The immutability of blockchains is critical for cryptocurrencies, but an imperative need arises for the redaction of on-chain data due to privacy-protecting laws like GPDR. Recently, Ateniese et al. (EuroS&P 2017) proposed an elegant solution to this problem based on chameleon hash functions, followed by many subsequent works. While these works offered a solution to the permissioned blockchain, the approaches were not efficient enough for the permissionless setting, in terms of either security (which may cause inconsistent historical transactions) or performance (only up to a few hundred nodes). In this paper, we investigate this problem and present Wolverine, a redactable permissionless blockchain. First, we present a formal redactable blockchain model, carefully considering transaction consistency. Next, towards a practical scheme, we introduce the novel concept of non-interactive chameleon hash (NITCH). NITCHs dynamically distribute a trapdoor key among a group and each party in the group can compute its partial share without communicating with others. Anyone who possesses enough shares can then find a valid hash collision. To prevent the static group from being compromised after a sufficiently long time, we provide a generic transform from NITCHs to decentralized random beacons (DRBs) and design a committee evolution protocol based on DRBs that refresh the group after every fixed interval of time. Based on NITCH and the committee evolution protocol, we construct Wolverine which offers important features such as scalability, transaction consistency, and public accountability. Finally, we demonstrate the practicality of Wolverine by giving a proof-of-concept implementation based on Bitcoin in Golang.

中文翻译：

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Wolverine：可扩展且交易一致的可编辑无许可区块链


区块链的不变性对于加密货币至关重要，但由于 GDPR 等隐私保护法，迫切需要对链上数据进行编辑。最近，Ateniese 等人。 （EuroS&P 2017）基于变色龙哈希函数针对这个问题提出了一种优雅的解决方案，随后出现了许多后续工作。虽然这些工作为许可区块链提供了解决方案，但这些方法对于无许可设置来说不够有效，无论是安全性（这可能会导致历史交易不一致）还是性能（最多只能有数百个节点）。在本文中，我们研究了这个问题并提出了 Wolverine，一个可编辑的无需许可的区块链。首先，我们提出一个正式的可编辑区块链模型，仔细考虑交易一致性。接下来，针对一个实用的方案，我们引入了非交互式变色龙哈希（NITCH）的新概念。 NITCH 在组中动态分配陷门密钥，组中的每一方都可以计算其部分份额，而无需与其他方通信。任何拥有足够份额的人都可以找到有效的哈希冲突。为了防止静态组在足够长的时间后受到损害，我们提供了从 NITCH 到去中心化随机信标（DRB）的通用转换，并设计了基于 DRB 的委员会演化协议，该协议在每个固定时间间隔后刷新组。基于 NITCH 和委员会进化协议，我们构建了 Wolverine，它提供了可扩展性、交易一致性和公共责任等重要功能。最后，我们通过在 Golang 中给出基于比特币的概念验证实现来展示 Wolverine 的实用性。