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 Verma’s 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. Verma’s 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.