Vigenère cipher online

How does the Vigenère cipher work?

What is this method?

Uses a repeating keyword to apply a different shift to each letter.

How does it work step by step?

Each keyword letter represents a shift from 0 to 25. The key repeats above the message, so the same plaintext letter may be encoded differently depending on the corresponding key letter.

Example and practical use

Enter a message and the keyword “REBUS”. Successive key letters choose a different shift for every letter of the text.

How to use the tool

Choose encryption or decryption, enter a message and set the parameters required by the Vigenère cipher. The result is calculated locally in your browser and can be copied or shared without sending the text to a server.

History of the cipher

The method grew from ideas by Alberti and Trithemius and was later associated with Blaise de Vigenère. In the nineteenth century it was called the “indecipherable cipher” before effective attacks became known.

Security and limitations

This tool is educational. Classical ciphers can usually be broken with frequency analysis, repetition patterns or a small search through possible keys, so they should not protect confidential information.