Quantum Cryptographic Key Distribution in Optical Communication Networks

Abstract

In this thesis, several novel secure optical communication network models are presented. The security of these network models is achieved using quantum cryptographic-key distribution. Both point-to-point and multiple access broadcast networks are considered. Furthermore, in developing these models, the simplicity, generality and flexibility are highly maintained. Thus, it is possible to use these models efficiently for software simulation purposes. Each secure optical communication network model is assumed to be composed of N communication nodes (stations) that are connected by three types of fiber optic channels. These are the quantum, authenticated public, and timing channels. Errors can occur in quantum transmission due to eavesdropping and system inefficiencies. Thus, an error elimination technique is implemented. In this technique, several rounds of random permutations and block parity comparisons are done between the transmitter and receiver. Then, another strategy of random subset parity comparisons is performed. Blocks or subsets of discordant parities are subjected to a bisective search to find error locations and eliminate them. After all quantum transmission errors are discovered and discarded, an important mathematical technique called privacy amplification is implemented. Using this technique, eavesdropper information about the final cryptographic key is reduced to an arbitrarily value smaller than one bit. This is essentially achieved by publicly choosing length-reducing transformations to apply to primary keys so that partial eavesdropper information about inputs conveys almost no knowledge of the outputs. In the designing of secure models for multiple access broadcast networks, both of broadcasting and multicasting quantum transmission modes are enabled. This is done via introducing electro-optic switches in the implementation of quantum channels. Hence, the efficiency of quantum cryptography protocols can significantly be increased, in many situations. All networks quantum cryptography protocols are simulated via the object oriented programming (OOP) approach using the Borland C ++ Compiler Version 4.5. Simulation results for both error elimination and privacy amplification stages are presented. It is important to mention that all the described protocols are secure even against an enemy possessing unlimited computing power.