About the Vigenère Cipher
The Vigenère cipher shifts each letter of your message by an amount set by a repeating keyword. It was long thought unbreakable and was called le chiffre indéchiffrable. This tool encrypts and decrypts with any keyword made of letters, keeps upper and lower case, and leaves spaces, numbers and punctuation unchanged without using up a key letter. Type your text and a keyword and the Vigenère cipher appears at once, with a few related figures underneath, and you can copy the result with one tap. The sums run in your browser, so nothing you enter is uploaded.
Updated October 2026
How to use the Vigenère Cipher
- 1Enter your text and a keyword.
- 2Pick the units or options from the menus if the Vigenère cipher tool offers them.
- 3Read the Vigenère cipher in the large result box.
- 4Look at the extra rows for related figures.
- 5Press Copy result to keep the answer.
When you need the Vigenère cipher
People use it for puzzles, classes about cryptography and escape rooms. Learners compare it with the Caesar cipher to see why using several shifts is stronger.
A longer, random keyword is harder to break. A one-letter key turns the cipher back into a Caesar cipher, and a key as long as the message that is never reused becomes the unbreakable one-time pad.
How the Vigenère cipher is worked out
For each letter, shift by the next key letter (A = 0, B = 1 …). Encrypting adds the shift and decrypting subtracts it, wrapping around after Z. ATTACK AT DAWN with the key LEMON becomes LXFOPV EF RNHR. Decrypting with the same key returns the original message.
Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.
- Encrypt and decrypt
- Keeps case and punctuation
- Any keyword
Mistakes to avoid with Vigenère cipher
It is not secure by modern standards, since methods such as the Kasiski test can find the key length. Do not use it for real secrets; use proper encryption.
On phone and computer
On a phone, type into the boxes one after another and read the Vigenère cipher underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the Vigenère cipher move. The vigenère cipher works the same on both.
Checking your Vigenère cipher by hand
A good habit is to test the vigenère cipher with a case you already know. ATTACK AT DAWN with the key LEMON becomes LXFOPV EF RNHR. Decrypting with the same key returns the original message.
If your own figures give a surprising answer, repeat the working yourself: For each letter, shift by the next key letter (A = 0, B = 1 …). Encrypting adds the shift and decrypting subtracts it, wrapping around after Z. Small differences usually come from rounding, from mixing units, or from a typing slip in one of the inputs. A keyword makes the cipher harder to read than a plain shift. Try the ROT13 and Caesar Cipher for a simple shift, the Atbash Cipher for a mirrored alphabet, and the Rail Fence Cipher for a pattern of rows.
Features
- Letters-only key
- Not for real secrets
- A longer key is stronger
- Clear messages when the Vigenère cipher inputs make no sense
- Copy the result with one tap
- Private: nothing is uploaded
Frequently asked questions
How do I calculate Vigenère cipher?
For each letter, shift by the next key letter (A = 0, B = 1 …). Encrypting adds the shift and decrypting subtracts it, wrapping around after Z. ATTACK AT DAWN with the key LEMON becomes LXFOPV EF RNHR. Decrypting with the same key returns the original message.
What is the formula for Vigenère cipher?
For each letter, shift by the next key letter (A = 0, B = 1 …). Encrypting adds the shift and decrypting subtracts it, wrapping around after Z. The vigenère cipher applies it exactly and rounds only the displayed answer to six significant figures.
Is the Vigenère cipher secure?
Not any more. Statistical attacks break it, so it is for fun and learning.
What if my key has numbers?
Only letters are used in the key.
Does it keep spaces?
Yes. Spaces and punctuation stay and do not consume a key letter.
Is this vigenère cipher free and private?
Yes. It is free, needs no account and runs in your browser, so the numbers you type are not uploaded or stored.