Cryptology - Unofficial St. Mary's College of California Web Site

7.2. TRITHEMIUS, THE FATHER OF BIBLIOGRAPHY 111
(3) Decipher JCQNGI RRIIZMVJ MUZLLAZ BUIVSTEBZ. Hint: The first letter of
each word is the key.
(4) Decipher LZWS XYXY RDGGV SBHSFJWOO CQNBRMNJ KVVYH Hint: the last
letter of the word is the key. 3
⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄ ⋄
Look again at part (1) of this example. The i in Vatican became O but the i
in City became K. Similarly, the t once became D and once V. A single plaintext
letter was enciphered to different ciphertext letters! This is the trademark of a
polyalphabetic cipher. A monoalphabetic (mono = one) cipher uses only
one ciphertext alphabet throughout the message, so each plaintext letter can
become only one ciphertext letter. A polyalphabetic cipher (Poly = many)
provides for several ciphertext alphabet, which allows each plaintext letter to
become several different ciphertext letters.
As we will see, that the same plaintext letter can become different ciphertext
letters provides for a very strong cipher. The weakness of Alberti’s method is
a bit more subtle. Can you find it (Try to decipher parts (1) or (2) from the
example.) 4
7.2 Trithemius, the Father of Bibliography
Johannes Trithemius (February 2, 1462 – December 15, 1516) is the second of
our four developers. By the age of 22, Trithemius was the abbot of the Benedictine
abbey of Saint Martin. His most important work, Liber de scriptoribus
ecclesiasticis, was a chronological list of about 7000 theological works, it was
published in 1494 and led to his title.
In 1499 he wrote Stenanographia, meaning “covered writing”. In it are some
examples of simple substitutions (swapping all i’s and t’s with each other, for
instance) and some null ciphers. (These ciphers appear like normal correspondence
but hide messages within them, for example, by having only certain
letters be meaningful, such as the initial letters in “Can’t order donuts every
Sunday”.) The third portion was a study of what we’d now call magic and the
occult. This portion brought him fame and notoriety and in 1609 the book was
placed on the Catholic Church’s Index of Prohibited Books.
Starting in 1508 Trithemius published the six-part Polygraphia (“many ways
of writing”). In Book V appears the world’s first known tableau, or table. The
simplest tableau is known as Trithemius’ tabula recta, and appears as Figure
7.1. (Trithememius’ recta came from the Latin alphabet, and so was 24 × 24,
rather than 26 × 26.)
3 (2) TCIBHOWB TK KIVMZ, (3) The XZ=pope arrives in ZZ=Rome on thursday, (4) The
ZAZ=pope will enter the side door.
4 We must include the keyletter(s) with the message. If the method is simply “use the first
letter of the words as the key”, then that letter is enciphered and is hard to determine!