Newbies
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Hello. If the a word in a sentence doesn’t make sense and it is on the website as that as well, should I just decrypt it as it is or do something else?
[EDIT, Harry: ALWAYS DECRYPT IT AS IT IS. It might just be a mistake, but it might not and in both cases we will mark your answer against a decrypt of what is published!]
Hi just how hard will the challenges get in a scale from 1-10? And when will we stop getting hints or tips to help us? I’m quite scared because this is my first time doing the National Cipher Challenge.
[EDIT, Harry: Ooooh, at least 12 on a scale of 1-10! Seriously, they do get pretty hard by the end, and not everyone will crack them all. The real question is, how far can you get this first time! And can you beat that next year? Good luck!!!]
Hi Harry.
It’s not cheating if you use websites to help, is it? Also, if you get the feeling that one of your peers are copying you, what should you do?
Thanks
from CipherGirl1, Jelly Bean Panda and Rick Astley 🙂[EDIT, Harry: It’s not really cheating at this point in the competition. We are still doing practice rounds and people are finding their feet. Later on websites will be less helpful (especially at the devilish end!) and for prizes we ask that submissions are all your own work. As for copying, again, this is still practice and we are all friends here, so I would not take that too seriously. Later on you might want to be a bit more circumspect!]
Dear Harry, me and my group don’t really understand frequency analysis and we’ve looked at numerous websites. Please can you explain the steps of using frequency analysis to us? Many thanks, the Encryptic Enterprise.
[EDIT, water_biscuit (I hope I’ll do!): Before how to do it, I’ll start with the point of the exercise: it begins with the observation that English uses (for example) the letter ‘e’ far more than the letter ‘z’. It turns out that it does so in a pretty predictable way: in any sufficiently long (and typical) English text, the letter ‘e’ accounts for around 12.5% of the all letters, ‘t’ for about 9% and so on, all the way down to ‘z’ at less than 0.1%. (I got these numbers from here: you can get slightly different numbers depending on how and what you count, but the basic pattern is always the same.)
So the aim of frequency analysis is to exploit this predictable pattern. If I have good reason to believe I’m dealing with a Caesar shift, and I can identify which letter occurs most frequently (particularly if it’s about 12.5%!) then there’s a good chance that if I line it up with ‘e’, I’ll be able to decode it. If I’m dealing with an affine cipher, them two letters and some maths is usually enough to work out what’s going on and how to decode it. So I might also guess which letter is ‘t’.
How you count is up to you: by hand is one (pretty tedious) option; another trick is to use find and replace in Word (find ‘a’, replace with ‘a’, and click “replace all”, which will tell you how many “replacements” it carried out). Or you could think about starting to write some code, or maybe using Excel, to do it for you. But having got the data, you can have a look at it: see if you can see a letter appearing a lot. Try lining it up with ‘e, and see if English comes out when you start to decode. If not, but the letters vary a lot, and in a similar pattern to the list at the link, it is probably still a substitution of some kind.
If I’ve got some substitution cipher, then having good guesses at a few letters will usually give me something to start from as I try and work out the rest. While you can get somewhere just with single letter frequencies, it can also be worth looking at how they appear in relation to one another. One example is ‘the’, which is the most common three letter word in English. Spot that and you’ve got three letters. Or you could ask “which letters can appear twice in a row?”. Or perhaps a long repeated section is an important word in the cipher (maybe ‘the shadow archive’ will appear more than once in some challenges this year, for example). Putting together lots of ideas like that, after maybe a few dead ends, will usually lead you to the right answer!
If I have a more complicated cipher, there is still useful information to be got from frequency analysis. But I think I’ve given you enough (maybe too much) information for the time being – see if you can get the hang of the technique in simple cases, and then maybe have another look at online tutorials!
(If you look at the codebreaking guide, you can see a worked example, as well as another explanation. I hope some of that was helpful!)]
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