public function encrypt($x)
    {
        $t = ''; // 16-byte block
        $y = ''; // returned cipher text;

        // put a 16-byte block into t
        $xsize = strlen($x);
        for ($i = 0; $i < $xsize; $i += 16) {
            for ($j = 0; $j < 16; ++$j) {
                // @codeCoverageIgnoreStart
                if (($i + $j) < $xsize) {
                    $t[$j] = $x[$i + $j];
                } else {
                    $t[$j] = chr(0);
                }
                // @codeCoverageIgnoreEnd
            }

            $y .= $this->encryptBlock($t);
        }

        return $y;
    }