Blockchain-enabled reliable outsourced decryption CP-ABE using responsive zkSNARK for mobile computing

Ciphertext-Policy Attribute-Based Encryption (CP-ABE) is a promising solution for access control in mobile computing. However, the heavy decryption overhead hinders its widespread adoption. A general approach to address this issue is to outsource decryption to a decryption cloud server (DCS). Existing schemes achieve verifiability but lack an effective exemption mechanism to protect honest DCS from false claims. In this paper, we propose a blockchain-enabled reliable outsourced decryption CP-ABE framework that achieves both verifiability and exemptibility without adding redundant information to the ciphertext. We use zkSNARK to verify outsourced results on blockchain efficiently and introduce a challenge-response mechanism to address the high cost of proof generation. Moreover, our framework ensures fair incentive and enables decentralized outsourcing through blockchain. Finally, we implement and evaluate our scheme on Ethereum to demonstrate its feasibility and efficiency. While maintaining almost the same decryption cost, our gas usage is 11$\times$ to 140$\times$ in the happy case and 4$\times$ to 55$\times$ in the challenge case lower than the scheme of Ge et al. (TDSC’24) in attribute numbers from 5 to 60. Building upon the proposed framework, we demonstrate its application in the data sharing of electric vehicles, enabling a more extensive use of mobile computing resources.