Security of Quantum Cryptosystems

Conventional secure communications rely on classical complexity-based ciphers and physical distribution of cryptographic keys. Classical cryptography is based on the assumption that certain problems cannot be solved efficiently. Due to technological advan ces, it is only believed to be a matter of time before classical cryptosystems, at least in their present form, break down. Quantum cryptography exploits principles of quantum mechanics to enable provable secure distribution of private information. Initia l studies and general theoretical proofs show that the basis of security roots in the laws of quantum physics, and is in principle perfect. However, it has been realized that the real level of security will be determined by imperfections and loopholes in real-world equipment. We aim to identify security loopholes and take into account imperfections in quantum cryptosystems in order to evaluate and specify measures to minimize degradation of security and eliminate loopholes. Five main tasks have been ident ified: 1. General quantum information theory. Study general quantum information theory, its application to quantum cryptography, and in particular the "regime of hope". 2. Theoretical security proof with imperfections. Quantify the security in terms o f different kind of possible imperfections in the systems. Several protocols, encodings, and equipment schemes will be investigated. 3. Faked states attack. Study faked states attack both theoretically and experimentally. A comparison of the vulnerabilit y to different attacks on the different equipment schemes will be made. 4. Eavesdropping using high-power laser pulses. Study the possibility of utilizing high-power external laser pulses to make irreversible changes in Alice's and Bob's setups that faci litate eavesdropping. 5. Measures to eliminate security loopholes. Make recommendations, specify measures to protect from the attacks, and eliminate lookholes.