docs: function encode(password, cb) {
    var secret_key = conf.secret_key
      , iterations = conf.pbkdf2_iterations
      , keylen = conf.pbkdf2_keylen;
  
    crypto.pbkdf2(password, secret_key, iterations, keylen, function(err, derivedKey) {
      var str;
  
      if(err) {
        cb(err);
      } else {
        str = new Buffer(derivedKey).toString('base64');
        cb(null, str);
      }
    });
  }