Vigenere Cipher
Encrypt and decrypt text using the Vigenere cipher with a customizable keyword.
About Vigenere Cipher
Our free online Vigenere Cipher tool allows you to encrypt and decrypt text using one of the most famous polyalphabetic substitution ciphers. The Vigenere cipher uses a keyword to shift each letter of the plaintext by a different amount, making it significantly more secure than simple substitution ciphers.
Developed in the 16th century by Blaise de Vigenere, this cipher was known as "le chiffre indechiffrable" (the indecipherable cipher) for centuries. It wasn't until the 19th century that Charles Babbage and Friedrich Kasiski developed methods to break it.
This tool processes your input entirely in the browser using JavaScript, ensuring your data never leaves your device. Encrypt or decrypt Vigenere cipher messages instantly with any alphabetic keyword.
The auto-convert feature updates the output in real-time as you type or change the keyword, making it convenient for experimenting with different keys and understanding how polyalphabetic substitution works.
Features
Fast Conversion
Encrypt and decrypt text instantly with no registration or limits. Completely free to use.
Auto-Convert
Automatically update the output as you type for real-time encryption and decryption.
Keyword-Based
Use any alphabetic keyword for flexible and personalized encryption and decryption.
One-Click Copy
Copy the encrypted or decrypted text to clipboard with a single click.
Preserves Formatting
Non-alphabetic characters like numbers, spaces, and punctuation are preserved unchanged.
Privacy First
All processing happens in your browser. Your data never leaves your device.
How to Use
Select Mode
Choose Encrypt to encode your text, or Decrypt to decode a Vigenere cipher message.
Enter Your Keyword
Type your encryption keyword. Only letters are used; the key is repeated to match the message length.
Enter Your Text
Type or paste your text into the input editor on the left.
Convert and Copy
Click Convert or enable auto-convert. Copy the result to your clipboard with one click.
Frequently Asked Questions
What is a Vigenere cipher?
A Vigenere cipher is a polyalphabetic substitution cipher that uses a keyword to shift each letter of the plaintext. Each letter of the keyword determines the shift amount for the corresponding letter in the message, making it more secure than simple substitution ciphers.
How does the Vigenere cipher work?
Each letter of the keyword is converted to a shift value (A=0, B=1, ..., Z=25). The keyword is repeated to match the length of the message. Each plaintext letter is then shifted by the corresponding keyword letter's value. For decryption, the shift is reversed.
How secure is the Vigenere cipher?
The Vigenere cipher was considered unbreakable for centuries, but methods like the Kasiski examination and Friedman test can crack it with sufficient ciphertext. It is not secure by modern standards but remains an important historical cipher.
What happens to non-letter characters?
Non-alphabetic characters such as numbers, spaces, and punctuation are not modified and do not consume a letter from the keyword. They pass through unchanged.
Is this Vigenere cipher tool free?
Yes, it is completely free to use with no registration, sign-up, or limits. You can use it as many times as you need for personal, educational, or commercial projects.
Does it work offline?
Yes, once the page is loaded, all Vigenere cipher encryption and decryption happens entirely in your browser using JavaScript. No server communication is needed after the initial page load.