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'ABNF') (Obsoleted by RFC 4234) ** Downref: Normative reference to an Informational RFC: RFC 1704 (ref. 'AUTH') ** Obsolete normative reference: RFC 3548 (ref. 'BASE64') (Obsoleted by RFC 4648) ** Obsolete normative reference: RFC 2831 (ref. 'DIGEST-MD5') (Obsoleted by RFC 6331) -- No information found for draft-ietf-nntpext-base- - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'NNTP' -- No information found for draft-ietf-nntpext-tls-nntp- - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'NNTP-TLS' -- No information found for draft-ietf-sasl-rfc2222bis- - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'SASL' -- No information found for draft-ietf-sasl-saslprep- - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'SASLprep' -- No information found for draft-hoffman-rfc3454bis- - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'StringPrep' -- No information found for draft-ietf-sasl-crammd5- - is the name correct? -- No information found for draft-ietf-sasl-gssapi- - is the name correct? -- No information found for draft-ietf-sasl-plain- - is the name correct? -- Obsolete informational reference (is this intentional?): RFC 2821 (ref. 'SMTP') (Obsoleted by RFC 5321) Summary: 15 errors (**), 0 flaws (~~), 8 warnings (==), 22 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 NNTP Extensions Working Group J. Vinocur 3 Internet Draft Cornell University 4 Updates: 2970 (if approved) K. Murchison 5 Expires: September 2005 Oceana Matrix Ltd. 6 C. Newman 7 Sun Microsystems 8 March 2005 10 NNTP Extension for Authentication 11 draft-ietf-nntpext-authinfo-07 13 Status of this memo 15 By submitting this Internet-Draft, I certify that any applicable 16 patent or other IPR claims of which I am aware have been disclosed, 17 and any of which I become aware will be disclosed, in accordance 18 with RFC 3668. 20 Internet-Drafts are working documents of the Internet Engineering 21 Task Force (IETF), its areas, and its working groups. Note that 22 other groups may also distribute working documents as 23 Internet-Drafts. 25 Internet-Drafts are draft documents valid for a maximum of six 26 months and may be updated, replaced, or obsoleted by other 27 documents at any time. It is inappropriate to use Internet-Drafts 28 as reference material or to cite them other than as "work in 29 progress." 31 The list of current Internet-Drafts can be accessed at 32 http://www.ietf.org/ietf/1id-abstracts.txt. 34 The list of Internet-Draft Shadow Directories can be accessed at 35 http://www.ietf.org/shadow.html. 37 Copyright Notice 39 Copyright (C) The Internet Society (2005). 41 Abstract 43 This document defines an extension the Network News Transport 44 Protocol [NNTP] which allows a client to indicate an authentication 45 mechanism to the server, perform an authentication protocol 46 exchange, and optionally negotiate a security layer for subsequent 47 protocol interactions during the remainder of an NNTP session. 49 Section 3.1 of [NNTP-COMMON] summarizes some ad-hoc authentication 50 methods currently used in the NNTP protocol. This document updates 51 and formalizes the AUTHINFO USER/PASS authentication method and 52 deprecates the AUTHINFO SIMPLE and AUTHINFO GENERIC authentication 53 methods. Additionally, this document defines a profile of the 54 Simple Authentication and Security Layer [SASL] for NNTP. 56 Table of Contents 58 0. Changes from Previous Version ............................ 2 59 1. Introduction ............................................. 3 60 1.1. Conventions Used in this Document ................... 3 61 2. The AUTHINFO Extension ................................... 4 62 2.1. Advertising the AUTHINFO Extension .................. 4 63 2.2. Authenticating with the AUTHINFO Extension .......... 5 64 2.3. AUTHINFO USER/PASS Command .......................... 6 65 2.3.1. Usage .......................................... 6 66 2.3.2. Description .................................... 7 67 2.3.3. Examples ....................................... 8 68 2.4. AUTHINFO SASL Command ............................... 9 69 2.4.1. Usage .......................................... 9 70 2.4.2. Description .................................... 10 71 2.4.3. Examples ....................................... 13 72 3. Augmented BNF Syntax for the AUTHINFO Extension .......... 15 73 3.1. Commands ............................................ 16 74 3.2. Command Continuation ................................ 16 75 3.3. Responses ........................................... 16 76 3.4. Capability entries .................................. 17 77 3.5. General non-terminals ............................... 17 78 4. Summary of Response Codes ................................ 17 79 5. Authentication Tracking/Logging .......................... 18 80 6. Security Considerations .................................. 18 81 7. IANA Considerations ...................................... 19 82 7.1. IANA Considerations for SASL/GSSAPI services ........ 19 83 7.2. IANA Considerations for NNTP extensions ............. 19 84 8. References ............................................... 20 85 8.1. Normative References ................................ 20 86 8.2. Informative References .............................. 21 87 9. Authors' Addresses ....................................... 21 88 10. Acknowledgments ......................................... 22 89 11. Intellectual Property Rights ............................ 22 90 12. Copyright ............................................... 23 92 0. Changes from Previous Version 94 Added: 95 o Example of an incorrectly encoded SASL response and the resulting 96 504 reply. 98 Changed: 99 o Renamed response-sasl-content to sasl-response-content. 101 Clarified: 102 o 2.1: AUTHINFO MUST NOT be advertised after successful 103 authentication. 105 1. Introduction 107 Although NNTP [NNTP] has traditionally been used to provide public 108 access to newsgroups, authentication is often useful, for example 109 to control resource consumption, to allow abusers of the POST 110 command to be identified, and to restrict access to "local" 111 newsgroups. 113 The ad-hoc AUTHINFO USER and AUTHINFO PASS commands, documented in 114 [NNTP-COMMON], provide a very weak authentication mechanism in 115 widespread use by the installed base. Due to their ubiquity they 116 are formalized in this specification but, because of their 117 insecurity, only for use in combination with appropriate security 118 layers. 120 The ad-hoc AUTHINFO GENERIC command, also documented in [NNTP- 121 COMMON] but much less ubiquitous, provided an NNTP-specific 122 equivalent of the generic SASL [SASL] facility. This document 123 deprecates AUTHINFO GENERIC in favor of an AUTHINFO SASL 124 replacement so that NNTP can benefit from authentication mechanisms 125 developed for other SASL-enabled application protocols including 126 SMTP, POP, IMAP, LDAP, and BEEP. 128 This specification is to be read in conjunction with the NNTP base 129 specification [NNTP]. Except where specifically stated otherwise, 130 in the case of a conflict between these two documents [NNTP] takes 131 precedence over this one. 133 It is also recommended that this specification be read in 134 conjunction with the SASL base specification [SASL]. 136 1.1. Conventions Used in this Document 138 The notational conventions used in this document are the same as 139 those in [NNTP] and any term not defined in this document has the 140 same meaning as in that one. 142 The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD 143 NOT", "MAY", and "OPTIONAL" in this document are to be interpreted 144 as described in "Key words for use in RFCs to Indicate Requirement 145 Levels" [KEYWORDS]. 147 Terms related to authentication are defined in "On Internet 148 Authentication" [AUTH]. 150 In the examples, commands from the client are indicated with [C], 151 and responses from the server are indicated with [S]. 153 2. The AUTHINFO Extension 155 The AUTHINFO extension is used to authenticate a user. Note that 156 authorization is a matter of site policy, not network protocol, and 157 is therefore not discussed in this document. The server determines 158 authorization in whatever manner is defined by its implementation 159 as configured by the site administrator. 161 This extension provides three new commands: AUTHINFO USER, AUTHINFO 162 PASS, and AUTHINFO SASL. The capability label for this extension 163 is AUTHINFO. 165 2.1. Advertising the AUTHINFO Extension 167 A server MUST implement at least one of the AUTHINFO USER or 168 AUTHINFO SASL commands in order to advertise the AUTHINFO 169 capability in the response to the CAPABILITIES command. However, 170 this capability MUST NOT be advertised after successful 171 authentication (see section 2.2). This capability MAY be 172 advertised both before and after any use of MODE READER, with the 173 same semantics. 175 The AUTHINFO capability label contains an argument list detailing 176 which authentication commands are available. 178 The "USER" argument indicates that AUTHINFO USER/PASS is supported 179 as defined by Section 2.3 of this document. The "USER" argument 180 MUST NOT be advertised, and the AUTHINFO USER/PASS commands SHOULD 181 NOT be provided, unless a strong encryption layer (e.g. TLS [NNTP- 182 TLS]) is in use or backward compatibility dictates otherwise. 184 The "SASL" argument indicates that AUTHINFO SASL is supported as 185 defined by Section 2.4 of this document. If the server advertises 186 the "SASL" argument, then it MUST also advertise the "SASL" 187 capability in response to the CAPABILITIES command. The SASL 188 capability is followed by a whitespace-separated list of available 189 SASL mechanism names. 191 The server may list the AUTHINFO capability with no arguments, 192 which indicates that it complies with this specification and does 193 not permit any authentication commands in its current state. In 194 this case, the client MUST NOT attempt to utilize any AUTHINFO 195 commands, even if it contains logic to do so (e.g. for backward 196 compatibility with servers that are not compliant with this 197 specification). 199 Future extensions may add additional arguments to this capability. 200 Unrecognized arguments SHOULD be ignored or brought to the 201 attention of the user. 203 As the AUTHINFO command is related to security, cached results of 204 CAPABILITIES from a previous session MUST NOT be relied on, as per 205 section 11.6 of [NNTP]. 207 Example (here, the STARTTLS extension [NNTP-TLS] is also in use): 208 [C] CAPABILITIES 209 [S] 101 Capability list: 210 [S] VERSION 2 211 [S] READER 212 [S] IHAVE 213 [S] STARTTLS 214 [S] AUTHINFO SASL 215 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI 216 [S] LIST ACTIVE NEWSGROUPS 217 [S] . 218 [C] STARTTLS 219 [S] 382 Continue with TLS negotiation 220 [TLS negotiation proceeds, further commands protected by TLS layer] 221 [C] CAPABILITIES 222 [S] 101 Capability list: 223 [S] VERSION 2 224 [S] READER 225 [S] IHAVE 226 [S] AUTHINFO USER SASL 227 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI PLAIN EXTERNAL 228 [S] LIST ACTIVE NEWSGROUPS 229 [S] . 231 2.2. Authenticating with the AUTHINFO Extension 233 An NNTP server responds to a client command with a 480 response to 234 indicate that the client MUST authenticate and/or authorize in 235 order to use that command or access the indicated resource. Use of 236 the AUTHINFO command as described below is one such way that a 237 client can authenticate/authorize to the server. The client MAY 238 therefore use an AUTHINFO command after receiving a 480 response. 239 A client intending to use an AUTHINFO command SHOULD issue the 240 CAPABILITIES command to obtain the available authentication 241 commands and mechanisms before attempting authentication. 243 If a server advertises the AUTHINFO capability, a client MAY 244 attempt the first step of authentication at any time during a 245 session to acquire additional privileges without having received a 246 480 response. Servers SHOULD accept such unsolicited 247 authentication requests. A server MUST NOT under any circumstances 248 reply to an AUTHINFO command with a 480 response. 250 A client MUST NOT under any circumstances continue with any steps 251 of authentication beyond the first, unless the response code from 252 the server indicates that the authentication exchange is welcomed. 253 In particular, anything other than a 38x response code indicates 254 that the client MUST NOT continue the authentication exchange. 256 After a successful authentication, the client MUST NOT issue 257 another AUTHINFO command in the same session. A server MUST NOT 258 return the AUTHINFO capability in response to a CAPABILITIES 259 command and a server MUST reject any subsequent AUTHINFO commands 260 with a 502 response. Additionally, the client MUST NOT issue a 261 MODE READER command after authentication and a server MUST NOT 262 advertise the MODE-READER capability. 264 In agreement with [SASL], the server MUST continue to advertise the 265 SASL capability in response to a CAPABILITIES command with the same 266 list of SASL mechanisms as before authentication (thereby enabling 267 the client to detect a possible active down-negotiation attack). 268 Other capabilities returned in response to a CAPABILITIES command 269 received after authentication MAY be different than those returned 270 before authentication. For example, an NNTP server may not want to 271 advertise support for a specific extension unless a client has been 272 authenticated. 274 It should be noted that a server may perform a successful 275 authentication exchange with a client and yet still deny access to 276 some or all resources; the permanent 502 response indicates a 277 resource is unavailable even though authentication has been 278 performed (this is in contrast to the temporary 480 error 279 indicating that a resource is unavailable now but may become 280 available after authentication). 282 2.3. AUTHINFO USER/PASS Command 284 This section supersedes the definition of the AUTHINFO USER and 285 AUTHINFO PASS commands as documented in Section 3.1.1 of [NNTP- 286 COMMON]. 288 2.3.1. Usage 289 These commands MUST NOT be pipelined. 291 Syntax 292 AUTHINFO USER username 293 AUTHINFO PASS password 295 Responses 296 281 Authentication accepted 297 381 Password required [1] 298 481 Authentication failed/rejected 299 482 Authentication commands issued out of sequence 300 502 Command unavailable [2] 302 [1] Only valid for AUTHINFO USER. Note that unlike traditional 3xx 303 codes which indicate that the client may continue the current 304 command, the legacy 381 code means that the AUTHINFO PASS command 305 must be used to complete the authentication exchange. 307 [2] If authentication has already occurred, AUTHINFO USER/PASS are 308 not valid commands (see section 2.2). 310 NOTE: Notwithstanding section 3.2.1 of [NNTP], the server MUST NOT 311 return 480 in response to AUTHINFO USER/PASS. 313 Parameters 314 username = UTF-8 string identifying the user/client 315 password = UTF-8 string representing the user's password 317 2.3.2. Description 319 The AUTHINFO USER and AUTHINFO PASS commands are used to present 320 clear text credentials to the server. These credentials consist of 321 a username or a username plus a password (the distinction is that a 322 password is expected to be kept secret while a username is not; 323 this does not directly affect the protocol but may have an impact 324 on user interfaces). The username is supplied through the AUTHINFO 325 USER command, and the password through the AUTHINFO PASS command. 327 If the server requires only a username, it MUST NOT give a 381 328 response to AUTHINFO USER and MUST give a 482 response to AUTHINFO 329 PASS. 331 If the server requires both username and password, the former MUST 332 be sent before the latter. The server will need to cache the 333 username until the password is received; it MAY require the 334 password to be sent in the immediately next command (in other 335 words, only caching the username until the next command is sent). 336 The server: 338 - MUST return a 381 response to AUTHINFO USER; 339 - MUST return a 482 response to AUTHINFO PASS if there is no 340 cached username; 341 - MUST use the argument of the most recent AUTHINFO USER for 342 authentication; 343 - MUST NOT return a 381 response to AUTHINFO PASS. 345 The server MAY determine whether or not a password is needed based 346 on the username. Thus the same server can respond with both 381 347 and other response codes to AUTHINFO USER. 349 The AUTHINFO PASS command permits the client to use a clear-text 350 password to authenticate. A compliant implementation MUST NOT 351 implement this command without also implementing support for TLS 352 [NNTP-TLS]. Use of this command without an active strong 353 encryption layer is deprecated, as it exposes the user's password 354 to all parties on the network between the client and the server. 355 Any implementation of this command SHOULD be configurable to 356 disable it whenever a strong encryption layer such as that provided 357 by [NNTP-TLS] is not active, and this configuration SHOULD be the 358 default. The server will use the 483 response code to indicate 359 that the datastream is insufficiently secure for the command being 360 attempted. 362 Usernames and passwords MUST use the UTF-8 [UTF-8] character set 363 and a client MUST convert any user input to UTF-8 if necessary. 365 Note that a server MAY, but is not required to, allow white space 366 characters in usernames and passwords. A server implementation MAY 367 blindly split command arguments at white space and therefore not 368 preserve the exact sequence of white space characters in the 369 username or password. Therefore a client SHOULD scan the username 370 and password for whitespace, and if detected, warn the user of the 371 likelihood of problems. The SASL PLAIN [PLAIN] mechanism is 372 recommended as an alternative, as it does not suffer from these 373 issues. 375 2.3.3. Examples 377 Example of successful AUTHINFO USER: 379 [C] AUTHINFO USER wilma 380 [S] 281 Authentication accepted 382 Example of successful AUTHINFO USER/PASS: 384 [C] AUTHINFO USER fred 385 [S] 381 Enter passphrase 387 [C] AUTHINFO PASS flintstone 388 [S] 281 Authentication accepted 390 Example of AUTHINFO USER/PASS requiring a security layer: 392 [C] AUTHINFO USER fred@stonecanyon.example 393 [S] 483 Encryption or stronger authentication required 395 Example of failed AUTHINFO USER/PASS: 397 [C] AUTHINFO USER barney 398 [S] 381 Enter passphrase 399 [C] AUTHINFO PASS flintstone 400 [S] 481 Authentication failed 402 Example of AUTHINFO PASS before AUTHINFO USER: 404 [C] AUTHINFO PASS flintstone 405 [S] 482 Authentication commands issued out of sequence 407 2.4. AUTHINFO SASL Command 409 This section defines a formal profile of the Simple Authentication 410 and Security Layer [SASL]. The use of the AUTHINFO GENERIC command 411 as documented in Section 3.1.3 of [NNTP-COMMON] as a way to perform 412 SASL authentication is deprecated in favor of the AUTHINFO SASL 413 command. A server SHOULD NOT advertise AUTHINFO GENERIC in the 414 list of capabilities returned by CAPABILITIES. 416 2.4.1. Usage 418 This command MUST NOT be pipelined. 420 Syntax 421 AUTHINFO SASL mechanism [initial-response] 423 This command MAY exceed 512 octets. The maximum length of this 424 command is increased to that which can accommodate the largest 425 encoded initial response possible for any of the SASL mechanisms 426 supported by the implementation. 428 Responses 429 281 Authentication accepted 430 283 challenge Authentication accepted (with success data) [1] 431 383 challenge Continue with SASL exchange [1] 432 481 Authentication failed/rejected 433 482 SASL protocol error 434 502 Command unavailable [2] 436 [1] These responses MAY exceed 512 octets. The maximum length of 437 these responses is increased to that which can accommodate the 438 largest encoded challenge possible for any of the SASL mechanisms 439 supported by the implementation. 441 [2] If authentication has already occurred, AUTHINFO SASL is not a 442 valid command (see section 2.2). 444 NOTE: Notwithstanding section 3.2.1 of [NNTP], the server MUST NOT 445 return 480 in response to AUTHINFO USER/PASS. 447 Parameters 448 mechanism = String identifying a [SASL] authentication 449 mechanism. 450 initial-response = Optional initial client response. If present, 451 the response MUST be encoded as specified in 452 Section 3 of [BASE64]. [3] 453 challenge = Server challenge. The challenge MUST be 454 encoded as specified in Section 3 of [BASE64]. 456 [3] This argument MAY exceed 497 octets. The maximum length of 457 this argument is increased to that which can accommodate the 458 largest encoded initial response possible for any of the SASL mech- 459 anisms supported by the implementation. 461 2.4.2. Description 463 The AUTHINFO SASL command initiates a [SASL] authentication 464 exchange between the client and the server. The client identifies 465 the SASL mechanism to use with the first parameter of the AUTHINFO 466 SASL command. If the server supports the requested authentication 467 mechanism, it performs the SASL exchange to authenticate the user. 468 Optionally, it also negotiates a security layer for subsequent 469 protocol interactions during this session. If the requested 470 authentication mechanism is invalid (e.g. is not supported), the 471 server rejects the AUTHINFO SASL command with a 503 reply. If the 472 requested authentication mechanism requires an encryption layer, 473 the server rejects the AUTHINFO SASL command with a 483 reply. 475 The service name specified by this protocol's profile of SASL is 476 "nntp". 478 The SASL authentication exchange consists of a series of server 479 challenges and client responses that are specific to the chosen 480 [SASL] mechanism. 482 A server challenge is sent as a 383 reply with a single argument 483 containing the [BASE64] encoded string supplied by the SASL 484 mechanism. A server challenge that has zero length MUST be sent as 485 a single equals sign ("=") and not omitted (in order to comply with 486 the [NNTP] requirement that responses always have the same number 487 of arguments). 489 A client response consists of a line containing a [BASE64] encoded 490 string. A client response that has zero length MUST be sent as a 491 single equals sign ("=") and not omitted (for consistency with the 492 server challenge format). If the client wishes to cancel the 493 authentication exchange, it issues a line with a single "*". If 494 the server receives such a response, it MUST reject the AUTHINFO 495 SASL command by sending a 481 reply. 497 Note that these [BASE64] strings can be much longer than normal 498 NNTP responses. Clients and servers MUST be able to handle the 499 maximum encoded size of challenges and responses generated by their 500 supported authentication mechanisms. This requirement is 501 independent of any line length limitations the client or server may 502 have in other parts of its protocol implementation. 504 The optional initial response argument to the AUTHINFO SASL command 505 is used to save a round trip when using authentication mechanisms 506 that support an initial client response. If the initial response 507 argument is omitted and the chosen mechanism requires an initial 508 client response, the server MUST proceed as defined in section 5.1 509 of [SASL]. In NNTP, a server challenge that contains no data is 510 equivalent to a zero length challenge and is encoded as a single 511 equals sign ("="). 513 Note that the [BASE64] encoded initial response argument can exceed 514 497 octets and therefore the AUTHINFO SASL command can exceed 512 515 octets. Clients SHOULD, and servers MUST be able to handle the 516 maximum encoded size of initial responses possible for their 517 supported authentication mechanisms. This requirement is 518 independent of any command or argument length limitations the 519 client or server may have in other parts of its protocol 520 implementation. 522 If use of the initial response argument would cause the AUTHINFO 523 SASL command to exceed 512 octets, the client MAY choose to omit 524 the initial response parameter (and instead proceed as defined in 525 section 5.1 of [SASL]). 527 If the client is transmitting an initial response of zero length, 528 it MUST instead transmit the response as a single equals sign 529 ("="). This indicates that the response is present, but contains 530 no data. 532 If the client uses an initial-response argument to the AUTHINFO 533 SASL command with a SASL mechanism that does not support an initial 534 client response, the server MUST reject the AUTHINFO SASL command 535 with a 482 reply. 537 If the server cannot [BASE64] decode any client response, it MUST 538 reject the AUTHINFO SASL command with a 504 reply. If the client 539 cannot BASE64 decode any of the server's challenges, it MUST cancel 540 the authentication using the "*" response. In particular, servers 541 and clients MUST reject (and not ignore) any character not 542 explicitly allowed by the BASE64 alphabet, and MUST reject any 543 sequence of BASE64 characters that contains the pad character ('=') 544 anywhere other than the end of the string (e.g. "=AAA" and 545 "AAA=BBB" are not allowed). 547 The authorization identity generated by this [SASL] exchange is a 548 simple username, and both client and server MUST use the [SASLprep] 549 profile of the [StringPrep] algorithm to prepare these names for 550 transmission or comparison. If preparation of the authorization 551 identity fails or results in an empty string (unless it was 552 transmitted as the empty string), the server MUST fail the 553 authentication with a 481 reply. 555 Should the client successfully complete the exchange, the server 556 issues either a 281 or 283 reply. If the server is unable to 557 authenticate the client, it MUST reject the AUTHINFO SASL command 558 with a 481 reply. If an AUTHINFO command fails, the client MAY 559 proceed without authentication. Alternatively, the client MAY try 560 another authentication mechanism, or present different credentials 561 by issuing another AUTHINFO command. 563 If the SASL mechanism returns additional data on success (e.g. 564 server authentication), the NNTP server issues a 283 reply with a 565 single argument containing the [BASE64] encoded string supplied by 566 the SASL mechanism. If no additional data is returned on success, 567 the server issues a 281 reply. 569 If a security layer is negotiated during the SASL exchange, it 570 takes effect for the client on the octet immediately following the 571 CRLF that concludes the last response generated by the client. For 572 the server, it takes effect immediately following the CRLF of its 573 success reply. 575 When a security layer takes effect, the NNTP protocol is reset to 576 the state immediately after the initial greeting response (see 5.1 577 of [NNTP]) has been sent, with the exception that if a MODE READER 578 command has been issued, the effects of it (if any) are not 579 reversed. The server MUST discard any knowledge obtained from the 580 client, such as the current newsgroup and article number, that was 581 not obtained from the SASL negotiation itself. Likewise, the 582 client SHOULD discard and MUST NOT rely on any knowledge obtained 583 from the server, such as the capability list, that was not obtained 584 from the SASL negotiation itself. (Note that a client MAY compare 585 the advertised SASL mechanisms before and after authentication in 586 order to detect an active down-negotiation attack.) 588 When both TLS [NNTP-TLS] and SASL security layers are in effect, 589 the TLS encoding MUST be applied after the SASL encoding (the 590 cleartext data is always SASL encoded first and then the resultant 591 data is TLS encoded). 593 To ensure interoperability, client and server implementations of 594 this extension MUST implement the [DIGEST-MD5] SASL mechanism. 596 If AUTHINFO USER/PASS and AUTHINFO SASL are both implemented, the 597 SASL [PLAIN] mechanism SHOULD also be implemented, as the 598 functionality of DIGEST-MD5 is insufficient for some environments 599 (e.g. the server may need to pass the plaintext password off to an 600 external authentication service). The SASL PLAIN mechanism is 601 preferred over AUTHINFO USER, even if there is not a strong 602 encryption layer active, because it eliminates limitations that 603 AUTHINFO USER/PASS has with regards to white space characters being 604 used in usernames and passwords. 606 2.4.3. Examples 608 Example of the [PLAIN] SASL mechanism under a TLS layer, using an 609 initial client response: 611 [C] CAPABILITIES 612 [S] 101 Capability list: 613 [S] VERSION 2 614 [S] READER 615 [S] STARTTLS 616 [S] AUTHINFO SASL 617 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI 618 [S] LIST ACTIVE NEWSGROUPS 619 [S] . 620 [C] STARTTLS 621 [S] 382 Continue with TLS negotiation 622 [TLS negotiation proceeds, further commands protected by TLS layer] 623 [C] CAPABILITIES 624 [S] 101 Capability list: 625 [S] VERSION 2 626 [S] READER 627 [S] AUTHINFO USER SASL 629 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI PLAIN EXTERNAL 630 [S] LIST ACTIVE NEWSGROUPS 631 [S] . 632 [C] AUTHINFO SASL PLAIN AHRlc3QAMTIzNA== 633 [S] 281 Authentication accepted 635 Example of the EXTERNAL SASL mechanism under a TLS layer, using the 636 authorization identity derived from the client TLS certificate, and 637 thus a zero-length initial client response (commands prior to 638 AUTHINFO SASL are the same as the previous example and have been 639 omitted): 641 [C] AUTHINFO SASL EXTERNAL = 642 [S] 281 Authentication accepted 644 Example of the [DIGEST-MD5] SASL mechanism, which includes a server 645 challenge and server success data (whitespace has been inserted for 646 clarity; base64-encoded data is actually sent as a single line with 647 no embedded whitespace): 649 [C] AUTHINFO SASL DIGEST-MD5 650 [S] 383 bm9uY2U9InNheUFPaENFS0dJZFBNSEMwd3RsZUxxT0ljT0kyd1FZSWU0 651 enplQXR1aVE9IixyZWFsbT0iZWFnbGUub2NlYW5hLmNvbSIscW9wPSJhdXRo 652 LGF1dGgtaW50LGF1dGgtY29uZiIsY2lwaGVyPSJyYzQtNDAscmM0LTU2LHJj 653 NCxkZXMsM2RlcyIsbWF4YnVmPTQwOTYsY2hhcnNldD11dGYtOCxhbGdvcml0 654 aG09bWQ1LXNlc3M= 655 [C] dXNlcm5hbWU9InRlc3QiLHJlYWxtPSJlYWdsZS5vY2VhbmEuY29tIixub25j 656 ZT0ic2F5QU9oQ0VLR0lkUE1IQzB3dGxlTHFPSWNPSTJ3UVlJZTR6emVBdHVp 657 UT0iLGNub25jZT0iMFkzSlFWMlRnOVNjRGlwK08xU1ZDMHJoVmcvLytkbk9J 658 aUd6LzdDZU5KOD0iLG5jPTAwMDAwMDAxLHFvcD1hdXRoLWNvbmYsY2lwaGVy 659 PXJjNCxtYXhidWY9MTAyNCxkaWdlc3QtdXJpPSJubnRwL2xvY2FsaG9zdCIs 660 cmVzcG9uc2U9ZDQzY2Y2NmNmZmE5MDNmOWViMDM1NmMwOGEzZGIwZjI= 661 [S] 283 cnNwYXV0aD1kZTJlMTI3ZTVhODFjZGE1M2Q5N2FjZGEzNWNkZTgzYQ== 663 Example of a failed authentication due to bad [GSSAPI] credentials. 664 Note that while the mechanism can utilize the initial response, the 665 client chooses not to use it because of its length, resulting in a 666 zero-length server challenge (here whitespace has been inserted for 667 clarity; base64-encoded data is actually sent as a single line with 668 no embedded whitespace): 670 [C] AUTHINFO SASL GSSAPI 671 [S] 383 = 672 [C] YIICOAYJKoZIhvcSAQICAQBuggInMIICI6ADAgEFoQMCAQ6iBwMFACAAAACj 673 ggE/YYIBOzCCATegAwIBBaEYGxZURVNULk5FVC5JU0MuVVBFTk4uRURVoiQw 674 IqADAgEDoRswGRsEbmV3cxsRbmV0bmV3cy51cGVubi5lZHWjge8wgeygAwIB 675 EKEDAgECooHfBIHcSQfLKC8vm2i17EXmomwk6hHvjBY/BnKnvvDTrbno3198 676 vlX2RSUt+CjuAKhcDcj4DW0gvZEqH7t5v9yWedzztlpaThebBat6hQNr9NJP 677 ozh1/+74HUwhGWb50KtjuftO/ftQ8q0nTuYKgIq6PM4tp2ddo1IfpjfdNR9E 678 95GFi3y1uBT7lQOwtQbRJUjPSO3ijdue9V7cNNVmYsBsqNsaHhvlBJEXf4WJ 679 djH8yG+Dw/gX8fUTtC5fDpB5zLt01mkSXh6Wc4UhqQtwZBI2t/+TpX1okbg6 680 Hr1ZZupeH6SByjCBx6ADAgEQooG/BIG8GnCmcXWtqhXh48dGTLHQgJ04K5Fj 681 RMMq2qPSbiha9lq0osqR2KAnQA6LioWYxU+6yPKpBDSC5WOT441fUfkM8iAL 682 kW3uNc+luFCGcnDsacrmoVU7Y6Akcp9m7Fm7orRc+TWSWPpBg3OR2oG3ATW0 683 0NAz8TT06VOLVxIMUTINKdYVI/Ja7f3sy+/N4LGkJqScCQOwlo5tfDWn/UQF 684 iTWo5Zw435rH8pjy2smQCnqC14v3NMAWTu4j+dzHUNw= 685 [S] 481 Authentication error 687 Example of a client aborting in the midst of an exchange: 689 [C] AUTHINFO SASL GSSAPI 690 [S] 383 = 691 [C] * 692 [S] 481 Authentication aborted as requested 694 Example of attempting to use a mechanism that is not supported by 695 the server: 697 [C] AUTHINFO SASL EXAMPLE 698 [S] 503 Mechanism not recognized 700 Example of attempting to use a mechanism that requires a security 701 layer: 703 [C] AUTHINFO SASL PLAIN 704 [S] 483 Encryption or stronger authentication required 706 Example of using an initial response with a mechanism that doesn't 707 support it (server must start the exchange): 709 [C] AUTHINFO SASL CRAM-MD5 AHRlc3QAMTIzNA== 710 [S] 482 SASL protocol error 712 Example of a failed authentication due to an incorrectly encoded 713 response: 715 [C] AUTHINFO SASL CRAM-MD5 716 [S] 383 PDE1NDE2NzQ5My4zMjY4MzE3QHRlc3RAZXhhbXBsZS5jb20+ 717 [C] abcd=efg 718 [S] 504 Base64 encoding error 720 3. Augmented BNF Syntax for the AUTHINFO Extension 722 This section describes the syntax of the AUTHINFO extension. It 723 extends the syntax in [NNTP], and non-terminals not defined in this 724 document are defined there. 726 3.1. Commands 728 This syntax extends the non-terminal "command", which represents an 729 NNTP command. 731 command =/ authinfo-sasl-command / 732 authinfo-user-command / 733 authinfo-pass-command 735 authinfo-sasl-command = "AUTHINFO" WS "SASL" WS mechanism 736 [WS initial-response] 737 authinfo-user-command = "AUTHINFO" WS "USER" WS username 738 authinfo-pass-command = "AUTHINFO" WS "PASS" WS password 740 initial-response = base64-opt 741 username = 1*user-pass-char 742 password = 1*user-pass-char 743 user-pass-char = P-CHAR 745 NOTE: A server implementation MAY parse AUTHINFO USER and AUTHINFO 746 PASS specially as to allow white space to be used within the 747 username or password. Such implementations accept the additional 748 syntax (making these two items inconsistent with "token" in section 749 9.7 of [NNTP]): 751 user-pass-char =/ SP / TAB 753 In doing so, the grammar can become ambiguous if the username or 754 password begins or ends with white space. To solve this ambiguity, 755 such implementations typically treat everything after the first 756 white space character following "USER"/"PASS", up to, but not 757 including, the CRLF as the username/password. 759 3.2. Command Continuation 761 This syntax extends the non-terminal "command-continuation", which 762 represents the further material sent by the client in the case of 763 multi-stage commands. 765 command-continuation =/ authinfo-sasl-continuation 766 authinfo-sasl-continuation = ("*" / base64-opt) CRLF 767 ; client must send a continuation following each 768 ; "383" response from the server 770 3.3. Responses 771 This syntax extends the non-terminal "simple-response-content", 772 which represents an initial response line sent by the server. 774 simple-response-content =/ sasl-response-content 775 sasl-response-content = "283" SP base64 / "383" SP base64-opt 777 3.4. Capability entries 779 This syntax extends the non-terminal "capability-entry", which rep- 780 resents a capability that may be advertised by the server. 782 capability-entry =/ authinfo-capability / 783 sasl-capability 785 authinfo-capability = "AUTHINFO" *(WS authinfo-variant) 786 authinfo-variant = "USER" / "SASL" 787 sasl-capability = "SASL" 1*(WS mechanism) 789 3.5. General non-terminals 791 base64-opt = "=" / base64 793 mechanism = 1*20mech-char 794 mech-char = UPPER / DIGIT / "-" / "_" 796 4. Summary of Response Codes 798 This section contains a list of every new response code defined in 799 this document, whether it is multi-line, which commands can 800 generate it, what arguments it has, and what its meaning is. 802 Response code 281 803 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 804 Meaning: authentication accepted 806 Response code 283 807 Generated by: AUTHINFO SASL 808 1 argument: challenge 809 Meaning: authentication accepted (with success data) 811 Response code 381 812 Generated by: AUTHINFO USER 813 Meaning: password required via AUTHINFO PASS command. Note 814 that this code is used for backwards compatibility and does 815 not conform to the traditional use of 3xx codes. 817 Response code 383 818 Generated by: AUTHINFO SASL 819 1 argument: challenge 820 Meaning: continue with SASL exchange 822 Response code 481 823 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 824 Meaning: authentication failed/rejected 826 Response code 482 827 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 828 Meaning: authentication commands issued out of sequence or 829 SASL protocol error 831 5. Authentication Tracking/Logging 833 This section contains implementation suggestions and notes of best 834 current practice, and does not specify further network protocol 835 requirements. 837 Once authenticated, the authorization identity presented in the 838 AUTHINFO exchange (username when using USER/PASS) SHOULD be 839 included in an audit trail associating the identity with any 840 articles supplied during a POST operation, and this configuration 841 SHOULD be the default. This may be accomplished, for example, by 842 inserting headers in the posted articles or by a server logging 843 mechanism. The server MAY provide a facility for disabling the 844 procedure described above, as some users or administrators may 845 consider it a violation of privacy. 847 6. Security Considerations 849 Security issues are discussed throughout this memo. 851 Before the [SASL] negotiation has begun, any protocol interactions 852 may have been performed in the clear and may have been modified by 853 an active attacker. For this reason, clients and servers MUST 854 discard any sensitive knowledge obtained prior to the start of the 855 SASL negotiation upon the establishment of a security layer. 857 Servers MAY implement a policy whereby the connection is dropped 858 after a number of failed authentication attempts. If they do so, 859 they SHOULD NOT drop the connection until at least 3 attempts at 860 authentication have failed. 862 Implementations MUST support a configuration where authentication 863 mechanisms that are vulnerable to passive eavesdropping attacks 864 (such as AUTHINFO USER/PASS and SASL [PLAIN]) are not advertised or 865 used without the presence of an external security layer such as TLS 866 [NNTP-TLS]. 868 When multiple authentication mechanisms are permitted by both 869 client and server, an active attacker can cause a down-negotiation 870 to the weakest mechanism. For this reason, both clients and 871 servers SHOULD be configurable to forbid use of weak mechanisms. 872 The minimum strength acceptable is a policy decision which is 873 outside the scope of this specification. 875 7. IANA Considerations 877 7.1. IANA Considerations for SASL/GSSAPI services 879 Please register the SASL/GSSAPI service name "nntp". This service 880 name refers to authenticated use of Usenet news service when 881 provided via the [NNTP] protocol. 883 o Published Specification: This document. 885 o Author, Change Controller, and Contact for Further Information: 886 Author of this document. 888 7.2. IANA Considerations for NNTP extensions 890 Below is a formal definition of the AUTHINFO extension as required 891 by Section 3.3.3 of [NNTP] for the IANA registry. may 892 o This extension provides an extensible mechanism for NNTP 893 authentication via a variety of methods. 895 o The capability label for this extension is "AUTHINFO". 897 o The "AUTHINFO" capability label has two possible optional 898 arguments "USER" and "SASL" (as defined in Section 2.1) 899 indicating which variants of the AUTHINFO command are supported. 901 o This extension also provides the "SASL" capability label whose 902 arguments list the available SASL mechanisms. 904 o This extension defines three new commands, AUTHINFO USER, 905 AUTHINFO PASS, and AUTHINFO SASL, whose behavior, arguments, and 906 responses are defined in Sections 2.3 and 2.4. 908 o This extension does not associate any new responses with pre- 909 existing NNTP commands. 911 o This extension may affect the overall behavior of both server 912 and client, in that the AUTHINFO SASL command may require that 913 subsequent communication be transmitted via an intermediary 914 security layer. 916 o The length of the AUTHINFO SASL command (as defined in this 917 document) may exceed 512 octets. The maximum length of this 918 command is increased to that which can accommodate the largest 919 initial response possible for any of the SASL mechanisms 920 supported by the implementation. 922 o This extension defines two new responses, 283 and 383, whose 923 lengths may exceed 512 octets. The maximum length of these 924 responses is increased to that which can accommodate the largest 925 challenge possible for any of the SASL mechanisms supported by 926 the implementation. 928 o This extension does not alter pipelining, but AUTHINFO commands 929 cannot be pipelined. 931 o Use of this extension may alter the capabilities list; once the 932 AUTHINFO command has been used successfully, the AUTHINFO 933 capability can no longer be advertised by CAPABILITIES. 934 Additionally, the MODE-READER capability MUST NOT be advertised 935 after successful authentication. 937 o This extension does not cause any pre-existing command to 938 produce a 401, 480, or 483 response. 940 o This extension is unaffected by any use of the MODE READER 941 command, however the MODE READER command MUST NOT be used in the 942 same session following successful authentication. 944 o Published Specification: This document. 946 o Author, Change Controller, and Contact for Further Information: 947 Author of this document. 949 8. References 951 8.1. Normative References 953 [ABNF] Crocker, D., Overell, P., "Augmented BNF for Syntax 954 Specifications: ABNF", RFC 2234, November 1997. 956 [AUTH] Haller, N., Atkinson, R., "On Internet Authentication", 957 RFC 1704, Bell Communications Research, October 1994. 959 [BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data 960 Encodings", RFC 3548, July 2003. 962 [DIGEST-MD5] Leach, P., Newman, C., "Using Digest Authentication as 963 a SASL Mechanism", RFC 2831, May 2000. 965 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 966 Requirement Levels", RFC 2119, Harvard University, March 1997. 968 [NNTP] Feather, C., "Network News Transport Protocol", 969 draft-ietf-nntpext-base-*.txt, Work in Progress. 971 [NNTP-TLS] Vinocur, J., Murchison, K., Newman, C., "Using TLS with NNTP", 972 draft-ietf-nntpext-tls-nntp-*.txt, Work in Progress. 974 [SASL] Melnikov, A., "Simple Authentication and Security Layer 975 (SASL)", draft-ietf-sasl-rfc2222bis-*.txt, Work in Progress. 977 [SASLprep] Zeilega, K., "SASLprep: Stringprep profile for user names 978 and passwords", draft-ietf-sasl-saslprep-*.txt, Work in Progress. 980 [StringPrep] Hoffman, P. and Blanchet, M., "Preparation of 981 Internationalized Strings ("stringprep")", 982 draft-hoffman-rfc3454bis-*.txt, Work in Progress. 984 8.2. Informative References 986 [CRAM-MD5] Nerenberg, L., "The CRAM-MD5 SASL Mechanism", draft- 987 ietf-sasl-crammd5-*.txt, Work in Progress. 989 [GSSAPI] Melnikov, A., "SASL GSSAPI Mechanisms", draft-ietf-sasl- 990 gssapi-*.txt, Work in Progress. 992 [NNTP-COMMON] Barber, S., "Common NNTP Extensions", RFC 2980, 993 Academ Consulting Services, October 2000. 995 [PLAIN] Zeilenga, K., "The Plain SASL Mechanism", draft-ietf-sasl- 996 plain-*.txt, Work in Progress. 998 [SMTP] Klensin, J., "Simple Mail Transport Protocol", RFC 2821, 999 AT&T Laboratories, April 2001. 1001 [UTF-8] Yergeau, F. "UTF-8, a transformation format of ISO 10646", 1002 RFC 3629, Alis Technologies, November 2003. 1004 9. Authors' Addresses 1006 Jeffrey M. Vinocur 1007 Department of Computer Science 1008 Upson Hall 1009 Cornell University 1010 Ithaca, NY 14853 USA 1012 Email: vinocur@cs.cornell.edu 1013 Kenneth Murchison 1014 Oceana Matrix Ltd. 1015 21 Princeton Place 1016 Orchard Park, NY 14127 USA 1018 Email: ken@oceana.com 1020 Chris Newman 1021 Sun Microsystems 1022 1050 Lakes Drive, Suite 250 1023 West Covina, CA 91790 USA 1025 Email: cnewman@iplanet.com 1027 10. Acknowledgments 1029 A significant amount of the authentication text was originally from 1030 the NNTP revision or common authentication specs written by Stan 1031 Barber. A significant amount of the SASL text was lifted from the 1032 revisions to RFC 1734 and RFC 2554 by Rob Siemborski. 1034 Special acknowledgment also goes to Russ Allbery, Clive Feather, 1035 and others who commented privately on intermediate revisions of 1036 this document, as well as the members of the IETF NNTP Working 1037 Group for continual (yet sporadic) insight in discussion. 1039 11. Intellectual Property Rights 1041 The IETF takes no position regarding the validity or scope of any 1042 intellectual property or other rights that might be claimed to 1043 pertain to the implementation or use of the technology described in 1044 this document or the extent to which any license under such rights 1045 might or might not be available; neither does it represent that it 1046 has made any effort to identify any such rights. Information on 1047 the IETF's procedures with respect to rights in standards-track and 1048 standards-related documentation can be found in BCP-11. Copies of 1049 claims of rights made available for publication and any assurances 1050 of licenses to be made available, or the result of an attempt made 1051 to obtain a general license or permission for the use of such 1052 proprietary rights by implementers or users of this specification 1053 can be obtained from the IETF Secretariat. 1055 The IETF invites any interested party to bring to its attention any 1056 copyrights, patents or patent applications, or other proprietary 1057 rights which may cover technology that may be required to practice 1058 this standard. Please address the information to the IETF 1059 Executive Director. 1061 12. Copyright 1063 Copyright (C) The Internet Society (2005). This document is 1064 subject to the rights, licenses and restrictions contained in BCP 1065 78, and except as set forth therein, the authors retain all their 1066 rights." 1068 This document and the information contained herein are provided on 1069 an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 1070 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND 1071 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, 1072 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT 1073 THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR 1074 ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A 1075 PARTICULAR PURPOSE.