Paper 2008/053

Breaking One-Round Key-Agreement Protocols in the Random Oracle Model

Miroslava Sotakova

Abstract

In this work we deal with one-round key-agreement protocols, called Merkle's Puzzles, in the random oracle model, where the players Alice and Bob are allowed to query a random permutation oracle $n$ times. We prove that Eve can always break the protocol by querying the oracle $O(n^2)$ times. The long-time unproven optimality of the quadratic bound in the fully general, multi-round scenario has been proven recently by Barak and Mahmoody-Ghidary. The results in this paper have been found independently of their work.