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Vigenere Cipher

Vigenere Cipher

Encrypt and decrypt text with the Vigenere cipher using a custom keyword and selectable alphabet. One of the most famous polyalphabetic ciphers in classical cryptography.

Input
0 chars · 0 bytes
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Result
✓ Polyalphabetic substitution cipher ✓ Customizable keyword ✓ We never store your messages ✓ Processed on our server
Examples
Encrypt ATTACK AT DAWN Key: LEMON
Input ATTACK AT DAWN
Output LXFOPV EF RNHR

Keyword: LEMON. Mode: encrypt. Each keyword letter creates a different Caesar-style shift.

Decrypt LXFOPV EF RNHR Key: LEMON
Input LXFOPV EF RNHR
Output ATTACK AT DAWN

Keyword: LEMON. Mode: decrypt. The same keyword restores the original message.

Repeating keyword example Key: KEY
Input HELLO WORLD
Output RIJVS UYVJN

Keyword: KEY. The keyword is repeated automatically when the text is longer than the key.

Preserve spaces and punctuation Key: SECRET
Input HELLO, WORLD!
Output ZINCS, PGVNU!

Only alphabet characters are encrypted. Spaces, punctuation marks, and other symbols remain unchanged.

How Vigenere cipher works

The Vigenere cipher is a polyalphabetic substitution cipher that uses a keyword to determine how each letter in the message is shifted. Unlike the Caesar cipher, which uses a single shift value, Vigenere applies a different shift for each character based on the corresponding letter of the keyword.

If the keyword is shorter than the message, it is repeated until the entire text is processed. Each keyword letter defines a Caesar-style shift, creating a sequence of changing substitutions across the message.

This approach makes simple frequency analysis more difficult and historically made the Vigenere cipher one of the most important classical encryption methods.

Vigenere vs Caesar cipher

The Caesar cipher uses a single constant shift for the entire message. The Vigenere cipher improves on this idea by using a keyword that changes the shift from letter to letter.

Because multiple substitutions are used throughout the text, Vigenere is generally more resistant to basic cryptanalysis than Caesar. However, it is still considered insecure by modern standards.

History of the Vigenere cipher

The Vigenere cipher is named after the French diplomat Blaise de Vigenere, who described a related polyalphabetic encryption method in the 16th century. For centuries it was considered one of the strongest practical ciphers available.

Because it resisted simple frequency analysis, the cipher earned the nickname 'the indecipherable cipher' before more advanced cryptanalytic techniques were developed.

FAQ

A Vigenere key is a word or phrase used to generate the sequence of shifts applied during encryption and decryption.

Yes. The Vigenere cipher changes the shift value throughout the message, while the Caesar cipher uses only one constant shift.

Spaces, punctuation marks, numbers, and other non-alphabet characters are usually preserved and are not encrypted.

Yes. The keyword is automatically repeated until the entire message has been processed.

No. While it is much stronger than simple substitution ciphers, modern cryptanalysis can break Vigenere-encrypted messages relatively easily.

The cipher is traditionally associated with Blaise de Vigenere, although similar polyalphabetic techniques existed before his work.
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