Breaking Toy Ciphers: A Hands-On Intro to Applied Cryptography

A break-it-then-build-it course: no memorizing definitions, no proof-grinding. In every
session an AI mentor walks you through writing an attack, running it, and watching ciphertext
shatter into plaintext in front of you. We start by cracking the weakest toy ciphers —
single-byte XOR falls to frequency analysis in a blink, a repeating key gives away its length
to Hamming distance, a padding oracle decrypts without ever holding the key — so your intuition
grows out of the thrill of breaking things. Once you've broken enough, you turn around and build:
a toy RSA from scratch, a Diffie-Hellman handshake, hashing and HMAC, plus faithful re-creations
of real-world attacks like the e=3 cube root, length extension, and CBC bit-flipping. Everything
is pure-Python stdlib, offline, sub-second, and deterministic — every line you run is one you wrote.
By the end you'll finally know what's inside the box of the HTTPS, JWT, and signatures you use daily.