Research On Some Issues Of Quantum Cryptosystem

According to the Moore's law, the computer power will double for constant cost roughly once every two years. The difficulty for breaking a cryptosystem has been reducing continually, which brings great threat to the classical cryptosystem based on computational complexity. On the other hand, the growth of the computer's computing power requires higher integration and smaller typical component dimension, and finally this power would be disturbed by the quantum effects. People have to start a new generation of computing technology, i.e. quantum computing, which utilizes quantum properties such as qubit, phase and perfect correlation. Since the concept of quantum computing came into being twenty years ago, people have realized the threat of quantum parallelism to the classical cryptosystem gradually. To withstand this kind of attack, perhaps the communicators can only come to quantum cryptosystem for help.The contributions of this thesis are mainly on quantum key distribution, quantum identity verification, quantum secret sharing, and quantum encryption. They are distributed as follows:As to the quantum key distribution (QKD) and entanglement swapping (ES), we propose two QKD protocols based on ES between two Bell states. One is for the two-level systems and the other for the d-level ones. Furthermore, we investigate their security respectively in detail. Using the theory of quadratic residue, we prove that ES between two Bell states exhibits very different features for two-level systems and d-level ones. This result strengthens the claim that a protocol in high dimension systems is more secure than its analog in two-level systems, and is instructive for designing quantum cryptography protocols.With regard to the quantum identity verification (QIV), since most of...