The first developments in the USSR in the field of cryptographic protection of information date back to the beginning of the 20s. They were aimed at encrypting the speech signal. Developments were based on the principles of single-sideband modulation of electrical sound signals, heterodyne frequency conversion, registration of speech signals on a magnetic medium, for example, wire, and other similar inventions.
Soviet scientist, corresponding member of the USSR Academy of Sciences Mikhail Aleksandrovich Bonch-Bruevich in 1920 proposed a modernized version of the temporary reshuffle. What it is? Imagine that the speech to be classified is recorded on magnetic tape. After recording, the tape is cut into small fragments, which are then glued together according to a predetermined permutation algorithm. In such a mixed form, the flow of information is sent to the channel of the telephone line. The simple principle of turning the audio information flow was proposed back in 1900 by the Danish engineer Waldemar Poulsen and was called the time inversion. Eighteen years later, Scandinavian engineer Eric Magnus Campbell Tigerstedt refined Poulson's idea by proposing temporary permutations. As a result, the receiver-telephone only needs to know about the original algorithm (key) for rearranging fragments and restore the sound information. Bonch-Bruyevich made everything much more complicated by proposing in each segment of several segments to carry out a permutation according to a special cycle.
Mikhail Alexandrovich Bonch-Bruevich
The practical implementation of domestic developments was carried out at the Research Institute of Communications of the Red Army, when, during 1927-28, 6 hydroelectric power station devices designed by N. G. Suetin were created for the OGPU and border guards. Also, the institute carried out work on the further modernization of the secret field telephone to the model of GES-4. The importance of the topic of classifying telephone conversations in the USSR is evidenced by the fact that a whole bunch of departments were involved in this problem: the People's Commissariat of Post and Telegraph, the mentioned Institute of Communications of the Red Army, the Comintern Plant, the Research Institute of Communications and Telemechanics of the Navy, Research Institute No. 20 of the People's Commissariat of Electrical Industry and a special laboratory NKVD. Already in the 30s, high-frequency government communication lines were put into operation between Moscow and Leningrad, as well as Moscow and Kharkov. The Krasnaya Zarya plant launched the serial production of three-channel high-frequency telephony equipment SMT-34 (range 10, 4-38, 4 kHz), which met the requirements for speech clarity at a distance of 2000 km. By the middle of 1931, it was possible to establish more or less acceptable HF communication between Moscow and the capitals of most of the Union republics, military districts and regional centers.
But even such a connection, given the proper level of professionalism of the spies, could be easily intercepted, since it protected only from direct eavesdropping. In fact, a high-frequency current flowed through the wires, which was not perceived by the human ear without special treatment. A detector receiver of the simplest design solved this problem, and telephone conversations of the highest level could be tapped without problems. Interestingly, the former People's Commissar of Internal Affairs Yagoda admitted during interrogations that he deliberately hindered the development of new equipment for protecting communication lines, since he did not understand how to conduct total wiretapping of telephone conversations with new secrecy technologies.
The Soviet Union, in addition to everything, felt its own lag in the development of automatic telephone exchanges, which had to be purchased from the German Telefunken. The procedure for importing such equipment into the Union was amusing: all the labels were removed from the equipment and in a clean eye they presented it with their own development. Signing of a non-aggression pact between the USSR and Germany in 1939 was indicative. Stalin conducted all negotiations with Hitler by means of the Siemens telephone scrambler and the Enigma encryption machine brought from Germany. The USSR did not have its own equipment of this class. After finishing the negotiations, Stalin invited Ribbentrop, Molotov and his company to his place and solemnly proclaimed: "Hitler agrees with the terms of the contract!" Later, everyone who, in one way or another, ensured direct communication between Stalin and the Fuhrer, either died under mysterious circumstances, or disappeared in prisons.
Molotov signs the pact on August 23, 1939
Molotov and Ribbentrop after the signing of the Soviet-German Treaty of Friendship and the Border Between the USSR and Germany
The potential vulnerability of government HF communications was first announced in a report by senior technical engineer M. Ilyinsky on August 8, 1936. At that time, agents of foreign special services in the personnel serving communication lines were considered as malefactors. In 1936, special tests were carried out near Minsk, during which a long-wave antenna intercepted telephone conversations at a distance of 50 meters from the communication line. In 1937, agents reported that there was an unauthorized connection on the Moscow-Warsaw line in Poland. A year later, the head of the government communications department, I. Vorobyov, wrote a report in which he raised the alarm about the complete lack of secrecy in the Kremlin's long-distance negotiations. They reacted quickly and laid a special cable to connect the HF communication with the telephone exchange of the Kremlin. But the rest of the buildings of the government of the USSR continued to use the city telephone network.
After a large volume of warnings about discrediting the secrecy of negotiations, the People's Commissariat of Communications began to develop special protective filters for equipping long-distance telephone lines with them. At the beginning of 1941, a special device was put into operation in Tallinn - a "noise curtain", which significantly complicated the interception of HF communications by radio equipment. Later, this know-how began to be widely used in the government departments of Moscow and Leningrad. For all the counterintelligence's concern with the problems of Western espionage on the territory of the USSR, the problem of manning the HF communication lines was somehow missed. Only on May 5, 1941, a decree appeared, transferring all classified communications to the category of government communications.
With an obvious internal shortage of its own classified equipment, the management had to turn to foreign companies for help. The Americans supplied the USSR with a single spectrum inverter for the Moscow radiotelephone center, and the Germans from Siemens in 1936 tested their encoder on the Moscow-Leningrad line. But for obvious reasons, it was impossible to fully rely on the reliability of such a telephone connection.
By 1937, the leadership of the relevant departments presented fairly simple requirements for Western manufacturers: a compact device was required that could protect against decryption using a radio receiver. The condition of protection against decryption of information using a technique of a similar complexity was not even mentioned. Requests went to Switzerland (Hasler), Sweden (Ericsson), Great Britain (Standart Telephone and Cables), Belgium (Automatik Electric), Germany (Lorenz, Siemens & Halske) and the USA (Bell Telephone). But it all ended ingloriously - most of the companies refused, and the rest asked for an incredible 40-45 thousand dollars for those times just for the development.
The building of the telephone factory "Krasnaya Zarya" (late 19th - early 20th centuries)
As a result, devices for automatic encryption of telephone conversations, called EU inverters, went into series at the Krasnaya Zarya plant. The abbreviation is derived from the names of the main developers - K. P. Egorov and G. V. Staritsyn. They did not stop there, and by 1938 they mastered a more complex device ES-2, which was distinguished by the ability to transmit no more than 30% of all readable text to a subscriber - everything else was lost. But the encryption went in full without loss. We tested the EC-2 on the Moscow - Sochi line in August 36th and came to the conclusion that the equipment requires high quality communication channels.
Despite all the difficulties of use, on January 5, 1938, a decree was issued on the launch into production of the first domestic apparatus for automatically classifying telephone conversations. It was assumed that the NKVD will receive twelve half-sets of racks by May 1 to equip government communications with them.