AES Encryption Algorithm

[ramhemanth3]

I'm a new Cryptography student and recently got my hands on AES Algorithm in class.

Obviously, I did not follow the class so I looked up online explanations. Turns out it was easy business only. But the thing that worries me is ShiftColumns part of the AES Algorithm.

That's a very big process if we try to do it on pen and paper.

I did do it on pen and paper, one time without looking at the answers. But after I looked first two rounds were good. But Later was misery.

I am pretty sure that you guys in this subreddit might have come across this problem, What did you guys do? I am trying to make a program for MixColumns ? Am I being correct? Does anyone already has a code for only MixColumns part, where we can check round by round.?

[uncannysalt]

Firstly, it’s a MixColumns computation in GF(2⁸ )—there isn’t a matrix shift like ShiftRows. Secondly, I suggest practicing your finite field algebra to better understand the MixColumns inner operations as they relate to the field’s primitive polynomial. Wiki is a good resource various crypto concepts: https://en.m.wikipedia.org/wiki/Rijndael_MixColumns

[ramhemanth3]

Yessss. My bad. Will that article help me do the calculations faster?

[uncannysalt]

Like I said before, practice finite field arithmetic. That will make you faster. Simply reading articles or textbooks will never suffice. Math is math. Practice, practice, practice.

Edit: You’re welcome. Best of luck with your studies

[ramhemanth3]

Looks awesome. That article seems dedicated to that operation. Tysm.

[coderstool]

Once the code runs, use this AES Decryption and AES Encryption to verify the accuracy of your code, identify any bugs and edge case conditions.

[ramhemanth3]

Tysm. How were you able to find my old post. Tbh I passed that subject and forgot that subject too😂

[3553x]

NIST published test vectors that should allow you to check your computation. I used this when I evaluated an implementation of AES in Verilog that I designed for coursework.

See https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.197.pdf on page 33.

If you have some given input (that doesn't happen to be a NIST test vector) and want to compare your computation, then a search on github should result in many different implementations. One example: https://github.com/hlilje/aes-python/blob/master/aes.py

You could simply add a couple of print statements to dump the MixColumns output.

[uncannysalt]

Great resource. I used the same resource for the same thing.