An Expressive Fully Policy-Hidden Ciphertext Policy Attribute-Based Encryption Scheme With Credible Verification Based on Blockchain

As the public cloud becomes one of the leading ways in data-sharing nowadays, data confidentiality and user privacy are increasingly critical. Partially policy-hidden ciphertext policy attribute-based encryption (CP-ABE) can effectively protect data confidentiality while reducing privacy leakage by hiding part of the access structure. However, it cannot satisfy the need of data sharing in the public cloud with complex users and large amounts of data, both in terms of less expressive access structures and limited granularity of policy hiding. Moreover, the verification of access right to shared data and correctness of decryption are ignored or conducted by an untrusted third party, and the prime-order groups are seldom considered in the expressive policy-hidden schemes. This article proposes a fully policy-hidden CP-ABE scheme constructed on linear secret sharing scheme (LSSS) access structure and prime-order groups for public cloud data sharing. To help users decrypt, hidden vector encryption (HVE) with a "convert step" is applied, which is more compatible with CP-ABE. Meanwhile, decentralized credible verification of access right to shared data and correctness of decryption based on blockchain are also provided. We prove the security of our scheme rigorously and compare the scheme with others comprehensively. The results show that our scheme performs better.