Vigenère Cipher Decoder
Encode and decode Vigenère ciphers with a keyword. Great for classical cipher puzzles and CTFs.
Plaintext
This page is dedicated to Vigenère Cipher Decoder.
Letters only.
Offset shifts the starting zig-zag position before placing the first character.
Ciphertext
Vigenère Cipher Decoder — explanation, history & tips
Family: Polyalphabetic substitution
Era: 1500s–1800s
Strength: Weak (by modern standards)
The Vigenère cipher uses a repeating keyword to apply a different Caesar shift to each letter. Enter your keyword and this tool will encode or decode instantly, which is especially useful when you’re testing multiple keywords while solving puzzles.
- Pick Encode or Decode.
- Enter text (left for encode, right for decode).
- Type a keyword (letters only).
- The output updates instantly as you edit.
History (quick)
Popularised in Renaissance Europe and long nicknamed “le chiffre indéchiffrable” (“the indecipherable cipher”). It’s stronger than Caesar because the shifts change each letter, but it can be broken with techniques like Kasiski examination and index of coincidence.
Quick FAQs
Do I repeat the keyword?
Yes—Vigenère repeats the keyword to match the message length.
How do you break Vigenère without the key?
Estimate key length (Kasiski / index of coincidence), then solve each Caesar-like column with frequency analysis.
Are spaces/punctuation encrypted?
Most implementations leave non-letters unchanged; the keyword typically advances only on letters.
Want to decode with no key? Try our Cipher Breaker →