[General] How to Retrieve Proof Parameters for ETH Claim on L1 from zkSync Era?

[mihailo-maksa]

Team or Project

Kelp DAO

Environment

Mainnet

L2 block number

No response

Provide a brief description of the functionality you're trying to implement and the issue you are running into.

We're implementing a functionality in our contracts to bridge ETH from zkSync Era (L2) to Ethereum Mainnet (L1). However, we're encountering challenges with the claim transaction on Mainnet. Specifically, we're unsure how to obtain the correct proof parameters required for the L1 finalizeEthWithdrawal function, which must be called after the 24-hour bridging delay. Is there an API or other recommended and reliable method to fetch these proof parameters?

Repo Link (Optional)

No response

Additional Details

No response

[gleenai[bot]]

To retrieve the proof parameters required for the finalizeEthWithdrawal function on Ethereum Mainnet after bridging ETH from ZKsync Era, you can utilize the Prover API provided by ZKsync. This API is designed to help you fetch batch proof inputs that are necessary for finalizing withdrawals on L1.

Here are the relevant endpoints you might find useful:

1. /proof_generation_data - This endpoint allows you to retrieve the latest batch proof inputs, which are very similar to the internal workings of ZKsync's provers.
2. /proof_generation_data/{batch_number} - Use this endpoint to get inputs for a specific batch proof, which is useful for testing or benchmarking purposes.

Please note that not all batches have proof inputs available, and batch data is only available for a finite amount of time (30 days from the time of writing). After this period, the data is deleted, and ZKsync cannot verify batches older than this timeframe.

For more detailed information on setting up and using the Prover API, you can refer to the From Integration to Verification: Completing the First Steps in ZKsync documentation.

For further discussions and support, you may also visit the ZKsync developers discussions on Github.

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[bxpana]

Thanks for the post! Will check this out and get back to you

[mihailo-maksa]

Sounds good, thank you!

[popzxc]

Hey @mihailo-maksa! Yes, there are APIs for that.
You can take a look at how fetching withdrawal parameters is implemented in zksync-ethers. Corresponding RPC method iszks_getL2ToL1LogProof.

Basically, what you need is to identify the log that corresponds to the withdrawal L2 -> L1 message on l2 and then retreive a proof for it.

One caveat you should be aware of is that there might be multiple withdrawals in a single transaction (which is why index needs to be passed in the function above).

[mihailo-maksa]

Hey @popzxc, thanks for sharing this, it was very helpful!

I was also wondering if this would work in case in which a call to withdraw on L2 is done via some other function on the L2 smart contract?

e.g. suppose that there is an L2Vault contract on zkSync Era that has a bridgeAssets method on it, callable only by the contract owner, and within this bridgeAssets function, there is a call to withdraw to initiate the withdrawal of ETH from L2 --> L1

[popzxc]

Absolutely, you only need to extract the log that corresponds to the L2->L1 message initiating a withdrawal. How withdrawal was initiated is not important.
Moreover, the algorithm is the same for any form of L2->L1 communication.

[mihailo-maksa]

Sounds good, thank you for the detailed answer!