Question 1

What is the Vigenère cipher?

Accepted Answer

The Vigenère cipher is a classical polyalphabetic substitution cipher invented in 1553 by Giovan Battista Bellaso. Each letter of the plaintext is shifted by a different amount based on a repeating keyword, making frequency analysis much harder than simple Caesar ciphers.

Question 2

Is Vigenère cipher secure today?

Accepted Answer

No. The Vigenère cipher is a historical cipher used for educational and entertainment purposes. It can be broken with Kasiski examination and frequency analysis. For real-world security, use modern authenticated ciphers like AES-256-GCM.

Question 3

What is autokey mode?

Accepted Answer

Autokey Vigenère uses the plaintext itself as part of the key stream after the initial keyword. The keystream becomes KEY + PLAINTEXT, which prevents simple Kasiski analysis based on key repetition. You can enable it under Mode.

Question 4

Does it preserve case and punctuation?

Accepted Answer

Yes. By default, the cipher only shifts letters and preserves case, digits, punctuation and whitespace. You can switch to A-Z only or full ASCII using the Alphabet dropdown.