SEG – A Provably Secure Variant of El-Gamal

The Zheng-Seberry (ZS) [9] encryption scheme was published in 1993 and was one of the first practical schemes that was considered secure against an adaptively chosen ciphertext adversary. This paper shows that the semantic security of the one-way hash variant of the ZS scheme is actually insecure against an adaptively chosen ciphertext adversary. Attempts to modify the ZS scheme resulted in a variant of El-Gamal that is provably secure against an adaptively chosen ciphertext adversary using standard public-key cryptography assumptions i.e. not the random oracle model.