Andrew Swanston - The King's Spy

The king’s summons came the next morning. Master Hill was to attend his majesty in the Great Hall at once. Thomas made ready, the papers again inside his shirt, and left immediately. The king sat in his customary place at the far end of the hall, and Thomas approached in the manner in which he had been instructed. The king clearly enjoyed observing his subjects like this, otherwise he would meet them in his apartments. He sat quite still, and waited. As before, he was surrounded by courtiers, including Rush, and, as before, he spoke quietly.

‘Master Hill, I am persuaded by Master Rush that it would be wise to demand from you a description of the cipher you claim has never before been broken, and an explanation of the manner in which you broke it.’

Thomas had been half expecting this. ‘That I will certainly do, your majesty, if you wish it. However, since I do not believe that there is anyone else in England who has the means to break the cipher, I suggest, with respect, that an understanding of the decryption technique would be best kept to as few as possible. It may yet prove as great an asset as a loyal army.’

The king took a moment to consider this. ‘Very well. You will demonstrate the cipher only to Master Rush and to me. We will begin at once.’ While servants brought paper and ink, and all the courtiers but Rush left the hall, Thomas took out his papers and laid the square he had written out and the original message on a table beside the king’s seat. He began with the square.

‘This is a Vigenère square, your majesty. The letters of the alphabet form the top row, and the first column. A message is encrypted by use of a keyword, which dictates the encrypted letter which will replace each letter of the text. The intercepted message I decrypted used the keyword PARIS. Thus, the first letter of the message, F, was replaced by U.’ He traced with a quill the column headed by F to where it intersected the row starting with P. ‘The second letter of the message, R, was replaced by itself, because the second letter of the keyword is A.’ He pointed to the first letter of the final row.

‘What is the purpose in encrypting a letter as itself?’

‘Unless the receiver of the message knows the keyword, your majesty, it is as good an encryption as any. Without the keyword, he cannot know, or even guess, that the letter A appears in it.’

‘And how did you discover that the keyword used in this message was PARIS?’ asked Rush.

Thomas explained how he had realized that the square created a number of single alphabetic ciphers rather than one poly-alphabetic one, and that he had found the length of the keyword, and thus the number of ciphers, by analysing the frequency of repeated letter sequences.

The king did not immediately grasp the importance of this. ‘And in what way did this lead you to a successful outcome?’ he asked suspiciously. Thomas explained the theories of frequency analysis, and how he had applied them, once he had identified the five ciphers in use.

‘I was fortunate, your majesty, in that, in a text of this length, there were sufficient letters in each cipher to make analysis by letter frequency viable. Even then, it was not entirely straightforward.’

‘Master Rush, do you understand this?’ asked the king.

‘I do, your majesty. Master Hill’s explanation seems to me to be plausible, although one wonders why, if he was able to decrypt the message with comparative ease, the cipher has remained unbroken for so long.’

‘Prison walls, Master Rush,’ replied Thomas sharply. ‘Prison walls led me to the solution. When one has nothing to do but sit on an excrement-covered floor and stare at a stone wall, it helps to con centrate the mind. I recommend it to you.’

Rush ignored the remark. ‘This is the original message, is it not? Did you make a copy?’

‘I did.’

‘Then perhaps we may have it. We should keep both original and copy in a safe place.’

Thomas handed the copy to Rush, who examined it closely, as if looking for differences. With a smile, he placed it on the table beside the original. ‘Your majesty will see that both original and copy were written by the same hand.’

The king peered at the papers. ‘It would seem so. How do you account for this, Master Hill?’

‘When decrypting a message, it is my habit to put myself, as far as I can, in the shoes of the encrypter. Thus, I try to copy his hand.’

‘Then you have done it as well as any forger,’ said Rush. ‘His majesty might find it difficult to believe this claim.’

‘By your leave, your majesty,’ Thomas replied, ‘if Master Rush would write a sentence or two in his own hand, I will reproduce it so that you are unable to tell the two apart.’

‘What would you like me to write?’ asked Rush.

‘Let us try “One eye is brown yet the other is blue”. That should be sufficient.’

Rush wrote the sentence and passed the quill to Thomas. With a quick glance at Rush’s script, he wrote a copy underneath. It was an exact match.

‘This proves only that, in addition to being a traitor and a murderer, this man may be a forger, your majesty.’ Rush spat out the words. The king looked thoughtful.

‘You are a man of many talents, Master Hill. I would not want you for an enemy, and I would like to be convinced, as the queen is, that you are our friend. Until I am, however, you will remain in Christ Church. Master Rush will conduct further inquiries.’

And how exactly will Master Rush do that? wondered Thomas, on his way back to his rooms. Threats? Torture? An accident? All three?

Even in time of war, the king and his household did not believe in stinting themselves, and for two days Thomas enjoyed the offerings of the king’s own cooks, who laboured day and night to keep his majesty happy. Breakfasts of buttered eggs and lamb cutlets and dinners of roasted venison and beef, washed down with excellent wines purloined from the college cellars, did their best to keep his spirits up. The meals were brought to him in his rooms by a young kitchen boy, who must have been told to say nothing to the gentleman he was serving. Even Thomas’s polite enquiry as to the boy’s name was met with blank silence. They were a strange two days. Imprisoned in the college, suspected of treason and murder, yet dining on royal food and drinking royal wine, both served by a silent boy. Luckily, his predecessor must have been a scholarly man, with an interest in ancient history. At least he had Plutarch and Tacitus for company.

The king’s summons came on the third morning. A guard escorted Thomas to the hall, where the king waited with his courtiers around him, the Master of the Revels and the Court Painter among them. Just what we need, thought Thomas, dancing and portraits. Enough to frighten away any pikeman. To Thomas’s surprise, Rush was not there.

‘Master Hill, it appears that your skills are needed once more. Another message has been intercepted,’ said the king, waving a paper at him. ‘It was hidden in a sword case, and captured near Reading. With Master Rush away on important business, it has been delivered to me. Kindly tell me what you make of it.’

Thomas took the paper from the king’s outstretched hand. The message was short — only two and a half lines — and written in a hand he did not know. He quickly counted the letters. There were one hundred and thirty-four. No numbers and no spaces. No clues at all. ‘Other than that it is short, your majesty,’ he replied, ‘I can tell you nothing. I shall need time to study it.’

‘Time, Master Hill, is one thing we do not have. The queen will soon leave Oxford, and this message must be decoded before she does. She must not be put in any danger. How long will you need?’