Linkability of Some Blind Signature Schemes

Unforgeability and blindness are two important properties of blind signature. The latter means that after interacting with various users, the signer is unable to link a valid message-signature pair. In ICCSA 2006, Zhang et al. showed that a signer in an identity-based blind signature scheme proposed by Huang et al. is able to link a valid messagesignature pair obtained by some user. They also presented an improved scheme to overcome this flaw. In ICICIC 2006, Zhang and Zou showed that the identity-based blind signature scheme proposed by Zhang and Kim also suffered from the similar linkability attack. In this paper, we first show that the so-called linkability can be shown for Zhang et al.’s improved scheme as well. We then point out that the linkability attack against the Huang et al. scheme and the Zhang-Kim scheme is invalid.