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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 10, 2010 Isode Ltd 6 C. Newman 7 N. Williams 8 Sun Microsystems 9 October 7, 2009 11 Salted Challenge Response (SCRAM) SASL and GSS-API Mechanism 12 draft-ietf-sasl-scram-09.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 10, 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 . . . . . . . . . . . . . 22 85 8.1. GSS-API Principal Name Types for SCRAM . . . . . . . . 22 86 8.2. GSS-API Per-Message Tokens for SCRAM . . . . . . . . . 22 87 8.3. GSS_Pseudo_random() for SCRAM . . . . . . . . . . . . 23 88 9. Security Considerations . . . . . . . . . . . . . . . 24 89 10. IANA Considerations . . . . . . . . . . . . . . . . . 26 90 11. Acknowledgements . . . . . . . . . . . . . . . . . . . 28 91 Appendix A. Other Authentication Mechanisms . . . . . . . . . . . 29 92 Appendix B. Design Motivations . . . . . . . . . . . . . . . . . . 30 93 Appendix C. Internet-Draft Change History . . . . . . . . . . . . 31 94 12. References . . . . . . . . . . . . . . . . . . . . . . 33 95 12.1. Normative References . . . . . . . . . . . . . . . . . 33 96 12.2. Normative References for GSS-API implementors . . . . 33 97 12.3. Informative References . . . . . . . . . . . . . . . . 34 98 Authors' Addresses . . . . . . . . . . . . . . . . . . 36 100 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 a Unicode normalization algorithm to a UTF-8 170 [RFC3629] encoded "str". The resulting string is also in UTF-8. 171 Implementations SHOULD use the SASLPrep profile [RFC4013] of the 172 "stringprep" algorithm [RFC3454] as the normalization algorithm. 173 When applying SASLPrep, "str" is treated as a "stored strings", 174 which means that unassigned Unicode codepoints are prohibited (see 175 Section 7 of [RFC3454]). 177 o HMAC(key, str): Apply the HMAC keyed hash algorithm (defined in 178 [RFC2104]) using the octet string represented by "key" as the key 179 and the octet string "str" as the input string. The size of the 180 result is the hash result size for the hash function in use. For 181 example, it is 20 octets for SHA-1 (see [RFC3174]). 183 o H(str): Apply the cryptographic hash function to the octet string 184 "str", producing an octet string as a result. The size of the 185 result depends on the hash result size for the hash function in 186 use. 188 o XOR: Apply the exclusive-or operation to combine the octet string 189 on the left of this operator with the octet string on the right of 190 this operator. The length of the output and each of the two 191 inputs will be the same for this use. 193 o Hi(str, salt, i): 195 U0 := HMAC(str, salt + INT(1)) 196 U1 := HMAC(str, U0) 197 U2 := HMAC(str, U1) 198 ... 199 Ui-1 := HMAC(str, Ui-2) 200 Ui := HMAC(str, Ui-1) 202 Hi := U0 XOR U1 XOR U2 XOR ... XOR Ui 204 where "i" is the iteration count, "+" is the string concatenation 205 operator and INT(g) is a four-octet encoding of the integer g, 206 most significant octet first. 208 Hi() is, essentially, PBKDF2 [RFC2898] with HMAC() as the PRF and 209 with dkLen == output length of HMAC() == output length of H(). 211 2. Introduction 213 This specification describes a family of authentication mechanisms 214 called the Salted Challenge Response Authentication Mechanism (SCRAM) 215 which addresses the requirements necessary to deploy a challenge- 216 response mechanism more widely than past attempts (see Appendix A and 217 Appendix B). When used in combination with Transport Layer Security 218 (TLS, see [RFC5246]) or an equivalent security layer, a mechanism 219 from this family could improve the status-quo for application 220 protocol authentication and provide a suitable choice for a 221 mandatory-to-implement mechanism for future application protocol 222 standards. 224 For simplicity, this family of mechanisms does not presently include 225 negotiation of a security layer [RFC4422]. It is intended to be used 226 with an external security layer such as that provided by TLS or SSH, 227 with optional channel binding [RFC5056] to the external security 228 layer. 230 SCRAM is specified herein as a pure Simple Authentication and 231 Security Layer (SASL) [RFC4422] mechanism, but it conforms to the new 232 bridge between SASL and the Generic Security Services Application 233 Programming Interface (GSS-API) called "GS2" [I-D.ietf-sasl-gs2]. 234 This means that this document defines both, a SASL mechanism and a 235 GSS-API mechanism. 237 SCRAM provides the following protocol features: 239 o The authentication information stored in the authentication 240 database is not sufficient by itself to impersonate the client. 241 The information is salted to prevent a pre-stored dictionary 242 attack if the database is stolen. 244 o The server does not gain the ability to impersonate the client to 245 other servers (with an exception for server-authorized proxies). 247 o The mechanism permits the use of a server-authorized proxy without 248 requiring that proxy to have super-user rights with the back-end 249 server. 251 o Mutual authentication is supported, but only the client is named 252 (i.e., the server has no name). 254 o When used as a SASL mechanism, SCRAM is capable of transporting 255 authorization identities (see [RFC4422], Section 2) from the 256 client to the server. 258 A separate document defines a standard LDAPv3 [RFC4510] attribute 259 that enables storage of the SCRAM authentication information in LDAP. 260 See [I-D.melnikov-sasl-scram-ldap]. 262 For an in-depth discussion of why other challenge response mechanisms 263 are not considered sufficient, see appendix A. For more information 264 about the motivations behind the design of this mechanism, see 265 appendix B. 267 3. SCRAM Algorithm Overview 269 The following is a description of a full, uncompressed SASL SCRAM 270 authentication exchange. Nothing in SCRAM prevents either sending 271 the client-first message with the SASL authentication request defined 272 by an application protocol ("initial client response"), nor sending 273 the server-final message as additional data of the SASL outcome of 274 authentication exchange defined by an application protocol. See 275 [RFC4422] for more details. 277 Note that this section omits some details, such as client and server 278 nonces. See Section 5 for more details. 280 To begin with, the SCRAM client is in possession of a username and 281 password (*) (or a ClientKey/ServerKey, or SaltedPassword). It sends 282 the username to the server, which retrieves the corresponding 283 authentication information, i.e. a salt, StoredKey, ServerKey and the 284 iteration count i. (Note that a server implementation may choose to 285 use the same iteration count for all accounts.) The server sends the 286 salt and the iteration count to the client, which then computes the 287 following values and sends a ClientProof to the server: 289 (*) - Note that both the username and the password MUST be encoded in 290 UTF-8 [RFC3629]. 292 Informative Note: Implementors are encouraged to create test cases 293 that use both username passwords with non-ASCII characters. In 294 particular, it's useful to test characters whose "Unicode 295 Normalization Form C" and "Unicode Normalization Form KC" are 296 different. Some examples of such characters include Vulgar Fraction 297 One Half (U+00BD) and Acute Accent (U+00B4). 299 SaltedPassword := Hi(Normalize(password), salt, i) 300 ClientKey := HMAC(SaltedPassword, "Client Key") 301 StoredKey := H(ClientKey) 302 AuthMessage := client-first-message-bare + "," + 303 server-first-message + "," + 304 client-final-message-without-proof 305 ClientSignature := HMAC(StoredKey, AuthMessage) 306 ClientProof := ClientKey XOR ClientSignature 307 ServerKey := HMAC(SaltedPassword, "Server Key") 308 ServerSignature := HMAC(ServerKey, AuthMessage) 310 The server authenticates the client by computing the ClientSignature, 311 exclusive-ORing that with the ClientProof to recover the ClientKey 312 and verifying the correctness of the ClientKey by applying the hash 313 function and comparing the result to the StoredKey. If the ClientKey 314 is correct, this proves that the client has access to the user's 315 password. 317 Similarly, the client authenticates the server by computing the 318 ServerSignature and comparing it to the value sent by the server. If 319 the two are equal, it proves that the server had access to the user's 320 ServerKey. 322 The AuthMessage is computed by concatenating messages from the 323 authentication exchange. The format of these messages is defined in 324 Section 7. 326 4. SCRAM Mechanism Names 328 A SCRAM mechanism name is a string "SCRAM-" followed by the 329 uppercased name of the underlying hash function taken from the IANA 330 "Hash Function Textual Names" registry (see http://www.iana.org), 331 optionally followed by the suffix "-PLUS" (see below). Note that 332 SASL mechanism names are limited to 20 characters, which means that 333 only hash function names with lengths shorter or equal to 9 334 characters (20-length("SCRAM-")-length("-PLUS") can be used. For 335 cases when the underlying hash function name is longer than 9 336 characters, an alternative 9 character (or shorter) name can be used 337 to construct the corresponding SCRAM mechanism name, as long as this 338 alternative name doesn't conflict with any other hash function name 339 from the IANA "Hash Function Textual Names" registry. In order to 340 prevent future conflict, such alternative name SHOULD be registered 341 in the IANA "Hash Function Textual Names" registry. 343 For interoperability, all SCRAM clients and servers MUST implement 344 the SCRAM-SHA-1 authentication mechanism, i.e. an authentication 345 mechanism from the SCRAM family that uses the SHA-1 hash function as 346 defined in [RFC3174]. 348 The "-PLUS" suffix is used only when the server supports channel 349 binding to the external channel. If the server supports channel 350 binding, it will advertise both the "bare" and "plus" versions of 351 whatever mechanisms it supports (e.g., if the server supports only 352 SCRAM with SHA-1 then it will advertise support for both SCRAM-SHA-1 353 and SCRAM-SHA-1-PLUS); if the server does not support channel 354 binding, then it will advertise only the "bare" version of the 355 mechanism (e.g., only SCRAM-SHA-1). The "-PLUS" exists to allow 356 negotiation of the use of channel binding. See Section 6. 358 5. SCRAM Authentication Exchange 360 SCRAM is a SASL mechanism whose client response and server challenge 361 messages are text-based messages containing one or more attribute- 362 value pairs separated by commas. Each attribute has a one-letter 363 name. The messages and their attributes are described in 364 Section 5.1, and defined in Section 7. 366 SCRAM is a client-first SASL mechanism (See [RFC4422], Section 5, 367 item 2a), and returns additional data together with a server's 368 indication of a successful outcome. 370 This is a simple example of a SCRAM-SHA-1 authentication exchange 371 when the client doesn't support channel bindings: 373 C: n,,n=Chris Newman,r=ClientNonce 374 S: r=ClientNonceServerNonce,s=PxR/wv+epq,i=128 375 C: c=biwsCg==,r=ClientNonceServerNonce,p=WxPv/siO5l+qxN4 376 S: v=WxPv/siO5l+qxN4 378 [[anchor5: Note that the all hashes above are fake and will be fixed 379 during AUTH48.]] 381 With channel-binding data sent by the client this might look like 382 this (see [tls-server-end-point] for the definition of tls-server- 383 end-point TLS channel binding): 385 C: p=tls-server-end-point,,n=Chris Newman,r=ClientNonce 386 S: r=ClientNonceServerNonce,s=PxR/wv+epq,i=128 387 C: c=cD10bHMtc2VydmVyLWVuZC1wb2ludCwsy1hFtXOnZ+ySrQM6srFp 388 l/77uqvtxrg7nBY1BetEr/g=,r=ClientNonceServerNonce,p=Wx 389 Pv/siO5l+qxN4 390 S: v=WxPv/siO5l+qxN4 392 [[anchor6: Note that all hashes above are fake and will be fixed 393 during AUTH48.]] 395 First, the client sends the "client-first-message" containing: 397 o a GS2 header consisting of a flag indicating whether channel 398 binding is supported-but-not-used, not supported, or used, and an 399 optional SASL authorization identity; 401 o SCRAM username and a random, unique nonce attributes. 403 Note that the client's first message will always start with "n", "y" 404 or "p", otherwise the message is invalid and authentication MUST 405 fail. This is important, as it allows for GS2 extensibility (e.g., 406 to add support for security layers). 408 In response, the server sends a "server-first-message" containing the 409 user's iteration count i, the user's salt, and appends its own nonce 410 to the client-specified one. 412 The client then responds by sending "client-final-message" with the 413 same nonce and a ClientProof computed using the selected hash 414 function as explained earlier. 416 The server verifies the nonce and the proof, verifies that the 417 authorization identity (if supplied by the client in the first 418 message) is authorized to act as the authentication identity, and, 419 finally, it responds with a "server-final-message", concluding the 420 authentication exchange. 422 The client then authenticates the server by computing the 423 ServerSignature and comparing it to the value sent by the server. If 424 the two are different, the client MUST consider the authentication 425 exchange to be unsuccessful and it might have to drop the connection. 427 5.1. SCRAM Attributes 429 This section describes the permissible attributes, their use, and the 430 format of their values. All attribute names are single US-ASCII 431 letters and are case-sensitive. 433 Note that the order of attributes in client or server messages is 434 fixed, with the exception of extension attributes (described by the 435 "extensions" ABNF production), which can appear in any order in the 436 designated positions. See the ABNF section for authoritative 437 reference. 439 o a: This is an optional attribute, and is part of the GS2 440 [I-D.ietf-sasl-gs2] bridge between the GSS-API and SASL. This 441 attribute specifies an authorization identity. A client may 442 include it in its first message to the server if it wants to 443 authenticate as one user, but subsequently act as a different 444 user. This is typically used by an administrator to perform some 445 management task on behalf of another user, or by a proxy in some 446 situations. 448 Upon the receipt of this value the server verifies its 449 correctness according to the used SASL protocol profile. 450 Failed verification results in failed authentication exchange. 452 If this attribute is omitted (as it normally would be), the 453 authorization identity is assumed to be derived from the 454 username specified with the (required) "n" attribute. 456 The server always authenticates the user specified by the "n" 457 attribute. If the "a" attribute specifies a different user, 458 the server associates that identity with the connection after 459 successful authentication and authorization checks. 461 The syntax of this field is the same as that of the "n" field 462 with respect to quoting of '=' and ','. 464 o n: This attribute specifies the name of the user whose password is 465 used for authentication (a.k.a. "authentication identity" 466 [RFC4422]). A client MUST include it in its first message to the 467 server. If the "a" attribute is not specified (which would 468 normally be the case), this username is also the identity which 469 will be associated with the connection subsequent to 470 authentication and authorization. 472 Before sending the username to the server, the client SHOULD 473 prepare the username using the "SASLPrep" profile [RFC4013] of 474 the "stringprep" algorithm [RFC3454] treating it as a query 475 string (i.e., unassigned Unicode code points are allowed). If 476 the preparation of the username fails or results in an empty 477 string, the client SHOULD abort the authentication exchange 478 (*). 480 (*) An interactive client can request a repeated entry of the 481 username value. 483 Upon receipt of the username by the server, the server SHOULD 484 prepare it using the "SASLPrep" profile [RFC4013] of the 485 "stringprep" algorithm [RFC3454] treating it as a query string 486 (i.e., unassigned Unicode code points are allowed). If the 487 preparation of the username fails or results in an empty 488 string, the server SHOULD abort the authentication exchange. 489 Whether or not the server prepares the username using 490 "SASLPrep", it MUST use it as received in hash calculations. 492 The characters ',' or '=' in usernames are sent as '=2C' and 493 '=3D' respectively. If the server receives a username which 494 contains '=' not followed by either '2C' or '3D', then the 495 server MUST fail the authentication. 497 o m: This attribute is reserved for future extensibility. In this 498 version of SCRAM, its presence in a client or a server message 499 MUST cause authentication failure when the attribute is parsed by 500 the other end. 502 o r: This attribute specifies a sequence of random printable ASCII 503 characters excluding ',' which forms the nonce used as input to 504 the hash function. No quoting is applied to this string. As 505 described earlier, the client supplies an initial value in its 506 first message, and the server augments that value with its own 507 nonce in its first response. It is important that this value be 508 different for each authentication (see [RFC4086] for more details 509 on how to achieve this). The client MUST verify that the initial 510 part of the nonce used in subsequent messages is the same as the 511 nonce it initially specified. The server MUST verify that the 512 nonce sent by the client in the second message is the same as the 513 one sent by the server in its first message. 515 o c: This REQUIRED attribute specifies the base64-encoded GS2 header 516 and channel-binding data. It is sent by the client in its second 517 authentication message. The attribute data consist of: 519 * the GS2 header from the client's first message (recall that the 520 GS2 header contains a channel binding flag and an optional 521 authzid). This header is going to include channel binding type 522 prefix (see [RFC5056]), if and only if the client is using 523 channel binding; 525 * followed by the external channel's channel binding data, if and 526 only if the client is using channel binding. 528 o s: This attribute specifies the base64-encoded salt used by the 529 server for this user. It is sent by the server in its first 530 message to the client. 532 o i: This attribute specifies an iteration count for the selected 533 hash function and user, and MUST be sent by the server along with 534 the user's salt. 536 For SCRAM-SHA-1/SCRAM-SHA-1-PLUS SASL mechanism servers SHOULD 537 announce a hash iteration-count of at least 4096. Note that a 538 client implementation MAY cache ClientKey&ServerKey (or just 539 SaltedPassword) for later reauthentication to the same service, 540 as it is likely that the server is going to advertise the same 541 salt value upon reauthentication. This might be useful for 542 mobile clients where CPU usage is a concern. 544 o p: This attribute specifies a base64-encoded ClientProof. The 545 client computes this value as described in the overview and sends 546 it to the server. 548 o v: This attribute specifies a base64-encoded ServerSignature. It 549 is sent by the server in its final message, and is used by the 550 client to verify that the server has access to the user's 551 authentication information. This value is computed as explained 552 in the overview. 554 5.2. Compliance with SASL mechanism requirements 556 This section describes compliance with SASL mechanism requirements 557 specified in Section 5 of [RFC4422]. 559 1) "SCRAM-SHA-1" and "SCRAM-SHA-1-PLUS". 561 2a) SCRAM is a client-first mechanism. 563 2b) SCRAM sends additional data with success. 565 3) SCRAM is capable of transferring authorization identities from the 566 client to the server. 568 4) SCRAM does not offer any security layers (SCRAM offers channel 569 binding instead). 571 5) SCRAM has a hash protecting the authorization identity. 573 6. Channel Binding 575 SCRAM supports channel binding to external secure channels, such as 576 TLS. Clients and servers may or may not support channel binding, 577 therefore the use of channel binding is negotiable. SCRAM does not 578 provide security layers, however, therefore it is imperative that 579 SCRAM provide integrity protection for the negotiation of channel 580 binding. 582 Use of channel binding is negotiated as follows: 584 o Servers SHOULD advertise both non-PLUS (SCRAM-) and 585 the PLUS-variant (SCRAM--PLUS) SASL mechanism 586 names. If the server cannot support channel binding, it MAY 587 advertise only the non-PLUS variant. If the server would never 588 succeed authentication of the non-PLUS variant due to policy 589 reasons, it MAY advertise only the PLUS-variant. 591 o If the client negotiates mechanisms then the client MUST select 592 SCRAM--PLUS if offered by the server and the client 593 wants to select SCRAM with the given hash function. Otherwise 594 (the client does not negotiate mechanisms), if the client has no 595 prior knowledge about mechanisms supported by the server and 596 wasn't explicitly configured to use a particular variant of the 597 SCRAM mechanism, then it MUST select only SCRAM- 598 (not suffixed with "-PLUS"). 600 o If the client supports channel binding and the server appears to 601 support it (i.e., the client sees SCRAM--PLUS), or 602 if the client wishes to use channel binding but the client does 603 not negotiate mechanisms, then the client MUST set the GS2 channel 604 binding flag to "p" in order to indicate the channel binding type 605 it is using and it MUST include the channel binding data for the 606 external channel in the computation of the "c=" attribute (see 607 Section 5.1). 609 o If the client supports channel binding but the server does not 610 appear to (i.e., the client did not see SCRAM-- 611 PLUS) then the client MUST either fail authentication or it MUST 612 choose the non-PLUS mechanism and set the GS2 channel binding flag 613 to "y" and MUST NOT include channel binding data for the external 614 channel in the computation of the "c=" attribute (see 615 Section 5.1). 617 o If the client does not support channel binding then the client 618 MUST set the GS2 channel binding flag to "n" and MUST NOT include 619 channel binding data for the external channel in the computation 620 of the "c=" attribute (see Section 5.1). 622 o Upon receipt of the client first message the server checks the GS2 623 channel binding flag (gs2-cb-flag). 625 * If the flag is set to "y" and the server supports channel 626 binding the server MUST fail authentication. This is because 627 if the client sets the GS2 channel binding flag set to "y" then 628 the client must have believed that the server did not support 629 channel binding -- if the server did in fact support channel 630 binding then this is an indication that there has been a 631 downgrade attack (e.g., an attacker changed the server's 632 mechanism list to exclude the -PLUS suffixed SCRAM mechanism 633 name(s)). 635 * If the channel binding flag was "p" and the server does not 636 support the indicated channel binding type then the server MUST 637 fail authentication. 639 The server MUST always validate the client's "c=" field. The server 640 does this by constructing the value of the "c=" attribute and then 641 checking that it matches the client's c= attribute value. 643 For more discussions of channel bindings, and the syntax of the 644 channel binding data for various security protocols, see [RFC5056]. 646 6.1. Default Channel Binding 648 A default channel binding type agreement process for all SASL 649 application protocols that do not provide their own channel binding 650 type agreement is provided as follows. 652 'tls-unique' is the default channel binding type for any application 653 that doesn't specify one. 655 Servers MUST implement the "tls-unique" [tls-unique] 656 [I-D.altman-tls-channel-bindings] channel binding type, if they 657 implement any channel binding. Clients SHOULD implement the "tls- 658 unique" [tls-unique] [I-D.altman-tls-channel-bindings] channel 659 binding type, if they implement any channel binding. Clients and 660 servers SHOULD choose the highest- layer/innermost end-to-end TLS 661 channel as the channel to bind to. 663 Servers MUST choose the channel binding type indicated by the client, 664 or fail authentication if they don't support it. 666 7. Formal Syntax 668 The following syntax specification uses the Augmented Backus-Naur 669 Form (ABNF) notation as specified in [RFC5234]. "UTF8-2", "UTF8-3" 670 and "UTF8-4" non-terminal are defined in [RFC3629]. 672 ALPHA = 673 DIGIT = 674 UTF8-2 = 675 UTF8-3 = 676 UTF8-4 = 678 attr-val = ALPHA "=" value 679 ;; Generic syntax of any attribute sent 680 ;; by server or client 682 value = 1*value-char 684 value-safe-char = %x01-2B / %x2D-3C / %x3E-7F / 685 UTF8-2 / UTF8-3 / UTF8-4 686 ;; UTF8-char except NUL, "=", and ",". 688 value-char = value-safe-char / "=" 690 printable = %x21-2B / %x2D-7E 691 ;; Printable ASCII except ",". 692 ;; Note that any "printable" is also 693 ;; a valid "value". 695 base64-char = ALPHA / DIGIT / "/" / "+" 697 base64-4 = 4base64-char 699 base64-3 = 3base64-char "=" 701 base64-2 = 2base64-char "==" 703 base64 = *base64-4 [base64-3 / base64-2] 705 posit-number = %x31-39 *DIGIT 706 ;; A positive number 708 saslname = 1*(value-safe-char / "=2C" / "=3D") 709 ;; Conforms to 711 authzid = "a=" saslname 712 ;; Protocol specific. 714 cb-name = 1*(ALPHA / DIGIT / "." / "-") 715 ;; See RFC 5056 section 7. 716 ;; E.g. "tls-server-end-point" or 717 ;; "tls-unique" 719 gs2-cbind-flag = "p=" cb-name / "n" / "y" 720 ;; "n" -> client doesn't support channel binding 721 ;; "y" -> client does support channel binding 722 ;; but thinks the server does not. 723 ;; "p" -> client requires channel binding. 724 ;; The selected channel binding follows "p=". 726 gs2-header = gs2-cbind-flag "," [ authzid ] "," 727 ;; GS2 header for SCRAM 728 ;; (the actual GS2 header includes an optional 729 ;; flag to indicate that the GSS mechanism is not 730 ;; "standard" but since SCRAM is "standard" we 731 ;; don't include that flag). 733 username = "n=" saslname 734 ;; Usernames are prepared using SASLPrep. 736 reserved-mext = "m=" 1*(value-char) 737 ;; Reserved for signalling mandatory extensions. 738 ;; The exact syntax will be defined in 739 ;; the future. 741 channel-binding = "c=" base64 742 ;; base64 encoding of cbind-input 744 proof = "p=" base64 746 nonce = "r=" c-nonce [s-nonce] 747 ;; Second part provided by server. 749 c-nonce = printable 751 s-nonce = printable 753 salt = "s=" base64 755 verifier = "v=" base64 756 ;; base-64 encoded ServerSignature. 758 iteration-count = "i=" posit-number 759 ;; A positive number 761 client-first-message-bare = 763 [reserved-mext ","] 764 username "," nonce ["," extensions] 766 client-first-message = 767 gs2-header client-first-message-bare 769 server-first-message = 770 [reserved-mext ","] nonce "," salt "," 771 iteration-count ["," extensions] 773 client-final-message-without-proof = 774 channel-binding "," nonce ["," 775 extensions] 777 client-final-message = 778 client-final-message-without-proof "," proof 780 gss-server-error = "e=" value 781 server-final-message = gss-server-error / 782 verifier ["," extensions] 783 ;; The error message is only for the GSS-API 784 ;; form of SCRAM, and it is OPTIONAL to 785 ;; implement it. 787 extensions = attr-val *("," attr-val) 788 ;; All extensions are optional, 789 ;; i.e. unrecognized attributes 790 ;; not defined in this document 791 ;; MUST be ignored. 793 cbind-data = 1*OCTET 795 cbind-input = gs2-header [ cbind-data ] 796 ;; cbind-data MUST be present for 797 ;; gs2-cbind-flag of "p" and MUST be absent 798 ;; for "y" or "n". 800 8. SCRAM as a GSS-API Mechanism 802 This section and its sub-sections and all normative references of it 803 not referenced elsewhere in this document are INFORMATIONAL for SASL 804 implementors, but they are NORMATIVE for GSS-API implementors. 806 SCRAM is actually also GSS-API mechanism. The messages are the same, 807 but a) the GS2 header on the client's first message and channel 808 binding data is excluded when SCRAM is used as a GSS-API mechanism, 809 and b) the RFC2743 section 3.1 initial context token header is 810 prefixed to the client's first authentication message (context 811 token). 813 The GSS-API mechanism OID for SCRAM-SHA-1 is (see Section 10). 815 8.1. GSS-API Principal Name Types for SCRAM 817 SCRAM does not name acceptors. Therefore only GSS_C_NO_NAME and 818 names of type GSS_C_NT_ANONYMOUS shall be allowed as the target name 819 input of GSS_Init_sec_context() when using a SCRAM mechanism. 821 SCRAM supports only a single name type for initiators: 822 GSS_C_NT_USER_NAME. GSS_C_NT_USER_NAME is the default name type for 823 SCRAM. 825 There is no name canonicalization procedure for SCRAM beyond applying 826 SASLprep as described in Section 5.1. 828 The query, display and exported name syntax for SCRAM principal names 829 is the same: there is no syntax -- SCRAM principal names are free- 830 form. (The exported name token does, of course, conform to [RFC2743] 831 section 3.2, but the "NAME" part of the token is just a SCRAM user 832 name.) 834 8.2. GSS-API Per-Message Tokens for SCRAM 836 The per-message tokens for SCRAM as a GSS-API mechanism SHALL be the 837 same as those for the Kerberos V GSS-API mechanism [RFC4121] (see 838 Section 4.2 and sub-sections), using the Kerberos V "aes128-cts-hmac- 839 sha1-96" enctype [RFC3962]. 841 The 128-bit session "protocol key" SHALL be derived by using the 842 least significant (right-most) 128 bits of HMAC(StoredKey, "GSS-API 843 session key" || ClientKey || AuthMessage). "Specific keys" are then 844 derived as usual as described in Section 2 of [RFC4121], [RFC3961] 845 and [RFC3962]. 847 The terms "protocol key" and "specific key" are Kerberos V5 terms 849 [RFC3961]. 851 SCRAM does support PROT_READY, and is PROT_READY on the initiator 852 side first upon receipt of the server's reply to the initial security 853 context token. 855 8.3. GSS_Pseudo_random() for SCRAM 857 The GSS_Pseudo_random() [RFC4401] for SCRAM SHALL be the same as for 858 the Kerberos V GSS-API mechanism [RFC4402]. There is no acceptor- 859 asserted sub-session key for SCRAM, thus GSS_C_PRF_KEY_FULL and 860 GSS_C_PRF_KEY_PARTIAL are equivalent for SCRAM's GSS_Pseudo_random(). 861 The protocol key to be used for the GSS_Pseudo_random() SHALL be the 862 same as the key defined in Section 8.2. 864 9. Security Considerations 866 If the authentication exchange is performed without a strong security 867 layer (such as TLS with data confidentiality), then a passive 868 eavesdropper can gain sufficient information to mount an offline 869 dictionary or brute-force attack which can be used to recover the 870 user's password. The amount of time necessary for this attack 871 depends on the cryptographic hash function selected, the strength of 872 the password and the iteration count supplied by the server. An 873 external security layer with strong encryption will prevent this 874 attack. 876 If the external security layer used to protect the SCRAM exchange 877 uses an anonymous key exchange, then the SCRAM channel binding 878 mechanism can be used to detect a man-in-the-middle attack on the 879 security layer and cause the authentication to fail as a result. 880 However, the man-in-the-middle attacker will have gained sufficient 881 information to mount an offline dictionary or brute-force attack. 882 For this reason, SCRAM allows to increase the iteration count over 883 time. (Note that a server that is only in posession of "StoredKey" 884 and "ServerKey" can't automatic increase the iteration count upon 885 successful authentication. Such increase would require resetting 886 user's password.) 888 If the authentication information is stolen from the authentication 889 database, then an offline dictionary or brute-force attack can be 890 used to recover the user's password. The use of salt mitigates this 891 attack somewhat by requiring a separate attack on each password. 892 Authentication mechanisms which protect against this attack are 893 available (e.g., the EKE class of mechanisms). RFC 2945 [RFC2945] is 894 an example of such technology. The WG selected not to use EKE like 895 mechanisms as basis for SCRAM. 897 If an attacker obtains the authentication information from the 898 authentication repository and either eavesdrops on one authentication 899 exchange or impersonates a server, the attacker gains the ability to 900 impersonate that user to all servers providing SCRAM access using the 901 same hash function, password, iteration count and salt. For this 902 reason, it is important to use randomly-generated salt values. 904 SCRAM does not negotiate a hash function to use. Hash function 905 negotiation is left to the SASL mechanism negotiation. It is 906 important that clients be able to sort a locally available list of 907 mechanisms by preference so that the client may pick the most 908 preferred of a server's advertised mechanism list. This preference 909 order is not specified here as it is a local matter. The preference 910 order should include objective and subjective notions of mechanism 911 cryptographic strength (e.g., SCRAM with a successor to SHA-1 may be 912 preferred over SCRAM with SHA-1). 914 Note that to protect the SASL mechanism negotiation applications 915 normally must list the server mechs twice: once before and once after 916 authentication, the latter using security layers. Since SCRAM does 917 not provide security layers the only ways to protect the mechanism 918 negotiation are: a) use channel binding to an external channel, or b) 919 use an external channel that authenticates a user-provided server 920 name. 922 SCRAM does not protect against downgrade attacks of channel binding 923 types. The complexities of negotiation a channel binding type, and 924 handling down-grade attacks in that negotiation, was intentionally 925 left out of scope for this document. 927 A hostile server can perform a computational denial-of-service attack 928 on clients by sending a big iteration count value. 930 See [RFC4086] for more information about generating randomness. 932 10. IANA Considerations 934 IANA is requested to add the following family of SASL mechanisms to 935 the SASL Mechanism registry established by [RFC4422]: 937 To: iana@iana.org 938 Subject: Registration of a new SASL family SCRAM 940 SASL mechanism name (or prefix for the family): SCRAM-* 941 Security considerations: Section 7 of [RFCXXXX] 942 Published specification (optional, recommended): [RFCXXXX] 943 Person & email address to contact for further information: 944 IETF SASL WG 945 Intended usage: COMMON 946 Owner/Change controller: IESG 947 Note: Members of this family must be explicitly registered 948 using the "IETF Review" [RFC5226] registration procedure. 949 Reviews must be requested on the SASL WG mailing list. 951 "IETF Review" [RFC5226] registration procedure MUST be used for 952 registering new mechanisms in this family. The SASL mailing list 953 (or a successor designated by the responsible 954 Security AD) MUST be used for soliciting reviews on such 955 registrations. 957 Note to future SCRAM- mechanism designers: each new SCRAM- SASL 958 mechanism MUST be explicitly registered with IANA and MUST comply 959 with SCRAM- mechanism naming convention defined in Section 4 of this 960 document. 962 IANA is requested to add the following entries to the SASL Mechanism 963 registry established by [RFC4422]: 965 To: iana@iana.org 966 Subject: Registration of a new SASL mechanism SCRAM-SHA-1 968 SASL mechanism name (or prefix for the family): SCRAM-SHA-1 969 Security considerations: Section 7 of [RFCXXXX] 970 Published specification (optional, recommended): [RFCXXXX] 971 Person & email address to contact for further information: 972 IETF SASL WG 973 Intended usage: COMMON 974 Owner/Change controller: IESG 975 Note: 977 To: iana@iana.org 978 Subject: Registration of a new SASL mechanism SCRAM-SHA-1-PLUS 980 SASL mechanism name (or prefix for the family): SCRAM-SHA-1-PLUS 981 Security considerations: Section 7 of [RFCXXXX] 982 Published specification (optional, recommended): [RFCXXXX] 983 Person & email address to contact for further information: 984 IETF SASL WG 985 Intended usage: COMMON 986 Owner/Change controller: IESG 987 Note: 989 This document also requests IANA to assign a GSS-API mechanism OID 990 for SCRAM-SHA-1 from the iso.org.dod.internet.security.mechanisms 991 prefix (see "SMI Security for Mechanism Codes" registry). 993 11. Acknowledgements 995 This document benefited from discussions on the SASL WG mailing list. 996 The authors would like to specially thank Dave Cridland, Simon 997 Josefsson, Jeffrey Hutzelman, Kurt Zeilenga, Pasi Eronen, Ben 998 Campbell and Peter Saint-Andre for their contributions to this 999 document. 1001 Appendix A. Other Authentication Mechanisms 1003 The DIGEST-MD5 [I-D.ietf-sasl-digest-to-historic] mechanism has 1004 proved to be too complex to implement and test, and thus has poor 1005 interoperability. The security layer is often not implemented, and 1006 almost never used; everyone uses TLS instead. For a more complete 1007 list of problems with DIGEST-MD5 which lead to the creation of SCRAM 1008 see [I-D.ietf-sasl-digest-to-historic]. 1010 The CRAM-MD5 SASL mechanism, while widely deployed has also some 1011 problems, in particular it is missing some modern SASL features such 1012 as support for internationalized usernames and passwords, support for 1013 passing of authorization identity, support for channel bindings. It 1014 also doesn't support server authentication. For a more complete list 1015 of problems with CRAM-MD5 see [I-D.ietf-sasl-crammd5-to-historic]. 1017 The PLAIN [RFC4616] SASL mechanism allows a malicious server or 1018 eavesdropper to impersonate the authenticating user to any other 1019 server for which the user has the same password. It also sends the 1020 password in the clear over the network, unless TLS is used. Server 1021 authentication is not supported. 1023 Appendix B. Design Motivations 1025 The following design goals shaped this document. Note that some of 1026 the goals have changed since the initial version of the document. 1028 o The SASL mechanism has all modern SASL features: support for 1029 internationalized usernames and passwords, support for passing of 1030 authorization identity, support for channel bindings. 1032 o The protocol supports mutual authentication. 1034 o The authentication information stored in the authentication 1035 database is not sufficient by itself to impersonate the client. 1037 o The server does not gain the ability to impersonate the client to 1038 other servers (with an exception for server-authorized proxies), 1039 unless such other servers allow SCRAM authentication and use the 1040 same salt and iteration count for the user. 1042 o The mechanism is extensible, but [hopefully] not overengineered in 1043 this respect. 1045 o Easier to implement than DIGEST-MD5 in both clients and servers. 1047 Appendix C. Internet-Draft Change History 1049 (RFC Editor: Please delete this section and all subsections.) 1051 Changes since -10 1053 o Converted the source for this I-D to XML. 1055 o Added text to make SCRAM compliant with the new GS2 design. 1057 o Added text on channel binding negotiation. 1059 o Added text on channel binding, including a reference to RFC5056. 1061 o Added text on SCRAM as a GSS-API mechanism. This noted as not 1062 relevant to SASL-only implementors -- the normative references for 1063 SCRAM as a GSS-API mechanism are segregated as well. 1065 Changes since -07 1067 o Updated References. 1069 o Clarified purpose of the m= attribute. 1071 o Fixed a problem with authentication/authorization identity's ABNF 1072 not allowing for some characters. 1074 o Updated ABNF for nonce to show client-generated and server- 1075 generated parts. 1077 o Only register SCRAM-SHA-1 with IANA and require explicit 1078 registrations of all other SCRAM- mechanisms. 1080 Changes since -06 1082 o Removed hash negotiation from SCRAM and turned it into a family of 1083 SASL mechanisms. 1085 o Start using "Hash Function Textual Names" IANA registry for SCRAM 1086 mechanism naming. 1088 o Fixed definition of Hi(str, salt, i) to be consistent with 1089 [RFC2898]. 1091 o Clarified extensibility of SCRAM: added m= attribute (for future 1092 mandatory extensions) and specified that all unrecognized 1093 attributes must be ignored. 1095 Changes since -05 1097 o Changed the mandatory to implement hash algorithm to SHA-1 (as per 1098 WG consensus). 1100 o Added text about use of SASLPrep for username canonicalization/ 1101 validation. 1103 o Clarified that authorization identity is canonicalized/verified 1104 according to SASL protocol profile. 1106 o Clarified that iteration count is per-user. 1108 o Clarified how clients select the authentication function. 1110 o Added IANA registration for the new mechanism. 1112 o Added missing normative references (UTF-8, SASLPrep). 1114 o Various editorial changes based on comments from Hallvard B 1115 Furuseth, Nico William and Simon Josefsson. 1117 Changes since -04 1119 o Update Base64 and Security Glossary references. 1121 o Add Formal Syntax section. 1123 o Don't bother with "v=". 1125 o Make MD5 mandatory to implement. Suggest i=128. 1127 Changes since -03 1129 o Seven years have passed, in which it became clear that DIGEST-MD5 1130 suffered from unacceptably bad interoperability, so SCRAM-MD5 is 1131 now back from the dead. 1133 o Be hash agnostic, so MD5 can be replaced more easily. 1135 o General simplification. 1137 12. References 1139 12.1. Normative References 1141 [RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed- 1142 Hashing for Message Authentication", RFC 2104, 1143 February 1997. 1145 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1146 Requirement Levels", BCP 14, RFC 2119, March 1997. 1148 [RFC3174] Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1 1149 (SHA1)", RFC 3174, September 2001. 1151 [RFC3454] Hoffman, P. and M. Blanchet, "Preparation of 1152 Internationalized Strings ("stringprep")", RFC 3454, 1153 December 2002. 1155 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 1156 10646", STD 63, RFC 3629, November 2003. 1158 [RFC4013] Zeilenga, K., "SASLprep: Stringprep Profile for User Names 1159 and Passwords", RFC 4013, February 2005. 1161 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 1162 Security Layer (SASL)", RFC 4422, June 2006. 1164 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 1165 Encodings", RFC 4648, October 2006. 1167 [RFC5056] Williams, N., "On the Use of Channel Bindings to Secure 1168 Channels", RFC 5056, November 2007. 1170 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 1171 Specifications: ABNF", STD 68, RFC 5234, January 2008. 1173 12.2. Normative References for GSS-API implementors 1175 [I-D.ietf-sasl-gs2] 1176 Josefsson, S. and N. Williams, "Using GSS-API Mechanisms 1177 in SASL: The GS2 Mechanism Family", draft-ietf-sasl-gs2-12 1178 (work in progress), April 2009. 1180 [RFC2743] Linn, J., "Generic Security Service Application Program 1181 Interface Version 2, Update 1", RFC 2743, January 2000. 1183 [RFC3961] Raeburn, K., "Encryption and Checksum Specifications for 1184 Kerberos 5", RFC 3961, February 2005. 1186 [RFC3962] Raeburn, K., "Advanced Encryption Standard (AES) 1187 Encryption for Kerberos 5", RFC 3962, February 2005. 1189 [RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos 1190 Version 5 Generic Security Service Application Program 1191 Interface (GSS-API) Mechanism: Version 2", RFC 4121, 1192 July 2005. 1194 [RFC4401] Williams, N., "A Pseudo-Random Function (PRF) API 1195 Extension for the Generic Security Service Application 1196 Program Interface (GSS-API)", RFC 4401, February 2006. 1198 [RFC4402] Williams, N., "A Pseudo-Random Function (PRF) for the 1199 Kerberos V Generic Security Service Application Program 1200 Interface (GSS-API) Mechanism", RFC 4402, February 2006. 1202 [tls-unique] 1203 Zhu, L., "Registration of TLS unique channel binding 1204 (generic)", IANA http://www.iana.org/assignments/ 1205 channel-binding-types/tls-unique, July 2008. 1207 12.3. Informative References 1209 [I-D.altman-tls-channel-bindings] 1210 Altman, J., Williams, N., and L. Zhu, "Channel Bindings 1211 for TLS", draft-altman-tls-channel-bindings-07 (work in 1212 progress), October 2009. 1214 [I-D.ietf-sasl-crammd5-to-historic] 1215 Zeilenga, K., "CRAM-MD5 to Historic", 1216 draft-ietf-sasl-crammd5-to-historic-00 (work in progress), 1217 November 2008. 1219 [I-D.ietf-sasl-digest-to-historic] 1220 Melnikov, A., "Moving DIGEST-MD5 to Historic", 1221 draft-ietf-sasl-digest-to-historic-00 (work in progress), 1222 July 2008. 1224 [I-D.melnikov-sasl-scram-ldap] 1225 Melnikov, A., "LDAP schema for storing SCRAM secrets", 1226 draft-melnikov-sasl-scram-ldap-02 (work in progress), 1227 July 2009. 1229 [RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson, 1230 "Remote Authentication Dial In User Service (RADIUS)", 1231 RFC 2865, June 2000. 1233 [RFC2898] Kaliski, B., "PKCS #5: Password-Based Cryptography 1234 Specification Version 2.0", RFC 2898, September 2000. 1236 [RFC2945] Wu, T., "The SRP Authentication and Key Exchange System", 1237 RFC 2945, September 2000. 1239 [RFC4086] Eastlake, D., Schiller, J., and S. Crocker, "Randomness 1240 Requirements for Security", BCP 106, RFC 4086, June 2005. 1242 [RFC4510] Zeilenga, K., "Lightweight Directory Access Protocol 1243 (LDAP): Technical Specification Road Map", RFC 4510, 1244 June 2006. 1246 [RFC4616] Zeilenga, K., "The PLAIN Simple Authentication and 1247 Security Layer (SASL) Mechanism", RFC 4616, August 2006. 1249 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", 1250 RFC 4949, August 2007. 1252 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1253 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1254 May 2008. 1256 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 1257 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 1259 [tls-server-end-point] 1260 Zhu, L., "Registration of TLS server end-point channel 1261 bindings", IANA http://www.iana.org/assignments/ 1262 channel-binding-types/tls-server-end-point, July 2008. 1264 Authors' Addresses 1266 Abhijit Menon-Sen 1267 Oryx Mail Systems GmbH 1269 Email: ams@oryx.com 1271 Alexey Melnikov 1272 Isode Ltd 1274 Email: Alexey.Melnikov@isode.com 1276 Chris Newman 1277 Sun Microsystems 1278 1050 Lakes Drive 1279 West Covina, CA 91790 1280 USA 1282 Email: chris.newman@sun.com 1284 Nicolas Williams 1285 Sun Microsystems 1286 5300 Riata Trace Ct 1287 Austin, TX 78727 1288 USA 1290 Email: Nicolas.Williams@sun.com