Verifiable and Redactable Blockchains With Fully Editing Operations.

Blockchain technology has been highly praised for its immutability, attracting considerable attention in the academic and industrial community. However, since permanent storage in blockchains would result in copyright disputes and harmful information spreads, it is desired to equip blockchains with mutability nowadays for legal and moral duty restrictions. A redactable blockchain is a variation, which enables the editing of block objects without affecting other blocks in the blockchain. Most existing redactable blockchains can only support editing operations such as modification and deletion, rather than insertion. However, insertion is necessary for some scenarios, especially when patching codes are needed for smart contracts and mistaken deletions occur. In addition, we argue that the verifiability of blockchains is also significantly important, especially for the redactable ones, in which one block may have multiple versions. Hence, an efficient mechanism is required to invalidate history versions and incent distributed adoptions of editing operations. In this paper, we propose a verifiable and redactable blockchain with fully editing operations for the first time. One distinguishable property is the simultaneous achievement of fully editability of block objects and verifiability of blockchain state, with acceptable extra cost. Specifically, we construct the redactable blockchain based on a double trapdoor chameleon hash family, enabling computationally efficient and key-exposure resistant block editing. Additionally, we combine trapdoorless universal accumulators and the largest sequence number principle to make the blockchain state verifiable. Furthermore, we present a comprehensive analysis and extensive experiments to demonstrate the security and feasibility of the proposed redactable blockchain.