Cryptology ePrint Archive: Report 2004/362

A new security proof for Damgård's ElGamal

Kristian Gjøsteen

Abstract: We provide a new security proof for a variant of ElGamal proposed by Damgård, showing that it is secure against non-adaptive chosen ciphertext. Unlike previous security proofs for this cryptosystem, which rely on somewhat problematic assumptions, our computational problem is similar to accepted problems such the Gap and Decision Diffie-Hellman problems.

Category / Keywords: public-key cryptography / subgroup membership problem, hash proof system

Date: received 20 Dec 2004, last revised 17 Mar 2005

Contact author: kristian gjosteen at math ntnu no

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Version: 20050317:203701 (All versions of this report)

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