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rfc:rfc2941

Network Working Group T. Ts'o, Editor Request for Comments: 2941 VA Linux Systems Obsoletes: 1416 J. Altman Category: Standards Track Columbia University

                                                         September 2000
                    Telnet Authentication Option

Status of this Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

 This document describes the authentication option to the telnet [1]
 protocol as a generic method for negotiating an authentication type
 and mode including whether encryption should be used and if
 credentials should be forwarded.  While this document summarizes
 currently utilized commands and types it does not define a specific
 authentication type.  Separate documents are to be published defining
 each authentication type.
 This document updates a previous specification of the telnet
 authentication option, RFC 1416 [2], so that it can be used to
 securely enable the telnet encryption option [3].

1. Command Names and Codes

    AUTHENTICATION          37
        Authentication Commands
        IS                       0
        SEND                     1
        REPLY                    2
        NAME                     3
        Authentication Types
        NULL                     0
        KERBEROS_V4              1

Ts'o & Altman Standards Track [Page 1] RFC 2941 Telnet Authentication Option September 2000

        KERBEROS_V5              2
        SPX*                     3
        MINK*                    4
        SRP                      5
        RSA*[also used by SRA*]  6
        SSL*                     7
        [unassigned]             8
        [unassigned]             9
        LOKI*                   10
        SSA*                    11
        KEA_SJ                  12
        KEA_SJ_INTEG            13
        DSS                     14
        NTLM*                   15
     Authentication types followed by (*) were never submitted to the
     IETF for consideration as an Internet standard.
     Following historical practice, future authentication type numbers
     and authentication modifiers will be assigned by the IANA under a
     First Come First Served policy as outlined by RFC 2434 [4].
     Despite the fact that authentication type numbers are allocated
     out of an 8-bit number space (as are most values in the telnet
     specification) it is not anticipated that the number space is or
     will become in danger of being exhausted.  However, if this
     should become an issue, when over 50% of the number space becomes
     allocated, the IANA shall refer allocation requests to either the
     IESG or a designated expert for approval.  IANA is instructed not
     to issue new suboption values without submission of documentation
     of their use.
        Modifiers
        AUTH_WHO_MASK        1
        AUTH_CLIENT_TO_SERVER    0
        AUTH_SERVER_TO_CLIENT    1
        AUTH_HOW_MASK        2
        AUTH_HOW_ONE_WAY         0
        AUTH_HOW_MUTUAL          2
        ENCRYPT_MASK        20
        ENCRYPT_OFF              0
        ENCRYPT_USING_TELOPT     4
        ENCRYPT_AFTER_EXCHANGE  16
        ENCRYPT_RESERVED        20
        INI_CRED_FWD_MASK    8
        INI_CRED_FWD_OFF         0

Ts'o & Altman Standards Track [Page 2] RFC 2941 Telnet Authentication Option September 2000

        INI_CRED_FWD_ON          8

2. Command Meanings

 This document makes reference to a "server" and a "client".  For the
 purposes of this document, the "server" is the side of the connection
 that performed the passive TCP open (TCP LISTEN state), and the
 "client" is the side of the connection that did the active open.
 IAC WILL AUTHENTICATION
    The client side of the connection sends this command to indicate
    that it is willing to send and receive authentication information.
 IAC DO AUTHENTICATION
    The servers side of the connection sends this command to indicate
    that it is willing to send and receive authentication information.
 IAC WONT AUTHENTICATION
    The client side of the connection sends this command to indicate
    that it refuses to send or receive authentication information; the
    server side must send this command if it receives a DO
    AUTHENTICATION command.
 IAC DONT AUTHENTICATION
    The server side of the connection sends this command to indicate
    that it refuses to send or receive authentication information; the
    client side must send this command if it receives a WILL
    AUTHENTICATION command.
 IAC SB AUTHENTICATION SEND authentication-type-pair-list IAC SE
    The sender of this command (the server) requests that the remote
    side send authentication information for one of the authentication
    types listed in "authentication-type-pair-list".  The
    "authentication-type-pair-list" is an ordered list of
    "authentication-type" pairs.  Only the server side (DO
    AUTHENTICATION) is allowed to send this.
 IAC SB AUTHENTICATION IS authentication-type-pair <auth data> IAC SE
    The sender of this command (the client) is sending the
    authentication information for authentication type
    "authentication-type-pair".  Only the client side (WILL
    AUTHENTICATION) is allowed to send this.

Ts'o & Altman Standards Track [Page 3] RFC 2941 Telnet Authentication Option September 2000

 IAC SB AUTHENTICATION REPLY authentication-type-pair <auth data> IAC
 SE
    The sender of this command (the server) is sending a reply to the
    the authentication information received in a previous IS command.
    Only the server side (DO AUTHENTICATION) is allowed to send this.
 IAC SB AUTHENTICATION NAME remote-user IAC SE
    This optional command is sent to specify the account name on the
    remote host that the user wishes to be authorized to use.  Note
    that authentication may succeed, and the authorization to use a
    particular account may still fail.  Some authentication mechanisms
    may ignore this command.
 The "authentication-type-pair" is two octets, the first is the
 authentication type, and the second is a modifier to the type.  The
 authentication type may or may not include built-in encryption.  For
 instance, when the Kerberos 4 authentication type is negotiated
 encryption must be negotiated with the telnet ENCRYPT option.
 However, the SSL and KEA_SJ authentication types provide an encrypted
 channel as part of a successful telnet AUTH option negotiation.
 There are currently five one bit fields defined in the modifier.  The
 first two of these bits are processed as a pair, the AUTH_WHO_MASK
 bit and the AUTH_HOW_MASK bit.  There are four possible combinations
 of these two bits:
    AUTH_CLIENT_TO_SERVER
    AUTH_HOW_ONE_WAY
       The client will send authentication information about the local
       user to the server.  If the negotiation is successful, the
       server will have authenticated the user on the client side of
       the connection.
    AUTH_SERVER_TO_CLIENT
    AUTH_HOW_ONE_WAY
       The server will authenticate itself to the client.  If the
       negotiation is successful, the client will know that it is
       connected to the server that it wants to be connected to.
    AUTH_CLIENT_TO_SERVER
    AUTH_HOW_MUTUAL
       The client will send authentication information about the local
       user to the server, and then the server will authenticate

Ts'o & Altman Standards Track [Page 4] RFC 2941 Telnet Authentication Option September 2000

       itself to the client.  If the negotiation is successful, the
       server will have authenticated the user on the client side of
       the connection, and the client will know that it is connected
       to the server that it wants to be connected to.
    AUTH_SERVER_TO_CLIENT
    AUTH_HOW_MUTUAL
       The server will authenticate itself to the client, and then the
       client will authenticate itself to the server.  If the
       negotiation is successful, the client will know that it is
       connected to the server that it wants to be connected to, and
       the server will know that the client is who it claims to be.
    The third and fifth bits in the modifier are the ENCRYPT_MASK
    bits.  These bits are used to determine if and how encryption
    should be enabled.  Of the four possible combinations only three
    are currently defined:
       ENCRYPT_OFF
          Encryption will not be used for this session.  TELOPT
          ENCRYPT SHOULD NOT be negotiated.  This mode MUST be used
          with all AUTH types that do not provide a shared secret to
          be used as a session key.
       ENCRYPT_USING_TELOPT
          Encryption will be negotiated via the use of TELOPT ENCRYPT.
          Immediately after authentication has completed TELOPT
          ENCRYPT MUST be negotiated in both directions.  This is
          required to occur before credentials forwarding; other
          telnet options are negotiated; or any user data is
          transmitted.  A failure to successfully negotiate TELOPT
          ENCRYPT in either direction MUST result in immediate session
          termination.
       ENCRYPT_AFTER_EXCHANGE
          Encryption will be activated in both directions immediately
          after the successful exchange of the shared secret to be
          used as the session key.  The encryption algorithm to be
          used MUST be implied by the AUTH type.
    The fourth bit field in the modifier is the INI_CRED_FWD_MASK bit.
    This bit is either set to INI_CRED_FWD_ON or INI_CRED_FWD_OFF.
    This bit is set by the client to advise the server to expect
    forwarded credentials from the client.

Ts'o & Altman Standards Track [Page 5] RFC 2941 Telnet Authentication Option September 2000

       INI_CRED_FWD_OFF
          The client will not be forwarding credentials to the server.
          This mode must be used if the selected authentication method
          does not support credentials forwarding.
       INI_CRED_FWD_ON
          Once authentication, and perhaps encryption, completes, the
          client will immediately forward authentication credentials
          to the server.
    The motivation for this advisory bit is that the server may wish
    to wait until the forwarded credentials have been sent before
    starting any operating system specific login procedures which may
    depend on these credentials.  Note that credentials forwarding may
    not be supported by all authentication mechanisms.  It is a
    protocol error to set this bit if the underlying authentication
    mechanism does not support credentials forwarding.
    Credentials forwarding MUST NOT be performed if
    AUTH_CLIENT_TO_SERVER|AUTH_HOW_ONE_WAY was used since the identity
    of the server can not be assured.  Credentials SHOULD NOT be
    forwarded if the telnet connection is not protected using some
    encryption or integrity protection services.
    Note that older implementations of the telnet authentication
    option will not understand the ENCRYPT_MASK and INI_CRED_FWD_MASK
    bits.  Hence an implementation wishing to offer these bits should
    offer authentication type pairs with these bits both set and not
    set if backwards compatibility is required.

3. Default Specification

 The default specification for this option is
    WONT AUTHENTICATION DONT AUTHENTICATION
 meaning there will not be any exchange of authentication information.

4. Motivation

 One of the deficiencies of the Telnet protocol is that in order to
 log into remote systems, users have to type their passwords, which
 are passed in clear text through the network.  If the connections go
 through untrusted networks, there is the possibility that passwords
 will be compromised by someone watching the packets while in transit.

Ts'o & Altman Standards Track [Page 6] RFC 2941 Telnet Authentication Option September 2000

 The purpose of the AUTHENTICATION option is to provide a framework
 for the passing of authentication information through the TELNET
 session, and a mechanism to enable encryption of the data stream as a
 side effect of successful authentication or via subsequent use of the
 telnet ENCRYPT option.  This means that: 1) the users password will
 not be sent in clear text across the network, 2) if the front end
 telnet process has the appropriate authentication information, it can
 automatically send the information, and the user will not have to
 type any password.  3) once authentication has succeeded, the data
 stream can be encrypted to provide protection against active attacks.
 It is intended that the AUTHENTICATION option be general enough that
 it can be used to pass information for any authentication and
 encryption system.

5. Security Implications

 The ability to negotiate a common authentication mechanism between
 client and server is a feature of the authentication option that
 should be used with caution.  When the negotiation is performed, no
 authentication has yet occurred.  Therefore each system has no way of
 knowing whether or not it is talking to the system it intends.  An
 intruder could attempt to negotiate the use of an authentication
 system which is either weak, or already compromised by the intruder.
 If the authentication type requires that encryption be enabled as a
 separate optional negotiation (the ENCRYPT option), it will provide a
 window of vulnerability from when the authentication completes, up to
 and including the negotiation to turn on encryption by an active
 attacker.  An active attack is one where the underlying TCP stream
 can be modified or taken over by the active attacker.  If the server
 only offers authentication type pairs that include the
 ENCRYPT_USING_TELOPT set in the ENCRYPT_MASK field, this will avoid
 the window of vulnerability, since both parties will agree that
 telnet ENCRYPT option must be successfully negotiated immediately
 following the successful completion of telnet AUTH.
 Other authentication types link the enabling of encryption as a side
 effect of successful authentication.  This will also provide
 protection against the active attacker.  The ENCRYPT_AFTER_EXCHANGE
 bit allows these authentication types to negotiate encryption so that
 it can be made optional.
 Another opportunity for active attacks is presented when encryption
 may be turned on and off without re-authentication.  Once encryption
 is disabled, an attacker may hijack the telnet stream, and interfere
 with attempts to restart encryption.  Therefore, a client SHOULD NOT

Ts'o & Altman Standards Track [Page 7] RFC 2941 Telnet Authentication Option September 2000

 support the ability to turn off encryption.  Once encryption is
 disabled, if an attempt to re-enable encryption fails, the client
 MUST terminate the telnet connection.
 It is important that in both cases the authentication type pair be
 integrity protected at the end of the authentication exchange.  This
 must be specified for each authentication type to ensure that the
 result of the telnet authentication option negotiation is agreed to
 by both the client and the server.  Some authentication type
 suboptions may wish to include all of the telnet authentication
 negotiation exchanges in the integrity checksum, to fully protect the
 entire exchange.
 Each side MUST verify the consistency of the auth-type-pairs in each
 message received.  Any variation in the auth-type-pair MUST be
 treated as a fatal protocol error.

6. Implementation Rules

 WILL and DO are used only at the beginning of the connection to
 obtain and grant permission for future negotiations.
 The authentication is only negotiated in one direction; the server
 must send the "DO", and the client must send the "WILL".  This
 restriction is due to the nature of authentication; there are three
 possible cases; server authenticates client, client authenticates
 server, and server and client authenticate each other.  By only
 negotiating the option in one direction, and then determining which
 of the three cases is being used via the suboption, potential
 ambiguity is removed.  If the server receives a "DO", it must respond
 with a "WONT".  If the client receives a "WILL", it must respond with
 a "DONT".
 Once the two hosts have exchanged a DO and a WILL, the server is free
 to request authentication information.  In the request, a list of
 supported authentication types is sent.  Only the server may send
 requests ("IAC SB AUTHENTICATION SEND authentication-type-pair-list
 IAC SE").  Only the client may transmit authentication information
 via the "IAC SB AUTHENTICATION IS authentication-type ... IAC SE"
 command.  Only the server may send replies ("IAC SB AUTHENTICATION
 REPLY authentication-type ... IAC SE").  As many IS and REPLY
 suboptions may be exchanged as are needed for the particular
 authentication scheme chosen.
 If the client does not support any of the authentication types listed
 in the authentication-type-pair-list, a type of NULL should be used
 to indicate this in the IS reply.  Note that if the client responds
 with a type of NULL, the server may choose to close the connection.

Ts'o & Altman Standards Track [Page 8] RFC 2941 Telnet Authentication Option September 2000

 When the server has concluded that authentication cannot be
 negotiated with the client it should send IAC DONT AUTH to the
 client.
 The order of the authentication types MUST be ordered to indicate a
 preference for different authentication types, the first type being
 the most preferred, and the last type the least preferred.
 As long as the server is WILL AUTH it may request authentication
 information at any time.  This is done by sending a new list of
 supported authentication types.  Requesting authentication
 information may be done as a way of verifying the validity of the
 client's credentials after an extended period of time or to negotiate
 a new session key for use during encryption.

7. User Interface

 Normally protocol specifications do not address user interface
 specifications.  However, due to the fact that the user will probably
 want to be able to configure the authentication and encryption and
 know whether or not the negotiations succeeded, some guidance needs
 to be given to implementors to provide some minimum level of user
 control.
 The user MUST be able to specify whether or not authentication is to
 be used, and whether or not encryption is to used if the
 authentication succeeds.  There SHOULD be at least four settings,
 REQUIRE, PROMPT, WARN and DISABLE.  Setting the authentication switch
 to REQUIRE means that if the authentication fails, then an
 appropriate error message must be displayed and the TELNET connection
 must be terminated.  Setting the authentication switch to PROMPT
 means that if the authentication fails, then an appropriate error
 message must be displayed and the user must be prompted for
 confirmation before continuing the TELNET session.  Setting the
 authentication switch to WARN means that if the authentication fails,
 then an appropriate error message must be displayed before continuing
 the TELNET session.  Setting the authentication switch to DISABLE
 means that authentication will not be attempted.  The encryption
 switch SHOULD have the same settings as the authentication switch;
 however its settings are only used when authentication succeeds.  The
 default setting for both switches should be WARN.  Both of these
 switches may be implemented as a single switch, though having them
 separate gives more control to the user.

Ts'o & Altman Standards Track [Page 9] RFC 2941 Telnet Authentication Option September 2000

8. Example

 The following is an example of use of the option:
 Client                           Server
                                  IAC DO AUTHENTICATION
 IAC WILL AUTHENTICATION
 [ The server is now free to request authentication information.
   ]
                                  IAC SB AUTHENTICATION SEND
                                  KERBEROS_V4 CLIENT|MUTUAL
                                  KERBEROS_V4 CLIENT|ONE_WAY IAC
                                  SE
 [ The server has requested mutual Kerberos authentication, but is
   willing to do just one-way Kerberos authentication.  The client
   will now respond with the name of the user that it wants to log
   in as, and the Kerberos ticket.  ]
 IAC SB AUTHENTICATION NAME "joe"
 IAC SE
 IAC SB AUTHENTICATION IS
 KERBEROS_V4 CLIENT|MUTUAL AUTH 4
 7 1 67 82 65 89 46 67 7 9 77 0
 48 24 49 244 109 240 50 208 43
 35 25 116 104 44 167 21 201 224
 229 145 20 2 244 213 220 33 134
 148 4 251 249 233 229 152 77 2
 109 130 231 33 146 190 248 1 9
 31 95 94 15 120 224 0 225 76 205
 70 136 245 190 199 147 155 13
 IAC SE
 [ The server responds with an ACCEPT command to state that the
   authentication was successful.  ]
                                  IAC SB AUTHENTICATION REPLY
                                  KERBEROS_V4 CLIENT|MUTUAL ACCEPT
                                  IAC SE
 [ Next, the client sends across a CHALLENGE to verify that it is
   really talking to the right server.  ]
 IAC SB AUTHENTICATION IS
 KERBEROS_V4 CLIENT|MUTUAL
 CHALLENGE xx xx xx xx xx xx xx
 xx IAC SE
 [ Lastly, the server sends across a RESPONSE to prove that it
   really is the right server.
                                    IAC SB AUTHENTICATION REPLY
                                    KERBEROS_V4 CLIENT|MUTUAL
                                    RESPONSE yy yy yy yy yy yy yy yy
                                    IAC SE

Ts'o & Altman Standards Track [Page 10] RFC 2941 Telnet Authentication Option September 2000

 The following is an example of use of the option with encryption
 negotiated via telnet ENCRYPT:
 Client                           Server
                                  IAC DO AUTHENTICATION
 IAC WILL AUTHENTICATION
 [ The server is now free to request authentication information.
   ]
                                  IAC SB AUTHENTICATION SEND
                                  KERBEROS_V4
                                  CLIENT|MUTUAL|ENCRYPT_USING_TELOPT
                                  KERBEROS_V4 CLIENT|ONE_WAY IAC
                                  SE
 [ The server has requested mutual Kerberos authentication, but is
   willing to do just one-way Kerberos authentication.  In both
   cases it is willing to encrypt the data stream.  The client
   will now respond with the name of the user that it wants to log
   in as, and the Kerberos ticket.  ]
 IAC SB AUTHENTICATION NAME "joe"
 IAC SE
 IAC SB AUTHENTICATION IS
 KERBEROS_V4
 CLIENT|MUTUAL|ENCRYPT_USING_TELOPT
 AUTH 4 7 1 67 82 65 89 46 67 7 9
 77 0 48 24 49 244 109 240 50 208
 43 35 25 116 104 44 167 21 201
 224 229 145 20 2 244 213 220 33
 134 148 4 251 249 233 229 152 77
 2 109 130 231 33 146 190 248 1 9
 31 95 94 15 120 224 0 225 76 205
 70 136 245 190 199 147 155 13
 IAC SE
 [ The server responds with an ACCEPT command to state that the
   authentication was successful.  ]
                                  IAC SB AUTHENTICATION REPLY
                                  KERBEROS_V4
                                  CLIENT|MUTUAL|ENCRYPT_USING_TELOPT
                                  ACCEPT IAC SE
 [ Next, the client sends across a CHALLENGE to verify that it is
   really talking to the right server.  ]
 IAC SB AUTHENTICATION IS
 KERBEROS_V4
 CLIENT|MUTUAL|ENCRYPT_USING_TELOPT

Ts'o & Altman Standards Track [Page 11] RFC 2941 Telnet Authentication Option September 2000

 CHALLENGE xx xx xx xx xx xx xx
 xx IAC SE
 [ The server sends across a RESPONSE to prove that it really is
   the right server.  ]
                                  IAC SB AUTHENTICATION REPLY
                                  KERBEROS_V4
                                  CLIENT|MUTUAL|ENCRYPT_USING_TELOPT
                                  RESPONSE yy yy yy yy yy yy yy yy
                                  IAC SE
 [ At this point, the client and server begin to negotiate the
   telnet ENCRYPT option in each direction for a secure channel.
   If the option fails in either direction for any reason the
   connection must be immediately terminated.  ]
 The following is an example of use of the option with integrated
 encryption:
 Client                           Server
                                  IAC DO AUTHENTICATION
 IAC WILL AUTHENTICATION
 [ The server is now free to request authentication information.
   ]
                                  IAC SB AUTHENTICATION SEND
                                  KEA_SJ
                                  CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE
                                  IAC SE
 [ The server has requested mutual KEA authentication with
   SKIPJACK encryption.  The client will now respond with the name
   of the user that it wants to log in as and the KEA cert.  ]
 IAC SB AUTHENTICATION NAME "joe"
 IAC SE IAC SB AUTHENTICATION IS
 KEA_SJ
 CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE
 '1' CertA||Ra IAC SE
 [ The server responds with its KEA Cert.  ]
                                  IAC SB AUTHENTICATION REPLY
                                  KEA_SJ
                                  CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE
                                  '2'
                                  CertB||Rb||IVb||Encrypt(NonceB)
                                  IAC SE
 [ Next, the client sends across a CHALLENGE to verify that it is
   really talking to the right server.  ]
 IAC SB AUTHENTICATION IS KEA_SJ
 CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE
 '3' IVa||Encrypt( NonceB xor
 0x0C18 || NonceA ) IAC SE

Ts'o & Altman Standards Track [Page 12] RFC 2941 Telnet Authentication Option September 2000

 [ At this point, the client begins to encrypt the outgoing data
   stream, and the server, after receiving this command, begins to
   decrypt the incoming data stream.  Lastly, the server sends
   across a RESPONSE to prove that it really is the right server.
   ]
                                  IAC SB AUTHENTICATION REPLY
                                  KEA_SJ
                                  CLIENT|MUTUAL|ENCRYPT_AFTER_EXCHANGE
                                  '4' Encrypt( NonceA xor 0x0C18 )
                                  IAC SE
 [ At this point, the server begins to encrypt its outgoing data
   stream, and the client, after receiving this command, begins to
   decrypt its incoming data stream.  ]
 It is expected that any implementation that supports the Telnet
 AUTHENTICATION option will support all of this specification.

9. Security Considerations

 This memo describes a general framework for adding authentication and
 encryption to the telnet protocol.  The actual authentication
 mechanism is described in the authentication suboption
 specifications, and the security of the authentication option is
 dependent on the strengths and weaknesses of the authentication
 suboption.
 It should be noted that the negotiation of the authentication type
 pair is not protected, thus allowing an attacker to force the result
 of the authentication to the weakest mutually acceptable method.
 (For example, even if both sides of the negotiation can accept a
 "strong" mechanism and a "40-bit" mechanism, an attacker could force
 selection of the "40-bit" mechanism.)  An implementation should
 therefore only accept an authentication mechanism to be negotiated if
 it is willing to trust it as being secure.
 It should also be noted that the negotiation of the username in the
 IAC SB AUTHENTICATION NAME name IAC SE message is not protected.
 Implementations should verify the value by a secure method before
 using this untrusted value.

11. Acknowledgements

 Many people have worked on this document over the span of many years.
 Dave Borman was a document editor and author of much of the original
 text.  Other folks who have contributed ideas and suggestions to this
 text include: David Carrel, Jeff Schiller, and Richard Basch.

Ts'o & Altman Standards Track [Page 13] RFC 2941 Telnet Authentication Option September 2000

10. References

 [1] Postel, J. and J. Reynolds, "Telnet Protocol Specification", STD
     8, RFC 854, May 1983.
 [2] Borman D., "Telnet Authentication Option", RFC 1416, February
     1993.
 [3] Ts'o, T., "Telnet Data Encryption Option", RFC 2946, September
     2000.
 [4] Alvestrand, H. and T. Narten, "Guidelines for Writing an IANA
     Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

12. Authors' Addresses

 Theodore Ts'o, Editor
 VA Linux Systems
 43 Pleasant St.
 Medford, MA 02155
 Phone: (781) 391-3464
 EMail: tytso@mit.edu
 Jeffrey Altman
 Columbia University
 Watson Hall Room 716
 612 West 115th Street
 New York NY 10025
 Phone: +1 (212) 854-1344
 EMail: jaltman@columbia.edu
 Mailing List: telnet-wg@BSDI.COM

Ts'o & Altman Standards Track [Page 14] RFC 2941 Telnet Authentication Option September 2000

13. Full Copyright Statement

 Copyright (C) The Internet Society (2000).  All Rights Reserved.
 This document and translations of it may be copied and furnished to
 others, and derivative works that comment on or otherwise explain it
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Ts'o & Altman Standards Track [Page 15]

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