Cryptography Reference
In-Depth Information
cryptanalysis. He wrote thirteen rules for symbol substitution ciphers. Later,
another Italian, Giovani Soro, was appointed
Cipher Secretary
for Venice in
1506. Soro's cryptanalytic prowess gained him two assistants and an oGce in
the Doge's Palace above the Sala di Segret, in 1542. (The
Doge's Palace
was
the oGcial residence of the doges in Venice. The
Doge
(from the Latin
dux
or
leader
,or
duke
, in English) was the highest o
G
cial of the republic of Venice for
more than a millennium (roughly 800-1800 AD). They represented the virtual
emblem of the sovereignty of the Venetian State.) Soro, and his highly placed
assistants, worked on the most elevated level of security, deciphering all messages
from foreign powers, intercepted by the Venetians.
Cryptographic assistants were also available at the Vatican. The practice
became of such high consequence to the popes that the oGce of
Cipher Sec-
retary to the Pontiff
was established in 1555. The first of these was Triphon
Benicio de Assisi. Assisi assisted Pope Paul IV during warring times with King
Philip II of Spain. In 1557, Assisi was adept at deciphering the King's cryp-
tograms. By September 12, 1557, peace was made, due in no small measure to
the cryptanalytic skills of Assisi.
In the late 1580s, the Argentis, a family of cryptologists, took over the cipher
secretariat. They were the first to institute certain cryptanalytic methods, use
of which later became widespread. This included a
mnemonic
or
memory aid
key to mix a cipher alphabet. Of great interest to us is Matteo Argenti, who
wrote a 135-page topic on cryptology, which many consider to be the height of
Renaissance cryptography. The Argentis distributed polyalphabetic ciphers to
cardinals for their personal use, but failed to trust them for the bulk of their
cryptographic traGc. When they used these ciphers, they employed relatively
long keys, for reasons cited below.
It was Matteo Argenti who laid claims to being able to cryptanalyze certain
autokey polyalphabetic ciphers. Yet part of this success was due to the use
of “weak keys”, some of which could be easily guessed. However, by the time
Vigenere had developed his ideas and they were refined, the methods of mix-
ing alphabets and using large keys was suGcient to thwart the cryptanalysts of
the day. Nevertheless, the nomenclators (discussed earlier, see page 40), held
sway for three more centuries over its more powerful cousin, the polyalphabetic
autokey cipher. The reasons for this stem from the user more than the cipher.
Cryptographers of the day were not enamored with the slowness of polyalpha-
betic ciphers, of having to always keep track of cipher alphabets, and what they
perceived as a lack of precision, too much room for errors, and so on. Although
not popular in the main, polyalphabetic ciphers did play a role, often a vital
one at the time. We will learn more about this in the next section.
We close this section with Sir Francis Bacon, (1566-1626) whom we already
discussed on page 36. He developed a steganographic device where one sim-
ply changes the typeface of random text to hide the existence of a message.
He also invented a cipher, called
the bilateral cipher
(which today would be
known as 5-bit encryption), in which he used a combination of substitution and
steganography.
In the Chapter 2, we have another 500 years to put under the microscope.
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