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?