Key Generation: Foundations and a New Quantum Approach

The fundamental security and efficiency considerations for fresh key generation will be described. It is shown that the attacker´s optimal probability of finding the generated key is an indispensable measure of security and that this probability limits the possibility of privacy amplification and the amount of fresh key that can be generated. A new approach to quantum cryptography to be called keyed communication in quantum noise (KCQ) is developed on the basis of quantum detection and communication theory for classical information transmission. KCQ key generation schemes with coherent states of considerable energy will be described. The possibility of fresh key generation is demonstrated for binary and N-ary detection systems under heterodyne attacks. The security issues of these schemes will be discussed and compared with BB84. The emphasis throughout is on concrete finite bit-length protocols.