Decoding a Playfair Cipher – Escape the Room in Cozumel

Though named after Lord Playfair, who insisted on using this method of encryption, the Playfair cipher was was invented by Charles Wheatstone in 1854 and was subsequently used by English-speaking militaries during both World War I and II. It is the first digraph code meaning that decoding the cipher is performed on blocks of two letters at a time. With the advent of computerized code breaking methods the Playfair is no longer considered safe or secure.

Hint: You will see this puzzle in Cozumel Detective Agency room escape experiences and live action puzzle hunt spy games in Cozumel, Mexico.

Once you have the all important key, deciphering a Playfair encrypted message isn’t difficult. See the video and the accompanying information below!

Once you know the key, the rest is very simple. You only need a pencil and paper to work out deciphering the rest of the coded message.

1. Draw a 5 block by 5 block grid.

2. Fill the key, one letter at a time and one letter per block, into the grid starting at the top left block. Work across the grid moving from left to right, one row at a time and from top to bottom.

Decoding a Playfair Cipher Tutorial3. Then fill in the rest of the grid in alphabetical order omitting all of the letters all ready included in the key. Because there are 26 letters in the English alphabet and only 25 block in the grid, some Playfair ciphers omit the letter ‘Q’ or substitute the letter “I” in place of “J”; it’s important to know which rules you are working with.

4. Next, draw a box around each cipher letter pairs you will find in grid and replace letters in cipher with decoded letters following these rules:

  • If the resulting box uses more than one row or column then replace the cipher letters with the decoded letters you find in the opposite corner of the same row.
  • If the resulting box forms a single row then replace each cipher letter with the decoded letter to its left in the same row; replace cipher letters in the first (furthest left) with the letter from the last column (furthest right) in the same row.
  • If cipher letters are in the same column, replace them with the decoded letters above them in the same column. Decode ciphers in the top row with the letters from the bottom row of the same column.

5. Lastly, make sense of the message by removing all unnecessary “X”s from the deciphered letters, add any “Q”s that are missing and fix spacing to read the deciphered message!

The Playfair cipher is used in many escape the room games around the English-speaking world due to its complexity, ease of use and the ease with which escape room game players can learn it while immersed in a game. Players of our room escape games in Cozumel have always enjoyed discovering and using this method of encryption (and a few have even sent their testimonials back to us encrypted using the Playfair cipher)!

Cozumel Detective Adventures LogoThe Cozumel Detective Adventures’ “Spycraft 101” article series was created for our arriving detectives to study up before heading to Cozumel and participating in our Cozumel Escape Room adventures, live action ISpy Cozumel spy game and our exciting underwater puzzle hunt, Sea Hunt Cozumel!

Every spy worth his salt is well-versed in the techniques used in espionage and the activity of intelligence.

We want to help you be the very best Cozumel Detective Agent you can be!

Solve the Puzzle. Save the Day!™

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