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

ABSTRACT 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.