Abstract: A single decryption private key is subordinate to multiple users in traditional ciphertext attribute-based encryption schemes, which makes it possible for malicious users or semi-trusted attribute authorities to reveal the decryption private key to third unauthorized parties in order to gain benefits. Moreover, the decryption stage requires numerous pairing calculations, resulting to a huge burden to the end users with limited computing power. To address these issues, this paper proposes an accountable and verifiable outsourced decryption for ciphertext-policy attribute-based encryption. By deploying verifiable outsourcing decryption technology, the majority of the encryption overhead is shifted to the decryption agents , such that the computational load on end users can be reduced. By embedding user identity information and secret information that remains invisible to attribute authority into the user's private key, public accountability of both users and attribute authority is achieved. Security analysis demonstrates that our proposed scheme provides selective security, accountability, and verifiability of outsourcing decryption under the standard model. Performance analysis also indicates that the decryption cost of this scheme mainly lies on the decryption agent side, making it applicable for mobile device users with limited resources.

Key words: attribute-based encryption, accountable, outsourced decryption, verifiable