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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Robert Siemborski 3 INTERNET-DRAFT Carnegie Mellon University 4 Intended Category: Proposed Standard December, 2003 6 POP3 SASL Authentication Mechanism 8 10 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Task Force 15 (IETF), its areas, and its working groups. Note that other groups 16 may also distribute working documents as Internet-Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six 19 months and may be updated, replaced, or obsoleted by other documents 20 at any time. It is inappropriate to use Internet Drafts as 21 reference material or to cite them other than as "work in progress." 23 The list of current Internet-Drafts can be accessed at 24 http://www.ietf.org/ietf/1id-abstracts.txt 26 The list of Internet-Draft Shadow Directories can be accessed at 27 http://www.ietf.org/shadow.html. 29 Distribution of this memo is unlimited. 31 Abstract 33 This document defines a profile of the Simple Authentication and 34 Security Layer (SASL) for the Post Office Protocol (POP3). This 35 extension allows a POP3 client to indicate an authentication 36 mechanism to the server, perform an authentication protocol 37 exchange, and optionally negotiate a security layer for subsequent 38 protocol interactions during this session. 40 In order to consolidate all of the authentication related 41 information for POP3 into a single document, this document obsoletes 42 RFC 1734 and RFC 3206, replacing them as a Proposed Standard. It 43 also updates information contained in Section 6.3 and Section 8 of 44 RFC 2449. 46 POP3 SASL Authentication Mechanism December, 2003 48 Table of Contents 50 1. How to Read This Document . . . . . . . . . . . . . . . . . . . . 3 51 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 3. The SASL Capability . . . . . . . . . . . . . . . . . . . . . . . 3 53 4. The AUTH Command . . . . . . . . . . . . . . . . . . . . . . . . 4 54 4.1. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 7 55 4.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 56 5. Extended POP3 Response Codes . . . . . . . . . . . . . . . . . . 10 57 5.1. The LOGIN-DELAY Response Code . . . . . . . . . . . . . . . . . 10 58 5.2. The IN-USE Response Code . . . . . . . . . . . . . . . . . . . 10 59 5.3. The AUTH Response Code . . . . . . . . . . . . . . . . . . . . 11 60 5.3.1. The AUTH-RESP-CODE Capability . . . . . . . . . . . . . . . . 11 61 5.4. The SYS Response Code . . . . . . . . . . . . . . . . . . . . . 12 62 6. Security Considerations . . . . . . . . . . . . . . . . . . . . . 12 63 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 13 64 8. Protocol Actions . . . . . . . . . . . . . . . . . . . . . . . . 13 65 9. Intellectual Property Rights . . . . . . . . . . . . . . . . . . 13 66 10. Copyright . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 67 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 68 12. Changes From RFC 1734, RFC 2449, and RFC 3206 . . . . . . . . . 16 69 13. Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16 70 14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 16 72 POP3 SASL Authentication Mechanism December, 2003 74 1. How to Read This Document 76 The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD 77 NOT", "RECOMMENDED", and "MAY" in this document are to be 78 interpreted as defined in "Key words for use in RFCs to Indicate 79 Requirement Levels" [KEYWORDS] 81 In examples, "C:" and "S:" indicate lines sent by the client and 82 server respectively. 84 2. Introduction 86 The [POP3] AUTH command [POP3-AUTH] in has suffered several problems 87 in its specification. The first is that it was very similar to a 88 [SASL] framework, but pre-dated the initial SASL specification. It 89 was therefore missing some key components, such as a way to list the 90 available authentication mechanisms. 92 Later, [POP3-EXT] attempted to remedy this situation by adding the 93 CAPA command and allowing an initial client response to the AUTH 94 command, however problems in the clarity of the specification of how 95 the initial client response was to be handled remained. 97 Additionally, there is yet another document, [POP3-CODES], that 98 provides additional response codes that are useful during 99 authentication. Together, this means creating a full POP3 AUTH 100 implementaiton requires an understanding of material in atleast six 101 different documents. 103 This document attempts to combine all of the POP3 SASL 104 authentication related details into a single document, in addition 105 to clarifying and updating the older specifications where 106 appropriate. 108 3. The SASL Capability 110 This section supercedes the definition of the SASL Capability in 111 section 6.3 of [POP3-EXT]. 113 CAPA tag: 114 SASL 116 Arguments: 117 Supported SASL Mechanisms 119 Standard Commands Affected 120 None 122 POP3 SASL Authentication Mechanism December, 2003 124 Announced states / possible differences: 125 both / no 127 Commands valid in states: 128 AUTHORIZATION 130 Specification Reference: 131 This Document, [SASL] 133 Discussion 134 The SASL capability permits the use of the AUTH command (as 135 defined in section 4 of this document) to begin a [SASL] 136 negotiation. The arguments to the SASL capability is a space- 137 separated list of SASL mechanisms which are supported. 139 If a server either does not support the CAPA command or does not 140 advertise the SASL capability, clients SHOULD NOT attempt the 141 AUTH command. If a client does attempt the AUTH command in such 142 a situation, it MUST NOT supply the client initial response 143 parameter (for backwards compatibility with [POP3-AUTH]). 145 Note that the list of available mechanisms MAY change after a 146 successful STLS command [POP3-TLS]. Additionally, 147 implementations MAY choose to omit the SASL capability after a 148 successful AUTH command has been completed. 150 Example 152 S: +OK pop.example.com BlurdyBlurp POP3 server ready 153 C: CAPA 154 S: +OK List of capabilities follows 155 S: SASL KERBEROS_V4 GSSAPI ANONYMOUS 156 S: STLS 157 S: IMPLEMENTATION BlurdyBlurp POP3 server 158 S: . 160 4. The AUTH Command 162 AUTH mechanism [initial-response] 164 Arguments: 165 mechanism: A string identifying a [SASL] authentication 166 mechanism. 168 initial-response: An optional initial client response. If 169 present, this response MUST be encoded as specified in Section 170 3 of [BASE64]. 172 POP3 SASL Authentication Mechanism December, 2003 174 Restrictions: 175 After an AUTH command has been successfully completed, no more 176 AUTH commands may be issued in the same session. After a 177 successful AUTH command completes, a server MUST reject any 178 further AUTH commands with a -ERR reply. 180 The AUTH command may only be given during the AUTHORIZATION 181 state. 183 Discussion: 184 The AUTH command initiates a [SASL] authentication exchange 185 between the client and the server. The client identifies the 186 SASL mechanism to use with the first parameter of the AUTH 187 command. If the server supports the requested authentication 188 mechanism, it performs the SASL exchange to authenticate the 189 user. Optionally, it also negotiates a security layer for 190 subsequent protocol interactions during this session. If the 191 requested authentication mechanism is not supported, the 192 server rejects the AUTH command with a -ERR reply. 194 The authentication protocol exchange consists of a series of 195 server challenges and client responses that are specific to 196 the chosen [SASL] mechanism. 198 A server challenge is sent as a line consisting of a "+" 199 character followed by a single space and a string encoded as 200 specified in Section 3 of [BASE64]. This challenge MUST NOT 201 contain any text other than the BASE64 encoded challenge. 203 A client response consists of a line containing a string 204 encoded as defined in Section 3 of [BASE64]. If the client 205 wishes to cancel the authentication exchange, it issues a line 206 with a single "*". If the server receives such a response, it 207 MUST reject the AUTH command by sending a -ERR reply. 209 The optional initial response argument to the AUTH command is 210 used to save a round trip when using authentication mechanisms 211 that support an initial client response. If the initial 212 response argument is omitted and the chosen mechanism requires 213 an initial client response, the server MUST proceed as defined 214 in section 5.1 of [SASL]. In POP3, a server challenge with no 215 data is defined as line with only a "+" followed by a single 216 space. It MUST NOT contain any other data. 218 For the purposes of the initial client response, the line 219 length limitation defined in [POP3-EXT] still applies. If a 220 client initial send would cause the AUTH command to exceed 221 this length, the client MUST NOT use the initial response 223 POP3 SASL Authentication Mechanism December, 2003 225 parameter (and instead proceed as defined in section 5.1 of 226 [SASL]). 228 If the client needs to send a zero-length initial response, 229 the client MUST transmit the response as a single equals sign 230 ("="). This indicates that the response is present, but 231 contains no data. 233 If the client uses an initial-response argument to the AUTH 234 command with a SASL mechanism that does not support an initial 235 client send, the server MUST reject the AUTH command with a 236 -ERR reply. 238 If the server cannot [BASE64] decode any client response, it 239 MUST reject the AUTH command with a -ERR reply. If the client 240 cannot BASE64 decode any of the server's challenges, it MUST 241 cancel the authentication using the "*" response. In 242 particular, servers and clients MUST reject (and not ignore) 243 any character not explicitly allowed by the BASE64 alphabet, 244 and MUST reject any sequence of BASE64 characters that 245 contains the pad character ('=') anywhere other than the end 246 of the string (e.g. "=AAA" and "AAA=BBB" are not allowed). 248 Note that these [BASE64] strings (excepting the initial client 249 response) may be of arbitrarily length. Clients and servers 250 MUST be able to handle the maximum encoded size of challenges 251 and responses generated by their supported authentication 252 mechanisms. This requirement is independent of any line 253 length limitations the client or server may have in other 254 parts of its protocol implementation. 256 If the server is unable to authenticate the client, it MUST 257 reject the AUTH command with a -ERR reply. Should the client 258 successfully complete the exchange, the server issues a +OK 259 reply. Additionally, upon success, the POP3 session enters 260 the TRANSACTION state. 262 The authorization identity generated by this [SASL] exchange 263 is a simple username, and MUST use the [SASLprep] profile of 264 the [StringPrep] algorithm to prepare these names for 265 matching. If preparation of the authorization identity fails 266 or results in an empty string (unless it was transmitted as 267 the empty string), the server MUST fail the authentication. 269 If a security layer is negotiated during the SASL exchange, it 270 takes effect for the client on the octet immediately following 271 the CRLF that concludes the last response generated by the 272 client. For the server, it takes effect immediately following 274 POP3 SASL Authentication Mechanism December, 2003 276 the CRLF of its success reply. 278 When a security layer takes effect, the server MUST discard 279 any knowledge previously obtained from the client, which was 280 not obtained from the SASL negotiation itself. Likewise, the 281 client MUST discard any knowledge obtained from the server, 282 such as the list of available POP3 service extensions. After 283 a security layer is established, the server SHOULD NOT 284 advertise either the SASL or the STLS extension. 286 When both [TLS] and SASL security layers are in effect, the 287 TLS encoding MUST be applied after the SASL encoding, 288 regardless of the order in which the layers were negotiated. 290 The service name specified by this protocol's profile of SASL 291 is "pop". 293 If an AUTH command fails, the client may try another 294 authentication mechanism or present different credentials by 295 issuing another AUTH command (or by using one of the other 296 [POP3] authentication mechanisms). Likewise, the server MUST 297 behave as if the client had not issued the AUTH command. 299 To ensure interoperability, client and server implementations 300 of this extension MUST implement the [DIGEST-MD5] SASL 301 mechanism. 303 <> 315 4.1. Formal Syntax 317 The following syntax specification uses the Augmented Backus-Naur 318 Form notation as specified in [ABNF]. 320 Except as noted otherwise, all alphabetic characters are case- 321 insensitive. The use of upper or lower case characters to define 323 POP3 SASL Authentication Mechanism December, 2003 325 token strings is for editorial clarity only. Implementations MUST 326 accept these strings in a case-insensitive fashion. 328 UPALPHA = %x41-5A ;; Uppercase: A-Z 330 LOALPHA = %x61-7A ;; Lowercase: a-z 332 ALPHA = UPALPHA / LOALPHA ;; case insensitive 334 DIGIT = %x30-39 ;; Digits 0-9 336 AUTH_CHAR = ALPHA / DIGIT / "-" / "_" 338 auth_type = 1*20AUTH_CHAR 340 auth_command = "AUTH" SPACE auth_type [SPACE (base64 / "=")] 341 *(CRLF [base64]) CRLF 343 base64 = base64_terminal / 344 ( 1*(4base64_CHAR) [base64_terminal] ) 346 base64_char = UPALPHA / LOALPHA / DIGIT / "+" / "/" 347 ;; Case-sensitive 349 base64_terminal = (2base64_char "==") / (3base64_char "=") 351 continue_req = "+" SPACE [base64] CRLF 353 CR = %x0C ;; ASCII CR, carriage return 355 CRLF = CR LF 357 LF = %x0A ;; ASCII LF, line feed 359 SPACE = %x20 ;; ASCII SP, space 361 4.2. Examples 363 Here is an example of a client attempting AUTH PLAIN under TLS and 364 making use of the initial client response: 366 POP3 SASL Authentication Mechanism December, 2003 368 S: +OK pop.example.com BlurdyBlurp POP3 server ready 369 C: CAPA 370 S: +OK List of capabilities follows 371 S: SASL KERBEROS_V4 GSSAPI ANONYMOUS 372 S: STLS 373 S: IMPLEMENTATION BlurdyBlurp POP3 server 374 S: . 375 C: STLS 376 S: +OK Begin TLS negotiation now 377 ... TLS negotiation proceeds, further commands protected by TLS layer ... 378 C: CAPA 379 S: +OK List of capabilities follows 380 S: SASL PLAIN KERBEROS_V4 GSSAPI ANONYMOUS 381 S: IMPLEMENTATION BlurdyBlurp POP3 server 382 S: . 383 C: AUTH PLAIN dGVzdAB0ZXN0AHRlc3Q= 384 S: +OK Maildrop locked and ready 386 Here is another client that is attempting AUTH PLAIN under a TLS 387 layer, this time without the initial response. Parts of the 388 negotiation before the TLS layer was established have been omitted: 390 ... TLS negotiation proceeds, further commands protected by TLS layer ... 391 C: CAPA 392 S: +OK List of capabilities follows 393 S: SASL PLAIN KERBEROS_V4 GSSAPI ANONYMOUS 394 S: IMPLEMENTATION BlurdyBlurp POP3 server 395 S: . 396 C: AUTH PLAIN 397 (note that there is a space following the '+' on the following line) 398 S: + 399 C: dGVzdAB0ZXN0AHRlc3Q= 400 S: +OK Maildrop locked and ready 402 Here is an example using a mechanism which does not support an 403 initial client send, and includes server challenges: 405 POP3 SASL Authentication Mechanism December, 2003 407 S: +OK pop.example.com BlurdyBlurp POP3 server ready 408 C: CAPA 409 S: +OK List of capabilities follows 410 S: SASL KERBEROS_V4 GSSAPI ANONYMOUS 411 S: STLS 412 S: IMPLEMENTATION BlurdyBlurp POP3 server 413 S: . 414 C: AUTH KERBEROS_V4 415 S: + ezLUFA== 416 (the following lines are broken for editorial clarity only) 417 C: BAYFQU5EUkVXLkNNVS5FRFUAOCCXeMiVyFe9K6Nwne7+sPLgIoF9YQ5ePfxUsMlJAf 418 C7aoNySU8nrqS9m8JAddsUeuyc5HFXXovaKLrZNo2bTLH0Lyolwy0W9ryJDojbKmHy 419 zSMqFsGD4EL0 420 S: + Z74fTwDw7KQ= 421 C: vSAF7ha6qotK2UHUgKlsEA== 422 S: +OK Maildrop locked and ready 423 ... at this point a security layer has been established and additional 424 commands and responses proceed within it ... 426 5. Extended POP3 Response Codes 428 This section defines four POP3 response codes which can be used to 429 determine the reason for a failed login (provided that the server 430 advertises the RESP-CODES capability [POP3-EXT]). These definitions 431 supercede those in [POP3-EXT] and [POP3-CODES]. 433 It is RECOMMENDED that server applications use these codes when 434 possible to allow clients a straightforward, interoperable way to 435 determine the cause of an authentication failure (as opposed to 436 parsing error text). 438 5.1. The LOGIN-DELAY Response Code 440 This occurs on an -ERR response to an AUTH, USER (see note), PASS or 441 APOP command and indicates that the user has logged in recently and 442 will not be allowed to login again until the login delay period has 443 expired. 445 Please see the Security Considerations section of this document for 446 an important note about returning this code in response to the USER 447 command. 449 5.2. The IN-USE Response Code 451 This occurs on an -ERR response to an AUTH, APOP, or PASS command. 452 It indicates the authentication was successful, but the user's 453 maildrop is currently in use (probably by another POP3 client). 455 POP3 SASL Authentication Mechanism December, 2003 457 5.3. The AUTH Response Code 459 The AUTH response code informs the client that there is a problem 460 with the user's credentials. This might be an incorrect password, 461 an unknown user name, an expired account, an attempt to authenticate 462 in violation of policy (such as from an invalid location or during 463 an unauthorized time), or some other problem. 465 The AUTH response code is valid with an -ERR response to any 466 authentication command including AUTH, USER (see the note in the 467 Security Considerations section of this document), PASS, or APOP. 469 Servers which include the AUTH response code with any authentication 470 failure SHOULD support the CAPA command [POP3-EXT] and SHOULD 471 include the AUTH-RESP-CODE capability (defined in the next section) 472 in the CAPA response. AUTH-RESP-CODE assures the client that only 473 errors with the AUTH code are caused by credential problems. 475 5.3.1. The AUTH-RESP-CODE Capability 477 CAPA tag: 478 AUTH-RESP-CODE 480 Arguments: 481 none 483 Added commands: 484 none 486 Standard commands affected: 487 none 489 Announced states / possible differences: 490 both / no 492 Commands valid in states: 493 n/a 495 Specification reference: 496 this document 498 Discussion: 499 The AUTH-RESP-CODE capability indicates that the server includes 500 the AUTH response code with any authentication error caused by a 501 problem with the user's credentials. 503 POP3 SASL Authentication Mechanism December, 2003 505 5.4. The SYS Response Code 507 The SYS response code announces that a failure is due to a system 508 error, as opposed to the user's credentials or an external 509 condition. It is hierarchical, with two possible second-level 510 codes: TEMP and PERM. (Case is not significant at any level of the 511 hierarchy.) 513 SYS/TEMP indicates a problem which is likely to be temporary in 514 nature, and therefore there is no need to alarm the user, unless the 515 failure persists. Examples might include a central resource which 516 is currently locked or otherwise temporarily unavailable, 517 insufficient free disk or memory, etc. 519 SYS/PERM is used for problems which are unlikely to be resolved 520 without intervention. It is appropriate to alert the user and 521 suggest that the organization's support or assistance personnel be 522 contacted. Examples include corrupted mailboxes, system 523 configuration errors, etc. 525 The SYS response code is valid with an -ERR response to any command. 527 6. Security Considerations 529 Security issues are discussed throughout this memo. 531 Before the [SASL] negotiation has begun, any protocol interactions 532 are performed in the clear and may be modified by an active 533 attacker. For this reason, clients and servers MUST discard any 534 knowledge obtained prior to the start of the SASL negotiation upon 535 the establishment of a security layer. 537 Servers MAY implement a policy whereby the connection is dropped 538 after a number of failed authentication attempts. If they do so, 539 they SHOULD NOT drop the connection until atleast 3 attempts to 540 authenticate have failed. 542 Implementations MUST support a configuration where [SASL] mechanisms 543 that are vulnerable to passive eavesdropping attacks (such as 544 [PLAIN]) are not advertised or used without the presence of an 545 external security layer such as [TLS]. 547 Returning the LOGIN-DELAY or AUTH response codes to the USER command 548 avoids the work of authenticating the user but is likely to reveal 549 information to the client about the existence of the account in 550 question. Unless the server is operating in an environment where 551 user names are not secret (for example, many popular email clients 552 advertise the POP server and user name in an outgoing mail header), 554 POP3 SASL Authentication Mechanism December, 2003 556 or where server access is restricted, or the server can verify that 557 the connection is to the same user, the the server SHOULD NOT issue 558 this response code to the USER command. The server still saves the 559 cost of opening the maildrop, which in some environments is the most 560 expensive step. 562 7. IANA Considerations 564 This document requests that the IANA update the entry for the "pop" 565 SASL protocol name to point at this document. 567 This document requests that the IANA update the entry for the SASL 568 POP3 capability to be as defined in Section 3 of this document. 570 This document requests that the IANA update the entry for the LOGIN- 571 DELAY, IN-USE, AUTH, SYS/TEMP, and SYS/PERM POP3 response codes to 572 this document. 574 This document requests that the IANA update the entry for the AUTH- 575 RESP-CODE capability to be as defined in Section 5.3.1 of this 576 document. 578 8. Protocol Actions 580 [RFC Editor: Remove this section before publication] 582 This document obsoletes RFC 1734 and replaces it as a Proposed 583 Standard. By moving RFC 1734 to Historic, RFC 1731 can also be 584 moved to Historic (as RFC 1734 was the last document to have a 585 normative reference). 587 This document obsoletes RFC 3206 and replaces it as a Proposed 588 Standard. 590 It also updates information contained in Section 6.3 and Section 8 591 of RFC 2449. 593 9. Intellectual Property Rights 595 The IETF takes no position regarding the validity or scope of any 596 intellectual property or other rights that might be claimed to 597 pertain to the implementation or use of the technology described in 598 this document or the extent to which any license under such rights 599 might or might not be available; neither does it represent that it 600 has made any effort to identify any such rights. Information on the 601 IETF's procedures with respect to rights in standards-track and 602 standards-related documentation can be found in BCP-11. Copies of 603 claims of rights made available for publication and any assurances 605 POP3 SASL Authentication Mechanism December, 2003 607 of licenses to be made available, or the result of an attempt made 608 to obtain a general license or permission for the use of such 609 proprietary rights by implementors or users of this specification 610 can be obtained from the IETF Secretariat. 612 The IETF invites any interested party to bring to its attention any 613 copyrights, patents or patent applications, or other proprietary 614 rights which may cover technology that may be required to practice 615 this standard. Please address the information to the IETF Executive 616 Director. 618 10. Copyright 620 Copyright (C) The Internet Society (2003). All Rights Reserved. 622 This document and translations of it may be copied and furnished to 623 others, and derivative works that comment on or otherwise explain it 624 or assist in its implementation may be prepared, copied, published 625 and distributed, in whole or in part, without restriction of any 626 kind, provided that the above copyright notice and this paragraph 627 are included on all such copies and derivative works. However, this 628 document itself may not be modified in any way, such as by removing 629 the copyright notice or references to the Internet Society or other 630 Internet organizations, except as needed for the purpose of 631 developing Internet standards in which case the procedures for 632 copyrights defined in the Internet Standards process must be 633 followed, or as required to translate it into languages other than 634 English. 636 This document and the information contained herein is provided on an 637 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 638 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 639 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 640 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 641 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 643 POP3 SASL Authentication Mechanism December, 2003 645 11. References 647 The following documents contain normative definitions or 648 specifications that are necessary for correct understanding of this 649 protocol: 651 [BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data 652 Encodings", RFC 3548, July 2003. 654 [DIGEST-MD5] 655 Leach, P., Melnikov, A., and Newman C., "Using Digest 656 Authentication as a SASL Mechanism", draft-ietf-sasl- 657 rfc2831bis-*.txt, a work in progress. 659 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 660 Requirement Levels", BCP 14, RFC 2119, March 1997 662 [POP3] Myers, J. and Rose, M., "Post Office Protocol - Version 3", 663 STD 53, RFC 1939, May 1996. 665 [POP3-EXT] Gellens, R., Newman, C., and Lundblade, L., "POP3 Extension 666 Mechanism", RFC 2449, November 1998. 668 [POP3-TLS] Newman, C., "Using TLS with IMAP, POP3, and ACAP", RFC 2595, 669 June 1999. 671 [SASL] Melnikov, A., "Simple Authentication and Security Layer 672 (SASL)", draft-ietf-sasl-rfc2222bis-*.txt, a work in 673 progress. 675 [SASLprep] Zeilega, K., "SASLprep: Stringprep profile for user names 676 and passwords", draft-ietf-sasl-saslprep-*.txt, a work in 677 progress 679 [StringPrep] 680 Hoffman, P. and Blanchet, M., "Preparation of 681 Internationalized Strings ("stringprep")", draft-hoffman- 682 rfc3454bis-*.txt, a work in progress 684 The following references are for informational purposes only: 686 [PLAIN] Zeilenga, K., "The Plain SASL Mechanism", draft-ietf-sasl- 687 plain-*.txt, a work in progress. 689 [POP3-AUTH] Myers, J., "POP3 AUTHentication Command", RFC 1734, January 690 1994. 692 [POP3-CODES] 694 POP3 SASL Authentication Mechanism December, 2003 696 Gellens, R., "The SYS and AUTH POP Response Codes", RFC 697 3206, February 2002. 699 [TLS] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC 700 2246, January 1999. 702 12. Changes From RFC 1734, RFC 2449, and RFC 3206 704 1. The SASL-based semantics defined in RFC 2449 are now 705 normative for the AUTH extension. 707 2. Clarifications and examples of the proper behavior of 708 initial client response handling. 710 3. Minimum requirement of support for DIGEST-MD5. 712 4. Clarify ordering of TLS and SASL security layers. 714 5. Update references to newer versions of various 715 specifications. 717 6. Clarify that the mechanism list can change. 719 7. Add the use of the SASLprep profile for preparing 720 authorization identities. 722 8. General other editorial clarifications. 724 9. Consolidation of all applicable information into a 725 single document. 727 13. Author's Address: 729 Robert Siemborski 730 Carnegie Mellon, Andrew Systems Group 731 Cyert Hall 207 732 5000 Forbes Avenue 733 Pittsburgh, PA 15213 734 +1 412 268 7456 735 rjs3+@andrew.cmu.edu 737 14. Acknowledgments: 739 The author would like to acknowledge the contributions of John 740 Myers, Randall Gellens, Chris Newman, Laurence Lundblade, and other 741 contributors to RFC 1734, RFC 2554, and RFC 3206, on which this 742 document draws heavily. 744 POP3 SASL Authentication Mechanism December, 2003 746 The author would also like to thank Ken Murchison, Alexey Melnikov, 747 and Mark Crispin for the time they devoted to reviewing early drafts 748 of this document.