Smelling traps now, Vasco was wary. “I shall report to Missier Grande, of course. He will probably send me to return the documents to Circospetto, but that will be his decision.”
Nostradamus nodded. “But Sciara reports to the Grand Chancellor. I must be confident that my information will not disappear in some unfortunate accident. Take a chair. No, on second thought take Alfeo’s, where I can see you more easily. My neck, you know…”
I never heard him complain of his neck before, but he was certainly up to something. Suppressing outrage at being evicted from my rightful place, I yielded it to Vasco and then stood over him to watch.
“Alfeo, give the vizio a sheet of paper and a pen. Good. Now, if you please, lustrissimo, write the alphabet along the top. Capitals are easier.”
“May I help him?” I murmured, but Vasco managed to win through on his own:
A B C D E F G H I J L M N O P Q R S T U V X Z
The Maestro had even worse torment in store for him. “Now, write B under A and the rest of the alphabet until you reach Z again, and complete the row with an A.”
I was already flipping through Giovan Batista Belaso’s La cifra del Sig to find the illustration.
“You see where you are going?” the Maestro said. “The next row would begin with C, yes? You would end by listing all Caesar alphabets possible with an alphabet of twenty-three letters. If you were to include some of the barbaric runes that northern tribes like the English and Germans use, you would have more.”
Vasco nodded uncertainly.
“Alfeo told you how easy it is to break a Caesar cipher. But if you use several Caesars by turn, then the cipher becomes unbreakable! Or so the sagacious Belaso believed and later authorities have agreed. The only thing you need to establish in advance with your correspondent is the order in which you will use the alphabets. No? Well, let us attempt an example. A little farther down the page write the sentence, ‘Sciara, who is furtive.’ In uppercase letters, if you please.”
Vasco wrote, SCIARA, CHE E CIRCOSPETTO.
“And then put it in five-letter groups, as Algol does.”
SCIAR ACHEE CIRCO SPETT O
The Maestro pressed his fingertips together, enjoying his lecture. “Now we shall apply the key, and in this case the word will be VIRTU, as that was Algol’s choice. The man has a sense of irony, if not humor. Pray write that under each of the groups.”
“Excellent. Now leave a line and write out the normal alphabet again. Good. Under it write the Caesars you will use to encipher your plaintext.” He frowned at Vasco’s blank stare-he is accustomed to dealing with my less-circumscribed intelligence. “The first row, you begin with a V… VXZAB…and end with U. The next begins IJLMN…”
It took a while and Vasco’s rows and columns were not as straight as might be desired, but he got there. The Maestro was beaming.
“Excellent! We’ll make a scribe out of you yet. Now to begin the encipherment! Under the first letter of the plaintext, S, you see the V of VIRTU, yes? So you find S in the normal alphabet, the one that begins with A, and go down to the alphabet that begins with V and what letter do you find?”
Thoroughly bewildered, Vasco did not find any, so I directed him to P, and he wrote it underneath the S, as instructed. The next letter, C, on the I alphabet, came out as B, and so on. By the time he reached the middle of the second group, he was managing by himself and I was making admiring noises.
SCIAR ACHEE CIRCO SPETT O
“This is absolutely brilliant!” I said. “How in the world did you do it?”
The Maestro made no effort to appear modest. “The pattern you noticed indicated that a letter’s position within each group was important, so I tried a frequency analysis on the initial letter of each group. It showed too many B ’s, so I hypothesized that B stood for either E or A, in which case the Caesar alphabet began with either V or B. Then I tried the second letter of each group, and so on. A rigorous analysis would require more plaintext than just one page, but I found enough clues to work out that the key must be VIRTU . It was not so difficult once I recalled the theories of Trithemius, Cardano, Porta, and so on. I’m astonished Sciara and his rabble did not see it. I admit, though,” he added, being hypocritically gracious, “that I have never heard of polyalphabetic substitution ever being used in practice.”
He had been lucky. Che is not merely a common word in itself; that combination of letters appears in many words in both Tuscan and Veneziano. Whenever it fell in the middle of a five-letter group, it had enciphered as my initials, which had caught my eye. In any other position it was represented by some other triplet, and with another key word it might always be. Then we would not have noticed the repetition. The best ciphers are broken because of human error, Nostradamus had told us, and Algol should never have left the ciphertext in five-letter groupings. That was incredible carelessness.
Vasco, meanwhile had completed the enciphering and was staring in bewilderment at the result:
PBLTN VLAZA ZRJVJ L
He had not even noticed my LAZ in there.
“So there you are, Vizio,” the Maestro said. “That is how it is enciphered. Now let us try some deciphering. We need to know if the same keyword will work for all four intercepted messages. Page one of one, if you please.”
With surprisingly little help from me, Vasco managed to reverse the process and start recovering the original plaintext:
He stopped. “This is gibberish!”
The Maestro sighed. “Perhaps the key word is not the same, then.” He was carefully not looking at me, who could read over Vasco’s shoulder. Unlike Vasco, though, I was reading: 11 Agosto. Il Consiglio dei Deci…*
“Let us try the final dispatch then. Page one of four, please.”
Again Vasco balked after a few groups, but this time a ray broke through the clouds. “Wait a moment! They begin with dates!”
15 Settembre. Il presidio…*
“Why, so they do!” I cried.
The game was over. Vasco hastily covered his work with his hands.
“You don’t need to see this!”
“Of course not,” the Maestro agreed. “You can let Missier Grande into the secret and he can decipher the rest.”
But I was confident that the Maestro himself would break the news to Circospetto, so he could watch Sciara gnash his fangs in mortification. Vasco looked at him as if suspecting the sort of elaborate hoax that I love to play on him every time I get the chance, but which the Maestro considers beneath his dignity.
“This nonsense will translate everything?”
Nostradamus sighed and opened a drawer. “Here is a deciphered version of the page you left in the dining room.”
It was his own version, and Vasco needed some time to decipher the scrawl and artificial letter groups. As he did, he grew paler and paler.
“The interesting thing,” the Maestro remarked, and now he was looking at me, although his expression gave away nothing, “was that Circospetto lied to us.”
“Yes, he did,” I agreed. Today was September 23. If Algol’s fourth dispatch reported news of events on September 15, there had not been time for it to reach Constantinople and the Republic’s spy there to copy it and report back to Venice. Of all the states Algol might be working for, even Rome, the closest, would require almost impossible timing. If the Ten were opening Algol’s mail right here in the city, why did they not know the sender?