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permit2

Permit2 introduces a low-overhead, next generation token approval/meta-tx system to make token approvals easier, more secure, and more consistent across applications.

Deployments

Address

0x31c2F6fcFf4F8759b3Bd5Bf0e1084A055615c768

Supported Blockchains

  • BSC Mainnet
  • BSC Testnet
  • Goerli

Features

  • Signature Based Approvals: Any ERC20 token, even those that do not support EIP-2612, can now use permit style approvals. This allows applications to have a single transaction flow by sending a permit signature along with the transaction data when using Permit2 integrated contracts.
  • Batched Token Approvals: Set permissions on different tokens to different spenders with one signature.
  • Signature Based Token Transfers: Owners can sign messages to transfer tokens directly to signed spenders, bypassing setting any allowance. This means that approvals aren't necessary for applications to receive tokens and that there will never be hanging approvals when using this method. The signature is valid only for the duration of the transaction in which it is spent.
  • Batched Token Transfers: Transfer different tokens to different recipients with one signature.
  • Safe Arbitrary Data Verification: Verify any extra data by passing through a witness hash and witness type. The type string must follow the EIP-712 standard.
  • Signature Verification for Contracts: All signature verification supports EIP-1271 so contracts can approve tokens and transfer tokens through signatures.
  • Non-monotonic Replay Protection: Signature based transfers use unordered, non-monotonic nonces so that signed permits do not need to be transacted in any particular order.
  • Expiring Approvals: Approvals can be time-bound, removing security concerns around hanging approvals on a wallet’s entire token balance. This also means that revoking approvals do not necessarily have to be a new transaction since an approval that expiries will no longer be valid.
  • Batch Revoke Allowances: Remove allowances on any number of tokens and spenders in one transaction.

Architecture

Permit2 is the union of two contracts: AllowanceTransfer and SignatureTransfer.

The SignatureTransfer contract handles all signature-based transfers, meaning that an allowance on the token is bypassed and permissions to the spender only last for the duration of the transaction that the one-time signature is spent.

The AllowanceTransfer contract handles setting allowances on tokens, giving permissions to spenders on a specified amount for a specified duration of time. Any transfers that then happen through the AllowanceTransfer contract will only succeed if the proper permissions have been set.

Integrating with Permit2

Before integrating contracts can request users’ tokens through Permit2, users must approve the Permit2 contract through the specific token contract. To see a detailed technical reference, visit the Uniswap documentation site.

Note on viaIR compilation

Permit2 uses viaIR compilation, so importing and deploying it in an integration for tests will require the integrating repository to also use viaIR compilation. This is often quite slow, so can be avoided using the precompiled DeployPermit2 utility:

import {DeployPermit2} from "permit2/test/utils/DeployPermit2.sol";

contract MyTest is DeployPermit2 {
    address permit2;

    function setUp() public {
        permit2 = deployPermit2();
    }
}

Bug Bounty

This repository is subject to the Uniswap Labs Bug Bounty program, per the terms defined here.

Contributing

You will need a copy of Foundry installed before proceeding. See the installation guide for details.

Setup

git clone https://github.com/Uniswap/permit2.git
cd permit2
forge install

Lint

forge fmt [--check]

Run Tests

# unit
forge test

# integration
source .env
FOUNDRY_PROFILE=integration forge test

Update Gas Snapshots

forge snapshot

Deploy

Run the command below. Remove --broadcast, ---rpc-url, --private-key and --verify options to test locally

forge script --broadcast --rpc-url <RPC-URL> --private-key <PRIVATE_KEY> --verify script/DeployPermit2.s.sol:DeployPermit2

Acknowledgments

Inspired by merklejerk's permit-everywhere contracts which introduce permit based approvals for all tokens regardless of EIP2612 support.