Question 1

What is the Vigenère cipher?

Accepted Answer

The Vigenère cipher is a polyalphabetic substitution cipher that uses a keyword. Each letter of the keyword shifts the plaintext by a different amount, repeating the keyword across the message. This makes it much harder to break than a simple Caesar cipher.

Question 2

How does the Vigenère cipher work?

Accepted Answer

Convert each plaintext letter to a number (A=0), convert each key letter to a number, add them modulo 26 to get the cipher letter. To decrypt, subtract the key value instead. The keyword repeats cyclically across the whole message.

Question 3

What makes Vigenère stronger than Caesar?

Accepted Answer

A Caesar cipher uses one fixed shift, so it has 25 possible keys. Vigenère uses a keyword, so the shift changes per letter. With a key of length n, it behaves like n interleaved Caesar ciphers, and brute-force becomes exponentially harder.

Question 4

Is my data safe?

Accepted Answer

Yes — everything is processed locally in your browser. Your text and key never leave your device.

Question 5

What should my key be?

Accepted Answer

Any word or phrase containing only letters. A longer key makes the cipher harder to crack. Example: 'LEMON' is the classic example key. Non-letter characters in the key are ignored.

Vigenère Cipher Encoder & Decoder

Keyword

Input

Result

How it works

Vigenère Cipher Encoder & Decoder

Keyword

Input

Result

How it works

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