Study Of Some Problems Of Quantum Cryptography And Theoretical Security Of Cryptosystem

Internet makes resource-sharing and data communication possible, that has brought great convenience to scientific research, military and social life. But with more and more people join Internet, a lot of issues of information security appear. Cryptography is the core of the information security. Cryptographical technologies in national key infrastructure are impossible to introduce, we can only develop them independently. A lot of applied cryptosystems we use now are computational secure, but with the progress of computational power and cryptanalytic technique, the cryptosystems that are computational secure will become more and more insecure, so it will be more and more important to study theoretical security of cryptosystem. In order to gain the error detection ability of key, the thesis brings forward the concept of perfect security besides redundancy, and designs algorithms that meet perfect security besides redundancy. The thesis analyses the difficulties to realize perfect secrecy and the security of ideal secrecy , and proposes new concepts of security, such as key authentic degree, and designs a new cryptosystem based on the concepts.As quantum cryptography is thought to be unbreakable, the thesis suggests man-in-the-middle attack on BB84 protocol and the methods to defense against the attack. At the same time, the thesis brings forword a new quantum encryption protocol and analyses its security. The protocol that combines error correcting code, traditional cipher and quantum mechanics uses shared key and single quantum to transfer private message.