Comment on Security and Improvement of Partial Blind Signature Scheme and Revocable Certificateless Signature Scheme

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Partial blind signature scheme (BLD-SS) can protect the specific content of the signed message by adding factor to blind the signed message and can also prevent the misuse of the signature by adding common information negotiated in advance. Revocable certificateless signature scheme (RCSS) can prevent the user’s privacy from leaking by adding time key in the signature process and signature verification process. BLD-SS and RCSS both have wide applications in electronic-voting, electronic-cash system and other fields. In this paper, it presents a security analysis on a partial blind signature scheme and a revocable signature scheme proposed recently. It points out that the BLD-SS does not satisfy the unforgeability. A malicious user can forge a partial blind signature on any message and any common information without known from PKG (Private Key Generation). It also shows that the RCSS does not satisfy the unforgeability. A malicious enemy can forge a signature on any message and on any user. The PKG also cannot update the time key immediately when a user’s key is leaked or his identity is expired. In order to overcome these problems, it proposes some simple improvement methods which are almost the same efficiency with the original signature scheme.