Abstract: At present, the security of the identity based proactive threshold proxy signature schemes was almost proven in the random oracle model, and the threshold value of these schemes was almost changeless. It is more practical to design threshold proxy signature scheme in the standard model, compared with the existing ones. Aiming at the two problems pointed out above, this paper presented a proactive threshold proxy signature scheme by using the hardness of the computational DifficHellman problem with changeable threshold value, based on the modification of Paterson' proposed identity based signature scheme. At last, the scheme's correctness was exactly proven in terms of bilinear pairing technique and its security analysis and prove were given in detail in the assumption of the computational Diffie-Hellman problem, therefore, this scheme was proven secure and reliable.

Key words: Proactive threshold proxy signature, Standard model, Identity based cryptography, Computational Diffie-Hellman problem