Vigenère Cipher

Encrypt and decrypt text with a Vigenère cipher keyword — free online cipher tool.

About

About the Vigenère Cipher

Encodes or decodes text with a Vigenère cipher, shifting each letter by an amount set by a repeating keyword.

Puzzle setters use it to create a harder-to-crack cipher than a simple Caesar shift, while students learning cryptography see how a keyword-based cipher works in practice. It's one of many free text tools on Toolapt, and like every tool here, it's free to use with no sign-up and no limit on how many times you run it.

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Guide

Using the Vigenère Cipher

  1. 1

    Step 1

    Type or paste your text into the Input box.

  2. 2

    Step 2

    Enter a keyword — the same keyword is needed to encode and later decode the message.

  3. 3

    Step 3

    Click Encode to encrypt the text, or Decode to reverse it using the same keyword.

  4. 4

    Step 4

    Click Copy to copy the result, or Clear to start over.

  • Encodes and decodes text using a Vigenère cipher with any keyword you choose
  • Shifts each letter by an amount that changes across the message, based on the repeating keyword
  • Leaves numbers, punctuation and spacing untouched, shifting only letters
  • Preserves letter case, so uppercase stays uppercase and lowercase stays lowercase
  • Works entirely in your browser — no installs and no sign-up
  • Free to use, with no limit on how many times you run it
  • Fully responsive, so it works just as well on a phone as on a desktop

Puzzle setters

Puzzle setters use the Vigenère Cipher for creating a harder-to-crack encoded message than a simple Caesar shift.

Students learning cryptography

Students learning cryptography use the Vigenère Cipher for seeing how a keyword-based polyalphabetic cipher works compared to a single-shift cipher.

History and cryptography enthusiasts

History and cryptography enthusiasts use the Vigenère Cipher for exploring one of the most famous historical ciphers, once called "le chiffre indéchiffrable".

Hobbyist coders

Hobbyist coders use the Vigenère Cipher for testing basic keyword-shift encoding logic before building it into their own project.

Examples

Vigenère Cipher examples

3 worked examples

01

Encoding a classic message

Encoding ATTACKATDAWN with the keyword LEMON produces LXFOPVEFRNHR, the textbook Vigenère example, since each letter is shifted by the amount its repeating LEMONLEMONLE key letter represents.

02

Decoding it back

Entering LXFOPVEFRNHR with the same keyword LEMON and clicking Decode returns the original ATTACKATDAWN.

03

Keeping case and spacing

Encoding "Attack at dawn" with keyword LEMON gives "Lxfopv ef rnhr" — spaces pass through untouched and letter case is preserved even though only letters are shifted.

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FAQ

Frequently asked questions

Quick answers to common questions about the Vigenère Cipher.

What does the Vigenère Cipher tool do?

It encodes or decodes text using a Vigenère cipher, shifting each letter by an amount determined by a repeating keyword you choose.

Is the Vigenère Cipher tool free to use?

Yes. It's free, with no sign-up, no watermark and no limit on how many times you use it.

Is my text safe when I use this tool?

Yes. Your text and keyword are processed entirely on your own device — nothing is sent to a server.

How is a Vigenère cipher different from a Caesar cipher?

A Caesar cipher shifts every letter by the same fixed amount, while a Vigenère cipher shifts each letter by an amount that changes according to a repeating keyword, making it harder to break by simple analysis.

Do I need the same keyword to decode a message?

Yes. You must enter the exact same keyword used to encode the message in order to decode it back to the original text.

Is the Vigenère cipher secure for real secrets?

No. While historically considered strong, it's now easily broken with modern cryptanalysis techniques, so it's best used for puzzles, learning and novelty rather than genuine security.

Does the cipher affect numbers and punctuation?

No. Only letters are shifted; numbers, spaces and punctuation are left exactly as they are.

Does this tool have any limitations?

It only shifts standard Latin letters A-Z and uses a Latin-letter keyword; it doesn't support accented letters or non-Latin scripts.

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