Abstract: Based on the verifiably encrypted signature scheme without random oracles recently proposed by Gorantla et al.，a new scheme of optimistic fair exchange of digital signatures is proposed in this paper.The two players firstly exchange their verifiably encrypted signature on agreed-upon messages then their ordinary signature after the verification of each other’s verifiably encrypted signature.If one of them executes the protocol dishonestly，the other can resort to a trusted third party so as to get the purpose of fair exchange of signatures.The proposed scheme has properties of short signature，low computation and verification cost.It can realize exchange of digital signatures fairly and efficiently.

Key words: fair exchange, digital signature, verifiably encrypted signature

摘要： 基于Gorantla等最近提出的标准模型下可证安全的可验证加密签名，提出了一个优化的公平数字签名交换方案。签名交换双方首先交换他们的可验证加密签名，验证通过以后再交换他们的真实签名，如果其中一方不能诚实地执行协议，则另一方可求助可信任第三方以达到公平交换的目的。提出的方案具有签名长度短、计算量小等优点，可以公平且有效地实现数字签名的交换。

关键词: 公平交换, 数字签名, 可验证加密签名