PopCo by Scarlett Thomas Page B

wasn’t a Caesar shift cipher, that’s for sure: you can tell one of those just by looking at it. A Caesar shift cipher is one of the most simple of all substitution ciphers, and involves one of two identical alphabets being simply ‘shifted’ one way or the other. If ‘a’, for example, is enciphered as Z then that’s a shift of minus-one. Every letter will be enciphered as the one just behind it in the alphabet. In this system, with a shift of minus-one, if you found a C in the ciphertext, you’d know it was actually a ‘d’ and so on. One of the most famous contemporary uses of a Caesar shift cipher is, according to SF geeks, in the naming of the fictional computer HAL from 2001, A Space Odyssey . Taking into account a Caesar shift of minus-one, HAL of course reads IBM . I used to have a little Caesar-shift wheel, where you could set the letter A to any other letter in the alphabet and the rest would just follow from there. But I did so many of those things when I was a kid that I eventually didn’t need the wheel, and somehow became familiar with twenty-six different ways of, for example, spelling the word ‘and’. BOE, CPF, DQG and so on. It must have been when I was nine or ten, and my grandfather communicated with me almost exclusively in this way until I learnt more sophisticated methods of cryptanalysis, at which point he began using more complicated ciphers to leave me notes that said things like: ‘Gone to the shop for milk’, or ‘Back later’.
    Another thing about Caesar shift ciphers, like almost all ciphers, is that they have their own little conventions that you can look out for. The text in my pocket starts with the letters XYC, if I remember correctly. Caesar shift ciphertexts don’t usually start with two consecutive letters for the simple reason that not many sets of two consecutive letters in the English alphabet actually form the beginnings of sensible, common words. You’ve got A and B, which are pretty rare together at the beginning of words; S and T, which are the main two to watch out for – but I’ve already done it in my head and it’s not S and T (the third letter would be X if it were); H and I, N and O, O and P, and of course D and E, which, rather worryingly, do start the word death . But, if this were a Caesar shift cipher and the first two letters were D and E, then the third would be I. Unless someone’s writing to me about a deity this isn’t very likely. The thing to watch out for, though, is that the Caesar shift could merely be the first layer of code and that when you lookat the beginning of a message you may actually be looking at the end. Sometimes people will write something out backwards and then apply a simple Caesar code to it. But this doesn’t feel like that.
    The five most common words that begin coded communications are: Meet, The, Take, Enemy and Go . The ten most common words in the English language are the, of, to, and, is, a, an, it, you and that . The most common letter found in standard English language texts is always E, followed by T and then A, O, N, R, I and S (in various orders depending on which frequency analysis you read). The most common digraph in English is ‘th’. More than half of all English words end with E, T, D or S. The most common letters beginning words in English are T, O, A, W, B, C, D, S and F.
    I wonder what the bloody message does say, and prickle slightly. I wish I had time to just crack it now. It could turn out to be nothing at all, which would make me feel so much better. Maybe it is from Dan but contains such a small message, or joke or whatever, that there’s no reason for it to be hidden in his face. Perhaps he has even forgotten that he put it there. He’s never written to me in code before, though. Why would he start now? Don’t worry, Alice. You just decided not to worry . OK. I drink all my wine and accept Dan’s top-up. That feels a bit better. ‘Thanks,’ I say.
    Dan’s putting a small red hardback