The Alchemist's Code

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: