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In this paper, wc address the question of providing security proofs for signature schemes in the so-called random oracle model [l]. In particular, we establish the generality of this technique against adapt,ively chosen message attacks. Our main application achieves such a security proof for a slight variant of the El Garrial signature schemc [4]where comniitted values are hashed together with the message. This is a rather surprising result since the original El Gamal is, as RSA [ll], subject to cxistcnt,ial forgery.U. Maurer (Ed.): Advances in Cryptology -

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International audienceThe aim of electronic voting schemes is to provide a set of protocols that allow voters to cast ballots while a group of authorities collect the votes and output the final tally. In this paper we describe a practical multi-candidate election scheme that guarantees privacy of voters, public verifiablity and robustness against a coalition of malicious authorities. Furthermore, we address the problem of receipt-freeness and incoercibility of voters. Our new scheme is based on the Paillier cryptosystem and on some related zero-knowledge proof techniques. The voting schemes are very practical and can be efficiently implemented in a real system