CR²-ABE: A Blockchain-Assisted Coercion-Resistant and Revocable Attribute-Based Encryption for IoMT

The Internet of Medical Things (IoMT) has rapidly developed due to its ability to enhance the efficiency of medical data collection and utilization. Encryption technology is vital for ensuring IoMT data security and privacy. However, existing solutions often fail when secret keys or random numbers are exposed under coercion, undermining their effectiveness and security. Additionally, medical data stored on cloud platforms is vulnerable to risks, such as tampering or loss. To address these challenges, we propose CR2-ABE, a novel encryption scheme specifically designed for the IoMT environment. CR2-ABE combines chameleon hash functions and deniable encryption techniques, enabling medical data owners and recipients to present deceptive messages under coercion, thereby enhancing the coercion resistance of sensitive medical data. Moreover, CR2-ABE employs ciphertext-policy attribute-based encryption (CP-ABE) to facilitate fine-grained access control for medical data, while also leveraging blockchain technology to ensure data integrity and tamper resistance within cloud services. In terms of user management, CR2-ABE implements a policy revocation mechanism that operates directly on ciphertexts using software Guard extensions (SGX). We rigorously prove the correctness and semantic security of CR2-ABE, demonstrating its resilience against coercion attacks. Comprehensive evaluation results show that CR2-ABE exhibits significant performance improvements in key generation, encryption, decryption, and policy revocation compared to other solutions. Therefore, CR2-ABE possesses strong security and scalability.