Sign data with private key inside a truffle test file

Question

I've got a contract method that checks the signer of a message using the solidity ecrecover function. In my truffle test file I now want to check if this is done correctly. Therefore I need to sign a message within the testfile using a private key.

Using this

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

does not work with error "Method personal_sign not supported."

Any idea how to do this? Thanks for you help!

Answer 1

I went through exactly the same problem a couple of days ago and it seems that the personal_sign method is rarely exposed for security reason.

I sorted this out using a random private key and a JavaScript library called ethereumjs-util

var EthUtil             = require('ethereumjs-util');

const messageToSign = "hello world";
const privateKey = "43f2ee33c522046e80b67e96ceb84a05b60b9434b0ee2e3ae4b1311b9f5dcc46";

var msgHash = EthUtil.hashPersonalMessage(new Buffer(messageToSign));
var signature = EthUtil.ecsign(msgHash, new Buffer(privateKey, 'hex')); 
var signatureRPC = EthUtil.toRpcSig(signature.v, signature.r, signature.s)

console.log(signatureRPC);

That returns:

0xd74a20b5a5b58185cc701e9d1349f240ff04154ab600266748bd45986104f0a62b8b827e2ba4a0da018efffb0ea16506503f4292538d791232ce574ac283e47c00

---

Working Code is available on my github

Answer 2

Since you cannot use the addresses available under the accounts to sign, the best way is to create one (or more) address(es) using web3.eth.accounts.wallet.create(x) (where x = number of accounts you want to generate).

Within your truffle test, you can create the wallet in the before(...) hook, and reference the newly created address(es) to some globally scoped variables.

contract("Your Contract", async (accounts) => {
let firstAccount,
    secondAccount,
    thirdAccount

before(async () => {
    await web3.eth.accounts.wallet.create(3) // create 3 accounts

    firstAccount = web3.eth.accounts.wallet[0]
    secondAccount = web3.eth.accounts.wallet[1]
    thirdAccount = web3.eth.accounts.wallet[2]
})

// tests here...


})

Each newly created address will have both property and method attach to them (see web3 docs):

• privateKey (see example of returned object for wallet.add in web3 docs)
• sign(...) (see web3 docs)

Both give you two ways to sign your message.

via web3.eth.accounts.wallet[...].sign(...)

let signature = web3.eth.accounts.wallet[firstAccount].sign("Message To Sign").signature

or alternatively

via web3.eth.accounts.sign(...), using privateKey

let signature = web3.eth.accounts.sign("Message To Sign", firstAccount.privateKey).signature

NB: you can also use object destructuring syntax to extract the signature (from the object returned by both signing methods). This also make the code shorter and a bit easier to read.

// first method
let { signature } = web3.eth.accounts.wallet[firstAccount].sign("Message To Sign")
// second method
let { signature } = web3.eth.accounts.sign("Message To Sign", firstAccount.privateKey)

Answer 3

There is no need to hardcode a private key or import a dependency. The accounts supplied by truffle+ganache are accessible in the web3.eth provider.

You can use web3.eth.sign to sign arbitrary data. It will hash the data using keccak256 and sign the hash. It is async so you have to await it, and it returns the 65-byte signature.

const sig = await web3.eth.sign(data, fromAccount)
const txSig = await web3.eth.signTransaction(tx, fromAccount)