Online/Offline and Fine-Grained Controllable Editing with Accountability and Revocability in Blockchains

Editable or rewritable blockchains offer a vital solution where flexibility and adaptability are paramount. They cater to scenarios where errors, regulatory compliance, privacy concerns, governance, and developmental stages demand a certain level of malleability in recorded data. One of the techniques for achieving editable blockchains is the use of policy-based chameleon hash functions (PCH). This enables the rewriting operations to be controlled and ensures that only specific entities with attributes that meet the predefined policies can edit the contents on the blockchains. However, PCH-based editable blockchains do not prevent malicious entities to leak their rewriting trapdoors to other unauthorized parties. Therefore, tracking of malicious key abusers is desirable in such solution. Tian et al. at ACSAC 2020 proposed a blockchain that is editable and incorporates black-box accountability, allowing for the identification of individuals who maliciously modify content. However, the key delegation of their scheme has problems with the calculation \(s{{k}_{0,1}}={{h}^{{{b}_{1}}\cdot \left( {{r}_{1}}+{{z}_{1}} \right) }}\) and \(s{{k}_{0,2}}={{h}^{{{b}_{2}}\cdot \left( {{r}_{2}}+{{z}_{2}} \right) }}\) . In addition, the current approaches cannot meet the efficient fine-grained accountable and revocable editing. Motivated by the research of Tian et. al, a fine-grained controllable and editable blockchain based on online/offline policy-based chameleon hash with accountability and revocability (OPCHAR) is proposed. It achieves the black-box accountability mechanism with a correct key delegation algorithm and realizes that the authorized organization can identify malicious modifiers and append them to the revocation list. Furthermore, unlike the traditional revocable attribute encryption, to prevent accused users from leaking the previously obtained chameleon hash ephemeral trapdoor, the authorized organization can generate a new ephemeral trapdoor to re-adapt transactions modified by malicious users to achieve revocability, rather than by invoking a centralized semi-trusted third party (e.g., cloud). Additionally, we use online/offline techniques to perform hash and adaption algorithms. Finally, the implementation demonstrates that our scheme has a superior performance. In particular, the hash algorithm consistently maintains a running time of 0.02 s.