AES encryption in PHP

Question

PHP doesn't have a built-in functions for AES (specifically, AES-128) encoding/decoding, so I've had to implement my own, and this is what I have come up to (of course, taken from different many sources, mostly not coded by me).

My question is, are these correct? Not the code itself, but what they do. The correctness of the algorithm. I have tested them, and they apparently do work. But there might be a subtle error that I'm overlooking...

---

Encoding algorithm:

function aes128_encode($data, $mode)
{
        switch ($mode) {
        case "ECB":
        case "CBC":
            if ($mode === "ECB") {
                $cipher = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_ECB, '');
            } else {
                $cipher = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
            }

            $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($cipher), MCRYPT_RAND);
            $key = substr(CIPHERKEY, 0, mcrypt_enc_get_key_size($cipher));

            if (mcrypt_generic_init($cipher, $key, $iv) != 1) {
                $cipherData = mcrypt_generic($cipher, $data);

                mcrypt_generic_deinit($cipher);
                mcrypt_module_close($cipher);

                if ($mode === "ECB") {
                    $sanitizedCipherData = trim(base64_encode($cipherData)); 
                } else {
                    $sanitizedCipherData = trim(base64_encode($iv)."_".base64_encode($cipherData));
                }

                return $sanitizedCipherData;
            } else {
                return false;
            }
            break;

        default:
            return false;
            break;
        }
    }

---

Decoding algorithm:

function aes128_decode($data, $mode)
{
    switch ($mode) {
    case "ECB":
        $cipher = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_ECB, '');
        $key = substr(CIPHERKEY, 0, mcrypt_enc_get_key_size($cipher));

        // Fake iv to call mcrypt_generic_init
        $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($cipher), MCRYPT_RAND);
        $cipherData = base64_decode($data);

        if (mcrypt_generic_init($cipher, $key, $iv) != -1) {
            $originalData = mdecrypt_generic($cipher, $cipherData);
            mcrypt_generic_deinit($cipher);
            mcrypt_module_close($cipher);

            return $originalData;
        } else {
            return false;
        }
        break;

    case "CBC":
        $cipher = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
        $key = substr(CIPHERKEY, 0, mcrypt_enc_get_key_size($cipher));
        $parts = explode("_", $data);
        $iv = base64_decode($parts[0]); 
        $cipherData = base64_decode($parts[1]);

        if (mcrypt_generic_init($cipher, $key, $iv) != -1) {
            $originalData = mdecrypt_generic($cipher, $cipherData);
            mcrypt_generic_deinit($cipher);
            mcrypt_module_close($cipher);

            return $originalData;
        } else {
            return false;
        }
        break;

    default:
        return false;
        break;
    }
}

---

NOTE: The $mode variable indicates which mode of operation will be used (ECB or CBC). The CIPHERKEY is a constant with a randomized value that should be only known by the admin of the website.

Answer 1

Implementing AES alone is very risky, mainly because it is very easy to make a mistake. I strongly recommend you use phpseclib for this.

Also you should not use ECB mode unless you are encrypting only 1 block.

Answer 2

As I understand it, the only difference between AES and Rijndael is that AES is restricted to a 128-bit block size and can only use key sizes of 128, 192, and 256 bit. So if you are using Rijndael_128 with one of those three key lengths then you are uses AES.

If you must have something that says AES, then, as Chris Smith said, use phpseclib.

Answer 3

PHP may not have a built-in AES Encryption library but free one exist for ECB or for other type you may check that open source project. I strongly suggest to not reinvent the wheel because it can be error prone.