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?
Find the frequency distribution for ordinary English, and use it to help you crack the code.
How can Agent X transmit data on a faulty line and be sure that her message will get through?
This problem follows on from Substitution Cipher and Transposition Cipher
Below is a secret message. It's been double encrypted, first using a substitution cipher and then using a transposition cipher. Can you decipher it?
If you want to work on a computer, you can download the ciphertext as a text file here.
You can then use our Cipher Challenge Toolkit to help you decrypt it.
If you are interested in code breaking you might enjoy the Secondary Cipher Challenge.