Dmitry Kronberg

Quantum cryptography provides everlasting secure communication - a property unattainable by classical or post-quantum cryptography. Traditionally, quantum cryptography proclaims everlasting security by relying on principles such as the 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 other, nontraditional quantum effects and techniques boost quantum cryptography performance while maintaining everlasting security of communication. In particular, legitimate users can exploit the physical properties of optical fiber channels - specifically, that all losses are caused by Rayleigh scattering and are therefore homogeneously distributed. This quantum property can be combined with quantum tomography of the fiber channel, which reveals the spatial loss distribution and potential eavesdropping attempts. Finally, we present a detailed framework for constructing a security statement applicable to arbitrary cryptographic solutions and distinguish it from formal security theorems proven within idealized mathematical models of cryptographic setups.

An important problem for QKD at long distances is the PLOB bound. It follows from the fact that an eavesdropper can perform any actions with the quantum states sent over the quantum channel, which is a standart assumption in QKD. Here, we propose an alternative model which explicitly uses the restrictions of quantum thermodynamics, which prevent the eavesdropper from exploiting all the photons lost in the channel. We consider this solution as chanel device dependent (CDD) QKD which is better at long distances than conventional QKD with trusted nodes.