Redactable Blockchain Supporting Rewriting Authorization Without Trapdoor Exposure

Blockchain technology, known for its decentralization and immutability, has been widely applied across various domains. However, this immutability reveals limitations in adapting to rapidly changing legal environments and preventing malicious misuse. To introduce a degree of flexibility, various transaction-level redactable blockchain solutions have been proposed. Yet, current schemes grant modifiers redaction privileges by providing access to the trapdoor, potentially posing risks of malicious dissemination and abuse of the trapdoor. In this paper, we first propose an RSA-based threshold chameleon hash (TCH) construction, allowing the distribution of the trapdoor among a group of authorities. Building on TCH, we develop a threshold policy-based chameleon hash (TPCH). Compared to the Policy-Based Chameleon Hash (PCH) proposed by Derler at NDSS'19, our TPCH supports authorization without exposing the trapdoor. Furthermore, leveraging TPCH, we introduce a novel transaction-level redactable blockchain (TPRB). TPRB supports decentralized authorization without trapdoor exposure and fine-grained rewriting control. Finally, through implementation and evaluation, we demonstrate the practicality and efficiency of our TCH and TPCH schemes.