Cryptography
Cryptography gets taught as math homework — long proofs, Greek letters, modular arithmetic. Forget that. This section is not that. You do not need to build a cipher. You need to know what each tool does, what it promises, and what happens when someone uses it wrong. That last part is the one that gets people fired.
Here is why you should care, even if you never implement a single algorithm yourself.
It is what makes the internet trustworthy. Every time you log into a site over HTTPS, cryptography is doing three jobs at once: proving the site is who it says it is, keeping your password unreadable in transit, and catching anyone who tries to tamper with the data. Without it, the internet is a room where everyone can hear and edit everyone else’s mail.
It shows up in every CTF. Capture-the-flag competitions run a cryptography (crypto) category almost every time — a challenge track built entirely around this stuff. You do not need to be a mathematician to solve these. You need to recognize the primitive, know what it promises, and spot where a real implementation cut a corner.
Misusing it is one of the most common real-world vulnerabilities. Broken cryptography rarely means someone found a flaw in the math. The math is usually fine — mathematicians have beaten on these algorithms for decades. It fails because someone reused a key, rolled their own cipher, or hardcoded a password in the source code. That is a mistake you can learn to spot, and avoid, without ever touching a proof.
What’s In This Section
Two pages. Read them in order — the first gives you the vocabulary, the second shows you where it is actually used and how it actually breaks.
The Building Blocks
The primitives: hashing, symmetric encryption, asymmetric (public-key) encryption, digital signatures, key exchange, and randomness. Each one explained by the problem it solves, not by the equation behind it. Start here: The Building Blocks.
Crypto in the Real World
Where those primitives actually show up: TLS (the “S” in HTTPS), end-to-end encrypted messaging, and the CTF crypto category. Then the part that matters most — how crypto fails in practice, and it is almost never the math. Continue to: Crypto in the Real World.
One honest warning before you start: this section will not make you able to design a cryptographic algorithm. Nobody should be doing that outside of academic research — that is exactly the mistake covered in the second page. The goal here is smaller and more useful: read a system, know what protects it, and know what to ask when someone tells you it is “encrypted.”
- The Building Blocks The six cryptographic primitives explained by what problem each one solves, not by the math behind it.
- Crypto in the Real World How the primitives from the last page show up in HTTPS and encrypted messaging, and the specific mistakes that keep breaking them.