In recent years, with the rapid growth of the Internet of Things (IoT) devices, IoT has received extensive attention and research from both academic and industrial fields. The Internet of Everything makes data closer to us, can better serve us, and greatly facilitate our lives. Currently, most IoT solutions rely on the centralized server-client paradigm, which incurs heavy storage and computation burden on servers, and even leads to the single point failure threat.

Blockchain is a decentralized and untrustworthy distributed database technology. Its decentralization, tamper-resistance, transparentness, and security features have made blockchain technology widely used, and provide a new idea for solving data security and privacy issues in the IoT environment. Although the application of blockchain technology to data security and privacy issues in the context of IoT has many advantages, the combination of the two also presents some new challenges, including a series of problems such as poor scalability, data retrieval efficiency, data mining, and the limitations brought by the blockchain itself. Thus, the security and privacy concerns in blockchain-based IoT applications make data sharing and mining over encrypted data challenging issues. Therefore, it is urgent and necessary to design and develop solutions for privacy-preserving data sharing and data mining in the context of IoT in combination with blockchain technology.

The aim of this Special Issue is to collect original research and review articles with a focus on the latest developments in the use of blockchain technology to achieve secure data retrieval, privacy protection, and machine learning-based data mining in IoT applications.

Potential topics include but are not limited to the following:

• Blockchain-based access control for shared data in IoT
• Public data auditing based on blockchain in IoT
• Encrypted textual data search based on the blockchain in IoT
• Verifiability of search results based on the blockchain in IoT
• Data deduplication over encrypted cloud data using blockchain
• Encrypted image search in the blockchain-based IoT applications
• Attacks on searchable encryption schemes based on the blockchain in IoT
• Different types of encrypted data search based on the blockchain in IoT
• Threat model and risk assessment in blockchain-based IoT
• Secure data computation based on the blockchain in the IoT
• Machine learning algorithms in blockchain for IoT
• Novel security architectures in blockchain-based IoT data mining
• Privacy preservation in blockchain-based data mining
• Defense countermeasures of blockchain-based data mining
• Federated learning in blockchain-based computing