PIRB: Privacy-Preserving Identity-Based Redactable Blockchains with Accountability

Abstract

In this paper, we propose a privacy-preserving identity-based redactable blockchain (PIRB), the first identity-based redactable blockchain that supports flexible policies while maintaining accountability. Based on digital identities, PIRB enables a knowledge owner to set one policy for a batch of users while preserving policy privacy. Furthermore, similar to state-of-the-art solutions, PIRB draws inspiration from the proxy re-encryption technique to enforce user accountability. The design of PIRB entails addressing two primary technical challenges: firstly, achieving a flexible policy while upholding policy privacy; secondly, establishing accountability measures. To tackle the former challenge, we propose an enhanced identity-based encryption scheme that integrates polynomial function techniques. To address the latter challenge, a distinct identifier is generated for each user and subsequently concealed within the user’s secret key. Specifically, following existing schemes, we present the first scheme PIRB-I to cater to one-way access control scenarios, empowering owners to define access policies for designated editors. Additionally, recognizing the needs on the editor side for owner selection, we enhance PIRB-I through the introduction of matchmaking encryption, thereby supporting bilateral access control in a framework denoted as the second scheme PIRB-II. Notably, PIRB-I and PIRB-II involve a trade-off between computational and communication complexities. Specifically, when contrasted with PIRB-I, PIRB-II facilitates editors in owner selection, thereby mitigating editors’ communication overheads at the cost of increased computational overheads during policy generation and matching. Theoretical analysis demonstrates the inherent trade-off complexity and the resilience exhibited by PIRB-I and PIRB-II against chosen-plaintext attacks. Extensive experimentation on the FISCO blockchain shows that, compared with the state-of-the-art works, PIRB-I and PIRB-II achieve 200 times and 100 times computational efficiency improvements and 50 times and 60 times communication efficiency improvements on average, respectively.