rfc2951.txt

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       Cn is the nth character in the TELNET stream.
       Hn = SHA-1( Hn-1||Cn ), where Hn is the hash value
            associated with the nth character in the stream.
       ICVn is set to the three most significant bytes of Hn.
       Transmit Encrypt( Cn||ICVn ).

   The ciphertext that is transmitted is the SKIPJACK CFB-32 encryption
   of ( Cn||ICVn ).  The receiving end of the TELNET link reverses the
   process, first decrypting the ciphertext, separating Cn and ICVn,
   recalculating Hn, recalculating ICVn, and then comparing the received
   ICVn with the recalculated ICVn.  Integrity is indicated if the
   comparison succeeds, and Cn can then be processed normally as part of
   the TELNET stream.  Failure of the comparison indicates some loss of
   integrity, whether due to active manipulation or loss of
   cryptographic synchronization.  In either case, the only recourse is
   to drop the TELNET connection and start over.

   For SKIPJACK with stream integrity, the two-octet authentication type
   pair is KEA_SJ_INTEG AUTH_CLIENT_TO_SERVER | AUTH_HOW_MUTUAL |
   ENCRYPT_AFTER_EXCHANGE | INI_CRED_FWD_OFF.  This indicates that the
   KEA SKIPJACK with integrity mechanism will be used for mutual
   authentication and TELNET stream encryption.  Figure 2 illustrates
   the authentication mechanism of KEA SKIPJACK with stream integrity.




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RFC 2951       TELNET Authentication Using KEA & SKIPJACK September 2000


---------------------------------------------------------------------
 Client (Party A)                   Server (Party B)

                                    <-- IAC DO AUTHENTICATION

 IAC WILL AUTHENTICATION        -->

                                    <-- IAC SB AUTHENTICATION SEND
                                        <list of authentication options>
                                        IAC SE

 IAC SB AUTHENTICATION
 NAME <user name>               -->

 IAC SB AUTHENTICATION IS
 KEA_SJ_INTEG
 AUTH_CLIENT_TO_SERVER |
     AUTH_HOW_MUTUAL |
     ENCRYPT_AFTER_EXCHANGE |
     INI_CRED_FWD_OFF
 KEA_CERTA_RA
 CertA||Ra IAC SE               -->

                                    <-- IAC SB AUTHENTICATION REPLY
                                        KEA_SJ_INTEG
                                        AUTH_CLIENT_TO_SERVER |
                                            AUTH_HOW_MUTUAL |
                                            ENCRYPT_AFTER_EXCHANGE |
                                            INI_CRED_FWD_OFF
                                        IVA_RESPONSEB_NONCEA
                                        KEA_CERTB_RB_IVB_NONCEB
                                        CertB||Rb||IVb||
                                            Encrypt( NonceB )
                                        IAC SE

 IAC SB AUTHENTICATION IS
 KEA_SJ_INTEG
 AUTH_CLIENT_TO_SERVER |
     AUTH_HOW_MUTUAL |
     ENCRYPT_AFTER_EXCHANGE |
     INI_CRED_FWD_OFF
 KEA_IVA_RESPONSEB_NONCEA
 IVa||Encrypt( (NonceB XOR 0x0D12)||NonceA )
 IAC SE                         -->







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RFC 2951       TELNET Authentication Using KEA & SKIPJACK September 2000


 Client (Party A)                   Server (Party B)

 <client begins encryption>
                                    <-- IAC SB AUTHENTICATION REPLY
                                        KEA_SJ_INTEG
                                        AUTH_CLIENT_TO_SERVER |
                                            AUTH_HOW_MUTUAL |
                                            ENCRYPT_AFTER_EXCHANGE |
                                            INI_CRED_FWD_OFF
                                        KEA_RESPONSEA
                                        Encrypt( NonceA XOR 0x0D12 )
                                        IAC SE

                                        <server begins encryption>
---------------------------------------------------------------------
                              Figure 2

4.0.  Security Considerations

   This entire memo is about security mechanisms.  For KEA to provide
   the authentication discussed, the implementation must protect the
   private key from disclosure.  Likewise, the SKIPJACK keys must be
   protected from disclosure.

   Implementations must randomly generate KEA private keys,
   initialization vectors (IVs), and nonces.  The use of inadequate
   pseudo-random number generators (PRNGs) to generate cryptographic
   keys can result in little or no security.  An attacker may find it
   much easier to reproduce the PRNG environment that produced the keys,
   searching the resulting small set of possibilities, rather than brute
   force searching the whole key space.  The generation of quality
   random numbers is difficult.  RFC 1750 [8] offers important guidance
   in this area, and Appendix 3 of FIPS Pub 186 [9] provides one quality
   PRNG technique.

   By linking the enabling of encryption as a side effect of successful
   authentication, protection is provided against an active attacker.
   If encryption were enabled as a separate negotiation, it would
   provide a window of vulnerability from when the authentication
   completes, up to and including the negotiation to turn on encryption.
   The only safe way to restart encryption, if it is turned off, is to
   repeat the entire authentication process.









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RFC 2951       TELNET Authentication Using KEA & SKIPJACK September 2000


5. IANA Considerations

   The authentication types KEA_SJ and KEA_SJ_INTEG and their associated
   suboption values are registered with IANA.  Any suboption values used
   to extend the protocol as described in this document must be
   registered with IANA before use.  IANA is instructed not to issue new
   suboption values without submission of documentation of their use.

6.0.  Acknowledgements

   We would like to thank William Nace for support during implementation
   of this specification.

7.0.  References

   [1] Postel, J. and J. Reynolds, "TELNET Protocol Specification", ASTD
       8, RFC 854, May 1983.

   [2] Ts'o, T. and J. Altman, "Telnet Authentication Option", RFC 2941,
       September 2000.

   [3] Secure Hash Standard. FIPS Pub 180-1. April 17, 1995.

   [4] "SKIPJACK and KEA Algorithm Specification", Version 2.0, May 29,
       1998. Available from http://csrc.nist.gov/encryption/skipjack-
       kea.htm

   [5] Postel, J. and J. Reynolds, "TELNET Option Specifications", STD
       8, RFC 855, May 1983.

   [6] Housley, R., Ford, W., Polk, W. and D. Solo, "Internet X.509
       Public Key Infrastructure: X.509 Certificate and CRL Profile",
       RFC 2459, January 1999.

   [7] Housley, R. and W. Polk, "Internet X.509 Public Key
       Infrastructure - Representation of Key Exchange Algorithm (KEA)
       Keys in Internet X.509 Public Key Infrastructure Certificates",
       RFC 2528, March 1999.

   [8] Eastlake, D., Crocker, S. and J. Schiller, "Randomness
       Recommendations for Security", RFC 1750, December 1994.

   [9) National Institute of Standards and Technology.  FIPS Pub 186:
       Digital Signature Standard.  19 May 1994.







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RFC 2951       TELNET Authentication Using KEA & SKIPJACK September 2000


8.0.  Authors' Addresses

   Russell Housley
   SPYRUS
   381 Elden Street, Suite 1120
   Herndon, VA 20170
   USA

   EMail: [e-mail]


   Todd Horting
   SPYRUS
   381 Elden Street, Suite 1120
   Herndon, VA 20170
   USA

   EMail: [e-mail]


   Peter Yee
   SPYRUS
   5303 Betsy Ross Drive
   Santa Clara, CA 95054
   USA

   EMail: [e-mail]
























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RFC 2951       TELNET Authentication Using KEA & SKIPJACK September 2000


9.  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.



















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