RotWord in Rijndael's Algorithm 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 &amp; 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 --&gt; +----+ 
| 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?
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)