Efficient certificateless threshold signatures without random oracles

This paper defines the security notion for Certificateless Threshold Signatures (CLTHS). Different from the adversarial model defined by Wang, et al. (2007), our definition considers Type I and Type II adversary separately. At the same time, the authors develop the simulatability and relationship between certificateless threshold signature and the underlying certificateless signature. We also propose the first CLTHS scheme which is proved existentially unforgeable against adaptively chosen message attack without random oracles. Compared with the previous scheme by Wang, et al. (2007), our scheme does not use hash function and is more efficient.