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'12' ** Downref: Normative reference to an Informational RFC: RFC 2104 (ref. '13') -- Possible downref: Non-RFC (?) normative reference: ref. '14' ** Obsolete normative reference: RFC 2002 (ref. '15') (Obsoleted by RFC 3220) Summary: 7 errors (**), 0 flaws (~~), 4 warnings (==), 12 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 J. Arkko 3 Internet Draft Ericsson 4 Document: draft-arkko-pppext-eap-aka-01.txt H. Haverinen 5 Expires: December 2001 Nokia 6 November 2001 8 EAP AKA Authentication 10 Status of this Memo 12 This document is an Internet-Draft and is in full conformance 13 with all provisions of Section 10 of RFC2026. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as Internet- 18 Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six 21 months and may be updated, replaced, or obsoleted by other documents 22 at any time. It is inappropriate to use Internet-Drafts as 23 reference material or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 Abstract 32 This document specifies an Extensible Authentication Protocol (EAP) 33 mechanism for authentication and session key distribution using the 34 UMTS AKA authentication mechanism. AKA is based on symmetric keys, 35 and runs typically in a UMTS Subscriber Identity Module, a smart 36 card like device. AKA provides also backward compatibility to GSM 37 authentication, making it possible to use EAP AKA for authenticating 38 both GSM and UMTS subscribers. 40 Table of Contents 42 Status of this Memo................................................1 43 Abstract...........................................................1 44 1. Introduction and Motivation.....................................2 45 2. Conventions used in this document...............................3 46 3. Protocol Overview...............................................5 47 4. IMSI Privacy Support...........................................10 48 5. Message Format.................................................12 50 EAP AKA Authentication November 2001 52 6. Messages.......................................................13 53 6.1. EAP-Response/Identity........................................13 54 6.2. EAP-Request/USIM-Challenge...................................14 55 6.3. EAP-Response/USIM-Challenge..................................18 56 6.4. EAP-Response/USIM-Authentication-Reject......................20 57 6.5. EAP-Response/USIM-Synchronization-Failure....................20 58 6.6. EAP-Request/USIM-IMSI........................................21 59 6.7. EAP-Response/USIM-IMSI.......................................22 60 7. Interoperability with GSM......................................23 61 8. IANA and Protocol Numbering Considerations.....................24 62 9. Security Considerations........................................24 63 10. Intellectual Property Right Notices...........................24 64 Acknowledgements..................................................25 65 Authors' Addresses................................................25 67 1. Introduction and Motivation 69 This document specifies an Extensible Authentication Protocol (EAP) 70 mechanism for authentication and session key distribution using the 71 UMTS AKA authentication mechanism [1]. The Universal Mobile 72 Telecommunications System (UMTS) is a global third generation mobile 73 network standard. 75 AKA is based on challenge-response mechanisms and symmetric 76 cryptography. AKA typically runs in a UMTS Subscriber Identity 77 Module (USIM), a smart card like device. However, the applicability 78 of AKA is not limited to client devices with smart cards, but the 79 AKA mechanisms could also be implemented in host software, for 80 example AKA also provides backward compatibility to the GSM 81 authentication mechanism [2]. Compared to the GSM mechanism, AKA 82 provides substantially longer key lengths and the authentication of 83 the server side as well as the client side. 85 The introduction of AKA inside EAP allows several new applications. 86 These include the following: 88 - The use of the AKA also as a secure PPP authentication method in 89 devices that already contain an USIM. 91 - The use of the third generation mobile network authentication 92 infrastructure in the context of wireless LANs and IEEE 801.1x 93 technology through EAP over Wireless [3, 4]. 95 - Relying on AKA and the existing infrastructure in a seamless way 96 with any other technology that can use EAP. 98 AKA works in the following manner: 100 - The USIM and the home environment have agreed on a secret key 101 beforehand. 103 EAP AKA Authentication November 2001 105 - The actual authentication process starts by having the home 106 environment produce an authentication vector, based on the secret 107 key and a sequence number. The authentication vector contains a 108 random part RAND, an authenticator part AUTN used for 109 authenticating the network to the USIM, an expected result part 110 XRES, a session key for integrity check IK, and a session key for 111 encryption CK. 113 - The RAND and the AUTN are delivered to the USIM. 115 - The USIM verifies the AUTN, again based on the secret key and the 116 sequence number. If this process is successful (the AUTN is valid 117 and the sequence number used to generate AUTN is within the 118 correct range), the USIM produces an authentication result, RES 119 and sends this to the home environment. 121 - The home environment verifies the correct result from the USIM. If 122 the result is correct, IK and CK can be used to protect further 123 communications between the USIM and the home environment. 125 When verifying AUTN, the USIM may detect that the sequence number 126 the network uses is not within the correct range. In this case, the 127 USIM calculates a sequence number synchronization parameter AUTS and 128 sends it to the network. AKA authentication may then be retried with 129 a new authentication vector generated using the synchronized 130 sequence number. 132 For a specification of the AKA mechanisms and how the cryptographic 133 values AUTN, RES, IK, CK and AUTS are calculated, see reference [1]. 135 It is also possible that the home environment delegates the actual 136 authentication task to an intermediate node. In this case the 137 authentication vector or parts of it are delivered to the 138 intermediate node, enabling it to perform the comparison between RES 139 and XRES, and possibly also use CK and IK. In EAP AKA, the EAP 140 server node is such an intermediate node. 142 In the third generation mobile networks, AKA is used both for radio 143 network authentication and IP multimedia service authentication 144 purposes. Different user identities and formats are used for these; 145 the radio network uses the International Mobile Subscriber 146 Identifier (IMSI), whereas the IP multimedia service uses the 147 Network Access Identifier (NAI) [5]. 149 2. Conventions used in this document 151 The following terms will be used through this document: 153 AAA protocol 155 Authentication, Authorization and Accounting protocol 157 EAP AKA Authentication November 2001 159 AAA server 161 In this document, AAA server refers to the network element that 162 resides on the border of Internet AAA network and GSM network. 163 Cf. EAP server 165 AKA 167 Authentication and Key Agreement 169 AuC 171 Authentication Centre. The mobile network element that can 172 authorize subscribers either in GSM or in UMTS networks. 174 EAP 176 Extensible Authentication Protocol [6]. 178 EAP server 180 The network element that terminates the EAP protocol. Typically, 181 the EAP server functionality is implemented in a AAA server. 183 GSM 185 Global System for Mobile communications. 187 NAI 189 Network Access Identifier [5]. 191 AUTN 193 Authentication value generated by the AuC which together with the 194 RAND authenticates the server to the client, 128 bits [1]. 196 AUTS 198 A value generated by the client upon experiencing a 199 synchronization failure, 112 bits. 201 RAND 203 Random number generated by the AuC, 128 bits [1]. 205 RES 207 Authentication result from the client, which together with the 208 RAND authenticates the client to the server, 128 bits [1]. 210 SQN 212 Sequence number used in the authentication process, 48 bits [1]. 214 EAP AKA Authentication November 2001 216 SIM 218 Subscriber Identity Module. SIM cards are smart cards distributed 219 by GSM operators. 221 SRES 223 The authentication result parameter in GSM, corresponds to the 224 RES parameter in UMTS aka, 32 bits. 226 USIM 228 UMTS Subscriber Identity Module. These cards are smart cards 229 Similar to SIMs and are distributed by UMTS operators. 231 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 232 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 233 this document are to be interpreted as described in RFC 2119 [7] 235 3. Protocol Overview 237 In this document, the term EAP Server refers to the network element 238 that terminates the EAP protocol. Usually the EAP server is separate 239 from the authenticator device, which is the network element closest 240 to the client, such as a Network Access Server (NAS) or an IEEE 241 802.1X bridge. Typically, the authenticator does not contain the EAP 242 server functionality, but the EAP server functionality is 243 implemented on a separate AAA server with whom the authenticator 244 communicates using an AAA protocol. (The exact AAA communications is 245 outside the scope of this document, however.) 247 The below message flow shows the basic successful authentication 248 case with the EAP AKA. The EAP AKA uses two roundtrips to authorize 249 the user and generate session keys. As in other EAP schemes, first 250 an identity request/response message pair is exchanged. (For this 251 particular EAP protocol, the identity request is defined to be 252 optional, to shorten the authentication process to a minimal one.) 254 Next, the EAP server starts the actual AKA protocol by sending an 255 EAP-Request/USIM-Challenge message. This message contains a random 256 number (RAND) and an authorization vector (AUTN). The EAP- 257 Request/USIM-Challenge message MAY optionally contain encrypted 258 data, which is used for IMSI privacy support, as described in 259 Section 4. The encrypted data is not shown in the figures of this 260 section. The client runs the AKA algorithm (perhaps inside an USIM) 261 and verifies the AUTN. If this is successful, the client is talking 262 to a legitimate EAP server and proceeds to send the EAP- 263 Response/USIM-Challenge. This message contains a result parameter 264 that allows the EAP server in turn to verify that the client is a 265 legitimate one. 267 EAP AKA Authentication November 2001 269 Client Authenticator 270 | | 271 | EAP-Request/Identity (optional) | 272 |<------------------------------------------------------| 273 | | 274 | EAP-Response/Identity | 275 | (Includes user's NAI) | 276 |------------------------------------------------------>| 277 | | 278 | +------------------------------+ 279 | | Server runs UMTS algorithms, | 280 | | generates RAND and AUTN. | 281 | +------------------------------+ 282 | | 283 | EAP-Request/USIM-Challenge | 284 | (RAND, AUTN) | 285 |<------------------------------------------------------| 286 | | 287 +-------------------------------------+ | 288 | Client runs UMTS algorithms on USIM,| | 289 | verifies AUTN, derives RES | | 290 | and session key | | 291 +-------------------------------------+ | 292 | | 293 | EAP-Response/USIM-Challenge | 294 | (RES) | 295 |------------------------------------------------------>| 296 | | 297 | +------------------------------+ 298 | | Server checks the given RES, | 299 | | and finds it correct. | 300 | +------------------------------+ 301 | | 302 | EAP-Success | 303 |<------------------------------------------------------| 305 When EAP AKA is run in the GSM compatible mode, the message flow is 306 otherwise identical to the message flow below except that the AUTN 307 attribute is not included in EAP-Request/USIM-Challenge packet. 309 The second message flow shows how the EAP server rejects the Client 310 due to failed authentication. The same flow is also used in the GSM 311 compatible mode, except that the AUTN parameter is not included in 312 the EAP-Request/USIM-Challenge packet. 314 EAP AKA Authentication November 2001 316 Client Authenticator 317 | | 318 | EAP-Request/Identity (optional) | 319 |<------------------------------------------------------| 320 | | 321 | EAP-Response/Identity | 322 | (Includes user's NAI) | 323 |------------------------------------------------------>| 324 | | 325 | +------------------------------+ 326 | | Server runs UMTS algorithms, | 327 | | generates RAND and AUTN. | 328 | +------------------------------+ 329 | | 330 | EAP-Request/USIM-Challenge | 331 | (RAND, AUTN) | 332 |<------------------------------------------------------| 333 | | 334 +-------------------------------------+ | 335 | Client runs UMTS algorithms on USIM,| | 336 | possibly verifies AUTN, and sends an| | 337 | invalid response | | 338 +-------------------------------------+ | 339 | | 340 | EAP-Response/USIM-Challenge | 341 | (RES) | 342 |------------------------------------------------------>| 343 | | 344 | +------------------------------+ 345 | | Server checks the given RES, | 346 | | and finds it incorrect. | 347 | +------------------------------+ 348 | | 349 | EAP-Failure | 350 |<------------------------------------------------------| 352 The next message flow shows the client rejecting the AUTN of the EAP 353 server. This flow is not used in the GSM compatible mode. 355 EAP AKA Authentication November 2001 357 Client Authenticator 358 | | 359 | EAP-Request/Identity (optional) | 360 |<------------------------------------------------------| 361 | | 362 | EAP-Response/Identity | 363 | (Includes user's NAI) | 364 |------------------------------------------------------>| 365 | | 366 | +------------------------------+ 367 | | Server runs UMTS algorithms, | 368 | | generates RAND and a bad AUTN| 369 | +------------------------------+ 370 | | 371 | EAP-Request/USIM-Challenge | 372 | (RAND, AUTN) | 373 |<------------------------------------------------------| 374 | | 375 +-------------------------------------+ | 376 | Client runs UMTS algorithms on USIM | | 377 | and discovers AUTN that can not be | | 378 | verified | | 379 +-------------------------------------+ | 380 | | 381 | EAP-Response/USIM-Authentication-Reject | 382 |------------------------------------------------------>| 383 | | 384 | | 385 | EAP-Failure | 386 |<------------------------------------------------------| 388 Networks that are not UMTS aware use the GSM compatible version of 389 this protocol even for UMTS subscribers. In this case, the AUTN 390 parameter is not included in the EAP-Request/USIM-Challenge packet. 391 If a UMTS capable client does not want to accept the use of the GSM 392 compatible mode, the client can reject the authentication with the 393 EAP-Response/Nak message [6], as shown in the following figure: 395 EAP AKA Authentication November 2001 397 Client Authenticator 398 | | 399 | EAP-Request/Identity (optional) | 400 |<------------------------------------------------------| 401 | | 402 | EAP-Response/Identity | 403 | (Includes user's NAI) | 404 |------------------------------------------------------>| 405 | | 406 | +------------------------------+ 407 | | Server runs GSM algorithms, | 408 | | generates RAND | 409 | +------------------------------+ 410 | | 411 | EAP-Request/USIM-Challenge | 412 | (RAND) | 413 |<------------------------------------------------------| 414 | | 415 +-------------------------------------+ | 416 | Client does not accept the GSM | | 417 | compatible version of this protocol.| | 418 +-------------------------------------+ | 419 | | 420 | EAP-Response/Nak | 421 |------------------------------------------------------>| 422 | | 423 | | 424 | EAP-Failure | 425 |<------------------------------------------------------| 427 The AKA uses shared secrets between the Client and the Client's home 428 operator together with a sequence number to actually perform an 429 authentication. In certain circumstances it is possible for the 430 sequence numbers to get out of sequence. Here's what happens then: 432 EAP AKA Authentication November 2001 434 Client Authenticator 435 | | 436 | EAP-Request/Identity (optional) | 437 |<------------------------------------------------------| 438 | | 439 | EAP-Response/Identity | 440 | (Includes user's NAI) | 441 |------------------------------------------------------>| 442 | | 443 | +------------------------------+ 444 | | Server runs UMTS algorithms, | 445 | | generates RAND and AUTN. | 446 | +------------------------------+ 447 | | 448 | EAP-Request/USIM-Challenge | 449 | (RAND, AUTN) | 450 |<------------------------------------------------------| 451 | | 452 +-------------------------------------+ | 453 | Client runs UMTS algorithms on USIM | | 454 | and discovers AUTN that contains an | | 455 | inappropriate sequence number | | 456 +-------------------------------------+ | 457 | | 458 | EAP-Response/USIM-Synchronization-Failure | 459 | (AUTS) | 460 |------------------------------------------------------>| 461 | | 462 | +---------------------------+ 463 | | Perform resynchronization | 464 | | towards the AAA using | 465 | | AUTS and the sent RAND | 466 | +---------------------------+ 467 | | 469 After the resynchronization process takes place in the server and 470 AAA side, the process continues by the server side sending a new 471 EAP-Request/USIM-Challenge message. 473 4. IMSI Privacy Support 475 In the very first connection to an EAP server, the client always 476 transmits the cleartext IMSI in the EAP-Response/Identity packet. In 477 subsequent connections, the optional IMSI privacy support can be 478 used to hide the IMSI and to make the connections unlinkable to a 479 passive eavesdropper. 481 The EAP-Request/USIM-Challenge message MAY include an encrypted 482 pseudonym in the value field of the AT_ENCR_DATA attribute. The 483 AT_IV and AT_MAC attributes are also used to transport the pseudonym 484 to the client, as described in Section 6.2. Because the IMSI privacy 485 support is optional to implement, the client MAY ignore the AT_IV, 486 AT_ENCR_DATA, and AT_MAC attributes and always transmit the IMSI in 487 the EAP-Response/Identity packet. 489 EAP AKA Authentication November 2001 491 On receipt of the EAP-Request/USIM-Challenge, the client verifies 492 the AT_AUTN attribute before looking at the AT_ENCR_DATA or AT_MAC 493 attributes. If the AUTN is invalid, then the client MUST ignore the 494 AT_IV, AT_ENCR_DATA and AT_MAC attributes. If AUTN is valid, then 495 the client MAY derive the K_encr and K_int keys as described in 496 Section 6.2 and verify the AT_MAC attribute. If the AT_MAC attribute 497 is valid, then the client MAY decrypt the encrypted data and use the 498 pseudonym in the next authentication. If the MAC is invalid, then 499 the encrypted data MUST be ignored and the whole EAP packet MAY be 500 silently ignored. 502 The EAP server produces pseudonyms in an implementation-dependent 503 manner. Please see [8] for examples on how to produce pseudonyms. 504 The pseudonyms need to be reversible to the IMSI only on the EAP 505 server. Regardless of construction method, the pseudonym MUST 506 conform to the grammar specified for the username portion of an NAI. 508 On the next connection to the EAP server, the client MAY transmit 509 the received pseudonym in the first EAP-Response/Identity packet. 510 The client concatenates the received pseudonym with the "@" 511 character and the NAI realm portion. The client MUST use the same 512 realm portion that it used in the connection when it received the 513 pseudonym. 515 If the EAP server fails to decode the pseudonym to a known client 516 name, then the EAP server requests the regular IMSI (non-pseudonym 517 identity) by issuing the EAP-Request/USIM-IMSI packet to the client. 518 This packet includes no attributes. The client responds with the 519 EAP-Response/USIM-IMSI, which includes the client's IMSI in the 520 clear. This case is illustrated in the figure below. 522 Client Authenticator 523 | | 524 | EAP-Request/Identity | 525 |<------------------------------------------------------| 526 | | 527 | EAP-Response/Identity | 528 | (Includes a pseudonym) | 529 |------------------------------------------------------>| 530 | | 531 | +------------------------------+ 532 | | Server fails to decode the | 533 | | Pseudonym. | 534 | +------------------------------+ 535 | | 536 | EAP-Request/USIM-IMSI | 537 |<------------------------------------------------------| 538 | | 539 | | 540 | EAP-Response/USIM-IMSI | 541 | (IMSI) | 542 |------------------------------------------------------>| 543 | | 545 EAP AKA Authentication November 2001 547 After receiving the EAP-Response/USIM-IMSI packet, the EAP server 548 issues the EAP-Request/USIM-Challenge and the authentication 549 proceeds as usual. 551 Because the keys that are used to protect the pseudonym are derived 552 from the AKA cipher key (CK) and the AKA integrity key (IK), the 553 IMSI privacy support is not available when EAP AKA is used in the 554 GSM compatible mode. 556 5. Message Format 558 The Type-Data of the EAP AKA packets begins with a 1-octet Subtype 559 field, which is followed by a 2-octet reserved field. The rest of 560 the Type-Data consists of attributes that are encoded in Type, 561 Length, Value format. The figure below shows the generic format of 562 an attribute. 564 0 1 2 3 565 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 1 566 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 567 |Attribute Type | Length | Value... 568 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 570 Attribute Type 572 Indicates the particular type of attribute. The attribute type 573 values are listed in Section 8. 575 Length 577 Indicates the length of this attribute in multiples of 4 bytes. 578 The maximum length of an attribute is 1024 bytes. The length 579 includes the Attribute Type and Length bytes. 581 Value 583 The particular data associated with this attribute. This field is 584 always included and it may be two or more bytes in length. The 585 type and length fields determine the format and length of the 586 value field. 588 When an attribute numbered within the range 0 through 127 is 589 encountered but not recognized, the EAP/USIM message containing that 590 attribute MUST be silently discarded. These attributes are called 591 non-skippable attributes. 593 When an attribute numbered in the range 128 through 255 is 594 encountered but not recognized that particular attribute is ignored, 595 but the rest of the attributes and message data MUST still be 596 processed. The Length field of the attribute is used to skip the 597 attribute value in searching for the next attribute. These 598 attributes are called skippable attributes. 600 EAP AKA Authentication November 2001 602 Unless otherwise specified, the order of the attributes in an EAP 603 AKA message is insignificant, and an EAP AKA implementation should 604 not assume a certain order to be used. 606 Attributes can be encapsulated within other attributes. In other 607 words, the value field of an attribute type can be specified to 608 contain other attributes. 610 6. Messages 612 6.1. EAP-Response/Identity 614 In the beginning of EAP authentication, the Authenticator issues the 615 EAP-Request/Identity packet to the client. The client responds with 616 EAP-Response/Identity, which contains the user's identity. The 617 formats of these packets are specified in [6]. 619 The EAP AKA mechanism uses the NAI format [5] as the identity. 620 In order to facilitate the use of the existing cellular roaming 621 infrastructure, the subscriber's IMSI is used as the client 622 identifier. When IMSI privacy is not used, the EAP AKA client 623 transmits the user's IMSI within the NAI in the EAP 624 Response/Identity packet. The NAI is of the format "0imsi@realm". In 625 other words, the first character is the digit zero (ASCII value 626 0x30), followed by the IMSI, followed by the @ character and the 627 realm. The IMSI is an ASCII string that consists of not more than 15 628 decimal digits (ASCII values between 0x30 and 0x39) as specified in 629 [9]. 631 When the optional IMSI privacy support is used, the client MAY use 632 the pseudonym received as part of the previous authentication 633 sequence as the user name portion of the NAI, as specified in 634 Section 4. 636 The AAA network routes AAA requests to the correct AAA server using 637 the realm part of the NAI. Because cellular roaming can be used with 638 EAP AKA, the AAA request can be routed to an AAA server in the 639 visited network instead of the server indicated in the NAI realm. 640 The operators need to agree on this special AAA routing in advance. 641 It is recommended that operators should reserve the realm portion of 642 NAI for EAP AKA users exclusively, so that exactly the same realm is 643 not used with other authentication methods. This convention makes it 644 easy to recognize that the NAI identifies a UMTS or GSM subscriber 645 of this operator, which may be useful when configuring the routing 646 rules in the visited AAA networks. 648 In the EAP AKA protocol, the EAP-Request/Identity message is 649 optional when applicable. If the client can positively determine 650 that it has to authenticate, it MAY send an unsolicited EAP- 651 Response/Identity to the authenticator with an EAP Identifier value 652 it has picked up itself. The client MUST NOT send an unsolicited 653 EAP-Response/Identity if it has already received an EAP- 654 Request/Identity packet. The client MUST send an EAP- 655 Response/Identity to all received EAP-Request/Identity packets, 657 EAP AKA Authentication November 2001 659 using the Identifier value in the EAP-Request/Identity. If the 660 authenticator receives an unsolicited EAP-Response/Identity, it 661 SHOULD process the packet as if it had requested it. If the 662 authenticator receives an EAP-Response/Identity with an incorrect 663 Identifier value in response to the first EAP-Request/Identity it 664 has sent to the client, then the authenticator SHOULD still accept 665 the EAP-Response/Identity packet. 667 6.2. EAP-Request/USIM-Challenge 669 The format of the EAP-Request/USIM-Challenge packet is shown below. 671 EAP AKA Authentication November 2001 673 0 1 2 3 674 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 1 675 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 676 | Code | Identifier | Length | 677 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 678 | Type | Subtype | Reserved | 679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 680 | AT_RAND | Length = 5 | Reserved | 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | | 683 | RAND | 684 | | 685 | | 686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 | AT_AUTN | Length = 5 | Reserved | 688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 689 | | 690 | AUTN (optional) | 691 | | 692 | | 693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 694 | AT_IV | Length = 5 | Reserved | 695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 696 | | 697 | Initialization Vector (optional) | 698 | | 699 | | 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | AT_ENCR_DATA | Length | Reserved | 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 | | 704 | Encrypted Data (optional) | 705 | | 706 | | 707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 708 | AT_MAC | Length = 6 | Reserved | 709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 | | 711 | MAC (optional) | 712 | | 713 | | 714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 716 The semantics of the fields is described below: 718 Code 720 1 for Request 722 Identifier 724 See [6] 726 EAP AKA Authentication November 2001 728 Length 730 The length of the EAP Request packet. 732 Type 734 TBD 736 Subtype 738 1 for USIM-Challenge 740 Reserved 742 Set to zero when sending, ignored on reception. 744 AT_RAND 746 The value field of this attribute contains two reserved bytes 747 followed by the AKA RAND parameter, 16 bytes (128 bits). The 748 reserved bytes are set to zero when sending and ignored on 749 reception. The AT_RAND attribute MUST be present in EAP- 750 Request/USIM-Challenge. 752 AT_AUTN 754 The value field of this attribute contains two reserved bytes 755 followed by the AKA AUTN parameter, 16 bytes (128 bits). The 756 reserved bytes are set to zero when sending and ignored on 757 reception. The AT_AUTN attribute MUST NOT be included in the GSM 758 compatible mode of this protocol; otherwise it MUST be included. 760 AT_IV 762 The value field contains two reserved bytes followed by a 16-byte 763 initialization vector required by the AT_ENCR_DATA attribute. The 764 reserved bytes are set to zero when sending and ignored on 765 reception. This attribute MUST be included if and only if the 766 AT_ENCR_DATA is included. Messages that do not meet this 767 condition MUST be silently discarded. 769 AT_ENCR_DATA 771 The AT_ENCR_DATA MAY is optional. The value field of this 772 attribute consists of two reserved bytes followed by bytes 773 encrypted using the Advanced Encryption Standard (AES) [10] in 774 the Cipher Block Chaining (CBC) mode of operation, using the 775 initialization vector from the AT_IV attribute. The reserved 776 bytes are set to zero when sending and ignored on reception. 777 Please see [11] for a description of the CBC mode. 779 The encryption key (K_encr) is derived from the AKA Cipher Key 780 (CK) with the following formula. The result of the SHA-1 hash 781 value [12] is truncated to 128 bits by ignoring the 32 rightmost 783 EAP AKA Authentication November 2001 785 bits. The notation A|0 denotes A concatenated with the byte zero 786 0x00. 788 K_encr = 128 leftmost bits of SHA1(CK|0) 790 The plaintext consists of nested attributes as described below. 792 AT_MAC 794 This attribute is optional, but it MUST be included whenever the 795 AT_ENCR_DATA attribute is included. Messages that do not meet 796 this condition MUST be silently discarded. 798 The value field of the AT_MAC attribute contains two reserved 799 bytes followed by a message authentication code (MAC). The MAC is 800 calculated over the whole EAP packet with the exception that the 801 value field of the MAC attribute is set to zero when calculating 802 the MAC. The reserved bytes are set to zero when sending and 803 ignored on reception. 805 The MAC algorithm is HMAC-SHA1 [13] keyed hash value, so the 806 length of the MAC is 20 bytes. 808 The integrity protection key (K_int) used in the calculation of 809 the MAC is derived from the AKA integrity key (IK) with the 810 following formula. The notation A|0 denotes A concatenated with 811 the byte zero 0x00. 813 K_int = SHA1(IK|0) 815 The AT_IV, AT_ENCR_DATA and AT_MAC attributes are used for IMSI 816 privacy. The plaintext of the AT_ENCR_DATA value field consists of 817 nested attributes, which are shown below. Later versions of this 818 protocol MAY specify additional attributes to be included within the 819 encrypted data. 821 0 1 2 3 822 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 1 823 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 824 | AT_PSEUDONYM | Length | Actual Pseudonym Length | 825 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 826 | | 827 | Pseudonym | 828 | | 829 | | 830 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 831 | AT_PADDING | Length | Padding... | 832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 833 | | 834 | | 835 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 837 EAP AKA Authentication November 2001 839 AT_PSEUDONYM 841 This attribute is optional. The value field of this attribute 842 begins with 2-byte actual pseudonym length, which specifies the 843 length of the pseudonym in bytes. This field is followed by a 844 pseudonym user name, of the indicated actual length, that the 845 client can use in the next authentication, as described in 846 Section 4. The user name does not include any terminating null 847 characters. Because the length of the attribute must be a 848 multiple of 4 bytes, the sender pads the pseudonym with zero 849 bytes when necessary. 851 AT_PADDING 853 The encryption algorithm requires the length of the plaintext to 854 be a multiple of 16 bytes. The sender may need to include the 855 AT_PADDING attribute as the last attribute within AT_ENCR_DATA. 856 The AT_PADDING attribute is not included if the total length of 857 other nested attributes within the AT_ENCR_DATA attribute is a 858 multiple of 16 bytes. As usual, the Length of the Padding 859 attribute includes the Attribute Type and Attribute Length 860 fields. The Length of the Padding attribute is 4, 8 or 12 bytes. 861 It is chosen so that the length of the value field of the 862 AT_ENCR_DATA attribute becomes a multiple of 16 bytes. The actual 863 pad bytes in the value field are set to zero (0x00) on sending. 864 The recipient of the message MUST verify that the pad bytes are 865 set to zero, and silently drop the message if this verification 866 fails. 868 6.3. EAP-Response/USIM-Challenge 870 The format of the EAP-Response/USIM-Challenge packet is shown below. 872 EAP-Response/USIM-Challenge MAY include the AT_MAC attribute to 873 integrity protect the EAP packet. Later versions of this protocol 874 MAY make use of the AT_ENCR_DATA and AT_IV attributes in this 875 message to include encrypted (skippable) attributes. AT_MAC, 876 AT_ENCR_DATA and AT_IV attributes are not shown in the figure below. 877 If present, they are processed as in EAP-Request/USIM-Challenge 878 packet. The EAP server MUST process EAP-Response/USIM-Challenge 879 messages that include these attributes even if the server did not 880 implement these optional attributes. 882 EAP AKA Authentication November 2001 884 0 1 2 3 885 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 1 886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 887 | Code | Identifier | Length | 888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 889 | Type | Subtype | Reserved | 890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 891 | AT_RES | Length | RES Length | 892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 893 | | 894 | RES | 895 | | 896 | | 897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 899 The semantics of the fields is described below: 901 Code 903 2 for Response 905 Identifier 907 See [6] 909 Length 911 The length of the EAP Response packet. 913 Type 915 TBD 917 Subtype 919 1 for USIM-Challenge 921 Reserved 923 Set to zero when sending, ignored on reception. 925 AT_RES 927 This attribute MUST be included in EAP-Response/USIM-Challenge. 928 The value field of this attribute begins with the 2-byte RES 929 Length, which is identifies the exact length of the RES (or SRES) 930 in bits. The RES length is followed by the UMTS AKA RES or GSM 931 SRES parameter. According to the specification [14] the length of 932 the AKA RES can vary between 32 and 128 bits. The GSM SRES 933 parameter is always 32 bits long. Because the length of the 934 AT_RES attribute must be a multiple of 4 bytes, the sender pads 935 the RES with zero bits where necessary. 937 EAP AKA Authentication November 2001 939 6.4. EAP-Response/USIM-Authentication-Reject 941 The format of the EAP-Response/USIM-Authentication-Reject packet is 942 shown below. 944 0 1 2 3 945 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 1 946 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 947 | Code | Identifier | Length | 948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 949 | Type | Subtype | Reserved | 950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 952 The semantics of the fields is described below: 954 Code 956 2 for Response 958 Identifier 960 See [6] 962 Length 964 The length of the EAP Response packet. 966 Type 968 TBD 970 Subtype 972 2 for USIM-Authentication-Reject 974 Reserved 976 Set to zero on sending, ignored on reception. 978 6.5. EAP-Response/USIM-Synchronization-Failure 980 The format of the EAP-Response/USIM-Synchronization-Failure packet 981 is shown below. 983 EAP AKA Authentication November 2001 985 0 1 2 3 986 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 1 987 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 988 | Code | Identifier | Length | 989 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 990 | Type | Subtype | Reserved | 991 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| 992 | AT_AUTS | Length = 4 | | 993 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 994 | | 995 | AUTS | 996 | | 997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 999 The semantics of the fields is described below: 1001 Code 1003 2 for Response 1005 Identifier 1007 See [6] 1009 Length 1011 The length of the EAP Response packet, 20. 1013 Type 1015 TBD 1017 Subtype 1019 4 for USIM-Synchronization-Failure 1021 AT_AUTS 1023 This attribute MUST be included in EAP-Response/USIM- 1024 Synchronization-Failure. The value field of this attribute 1025 contains the AKA AUTS parameter, 112 bits (14 bytes). 1027 6.6. EAP-Request/USIM-IMSI 1029 The format of the EAP-Request/USIM-IMSI packet is shown below. 1031 0 1 2 3 1032 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 1033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1034 | Code | Identifier | Length | 1035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1036 | Type | Subtype | Reserved | 1037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1039 EAP AKA Authentication November 2001 1041 The semantics of the fields is described below: 1043 Code 1045 1 for Request 1047 Identifier 1049 See [6] 1051 Length 1053 The length of the EAP Request packet. 1055 Type 1057 TBD 1059 Subtype 1061 5 for USIM-IMSI 1063 Reserved 1065 Set to zero on sending, ignored on reception. 1067 6.7. EAP-Response/USIM-IMSI 1069 The format of the EAP-Response/USIM-IMSI packet is shown below. 1071 0 1 2 3 1072 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 1073 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1074 | Code | Identifier | Length | 1075 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1076 | Type | Subtype | Reserved | 1077 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1078 | AT_IMSI | Length = 5 | Reserved | 1079 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1080 | | 1081 | IMSI | 1082 | | 1083 | | 1084 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1086 The semantics of the fields is described below: 1088 Code 1090 2 for Response 1092 EAP AKA Authentication November 2001 1094 Identifier 1096 See [6] 1098 Length 1100 The length of the EAP Response packet. 1102 Type 1104 TBD 1106 Subtype 1108 5 for USIM-IMSI 1110 Reserved 1112 Set to zero on sending, ignored on reception. 1114 AT_IMSI 1116 This attribute MUST be included in EAP-Response/USIM-IMSI. The 1117 value field of this attribute contains two reserved bytes 1118 followed by the IMSI, represented as an ASCII string that 1119 consists of not more than 15 decimal digits (ASCII values between 1120 0x30 and 0x39) [9]. The reserved bytes are set to zero on sending 1121 and ignored on reception. The IMSI characters are followed by one 1122 or more "F" characters (ASCII value 0x46). They are included to 1123 make the length of the value field 16 bytes. 1125 7. Interoperability with GSM 1127 The EAP AKA protocol is able to authenticate both UMTS and GSM 1128 users, if the subscriber's operator's network is UMTS aware. This is 1129 because the home network will be able to determine from the 1130 subscriber records whether the subscriber is equipped with a UMTS 1131 USIM or a GSM SIM. A UMTS aware home network will hence always use 1132 UMTS AKA with UMTS subscribers and GSM authentication with GSM 1133 subscribers. With GSM subscribers, the EAP AKA protocol is always 1134 used in the GSM compatible mode. 1136 It is not possible to use a GSM AuC to authenticate UMTS 1137 subscribers. (Note that if the home network doesn't support an 1138 authentication method it should not distribute SIMs for that 1139 method.) 1141 However, it is possible that the node actually terminating EAP and 1142 the node that stores the authentication keys (AuC) are separate, and 1143 support different authentication types. If the node terminating EAP 1144 is GSM-only but AuC is UMTS-aware, then authentication can still be 1145 achieved using the GSM compatible version of EAP AKA. This 1146 authentication will be weaker, since the GSM compatible mode does 1148 EAP AKA Authentication November 2001 1150 not provide for mutual authentication. Section 6.8.1.1 in [1] 1151 specifies how the GSM SRES parameter and the Kc key can be 1152 calculated on the USIM and the AuC. If a UMTS terminal does not want 1153 to accept the GSM compatible version of this protocol, then it can 1154 reject the authentication with the EAP-Response/USIM-GSM- 1155 Authentication-Reject packet. 1157 In conclusion, the following table shows which variant of the EAP 1158 AKA protocol should be run under different conditions: 1160 SIM EAP node AuC EAP AKA mode 1161 ---------------------------------------------------- 1162 GSM (any) (any) GSM 1163 UMTS (any) GSM (illegal) 1164 UMTS GSM GSM+UMTS GSM 1165 UMTS GSM+UMTS GSM+UMTS UMTS 1167 8. IANA and Protocol Numbering Considerations 1169 IANA has assigned the number TBD for EAP AKA authentication. 1171 EAP AKA messages include a Subtype field. The following Subtypes are 1172 specified: 1174 USIM-Challenge..................................1 1175 USIM-Authentication-Reject......................2 1176 USIM-Synchronization-Failure....................4 1177 USIM-IMSI.......................................5 1179 The Subtype-specific data is composed of attributes, which have 1180 attribute type numbers. The following attribute types are specified: 1182 AT_RAND.........................................1 1183 AT_AUTN.........................................2 1184 AT_RES..........................................3 1185 AT_AUTS.........................................4 1186 AT_IMSI.........................................5 1187 AT_PADDING......................................6 1189 AT_IV.........................................129 1190 AT_ENCR_DATA..................................130 1191 AT_MAC........................................131 1192 AT_PSEUDONYM..................................132 1194 9. Security Considerations 1196 Implementations running the EAP AKA protocol will rely on the 1197 security of the AKA scheme, and the secrecy of the symmetric keys 1198 stored in the USIM and the AuC. 1200 10. Intellectual Property Right Notices 1202 EAP AKA Authentication November 2001 1204 On IPR related issues, Nokia and Ericsson refer to the their 1205 respective statements on patent licensing. Please see 1206 http://www.ietf.org/ietf/IPR/NOKIA and 1207 http://www.ietf.org/ietf/IPR/ERICSSON-General 1209 Acknowledgements 1211 The authors wish to thank Rolf Blom of Ericsson, Bernard Aboba of 1212 Microsoft, Arne Norefors of Ericsson, N.Asokan of Nokia and Jukka- 1213 Pekka Honkanen of Nokia for interesting discussions in this problem 1214 space. 1216 The IMSI privacy support is based on the identity privacy support of 1217 [8]. The attribute format is based on the extension format of Mobile 1218 IPv4 [15]. 1220 Authors' Addresses 1222 Jari Arkko 1223 Ericsson 1224 02420 Jorvas Phone: +358 40 5079256 1225 Finland Email: jari.arkko@ericsson.com 1227 Henry Haverinen 1228 Nokia Mobile Phones 1229 P.O. Box 88 1230 33721 Tampere Phone: +358 50 594 4899 1231 Finland E-mail: henry.haverinen@nokia.com 1233 References 1235 [1] 3GPP Technical Specification 3GPP TS 33.102 V3.6.0: "Technical 1236 Specification Group Services and System Aspects; 3G Security; 1237 Security Architecture (Release 1999)", 3rd Generation 1238 Partnership Project, November 2000. 1240 [2] GSM Technical Specification GSM 03.20 (ETS 300 534): "Digital 1241 cellular telecommunication system (Phase 2); Security related 1242 network functions", European Telecommunications Standards, 1243 Institute, August 1997. 1245 [3] IEEE P802.1X/D11, "Standards for Local Area and Metropolitan 1246 Area Networks: Standard for Port Based Network Access 1247 Control", March 2001 1249 [4] IEEE Draft 802.11eS/D1, "Draft Supplement to STANDARD FOR 1250 Telecommunications and Information Exchange between Systems - 1251 LAN/MAN Specific Requirements - Part 11: Wireless Medium 1252 Access Control (MAC) and physical layer (PHY) specifications: 1253 Specification for Enhanced Security", March 2001 1255 [5] Aboba, B. and M. Beadles, "The Network Access Identifier", RFC 1256 2486, January 1999. 1258 EAP AKA Authentication November 2001 1260 [6] L. Blunk, J. Vollbrecht, "PPP Extensible Authentication 1261 Protocol (EAP)", RFC 2284, March 1998. 1263 [7] S. Bradner, "Key words for use in RFCs to indicate Requirement 1264 Levels", RFC 2119, March 1997. 1266 [8] J. Carlson, B. Aboba, H. Haverinen, "EAP SRP-SHA1 1267 Authentication Protocol", draft-ietf-pppext-eap-srp-03.txt, 1268 July 2001 (work-in-progress) 1270 [9] GSM Technical Specification GSM 03.03 (ETS 300 523): "Digital 1271 cellular telecommunication system (Phase 2); Numbering, 1272 addressing and identification", European Telecommunications 1273 Standards Institute, April 1997. 1275 [10] Federal Information Processing Standard (FIPS) draft standard, 1276 "Advanced Encryption Standard (AES)", 1277 http://csrc.nist.gov/publications/drafts/dfips-AES.pdf, 1278 September 2001 1280 [11] US National Bureau of Standards, "DES Modes of Operation", 1281 Federal Information Processing Standard (FIPS) Publication 81, 1282 December 1980. 1284 [12] Federal Information Processing Standard (FIPS) Publication 1285 180-1, "Secure Hash Standard," National Institute of Standards 1286 and Technology, U.S. Department of Commerce, April 17, 1995. 1288 [13] H. Krawczyk, M. Bellare, R. Canetti, "HMAC: Keyed-Hashing for 1289 Message Authentication", RFC2104, February 1997 1291 [14] 3GPP Technical Specification 3GPP TS 33.105 V3.5.0: "Technical 1292 Specification Group Services and System Aspects; 3G Security; 1293 Cryptographic Algorithm Requirements (Release 1999)", 1294 3rdGeneration Partnership Project, October 2000 1296 [15] C. Perkins (editor), "IP Mobility Support", RFC 2002, October 1297 1996