Puzzle tools
Vigenère cipher
Type your message and the keyword: the tool applies the Vigenère square letter by letter. Decoding needs the same keyword that was used to encode.
How does the Vigenère cipher work?
It is a Caesar cipher whose shift changes at every letter. Write the keyword under the message, repeating it as often as needed. Each keyword letter gives the shift for the letter above it: A shifts by 0, B by 1, C by 2… up to Z, which shifts by 25.
To decode, move each letter back by the shift its keyword letter gives. Spaces and punctuation are kept and do not use up a keyword letter.
Example
Message: “ATTACK AT DAWN”. Keyword: LEMON. Line up L, E, M, O, N, L, E… under the message, then shift: A + L gives L, T + E gives X, T + M gives F, and so on. Result: “LXFOPV EF RNHR”.
A bit of history
First described by Giovan Battista Bellaso in 1553 and later credited to Blaise de Vigenère, it was nicknamed “the indecipherable cipher” for almost three centuries. It took Charles Babbage and Friedrich Kasiski, in the 19th century, to find a reliable way to break it without the key.
Using it in an escape game
Vigenère makes a two-step puzzle: find the keyword, then decode. Hide the keyword in another clue (a book title, an engraved name, the answer to an earlier puzzle): that’s what makes the discovery so satisfying.
For beginners, pick a short keyword and hand out the Vigenère square as a document, or a link to this page.
Frequently asked questions
Can Vigenère be broken without the key?
Yes, but it takes work: guess the key length (Kasiski examination or index of coincidence), then break each column like a Caesar cipher. In an escape game, the key should be findable elsewhere.
Can the keyword contain spaces or digits?
Only letters count. Spaces and digits in the key are ignored, and accents are removed (é counts as e).
What is the Vigenère square?
A table of 26 rows where each row is the alphabet shifted one more place. The encoded letter sits where the message letter’s column meets the key letter’s row. The tool does that lookup for you.
Turn your message into a puzzle
On In-Evasion you build a free online escape game: every puzzle has its code, each code found opens the next one, and your players solve it all together on a shared board.