How to get private keys on Truffle from Ganache accounts

Question

Doing some ERC-735 tests on truffle+ganache I got stuck when creating claim signatures. They need to be signed from my ganache account, but I don't know its private key. The code to be used is this:

const messageToSign = "hello world";
const privateKey = "43f2ee33c522046e80b67e96ceb84a05b60b9434b0ee2e3ae4b1311b9f5dcc46";
var msgHash = EthUtil.hashPersonalMessage(new Buffer(messageToSign));
var sig = EthUtil.ecsign(msgHash, new Buffer(privateKey, 'hex')); 
var signatureRPC = EthUtil.toRpcSig(sig.v, sig.r, sig.s)
console.log(signatureRPC);

As explained on Sign data with private key inside a truffle test file there was a method to sign messages from Truffle using:

let signedMessage = await web3.personal.sign("data", accounts[0])

but it is now deprecated, it throws "Method personal_sign not supported" error, so a solution seems to be an explicit signing using private key (code above).

How can I get the private key from ganache? or even better, can I get the private key from truffle?

Answer 1

You can start ganache with a mnemonic as a parameter ( -m 'jar boss sister abuse equal ....'). Doing this, you'll:

• be guaranteed to have the same addresses generated with each run

• be able to derive the private keys from that mnemonic

  const bip39 = require('bip39');
  const hdkey = require('ethereumjs-wallet/hdkey');
  const wallet = require('ethereumjs-wallet');
  
  const seed = bip39.mnemonicToSeed(mnemonic); // mnemonic is the string containing the words
  const hdk = hdkey.fromMasterSeed(seed);
  const addr_node = hdk.derivePath("m/44'/60'/0'/0/0"); //m/44'/60'/0'/0/0 is derivation path for the first account. m/44'/60'/0'/0/1 is the derivation path for the second account and so on
  const addr = addr_node.getWallet().getAddressString(); //check that this is the same with the address that ganache list for the first account to make sure the derivation is correct
  const private_key = addr_node.getWallet().getPrivateKey();