by James Becker
“I don’t think I can face starting the decryption right now,” she said. “I need a caffeine injection as a matter of some urgency, and this time I’m buying.”
“Good idea.”
Mallory stood up as well, closed the lid on his laptop and unplugged the charger cable, then slid the computer back into his bag.
Robin looked at him quizzically.
“I can’t afford to lose this machine,” Mallory said simply. “I do a lot of my work for my clients offsite, and so I have a lot of commercially sensitive material on this computer as well as some expensive utility programs, plus all my personal stuff. So where I go, the laptop goes.”
“Even fifty yards down the road for a coffee?”
“Even fifty yards down the road for a coffee,” Mallory confirmed.
Robin locked the apartment door behind her and at the bottom of the spiral staircase she opened the rear door to the shop and led the way inside.
A pleasant-looking middle-aged woman turned around from her seat behind the counter as they walked in, lowering the novel she had been reading as she did so.
“Betty,” Robin said, “this is David Mallory. He’s helping me with a little project I’m working on.” She turned to Mallory. “Betty runs the place,” she went on. “I simply couldn’t manage the shop without her. I know that’s a cliché, but in this case it also happens to be absolutely true.”
The coffee in the café Robin had selected was far better than it had been in the one where they had met. Somewhat revived and fortified, they were back in her office within twenty minutes, and Mallory started work on the decryption almost immediately. And almost immediately he ran into problems.
“You’re quite right,” he said. “It’s only the first nine words that I can decode using the Atbash cipher with the eleven-place shift to the left. It doesn’t work for the tenth word, nor the eleventh or twelfth.” He thought for a few seconds, then continued. “I suppose realistically there are only two possibilities. Either whoever wrote this switched to a different type of encryption method, or they simply used a different shift but carried on using Atbash.”
“If it’s medieval, and I still think that’s the most likely period, then I have no idea what other possible types of cipher were around, if any. Do you know?”
“Oddly enough, yes. Ciphers of various sorts have been around for a long time. Researchers have identified three kinds of monoalphabetic ciphers in the Old Testament, and there are even records of an early type of steganography—that’s a technique for hiding a message inside another medium—using wax tablets from around the fifth century BC. The idea was to scratch the real message in plaintext on a block of wood used as the backing for a wax tablet, then apply the normal wax surface to hide it and write another, entirely innocent, message on the wax. Melt the wax off the wood, and then the important message could be read.”
Mallory laughed shortly.
“That was a fairly efficient method of sending a hidden message, because it could travel as fast as the messenger could run or a horse could gallop, but there was another classic example of steganography that was a lot slower. According to Herodotus, in ancient Greece a vital message about Persian invasion plans was tattooed on the shaved scalp of a slave. Weeks later, when his hair had grown long enough to hide the tattoo, he was sent off to the recipient of the message, his head was shaved again, and the warning was delivered, but that was obviously a really slow option.”
“I’ve actually heard of steganography,” Robin said. “That includes things like microdots, doesn’t it?”
“Microdots and almost everything else, yes. There was a famous case back in the sixties when an American serviceman who’d been captured by the North Vietnamese blinked his eyelids to spell out the word torture in Morse code during a press conference he was forced to attend, which is one of the more unusual examples. These days, because of digital transmission media, you can hide data or images in almost everything from pictures to sound files and documents.
“One very simple and obvious way of doing that would be to include a passage of text in a blank area of a word-processing document, and to make the text the same color as the background. It would be invisible to anyone reading the document, but if the recipient knows where it is he can simply highlight the block, change the text color, and read it. But more usually the text would be shrunk down to the size of a full stop or other punctuation mark and embedded somewhere in a document, or reduced to the size of a single pixel and then hidden in an image file of some type.
“Then there was a thing called a Polybius square, developed by a Greek historian in the second century BC, which was used to convert letters into numbers, most commonly employed in signaling. A variant of that is still in use today. And it was most probably Julius Caesar who used what you might call a shifted Atbash in his military communications, usually without reversing the cipher alphabet, and a monoalphabetic cipher of that kind is still known today as a Caesar alphabet. He also did things like substituting Greek for Latin letters. Coming a bit more up to date, the Vikings used simple encryption methods in some of their rune stones, and in the thirteenth century, Roger Bacon wrote quite a lot about the cryptography methods that were then in common use. Techniques for encrypting messages and information have been around in various forms for a long time. There’s even a section in the Kama Sutra about the importance of using and understanding ciphers.”
“The Kama Sutra?” Robin asked. “I thought that dealt with slightly more interesting subjects, like sex.”
“It does.” Mallory grinned. “And those are the only bits that everybody reads, but there’s a lot more in that work than just finding the right—or even the wrong—position to adopt when you’re in bed with somebody.”
He looked back at the printed text in front of him.
“But almost all of these methods were various types of substitution ciphers,” he finished, pointing at the paper he had been scribbling on, “and I’m pretty certain that this is just a kind of Atbash, nothing more complicated than that. And using this method of shifting, there are only twenty-six possible alternative keys, or fifty-two if we include the nonreversed cipher alphabets. I’ll write out all of them and then we’ll pick a word that’s fairly short, four or five letters, something like that, and try each of them until we find the one that decodes it.”
Writing them all out was laborious, but easy, not least because Robin did half of them.
“I’ll start from the beginning,” Mallory said, “with a right shift of one place, and see where that gets us.”
The short answer was nowhere, because it didn’t work. Nor did the right shift of two, but when he tried the next possible key, right-shifted three places, the first four-letter word he had selected deciphered as deus.
“That looks like Latin,” he said.
“That’s because it is,” Robin confirmed. “It’s the Latin word for God.”
Mallory quickly decoded the nine words that followed the first group he had deciphered.
“If the guy who wrote this was following a pattern,” he said, “I’ll probably need to use a different key for the next word.”
But to his surprise, he decrypted the next word, the nineteenth in the manuscript, using the same key, and did the same with the following eight. However, the twenty-eighth word refused to decipher using that key, and Mallory took several minutes, trying each possible Atbash key until it finally yielded to a left shift of seven. That worked for the next eight words, but not for the ninth.
“That’s interesting,” he said. “There’s obviously something important about the number nine, because I’ve now used three different Atbash ciphers, two of them decoding nine words each and the other one decoding eighteen, which is of course nine multiplied by two. I’ll bet this cipher works either for nine words or for a multiple of nine.”
It did. The thirty-seventh word didn’t d
ecode until Mallory tried a left shift of eight, and then he was able to decipher the next eight words to make a total of nine for that particular key. The next group decoded using Atbash shifted eleven places left, and the following eighteen using a right shift of three.
“He’s starting to repeat himself,” Mallory said, “and that might make it a bit easier—or at least quicker—to sort out the rest.”
The first section of the document was eighty-three words in length, and because Mallory could guess where the cipher changed and what the subsequent one was likely to be, he made short work of decrypting the text into Latin. But when he tried to decode the first word of the second paragraph or section, none of the keys he’d used before decrypted it, and in fact none of the twenty-six possible shifted Atbash keys worked, and nor did the keys using the nonreversed alphabet.
“I didn’t expect that,” he said. “This section has obviously been written using either a different encryption method or a different type of Atbash cipher. I know I told you that there weren’t that many alternative types of code in use in the Middle Ages, but I think we’re looking at one.”
“But however it was done,” Robin said, “it surely can’t be that sophisticated?”
“Probably not. Atbash is the simplest possible type of monoalphabetic substitution cipher, and it wouldn’t be that great a leap of logic for somebody who used that code to make the transition from it to another type of substitution cipher, but using a keyword or several keywords, instead of just the alphabet written forward or backward and shifted left or right.”
Robin looked slightly blank.
“Let me give you a very simple example.”
Mallory jotted down the letters A to F in a horizontal line on the paper, and then wrote BRANDY directly underneath them.
“Right, that’s the first part of the alphabet and let’s assume that BRANDY is the keyword you’ve chosen. Suppose you wanted to encode the word DECADE. You do it exactly the same as you’d do in Atbash: just read off the letters from the code word that correspond to the plaintext letters, so D would be enciphered as N, E as D, and so on. So using that code word, DECADE would be encrypted as NDABND. Two ciphers that are still in use today—the single and double substitution ciphers—use exactly the same technique. In theory, you can’t decrypt the text without knowing what the code word was, and certainly not with a double substitution cipher that uses two different code words that both have to be applied. You encrypt the plaintext using the first code word, then encrypt the enciphered text using the second code word, so it’s really difficult to crack. But that’s a comparatively recent technique, and I don’t believe that’s been used here.”
“You said that in theory you can’t crack it, but what about in practice? Is it possible?” Robin asked.
“In practice, the biggest problem in decoding encrypted text is usually time. Today, given enough computing power and sufficient time, almost any code can be cracked. That’s what places like GCHQ out at Cheltenham do. That’s their job over at Spook Central, the whole reason they’re there. They have banks of supercomputers, things like Crays, and they run what are called brute force attacks, trying every possible combination of letters, numbers, punctuation marks, and symbols against messages they believe are important. That technique only works because these computers can try tens or hundreds of millions of combinations every second. I don’t have access to a supercomputer, obviously, but with simple ciphers there are things you can do quite quickly to try to work out what at least some of the encrypted letters stand for. Have you ever heard about a technique called frequency analysis?”
“Oddly enough, yes, if you’re talking about an alphabet. In English, the most commonly used letters of the alphabet are, in order, E T A O I N. Don’t ask me how or why I remember that, but I just do.”
“Exactly,” Mallory said, looking at her with new respect. “Most people have never even heard of it. So looking back at my simple example using BRANDY as a code word, if you applied frequency analysis to the result, you could reasonably assume that either the encrypted letter N or D represented the plaintext letter E, and of course you’d be quite right: it’s D. The bigger the sample you have to work with, the more accurate the result is likely to be. Unfortunately I don’t know the frequency analysis details for Latin, so that method wouldn’t necessarily be much use to us here. And the other problem is that if the person who wrote this text decided to change the key every nine words, we might never be able to decipher it completely because we just wouldn’t have enough material to work with.”
“So, is there anything we can do?” Robin asked.
“That’s really where you come in. I’ve deciphered the first eighty-odd words of this, so we now have the Latin text. If you can translate that into English so that I can understand it, then we might find a clue.”
Ten minutes later, Robin passed Mallory a sheet of paper on which she had written out a translation of the Latin text. He took it eagerly, but the expression on his face changed as he read it. Then he put the paper on the desk and looked across at Robin.
“Unless I’m missing something,” he said, “this just looks like a waste of space. It’s a long rambling prayer or invocation about the importance of accepting God’s will and living a life based on a strict rule.”
Robin nodded.
“You haven’t missed anything, unless I’ve missed it, too. That’s exactly what it is, and it’s typically medieval in its sentiments. I really can’t think of any good reason why anyone would want to hide something like that away in the book safe. The important bit has got to be contained in the rest of the text, the part that we can’t decipher.”
She glanced at her watch. “I don’t know about you, but I’m getting hungry and it’s nearly seven, so let’s make tracks for a restaurant. You might have a sudden brain wave when you’re halfway through a chop or something.”
Mallory nodded. “A break often helps when you’re stuck on something, in my experience, so let’s go. You can tell me all about your life and your deprived childhood and your deepest fears and fantasies and dreams,” he added with a smile. “Or not. It’s entirely up to you.”
“I’ll keep my fantasies and dreams to myself, thank you very much, and my childhood was depressingly un-deprived.”
She watched Mallory shut the lid of his computer and put the laptop in his bag, along with the photocopies of the parchment and the sheets of paper they’d been working on.
“You really can leave that here, you know,” she said. “I’m sure it’ll be perfectly safe.”
“Sorry. The habit of a lifetime, but I’ll worry if I can’t see it.”
“Is that the only peculiarity about you?” Robin asked as she locked the door to her apartment and they started walking down the stairs. “Or have you got a whole raft of neuroses and psychoses that you’re just gasping to tell me about over a bowl of soup? In short: are you normal?”
“I think anyone’s definition of the word normal depends largely on where and when they’re standing, if you see what I mean. What was normal in Rome in the first century AD would have been considered completely abnormal in Victorian England. But as far as I’m aware, by the standards of this century and in this country, I’m pretty normal. I just tend to worry quite a lot about my laptop.”
“You could have given me the short answer,” Robin complained, leading the way down the alley to the street. “A simple yes would have done.”
13
Exeter Airport, Devon
“India Bravo Echo, Exeter Tower, land runway two six and take the taxiway on the left.”
“Thank you, Tower. Cleared to land and to turn south off the active. India Echo.”
The tower controller lifted his binoculars to his face as the pilot of the Cessna Citation X lifted the aircraft’s nose just prior to touchdown on the active runway. The main landing gear straddled the center line, both wheels t
ouching the concrete at the same moment, producing twin puffs of blue smoke and leaving a pair of short black skid marks. Moments later, the nose gear made contact with the runway and the high-performance executive jet began slowing rapidly, angling away from the centerline and toward the entrance to the taxiway, close to the western end of the runway. A few moments later, the pilot called the tower again.
“India Echo is clear of the active.”
“Roger.”
“Pretty aircraft,” the controller’s assistant remarked, watching the sleek white-painted jet move along the taxiway.
The controller nodded.
“Pretty, really expensive, and very quick,” he agreed. “Now that Concorde is no longer with us, what you’re looking at is the fastest civil aircraft in the world. For your fifteen million quid or so, you get a jet that’ll do better than point nine Mach, with a range of well over three thousand miles. Nice piece of kit. Don’t see that many of them here, and especially not with Italian registry.”
The assistant was still watching the aircraft.
“Maybe it’s the Mafia come to call,” he suggested.
“I think it’s a bit too high profile for them,” the controller replied. “Far more likely to be some fat Italian businessman on the take, traveling with a small flock of his mistresses.”
A few minutes later the pilot shut down the Cessna’s engines in the private aircraft parking area and the side door opened. Six heavily built men wearing dark suits emerged and walked briskly across to the ECA—Exeter Corporate Aviation—facility. Neither the controller nor the assistant saw them, because by then their attention was directed elsewhere on the airfield, but none of the new arrivals looked like businessmen, fat or otherwise.
About forty minutes after that, the six men drove away from the building in a pair of black Range Rovers, which they had hired while the aircraft was still in the air somewhere over France. They turned right out of the main gate and headed west along the A30 until they reached the Sowton Interchange, and there they turned south to follow the M5 Motorway, the second vehicle holding position about a hundred yards behind the first.