Blockchain-Based Ciphertext-Policy Attribute-Based Encryption for Controlled Multi-User Collaboration

As cloud computing technology continues to advance and mature, the public cloud has emerged as a predominant method for data sharing. Ciphertext-policy attribute-based encryption (CP-ABE) is recognized as a highly promising cryptographic approach that safeguards data confidentiality while improving sharing efficiency. However, as the demand for collaborative access increases, the shortcomings of existing schemes in controlled multi-user collaboration scenarios have become increasingly evident. In this paper, we propose a blockchain-based CP-ABE scheme for controlled multi-user collaboration. We convert the regular policy to collaborative policy by the collaborative attribute bounding to a ciphertext, and we present a collaborative access structure with attribute reuse to avoid an increase in computation and storage overhead. Furthermore, we design a collaborative channel driven by smart contracts to efficiently control the collaboration within the same group. Security analysis demonstrates that our scheme achieves IND-CPA security, ensures controlled collaboration, and resists user collusion. Additionally, we analyze the impact of blockchain security on the scheme. Performance comparisons indicate that our scheme is competitive, achieving a moderate performance in encryption, a 15% reduction in decryption overhead, and a 5% reduction in key generation overhead compared to state-of-the-art approaches, while completely eliminating the need for any collaborative communication overhead. These results align with the initial purpose of the scheme and demonstrate its feasibility in multi-user collaborative scenarios.