Code cracking puzzles

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Crack the code breaking puzzles and learn not just about codes but also language, calculating frequencies and percentages. They can be as simple or hard as you like.
Learn about:
  • cryptography algorithms
  • frequency analysis
  • algorithmic thinking
  • computational thinking


  • literacy for fun
  • histograms
  • tally charts
  • patterns in letters and digraphs


Frequency Analysis

Can you crack our cipher and read our secret computing joke? Learn about frequency analysis, use histograms and tally tables as well as your knowledge of patterns in letters in English.

One-time pads

onetimepadThe British used an uncrackable cipher doing the war – the one-time pad. Here you can make one with a pack of cards and our lookup table. For a simpler version that doesn’t need a lookup table, but more work to make the resources, make your own cards of 1-26.

We ask the question why aren’t they used more…

Firstly the one-time pad has to be massive – one number for every letter you ever want to send. Secondly, the key exchange problem. The whole one-time pad is the key. You have to share that first, and you can’t just send it unencrypted! If Eve reads the one-time pad when you send it, she can read all your messages from then on. Also you can’t memorise it, so it has to be written down. If it is stolen, whoever has it can read all your past messages if they recorded them. Worse, if Trudy breaks in and takes a copy of the one-time pad, then all your messages in future can be read too.


christmastreesnowman-PIXABAY1033346Christmas Cryptography

Can you decipher this Christmas word: ZOFLTS ?

The key is to give it a go on your computer when you are bored!

Decrypt a sinister christmas message from Herod

  •   Perhaps you can crack Herod’s message yourself, If not read on and learn about Caesar Ciphers, and cribs, or just imagine you are the  the recipient who knows the key and must just use that key to decrypt it.

The Great Fire of LondonFireOfLondon

  • Here is a message to decipher  hidden in  a description of the Great Fire of London to match the Stuart theme of the cipher.  It uses the Bacon Cipher invented by Sir Francis Bacon.

Bacon not Turkey this Christmaschristmas-pig-PIXABAY152729

  •  Decipher the message hidden in the carol ‘Silent Night’ in this Tudor/Stuart based code-cracking puzzle. It uses the Bacon Cipher invented by Sir Francis Bacon.

The Knight’s Templar Ciphertemplarflag

  •  The Knight’s Templar invented international banking and their cipher may have been part of it from the start. Do our code cracking puzzle sheet about them.

Other Puzzle Sheets

Other EXTERNAL Resources on Computer Security