Paper 2024/1915 Original: eprint.iacr.org/2024/1915 ↗

MULTISS: Long-Term Secure Distributed Storage over Remote QKD Networks

Abstract

We introduce MULTISS, a distributed storage protocol over multiple remote Quantum Key Distribution (QKD) networks that ensures long-term data confidentiality. MULTISS is designed to combine several QKD networks, as QKD links are inherently limited in range, and to connect these networks through classical cryptographic channels. It relies on a hierarchical secret sharing scheme that makes certain shares mandatory for the reconstruction of the original secret. Hence, MULTISS offers a secure distributed storage solution in a scenario that is compatible with the current deployment of quantum networks. We prove that MULTISS preserves the confidentiality of stored data even if an adversary (i) gains full access to all nodes of a subset of the QKD networks, or (ii) records all classical communications between distant QKD networks and compromises them at a later stage. We show that it provides strictly stronger security guarantees than existing QKD-storage protocols. Our protocol also includes a procedure to update the shares without reconstructing the original data. In addition, we provide a recovery mechanism that tolerates the complete compromise of some QKD networks. We further introduce a variant of the protocol, called the local-mode, that minimizes the communication overhead of the recovery procedure when deployed over specific network topologies.