Quantum Digital Signature Based on Single‐Qubit Without a Trusted Third‐Party

ABSTRACT We propose a novel quantum digital signature protocol that eliminates the need for a trusted third‐party, a common limitation in existing quantum signature schemes. While the concept of third‐party‐free quantum signatures has been discussed in earlier works, such as Gottesman and Chuang (2001), no concrete protocol with provable information‐theoretic security has been presented to date. Recent studies have explored computationally secure quantum signature schemes without trusted parties, but their security relies on assumptions about quantum computational hardness. In contrast, our protocol achieves information‐theoretic unforgeability based solely on the non‐cloning property of quantum states. It uses classical private keys and quantum public keys, and requires only single‐qubit operations. The scheme also satisfies key security properties, including asymmetry, undeniability, and expandability, making it suitable for implementation in near‐term quantum technologies.