NEW APPROACHES TO EAVESDROPPER INFORMATION BOUNDS IN QUANTUM CRYPTOGRAPHY PROBLEMS

Purpose of work is to review new aspects for the task of information extraction from ensembles of quantum states, dictated by practical tasks of quantum cryptography. Research methods: mathematical methods of quantum information theory, in particular, unambiguous discrimination of quantum states. Results of the study: the paper analyzes the literature on the topic of eavesdropper information bounds in quantum cryptography in the presence of channel attenuation, including in the absence of quantum memory. The features of application of the fundamental information bound to the eavesdropper information in the presence of attenuation, the threats of application of ad hoc countermeasures for unambiguous state discrimination attack are demonstrated. The problems of finding an effective postselective eavesdropping transformation, as well as measurement in the absence of eavesdropper’s quantum memory, are formulated. Scientific novelty: the scientific novelty consists in the integration of disparate approaches to the problem of eavesdropper information bounds in quantum cryptography and resisting attacks in case of lossy channel. The review describes the peculiarities of applying information bound to quantum cryptography problems and formalizes the challenges facing the eavesdropper under attenuation conditions.