Asset Bridging

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Overview

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Supported Token Types

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Bridge Asset Function

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Function Signature

function bridgeAsset(
    uint32 destinationNetwork,
    address destinationAddress,
    uint256 amount,
    address token,
    bool forceUpdateGlobalExitRoot,
    bytes calldata permitData
) external payable

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Parameters

• destinationNetwork: Network ID of the destination chain
• destinationAddress: Address to receive assets on destination chain
• amount: Amount of tokens to bridge
• token: Token contract address (0x0 for native gas token)
• forceUpdateGlobalExitRoot: Whether to update GER immediately
• permitData: Raw permit data for ERC20 tokens (optional)

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Process Steps

1. Validation: Check destination network is not the source network
2. Token Preparation: Handle token based on type (lock, burn, or transfer)
3. Event Emission: Emit BridgeEvent with transaction details
4. Tree Update: Add transaction to Local Exit Tree as leaf node

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Token Preparation Logic

Note that in case ETH is the native token, WETHToken will be at 0x0 address.

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Native Gas Token (ETH, Custom Gas Token)

// Bridge contract holds the tokens
// The native gas token is already transferred via msg.value
// No additional token transfer required

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WETH Token

// Burn WETH tokens from user's address
IWETH(token).burnFrom(msg.sender, amount);

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Foreign ERC20 Token (Not native to source chain)

// If the token contract is not originally from the source network, 
// burn the ERC20 token from user's address
IERC20(token).burnFrom(msg.sender, amount);

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Native ERC20 Token (Native to source chain)

// If the token contract is originally from the source network:
// 1. Execute permit if provided
if (permitData.length > 0) {
    IERC20Permit(token).permit(...);
}
// 2. Transfer tokens from user to bridge contract
IERC20(token).transferFrom(msg.sender, address(this), amount);

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Claim Asset Function

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Function Signature

function claimAsset(
    bytes32[_DEPOSIT_CONTRACT_TREE_DEPTH] calldata smtProofLocalExitRoot,
    bytes32[_DEPOSIT_CONTRACT_TREE_DEPTH] calldata smtProofRollupExitRoot,
    uint256 globalIndex,
    bytes32 mainnetExitRoot,
    bytes32 rollupExitRoot,
    uint32 originNetwork,
    address originTokenAddress,
    uint32 destinationNetwork,
    address destinationAddress,
    uint256 amount,
    bytes calldata metadata
) external

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Parameters

• smtProofLocalExitRoot: Merkle proof for Local Exit Root
• smtProofRollupExitRoot: Merkle proof for Rollup Exit Root
• globalIndex: Global index identifying the transaction
• mainnetExitRoot: Mainnet Exit Root at time of transaction
• rollupExitRoot: Rollup Exit Root at time of transaction
• originNetwork: Network ID of source chain
• originTokenAddress: Token address on source chain
• destinationNetwork: Network ID of destination chain
• destinationAddress: Address to receive assets
• amount: Amount of tokens to claim
• metadata: Additional metadata (if any)

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Process Steps

1. Validation: Verify destination network matches current chain
2. Proof Verification: Verify Merkle proofs against Global Exit Root
3. Duplicate Check: Ensure transaction hasn’t been claimed before
4. Token Transfer: Transfer tokens based on token type (see Token Transfer Logic below)
5. Claim Record: Mark transaction as claimed

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Token Transfer Logic

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Proof Verification Logic

// Construct Global Exit Root
bytes32 globalExitRoot = keccak256(abi.encodePacked(mainnetExitRoot, rollupExitRoot));

// Verify against synchronized GER
require(globalExitRoot == getGlobalExitRoot(), "Invalid global exit root");

// Verify Merkle proofs based on origin
if (originNetwork == 0) {
    // L1 to L2: Verify against mainnet exit root
    verifyMerkleProof(smtProofLocalExitRoot, mainnetExitRoot, globalIndex);
} else {
    // L2 to L2: Verify against rollup exit root
    verifyMerkleProof(smtProofLocalExitRoot, rollupExitRoot, globalIndex);
    verifyMerkleProof(smtProofRollupExitRoot, rollupExitRoot, globalIndex);
}

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Bridging Flows

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L1 to L2 Bridging

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L2 to L1 Bridging

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L2 to L2 Bridging