Codes and Ciphers - February 2012, Stage 3&4

We're celebrating the centenary of Turing's birth with lots of engaging tasks on codes and ciphers, devised with the help of James Grime of the Enigma project. We hope they stimulate interest in this intriguing field.

Problems

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Substitution Cipher

Age 11 to 14 Challenge Level:

Find the frequency distribution for ordinary English, and use it to help you crack the code.

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The Best Card Trick?

Age 11 to 16 Challenge Level:

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?

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Transposition Cipher

Age 11 to 16 Challenge Level:

Can you work out what size grid you need to read our secret message?

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Secondary Cipher Challenge Part 1

Age 11 to 16 Challenge Level:

Here is the start of a six-part challenge. Can you get to the end and crack the final message?

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Substitution Transposed

Age 11 to 16 Challenge Level:

Substitution and Transposition all in one! How fiendish can these codes get?

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Secret Transmissions

Age 14 to 16 Challenge Level:

How can Agent X transmit data on a faulty line and be sure that her message will get through?