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I know what bridges are and the problem they solve. The only problem now is I am trying to wrap my head around how they actually do what they do.

I found an answer similar to this question here, where it states:

Create 2 contracts on 2 chains, you then lock tokens on mainchain contract, listen off-chain (you choose Node.js/GoLang/Python/etc). You then listen for the event that is emitted when the lock (deposit) function executes and on the secondary chain the offchain trusted (whitelister/relayer/messenger) mints the equivalent amount of tokens. If you want to withdraw you burn your tokens on the secondary chain, then the offchain service unlocks the equivalent burned of tokens and transfers them to the users main-chain address.

Question I have is, how exactly do the token gets minted on the second chain? For example given a Ethereum/Polkadot bridge, how will a Dot token be minted on Polkadot? I ask because I assume tokens gets minted either via mining or validator (in proof of stake). So for bridging, how does the bridge manage to mint a new token when there is no mining or validating?

Also on the side of the originating chain, how does locking of coin works?

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  • Possibly good read: Blockchain bridges Commented Jun 17, 2022 at 13:45
  • @PaulRazvanBerg I read that piece but it does not provide the answer the the exact question of "how" Commented Jun 17, 2022 at 16:07
  • Your post describes all of the How. But maybe your question title should be modified to emphasise that you're asking about the gas transaction routines involved on both sides of the bridge?
    – user610620
    Commented Dec 9, 2022 at 16:49

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I know this is 2 months old, but in case you didn't already figure it out (take the following with a grain of salt, I'm also learning as I go!)

I've worked from ETH => Polygon so I can't assure you it's all the same, but in my case it works as follows

"Locking" tokens on mainnet simply means you give your tokens to the bridge, so now you don't own them at all, the bridge does, so they are stuck there until you bring them back

As for minting them on the other chain, polygon's web2 server is in charge of picking up a request from the Ethereum bridge to run some transactions on the other side, which are then received by the bridge on polygon

So, you can specify the address of the token you deployed on polygon, and make a request from Eth chain to interact with this specific polygon address, in our case it could be "mint x amount to this address"

These docs can obviously do a much better job at explaining than I can: https://docs.polygon.technology/docs/develop/ethereum-polygon/getting-started

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  • If your token is locked on the bridge as intended, what happens when you mistakenly lose access to the private key of the wallet from which you put them there in the first place? Is there any bridge code that resolves this circumstance, allowing for the rightful owner to recover their locked token, perhaps from a different private key?
    – user610620
    Commented Dec 9, 2022 at 16:50

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