In an arbitrated quantum signature scheme, the signatory signs the message and the receiver verifies the signature's validity with the assistance of the arbitrator. We present an arbitrated quantum signature scheme using two-particle entangled Bell states similar to the previous scheme using three-particle entangled Greenberger-Horne-Zeilinger states [G. H. Zeng and C. H. Keitel, Phys. Rev. A 65, 042312 (2002)]. The proposed scheme can preserve the merits in the original scheme while providing a higher efficiency in transmission and reducing the complexity of implementation.

Arbitrated quantum signature scheme using Bell states

A digital signature is a mathematical scheme for demonstrating the authenticity of a digital message or document. For signing quantum messages, some arbitrated quantum signature (AQS) schemes have been proposed. It was claimed that these AQS schemes could guarantee unconditional security. However, we show that they can be repudiated by the receiver Bob. To conquer this shortcoming, we construct an AQS scheme using a public board. The AQS scheme not only avoids being disavowed by the receiver but also preserves all merits in the existing schemes. Furthermore, we discover that entanglement is not necessary while all these existing AQS schemes depend on entanglement. Therefore, we present another AQS scheme without utilizing entangled states in the signing phase and the verifying phase. This scheme has three advantages: it does not utilize entangled states and it preserves all merits in the existing schemes; the signature can avoid being disavowed by the receiver; and it provides a higher efficiency in transmission and reduces the complexity of implementation.

Security analysis and improvements of arbitrated quantum signature schemes

A weak blind signature scheme based on quantum cryptography

In many circumstances, a shared key is needed to realize secure communication. Based on quantum mechanics principles, quantum key agreement (QKA) is a good method to establish a shared key by every party's fair participation. In this paper, we propose a novel three-party QKA protocol, which is designed by using Greenberger---Horne---Zeilinger (GHZ) states. To realize the protocol, the distributor of the GHZ states needs only one quantum communication with the other two parties, respectively, and everyone performs single-particle measurements simply. Then, we extend the three-party QKA protocol to arbitrary multiparty situation. At last, we discuss the security and fairness of the multiparty protocol. It shows that the new scheme is secure and fair to every participant.

Novel multiparty quantum key agreement protocol with GHZ states

To reply to the Comment on our original paper entitled ``Arbitrated quantum-signature scheme'' [Phys. Rev. A 65, 042312 (2002)], we present more detailed presentations and proofs of the quantum-signature scheme in our paper. We feel our further investigation has shown that the original quantum-signature scheme is secure and operationally well defined. In addition, proofs illustrate that the quantum-signature scheme with unknown quantum states is also suitable in principle.

Hyunsang Kim

Papers

Arbitrated quantum signature scheme with message recovery