Superchain WETH

Table of Contents

• Motivation and Constraints
  • Handling native assets other than ETH
  • Minimizing protocol complexity
• Constants
• SuperchainWETH
  • Invariants
    • deposit
    • withdraw
    • crosschainBurn
    • crosschainMint
    • sendETH
    • relayETH
• ETHLiquidity
  • Invariants
    • Global Invariants
    • burn
    • mint

Superchain WETH is an enhanced version of the standard WETH contract, enabling ETH interoperability across the Superchain. The Superchain WETH contract serves two primary functions:

1. Native ETH Transfers: It provides the sendETH and relayETH functions to transfer native ETH directly between interoperable chains that both use ETH as their native token. If the destination chain does not use ETH as its native asset, the transferred ETH is converted into the SuperchainWETH ERC20 token on the destination chain instead.
2. ERC20 Token: It extends the ERC20 contract, allowing ETH to be wrapped into the SuperchainWETH ERC20 token. This wrapped token can be transferred across interoperable chains via the SuperchainTokenBridge, serving as the entry point for ERC20 token interoperability.

Superchain WETH integrates with the ETHLiquidity contract to manage native ETH liquidity across chains, ensuring seamless cross-chain transfers of ETH in both its native and ERC20 forms.

Motivation and Constraints

ETH is the native asset of Ethereum and has by extension also become the native asset of many Ethereum L2 blockchains. In its role as a native asset, ETH can be used to pay for transaction fees and can be transferred from account to account via calls with attached value. ETH plays a significant role in the economics of most L2s and any protocol that enables interoperability between chains must be able to account for ETH.

Handling native assets other than ETH

Not all chains using the OP Stack use ETH as the native asset. We would like these chains to be able to interoperate with chains that do use ETH as a native asset. Certain solutions that might work when all chains use ETH as a native asset begin to break down when alternative native assets are introduced. For example, a protocol that burns the native asset on one chain and mints it on another will work if both chains use the same native asset but will obviously fail if either chain uses a different native asset.

Minimizing protocol complexity

Support for native ETH opens the door to unnecessary complexity. Any solution to this problem should aim to minimize the amount of protocol code required to support native ETH. This generally points towards an app-layer solution if possible but does not preclude a protocol-layer solution as long as we minimize implementation size.

Constants

SuperchainWETH

Invariants

deposit

• Reverts if triggered on a chain that does not use ETH as a native token.

withdraw

• Reverts if triggered on a chain that does not use ETH as a native token.

crosschainBurn

• Reverts if called by any address other than the SuperchainTokenBridge.
• Reverts if attempting to send more than the sender's available balance.
• Reduces the sender's balance by the sent amount.
• Emits a transfer event from sender to null address for the sent amount.
• Burns liquidity by sending the sent amount of ETH into the ETHLiquidity contract if native token is ETH.
  • Must not revert.
• Emits a CrosschainBurn event.

crosschainMint

• Reverts if called by any address other than the SuperchainTokenBridge.
• Mints liquidity from the ETHLiquidity contract if native token is ETH.
  • Must not revert.
• Increases the recipient's balance by the sent amount.
• Emits a transfer event from null address to recipient for the sent amount.
• Emits a CrosschainMint event.

sendETH

• Reverts if the msg.sender's balance is less than the msg.value being sent.
• Reverts if the to address is the zero address.
• Reverts if the native token on the source chain is not ETH.
• Transfers msg.value of ETH from the msg.sender to the ETHLiquidity contract.
• Sends a cross-chain message to the destination chain to call relayETH.
• Emits a SendETH event with details about the sender, recipient, amount, and destination chain.

relayETH

• Reverts if called by any address other than the L2ToL2CrossDomainMessenger.
• Reverts if the cross-domain sender is not SuperchainWETH on the source chain.
• If the destination chain uses ETH as its native token:
  • Transfers the relayed ETH to the recipient.
• If the destination chain uses a custom gas token:
  • Mints SuperchainWETH ERC-20 tokens to the recipient.
• Emits a RelayETH event with details about the sender, recipient, amount, and source chain.

ETHLiquidity

Invariants

Global Invariants

• Initial balance must be set to type(uint248).max (wei). Purpose for using type(uint248).max is to guarantees that the balance will be sufficient to credit all use within the SuperchainWETH contract but will never overflow on calls to burn because there is not ETH in the total ETH supply to cause such an overflow. Invariant that avoids overflow is maintained by SuperchainWETH but could theoretically be broken by some future contract that is allowed to integrate with ETHLiquidity. Maintainers should be careful to ensure that such future contracts do not break this invariant.

burn

• Must never be callable such that balance would increase beyond type(uint256).max.
  • This is an invariant and NOT a revert.
  • Maintained by considering total available ETH supply and the initial balance of ETHLiquidity.
• Reverts if called by any address other than SuperchainWETH.
• Reverts if called on a chain that does not use ETH as a native token.
• Accepts ETH value.
• Emits an event including address that triggered the burn and the burned ETH value.

mint

• Must never be callable such that balance would decrease below 0.
  • This is an invariant and NOT a revert.
  • Maintained by considering total available ETH supply and the initial balance of ETHLiquidity.
• Reverts if called by any address other than SuperchainWETH.
• Reverts if called on a chain that does not use ETH as a native token.
• Transfers requested ETH value to the sending address.
• Emits an event including address that triggered the mint and the minted ETH value.