On Eavesdropping in Quantum Cryptography through Side Channels of Information Leakage

Abstract

In quantum cryptography, in addition to attacks on transmitted quantum states, states in side channels of information leakage can be detected. The security of keys in real quantum cryptography systems cannot be analyzed without the inclusion of information leakage through side channels. A quantum-mechanical method has been proposed in this work to take into account key information leakage through side channels. This method is based on the detection of side electromagnetic radiation, active probing of a phase modulator at the transmitter station, and re-emission of avalanche detectors at the receiver side. The method takes into account joint collective measurements of quantum states in all channels of information leakage and operates at any intensity and structure of states in side channels. The choice of special prolate spheroidal functions makes it possible to “match” the quantum and classical descriptions of signals in side channels. A relation has been found between information leakage and the fundamental Holevo quantity. A transparent and intuitively clear physical interpretation of the results has been given.