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Filename : verify.js
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// Copyright 2015 Joyent, Inc.

var assert = require('assert-plus');
var crypto = require('crypto');
var sshpk = require('sshpk');
var utils = require('./utils');

var HASH_ALGOS = utils.HASH_ALGOS;
var PK_ALGOS = utils.PK_ALGOS;
var InvalidAlgorithmError = utils.InvalidAlgorithmError;
var HttpSignatureError = utils.HttpSignatureError;
var validateAlgorithm = utils.validateAlgorithm;

///--- Exported API

module.exports = {
  /**
   * Verify RSA/DSA signature against public key.  You are expected to pass in
   * an object that was returned from `parse()`.
   *
   * @param {Object} parsedSignature the object you got from `parse`.
   * @param {String} pubkey RSA/DSA private key PEM.
   * @return {Boolean} true if valid, false otherwise.
   * @throws {TypeError} if you pass in bad arguments.
   * @throws {InvalidAlgorithmError}
   */
  verifySignature: function verifySignature(parsedSignature, pubkey) {
    assert.object(parsedSignature, 'parsedSignature');
    if (typeof (pubkey) === 'string' || Buffer.isBuffer(pubkey))
      pubkey = sshpk.parseKey(pubkey);
    assert.ok(sshpk.Key.isKey(pubkey, [1, 1]), 'pubkey must be a sshpk.Key');

    var alg = validateAlgorithm(parsedSignature.algorithm);
    if (alg[0] === 'hmac' || alg[0] !== pubkey.type)
      return (false);

    var v = pubkey.createVerify(alg[1]);
    v.update(parsedSignature.signingString);
    return (v.verify(parsedSignature.params.signature, 'base64'));
  },

  /**
   * Verify HMAC against shared secret.  You are expected to pass in an object
   * that was returned from `parse()`.
   *
   * @param {Object} parsedSignature the object you got from `parse`.
   * @param {String} secret HMAC shared secret.
   * @return {Boolean} true if valid, false otherwise.
   * @throws {TypeError} if you pass in bad arguments.
   * @throws {InvalidAlgorithmError}
   */
  verifyHMAC: function verifyHMAC(parsedSignature, secret) {
    assert.object(parsedSignature, 'parsedHMAC');
    assert.string(secret, 'secret');

    var alg = validateAlgorithm(parsedSignature.algorithm);
    if (alg[0] !== 'hmac')
      return (false);

    var hashAlg = alg[1].toUpperCase();

    var hmac = crypto.createHmac(hashAlg, secret);
    hmac.update(parsedSignature.signingString);

    /*
     * Now double-hash to avoid leaking timing information - there's
     * no easy constant-time compare in JS, so we use this approach
     * instead. See for more info:
     * https://www.isecpartners.com/blog/2011/february/double-hmac-
     * verification.aspx
     */
    var h1 = crypto.createHmac(hashAlg, secret);
    h1.update(hmac.digest());
    h1 = h1.digest();
    var h2 = crypto.createHmac(hashAlg, secret);
    h2.update(new Buffer(parsedSignature.params.signature, 'base64'));
    h2 = h2.digest();

    /* Node 0.8 returns strings from .digest(). */
    if (typeof (h1) === 'string')
      return (h1 === h2);
    /* And node 0.10 lacks the .equals() method on Buffers. */
    if (Buffer.isBuffer(h1) && !h1.equals)
      return (h1.toString('binary') === h2.toString('binary'));

    return (h1.equals(h2));
  }
};