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Ts'o, Editor 2 Internet-Draft VA Linux Systems 3 draft-tso-telnet-auth-enc-05.txt April 2000 5 Telnet Authentication Option 7 Status of this Memo 9 This document is an Internet-Draft and is in full conformance with 10 all provisions of Section 10 of RFC2026. Internet-Drafts are working 11 documents of the Internet Engineering Task Force (IETF), its areas, 12 and its working groups. Note that other groups may also distribute 13 working documents as Internet-Drafts. 15 Internet-Drafts are draft documents valid for a maximum of six months 16 and may be updated, replaced, or obsoleted by other documents at any 17 time. It is inappropriate to use Internet-Drafts as reference 18 material or to cite them other than as "work in progress." 20 The list of current Internet-Drafts can be accessed at 21 http://www.ietf.org/ietf/1id-abstracts.txt 23 The list of Internet-Draft Shadow Directories can be accessed at 24 http://www.ietf.org/shadow.html. 26 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 27 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 28 document are to be interpreted as described in RFC 2119. 30 0. Abstract 32 This document describes the authentication option to the telnet[1] 33 protocol as a generic method for negotiating an authentication type 34 and mode including whether encryption should be used and if creden- 35 tials should be for- warded. While this document summarizes current- 36 ly utilized commands and types it does not define a specific authen- 37 tication type. Separate documents are to be published defining each 38 authentication type. 40 This document updates a previous specification of the telnet authen- 41 tication option, RFC 1409 [2], so that it can be used to its use can 42 be used to securely enable the telnet encryption option[3]. 44 1. Command Names and Codes 46 AUTHENTICATION 37 47 Authentication Commands 48 IS 0 49 SEND 1 50 REPLY 2 51 NAME 3 53 Authentication Types 54 NULL 0 55 KERBEROS_V4 1 56 KERBEROS_V5 2 57 SPX* 3 58 MINK* 4 59 SRP 5 60 RSA*[also used by SRA*] 6 61 SSL* 7 62 [unassigned] 8 63 [unassigned] 9 64 LOKI* 10 65 SSA* 11 66 KEA_SJ 12 67 KEA_SJ_INTEG 13 68 DSS 14 69 NTLM* 15 71 Authentication types followed by (*) were never submitted to the 72 IETF for consideration as an Internet standard. 74 Following historical practice, future authentication type numbers 75 and authentication modifiers will be assigned by the IANA under a 76 First Come First Served policy as outlined by RFC 2434 [4]. 77 Despite the fact that authentication type numbers are allocated out 78 of an 8-bit number space (as are most values in the telnet 79 specification) it is not anticipated that the number space is or 80 will become in danger of being exhausted. However, if this should 81 become an issue, when over 50% of the number space becomes allocated, 82 the IANA shall refer allocation requests to either the IESG or a 83 designated expert for approval. IANA is instructed not to issue new 84 suboption values without submission of documentation of their use. 86 Modifiers 87 AUTH_WHO_MASK 1 88 AUTH_CLIENT_TO_SERVER 0 89 AUTH_SERVER_TO_CLIENT 1 91 AUTH_HOW_MASK 2 92 AUTH_HOW_ONE_WAY 0 93 AUTH_HOW_MUTUAL 2 95 ENCRYPT_MASK 20 96 ENCRYPT_OFF 0 97 ENCRYPT_USING_TELOPT 4 98 ENCRYPT_AFTER_EXCHANGE 16 99 ENCRYPT_RESERVED 20 101 INI_CRED_FWD_MASK 8 102 INI_CRED_FWD_OFF 0 103 INI_CRED_FWD_ON 8 105 2. Command Meanings 107 This document makes reference to a "server" and a "client". For the 108 purposes of this document, the "server" is the side of the connection 109 that did the passive TCP open (TCP LISTEN state), and the "client" is 110 the side of the connection that did the active open. 112 IAC WILL AUTHENTICATION 114 The client side of the connection sends this command to indicate 115 that it is willing to send and receive authentication information. 117 IAC DO AUTHENTICATION 119 The servers side of the connection sends this command to indicate 120 that it is willing to send and receive authentication information. 122 IAC WONT AUTHENTICATION 124 The client side of the connection sends this command to indicate 125 that it refuses to send or receive authentication information; the 126 server side must send this command if it receives a DO AUTHENTICA- 127 TION command. 129 IAC DONT AUTHENTICATION 131 The server side of the connection sends this command to indicate 132 that it refuses to send or receive authentication information; the 133 client side must send this command if it receives a WILL AUTHENTI- 134 CATION command. 136 IAC SB AUTHENTICATION SEND authentication-type-pair-list IAC SE 138 The sender of this command (the server) requests that the remote 139 side send authentication information for one of the authentication 140 types listed in "authentication-type-pair-list". The "authentica- 141 tion-type-pair-list" is an ordered list of "authentication-type" 142 pairs. Only the server side (DO AUTHENTICATION) is allowed to 143 send this. 145 IAC SB AUTHENTICATION IS authentication-type-pair IAC SE 147 The sender of this command (the client) is sending the authentica- 148 tion information for authentication type "authentication-type- 149 pair". Only the client side (WILL AUTHENTICATION) is allowed to 150 send this. 152 IAC SB AUTHENTICATION REPLY authentication-type-pair IAC 153 SE 155 The sender of this command (the server) is sending a reply to the 156 the authentication information received in a previous IS command. 157 Only the server side (DO AUTHENTICATION) is allowed to send this. 159 IAC SB AUTHENTICATION NAME remote-user IAC SE 160 This optional command is sent to specify the account name on the 161 remote host that the user wishes to be authorized to use. Note 162 that authentication may succeed, and the authorization to use a 163 particular account may still fail. Some authentication mechanisms 164 may ignore this command. 166 The "authentication-type-pair" is two octets, the first is the au- 167 thentication type, and the second is a modifier to the type. The au- 168 thentication type may or may not include built-in encryption. For 169 instance, when the Kerberos 4 authentication type is negotiated en- 170 cryption must be negotiated with the telnet ENCRYPT option. However, 171 the SSL and KEA_SJ authentication types provide an encrypted channel 172 as part of a successful telnet AUTH option negotiation. 174 There are currently five one bit fields defined in the modifier. The 175 first two of these bits are processed as a pair, the AUTH_WHO_MASK 176 bit and the AUTH_HOW_MASK bit. There are four possible combinations 177 of these two bits: 179 AUTH_CLIENT_TO_SERVER 180 AUTH_HOW_ONE_WAY 182 The client will send authentication information about the local 183 user to the server. If the negotiation is successful, the 184 server will have authenticated the user on the client side of 185 the connection. 187 AUTH_SERVER_TO_CLIENT 188 AUTH_HOW_ONE_WAY 190 The server will authenticate itself to the client. If the ne- 191 gotiation is successful, the client will know that it is con- 192 nected to the server that it wants to be connected to. 194 AUTH_CLIENT_TO_SERVER 195 AUTH_HOW_MUTUAL 197 The client will send authentication information about the local 198 user to the server, and then the server will authenticate it- 199 self to the client. If the negotiation is successful, the 200 server will have authenticated the user on the client side of 201 the connection, and the client will know that it is connected 202 to the server that it wants to be connected to. 204 AUTH_SERVER_TO_CLIENT 205 AUTH_HOW_MUTUAL 207 The server will authenticate itself to the client, and then the 208 client will authenticate itself to the server. If the negotia- 209 tion is successful, the client will know that it is connected 210 to the server that it wants to be connected to, and the server 211 will know that the client is who it claims to be. 213 The third and fifth bits in the modifier are the ENCRYPT_MASK 214 bits. These bits are used to determine if and how encryption 215 should be enabled. Of the four possible combinations only three 216 are currently defined: 218 ENCRYPT_OFF 220 Encryption will not be used for this session. TELOPT EN- 221 CRYPT SHOULD NOT be negotiated. This mode MUST be used with 222 all AUTH types that do not provide a shared secret to be 223 used as a session key. 225 ENCRYPT_USING_TELOPT 227 Encryption will be negotiated via the use of TELOPT ENCRYPT. 228 Immediately after authentication has completed TELOPT EN- 229 CRYPT MUST be negotiated in both directions. This is re- 230 quired to occur before credentials forwarding; other telnet 231 options are negotiated; or any user data is transmitted. A 232 failure to successfully negotiate TELOPT ENCRYPT in either 233 direction MUST result in immediate session termination. 235 ENCRYPT_AFTER_EXCHANGE 237 Encryption will be activated in both directions immediately 238 after the successful exchange of the shared secret to be 239 used as the session key. The encryption algorithm to be 240 used MUST be implied by the AUTH type. 242 The fourth bit field in the modifier is the INI_CRED_FWD_MASK bit. 243 This bit is either set to INI_CRED_FWD_ON or INI_CRED_FWD_OFF. 244 This bit is set by the client to advise the server to expect for- 245 warded credentials from the client. 247 INI_CRED_FWD_OFF 249 The client will not be forwarding credentials to the server. 250 This mode must be used if the selected authentication method 251 does not support credentials forwarding. 253 INI_CRED_FWD_ON 255 Once authentication, and perhaps encryption, completes, the 256 client will immediately forward authentication credentials 257 to the server. 259 The motivation for this advisory bit is that the server may wish 260 to wait until the forwarded credentials have been sent before 261 starting any operating system specific login procedures which may 262 depend on these credentials. Note that credentials forwarding may 263 not be supported by all authentication mechanisms. It is a proto- 264 col error to set this bit if the underlying authentication mecha- 265 nism does not support credentials forwarding. 267 Credentials forwarding MUST NOT be performed if 268 AUTH_CLIENT_TO_SERVER|AUTH_HOW_ONE_WAY was used since the identity 269 of the server can not be assured. Credentials SHOULD NOT be for- 270 warded if the telnet connection is not protected using some en- 271 cryption or integrity protection services. 273 Note that older implementations of the telnet authentication op- 274 tion will not understand the ENCRYPT_MASK and INI_CRED_FWD_MASK 275 bits. Hence an implementation wishing to offer these bits should 276 offer authentication type pairs with these bits both set and not 277 set if backwards compatibility is required. 279 3. Default Specification 281 The default specification for this option is 283 WONT AUTHENTICATION 284 DONT AUTHENTICATION 286 meaning there will not be any exchange of authentication information. 288 4. Motivation 290 One of the deficiencies of the Telnet protocol is that in order to 291 log into remote systems, users have to type their passwords, which 292 are passed in clear text through the network. If the connections 293 goes through untrusted networks, there is the possibility that pass- 294 words will be compromised by someone watching the packets as they go 295 by. 297 The purpose of the AUTHENTICATION option is to provide a framework 298 for the passing of authentication information through the TELNET ses- 299 sion, and a mechanism to enable encryption of the data stream as a 300 side effect of successful authentication or via subsequent use of the 301 telnet ENCRYPT option. This means that: 1) the users password will 302 not be sent in clear text across the network, 2) if the front end 303 telnet process has the appropriate authentication information, it can 304 automatically send the information, and the user will not have to 305 type any password. 3) once authentication has succeeded, the data 306 stream can be encrypted to provide protection against active attacks. 308 It is intended that the AUTHENTICATION option be general enough that 309 it can be used to pass information for any authentication and encryp- 310 tion system. 312 5. Security Implications 314 The ability to negotiate a common authentication mechanism between 315 client and server is a feature of the authentication option that 316 should be used with caution. When the negotiation is performed, no 317 authentication has yet occurred. Therefore each system has no way of 318 knowing whether or not it is talking to the system it intends. An in- 319 truder could attempt to negotiate the use of an authentication system 320 which is either weak, or already compromised by the intruder. 322 If the authentication type requires that encryption be enabled as a 323 separate optional negotiation (the ENCRYPT option), it will provide a 324 window of vulnerability from when the authentication completes, up to 325 and including the negotiation to turn on encryption by an active at- 326 tacker. An active attack is one where the underlying TCP stream can 327 be modified or taken over by the active attacker. If the server only 328 offers authentication type pairs that include the ENCRYPT_US- 329 ING_TELOPT set in the ENCRYPT_MASK field, this will avoid the window 330 of vulnerability, since both parties will agree that telnet ENCRYPT 331 option must be successfully negotiated immediately following the suc- 332 cessful completion of telnet AUTH. 334 Other authentication types link the enabling of encryption as a side 335 effect of successful authentication. This will also provide protec- 336 tion against the active attacker. The ENCRYPT_AFTER_EXCHANGE bit al- 337 lows these authentication types to negotiate encryption so that it 338 can be made optional. 340 Another opportunity for active attacks is presented when encryption 341 may be turned on and off without re-authentication. Once encryption 342 is disabled, an attacker may hijack the telnet stream, and interfere 343 with attempts to restart encryption. Therefore, a client SHOULD NOT 344 support the ability to turn off encryption. Once encryption is dis- 345 abled, if an attempt to re-enable encryption fails, the client MUST 346 terminate the telnet connection. 348 It is important that in both cases the authentication type pair be 349 integrity protected at the end of the authentication exchange. This 350 must be specified for each authentication type to ensure that the re- 351 sult of the telnet authentication option negotiation is agreed to by 352 both the client and the server. Some authentication type suboptions 353 may wish to include all of the telnet authentication negotiation ex- 354 changes in the integrity checksum, to fully protect the entire ex- 355 change. 357 Each side MUST verify the consistency of the auth-type-pairs in each 358 message received. Any variation in the auth-type-pair MUST be treat- 359 ed as a fatal protocol error. 360 6. Implementation Rules 362 WILL and DO are used only at the beginning of the connection to ob- 363 tain and grant permission for future negotiations. 365 The authentication is only negotiated in one direction; the server 366 must send the "DO", and the client must send the "WILL". This re- 367 striction is due to the nature of authentication; there are three 368 possible cases; server authenticates client, client authenticates 369 server, and server and client authenticate each other. By only nego- 370 tiating the option in one direction, and then determining which of 371 the three cases is being used via the suboption, potential ambiguity 372 is removed. If the server receives a "DO", it must respond with a 373 "WONT". If the client receives a "WILL", it must respond with a 374 "DONT". 376 Once the two hosts have exchanged a DO and a WILL, the server is free 377 to request authentication information. In the request, a list of 378 supported authentication types is sent. Only the server may send re- 379 quests ("IAC SB AUTHENTICATION SEND authentication-type-pair-list IAC 380 SE"). Only the client may transmit authentication information via 381 the "IAC SB AUTHENTICATION IS authentication-type ... IAC SE" com- 382 mand. Only the server may send replies ("IAC SB AUTHENTICATION REPLY 383 authentication-type ... IAC SE"). As many IS and REPLY suboptions 384 may be exchanged as are needed for the particular authentication 385 scheme chosen. 387 If the client does not support any of the authentication types listed 388 in the authentication-type-pair-list, a type of NULL should be used 389 to indicate this in the IS reply. Note that if the client responds 390 with a type of NULL, the server may choose to close the connection. 391 When the server has concluded that authentication cannot be nego- 392 tiated with the client it should send IAC DONT AUTH to the client. 394 The order of the authentication types MUST be ordered to indicate a 395 preference for different authentication types, the first type being 396 the most preferred, and the last type the least preferred. 398 As long as the server is WILL AUTH it may request authentication in- 399 formation at any time. This is done by sending a new list of sup- 400 ported authentication types. Requesting authentication information 401 may be done as a way of verifying the validity of the client's cre- 402 dentials after an extended period of time or to negotiate a new ses- 403 sion key for use during encryption. 405 7. User Interface 407 Normally protocol specifications do not address user interface speci- 408 fications. However, due to the fact that the user will probably want 409 to be able to specify the things about authentication and encryption 410 and also know whether or not things succeeded, some guidance needs to 411 be given to implementors to provide some minimum level of user con- 412 trol. 414 The user MUST be able to specify whether or not authentication is to 415 be used, and whether or not encryption is to used if the authentica- 416 tion succeeds. There SHOULD be at least four settings, REQUIRE, 417 PROMPT, WARN and DISABLE. Setting the authentication switch to RE- 418 QUIRE means that if the authentication fails, then an appropriate er- 419 ror message must be displayed and the TELNET connection must be ter- 420 minated. Setting the authentication switch to PROMPT means that if 421 the authentication fails, then an appropriate error message must be 422 displayed and the user must be prompted for confirmation before con- 423 tinuing the TELNET session. Setting the authentication switch to 424 WARN means that if the authentication fails, then an appropriate er- 425 ror message must be displayed before continuing the TELNET session. 426 Setting the authentication switch to DISABLE means that authentica- 427 tion will not be attempted. The encryption switch SHOULD have the 428 same settings as the authentication switch; however its settings are 429 only used when authentication succeeds. The default setting for both 430 switches should be WARN. Both of these switches may be implemented 431 as a single switch, though having them separate gives more control to 432 the user. 434 8. Example 436 The following is an example of use of the option: 438 Client Server 439 IAC DO AUTHENTICATION 440 IAC WILL AUTHENTICATION 441 [ The server is now free to request authentication information. 442 ] 443 IAC SB AUTHENTICATION SEND 444 KERBEROS_V4 CLIENT|MUTUAL 445 KERBEROS_V4 CLIENT|ONE_WAY IAC 446 SE 447 [ The server has requested mutual Kerberos authentication, but is 448 willing to do just one-way Kerberos authentication. The client 449 will now respond with the name of the user that it wants to log 450 in as, and the Kerberos ticket. ] 451 IAC SB AUTHENTICATION NAME "joe" 452 IAC SE 453 IAC SB AUTHENTICATION IS 454 KERBEROS_V4 CLIENT|MUTUAL AUTH 4 455 7 1 67 82 65 89 46 67 7 9 77 0 456 48 24 49 244 109 240 50 208 43 457 35 25 116 104 44 167 21 201 224 458 229 145 20 2 244 213 220 33 134 459 148 4 251 249 233 229 152 77 2 460 109 130 231 33 146 190 248 1 9 461 31 95 94 15 120 224 0 225 76 205 462 70 136 245 190 199 147 155 13 463 IAC SE 464 [ The server responds with an ACCEPT command to state that the 465 authentication was successful. ] 466 IAC SB AUTHENTICATION REPLY 467 KERBEROS_V4 CLIENT|MUTUAL ACCEPT 468 IAC SE 469 [ Next, the client sends across a CHALLENGE to verify that it is 470 really talking to the right server. ] 471 IAC SB AUTHENTICATION IS 472 KERBEROS_V4 CLIENT|MUTUAL 473 CHALLENGE xx xx xx xx xx xx xx 474 xx IAC SE 475 [ Lastly, the server sends across a RESPONSE to prove that it 476 really is the right server. 477 IAC SB AUTHENTICATION REPLY 478 KERBEROS_V4 CLIENT|MUTUAL 479 RESPONSE yy yy yy yy yy yy yy yy 480 IAC SE 482 The following is an example of use of the option with encryption ne- 483 gotiated via telnet ENCRYPT: 485 Client Server 486 IAC DO AUTHENTICATION 487 IAC WILL AUTHENTICATION 488 [ The server is now free to request authentication information. 489 ] 490 IAC SB AUTHENTICATION SEND 491 KERBEROS_V4 492 ENCRYPT_USING_TELOPT|CLIENT|MUTUAL 493 KERBEROS_V4 CLIENT|ONE_WAY IAC 494 SE 495 [ The server has requested mutual Kerberos authentication, but is 496 willing to do just one-way Kerberos authentication. In both 497 cases it is willing to encrypt the data stream. The client 498 will now respond with the name of the user that it wants to log 499 in as, and the Kerberos ticket. ] 500 IAC SB AUTHENTICATION NAME "joe" 501 IAC SE 502 IAC SB AUTHENTICATION IS 503 KERBEROS_V4 504 ENCRYPT_USING_TELOPT|CLIENT|MUTUAL 505 AUTH 4 7 1 67 82 65 89 46 67 7 9 506 77 0 48 24 49 244 109 240 50 208 507 43 35 25 116 104 44 167 21 201 508 224 229 145 20 2 244 213 220 33 509 134 148 4 251 249 233 229 152 77 510 2 109 130 231 33 146 190 248 1 9 511 31 95 94 15 120 224 0 225 76 205 512 70 136 245 190 199 147 155 13 513 IAC SE 514 [ The server responds with an ACCEPT command to state that the 515 authentication was successful. ] 516 IAC SB AUTHENTICATION REPLY 517 KERBEROS_V4 518 CLIENT|MUTUAL|ENCRYPT_USING_TELOPT 519 ACCEPT IAC SE 520 [ Next, the client sends across a CHALLENGE to verify that it is 521 really talking to the right server. ] 522 IAC SB AUTHENTICATION IS 523 KERBEROS_V4 524 CLIENT|MUTUAL|ENCRYPT_USING_TELOPT 525 CHALLENGE xx xx xx xx xx xx xx 526 xx IAC SE 527 [ The server sends across a RESPONSE to prove that it really is 528 the right server. ] 529 IAC SB AUTHENTICATION REPLY 530 KERBEROS_V4 531 CLIENT|MUTUAL|ENCRYPT_USING_TELOPT 532 RESPONSE yy yy yy yy yy yy yy yy 533 IAC SE 534 [ At this point, the client and server begin to negotiate the 535 telnet ENCRYPT option in each direction for a secure channel. 536 If the option fails in either direction for any reason the 537 connection must be immediately terminated. ] 539 The following is an example of use of the option with integrated en- 540 cryption: 542 Client Server 543 IAC DO AUTHENTICATION 544 IAC WILL AUTHENTICATION 545 [ The server is now free to request authentication information. 546 ] 547 IAC SB AUTHENTICATION SEND 548 KEA_SJ 549 CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE 550 IAC SE 551 [ The server has requested mutual KEA authentication with 552 SKIPJACK encryption. The client will now respond with the name 553 of the user that it wants to log in as and the KEA cert. ] 554 IAC SB AUTHENTICATION NAME "joe" 555 IAC SE IAC SB AUTHENTICATION IS 556 KEA_SJ 557 CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE 558 '1' CertA||Ra IAC SE 560 [ The server responds with its KEA Cert. ] 561 IAC SB AUTHENTICATION REPLY 562 KEA_SJ 563 CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE 564 '2' 565 CertB||Rb||IVb||Encrypt(NonceB) 566 IAC SE 567 [ Next, the client sends across a CHALLENGE to verify that it is 568 really talking to the right server. ] 569 IAC SB AUTHENTICATION IS KEA_SJ 570 CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE 571 '3' IVa||Encrypt( NonceB xor 572 0x0C18 || NonceA ) IAC SE 573 [ At this point, the client begins to encrypt the outgoing data 574 stream, and the server, after receiving this command, begins to 575 decrypt the incoming data stream. Lastly, the server sends 576 across a RESPONSE to prove that it really is the right server. 577 ] 578 IAC SB AUTHENTICATION REPLY 579 KEA_SJ 580 CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE 581 '4' Encrypt( NonceA xor 0x0C18 ) 582 IAC SE 583 [ At this point, the server begins to encrypt its outgoing data 584 stream, and the client, after receiving this command, begins to 585 decrypt its incoming data stream. ] 587 It is expected that any implementation that supports the Telnet AU- 588 THENTICATION option will support all of this specification. 590 9. Security Considerations 592 This memo describes a general framework for adding authentication and 593 encryption to the telnet protocol. The actual authentication mecha- 594 nism is described in the authentication suboption specifications, and 595 the security of the authentication option is dependent on the 596 strengths and weaknesses of the authentication suboption. 598 It should also be noted that the negotiation of the authentication 599 type pair is not protected, thus allowing an attacker to force the 600 result of the authentication to the weakest mutually acceptable 601 method. (For example, even if both sides of the negotiation can ac- 602 cept a "strong" mechanism and a "40-bit" mechanism, an attacker could 603 force selection of the "40-bit" mechanism.) An implementation should 604 therefore only accept an authentication mechanism to be negotiated if 605 it is willing to trust it as being secure. 607 11. Acknowledgements 609 Many people have worked on this document over the span of many years. 611 Dave Borman was a document editor and author of much of the original 612 text. Other folks who have contributed ideas and suggestions to this 613 text include: David Carrel, Jeff Schiller, and Richard Basch. 615 10. References 617 [1] Reynolds, Joyce, and Postel, Jon, "Telnet Protocol Specifica- 618 tion", RFC 854, May 1983. 619 [2] D. Borman, "Telnet Authentication Option", RFC 1409, January 620 1993. 621 [3] Internet Engineering Task Force, "Telnet Data Encryption Option", 622 draft-tso-telnet-encryption-04.txt, T. Ts'o, Editor, VA Linux 623 Systems, April 2000. 624 [4] Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA 625 Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. 627 Author's Address 629 Theodore Ts'o, Editor 630 VA Linux Systems 631 43 Pleasant St. 632 Medford, MA 02155 633 Phone: (781) 391-3464 634 EMail: tytso@valinux.com 636 Jeffrey Altman 637 Columbia University 638 Watson Hall Room 716 639 612 West 115th Street 640 New York NY 10025 641 Phone: +1 (212) 854-1344 642 EMail: jaltman@columbia.edu 644 Mailing List: telnet-wg@BSDI.COM 646 Jeffrey Altman * Sr.Software Designer * Kermit-95 for Win32 and OS/2 647 The Kermit Project * Columbia University 648 612 West 115th St #716 * New York, NY * 10025 649 http://www.kermit-project.org/k95.html * kermit-support@kermit-project.org