Foundry Book

sign

Signature

function sign(uint256 privateKey, bytes32 digest) external returns (uint8 v, bytes32 r, bytes32 s);

Description

Signs a digest digest with private key privateKey, returning (v, r, s).

This is useful for testing functions that take signed data and perform an ecrecover to verify the signer.

Examples

address alice = vm.addr(1);
bytes32 hash = keccak256("Signed by Alice");
(uint8 v, bytes32 r, bytes32 s) = vm.sign(1, hash);
address signer = ecrecover(hash, v, r, s);
assertEq(alice, signer); // [PASS]

This is useful for testing functions that require a signature:

// SPDX-License-Identifier: UNLICENSED
pragma solidity 0.8.17;

import { ECDSA } from "@openzeppelin/contracts/utils/cryptography/ECDSA.sol";

contract SigningExample is Ownable {
    using ECDSA for bytes32;

    address public systemAddress;

    function setSystemAddress(address _address) external onlyOwner {
        systemAddress = _address;
    }

    function purchase(uint256 _amount, string calldata _nonce, bytes calldata _signature) external payable {
        require(isValidSignature(
            systemAddress,
            keccak256(abi.encodePacked(msg.sender, _amount, _nonce)),
            _signature
            ), "Invalid Signature"
        );

        // mint tokens
    }

    function isValidSignature(address _systemAddress, bytes32 hash, bytes memory signature) internal view returns (bool) {
        require(_systemAddress != address(0), "Missing System Address");

        bytes32 signedHash = hash.toEthSignedMessageHash();
        return signedHash.recover(signature) == _systemAddress;
    }

}

contract SigningExampleTest is Test {
    using ECDSA for bytes32;

    SigningExample public signingExample;

    uint256 internal userPrivateKey;
    uint256 internal signerPrivateKey;

    function setUp() public {
        signingExample = new SigningExample();

        userPrivateKey = 0xa11ce;
        signerPrivateKey = 0xabc123;

        address signer = vm.addr(signerPrivateKey);
        signingExample.setSystemAddress(signer);
    }

    function testPurchase() public {
        address user = vm.addr(userPrivateKey);
        address signer = vm.addr(signerPrivateKey);

        uint256 amount = 2;
        string memory nonce = 'QSfd8gQE4WYzO29';

        vm.startPrank(signer);
        bytes32 digest = keccak256(abi.encodePacked(user, amount, nonce)).toEthSignedMessageHash();
        (uint8 v, bytes32 r, bytes32 s) = vm.sign(signerPrivateKey, digest);
        bytes memory signature = abi.encodePacked(r, s, v); // note the order here is different from line above.
        vm.stopPrank();

        vm.startPrank(user);
        // Give the user some ETH, just for good measure
        vm.deal(user, 1 ether);

        signingExample.purchase(
            amount,
            nonce,
            signature
        );
        vm.stopPrank();
    }
}