Vigenère Cipher
What is a Vigenère Cipher?
Encrypt and decrypt text messages using the polyalphabetic Vigenère cipher substitution algorithm with custom secret keywords and Vigenère square matrices.
Why Use This Tool?
- Historical Cryptography Learning: Study classical polyalphabetic substitution ciphers.
- Geocaching & Puzzle Solvers: Crack Vigenère encrypted clues on puzzle websites and CTF challenges.
- Custom Keyword Ciphers: Encrypt text messages using secret shared key words.
How to Use
- Select Action: "Encrypt" or "Decrypt".
- Enter Secret Keyword (e.g. `LEMON`).
- Enter text message to view Vigenère ciphertext output.
Real Working Example
Input:
Text: "ATTACKATDAWN" | Keyword: "LEMON" | Action: Encrypt
Output Result:
Ciphertext: "LXFOPVEFRNHR"
Important Technical Details & Security Standards
- Polyalphabetic Shift Math: $C_i = (P_i + K_i) \pmod{26}$ where $P$ is plaintext letter and $K$ is repeated keyword letter.
- Preserves Non-Alphabetic Characters: Retains spaces, numbers, and punctuation while shifting alphabetic letters.
- Local Memory Execution: Fast in-browser processing.
Related Security & Crypto Tools
- ROT13 / Caesar Cipher: Monoalphabetic shift cipher.
- Base64 Encoder/Decoder: Encode Base64 text.
- Encrypt / Decrypt Text: AES-256 text encryption.
Frequently Asked Questions
What is the Vigenère cipher?
The Vigenère cipher is a method of encrypting alphabetic text using a series of interwoven Caesar ciphers based on the letters of a keyword.
Is the Vigenère cipher secure for modern privacy?
No, the Vigenère cipher can be broken using Kasiski examination and frequency analysis; modern security requires algorithms like AES-256.
What happens if the keyword is shorter than the text?
The secret keyword repeats sequentially until it matches the length of the text message.
Is it free?
Yes, 100% free.
Does it change numbers or punctuation?
No, standard Vigenère shifts only alphabetic letters (A-Z, a-z).
Is my text sent to an external server?
No, all encryption and decryption runs 100% locally in your web browser.