Study On The Security Of Quantum Cryptography

As an important branch of quantum information, quantum cryptography (QC, or Quantum Key Distribution, QKD) is the process of sharing a secret bit string, known as the key, between two cooperative players (traditionally called Alice and Bob). The major work about this paper is analyzing the security of the schemes for QC in theory. The security of the scheme for QC is a crucial problem. In the classical communication, the eavesdropper (traditionally called Eve) can get the information about the key shared by Alice and Bob, so does she in the QC. However, in QC, it is impossible for Eve to leave behind no clue to Alice and Bob to find her eavesdropping that she can in the classical communication. The clue is the disturbance in the final key. The analysis of the security will answer the question that how much disturbance will guarantee the key's absolute security. In this paper, the securities of six-state scheme and three-state scheme for QC are studied. The tolerate error rates (the disturbance above which, the key will be insecure.) of the schemes are offered in Chapter III and IV. By comparing the corresponding parameters, we come to the conclusion that one scheme for QC is more safer than the other scheme under one eavesdropping strategy is not say that it does so always.In Chapter V, by a classical probability module, a formula for the error rate in the process of quantum error correction is obtained. By this formula, the error rate of the key, which obtains some error bits, will be easily worked out during each step.