Vigenere Cipher Encrypt/Decrypt
Vigenere cipher encrypt/decrypt tool with keyword-based polyalphabetic substitution, live conversion, and one-click copy for classical cryptography lessons and algorithm practice.
Input text
Key settings
A-Z only
Mode
Only English letters are shifted by the Vigenere cipher. Spaces, numbers, and symbols remain unchanged.
Result
The result will appear here
Documentation
What is the Vigenere cipher?
The Vigenere cipher is a classical polyalphabetic substitution method. It uses a keyword to control per-letter shifts and is less obvious than a single-shift Caesar cipher.
How it works
Repeat the key to match the count of letters in the input, then apply encryption or decryption character by character.
C = (P + K) mod 26P = (C - K + 26) mod 26
Non-letter characters stay as they are and do not consume key positions.
Examples
| Plaintext | Key | Ciphertext |
|---|---|---|
HELLO | KEY | RIJVS |
ATTACKATDAWN | LEMON | LXFOPVEFRNHR |
RIJVS | KEY | HELLO |
Security note
Historically called the “indecipherable cipher,” Vigenere can still be broken with modern frequency analysis and Kasiski examination, so it is best for learning and demonstrations.
Use cases
- Classical cryptography teaching
- Classroom demos and algorithm walkthroughs
- Security coursework verification
- Puzzle challenges and playful text obfuscation
How to use
- Enter text and provide a letter-only key
- Choose encrypt or decrypt mode
- Review the real-time output or load examples for validation
- Copy the result for downstream use