本論文提出了一可於雜訊通道中運行的量子金鑰回收(Quantum Key Recycling)協定，此協定能根據量子通道的雜訊程度回收使用過的加密金鑰。我們發現現存能於雜訊通道中運行的量子金鑰回收協定具有一共通的安全漏洞，因此我們提出了不具此漏洞的量子金鑰回收協定，且我們提出的量子金鑰回收協定基於量子通道實際的雜訊程度提升金鑰回收率。我們亦證明了在本協定中回收的金鑰具有無條件安全性並具有通用可組合性(universal composability)。另一方面，我們亦分析了使用量子金鑰回收協定來進行金鑰分配的可行性。為了比較量子金鑰回收協定與量子金鑰分配(Quantum Key Distribution)協定分配金鑰的效率，我們定義了金鑰分享率(key sharing rate)來比較兩類協定。我們發現使用我們提出的量子金鑰回收協定在特定情況下具有更高的金鑰分享率。

This thesis proposes a new Quantum Key Recycling (QKR) protocol, which recycles used keys according to the error rate. The proposed QKR protocol can tolerate the noise in the quantum channel. The earlier studies [1-4] also proposed QKR protocols with noise tolerance. Unfortunately, there is a common security loophole in these protocols. The proposed QKR protocol is designed to avoid this security loophole, and the key recycling rate of the pre-shared keys is optimized depending on the noise level. The security proof shows the security of the recycled keys is universal composable. This thesis also answers the question that is there any benefit for the QKR protocols to distribute keys as compared to the Quantum Key Distribution (QKD) protocols? The key sharing rate, which is the other version of the key rate, is defined to compare the efficiency of the proposed QKR protocol with that of QKD protocols. The key sharing rate can be calculated for both the QKD protocols and the QKR protocols, and the key sharing rate of the proposed QKR is then calculated. According to the comparison of the key sharing rate, this thesis finds that if using the proposed QKR protocol to distribute keys, it is more efficient than BB84 in some situations.

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