Use the Vigenere Cipher Converter
Use this tool to Encrypt or Decrypt text with a repeating keyword. It preserves uppercase and lowercase letters. Digits, spaces, punctuation, and other characters outside A-Z/a-z stay unchanged and do not advance the keyword.
How to convert text
- Choose Encrypt or Decrypt.
- Check the Keyword field. It starts with
KEY. Type a different keyword if needed. - Type or paste text into the input. The result appears in the read-only output area when the input and keyword are valid.
- To load a file, use Upload to choose a file requested as
.txtortext/plain. You can also use Drop file; the tool reads the first dropped file as text without applying the picker's extension filter. - Use Copy or Download .txt below the result to save or reuse the converted text. Download saves it as
vigenere-cipher-output.txt.
Keyword validation and output behavior
Only A-Z/a-z characters in Keyword are used. Spaces, digits, and punctuation are stripped, and the remaining keyword is matched without regard to case.
A non-empty Keyword value containing no A-Z/a-z letters shows Keyword needs at least one letter (A-Z).
and produces no output. An empty Keyword clears the output without showing that message. Output is also cleared when the input text is empty. Decrypt text with the exact keyword used for encryption; another keyword produces garbled output.
How the cipher handles text
- The keyword letters repeat across the eligible text letters.
- Encrypt shifts letters forward through the alphabet, wrapping from Z to A.
- Decrypt shifts letters backward.
- Letter case is preserved.
- Digits, spaces, punctuation, and other non-A-Z/a-z characters pass through unchanged and do not consume a keyword position.
Files, copying, and downloads
The output is text-only. Upload opens a file picker requesting .txt and text/plain files. Drop file reads the first dropped file as text, even though it does not apply the same extension check. Download .txt creates vigenere-cipher-output.txt.
Limitations and privacy scope
The Vigenere cipher is not secure by modern standards. It is suitable for learning, puzzles, and simple text transformation, not for protecting sensitive data.
The inspected tool code performs conversion in browser JavaScript and reads selected files with the browser's FileReader. This confirms local processing in the tool code, but does not establish how shared site services such as analytics or hosting logs handle page activity.
Frequently Asked Questions
What is a Vigenere cipher?
It is a classic polyalphabetic substitution cipher that uses a repeating keyword. Each keyword letter determines the shift applied to the corresponding text letter.
How is the Vigenere cipher different from the Caesar cipher?
A Caesar cipher uses one fixed shift for the whole message. A Vigenere cipher uses a repeating keyword, so the shift changes across the message. A one-letter keyword behaves like a Caesar shift.
Does the keyword need to match to decrypt?
Yes. Use the exact keyword used for encryption and switch to Decrypt. A different keyword produces garbled output.
What characters can I use in the keyword?
Only A-Z/a-z letters are used. Spaces, digits, and punctuation are stripped, and the remaining keyword is case-insensitive.
What happens when Keyword contains no letters?
A non-empty Keyword value containing no A-Z/a-z letters shows Keyword needs at least one letter (A-Z).
An empty Keyword clears the output without showing that message.
Is the Vigenere cipher secure?
No, not by modern standards. It can be broken with cryptanalysis, especially with short keywords or long messages, so it should not protect sensitive information.
Is my text sent to a server?
The tool's conversion and selected-file reading run in browser JavaScript. The inspected tool code contains no upload request, but this does not verify all data flows from shared site services.