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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'C' is mentioned on line 726, but not defined == Missing Reference: 'S' is mentioned on line 727, but not defined -- Looks like a reference, but probably isn't: '1' on line 442 -- Looks like a reference, but probably isn't: '2' on line 447 -- Looks like a reference, but probably isn't: '3' on line 463 == Unused Reference: 'CRAM-MD5' is defined on line 1014, but no explicit reference was found in the text == Unused Reference: 'SMTP' is defined on line 1027, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2234 (ref. '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) -- No information found for draft-ietf-sasl-rfc2831bis- - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'DIGEST-MD5' -- 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' ** Obsolete normative reference: RFC 2222 (ref. 'SASL') (Obsoleted by RFC 4422, RFC 4752) ** Obsolete normative reference: RFC 4013 (ref. 'SASLprep') (Obsoleted by RFC 7613) ** Obsolete normative reference: RFC 3454 (ref. 'StringPrep') (Obsoleted by RFC 7564) -- Duplicate reference: RFC2222, mentioned in 'GSSAPI', was also mentioned in 'SASL'. -- Obsolete informational reference (is this intentional?): RFC 2222 (ref. 'GSSAPI') (Obsoleted by RFC 4422, RFC 4752) -- Obsolete informational reference (is this intentional?): RFC 2821 (ref. 'SMTP') (Obsoleted by RFC 5321) Summary: 10 errors (**), 0 flaws (~~), 7 warnings (==), 20 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: 2980 (if approved) K. Murchison 5 Expires: December 2005 Oceana Matrix Ltd. 6 C. Newman 7 Sun Microsystems 8 June 2005 10 NNTP Extension for Authentication 11 draft-ietf-nntpext-authinfo-09 13 Status of this memo 15 By submitting this Internet-Draft, each author represents that any 16 applicable patent or other IPR claims of which he or she is aware 17 have been or will be disclosed, and any of which he or she becomes 18 aware will be disclosed, in accordance with Section 6 of BCP 79. 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 This document updates and formalizes the AUTHINFO USER/PASS 50 authentication method specified in RFC 2980 and deprecates the 51 AUTHINFO SIMPLE and AUTHINFO GENERIC authentication methods. 52 Additionally, this document defines a profile of the Simple 53 Authentication and Security Layer (SASL) for NNTP. 55 Note to the RFC Editor 57 The normative references to RFC 2234, RFC 2222, and RFC 3454 and 58 the informative references to RFC 2195, RFC 2222, and RFC 2595 may 59 be replaced by draft-crocker-abnf-rfc2234bis, 60 draft-ietf-sasl-rfc2222bis, draft-hoffman-rfc3454bis, 61 draft-ietf-sasl-crammd5, draft-ietf-sasl-gssapi, and 62 draft-ietf-sasl-plain respectively should any or all of those 63 documents reach RFC status before this one. 65 The normative references to [NNTP] and [NNTP-TLS] are documents 66 which are expected to be published simultaneously with this one 67 and so can be replaced by references to the resulting RFCs. 69 Table of Contents 71 1. Introduction ............................................. 3 72 1.1. Conventions Used in this Document ................... 3 73 2. The AUTHINFO Extension ................................... 4 74 2.1. Advertising the AUTHINFO Extension .................. 4 75 2.2. Authenticating with the AUTHINFO Extension .......... 5 76 2.3. AUTHINFO USER/PASS Command .......................... 6 77 2.3.1. Usage .......................................... 6 78 2.3.2. Description .................................... 7 79 2.3.3. Examples ....................................... 8 80 2.4. AUTHINFO SASL Command ............................... 9 81 2.4.1. Usage .......................................... 9 82 2.4.2. Description .................................... 10 83 2.4.3. Examples ....................................... 13 84 3. Augmented BNF Syntax for the AUTHINFO Extension .......... 16 85 3.1. Commands ............................................ 16 86 3.2. Command Continuation ................................ 17 87 3.3. Responses ........................................... 17 88 3.4. Capability entries .................................. 17 89 3.5. General non-terminals ............................... 17 90 4. Summary of Response Codes ................................ 17 91 5. Authentication Tracking/Logging .......................... 18 92 6. Security Considerations .................................. 18 93 7. IANA Considerations ...................................... 19 94 7.1. IANA Considerations for SASL/GSSAPI services ........ 19 95 7.2. IANA Considerations for NNTP extensions ............. 20 96 8. References ............................................... 21 97 8.1. Normative References ................................ 21 98 8.2. Informative References .............................. 22 99 9. Authors' Addresses ....................................... 22 100 10. Acknowledgments ......................................... 23 101 11. Intellectual Property Rights ............................ 23 102 12. Copyright ............................................... 23 104 1. Introduction 106 Although NNTP [NNTP] has traditionally been used to provide public 107 access to newsgroups, authentication is often useful, for example 108 to control resource consumption, to allow abusers of the POST 109 command to be identified, and to restrict access to "local" 110 newsgroups. 112 The ad-hoc AUTHINFO USER and AUTHINFO PASS commands, documented in 113 [NNTP-COMMON], provide a very weak authentication mechanism in 114 widespread use by the installed base. Due to their ubiquity they 115 are formalized in this specification but, because of their 116 insecurity, only for use in combination with appropriate security 117 layers. 119 The ad-hoc AUTHINFO GENERIC command, also documented in 120 [NNTP-COMMON] but much less ubiquitous, provided an NNTP-specific 121 equivalent of the generic SASL [SASL] facility. This document 122 deprecates AUTHINFO GENERIC in favor of an AUTHINFO SASL 123 replacement so that NNTP can benefit from authentication mechanisms 124 developed for other SASL-enabled application protocols including 125 SMTP, POP, IMAP, LDAP, and BEEP. 127 This specification is to be read in conjunction with the NNTP base 128 specification [NNTP]. Except where specifically stated otherwise, 129 in the case of a conflict between these two documents [NNTP] takes 130 precedence over this one. 132 It is also recommended that this specification be read in 133 conjunction with the SASL base specification [SASL]. 135 1.1. Conventions Used in this Document 137 The notational conventions used in this document are the same as 138 those in [NNTP] and any term not defined in this document has the 139 same meaning as in that one. 141 The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD 142 NOT", "MAY", and "OPTIONAL" in this document are to be interpreted 143 as described in "Key words for use in RFCs to Indicate Requirement 144 Levels" [KEYWORDS]. 146 Terms related to authentication are defined in "On Internet 147 Authentication" [AUTH]. 149 In the examples, commands from the client are indicated with [C], 150 and responses from the server are indicated with [S]. 152 2. The AUTHINFO Extension 154 The AUTHINFO extension is used to authenticate a user. Note that 155 authorization is a matter of site policy, not network protocol, and 156 is therefore not discussed in this document. The server determines 157 authorization in whatever manner is defined by its implementation 158 as configured by the site administrator. 160 This extension provides three new commands: AUTHINFO USER, AUTHINFO 161 PASS, and AUTHINFO SASL. The capability label for this extension 162 is AUTHINFO. 164 2.1. Advertising the AUTHINFO Extension 166 A server MUST implement at least one of the AUTHINFO USER or 167 AUTHINFO SASL commands in order to advertise the AUTHINFO 168 capability in the response to the CAPABILITIES command. However, 169 this capability MUST NOT be advertised after successful 170 authentication (see section 2.2). This capability MAY be 171 advertised both before and after any use of MODE READER, with the 172 same semantics. 174 The AUTHINFO capability label contains an argument list detailing 175 which authentication commands are available. 177 The "USER" argument indicates that AUTHINFO USER/PASS is supported 178 as defined by Section 2.3 of this document. The "USER" argument 179 MUST NOT be advertised, and the AUTHINFO USER/PASS commands SHOULD 180 NOT be provided, unless a strong encryption layer (e.g. TLS 181 [NNTP-TLS]) is in use or backward compatibility dictates otherwise. 183 The "SASL" argument indicates that AUTHINFO SASL is supported as 184 defined by Section 2.4 of this document. If the server advertises 185 the "SASL" argument, then it MUST also advertise the "SASL" 186 capability in response to the CAPABILITIES command. The SASL 187 capability is followed by a whitespace-separated list of available 188 SASL mechanism names. 190 The server MAY list the AUTHINFO capability with no arguments, 191 which indicates that it complies with this specification and does 192 not permit any authentication commands in its current state. In 193 this case, the client MUST NOT attempt to utilize any AUTHINFO 194 commands, even if it contains logic to do so (e.g. for backward 195 compatibility with servers that are not compliant with this 196 specification). 198 Future extensions may add additional arguments to this capability. 199 Unrecognized arguments MUST be ignored by the client. 201 As the AUTHINFO command is related to security, cached results of 202 CAPABILITIES from a previous session MUST NOT be relied on, as per 203 section 12.6 of [NNTP]. However, a client MAY use such cached 204 results in order to detect active down-negotiation attacks. 206 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] 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 286 [NNTP-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 Should the client successfully present proper credentials, the 350 server issues a 281 reply. If the server is unable to authenticate 351 the client, it MUST reject the AUTHINFO USER/PASS command with a 352 481 reply. If an AUTHINFO USER/PASS command fails, the client MAY 353 proceed without authentication. Alternatively, the client MAY try 354 another authentication mechanism, or present different credentials 355 by issuing another AUTHINFO command. 357 The AUTHINFO PASS command permits the client to use a clear-text 358 password to authenticate. A compliant implementation MUST NOT 359 implement this command without also implementing support for TLS 360 [NNTP-TLS]. Use of this command without an active strong 361 encryption layer is deprecated, as it exposes the user's password 362 to all parties on the network between the client and the server. 363 Any implementation of this command SHOULD be configurable to 364 disable it whenever a strong encryption layer such as that provided 365 by [NNTP-TLS] is not active, and this configuration SHOULD be the 366 default. The server will use the 483 response code to indicate 367 that the datastream is insufficiently secure for the command being 368 attempted (see section 3.2.1 of [NNTP]). 370 Usernames and passwords MUST use the UTF-8 [UTF-8] character set 371 and a client MUST convert any user input to UTF-8 if necessary. 373 Note that a server MAY, but is not required to, allow white space 374 characters in usernames and passwords. A server implementation MAY 375 blindly split command arguments at white space and therefore not 376 preserve the exact sequence of white space characters in the 377 username or password. Therefore a client SHOULD scan the username 378 and password for whitespace, and if detected, warn the user of the 379 likelihood of problems. The SASL PLAIN [PLAIN] mechanism is 380 recommended as an alternative, as it does not suffer from these 381 issues. 383 2.3.3. Examples 384 Example of successful AUTHINFO USER: 386 [C] AUTHINFO USER wilma 387 [S] 281 Authentication accepted 389 Example of successful AUTHINFO USER/PASS: 391 [C] AUTHINFO USER fred 392 [S] 381 Enter passphrase 393 [C] AUTHINFO PASS flintstone 394 [S] 281 Authentication accepted 396 Example of AUTHINFO USER/PASS requiring a security layer: 398 [C] AUTHINFO USER fred@stonecanyon.example 399 [S] 483 Encryption or stronger authentication required 401 Example of failed AUTHINFO USER/PASS: 403 [C] AUTHINFO USER barney 404 [S] 381 Enter passphrase 405 [C] AUTHINFO PASS flintstone 406 [S] 481 Authentication failed 408 Example of AUTHINFO PASS before AUTHINFO USER: 410 [C] AUTHINFO PASS flintstone 411 [S] 482 Authentication commands issued out of sequence 413 2.4. AUTHINFO SASL Command 415 This section defines a formal profile of the Simple Authentication 416 and Security Layer [SASL]. The use of the AUTHINFO GENERIC command 417 as documented in Section 3.1.3 of [NNTP-COMMON] as a way to perform 418 SASL authentication is deprecated in favor of the AUTHINFO SASL 419 command. A server SHOULD NOT advertise AUTHINFO GENERIC in the 420 list of capabilities returned by CAPABILITIES. 422 2.4.1. Usage 424 This command MUST NOT be pipelined. 426 Syntax 427 AUTHINFO SASL mechanism [initial-response] 429 This command MAY exceed 512 octets. The maximum length of this 430 command is increased to that which can accommodate the largest 431 encoded initial response possible for any of the SASL mechanisms 432 supported by the implementation. 434 Responses 435 281 Authentication accepted 436 283 challenge Authentication accepted (with success data) [1] 437 383 challenge Continue with SASL exchange [1] 438 481 Authentication failed/rejected 439 482 SASL protocol error 440 502 Command unavailable [2] 442 [1] These responses MAY exceed 512 octets. The maximum length of 443 these responses is increased to that which can accommodate the 444 largest encoded challenge possible for any of the SASL mechanisms 445 supported by the implementation. 447 [2] If authentication has already occurred, AUTHINFO SASL is not a 448 valid command (see section 2.2). 450 NOTE: Notwithstanding section 3.2.1 of [NNTP], the server MUST NOT 451 return 480 in response to AUTHINFO SASL. 453 Parameters 454 mechanism = String identifying a [SASL] authentication 455 mechanism. 456 initial-response = Optional initial client response. 457 If present, the response MUST be encoded as 458 specified in Section 3 of [BASE64]. [3] 459 challenge = Server challenge. 460 The challenge MUST be encoded as specified 461 in Section 3 of [BASE64]. 463 [3] This argument MAY exceed 497 octets. The maximum length of 464 this argument is increased to that which can accommodate the 465 largest encoded initial response possible for any of the SASL 466 mechanisms supported by the implementation. 468 2.4.2. Description 470 The AUTHINFO SASL command initiates a [SASL] authentication 471 exchange between the client and the server. The client identifies 472 the SASL mechanism to use with the first parameter of the AUTHINFO 473 SASL command. If the server supports the requested authentication 474 mechanism, it performs the SASL exchange to authenticate the user. 475 Optionally, it also negotiates a security layer for subsequent 476 protocol interactions during this session. If the requested 477 authentication mechanism is invalid (e.g. is not supported), the 478 server rejects the AUTHINFO SASL command with a 503 reply (see 479 section 3.2.1 of [NNTP]). If the requested authentication 480 mechanism requires an encryption layer, the server rejects the 481 AUTHINFO SASL command with a 483 reply (see section 3.2.1 of 482 [NNTP]). 484 The service name specified by this protocol's profile of SASL is 485 "nntp". 487 The SASL authentication exchange consists of a series of server 488 challenges and client responses that are specific to the chosen 489 [SASL] mechanism. 491 A server challenge is sent as a 383 reply with a single argument 492 containing the [BASE64] encoded string supplied by the SASL 493 mechanism. A server challenge that has zero length MUST be sent as 494 a single equals sign ("=") and not omitted (in order to comply with 495 the [NNTP] requirement that responses always have the same number 496 of arguments). 498 A client response consists of a line containing a [BASE64] encoded 499 string. A client response that has zero length MUST be sent as a 500 single equals sign ("=") and not omitted (for consistency with the 501 server challenge format). If the client wishes to cancel the 502 authentication exchange, it issues a line with a single "*". If 503 the server receives such a response, it MUST reject the AUTHINFO 504 SASL command by sending a 481 reply. 506 Note that these [BASE64] strings can be much longer than normal 507 NNTP responses. Clients and servers MUST be able to handle the 508 maximum encoded size of challenges and responses generated by their 509 supported authentication mechanisms. This requirement is 510 independent of any line length limitations the client or server may 511 have in other parts of its protocol implementation. 513 The optional initial response argument to the AUTHINFO SASL command 514 is used to save a round trip when using authentication mechanisms 515 that support an initial client response. If the initial response 516 argument is omitted and the chosen mechanism requires an initial 517 client response, the server MUST proceed as defined in section 5.1 518 of [SASL]. In NNTP, a server challenge that contains no data is 519 equivalent to a zero length challenge and is encoded as a single 520 equals sign ("="). 522 Note that the [BASE64] encoded initial response argument can exceed 523 497 octets and therefore the AUTHINFO SASL command can exceed 512 524 octets. Clients SHOULD, and servers MUST be able to handle the 525 maximum encoded size of initial responses possible for their 526 supported authentication mechanisms. This requirement is 527 independent of any command or argument length limitations the 528 client or server may have in other parts of its protocol 529 implementation. 531 If use of the initial response argument would cause the AUTHINFO 532 SASL command to exceed 512 octets, the client MAY choose to omit 533 the initial response parameter (and instead proceed as defined in 534 section 5.1 of [SASL]). 536 If the client is transmitting an initial response of zero length, 537 it MUST instead transmit the response as a single equals sign 538 ("="). This indicates that the response is present, but contains 539 no data. 541 If the client uses an initial-response argument to the AUTHINFO 542 SASL command with a SASL mechanism that does not support an initial 543 client response, the server MUST reject the AUTHINFO SASL command 544 with a 482 reply. 546 If the server cannot [BASE64] decode any client response, it MUST 547 reject the AUTHINFO SASL command with a 504 reply (see section 548 3.2.1 of [NNTP]). If the client cannot BASE64 decode any of the 549 server's challenges, it MUST cancel the authentication using the 550 "*" response. In particular, servers and clients MUST reject (and 551 not ignore) any character not explicitly allowed by the BASE64 552 alphabet, and MUST reject any sequence of BASE64 characters that 553 contains the pad character ('=') anywhere other than the end of the 554 string (e.g. "=AAA" and "AAA=BBB" are not allowed). 556 The authorization identity generated by this [SASL] exchange is a 557 simple username, and both client and server MUST use the [SASLprep] 558 profile of the [StringPrep] algorithm to prepare these names for 559 transmission or comparison. If preparation of the authorization 560 identity fails or results in an empty string (unless it was 561 transmitted as the empty string), the server MUST fail the 562 authentication with a 481 reply. 564 Should the client successfully complete the exchange, the server 565 issues either a 281 or 283 reply. If the server is unable to 566 authenticate the client, it MUST reject the AUTHINFO SASL command 567 with a 481 reply. If an AUTHINFO SASL command fails, the client 568 MAY proceed without authentication. Alternatively, the client MAY 569 try another authentication mechanism, or present different 570 credentials by issuing another AUTHINFO command. 572 If the SASL mechanism returns additional data on success (e.g. 573 server authentication), the NNTP server issues a 283 reply with a 574 single argument containing the [BASE64] encoded string supplied by 575 the SASL mechanism. If no additional data is returned on success, 576 the server issues a 281 reply. 578 If a security layer is negotiated during the SASL exchange, it 579 takes effect for the client on the octet immediately following the 580 CRLF that concludes the last response generated by the client. For 581 the server, it takes effect immediately following the CRLF of its 582 success reply. 584 When a security layer takes effect, the NNTP protocol is reset to 585 the state immediately after the initial greeting response (see 5.1 586 of [NNTP]) has been sent, with the exception that if a MODE READER 587 command has been issued, the effects of it (if any) are not 588 reversed. The server MUST discard any knowledge obtained from the 589 client, such as the current newsgroup and article number, that was 590 not obtained from the SASL negotiation itself. Likewise, the 591 client SHOULD discard and MUST NOT rely on any knowledge obtained 592 from the server, such as the capability list, that was not obtained 593 from the SASL negotiation itself. (Note that a client MAY compare 594 the advertised SASL mechanisms before and after authentication in 595 order to detect an active down-negotiation attack.) 597 When both TLS [NNTP-TLS] and SASL security layers are in effect, 598 the TLS encoding MUST be applied after the SASL encoding (the 599 cleartext data is always SASL encoded first and then the resultant 600 data is TLS encoded). 602 To ensure interoperability, client and server implementations of 603 this extension MUST implement the [DIGEST-MD5] SASL mechanism. 605 If AUTHINFO USER/PASS and AUTHINFO SASL are both implemented, the 606 SASL [PLAIN] mechanism SHOULD also be implemented, as the 607 functionality of DIGEST-MD5 is insufficient for some environments 608 (e.g. the server may need to pass the plaintext password off to an 609 external authentication service). The SASL PLAIN mechanism is 610 preferred over AUTHINFO USER, even if there is not a strong 611 encryption layer active, because it eliminates limitations that 612 AUTHINFO USER/PASS has with regards to white space characters being 613 used in usernames and passwords. 615 2.4.3. Examples 617 Example of the [PLAIN] SASL mechanism under a TLS layer, using an 618 initial client response: 620 [C] CAPABILITIES 621 [S] 101 Capability list: 622 [S] VERSION 2 623 [S] READER 625 [S] STARTTLS 626 [S] AUTHINFO SASL 627 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI 628 [S] LIST ACTIVE NEWSGROUPS 629 [S] . 630 [C] STARTTLS 631 [S] 382 Continue with TLS negotiation 632 [TLS negotiation proceeds, further commands protected by TLS] 633 [C] CAPABILITIES 634 [S] 101 Capability list: 635 [S] VERSION 2 636 [S] READER 637 [S] AUTHINFO USER SASL 638 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI PLAIN EXTERNAL 639 [S] LIST ACTIVE NEWSGROUPS 640 [S] . 641 [C] AUTHINFO SASL PLAIN AHRlc3QAMTIzNA== 642 [S] 281 Authentication accepted 644 Example of the EXTERNAL SASL mechanism under a TLS layer, using the 645 authorization identity derived from the client TLS certificate, and 646 thus a zero-length initial client response (commands prior to 647 AUTHINFO SASL are the same as the previous example and have been 648 omitted): 650 [C] AUTHINFO SASL EXTERNAL = 651 [S] 281 Authentication accepted 653 Example of the [DIGEST-MD5] SASL mechanism, which includes a server 654 challenge and server success data (whitespace has been inserted for 655 clarity; base64-encoded data is actually sent as a single line with 656 no embedded whitespace): 658 [C] AUTHINFO SASL DIGEST-MD5 659 [S] 383 bm9uY2U9InNheUFPaENFS0dJZFBNSEMwd3RsZUxxT0ljT0kyd1FZSWU0 660 enplQXR1aVE9IixyZWFsbT0iZWFnbGUub2NlYW5hLmNvbSIscW9wPSJhdXRo 661 LGF1dGgtaW50LGF1dGgtY29uZiIsY2lwaGVyPSJyYzQtNDAscmM0LTU2LHJj 662 NCxkZXMsM2RlcyIsbWF4YnVmPTQwOTYsY2hhcnNldD11dGYtOCxhbGdvcml0 663 aG09bWQ1LXNlc3M= 664 [C] dXNlcm5hbWU9InRlc3QiLHJlYWxtPSJlYWdsZS5vY2VhbmEuY29tIixub25j 665 ZT0ic2F5QU9oQ0VLR0lkUE1IQzB3dGxlTHFPSWNPSTJ3UVlJZTR6emVBdHVp 666 UT0iLGNub25jZT0iMFkzSlFWMlRnOVNjRGlwK08xU1ZDMHJoVmcvLytkbk9J 667 aUd6LzdDZU5KOD0iLG5jPTAwMDAwMDAxLHFvcD1hdXRoLWNvbmYsY2lwaGVy 668 PXJjNCxtYXhidWY9MTAyNCxkaWdlc3QtdXJpPSJubnRwL2xvY2FsaG9zdCIs 669 cmVzcG9uc2U9ZDQzY2Y2NmNmZmE5MDNmOWViMDM1NmMwOGEzZGIwZjI= 670 [S] 283 cnNwYXV0aD1kZTJlMTI3ZTVhODFjZGE1M2Q5N2FjZGEzNWNkZTgzYQ== 672 Example of a failed authentication due to bad [GSSAPI] credentials. 673 Note that while the mechanism can utilize the initial response, the 674 client chooses not to use it because of its length, resulting in a 675 zero-length server challenge (here whitespace has been inserted for 676 clarity; base64-encoded data is actually sent as a single line with 677 no embedded whitespace): 679 [C] AUTHINFO SASL GSSAPI 680 [S] 383 = 681 [C] YIICOAYJKoZIhvcSAQICAQBuggInMIICI6ADAgEFoQMCAQ6iBwMFACAAAACj 682 ggE/YYIBOzCCATegAwIBBaEYGxZURVNULk5FVC5JU0MuVVBFTk4uRURVoiQw 683 IqADAgEDoRswGRsEbmV3cxsRbmV0bmV3cy51cGVubi5lZHWjge8wgeygAwIB 684 EKEDAgECooHfBIHcSQfLKC8vm2i17EXmomwk6hHvjBY/BnKnvvDTrbno3198 685 vlX2RSUt+CjuAKhcDcj4DW0gvZEqH7t5v9yWedzztlpaThebBat6hQNr9NJP 686 ozh1/+74HUwhGWb50KtjuftO/ftQ8q0nTuYKgIq6PM4tp2ddo1IfpjfdNR9E 687 95GFi3y1uBT7lQOwtQbRJUjPSO3ijdue9V7cNNVmYsBsqNsaHhvlBJEXf4WJ 688 djH8yG+Dw/gX8fUTtC5fDpB5zLt01mkSXh6Wc4UhqQtwZBI2t/+TpX1okbg6 689 Hr1ZZupeH6SByjCBx6ADAgEQooG/BIG8GnCmcXWtqhXh48dGTLHQgJ04K5Fj 690 RMMq2qPSbiha9lq0osqR2KAnQA6LioWYxU+6yPKpBDSC5WOT441fUfkM8iAL 691 kW3uNc+luFCGcnDsacrmoVU7Y6Akcp9m7Fm7orRc+TWSWPpBg3OR2oG3ATW0 692 0NAz8TT06VOLVxIMUTINKdYVI/Ja7f3sy+/N4LGkJqScCQOwlo5tfDWn/UQF 693 iTWo5Zw435rH8pjy2smQCnqC14v3NMAWTu4j+dzHUNw= 694 [S] 481 Authentication error 696 Example of a client aborting in the midst of an exchange: 698 [C] AUTHINFO SASL GSSAPI 699 [S] 383 = 700 [C] * 701 [S] 481 Authentication aborted as requested 703 Example of attempting to use a mechanism that is not supported by 704 the server: 706 [C] AUTHINFO SASL EXAMPLE 707 [S] 503 Mechanism not recognized 709 Example of attempting to use a mechanism that requires a security 710 layer: 712 [C] AUTHINFO SASL PLAIN 713 [S] 483 Encryption or stronger authentication required 715 Example of using an initial response with a mechanism that doesn't 716 support it (server must start the exchange): 718 [C] AUTHINFO SASL CRAM-MD5 AHRlc3QAMTIzNA== 719 [S] 482 SASL protocol error 721 Example of a failed authentication due to an incorrectly encoded 722 response: 724 [C] AUTHINFO SASL CRAM-MD5 725 [S] 383 PDE1NDE2NzQ5My4zMjY4MzE3QHRlc3RAZXhhbXBsZS5jb20+ 726 [C] abcd=efg 727 [S] 504 Base64 encoding error 729 3. Augmented BNF Syntax for the AUTHINFO Extension 731 This section describes the formal syntax of the AUTHINFO extension 732 using ABNF [ABNF]. It extends the syntax in section 9 of [NNTP], 733 and non-terminals not defined in this document are defined there. 734 The [NNTP] ABNF should be imported first before attempting to 735 validate these rules. 737 3.1. Commands 739 This syntax extends the non-terminal "command", which represents an 740 NNTP command. 742 command =/ authinfo-sasl-command / 743 authinfo-user-command / 744 authinfo-pass-command 746 authinfo-sasl-command = "AUTHINFO" WS "SASL" WS mechanism 747 [WS initial-response] 748 authinfo-user-command = "AUTHINFO" WS "USER" WS username 749 authinfo-pass-command = "AUTHINFO" WS "PASS" WS password 751 initial-response = base64-opt 752 username = 1*user-pass-char 753 password = 1*user-pass-char 754 user-pass-char = P-CHAR 756 NOTE: A server implementation MAY parse AUTHINFO USER and AUTHINFO 757 PASS specially as to allow white space to be used within the 758 username or password. Such implementations accept the additional 759 syntax (making these two items inconsistent with "token" in section 760 9.8 of [NNTP]): 762 user-pass-char =/ SP / TAB 764 In doing so, the grammar can become ambiguous if the username or 765 password begins or ends with white space. To solve this ambiguity, 766 such implementations typically treat everything after the first 767 white space character following "USER"/"PASS", up to, but not 768 including, the CRLF as the username/password. 770 3.2. Command Continuation 772 This syntax extends the non-terminal "command-continuation", which 773 represents the further material sent by the client in the case of 774 multi-stage commands. 776 command-continuation =/ authinfo-sasl-383-continuation 778 authinfo-sasl-383-continuation = ("*" / base64-opt) CRLF 780 3.3. Responses 782 This syntax extends the non-terminal "initial-response-content", 783 which represents an initial response line sent by the server. 785 initial-response-content =/ response-283-content / 786 response-383-content 788 response-283-content = "283" SP base64 789 response-383-content = "383" SP base64-opt 791 3.4. Capability entries 793 This syntax extends the non-terminal "capability-entry", which rep- 794 resents a capability that may be advertised by the server. 796 capability-entry =/ authinfo-capability / 797 sasl-capability 799 authinfo-capability = "AUTHINFO" *(WS authinfo-variant) 800 authinfo-variant = "USER" / "SASL" 801 sasl-capability = "SASL" 1*(WS mechanism) 803 3.5. General non-terminals 805 base64-opt = "=" / base64 806 mechanism = 1*20mech-char 807 mech-char = UPPER / DIGIT / "-" / "_" 809 4. Summary of Response Codes 811 This section contains a list of every new response code defined in 812 this document, whether it is multi-line, which commands can 813 generate it, what arguments it has, and what its meaning is. 815 Response code 281 816 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 817 Meaning: authentication accepted 819 Response code 283 820 Generated by: AUTHINFO SASL 821 1 argument: challenge 822 Meaning: authentication accepted (with success data) 824 Response code 381 825 Generated by: AUTHINFO USER 826 Meaning: password required via AUTHINFO PASS command. Note 827 that this code is used for backwards compatibility and does 828 not conform to the traditional use of 3xx codes. 830 Response code 383 831 Generated by: AUTHINFO SASL 832 1 argument: challenge 833 Meaning: continue with SASL exchange 835 Response code 481 836 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 837 Meaning: authentication failed/rejected 839 Response code 482 840 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 841 Meaning: authentication commands issued out of sequence or 842 SASL protocol error 844 5. Authentication Tracking/Logging 846 This section contains implementation suggestions and notes of best 847 current practice, and does not specify further network protocol 848 requirements. 850 Once authenticated, the authorization identity presented in the 851 AUTHINFO exchange (username when using USER/PASS) SHOULD be 852 included in an audit trail associating the identity with any 853 articles supplied during a POST operation, and this configuration 854 SHOULD be the default. This may be accomplished, for example, by 855 inserting headers in the posted articles or by a server logging 856 mechanism. The server MAY provide a facility for disabling the 857 procedure described above, as some users or administrators may 858 consider it a violation of privacy. 860 6. Security Considerations 861 Security issues are discussed throughout this memo. 863 In general, the security considerations of [SASL] and any 864 implemented SASL mechanisms are applicable here; only the most 865 important are highlighted specifically below. Also, this extension 866 is not intended to cure the security considerations described in 867 section 12 of [NNTP]; those considerations remain relevant to any 868 NNTP implementation. 870 Before the [SASL] negotiation has begun, any protocol interactions 871 may have been performed in the clear and may have been modified by 872 an active attacker. For this reason, clients and servers MUST 873 discard any sensitive knowledge obtained prior to the start of the 874 SASL negotiation upon the establishment of a security layer. 875 Furthermore, the CAPABILITIES command SHOULD be re-issued upon the 876 establishment of a security layer, and other protocol state SHOULD 877 be re-negotiated as well. 879 Servers MAY implement a policy whereby the connection is dropped 880 after a number of failed authentication attempts. If they do so, 881 they SHOULD NOT drop the connection until at least 3 attempts at 882 authentication have failed. 884 Implementations MUST support a configuration where authentication 885 mechanisms that are vulnerable to passive eavesdropping attacks 886 (such as AUTHINFO USER/PASS and SASL [PLAIN]) are not advertised or 887 used without the presence of an external security layer such as TLS 888 [NNTP-TLS]. 890 When multiple authentication mechanisms are permitted by both 891 client and server, an active attacker can cause a down-negotiation 892 to the weakest mechanism. For this reason, both clients and 893 servers SHOULD be configurable to forbid use of weak mechanisms. 894 The minimum strength acceptable is a policy decision which is 895 outside the scope of this specification. 897 7. IANA Considerations 899 7.1. IANA Considerations for SASL/GSSAPI services 901 Please register the SASL/GSSAPI service name "nntp". This service 902 name refers to authenticated use of Usenet news service when 903 provided via the [NNTP] protocol. 905 o Published Specification: This document. 907 o Author, Change Controller, and Contact for Further Information: 908 Author of this document. 910 7.2. IANA Considerations for NNTP extensions 912 This section gives a formal definition of the AUTHINFO extension as 913 required by Section 3.3.3 of [NNTP] for the IANA registry. 915 o This extension provides an extensible mechanism for NNTP 916 authentication via a variety of methods. 918 o The capability label for this extension is "AUTHINFO". 920 o The "AUTHINFO" capability label has two possible optional 921 arguments "USER" and "SASL" (as defined in Section 2.1) 922 indicating which variants of the AUTHINFO command are supported. 924 o This extension also provides the "SASL" capability label whose 925 arguments list the available SASL mechanisms. 927 o This extension defines three new commands, AUTHINFO USER, 928 AUTHINFO PASS, and AUTHINFO SASL, whose behavior, arguments, and 929 responses are defined in Sections 2.3 and 2.4. 931 o This extension does not associate any new responses with pre- 932 existing NNTP commands. 934 o This extension may affect the overall behavior of both server 935 and client, in that the AUTHINFO SASL command may require that 936 subsequent communication be transmitted via an intermediary 937 security layer. 939 o The length of the AUTHINFO SASL command (as defined in this 940 document) may exceed 512 octets. The maximum length of this 941 command is increased to that which can accommodate the largest 942 initial response possible for any of the SASL mechanisms 943 supported by the implementation. 945 o This extension defines two new responses, 283 and 383, whose 946 lengths may exceed 512 octets. The maximum length of these 947 responses is increased to that which can accommodate the largest 948 challenge possible for any of the SASL mechanisms supported by 949 the implementation. 951 o This extension does not alter pipelining, but AUTHINFO commands 952 cannot be pipelined. 954 o Use of this extension may alter the capabilities list; once the 955 AUTHINFO command has been used successfully, the AUTHINFO 956 capability can no longer be advertised by CAPABILITIES. 957 Additionally, the MODE-READER capability MUST NOT be advertised 958 after successful authentication. 960 o This extension does not cause any pre-existing command to 961 produce a 401, 480, or 483 response. 963 o This extension is unaffected by any use of the MODE READER 964 command, however the MODE READER command MUST NOT be used in the 965 same session following successful authentication. 967 o Published Specification: This document. 969 o Author, Change Controller, and Contact for Further Information: 970 Author of this document. 972 8. References 974 8.1. Normative References 976 [ABNF] Crocker, D., Overell, P., "Augmented BNF for Syntax 977 Specifications: ABNF", RFC 2234, November 1997. 979 [AUTH] Haller, N., Atkinson, R., "On Internet Authentication", 980 RFC 1704, October 1994. 982 [BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data 983 Encodings", RFC 3548, July 2003. 985 [DIGEST-MD5] Leach, P., Newman, C., Melnikov, A., 986 "Using Digest Authentication as a SASL Mechanism", 987 draft-ietf-sasl-rfc2831bis-*.txt, Work in Progress. 989 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 990 Requirement Levels", BCP 14, RFC 2119, March 1997. 992 [NNTP] Feather, C., "Network News Transport Protocol", 993 draft-ietf-nntpext-base-*.txt, Work in Progress. 995 [NNTP-TLS] Murchison, K., Vinocur, J., Newman, C., 996 "Using TLS with NNTP", draft-ietf-nntpext-tls-nntp-*.txt, 997 Work in Progress. 999 [SASL] Myers, J., "Simple Authentication and Security Layer 1000 (SASL)", RFC 2222, October 1997. 1002 [SASLprep] Zeilega, K., "SASLprep: Stringprep Profile for 1003 User Names and Passwords", RFC 4013, February 2005. 1005 [StringPrep] Hoffman, P. and Blanchet, M., "Preparation of 1006 Internationalized Strings ("stringprep")", 1007 RFC 3454, December 2002. 1009 [UTF-8] Yergeau, F. "UTF-8, a transformation format of ISO 10646", 1010 RFC 3629, November 2003. 1012 8.2. Informative References 1014 [CRAM-MD5] Klensin, J., Catoe, R., Krumviede, P., "IMAP/POP 1015 AUTHorize Extension for Simple Challenge/Response", RFC 2195, 1016 September 1997. 1018 [GSSAPI] Myers, J., "Simple Authentication and Security Layer 1019 (SASL)", RFC 2222, October 1997. 1021 [NNTP-COMMON] Barber, S., "Common NNTP Extensions", RFC 2980, 1022 October 2000. 1024 [PLAIN] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC 2595, 1025 June 1999. 1027 [SMTP] Klensin, J., "Simple Mail Transport Protocol", RFC 2821, 1028 April 2001. 1030 9. Authors' Addresses 1032 Jeffrey M. Vinocur 1033 Department of Computer Science 1034 Upson Hall 1035 Cornell University 1036 Ithaca, NY 14853 USA 1038 Email: vinocur@cs.cornell.edu 1040 Kenneth Murchison 1041 Oceana Matrix Ltd. 1042 21 Princeton Place 1043 Orchard Park, NY 14127 USA 1045 Email: ken@oceana.com 1047 Chris Newman 1048 Sun Microsystems 1049 1050 Lakes Drive, Suite 250 1050 West Covina, CA 91790 USA 1051 Email: Chris.Newman@sun.com 1053 10. Acknowledgments 1055 A significant amount of the authentication text was originally from 1056 the NNTP revision or common authentication specs written by Stan 1057 Barber. A significant amount of the SASL text was lifted from the 1058 revisions to RFC 1734 and RFC 2554 by Rob Siemborski. 1060 Special acknowledgment also goes to Russ Allbery, Clive Feather, 1061 and others who commented privately on intermediate revisions of 1062 this document, as well as the members of the IETF NNTP Working 1063 Group for continual (yet sporadic) insight in discussion. 1065 11. Intellectual Property Rights 1067 The IETF takes no position regarding the validity or scope of any 1068 Intellectual Property Rights or other rights that might be claimed 1069 to pertain to the implementation or use of the technology described 1070 in this document or the extent to which any license under such 1071 rights might or might not be available; nor does it represent that 1072 it has made any independent effort to identify any such rights. 1073 Information on the procedures with respect to rights in RFC 1074 documents can be found in BCP 78 and BCP 79. 1076 Copies of IPR disclosures made to the IETF Secretariat and any 1077 assurances of licenses to be made available, or the result of an 1078 attempt made to obtain a general license or permission for the use 1079 of such proprietary rights by implementers or users of this 1080 specification can be obtained from the IETF on-line IPR repository 1081 at http://www.ietf.org/ipr. 1083 The IETF invites any interested party to bring to its attention any 1084 copyrights, patents or patent applications, or other proprietary 1085 rights that may cover technology that may be required to implement 1086 this standard. Please address the information to the IETF at 1087 ietf-ipr@ietf.org. 1089 12. Copyright 1091 Copyright (C) The Internet Society (2005). 1093 This document is subject to the rights, licenses and restrictions 1094 contained in BCP 78, and except as set forth therein, the authors 1095 retain all their rights. 1097 This document and the information contained herein are provided on 1098 an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 1099 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND 1100 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, 1101 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT 1102 THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR 1103 ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A 1104 PARTICULAR PURPOSE.