vETH

On this page, you can find the contracts and their interactions involved when bridging to and from Ethereum (L1 - $ETH) and Cronos zkEVM (L2 - $vETH ), it includes:

[L1 -> L2] Minting $vETH with $ETH

[L2 -> L1] Withdrawing $ETH from $vETH

[L1 -> L2] Minting $vETH with $ETH

From Ethereum mainnet (L1) to Cronos zkEVM mainnet (L2)

For bridging $ETH (Ethereum Mainnet) to $vETH (Cronos zkEVM Mainnet), we would need to:

  1. Mint and bridge $ybETH from Ethereum to Cronos zkEVM Mainnet with $ETH;

  2. Mint $vETH with $ybETH on Cronos zkEVM Mainnet.

To bridge $ETH from Ethereum mainnet -> Cronos zkEVM mainnet, and obtain $vETH, we would need to interact with:

Step 1) Calculating the amount of $ybETH to Bridge

On Ethereum, use ybETH contract to call the convertToShare function:

ybETH.convertToShare(ethAmount)
ParametersComments

ethAmount

The amount of $ETH (with 18 decimals) to be used to mint $ybETH.

Keep this amount for later steps.

Step 2) Minting And Bridging $ybETH

On Ethereum, call the mintAndBridge function on the ybETHBridge contract:

function mintAndBridge(
        address _l2Receiver,
        uint256 _amount,
        uint256 _l2GasLimit,
        uint256 _l2GasPerPubdataByteLimit,
        address _refundRecipient
    )
ParametersComments

_l2Receiver

The address on Cronos zkEVM that will receive $ybETH

_amount

The amount of $ETH to mint and bridge $ybETH, as calculate in Step 1

_l2Gaslimit

Maximum amount of L2 gas that transaction can consume during execution on L2. Reference value: 500,000

_l2GasPerPubdataByteLimit

The maximum amount of L2 gas that the operator may charge the user for a single byte of pubdata. Reference value: 800

_refundRecipient

Address to collect refund, if bridging is unsuccessful.

This will mint $ybETH on Ethereum and bridge it to the _l2Receiver address.

Step 3) Approving $ybETH to be spend by $vETH contract

On Cronos zkEVM, call approve on the $ybETH contract to approve $vETH to spend $ybETH with appropriate amount.

Step 4) Minting of $vETH

On Cronos zkEVM, call mint on $vETH contract , to mint $vETH

function mint(
         address _receiver,
         uint256 _ybEthAmount
         )
ParametersComments

_receiver

Address to receive the minted $vETH tokens

_ybEthAmount

Amount of $ybETH to be used to mint $vETH

This will mint $vETH into the _receiver address.

[L2 -> L1] Withdrawing $ETH from $vETH

From Cronos zkEVM mainnet (L2) -> Ethereum mainnet (L1)

For withdrawing $vETH (Cronos zkEVM Mainnet) and get $ETH (Ethereum Mainnet) , we would need to:

  1. [On Cronos zkEVM] Use $vETH to redeem $ybETH;

  2. [On Cronos zkEVM] Bridge $ybETH to Ethereum;

  3. [On Ethereum] Obtain vnoNFT by burning $ybETH

  4. [On Ethereum] Withdraw $ETH by buringvnoNFT.

To redeem $vETH from Cronos zkEVM mainnet, and withdraw $ETH on Ethereum mainnet we would need to interact with the following contracts:

Step 1) Approving $vETH to be spend by vETH contract

On Cronos zkEVM, call approve on the $vETH contract to approve $vETH spend with appropriate amount.

Step 2) Redeeming $vETH for $ybETH

On Cronos zkEVM, call redeem on the vETH contract, to burn $vETH and redeem $ybETH

function redeem(
        address _receiver,
        uint256 _vethAmount
    )
ParametersComments

_receiver

Address to receive $ybETH on Cronos zkEVM

_vethAmount

Amount of vETH that will be burned to redeem ybETH

Once done, corresponding $ybETH will be transfer to the _reciever address

Step 3) Approving $ybETH to be spend by the L2Bridge

On Cronos zkEVM, call approve on the ybETH contract, to approve L2Bridge to spend $ybETH.

Step 4) Withdrawing $ybETH and store withdrawal hash

On Cronos zkEVM, call withdraw on the L2Bridge contract

function withdraw(
        address _l1Receiver, 
        address _l2Token, 
        uint256 _amount)
ParametersComments

_l1Receiver

Address on Ethereum to receive the token

_l2Token

The token to be withdrawn, the Cronos zkEVM contract address $ybETH in this case.

_amount

amount of tokens to be withdrawn, note $ybETH has 18 decimals

Keep the transaction hash for later use in Step 5. This withdraws $ybETH from Cronos zkEVM to Ethereum. It takes at least 24 hours before the withdrawal can be finalized on Ethereum. Store the transaction hash from the withdrawal transaction; you will need it to finalize the withdrawal.

Step 5) Gathering information for $ybETH withdrawal on L1

Extra information for the L2 -> L1 transaction is required for the next step in claiming the $ybETH on L1. This information can be gathered by finalizeWithdrawalParams, using zksync-ethers package

finalizeWithdrawalParams(withdrawalHash)

This takes the L2 withdrawal hash as parameters and returns the parameters required for finalizing a withdrawal in the next step.

Example outputs:

{
  l1BatchNumber: 18,
  l2MessageIndex: 59,
  l2TxNumberInBlock: 2919,
  message: '0x6c0960f935f448644c86dbda241ecb57f18a15c80f35a066000000000000000000000000000000000000000000000a2a15d09519be000000',
  sender: '0x000000000000000000000000000000000000800a',
  proof: [
    '0x23ff0fb003a6a6e111f87cff02afc8680944c711abbe792f07ab4206e9efb9a3',
    '0x09fece9c46307f2a0976a3a9b57873e453cf0f4773c2377dcd19f054166aef22',
    '0x33c106ae5601983b53c751129d1921c17e40b69aa3fdbfaf07b7a0e0750d35e4',
    '0x952ffa5de22d99815d9513dd7454949edb2a1cbcf86008f6fa8b169ffe9b4aee',
    '0x8f10560a0b5412ca2e0578fb9266f55411f357d52c8fc3b2cad43b9877a559a6',
    '0x8e70b93d3c90798df26473a3ad32a86170e8d52023a4044cf1d4c2d645471b14',
    '0xdfaacb39891bbbf4509af408239b97a6f5ef715a5c299ba1f3625c20aec4ef8f',
    '0xb04e5ee349086985f74b73971ce9dfe76bbed95c84906c5dffd96504e1e5396c',
    '0xac506ecb5465659b3a927143f6d724f91d8d9c4bdb2463aee111d9aa869874db',
    '0x124b05ec272cecd7538fdafe53b6628d31188ffb6f345139aac3c3c1fd2e470f',
    '0xc3be9cbd19304d84cca3d045e06b8db3acd68c304fc9cd4cbffe6d18036cb13f',
    '0xfef7bd9f889811e59e4076a0174087135f080177302763019adaf531257e3a87',
    '0xa707d1c62d8be699d34cb74804fdd7b4c568b6c1a821066f126c680d4b83e00b',
    '0xf6e093070e0389d2e529d60fadb855fdded54976ec50ac709e3a36ceaa64c291'
  ]
}

Step 6) Claiming the $ybETH on L1

Once the transaction in Step 4 has been finalized on L1, we can claim the withdrawn $ybETH from the Shared Bridge contract by calling its finalizeWithdrawal function. The inputs can be found in Step 5,

    function finalizeWithdrawal(
            uint256   _chainId,
            uint256   _l2BatchNumber,
            uint256   _l2MessageIndex,
            uint16    _l2TxNumberInBatch,
            bytes calldata _message,
            bytes32 calldata _merkleProof
        )
ParametersComments

_chainId

Chain id for Cronos zkEVM, which is 388

_l2BatchNumber

The L2 batch number where the withdrawal was processed, obtained in Step 5.

_l2MessageIndex

The position in the L2 logs Merkle tree of the l2Log that was sent with the message, obtained in Step 5.

_l2TxNumberInBatch

The L2 transaction number in the batch, in which the log was sent, obtained in Step 5.

_message

The L2 withdraw data, stored in an L2 -> L1 message, obtained in Step 5.

_merkleProof

The Merkle Proof, obtained in Step 5.

Once finalizeWithdrawal is completed, the withdrawn amount of $ybETH will go into the receiver's wallet on Ethereum.

We can use zksync-ethers package isWithdrawalFinalized call to confirm whether the withdrawal transaction is finalized on the L1 network.

isWithdrawalFinalized(withdrawalHash)
ParametersComments

withdrawalHash

The transaction hash of the L2 transaction includes the withdrawal transaction from Step 4

Step 7) Approving $ybETH to be spend by ybETH contract

On Ethereum, call approve on the $ybETH contract, to approve the contract to spend $ybETH.

Step 8) Requesting $ETH withdrawal

On Ethereum, call requestUnbond to request a unbonding of the staked $ETH.

function requestUnbond(
        uint256 _shareAmount, 
        address _receiver
        )
ParametersComments

_shareAmount

The amount of $ybETH that is to be burned to unbond $ETH

_receiver

The wallet address on ethereum to receive the receipt NFT. This NFT is needed to withdraw the $ETH once the unbond period has ended

This will burn $ybETH and mint a receipt NFT - Veno Unstaked ETH (vnoNFT) to the _receiver address. The unbonding procress takes 1~10 days, hold on to the NFT to claim the $ETH once it's ready. Store the tokenId of the received NFT; it is needed to withdraw the $ETH in the next steps.

Step 9) Approving NFT to be spend by ybETH contract

On Ethereum, call setApprovalForAll on the vnoNFT contract, to approve $ybETH to transfer your vnoNFT obtained in Step 8). 

setApprovalForAll(address operator, bool _approved)
ParametersComments

operator

$ybETH contract address on Ethereum

_approved

Set to "True" to grant approval.

Step 10) Withdrawing $ETH

On Ethereum, call unbondfunction on the ybETH contract to burn the receipt NFT and receive the underlying unstaked $ETH.

 function unbond(
        uint256 _tokenId, 
        address _receiver
        )
ParametersComments

_tokenId

The tokenId of the receipt NFT, recieved in Step 7

_receiver

The address on Ethereum to receive $ETH

This transaction burns the receipt NFT and sends the unstaked $ETH to the specified receiver.

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