Vigenere Cipher Calculator
Pick a short message and keyword, letter by letter, to encrypt or decrypt them using the classic Vigenere cipher.
What this calculator does
The Vigenere cipher is a classic polyalphabetic substitution cipher from the 16th century that shifts each letter of a message by an amount determined by a repeating keyword, making it much harder to break than a simple single-shift (Caesar) cipher.
How it works
Choose a short message and a keyword, letter by letter, using the dropdowns (only A–Z letters are supported, matching the traditional cipher). Each message letter is shifted forward (to encrypt) or backward (to decrypt) in the alphabet by the position of the corresponding keyword letter, repeating the keyword as needed to cover the whole message.
This is a historical cipher included for educational purposes; it is not considered cryptographically secure by modern standards and should not be used to protect sensitive information.