PHP aes算法

function aes128cbcEncrypt($key, $text)
{
    /**
     * Open the cipher
     */
    $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
    if (! $td)
    {
        throw new GeneralSecurityException('Invalid mcrypt cipher, check your libmcrypt library and php-mcrypt extention');
    } 
    // replaced MCRYPT_DEV_RANDOM with MCRYPT_RAND since windows doesn't have /dev/rand :)
    srand((double)microtime() * 1000000);
    $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
    /**
     * Intialize encryption
     */
    mcrypt_generic_init($td, $key, $iv);
    /**
     * Encrypt data
     */
    $encrypted = mcrypt_generic($td, $text);
    /**
     * Terminate encryption handler
     */
    mcrypt_generic_deinit($td);
    /**
     * AES-128-CBC encryption.  The IV is returned as the first 16 bytes  
     * of the cipher text.
     */
    return $iv . $encrypted;
} 

function aes128cbcDecrypt($key, $encrypted_text)
{
    /**
     * Open the cipher
     */
    $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
    if (is_callable('mb_substr'))
    {
        $iv = mb_substr($encrypted_text, 0, Crypto_CIPHER_BLOCK_SIZE, 'latin1');
    } 
    else
    {
        $iv = substr($encrypted_text, 0, Crypto_CIPHER_BLOCK_SIZE);
    } 
    /**
     * Initialize encryption module for decryption
     */
    mcrypt_generic_init($td, $key, $iv);
    /**
     * Decrypt encrypted string
     */
    if (is_callable('mb_substr'))
    {
        $encrypted = mb_substr($encrypted_text, Crypto_CIPHER_BLOCK_SIZE, mb_strlen($encrypted_text, 'latin1'), 'latin1');
    } 
    else
    {
        $encrypted = substr($encrypted_text, Crypto_CIPHER_BLOCK_SIZE);
    } 
    $decrypted = mdecrypt_generic($td, $encrypted);
    /**
     * Terminate decryption handle and close module
     */
    mcrypt_generic_deinit($td);
    mcrypt_module_close($td);
    /**
     * Show string
     */
    return trim($decrypted);
} 
define('Crypto_CIPHER_BLOCK_SIZE', 16);
$a = aes128cbcEncrypt('pass', 'this is text');
echo base64_encode($a) . "/r/n";
$b = aes128cbcDecrypt('pass', $a);
echo $b . "/r/n";
$c = aes128cbcDecrypt('pass', base64_decode(base64_encode($a)));
echo $c . "/r/n";
?>