR_DATA value field consists of nested
2761 attributes. The nested attributes MAY include AT_PADDING (as
2762 specified in Section 10.12). If the server supports identity privacy
2763 and wants to communicate a pseudonym to the peer for the next full
2764 authentication, then the nested encrypted attributes include the
2765 AT_NEXT_PSEUDONYM attribute. If the server supports
2766 re-authentication and wants to communicate a fast re-authentication
2767 identity to the peer, then the nested encrypted attributes include
2768 the AT_NEXT_REAUTH_ID attribute.
2770 When processing this message, the peer MUST process AT_RAND before
2771 processing other attributes. Only if AT_RAND is verified to be
2772 valid, the peer derives keys and verifies AT_MAC. The operation in
2773 case an error occurs is specified in Section 6.3.1.
2775 9.4. EAP-Response/SIM/Challenge
2777 The peer sends EAP-Response/SIM/Challenge in response to a valid
2778 EAP-Request/SIM/Challenge.
2780 Sending this packet indicates that the peer has successfully
2781 authenticated the server and that the EAP exchange will be accepted
2782 by the peer's local policy. Hence, if these conditions are not met,
2783 then the peer MUST NOT send EAP-Response/SIM/Challenge, but the peer
2784 MUST send EAP-Response/SIM/Client-Error.
2786 The AT_MAC attribute MUST be included. For EAP-
2787 Response/SIM/Challenge, the MAC code is calculated over the following
2792 The EAP packet is represented as specified in Section 8.1. The EAP
2793 packet bytes are immediately followed by the two or three SRES values
2794 concatenated, denoted above with the notation n*SRES. The SRES
2795 values are used in the same order as the corresponding RAND
2796 challenges in the server's AT_RAND attribute.
2802 Haverinen & Salowey Informational [Page 50]
2804 RFC 4186 EAP-SIM Authentication January 2006
2807 The AT_RESULT_IND attribute MAY be included if it was included in
2808 EAP-Request/SIM/Challenge. The usage of this attribute is discussed
2811 Later versions of this protocol MAY make use of the AT_ENCR_DATA and
2812 AT_IV attributes in this message to include encrypted (skippable)
2813 attributes. The EAP server MUST process EAP-Response/SIM/Challenge
2814 messages that include these attributes even if the server did not
2815 implement these optional attributes.
2817 9.5. EAP-Request/SIM/Re-authentication
2819 The server sends the EAP-Request/SIM/Re-authentication message if it
2820 wants to use fast re-authentication, and if it has received a valid
2821 fast re-authentication identity in EAP-Response/Identity or
2822 EAP-Response/SIM/Start.
2824 AT_MAC MUST be included. No message-specific data is included in the
2825 MAC calculation. See Section 10.14.
2827 The AT_RESULT_IND attribute MAY be included. The usage of this
2828 attribute is discussed in Section 6.2.
2830 The AT_IV and AT_ENCR_DATA attributes MUST be included. The
2831 plaintext consists of the following nested encrypted attributes,
2832 which MUST be included: AT_COUNTER and AT_NONCE_S. In addition, the
2833 nested encrypted attributes MAY include the following attributes:
2834 AT_NEXT_REAUTH_ID and AT_PADDING.
2836 9.6. EAP-Response/SIM/Re-authentication
2838 The client sends the EAP-Response/SIM/Re-authentication packet in
2839 response to a valid EAP-Request/SIM/Re-authentication.
2841 The AT_MAC attribute MUST be included. For
2842 EAP-Response/SIM/Re-authentication, the MAC code is calculated over
2847 The EAP packet is represented as specified in Section 8.1. It is
2848 followed by the 16-byte NONCE_S value from the server's AT_NONCE_S
2851 The AT_IV and AT_ENCR_DATA attributes MUST be included. The nested
2852 encrypted attributes MUST include the AT_COUNTER attribute. The
2853 AT_COUNTER_TOO_SMALL attribute MAY be included in the nested
2858 Haverinen & Salowey Informational [Page 51]
2860 RFC 4186 EAP-SIM Authentication January 2006
2863 encrypted attributes, and it is included in cases specified in
2864 Section 5. The AT_PADDING attribute MAY be included.
2866 The AT_RESULT_IND attribute MAY be included if it was included in
2867 EAP-Request/SIM/Re-authentication. The usage of this attribute is
2868 discussed in Section 6.2.
2870 Sending this packet without AT_COUNTER_TOO_SMALL indicates that the
2871 peer has successfully authenticated the server and that the EAP
2872 exchange will be accepted by the peer's local policy. Hence, if
2873 these conditions are not met, then the peer MUST NOT send
2874 EAP-Response/SIM/Re-authentication, but the peer MUST send
2875 EAP-Response/SIM/Client-Error.
2877 9.7. EAP-Response/SIM/Client-Error
2879 The peer sends EAP-Response/SIM/Client-Error in error cases, as
2880 specified in Section 6.3.1.
2882 The AT_CLIENT_ERROR_CODE attribute MUST be included.
2884 The AT_MAC, AT_IV, or AT_ENCR_DATA attributes MUST NOT be used with
2887 9.8. EAP-Request/SIM/Notification
2889 The usage of this message is specified in Section 6. The
2890 AT_NOTIFICATION attribute MUST be included.
2892 The AT_MAC attribute MUST be included if the P bit of the
2893 notification code in AT_NOTIFICATION is set to zero, and MUST NOT be
2894 included in cases when the P bit is set to one. The P bit is
2895 discussed in Section 6.
2897 No message-specific data is included in the MAC calculation. See
2900 If EAP-Request/SIM/Notification is used on a fast re-authentication
2901 exchange, and if the P bit in AT_NOTIFICATION is set to zero, then
2902 AT_COUNTER is used for replay protection. In this case, the
2903 AT_ENCR_DATA and AT_IV attributes MUST be included, and the
2904 encapsulated plaintext attributes MUST include the AT_COUNTER
2905 attribute. The counter value included in AT_COUNTER MUST be the same
2906 as in the EAP-Request/SIM/Re-authentication packet on the same fast
2907 re-authentication exchange.
2914 Haverinen & Salowey Informational [Page 52]
2916 RFC 4186 EAP-SIM Authentication January 2006
2919 9.9. EAP-Response/SIM/Notification
2921 The usage of this message is specified in Section 6. This packet is
2922 an acknowledgement of EAP-Request/SIM/Notification.
2924 The AT_MAC attribute MUST be included in cases when the P bit of the
2925 notification code in AT_NOTIFICATION of EAP-Request/SIM/Notification
2926 is set to zero, and MUST NOT be included in cases when the P bit is
2927 set to one. The P bit is discussed in Section 6.
2929 No message-specific data is included in the MAC calculation, see
2932 If EAP-Request/SIM/Notification is used on a fast re-authentication
2933 exchange, and if the P bit in AT_NOTIFICATION is set to zero, then
2934 AT_COUNTER is used for replay protection. In this case, the
2935 AT_ENCR_DATA and AT_IV attributes MUST be included, and the
2936 encapsulated plaintext attributes MUST include the AT_COUNTER
2937 attribute. The counter value included in AT_COUNTER MUST be the same
2938 as in the EAP-Request/SIM/Re-authentication packet on the same fast
2939 re-authentication exchange.
2943 This section specifies the format of message attributes. The
2944 attribute type numbers are specified in the IANA considerations
2945 section of the EAP-AKA specification [EAP-AKA].
2947 10.1. Table of Attributes
2949 The following table provides a guide to which attributes may be found
2950 in which kinds of messages, and in what quantity. Messages are
2951 denoted with numbers in parentheses as follows: (1)
2952 EAP-Request/SIM/Start, (2) EAP-Response/SIM/Start, (3)
2953 EAP-Request/SIM/Challenge, (4) EAP-Response/SIM/Challenge, (5)
2954 EAP-Request/SIM/Notification, (6) EAP-Response/SIM/Notification, (7)
2955 EAP-Response/SIM/Client-Error, (8) EAP-Request/SIM/Re-authentication,
2956 and (9) EAP-Response/SIM/Re-authentication. The column denoted with
2957 "Encr" indicates whether the attribute is a nested attribute that
2958 MUST be included within AT_ENCR_DATA, and the column denoted with
2959 "Skip" indicates whether the attribute is a skippable attribute.
2961 "0" indicates that the attribute MUST NOT be included in the message,
2962 "1" indicates that the attribute MUST be included in the message,
2963 "0-1" indicates that the attribute is sometimes included in the
2964 message, and "0*" indicates that the attribute is not included in the
2965 message in cases specified in this document, but MAY be included in
2966 future versions of the protocol.
2970 Haverinen & Salowey Informational [Page 53]
2972 RFC 4186 EAP-SIM Authentication January 2006
2975 Attribute (1) (2) (3) (4) (5) (6) (7) (8) (9) Encr Skip
2976 AT_VERSION_LIST 1 0 0 0 0 0 0 0 0 N N
2977 AT_SELECTED_VERSION 0 0-1 0 0 0 0 0 0 0 N N
2978 AT_NONCE_MT 0 0-1 0 0 0 0 0 0 0 N N
2979 AT_PERMANENT_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N
2980 AT_ANY_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N
2981 AT_FULLAUTH_ID_REQ 0-1 0 0 0 0 0 0 0 0 N N
2982 AT_IDENTITY 0 0-1 0 0 0 0 0 0 0 N N
2983 AT_RAND 0 0 1 0 0 0 0 0 0 N N
2984 AT_NEXT_PSEUDONYM 0 0 0-1 0 0 0 0 0 0 Y Y
2985 AT_NEXT_REAUTH_ID 0 0 0-1 0 0 0 0 0-1 0 Y Y
2986 AT_IV 0 0 0-1 0* 0-1 0-1 0 1 1 N Y
2987 AT_ENCR_DATA 0 0 0-1 0* 0-1 0-1 0 1 1 N Y
2988 AT_PADDING 0 0 0-1 0* 0-1 0-1 0 0-1 0-1 Y N
2989 AT_RESULT_IND 0 0 0-1 0-1 0 0 0 0-1 0-1 N Y
2990 AT_MAC 0 0 1 1 0-1 0-1 0 1 1 N N
2991 AT_COUNTER 0 0 0 0 0-1 0-1 0 1 1 Y N
2992 AT_COUNTER_TOO_SMALL 0 0 0 0 0 0 0 0 0-1 Y N
2993 AT_NONCE_S 0 0 0 0 0 0 0 1 0 Y N
2994 AT_NOTIFICATION 0 0 0 0 1 0 0 0 0 N N
2995 AT_CLIENT_ERROR_CODE 0 0 0 0 0 0 1 0 0 N N
2997 It should be noted that attributes AT_PERMANENT_ID_REQ,
2998 AT_ANY_ID_REQ, and AT_FULLAUTH_ID_REQ are mutually exclusive; only
2999 one of them can be included at the same time. If one of the
3000 attributes AT_IV and AT_ENCR_DATA is included, then both of the
3001 attributes MUST be included.
3003 10.2. AT_VERSION_LIST
3005 The format of the AT_VERSION_LIST attribute is shown below.
3008 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
3009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3010 | AT_VERSION_L..| Length | Actual Version List Length |
3011 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3012 | Supported Version 1 | Supported Version 2 |
3013 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3016 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3017 | Supported Version N | Padding |
3018 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3020 This attribute is used in version negotiation, as specified in
3021 Section 4.1. The attribute contains the version numbers supported by
3022 the EAP-SIM server. The server MUST only include versions that it
3026 Haverinen & Salowey Informational [Page 54]
3028 RFC 4186 EAP-SIM Authentication January 2006
3031 implements and that are allowed in its security policy. The server
3032 SHOULD list the versions in the order of preference, with the most
3033 preferred versions listed first. At least one version number MUST be
3034 included. The version number for the protocol described in this
3035 document is one (0001 hexadecimal).
3037 The value field of this attribute begins with 2-byte Actual Version
3038 List Length, which specifies the length of the Version List in bytes,
3039 not including the Actual Version List Length attribute length. This
3040 field is followed by the list of the versions supported by the
3041 server, which each have a length of 2 bytes. For example, if there
3042 is only one supported version, then the Actual Version List Length is
3043 2. Because the length of the attribute must be a multiple of 4
3044 bytes, the sender pads the value field with zero bytes when
3047 10.3. AT_SELECTED_VERSION
3049 The format of the AT_SELECTED_VERSION attribute is shown below.
3052 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
3053 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3054 | AT_SELECTED...| Length = 1 | Selected Version |
3055 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3057 This attribute is used in version negotiation, as specified in
3058 Section 4.1. The value field of this attribute contains a two-byte
3059 version number, which indicates the EAP-SIM version that the peer
3064 The format of the AT_NONCE_MT attribute is shown below.
3067 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
3068 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3069 |AT_NONCE_MT | Length = 5 | Reserved |
3070 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3075 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3082 Haverinen & Salowey Informational [Page 55]
3084 RFC 4186 EAP-SIM Authentication January 2006
3087 The value field of the NONCE_MT attribute contains two reserved bytes
3088 followed by a random number freshly generated by the peer (16 bytes
3089 long) for this EAP-SIM authentication exchange. The random number is
3090 used as a seed value for the new keying material. The reserved bytes
3091 are set to zero upon sending and ignored upon reception.
3093 The peer MUST NOT re-use the NONCE_MT value from a previous EAP-SIM
3094 authentication exchange. If an EAP-SIM exchange includes several
3095 EAP/SIM/Start rounds, then the peer SHOULD use the same NONCE_MT
3096 value in all EAP-Response/SIM/Start packets. The peer SHOULD use a
3097 good source of randomness to generate NONCE_MT. Please see [RFC4086]
3098 for more information about generating random numbers for security
3101 10.5. AT_PERMANENT_ID_REQ
3103 The format of the AT_PERMANENT_ID_REQ attribute is shown below.
3106 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
3107 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3108 |AT_PERM..._REQ | Length = 1 | Reserved |
3109 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3111 The use of the AT_PERMANENT_ID_REQ is defined in Section 4.2. The
3112 value field contains only two reserved bytes, which are set to zero
3113 on sending and ignored on reception.
3117 The format of the AT_ANY_ID_REQ attribute is shown below.
3120 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
3121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3122 |AT_ANY_ID_REQ | Length = 1 | Reserved |
3123 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3125 The use of the AT_ANY_ID_REQ is defined in Section 4.2. The value
3126 field contains only two reserved bytes, which are set to zero on
3127 sending and ignored on reception.
3138 Haverinen & Salowey Informational [Page 56]
3140 RFC 4186 EAP-SIM Authentication January 2006
3143 10.7. AT_FULLAUTH_ID_REQ
3145 The format of the AT_FULLAUTH_ID_REQ attribute is shown below.
3148 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
3149 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3150 |AT_FULLAUTH_...| Length = 1 | Reserved |
3151 +---------------+---------------+-------------------------------+
3153 The use of the AT_FULLAUTH_ID_REQ is defined in Section 4.2. The
3154 value field contains only two reserved bytes, which are set to zero
3155 on sending and ignored on reception.
3159 The format of the AT_IDENTITY attribute is shown below.
3162 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
3163 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3164 | AT_IDENTITY | Length | Actual Identity Length |
3165 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3167 . Identity (optional) .
3170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3172 The use of the AT_IDENTITY is defined in Section 4.2. The value
3173 field of this attribute begins with a 2-byte actual identity length,
3174 which specifies the length of the identity in bytes. This field is
3175 followed by the subscriber identity of the indicated actual length.
3176 The identity is the permanent identity, a pseudonym identity, or a
3177 fast re-authentication identity. The identity format is specified in
3178 Section 4.2.1. The same identity format is used in the AT_IDENTITY
3179 attribute and the EAP-Response/Identity packet, with the exception
3180 that the peer MUST NOT decorate the identity it includes in
3181 AT_IDENTITY. The identity does not include any terminating null
3182 characters. Because the length of the attribute must be a multiple
3183 of 4 bytes, the sender pads the identity with zero bytes when
3194 Haverinen & Salowey Informational [Page 57]
3196 RFC 4186 EAP-SIM Authentication January 2006
3201 The format of the AT_RAND attribute is shown below.
3204 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
3205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3206 | AT_RAND | Length | Reserved |
3207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3214 The value field of this attribute contains two reserved bytes
3215 followed by n GSM RANDs, each 16 bytes long. The value of n can be
3216 determined by the attribute length. The reserved bytes are set to
3217 zero upon sending and ignored upon reception.
3219 The number of RAND challenges (n) MUST be two or three. The peer
3220 MUST verify that the number of RAND challenges is sufficient
3221 according to the peer's policy. The server MUST use different RAND
3222 values. In other words, a RAND value can only be included once in
3223 AT_RAND. When processing the AT_RAND attribute, the peer MUST check
3224 that the RANDs are different.
3226 The EAP server MUST obtain fresh RANDs for each EAP-SIM full
3227 authentication exchange. More specifically, the server MUST consider
3228 RANDs it included in AT_RAND to be consumed if the server receives an
3229 EAP-Response/SIM/Challenge packet with a valid AT_MAC, or an
3230 EAP-Response/SIM/Client-Error with the code "insufficient number of
3231 challenges" or "RANDs are not fresh". However, in other cases (if
3232 the server does not receive a response to its
3233 EAP-Request/SIM/Challenge packet, or if the server receives a
3234 response other than the cases listed above), the server does not need
3235 to consider the RANDs to be consumed, and the server MAY re-use the
3236 RANDs in the AT_RAND attribute of the next full authentication
3250 Haverinen & Salowey Informational [Page 58]
3252 RFC 4186 EAP-SIM Authentication January 2006
3255 10.10. AT_NEXT_PSEUDONYM
3257 The format of the AT_NEXT_PSEUDONYM attribute is shown below.
3260 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
3261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3262 | AT_NEXT_PSEU..| Length | Actual Pseudonym Length |
3263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
projects / strongswan.git / blob