Cryptopals

Over the recent Christmas break, I picked up the Cryptopals challenges again. After a four-year hiatus, I finally sat down to give the AES implementation another go, only to realize that I had misread the purpose of the challenge and was making it so much harder for myself.

This group of challenges focuses on AES ECB (Electronic Code Book), implementing CBC (Cipher Block Chaining) yourself, and decrypting an AES ECB ciphertext with a padding oracle.

I’ve recently started the cryptopals crypto challenges, and, frankly, even the basics are kicking my ass. However, I seem to be enjoying them, and I’m finally starting to understand some of the Computer Science topics I really should have listened to at University. If you are like me and prefer learning by getting your hands dirty and hacking some code together, then I highly recommend working through some of these challenges.

We’ve all used Convert.ToBase64String() but what is it actually happening under the covers? Sure, it’s taking a value and representing it using only characters from a range of 64 characters, but how exactly does it do that? Up until now, I probably couldn’t have told you.

My favorite example for understanding how Base64 encoding works is actually from Wikipedia...

The next few challenges cover implementing and then breaking the Caesar and Vigenère ciphers. These ciphers usually serve as the introduction to most cryptography books, as a history lesson of what we used to use and how easy they are to break. However, with cryptopals, we take this academic knowledge and turn it into practice.