A partially blind signature is an extension of a blind signature that allows a signer to sign a partially blinded message that includes pre-agreed upon information, such as an expiration date, or collateral conditions on the resulting signatures. Partially blind signatures are more useful than blind signatures in many applications, such as electronic cash (e-cash) systems. The concept of partially blind signatures was introduced by Abe and Fujisaki [1].

The security of a partially blind signature scheme depends on three requirements: completeness, partial blindness, and nonforgeability. Huang and Chang [2] proposed a new efficient partially blind signature scheme based on the discrete logarithm and Chinese remainder theorems. This paper shows that this scheme is not secure. Specifically, this scheme does not meet the partial blindness property: a malicious user (requester) can prepare special public information, and then remove the original information from the signer’s signature to obtain a partially blind signature with this new special information. For example, if this signature scheme is used to design an e-cash system, and includes an expiration date and a face value as common information in each e-cash item issued by the bank, then any malicious user can first withdraw an e-cash item from the bank, use it, and then replace this common information with other information (a new expiration date and a new value, for example).

This paper makes a correction to the Huang-Chang partially blind signature scheme, avoiding a weakness in the blindness property of the algorithm. With this improvement, the Huang-Chang scheme becomes a good partially blind signature scheme for many applications.