Wrapped Fungible Token Example Application

This example application implements a wrapped (bridged) fungible token, used by the EVM↔Linera bridge. It extends the base fungible token with Mint and Burn operations whose authority is restricted to a single registered application — the authorized caller — on a designated mint chain. In the bridge, that authorized caller is the evm-bridge application.

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 supply control (Mint/Burn) gated to a registered authorized caller.

Authorization

Mint and Burn are driven only by the registered authorized caller, and only on the designated mint chain. Two checks, both mandatory:

• The cross-application caller must equal the application registered via RegisterAuthorizedCaller.
• The operation must run on mint_chain_id (a WrappedParameters field).

RegisterAuthorizedCaller is itself restricted to the mint chain — the only chain where the authorized caller is consulted — and requires an authenticated signer. The caller is registered after creation rather than passed as a parameter, so an authorized caller that takes this token's id as a creation parameter can be created first (see Deployment).

There is no signer check on Mint/Burn: the authorized caller is trusted to validate its own input, so whoever relays the request is irrelevant. This keeps relaying permissionless.

Operations

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

• Mint { target_account, amount } — creates new tokens; authorized caller only, on the mint chain.
• Burn { owner, amount } — burns tokens from an account; authorized caller only, on the mint chain.
• RegisterAuthorizedCaller { app_id } — registers the application allowed to Mint/Burn; mint chain only, requires an authenticated signer.

Deployment

The wrapped fungible token is deployed as part of the EVM↔Linera bridge. Because the evm-bridge application takes this token's id as a creation parameter, the token is created first:

1. Deploy wrapped-fungible.
2. Deploy the evm-bridge application, pointing it at the wrapped-fungible app id.
3. On the mint chain, register the bridge as the authorized caller via RegisterAuthorizedCaller.

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