EAVESDROPPING ON QUANTUM-CRYPTOGRAPHICAL SYSTEMS

Quantum cryptography cannot prevent eavesdropping, but any eavesdroppi ng attempt can be detected by the legitimate users of the communicatio n channel. This is because eavesdropping affects the quantum state of the information carriers and results in an abnormal error rate. In thi s paper, we analyze various eavesdropping techniques, which may be eit her translucent or opaque to the transmitted photons, and we estimate the error rate above which the key distribution is deemed unsafe and s hould be abandoned.