New attack strategies for quantum cryptography protocols

In the anaysis of cryptographic security of quantum key distribution protocols, two types of the results can be distinguished: lower security bounds, i.e. security proofs, and upper bounds, which imply designing a specific algorithm for the eavesdropper to obtain the transmitted information. The main restriction for the eavesdropper in quantum cryptography is that they can perform only unitary operations, and their task is to obtain maximum information under this constraint. An approach has been developed, which in some cases combines the two basic attacks for quantum cryptography in communication lines with attenuation: beam splitting attack and unambiguous state discrimination attack. Using this approach, we obtain better upper bounds for both short and long communication lines. Based on this approach, new attacks have been proposed for strong reference B92, differential phase shift and coherent one-way quantum cryptography protocols.