Overview

Permit2 is a shared approval and signature-transfer contract used by Ring routing flows. It is composed of SignatureTransfer and AllowanceTransfer. The SignatureTransfer contract handles signature-based transfers, meaning that a direct allowance on the token is bypassed and spender permissions last only for the duration of the transaction where the one-time signature is spent. The AllowanceTransfer contract handles token allowances with specified amounts and durations.

Resources

A great explanation of the Permit2 contract and example usage.

Approving Permit2

Before integrating contracts can request users’ tokens through Permit2, users must approve the Permit2 contract through the specific token contract by calling something like:

USDC.approve(permit2Address, totalAmount);

To get the maximal benefits from Permit2, users should do a max approval on the contract where:

totalAmount = type(uint256).max;