分析指出基于签密的并发签名方案是不抗接收者伪造的,即在没有签名者的关键数与密钥的情况下,接收者利用签名者的有效模糊签名便可恢复出签密消息,且可以以签名者身份伪造任意消息的模糊签名.因此,基于该签密并发签名方案的公平交易协议也是不安全的,进而提出了一个改进的基于签密的并发方案,弥补了原并发签名方案的安全缺陷,从而保证了公平交易协议的安全性. The analysis shows that the scheme based on signcryption is not against the forgery of the receiver. That is to say, without the key number and key of the signer, the receiver can recover the signcryption message by using the signifier’s effective fuzzy signature, and We can falsify the ambiguous signature of arbitrary message as the signer.As a result, the fair trade protocol based on the signcryption and concurrent signcryption scheme is also insecure, and then an improved signcryption-based concurrency scheme is proposed to make up the original concurrency signature scheme Security flaws, thus ensuring the fair trade agreement security.