Improvement of Identity-Based Threshold Proxy Signature Scheme with Known Signers

0 IntroductionIdentity-based (ID-based) cryptography1]is rapidly emer-gingin recent years .The concept of the proxy signature scheme was first in-troduced by Mamboet al2]in 1996 .The concept of thresholdproxy signature was proposed3 ,4]. Apractical and secure (t,n) threshold proxy signature scheme should satisfy the secre-cy,the proxy protected,the unforgeability,the non-repudia-tion,the ti me constraint ,andthe known signers5].In 2006 , Baoet al6]proposed an ID-based thresholdproxy si…

Improvement of Identity-Based Threshold Proxy Signature Scheme with Known Signers

In 2006, Baoet al proposed an identity-based threshold proxy signature scheme with known signers. In this paper, we show that Baoet al 's scheme is vulnerable to the forgery attack. An adversary can forge a valid threshold proxy signature for any message with knowing a previously valid threshold proxy signature. In addition, their scheme also suffers from the weakness that the proxy signers might change the threshold value. That is, the proxy signers can arbitrarily modify the threshold strategy without being detected by the original signer or verifiers, which might violate the original signer's intent. Furthermore, we propose an improved scheme that remedies the weaknesses of Baoet al 's scheme. The improved scheme satisfies all secure requirements for threshold proxy signature. Foundation item: Supported by the National Natural Science Foundation of China (60473029) Biography: LI Fagen (1979-), male, Ph. D. candidate, research direction: cryptography and information security.