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Every time I have used a code-breaking activity in my lessons I have relished how pupils are captivated and keen to decode the secret message first. With exams finished, I decided to organise a cryptanalysis project for the 60 pupils in the parallel year 9 top sets that would really give them an opportunity to test themselves in an exciting area of maths in which there is a recognised shortage of recruits.
I arranged to take both classes off timetable for three one-hour lessons with the following structure:
LESSON 1: History of codebreaking
LESSON 2: Spy School
LESSON 3: Cryptanalysis Exercise
Given the proximity to the end of the year, I tried to draw in a range of different maths and history teachers, and an outsider speaker, in order to maintain an intensity that would mirror the WWII backdrop against the activities were framed. I approached David Stupples, a Professor of Systems and Cryptography at City University’s School of Engineering and Mathematical Sciences, who kindly agreed not only to present a lecture on the history of cryptography, but, moreover, to actually bring in a genuine WWII Enigma machine! He drew on early examples of codes from the ancient Egyptians and Romans before exploring the mathematics behind modern codebreaking. This led on to an opportunity for pupils to get up close with the Enigma machine and then try to use factorials to find out how many combinations were possible (1.075×1023). He continued by exploring the fundamental role codebreaking played in winning the war as analysts at Bletchley Park intercepted and deciphered German messages sent using Enigma. Finally he rounded off his talk progressing through the Cold War and looking at the role of cryptanalysts at GCHQ today in countering cyber-crime and cyber-terrorism.
For the Spy School I used activities that I had adapted from Charlotte King (@Chk_ing) after reading her article ‘My best lesson’ in The Guardian. The session was introduced by a history teacher who set the contextual backdrop and emphasised the importance of decoding German U-boat messages in order to ensure Britain received sufficient supplies through the war. Five maths teachers then took a 10 minute session each to cover; the Caesar cipher, the Pipgpen cipher, the transposition cipher, frequency analysis and the Vigenère square. As the last section came to a close, I used graphics from Mathew John James (@MatthewJohnJone) to simulate my computer being hacked by military intelligence. This set the scene for the final session of the day when pupils were provided with a series of coded messages which would require them to apply all the skills they had learned at Spy School to successfully decipher.
Incredibly, five groups successfully deciphered all of the codes before the end of the day which was tremendous testament to their enthusiasm and determination. This enabled pupils to access a final challenge: the chance to go down in history as a master cryptanalyst. I had previously come across an article on CIA Analyst David Stein who had taken more than seven years labouring over piles of gibberish to finally crack three of the four coded messages encrypted in the KYRPTOS sculpture at CIA headquarters. The fourth, however, remains unsolved and hence provided a unique opportunity for pupils to launch their cryptography career:
The staff were hugely impressed by the collaborative spirit within groups and the intense level of competition between them as they pitted their mathematical abilitites against each other to crack the codes first. In summary, Professor Stupples emphasised that this was not merely a historical exercise as, in years to come, GCHQ would be relying on people like them to continue to protect the UK from hostile actions!
Download all resources (including Professor Stupples’ presentation) here.