Cryptography Reference
In-Depth Information
of other civilizations. The Romans used monoalphabetic
substitution with a simple cyclic displacement of the
alphabet. Julius Caesar employed a shift of three positions
so that plaintext A was encrypted as D, while Augustus
Caesar used a shift of one position so that plaintext A was
enciphered as B. As many moviegoers noticed, HAL, the
computer in
2001: A Space Odyssey
(1968), encrypts to IBM
using Augustus's cipher.
The first people to understand clearly the principles
of cryptography and to elucidate the beginnings of crypt-
analysis were the Arabs. They devised and used both
substitution and transposition ciphers and discovered
the use of both letter frequency distributions and prob-
able plaintext in cryptanalysis. As a result, by about 1412,
al-Kalka-shand
-
could include a respectable, if elemen-
tary, treatment of several cryptographic systems in his
encyclopaedia
Şubı
-
al-a
-
shı
-
and give explicit instructions
on how to cryptanalyze ciphertext using letter frequency
counts complete with lengthy examples to illustrate the
technique.
European cryptology dates from the Middle Ages,
when it was developed by the Papal States and the Italian
city-states. The first European manual on cryptography (
c
.
1379) was a compilation of ciphers by Gabriele de Lavinde
of Parma, who served Pope Clement VII. This manual,
now in the Vatican archives, contains a set of keys for 24
correspondents and embraces symbols for letters, nulls,
and several two-character code equivalents for words and
names. The first brief code vocabularies, called nomencla-
tors, were gradually expanded and became the mainstay
well into the 20th century for diplomatic communica-
tions of nearly all European governments. In 1470 Leon
Battista Alberti published
Trattati in cifra
(“Treatise on
Ciphers”), in which he described the first cipher disk; he
prescribed that the setting of the disk should be changed
