Classical Ciphers

Shift every letter by a fixed amount.

A repeating key defeats simple frequency analysis.

Every letter gets its own unique stand-in.

Electromechanical permutation — self-inverse by design.

The technique that broke every classical cipher.

The only theoretically unbreakable cipher — and why nobody uses it.

Rearranging letters instead of replacing them. Rail fence to ADFGVX.

Beyond Vigenère: Beaufort, autokey, Trithemius.

The attacker's toolkit: ciphertext-only, known-plaintext, chosen-plaintext, Kasiski, Friedman.