Details of the ShuttleFlow protocol, a cross-chain bridge of Conflux assets

A view of the, back

In 2019, DeFi open finance (hereinafter referred to as DeFi) attracted a large number of investors with more transparent and more efficient capital liquidity and more attractive deposit and loan interest rates than traditional finance, and became the most high-profile track in the digital currency application layer.

Various DeFi products have been launched as investors move their assets across the Ethereum network to participate in the DeFi ecosystem. By the end of 2019, the total value of DeFi's ecological lock-in on Ethereum had grown to $651.6 million. Thanks to the proliferation of well-known DeFi platforms such as MakerDao and Compound, Ethereum is giving birth to a new digital financial system.

At the same time, since most DeFi applications are currently based on Ethereum, the development of DeFi is also limited by the limited assets and low performance limitations of Ethereum and cannot be used on a large scale.

In March 2020, a series of black swan events caused the collapse of bitcoin, Ethereum and other mainstream digital currencies. The DeFi ecology on Ethereum triggered a series of mysterious events due to the performance bottleneck of Ethereum, which greatly frustrated and questioned the already weak DeFi market. This unexpected event accelerated the demand for high-performance infrastructure from the community.

In addition, the lack of quality assets has become a bottleneck for DeFi. As we all know, BTC is the largest digital currency asset by market value. Bitcoin now has a market value of more than $100bn, about eight times that of ethereum. In order to further introduce bitcoin traffic to expand the ecology, the application on ethereum can only bring other publicly linked assets into the ecology of ethereum by transiting mainstream currencies such as bitcoin across the chain. However, most of the cross-chain assets on ethereum are plagued by the uneven quality of the issuer and the extremely limited issuance scale under single endorsement, which not only limits the growth rate of DeFi, but also makes DeFi face a critical liquidity crisis in extreme cases.

Ethereum 2.0 is still on its way, and it remains to be seen whether the PoS mechanism will pass the security test, but the high-performance, high-security Conflux was first revealed during DeFi's much-questioned "darkest moment". To promote the DeFi ecosystem, the Conflux technical team has developed an asset cross-chain protocol called "ShuttleFlow" that will provide users with a safer, more efficient and more convenient asset cross-chain bridge. Shuttle, which means "Shuttle", "Flow" and "flowing water", embodies the vision of enabling cross-chain assets to pass freely among common links like flowing water through the asset cross-chain bridge of Conflux.

2. Existing cross-chain schemes

Since bitcoin, ethereum and other public chains are independent of each other, the assets on the chain cannot be directly circulated for matchmaking. There are two main solutions, namely cross-chain atom exchange and cross-chain atom mapping.

Cross-chain atomic exchange is performed by hashing time locking contracts. The trading party must complete the transaction within the specified time and provide the transaction private key. Although this transaction method is safe, it requires both parties to be online at the same time, takes a long time to confirm, and is not friendly to ordinary small transactions.

Cross-chain atomic mapping is to lock the assets of one chain and cast the same amount of assets to another chain at the same time 1:1, so as to realize the fast matching between assets in another chain. Take BTC for example, there are currently several ethereum publishers casting ERC20 BTC with this solution. Such as wBTC, tBTC, imBTC, hBTC, etc.

Conficuux ShuttleFlow selects how to map a cross-chain asset by cross-chain atom mapping.

Iii. Asset cross-chain bridge Conflux ShuttleFlow

Conjuction ShuttleFlow will form a cross-chain asset management alliance (hereinafter referred to as the "alliance") in conjunction with major players in the conjuction ecosystem, including well-known wallets, custoders and decentralized trading platforms, to map cross-chain assets in a 2/3 multi-signature manner and constitute the first-level release and acceptance of cross-chain assets on conjucux.

Taking BTC as an example, after the user transfers BTC to the designated user's BTC collection wallet, the alliance automatically listens to the coinage request and issues 1:1 cBTC anchoring BTC on conficuux in the form of multiple signatures, providing coinage and acceptance services, and coinage cBTC to the designated conficuux wallet address.

Specific solutions are as follows:

Create a multi-signature account on Bitcoin to lock up the BTC collateral required for casting cBTC. On conficux, a smart contract is deployed to manage and document the casting and acceptance of cBTC. The oversigned BTC account and c

The BTC's smart contracts are jointly managed by the members of the aforementioned alliance. Each member runs an alliance node. This node is responsible for listening for validating events on the Bitcoin and Conflux chains, as well as for the corresponding transaction actions after the commit event occurs.

Coinage acceptance process of alliance oversigned:

COINS process

1. The Bitcoin account of A member of the federation A submits A transaction on Bitcoin to the federation's multi-signature BTC account, making A coinage request to "concoct x cBTC to concoct account B", in which A needs to actually remit x BTC to the multi-signature BTC account. Where, information for Conflux account B is stored in the op_return of the Bitcoin transaction (up to 83 bytes).

2. The union node listens for coin requests in the oversigned account on Bitcoin.

3. After the alliance node listens to the request, verify the request:
3.1. Wait for finality of the corresponding transaction on Bitcoin and x BTC to be confirmed to the account.
3.2. Check that the target account address B indicated in op_return is A legal address. If the address is not legal, you can apply for A refund. Or apply to update the address, the new address is legal, according to the normal procedures continue.

4. If the casting request is verified to be correct, the federation node shall sign and broadcast the coinage operation "x cBTC to conf account B" on conf ux to other federation nodes.

5. Each alliance node collects signatures independently:

5.1. When an alliance node receives signatures for the operation from more than 2/3 of the nodes, the operation and the signatures received are submitted to the cBTC smart contract on conficux for coinage, and repeated submissions are ignored.
5.2. After the contract is minted, x CBTCS are automatically added to Conflux account B.

Acceptance process

1. A federation member's Conflux account B submits A transaction to the cBTC smart contract, making an acceptance request to "accept x BTC to Bitcoin account A". In this transaction, B needs to actually transfer x cBTC to the smart contract, and the transferred x cBTC will be directly destroyed. Where, the information of the Bitcoin account A is specified in the request parameters.

2. The federation node listens for the acceptance request in the cBTC contract on conficux.

3. After the alliance node listens to the request, it waits for the corresponding transaction to be confirmed to finality on conficux and x cBTC to be confirmed to be destroyed.

4. If the acceptance request is verified to be correct, the union node shall sign the acceptance operation "accept x BTC to Bitcoin account A" on Bitcoin and broadcast it to other union nodes.

5. Each alliance node collects signatures independently:

5.1. When an alliance node receives the signature of the operation from more than 2/3 of the nodes, the operation and the signature received are submitted to the multi-signature account on Bitcoin for acceptance operation, and the repeated submission is directly ignored.

5.2. After the over-signed accounts perform acceptance operation, x BTC will automatically accept Bitcoin account A.

Iv. One-key asset cross-chain experience adaptation to multiple application scenarios

Users' demand for cross-chain assets is generally linked to scenarios, such as DEX's transaction scenario and Lending's Lending scenario, which requires users to first cross the asset chain and then recharge the asset to the corresponding scenario for use. This process requires the user to understand the existence of intermediate assets, such as wBTC, etc., with a high cognitive threshold and a long operation path.

ShuttleFlow protocol combines two steps of users' asset cross-chain operation and DApp operation with one step through the original multi-scenario asset cross-chain collection address to carry out one-key encapsulation, so that ordinary users do not need to perceive the intermediate process of asset cross-chain, and realize "transfer is cross-chain, cross-chain is experience".

An example is an application scenario using DEX decentralized exchanges on the conficuux chain. If users want to use a decentralised exchange on the conficuux chain, they do not have to go through the multiple and complicated steps of transferring from the central exchange to the wallet on the conficuux chain, from the wallet authorization to the decentralised exchange. Simply obtain the custom collection address from the DEX application end, withdraw COINS directly from the wallet on the central exchange/other chains to this address, then you can instantly receive multiple COINS in the DEX account, achieve one-key completion of asset cross-chain, and support direct transaction. In the process of user's one-key recharge, cross-chain alliance has completed the behavior of multiple COINS to the user's DEX account, so that users can enjoy high security while having the use experience no less than the centralized exchange.

5. Hot and cold wallet system -- to secure and lock assets

Conficux will work with a number of organizations, including well-known wallet parties, custodian and decentralized trading platforms, to be an acceptor of cross-chain assets, adding multiple insurances to assets and making them safer and more reliable. The coinage process for each currency will involve a user collection wallet and an alliance escrow wallet. ShuttleFlow automatically transfers users' assets to the collection wallet into the alliance managed wallet. Everyone can publicly audit and trace the casting and destruction of all cross-chain assets, ensuring that each cross-chain asset corresponds to the original chain asset of equal value.

To further ensure asset security, the alliance managed wallet will be divided into two management modes, cold wallet and hot wallet, to double lock the asset security. ShuttleFlow will set an upper and lower limit for the alliance's multi-mint and acceptance amounts: check the upper limit once a day, and if the assets in the hot wallet are higher than the upper limit, the excess will be automatically transferred to a safer cold wallet for safekeeping to improve security. Check the lower bound in real time. If the assets in the hot wallet are lower than the lower bound, alliance members will be reminded to initiate multi-signing to transfer part of the assets in the cold wallet to the hot wallet.

Vi. ShuttleFlow alliance governance model

In the ShuttleFlow alliance ecosystem, each alliance member will independently maintain one co-sign node and keep the private key of multi-sign authorization. Conflux strives to achieve efficient governance of the alliance ecosystem by:

Directed invitation system: alliance members will be determined in the form of directed invitation system, with a maximum of 11 highly trusted partners that are ecologically bound to Conflux DeFi. In order for the ecosystem to grow rapidly, the ficux foundation will provide options for early alliance members.

Early stage governance: early alliance ecology has a variety of proposals that require decision making, such as iteration of alliance members, support for new currency, and various parameters such as withdrawal fees. Due to the frequent iterations of early business with market changes, in order to shorten the decision-making chain and rapidly promote business, the Conflux foundation will organize consensus meetings among alliance members under the chain to make proposals and resolutions.

Stability stage governance: with the ecological development and maturity, after the cross-chain Alliance business is stable, the cross-chain Alliance will build a legal Cross Chain Alliance DAO, and DAO will govern the ShuttleFlow Alliance ecology. With autonomy, alliance members can coordinate the development of resources, and even make decisions on how to control risks, etc., and will benefit from ecological services.

Vii. ShuttleFlow development plan

ShuttleFlow is an important link for DeFi's ecological development on the network of Conflux and an asset inflow port for the entire DeFi ecosystem. The conficux network and ecology will launch the first phase of the conficux network and ecosystem process in mid-to-late April, and the first decentralized trading application developed based on the conficux decentralized exchange protocol BoomFlow will begin trial operation after the first phase of conficux network is launched. ShuttleFlow will be launched in conjunction with DEX based on the Conflux BoomFlow protocol.

ShuttleFlow V1.0 has been developed, is being audited, and is scheduled to be open source after the audit. We will continue to work on ShuttleFlow V2.0 and support more public links and its on-board asset protocols.

There is no doubt that ShuttleFlow support across the chain on the asset has a broad application scenario, these assets across the chain can not only directly into DEX Conflux chain and other DeFi products as high quality liquid assets, in the next step plan will also support more public chain, support multiple public assets across each other on the chain chain operations, to be a universal across the chain of assets. The ecological blueprint of DeFi on the confeux network is not limited to the development of confeux network, but rather to a decentralized trading platform that extends to multiple public chains to enhance the liquidity of digital assets in the entire blockchain world while ensuring asset security.

We are well aware that the DeFi market is still young, and conficux has planted a seed. We hope to work with more partners who are willing to expand the cross-chain asset blueprint, to provide more application scenarios and better assets for DeFi, and work with conficux to grow this seed into a great tree.

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