Security Analysis of a Proxy Signature Scheme over Braid Groups

Delegation of powers is a common practice in the real world. To realized the delegation of powers electronically, Mambo,Usuda and Okamoto proposed the first proxy signature scheme in 1996. Since then a number of new schemes and their improvements have been proposed. In 2008, Verma proposed a proxy signature scheme over braid groups. This paper analyzes Vermas scheme and found that this scheme suffers with the serious security flaws. In this scheme,the proxy signer is able to misuse his delegated signing capabilities and the original signer can not restrict the proxy signer for misuse her delegation power. As a result, the proposed scheme does not satisfy some essential security requirements. Vermas proposed scheme is also not secure against the original signer and proxy singer changing attacks. Thus, the proposed scheme is not only insecure against the attacks by original signer and proxy signer but also has pitfalls against the forgery attacks mounted by any antagonist

A Strong Blind Signature Scheme over Braid Groups

The rapid development of quantum computing makes public key cryptosystems not based on commutative algebraic systems hot topic. Because of the non-commutativity property, the braid group with braid index more than two becomes a new candidate for constructing cryptographic protocols. A strong blind signature scheme is proposed based on the difficulty of the one-more matching conjugacy problem in the braid groups, in which the signer can not relate the signature of the blinded message to that of the original message. The usage of random factor ensures that the blind signatures of the same message are different and avoids the weakness of simultaneous conjugating. The scheme can resist the adaptively chosen-message attack under the random oracle model

Linkability of Blind Signature Schemes over Braid Groups

Blindness and unforgeability are two essential security requirements of a secure blind signature scheme. Blindness means that after interacting with various users, the signer can never be able to link a valid message pair. Blindness is meaningless if after interacting with various users, the signer is able to link a valid message signature pair. This security vulnerability is known as linkability attack. Recently, Verma proposed two blind signature schemes over braid groups. Verma claimed that the proposed schemes are secure against all possible security vulnerabilities and also satisfy all essential securities properties.This paper reviews Verma’s proposed blind signature schemes and found that these scheme do not withstand against the linkability vulnerability

Analysis and improvement of a certificateless proxy blind signature

通过对葛荣亮等人提出的无证书代理盲签名方案进行分析,从中发现该方案会引起公钥替换攻击和恶意但是被动的kgC攻击。为了解决此方案的安全性缺陷,提出了一种改进方案。分析表明,改进的新方案满足无证书代理盲签名方案的所有安全性要求,并且拥有与原方案相同的计算效率。Through the cryptanalysis of a certificateless proxy blind signature scheme proposed by Ge Rong-liang,it find that this scheme can cause the public replacement attack and malicious-but-passive KGC attack.To avoid these attacks,this paper proposed a new improved scheme.Analysis result shows that the new improved shceme satisfies the requirements of proxy blind signature scheme and has the same computational efficiency compared with the original scheme.国家自然科学基金资助项目(11261060); 福建省自然科学基金资助项目(2012J01022); 新疆研究生科研创新资助项目(XJGRI2013130