Page 1 of 1

Deriving Rijndael Key from Plain and Cipher Text

Posted: Thu Jul 01, 2010 8:49 am
by jonesy246
I'm implementing a solution for managing licenses using PHP's mycrypt functions - see example #2 at http://www.php.net/manual/en/function.m ... e-open.php.

I'm not going to go into massive detail of how my solution works, but what I want to know is if a person knows the:

1) Plain text
2) Ciphered version of that plain text
3) Initiation vector used to create that cipher text

Can they derive the encryption key used to convert the plain text to cipher text? I'm using rijndael-128.

Re: Deriving Rijndael Key from Plain and Cipher Text

Posted: Wed Jul 14, 2010 8:23 am
by Mordred
Not, unless you're doing something stupid, or you use a very weak key.

Having said that, if an attacker has the means to know your plaintext, maybe you should revisit the need to encrypt it in the first place.