KCQ: A New Approach to Quantum Cryptography I. General Principles and Qubit Key Generation
Horace P. Yuen · arXiv (Cornell University) · 2003
A new principle of quantum cryptography to be called KCQ, keyed CDMA in quantum noise, is developed on the basis of quantum detection theory. By the use of a shared secret key that determines the quantum states generated for different data bit values, the users may employ the corresponding optimum quantum measurement to decode each data bit. This gives them a better error performance than an attacker who does not know the key, and an overall generation of a fresh key may be obtained from the resulting advantage. This principle is illustrated in the operation of a concrete qubit system which is secure against individual attack in a simple manner. Its security against joint attacks in the presence of noise is obtained with the introduction of two new techniques, data bit randomization via source coding and deliberate error randomization via keyless randomness introduced by the user. The criterion of bit error rate, which is more appropriate than mutual information, is used in a general security analysis of key generation schemes.The criterion of protocol efficiency and its sensitivity to system parameter fluctuation is proposed as another benchmark on the evaluation of key generation protocols. A brief sketch is given on the implementation of KCQ with coherent states of considerable energy and its use in direct encryption. Another technique, deliberate signal randomization, is introduced. Some qualitative comparison among the different key generation schemes are made from with a fundamental and a practical viewpoint. Detailed quantitative results on qubits and coherent-state KCQ schemes for key generation and direct encryption performance would be presented in future papers of this series. The apparent gaps in the unconditional security proofs of previous protocols are indicated in Appendix.