Cryptanalysis of the Quantum Blind Signature Scheme for Supply Chain Finance and Its Improvement

Recently, a quantum blind signature scheme based on the ‐state for quantum supply chain finance has been proposed, which utilizes blindness to protect the privacy of participating firms. However, our analysis found that this scheme cannot resist the intercept‐measurement‐resend attack and the entanglement‐measurement attack, and the blind operation is ineffective against the insider attacker. Importantly, the blind signer can achieve existential forgery through a valid signature. Then, an improved scheme was proposed that reduces quantum bit consumption, eliminates the need for quantum state swap tests, and extends the message space for signatures to the more universal classical bit space. We have constructed a security model that formally defines the security properties and adversary capabilities of the quantum blind signature. Through this model, the blindness and unforgeability of the improved scheme are reduced to the principles of quantum mechanics in four games. The vulnerabilities of the original scheme and the feasibility of the improved scheme in quantum computing have been verified through the Qiskit simulator.