crypt.js

var fs = require('fs'),
    assert = require('assert'),
    crypto = require('crypto');

var msg = "Gaur!";
fs.readFile('PrivateKey.pem', 'utf-8', function(e,pri) {
  var signer = crypto.createSign('sha256').update(msg);
  var signature = signer.sign(pri, output_format='base64');
  
  fs.readFile('PublicKey.pem', 'utf-8', function(e,pub) {
    var verifier = crypto.createVerify('sha256').update(msg);
    var verified = verifier.verify(pub, signature, signature_format='base64');
    assert.equal(verified, 1)
  });
});