Burdens of Proof: Cryptographic Culture and Evidence Law in the Age of Electronic Documents

Radio

26 Chapter 2 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 operations .24 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 communications 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 headquarters 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.25 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, organizational 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.”26 ...