Certificateless undeniable signatures from bilinear maps

Certificateless public-key cryptosystem avoids the inherent key escrow problem in identity-based public-key cryptosystem, and does not need expensive certificates in the public key infrastructure. This cryptographic primitive has received a significant attention since it was introduced, and lots of certificateless schemes have been proposed in the past years. In this paper, we propose an certificateless undeniable signature scheme based on bilinear maps. To formally analyze the security of the proposed scheme, we extend security notions of undeniable signatures in the traditional public key infrastructure to the certificateless setting. Under the formally defined security models, we prove that our proposed scheme satisfies all the security properties under certain standard assumptions in the random oracle model. Compared with existed certificateless undeniable signatures, the sign algorithm of our scheme is more efficient, the weakness is that the unforgeability of our scheme is proved in a weak model.