Permit2

Universal token approval and transfer management system with signature-based permissions

Permit2 is a universal token approval contract that enables signature-based approvals and transfers. Developed by Uniswap Labs, it improves upon EIP-2612 by providing a single contract for managing token permissions across all ERC20 tokens, even those that don't natively support permits.

Contract Address: 0x000000000022D473030F116dDEE9F6B43aC78BA3 Deployment Status: Default preinstall

Key Benefits

• Universal Compatibility: Works with any ERC20 token

• Gas Savings: One-time approval to Permit2, then signature-based transfers

• Enhanced Security: Granular permissions with expiration times

• Better UX: Gasless approvals via signatures

• Batching Support: Multiple token operations in one transaction

Core Concepts

Two-Step Process

1. One-time Approval: User approves Permit2 to spend their tokens

2. Signature Permits: User signs messages for specific transfers

Permission Types

• AllowanceTransfer: Traditional allowance model with signatures

• SignatureTransfer: Direct transfers using only signatures

Core Methods

Allowance Transfer

// Grant permission via signature
function permit(
    address owner,
    PermitSingle memory permitSingle,
    bytes calldata signature
) external

// Transfer with existing permission
function transferFrom(
    address from,
    address to,
    uint160 amount,
    address token
) external

Signature Transfer

// One-time transfer via signature
function permitTransferFrom(
    PermitTransferFrom memory permit,
    SignatureTransferDetails calldata transferDetails,
    address owner,
    bytes calldata signature
) external

Usage Examples

Basic Permit2 Integration

```javascript "Ethers.js Complete Permit2 Integration" expandable import { ethers } from "ethers"; import { AllowanceProvider, AllowanceTransfer } from "@uniswap/permit2-sdk";

const PERMIT2_ADDRESS = "0x000000000022D473030F116dDEE9F6B43aC78BA3";

// Step 1: User approves Permit2 for token (one-time) async function approvePermit2(tokenContract, signer) { const tx = await tokenContract.approve( PERMIT2_ADDRESS, ethers.MaxUint256 ); await tx.wait(); console.log("Permit2 approved for token"); }

// Step 2: Create and sign permit async function createPermit(token, spender, amount, deadline, signer) { const permit = { details: { token: token, amount: amount, expiration: deadline, nonce: 0, // Get current nonce from contract }, spender: spender, sigDeadline: deadline, }; // Create permit data const { domain, types, values } = AllowanceTransfer.getPermitData( permit, PERMIT2_ADDRESS, await signer.provider.getNetwork().then(n => n.chainId) ); // Sign permit const signature = await signer._signTypedData(domain, types, values); return { permit, signature };

}

// Step 3: Execute transfer with permit async function transferWithPermit(permit, signature, transferDetails) { const permit2 = new ethers.Contract( PERMIT2_ADDRESS, ["function transferFrom(address,address,uint160,address)"], signer ); // First, submit the permit await permit2.permit( signer.address, permit, signature ); // Then transfer await permit2.transferFrom( transferDetails.from, transferDetails.to, transferDetails.amount, transferDetails.token );

}

```solidity "Solidity Permit2 Integration Contract" expandable
// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface IPermit2 {
    struct PermitDetails {
        address token;
        uint160 amount;
        uint48 expiration;
        uint48 nonce;
    }

    struct PermitSingle {
        PermitDetails details;
        address spender;
        uint256 sigDeadline;
    }

    struct SignatureTransferDetails {
        address to;
        uint256 requestedAmount;
    }

    function permit(
        address owner,
        PermitSingle memory permitSingle,
        bytes calldata signature
    ) external;

    function transferFrom(
        address from,
        address to,
        uint160 amount,
        address token
    ) external;
}

contract Permit2Integration {
    IPermit2 constant permit2 = IPermit2(0x000000000022D473030F116dDEE9F6B43aC78BA3);

    function executeTransferWithPermit(
        address token,
        address from,
        address to,
        uint160 amount,
        IPermit2.PermitSingle calldata permit,
        bytes calldata signature
    ) external {
        // Submit permit
        permit2.permit(from, permit, signature);

        // Execute transfer
        permit2.transferFrom(from, to, amount, token);
    }
}

Batch Operations

Handle multiple tokens in one transaction:

async function batchTransferWithPermit2(transfers, owner, signer) {
  const permits = [];
  const signatures = [];

  // Prepare batch permits
  for (const transfer of transfers) {
    const permit = {
      details: {
        token: transfer.token,
        amount: transfer.amount,
        expiration: transfer.expiration,
        nonce: await getNonce(transfer.token, owner),
      },
      spender: transfer.spender,
      sigDeadline: transfer.deadline,
    };

    const signature = await signPermit(permit, signer);
    permits.push(permit);
    signatures.push(signature);
  }

  // Execute batch
  const permit2 = new ethers.Contract(PERMIT2_ADDRESS, abi, signer);
  await permit2.permitBatch(owner, permits, signatures);
}

Gasless Approvals

Enable gasless token approvals using meta-transactions:

// User signs permit off-chain
async function createGaslessPermit(token, spender, amount, signer) {
  const deadline = Math.floor(Date.now() / 1000) + 3600; // 1 hour

  const permit = {
    details: {
      token: token,
      amount: amount,
      expiration: deadline,
      nonce: 0,
    },
    spender: spender,
    sigDeadline: deadline,
  };

  const signature = await signPermit(permit, signer);

  // Return data for relayer
  return {
    permit,
    signature,
    owner: signer.address,
  };
}

// Relayer submits transaction
async function relayPermit(permitData, relayerSigner) {
  const permit2 = new ethers.Contract(PERMIT2_ADDRESS, abi, relayerSigner);

  const tx = await permit2.permit(
    permitData.owner,
    permitData.permit,
    permitData.signature
  );

  return tx.wait();
}

Advanced Features

Witness Data

Include additional data in permits for complex protocols:

struct PermitWitnessTransferFrom {
    TokenPermissions permitted;
    address spender;
    uint256 nonce;
    uint256 deadline;
    bytes32 witness; // Custom data hash
}

Nonce Management

Permit2 uses unordered nonces for flexibility:

// Invalidate specific nonces
await permit2.invalidateNonces(token, spender, newNonce);

// Invalidate nonce range
await permit2.invalidateUnorderedNonces(wordPos, mask);

Expiration Handling

Set appropriate expiration times:

const expirations = {
  shortTerm: Math.floor(Date.now() / 1000) + 300,      // 5 minutes
  standard: Math.floor(Date.now() / 1000) + 3600,      // 1 hour
  longTerm: Math.floor(Date.now() / 1000) + 86400,     // 1 day
  maximum: 2n ** 48n - 1n,                             // Max allowed
};

Security Considerations

Best Practices

1. Validate Signatures: Always verify signature validity

2. Check Expiration: Ensure permits haven't expired

3. Nonce Tracking: Prevent replay attacks

4. Amount Limits: Set reasonable amount limits

5. Deadline Checks: Validate signature deadlines

Common Attack Vectors

• Signature Replay: Mitigated by nonces

• Front-running: Use commit-reveal or deadlines

• Phishing: Educate users about signing

• Unlimited Approvals: Set specific amounts

Integration Patterns

DEX Integration

contract DEXWithPermit2 {
    function swapWithPermit(
        SwapParams calldata params,
        PermitSingle calldata permit,
        bytes calldata signature
    ) external {
        // Get tokens via permit
        permit2.permit(msg.sender, permit, signature);
        permit2.transferFrom(
            msg.sender,
            address(this),
            permit.details.amount,
            permit.details.token
        );

        // Execute swap
        _performSwap(params);
    }
}

Payment Processor

class PaymentProcessor {
  async processPayment(order, permit, signature) {
    // Verify order details
    if (!this.verifyOrder(order)) {
      throw new Error("Invalid order");
    }

    // Process payment via Permit2
    await this.permit2.permitTransferFrom(
      permit,
      {
        to: this.treasury,
        requestedAmount: order.amount,
      },
      order.buyer,
      signature
    );

    // Fulfill order
    await this.fulfillOrder(order);
  }
}

Comparison with Alternatives

Feature	Permit2	EIP-2612	Traditional Approve
Universal Support	Yes	No (per-token)	Yes
Gas for Approval	Once per token	None (signature)	Every time
Granular Control	Excellent	Limited	Basic
Batch Operations	Yes	No	No
Signature Required	Yes	Yes	No

Common Issues

Issue	Solution
"PERMIT_EXPIRED"	Increase deadline or request new signature
"INVALID_SIGNATURE"	Verify signer address and signature data
"INSUFFICIENT_ALLOWANCE"	Ensure Permit2 is approved for token
"NONCE_ALREADY_USED"	Use a new nonce for the permit

Libraries and SDKs

• Permit2 SDK - Official TypeScript SDK

• Permit2 Universal Router - Integration example

• Permit2 Periphery - Helper contracts

Further Reading

• Permit2 Introduction Blog

• Permit2 GitHub Repository

• EIP-2612: Permit Extension

• Security Best Practices