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    I really don’t understand this clue by Joan or the observation by michael1212. Can anyone please explain?



    @joan, do you mean reversing the words and keeping them in the same order, or reversing them along with the whole text?
    And does the punctuation stay where it is, or do you reverse it as if it were part of the word?



    Is the secret message obvious? I.e. when i find it, will i know that it’s that, and is it a part of the text, or is there some steganography?



    OFFICIAL CLUE: The cipher is something the Romans could easily implement and is based on the two principles of diffusion and confusion. We will say a bit more about this after the end of the challenge, but in practice there are two stages. First the text was encrypted using what we would now call a Hill cipher with vector length 12 (the ancients liked doing things in units of twelve) ignoring spaces and punctuation but then written down preserving the word structure. This provided an element of diffusion. Of course the Romans didn’t have matrix multiplication, so even though we can describe the cipher in this way, this particular Hill cipher doesn’t need that concept and is designed to be easy to implement by hand. Next the words were reversed (as in word -> drow) to confuse the cryptanalyst. You have seen similar things throughout the challenge, and again it is relatively easy to implement.

    To decipher the text you need to reverse the process, so first reverse all the words you see and then analyse the text bearing in mind that now you are trying to decipher a Hill cipher. You can actually get a long way by doing digram and trigram analysis at this point, and the fact that the word structure is there will help now. (With the words reverse it was hard to use that).

    Good luck and Happy New Year,

    Harry and the Elves



    OFFICIAL CLUE: @Cristina you just need to reverse each word, but keep them in the same order, e.g. “I am Joan.” Would become “I ma naoJ.” Hope this helps.



    OFFICIAL CLUE: about the secret message – when you have found it, yes you will know you have it. I will check in with Harry about clues for this as we are in the last few days.



    How do you solve a hill cipher? I am confused?



    I take my hat off to any ancient Romans trying to do any sort of multiplication (let alone matrix multiplication) with roman numerals!

    For those still struggling, I think that the non-Hill/matrix attack might be more accessible.

    As hill has been openly identified as one option, my suggestion is Autokey/Autoclave, a variant of the vigenere cipher and in my view a much more probable adaption of the ciphers developed in the Imperial Cipher School.

    You will still have to (i) find any primer, but @Tommo’s comments in this thread should help with that, then as the message starts to reveal itself, (ii) apply the period of 12 @michael1212’s insight should help with that one.



    I am still in the dark regarding the Hill cipher (solved it without matrices somewhere about Christmas Eve) nature of this… I will be very interested to see exactly how this relates to the method of solution which we used that bears more of a relation to evolution of the Vigenere cipher, where we treated every 12th character as a self-correction point



    Thanks Joan!



    Are we allowed to know the matrices for the Hill Cipher?



    Ok so apparently there was not a break over the holidays like I thought and I’ve been on holiday for the entire time so now I have a few days to compete the cipher and I’ll get hardly any points… that’s kind of unfair…



    @Flame of Ceaser I’m sorry that you thought there was a break in the competition. The dates were published on the website since the start. Hope you can still enjoy completing challenge 8.



    Yeah one of my teachers said we would get a break and my family plans holidays really early so it was already planned before the challenge even started.



    Will there be any more hints released for 8B?

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