You've helped them one at a time. The real understanding is how the ideas CONNECT — teach that next.
Caesar (the Caesar shift (one fixed shift for every letter)) ×Vigenère (the Vigenère keyword cipher (a rotating shift))
How is a Vigenère cipher built out of Caesar shifts?
Caesar then says: “With keyword "KEY", every letter shifts by the same amount — say +10 — the whole message.” — is that right?
The link: Vigenère is Caesar with a moving shift — that's exactly why it hides the letter-frequency pattern a single Caesar leaks.
Now they see it: the "unbreakable" cipher is really just Caesar, rotated by a keyword.
Mask (monoalphabetic substitution (each letter → one fixed substitute)) ×Sift (frequency analysis (breaking a cipher by counting letters))
Why can counting how often each symbol appears break a substitution cipher?
Mask then says: “Mask is safe from counting — swapping the letters scrambles how often each one shows up.” — is that right?
The link: Mask's fixed swap is exactly the weakness Sift attacks — the cipher and its cracker are two sides of one coin.
Now they see it: a cipher's strength is measured by what its BREAKER can and can't do.
Caesar (substitution — change WHICH letters) ×Rail (transposition — change WHERE letters sit (rail-fence))
What's the core difference between what Caesar does and what Rail does to a message?
Caesar then says: “Rail-fence encoding removes some letters, so the message gets shorter.” — is that right?
The link: Caesar and Rail are the two halves of cryptography — change the letters, or change their places. That's why frequency analysis breaks one but not the other.
Now they see it: every cipher is some mix of "swap the letters" and "shuffle their order".
Capstone — send one secret message
You're sending a secret note past a nosy classmate. Each part below needs ONE of the cast's ideas — bring in the right person for each.
Shift every letter forward by the same fixed amount.
Who do you bring in?
Make the shift CHANGE per letter using a secret keyword.
Who do you bring in?
Now scramble the ORDER of the letters without changing them.
Who do you bring in?
Turn the final letters into numbers to send over a number pad.
Who do you bring in?
The classmate intercepts a plain substitution note — crack it by counting letters.
Who do you bring in?
Notice what you just did: no single idea secured the message — you PICKED the right idea for each step and stacked them. That's what knowing cryptography really means.
The whole cast, working together — because you taught each one and saw how they fit.
Each idea is a person you teach. A filled circle is one you can teach; a solid line is a connection you've taught. Fill the map by teaching the cast + their connections.
