Cryptoanalysis of Certificateless Partially Blind Signature and Proxy Blind Signature Scheme

Blind signature and proxy signature are two important crytographical primitives. Unforgeability is a primitive property of digital signature, it assures that any one cannot produce a forged signature on a message except the signer. However, blindness is an important property which distinguish with other signatures. Recently, Rong et.al gave a certificateless partially blind signature scheme and Wang et.al gave a proxy blind signature scheme. They claimed that their schemes satisfy blindness and unforgeability of blind signature. Unfortunately, in the paper, we analyze the two blind signature schemes and the result shows that the two blind signature schemes are not secure. They exists a common flaw: linkability. Namely, the signer is able to link a valid message-signature pair obtained by some user.