On the Linkability and Security Analysis of Two Schnorr-Type Blind Signature Schemes

As a special digital signature, the blindness of blind signatures can protect the signed contents, this property makes it to distinguish from the other signatures. And it makes it play an important role in plays a central role in applications such as electronic voting and electronic cash system. Recently, Huang et. al and Wang et. al propose a Schnorr-type blind signature schemes, respectively. And they claimed that these schemes were secure. In the paper, we discuss the security Huang et.al´s scheme and Wang et.al´s scheme. And the result shows that the two blind signature schemes are insecure. Huang et.al´s scheme is universally forgeable, namely, any one can produce a forged signature on arbitrary a message. And Wang et.al´s scheme is linkable. Namely, it doesn´t´t satisfy the blindness of blind signature. It means that the signer is able to link a valid message-signature pair obtained by some user. Finally, we give the corresponding attack on the two schemes and analyze the reasons to produce such attack, then give an improved blind signature scheme.