Free Vigenere Cipher Tool

Simple frequency analysis does not work because each letter can encrypt to many different ciphertext letters. Without knowing the keyword length, the cipher seemed to have unlimited keys.

Charles Babbage (1850s) and Friedrich Kasiski found that repeated patterns in ciphertext reveal keyword length. Once the length is known, the cipher becomes multiple solvable Caesar ciphers.

Longer keywords are better. Random letters resist dictionary attacks. Avoid names, dates, and common words. But remember - Vigenere is not secure for real use regardless of keyword.

Caesar uses one shift for all letters (monoalphabetic). Vigenere uses different shifts based on keyword position (polyalphabetic). This makes Vigenere much harder to crack by frequency analysis.

A 26×26 grid called the tabula recta. Each row is the alphabet shifted by one position. Find the intersection of the plaintext column and keyword row to get the ciphertext letter.

No, Vigenere is easily broken with computer analysis. It is valuable for education and puzzles only. Use AES or other modern encryption for real security.