Multiparty Quantum Signature Schemes
This work addresses the need for secure digital signatures in electronic communications by providing a scalable quantum solution, though it is incremental as it builds on existing protocols.
The paper tackles the lack of multiparty quantum signature schemes by extending security definitions to quantum cases and generalizing a three-party protocol to multiple participants, proving its security against forging, repudiation, and non-transferability, with implementation feasibility using quantum key distribution networks.
Digital signatures are widely used in electronic communications to secure important tasks such as financial transactions, software updates, and legal contracts. The signature schemes that are in use today are based on public-key cryptography and derive their security from computational assumptions. However, it is possible to construct unconditionally secure signature protocols. In particular, using quantum communication, it is possible to construct signature schemes with security based on fundamental principles of quantum mechanics. Several quantum signature protocols have been proposed, but none of them has been explicitly generalized to more than three participants, and their security goals have not been formally defined. Here, we first extend the security definitions of Swanson and Stinson (2011) so that they can apply also to the quantum case, and introduce a formal definition of transferability based on different verification levels. We then prove several properties that multiparty signature protocols with information-theoretic security -- quantum or classical -- must satisfy in order to achieve their security goals. We also express two existing quantum signature protocols with three parties in the security framework we have introduced. Finally, we generalize a quantum signature protocol given in Wallden-Dunjko-Kent-Andersson (2015) to the multiparty case, proving its security against forging, repudiation and non-transferability. Notably, this protocol can be implemented using any point-to-point quantum key distribution network and therefore is ready to be experimentally demonstrated.