Try it yourself

Up to here you pressed a button in every chapter to see what an idea does. Now we turn it around: below you use those ideas for something. You make a key card you can keep on paper, you send a friend a message no one else can read, and you get the chip in your ID card to sign something.

Everything that happens here is real. No faked output, no "imagine that". The same calculations as your bank, your messaging app and the Belgian State.

1. Secret post: unbreakable messages
   Make your own key card, print it, swap it with your friends and send each other messages over WhatsApp that no one else can read.
2. The Belgian eID
   Put your ID card in a reader and watch everything from this site happen for real.
3. Signing a PDF with your eID
   Sign a real document with the chip in your ID card. Legally just as valid as with a pen.
4. Crack it yourself
   Four puzzles where the math is right but someone used it wrongly. Crack them yourself.
5. Build your own certificate
   Build a root certificate and a chain underneath it, break them with one letter, and find out why your browser still doesn't trust them.

On your own stuff. What you learn here about cracking weak cryptography, you try out on your own keys and on the puzzles waiting for you here. Not on someone else's systems — not even "just to see if it works". That's the difference between learning and breaking in, and only the first one is allowed.