Accountable Ciphertext-Policy Attribute-Based Encryption Scheme Supporting Public Verifiability and Nonrepudiation

Ciphertext-policy attribute-based encryption, denoted by CP-ABE, is a promising extension of identity-based encryption which enables fine-grained data access control by taking a set of attributes as users' public key. However, owing to the fact that an attribute set may be shared by multiple users, malicious users dare to share their decryption keys to others for profits. Furthermore, the central authority is able to issue arbitrary decryption keys for any unauthorized users. To prevent these two kinds of key abuses in CP-ABE system, we propose an accountable CP-ABE scheme which allows any third party to publicly verify the identity embedded in a leaked decryption key, allows an auditor to publicly check whether a malicious user or the authority should be responsible for an exposed decryption key, and the malicious user or the authority can't deny it. The proposed accountable CP-ABE scheme supports any LSSS realizable access structures. At last, the confidentiality and public verifiability of the proposed scheme can be proved to be tightly related to the atomic CP-ABE scheme and the signature scheme that it composed from.