There are many ways of signing a message with a private key.
Quite rightfully there are not many websites allowing you to do so - that would be a suicide to trust anyone with your private key.
However, with some precautions you can build a website yourself.
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:
- https://security.stackexchange.com/questions/118547/unpublished-modules-on-npm-could-an-attacker-take-advantage-of-their-former-not/118579
- https://github.com/joaojeronimo/rimrafall
- it's inherit property of any software...
- ...even if it open-source and has well-established reputation you never know
- (not being paranoid, just being aware of security implications)
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 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>
- provide user interface for inputting the key
- use https://wzrd.in/ to avoid installing files
- create standalone demo