Issuer-Free Adaptive Oblivious Transfer with Access Policy

Abstract

Due to the frequent use of Internet in our daily life, privacy is a major issue in designing any cryptographic primitive. Adaptive oblivious transfer with access policy (\(\mathsf{AOT}\)-\(\mathsf{AP}\)) is a widely used primitive to create privacy preserving databases in which different messages have different access policies, allowing only those receivers who have the necessary permissions to access the databases. We provide the first fully-simulatable \(\mathsf{AOT}\)-\(\mathsf{AP}\) without the third party called issuer. To achieve our goal, we present a new ciphertext policy attribute based encryption (CP-ABE), which is a variant of Water’s CP-ABE. The Boneh-Boyen signature is employed to control the malicious behavior of the parties, and proposed CP-ABE is used to encrypt each message of the database under some access policy. The proposed protocol is secure under \(q\)-Strong Diffie-Hellman and \(q\)-Decision Bilinear Diffie-Hellman Exponent assumptions in static corruption model in the presence of malicious adversary. Moreover, our \(\mathsf{AOT}\)-\(\mathsf{AP}\) is as efficient as the existing similar schemes.