Research On Escrow Protocol Based On Anonymous Coin

In e-commerce,the buyer and the seller do not trust each other,and a basic security re-quirement called “fair trading” is: if the buyer pays,then he/she must get the goods; if the seller ships the goods,such as a table,he/she must get the money.In real life,fair trading is guaran-teed by a centralized third-party platform such as Taobao,but there are a single point of failure and security risks which the administrators of third-party platform steal the money.In order to remove centralized third-party platform,the state of art works propose various escrow protocols based on blockchain: the buyer escrow cryptocurrencies on the blockchain,and the mediator intervenes when a dispute arises,so honest buyer gets his/her principal back,and honest seller gets paid.However,there are following defects in existing escrow protocols:(1)Availability defi-ciency,i.e.relying on the gratuitous dedication of the mediator.This will result in no mediator being willing to participate in the protocol.(2)Security deficiency,i.e.being vulnerable to de-nial of service attacks.The mediator can get additional fees by refusing to mediate the dispute.This will lead to higher transaction costs.(3)Privacy protection deficiency,i.e.the transaction amount is leaked.This leads to the possibility of an attack by the mediator increases as the transaction amount increases.To overcome these defects,this paper proposes a new escrow protocol for ethereum based on anonymous coin scheme.The solution of this paper is as follows:Firstly,the mediator incentive mechanism is introduced.Once there is a dispute between the buyer and the seller,the mediator can get a reward if he/she intervenes,and the reward is jointly paid by both parties to the transaction.In this way we overcome vailability deficiency.Secondly,the mediator punishment mechanism is introduced.The mediator needs to de-posit cryptocurrencies into the smart contract,and if the mediator refuses to mediate the dispute in subsequent actions,the deposit will be lost.This approach can force rational mediator to mediate the dispute,thus we overcome security deficiency.Lastly,a new anonymous coin scheme is proposed in this paper for solving amount dis-closure,which escrow anonymous coin to hide transaction amount instead of ordinary cryp-tocurrencies,thus overcoming privacy protection deficiency.Our anonymous coin scheme is an improvement on the Kosba’s scheme,because we find that the Kosba’s scheme has the fol-lowing deficiencies in the buying and selling transaction scenario:(1)Even if it is the same pair of transaction parties,each transaction still needs to use a different public key which causes trust cannot be accumulated.(2)Two trading partners could not exchange anonymous coin back to Ether.First of all,in order to allow both parties to use a fixed public key,we have improved the minting logic,using zero-knowledge proofs to hide the relationship between the public key and anonymous coins,and by simultaneously minting multiple anonymous coins and zero-knowledge proofs technology to hide the amount of the minted coins,thus we solve the problem of using a fixed public key to bring the transaction amount to be guessed in some cases,thereby allowing the use of fixed public keys.Finally,we added the function of exchang-ing back Ether,considering the use of anonymous coins only temporarily.