Cryptography Reference
In-Depth Information
Radio
The radio completed the communications revolution in modern warfare,
as well as fostering the growth and systematization of the second leg of
cryptology, that is, cryptanalysis. Because it provides military commanders
with a copy of every enemy ciphertext, the radio made cryptanalysis even
more important than cryptography, a weapon that could be depended
upon to continuously provide fresh information relevant to ongoing oper-
ations.
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After World War I, cryptanalysis thus became a permanent and
major element of military intelligence and espionage. The significance of
radio transmission for intelligence did not however lie solely in the ability
to cryptanalyze enemy texts, but also in analyzing patterns in communica-
tions themselves. On the Great War's Western Front, for example, French
intelligence personnel
recorded call-signs, volume of traffic, and correspondents for all stations. These soon
segregated themselves into four main networks, each of which, the French assumed,
belonged to a combat group. The patterns of correspondence defined the headquar-
ters stations and volume soon differentiated the fast-moving and fast-sending
cavalry stations from the infantry. Occasional clear-text signatures disclosed the
commanders' names. In this way, the French gradually built up a picture of the
German forces facing them. . . . Traffic analysis aided in delineating the enemy order
of battle, and frequently forewarned of important enemy activities by detecting an
increase in message volume.
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Increased reliance on cryptographic communication also gave rise to
new difficulties. As radio increased the number of messages pouring in and
out of army communication centers by an order of magnitude, organiza-
tional problems of scale and human factors impeded the efficiency of the
ciphering systems. The important resources devoted to cryptanalysis meant
the slightest mistake would be immediately exploited by the adversary,
while the pressures of military operations provided little of the serene
conditions propitious to the performance of complex ciphers. Training had
to be provided, as well as observed. Thus, “the great practical lesson of
World War I cryptology was the necessity of infusing an iron discipline in
the cryptographic personnel,” and the head of the French cryptologic
section sternly warned his cipher clerks: “Encode well or do not encode at
all. In transmitting cleartext, you give only a piece of information to the
enemy, and you know what it is; in encoding badly, you permit him to
read all your correspondence and that of your friends.”
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