[next_xibalba]

Slightly off topic:

In school I only took one cryptography class (it was bundled with networking, at that), and to this day I still think it contained some of the most amazing concepts I've ever learned. Public-key cryptography being on the short list along with cryptographic hash functions. Maybe it's my particular bias, or maybe cryptography has just attracted some of the most creative genius' of the 20th century.

[Aachen]

What I find the most mind-blowing is that you can do a diffie-hellman-merkle key exchange in a room full of people, everyone can hear you, but the two participants are the only ones in possession of the encryption key after exchanging three messages (once to establish the parameters, once to convey one computed number in each direction). The math is simple enough to do by heart, at least as a demonstration (of course, it's not possible to compute numbers in your head that are so large a computer, doing billions of calculations per second, cannot simply iterate over all possible values and thus break it; but the principle works)

Didn't get this in school unfortunately. They made us implement DES S-boxes iirc and Caesar cipher breaking... all very relevant and foundational knowledge for non-mathematicians who will never design a secure cipher