Secret writing that no one can crack

Every time you send a message, something happens that no supercomputer on Earth can undo. Not because it's secret — the formulas are just sitting on Wikipedia. But because the math behind it is so clever that knowing how it works doesn't get you a single step further.

This site lets you take that math into your own hands. No video, no picture of a padlock with a little key. Every chapter has buttons, and behind those buttons runs the exact same code your bank, WhatsApp and your ID card use. You make a key, you encrypt something, you change one letter and you watch it all fall apart.

You need nothing for this except this browser. No prior knowledge, no advanced math. Every word you might not know gets explained right when you need it.

What you're going to discover

1. Base64: not encryption
   Why something that looks like secret writing usually isn't — and how you "crack" it in two seconds.
2. Hash functions
   How you turn a book into a 64-character fingerprint, and why no one can get the book back out of it.
3. Why password hashes break
   What really happens when a site gets "hacked", and why a good password survives anyway.
4. Symmetric encryption
   Julius Caesar's secret writing, and what's been improved on it in 2000 years.
5. Agreeing a secret in public
   Two people agree on a secret while everyone is listening in. Check the trick yourself on a clock face of 23.
6. Asymmetric encryption
   A lock anyone can click shut but only you can open — it sounds impossible and still works.
7. Practical applications
   Signatures, certificates and the padlock in your browser — the same handful of ideas, stacked differently each time.
8. Try it yourself
   Make your own key card, send unreadable messages and have the chip in your ID card sign something.

Three agreements