Cryptanalysis of a sessional blind signature based on quantum cryptography

A digital signature is a mathematical scheme for demonstrating the authenticity of a digital message or document. A blind signature is a form of digital signature in which the content of a message is disguised (blinded) before it is signed to protect the privacy of the message from the signatory. For signing quantum messages, some quantum blind signature protocols have been proposed. Recently, Khodambashi et al. (Quantum Inf Process 13:121, 2014) proposed a sessional blind signature based on quantum cryptography. It was claimed that these protocol could guarantee unconditional security. However, after our analysis, we find that the signature protocol will cause the key information leakage in the view of information theory. Taking advantage of loophole, the message sender can succeed in forging the signature without the knowledge of the whole exact key between the verifier and him. To conquer this shortcoming, we construct an improved protocol based on it and the new protocol can resist the key information leakage attacks.