Andrew Swanston - The King's Spy

Before Fayne knew it, Thomas had landed two more punches, and stepped nimbly out of his reach. The first blackened an eye, the second split a lip. The handsome face was twisted and bloody. Fayne, though, was strong. He shook off the blows and swung a fist at Thomas. It was slow and cumbersome, but brushed Thomas’s shoulder, knocking him slightly off balance. Fayne saw his chance and grabbed Thomas’s throat. Thomas found himself pushed back against the wall, struggling to take a breath. Fayne hissed at him through the blood, ‘Now, bookseller, now I’ll break your neck.’

Thomas knew he had to move fast. He grabbed Fayne’s hair with his left hand and got his right hand under Fayne’s nose. He pulled the hair backwards and pushed as hard as he could with the ball of his thumb. No attacker’s nose could resist that, and Fayne’s head was forced back and away until he had to release his grip on Thomas’s throat. The moment he did so, Thomas kicked him hard on the knee and landed two more blows to his nose, drawing more blood. Fayne subsided to the ground with a grunt of pain, his hands covering his face. It was over. Thomas could see no point in waiting for the mewling oaf to recover, and, with a bow to the ladies, adjusted his dress and left them to offer their friend whatever assistance they could.

Just as it had the first time, the icy calm departed as quickly as it had come. And when it did, it left a void. Thomas was drained of strength and emotion. He lay on his bed and closed his eyes. He had always regarded violence as a form of weakness, and he knew he had been weak. He should have ignored Fayne. He should not have allowed himself to be provoked. Perhaps it had been Jane’s refusal to see him, perhaps a reaction to the battle and his journey from Newbury, perhaps neither. ‘You are a feeble fellow, Thomas Hill,’ he said to himself, ‘and I trust you will not allow such a thing to happen again.’

Abraham was blunt to the point of rudeness. ‘You will not give up, Thomas, until I say you can. And I am unlikely ever to do so. I have told the king that you are the most accomplished cryptographer in England, and you are not to embarrass me by quitting.’

‘Abraham, I’ve tried everything. The cipher is unbreakable. I cannot do it.’

‘You can, Thomas, and you will. There will be a way. Find it.’

Thomas sighed in resignation. ‘Oh very well, Abraham, for you I’ll keep trying. I wouldn’t do it for anyone else.’

‘Good. Go now and begin again. I wish to be informed the moment you have made progress.’

‘Rest assured that you will be the first to know if there is even a hint of it.’

For two days, he laboured on the message and his square, trying all manner of approaches — some logical, others absurd, all futile. None worked. On the third morning, he sat at his table and tried again.

Can there really be such a thing as an unbreakable cipher? he asked himself for the hundredth time. Monsieur Vigenère thought so, and so far he was right. Twenty-six possible substitutions for each letter, determined by an agreed keyword, from whose own letters the encryption row was taken. If the keyword were THOMAS, a single letter in the text might have been encrypted according to any of the rows starting with T, H, O, M, A or S. It would not respond to analysis of frequencies. Yet the more he thought about it, the more Thomas’s logical mind could not accept the concept of an unbreakable cipher. That the square had not yet been broken did not mean it never would be. Abraham was right. There would be a way.

Putting himself in the shoes of an encrypter, he wrote down five repetitions of his keyword THOMAS, and, underneath them, his ‘message’ in plain text.

T H OM A S T H O M A S T H O M A S T H OM A S T H OMA S

O N E E Y E I S B R O W N Y E T T H E O T H E R I S B L UE

Then, using the square he had already constructed, he en coded each letter of his message according to the letter above it, which indicated which row of the square to use. This gave him a third, enciphered line:

H U S Q Y W B Z P D O O G F S F T Z X V H T E J B Z P X UW

The recipient of this message would decrypt it by reversing the process, as long as he knew the keyword, or the sequence of rows to be used, which could, less securely, be communicated by numbers. But as the numbers had proved time-consuming and unhelpful, Thomas had decided that they were codes and that he would return to the letters. Two things stuck out from his encryption. Double letters were coincidental, and would be no help in decryption, and any letter encrypted according to the letter A would appear as itself. Without his knowing if there were any As in the keyword, this too was unhelpful. He also noticed, however, that the sequence of letters BZP appeared twice, because they happened to coincide twice with the plain text letters ISB. A thought struck him. He knew why BZP appeared twice because he knew what the keyword was. In a Vigenère square, single-letter repetitions were meaningless, but repetitions of sequences might not be.

For an hour he pondered the question. The answer did not leap at him as it did to Archimedes in his bath, it crept up slowly. If he just knew the length of the keyword it would be a start. Common letter sequences, such as THE, AND and TION, would have been repeated in the text, and would sometimes have coincided with repeats of the letters of the keyword, thus leading to repetitions in the en crypted text. If he measured the distances in letters between each repeated sequence, he should be able to calculate the length of the keyword. In his ‘message’ BZP were letters seven to nine, and twenty-five to twenty-seven. So the start of the second sequence fell eighteen letters after the start of the first. His keyword, THOMAS, had six letters. Eighteen was divisible by six. The letters of the keyword had been repeated exactly three times before meeting the same plain-text sequence of letters again. It was a matter of simple arithmetic. Then an awkward thought occurred. Eighteen was also divisible by one, two, three, nine and itself. Not so simple, after all. Time for another stroll. He locked his door and set off.

Outside Pembroke, Thomas turned left towards the ancient castle. Head down and lost in thought, he barely noticed the beggars and whores who infested this part of the town. Jumbles of letters and numbers tumbled about in his mind, as if trying to make some sort of sense but never quite managing it. He walked round the castle and back towards St Ebbe’s. Could he find the length of the keyword from repeating sequences of letters, and, if so, how could he use it? He felt the vague stirring of an idea.

He did not see the boys until it was too late. Three of them came hurtling towards him, and, before he could move aside, knocked him off his feet into a drain. At least they had the grace to stop and help him up, dusting him down and enquiring if he was hurt. Although he knew that his shoulder was bruised, he assured them that he was only shaken, and advised them to take more care in future. They promised to do so and offered to help him home. Not wishing to be helped, he declined the offer and walked alone back to Pembroke, conscious that he looked and smelt exactly as if he had fallen into a drain.

For once, Silas was not on sentry duty, so he did not have to undergo an inquisition. At the door to his room, he reached into his pocket for the key. It was not there. He tried the other pocket. Not there either. ‘Damnation,’ he said out loud, ‘it’s in that shit-filled drain. And it’ll have to stay there.’

He returned to find Silas back at his post. Having offered a feeble lie for his condition and for the loss of the key, he was grudgingly given a replacement. ‘I keep three keys for each lock, sir. One for the gentleman, one for me and one spare. Now you’ve lost yours, I’ve got no spare until I can get another made, and only the good Lord knows when that will be. The forges are all busy sharpening swords and shoeing horses.’