Paper 2008/301

Accountability of Perfect Concurrent Signature

Yunfeng Li, Dake He, and Xianhui Lu

Abstract

Concurrent signature provided a novel idea for fair exchange protocol without trusted third party. Perfect Concurrent Signature is proposed to strengthen theambiguity of the concurrent signature. Wang et al, pointed out there exist an attack against the fairness of Perfect Concurrent Signature and proposed the improved perfect concurrent signature. This paper find that in proposed (perfect) concurrent signature protocol, no matter two party or multi-party, the signer could bind multiple messages with one keystone set but let the other signers know only one of the messages. This is a new unfair case in the application of concurrent signature. Based on this observation, we propose that accountability should be one of the security properties of (perfect) concurrent signature and we give the definition of accountability of concurrent signature. To illustrate this idea, we give an attack scene against the accountability of improved perfect concurrent signature proposed by Wang et al, and propose an update version of perfect concurrent signature to avoid such attack.