依赖PHP自身的mcrypt扩展

class aes {
 
    // CRYPTO_CIPHER_BLOCK_SIZE 32
     
    private $_secret_key = 'default_secret_key';
     
    public function setKey($key) {
        $this->_secret_key = $key;
    }
     
    public function encode($data) {
        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_256,'',MCRYPT_MODE_CBC,'');
        $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td),MCRYPT_RAND);
        mcrypt_generic_init($td,$this->_secret_key,$iv);
        $encrypted = mcrypt_generic($td,$data);
        mcrypt_generic_deinit($td);
         
        return $iv . $encrypted;
    }
     
    public function decode($data) {
        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_256,'',MCRYPT_MODE_CBC,'');
        $iv = mb_substr($data,0,32,'latin1');
        mcrypt_generic_init($td,$this->_secret_key,$iv);
        $data = mb_substr($data,32,mb_strlen($data,'latin1'),'latin1');
        $data = mdecrypt_generic($td,$data);
        mcrypt_generic_deinit($td);
        mcrypt_module_close($td);
         
        return trim($data);
    }
}
 
$aes = new aes();
$aes->setKey('key');
 
// 加密
$string = $aes->encode('string');
// 解密
$aes->decode($string);
?>