# A Hybrid Encryption Scheme for Quantum Secure Video Conferencing Combined with Blockchain
###### Abstract
However, in the existing scheme, although the video security problem can be solved well, the key is pseudo-randomly generated according to the traditional key negotiation process, and the security mainly depends on some number theoretic problems with computational complexity, such as the discrete logarithm problem, integer factorization problem, and elliptic curve discrete logarithm problem. With the development and implementation of high-performance computers, especially quantum computing technology, the existing encryption system that guarantees security based on computational complexity will pose a serious threat [11]. In order to deal with the security threat brought by quantum computing, a quantum secure communication scheme based on the quantum key distribution (QKD) can be adopted [12]. Quantum communication uses a single photon as the information carrier, and the single photon is inseparable. An eavesdropper cannot obtain the key information by stealing half a photon and measuring its state. The eavesdropper can measure the state of a single photon after intercepting it, but the Heisenberg uncertainty principle in quantum mechanics detects the eavesdropper's measurement of the photon, thereby verifying the security of the key established by the two communicating parties. The eavesdropper can also steal the information by copying the quantum state of the single photon, but the no-cloning theorem guarantees that an unknown quantum state cannot be exactly replicated. The QKD method realizes the generation of a key with theoretical absolute randomness and does not require a third party to transmit the key. Therefore, QKD does not depend on the complexity of computing to ensure communication security, so that the security of quantum cryptosystems will not be threatened by the continuous improvement of computing power and the mathematical level, thus ensuring the security of the encrypted information of the quantum cryptography system. This paper proposes a hybrid encryption scheme for quantum secure video conferencing combined with blockchain, aiming at solving the security problem of data information in a classical video conference system. Firstly, the QKD network based on time phase coding technology running on commercial optical fiber is effectively combined with the classical video conference system network. The QKD network generates theoretically absolutely secure quantum keys and uses quantum keys to encrypt audio and video data information. Then, due to the low key rate of the QKD network, it cannot satisfy the one-time pad encryption of all audio and video data. A hybrid encryption scheme is proposed, that is the main site selects classical key encryption and quantum key encryption according to the security level of video conference content. Secondly, the QKD network runs in the actual commercial optical fiber, and the key distribution is easily affected by external factors. Therefore, a real-time monitoring function is designed to display the network operation status on the interface of the video conference system to ensure the stable operation of the system. Finally, with the advantages of blockchain technology, such as tamper-proofness, decentralization, and traceability, the meeting minutes are encrypted and uploaded to the blockchain (alliance chain). A cache-efficient query method based on B+ tree is designed to facilitate viewing of the meeting minutes. The blockchain information is uploaded to the cache layer, and the keyword index in the block is used as the index address. The leaf nodes in the B+ tree store the index address of meeting minutes and the ciphertext. To solve the conflict of index addresses, the leaf nodes store the ciphertext in an adaptive space. The layers above the leaf nodes are used as indexes. Compared with the classical video conferencing system, the main contributions of this paper include the following four aspects:  
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