2
$\begingroup$

I am currently learning Rijndael's Algorithm through this site where there is a slide show animation step-by-step.
I understand nearly all of the encryption process except part of Add Round Key.
Looking at slides 16 & 17, it says:

Applying the RotWord ... to the previous word Wi-1

What is the RotWord and how do we apply it? Is it the same transformation in all rounds?

I can deduct (from the result on slide 17) that the RotWord transformation has done a shift upwards by 1 on the word:

+----+                 +----+ 
| 09 |                 | CF | 
+----+                 +----+ 
| CF |                 | 4F |  
+----+ --- RotWord --> +----+ 
| 4F |                 | 3C |
+----+                 +----+
| 3C |                 | 09 |
+----+                 +----+

Is my assumption of this transformation correct?
If so, will the amount shifted by change every round or does it remain constant?

$\endgroup$
  • 1
    $\begingroup$ Yes. See also en.wikipedia.org/wiki/Advanced_Encryption_Standard. There is a pseudo-code in NIST's AES standard document. I have a Python code that very closely follows that pseudo-code in s13.zetaboards.com/Crypto/topic/7385224/1/ $\endgroup$ – Mok-Kong Shen Aug 3 '16 at 8:28
  • $\begingroup$ @Mok-KongShen: if this is an answer, please submit it as an answer (so that it can be accepted) $\endgroup$ – poncho Aug 3 '16 at 21:14
2
$\begingroup$

Yes. See also en.wikipedia.org/wiki/Advanced_Encryption_Standard. There is a pseudo-code in NIST's AES standard document which is very helpful for implementors. I have a Python code that very closely follows that pseudo-code in s13.zetaboards.com/Crypto/7385224/1/. For details of the design of AES, see J. Daemen, V. Rijmen, The Design of Rijndael. (Springer-Verlag, 2002)

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.