In 1996, Mambo et al. introduced the concept of proxy signature. However, a proxy signature only provides the delegated authenticity and doesn't provide the confidentiality. Chan and Wei proposed a threshold proxy signcryption scheme (denoted as Chan-Wei scheme), which extended the concept of proxy signature. In this paper, the authors demonstrate Chan-Wei scheme does not satisfy strong unforgeablity, strong nonrepudiation and strong identifiability. Based on Chan-Wei scheme, a nonrepudiable threshold proxy signcryption scheme with known proxy agents is proposed. The proposed scheme overcomes the weaknesses of Chan-Wei scheme. Completeness proof and security analysis of the proposed scheme are presented. In addition, compared with Chan-Wei scheme, the proposed scheme exactly finds out which proxy agents present bogus secret shadow or tamper secret shadow.%1996年,Mambo等人提出了代理签名概念.但是,代理签名仅能提供授权的认证而不能提供保密性.Chan和Wei提出一个门限代理签密方案(记为Chan-Wei方案),扩展了代理签名的概念.指出他们的方案不满足强不可伪造性、强不可否认性和强识别性.基于Chan-Wei方案,提出一个能够克服Chan-Wei方案缺点的不可否认门限代理签密方案.给出方案的完备性证明和安全性分析.此外,与Chan-Wei方案相比,所提出的方案能够确切地发现哪些代理人提供假子密钥或篡改子密钥.
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