How to sign a message with a private key. - acetronaut/wiki GitHub Wiki

There are many ways of signing a message with a private key.

Quite rightfully there are not many websites allowing you to do so - it would be suicide to trust anyone with your private key.

However, with some precautions you can build a website yourself.

Browser method - only website you fully trust and control

Why don't you build it yourself? For that reason we will use:

You'll need to have node and browserify installed. Start with installing node and then npm install browserify -g

We will create a file with required libraries, let's call it dependencies.js

module.exports = {
  base58: require('bs58'),
  bitcoin: require('bitcoinjs-lib'),
  bitcoinMessage: require('bitcoinjs-message'),
  ecurve: require('ecurve'),
  BigInteger: require('bigi')
}

We also need to install these libraries locally:

npm install bs58 bitcoinjs-lib bitcoinjs-message ecurve bigi

WARNING: Installing from npm can also be dangerous, see links below:

As you mentioned you cannot republish a file of a particular version. By setting an exact version in your dependencies your application will only download this version. If an attacker was to gain control of the package they could only push malicious code to users of a later package.

From here we can use browserify to make it available in the browser:

browserify index.js --standalone library > bitcoin.js

Now let's create a super simple webpage:

<!DOCTYPE html>
<html>
  <head>
    <meta charset="UTF-8">
    <title>Signing message with private key</title>
    <script src="bitcoin.js"></script>
	<script>
		var keyPair = library.bitcoin.ECPair.fromWIF('5KYZdUEo39z3FPrtuX2QbbwGnNP5zTd7yyr2SC1j299sBCnWjss')
		var privateKey = keyPair.d.toBuffer(32)
		var message = 'This is an example of a signed message.'
		var messagePrefix = library.bitcoin.networks.bitcoin.messagePrefix
		 
		var signature = library.bitcoinMessage.sign(message, messagePrefix, privateKey, keyPair.compressed)
		console.log(signature.toString('base64'))
	</script>
  </head>
  <body>
  
  </body>
</html>

TODO:

  • provide user interface for inputting the key
  • use https://wzrd.in/ to avoid installing files
  • create standalone demo

Alternative: myetherwallet

Myetherwallet is a trustless open-source application that allows you to interact with the ethereum network without running a full client. You can create and manage wallets without uploading your private key.

To sign a message perform the following steps:

  • go to https://www.myetherwallet.com/
  • click "View wallet info" tab
  • chose how you would like to access your wallet and decrypt it locally
  • scroll to the section "Sign or verify message" on the page bottom
  • enter your message and optionally enter a date before clicking the "Sign message" button
⚠️ **GitHub.com Fallback** ⚠️