The pattern allows you to create your own secret coded message. It looks random but anyone who knows that it is a code should be able to crack it using a little logic.

Quote from something I wrote some time ago, relating to 2003:

It was Easter Conference time again. As usual there were many interesting ideas to play with but the real highlight was meeting Simon Singh, author of Fermat’s Last Theorem and The Code Book. I had previously listened to the reading of The Code Book on Radio 4. I found it fascinating but it was nothing compared with the impact of the man himself. Simon gave an amazing talk about many different types of encryption. I learned a great deal but the I-could-knit-that-moment came from the simplest code of all, where one letter or number is substituted for another. I could substitute colours instead. I told Simon of my plan and that I would send him a picture when it was complete.

It didn’t take long to finish. The planning presented a few problems. We needed twenty-six colours to represent the letters of the alphabet. It caused a similar problem to that we had with Counting Pane many years before. It is just not possible to find so many colours that can be easily identified. To crack the code it had to be possible to tell the difference between the twenty-six symbols. We could manage thirteen colours so each had to be used twice in obviously different ways. Thirteen could be knitted, thirteen could be crochet, with the same lacy holes I had recently used for Surface Tension. That was one problem solved.

The next challenge was to decide on the message and the number of squares to be used. We weren’t even sure how many letters we needed to use for there to be enough clues to crack the code. More by chance than anything else we decided on a 16 x 16 square, giving 256 squares altogether. We later discovered that half this number would be enough to crack most simple messages.

Cracking this type of code relies on knowing the frequency of the letters in a normal piece of writing and this is generally the same whether you are reading a child’s book or an academic tome. The most frequent letter is E, followed by A, H, N, O, S, and T (not necessarily in that order). When the same 3 letter word appears more than once in a sentence it will probably be THE or AND. If it ends in E it will probably be THE so all the other Ts, Hs and Es can be identified. A 3 letter word at the beginning of a sentence is not likely to be AND. A word of one letter is very likely to be A or I. Two squares the same, next to each other, means there must be a double letter. B, L, and P commonly occur as double letters, others are rarer or non-existent. These clues will work for almost all messages, unless there are a lot of proper nouns, which are more unpredictable.

We decided on a message that was relevant to the afghan itself, which left us with two more problems. The first was how we should represent spaces between words. On paper, a space shows where a word ends but we couldn’t leave a hole. The solution was to use a ‘background’ colour of navy blue. Spaces between words were navy crochet squares; spaces between sentences were navy knitted squares. This left the final problem of fitting the message, including these squares, into the total of 256. A little juggling and rewording provided a suitable solution. The afghan was named Code Comfort. The message says:

the inspiration for this hanging was the code book by simon singh if you are reading this message you have already cracked the code it has knit and crochet squares in each colour it is not possible to find a different colour for each letter of the alphabet

The afghan had a code-cracking cushion to accompany it. This was a cylinder of squares in the same colours with the letters they represent embroidered on to them. Anyone unable to crack the code could check the colours against the cushion to find the message.