Break a classical cipher yourself, meet the one provably unbreakable scheme and its fatal catch, then share a secret over a public channel with plain arithmetic.
3 units, about 3 hours. Free.
Break a Caesar cipher automatically and explain why letter patterns defeat substitution.
2Implement one-time pad encryption, prove key reuse leaks plaintext, and state why the perfect cipher is impractical.
3Use hash functions correctly for integrity and passwords, and perform a Diffie-Hellman exchange by hand.