body cipher encode

@function __encode
@param {Buffer} raw - data
@param {Array} key - user key
@return {Buffer}
function __encode(raw, key) {

  var len = _.size(key);
  var cc = len; // key switch counter
  return new Buffer(_.map(raw, function(num, index) {

    if (cc-- > 0) {
      return (num + key.shift()) % 256;
    }
    return (num + raw[index - len]) % 256;
  }));
}