# A Hybrid Encryption Scheme for Quantum Secure Video Conferencing Combined with Blockchain
## 5 Security Analysis  
(1) Data security:  
Key security ensures the security of communication data. Existing key distribution schemes generally use assumed secure channels to transmit key system parameters or the two communicating parties can only meet privately to exchange keys. In practical applications, due to the complexity of the network, there are security problems such as eavesdropping or cracking, so the quantum key distribution mechanism is introduced. The system makes full use of the security characteristics of the quantum key distribution and generates a theoretically absolutely secure symmetric key through the quantum channel. Encrypting data through \"one-time pad\" can effectively prevent monitoring and theft and strengthen the data security of the existing scheme.  
Assuming that the attacker knows the user's communication address information, during the operation of the video conference system, the Wireshark tool is used to successfully intercept the network data packet \(\{C_{0},C_{1},C_{2}\cdots C_{n}\}\) of important data, but the encrypted quantum key is private and updated in real-time, so \(\{C_{0},C_{1},C_{2}\cdots C_{n}\}\) is indistinguishable in the form of ciphertext. For example, the attacker constructs a pair of information \((m_{0},m_{1})\), \(m_{0},m_{1}\in M\), and \((m_{0},m_{1})\), which is encrypted by quantum key encryption method \(En_{opt}(qk,M)\), respectively, where \(qk\) is the real-time update by the QKD network. By repeated encryption, the ciphertext \((c_{i},c_{j})\) obtained by each plaintext \((m_{0},m_{1})\) is different, that is the attacker does not know which plaintext \((m_{0},m_{1})\) corresponds to \((c_{i},c_{j})\). Therefore, it can effectively resist eavesdropping attacks.  
Assume that the attacker can access the alliance chain and query the meeting minutes' information through the keyword index. The attacker constructs the keyword \(kw^{\prime}\) through the collision attack of the hash function, calculates \(hkw=Hash(kw^{\prime})\), and uses the query function of the alliance chain to obtain the ciphertext \(C\) of the meeting minutes associatedwith \(hkw^{\prime}\). Similarly, because the ciphertext \(C\) stored in the blockchain is indistinguishable, the attacker cannot decrypt \(C\) and obtain the plaintext \(M\) of the meeting minutes. At the same time, due to the one-way characteristic of the hash function, the original data cannot be deduced by collision attack, so the video conference communication data and meeting minutes' data are safe.  
(2) System stability:  
Because of the influence of the channel, environment, eavesdropping, and other factors, quantum keys cannot be generated. In order to ensure the stable operation of the system, two encryption schemes are provided, namely the \"one-time pad + AES\" quantum key encryption scheme and the \"AES\" classical key encryption scheme. The two schemes can be switched at any time when the system is running. When the security level of the conference content is high, the user switches the quantum key encryption scheme. When the quantum key is sufficient, the system uses the \"one-time pad\" encryption scheme; when the quantum key capacity is insufficient, the system will automatically switch to the \"AES\" encryption scheme, and there will not be a crash. When the security level of the conference content is low, the user can switch to the classical key encryption scheme without consuming quantum keys. At the same time, in order to monitor whether the QKD network is running normally, a heartbeat monitoring mechanism is set to determine \(T\geq T_{Heartbeat}\), so that the user can grasp the real-time dynamics of the QKD network and ensure the stable operation of the video conference system.