Paper 2024/1915

MUTLISS: a protocol for long-term secure distributed storage over multiple remote QKD networks

Abstract

We introduce MULTISS, a new distributed storage protocol over multiple remote Quantum Key Distribution (QKD) networks that ensures long-term data confidentiality. Our protocol extends LINCOS, a secure storage protocol that uses Shamir secret sharing to distribute data in a single QKD network. Instead MULTISS uses a hierarchical secret scheme that makes certain shares mandatory for the reconstruction of the original secret. We prove that MULTISS ensures that the stored data remain secure even if an eavesdropper (1) gets full access to all storage servers of some of the QKD networks or (2) stores and breaks later all the classical communication between the QKD networks. We demonstrate that this is strictly more secure than LINCOS which is broken as soon as one QKD network is compromised. Our protocol, like LINCOS, has a procedure to update the shares stored in each QKD network without reconstructing the original data. In addition, we provide a procedure to recover from a full compromission of one of the QKD network. In particular, we introduce a version of the protocol that can only be implemented over a restricted network topologies, but minimizes the communication required in the recovery procedure. In practice, the MULTISS protocol is designed for the case of several QKD networks at the metropolitan scale connected to each other through channels secured by classical cryptography. Hence, MULTISS offers a secure distributed storage solution in a scenario that is compatible with the current deployment of quantum networks.