Calculator
Key tools
The square is filled with the keyword's letters, each the first time it appears, then with the rest of the alphabet in order. Only letters count, and J is written as I.
The square below can also be edited cell by cell; it is then a custom square with no keyword.
Automatic Playfair solving is unreliable on short ciphertext. More text usually produces better results.
Advanced hints
A word or phrase you believe is in the plaintext. Solutions that contain it are ranked higher; it does not constrain the search, because in Playfair a known word does not pin down key letters the way it does in a simple substitution.
Background searching is not available here, most likely because this page was opened as a file instead of from a web server. Searches still work, but the page pauses while one runs, shows no progress, and cannot be stopped; Strong and Maximum effort can take a long while.
Several plausible solutions were found. More ciphertext may improve the result.
Search details
Prepare the message
- Original
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- Normalized
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- Prepared digraphs
Key square
in, solid border: the two letters of the pair. out, dashed border: the letters they become. A tinted line is the shared row or column. Edit any cell to change the key: the letter you type trades places with the cell that held it.
How your message is transformed
| Pair | Positions | Rule | Result |
|---|
Choose a row to see that digraph on the key square. Putting the cursor on a letter of your input chooses its digraph too.
Why are repeated letters separated?
Every Playfair rule moves two letters that sit in different cells of the square. A pair made of the same letter twice has only one cell, so there is nothing to move it relative to. A filler letter is therefore inserted between the two, and each is encrypted in a pair of its own.
If the doubled letter is the filler itself, a second filler is used: Q after an X.
Why do I and J share a cell?
A 5×5 square has 25 cells and the English alphabet has 26 letters, so one letter has to go. The standard Playfair convention writes J as I. The reader of the decrypted message decides from the context which was meant: IUST is easily read as JUST.
How does the rectangle rule work?
When the two letters are in different rows and different columns, they mark two opposite corners of a rectangle. Each letter moves along its own row to the other corner on that row, which is the column of the other letter. Doing the same again brings both letters back, so the rule is the same for encryption and decryption.
What happens to filler letters after decryption?
They are still there. Decryption gives back exactly what was encrypted, and that includes every X or Q inserted to separate a double or to complete the last pair. The receiver removes them by reading: HELXLO is obviously HELLO.
No rule can remove them with certainty, because a genuine X can stand in the same place, so this page marks the letters that could be fillers and deletes nothing.
Related topics
The Caesar, Affine and Substitution ciphers replace single letters, always the same way. Playfair differs because it encrypts pairs: the same letter becomes different letters depending on its partner, which hides single-letter frequencies, though not the frequencies of pairs.
The Vigenère Cipher hides letter frequencies in a different way, by changing the substitution from one position to the next.