This article presents optimization results on the MOVA undeniable signature scheme presented last year by Monnerat and Vaudenay at PKC'04 as well as its generalization proposed at Asiacrypt'04 which is based on a secret group homomorphism. The original MOVA scheme uses characters on $\zz_n^*$ and some additional candidate homomorphisms were proposed with its generalization. We give an overview of the expected performance of the MOVA scheme depending on the group homomorphism. Our optimizations focus on the quartic residue symbol and a homomorphism based on the computation of a discrete logarithm in a hidden subgroup of $\zz_n^*$. We demonstrate that the latter provides a signature generation which is three times faster than RSA.
