Attribute-Based Encryption With Payable Outsourced Decryption Using Blockchain and Responsive Zero Knowledge Proof

TL;DR

This paper introduces a blockchain-based payable outsourced decryption scheme for Attribute-Based Encryption that ensures verifiability, exemptibility, fairness, and decentralization, with practical implementation and efficiency demonstrated on Ethereum.

Contribution

It presents a novel blockchain and zero-knowledge proof-based scheme enabling payable outsourced decryption with verifiability and exemptibility without ciphertext overhead.

Findings

Efficient verification of outsourced decryption results using zero-knowledge proofs.

Reduced gas costs in Ethereum implementation compared to previous schemes.

Achieved fairness and decentralization in outsourced decryption process.

Abstract

Attribute-Based Encryption (ABE) is a promising solution for access control in cloud services. However, the heavy decryption overhead hinders its widespread adoption. A general approach to address this issue is to outsource decryption to decryption cloud service(DCS). Existing schemes have utilized various methods to enable users to verify outsourced results; however, they lack an effective mechanism to achieve exemptibility which enables the honest DCS to escape from wrong claims. And it is impractical to assume that the DCS will provide free services. In this paper, we propose a blockchain-based payable outsourced decryption ABE scheme that achieves both verifiability and exemptibility without adding redundant information to ABE ciphertext. We use zero-knowledge proof to verify outsourced results on blockchain and introduce an optional single-round challenge game under optimistic assumption to address the high cost of proof generation. Moreover, our system achieves fairness and decentralized outsourcing to protect the interests of all parties. Finally, we implement and evaluate our scheme on Ethereum to demonstrate its feasibility and efficiency, the gas usage in attribute numbers from 5 to 60 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'23).