Permit Signature

Permit Signature Explained in Detail

A permit signature authorizes a contract action with off-chain signed data. In ERC20 tokens, EIP-2612 uses permit to set allowance without an on-chain approve transaction from the owner.

Anyone can submit a valid permit. The security comes from the signed fields and validation rules, not from who relays it.

Smart contract example

permit(owner, spender, value, deadline, v, r, s);

The signature should bind owner, spender, value, nonce, deadline, chain, and verifying contract.

Permit Signature in Auditing

Permit flows move authorization off-chain. If nonce, deadline, domain separator, or signature checks are wrong, attackers may replay approvals or redirect them.

Auditors review permit as both token logic and signature logic.

Red flags in code

• No nonce or nonce is consumed at the wrong time.

• Expired permits are accepted.

• Chain ID or verifying contract is missing from the signed domain.

• Raw ecrecover accepts zero address or malleable signatures.

• The product promises contract-wallet support but only EOA signatures are accepted.

How to test or review it

• Submit the same permit twice and expect the second call to fail.

• Mutate signer, spender, value, nonce, deadline, chain, and domain.

• Test expired signatures and invalid signature formats.

• Test permit plus action flows when another relayer front-runs the permit.

• Check whether contract signatures are required for the product's wallet model.