“You know the doge is a great book collector and the Maestro is an expert on old books? He’s examining some very rare documents for the doge, so valuable that the doge sent the vizio along to guard them.” That was as close to the truth as I could come and it satisfied the youngsters, although probably not Mama, who never missed a word of any conversation, spoken or unspoken. Hating myself for even that much deception, I beat a fast retreat with a mug of hot water and another of khave.
I checked that both doors were bolted as well as locked.
As soon as I had shaved, I took my tarot deck from under my pillow and tried another reading. It was no more informative than the last one and I tucked the deck away again, fearing that any more attempts to force it might desensitize it. My tarot skill had apparently become as useless as the Maestro’s clairvoyance, which confirmed what I already suspected-that whatever we were up against would not be deterred by bolted doors or Filiberto Vasco’s sword.
When Vasco returned, he found me at my side of the big desk behind a pile of every book on cryptography in the Maestro’s library-Roger Bacon, Johannes Trithemius, Girolamo Cardano, Leon Battista Alberti, Giovani Porta, Blaise de Vigenere. Al-Kindi was there, too, but I can’t read Arabic. Needless to say, I had made small progress with those I could read.
“No sign of the Maestro,” I said. “May I have a look at the evidence?” You cannot conceive how much it hurt me to sound humble.
The vizio could, though, and smirked. “What for?”
“Not the ciphertext, just Circospetto ’s notes.”
He had the effrontery to make himself comfortable in the Maestro’s chair and beam across at me. “Why?”
“I have an idea and I wanted to see if the Ten’s gnomes thought to check for it.”
“What sort of idea?”
“About nomenclators.”
“What’s a nomenclator?”
“This frantic impulse to exercise your brain after so many years of disuse may do serious damage.”
He just smiled.
“I taught you last night,” I said with saintly patience, while silently vowing epochal revenge, “that a simple Caesar alphabet cipher is too easy to break. The most popular way to improve it is to add more symbols, usually numbers. So you have, say, 32 standing for D, 14 for N, and a dozen or so different codes for a very common letter like E -and so on. Then you start adding symbols for common words, perhaps 42 for the and 51 for and. That sort of list is called a nomenclator. It makes the cipher harder to break, but not much. Carry it too far and you’re writing a whole codebook, with numbers for King of Denmark, Venice, Janissary regiment, and Lord knows what. That’s more secure, but then your spy can’t carry the cipher in his head anymore and has to lug a book around with him. If the enemy captures it, a codebook is enough evidence to hang him and reveal all your coded correspondence, past, present, and future. If a Caesar alphabet is compromised, you only have to change the key, which is a single number, whereas replacing a codebook is a huge task. But codebooks are how most states encipher their dispatches.”
Vasco nodded as if he understood. He does have a certain low animal cunning. “Algol doesn’t use numbers.”
“No, he uses twenty-three letters, and if he is pairing them up he has hundreds of couplets available. So the first thing the Maestro asked was if Sciara’s gnomes had checked for couplet frequency. Perhaps GX stands for A, NT for B, EO for King of France, understand? Now you pass me the notes and I’ll tell you what to look for in the ciphertext and if we’re quick about it we may have this thing broken before the Maestro comes.”
“And if we’re really lucky, angels may appear to transport you to Paradise.”
I thought that was the end and the pleasure of refusing me had overridden his duty, but then he shrugged and opened the satchel. He held out the work notes, making me stand up to reach them.
“So what do I look for?” he asked.
“My initials. LAZ, for Luca Alfeo Zeno. How many times can you see those letters together? I know they appear more often than they should.” I set to work reading what Sciara’s team had tried, ignoring more scoffing from Vasco.
Sciara’s notes were thorough and detailed. I learned that the ciphertext comprised four Algol dispatches, varying in length from three pages to nine, twenty-four pages in all. The Ten’s cryptologists had tested for letter frequency and couplet frequency and even “word” frequency, although the five-letter groups could not be real words. Their conclusion was that the distribution of letters was not truly random, but not skewed enough for a substitution cipher, such as a Caesar, or a transposition cipher, which is a gigantic anagram. They suspected that all four dispatches had been written using the same code, so very likely it was a nomenclator.
They had not tested for triplets, though. Of course my own initials in a page of meaningless text will always jump out at me, and the previous evening I had seen them twice on one page when I was looking over the Maestro’s shoulder. After a few minutes of angry muttering, Vasco announced that he had found my initials seven times, and at least once in each of the four dispatches. We had grasped a thread in the labyrinth! That ought to lead somewhere.
But where? There were thousands of other three-letter combinations to look for, and the only sensible next move I could think of was to hand the problem back to Sciara and tell him to put his legions to work on triplet frequencies. I suggested we each try to find another repeating triplet.
Eventually the thump of the Maestro’s staff on the terrazzo outside announced his approach and Vasco hastily vacated his chair. The old man came hobbling in, looking murderous.
“Make any sense of it?” he growled at me, with a wave at the slate table.
“Nine words,” I said. “That’s all.”
He grunted, meaning that he had reached the same conclusion.
“And my tarot doesn’t work either.”
He seemed unsurprised. “Why do you think he’s called Algol? Vizio , who named the unknown that and why?”
“I have no idea, Doctor.”
More grunt.
I doubted that Algol would turn out to be a true ghoul, a monster that haunts graveyards and eats corpses, but he might well be a demonologist, and the laws of demonology dictate that anyone who employs demons will soon find that the shoe is on the other hoof and the demons are employing him.
Vasco was looking puzzled. I thought it kinder to leave him that way.
“Can you break a nomenclator in an unknown language?” I asked.
The Maestro’s scowl darkened. “Given time and enough text to work on, yes. But there are far more good ciphers than good people using them. When a cipher is broken, it is almost always because the operator was careless. Human error damns us all! If we look hard enough and long enough, we will find that he has made a mistake somewhere.”
That was my cue. “He likes my initials. He used them seven times.”
The effect on the Maestro was dramatic. He sat up straight and his eyes blazed with excitement. “Where? Show me!”
Two minutes later he snapped, “Bring me the pastels!”
I fetched our box of pastels.
We marked every LAZ in red. After another ten minutes or so we had located and highlighted four more triplets that were repeated at least once. Nostradamus told me to round up the three oldest Angeli children currently available. Reading and writing are uncommon skills among the citizen class, but I taught Mama and she teaches all her children.
Archangelo was on a ladder, dusting the tops of high pictures in the salone, and so was happy to be recruited. Corrado and Christoforo happened to come running up the stairs as I emerged from the atelier and were not, but they brightened when I chivied them into the dining room and they saw the pile of shiny soldi in front of the Maestro. Most of the time he is as tight as a coffin lid where money is concerned, but he has little idea of how much it means to adolescents and often tips them extravagantly.