# Codes and Ciphers - February 2012, All Stages

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

### What Was in the Box?

##### Age 5 to 7 Challenge Level:

This big box adds something to any number that goes into it. If you know the numbers that come out, what addition might be going on in the box?

### What's Happening?

##### Age 5 to 7 Challenge Level:

Shapes are added to other shapes. Can you see what is happening? What is the rule?

### What's in a Name?

##### Age 5 to 7 Challenge Level:

Here's a very elementary code that requires young children to read a table, and look for similarities and differences.

### Unlocking the Case

##### Age 7 to 11 Challenge Level:

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?

### It's a Scrabble

##### Age 7 to 11 Challenge Level:

Letters have different values in Scrabble - how are they decided upon? And would the values be the same for other languages?

### Some Secret Codes

##### Age 7 to 11 Challenge Level:

Can you follow the rule to decode the messages?

### Substitution Cipher

##### Age 11 to 14 Challenge Level:

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

### 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?

### Transposition Cipher

##### Age 11 to 16 Challenge Level:

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

### 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?

### Substitution Transposed

##### Age 11 to 16 Challenge Level:

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

### 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?

### More Secret Transmissions

##### Age 16 to 18 Challenge Level:

In 'Secret Transmissions', Agent X could send four-digit codes error free. Can you devise an error-correcting system for codes with more than four digits?

### Probably a Code?

##### Age 16 to 18 Challenge Level:

Is the regularity shown in this encoded message noise or structure?

### Stage 5 Cipher Challenge

##### Age 16 to 18 Challenge Level:

Can you crack these very difficult challenge ciphers? How might you systematise the cracking of unknown ciphers?