A case is found with a combination lock. There is one clue about the number needed to open the case. Can you find the number and open the case?
Letters have different values in Scrabble - how are they decided upon? And would the values be the same for other languages?
Can you follow the rule to decode the messages?
Find the frequency distribution for ordinary English, and use it to help you crack the code.
Time for a little mathemagic! Choose any five cards from a pack and show four of them to your partner. How can they work out the fifth?
Can you work out what size grid you need to read our secret message?
Here is the start of a six-part challenge. Can you get to the end and crack the final message?
Substitution and Transposition all in one! How fiendish can these codes get?
We had the most blogs yet for this task, many from Brynmill School in Swansea. These and others can be viewed at our Infinities blog. Randley School in England also sent in a number of observations from their children, Olivia, Anna, Jamie and Harvi.
Go to last month's problems to see more solutions.
Simon Singh describes PKC, its origins, and why the science of code making and breaking is such a secret occupation.
Dr James Grime takes an Enigma machine in to schools. Here he describes how the code-breaking work of Turing and his contemporaries helped to win the war.
The Enigma Project's James Grime has created a video code challenge. Watch it here!