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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NETWORK WORKING GROUP A. Menon-Sen 3 Internet-Draft Oryx Mail Systems GmbH 4 Intended status: Standards Track A. Melnikov 5 Expires: April 16, 2010 Isode Ltd 6 C. Newman 7 N. Williams 8 Sun Microsystems 9 October 13, 2009 11 Salted Challenge Response (SCRAM) SASL and GSS-API Mechanism 12 draft-ietf-sasl-scram-10.txt 14 Status of this Memo 16 This Internet-Draft is submitted to IETF in full conformance with the 17 provisions of BCP 78 and BCP 79. 19 Internet-Drafts are working documents of the Internet Engineering 20 Task Force (IETF), its areas, and its working groups. Note that 21 other groups may also distribute working documents as Internet- 22 Drafts. 24 Internet-Drafts are draft documents valid for a maximum of six months 25 and may be updated, replaced, or obsoleted by other documents at any 26 time. It is inappropriate to use Internet-Drafts as reference 27 material or to cite them other than as "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/ietf/1id-abstracts.txt. 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html. 35 This Internet-Draft will expire on April 16, 2010. 37 Copyright Notice 39 Copyright (c) 2009 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents in effect on the date of 44 publication of this document (http://trustee.ietf.org/license-info). 45 Please review these documents carefully, as they describe your rights 46 and restrictions with respect to this document. 48 Abstract 50 The secure authentication mechanism most widely deployed and used by 51 Internet application protocols is the transmission of clear-text 52 passwords over a channel protected by Transport Layer Security (TLS). 53 There are some significant security concerns with that mechanism, 54 which could be addressed by the use of a challenge response 55 authentication mechanism protected by TLS. Unfortunately, the 56 challenge response mechanisms presently on the standards track all 57 fail to meet requirements necessary for widespread deployment, and 58 have had success only in limited use. 60 This specification describes a family of Simple Authentication and 61 Security Layer (SASL, RFC 4422) authentication mechanisms called the 62 Salted Challenge Response Authentication Mechanism (SCRAM), which 63 addresses the security concerns and meets the deployability 64 requirements. When used in combination with TLS or an equivalent 65 security layer, a mechanism from this family could improve the 66 status-quo for application protocol authentication and provide a 67 suitable choice for a mandatory-to-implement mechanism for future 68 application protocol standards. 70 Table of Contents 72 1. Conventions Used in This Document . . . . . . . . . . 4 73 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 4 74 1.2. Notation . . . . . . . . . . . . . . . . . . . . . . . 5 75 2. Introduction . . . . . . . . . . . . . . . . . . . . . 7 76 3. SCRAM Algorithm Overview . . . . . . . . . . . . . . . 9 77 4. SCRAM Mechanism Names . . . . . . . . . . . . . . . . 11 78 5. SCRAM Authentication Exchange . . . . . . . . . . . . 12 79 5.1. SCRAM Attributes . . . . . . . . . . . . . . . . . . . 13 80 5.2. Compliance with SASL mechanism requirements . . . . . 16 81 6. Channel Binding . . . . . . . . . . . . . . . . . . . 17 82 6.1. Default Channel Binding . . . . . . . . . . . . . . . 18 83 7. Formal Syntax . . . . . . . . . . . . . . . . . . . . 19 84 8. SCRAM as a GSS-API Mechanism . . . . . . . . . . . . . 23 85 8.1. GSS-API Principal Name Types for SCRAM . . . . . . . . 23 86 8.2. GSS-API Per-Message Tokens for SCRAM . . . . . . . . . 23 87 8.3. GSS_Pseudo_random() for SCRAM . . . . . . . . . . . . 24 88 9. Security Considerations . . . . . . . . . . . . . . . 25 89 10. IANA Considerations . . . . . . . . . . . . . . . . . 27 90 11. Acknowledgements . . . . . . . . . . . . . . . . . . . 29 91 Appendix A. Other Authentication Mechanisms . . . . . . . . . . . 30 92 Appendix B. Design Motivations . . . . . . . . . . . . . . . . . . 31 93 Appendix C. Internet-Draft Change History . . . . . . . . . . . . 32 94 12. References . . . . . . . . . . . . . . . . . . . . . . 34 95 12.1. Normative References . . . . . . . . . . . . . . . . . 34 96 12.2. Normative References for GSS-API implementors . . . . 34 97 12.3. Informative References . . . . . . . . . . . . . . . . 35 98 Authors' Addresses . . . . . . . . . . . . . . . . . . 37 100 1. Conventions Used in This Document 102 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 103 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 104 document are to be interpreted as described in [RFC2119]. 106 Formal syntax is defined by [RFC5234] including the core rules 107 defined in Appendix B of [RFC5234]. 109 Example lines prefaced by "C:" are sent by the client and ones 110 prefaced by "S:" by the server. If a single "C:" or "S:" label 111 applies to multiple lines, then the line breaks between those lines 112 are for editorial clarity only, and are not part of the actual 113 protocol exchange. 115 1.1. Terminology 117 This document uses several terms defined in [RFC4949] ("Internet 118 Security Glossary") including the following: authentication, 119 authentication exchange, authentication information, brute force, 120 challenge-response, cryptographic hash function, dictionary attack, 121 eavesdropping, hash result, keyed hash, man-in-the-middle, nonce, 122 one-way encryption function, password, replay attack and salt. 123 Readers not familiar with these terms should use that glossary as a 124 reference. 126 Some clarifications and additional definitions follow: 128 o Authentication information: Information used to verify an identity 129 claimed by a SCRAM client. The authentication information for a 130 SCRAM identity consists of salt, iteration count, the "StoredKey" 131 and "ServerKey" (as defined in the algorithm overview) for each 132 supported cryptographic hash function. 134 o Authentication database: The database used to look up the 135 authentication information associated with a particular identity. 136 For application protocols, LDAPv3 (see [RFC4510]) is frequently 137 used as the authentication database. For network-level protocols 138 such as PPP or 802.11x, the use of RADIUS [RFC2865] is more 139 common. 141 o Base64: An encoding mechanism defined in [RFC4648] which converts 142 an octet string input to a textual output string which can be 143 easily displayed to a human. The use of base64 in SCRAM is 144 restricted to the canonical form with no whitespace. 146 o Octet: An 8-bit byte. 148 o Octet string: A sequence of 8-bit bytes. 150 o Salt: A random octet string that is combined with a password 151 before applying a one-way encryption function. This value is used 152 to protect passwords that are stored in an authentication 153 database. 155 1.2. Notation 157 The pseudocode description of the algorithm uses the following 158 notations: 160 o ":=": The variable on the left hand side represents the octet 161 string resulting from the expression on the right hand side. 163 o "+": Octet string concatenation. 165 o "[ ]": A portion of an expression enclosed in "[" and "]" may not 166 be included in the result under some circumstances. See the 167 associated text for a description of those circumstances. 169 o Normalize(str): Apply the SASLPrep profile [RFC4013] of the 170 "stringprep" algorithm [RFC3454] as the normalization algorithm to 171 a UTF-8 [RFC3629] encoded "str". The resulting string is also in 172 UTF-8. When applying SASLPrep, "str" is treated as a "stored 173 strings", which means that unassigned Unicode codepoints are 174 prohibited (see Section 7 of [RFC3454]). Note that 175 implementations MUST either implement SASLPrep, or disallow use of 176 non US-ASCII Unicode codepoints in "str". 178 o HMAC(key, str): Apply the HMAC keyed hash algorithm (defined in 179 [RFC2104]) using the octet string represented by "key" as the key 180 and the octet string "str" as the input string. The size of the 181 result is the hash result size for the hash function in use. For 182 example, it is 20 octets for SHA-1 (see [RFC3174]). 184 o H(str): Apply the cryptographic hash function to the octet string 185 "str", producing an octet string as a result. The size of the 186 result depends on the hash result size for the hash function in 187 use. 189 o XOR: Apply the exclusive-or operation to combine the octet string 190 on the left of this operator with the octet string on the right of 191 this operator. The length of the output and each of the two 192 inputs will be the same for this use. 194 o Hi(str, salt, i): 196 U0 := HMAC(str, salt + INT(1)) 197 U1 := HMAC(str, U0) 198 U2 := HMAC(str, U1) 199 ... 200 Ui-1 := HMAC(str, Ui-2) 201 Ui := HMAC(str, Ui-1) 203 Hi := U0 XOR U1 XOR U2 XOR ... XOR Ui 205 where "i" is the iteration count, "+" is the string concatenation 206 operator and INT(g) is a four-octet encoding of the integer g, 207 most significant octet first. 209 Hi() is, essentially, PBKDF2 [RFC2898] with HMAC() as the PRF and 210 with dkLen == output length of HMAC() == output length of H(). 212 2. Introduction 214 This specification describes a family of authentication mechanisms 215 called the Salted Challenge Response Authentication Mechanism (SCRAM) 216 which addresses the requirements necessary to deploy a challenge- 217 response mechanism more widely than past attempts (see Appendix A and 218 Appendix B). When used in combination with Transport Layer Security 219 (TLS, see [RFC5246]) or an equivalent security layer, a mechanism 220 from this family could improve the status-quo for application 221 protocol authentication and provide a suitable choice for a 222 mandatory-to-implement mechanism for future application protocol 223 standards. 225 For simplicity, this family of mechanisms does not presently include 226 negotiation of a security layer [RFC4422]. It is intended to be used 227 with an external security layer such as that provided by TLS or SSH, 228 with optional channel binding [RFC5056] to the external security 229 layer. 231 SCRAM is specified herein as a pure Simple Authentication and 232 Security Layer (SASL) [RFC4422] mechanism, but it conforms to the new 233 bridge between SASL and the Generic Security Services Application 234 Programming Interface (GSS-API) called "GS2" [I-D.ietf-sasl-gs2]. 235 This means that this document defines both, a SASL mechanism and a 236 GSS-API mechanism. 238 SCRAM provides the following protocol features: 240 o The authentication information stored in the authentication 241 database is not sufficient by itself to impersonate the client. 242 The information is salted to prevent a pre-stored dictionary 243 attack if the database is stolen. 245 o The server does not gain the ability to impersonate the client to 246 other servers (with an exception for server-authorized proxies). 248 o The mechanism permits the use of a server-authorized proxy without 249 requiring that proxy to have super-user rights with the back-end 250 server. 252 o Mutual authentication is supported, but only the client is named 253 (i.e., the server has no name). 255 o When used as a SASL mechanism, SCRAM is capable of transporting 256 authorization identities (see [RFC4422], Section 2) from the 257 client to the server. 259 A separate document defines a standard LDAPv3 [RFC4510] attribute 260 that enables storage of the SCRAM authentication information in LDAP. 261 See [I-D.melnikov-sasl-scram-ldap]. 263 For an in-depth discussion of why other challenge response mechanisms 264 are not considered sufficient, see appendix A. For more information 265 about the motivations behind the design of this mechanism, see 266 appendix B. 268 3. SCRAM Algorithm Overview 270 The following is a description of a full, uncompressed SASL SCRAM 271 authentication exchange. Nothing in SCRAM prevents either sending 272 the client-first message with the SASL authentication request defined 273 by an application protocol ("initial client response"), nor sending 274 the server-final message as additional data of the SASL outcome of 275 authentication exchange defined by an application protocol. See 276 [RFC4422] for more details. 278 Note that this section omits some details, such as client and server 279 nonces. See Section 5 for more details. 281 To begin with, the SCRAM client is in possession of a username and 282 password (*) (or a ClientKey/ServerKey, or SaltedPassword). It sends 283 the username to the server, which retrieves the corresponding 284 authentication information, i.e. a salt, StoredKey, ServerKey and the 285 iteration count i. (Note that a server implementation may choose to 286 use the same iteration count for all accounts.) The server sends the 287 salt and the iteration count to the client, which then computes the 288 following values and sends a ClientProof to the server: 290 (*) - Note that both the username and the password MUST be encoded in 291 UTF-8 [RFC3629]. 293 Informative Note: Implementors are encouraged to create test cases 294 that use both username passwords with non-ASCII codepoints. In 295 particular, it's useful to test codepoints whose "Unicode 296 Normalization Form C" and "Unicode Normalization Form KC" are 297 different. Some examples of such codepoints include Vulgar Fraction 298 One Half (U+00BD) and Acute Accent (U+00B4). 300 SaltedPassword := Hi(Normalize(password), salt, i) 301 ClientKey := HMAC(SaltedPassword, "Client Key") 302 StoredKey := H(ClientKey) 303 AuthMessage := client-first-message-bare + "," + 304 server-first-message + "," + 305 client-final-message-without-proof 306 ClientSignature := HMAC(StoredKey, AuthMessage) 307 ClientProof := ClientKey XOR ClientSignature 308 ServerKey := HMAC(SaltedPassword, "Server Key") 309 ServerSignature := HMAC(ServerKey, AuthMessage) 311 The server authenticates the client by computing the ClientSignature, 312 exclusive-ORing that with the ClientProof to recover the ClientKey 313 and verifying the correctness of the ClientKey by applying the hash 314 function and comparing the result to the StoredKey. If the ClientKey 315 is correct, this proves that the client has access to the user's 316 password. 318 Similarly, the client authenticates the server by computing the 319 ServerSignature and comparing it to the value sent by the server. If 320 the two are equal, it proves that the server had access to the user's 321 ServerKey. 323 The AuthMessage is computed by concatenating messages from the 324 authentication exchange. The format of these messages is defined in 325 Section 7. 327 4. SCRAM Mechanism Names 329 A SCRAM mechanism name is a string "SCRAM-" followed by the 330 uppercased name of the underlying hash function taken from the IANA 331 "Hash Function Textual Names" registry (see http://www.iana.org), 332 optionally followed by the suffix "-PLUS" (see below). Note that 333 SASL mechanism names are limited to 20 octets, which means that only 334 hash function names with lengths shorter or equal to 9 octets (20- 335 length("SCRAM-")-length("-PLUS") can be used. For cases when the 336 underlying hash function name is longer than 9 octets, an alternative 337 9 octet (or shorter) name can be used to construct the corresponding 338 SCRAM mechanism name, as long as this alternative name doesn't 339 conflict with any other hash function name from the IANA "Hash 340 Function Textual Names" registry. In order to prevent future 341 conflict, such alternative name SHOULD be registered in the IANA 342 "Hash Function Textual Names" registry. 344 For interoperability, all SCRAM clients and servers MUST implement 345 the SCRAM-SHA-1 authentication mechanism, i.e. an authentication 346 mechanism from the SCRAM family that uses the SHA-1 hash function as 347 defined in [RFC3174]. 349 The "-PLUS" suffix is used only when the server supports channel 350 binding to the external channel. If the server supports channel 351 binding, it will advertise both the "bare" and "plus" versions of 352 whatever mechanisms it supports (e.g., if the server supports only 353 SCRAM with SHA-1 then it will advertise support for both SCRAM-SHA-1 354 and SCRAM-SHA-1-PLUS); if the server does not support channel 355 binding, then it will advertise only the "bare" version of the 356 mechanism (e.g., only SCRAM-SHA-1). The "-PLUS" exists to allow 357 negotiation of the use of channel binding. See Section 6. 359 5. SCRAM Authentication Exchange 361 SCRAM is a SASL mechanism whose client response and server challenge 362 messages are text-based messages containing one or more attribute- 363 value pairs separated by commas. Each attribute has a one-letter 364 name. The messages and their attributes are described in 365 Section 5.1, and defined in Section 7. 367 SCRAM is a client-first SASL mechanism (See [RFC4422], Section 5, 368 item 2a), and returns additional data together with a server's 369 indication of a successful outcome. 371 This is a simple example of a SCRAM-SHA-1 authentication exchange 372 when the client doesn't support channel bindings: 374 C: n,,n=Chris Newman,r=ClientNonce 375 S: r=ClientNonceServerNonce,s=PxR/wv+epq,i=128 376 C: c=biwsCg==,r=ClientNonceServerNonce,p=WxPv/siO5l+qxN4 377 S: v=WxPv/siO5l+qxN4 379 [[anchor5: Note that the all hashes above are fake and will be fixed 380 during AUTH48.]] 382 With channel-binding data sent by the client this might look like 383 this (see [tls-server-end-point] for the definition of tls-server- 384 end-point TLS channel binding): 386 C: p=tls-server-end-point,,n=Chris Newman,r=ClientNonce 387 S: r=ClientNonceServerNonce,s=PxR/wv+epq,i=128 388 C: c=cD10bHMtc2VydmVyLWVuZC1wb2ludCwsy1hFtXOnZ+ySrQM6srFp 389 l/77uqvtxrg7nBY1BetEr/g=,r=ClientNonceServerNonce,p=Wx 390 Pv/siO5l+qxN4 391 S: v=WxPv/siO5l+qxN4 393 [[anchor6: Note that all hashes above are fake and will be fixed 394 during AUTH48.]] 396 First, the client sends the "client-first-message" containing: 398 o a GS2 header consisting of a flag indicating whether channel 399 binding is supported-but-not-used, not supported, or used, and an 400 optional SASL authorization identity; 402 o SCRAM username and a random, unique nonce attributes. 404 Note that the client's first message will always start with "n", "y" 405 or "p", otherwise the message is invalid and authentication MUST 406 fail. This is important, as it allows for GS2 extensibility (e.g., 407 to add support for security layers). 409 In response, the server sends a "server-first-message" containing the 410 user's iteration count i, the user's salt, and appends its own nonce 411 to the client-specified one. 413 The client then responds by sending "client-final-message" with the 414 same nonce and a ClientProof computed using the selected hash 415 function as explained earlier. 417 The server verifies the nonce and the proof, verifies that the 418 authorization identity (if supplied by the client in the first 419 message) is authorized to act as the authentication identity, and, 420 finally, it responds with a "server-final-message", concluding the 421 authentication exchange. 423 The client then authenticates the server by computing the 424 ServerSignature and comparing it to the value sent by the server. If 425 the two are different, the client MUST consider the authentication 426 exchange to be unsuccessful and it might have to drop the connection. 428 5.1. SCRAM Attributes 430 This section describes the permissible attributes, their use, and the 431 format of their values. All attribute names are single US-ASCII 432 letters and are case-sensitive. 434 Note that the order of attributes in client or server messages is 435 fixed, with the exception of extension attributes (described by the 436 "extensions" ABNF production), which can appear in any order in the 437 designated positions. See the ABNF section for authoritative 438 reference. 440 o a: This is an optional attribute, and is part of the GS2 441 [I-D.ietf-sasl-gs2] bridge between the GSS-API and SASL. This 442 attribute specifies an authorization identity. A client may 443 include it in its first message to the server if it wants to 444 authenticate as one user, but subsequently act as a different 445 user. This is typically used by an administrator to perform some 446 management task on behalf of another user, or by a proxy in some 447 situations. 449 Upon the receipt of this value the server verifies its 450 correctness according to the used SASL protocol profile. 451 Failed verification results in failed authentication exchange. 453 If this attribute is omitted (as it normally would be), the 454 authorization identity is assumed to be derived from the 455 username specified with the (required) "n" attribute. 457 The server always authenticates the user specified by the "n" 458 attribute. If the "a" attribute specifies a different user, 459 the server associates that identity with the connection after 460 successful authentication and authorization checks. 462 The syntax of this field is the same as that of the "n" field 463 with respect to quoting of '=' and ','. 465 o n: This attribute specifies the name of the user whose password is 466 used for authentication (a.k.a. "authentication identity" 467 [RFC4422]). A client MUST include it in its first message to the 468 server. If the "a" attribute is not specified (which would 469 normally be the case), this username is also the identity which 470 will be associated with the connection subsequent to 471 authentication and authorization. 473 Before sending the username to the server, the client SHOULD 474 prepare the username using the "SASLPrep" profile [RFC4013] of 475 the "stringprep" algorithm [RFC3454] treating it as a query 476 string (i.e., unassigned Unicode code points are allowed). If 477 the preparation of the username fails or results in an empty 478 string, the client SHOULD abort the authentication exchange 479 (*). 481 (*) An interactive client can request a repeated entry of the 482 username value. 484 Upon receipt of the username by the server, the server MUST 485 either prepare it using the "SASLPrep" profile [RFC4013] of the 486 "stringprep" algorithm [RFC3454] treating it as a query string 487 (i.e., unassigned Unicode codepoints are allowed) or otherwise 488 be prepared to do SASLprep-aware string comparisons and/or 489 index lookups. If the preparation of the username fails or 490 results in an empty string, the server SHOULD abort the 491 authentication exchange. Whether or not the server prepares 492 the username using "SASLPrep", it MUST use it as received in 493 hash calculations. 495 The characters ',' or '=' in usernames are sent as '=2C' and 496 '=3D' respectively. If the server receives a username which 497 contains '=' not followed by either '2C' or '3D', then the 498 server MUST fail the authentication. 500 o m: This attribute is reserved for future extensibility. In this 501 version of SCRAM, its presence in a client or a server message 502 MUST cause authentication failure when the attribute is parsed by 503 the other end. 505 o r: This attribute specifies a sequence of random printable ASCII 506 characters excluding ',' which forms the nonce used as input to 507 the hash function. No quoting is applied to this string. As 508 described earlier, the client supplies an initial value in its 509 first message, and the server augments that value with its own 510 nonce in its first response. It is important that this value be 511 different for each authentication (see [RFC4086] for more details 512 on how to achieve this). The client MUST verify that the initial 513 part of the nonce used in subsequent messages is the same as the 514 nonce it initially specified. The server MUST verify that the 515 nonce sent by the client in the second message is the same as the 516 one sent by the server in its first message. 518 o c: This REQUIRED attribute specifies the base64-encoded GS2 header 519 and channel-binding data. It is sent by the client in its second 520 authentication message. The attribute data consist of: 522 * the GS2 header from the client's first message (recall that the 523 GS2 header contains a channel binding flag and an optional 524 authzid). This header is going to include channel binding type 525 prefix (see [RFC5056]), if and only if the client is using 526 channel binding; 528 * followed by the external channel's channel binding data, if and 529 only if the client is using channel binding. 531 o s: This attribute specifies the base64-encoded salt used by the 532 server for this user. It is sent by the server in its first 533 message to the client. 535 o i: This attribute specifies an iteration count for the selected 536 hash function and user, and MUST be sent by the server along with 537 the user's salt. 539 For SCRAM-SHA-1/SCRAM-SHA-1-PLUS SASL mechanism servers SHOULD 540 announce a hash iteration-count of at least 4096. Note that a 541 client implementation MAY cache ClientKey&ServerKey (or just 542 SaltedPassword) for later reauthentication to the same service, 543 as it is likely that the server is going to advertise the same 544 salt value upon reauthentication. This might be useful for 545 mobile clients where CPU usage is a concern. 547 o p: This attribute specifies a base64-encoded ClientProof. The 548 client computes this value as described in the overview and sends 549 it to the server. 551 o v: This attribute specifies a base64-encoded ServerSignature. It 552 is sent by the server in its final message, and is used by the 553 client to verify that the server has access to the user's 554 authentication information. This value is computed as explained 555 in the overview. 557 5.2. Compliance with SASL mechanism requirements 559 This section describes compliance with SASL mechanism requirements 560 specified in Section 5 of [RFC4422]. 562 1) "SCRAM-SHA-1" and "SCRAM-SHA-1-PLUS". 564 2a) SCRAM is a client-first mechanism. 566 2b) SCRAM sends additional data with success. 568 3) SCRAM is capable of transferring authorization identities from the 569 client to the server. 571 4) SCRAM does not offer any security layers (SCRAM offers channel 572 binding instead). 574 5) SCRAM has a hash protecting the authorization identity. 576 6. Channel Binding 578 SCRAM supports channel binding to external secure channels, such as 579 TLS. Clients and servers may or may not support channel binding, 580 therefore the use of channel binding is negotiable. SCRAM does not 581 provide security layers, however, therefore it is imperative that 582 SCRAM provide integrity protection for the negotiation of channel 583 binding. 585 Use of channel binding is negotiated as follows: 587 o Servers SHOULD advertise both non-PLUS (SCRAM-) and 588 the PLUS-variant (SCRAM--PLUS) SASL mechanism 589 names. If the server cannot support channel binding, it MAY 590 advertise only the non-PLUS variant. If the server would never 591 succeed authentication of the non-PLUS variant due to policy 592 reasons, it MAY advertise only the PLUS-variant. 594 o If the client negotiates mechanisms then the client MUST select 595 SCRAM--PLUS if offered by the server and the client 596 wants to select SCRAM with the given hash function. Otherwise 597 (the client does not negotiate mechanisms), if the client has no 598 prior knowledge about mechanisms supported by the server and 599 wasn't explicitly configured to use a particular variant of the 600 SCRAM mechanism, then it MUST select only SCRAM- 601 (not suffixed with "-PLUS"). 603 o If the client supports channel binding and the server appears to 604 support it (i.e., the client sees SCRAM--PLUS), or 605 if the client wishes to use channel binding but the client does 606 not negotiate mechanisms, then the client MUST set the GS2 channel 607 binding flag to "p" in order to indicate the channel binding type 608 it is using and it MUST include the channel binding data for the 609 external channel in the computation of the "c=" attribute (see 610 Section 5.1). 612 o If the client supports channel binding but the server does not 613 appear to (i.e., the client did not see SCRAM-- 614 PLUS) then the client MUST either fail authentication or it MUST 615 choose the non-PLUS mechanism and set the GS2 channel binding flag 616 to "y" and MUST NOT include channel binding data for the external 617 channel in the computation of the "c=" attribute (see 618 Section 5.1). 620 o If the client does not support channel binding then the client 621 MUST set the GS2 channel binding flag to "n" and MUST NOT include 622 channel binding data for the external channel in the computation 623 of the "c=" attribute (see Section 5.1). 625 o Upon receipt of the client first message the server checks the GS2 626 channel binding flag (gs2-cb-flag). 628 * If the flag is set to "y" and the server supports channel 629 binding the server MUST fail authentication. This is because 630 if the client sets the GS2 channel binding flag set to "y" then 631 the client must have believed that the server did not support 632 channel binding -- if the server did in fact support channel 633 binding then this is an indication that there has been a 634 downgrade attack (e.g., an attacker changed the server's 635 mechanism list to exclude the -PLUS suffixed SCRAM mechanism 636 name(s)). 638 * If the channel binding flag was "p" and the server does not 639 support the indicated channel binding type then the server MUST 640 fail authentication. 642 The server MUST always validate the client's "c=" field. The server 643 does this by constructing the value of the "c=" attribute and then 644 checking that it matches the client's c= attribute value. 646 For more discussions of channel bindings, and the syntax of the 647 channel binding data for various security protocols, see [RFC5056]. 649 6.1. Default Channel Binding 651 A default channel binding type agreement process for all SASL 652 application protocols that do not provide their own channel binding 653 type agreement is provided as follows. 655 'tls-unique' is the default channel binding type for any application 656 that doesn't specify one. 658 Servers MUST implement the "tls-unique" [tls-unique] 659 [I-D.altman-tls-channel-bindings] channel binding type, if they 660 implement any channel binding. Clients SHOULD implement the "tls- 661 unique" [tls-unique] [I-D.altman-tls-channel-bindings] channel 662 binding type, if they implement any channel binding. Clients and 663 servers SHOULD choose the highest- layer/innermost end-to-end TLS 664 channel as the channel to bind to. 666 Servers MUST choose the channel binding type indicated by the client, 667 or fail authentication if they don't support it. 669 7. Formal Syntax 671 The following syntax specification uses the Augmented Backus-Naur 672 Form (ABNF) notation as specified in [RFC5234]. "UTF8-2", "UTF8-3" 673 and "UTF8-4" non-terminal are defined in [RFC3629]. 675 ALPHA = 676 DIGIT = 677 UTF8-2 = 678 UTF8-3 = 679 UTF8-4 = 681 attr-val = ALPHA "=" value 682 ;; Generic syntax of any attribute sent 683 ;; by server or client 685 value = 1*value-char 687 value-safe-char = %x01-2B / %x2D-3C / %x3E-7F / 688 UTF8-2 / UTF8-3 / UTF8-4 689 ;; UTF8-char except NUL, "=", and ",". 691 value-char = value-safe-char / "=" 693 printable = %x21-2B / %x2D-7E 694 ;; Printable ASCII except ",". 695 ;; Note that any "printable" is also 696 ;; a valid "value". 698 base64-char = ALPHA / DIGIT / "/" / "+" 700 base64-4 = 4base64-char 702 base64-3 = 3base64-char "=" 704 base64-2 = 2base64-char "==" 706 base64 = *base64-4 [base64-3 / base64-2] 708 posit-number = %x31-39 *DIGIT 709 ;; A positive number 711 saslname = 1*(value-safe-char / "=2C" / "=3D") 712 ;; Conforms to 714 authzid = "a=" saslname 715 ;; Protocol specific. 717 cb-name = 1*(ALPHA / DIGIT / "." / "-") 718 ;; See RFC 5056 section 7. 719 ;; E.g. "tls-server-end-point" or 720 ;; "tls-unique" 722 gs2-cbind-flag = "p=" cb-name / "n" / "y" 723 ;; "n" -> client doesn't support channel binding 724 ;; "y" -> client does support channel binding 725 ;; but thinks the server does not. 726 ;; "p" -> client requires channel binding. 727 ;; The selected channel binding follows "p=". 729 gs2-header = gs2-cbind-flag "," [ authzid ] "," 730 ;; GS2 header for SCRAM 731 ;; (the actual GS2 header includes an optional 732 ;; flag to indicate that the GSS mechanism is not 733 ;; "standard" but since SCRAM is "standard" we 734 ;; don't include that flag). 736 username = "n=" saslname 737 ;; Usernames are prepared using SASLPrep. 739 reserved-mext = "m=" 1*(value-char) 740 ;; Reserved for signalling mandatory extensions. 741 ;; The exact syntax will be defined in 742 ;; the future. 744 channel-binding = "c=" base64 745 ;; base64 encoding of cbind-input 747 proof = "p=" base64 749 nonce = "r=" c-nonce [s-nonce] 750 ;; Second part provided by server. 752 c-nonce = printable 754 s-nonce = printable 756 salt = "s=" base64 758 verifier = "v=" base64 759 ;; base-64 encoded ServerSignature. 761 iteration-count = "i=" posit-number 762 ;; A positive number 764 client-first-message-bare = 766 [reserved-mext ","] 767 username "," nonce ["," extensions] 769 client-first-message = 770 gs2-header client-first-message-bare 772 server-first-message = 773 [reserved-mext ","] nonce "," salt "," 774 iteration-count ["," extensions] 776 client-final-message-without-proof = 777 channel-binding "," nonce ["," 778 extensions] 780 client-final-message = 781 client-final-message-without-proof "," proof 783 server-error = "e=" server-error-value 785 server-error-value = "invalid-encoding" / 786 "extensions-not-supported" / ; unrecognized 'm' value 787 "invalid-proof" / 788 "channel-bindings-dont-match" / 789 "server-does-support-channel-binding" / 790 ; server does not support channel binding 791 "channel-binding-not-supported" / 792 "unsupported-channel-binding-type" / 793 "unknown-user" / 794 "invalid-username-encoding" / 795 ; invalid username encoding (invalid UTF-8 or 796 ; SASLprep failed) 797 "no-resources" / 798 "other-error" / 799 server-error-value-ext 800 ; Unrecognized errors should be treated as "other-error". 801 ; In order to prevent information disclosure the server 802 ; may substitute the real reason with "other-error". 804 server-error-value-ext = value 805 ; Additional error reasons added by extensions 806 ; to this document. 808 server-final-message = (server-error / verifier) 809 ["," extensions] 810 ;; The error message is only for the GSS-API 811 ;; form of SCRAM, and it is OPTIONAL to 812 ;; implement it. 814 extensions = attr-val *("," attr-val) 815 ;; All extensions are optional, 816 ;; i.e. unrecognized attributes 817 ;; not defined in this document 818 ;; MUST be ignored. 820 cbind-data = 1*OCTET 822 cbind-input = gs2-header [ cbind-data ] 823 ;; cbind-data MUST be present for 824 ;; gs2-cbind-flag of "p" and MUST be absent 825 ;; for "y" or "n". 827 8. SCRAM as a GSS-API Mechanism 829 This section and its sub-sections and all normative references of it 830 not referenced elsewhere in this document are INFORMATIONAL for SASL 831 implementors, but they are NORMATIVE for GSS-API implementors. 833 SCRAM is actually also GSS-API mechanism. The messages are the same, 834 but a) the GS2 header on the client's first message and channel 835 binding data is excluded when SCRAM is used as a GSS-API mechanism, 836 and b) the RFC2743 section 3.1 initial context token header is 837 prefixed to the client's first authentication message (context 838 token). 840 The GSS-API mechanism OID for SCRAM-SHA-1 is (see Section 10). 842 8.1. GSS-API Principal Name Types for SCRAM 844 SCRAM does not name acceptors. Therefore only GSS_C_NO_NAME and 845 names of type GSS_C_NT_ANONYMOUS shall be allowed as the target name 846 input of GSS_Init_sec_context() when using a SCRAM mechanism. 848 SCRAM supports only a single name type for initiators: 849 GSS_C_NT_USER_NAME. GSS_C_NT_USER_NAME is the default name type for 850 SCRAM. 852 There is no name canonicalization procedure for SCRAM beyond applying 853 SASLprep as described in Section 5.1. 855 The query, display and exported name syntax for SCRAM principal names 856 is the same: there is no syntax -- SCRAM principal names are free- 857 form. (The exported name token does, of course, conform to [RFC2743] 858 section 3.2, but the "NAME" part of the token is just a SCRAM user 859 name.) 861 8.2. GSS-API Per-Message Tokens for SCRAM 863 The per-message tokens for SCRAM as a GSS-API mechanism SHALL be the 864 same as those for the Kerberos V GSS-API mechanism [RFC4121] (see 865 Section 4.2 and sub-sections), using the Kerberos V "aes128-cts-hmac- 866 sha1-96" enctype [RFC3962]. 868 The 128-bit session "protocol key" SHALL be derived by using the 869 least significant (right-most) 128 bits of HMAC(StoredKey, "GSS-API 870 session key" || ClientKey || AuthMessage). "Specific keys" are then 871 derived as usual as described in Section 2 of [RFC4121], [RFC3961] 872 and [RFC3962]. 874 The terms "protocol key" and "specific key" are Kerberos V5 terms 876 [RFC3961]. 878 SCRAM does support PROT_READY, and is PROT_READY on the initiator 879 side first upon receipt of the server's reply to the initial security 880 context token. 882 8.3. GSS_Pseudo_random() for SCRAM 884 The GSS_Pseudo_random() [RFC4401] for SCRAM SHALL be the same as for 885 the Kerberos V GSS-API mechanism [RFC4402]. There is no acceptor- 886 asserted sub-session key for SCRAM, thus GSS_C_PRF_KEY_FULL and 887 GSS_C_PRF_KEY_PARTIAL are equivalent for SCRAM's GSS_Pseudo_random(). 888 The protocol key to be used for the GSS_Pseudo_random() SHALL be the 889 same as the key defined in Section 8.2. 891 9. Security Considerations 893 If the authentication exchange is performed without a strong security 894 layer (such as TLS with data confidentiality), then a passive 895 eavesdropper can gain sufficient information to mount an offline 896 dictionary or brute-force attack which can be used to recover the 897 user's password. The amount of time necessary for this attack 898 depends on the cryptographic hash function selected, the strength of 899 the password and the iteration count supplied by the server. An 900 external security layer with strong encryption will prevent this 901 attack. 903 If the external security layer used to protect the SCRAM exchange 904 uses an anonymous key exchange, then the SCRAM channel binding 905 mechanism can be used to detect a man-in-the-middle attack on the 906 security layer and cause the authentication to fail as a result. 907 However, the man-in-the-middle attacker will have gained sufficient 908 information to mount an offline dictionary or brute-force attack. 909 For this reason, SCRAM allows to increase the iteration count over 910 time. (Note that a server that is only in posession of "StoredKey" 911 and "ServerKey" can't automatic increase the iteration count upon 912 successful authentication. Such increase would require resetting 913 user's password.) 915 If the authentication information is stolen from the authentication 916 database, then an offline dictionary or brute-force attack can be 917 used to recover the user's password. The use of salt mitigates this 918 attack somewhat by requiring a separate attack on each password. 919 Authentication mechanisms which protect against this attack are 920 available (e.g., the EKE class of mechanisms). RFC 2945 [RFC2945] is 921 an example of such technology. The WG selected not to use EKE like 922 mechanisms as basis for SCRAM. 924 If an attacker obtains the authentication information from the 925 authentication repository and either eavesdrops on one authentication 926 exchange or impersonates a server, the attacker gains the ability to 927 impersonate that user to all servers providing SCRAM access using the 928 same hash function, password, iteration count and salt. For this 929 reason, it is important to use randomly-generated salt values. 931 SCRAM does not negotiate a hash function to use. Hash function 932 negotiation is left to the SASL mechanism negotiation. It is 933 important that clients be able to sort a locally available list of 934 mechanisms by preference so that the client may pick the most 935 preferred of a server's advertised mechanism list. This preference 936 order is not specified here as it is a local matter. The preference 937 order should include objective and subjective notions of mechanism 938 cryptographic strength (e.g., SCRAM with a successor to SHA-1 may be 939 preferred over SCRAM with SHA-1). 941 Note that to protect the SASL mechanism negotiation applications 942 normally must list the server mechs twice: once before and once after 943 authentication, the latter using security layers. Since SCRAM does 944 not provide security layers the only ways to protect the mechanism 945 negotiation are: a) use channel binding to an external channel, or b) 946 use an external channel that authenticates a user-provided server 947 name. 949 SCRAM does not protect against downgrade attacks of channel binding 950 types. The complexities of negotiation a channel binding type, and 951 handling down-grade attacks in that negotiation, was intentionally 952 left out of scope for this document. 954 A hostile server can perform a computational denial-of-service attack 955 on clients by sending a big iteration count value. 957 See [RFC4086] for more information about generating randomness. 959 10. IANA Considerations 961 IANA is requested to add the following family of SASL mechanisms to 962 the SASL Mechanism registry established by [RFC4422]: 964 To: iana@iana.org 965 Subject: Registration of a new SASL family SCRAM 967 SASL mechanism name (or prefix for the family): SCRAM-* 968 Security considerations: Section 7 of [RFCXXXX] 969 Published specification (optional, recommended): [RFCXXXX] 970 Person & email address to contact for further information: 971 IETF SASL WG 972 Intended usage: COMMON 973 Owner/Change controller: IESG 974 Note: Members of this family must be explicitly registered 975 using the "IETF Review" [RFC5226] registration procedure. 976 Reviews must be requested on the SASL WG mailing list. 978 "IETF Review" [RFC5226] registration procedure MUST be used for 979 registering new mechanisms in this family. The SASL mailing list 980 (or a successor designated by the responsible 981 Security AD) MUST be used for soliciting reviews on such 982 registrations. 984 Note to future SCRAM- mechanism designers: each new SCRAM- SASL 985 mechanism MUST be explicitly registered with IANA and MUST comply 986 with SCRAM- mechanism naming convention defined in Section 4 of this 987 document. 989 IANA is requested to add the following entries to the SASL Mechanism 990 registry established by [RFC4422]: 992 To: iana@iana.org 993 Subject: Registration of a new SASL mechanism SCRAM-SHA-1 995 SASL mechanism name (or prefix for the family): SCRAM-SHA-1 996 Security considerations: Section 7 of [RFCXXXX] 997 Published specification (optional, recommended): [RFCXXXX] 998 Person & email address to contact for further information: 999 IETF SASL WG 1000 Intended usage: COMMON 1001 Owner/Change controller: IESG 1002 Note: 1004 To: iana@iana.org 1005 Subject: Registration of a new SASL mechanism SCRAM-SHA-1-PLUS 1007 SASL mechanism name (or prefix for the family): SCRAM-SHA-1-PLUS 1008 Security considerations: Section 7 of [RFCXXXX] 1009 Published specification (optional, recommended): [RFCXXXX] 1010 Person & email address to contact for further information: 1011 IETF SASL WG 1012 Intended usage: COMMON 1013 Owner/Change controller: IESG 1014 Note: 1016 This document also requests IANA to assign a GSS-API mechanism OID 1017 for SCRAM-SHA-1 from the iso.org.dod.internet.security.mechanisms 1018 prefix (see "SMI Security for Mechanism Codes" registry). 1020 11. Acknowledgements 1022 This document benefited from discussions on the SASL WG mailing list. 1023 The authors would like to specially thank Dave Cridland, Simon 1024 Josefsson, Jeffrey Hutzelman, Kurt Zeilenga, Pasi Eronen, Ben 1025 Campbell and Peter Saint-Andre for their contributions to this 1026 document. 1028 Appendix A. Other Authentication Mechanisms 1030 The DIGEST-MD5 [I-D.ietf-sasl-digest-to-historic] mechanism has 1031 proved to be too complex to implement and test, and thus has poor 1032 interoperability. The security layer is often not implemented, and 1033 almost never used; everyone uses TLS instead. For a more complete 1034 list of problems with DIGEST-MD5 which lead to the creation of SCRAM 1035 see [I-D.ietf-sasl-digest-to-historic]. 1037 The CRAM-MD5 SASL mechanism, while widely deployed has also some 1038 problems, in particular it is missing some modern SASL features such 1039 as support for internationalized usernames and passwords, support for 1040 passing of authorization identity, support for channel bindings. It 1041 also doesn't support server authentication. For a more complete list 1042 of problems with CRAM-MD5 see [I-D.ietf-sasl-crammd5-to-historic]. 1044 The PLAIN [RFC4616] SASL mechanism allows a malicious server or 1045 eavesdropper to impersonate the authenticating user to any other 1046 server for which the user has the same password. It also sends the 1047 password in the clear over the network, unless TLS is used. Server 1048 authentication is not supported. 1050 Appendix B. Design Motivations 1052 The following design goals shaped this document. Note that some of 1053 the goals have changed since the initial version of the document. 1055 o The SASL mechanism has all modern SASL features: support for 1056 internationalized usernames and passwords, support for passing of 1057 authorization identity, support for channel bindings. 1059 o The protocol supports mutual authentication. 1061 o The authentication information stored in the authentication 1062 database is not sufficient by itself to impersonate the client. 1064 o The server does not gain the ability to impersonate the client to 1065 other servers (with an exception for server-authorized proxies), 1066 unless such other servers allow SCRAM authentication and use the 1067 same salt and iteration count for the user. 1069 o The mechanism is extensible, but [hopefully] not overengineered in 1070 this respect. 1072 o Easier to implement than DIGEST-MD5 in both clients and servers. 1074 Appendix C. Internet-Draft Change History 1076 (RFC Editor: Please delete this section and all subsections.) 1078 Changes since -10 1080 o Converted the source for this I-D to XML. 1082 o Added text to make SCRAM compliant with the new GS2 design. 1084 o Added text on channel binding negotiation. 1086 o Added text on channel binding, including a reference to RFC5056. 1088 o Added text on SCRAM as a GSS-API mechanism. This noted as not 1089 relevant to SASL-only implementors -- the normative references for 1090 SCRAM as a GSS-API mechanism are segregated as well. 1092 Changes since -07 1094 o Updated References. 1096 o Clarified purpose of the m= attribute. 1098 o Fixed a problem with authentication/authorization identity's ABNF 1099 not allowing for some characters. 1101 o Updated ABNF for nonce to show client-generated and server- 1102 generated parts. 1104 o Only register SCRAM-SHA-1 with IANA and require explicit 1105 registrations of all other SCRAM- mechanisms. 1107 Changes since -06 1109 o Removed hash negotiation from SCRAM and turned it into a family of 1110 SASL mechanisms. 1112 o Start using "Hash Function Textual Names" IANA registry for SCRAM 1113 mechanism naming. 1115 o Fixed definition of Hi(str, salt, i) to be consistent with 1116 [RFC2898]. 1118 o Clarified extensibility of SCRAM: added m= attribute (for future 1119 mandatory extensions) and specified that all unrecognized 1120 attributes must be ignored. 1122 Changes since -05 1124 o Changed the mandatory to implement hash algorithm to SHA-1 (as per 1125 WG consensus). 1127 o Added text about use of SASLPrep for username canonicalization/ 1128 validation. 1130 o Clarified that authorization identity is canonicalized/verified 1131 according to SASL protocol profile. 1133 o Clarified that iteration count is per-user. 1135 o Clarified how clients select the authentication function. 1137 o Added IANA registration for the new mechanism. 1139 o Added missing normative references (UTF-8, SASLPrep). 1141 o Various editorial changes based on comments from Hallvard B 1142 Furuseth, Nico William and Simon Josefsson. 1144 Changes since -04 1146 o Update Base64 and Security Glossary references. 1148 o Add Formal Syntax section. 1150 o Don't bother with "v=". 1152 o Make MD5 mandatory to implement. Suggest i=128. 1154 Changes since -03 1156 o Seven years have passed, in which it became clear that DIGEST-MD5 1157 suffered from unacceptably bad interoperability, so SCRAM-MD5 is 1158 now back from the dead. 1160 o Be hash agnostic, so MD5 can be replaced more easily. 1162 o General simplification. 1164 12. References 1166 12.1. Normative References 1168 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 1169 Hashing for Message Authentication", RFC 2104, 1170 February 1997. 1172 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1173 Requirement Levels", BCP 14, RFC 2119, March 1997. 1175 [RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 1176 (SHA1)", RFC 3174, September 2001. 1178 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 1179 Internationalized Strings ("stringprep")", RFC 3454, 1180 December 2002. 1182 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 1183 10646", STD 63, RFC 3629, November 2003. 1185 [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names 1186 and Passwords", RFC 4013, February 2005. 1188 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 1189 Security Layer (SASL)", RFC 4422, June 2006. 1191 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 1192 Encodings", RFC 4648, October 2006. 1194 [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure 1195 Channels", RFC 5056, November 2007. 1197 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1198 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1200 12.2. Normative References for GSS-API implementors 1202 [I-D.ietf-sasl-gs2] 1203 Josefsson, S. and N. Williams, "Using GSS-API Mechanisms 1204 in SASL: The GS2 Mechanism Family", draft-ietf-sasl-gs2-12 1205 (work in progress), April 2009. 1207 [RFC2743] Linn, J., "Generic Security Service Application Program 1208 Interface Version 2, Update 1", RFC 2743, January 2000. 1210 [RFC3961] Raeburn, K., "Encryption and Checksum Specifications for 1211 Kerberos 5", RFC 3961, February 2005. 1213 [RFC3962] Raeburn, K., "Advanced Encryption Standard (AES) 1214 Encryption for Kerberos 5", RFC 3962, February 2005. 1216 [RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos 1217 Version 5 Generic Security Service Application Program 1218 Interface (GSS-API) Mechanism: Version 2", RFC 4121, 1219 July 2005. 1221 [RFC4401] Williams, N., "A Pseudo-Random Function (PRF) API 1222 Extension for the Generic Security Service Application 1223 Program Interface (GSS-API)", RFC 4401, February 2006. 1225 [RFC4402] Williams, N., "A Pseudo-Random Function (PRF) for the 1226 Kerberos V Generic Security Service Application Program 1227 Interface (GSS-API) Mechanism", RFC 4402, February 2006. 1229 [tls-unique] 1230 Zhu, L., "Registration of TLS unique channel binding 1231 (generic)", IANA http://www.iana.org/assignments/ 1232 channel-binding-types/tls-unique, July 2008. 1234 12.3. Informative References 1236 [I-D.altman-tls-channel-bindings] 1237 Altman, J., Williams, N., and L. Zhu, "Channel Bindings 1238 for TLS", draft-altman-tls-channel-bindings-07 (work in 1239 progress), October 2009. 1241 [I-D.ietf-sasl-crammd5-to-historic] 1242 Zeilenga, K., "CRAM-MD5 to Historic", 1243 draft-ietf-sasl-crammd5-to-historic-00 (work in progress), 1244 November 2008. 1246 [I-D.ietf-sasl-digest-to-historic] 1247 Melnikov, A., "Moving DIGEST-MD5 to Historic", 1248 draft-ietf-sasl-digest-to-historic-00 (work in progress), 1249 July 2008. 1251 [I-D.melnikov-sasl-scram-ldap] 1252 Melnikov, A., "LDAP schema for storing SCRAM secrets", 1253 draft-melnikov-sasl-scram-ldap-02 (work in progress), 1254 July 2009. 1256 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 1257 "Remote Authentication Dial In User Service (RADIUS)", 1258 RFC 2865, June 2000. 1260 [RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography 1261 Specification Version 2.0", RFC 2898, September 2000. 1263 [RFC2945] Wu, T., "The SRP Authentication and Key Exchange System", 1264 RFC 2945, September 2000. 1266 [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 1267 Requirements for Security", BCP 106, RFC 4086, June 2005. 1269 [RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol 1270 (LDAP): Technical Specification Road Map", RFC 4510, 1271 June 2006. 1273 [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and 1274 Security Layer (SASL) Mechanism", RFC 4616, August 2006. 1276 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 1277 RFC 4949, August 2007. 1279 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1280 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1281 May 2008. 1283 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1284 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1286 [tls-server-end-point] 1287 Zhu, L., "Registration of TLS server end-point channel 1288 bindings", IANA http://www.iana.org/assignments/ 1289 channel-binding-types/tls-server-end-point, July 2008. 1291 Authors' Addresses 1293 Abhijit Menon-Sen 1294 Oryx Mail Systems GmbH 1296 Email: ams@oryx.com 1298 Alexey Melnikov 1299 Isode Ltd 1301 Email: Alexey.Melnikov@isode.com 1303 Chris Newman 1304 Sun Microsystems 1305 1050 Lakes Drive 1306 West Covina, CA 91790 1307 USA 1309 Email: chris.newman@sun.com 1311 Nicolas Williams 1312 Sun Microsystems 1313 5300 Riata Trace Ct 1314 Austin, TX 78727 1315 USA 1317 Email: Nicolas.Williams@sun.com