Vigenère Cipher
Encrypt and decrypt text with the Vigenère cipher using a secret keyword. A classic polyalphabetic substitution cipher with case-preserving output. Free online cryptography tool for students, CTF challenges, and puzzle solving — 100% client-side, no signup.
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What is Vigenère Cipher?
The Vigenère cipher is a classical polyalphabetic substitution cipher that encrypts text by shifting each letter according to a repeating secret keyword, defeating simple single-alphabet frequency analysis.
Key Benefits
- Stronger than Caesar
- Keyword-based
- Case preserving
- Educational
Common Use Cases
- •Cryptography study
- •CTF challenges
- •Escape rooms
- •Secret messages
How to Use the Vigenère Cipher
- Pick mode: Choose Encrypt or Decrypt.
- Enter keyword: Type a secret keyword (letters only).
- Paste text: Enter the plaintext or ciphertext to transform.
- Copy result: Copy the output, or hit Swap to reverse.
Key Features
- Encrypt and decrypt with a keyword
- Classic polyalphabetic cipher
- Preserves letter case
- Ignores non-alphabetic characters
- One-click swap between modes
- Case-insensitive keyword