改进的指定接收者签名方案

提出了两个新的指定接收者签名方案。内部攻击者要伪造签名，等价于伪造Schnorr签名，外部攻击者要验证签名，等价于解Diffie-Hellman问题。二者的计算复杂度均比Cao-Li-Li方案和Zhang-Cai-Xian方案更小，第一个方案保持了Cao-Li-Li方案中同时有保密性和认证性的优点，又克服了Cao-Li-Li方案中利用冗余信息来验证签名的不足。以他们为基础，还构造了两个高效的共享验证签名方案。

Improved signature schemes with specified receiver

Two new signature schemes with specified receiver were proposed in this paper. In both the schemes , forging signatures by the inside attacker is provably equivalent to forging Schnorr signature, and verifying the validity of the signature by the outside attacker is equivalent to breaking the Diffie-Hellman problem. The compu- tational complexity of the new schemes is smaller than those proposed by Cao-Li-Li and zhang-Cai-Xiao. Comparing to the sch- eme proposed by Cao-Li-Li, our first scheme inherent its advantage that enjoying both the authentication and secr- ecy, and overcomes its disadvantage that using checksum to verify validity of the signature. Based the proposed schemes, we construct two novel efficient threshold shared verification signature schemes.