On the security of an ID-based anonymous proxy signature scheme and its improved scheme

Abstract

As an important delegation technique, proxy signature was introduced in 1996 by Mambo, Usuda, and Okamoto. And many variants of proxy signature schemes have been proposed. In some cases, to protect privacy of proxy signer, the identity of proxy signer is hidden. Recently, to satisfy the requirement of proxy signer’s privacy protection, Hu et al. gave an enhanced ID-based anonymous proxy signature scheme from pairings, in which it allows that proxy signature produces an anonymous signature on behalf of original signer, and the identity of proxy signer is hidden. Meanwhile, it also allows the original signer to trace the actual identity of proxy signer. Unfortunately, in this paper, by analysing the scheme, we show that the scheme is insecure. It is universally forgeable, namely, anyone can produce an anonymous proxy signature on an arbitrary message. And the original signer can not also trace the actual identity of proxy signer. Finally, we give the corresponding attacks on the scheme and the reasons to produce suck attacks. To overcome our attacks, we proposed an improved scheme based on bilinear map of composite order.