var EC = require("elliptic").ec;
var ec = new EC("secp256k1");
var crypto = require('crypto');

/**
* Retrieve public key from a private key
* @param {string} privateKey Private key from where extract the public key
* @returns {string} Public key as hexadicemal
*/
function getPublicKey (privateKey) {
	var pubKey = privateKey.getPublic()
	var publicKey = pubKey.encode('hex');
	return publicKey;
}

/**
* Sign an message
* @params {string} message Message to sign
* @params {string} privateKey Private key to sign the message
* @returns {Array} Array of integer from the signature of the message signed
*/
function createSignature (message, privateKey) {
	var privKey = ec.keyFromPrivate(privateKey, 'hex')
	var signature = ec.sign(message, privKey)
	return signature.toDER()
}

/**
* Check a signature with a public key
* @params {string} message Message in the signature
* @params {string} publicKey Public key used to check the signature
* @params {Array} signature Array of integer from the signature serialized
*/
function checkSignature (message, publicKey, signature) {
	var _publicKey = ec.keyFromPublic(publicKey, 'hex')
	var checkresult = _publicKey.verify(message, signature)
	return checkresult
}

/**
* Hash a message with as SHA256
* @params {string} message Message to hash
* @returns {string} Hashed message
*/
function hashMessage (message) {
  var message = new Buffer(message, 'utf8')
  var shaMsg = crypto.createHash('sha256').update(message).digest()
  return shaMsg
}

var message = hashMessage('test')
var prvKey = '6fb63b7bdee06a3554e9b20881e982d8dd92e6be08f2797e29dff98fb473c1d1'
var privateKey = ec.keyFromPrivate(prvKey, 'hex')
var publicKey = getPublicKey(privateKey)

var signature = createSignature(message, privateKey)
var result = checkSignature(message, publicKey, signature)

console.log(result)