Vigenère Cipher Encoder + Decoder

The Vigenère cipher uses a keyword to shift each letter by a different amount — much harder to break than Caesar (which uses a single shift). Designed in the 16th century, "broke" in the 19th. Still useful for puzzles, CTF challenges, and teaching cryptanalysis.

How to use the Vigenère Cipher Encoder + Decoder

Pick encrypt or decrypt. Type a key (letters only). Non-letter characters pass through unchanged. Case is preserved on output.