Vigenère & Polyalphabetic Ciphers
Understand how multiple alphabets defeat frequency analysis.
Welcome
The Vigenère cipher defeated frequency analysis for 300 years by using multiple Caesar alphabets in rotation, keyed by a repeating keyword.
Core Concept
Given key 'KEY' and plaintext 'HELLO': H+K=R, E+E=I, L+Y=J, L+K=V, O+E=S → ciphertext 'RIJVS'. Different letters encrypt the same plaintext letter differently.
All lessons in this course
- Caesar Cipher Mechanics
- Atbash & Affine Ciphers
- Vigenère & Polyalphabetic Ciphers
- Frequency Analysis & Cryptanalysis Basics