Themis is a trusted blockchain infrastructure based on a group hosting protocol, which solves the problem of fair exchange using digital assets as a medium and helps build a new generation of trust network. Themis provides decentralized digital asset custody services to solve the problem of fair exchange using digital currency as a medium, which can be applied to digital asset e-commerce payment, digital asset over-the-counter transactions, digital asset custody account custody, etc. Themis provides third-party escrow services (similar to the role of Alipay in online shopping), issues tokens Global Escrow Token (GET) on the chain, introduces group escrow mechanisms and reputation mechanisms based on economic incentives to motivate blockchain nodes, and uses Escrow contracts and arbitration contracts realize peer-to-peer fair exchange between digital currencies, digital currencies and real assets.

Design goals

Themis is a decentralized fair exchange system, similar to Alipay in the digital currency world, which solves the problem of fair exchange using digital currency as the medium. Technically, Themis should be able to meet the following requirements:
Fairness: After the exchange is over, either both parties to the exchange can get the desired target (such as digital currency, digital assets, physical goods), or neither can get it (All-or-nothing);
Security: Digital currency cannot be taken away by anyone without authorization during the exchange process;
Passivity: If there is no dispute, no third party is required to participate;
Correctness: Ensure Transactions and dispute resolution are executed in accordance with pre-agreed rules;
Reliability: After a dispute occurs, avoid the problem of fund lock
caused by the custodian’s non-execution of the arbitration resolution, that is, avoid single point of failure and denial of service;
Privacy Sexuality: In the absence of disputes, the third party cannot know whether the transaction is completed, and non-transaction related parties cannot know whether there is a dispute.

Application scenario

Peer-to-point escrow payment
Themis can provide decentralized digital currency escrow payment for P2P online markets (such as OpenBazaar) to achieve direct transactions between buyers and sellers; Themis can connect e-commerce The platform digital currency payment system generates a corresponding escrow account on the original chain through Themis, and conducts decentralized custody of digital currency transaction behavior. During the transaction, the buyer entrusts the digital currency that needs to be paid into the escrow account. According to the delivery of the physical goods, after the delivery is officially confirmed, the buyer sends a confirmation instruction to the seller, and the seller can obtain the digital currency from the escrow account. This mechanism can effectively solve the problem that digital currency payment and physical commodity delivery cannot be completed at the same time.
In the practical application of e-commerce, Themis platform will provide buyers with advance payment protection. For example, within 7 days after confirmation of receipt, 5% of the seller's funds will be left in the platform account through the smart contract as a deposit; if there is a dispute within 7 days, Themis can use the money in the deposit pool to pay the buyer first, and then the platform will Negotiate refunds with the seller. This can further improve buyer satisfaction and at the same time increase credit for sellers.
Digital Currency Transaction Exchange
Themis is a set of fair trade system based on blockchain, which can not only meet the needs of fair exchange between digital currency and physical goods, but also meet the needs of different digital currencies. Transaction exchange requirements, providing fair exchange guarantees for various centralized and decentralized digital currency exchange transactions.
Themis supports over-the-counter transactions of digital currencies, and can provide decentralized security custody services for Bitcoin, Ethereum, and other blockchain-based cryptographic digital currencies. By generating corresponding custody accounts on the original chain, the The demand for transaction exchange between different digital currencies provides a fair exchange guarantee for digital currency cross-chain transactions.
Supervisory account security custody
Custody service is an important means to ensure the safety of users' funds in traditional finance. For example, after opening an account, a securities company needs to open a bank custody account, and a P2P online loan needs to open a custody account. For private equity funds, crowdfunding funds, and newly emerging ICO investment funds, etc., because there is no fund custody, or a third-party centralized custody mechanism is adopted, the investment objects, investment ratios and investment income of the custody funds are opaque, which is likely to cause information distortion and Moral Hazard.
As a highly scalable smart contract cluster, Themis can provide a distributed ledger interface and provide decentralized custody services for digital currency fund supervision accounts, which can effectively guarantee the security of investment funds, project traceability and investment profits allocation rationalization etc. With the vigorous development of the digital economy, many digital currency financial products and application scenarios will be derived in the future, such as digital currency lending, digital currency futures and options, digital currency ETF funds, cross-chain digital currency transactions, etc., can all be carried out safely through the Themis system Trusteeship to ensure the safety of funds.
Multi-subject transaction asset custody
In the supply chain finance, real estate, large-scale equipment and other transactions, due to the large number of transaction subjects, long transaction links and strong transaction dependence, it is easy to cause moral hazard and the issue of dishonesty of transaction subjects.
Themis can host funds that need to be escrowed in multi-agent transactions, such as deposits, first payments, commissions, balance payments, etc., in the form of digital currencies by establishing smart contracts based on multi-subject responsibilities and equity trigger condition instructions. . When the transaction progresses to the corresponding stage, the corresponding transaction subject triggers the smart contract by inputting the corresponding instruction to realize fair transaction and delivery of rights and interests. If one party to the transaction has a dispute over the transaction, it can use the Themis group hosting service agreement and fair arbitration mechanism to initiate an arbitration request. Each member of the group hosting party will arbitrate, vote, and form a ruling on the dispute, and the winner will be able to unlock it Escrow account.

Overall structure

DPoSR consensus mechanism. Themis will improve the existing Delegated Proof of Stake (DPoS) protocol, and propose a new consensus mechanism DPoSR (Deposit based Proof of Stake and Reputation), which is a bond-based proof of stake and reputation protocol, adding the reputation of nodes participating in dispute processing In the consensus mechanism, at the same time, nodes need to pay a deposit in order to compete for trustee qualifications. The probability of a node becoming a trusted node is closely related to its security deposit, equity and reputation it owns.
Margin mechanism. Nodes need to pay a certain price to compete for trustee qualifications, that is, to pay a deposit on Themis. If the node does evil, the security deposit will be confiscated by the system. The trustee will be paid for maintaining the system operation, that is, sharing the block transaction fee with other trustees. Remuneration forms positive feedback to it, thereby motivating trustees to work harder to maintain system security. Since blocks are signed by delegates in turn, if a delegate misses signing a block due to being offline, he will face the risk of being replaced by other candidate delegates. Therefore, in order to make a profit, the trustee must ensure sufficient online time.
Cost node incentive mechanism. The custodian node obtains the corresponding number of key shares according to the rights and interests it holds, and calculates the corresponding signature shares and attaches them to the transaction, and then obtains the handling fee according to the key share ratio. If the escrow node correctly provides the key share, it will get the transaction fee corresponding to its security deposit; if it is offline or loses the key share, it cannot participate in the arbitration transaction and cannot obtain the transaction fee. Nodes can be de-escrowed for providing false or wrong key shares. To sum up, the incentive mechanism will motivate the escrow node to provide the correct key share, stay online and keep its own key share safely.
Reputation management mechanism. On the one hand, nodes in Themis participate in dispute resolution and give arbitration opinions; on the other hand, they continue to anonymously evaluate the dispute resolution opinions given by other users. Here we will create a practical anonymous reputation mechanism that can quickly update reputation values ​​in a large user base while meeting users' privacy needs. The reputation system will accurately calculate the feedback of other users in the system on the results of a user's arbitration opinion, and quickly update the user's reputation value. The level of reputation value is directly related to the probability of a user becoming an arbitration node, that is, a user with a lower reputation value is more difficult to be selected as an arbitration node.
Common node incentive mechanism. Only those who have enough rights and interests on Themis can be selected as hosting nodes and participate in hosting. Other nodes that have not become hosting nodes are called ordinary nodes. Ordinary nodes cannot participate in custody but can entrust the rights they hold to trusted escrow nodes. The entrusted escrow nodes will distribute the transaction fees obtained by verifying transactions to ordinary nodes according to the proportion of entrusted rights and interests. If the hosting node is punished, the ordinary node will also bear the corresponding loss. This incentive mechanism ensures that equity owners on Themis can obtain benefits related to their equity, and also encourages them to entrust their equity to trusted nodes, thereby improving the security and stability of Themis.

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