ID-based Proxy blind signature scheme with unlinkability

A proxy blind signature allows the designated proxy signer using the proxy private key to generate a blind signature on behalf of the original signer. It can be adopted in such applications as e-commerce or e-lottery. In 2008, Chen et al. presented an ID-based proxy blind signature scheme which combined the advantages of proxy signature and of blind signature and claimed that their scheme was secure. However, Chen et al.'s scheme does not satisfy the unlinkability requirement. Moreover, by computing the original signer's private key, the proxy signer can forge the signing capabilities of the original signer and even award the signing capabilities to others. The paper presents a proxy key generation algorithm attack and a linkability attack to show Chen et al.'s vulnerability mentioned above. An improved proxy blind signature scheme is proposed, which can not only resist the above two attacks, but also has other required properties of a proxy blind signature scheme. In addition, the efficiency of improved scheme is higher than that of others.