Q1. How crosschained BTC to wanBTC is realized?
A: Please read this article for general idea:
https://www.explorewanchain.org/#/technology/cross-chain
Codes on Githhub Repo:https://github.com/wanchain/wanchain-crosschain-contracts/tree/btc_wan_cross
Q2. About Storeman Group
Threshold + MPC method to manage cross-chain assets, is it managed through multiple groups? How many groups are there, and how to manage different groups?
A: The previous design was that each cross-chain bridge (two chains or called one pair) use one storeman group with 21 nodes. The latest research update is that cross-chain bridges will share a combined Storeman group to enhance the utilization and security of collaterals. The number of nodes in this combined group can be expanded.
More details please refer to this article:
https://medium.com/wanchain-foundation/understanding-wanchain-two-way-bridge-and-direct-bridge-7f6088617734
Q3. Does each group involve 21 nodes, and requires at least 16 signatures, and generates one address?
A: It is now a Storeman group of 21 nodes, which can be expanded. The required threshold signature is 15, and aone address is generated.
Q4. When one Storeman group is switching to a new group, do other groups need to re-generate key fragments?
A: Different groups are independent. Every time when a new Storeman group election is selected to replace the old one, it is necessary to re-produce the key fragments.
Q5. If a Storeman node commits malicious behavior and needs to be slashed and expelled, how to deal with it? When it comes to adding or expelling nodes, does the protocol itself support dynamic adding and removing of a node?
A: When we started the project back in 2017, the theoretical reference was: “Robust Threshold DSS Signatures” and after 3 years of evolution, now we implemented using this reference: “Fast Multiparty Threshold ECDSA with Fast Trustless Setup”. The procedure for dealing with malicious behavior is that: the node’s own collaterals (currently is his staked WAN coins) will be slashed by a percentage when the malicious action occurs for the first time; and after that, if such malicious actions are committed again, the collaterals deduction will continue until all staked WAN coins are finished. After that, the MPC will not use any data provided by this node. We do not support dynamic node changes during the current group work cycle. The current design is when a new elections will be held on the 1st-7th of each calendar month, the balances of cross-chain assets of the previous group will be handed over to the newly selected group on 8th-9th, and new cycle of work will begin on the 10th. Adding or removing nodes will happen that the moment.
P.S. In addition, our research team has been studying how to achieve dynamic changes of nodes. It is also hoped that it will be an quite important milestone for the next technological implementation.
Q6. When signing the execution of cross-chain assets, is it necessary for at least 16 nodes to be online at the same time to sign and how many rounds of signing? How was this interaction cost considered?
A: Firstly, our protocol needs 15 nodes are online to sign, not 16. Interactions between these nodes: for BTC-WAN, it needs 3 rounds; and for ETH-WAN it requires 2 rounds. The cost has been verified and approved by engineering implementation that it fully meets cross-chain requirements (speed, cost); and it can be expanded to large-scale node adoptions easily (scalability).
Q7. I think Storeman group’s participation in the cross-chain execution is a very essential mechanism. Is the collateralized funds valued in fiat currency? How can the Oracle ensure stable execution of different prices and will not make permission switching errors? Where does the rewards to Storeman nodes come from?
A: The collaterals now are WAN coins and WAN is valued by its fiat USD price coming from exchanges. When executing other assets such as ETH and BTC, the protocol follows the 150% over-collateralization rule currently. Storeman group’s WAN coins are priced in USD value to make sure the collaterals are 150% more than crosschain assets.
When user transfer WAN to Ethereum for example, collaterals, which are the WAN coins are priced based on a 1:1 matching amount, regardless of fiat factor.
The Oracle in Storeman is completely decentralized and adopts the design idea of “Signature is Consensus, SOC”. The decentralized design does not involve the issue of any permission switching. In addition, the rewards for Storeman now is from reserved WAN coins by the Foundation as illustrated clearly in its whitepaper. And we expect that with more adoptions of crosschain operations in the near future, the service fee for crosschain operation will be charged for each transaction, and these rewards will 100% go to Storeman nodes.
Q8. Cross-chain assets need to map ‘Issued ‘tokens. Whether the number of mapping issued tokens is correct is crucial. What is the purpose of adding HLTC to cross-chain?
A: My understand that ‘issue’ here means mint, which is exactly in accordance with the one-to-one mapping between locked and minted numbers. This is how it works: once the cross-chain transaction is proposed by the user, after the Storeman group will construct one transaction, and the request as well as the number of minted tokens are passed to each node of the group for verification and signing. Nodes will only sign if the number of minted token is exactly the same as the number of locked amount. Therefore, as long as the cross-chain process is successful, the number of minted token must be commonly agreed in the Storeman group, that is, the idea of “Signature is Consensus, SOC” mentioned above. The old version of the cross-chain mechanism adopts HTLC to ensure the atomic swap; but after the new cross-chain mechanism is updated, the combined open Storeman design no longer needs HTLC to ensure the atomic swap. Thus HTLC has been removed from the protocol.
More to read about other details of Wanchain’s crosschain design and implementation, please refer to these articles:
Comparative Analysis of wanBTC with tBTC https://medium.com/wanchain-foundation/comparative-analysis-of-wanbtc-with-tbtc-620b87bb9846
Understanding Wanchain Two-Way Bridge and Direct Bridge for crosschain operations https://medium.com/wanchain-foundation/understanding-wanchain-two-way-bridge-and-direct-bridge-7f6088617734?source=collection_home---4------1-----------------------
Universal Multichain Bridges with Shared Staking Assets https://medium.com/wanchain-foundation/universal-multichain-bridges-with-shared-staking-assets-e2a50669f016
About Wanchain
Wanchain is the infrastructure connecting the decentralized financial world. Wanchain’s live cross-blockchain solution is EVM-based, includes optional private transactions, and provides a decentralized, permissionless, and secure approach for interoperability. Wanchain has employees globally with teams in China, the USA, and other team members around the world in Asia, Africa, and Europe.
Written by:
Li Ni
VP of Operations at Wanchain
