Blockchain is a new model of application for distributed ledgers, peer-to-peer transmission, consensus mechanisms, encryption algorithms, and other computer technologies. A blockchain, a significant aspect of many cryptocurrencies, is essentially a decentralized database, where a set of sequenced blocks are associated with each other through cryptographic methods. Each block contains a batch of information of network transactions, which is devoted to verifying the validity of its information and generating the next block. The application of blockchain technology has been extended to digital finance, Internet of Things, intelligent manufacturing, supply chain management, and digital asset trading, among many other fields.

Due to the wide application of blockchain, the security and performance of blockchain systems have drawn much attention and are the focus of significant research. The security of blockchain systems faces many challenges, for example, there are many ¬¬leaks in its mechanism, such as algorithm leaks, protocol leaks, user leaks, implementation leaks, or system leaks. Another challenge is the various attacks on the blockchain system, such as 51% attacks, eclipse attacks, routing attacks, or DDoS attacks. The privacy risk for blockchain systems is increasingly prominent. All transaction information records in the blockchain must be open to all nodes, which should be recorded and stored synchronously on all user sides. Through attacks in the network layer, transaction layer, or application layer, the attacker can obtain the data to analyze and extract the users’ information. In addition, data security and supervision are also faced with challenges. The data storage structure of blockchains determines that the blockchain is difficult to tamper with. In addition, the anonymity of blockchain brings great challenges to data security and network supervision.

The aim of this Special Issue is to make a point of the current situation as well as to evaluate the state of the art in blockchain systems and solicit original research articles to provide a forum for researchers working on the security and performance of blockchain systems. Review articles discussing the state of the art are also welcome.

Potential topics include but are not limited to the following:

• Attacks in blockchain systems
• Optimization of consensus mechanisms
• New consensus algorithms
• Blockchain transaction execution process optimization
• Cryptographic algorithm security
• Blockchain system encryption privacy protocol design
• Blockchain data structure optimization
• Blockchain system query optimization
• Blockchain system data model design
• Smart contract security
• Optimization of smart contract virtual machines
• Application system security based on blockchain
• Blockchain regulation and governance technologies
• Cross-chain transaction security