I like teaching people, and I strongly believe in learning by solving challenges. That’s why I’ve prepared quite a few CTF-like tasks teaching security basics - like cryptography.

They are meant to be used as a part of lecture, but have enough context to be solved without a formal introduction.

Cryptography

Pseudo-randomness

Your task is to predict the next number generated by this RNG.

• LCG challenge

Symmetric Ciphers

They say that “encryption is not authentication”. Prove them right by circumventing the simulated “session” mechanism implemented using various encryption methods.

• Stream cipher (RC4) challenge
• ECB mode challenge
• CBC mode challenge
• CTR mode challenge

Final Assignments

(unsolvable without source code, I’ll add it here someday)

• Crypto final assignment 2022: nc mimcrypto2022.var.tailcall.net 30006
• Crypto final assignment 2023: nc mimcrypto2023.var.tailcall.net 30007

Reverse Engineering

• RE final assignment 2024

More challenges

I actually created dozens (really) more CTF challenges, but most of them are not hosted anywhere anymore. A great collection of tasks - including mine - that I recommend is hack.cert.pl.