St Thomas of Canterbury, 18 January 2019

I started our second week of Bletchley Juniors Codebreaking Club with some pinprick codes. I had prepared by cutting out some newspaper articles and finding some jokes and punchlines that I thought the children would like. (“Why did the chicken cross the playground?” “To get to the other slide”. Admit it, that one is not that bad). The intention was to give one child the joke and another child the punchline. I used a pin to prick a hole above letters in the newspaper article which corresponded to letters in the joke.

I gave one article to the children and asked them to see how the message was hidden. None of them could: when you hold the article and look down you cannot see the tiny pinpricks. I asked the children to hold it up to the light. One child said they could see ‘sparkles’: when light is behind the newspaper each pinprick is revealed. However, things did not work quite as well as I had planned. When I tested this at home using my ceiling light fitting, it worked perfectly. But the light is very different in the school hall: the ceiling is much higher, the light fittings are different, and it was tricky for the children to see all the pinpricks. We went over to the doors, and were able to get just enough light through the windows (it is January) to read the messages, giving the children a bit of help. The lesson I learnt was to test things like this in the school environment first, as I cannot assume that something that works at home can be replicated in the school hall. On the other hand, the fact that the messages were hard to read does prove that the pinprick code is a useful way to hide a message from someone who does not know where to look for it.

The second part of the session used a book cipher. I had borrowed several copies of the same novel from Year 6. I had written a message for each child, then encoded the message as a book cipher. Each letter was encoded as a set of numbers e.g. 17, 3, 4, where 17 is the page number, 3 is the row, and 4 means count four letters along starting on the left. I wrote out the ciphers in a long list, one per row. After prompting them to write each letter out again along one row, each child was able to decode their message. I think they enjoyed having a message that was personal to them, based on their interests. We ended the session by reading out the jokes from earlier. I am pleased to report the chicken joke got the biggest laugh.

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