Editable Blockchain Based On Chameleon Hash Function And Its Application

In the traditional blockchain,the two representative features of decentralization and non tamperability build a trust mechanism for it,which makes the technology have broad prospects in the fields of digital currency,deposit certificate anti-counterfeiting and so on.Decentralization refers to the equal status of all nodes in the blockchain network to jointly store and record the data in the system and maintain the stability of the system.Non tamperability means that after the transaction and other data are verified and agreed and written into the blockchain,no one can modify the data,and the linked data will be permanently stored in the blockchain.However,in the practical application of blockchain technology,due to system failure or personal malice,sometimes wrong data and false messages will be put on the blockchain.We call this kind of data bad data.The permanent storage of bad data on the chain pollutes the blockchain and reduces its credibility,which has a negative impact on the security of blockchain information content and even the public opinion environment.Therefore,blockchain technology urgently needs safe and controllable technical means to modify the bad data on the chain.The development of editable blockchain technology endows the blockchain with the function of controllable editing.However,due to the problem of centralization of editing rights,there is a risk of abuse of editing rights,which is also contrary to the concept of decentralization of blockchain.At the same time,with the development of blockchain in enhancing the privacy of user transaction information,the ability of user transaction privacy protection has been greatly strengthened,but the transaction is also difficult to audit.Although there are some solutions that can realize the audit function of transactions,these solutions can only identify illegal transactions,and there is often nothing to do with those illegal transactions that have been put on the chain.This thesis intends to focus on the editable blockchain technology with decentralized editing rights and the blockchain technology with auditable transaction information and revocable illegal transactions,mainly including the following two points:(1)Aiming at the centralization of editing rights in editable blockchain,this thesis proposes a decentralized editable blockchain(DEB)scheme.In order to realize the legal editing of blockchain data and the decentralization of editing rights,the scheme has been improved in two aspects:technology and application scenarios.In terms of technology,the scheme uses chameleon hash function with temporary trap door,so that the editing operation of the block can be performed only with the authorization of the participant holding the temporary trap door.In terms of application scenarios,two roles of editing request review center and block registration center are introduced to realize the decentralization of editing rights.Among them,the editing request audit center manages the chameleon hash private key and is responsible for auditing the editing request;The block registration center manages the temporary trap door corresponding to each block and is responsible for the registration of new blocks.When the blockchain performs editing operations,the editing executor needs to use the chameleon hash private key and the temporary trap door of the block to be edited to edit the block at the same time,and other users can verify the legitimacy of the editing results.The scheme meets the editability,public key only non editable and private key only non editable,which ensures that any party in the system can not perform editing operation by itself,which makes the scheme have good decentralized nature.Simulation experiments show that the execution time of each stage of the scheme is milliseconds,so the scheme has high execution efficiency.(2)In order to give consideration to transaction data privacy and transaction auditability,and revoke illegal transactions that have been linked,this thesis proposes a blockchain(TARB)scheme that can realize transaction auditability and revocation of illegal transactions.In this scheme,the Paillier homomorphic encryption algorithm is used to encrypt the transaction data,so that other users can not confirm the exact information of the transaction except the transaction auditor.At the same time,the validity of the transaction can be verified to other users.In order to realize the cancellation of illegal transactions,the scheme first improves the Merkle tree in the block to adapt to the block editing technology based on chameleon hash function,then abstracts the concept of unspent transaction output(utxo)in the bitcoin system,and puts forward the concepts of available utxo pool,input utxo pool and output utxo pool respectively,ensure that other transactions will not be affected during the cancellation of transactions.The scheme meets the requirements of auditability,public verifiability of transaction,unforgeability of transaction certificate and revocability of illegal transaction.In the simulation experiment,the execution time of each algorithm is in the order of milliseconds,and the scheme has high execution efficiency.