System transactions

Transactions on Signet can originate from Ethereum. When the Signet node observes specific events from the Passage or Transactor contracts on the host chain, it creates corresponding transactions on the rollup.

Three host-chain event types produce system transactions:

System transactions execute last in the block, after all user-submitted transactions. Processing order within that group is:

1. Enter
2. EnterToken
3. Transact

A single host transaction can produce multiple system transactions. For example, the Transactor’s enterTransact function emits both an Enter event and a Transact event, producing two system transactions in the same block.

MagicSig

System transactions are not signed by a private key. The signature field carries a MagicSig with three fields:

• Event type: Enter, EnterToken, or Transact
• Transaction hash: the host-chain transaction that emitted the event
• Event index: position of the event within the transaction’s logs

The s value of the signature begins with the sentinel 0xffeeddcc, which exceeds the secp256k1 curve order. This makes it impossible to confuse a MagicSig with a real ECDSA signature on any EIP-2 chain.

For Transact events, the MagicSig also encodes the sender address and whether address aliasing was applied.

See the MagicSig documentation for the full wire format specification.

Native asset mints

When USDC or USDT is deposited through Passage (EnterToken event), the node mints native USD directly to the recipient’s balance. This is not an EVM transaction. The node increases the account balance directly, without executing contract code.

Amounts are normalized from the host token’s decimals to 18. For example, 1 USDC (10**6 on Ethereum) becomes 10**18 wei of native USD on Signet.

The node emits a MintNative system log from MINTER_ADDRESS:

event MintNative(
    bytes32 indexed txHash,
    uint64 indexed logIndex,
    address indexed recipient,
    uint256 amount
);

MINTER_ADDRESS is 0x00000000000000000000746f6b656e61646d696e.

Token mints

ETH deposits (Enter) and non-USD token deposits (EnterToken) produce a token mint transaction. The node calls mint(recipient, amount) on the corresponding rollup-side ERC-20 contract.

These transactions run from MINTER_ADDRESS with zero gas cost.

Transaction properties:

• from: MINTER_ADDRESS
• to: the rollup token contract
• value: 0
• nonce: next nonce for MINTER_ADDRESS
• input: ABI-encoded mint(address recipient, uint256 amount)
• max_fee_per_gas: 0
• max_priority_fee_per_gas: 0

The node emits a MintToken system log from MINTER_ADDRESS:

event MintToken(
    bytes32 indexed txHash,
    uint64 indexed logIndex,
    address indexed recipient,
    address hostToken,
    uint256 amount
);

Transact

When the host Transactor emits a Transact event, the node creates a transaction on Signet from the caller’s address. This allows Ethereum contracts to own assets on Signet and trigger execution there, using their Ethereum address as the sender.

Transaction properties:

• from: the host-chain msg.sender, aliased if the sender is a smart contract
• to: as specified in the event
• value: as specified in the event (USD wei)
• input: as specified in the event
• nonce: next nonce for the sender’s Signet account
• gas_limit: as specified in the event
• max_fee_per_gas: as specified in the event
• max_priority_fee_per_gas: 0