Abstract:

A perfect concurrent signature protocol proposed by Huang et al in 2007 is analyzed. Two attacks are given out to show that there are two weaknesses in Huang's protocol: firstly, both participators A and B can change the signed messages after the concurrent signature protocol is completed; secondly, both A and B can forge a concurrent signature themselves. To prevent such forgery attacks, an improved protocol is proposed by adding authentication to the keystone information, and then the security of the improvement is analyzed.

Key words: Concurrent Signature, Perfect Concurrent Signature, Fair Contract Signing, Ring Signature