Vigenere CipherEncrypt and decrypt text using the Vigenere cipher with a keyword.
Vigenere Cipher
Encrypt and decrypt text using the Vigenere cipher with a keyword.
Enter Input
Type or paste your input.
View Output
Results appear in real time.
Copy Result
Click Copy to copy the output.
What Is Vigenere Cipher?
Polyalphabetic substitution cipher from the 16th century. Keyword determines different shifts per letter. Called le chiffre indechiffrable for 300 years until Kasiski (1863). Only letter keyword chars used. Pure JavaScript.
Why Use Our Vigenere Cipher?
- Fast, accurate processing
- 100% client-side — data never leaves your browser
- Free online tool with no signup required
- Mobile-friendly with 44px touch targets
Common Use Cases
Development
Use in software development workflows.
Security
Cryptographic and security applications.
Education
Learn about algorithms and techniques.
Verification
Verify and validate data integrity.
Technical Guide
C[i] = (P[i] + K[i mod keyLen]) mod 26. D[i] = (C[i] - K[i mod keyLen] + 26) mod 26. Keyword cleaned to uppercase. Key index advances only for letters.
Tips & Best Practices
- 1All processing happens in your browser
- 2Results are deterministic for the same input
- 3Use Copy button to quickly grab output
- 4Works on mobile devices with touch-friendly interface
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Encoding & CryptoFrequently Asked Questions
QIs this tool free?
QIs my data secure?
QDoes it work on mobile?
QWhat browsers are supported?
QCan I use this offline?
About Vigenere Cipher
Vigenere Cipher is a free online tool from FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration required. No ads. Just fast, reliable tools.