1 2 3NETWORK WORKING GROUP L. Zhu 4Internet-Draft K. Damour 5Updates: 4178 (if approved) D. McPherson 6Intended status: Informational Microsoft Corporation 7Expires: January 15, 2009 July 14, 2008 8 9 10 The Extended GSS-API Negotiation Mechanism (NEGOEX) 11 draft-zhu-negoex-01 12 13Status of this Memo 14 15 By submitting this Internet-Draft, each author represents that any 16 applicable patent or other IPR claims of which he or she is aware 17 have been or will be disclosed, and any of which he or she becomes 18 aware will be disclosed, in accordance with Section 6 of BCP 79. 19 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as Internet- 23 Drafts. 24 25 Internet-Drafts are draft documents valid for a maximum of six months 26 and may be updated, replaced, or obsoleted by other documents at any 27 time. It is inappropriate to use Internet-Drafts as reference 28 material or to cite them other than as "work in progress." 29 30 The list of current Internet-Drafts can be accessed at 31 http://www.ietf.org/ietf/1id-abstracts.txt. 32 33 The list of Internet-Draft Shadow Directories can be accessed at 34 http://www.ietf.org/shadow.html. 35 36 This Internet-Draft will expire on January 15, 2009. 37 38Abstract 39 40 This document defines the Extended Generic Security Service 41 Application Program Interface (GSS-API) Negotiation Mechanism 42 (NegoEx). NegoEx is a pseudo-security mechanism that logically 43 extends the SPNEGO protocol as defined in RFC4178. 44 45 The NegoEx protocol itself is a security mechanism negotiated by 46 SPNEGO. When selected as the common mechanism, NegoEx OPTIONALLY 47 adds a pair of meta-data messages for each negotiated security 48 mechanism. The meta-data exchange allows security mechanisms to 49 exchange auxiliary information such as trust configurations, thus 50 NegoEx provides additional flexibility than just exchanging object 51 52 53 54Zhu, et al. Expires January 15, 2009 [Page 1] 55 56Internet-Draft NEGOEX July 2008 57 58 59 identifiers in SPNEGO. 60 61 NegoEx preserves the optimistic token semantics of SPNEGO and applies 62 that recursively. Consequently a context establishment mechanism 63 token can be included in the initial NegoEx message, and NegoEx does 64 not require an extra round-trip when the initiator's optimistic token 65 is accepted by the target. 66 67 Similar to SPNEGO, NegoEx defines a few new GSS-API extensions that a 68 security mechanism MUST support in order to be negotiated by NegoEx. 69 This document defines these GSS-API extensions. 70 71 Unlike SPNEGO however, NegoEx defines its own way for signing the 72 protocol messages in order to protect the protocol negotiation. The 73 NegoEx message signing or verification can occur before the security 74 context for the negotiated real security mechanism is fully 75 established. 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110Zhu, et al. Expires January 15, 2009 [Page 2] 111 112Internet-Draft NEGOEX July 2008 113 114 115Table of Contents 116 117 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 118 2. Requirements Terminology . . . . . . . . . . . . . . . . . . . 6 119 3. Presentation Language and Primitive Data Types . . . . . . . . 6 120 3.1. Basic Block Size . . . . . . . . . . . . . . . . . . . . . 7 121 3.2. Miscellaneous . . . . . . . . . . . . . . . . . . . . . . 7 122 3.3. Constants . . . . . . . . . . . . . . . . . . . . . . . . 7 123 3.4. Numbers . . . . . . . . . . . . . . . . . . . . . . . . . 7 124 3.5. Enum Types . . . . . . . . . . . . . . . . . . . . . . . . 7 125 3.6. Typedef Declarations . . . . . . . . . . . . . . . . . . . 8 126 3.7. Array Types . . . . . . . . . . . . . . . . . . . . . . . 8 127 3.8. Vector Types . . . . . . . . . . . . . . . . . . . . . . . 8 128 3.9. Constructed Types . . . . . . . . . . . . . . . . . . . . 9 129 4. Cryptographic Computations . . . . . . . . . . . . . . . . . . 10 130 5. The NegoEx Protocol . . . . . . . . . . . . . . . . . . . . . 11 131 5.1. Generation of the Initiator Initial Token . . . . . . . . 11 132 5.2. Receipt of the Initial Initiator Token and Generation 133 of the Initial Acceptor Response . . . . . . . . . . . . . 13 134 5.3. Receipt of the Acceptor Initial Response and 135 Completion of Authentication after the Negotiation 136 Phrase . . . . . . . . . . . . . . . . . . . . . . . . . . 14 137 5.4. Finalizing Negotiation . . . . . . . . . . . . . . . . . . 15 138 5.5. High-level NegoEx Message Flow . . . . . . . . . . . . . . 15 139 6. Supporting GSS-API Extensions . . . . . . . . . . . . . . . . 16 140 6.1. GSS_Query_meta_data . . . . . . . . . . . . . . . . . . . 16 141 6.2. GSS_Exchange_meta_data . . . . . . . . . . . . . . . . . . 16 142 6.3. GSS_Query_mechanism_info . . . . . . . . . . . . . . . . . 16 143 6.4. GSS_Query_context_attr . . . . . . . . . . . . . . . . . . 16 144 7. Security Considerations . . . . . . . . . . . . . . . . . . . 16 145 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17 146 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 147 10. Normative References . . . . . . . . . . . . . . . . . . . . . 17 148 Appendix A. Protocol Data Structures and Constant Values . . . . 17 149 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 150 Intellectual Property and Copyright Statements . . . . . . . . . . 22 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166Zhu, et al. Expires January 15, 2009 [Page 3] 167 168Internet-Draft NEGOEX July 2008 169 170 1711. Introduction 172 173 If more than one GSS-API mechanism is shared between the initator and 174 the acceptor, the Simple and Protected (GSS-API) Negotiation 175 Mechanism (SPNEGO) as defined in [RFC4178] can be deployed to choose 176 a mutually preferred one. This pseudo mechanism does well in the 177 most basic scenarios but suffers from a couple of drawbacks, notably: 178 179 o First, the SPNEGO negotiation model is inefficient when 180 negotiating based on mechanism specific configuration information. 181 SPNEGO negotiation is based on exchanging object identifiers only, 182 and it does not allow exchange of auxiliary information in any 183 other from. This is inefficient and often impractical in that one 184 object identifier effectively conveys only one bit of information. 185 186 o Secondly, the SPNEGO negotiation model is inadequate when the 187 choice cannot be made by the acceptor in the initial response. In 188 SPNEGO, the negotiation information is sent one-way from the 189 initiator for the acceptor to make a choice, and the acceptor must 190 choose one when it makes the initial response. This negotiation 191 model is counter intuitive. The selection of a security mechanism 192 is typically the result of selecting one type of credentials from 193 the available set, and the initiator typically does not wish to 194 reveal credentials information often associated with user 195 identities. In practice, in order to operate in this model, the 196 Kerberos GSS-API mechanism [RFC4121] must acquire the context 197 establishment token in the initial call to GSS_Init_sec_context(). 198 If the initiator fails to acquire the initial Kerberos GSS-API 199 context token, it must not offer Kerberos; otherwise the SPNEGO 200 context negotiation will fail without being able to select the 201 next available mechanism that could work. Obtaining the initial 202 Kerberos GSS-API context token may require multiple round-trips of 203 network calls and the cost of the operation can be substantial. 204 It is suboptimal when multiple GSS-API mechanisms have to add the 205 extra cost that would not exist if the negotiated security 206 mechanism were selected based on configuration. 207 208 The Extended Generic Security Service Application Program Interface 209 (GSS-API) Negotiation Mechanism (NegoEx) is defined to address these 210 concerns. NegoEx is a pseudo security mechanism that is negotiated 211 by SPNEGO, and when negotiated, it can recursively negotiate real 212 security mechanisms. 213 214 Any security mechanism negotiated by NegoEx MUST support integrity 215 protection. 216 217 The basic form of NegoEx works as follows: 218 219 220 221 222Zhu, et al. Expires January 15, 2009 [Page 4] 223 224Internet-Draft NEGOEX July 2008 225 226 227 1. The initiator proposes a list of mechanisms in decreasing 228 preference order. For each of these mechanism, NegoEx 229 OPTIOINALLY includes a mechanism specific meta-data token. GSS- 230 API extensions are defined later in this document for NegoEx to 231 query the meta-data token for inclusion in the NegoEx message. 232 233 2. The acceptor then passes the meta-data token from the initiator 234 to the intended security mechanism. A meta-data token for a 235 security mechanism not supported on the acceptor side is ignored. 236 New GSS-API extensions are defined later in this document for a 237 security mechanism to consume the meta-data token. When 238 processing the received meta-data tokens, a security mechanism 239 that reports a failure is removed from the set of mutually 240 supported mechanisms. The acceptor then responds with the list 241 of mutually supported mechanisms in decreasing preference order. 242 For each of these mechanism, NegoEx again OPTIOINALLY supplies a 243 mechanism specific meta-data token in the response. These meta- 244 data tokens are returned to NegoEx via new GSS-API extensions as 245 described in the initial step. 246 247 3. The initiator then passes the meta-data tokens to the intended 248 security mechanisms by invoking the new GSS-API extensions. When 249 processing the received meta-data token, a security mechanism 250 that reports a failure is removed from the set of mutually 251 supported mechanisms for this negotiation context. The initiator 252 then selects one from the set of mutually-supported mechanisms. 253 If more than one security mechanism is available, unless 254 otherwise specified, the preferred one in the acceptor's 255 preference order SHOULD be selected. Once the common security 256 mechanism is identified, the security mechanism may also 257 negotiate mechanism-specific options during its context 258 establishments. This will be inside the mechanism tokens, and 259 invisible to the NegoEx protocol. 260 261 4. The selected security mechanism provides keying materials to 262 NegoEx, and NegoEx then signs and verifies the negotiation NegoEx 263 messages to protect the negotiation. 264 265 5. The initiator and the acceptor proceed to exchange tokens until 266 the GSS-API context for selected security mechanism is 267 established. Once the security context is established, the per- 268 message tokens are generated and verified in accordance with the 269 selected security mechanism. 270 271 NegoEx does not work outside of SPNEGO. When negotiated by SPNEGO, 272 NegoEx uses the concepts developed in the GSS-API specification 273 [RFC2743]. The negotiation data is encapsulated in context-level 274 tokens. Therefore, callers of the GSS-API do not need to be aware of 275 276 277 278Zhu, et al. Expires January 15, 2009 [Page 5] 279 280Internet-Draft NEGOEX July 2008 281 282 283 the existence of the negotiation tokens but only of the SPENGO 284 pseudo-security mechanism. 285 286 In its basic form NegoEx requires at least one extra round-trip. 287 Network connection setup is a critical performance characteristic of 288 any network infrastructure and extra round trips over WAN links, 289 packet radio networks, etc. really make a difference. In order to 290 avoid such an extra round trip the initial security token of the 291 preferred mechanism for the initiator may be embedded in the initial 292 NegoEx token. The optimistic mechanism token may be accompanied by 293 the meta-data tokens and the optimistic mechanism token MUST be that 294 of the first mechanism in the list of the mechanisms proposed by the 295 initiator. The NegoEx message that contains signatures for 296 protecting the NegoEx negotiation can also be included along with the 297 mechanism token. If the target preferred mechanism matches the 298 initiator's preferred mechanism, and when the NegoEx negotiation 299 protection messages are included along with the mechanism token, no 300 additional round trips are incurred by using the NegoEx protocol with 301 SPNEGO. 302 303 NegoEx does not update the ASN.1 structures of SPNEGO in that a large 304 deployment of SPNEGO does not have the ASN.1 extensibility marker in 305 the message definition. There is no change to the SPNEGO messages. 306 307 NegoEx does not use ASN.1 encoding and it uses simple C structures 308 encoded in little endian for all its messages. 309 310 The rest of the document is organized as follows: Section 3 defines 311 the encoding of NegoEx data structures and all the primitive data 312 types. Section 4 describes the cryptographic framework required by 313 the NegoEx for protecting the NegoEx negotiation. Section 5 defines 314 the NegoEx messages and the NegoEx protocol. Section 6 defines the 315 new GSS-API extensions that a security mechanism MUST support in 316 order to be negotiated by NegoEx. These then are followed by the 317 security considerations section. Lastly Appendix A contains all the 318 protocol constructs and constants. 319 320 3212. Requirements Terminology 322 323 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 324 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 325 document are to be interpreted as described in [RFC2119]. 326 327 3283. Presentation Language and Primitive Data Types 329 330 The following very basic and somewhat casually defined presentation 331 332 333 334Zhu, et al. Expires January 15, 2009 [Page 6] 335 336Internet-Draft NEGOEX July 2008 337 338 339 syntax will be used in all NegoEx messages. Although it resembles 340 the programming language "C" in its syntax, it would be risky to draw 341 too many parallels. The purpose of this presentation language is to 342 document NegoEx only; it has no general application beyond that 343 particular goal. 344 345 This section also defines all the primitive data types. The 346 semantics of the data types is explained in the next section. 347 3483.1. Basic Block Size 349 350 The representation of all data items is explicitly specified. The 351 basic data block size is one octet. Multiple octet data items are 352 concatenations of octets, from left to right, from top to bottom 353 Unless otherwise specific a multi-octet numeric is in little endian 354 order with the least significant octet first. 355 3563.2. Miscellaneous 357 358 Comments start with "//"' and continue until the end of the line. 359 3603.3. Constants 361 362 Constants are denoted using "#define" followed by the symbolic name 363 and then the constant value. 364 3653.4. Numbers 366 367 UCHAR is the data type for a one-octet number. 368 369 ULONG is the data type for a 4-octet number encoded in little enidan. 370 371 USHORT is the data type for a 2-octet number encoded in little 372 endian. 373 374 ULONG64 is the data type for a 8-octet number encoded in little 375 endian. 376 377 GUID is the data type for a 16-octet number encoded in little endian. 378 3793.5. Enum Types 380 381 An enum type is the data type for a number with a small number of 382 permissible values. An instance of an enum type is a 4-octet number 383 encoded in little endian. 384 385 The definition of an enum type follows the simple "C" convention. 386 387 388 389 390Zhu, et al. Expires January 15, 2009 [Page 7] 391 392Internet-Draft NEGOEX July 2008 393 394 395 MESSAGE_TYPE is an enum type defined as follows: 396 397 enum 398 { 399 MESSAGE_TYPE_INITIATOR_NEGO = 0, 400 MESSAGE_TYPE_ACCEPTOR_NEGO, 401 MESSAGE_TYPE_INITIATOR_META_DATA, 402 MESSAGE_TYPE_ACCEPTOR_META_DATA, 403 MESSAGE_TYPE_CHALLENGE, 404 // an exchange message from the acceptor 405 MESSAGE_TYPE_AP_REQUEST, 406 // an exchange message from the initiator 407 MESSAGE_TYPE_VERIFY, 408 MESSAGE_TYPE_ALERT, 409 } MESSAGE_TYPE; 410 411 MESSAGE_TYPE_INITIATOR_NEGO has the value 0, and MESSAGE_TYPE_ALERT 412 has the value 7. 413 4143.6. Typedef Declarations 415 416 A typedef creates a synonym for the type. This is used to create 417 more meaningful names for existing types. 418 419 The following two type synonyms are defined. 420 421 typedef GUID AUTH_SCHEME; 422 typedef GUID CONVERSATION_ID; 423 4243.7. Array Types 425 426 Arrays are a data structure which holds multiple variables of the 427 same data type consecutively and the number of elements is fixed. An 428 array is declared using "C" convention. For example, the following 429 defines an array of 32 octets. 430 431 UCHAR Random[32]; 432 4333.8. Vector Types 434 435 Vectors are a data structure which holds multiple variables of the 436 same data type consecutively and the number of elements is not fixed. 437 A vector contains a fixed length header followed by a variable length 438 payload. The header of a vector structure contains the count of 439 elements and the offset to the payload. In this document all the 440 offset fields start from the beginning of the containing NegoEx 441 message. The size of each element is specified by the vector type 442 definition. 443 444 445 446Zhu, et al. Expires January 15, 2009 [Page 8] 447 448Internet-Draft NEGOEX July 2008 449 450 451 The following vector types are defined. 452 453 struct 454 { 455 ULONG ByteArrayOffset; // each element contains an octet/byte 456 ULONG ByteArrayLength; 457 } BYTE_VECTOR; 458 459 BYTE_VECTOR encapsulates a variable length array of octets (or bytes) 460 that are stored consecutively. Each element in is a byte (8 bits). 461 462 struct 463 { 464 ULONG AuthSchemeArrayOffset; 465 // each element contains an AUTH_SCHEME 466 USHORT AuthSchemeCount; 467 } AUTH_SCHEME_VECTOR; 468 469 AUTH_SCHEME_VECTOR encapsulates a variable length array of 470 AUTH_SCHEMEs that are stored consecutively. Each element is a 471 structure of the type AUTH_SCHEME. 472 473 struct 474 { 475 ULONG ExtensionArrayOffset; 476 // each element contains an EXTENSION 477 USHORT ExtensionCount; 478 } EXTENSION_VECTOR; 479 480 EXTENSION_VECTOR encapsulates a variable length array of EXTENSIONs 481 that are stored consecutively. Each element is a structure of the 482 type EXTENSION. 483 4843.9. Constructed Types 485 486 Structure types may be constructed from primitive types for 487 convenience. Each specification declares a new, unique type. The 488 syntax for definition is much like that of C. 489 490 struct { 491 T1 f1; 492 T2 f2; 493 ... 494 Tn fn; 495 } T; 496 497 498 Structure definitions may be embedded. 499 500 501 502Zhu, et al. Expires January 15, 2009 [Page 9] 503 504Internet-Draft NEGOEX July 2008 505 506 507 The following types are defined as constructed types: 508 509 struct 510 { 511 ULONG ExtensionType; // negative extensions are critical 512 BYTE_VECTOR ExtensionValue; 513 } EXTENSION; 514 515 An extension has two fields. The ExtensionType field indicates how 516 the extension data should be interpreted. The ExtensionValue field 517 contains the extension data. 518 519 // 520 // schemes defined for the checksum in the VERIFY message 521 // 522 523 struct 524 { 525 ULONG cbHeaderLength; 526 ULONG ChecksumScheme; 527 ULONG ChecksumType; // in the case of RFC3961 scheme, this is 528 // the RFC3961 checksum type 529 BYTE_VECTOR ChecksumValue; 530 } CHECKSUM; 531 532 The CHECKSUM structure contains 4 fields. The cbHeaderLength length 533 contains the length of the structure defintion in octets, and this 534 field has a value of 20. 535 536 The ChecksumScheme field describes how checksum is computed and 537 verified. Currently only one value is defined. 538 539 #define CHECKSUM_SCHEME_RFC3961 1 540 541 When the value of the ChecksumScheme field is 1 542 (CHECKSUM_SCHEME_RFC3961), the ChecksumValue field contains a 543 sequence of octets computed according to [RFC3961] and the 544 ChecksumType field contains the checksum type value defined according 545 to [RFC3961]. 546 547 5484. Cryptographic Computations 549 550 The message signing and verification in NegoEx is based on [RFC3961]. 551 [RFC3961] is used here as a generic framework and this application is 552 not Kerberos specific. 553 554 A security mechanism MUST support [RFC3961] in order to be negotiated 555 556 557 558Zhu, et al. Expires January 15, 2009 [Page 10] 559 560Internet-Draft NEGOEX July 2008 561 562 563 by NegoEx. 564 565 5665. The NegoEx Protocol 567 568 This section describes the NegoEx protocol and it defines NegoEx 569 messages in the order that the messages can appear on the wire. The 570 enum type MESSAGE_TYPE defined in Section 3.5 lists all NegoEx 571 message types. A GSS-API context token for NegoEx consists of one or 572 more NegoEx messages. If there are more than one NegoEx message, 573 these messages are concatenated together. The smallest data unit for 574 NegoEx to compute the checksum for negotiation protection is a NegoEx 575 message. Note that NegoEx is not a GSS-API mechanism itself and the 576 initial NegoEx context establishment token does not follow the 577 mechanism-independent token format defined in Section 3.1 of 578 [RFC2743]. 579 580 A security mechanism negotiated by NegoEx is identified by a unique 581 identifier of the data type AUTH_SCHEME defined in Section 3.5. The 582 value of the security mechanism is returned to NegoEx via the 583 GSS_Query_mechanism_info() GSS-API extension as defined in Section 6. 584 585 The object identifier of the NegoEx within SPNEGO is iso(1) 586 identified-organization(3) dod(6) internet(1) private(4) 587 enterprise(1) microsoft (311) security(2) mechanisms(2) negoex(30). 588 Note that NegoEx does not work outside of SPNEGO and it is not GSS- 589 API mechanism. 590 5915.1. Generation of the Initiator Initial Token 592 593 The GSS-API initiator makes the first call to GSS_Init_sec_context() 594 with no input token, and the output token starts as a NEGO_MESSAGE 595 message with the MESSAGE_TYPE_INITIATOR_NEGO message type. 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614Zhu, et al. Expires January 15, 2009 [Page 11] 615 616Internet-Draft NEGOEX July 2008 617 618 619 struct 620 { 621 ULONG64 Signature; // contains MESSAGE_SIGNATURE 622 MESSAGE_TYPE MessageType; 623 ULONG SequenceNum; // the message sequence number of this, 624 // conversation, starting with 0 and sequentially 625 // incremented 626 ULONG cbHeaderLength; // the header length of this message, 627 // including the message specific header, excluding the 628 // payload 629 ULONG cbMessageLength; // the length of this message 630 CONVERSATION_ID ConversationId; 631 } MESSAGE_HEADER; 632 633 struct 634 { 635 MESSAGE_HEADER Header; 636 // MESSAGE_TYPE_INITIATOR_NEGO for the initiator, 637 // MESSAGE_TYPE_ACCEPTOR_NEGO for the acceptor 638 UCHAR Random[32]; 639 ULONG64 ProtocolVersion; 640 // version of the protocol, this contains 0 641 AUTH_SCHEME_VECTOR AuthSchemes; 642 EXTENSION_VECTOR Extensions; 643 } NEGO_MESSAGE; 644 645 The initiator randomly generates a ConversationID and fills the 646 common header. The ConversationID in subsequent NegoEx messages MUST 647 remain the same. The initiator also fills the Random field using a 648 secure random number generator. The initiator fills the AuthSchemes 649 with available security mechanisms supported by the initiator in 650 decreasing preference order. 651 652 The extensions field contains NegoEx extensions for future 653 extensibility. There is no extension defined in this document. All 654 negative extension types (the highest bit is set to 1) are critical. 655 If the receiver does not understand a critical extension, the 656 authentication attempt must be rejected. 657 658 The initiator can OPTIONALLY include a meta-data token, one for each 659 available security mechanism. 660 661 A meta-data token is returned to NegoEx for a security mechanism 662 using GSS_Query_meta_data() extension as defined in Section 6. A 663 meta-data token is encapsulated in an EXCHANGE message with the 664 message type MESSAGE_TYPE_INITIATOR_META_DATA. 665 666 667 668 669 670Zhu, et al. Expires January 15, 2009 [Page 12] 671 672Internet-Draft NEGOEX July 2008 673 674 675 struct 676 { 677 MESSAGE_HEADER Header; 678 // MESSAGE_TYPE_CHALLENGE for the acceptor, 679 // or MESSAGE_TYPE_AP_REQUEST for the initiator 680 // MESSAGE_TYPE_INITIATOR_META_DATA for 681 // the initiator metadata 682 // MESSAGE_TYPE_ACCEPTOR_META_DATA for 683 // the acceptor metadata 684 AUTH_SCHEME AuthScheme; 685 BYTE_VECTOR Exchange; 686 // contains the opaque handshake message for the 687 // authentication scheme 688 } EXCHANGE_MESSAGE; 689 690 The AuthScheme field signifies the security mechanism for which the 691 EXCHANGE message is targeted. If a security mechanism fails to 692 produce the metadata token, it should be removed from the list of 693 supported security mechanism for this negotiation context. 694 695 If there are more than one exchange messages, the order in which the 696 exchange message is included bears no significance. In other words, 697 the exchange messages are in an unordered set. The NEGO_MESSAGE MAY 698 be followed by a set of MESSAGE_TYPE_INITIATOR_META_DATA messages as 699 described above, in which case all the NegoEx messages concatenated 700 are returned as a single input token. 701 702 The first mechanism in the initiator proposed list can OPTIONALLY 703 include its initial context context in an AP_REQUEST message. 704 705 Both an AP_REQUSET(short for MESSAGE_TYPE_AP_REQUEST) message and a 706 INITIATOR_META_DATA(short for MESSAGE_TYPE_INITIATOR_META_DATA) 707 message are instances of the EXCHANGE_MESSAGE structure with 708 different message type values. An AP_REQUEST message contains the 709 type MESSAGE_TYPE_AP_REQUEST while an INITIATOR_META_DATA message 710 contains the type MESSAGE_TYPE_INITIATOR_META_DATA. 711 7125.2. Receipt of the Initial Initiator Token and Generation of the 713 Initial Acceptor Response 714 715 Upon receipt of the NEGO_MESSAGE from the initiator, the acceptor 716 verifies the NEGO_MESSAGE to make sure it is well-formed. The 717 acceptor then computes the list of authentication schemes that are 718 mutually supported by examining the set of security mechanisms 719 proposed by the initiator and the meta-data tokens from the 720 initiator. The meta-data tokens are passed to the security mechanism 721 via GSS_Exchange_meta_data() as defined in Section 6. 722 723 724 725 726Zhu, et al. Expires January 15, 2009 [Page 13] 727 728Internet-Draft NEGOEX July 2008 729 730 731 The acceptor MUST examine the NegoEx extensions in the NEGO_MESSAGE. 732 If there is an unknown critical extension, the authentication must be 733 rejected. 734 735 The acceptor's response starts as a NEGO_MESSAGE but with the 736 MESSAGE_TYPE_ACCEPTOR_NEGO. The AuthSchemes field contains the list 737 of mutually supported security mechanism in decreasing preference 738 order of the acceptor. The acceptor does not need to honor the 739 preference order proposed by the initiator when computing its 740 preference list. 741 742 The acceptor can OPTIONALLY include a meta-data token, one for each 743 available security mechanism. 744 745 A meta-data token is returned to NegoEx for a security mechanism 746 using GSS_Query_meta_data() extension as defined in Section 6. A 747 meta-data token is encapsulated in an EXCHANGE message with the 748 message type MESSAGE_TYPE_ACCEPTOR_META_DATA. For a given security 749 mechanism if a meta-token is received from the initiator, 750 GSS_Query_meta_data() MUST be invoked on the acceptor side for that 751 security mechanism, and the output meta-data token, if present, MUST 752 be included in the NegoEx reply. 753 7545.3. Receipt of the Acceptor Initial Response and Completion of 755 Authentication after the Negotiation Phrase 756 757 Upon receipt of the initial response from the acceptor, the initial 758 verifies the NEGO_MESSAGE to make sure it is well-formed. The 759 initiator then computes the list of authentication schemes that are 760 mutually supported by examining the set of security mechanisms 761 returned by the acceptor and the meta-data tokens from the acceptor 762 The meta-data tokens are passed to the security mechanism via 763 GSS_Exchange_meta_data() as defined in Section 6. 764 765 The initiator MUST examine the NegoEx extensions in the NEGO_MESSAGE. 766 If there is an unknown critical extension, the authentication must be 767 rejected. 768 769 After the initial exchange of NEGO_MESSAGE messages, the initiator 770 MUST choose the negotiated security mechanism. The negotiated 771 security mechanism cannot be changed once it is selected. 772 773 The initiator and the acceptor can then proceed to exchange handshake 774 messages as determined by the negotiated security mechanism until its 775 authentication context is established. The context tokens of the 776 negotiated security mechanism are encapsulated in an 777 EXCHANGE_MESSAGE. If the context token is from the initiator, the 778 EXCHANGE_MESSAGE message has the message type 779 780 781 782Zhu, et al. Expires January 15, 2009 [Page 14] 783 784Internet-Draft NEGOEX July 2008 785 786 787 MESSAGE_TYPE_AP_REQUEST; otherwise, the message type is 788 MESSAGE_TYPE_CHALLENGE. 789 7905.4. Finalizing Negotiation 791 792 Whenever there is a shared key established returned by 793 GSS_Query_context_attr(NEGOEX_SESSION_KEYS) as defined in Section 6,, 794 a VERIFY message is produced and included in the output token. The 795 returned protocol key is used as the base key in the parlance of 796 RFC3961 to sign all the NegoEx messages in the negotiation context. 797 798 A VERIFY message is a VERIFY_MESSAGE structure. The AuthScheme field 799 signifies from which security mechanism the protocol key was 800 obtained. The checksum is computed based on RFC3961 and the key 801 usage number is 23 for the message is signed by the initiator, 25 802 otherwise. The checksum is performed over all the previous NegoEx 803 messages in the context negotiation. 804 805 struct 806 { 807 MESSAGE_HEADER Header; // MESSAGE_TYPE_VERIFY 808 AUTH_SCHEME AuthScheme; 809 CHECKSUM Checksum; 810 // contains the checksum of all the previously 811 // exchanged messages in the order they were sent. 812 } VERIFY_MESSAGE; 813 814 Note that the VERIFY_MESSAGE message can be included before the 815 security context for the negotiated security mechanism is fully 816 established. 817 8185.5. High-level NegoEx Message Flow 819 820 The following text art summarizes the protocol message flow: 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838Zhu, et al. Expires January 15, 2009 [Page 15] 839 840Internet-Draft NEGOEX July 2008 841 842 843 INITIATOR_NEGO 844 *INITIATOR_META_DATA 845 *AP_REQUEST 846 ---------> 847 ACCEPTOR_NEGO 848 ACCEPTOR_META_DATA*+ 849 --------- CHALLENGE* 850 851 . 852 . 853 *AP_REQUEST 854 VERIFY ---------> 855 CHALLENGE* 856 -------- VERIFY 857 * Indicates optional or situation-dependent messages that are 858 not always sent. 859 + Indicates there can be more than one instance. 860 861 8626. Supporting GSS-API Extensions 863 864 This section defined all the required GSS-API extensions required by 865 NegoEx. 866 8676.1. GSS_Query_meta_data 868 869 TBD. 870 8716.2. GSS_Exchange_meta_data 872 873 TBD. 874 8756.3. GSS_Query_mechanism_info 876 877 TBD. 878 8796.4. GSS_Query_context_attr 880 881 TBD. 882 883 8847. Security Considerations 885 886 TBD. 887 888 889 890 891 892 893 894Zhu, et al. Expires January 15, 2009 [Page 16] 895 896Internet-Draft NEGOEX July 2008 897 898 8998. Acknowledgements 900 901 TBD. 902 903 9049. IANA Considerations 905 906 There is no action required for IANA. 907 908 90910. Normative References 910 911 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 912 Requirement Levels", BCP 14, RFC 2119, March 1997. 913 914 [RFC2743] Linn, J., "Generic Security Service Application Program 915 Interface Version 2, Update 1", RFC 2743, January 2000. 916 917 [RFC3961] Raeburn, K., "Encryption and Checksum Specifications for 918 Kerberos 5", RFC 3961, February 2005. 919 920 [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The 921 Kerberos Network Authentication Service (V5)", RFC 4120, 922 July 2005. 923 924 [RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos 925 Version 5 Generic Security Service Application Program 926 Interface (GSS-API) Mechanism: Version 2", RFC 4121, 927 July 2005. 928 929 [RFC4178] Zhu, L., Leach, P., Jaganathan, K., and W. Ingersoll, "The 930 Simple and Protected Generic Security Service Application 931 Program Interface (GSS-API) Negotiation Mechanism", 932 RFC 4178, October 2005. 933 934 935Appendix A. Protocol Data Structures and Constant Values 936 937 This section complies all the protocol data structures and constant 938 values. 939 940 #define MESSAGE_SIGNATURE 0x535458454f47454ei64 941 // "NEGOEXTS" 942 943 struct 944 { 945 ULONG ByteArrayOffset; // each element contains a byte 946 ULONG ByteArrayLength; 947 948 949 950Zhu, et al. Expires January 15, 2009 [Page 17] 951 952Internet-Draft NEGOEX July 2008 953 954 955 } BYTE_VECTOR; 956 957 struct 958 { 959 ULONG AuthSchemeArrayOffset; 960 // each element contains an AUTH_SCHEME 961 USHORT AuthSchemeCount; 962 } AUTH_SCHEME_VECTOR; 963 964 struct 965 { 966 ULONG ExtensionArrayOffset; 967 // each element contains an EXTENSION 968 USHORT ExtensionCount; 969 } EXTENSION_VECTOR; 970 971 struct 972 { 973 ULONG ExtensionType; // negative extensions are critical 974 BYTE_VECTOR ExtensionValue; 975 } EXTENSION; 976 977 // 978 // schemes defined for the checksum in the VERIFY message 979 // 980 981 #define CHECKSUM_SCHEME_RFC3961 1 982 983 struct 984 { 985 ULONG cbHeaderLength; 986 ULONG ChecksumScheme; 987 ULONG ChecksumType; // in the case of RFC3961 scheme, this is 988 // the RFC3961 checksum type 989 BYTE_VECTOR ChecksumValue; 990 } CHECKSUM; 991 992 typedef GUID AUTH_SCHEME; 993 typedef GUID CONVERSATION_ID; 994 995 enum 996 { 997 MESSAGE_TYPE_INITIATOR_NEGO = 0, 998 MESSAGE_TYPE_ACCEPTOR_NEGO, 999 MESSAGE_TYPE_INITIATOR_META_DATA, 1000 MESSAGE_TYPE_ACCEPTOR_META_DATA, 1001 MESSAGE_TYPE_CHALLENGE, 1002 // an exchange message from the acceptor 1003 1004 1005 1006Zhu, et al. Expires January 15, 2009 [Page 18] 1007 1008Internet-Draft NEGOEX July 2008 1009 1010 1011 MESSAGE_TYPE_AP_REQUEST, 1012 // an exchange message from the initiator 1013 MESSAGE_TYPE_VERIFY, 1014 MESSAGE_TYPE_ALERT, 1015 } MESSAGE_TYPE; 1016 1017 struct 1018 { 1019 ULONG64 Signature; // contains MESSAGE_SIGNATURE 1020 MESSAGE_TYPE MessageType; 1021 ULONG SequenceNum; // the message sequence number of this, 1022 // conversation, starting with 0 and sequentially 1023 // incremented 1024 ULONG cbHeaderLength; // the header length of this message, 1025 // including the message specific header, excluding the 1026 // payload 1027 ULONG cbMessageLength; // the length of this message 1028 CONVERSATION_ID ConversationId; 1029 } MESSAGE_HEADER; 1030 1031 struct 1032 { 1033 MESSAGE_HEADER Header; 1034 // MESSAGE_TYPE_INITIATOR_NEGO for the initiator, 1035 // MESSAGE_TYPE_ACCEPTOR_NEGO for the acceptor 1036 UCHAR Random[32]; 1037 ULONG64 ProtocolVersion; 1038 // version of the protocol, this contains 0 1039 AUTH_SCHEME_VECTOR AuthSchemes; 1040 EXTENSION_VECTOR Extensions; 1041 } NEGO_MESSAGE; 1042 1043 struct 1044 { 1045 MESSAGE_HEADER Header; 1046 // MESSAGE_TYPE_CHALLENGE for the acceptor, 1047 // or MESSAGE_TYPE_AP_REQUEST for the initiator 1048 // MESSAGE_TYPE_INITiATOR_META_DATA for 1049 // the initiator metadata 1050 // MESSAGE_TYPE_ACCEPTOR_META_DATA for 1051 // the acceptor metadata 1052 AUTH_SCHEME AuthScheme; 1053 BYTE_VECTOR Exchange; 1054 // contains the opaque handshake message for the 1055 // authentication scheme 1056 } EXCHANGE_MESSAGE; 1057 1058 struct 1059 1060 1061 1062Zhu, et al. Expires January 15, 2009 [Page 19] 1063 1064Internet-Draft NEGOEX July 2008 1065 1066 1067 { 1068 MESSAGE_HEADER Header; // MESSAGE_TYPE_VERIFY 1069 AUTH_SCHEME AuthScheme; 1070 CHECKSUM Checksum; 1071 // contains the checksum of all the previously 1072 // exchanged messages in the order they were sent. 1073 } VERIFY_MESSAGE; 1074 1075 struct 1076 { 1077 ULONG AlertType; 1078 BYTE_VECTOR AlertValue; 1079 } ALERT; 1080 1081 // 1082 // alert types 1083 // 1084 1085 #define ALERT_TYPE_PULSE 1 1086 1087 // 1088 // reason codes for the heartbeat message 1089 // 1090 1091 #define ALERT_VERIFY_NO_KEY 1 1092 1093 struct 1094 { 1095 ULONG cbHeaderLength; 1096 ULONG Reason; 1097 } ALERT_PULSE; 1098 1099 struct 1100 { 1101 ULONG AlertArrayOffset; // the element is an ALERT 1102 USHORT AlertCount; // contains the number of alerts 1103 } ALERT_VECTOR; 1104 1105 struct 1106 { 1107 MESSAGE_HEADER Header; 1108 AUTH_SCHEME AuthScheme; 1109 ULONG ErrorCode; // an NTSTATUS code 1110 ALERT_VECTOR Alerts; 1111 } ALERT_MESSAGE; 1112 1113 1114 1115 1116 1117 1118Zhu, et al. Expires January 15, 2009 [Page 20] 1119 1120Internet-Draft NEGOEX July 2008 1121 1122 1123Authors' Addresses 1124 1125 Larry Zhu 1126 Microsoft Corporation 1127 One Microsoft Way 1128 Redmond, WA 98052 1129 US 1130 1131 Email: lzhu@microsoft.com 1132 1133 1134 Kevin Damour 1135 Microsoft Corporation 1136 One Microsoft Way 1137 Redmond, WA 98052 1138 US 1139 1140 Email: kdamour@microsoft.com 1141 1142 1143 Dave McPherson 1144 Microsoft Corporation 1145 One Microsoft Way 1146 Redmond, WA 98052 1147 US 1148 1149 Email: davemm@microsoft.com 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174Zhu, et al. Expires January 15, 2009 [Page 21] 1175 1176Internet-Draft NEGOEX July 2008 1177 1178 1179Full Copyright Statement 1180 1181 Copyright (C) The IETF Trust (2008). 1182 1183 This document is subject to the rights, licenses and restrictions 1184 contained in BCP 78, and except as set forth therein, the authors 1185 retain all their rights. 1186 1187 This document and the information contained herein are provided on an 1188 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1189 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1190 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1191 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1192 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1193 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1194 1195 1196Intellectual Property 1197 1198 The IETF takes no position regarding the validity or scope of any 1199 Intellectual Property Rights or other rights that might be claimed to 1200 pertain to the implementation or use of the technology described in 1201 this document or the extent to which any license under such rights 1202 might or might not be available; nor does it represent that it has 1203 made any independent effort to identify any such rights. Information 1204 on the procedures with respect to rights in RFC documents can be 1205 found in BCP 78 and BCP 79. 1206 1207 Copies of IPR disclosures made to the IETF Secretariat and any 1208 assurances of licenses to be made available, or the result of an 1209 attempt made to obtain a general license or permission for the use of 1210 such proprietary rights by implementers or users of this 1211 specification can be obtained from the IETF on-line IPR repository at 1212 http://www.ietf.org/ipr. 1213 1214 The IETF invites any interested party to bring to its attention any 1215 copyrights, patents or patent applications, or other proprietary 1216 rights that may cover technology that may be required to implement 1217 this standard. Please address the information to the IETF at 1218 ietf-ipr@ietf.org. 1219 1220 1221 1222 1223 1224 1225 1226 1227 1228 1229 1230Zhu, et al. Expires January 15, 2009 [Page 22] 1231 1232 1233