Security proofs for signature schemes

Abstract

In this paper, we address the question of providing security proofs for signature schemes in the so-called random oracle model [1]. In particular, we establish the generality of this technique against adaptively chosen message attacks. Our main application achieves such a security proof for a slight variant of the El Gamal signature scheme [4] where committed values are hashed together with the message. This is a rather surprising result since the original El Gamal is, as RSA [11], subject to existential forgery.