‘In that case, kindly report to me this evening on your progress or immediately if the cipher begins to reveal itself. This could be a matter of the greatest importance.’
Alone in his room, Thomas studied the message.
So, 172 letters in four lines, with neither breaks nor numbers. He began as he always had, by trying to envisage the sender of the message. What kind of man was he? Was he fat or thin, short or tall? How old was he? Where might he have learned the science of encryption?
Nothing much came to mind, probably because the message was short and there was nothing distinctive about the hand. He wondered if it contained misspellings or nulls. Probably not, due to the length. He studied it again, trying to work out a way into the cipher. He noted the two double F’s and three instances of JP, but little else. Time to count letters. He wrote out a chart and began.
When he had finished, he had:
Sixteen of S, thirteen of B, eleven of F and ten each of G and W made them good choices for E, A and T. As there were double FF’s, in a simple substitution cipher F could not be A, so it should be E or T. N, with no appearances, would be Z or X. He would work from there.
By that evening, his head ached, he had cramp in his right hand from holding the quill and, having eaten nothing since breakfast, he was starving. He knew very little more about the message than he had eight hours earlier, except that it had not been encrypted with a simple cipher. None of the standard techniques had worked, but before trying a new approach he needed to rest.
First, though, his lordship expected a report. Again the secretary showed him into the library. ‘Ah, Master Hill,’ said Willoughby, ‘what do you have to tell me?’
‘Other than that I have eliminated the most obvious cipher systems, very little, I fear, my lord. It is more complicated than I had expected. I suspect a double or triple substitution cipher. I will break it but it will take more time.’
‘Only to be expected, I suppose. Ayscue’s no fool. He won’t know about you but he’ll assume we have some expertise in these matters.’
‘Quite so, my lord. I shall resume first thing tomorrow.’
‘Good. This could be vital, Master Hill. It might just tip the scales sufficiently for Ayscue to go home. We must read the message. I depend upon you.’
After a frugal supper – he had always tried not to overindulge while working on a problem – Thomas went reluctantly to the bedroom prepared for him. He did not expect much sleep. A mind stimulated by eight hours of thinking and figuring does not readily submit to sleep and it was not until the early hours that he eventually nodded off.
He was awoken at dawn by a knocking on the door. Squinting against the morning light, he managed a gruff ‘Enter’ and was rewarded by the sight of a plump girl bearing a tray.
‘Good morning, sir. I’m Annie. I’ve brought your breakfast. Shall I put it on the table?’
‘Thank you, Annie.’ Annie put the tray down, and came over to the bed. It was a large bed, equipped with cushions for the head and a light cotton sheet. In Barbados, no more was needed.
‘His lordship says I’m to ask if there’s anything else you might want,’ said Annie. Thomas opened his eyes fully and looked at her. His lordship says that, does he? he thought. Whatever can he mean? She was pretty enough in her way. About twenty, blonde and buxom. Built for comfort rather than conversation.
Annie smiled encouragingly. ‘Anything that might help with your work, he said.’
Thomas hesitated. ‘I am, er, a little unpractised, Annie.’
Annie giggled. ‘Don’t you worry about that, sir. Just you lie back and let Annie take care of things.’ And having slipped out of her smock, Annie joined Thomas on the bed.
An hour later, breakfast forgotten, Annie had carried out his lordship’s instructions with the utmost diligence. ‘Well, Annie,’ said Thomas, stretching out while she dressed, ‘let’s hope your contribution to our efforts proves successful. I certainly feel better for it.’
‘That’s good, sir. If you need any more help with your work just send a message to the kitchen. Now better eat your breakfast. Goodbye, sir.’
By the time he had eaten two cold cutlets, a chunk of bread and a piece of cheese, all washed down with good ale, Thomas was ready to return to the message. Something was nagging at his mind. What was it? He thought of Abraham Fletcher, cruelly murdered by Rush. Abraham and he used to amuse themselves by sending each other encrypted and coded messages and challenging the other to break them. Was this a cipher one of them had used? Or had he come across it elsewhere?
He looked again at the text. He would begin on double substitutions, each letter being encrypted alternately with each substitution. A double substitution would render the double FF’s and the repetitions of JP irrelevant, and would be laborious to unravel. A shortcut would be useful. As he had told Lord Willoughby, military messages seldom carried names but if this one did, it would most probably be the name of the sender and would appear at the end. He should have thought of it earlier; it was worth a try. He would assume that the letters AORDTG were AYSCUE, and proceed from there. If he was wrong, he would soon find out and not much time would have been wasted.
It took all day, but, by evening, he had done it. The letters AORDTG did indeed represent AYSCUE and two substitutions had been used. No nulls and no misspellings.
Thomas’s second chart revealed the substitutions:
A double Caesar shift, named after the man who had used it to send reports home to Rome when on campaign in Gaul or Germania, using the five vowels to make the shift, in the first substitution at the beginning of the alphabet and in the second at the end. Easy to remember and for the sender and recipient easy to encrypt and decrypt. His lordship’s advisers could not be very experienced cryptographers and he was cross with himself for not having thought of this cipher earlier.
He went to find Willoughby’s steward, who showed him into the library where his lordship was enjoying some refreshment. ‘Master Hill, good evening. Will you take a glass of madeira? Better news, I trust.’
‘Thank you, my lord, I should enjoy a glass. And better news there is.’
As the steward poured his drink, Thomas handed Willoughby the message written out in plain English text. His lordship read it aloud.
‘To Modyford. Confirm strength of your force and state of readiness. Our landings will follow immediately after your declaration. We shall have the advantage of numbers and, God willing, we shall prevail. Ayscue.’
‘Are you sure of this?’
‘Quite sure, your lordship. It turned out to be a double substitution based upon moving the vowels to the beginning and the end of the encryption alphabets.’
Willoughby beamed at him. ‘Then you have done us all a considerable service.’
‘I regret that it took so long, my lord. I was a little out of practice.’
‘No matter. This has come as no surprise. Colonel Modyford’s loyalties have always been in doubt. At least now we know where we stand and we have time to take steps. Had it been otherwise we might have found ourselves trapped.’
‘I am pleased to have been of service, my lord.’
‘And you shall be rewarded for it. You shall dine with me tonight and return to the Lytes tomorrow,’ he said, adding with a discreet cough, ‘I do hope you’ve found our hospitality to your liking.’