‘Monks may be recluses, friars are not. I choose to live in the same world as you. I find both qualities useful.’
‘And you don’t behave like a man of the church. You travelled to Romsey to fetch me, disguised me as one of your own, pro tected me from Rush and brought Jane to visit me in the abbey.’
‘Were these not Christian actions, Thomas? Except, perhaps, for the last, and that was a simple act of kindness to you both. Even a Franciscan knows worldly love when he sees it. Rest assured, Thomas, I am what I appear.’
‘As you wish.’ They made another circuit of the quadrangle. ‘Now, this accursed message. We’d better break it or I may not be anything much longer. This is what I think. We’ve tried everything I know and achieved nothing. I’m afraid it’s Vigenère again, this time without codewords.’
‘Why would the numbers have been omitted?’ asked Simon.
‘The strength of codes is that they can be quickly decoded by the intended recipient. In the case of the square, they also make the frequency analysis harder by reducing the number of letters in the text. This is a very short message, which in itself is protection against decryption. If the keyword has, say, five letters, there will be no more than twenty-seven letters in each group. Too few to be much use, although I shall of course try.’
‘And do you see Rush behind it?’
‘I do. He’s no fool. He suggested to the king that I show them how the decryption of the last message worked, and he’s realized that, unless the text is short, the length of a keyword can be worked out. And he may have inserted nulls or misspellings, or both, to throw unwelcome hounds off his scent. Why otherwise would the encryption be as it is? If Rush wrote this message, it may well concern the queen, and we must discover its contents.’
‘So a long night of counting letters and looking for vowels, is that it, Thomas?’
‘It is.’
‘I would gladly offer to help, but the queen will expect me for her evening devotions.’
‘Of course. I’m used to working alone.’ They came to the college gate. ‘Now be off with you, and please ask Jane to visit soon.’
‘I shall. Goodbye, Thomas. I’ll offer a prayer for you.’
The long day did indeed turn into a long night. Every effort to pin down just one letter of the keyword had failed, and Thomas was losing heart. Twelve hours of toil had achieved nothing. By the early hours, he had tried everything he could think of, and had even guessed keywords that might have dictated the alphabetic shift. Nothing had worked. Tomorrow’s meeting with the king would not be a pleasant experience, but he had to plead for more time.
The next morning, the king was in no mood for explanations or excuses. ‘So, Master Hill, am I to understand that you have made no progress whatever?’ he asked, impatiently tapping his stick on the floor. Tobias Rush stood at his shoulder.
‘I have made progress by the elimination of simple ciphers, your majesty,’ replied Thomas, trying to keep his voice steady. ‘This message has been encrypted by a very cautious man indeed. He hid it, encrypted it with some complex method, which I am now sure is the Vigenère cipher, and may also have left false trails.’
‘I would be a great deal more pleased if you were able to tell me that you had broken the cipher, as would Master Rush.’
‘Indeed I would, your majesty,’ agreed Rush, with a smirk that the king could not see. ‘As you know, I was unconvinced by Master Hill’s explanation of his previous effort and his lack of progress now reinforces my view. I wonder whether your majesty would be well advised to entrust the message to another, more reliable man. I have someone suitable in mind. Master Hill would not then be needed and could be sent home, or, if your majesty wished, held at your pleasure.’
The king raised an eyebrow. ‘What have you to say to that, Master Hill?’
Thomas knew he had to take care. Rush would have him thrown back into that cell as quick as you like. ‘I am at your majesty’s service. I ask you to believe me when I say that I have made progress, and am confident of success. We are dealing with a very complex cipher, with only one hundred and thirty-six letters to work on, and anyone taking over from me would wish to start again using his own techniques. He would not wish, as I would not, to accept the workings of someone else. That would create more delay, which could be fatal to our cause.’
‘So what is to be done?’
‘I need more time, your majesty. All ciphers can be broken. It just takes time.’
The king hesitated. ‘You have already tried my patience, and I am reluctant to delay the queen’s departure any longer. If you cannot bring me the decrypted message by tomorrow morning, you will be released from your duties. In that case, Master Rush will advise me on what further course of action to take. Good day, Master Hill.’
A stay of execution, thought Thomas, walking back to his room. Damocles’ sword still held by a thread above his head. Twenty-four hours to break the cipher. To work, Thomas, to work.
His room was just as he had left it, except for one thing. His working papers — all but the original message under his shirt — had gone. While he had been with the king, Thomas had had an unwelcome visitor. Another one. A tidy one, but nevertheless un welcome. And there was only one person who could have arranged it, knowing for certain that Thomas would be otherwise engaged. Not that there was the slightest reason to inform the king, or anyone else. Rush would simply accuse Thomas of destroying the papers himself in order to provide an excuse for failing to decrypt the message. And, on reflection, perhaps it was not such a bad thing. An uncluttered table might help unclutter the mind. He still had the message itself, and could, without much difficulty, resume where he had left off. Rush might even assume that the copy that had been taken was the original, and that Thomas had no other. All the more reason to surprise the repulsive creature.
He started by reworking the distribution arising from a seven-letter keyword. When the first letter threw up impossible combinations, he knew he was wasting his time. Not enough letters, with or without tricks. Unclutter the mind, forget this approach, Thomas, and think of something else.
But what else? How could he break a Vigenère cipher without being able to attack it by frequency analysis? And a Vigenère cipher he was now quite sure it was. Anything else would by now have revealed itself, and it was just what the devious Rush would have done. Find his enemy’s strength and render it useless. A short message, the cipher and tricks. Unbreakable.
But break it he must. He would count each letter distribution separately, starting with a four-letter keyword and working his way up to eight. The chances of its being longer were remote. Too complicated and time-consuming to encrypt and decrypt. If he learned nothing from that, he would have to look for nulls, just as he had before, only this time in the context of the square. He’d need Simon’s prayers, or the meeting next morning with the king would be his last.
It started badly. The first letter of a hypothetical four-letter keyword yielded four Is, four Ts and six voids, and the other three letters produced similar distributions. Quite useless. Five- and six-letter keywords were no better. Shapeless distributions, offering no clues as to where the most common and uncommon letters hid. After fifteen separate counts, Thomas started making mistakes. He had to rewrite the list of letters produced by the third letter of a seven-letter keyword, and miscounted twice.
Thomas was standing by the window deep in thought when Simon burst in carrying a sack. He was ashen. ‘Thomas, Jane has been attacked. She was found this morning in the river, unconscious and having lost much blood.’
‘Is she alive?’ Please God, he thought, let her be alive.
‘She is. Just.’
‘Who did this to her?’
‘We don’t know. She was found by a student walking beside the river. It must have been shortly after the attack or she’d have been dead. He dragged her out and carried her to Magdalen. An officer’s wife there recognized her and sent word to Merton. She’s there now.’