# Wide Area Key Distribution Network Based on a Quantum Key Distribution System
## 6 Discussion and Conclusions  
Considering the key rate and the requirements of multiple-endpoint long-distance communication, the public-XOR-key scheme is more efficient and practical than the BBN protocol, re-encryption protocol and STR. In this paper, we extend the chain structure of the public-XOR-key scheme with two endpoints to the complex network with multiple endpoints. In the complex network with multiple endpoints, the practical contributions are as follows: (1) The relay nodes do not need to store the QKD keys. (2) The relay nodes do not need to store the XOR results of the QKD keys secretly, which reduces the storage. (3) The relay nodes do not participate in the transmission of the key, which \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **[PERSON]’s Model** & **Model of QKD Network** \\ \hline Keys & \(K\) & \(S\) \\ Plaintext & \(M\) & \(QK\) \\ Ciphertext & \(C\) & \(C\) \\ Rate of language & \(H_{L}\) & \(H(p)\) \\ Redundancy of language & \(R_{L}\) & \(I_{0}\) \\ Unicity distance & \(1/R_{L}\) & \(1/I_{0}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The contrast between [PERSON]’s model and the model of the quantum key distribution (QKD) network. reduces the communication traffic to a certain extent. A particularly important contribution is the proof of the security of the scheme. On the one hand, compared with the security of re-encryption key distribution scheme whose XOR keys are not announced, the security of the key distribution scheme we proposed and the re-encryption scheme is equivalent. Our scheme can not only improve the practical performance and simplify the system's complexity, but also ensure that the security is not reduced. Even though the adversary obtains partial information about the QKD keys in our scheme, she cannot confirm the shared key. On the other hand, we discuss the information leakage of the practical key distribution networks from the perspective of the unicity distance. The unicity distance of the practical QKD network is infinity, which bears out that our scheme is secure and [PERSON] can never obtain the shared key. The major advantages of our scheme are as follows. * The superiority of the practical performance: (i) The relay nodes need not store the QKD keys. Even if [PERSON] attacks the relay nodes, she cannot access the QKD keys and plaintext. The scheme reduces the storage of QKD keys and increases the practical security of the system. (ii) The relay nodes need not store the XOR results of the QKD keys secretly, which reduces the storage. It is difficult for actual network to ensure the absolute security of the data storage. The secret storage is avoided in our scheme. (iii) There is no re-generation keys in our scheme. In our scheme, the keys shared by endpoints are exactly the QKD keys and it is no need to generated random numbers from point to point. (iv) The relay nodes do not participate in the transmission of the key, which reduces the communication traffic to a certain extent. * The superiority of security: (i) we analyze the information leakage of public-XOR-key scheme and re-encryption scheme in the threat model and prove the security of the schemes. Even though the adversary obtains partial information about the QKD keys, she cannot confirm the shared key. (ii) We discuss the information leakage of the practical key distribution networks from the perspective of the unicity distance. The unicity distance of the practical QKD network is infinity, which bears out that our scheme is secure and [PERSON] can never obtain the shared key. The security analysis of complex network structures are worthy for the further study. In addition, we analyze the reason why the unicity distance of the practical system is different from that in theory. In fact, this system is a typical example of that the same plaintext is encrypted with different keys. It can be analyzed as [PERSON]'s ciphertext-only attack model because the encryption and decryption algorithms are XOR, where the order of operations can be exchanged.