1 2 3 4NETWORK WORKING GROUP A. Menon-Sen 5Internet-Draft Oryx Mail Systems GmbH 6Intended status: Standards Track A. Melnikov 7Expires: September 24, 2009 Isode Ltd 8 C. Newman 9 N. Williams 10 Sun Microsystems 11 March 23, 2009 12 13 14 Salted Challenge Response (SCRAM) SASL Mechanism 15 draft-newman-auth-scram-11.txt 16 17Status of this Memo 18 19 This Internet-Draft is submitted to IETF in full conformance with the 20 provisions of BCP 78 and BCP 79. 21 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that 24 other groups may also distribute working documents as Internet- 25 Drafts. 26 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 31 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 34 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 37 38 This Internet-Draft will expire on September 24, 2009. 39 40Copyright Notice 41 42 Copyright (c) 2009 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 44 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents in effect on the date of 47 publication of this document (http://trustee.ietf.org/license-info). 48 Please review these documents carefully, as they describe your rights 49 and restrictions with respect to this document. 50 51 52 53 54 55Menon-Sen, et al. Expires September 24, 2009 [Page 1] 56 57Internet-Draft SCRAM March 2009 58 59 60Abstract 61 62 The secure authentication mechanism most widely deployed and used by 63 Internet application protocols is the transmission of clear-text 64 passwords over a channel protected by Transport Layer Security (TLS). 65 There are some significant security concerns with that mechanism, 66 which could be addressed by the use of a challenge response 67 authentication mechanism protected by TLS. Unfortunately, the 68 challenge response mechanisms presently on the standards track all 69 fail to meet requirements necessary for widespread deployment, and 70 have had success only in limited use. 71 72 This specification describes a family of authentication mechanisms 73 called the Salted Challenge Response Authentication Mechanism 74 (SCRAM), which addresses the security concerns and meets the 75 deployability requirements. When used in combination with TLS or an 76 equivalent security layer, a mechanism from this family could improve 77 the status-quo for application protocol authentication and provide a 78 suitable choice for a mandatory-to-implement mechanism for future 79 application protocol standards. 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111Menon-Sen, et al. Expires September 24, 2009 [Page 2] 112 113Internet-Draft SCRAM March 2009 114 115 116Table of Contents 117 118 1. Conventions Used in This Document . . . . . . . . . . 4 119 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 4 120 1.2. Notation . . . . . . . . . . . . . . . . . . . . . . . 5 121 2. Introduction . . . . . . . . . . . . . . . . . . . . . 7 122 3. SCRAM Algorithm Overview . . . . . . . . . . . . . . . 9 123 4. SCRAM Mechanism Names . . . . . . . . . . . . . . . . 10 124 5. SCRAM Authentication Exchange . . . . . . . . . . . . 11 125 5.1. SCRAM Attributes . . . . . . . . . . . . . . . . . . . 12 126 6. Channel Binding . . . . . . . . . . . . . . . . . . . 15 127 6.1. Channel Binding to TLS Channels . . . . . . . . . . . 16 128 7. Formal Syntax . . . . . . . . . . . . . . . . . . . . 17 129 8. SCRAM as a GSS-API Mechanism . . . . . . . . . . . . . 20 130 8.1. GSS-API Principal Name Types for SCRAM . . . . . . . . 20 131 8.2. GSS-API Per-Message Tokens for SCRAM . . . . . . . . . 20 132 8.3. GSS_Pseudo_random() for SCRAM . . . . . . . . . . . . 21 133 9. Security Considerations . . . . . . . . . . . . . . . 22 134 10. IANA Considerations . . . . . . . . . . . . . . . . . 24 135 11. Acknowledgements . . . . . . . . . . . . . . . . . . . 25 136 Appendix A. Other Authentication Mechanisms . . . . . . . . . . . 26 137 Appendix B. Design Motivations . . . . . . . . . . . . . . . . . . 27 138 Appendix C. SCRAM Examples and Internet-Draft Change History . . . 28 139 12. References . . . . . . . . . . . . . . . . . . . . . . 31 140 12.1. Normative References . . . . . . . . . . . . . . . . . 31 141 12.2. Normative References for GSS-API implementors . . . . 31 142 12.3. Informative References . . . . . . . . . . . . . . . . 32 143 Authors' Addresses . . . . . . . . . . . . . . . . . . 34 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167Menon-Sen, et al. Expires September 24, 2009 [Page 3] 168 169Internet-Draft SCRAM March 2009 170 171 1721. Conventions Used in This Document 173 174 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 175 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 176 document are to be interpreted as described in [RFC2119]. 177 178 Formal syntax is defined by [RFC5234] including the core rules 179 defined in Appendix B of [RFC5234]. 180 181 Example lines prefaced by "C:" are sent by the client and ones 182 prefaced by "S:" by the server. If a single "C:" or "S:" label 183 applies to multiple lines, then the line breaks between those lines 184 are for editorial clarity only, and are not part of the actual 185 protocol exchange. 186 1871.1. Terminology 188 189 This document uses several terms defined in [RFC4949] ("Internet 190 Security Glossary") including the following: authentication, 191 authentication exchange, authentication information, brute force, 192 challenge-response, cryptographic hash function, dictionary attack, 193 eavesdropping, hash result, keyed hash, man-in-the-middle, nonce, 194 one-way encryption function, password, replay attack and salt. 195 Readers not familiar with these terms should use that glossary as a 196 reference. 197 198 Some clarifications and additional definitions follow: 199 200 o Authentication information: Information used to verify an identity 201 claimed by a SCRAM client. The authentication information for a 202 SCRAM identity consists of salt, iteration count, the "StoredKey" 203 and "ServerKey" (as defined in the algorithm overview) for each 204 supported cryptographic hash function. 205 206 o Authentication database: The database used to look up the 207 authentication information associated with a particular identity. 208 For application protocols, LDAPv3 (see [RFC4510]) is frequently 209 used as the authentication database. For network-level protocols 210 such as PPP or 802.11x, the use of RADIUS is more common. 211 212 o Base64: An encoding mechanism defined in [RFC4648] which converts 213 an octet string input to a textual output string which can be 214 easily displayed to a human. The use of base64 in SCRAM is 215 restricted to the canonical form with no whitespace. 216 217 o Octet: An 8-bit byte. 218 219 o Octet string: A sequence of 8-bit bytes. 220 221 222 223Menon-Sen, et al. Expires September 24, 2009 [Page 4] 224 225Internet-Draft SCRAM March 2009 226 227 228 o Salt: A random octet string that is combined with a password 229 before applying a one-way encryption function. This value is used 230 to protect passwords that are stored in an authentication 231 database. 232 2331.2. Notation 234 235 The pseudocode description of the algorithm uses the following 236 notations: 237 238 o ":=": The variable on the left hand side represents the octet 239 string resulting from the expression on the right hand side. 240 241 o "+": Octet string concatenation. 242 243 o "[ ]": A portion of an expression enclosed in "[" and "]" may not 244 be included in the result under some circumstances. See the 245 associated text for a description of those circumstances. 246 247 o HMAC(key, str): Apply the HMAC keyed hash algorithm (defined in 248 [RFC2104]) using the octet string represented by "key" as the key 249 and the octet string "str" as the input string. The size of the 250 result is the hash result size for the hash function in use. For 251 example, it is 20 octets for SHA-1 (see [RFC3174]). 252 253 o H(str): Apply the cryptographic hash function to the octet string 254 "str", producing an octet string as a result. The size of the 255 result depends on the hash result size for the hash function in 256 use. 257 258 o XOR: Apply the exclusive-or operation to combine the octet string 259 on the left of this operator with the octet string on the right of 260 this operator. The length of the output and each of the two 261 inputs will be the same for this use. 262 263 o Hi(str, salt): 264 265 266 267 U0 := HMAC(str, salt + INT(1)) 268 U1 := HMAC(str, U0) 269 U2 := HMAC(str, U1) 270 ... 271 Ui-1 := HMAC(str, Ui-2) 272 Ui := HMAC(str, Ui-1) 273 274 Hi := U0 XOR U1 XOR U2 XOR ... XOR Ui 275 276 277 278 279Menon-Sen, et al. Expires September 24, 2009 [Page 5] 280 281Internet-Draft SCRAM March 2009 282 283 284 where "i" is the iteration count, "+" is the string concatenation 285 operator and INT(g) is a four-octet encoding of the integer g, 286 most significant octet first. 287 288 o This is, essentially, PBKDF2 [RFC2898] with HMAC() as the PRF and 289 with dkLen == output length of HMAC() == output length of H(). 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335Menon-Sen, et al. Expires September 24, 2009 [Page 6] 336 337Internet-Draft SCRAM March 2009 338 339 3402. Introduction 341 342 This specification describes a family of authentication mechanisms 343 called the Salted Challenge Response Authentication Mechanism (SCRAM) 344 which addresses the requirements necessary to deploy a challenge- 345 response mechanism more widely than past attempts. When used in 346 combination with Transport Layer Security (TLS, see [RFC5246]) or an 347 equivalent security layer, a mechanism from this family could improve 348 the status-quo for application protocol authentication and provide a 349 suitable choice for a mandatory-to-implement mechanism for future 350 application protocol standards. 351 352 For simplicity, this family of mechanism does not presently include 353 negotiation of a security layer. It is intended to be used with an 354 external security layer such as that provided by TLS or SSH, with 355 optional channel binding [RFC5056] to the external security layer. 356 357 SCRAM is specified herein as a pure Simple Authentication and 358 Security Layer (SASL) [RFC4422] mechanism, but it conforms to the new 359 bridge between SASL and the Generic Security Services Application 360 Programming Interface (GSS-API) called "GS2" [ref-needed]. This 361 means that SCRAM is actually both, a GSS-API and SASL mechanism. 362 363 SCRAM provides the following protocol features: 364 365 o The authentication information stored in the authentication 366 database is not sufficient by itself to impersonate the client. 367 The information is salted to prevent a pre-stored dictionary 368 attack if the database is stolen. 369 370 o The server does not gain the ability to impersonate the client to 371 other servers (with an exception for server-authorized proxies). 372 373 o The mechanism permits the use of a server-authorized proxy without 374 requiring that proxy to have super-user rights with the back-end 375 server. 376 377 o A standard attribute is defined to enable storage of the 378 authentication information in LDAPv3 (see [RFC4510]). 379 380 o Mutual authentication is supported, but only the client is named 381 (i.e., the server has no name). 382 383 For an in-depth discussion of why other challenge response mechanisms 384 are not considered sufficient, see appendix A. For more information 385 about the motivations behind the design of this mechanism, see 386 appendix B. 387 388 389 390 391Menon-Sen, et al. Expires September 24, 2009 [Page 7] 392 393Internet-Draft SCRAM March 2009 394 395 396 Comments regarding this draft may be sent either to the 397 ietf-sasl@imc.org mailing list or to the authors. 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447Menon-Sen, et al. Expires September 24, 2009 [Page 8] 448 449Internet-Draft SCRAM March 2009 450 451 4523. SCRAM Algorithm Overview 453 454 Note that this section omits some details, such as client and server 455 nonces. See Section 5 for more details. 456 457 To begin with, the client is in possession of a username and 458 password. It sends the username to the server, which retrieves the 459 corresponding authentication information, i.e. a salt, StoredKey, 460 ServerKey and the iteration count i. (Note that a server 461 implementation may chose to use the same iteration count for all 462 account.) The server sends the salt and the iteration count to the 463 client, which then computes the following values and sends a 464 ClientProof to the server: 465 466 467 SaltedPassword := Hi(password, salt) 468 ClientKey := H(SaltedPassword) 469 StoredKey := H(ClientKey) 470 AuthMessage := client-first-message + "," + 471 server-first-message + "," + 472 client-final-message-without-proof 473 ClientSignature := HMAC(StoredKey, AuthMessage) 474 ClientProof := ClientKey XOR ClientSignature 475 ServerKey := HMAC(SaltedPassword, salt) 476 ServerSignature := HMAC(ServerKey, AuthMessage) 477 478 479 The server authenticates the client by computing the ClientSignature, 480 exclusive-ORing that with the ClientProof to recover the ClientKey 481 and verifying the correctness of the ClientKey by applying the hash 482 function and comparing the result to the StoredKey. If the ClientKey 483 is correct, this proves that the client has access to the user's 484 password. 485 486 Similarly, the client authenticates the server by computing the 487 ServerSignature and comparing it to the value sent by the server. If 488 the two are equal, it proves that the server had access to the user's 489 ServerKey. 490 491 The AuthMessage is computed by concatenating messages from the 492 authentication exchange. The format of these messages is defined in 493 Section 7. 494 495 496 497 498 499 500 501 502 503Menon-Sen, et al. Expires September 24, 2009 [Page 9] 504 505Internet-Draft SCRAM March 2009 506 507 5084. SCRAM Mechanism Names 509 510 A SCRAM mechanism name is a string "SCRAM-HMAC-" followed by the 511 uppercased name of the underlying hashed function taken from the IANA 512 "Hash Function Textual Names" registry (see http://www.iana.org), 513 optionally followed by the suffix "-PLUS" (see below).. 514 515 For interoperability, all SCRAM clients and servers MUST implement 516 the SCRAM-HMAC-SHA-1 authentication mechanism, i.e. an authentication 517 mechanism from the SCRAM family that uses the SHA-1 hash function as 518 defined in [RFC3174]. 519 520 The "-PLUS" suffix is used only when the server supports channel 521 binding to the external channel. In this case the server will 522 advertise both, SCRAM-HMAC-SHA-1 and SCRAM-HMAC-SHA-1-PLUS, otherwise 523 the server will advertise only SCRAM-HMAC-SHA-1. The "-PLUS" exists 524 to allow negotiation of the use of channel binding. See Section 6. 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559Menon-Sen, et al. Expires September 24, 2009 [Page 10] 560 561Internet-Draft SCRAM March 2009 562 563 5645. SCRAM Authentication Exchange 565 566 SCRAM is a text protocol where the client and server exchange 567 messages containing one or more attribute-value pairs separated by 568 commas. Each attribute has a one-letter name. The messages and 569 their attributes are described in Section 5.1, and defined in 570 Section 7. 571 572 This is a simple example of a SCRAM-HMAC-SHA-1 authentication 573 exchange: 574 575 576 C: n,n=Chris Newman,r=ClientNonce 577 S: r=ClientNonceServerNonce,s=PxR/wv+epq,i=128 578 C: r=ClientNonceServerNonce,p=WxPv/siO5l+qxN4 579 S: v=WxPv/siO5l+qxN4 580 581 582 With channel-binding data sent by the client this might look like 583 this: 584 585 586 C: p,n=Chris Newman,r=ClientNonce 587 S: r=ClientNonceServerNonce,s=PxR/wv+epq,i=128 588 C: c=0123456789ABCDEF,r=ClientNonceServerNonce,p=WxPv/siO5l+qxN4 589 S: v=WxPv/siO5l+qxN4 590 591 592 <<Note that the channel-bind data above, as well as all hashes are 593 fake>> 594 595 First, the client sends a message containing: 596 597 o a GS2 header consisting of a flag indicating whether channel 598 binding is supported-but-not-used, not supported, or used, and the 599 SASL authzid (optional); 600 601 o SCRAM username and client nonce attributes. 602 603 Note that the client's first message will always start with "n", "y" 604 or "p", otherwise the message is invalid and authentication MUST 605 fail. This is important, as it allows for GS2 extensibility (e.g., 606 to add support for security layers). 607 608 In response, the server sends the user's iteration count i, the 609 user's salt, and appends its own nonce to the client-specified one. 610 The client then responds with the same nonce and a ClientProof 611 computed using the selected hash function as explained earlier. In 612 613 614 615Menon-Sen, et al. Expires September 24, 2009 [Page 11] 616 617Internet-Draft SCRAM March 2009 618 619 620 this step the client can also include an optional authorization 621 identity. The server verifies the nonce and the proof, verifies that 622 the authorization identity (if supplied by the client in the second 623 message) is authorized to act as the authentication identity, and, 624 finally, it responds with a ServerSignature, concluding the 625 authentication exchange. The client then authenticates the server by 626 computing the ServerSignature and comparing it to the value sent by 627 the server. If the two are different, the client MUST consider the 628 authentication exchange to be unsuccessful and it might have to drop 629 the connection. 630 6315.1. SCRAM Attributes 632 633 This section describes the permissible attributes, their use, and the 634 format of their values. All attribute names are single US-ASCII 635 letters and are case-sensitive. 636 637 o a: This is an optional attribute, and is part of the GS2 [ref- 638 needed] bridge between the GSS-API and SASL. This attribute 639 specifies an authorization identity. A client may include it in 640 its second message to the server if it wants to authenticate as 641 one user, but subsequently act as a different user. This is 642 typically used by an administrator to perform some management task 643 on behalf of another user, or by a proxy in some situations. 644 645 Upon the receipt of this value the server verifies its 646 correctness according to the used SASL protocol profile. 647 Failed verification results in failed authentication exchange. 648 649 If this attribute is omitted (as it normally would be), or 650 specified with an empty value, the authorization identity is 651 assumed to be derived from the username specified with the 652 (required) "n" attribute. 653 654 The server always authenticates the user specified by the "n" 655 attribute. If the "a" attribute specifies a different user, 656 the server associates that identity with the connection after 657 successful authentication and authorization checks. 658 659 The syntax of this field is the same as that of the "n" field 660 with respect to quoting of '=' and ','. 661 662 o n: This attribute specifies the name of the user whose password is 663 used for authentication. A client must include it in its first 664 message to the server. If the "a" attribute is not specified 665 (which would normally be the case), this username is also the 666 identity which will be associated with the connection subsequent 667 to authentication and authorization. 668 669 670 671Menon-Sen, et al. Expires September 24, 2009 [Page 12] 672 673Internet-Draft SCRAM March 2009 674 675 676 Before sending the username to the server, the client MUST 677 prepare the username using the "SASLPrep" profile [RFC4013] of 678 the "stringprep" algorithm [RFC3454]. If the preparation of 679 the username fails or results in an empty string, the client 680 SHOULD abort the authentication exchange (*). 681 682 (*) An interactive client can request a repeated entry of the 683 username value. 684 685 Upon receipt of the username by the server, the server SHOULD 686 prepare it using the "SASLPrep" profile [RFC4013] of the 687 "stringprep" algorithm [RFC3454]. If the preparation of the 688 username fails or results in an empty string, the server SHOULD 689 abort the authentication exchange. 690 691 The characters ',' or '=' in usernames are sent as '=2C' and 692 '=3D' respectively. If the server receives a username which 693 contains '=' not followed by either '2C' or '3D', then the 694 server MUST fail the authentication. 695 696 o m: This attribute is reserved for future extensibility. In this 697 version of SCRAM, its presence in a client or a server message 698 MUST cause authentication failure when the attribute is parsed by 699 the other end. 700 701 o r: This attribute specifies a sequence of random printable 702 characters excluding ',' which forms the nonce used as input to 703 the hash function. No quoting is applied to this string (<<unless 704 the binding of SCRAM to a particular protocol states otherwise>>). 705 As described earlier, the client supplies an initial value in its 706 first message, and the server augments that value with its own 707 nonce in its first response. It is important that this be value 708 different for each authentication. The client MUST verify that 709 the initial part of the nonce used in subsequent messages is the 710 same as the nonce it initially specified. The server MUST verify 711 that the nonce sent by the client in the second message is the 712 same as the one sent by the server in its first message. 713 714 o c: This REQUIRED attribute specifies base64-encoded of a header 715 and the channel-binding data. It is sent by the client in its 716 second authentication message. The header consist of: 717 718 * the GS2 header from the client's first message (recall: a 719 channel binding flag and an optional authzid); 720 721 * followed by the external channel's channel binding type prefix 722 (see [RFC5056], if and only if the client is using channel 723 binding; 724 725 726 727Menon-Sen, et al. Expires September 24, 2009 [Page 13] 728 729Internet-Draft SCRAM March 2009 730 731 732 * followed by the external channel's channel binding data, if and 733 only if the client is using channel binding. 734 735 o s: This attribute specifies the base64-encoded salt used by the 736 server for this user. It is sent by the server in its first 737 message to the client. 738 739 o i: This attribute specifies an iteration count for the selected 740 hash function and user, and must be sent by the server along with 741 the user's salt. 742 743 For SCRAM-HMAC-SHA-1 SASL mechanism servers SHOULD announce a 744 hash iteration-count of at least 128. 745 746 o p: This attribute specifies a base64-encoded ClientProof. The 747 client computes this value as described in the overview and sends 748 it to the server. 749 750 o v: This attribute specifies a base64-encoded ServerSignature. It 751 is sent by the server in its final message, and is used by the 752 client to verify that the server has access to the user's 753 authentication information. This value is computed as explained 754 in the overview. 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783Menon-Sen, et al. Expires September 24, 2009 [Page 14] 784 785Internet-Draft SCRAM March 2009 786 787 7886. Channel Binding 789 790 SCRAM supports channel binding to external secure channels, such as 791 TLS. Clients and servers may or may not support channel binding, 792 therefore the use of channel binding is negotiable. SCRAM does not 793 provide security layers, however, therefore it is imperative that 794 SCRAM provide integrity protection for the negotiation of channel 795 binding. 796 797 Use of channel binding is negotiated as follows: 798 799 o The server advertises support for channel binding by advertising 800 both, SCRAM-HMAC-<hash-function> and SCRAM-HMAC-<hash-function>- 801 PLUS. 802 803 o If the client negotiates mechanisms then client MUST select SCRAM- 804 HMAC-<hash-function>-PLUS if offered by the server. Otherwise, if 805 the client does not negotiate mechanisms then it MUST select only 806 SCRAM-HMAC-<hash-function> (not suffixed with "-PLUS"). 807 808 o If the client and server both support channel binding, or if the 809 client wishes to use channel binding but the client does not 810 negotiate mechanisms, the client MUST set the GS2 channel binding 811 flag to "p" and MUST include channel binding data for the external 812 channel in the computation of the "c=" attribute (see 813 Section 5.1). 814 815 o If the client supports channel binding but the server does not 816 then the client MUST set the GS2 channel binding flag to "y" and 817 MUST NOT include channel binding data for the external channel in 818 the computation of the "c=" attribute (see Section 5.1). 819 820 o If the client does not support channel binding then the client 821 MUST set the GS2 channel binding flag to "n" and MUST NOT include 822 channel binding data for the external channel in the computation 823 of the "c=" attribute (see Section 5.1). 824 825 o If the server receives a client first message with the GS2 channel 826 binding flag set to "y" and the server supports channel binding 827 the server MUST fail authentication. This is because if the 828 client sets the GS2 channel binding flag set to "y" then the 829 client must have believed that the server did not support channel 830 binding -- if the server did in fact support channel binding then 831 this is an indication that there has been a downgrade attack 832 (e.g., an attacker changed the server's mechanism list to exclude 833 the -PLUS suffixed SCRAM mechanism name(s)). 834 835 The server MUST always validate the client's "c=" field. The server 836 837 838 839Menon-Sen, et al. Expires September 24, 2009 [Page 15] 840 841Internet-Draft SCRAM March 2009 842 843 844 does this by constructing the value of the "c=" attribute and then 845 checking that it matches the client's c= attribute value. 846 8476.1. Channel Binding to TLS Channels 848 849 If an external TLS channel is to be bound into the SCRAM 850 authentication, and if the channel was established using a server 851 certificate to authenticate the server, then the SCRAM client and 852 server MUST use the 'tls-server-end-point' channel binding type. See 853 the IANA Channel Binding Types registry. 854 855 If an external TLS channel is to be bound into the SCRAM 856 authentication, and if the channel was established without the use of 857 any server certificate to authenticate the server, then the SCRAM 858 client and server MUST use the 'tls-unique' channel binding type. 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895Menon-Sen, et al. Expires September 24, 2009 [Page 16] 896 897Internet-Draft SCRAM March 2009 898 899 9007. Formal Syntax 901 902 The following syntax specification uses the Augmented Backus-Naur 903 Form (ABNF) notation as specified in [RFC5234]. "UTF8-2", "UTF8-3" 904 and "UTF8-4" non-terminal are defined in [RFC3629]. 905 906 907 ALPHA = <as defined in RFC 5234 appendix B.1> 908 DIGIT = <as defined in RFC 5234 appendix B.1> 909 UTF8-2 = <as defined in RFC 3629 (STD 63)> 910 UTF8-3 = <as defined in RFC 3629 (STD 63)> 911 UTF8-4 = <as defined in RFC 3629 (STD 63)> 912 913 generic-message = attr-val *("," attr-val) 914 ;; Generic syntax of any server challenge 915 ;; or client response 916 917 attr-val = ALPHA "=" value 918 919 value = *value-char 920 921 value-safe-char = %x01-2B / %x2D-3C / %x3E-7F / 922 UTF8-2 / UTF8-3 / UTF8-4 923 ;; UTF8-char except NUL, "=", and ",". 924 925 value-char = value-safe-char / "=" 926 927 base64-char = ALPHA / DIGIT / "/" / "+" 928 929 base64-4 = 4base64-char 930 931 base64-3 = 3base64-char "=" 932 933 base64-2 = 2base64-char "==" 934 935 base64 = *base64-4 [base64-3 / base64-2] 936 937 posit-number = %x31-39 *DIGIT 938 ;; A positive number 939 940 saslname = 1*(value-safe-char / "=2C" / "=3D") 941 ;; Conforms to <value> 942 943 authzid = "a=" saslname 944 ;; Protocol specific. 945 946 gs2-cbind-flag = "n" / "y" / "p" 947 ;; "n" -> client doesn't support channel binding 948 949 950 951Menon-Sen, et al. Expires September 24, 2009 [Page 17] 952 953Internet-Draft SCRAM March 2009 954 955 956 ;; "y" -> client does support channel binding 957 ;; but thinks the server does not. 958 ;; "p" -> client requires channel binding 959 gs2-header = gs2-cbind-flag [ authzid ] "," 960 ;; GS2 header for SCRAM 961 ;; (the actual GS2 header includes an optional 962 ;; flag to indicate that the GSS mechanism is not 963 ;; "standard" but since SCRAM is "standard" we 964 ;; don't include that flag). 965 966 username = "n=" saslname 967 ;; Usernames are prepared using SASLPrep. 968 969 reserved-mext = "m=" 1*(value-char) 970 ;; Reserved for signalling mandatory extensions. 971 ;; The exact syntax will be defined in 972 ;; the future. 973 974 ;;cbind-type = value 975 ;;cbind-input = gs2-header [ value ":" cbind-data ] 976 channel-binding = "c=" base64 977 ;; base64 encoding of cbind-input 978 979 proof = "p=" base64 980 981 nonce = "r=" c-nonce [s-nonce] 982 ;; Second part provided by server. 983 984 c-nonce = value 985 986 s-nonce = value 987 988 salt = "s=" base64 989 990 verifier = "v=" base64 991 ;; base-64 encoded ServerSignature. 992 993 iteration-count = "i=" posit-number 994 ;; A positive number 995 996 client-first-message = 997 gs2-header [reserved-mext ","] 998 username "," nonce ["," extensions] 999 1000 server-first-message = 1001 [reserved-mext ","] nonce "," salt "," 1002 iteration-count ["," extensions] 1003 1004 1005 1006 1007Menon-Sen, et al. Expires September 24, 2009 [Page 18] 1008 1009Internet-Draft SCRAM March 2009 1010 1011 1012 client-final-message-without-proof = 1013 [channel-binding ","] nonce ["," 1014 extensions] 1015 1016 client-final-message = 1017 client-final-message-without-proof "," proof 1018 1019 gss-server-error = "e=" value 1020 server-final-message = gss-server-error / 1021 verifier ["," extensions] 1022 ;; The error message is only for the GSS-API 1023 ;; form of SCRAM, and it is OPTIONAL to 1024 ;; implement it. 1025 1026 extensions = attr-val *("," attr-val) 1027 ;; All extensions are optional, 1028 ;; i.e. unrecognized attributes 1029 ;; not defined in this document 1030 ;; MUST be ignored. 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1045 1046 1047 1048 1049 1050 1051 1052 1053 1054 1055 1056 1057 1058 1059 1060 1061 1062 1063Menon-Sen, et al. Expires September 24, 2009 [Page 19] 1064 1065Internet-Draft SCRAM March 2009 1066 1067 10688. SCRAM as a GSS-API Mechanism 1069 1070 This section and its sub-sections and all normative references of it 1071 not referenced elsewhere in this document are INFORMATIONAL for SASL 1072 implementors, but they are NORMATIVE for GSS-API implementors. 1073 1074 SCRAM is actually also GSS-API mechanism. The messages are the same, 1075 but a) the GS2 header on the client's first message and channel 1076 binding data is excluded when SCRAM is used as a GSS-API mechanism, 1077 and b) the RFC2743 section 3.1 initial context token header is 1078 prefixed to the client's first authentication message (context 1079 token). 1080 1081 The GSS-API mechanism OID for SCRAM is <TBD> (see Section 10). 1082 10838.1. GSS-API Principal Name Types for SCRAM 1084 1085 SCRAM does not name acceptors. Therefore only GSS_C_NO_NAME and 1086 names of type GSS_C_NT_ANONYMOUS shall be allowed as the target name 1087 input of GSS_Init_sec_context() when using a SCRAM mechanism. 1088 1089 SCRAM supports only a single name type for initiators: 1090 GSS_C_NT_USER_NAME. GSS_C_NT_USER_NAME is the default name type for 1091 SCRAM. 1092 1093 There is no name canonicalization procedure for SCRAM beyond applying 1094 SASLprep as described in Section 5.1. 1095 1096 The query, display and exported name syntax for SCRAM principal names 1097 is the same: there is no syntax -- SCRAM principal names are free- 1098 form. (The exported name token does, of course, conform to [RFC2743] 1099 section 3.2, but the "NAME" part of the token is just a SCRAM user 1100 name.) 1101 11028.2. GSS-API Per-Message Tokens for SCRAM 1103 1104 The per-message tokens for SCRAM as a GSS-API mechanism SHALL BE the 1105 same as those for the Kerberos V GSS-API mechanism [RFC4121], using 1106 the Kerberos V "aes128-cts-hmac-sha1-96" enctype [RFC3962]. 1107 1108 The 128-bit session key SHALL be derived by using the least 1109 significant (right-most) 128 bits of HMAC(StoredKey, "GSS-API session 1110 key" || ClientKey || AuthMessage). 1111 1112 SCRAM does support PROT_READY, and is PROT_READY on the initiator 1113 side first upon receipt of the server's reply to the initial security 1114 context token. 1115 1116 1117 1118 1119Menon-Sen, et al. Expires September 24, 2009 [Page 20] 1120 1121Internet-Draft SCRAM March 2009 1122 1123 11248.3. GSS_Pseudo_random() for SCRAM 1125 1126 The GSS_Pseudo_random() [RFC4401] for SCRAM SHALL be the same as for 1127 the Kerberos V GSS-API mechanism [RFC4402]. There is no acceptor- 1128 asserted sub-session key for SCRAM, thus GSS_C_PRF_KEY_FULL and 1129 GSS_C_PRF_KEY_PARTIAL are equivalent for SCRAM's GSS_Pseudo_random(). 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174 1175Menon-Sen, et al. Expires September 24, 2009 [Page 21] 1176 1177Internet-Draft SCRAM March 2009 1178 1179 11809. Security Considerations 1181 1182 If the authentication exchange is performed without a strong security 1183 layer, then a passive eavesdropper can gain sufficient information to 1184 mount an offline dictionary or brute-force attack which can be used 1185 to recover the user's password. The amount of time necessary for 1186 this attack depends on the cryptographic hash function selected, the 1187 strength of the password and the iteration count supplied by the 1188 server. An external security layer with strong encryption will 1189 prevent this attack. 1190 1191 If the external security layer used to protect the SCRAM exchange 1192 uses an anonymous key exchange, then the SCRAM channel binding 1193 mechanism can be used to detect a man-in-the-middle attack on the 1194 security layer and cause the authentication to fail as a result. 1195 However, the man-in-the-middle attacker will have gained sufficient 1196 information to mount an offline dictionary or brute-force attack. 1197 For this reason, SCRAM includes the ability to increase the iteration 1198 count over time. 1199 1200 If the authentication information is stolen from the authentication 1201 database, then an offline dictionary or brute-force attack can be 1202 used to recover the user's password. The use of salt mitigates this 1203 attack somewhat by requiring a separate attack on each password. 1204 Authentication mechanisms which protect against this attack are 1205 available (e.g., the EKE class of mechanisms), but the patent 1206 situation is presently unclear. 1207 1208 If an attacker obtains the authentication information from the 1209 authentication repository and either eavesdrops on one authentication 1210 exchange or impersonates a server, the attacker gains the ability to 1211 impersonate that user to all servers providing SCRAM access using the 1212 same hash function, password, iteration count and salt. For this 1213 reason, it is important to use randomly-generated salt values. 1214 1215 SCRAM does not negotiate a hash function to use. Hash function 1216 negotiation is left to the SASL mechanism negotiation. It is 1217 important that clients be able to sort a locally available list of 1218 mechanisms by preference so that the client may pick the most 1219 preferred of a server's advertised mechanism list. This preference 1220 order is not specified here as it is a local matter. The preference 1221 order should include objective and subjective notions of mechanism 1222 cryptographic strength (e.g., SCRAM with a successor to SHA-1 may be 1223 preferred over SCRAM with SHA-1). 1224 1225 Note that to protect the SASL mechanism negotiation applications 1226 normally must list the server mechs twice: once before and once after 1227 authentication, the latter using security layers. Since SCRAM does 1228 1229 1230 1231Menon-Sen, et al. Expires September 24, 2009 [Page 22] 1232 1233Internet-Draft SCRAM March 2009 1234 1235 1236 not provide security layers the only ways to protect the mechanism 1237 negotiation are: a) use channel binding to an external channel, or b) 1238 use an external channel that authenticates a user-provided server 1239 name. 1240 1241 A hostile server can perform a computational denial-of-service attack 1242 on clients by sending a big iteration count value. 1243 1244 1245 1246 1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287Menon-Sen, et al. Expires September 24, 2009 [Page 23] 1288 1289Internet-Draft SCRAM March 2009 1290 1291 129210. IANA Considerations 1293 1294 IANA is requested to add the following entries to the SASL Mechanism 1295 registry established by [RFC4422]: 1296 1297 1298 To: iana@iana.org 1299 Subject: Registration of a new SASL mechanism SCRAM-HMAC-SHA-1 1300 1301 SASL mechanism name (or prefix for the family): SCRAM-HMAC-SHA-1 1302 Security considerations: Section 7 of [RFCXXXX] 1303 Published specification (optional, recommended): [RFCXXXX] 1304 Person & email address to contact for further information: 1305 IETF SASL WG <ietf-sasl@imc.org> 1306 Intended usage: COMMON 1307 Owner/Change controller: IESG <iesg@ietf.org> 1308 Note: 1309 1310 To: iana@iana.org 1311 Subject: Registration of a new SASL mechanism SCRAM-HMAC-SHA-1-PLUS 1312 1313 SASL mechanism name (or prefix for the family): SCRAM-HMAC-SHA-1-PLUS 1314 Security considerations: Section 7 of [RFCXXXX] 1315 Published specification (optional, recommended): [RFCXXXX] 1316 Person & email address to contact for further information: 1317 IETF SASL WG <ietf-sasl@imc.org> 1318 Intended usage: COMMON 1319 Owner/Change controller: IESG <iesg@ietf.org> 1320 Note: 1321 1322 1323 Note that even though this document defines a family of SCRAM-HMAC 1324 mechanisms, it doesn't register a family of SCRAM-HMAC mechanisms in 1325 the SASL Mechanisms registry. IANA is requested to prevent future 1326 registrations of SASL mechanisms starting with SCRAM-HMAC- without 1327 consulting the SASL mailing list <ietf-sasl@imc.org> first. 1328 1329 Note to future SCRAM-HMAC mechanism designers: each new SCRAM-HMAC 1330 SASL mechanism MUST be explicitly registered with IANA and MUST 1331 comply with SCRAM-HMAC mechanism naming convention defined in 1332 Section 4 of this document. 1333 1334 We hereby request that IANA assign a GSS-API mechanism OID for SCRAM. 1335 1336 1337 1338 1339 1340 1341 1342 1343Menon-Sen, et al. Expires September 24, 2009 [Page 24] 1344 1345Internet-Draft SCRAM March 2009 1346 1347 134811. Acknowledgements 1349 1350 The authors would like to thank Dave Cridland for his contributions 1351 to this document. 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380 1381 1382 1383 1384 1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399Menon-Sen, et al. Expires September 24, 2009 [Page 25] 1400 1401Internet-Draft SCRAM March 2009 1402 1403 1404Appendix A. Other Authentication Mechanisms 1405 1406 The DIGEST-MD5 [I-D.ietf-sasl-digest-to-historic] mechanism has 1407 proved to be too complex to implement and test, and thus has poor 1408 interoperability. The security layer is often not implemented, and 1409 almost never used; everyone uses TLS instead. For a more complete 1410 list of problems with DIGEST-MD5 which lead to the creation of SCRAM 1411 see [I-D.ietf-sasl-digest-to-historic]. 1412 1413 The CRAM-MD5 SASL mechanism, while widely deployed has also some 1414 problems, in particular it is missing some modern SASL features such 1415 as support for internationalized usernames and passwords, support for 1416 passing of authorization identity, support for channel bindings. It 1417 also doesn't support server authentication. For a more complete list 1418 of problems with CRAM-MD5 see [I-D.ietf-sasl-crammd5-to-historic]. 1419 1420 The PLAIN [RFC4616] SASL mechanism allows a malicious server or 1421 eavesdropper to impersonate the authenticating user to any other 1422 server for which the user has the same password. It also sends the 1423 password in the clear over the network, unless TLS is used. Server 1424 authentication is not supported. 1425 1426 1427 1428 1429 1430 1431 1432 1433 1434 1435 1436 1437 1438 1439 1440 1441 1442 1443 1444 1445 1446 1447 1448 1449 1450 1451 1452 1453 1454 1455Menon-Sen, et al. Expires September 24, 2009 [Page 26] 1456 1457Internet-Draft SCRAM March 2009 1458 1459 1460Appendix B. Design Motivations 1461 1462 The DIGEST-MD5 [I-D.ietf-sasl-digest-to-historic] mechanism has 1463 proved to be too complex to implement and test, and thus has poor 1464 interoperability. The security layer is often not implemented, and 1465 almost never used; everyone uses TLS instead. For a more complete 1466 list of problems with DIGEST-MD5 which lead to the creation of SCRAM 1467 see [I-D.ietf-sasl-digest-to-historic]. 1468 1469 The CRAM-MD5 SASL mechanism, while widely deployed has also some 1470 problems, in particular it is missing some modern SASL features such 1471 as support for internationalized usernames and passwords, support for 1472 passing of authorization identity, support for channel bindings. It 1473 also doesn't support server authentication. For a more complete list 1474 of problems with CRAM-MD5 see [I-D.ietf-sasl-crammd5-to-historic]. 1475 1476 The PLAIN [RFC4616] SASL mechanism allows a malicious server or 1477 eavesdropper to impersonate the authenticating user to any other 1478 server for which the user has the same password. It also sends the 1479 password in the clear over the network, unless TLS is used. Server 1480 authentication is not supported. 1481 1482 1483 1484 1485 1486 1487 1488 1489 1490 1491 1492 1493 1494 1495 1496 1497 1498 1499 1500 1501 1502 1503 1504 1505 1506 1507 1508 1509 1510 1511Menon-Sen, et al. Expires September 24, 2009 [Page 27] 1512 1513Internet-Draft SCRAM March 2009 1514 1515 1516Appendix C. SCRAM Examples and Internet-Draft Change History 1517 1518 <<To be written.>> 1519 1520 (RFC Editor: Please delete everything after this point) 1521 1522 Open Issues 1523 1524 o The appendices need to be written. 1525 1526 o Should the server send a base64-encoded ServerSignature for the 1527 value of the "v" attribute, or should it compute a ServerProof the 1528 way the client computes a ClientProof? 1529 1530 Changes since -10 1531 1532 o Converted the source for this I-D to XML. 1533 1534 o Added text to make SCRAM compliant with the new GS2 design. 1535 1536 o Added text on channel binding negotiation. 1537 1538 o Added text on channel binding, including a reference to RFC5056. 1539 1540 o Added text on SCRAM as a GSS-API mechanism. This noted as not 1541 relevant to SASL-only implementors -- the normative references for 1542 SCRAM as a GSS-API mechanism are segregated as well. 1543 1544 Changes since -07 1545 1546 o Updated References. 1547 1548 o Clarified purpose of the m= attribute. 1549 1550 o Fixed a problem with authentication/authorization identity's ABNF 1551 not allowing for some characters. 1552 1553 o Updated ABNF for nonce to show client-generated and server- 1554 generated parts. 1555 1556 o Only register SCRAM-HMAC-SHA-1 with IANA and require explicit 1557 registrations of all other SCRAM-HMAC- mechanisms. 1558 1559 Changes since -06 1560 1561 o Removed hash negotiation from SCRAM and turned it into a family of 1562 SASL mechanisms. 1563 1564 1565 1566 1567Menon-Sen, et al. Expires September 24, 2009 [Page 28] 1568 1569Internet-Draft SCRAM March 2009 1570 1571 1572 o Start using "Hash Function Textual Names" IANA registry for SCRAM 1573 mechanism naming. 1574 1575 o Fixed definition of Hi(str, salt) to be consistent with [RFC2898]. 1576 1577 o Clarified extensibility of SCRAM: added m= attribute (for future 1578 mandatory extensions) and specified that all unrecognized 1579 attributes must be ignored. 1580 1581 Changes since -05 1582 1583 o Changed the mandatory to implement hash algorithm to SHA-1 (as per 1584 WG consensus). 1585 1586 o Added text about use of SASLPrep for username canonicalization/ 1587 validation. 1588 1589 o Clarified that authorization identity is canonicalized/verified 1590 according to SASL protocol profile. 1591 1592 o Clarified that iteration count is per-user. 1593 1594 o Clarified how clients select the authentication function. 1595 1596 o Added IANA registration for the new mechanism. 1597 1598 o Added missing normative references (UTF-8, SASLPrep). 1599 1600 o Various editorial changes based on comments from Hallvard B 1601 Furuseth, Nico William and Simon Josefsson. 1602 1603 Changes since -04 1604 1605 o Update Base64 and Security Glossary references. 1606 1607 o Add Formal Syntax section. 1608 1609 o Don't bother with "v=". 1610 1611 o Make MD5 mandatory to implement. Suggest i=128. 1612 1613 Changes since -03 1614 1615 o Seven years have passed, in which it became clear that DIGEST-MD5 1616 suffered from unacceptably bad interoperability, so SCRAM-MD5 is 1617 now back from the dead. 1618 1619 o Be hash agnostic, so MD5 can be replaced more easily. 1620 1621 1622 1623Menon-Sen, et al. Expires September 24, 2009 [Page 29] 1624 1625Internet-Draft SCRAM March 2009 1626 1627 1628 o General simplification. 1629 1630 1631 1632 1633 1634 1635 1636 1637 1638 1639 1640 1641 1642 1643 1644 1645 1646 1647 1648 1649 1650 1651 1652 1653 1654 1655 1656 1657 1658 1659 1660 1661 1662 1663 1664 1665 1666 1667 1668 1669 1670 1671 1672 1673 1674 1675 1676 1677 1678 1679Menon-Sen, et al. Expires September 24, 2009 [Page 30] 1680 1681Internet-Draft SCRAM March 2009 1682 1683 168412. References 1685 168612.1. Normative References 1687 1688 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 1689 Hashing for Message Authentication", RFC 2104, 1690 February 1997. 1691 1692 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1693 Requirement Levels", BCP 14, RFC 2119, March 1997. 1694 1695 [RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 1696 (SHA1)", RFC 3174, September 2001. 1697 1698 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 1699 Internationalized Strings ("stringprep")", RFC 3454, 1700 December 2002. 1701 1702 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 1703 10646", STD 63, RFC 3629, November 2003. 1704 1705 [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names 1706 and Passwords", RFC 4013, February 2005. 1707 1708 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 1709 Security Layer (SASL)", RFC 4422, June 2006. 1710 1711 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 1712 Encodings", RFC 4648, October 2006. 1713 1714 [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure 1715 Channels", RFC 5056, November 2007. 1716 1717 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1718 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1719 172012.2. Normative References for GSS-API implementors 1721 1722 [RFC2743] Linn, J., "Generic Security Service Application Program 1723 Interface Version 2, Update 1", RFC 2743, January 2000. 1724 1725 [RFC3962] Raeburn, K., "Advanced Encryption Standard (AES) 1726 Encryption for Kerberos 5", RFC 3962, February 2005. 1727 1728 [RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos 1729 Version 5 Generic Security Service Application Program 1730 Interface (GSS-API) Mechanism: Version 2", RFC 4121, 1731 July 2005. 1732 1733 1734 1735Menon-Sen, et al. Expires September 24, 2009 [Page 31] 1736 1737Internet-Draft SCRAM March 2009 1738 1739 1740 [RFC4401] Williams, N., "A Pseudo-Random Function (PRF) API 1741 Extension for the Generic Security Service Application 1742 Program Interface (GSS-API)", RFC 4401, February 2006. 1743 1744 [RFC4402] Williams, N., "A Pseudo-Random Function (PRF) for the 1745 Kerberos V Generic Security Service Application Program 1746 Interface (GSS-API) Mechanism", RFC 4402, February 2006. 1747 174812.3. Informative References 1749 1750 [I-D.ietf-sasl-crammd5-to-historic] 1751 Zeilenga, K., "CRAM-MD5 to Historic", 1752 draft-ietf-sasl-crammd5-to-historic-00 (work in progress), 1753 November 2008. 1754 1755 [I-D.ietf-sasl-digest-to-historic] 1756 Melnikov, A., "Moving DIGEST-MD5 to Historic", 1757 draft-ietf-sasl-digest-to-historic-00 (work in progress), 1758 July 2008. 1759 1760 [I-D.ietf-sasl-rfc2831bis] 1761 Melnikov, A., "Using Digest Authentication as a SASL 1762 Mechanism", draft-ietf-sasl-rfc2831bis-12 (work in 1763 progress), March 2007. 1764 1765 [RFC2195] Klensin, J., Catoe, R., and P. Krumviede, "IMAP/POP 1766 AUTHorize Extension for Simple Challenge/Response", 1767 RFC 2195, September 1997. 1768 1769 [RFC2202] Cheng, P. and R. Glenn, "Test Cases for HMAC-MD5 and HMAC- 1770 SHA-1", RFC 2202, September 1997. 1771 1772 [RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography 1773 Specification Version 2.0", RFC 2898, September 2000. 1774 1775 [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 1776 Requirements for Security", BCP 106, RFC 4086, June 2005. 1777 1778 [RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol 1779 (LDAP): Technical Specification Road Map", RFC 4510, 1780 June 2006. 1781 1782 [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and 1783 Security Layer (SASL) Mechanism", RFC 4616, August 2006. 1784 1785 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 1786 RFC 4949, August 2007. 1787 1788 1789 1790 1791Menon-Sen, et al. Expires September 24, 2009 [Page 32] 1792 1793Internet-Draft SCRAM March 2009 1794 1795 1796 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1797 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1798 1799 1800 1801 1802 1803 1804 1805 1806 1807 1808 1809 1810 1811 1812 1813 1814 1815 1816 1817 1818 1819 1820 1821 1822 1823 1824 1825 1826 1827 1828 1829 1830 1831 1832 1833 1834 1835 1836 1837 1838 1839 1840 1841 1842 1843 1844 1845 1846 1847Menon-Sen, et al. Expires September 24, 2009 [Page 33] 1848 1849Internet-Draft SCRAM March 2009 1850 1851 1852Authors' Addresses 1853 1854 Abhijit Menon-Sen 1855 Oryx Mail Systems GmbH 1856 1857 Email: ams@oryx.com 1858 1859 1860 Alexey Melnikov 1861 Isode Ltd 1862 1863 Email: Alexey.Melnikov@isode.com 1864 1865 1866 Chris Newman 1867 Sun Microsystems 1868 1050 Lakes Drive 1869 West Covina, CA 91790 1870 USA 1871 1872 Email: chris.newman@sun.com 1873 1874 1875 Nicolas Williams 1876 Sun Microsystems 1877 5300 Riata Trace Ct 1878 Austin, TX 78727 1879 USA 1880 1881 Email: Nicolas.Williams@sun.com 1882 1883 1884 1885 1886 1887 1888 1889 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903Menon-Sen, et al. Expires September 24, 2009 [Page 34] 1904 1905