Free The King's Spy (Thomas Hill Trilogy 1) by Andrew Swanston Page A

have sufficed.’
    ‘How many keywords are there?’
    ‘Currently, twenty.’
    Thomas looked thoughtful. Twenty names withfixed codes, and twenty different keywords each month. Not difficult. Abraham passed Thomas the top sheet of paper.
    ‘This is an encrypted message, received three months ago. If you were the enemy, how long would it take you to decrypt it?’
    Thomas looked at it. It was six lines long, each line consisting of about fifty seemingly random letters. ‘This is about the right length for a military report, rather than a battlefield order. It looks like a substitution cipher, probably with a keyword. A simple shift would be too easy, and a cipher alphabet would be written down somewhere, which would make it vulnerable to capture. So I’d assume a keyword. With only one encrypted text to work with, perhaps a morning.’
    ‘That’s what I thought. Not secure from the attentions of a good cryptographer.’ Abraham passed over another sheet. ‘What about this one?’
    Again, Thomas studied the sheet for several minutes. ‘This message is shorter. It could be a military order. I guess that there are some coded words. Not knowing the context, I’d go about it as with the first message – frequencies and letter relationships – but if there are codes it would take longer.’
    Abraham smiled. ‘Your instincts are as good as ever, Thomas. Now what about this one?’
    Immediately Thomas said, ‘This is alpha-numeric.’ He imagined lines running through each number. ‘I think some of the numbers are nulls because there’s a pattern to them, but the others could be codes.’
    ‘Excellent. Now take these and practise your skills on them. Note that they may not all be what they seem.’ Abraham passed over the remaining papers. ‘Some of these are ours, others were intercepted. All incoming and outgoing messages will now be passed through me to you, for encryption and decryption. Next week you will need to send out the first half of a new keyword. Here is a list of all recipients. Please commit them to memory and destroy the list.’
    ‘And if I don’t, sir? Will I be confined to college?’
    Abraham could hear the raised eyebrows and the mocking smile, even though he could not see them.

C HAPTER 4

    ARMED WITH A handful of good duck-feather quills, a sharpening knife and a large pot of oak-apple ink supplied by Silas, Thomas set to work, starting with the simple task of memorizing the names of the twenty recipients of messages. He used a memory trick based on the vowels in each name which Abraham had taught him years ago, and most names surrendered without much of a fight. Within half an hour, he had them all.
    Next he counted the papers. There were twenty of them. Deciding to tackle them in the order in which Abraham had put them, he took the first one from the top of the pile. Twenty lines of ten letters each, written in a neat hand in brown ink and with spaces between every four or six letters, covered one side of the paper. Thomas held it up to the light, looking for unusualmarks or letter formations. There were none. He smiled. Kindly old Abraham had given him a simple substitution cipher to start with. On a blank sheet, he prepared a table with each letter of the alphabet across the top. Then he counted the number of times each letter occurred in the message, and wrote the number below it. He found that the letters C, F, and P appeared most often. They would probably represent E, A, and T, although not necessarily in that order. They were the three most commonly used letters in the alphabet, and if he could identify those he would be on the way to breaking the cipher. As C and P were preceded and followed by fifteen different letters, but F by only eight, F would represent T, which would appear between fewer letters than either E or A. Ignoring the spaces, which were merely intended to confuse, there were six instances of double Cs, but none of double Ps. C would represent E, leaving P as