A Provably Secure Ring Signature Scheme in Certificateless Cryptography

Ring signature is a kind of group-oriented signature. It allows amember of a group to sign messages on behalf of the group withoutrevealing his/her identity. Certificateless public key cryptography wasfirst introduced by Al-Riyami and Paterson in Asiacrypt 2003. Incertificateless cryptography, it does not require the use of certificatesto guarantee the authenticity of users’ public keys. Meanwhile, cer-tificateless cryptography does not have the key escrow problem, whichseems to be inherent in the Identity-based cryptography. In this paper,we propose a concrete certificateless ring signature scheme. The secu-rity models of certificateless ring signature are also formalized. Ournew scheme is provably secure in the random oracle model, with theassumption that the Computational Diffie-Hellman problem is hard.In addition, we also show that a generic construction of certificatelessring signature is insecure against the key replacement attack definedin our security models.