Registered Attribute-Based Encryption with Reliable Outsourced Decryption Based on Blockchain

TL;DR

This paper introduces a blockchain-based registered attribute-based encryption scheme with reliable outsourced decryption, enhancing decentralization, verifiability, and fairness in secure data sharing.

Contribution

It presents the first auditable RABE scheme with blockchain-supported reliable outsourced decryption, incorporating verifiability, fraud-proof, and fairness mechanisms.

Findings

Achieves verifiability of ciphertext transformations.

Ensures DCS cannot be falsely accused through zero-knowledge fraud proof.

Demonstrates feasibility and efficiency on Ethereum platform.

Abstract

Decentralized data sovereignty and secure data exchange are regarded as foundational pillars of the new era. Attribute-based encryption (ABE) is a promising solution that enables fine-grained access control in data sharing. Recently, Hohenberger et al. (Eurocrypt 2023) introduced registered ABE (RABE) to eliminate trusted authority and gain decentralization. Users generate their own public and secret keys and then register their keys and attributes with a transparent key curator. However, RABE still suffers from heavy decryption overhead. A natural approach to address this issue is to outsource decryption to a decryption cloud server (DCS). In this work, we propose the first auditable RABE scheme with reliable outsourced decryption (ORABE) based on blockchain. First, we achieve verifiability of transform ciphertext via a verifiable tag mechanism. Then, the exemptibility, which ensures that the DCS escapes false accusations, is guaranteed by zero knowledge fraud proof under the optimistic assumption. Additionally, our system achieves fairness and auditability to protect the interests of all parties through blockchain. Finally, we give concrete security and theoretical analysis and evaluate our scheme on Ethereum to demonstrate feasibility and efficiency.