# A Hybrid Encryption Scheme for Quantum Secure Video Conferencing Combined with Blockchain
## 2 Preliminaries
### Blockchain  
Blockchain consists of multiple nodes, each of which is independent and has the same status. Each node keeps certain information and relies on the consensus mechanism to ensure the consistency of stored data, which can be understood as a distributed ledger technology (DLT), and DLT is jointly maintained by these nodes. The characteristics of blockchain are that data are difficult to tamper with and forge and have traceability. The blockchain records the information of all transactions; the process is efficient and transparent, and the data are highly secure. According to the degree of openness of the nodes, it can be divided into three categories: public chain, alliance chain, and private chain. The public chain is completely developed externally, and users can directly participate anonymously and can access the network and blockchain without registration or authorization. The scope of application of the private chain is limited to private organizations, and the read and write privileges and participation in the blockchain are set according to the rules of private organizations. The alliance chain refers to a blockchain in which several institutions jointly participate in bookkeeping, that is alliance members reach a consensus through mutual trust of multiple centers. The data of the alliance chain only allows the member nodes in the system to read, write, and send transactions and record transaction data together. Compared with the public chain, the alliance chain has more advantages in high availability, high performance, programmability, and privacy protection. It is considered to be a \"partially decentralized\" or \"multi-center\" blockchain. The number of consortium chain nodes is limited, and most nodes only need to reach a consensus to trade, while the transaction speed is fast, so in real scenarios, the consortium chain is easier to use. In the alliance chain platform, Hyperledger is a classic case. Hyperledger is a collaborative open-source project of the Linux Foundation in 2015, aiming to promote cross-industry blockchain technology. It is a cooperative project of global cross-industry leaders and has become a global technology alliance in the field of blockchain. By creating enterprise-level, open-source distributed classification frameworks and code bases, it assists organizations to expand and build industry-specific applications, platforms, and hardware systems to support their respective transaction businesses. At present, blockchain has typical applications in all walks of life. Reference [32] designed a 2019-nCoV vaccine supply platform based on a blockchain platform. According to the tamper-proofness feature of the blockchain, it was used to verify identity, vaccine registration, storage, and side effect reporting. Reference [33] applied blockchain technology in the management of college students' transcripts. Reference [34] presented a land certificate management scheme based on blockchain. [PERSON] et al. [35] proposed a privacy protection scheme for electronic health records based on blockchain and homomorphic encryption, which solved the problem of electronic health record interaction. Using the combination of blockchain smart contracts and homomorphic encryption technology, the function of automatic claims' settlement was realized without revealing any sensitive user information. [PERSON] et al. [36] proposed an electronic evidence sharing scheme for the Internet of Vehicles based on signcryption and blockchain, using signcryption and proxy re-encryption technology to encrypt the electronic evidence of the Internet of Vehicles, storing evidence reports on the blockchain; the evidence ciphertext was stored in the cloud server. [PERSON] et al. [37] proposed a blockchain-based archive data protection and sharing method. This method stores archive data through a private Inter Planetary File System (IPFS) cluster and uses smart contract technology to realize the sharing and acquisition of archive data.