Wrapped Fungible Token Example Application

This example application implements a wrapped (bridged) fungible token for the EVM<>Linera bridge. It extends the base fungible token with minting, burning, and bridge-specific authorization.

Tokens are minted when a deposit proof from EVM is verified by the evm-bridge application, and burned automatically when transferred cross-chain to an Ethereum address (Address20) on the bridge chain.

How It Works

The wrapped fungible token shares the same account model as the fungible example: individual chains have accounts with owners and balances. It adds three bridge-specific features:

Minting

Minting creates new wrapped tokens backed by locked ERC-20 tokens on EVM. Authorization is configurable via WrappedParameters:

• bridge_app_id (optional): if set, minting is only allowed via cross-application call from the bridge app
• minter (optional): if set, the block signer must match this account
• mint_chain_id (optional): if set, minting is restricted to this chain

Each check is enforced only when the corresponding parameter is Some. A fully unconfigured token allows unrestricted minting.

Auto-Burning

When tokens are transferred cross-chain to an Address20 target (Ethereum address) on the designated bridge chain, they are automatically burned instead of credited. The contract emits a BurnEvent on the "burns" stream, which the off-chain relayer detects and forwards to the EVM bridge contract to release the corresponding ERC-20 tokens.

This replaces the previous flow where the relayer had to propose a separate Burn operation.

Operations

All standard fungible operations are supported (Transfer, TransferFrom, Approve, Claim, Balance, TickerSymbol), plus:

• Mint { target_account, amount } - Creates new tokens (subject to authorization checks)
• Burn { owner, amount } - Rejected at the contract level. Burning happens automatically via cross-chain transfer to an Address20 on the bridge chain.

Deployment

The wrapped fungible token is deployed as part of the EVM<>Linera bridge. The deployment order is:

1. Deploy the evm-bridge Linera application
2. Deploy wrapped-fungible with bridge_app_id pointing to the bridge app
3. Register the wrapped-fungible app ID in the bridge via RegisterFungibleApp

See examples/bridge-demo/setup.sh for the complete deployment script.