Introduction to Crypto

What is CTF Crypto?

Hey guys, Qu1ck5h0t here. I’m one of the crypto guys on the team, and I just so happen to be a founder/captain. I’m gonna walk you guys through the basics of CTF cryptography without the clanker slop (we have an unapologetically robophobic culture here at idk).

Here’s a secret they don’t tell you: fundamentally, it’s just maths. If you can read maths and read code, you’re golden. But if you’re here, chances are you can’t read maths. That’s fine, because that’s what I’m sacrificing my precious 1am time for instead of doing my chemistry coursework. But first, some yapping.

Why do CTF crypto?

Great question, because I’ve been asking myself this as well. Sure, most websites report the salary of a cryptographer to be somewhere between $100-200k USD, and although chances are you end up somewhere else in cyber, your crypto skills will come in use anywhere you go. So why do I do crypto? Because it makes my brain big! No, seriously, some say crypto is the hardest part of CTF and an argument I’d make in favour of that stance is that it’s the only CTF category that links maths and programming to real world attacks, or in other words you got a 3 in 1! Still not convinced? It’s really high demand since everybody wants to do web or forensics or rev. In fact, hard crypto challs are some of the hardest challs to AI solve, so you get to keep your job (as of 2026). Congratulations, you’re now an endangered species!

Ok now onto an overview of the cool stuff you’ll be doing.

There’s no way I can reasonably list everything you need to know on a single page, so here are the categories of the stuff we’ll go through

• Number theory and Lattices (assuming you know basic encoding and ciphers, this will get you a GOATED foundation that makes crypto easy)
• RSA Challs (super easy but often hidden in places that will make you cry)
• ECC (This stuff is pretty tough, but you’ll be fine if your foundations are good)
• Hash Functions (essentially weak hash + wordlists + birthday attack)
• Block Ciphers (remember kids, you can’t break AES but they’ll ALWAYS wrongly configure it)
• PRNG (if it doesn’t say CSPRNG, it can be broken. If it says CSPRNG and you see it in a chall, it’s not CSPRNG)
• Blockchain (actually I’ve seen people list this as its own category, and most blockchain challs are just smart contract exploits. I’ll run ya through the crypto aspects of it though, to give you an idea of what’s under the hood)
• Steganography (again, mostly a separate category but sometimes there’s a lot of maths in it and that’s where I’d claim a territory dispute)

Lastly, do PicoGym and Cryptohack along with whatever I write here. No, don’t go running off now, I just caught your attention :(

But seriously, those things help a lot. But more importantly, do real CTF challs in live CTFs. That’s how you actually get gud.

Fun fact: The cryptography docs on this site run on a perpetual, non exclusive, royalty free license shared with the docs hosted on my website (also writtem by me), which are (surprisingly)… the same docs