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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: July 2005 Oceana Matrix Ltd. 6 C. Newman 7 Sun Microsystems 8 January 2005 10 NNTP Extension for Authentication 11 draft-ietf-nntpext-authinfo-06 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 ................... 4 61 2. The AUTHINFO Extension ................................... 4 62 2.1. Advertising the AUTHINFO Extension .................. 4 63 2.2. Authenticating with the AUTHINFO Extension .......... 6 64 2.3. AUTHINFO USER/PASS Command .......................... 7 65 2.3.1. Usage .......................................... 7 66 2.3.2. Description .................................... 7 67 2.3.3. Examples ....................................... 9 68 2.4. AUTHINFO SASL Command ............................... 9 69 2.4.1. Usage .......................................... 10 70 2.4.2. Description .................................... 10 71 2.4.3. Examples ....................................... 14 72 3. Augmented BNF Syntax for the AUTHINFO Extension .......... 16 73 3.1. Commands ............................................ 16 74 3.2. Command Continuation ................................ 17 75 3.3. Responses ........................................... 17 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 ............................................... 21 85 8.1. Normative References ................................ 21 86 8.2. Informative References .............................. 21 87 9. Authors' Addresses ....................................... 22 88 10. Acknowledgments ......................................... 22 89 11. Intellectual Property Rights ............................ 22 90 12. Copyright ............................................... 23 92 0. Changes from Previous Version 94 New: 95 o Reintroduced the "SASL" capability to list available SASL mechs. 96 o Noted that MODE READER must not be used nor advertised after 97 authentication. 98 o Extended the length of the AUTHINFO SASL command to accommodate 99 large initial responses. 101 Changed: 102 o CAPABILITIES replaces LIST EXTENSIONS. 103 o Use of an unknown SASL mechanism results in 503 not 501. 104 o Use common language between this draft and STARTTLS regarding 105 unsolicited use of the extension and resetting of server state and 106 caching of info obtained prior to a security layer. 107 o Capabilities are now case-insensitive. 108 o Changed reference to IANA requirements in [NNTP] from Section 8 to 109 Section 3.3.4. 111 Clarified: 112 o Rewrote the CAPABILITIES after security layer text yet again. 113 o Neither the first WSP character following "USER"/"PASS" nor the 114 CRLF are part of the username/password. 115 o The MODE READER state change does not get discarded after a SASL 116 security layer is negotiated. 118 Outstanding issues: 119 o Make sure we correctly reference the text in [NNTP] regarding MODE 120 READER use after authentication. 122 1. Introduction 124 Although NNTP [NNTP] has traditionally been used to provide public 125 access to newsgroups, authentication is often useful, for example 126 to control resource consumption, to allow abusers of the POST 127 command to be identified, and to restrict access to "local" 128 newsgroups. 130 The ad-hoc AUTHINFO USER and AUTHINFO PASS commands, documented in 131 [NNTP-COMMON], provide a very weak authentication mechanism in 132 widespread use by the installed base. Due to their ubiquity they 133 are formalized in this specification but, because of their 134 insecurity, only for use in combination with appropriate security 135 layers. 137 The ad-hoc AUTHINFO GENERIC command, also documented in [NNTP- 138 COMMON] but much less ubiquitous, provided an NNTP-specific 139 equivalent of the generic SASL [SASL] facility. This document 140 deprecates AUTHINFO GENERIC in favor of an AUTHINFO SASL 141 replacement so that NNTP can benefit from authentication mechanisms 142 developed for other SASL-enabled application protocols including 143 SMTP, POP, IMAP, LDAP, and BEEP. 145 This specification is to be read in conjunction with the NNTP base 146 specification [NNTP]. Except where specifically stated otherwise, 147 in the case of a conflict between these two documents [NNTP] takes 148 precedence over this one. 150 It is also recommended that this specification be read in 151 conjunction with the SASL base specification [SASL]. 153 1.1. Conventions Used in this Document 155 The notational conventions used in this document are the same as 156 those in [NNTP] and any term not defined in this document has the 157 same meaning as in that one. 159 The key words "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD 160 NOT", "MAY", and "OPTIONAL" in this document are to be interpreted 161 as described in "Key words for use in RFCs to Indicate Requirement 162 Levels" [KEYWORDS]. 164 Terms related to authentication are defined in "On Internet 165 Authentication" [AUTH]. 167 In the examples, commands from the client are indicated with [C], 168 and responses from the server are indicated with [S]. 170 2. The AUTHINFO Extension 172 The AUTHINFO extension is used to authenticate a user. Note that 173 authorization is a matter of site policy, not network protocol, and 174 is therefore not discussed in this document. The server determines 175 authorization in whatever manner is defined by its implementation 176 as configured by the site administrator. 178 This extension provides three new commands: AUTHINFO USER, AUTHINFO 179 PASS, and AUTHINFO SASL. The capability label for this extension 180 is AUTHINFO. 182 2.1. Advertising the AUTHINFO Extension 184 A server MUST implement at least one of the AUTHINFO USER or 185 AUTHINFO SASL commands in order to advertise the AUTHINFO 186 capability in the response to the CAPABILITIES command. However, 187 this capability is not advertised after successful authentication 188 (see section 2.2). This capability MAY be advertised both before 189 and after any use of MODE READER, with the same semantics. 191 The AUTHINFO capability label contains an argument list detailing 192 which authentication commands are available. 194 The "USER" argument indicates that AUTHINFO USER/PASS is supported 195 as defined by Section 2.3 of this document. The "USER" argument 196 MUST NOT be advertised, and the AUTHINFO USER/PASS commands SHOULD 197 NOT be provided, unless a strong encryption layer (e.g. TLS [NNTP- 198 TLS]) is in use or backward compatibility dictates otherwise. 200 The "SASL" argument indicates that AUTHINFO SASL is supported as 201 defined by Section 2.4 of this document. If the server advertises 202 the "SASL" argument, then it MUST also advertise the "SASL" 203 capability in response to the CAPABILITIES command. The SASL 204 capability is followed by a whitespace-separated list of available 205 SASL mechanism names. 207 The server may list the AUTHINFO capability with no arguments, 208 which indicates that it complies with this specification and does 209 not permit any authentication commands in its current state. In 210 this case, the client MUST NOT attempt to utilize any AUTHINFO 211 commands, even if it contains logic to do so (e.g. for backward 212 compatibility with servers that are not compliant with this 213 specification). 215 Future extensions may add additional arguments to this capability. 216 Unrecognized arguments SHOULD be ignored or brought to the 217 attention of the user. 219 As the AUTHINFO command is related to security, cached results of 220 CAPABILITIES from a previous session MUST NOT be relied on, as per 221 section 11.6 of [NNTP]. 223 Example (here, the STARTTLS extension [NNTP-TLS] is also in use): 224 [C] CAPABILITIES 225 [S] 101 Capability list: 226 [S] VERSION 2 227 [S] READER 228 [S] IHAVE 229 [S] STARTTLS 230 [S] AUTHINFO SASL 231 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI 232 [S] LIST ACTIVE NEWSGROUPS 233 [S] . 234 [C] STARTTLS 235 [S] 382 Continue with TLS negotiation 236 [TLS negotiation proceeds, further commands protected by TLS layer] 237 [C] CAPABILITIES 238 [S] 101 Capability list: 239 [S] VERSION 2 240 [S] READER 241 [S] IHAVE 243 [S] AUTHINFO USER SASL 244 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI PLAIN EXTERNAL 245 [S] LIST ACTIVE NEWSGROUPS 246 [S] . 248 2.2. Authenticating with the AUTHINFO Extension 250 An NNTP server responds to a client command with a 480 response to 251 indicate that the client MUST authenticate and/or authorize in 252 order to use that command or access the indicated resource. Use of 253 the AUTHINFO command as described below is one such way that a 254 client can authenticate/authorize to the server. The client MAY 255 therefore use an AUTHINFO command after receiving a 480 response. 256 A client intending to use an AUTHINFO command SHOULD issue the 257 CAPABILITIES command to obtain the available authentication 258 commands and mechanisms before attempting authentication. 260 If a server advertises the AUTHINFO capability, a client MAY 261 attempt the first step of authentication at any time during a 262 session to acquire additional privileges without having received a 263 480 response. Servers SHOULD accept such unsolicited 264 authentication requests. A server MUST NOT under any circumstances 265 reply to an AUTHINFO command with a 480 response. 267 A client MUST NOT under any circumstances continue with any steps 268 of authentication beyond the first, unless the response code from 269 the server indicates that the authentication exchange is welcomed. 270 In particular, anything other than a 38x response code indicates 271 that the client MUST NOT continue the authentication exchange. 273 After a successful authentication, the client MUST NOT issue 274 another AUTHINFO command in the same session. A server MUST NOT 275 return the AUTHINFO capability in response to a CAPABILITIES 276 command and a server MUST reject any subsequent AUTHINFO commands 277 with a 502 response. Additionally, per section 3.4.2 of [NNTP], 278 the client MUST NOT issue a MODE READER command after 279 authentication and a server MUST NOT advertise the MODE-READER 280 capability. 282 In agreement with [SASL], the server MUST continue to advertise the 283 SASL capability in response to a CAPABILITIES command with the same 284 list of SASL mechanisms as before authentication (thereby enabling 285 the client to detect a possible active down-negotiation attack). 286 Other capabilities returned in response to a CAPABILITIES command 287 received after authentication MAY be different than those returned 288 before authentication. For example, an NNTP server may not want to 289 advertise support for a specific extension unless a client has been 290 authenticated. 292 It should be noted that a server may perform a successful 293 authentication exchange with a client and yet still deny access to 294 some or all resources; the permanent 502 response indicates a 295 resource is unavailable even though authentication has been 296 performed (this is in contrast to the temporary 480 error 297 indicating that a resource is unavailable now but may become 298 available after authentication). 300 2.3. AUTHINFO USER/PASS Command 302 This section supersedes the definition of the AUTHINFO USER and 303 AUTHINFO PASS commands as documented in Section 3.1.1 of [NNTP- 304 COMMON]. 306 2.3.1. Usage 308 These commands MUST NOT be pipelined. 310 Syntax 311 AUTHINFO USER username 312 AUTHINFO PASS password 314 Responses 315 281 Authentication accepted 316 381 Password required [1] 317 481 Authentication failed/rejected 318 482 Authentication commands issued out of sequence 319 502 Command unavailable [2] 321 [1] Only valid for AUTHINFO USER. Note that unlike traditional 3xx 322 codes which indicate that the client may continue the current 323 command, the legacy 381 code means that the AUTHINFO PASS command 324 must be used to complete the authentication exchange. 326 [2] If authentication has already occurred, AUTHINFO USER/PASS are 327 not valid commands (see section 2.2). 329 NOTE: Notwithstanding section 3.2.1 of [NNTP], the server MUST NOT 330 return 480 in response to AUTHINFO USER/PASS. 332 Parameters 333 username = UTF-8 string identifying the user/client 334 password = UTF-8 string representing the user's password 336 2.3.2. Description 338 The AUTHINFO USER and AUTHINFO PASS commands are used to present 339 clear text credentials to the server. These credentials consist of 340 a username or a username plus a password (the distinction is that a 341 password is expected to be kept secret while a username is not; 342 this does not directly affect the protocol but may have an impact 343 on user interfaces). The username is supplied through the AUTHINFO 344 USER command, and the password through the AUTHINFO PASS command. 346 If the server requires only a username, it MUST NOT give a 381 347 response to AUTHINFO USER and MUST give a 482 response to AUTHINFO 348 PASS. 350 If the server requires both username and password, the former MUST 351 be sent before the latter. The server will need to cache the 352 username until the password is received; it MAY require the 353 password to be sent in the immediately next command (in other 354 words, only caching the username until the next command is sent). 355 The server: 357 - MUST return a 381 response to AUTHINFO USER; 358 - MUST return a 482 response to AUTHINFO PASS if there is no 359 cached username; 360 - MUST use the argument of the most recent AUTHINFO USER for 361 authentication; 362 - MUST NOT return a 381 response to AUTHINFO PASS. 364 The server MAY determine whether or not a password is needed based 365 on the username. Thus the same server can respond with both 381 366 and other response codes to AUTHINFO USER. 368 The AUTHINFO PASS command permits the client to use a clear-text 369 password to authenticate. A compliant implementation MUST NOT 370 implement this command without also implementing support for TLS 371 [NNTP-TLS]. Use of this command without an active strong 372 encryption layer is deprecated, as it exposes the user's password 373 to all parties on the network between the client and the server. 374 Any implementation of this command SHOULD be configurable to 375 disable it whenever a strong encryption layer such as that provided 376 by [NNTP-TLS] is not active, and this configuration SHOULD be the 377 default. The server will use the 483 response code to indicate 378 that the datastream is insufficiently secure for the command being 379 attempted. 381 Usernames and passwords MUST use the UTF-8 [UTF-8] character set 382 and a client MUST convert any user input to UTF-8 if necessary. 384 Note that a server MAY, but is not required to, allow white space 385 characters in usernames and passwords. A server implementation MAY 386 blindly split command arguments at white space and therefore not 387 preserve the exact sequence of white space characters in the 388 username or password. Therefore a client SHOULD scan the username 389 and password for whitespace, and if detected, warn the user of the 390 likelihood of problems. The SASL PLAIN [PLAIN] mechanism is 391 recommended as an alternative, as it does not suffer from these 392 issues. 394 2.3.3. Examples 396 Example of successful AUTHINFO USER: 398 [C] AUTHINFO USER wilma 399 [S] 281 Authentication accepted 401 Example of successful AUTHINFO USER/PASS: 403 [C] AUTHINFO USER fred 404 [S] 381 Enter passphrase 405 [C] AUTHINFO PASS flintstone 406 [S] 281 Authentication accepted 408 Example of AUTHINFO USER/PASS requiring a security layer: 410 [C] AUTHINFO USER fred@stonecanyon.example 411 [S] 483 Encryption or stronger authentication required 413 Example of failed AUTHINFO USER/PASS: 415 [C] AUTHINFO USER barney 416 [S] 381 Enter passphrase 417 [C] AUTHINFO PASS flintstone 418 [S] 481 Authentication failed 420 Example of AUTHINFO PASS before AUTHINFO USER: 422 [C] AUTHINFO PASS flintstone 423 [S] 482 Authentication commands issued out of sequence 425 2.4. AUTHINFO SASL Command 427 This section defines a formal profile of the Simple Authentication 428 and Security Layer [SASL]. The use of the AUTHINFO GENERIC command 429 as documented in Section 3.1.3 of [NNTP-COMMON] as a way to perform 430 SASL authentication is deprecated in favor of the AUTHINFO SASL 431 command. A server SHOULD NOT advertise AUTHINFO GENERIC in the 432 list of capabilities returned by CAPABILITIES. 434 2.4.1. Usage 436 This command MUST NOT be pipelined. 438 Syntax 439 AUTHINFO SASL mechanism [initial-response] 441 This command MAY exceed 512 octets. The maximum length of this 442 command is increased to that which can accommodate the largest 443 encoded initial response possible for any of the SASL mechanisms 444 supported by the implementation. 446 Responses 447 281 Authentication accepted 448 283 challenge Authentication accepted (with success data) [1] 449 383 challenge Continue with SASL exchange [1] 450 481 Authentication failed/rejected 451 482 SASL protocol error 452 502 Command unavailable [2] 454 [1] These responses MAY exceed 512 octets. The maximum length of 455 these responses is increased to that which can accommodate the 456 largest encoded challenge possible for any of the SASL mechanisms 457 supported by the implementation. 459 [2] If authentication has already occurred, AUTHINFO SASL is not a 460 valid command (see section 2.2). 462 NOTE: Notwithstanding section 3.2.1 of [NNTP], the server MUST NOT 463 return 480 in response to AUTHINFO USER/PASS. 465 Parameters 466 mechanism = String identifying a [SASL] authentication 467 mechanism. 468 initial-response = Optional initial client response. If present, 469 the response MUST be encoded as specified in 470 Section 3 of [BASE64]. [3] 471 challenge = Server challenge. The challenge MUST be 472 encoded as specified in Section 3 of [BASE64]. 474 [3] This argument MAY exceed 497 octets. The maximum length of 475 this argument is increased to that which can accommodate the 476 largest encoded initial response possible for any of the SASL mech- 477 anisms supported by the implementation. 479 2.4.2. Description 480 The AUTHINFO SASL command initiates a [SASL] authentication 481 exchange between the client and the server. The client identifies 482 the SASL mechanism to use with the first parameter of the AUTHINFO 483 SASL command. If the server supports the requested authentication 484 mechanism, it performs the SASL exchange to authenticate the user. 485 Optionally, it also negotiates a security layer for subsequent 486 protocol interactions during this session. If the requested 487 authentication mechanism is invalid (e.g. is not supported), the 488 server rejects the AUTHINFO SASL command with a 503 reply. If the 489 requested authentication mechanism requires an encryption layer, 490 the server rejects the AUTHINFO SASL command with a 483 reply. 492 The service name specified by this protocol's profile of SASL is 493 "nntp". 495 The SASL authentication exchange consists of a series of server 496 challenges and client responses that are specific to the chosen 497 [SASL] mechanism. 499 A server challenge is sent as a 383 reply with a single argument 500 containing the [BASE64] encoded string supplied by the SASL 501 mechanism. A server challenge that has zero length MUST be sent as 502 a single equals sign ("=") and not omitted (in order to comply with 503 the [NNTP] requirement that responses always have the same number 504 of arguments). 506 A client response consists of a line containing a [BASE64] encoded 507 string. A client response that has zero length MUST be sent as a 508 single equals sign ("=") and not omitted (for consistency with the 509 server challenge format). If the client wishes to cancel the 510 authentication exchange, it issues a line with a single "*". If 511 the server receives such a response, it MUST reject the AUTHINFO 512 SASL command by sending a 481 reply. 514 Note that these [BASE64] strings can be much longer than normal 515 NNTP responses. Clients and servers MUST be able to handle the 516 maximum encoded size of challenges and responses generated by their 517 supported authentication mechanisms. This requirement is 518 independent of any line length limitations the client or server may 519 have in other parts of its protocol implementation. 521 The optional initial response argument to the AUTHINFO SASL command 522 is used to save a round trip when using authentication mechanisms 523 that support an initial client response. If the initial response 524 argument is omitted and the chosen mechanism requires an initial 525 client response, the server MUST proceed as defined in section 5.1 526 of [SASL]. In NNTP, a server challenge that contains no data is 527 equivalent to a zero length challenge and is encoded as a single 528 equals sign ("="). 530 Note that the [BASE64] encoded initial response argument can exceed 531 497 octets and therefore the AUTHINFO SASL command can exceed 512 532 octets. Clients SHOULD, and servers MUST be able to handle the 533 maximum encoded size of initial responses possible for their 534 supported authentication mechanisms. This requirement is 535 independent of any command or argument length limitations the 536 client or server may have in other parts of its protocol 537 implementation. 539 If use of the initial response argument would cause the AUTHINFO 540 SASL command to exceed 512 octets, the client MAY choose to omit 541 the initial response parameter (and instead proceed as defined in 542 section 5.1 of [SASL]). 544 If the client is transmitting an initial response of zero length, 545 it MUST instead transmit the response as a single equals sign 546 ("="). This indicates that the response is present, but contains 547 no data. 549 If the client uses an initial-response argument to the AUTHINFO 550 SASL command with a SASL mechanism that does not support an initial 551 client response, the server MUST reject the AUTHINFO SASL command 552 with a 482 reply. 554 If the server cannot [BASE64] decode any client response, it MUST 555 reject the AUTHINFO SASL command with a 504 reply. If the client 556 cannot BASE64 decode any of the server's challenges, it MUST cancel 557 the authentication using the "*" response. In particular, servers 558 and clients MUST reject (and not ignore) any character not 559 explicitly allowed by the BASE64 alphabet, and MUST reject any 560 sequence of BASE64 characters that contains the pad character ('=') 561 anywhere other than the end of the string (e.g. "=AAA" and 562 "AAA=BBB" are not allowed). 564 The authorization identity generated by this [SASL] exchange is a 565 simple username, and both client and server MUST use the [SASLprep] 566 profile of the [StringPrep] algorithm to prepare these names for 567 transmission or comparison. If preparation of the authorization 568 identity fails or results in an empty string (unless it was 569 transmitted as the empty string), the server MUST fail the 570 authentication with a 481 reply. 572 Should the client successfully complete the exchange, the server 573 issues either a 281 or 283 reply. If the server is unable to 574 authenticate the client, it MUST reject the AUTHINFO SASL command 575 with a 481 reply. If an AUTHINFO command fails, the client MAY 576 proceed without authentication. Alternatively, the client MAY try 577 another authentication mechanism, or present different credentials 578 by issuing another AUTHINFO command. 580 If the SASL mechanism returns additional data on success (e.g. 581 server authentication), the NNTP server issues a 283 reply with a 582 single argument containing the [BASE64] encoded string supplied by 583 the SASL mechanism. If no additional data is returned on success, 584 the server issues a 281 reply. 586 If a security layer is negotiated during the SASL exchange, it 587 takes effect for the client on the octet immediately following the 588 CRLF that concludes the last response generated by the client. For 589 the server, it takes effect immediately following the CRLF of its 590 success reply. 592 When a security layer takes effect, the NNTP protocol is reset to 593 the state immediately after the initial greeting response (see 5.1 594 of [NNTP]) has been sent, with the exception that if a MODE READER 595 command has been issued, the effects of it (if any) are not 596 reversed. The server MUST discard any knowledge obtained from the 597 client, such as the current newsgroup and article number, that was 598 not obtained from the SASL negotiation itself. Likewise, the 599 client SHOULD discard and MUST NOT rely on any knowledge obtained 600 from the server, such as the capability list, that was not obtained 601 from the SASL negotiation itself. (Note that a client MAY compare 602 the advertised SASL mechanisms before and after authentication in 603 order to detect an active down-negotiation attack.) 605 When both TLS [NNTP-TLS] and SASL security layers are in effect, 606 the TLS encoding MUST be applied after the SASL encoding (the 607 cleartext data is always SASL encoded first and then the resultant 608 data is TLS encoded). 610 To ensure interoperability, client and server implementations of 611 this extension MUST implement the [DIGEST-MD5] SASL mechanism. 613 If AUTHINFO USER/PASS and AUTHINFO SASL are both implemented, the 614 SASL [PLAIN] mechanism SHOULD also be implemented, as the 615 functionality of DIGEST-MD5 is insufficient for some environments 616 (e.g. the server may need to pass the plaintext password off to an 617 external authentication service). The SASL PLAIN mechanism is 618 preferred over AUTHINFO USER, even if there is not a strong 619 encryption layer active, because it eliminates limitations that 620 AUTHINFO USER/PASS has with regards to white space characters being 621 used in usernames and passwords. 623 2.4.3. Examples 625 Example of the [PLAIN] SASL mechanism under a TLS layer, using an 626 initial client response: 628 [C] CAPABILITIES 629 [S] 101 Capability list: 630 [S] VERSION 2 631 [S] READER 632 [S] STARTTLS 633 [S] AUTHINFO SASL 634 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI 635 [S] LIST ACTIVE NEWSGROUPS 636 [S] . 637 [C] STARTTLS 638 [S] 382 Continue with TLS negotiation 639 [TLS negotiation proceeds, further commands protected by TLS layer] 640 [C] CAPABILITIES 641 [S] 101 Capability list: 642 [S] VERSION 2 643 [S] READER 644 [S] AUTHINFO USER SASL 645 [S] SASL CRAM-MD5 DIGEST-MD5 GSSAPI PLAIN EXTERNAL 646 [S] LIST ACTIVE NEWSGROUPS 647 [S] . 648 [C] AUTHINFO SASL PLAIN AHRlc3QAMTIzNA== 649 [S] 281 Authentication accepted 651 Example of the EXTERNAL SASL mechanism under a TLS layer, using the 652 authorization identity derived from the client TLS certificate, and 653 thus a zero-length initial client response (commands prior to 654 AUTHINFO SASL are the same as the previous example and have been 655 omitted): 657 [C] AUTHINFO SASL EXTERNAL = 658 [S] 281 Authentication accepted 660 Example of the [DIGEST-MD5] SASL mechanism, which includes a server 661 challenge and server success data (whitespace has been inserted for 662 clarity; base64-encoded data is actually sent as a single line with 663 no embedded whitespace): 665 [C] AUTHINFO SASL DIGEST-MD5 666 [S] 383 bm9uY2U9InNheUFPaENFS0dJZFBNSEMwd3RsZUxxT0ljT0kyd1FZSWU0 667 enplQXR1aVE9IixyZWFsbT0iZWFnbGUub2NlYW5hLmNvbSIscW9wPSJhdXRo 668 LGF1dGgtaW50LGF1dGgtY29uZiIsY2lwaGVyPSJyYzQtNDAscmM0LTU2LHJj 669 NCxkZXMsM2RlcyIsbWF4YnVmPTQwOTYsY2hhcnNldD11dGYtOCxhbGdvcml0 670 aG09bWQ1LXNlc3M= 672 [C] dXNlcm5hbWU9InRlc3QiLHJlYWxtPSJlYWdsZS5vY2VhbmEuY29tIixub25j 673 ZT0ic2F5QU9oQ0VLR0lkUE1IQzB3dGxlTHFPSWNPSTJ3UVlJZTR6emVBdHVp 674 UT0iLGNub25jZT0iMFkzSlFWMlRnOVNjRGlwK08xU1ZDMHJoVmcvLytkbk9J 675 aUd6LzdDZU5KOD0iLG5jPTAwMDAwMDAxLHFvcD1hdXRoLWNvbmYsY2lwaGVy 676 PXJjNCxtYXhidWY9MTAyNCxkaWdlc3QtdXJpPSJubnRwL2xvY2FsaG9zdCIs 677 cmVzcG9uc2U9ZDQzY2Y2NmNmZmE5MDNmOWViMDM1NmMwOGEzZGIwZjI= 678 [S] 283 cnNwYXV0aD1kZTJlMTI3ZTVhODFjZGE1M2Q5N2FjZGEzNWNkZTgzYQ== 680 Example of a failed authentication due to bad [GSSAPI] credentials. 681 Note that while the mechanism can utilize the initial response, the 682 client chooses not to use it because of its length, resulting in a 683 zero-length server challenge (here whitespace has been inserted for 684 clarity; base64-encoded data is actually sent as a single line with 685 no embedded whitespace): 687 [C] AUTHINFO SASL GSSAPI 688 [S] 383 = 689 [C] YIICOAYJKoZIhvcSAQICAQBuggInMIICI6ADAgEFoQMCAQ6iBwMFACAAAACj 690 ggE/YYIBOzCCATegAwIBBaEYGxZURVNULk5FVC5JU0MuVVBFTk4uRURVoiQw 691 IqADAgEDoRswGRsEbmV3cxsRbmV0bmV3cy51cGVubi5lZHWjge8wgeygAwIB 692 EKEDAgECooHfBIHcSQfLKC8vm2i17EXmomwk6hHvjBY/BnKnvvDTrbno3198 693 vlX2RSUt+CjuAKhcDcj4DW0gvZEqH7t5v9yWedzztlpaThebBat6hQNr9NJP 694 ozh1/+74HUwhGWb50KtjuftO/ftQ8q0nTuYKgIq6PM4tp2ddo1IfpjfdNR9E 695 95GFi3y1uBT7lQOwtQbRJUjPSO3ijdue9V7cNNVmYsBsqNsaHhvlBJEXf4WJ 696 djH8yG+Dw/gX8fUTtC5fDpB5zLt01mkSXh6Wc4UhqQtwZBI2t/+TpX1okbg6 697 Hr1ZZupeH6SByjCBx6ADAgEQooG/BIG8GnCmcXWtqhXh48dGTLHQgJ04K5Fj 698 RMMq2qPSbiha9lq0osqR2KAnQA6LioWYxU+6yPKpBDSC5WOT441fUfkM8iAL 699 kW3uNc+luFCGcnDsacrmoVU7Y6Akcp9m7Fm7orRc+TWSWPpBg3OR2oG3ATW0 700 0NAz8TT06VOLVxIMUTINKdYVI/Ja7f3sy+/N4LGkJqScCQOwlo5tfDWn/UQF 701 iTWo5Zw435rH8pjy2smQCnqC14v3NMAWTu4j+dzHUNw= 702 [S] 481 Authentication error 704 Example of a client aborting in the midst of an exchange: 706 [C] AUTHINFO SASL GSSAPI 707 [S] 383 = 708 [C] * 709 [S] 481 Authentication aborted as requested 711 Example of attempting to use a mechanism that is not supported by 712 the server: 714 [C] AUTHINFO SASL EXAMPLE 715 [S] 503 Mechanism not recognized 717 Example of attempting to use a mechanism that requires a security 718 layer: 720 [C] AUTHINFO SASL PLAIN 721 [S] 483 Encryption or stronger authentication required 723 Example of using an initial response with a mechanism that doesn't 724 support it (server must start the exchange): 726 [C] AUTHINFO SASL CRAM-MD5 AHRlc3QAMTIzNA== 727 [S] 482 SASL protocol error 729 3. Augmented BNF Syntax for the AUTHINFO Extension 731 This section describes the syntax of the AUTHINFO extension. It 732 extends the syntax in [NNTP], and non-terminals not defined in this 733 document are defined there. 735 3.1. Commands 737 This syntax extends the non-terminal "command", which represents an 738 NNTP command. 740 command =/ authinfo-sasl-command / 741 authinfo-user-command / 742 authinfo-pass-command 744 authinfo-sasl-command = "AUTHINFO" WS "SASL" WS mechanism 745 [WS initial-response] 746 authinfo-user-command = "AUTHINFO" WS "USER" WS username 747 authinfo-pass-command = "AUTHINFO" WS "PASS" WS password 749 initial-response = base64-opt 750 username = 1*user-pass-char 751 password = 1*user-pass-char 752 user-pass-char = P-CHAR 754 NOTE: A server implementation MAY parse AUTHINFO USER and AUTHINFO 755 PASS specially as to allow white space to be used within the 756 username or password. Such implementations accept the additional 757 syntax (making these two items inconsistent with "token" in section 758 9.7 of [NNTP]): 760 user-pass-char =/ SP / TAB 762 In doing so, the grammar can become ambiguous if the username or 763 password begins or ends with white space. To solve this ambiguity, 764 such implementations typically treat everything after the first 765 white space character following "USER"/"PASS", up to, but not 766 including, the CRLF as the username/password. 768 3.2. Command Continuation 770 This syntax extends the non-terminal "command-continuation", which 771 represents the further material sent by the client in the case of 772 multi-stage commands. 774 command-continuation =/ authinfo-sasl-continuation 775 authinfo-sasl-continuation = ("*" / base64-opt) CRLF 776 ; client must send a continuation following each 777 ; "383" response from the server 779 3.3. Responses 781 This syntax extends the non-terminal "simple-response-content", 782 which represents an initial response line sent by the server. 784 simple-response-content =/ response-sasl-content 785 response-sasl-content = "283" SP base64 / "383" SP base64-opt 787 3.4. Capability entries 789 This syntax extends the non-terminal "capability-entry", which rep- 790 resents a capability that may be advertised by the server. 792 capability-entry =/ authinfo-capability / 793 sasl-capability 795 authinfo-capability = "AUTHINFO" *(WS authinfo-variant) 796 authinfo-variant = "USER" / "SASL" 797 sasl-capability = "SASL" 1*(WS mechanism) 799 3.5. General non-terminals 801 base64-opt = "=" / base64 803 mechanism = 1*20mech-char 804 mech-char = UPPER / DIGIT / "-" / "_" 806 4. Summary of Response Codes 808 This section contains a list of every new response code defined in 809 this document, whether it is multi-line, which commands can 810 generate it, what arguments it has, and what its meaning is. 812 Response code 281 813 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 814 Meaning: authentication accepted 816 Response code 283 817 Generated by: AUTHINFO SASL 818 1 argument: challenge 819 Meaning: authentication accepted (with success data) 821 Response code 381 822 Generated by: AUTHINFO USER 823 Meaning: password required via AUTHINFO PASS command. Note 824 that this code is used for backwards compatibility and does 825 not conform to the traditional use of 3xx codes. 827 Response code 383 828 Generated by: AUTHINFO SASL 829 1 argument: challenge 830 Meaning: continue with SASL exchange 832 Response code 481 833 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 834 Meaning: authentication failed/rejected 836 Response code 482 837 Generated by: AUTHINFO USER, AUTHINFO PASS, AUTHINFO SASL 838 Meaning: authentication commands issued out of sequence or 839 SASL protocol error 841 5. Authentication Tracking/Logging 843 This section contains implementation suggestions and notes of best 844 current practice, and does not specify further network protocol 845 requirements. 847 Once authenticated, the authorization identity presented in the 848 AUTHINFO exchange (username when using USER/PASS) SHOULD be 849 included in an audit trail associating the identity with any 850 articles supplied during a POST operation, and this configuration 851 SHOULD be the default. This may be accomplished, for example, by 852 inserting headers in the posted articles or by a server logging 853 mechanism. The server MAY provide a facility for disabling the 854 procedure described above, as some users or administrators may 855 consider it a violation of privacy. 857 6. Security Considerations 859 Security issues are discussed throughout this memo. 861 Before the [SASL] negotiation has begun, any protocol interactions 862 may have been performed in the clear and may have been modified by 863 an active attacker. For this reason, clients and servers MUST 864 discard any sensitive knowledge obtained prior to the start of the 865 SASL negotiation upon the establishment of a security layer. 867 Servers MAY implement a policy whereby the connection is dropped 868 after a number of failed authentication attempts. If they do so, 869 they SHOULD NOT drop the connection until at least 3 attempts at 870 authentication have failed. 872 Implementations MUST support a configuration where authentication 873 mechanisms that are vulnerable to passive eavesdropping attacks 874 (such as AUTHINFO USER/PASS and SASL [PLAIN]) are not advertised or 875 used without the presence of an external security layer such as TLS 876 [NNTP-TLS]. 878 When multiple authentication mechanisms are permitted by both 879 client and server, an active attacker can cause a down-negotiation 880 to the weakest mechanism. For this reason, both clients and 881 servers SHOULD be configurable to forbid use of weak mechanisms. 882 The minimum strength acceptable is a policy decision which is 883 outside the scope of this specification. 885 7. IANA Considerations 887 7.1. IANA Considerations for SASL/GSSAPI services 889 Please register the SASL/GSSAPI service name "nntp". This service 890 name refers to authenticated use of Usenet news service when 891 provided via the [NNTP] protocol. 893 o Published Specification: This document. 895 o Author, Change Controller, and Contact for Further Information: 896 Author of this document. 898 7.2. IANA Considerations for NNTP extensions 900 Below is a formal definition of the AUTHINFO extension as required 901 by Section 3.3.4 of [NNTP] for the IANA registry. may 902 o This extension provides an extensible mechanism for NNTP 903 authentication via a variety of methods. 905 o The capability label for this extension is "AUTHINFO". 907 o The "AUTHINFO" capability label has two possible optional 908 arguments "USER" and "SASL" (as defined in Section 2.1) 909 indicating which variants of the AUTHINFO command are supported. 911 o This extension also provides the "SASL" capability label whose 912 arguments list the available SASL mechanisms. 914 o This extension defines three new commands, AUTHINFO USER, 915 AUTHINFO PASS, and AUTHINFO SASL, whose behavior, arguments, and 916 responses are defined in Sections 2.3 and 2.4. 918 o This extension does not associate any new responses with pre- 919 existing NNTP commands. 921 o This extension may affect the overall behavior of both server 922 and client, in that the AUTHINFO SASL command may require that 923 subsequent communication be transmitted via an intermediary 924 security layer. 926 o The length of the AUTHINFO SASL command (as defined in this 927 document) may exceed 512 octets. The maximum length of this 928 command is increased to that which can accommodate the largest 929 initial response possible for any of the SASL mechanisms 930 supported by the implementation. 932 o This extension defines two new responses, 283 and 383, whose 933 lengths may exceed 512 octets. The maximum length of these 934 responses is increased to that which can accommodate the largest 935 challenge possible for any of the SASL mechanisms supported by 936 the implementation. 938 o This extension does not alter pipelining, but AUTHINFO commands 939 cannot be pipelined. 941 o Use of this extension may alter the capabilities list; once the 942 AUTHINFO command has been used successfully, the AUTHINFO 943 capability can no longer be advertised by CAPABILITIES. 944 Additionally, the MODE-READER capability MUST NOT be advertised 945 after successful authentication (as discussed in Section 3.4.2 946 of [NNTP]). 948 o This extension does not cause any pre-existing command to 949 produce a 401, 480, or 483 response. 951 o This extension is unaffected by any use of the MODE READER 952 command, however the MODE READER command MUST NOT be used in the 953 same session following successful authentication (as discussed 954 in Section 3.4.2 of [NNTP]). 956 o Published Specification: This document. 958 o Author, Change Controller, and Contact for Further Information: 959 Author of this document. 961 8. References 963 8.1. Normative References 965 [ABNF] Crocker, D., Overell, P., "Augmented BNF for Syntax 966 Specifications: ABNF", RFC 2234, November 1997. 968 [AUTH] Haller, N., Atkinson, R., "On Internet Authentication", 969 RFC 1704, Bell Communications Research, October 1994. 971 [BASE64] Josefsson, S., "The Base16, Base32, and Base64 Data 972 Encodings", RFC 3548, July 2003. 974 [DIGEST-MD5] Leach, P., Newman, C., "Using Digest Authentication as 975 a SASL Mechanism", RFC 2831, May 2000. 977 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate 978 Requirement Levels", RFC 2119, Harvard University, March 1997. 980 [NNTP] Feather, C., "Network News Transport Protocol", 981 draft-ietf-nntpext-base-*.txt, Work in Progress. 983 [NNTP-TLS] Vinocur, J., Murchison, K., Newman, C., "Using TLS with NNTP", 984 draft-ietf-nntpext-tls-nntp-*.txt, Work in Progress. 986 [SASL] Melnikov, A., "Simple Authentication and Security Layer 987 (SASL)", draft-ietf-sasl-rfc2222bis-*.txt, Work in Progress. 989 [SASLprep] Zeilega, K., "SASLprep: Stringprep profile for user names 990 and passwords", draft-ietf-sasl-saslprep-*.txt, Work in Progress. 992 [StringPrep] Hoffman, P. and Blanchet, M., "Preparation of 993 Internationalized Strings ("stringprep")", 994 draft-hoffman-rfc3454bis-*.txt, Work in Progress. 996 8.2. Informative References 998 [CRAM-MD5] Nerenberg, L., "The CRAM-MD5 SASL Mechanism", draft- 999 ietf-sasl-crammd5-*.txt, Work in Progress. 1001 [GSSAPI] Melnikov, A., "SASL GSSAPI Mechanisms", draft-ietf-sasl- 1002 gssapi-*.txt, Work in Progress. 1004 [NNTP-COMMON] Barber, S., "Common NNTP Extensions", RFC 2980, 1005 Academ Consulting Services, October 2000. 1007 [PLAIN] Zeilenga, K., "The Plain SASL Mechanism", draft-ietf-sasl- 1008 plain-*.txt, Work in Progress. 1010 [SMTP] Klensin, J., "Simple Mail Transport Protocol", RFC 2821, 1011 AT&T Laboratories, April 2001. 1013 [UTF-8] Yergeau, F. "UTF-8, a transformation format of ISO 10646", 1014 RFC 3629, Alis Technologies, November 2003. 1016 9. Authors' Addresses 1018 Jeffrey M. Vinocur 1019 Department of Computer Science 1020 Upson Hall 1021 Cornell University 1022 Ithaca, NY 14853 USA 1024 Email: vinocur@cs.cornell.edu 1026 Kenneth Murchison 1027 Oceana Matrix Ltd. 1028 21 Princeton Place 1029 Orchard Park, NY 14127 USA 1031 Email: ken@oceana.com 1033 Chris Newman 1034 Sun Microsystems 1035 1050 Lakes Drive, Suite 250 1036 West Covina, CA 91790 USA 1038 Email: cnewman@iplanet.com 1040 10. Acknowledgments 1042 A significant amount of the authentication text was originally from 1043 the NNTP revision or common authentication specs written by Stan 1044 Barber. A significant amount of the SASL text was lifted from the 1045 revisions to RFC 1734 and RFC 2554 by Rob Siemborski. 1047 Special acknowledgment also goes to Russ Allbery, Clive Feather, 1048 and others who commented privately on intermediate revisions of 1049 this document, as well as the members of the IETF NNTP Working 1050 Group for continual (yet sporadic) insight in discussion. 1052 11. Intellectual Property Rights 1054 The IETF takes no position regarding the validity or scope of any 1055 intellectual property or other rights that might be claimed to 1056 pertain to the implementation or use of the technology described in 1057 this document or the extent to which any license under such rights 1058 might or might not be available; neither does it represent that it 1059 has made any effort to identify any such rights. Information on 1060 the IETF's procedures with respect to rights in standards-track and 1061 standards-related documentation can be found in BCP-11. Copies of 1062 claims of rights made available for publication and any assurances 1063 of licenses to be made available, or the result of an attempt made 1064 to obtain a general license or permission for the use of such 1065 proprietary rights by implementers or users of this specification 1066 can be obtained from the IETF Secretariat. 1068 The IETF invites any interested party to bring to its attention any 1069 copyrights, patents or patent applications, or other proprietary 1070 rights which may cover technology that may be required to practice 1071 this standard. Please address the information to the IETF 1072 Executive Director. 1074 12. Copyright 1076 Copyright (C) The Internet Society (2005). This document is 1077 subject to the rights, licenses and restrictions contained in BCP 1078 78, and except as set forth therein, the authors retain all their 1079 rights." 1081 This document and the information contained herein are provided on 1082 an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE 1083 REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND 1084 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, 1085 EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT 1086 THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR 1087 ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A 1088 PARTICULAR PURPOSE.