Vigenère Cipher
Encode and decode with a keyword using the Vigenère, Beaufort or autokey cipher, and estimate the key length and key of a ciphertext. Free and private.
More options
This is not secure encryption: anyone can break it. Use AES encryption for real secrets.
Shortcuts: Ctrl+Enter run · Ctrl+Shift+C copy result · / search (use ⌘ on Mac)
Free Vigenère Cipher
A keyword decides how far each letter moves, so the same letter can become different letters. Choose a variant and enter your key. For a long ciphertext the tool estimates the key. It gives developers a quick browser-based way to solve a focused vigenère cipher task before moving the result into a project.
How to use Vigenère Cipher
Type the text and a key made of letters. When you decode a text with 100 or more letters, a key estimate is shown.
Common mistakes
- Expecting the estimate for a short text: at least 100 letters are needed.
- Using a key with digits or spaces: only the letters are used.
Frequently asked questions
How does the key work?
Each letter of the key is a Caesar shift. The first letter of the text uses the first key letter, the second uses the second, and the key repeats.
What are Beaufort and autokey?
Beaufort subtracts the letter from the key and is its own inverse. Autokey continues the key with the message itself, so it does not repeat.
How is the key estimated?
The index of coincidence of every n-th letter is about 0.065 for English and 0.038 for random letters. The shortest length that looks like English is chosen, then each column is solved as a Caesar shift.
Is anything uploaded?
No. The calculation runs in your browser and nothing you enter is sent to a server.
How do I use this vigenère cipher tool?
Use the interactive controls above; processing stays in your browser and the result is intended as a practical starting point for development work.
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