Security and Fairness in Multi-Party Quantum Secret Sharing Protocol

Quantum secret sharing (QSS) is a cryptographic protocol that leverages quantum mechanics to distribute a secret among multiple parties. With respect to the classical counterpart, in QSS the secret is encoded into quantum states and shared by a dealer such that only an authorized subsets of participants, i.e., the players, can reconstruct it. Several state-of-the-art studies aim to transpose classical Secret Sharing into the quantum realm, while maintaining their reliance on traditional network topologies (e.g., star, ring, fully-connected) and require that all the n players calculate the secret. These studies exploit the Greenberger-Horne-Zeilinger (GHZ) state, which is a type of maximally entangled quantum state involving three or more qubits. However, none of these works account for redundancy, enhanced security/privacy features or authentication mechanisms able to fingerprint players. To address these gaps, in this paper we introduce a new concept of QSS which leans on a generic distributed quantum-network, based on a threshold scheme, where all the players collaborate also to the routing of quantum information among them. The dealer, by exploiting a custom flexible weighting system, takes advantage of a newly defined quantum Dijkstra algorithm to select the most suitable subset of t players, out of the entire set on n players, to involve in the computation. To fingerprint and authenticate users, CRYSTAL-Kyber primitives are adopted, while also protecting each player's privacy by hiding their identities. We show the effectiveness and performance of the proposed protocol by testing it against the main classical and quantum attacks, thereby improving the state-of-the-art security measures.