Cryptoanlaysis of a Self-Certified Partially Blind Signature and a Proxy Blind Signature

As a special digital signature, blind signature allows allows a user to get a signature without giving the signer any information about the actual message or the resulting signature. Unforgeability is an important property of blind signature, it assures that any one cannot produce a forged signature on a message in a blind signature except the signer. Recently, Lin et.al gave a provably secure self certified partially blind signature scheme in ICC2008 and Yang et.al gave a proxy blind signature scheme based on DLP in ICESS2008. They claimed that their schemes were secure in their security model, respectively. In the paper, we analyze the two blind signature schemes and the result shows that the two blind signature schemes are not secure. They are universally forgeable in that any one can forge a blind signature on arbitrary a message. Finally, we give the corresponding attack and the improved discussion, respectively.