Text and key
The key is reduced to A-Z letters. For example, the key MOON repeats under the message: MOON MOON MOON...
Vigenère cipher
Encode or decode a message with a Vigenère key.
Codes
Use a keyword to encrypt or decrypt text with the Vigenère cipher. The conversion updates instantly and keeps the message structure visible.
Settings
Conversion direction
Only A-Z letters from the key are used. Accents in the text are converted to plain letters.
Source text
0 source char.
Result
Add source text.
Quick explanation
Enter text, choose encode or decode, then add the keyword. Letters are transformed with Vigenère, while spaces, digits, and punctuation stay visible.
Try this too
Need to compare A=0 and A=1?
Try Keyword shift to view key values, test A=0 or A=1, and enter a numeric sequence.
Additional information
Understanding the Vigenère cipher
The Vigenère cipher is a polyalphabetic cipher: instead of shifting every letter by the same amount as in Caesar cipher, it repeats a keyword and uses each key letter to choose a different shift.
A=0 convention
Vigenère usually uses A=0, B=1, C=2. If a puzzle may use A=0 or A=1, use Keyword shift.
Decoding
Decoding performs the reverse operation: each encrypted letter moves backward by the shift indicated by the keyword.
Simple example
| Step | Value | Explanation |
|---|---|---|
| Message | APP | Text to encode. |
| Key | KEY | K is 10, E is 4, Y is 24. |
| Result | KTE | A + K gives K, P + E gives T, P + Y gives E. |
For puzzle solving
Vigenère is common in treasure hunts, escape rooms, and hidden messages because the right keyword is enough to recover the text.
Simple case: Caesar
If the whole message uses one fixed shift, try the Caesar cipher.
Related tool
To see key values, compare A=0 and A=1, or enter a number sequence, use Keyword shift.
A bit of history
The cipher is associated with Blaise de Vigenère, a 16th-century diplomat and cryptographer, although several polyalphabetic ideas existed before him. To go further, read the Wikipedia article about the Vigenère cipher.
Related shift tools
If the shift is fixed, see the Caesar cipher. If that fixed shift is 13, ROT13 is the most direct tool.
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