Signature generation from just a private key and on-chain verification

This repo provides an example of how to generate a signature from just a private key as well as the accompanying contract to verify this signature.

The test case will:

1. Generate a new Ethereum account from a randomly generate mnemonic
2. Sign a message with the assoicated private key
3. Recover the associate address on-chain and verify the signature

Usage

https://github.com/AdamJLemmon/ethereum-signing.git
cd ethereum-signing
truffle develop
> test

Step-by-Step

Note: truffle version 4.1.14 and web3 version 0.20.6

Starting from the beginning a brand new account may be generated. The address and private key may be accessed directly from the new wallet:

const bip39 = require('bip39');
const hdkey = require('ethereumjs-wallet/hdkey');

const mnemonic = bip39.generateMnemonic();
const hdwallet = hdkey.fromMasterSeed(bip39.mnemonicToSeed(mnemonic));
const path = "m/44'/60'/0'/0/0";
const wallet = hdwallet.derivePath(path).getWallet();
const address = `0x${wallet.getAddress().toString('hex')}`;
const privateKey = wallet.getPrivateKey().toString('hex');

Then the data to be signed can be specified and the hash taken:

const messageToSign = 'adamjlemmon';
const hash = web3.sha3(messageToSign);

Finally, this data may be signed:

const sig = await generateSignature(hash, privateKey);

Where generateSignature is the following:

const ethUtil = require("ethereumjs-util");

module.exports = (dataToSign, privateKey) => {
  const msg = Buffer.from(dataToSign.replace("0x", ""), "hex");
  const msgHash = ethUtil.hashPersonalMessage(msg);
  const sig = ethUtil.ecsign(msgHash, new Buffer(privateKey, 'hex'));
  return ethUtil.toRpcSig(sig.v, sig.r, sig.s);
}