Blockchain‐Enabled Privacy‐Preserving Access Control for EHRs Sharing With Optimized User and Attribute Revocation

Electronic health records (EHRs) have become a crucial application in cloud computing environments, necessitating advanced privacy‐preserving access control mechanisms. Ciphertext policy attribute‐based encryption (CP‐ABE) is a widely recognized solution for secure access control in outsourced data environments. However, existing CP‐ABE models face challenges related to revocation efficiency, access policy exposure, and computational burden on data owners (DOs). Even though several research works have extensively tackled this issue, most rely on re‐encryption or ciphertext updates and outsourcing strategies to proxies. However, optimization for querying all affected ciphertexts to reduce re‐encryption/ciphertext update costs is often overlooked, and the cost associated with frequent blockchain transactions for ciphertext updates and revocation records has not been addressed. Furthermore, most works do not support both attribute and user revocation efficiently. To address these issues, we propose an enhanced revocable CP‐ABE‐based access control scheme with optimized revocation performance (R‐CP‐ABE‐ORP). This scheme integrates ciphertext aggregation, lazy re‐encryption with revocation tokens, proxy‐assisted lightweight re‐encryption (PRE‐LR), blockchain, and bloom filters for fast queries to significantly improve revocation efficiency. The proposed scheme ensures forward and backward security while maintaining efficient ciphertext update and policy enforcement mechanisms. Experimental evaluations confirm that the proposed scheme outperforms related works in revocation efficiency, computational cost, and query performance.