Vigenere Cipher
Encrypt and decrypt text with the Vigenere keyword cipher.
The classic keyword cipher
The Vigenere cipher shifts each letter by an amount set by a repeating keyword, which makes it much harder to crack than a single Caesar shift because the same letter encodes differently depending on its position. This tool encrypts and decrypts text with the keyword you supply, so you can set puzzles or study a piece of cryptographic history.
For example the key "KEY" shifts the first letter by K, the second by E, the third by Y, then repeats — spreading the pattern across the whole message.
Security note and privacy
Historically strong, Vigenere is trivially broken by modern methods and is not real security, so never use it for anything sensitive. Both the text and your key are processed in the browser and are never uploaded.
Frequently Asked Questions
How is it different from a Caesar cipher?
A repeating keyword sets a different shift for each position, so the same letter can encode differently depending on where it falls.
Do I need the key to decrypt?
Yes. You must enter the same keyword used to encrypt in order to recover the original text.
Are my text and key private?
Yes. Both are processed in your browser and neither is uploaded.
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