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    Welcome to the Forum for the 21st National Cipher Challenge, The Empty Vault.

    This is a great (and safe) place to give us feedback, to ask questions, to support one another and to spend some time getting to know the others taking part. To keep it that way we have a few simple rules:

    Be friendly
    Keep on topic (start a new thread if you want to veer off in a new direction)
    Don’t publish anything which you would be embarrassed about later
    Don’t publish anything which gives away your identity

    If you are unsure about anything or there is anything we can help with that you don’t want to make public, then email us at [email protected]. We are always pleased to hear from you.


    Idk how to code break i am new to this, where should i begin?


    I’ll let some of our more experienced codebreakers answer this too, but you could start by taking a look at the official BOSS guide to codebreaking which is linked at the top of the Resources page. Feel free to ask for advice and guidance in the forum though, that I what it is for.
    Good luck,


    Hi everyone, I did this last year for the first time with my school and it was such a cool experience. They aren’t doing it again, but I wanted to see how far I could make it on my own (I didn’t get past challenge 9A last time).

    It was so much fun to learn how to code break from scratch, a test of my maths and programming skills, but, honestly, one of the most fun aspects of the challenge was the story that unravelled after you finally decrypted the code. However, I kind of petered off after the last few challenges and didn’t get to the end, and some of it was going over my head already. So I wanted to ask, how much of last year’s tale is nescessary to understand this one?

    Regardless I hope everyone has a lot of fun this year,


    Hi, I have a question

    I’m currently entering with my team, do all team members have to submit their solutions to the challenge? or does only one person have to



    Dear RXIW, only the team captain can enter solutions for the team, the others won’t see that option on the Challenge page. Harry


    Hi how do I start programming from scratch? I’d learnt caeser shift and affine shift with some good ol’ maths headbutting, but it seems the most efficient way to learn deciphering Vinegere and beyond I must learn programming. Where do I start and do I need to download some apps?


    Generally the procedure I follow with a cipher is:

    Make a function to decrypt it, it should work every time

    Find a value to use in hill climbing – for most ciphers this is tetragram fitness, sometimes you can use other values like IOC for vigenere to help.

    Make a function to calculate the value – for fitness you need to download a corpus, record ngram frequencies and store the logarithm

    Make the hill climbing script – iterate through digram, trigram and tetragram fitness making random swaps. Break the script when the key has reached a stable position.

    Once you have one of these, the only thing that really changes between them is the decrypt function. Just try to work through it bit by bit until it works.


    Thanks to the University of Southampton for once again running the excellent National Cipher Challenge.

    I recognize that the competition is written mainly for UK secondary school and sixth form students of mathematics and computer science, but if there are any interested parties following proceedings, who don’t fit into that group, but who would still like to join a collaborative team, then please feel free to get in touch here. We won’t win any prizes, but it could be fun.


    I am stuck on 4B and i’m wondering if I need a code that wasn’t listed or explained.



    I know I won’t be eligible for prizes after I finish my sixth-form studies, but would I still be able to participate in the cipher challenge post-18?

    Really wish I knew about cipher challenge a few years earlier!

    [We would be delighted if you would. We have a number of fans who take part every year just for the fun of it, including a number of competition alumni, their teachers and some overseas participants. Glad you want to stick around! Harry]

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