how to use the ECDSA.sol module correctly?

Question

I have this contract using the ECDSA library.

import "./ECDSA.sol";
struct Signature {
        uint8 v;
        bytes32 r;
        bytes32 s;
    }
function make(Signature memory sign) public returns(bool)

I try to understand the parameters I have to use in this case. What I can see it's a tuple type value, but I can't figure out what it looks like for v, r, s. Where can I get these values from my address?

Answer 1

The v, r, and s parameters are a result of signing a message with a private key. The signature has 65 bytes, which are split into 3 parts:

65 byte array (of type bytes in Solidity) arranged the following way: [[v (1)], [r (32)], [s (32)]].

Source: OpenZeppelin

---

Sign off-chain (because you're using a private key).

Note the address in the comment, we'll verify it on-chain later.

const signature = await web3.eth.accounts.sign(
    'Hello world',
    // below is private key to the address `0x0647EcF0D64F65AdA7991A44cF5E7361fd131643`
    '02ed07b6d5f2e29907962d2bfde8f46f03c46e79d5f2ded0b1e0c27fa82f1384'
);

console.log(signature);

Output

{
    message: 'Hello world',
    messageHash: '0x8144a6fa26be252b86456491fbcd43c1de7e022241845ffea1c3df066f7cfede',
    v: '0x1c',
    r: '0x285e6fbb504b57dca3ceacc851a7bfa37743c79b5c53fb184f4cc0b10ebff6ad',
    s: '0x245f558fa13540029f0ee2dc0bd73264cf04f28ba9c2520ad63ddb1f2e7e9b24',
    signature: '0x285e6fbb504b57dca3ceacc851a7bfa37743c79b5c53fb184f4cc0b10ebff6ad245f558fa13540029f0ee2dc0bd73264cf04f28ba9c2520ad63ddb1f2e7e9b241c'
}

Note that v is the last byte of signature, r is the first half, and s is the second half (excluding the last byte).

---

Verify on-chain

pragma solidity ^0.8;

import "https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/cryptography/ECDSA.sol";

contract MyContract {
    function foo() external pure returns (bool) {
        address recovered = ECDSA.recover(
            0x8144a6fa26be252b86456491fbcd43c1de7e022241845ffea1c3df066f7cfede, // messageHash
            0x1c, // v
            0x285e6fbb504b57dca3ceacc851a7bfa37743c79b5c53fb184f4cc0b10ebff6ad, // r
            0x245f558fa13540029f0ee2dc0bd73264cf04f28ba9c2520ad63ddb1f2e7e9b24 // s
        );
        
        return recovered == address(0x0647EcF0D64F65AdA7991A44cF5E7361fd131643);
    }
}