Question

In PHP, which (decryptable) encryption algorithm is most secure one?
I mean MD5 can’t be decrypted back right?
I’ve found full working class with mcrypt (then encoded with base64 again) which can encrypt and decrypt back.

Sample mcrypt (Encrypt):

function encrypt($value) {
    if(!$value){return false;}
    $text = $value;
    $iv_size = mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB);
    $iv = mcrypt_create_iv($iv_size, MCRYPT_RAND);
    $crypttext = mcrypt_encrypt(MCRYPT_RIJNDAEL_256, $this->key, $text, MCRYPT_MODE_ECB, $iv);
    return trim($this->safe_b64encode($crypttext));
}

Then encode again with base64:

function safe_b64encode($string) {
    $data = base64_encode($string);
    $data = str_replace(array('+','/','='),array('-','_',''),$data);
    return $data;
}

(Sorry for the code just with the encrypt, without decrypt. I just giving sample.)
But I just want to know if there other more secure algorithm then using mcrypt.

Answer 1

You probably want MCRYPT_RIJNDAEL_256. Rijndael with blocksizes of 128, 192 and 256 bit is a generalization of AES which only supports a blocksize of 128 bit.

See: http://us.php.net/manual/en/mcrypt.ciphers.php and http://us.php.net/manual/en/book.mcrypt.php