I have legacy system that has data already encrypt, Wanted to decrypt all inside php8

[KhairulAzmi21]

I try the code below , but does not working to decypt data that has been encrpyted during legacy system .I believe legacy system using php7.1

anyone could explain why ?

if (!function_exists('decrypt')) {
    function decrypt($data, $key = '@bMp74Gx7k3E#2f6')
    {
        
        $module = @mcrypt_module_open('rijndael-256', '', MCRYPT_MODE_CBC, '');
        $key = byteSubstr($key, 0, mcrypt_enc_get_key_size($module));
        $ivSize = mcrypt_enc_get_iv_size($module);
        $iv = byteSubstr($data, 0, $ivSize);
        mcrypt_generic_init($module, $key, $iv);
        $decrypted = mdecrypt_generic($module, byteSubstr($data, $ivSize, byteLength($data)));
        mcrypt_generic_deinit($module);
        mcrypt_module_close($module);
        return rtrim($decrypted, "\0");
    }
}
```
```

if (!function_exists('byteSubstr')) {
    /**
     * Extract substring based on byte length.
     *
     * @param string $string
     * @param int $start
     * @param int $length
     * @param string $encoding
     * @return string
     */
    function byteSubstr($string, $start, $length = null)
    {
        if ($length === null) {
            $length = byteLength($string);
        }

        return mb_substr((string)$string, $start, $length, '8bit');
    }
}

```
```
if (!function_exists('byteLength')) {
    /**

     * Get the byte length of a string.
     *
     * @param string $string
     * @return int
     */
    function byteLength($string)
    {
        return mb_strlen((string)$string, '8bit');
    }
}
```