Abstract: A secure threshold proxy signature scheme was proposed. Conspiracy attack, that is, any t(t is threshold value) or more malicious proxy signatures may work together to reconstruct the secret polynomial of the proxy group and derive the secret keys of other members in the proxy group, consequently they can impersonate some other proxy signers to generate a valid threshold proxy signature. A large number of the schemes which were proposed require trusted party. So the trusted party becomes the attacked part. The proposed scheme can withstand the conspiracy attack, arbi- trarily signers of t still can't know the secure keys of other members in the proxy group, so they can't impersonate some other proxy signers to generate a valid threshold proxy signature. Furthermore, with regard to t of malicious signers impersonate the original signer, the original signer uses the second empower to solve, which only needs one secret channel between the original signer and the generation signer. It cannot distinguish the proxy signers by proxy signatures. In the scheme each participant's public key and private key and the group public key arc negotiated among all participants with no trusted party required. We shall try to avoid attacking the trusted party and the cheating between proxy signers, the security of this scheme is more efficient than other schemes.

Key words: Cryptography,Digital signature,Threshold proxy signature,Without a trusted party,Conspiracy attack