Cryptanalysis and improvement of a certificateless partially blind signature
Lin Zhang Cheng, Qiaoyan Wen · IET Information Security · 2015
Partially blind signature is an important technique in secure electronic cash (e‐cash) system. The first concrete certificateless partially blind signature (CLPBS) scheme for e‐cash was constructed in 2011. Recently it was found that this construction had a security weakness and a rescued scheme was given. Unfortunately, the formal security proof was not given. In this study, the authors first give cryptanalysis of their rescued scheme. They demonstrate that a malicious user in their rescued scheme can forge a signature on any message by replacing the signer's public key. In an e‐cash system, blind signatures issued by the bank are viewed as e‐cash. Once they apply their scheme to an untraceable e‐cash system, a malicious user can forge valid electronic coins (i.e. valid signatures) without being detected by the bank. It will result in loss of the bank. Then, they propose a newly improved CLPBS scheme which achieves the strongest security level and has higher computational efficiency than the rescued scheme published earlier. Finally, they give an example of potential application to e‐cash systems using their scheme.