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And that’s a wrap!

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    Congratulations to all of you who took part in this year’s National Cipher Challenge, we very much hope you enjoyed it! We will be contacting everyone who completed Challenge 7B before the first deadline to personally congratulate them and, if they might be in the running for a prize to discuss eligibility etc.

    The competition is about a lot more than prizes, and we hope you have learned a lot taking part. This year’s story was inspired by real events in the pre-war period and some of the characters were inspired by real individuals, though there is no evidence that the spyclists knew of, or tried to demolish, the Chain Home radar system. It was a key part of our defence against the air war and while several nations developed radar systems Chain Home was the first wide scale air defence system to be deployed and it heralded innovations that changed the world.

    We can’t be sure whether or not any of the original suspected spyclists were an important part of Nazi espionage, but Vernon Kell, head of MI6, certainly thought it possible and the police were asked to keep an eye on them. You might also be able to work out what the initials of several individuals stand for if you look up Nazi intelligence and Tirpitzufer, but of course the characters in this story are entirely fictitious. One who appears only briefly at the start of the story, Jessica, is based on a real Nazi spy and again, you might have fun trying to work out who she was. The history of that troubled time is fascinating, and I enjoyed learning about it. Once more though, the events depicted here are entirely the product of my twisted imagination, so don’t get too confused between fact and fantasy.

    Those of you who took part in the Special Edition of the challenge in the Spring learned about the attempts by British intelligence to prevent the Nazis from developing an atom bomb. That story overlaps this one, which is why Harry was mostly absent. The other difference is that much more of that story, including the main characters, was based on history. It is a fascinating tale of courage and initiative and well worth investigating. You can find our version at if you want to catch up.

    Next year will be the 20th official anniversary (though the Special Edition really made CC2020 the 20th national challenge) and we are starting to think about how we can make it really special. We introduced several new things to the competition over the last year or so, but if you have any ideas about how we can improve it, or ways in which we can encourage more people to take part, then let me know. You can post here, tweet or message us, or email [email protected].

    I need to finish with a special thank you to Madness. A stalwart of the competition for a long time now and Cipher Challenge archivist, this year’s final challenge was developed in partnership with him. I thoroughly enjoyed reading his deep insights into the clock cipher, and the beautifully produced technical reports were all his own work, as was the working model of a clock cipher machine that we posted about. The National cipher challenge is a community as much as a competition and we know that you all learn a lot from one another, so we hope that you will help us to keep the community alive. Madness has offered to make his codebreaking textbook available as a pdf on request, so if you would like a copy then email me and I will send you a link.

    It is a pleasure and privilege to be involved in this amazing group. I wish you all the very best and look forward to welcoming you all back to CC2021 in a few months.In the meantime, and especially while you are waiting to see the final standings, please keep the forum alive with your jokes, questions, puzzles, and challenges.

    Best wishes,



    It was fun. Where did you post the working model? I am happy to share the images for the laser-cutting.


    Thank you very much Madness. You have all the qualities of a good teacher.


    Thank you so much Harry (and Madness!). The competition was great fun – it was my first year so I didn’t manage to crack week 7 (although I got very close to getting 7A) and I learnt so much about cryptography and ciphers.

    [Thank you, we really enjoyed it too. Hope you and your friends will be back next year. Spread the word, Harry]


    Thanks Harry and Madness. this was our first year so we didn’t get 7b. Are you going to be releasing the encryption key… Or are you going to leave us hanging? This was a really fun after school challenge for us and my team enjoyed it, well apart from the stress of solving the ciphers before the deadline – some of my team are very competitive. I am sure that we will do next year’s challenge. Thanks once again.


    A thought about next year….
    It would be great if you could release instructions after the competition on how to solve the ciphers. For beginners especially I think this would be really helpful as it would help me to understand how the message was encrypted and learn more for next time.
    Thanks again Harry and the whole Cipher Challenge team.

    [Thank you, we will! If you look in the BOSS Training Division page you will find accounts by past winners of how they cracked the final challenge. We will do something similar this year, though you already have the fabulous technical reports by our experts telling you everything we know about the Clock Cipher! All the best, Harry]


    Thank you so much for your work in organising this challenge every year. You have inspired a generation of pupils, encouraged teamwork, highlighted the need for resilience and determination – whilst being such great fun with all the back stories. Love it love it love it.

    [Thank you very much! Please spread the word. We love doing this and would love it even more if everyone was taking part. Harry]


    Really well-organised and fun competition Harry, Madness and the rest of the team!

    Are we allowed to publicly discuss the methods to solving the challenges at this point or should we wait a bit until winners are decided?

    [I would prefer to postpone a bit until I have heard back from the potential winners. Not long I hope. Harry]


    Thank you for the challenge!

    [No problem, really glad you enjoyed it! Harry]


    Thank you so much Harry, Elves, Madness (and sponsors IBM, Cloud Digital, Bluespark Foundation, Engineering & Physical Sciences Research Council, Trinity College Cambridge, GCHQ, Netcraft and the Institute of Mathematics and its Applications).

    A great competition in very difficult circumstances. Hats off! Stay safe.

    [Thank you, our sponsors will be very pleased you said that! Best wishes, Harry]


    Honestly, thank you so much to all the team and all the competitors who made this possible.

    Top marks to all the Elves, who must dedicate so many hours scrolling through comments to be moderated, and for connecting the forum community.

    Well done all, and I cannot wait for next year.

    On that note, it is all over till next year right? Is there another challenge this spring like last year’s (which I have heard about on the forum)?

    Thank you for making this possible


    @Mattyrat2027, I have heard rumors from naughty elves that something evil is coming. Stay tuned.


    Forgot to post this but thank you to the people who made the challenges and made this all happen. This was my first year participating. 7B provided a great learning experience to me. I’ve also learnt a lot from the forums (especially the methods madness talks about) and hopefully I will be able to understand and implement some of these next year!

    Thanks again!


    Thanks to Harry, the elves, Madness and all others for making this possible! The challenges were greatly enjoyed and learning about ciphers is always a fun experience, either through the missions themselves or through the Forum. Hoping to be back next time for some more deciphering!


    Hi Harry, thank you for clarifying — please let me know when you receive all the responses from potential winners as the the cryptanalysis of 7B is so interesting that it would be cool to discuss it.

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