## Cryptology ePrint Archive: Report 2004/182

Simpler Session-Key Generation from Short Random Passwords

Abstract: Goldreich and Lindell (CRYPTO 01) recently presented the first protocol for password-authenticated key exchange in the standard model (with no common reference string or set-up assumptions other than the shared password). However, their protocol uses several heavy tools and has a complicated analysis.

We present a simplification of the Goldreich--Lindell (GL) protocol and analysis for the special case when the dictionary is of the form $D=\{0,1\}^d$, i.e. the password is a short random string (like an ATM PIN number). Our protocol can be converted into one for arbitrary dictionaries using a common reference string of logarithmic length. The security bound achieved by our protocol is somewhat worse than the GL protocol. Roughly speaking, our protocol guarantees that the adversary can break'' the scheme with probability at most $O(\mathrm{poly}(n)/|D|)^{\Omega(1)}$, whereas the GL protocol guarantees a bound of $O(1/|D|)$.

We also present an alternative, more natural definition of security than the augmented definition'' of Goldreich and Lindell, and prove that the two definitions are equivalent.

Category / Keywords: cryptographic protocols / Password authentication, key exchange

Publication Info: An extended abstract of this paper has appeared in the First Theory of Cryptography Conference (TCC 04).

Contact author: mnguyen at eecs harvard edu

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Short URL: ia.cr/2004/182

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