Quantum resources for everlasting communication security

Abstract Quantum cryptography provides communication with everlasting security—a property unattainable by classical or post-quantum cryptography. Traditionally, quantum cryptography proclaims everlasting security by relying on principles such as no-cloning theorem, Bell inequalities, or the uncertainty principle, along with the standard assumption that legitimate users have no control over the communication channel. In this study, we demonstrate that additional quantum effects and techniques can improve the performance of quantum cryptography while maintaining everlasting security. In particular, we study the recently introduced loss control-based QKD approach, which relies on the physical properties of optical fiber channels associated with Rayleigh scattering and on continuous monitoring of channel integrity. We show that achieving everlasting and future-proof security requires an additional assumption concerning the completeness of the mathematical description of the devices and, consequently, of the eavesdropper’s ensemble. Furthermore, we introduce a security statement framework that combines physical assumptions about a cryptographic implementation with formal mathematical security proofs. Applying this framework to loss control-based QKD, we derive the eavesdropper’s ensemble for an arbitrary number of local attack points and define channel-dependent QKD as a new class of QKD protocols. Finally, we propose a general criterion for identifying quantum cryptographic solutions based on whether the physical mechanism underlying security disappears in the classical limit.