/**
 * ECDSA public key recovery from signature
 * @param {Buffer} msgHash
 * @param {Number} v
 * @param {Buffer} r
 * @param {Buffer} s
 * @return {Buffer} publicKey
 */
exports.ecrecover = function (msgHash, v, r, s) {
  var signature = Buffer.concat([exports.setLength(r, 32), exports.setLength(s, 32)], 64)
  var recovery = v - 27
  if (recovery !== 0 && recovery !== 1) {
    throw new Error('Invalid signature v value')
  }
  var senderPubKey = secp256k1.recover(msgHash, signature, recovery)
  return secp256k1.publicKeyConvert(senderPubKey, false).slice(1)
}

/**
* Determines if the signature is valid
* @return {Boolean}
*/
verifySignature () {
  const msgHash = this.hash(false)
  // All transaction signatures whose s-value is greater than secp256k1n/2 are considered invalid.
  if (this._homestead && new BN(this.s).cmp(N_DIV_2) === 1) {
    return false
  }

  try {
    let v = ethUtil.bufferToInt(this.v)
    if (this._chainId > 0) {
      v -= this._chainId * 2 + 8
    }
    this._senderPubKey = ethUtil.ecrecover(msgHash, v, this.r, this.s)
  } catch (e) {
    return false
  }

  return !!this._senderPubKey
}

var sig = secp256k1.sign(msgHash, privateKey)
  var ret = {}
  ret.r = sig.signature.slice(0, 32)
  ret.s = sig.signature.slice(32, 64)
  ret.v = sig.recovery + 27