Subject: [IPsec] Dictionary-based key exchange (for mobile users)

From: "Pars Mutaf" <[email-masked]>
Date: Fri, 16 Nov 2007 19:50:45 +0100

Hello,
I would very much appreciate some feedback on the following
draft (very short). Thanks in advance.

Regards,
pars

--------cut here ---------

Network Working Group                                           P. Mutaf
Internet-Draft                                     Institut National des
                                                      Telecommunications
Expires: May 19, 2008                                  November 16, 2007

                     Dictionary-based Key Exchange
                         draft-mutaf-dke-00.txt

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   A dictionary-based key exchange protocol is proposed.  Two mobile
   host users that physically meet each other can use this protocol to
   authenticate each other.  PKI nor certificates are not needed.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Protocol description  . . . . . . . . . . . . . . . . . . . . . 3
   3.  Security considerations . . . . . . . . . . . . . . . . . . . . 3
   4.  IANA considerations . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   6.  Informative References  . . . . . . . . . . . . . . . . . . . . 4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 4
   Intellectual Property and Copyright Statements  . . . . . . . . . . 5

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1.  Introduction

   A dictionary-based key exchange protocol is proposed.  Two mobile
   host users that physically meet each other can use this protocol to
   authenticate each other.  PKI nor certificates are not needed.

2.  Protocol description

   The proposed protocol is briefly described below:

          Initiator              MitM                 Responder

                     Request RSA public key PK
           ----------------------------------------------->
                                  PK
         | <--------------------------------------------
      T  |
         | <========== Read 40-bit fingerprint ============
   human verification
   of 40-bit fingerprint

           -----------------{secret key}PK --------------->

   where
           PK: a one time RSA public key
           ===: voice channel, i.e. responder user tells the fingerprint
                to initiator user through oral communication.
           MitM: Man in the Middle

                                 Figure 1

   The octets of the fingerprint will typically be mapped to a
   dictionary of easy to pronounce and type well-known words.  For
   example, with a dictionary containing 256 words, each octet can be
   represented with one word in the dictionary, and only 40/8=5 words
   need to be checked.

   In T time units, MitM has to find a PK' giving the same fingerprint
   as PK, and returned it to the initiator before PK. 2^40 is large
   enough to assume that the attacker cannot reasonably succeed.

3.  Security considerations

   TBD.

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4.  IANA considerations

   None.

5.  Conclusion

   This document described a dictionary-based key exchange protocol.
   The idea of human verification of a public key fingerprint is not
   new.  A 40-bit fingerprint is normally too short and considered
   insecure (See for example [SB].).  In the proposed protocol, however,
   the fingerprint is used to authenticate a one-time public key that is
   used to exchange a secret key and possibly other material.

6.  Informative References

   [SB]  McCune, J. and J. McCune, "Seeing is Believing", Proceedings of
         the IEEE Symposium on Security and Privacy, Oakland, CA. May
         2005.

Author's Address

   Pars Mutaf
   Institut National des Telecommunications

   Email: [email-masked]

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