Cryptography Reference
In-Depth Information
table bearing his name and descriptions of the first plain-
text and ciphertext autokey systems.
By the time of the American Civil War, diplomatic
communications were generally secured using codes, and
cipher systems had become a rarity for this application
because of their perceived weakness and inefficiency.
Cipher systems prevailed, however, for military tactical
communications because of the difficulty of protect-
ing codebooks from capture or compromise in the field.
In the early history of the United States, codes were
widely used, as were book ciphers. Topic ciphers approxi-
mate onetime keys if the topic used is lost or unknown.
(A famous unsolved topic cipher is the Beale cipher [
c
.
1820], which purports to give the location of a buried
treasure in Bedford county, Virginia.) During the Civil
War the Union Army made extensive use of transposi-
tion ciphers, in which a key word indicated the order in
which columns of the array were to be read and in which
the elements were either plaintext words or code word
replacements for plaintext. The Confederate Army pri-
marily used the Vigenère cipher and on occasion simple
monoalphabetic substitution. While Union cryptana-
lysts solved most intercepted Confederate ciphers, the
Confederacy in desperation sometimes published Union
ciphers in newspapers, appealing for help from readers in
cryptanalyzing them.
world wars i and ii
During the first two years of World War I, code sys-
tems were used for high-command and diplomatic
communications, just as they had been for centuries, and
cipher systems were used almost exclusively for tactical
