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.