Abstract: Many variants of the ElGamal signature scheme have been proposed. The most famous is the DSA standard. If computing discrete logarithms is hard, then some of these schemes have been proven secure in an idealized model, either the random oracle or the generic group. We propose a generic but simple presentation of signature schemes with security based on the discrete logarithm. We show how they can be proven secure in idealized model, under which conditions. We conclude that none of the previously proposed digital signature schemes has optimal properties and we propose a scheme named PECDSA.