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?
How can Agent X transmit data on a faulty line and be sure that her message will get through?
This was a very popular problem and we received many useful suggestions on how to tackle it. Thank you all.
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.
Our toolkit removes the drudgery of codebreaking while leaving you to do the hard thinking!
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!