面向可信联盟的区块链账本可验证修改方法研究

Research on Verifiable Blockchain Ledger Redaction Method for Trusted Consortium

区块链历经十年发展,成为信息技术领域最被寄予厚望的颠覆性技术之一.区块链上链数据具有不可篡改性,历史区块数据一旦确认就不能变更.这保证了区块链历史数据的完整性和可验证,但另一方面,当区块链中出现数据管理需求,即历史区块中过期或无效交易需要被压缩、违法违规信息需要被管控删除时,这种特性也将阻碍区块链对有问题的数据进行修改.类似数据管理需求在联盟链、私有链中尤其突出.传统区块链利用哈希算法的碰撞困难,实现区块和交易的完整性验证.而变色龙哈希存在一个陷门,掌握陷门可以轻松找到哈希碰撞.基于这个特性,本文将该类哈希算法的陷门交给多方管理,从而在不影响前后区块的完整性验证的情况下,实现多方共识修改交易数据的功能.本文进一步对变色龙哈希进行改进,设计了一种适用于联盟链的多中心化的账本修改方案.考虑到交易修改功能的去中心化,即变色龙哈希的陷门不应生成、存放于单个节点的问题,改进后的算法允许联盟链的所有权限节点协作生成系统的变色龙哈希公私钥.同时,为了权衡时间、空间代价与安全性,设计了多种有关私钥生成与同步的共识机制,并对它们的空间开销、通信时间、安全程度等性能进行了对比.本文考虑了一些特殊情况下区块链系统的可用性和问责性.最后,利用改进后的变色龙哈希算法构建了原型链,实现了历史交易的管控功能,描述了数据管理功能的设计细节.实验表明,本文提出的账本修改方案,其最佳区块压缩率可达30%、算法执行速率整体达到毫秒级,且具有可证明的安全性.

After a decade of development,blockchain becomes one of the most disruptive innovations in information technology.Data on the blockchain has the strength of immutability.Once a historical block of data is confirmed,it cannot be revised any more.Such design guarantees the integrity and verifiability of blockchain historical data.But when there is a need of data maintenance in blockchain ledger,such as compression of expired or invalid transactions in historical blocks,removal of illegal information,immutability prevents a blockchain from redacting the data questioned.Such data maintenance requirements are particularly prominent for consortium and private blockchains.Therefore,redactable blockchain is of great value in these cases where a blockchain ledger is allowed compressing ledger data whose value fades away to save storage space,and when new regulations roll out a blockchain can adjust historical data accordingly without forking,in order to satisfying government supervision.Traditional blockchain can guarantee the integrity verification of blocks and transactions relying on the collision difficulty of hash algorithms.While chameleon hash algorithm contains a trap door or a private key,which one may utilize to find collisions easily.When applying in blockchain,the trap door of the hash algorithm can be handed over to multiple parties for management,to support the procedure of redacting transaction data by consensus without affecting the integrity verification of the neighboring blocks.The existing ledger redaction methods simply add modification and deletion functions to the blockchain system,without good adaption in the consensus procedure.Implementation of some existing methods replies on specific block structures or blockchain architectures.These methods lack universality and compatibility across various blockchain platforms,and they are restrained from being promoted in all the mainstream blockchains.Other existing methods supporting redaction operation require the intervention of trusted third parties or a centralized single node,which undermines the decentralization of the blockchain and is likely to cause single point of failure or trust issues.In order to solve these problems,in this paper,we optimize the original chameleon hash as a multiply centralized ledger redaction method for consortium blockchain.Considering the decentralization of the transaction redaction capability,that is,the trap door of the chameleon hash should not be generated and stored at a single node,the traditional chameleon hash is improved allowing all authority nodes of the consortium blockchain cooperatively generate the chameleon hash’s public and private keys.In order to evaluate time,space cost and security robustness,several private key generating and synchronizing consensus mechanisms are designed and benchmarked in all aspects.The usability and accountability of the blockchain system are considered in special cases.Finally,the improved chameleon hash algorithm is used to construct a prototype chain.We implement the management function for historical transactions and describe the design details of the function.Experiments show that,applying the ledger redaction method proposed,the best block compressing rate can reach 30%,while the algorithm executing rate achieves millisecond level,and the improved algorithm has proved safety.