Cryptology ePrint Archive: Report 2006/057

Key Exchange Using Passwords and Long Keys

Vladimir Kolesnikov and Charles Rackoff

Abstract: We propose a new model for key exchange (KE) based on a combination of different types of keys. In our setting, servers exchange keys with clients, who memorize short passwords and carry (stealable) storage cards containing long (cryptographic) keys. Our setting is a generalization of that of Halevi and Krawczyk \cite{HaleviKr99} (HK), where clients have a password and the public key of the server.

We point out a subtle flaw in the protocols of HK and demonstrate a practical attack on them, resulting in a full password compromise. We give a definition of security of KE in our (and thus also in the HK) setting and discuss many related subtleties. We define and discuss protection against denial of access (DoA) attacks, which is not possible in any of the previous KE models that use passwords. Finally, we give a very simple and efficient protocol satisfying all our requirements.

Category / Keywords: foundations / password-based key exchange, hybrid model, long key

Publication Info: Theory of Cryptography Conference 2006

Date: received 14 Feb 2006, last revised 23 Feb 2006

Contact author: vlad at cs utoronto ca

Available format(s): Postscript (PS) | Compressed Postscript (PS.GZ) | PDF | BibTeX Citation

Note: This is an extended version of the TCC 2006 publication with the same title. This version adds proofs of security and discussions on password updates and storing passords on the server.

Version: 20060223:202318 (All versions of this report)

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