Andrew Swanston - The King's Spy

Despite the length of the text, the sender did not reveal himself at all. Thomas studied the writer’s hand and tried to visualize him. He tried fat and thin, short and tall, old and young. He tried divining the man’s nature — mean, generous, kind, cruel. Nothing. After he had stared at the text for an hour, the man who had encrypted it remained hidden. Thomas’s magic, for once, was not working.

‘So much for art,’ he said aloud, ‘time to try science.’ Once again, he wrote out the letters of the alphabet across the top of a sheet of paper. Then he counted the number of times each letter appeared in the message. He wrote this number below each letter, and E, A and T under the highest numbers; then he examined the juxtaposition of each to other letters, found three instances of double letters, and concluded which encrypted letter represented each of them. He repeated the process to find the letters I, O, S and R, and tentatively applied this to the first few lines. For this exercise, all numbers were ignored. The result was nonsense. As he had expected, this was not a straightforward alphabetic cipher, either shifted by a keyword or mixed by a system of substitution. At least two substitutions had been used, perhaps more, and there was still the matter of the numbers. A double or even triple alphabetic substitution would eventually yield to close analysis and a little intuition, but it would take time. And Thomas’s instincts were shouting at him that this decryption was going to require all his skills. Hoping that sustenance would bring more success, he put down his quill and went to find food.

Fortified by an excellent mutton stew from Silas’s kitchen and half a bottle of claret from his cellar, Thomas lit a cheap tallow candle and started again. This time he attacked the forty-five numbers. He still suspected that they were codes for names, but needed to be certain. Assuming that the numbers were actually in sequences of three digits, the sixes being two names together, he found eight separate numbers, of which 769, 574, 852 and 775 were repeated once, and 371 occurred four times. That made a nomenclator almost certain, and decoding 371 would be a huge step forward. After two more hours, however, and four more candles, he had made no further progress. He had identified not a single word from the letters or numbers, and had no more idea what secrets they held than when Abraham had handed the paper to him. Beyond the facts that a complex system of encryption and encoding had been used, and that the message must be important, he still knew nothing about it. Without bothering to undress, he lay down and slept.

Next morning, Thomas went first to visit Abraham, hoping his old friend would provide an insight into the problem. He described the text in detail — forty-five numbers, 456 letters and 138 spaces. He told Abraham how he had approached the task, the old man nodding encouragingly as he did so, and finally he told him that he had learned nothing. They discussed poly-alphabetic substitutions, nomenclators, variable Caesar shifts, homophonic substitutions, keywords and codewords. At the end of the morning, they had agreed only that this was not a message intended to be decrypted quickly, even by someone with the key. It was too complex. So it was not a standard military despatch, and, although important, would not be battlefield-urgent. That made it of strategic rather than tactical value. There was no context, and there were no other clues. They still had no idea what it was about, who had written it or for whom it was intended. Abraham could tell from Thomas’s voice that he was tired and frustrated.

‘My best advice is that you put it away for today. Go for a walk. Hill’s magic might return with the dawn.’

Taking heed, Thomas spent the afternoon by the river, and the evening with his friend Montaigne. He fell asleep thinking of Polly and Lucy, and of Jane Romilly, who had stormed out of his room in a fierce temper.

The next three days were spent on the intercepted message. The marks on the paper had become his enemies. He tried a variety of double and triple alphabetic substitutions, he tried assuming that all the numbers were meaningless, that they hid keywords, that the message was in Latin, that it had been written backwards, and he even guessed at a few possible keywords to create alphabetic shifts, such as PARLIAMENT, OXFORD and PROTESTANT. The guesswork was futile without at least some facts, and he knew it. He gave it up when Montaigne tapped gently on his shoulder, and whispered in his ear, ‘Thomas Hill, have I taught you nothing? Rational thought is greatly superior to intuition. Think, don’t guess.’

On the fourth morning, he went again to see Abraham, and again reported his lack of progress. Abraham tried to be encouraging. ‘Thomas, you have made progress,’ he said. ‘You know a good many things that this cipher is not.’

‘Indeed. But if I have to eliminate all the things it is not before discovering what it is, I shall be even older than you when I finally do so.’

Abraham laughed, and then voiced the thought that both had so far left unspoken. ‘Could we be facing Vigenère, Thomas?’

‘It’s possible, of course, although the numbers must also be serving some purpose. Have you heard of a square used with numerical codes?’

‘I haven’t, but that doesn’t mean they don’t exist. If the numbers are codes, the cipher will work just as well if they are ignored.’

‘Abraham, a Vigenère cipher has never been broken, with or without word codes.’

‘I know. Trust a Frenchman to come up with such a diabolical thing. Tedious to encrypt, tedious to decrypt, and proof against even you, Thomas, unless you can divine the keyword.’

‘I can try, Abraham, but you know it’ll take a miracle.’

Abraham was thoughtful. ‘Perhaps not. Look again at the numbers. Could they be telling us which rows on the square to use? If so, the cipher would still be secure against anyone un familiar with Monsieur Vigenère.’ He picked up a thin strip of wood with a straight edge and passed it to Thomas. ‘If it’s Vigenère, you’ll need this.’

Thomas took the strip of wood. ‘Thank you. I’ll assume it’s Vigenère and try the numbers again. Prayers thrice daily, Abraham, please. I shall need them.’

That evening, Tobias Rush visited again. All in black, silver-topped cane in hand, he called to tell Thomas that his letter had been safely delivered to Margaret. ‘Was there a reply?’ asked Thomas hopefully.

‘Unfortunately, no. The courier had to reach Southampton by dusk and could not afford to wait,’ said Rush with a shrug. ‘No doubt your sister will find a way of writing back, however. Do let me know when she does.’ He paused. ‘And how did you enjoy the masque?’

‘Masque? Oh, the masque. Remarkable. A remarkable entertainment.’

‘Indeed. Their majesties have unerring eyes for beauty. And speaking of beauty, how did you find Lady Romilly? Well, I trust?’

‘Quite well. An unusual lady.’

‘You refer to her eyes, I imagine?’

‘In part, yes. They are striking. But not just her eyes. She’s a lady of spirit.’ As I am only too well aware, thought Thomas.

Rush smiled his thin smile, and changed the subject. ‘How goes your work, Master Hill?’ he asked, looking casually around the room. His working papers were underneath others on the table. Just as well, thought Thomas, although I must be more careful in future. Abraham had insisted on absolute secrecy, even from Master Rush. He dissembled. ‘Routine matters only. Not much has changed since I last worked with codes. I would prefer something more interesting.’

‘Oh? Have the enemy not offered you anything at all appro priate to your skills?’

‘Not as yet, sir.’