EIS-3 (Egorov-Ilyinsky-Staritsyn) - the device, which became serial in 1937, was intended for encryption of radiotelephones. The device was of the "masking" type, based on a simple inversion of the transmitted signal. Additionally, a high-pitched disturbing tone was fed into the communication channel. It was possible to listen to such conversations only with special equipment, but "amateur" interceptions with subsequent decryption were impossible. The Leningrad plant "Krasnaya Zarya" by that time was working at the limit of its capabilities - at the same time, in addition to the EIS-3, a whole series of equipment for simple classification ES-2M, MES, MES-2, MES-2A, MES-2AZh, PZh was sent to the special services 8 and PZh-8M. This made it possible by April 1, 1941, of the 134 government long-distance communication lines, to classify 66 inversion devices as secret.
In 1939, a novelty appeared in the government - a long-distance automation system for HF communication under the MA-5 index, providing communication for 5 subscribers via 10 channels, which made it possible to abandon telephone operators. There was also a variant of MA-3 for three subscribers. Before the war, there were 116 HF stations and 39 broadcasting stations in working order, which made it possible to serve 720 subscribers of the highest party and state leadership at once.
Stalin's phones in an underground bunker in Izmailovo
During the Great Patriotic War, the equipment of the EU series was used on all fronts to organize HF communications. However, simple classification by inversion was clearly insufficient, therefore, back in 1938, a "complex" encryption apparatus S-1 was developed and tested on the Moscow-Leningrad line. Later, the system was tested on the highways Moscow-Khabarovsk and Moscow-Kuibyshev-Tashkent. But the S-1 remained in single copies due to the high cost and complexity of manufacturing. For all this, S-1 did not give a decisive advantage in secrecy over the "simple" algorithm.
Telegraph communications were also encrypted. For this purpose, the S-380M device was used, which was not particularly resistant to burglary. The deciphering could easily be carried out by employees of the People's Commissariat of Communications, and this, given Stalin's difficult relationship with his leaders - Yagoda and Rykov, became a serious obstacle to the widespread introduction of such equipment. Since the beginning of the war, the "suitcase" security equipment SI-15 "Sinitsa" and SAU-16 "Snegir" became widespread, which provided communications to front commanders with communications on the road.
In general, the encryption of radio transmitting devices that appeared in the USSR before the war can be divided into several basic schemes:
- signal transformation by inversion of the frequency spectrum;
- encryption by inversion of conversational frequencies and "wobling" due to the frequency swing of the radio transmitter;
- dynamic inversion and rearrangement of two spectral bands at a given speed (SU-1 apparatus);
- transformation in accordance with a complex encryption system with dynamic rearrangement of three bands of the spectrum according to an arbitrary law and with an arbitrary speed within known limits (SET-2).
Despite all the efforts of domestic engineers, in 1940 the long-term result of their work was succinctly described: "The equipment for classifying telephone conversations, developed by the order of the NKVD by the Krasnaya Zarya plant, is weak and has no code."
Vladimir Alexandrovich Kotelnikov on a modern postal envelope and in his youth.
A kind of kind wizard in this situation was Vladimir Aleksandrovich Kotelnikov (1908-2005), who since 1938 headed the laboratories for classifying telephone and telegraph information at the Central Research Institute of Communications. Vladimir Kotelnikov can rightfully be considered one of the most outstanding Russian scientists - academician of the USSR Academy of Sciences, twice Hero of Socialist Labor, laureate of numerous prizes. His areas of interest included radio engineering, radar, radio astronomy, as well as the theory of anti-jamming communications. Many of his achievements are included in textbooks with the words "for the first time in the world." Vladimir Kotelnikov formulated and proved the sampling theorem on which all digital signal processing is based. His laboratory developed the "Moscow" hardware complex, in which, for the first time in the country, telegraph messages were classified by imposing cipher signs on the text. Kotelnikov's idea of imposing a cipher on the text became a fundamental breakthrough in the theory of encryption, becoming the basis for many subsequent generations of classified technology.
The device "Moskva" S-308-M is interesting. It was based on complex and rather bulky electromechanical assemblies, as well as drums filled with balls. During the rotation of the drums, through the system of pins from the slots, the balls were randomly rolled along six vertical tubes onto two moving telegraph tapes superimposed on each other through a "carbon copy". After that, the tapes were perforated according to such marks, which formed a random key, which was later sent to the places where the devices were installed. A photoelectric cell was responsible for reading the cipher from the key. The novelty was tested on the super-long communication line Moscow - Komsomolsk-on-Amur, and in the same 1938, an order was placed at plant No. 209 for 30 Moskva devices at once. The success of the development of Vladimir Kotelnikov was that the new system provided almost 100% protection of telegraph messages from decryption.
The very next year, Kotelnikov's laboratories received a new assignment to develop an encryptor for encrypting speech with increased resistance to unauthorized listening. The order came from the very department of the government HF communications of the Soviet Union. Alexander Mints, Konstantin Egorov and Viktor Vitorsky also took part in the development project. The group tried to ensure the secrecy of information transmission using the unique multichannel radio communication equipment they created, which for the first time used a single sideband. And it turned out: in 1939, on the Moscow-Khabarovsk highway, a speech encryption system using a new algorithm started working. Vladimir Kotelnikov came up with the idea of a potentially undisclosed cipher, which he formulated literally three days before the start of the Great Patriotic War.
In his memoirs, Kotelnikov writes: “Using a one-time key is also useful for classifying both wired and radio telephony. Only there, everything is much more complicated, and in the case of analog transmission of the speech spectrum, without converting it into digital, it is impossible to obtain absolutely stable classification. A high degree of durability can be obtained, but not absolute. With mosaic spectrum encryption, even if a one-time key is used, the system remains vulnerable, since each “piece” remains unencrypted by itself. That is why it is important to make the intervals as small as possible, but at the same time the quality of the transmitted speech is lost."
In the laboratory, under the leadership of Vladimir Kotelnikov, a new telephone scrambler of the "mosaic" type was developed, which combined frequency transformations of a speech signal with the permutation of its segments in time. The highlight of the device was the dynamic transformation, which changed according to the law of distribution of random variables, which was extremely difficult to decipher even for high-class specialists. The system produced quasi-random permutations of hundred-millisecond speech segments that were known only to the recipient, as well as two frequency bands with speech signal inversion.
Another brainchild of the Kotelnikov group was the first cavity vocoder in the USSR, the name of which comes from the English combination voice coder - a voice encoder. The device was brought to a working prototype, which was tested and showed the fundamental possibility of compressing a speech signal. Kotelnikov wrote in this regard: “In order to make it more difficult to decipher the transmitted speech, it was important to make the“segments”into which we split it, as short as possible. And this is a problem, because then the quality of the transmitted speech deteriorated. I began to think how to transfer speech not all completely, but somehow to compress its spectrum. I began to examine the spectrum of sounds in order to understand which frequencies are defining … At this time, I caught my eye a link to an article by Homer Dudley, published in October 1940, where it was said that he had made a speech converter - a vocoder. I rushed to look, but it turned out that nothing concrete was written there. But all the same it was very useful: he has the same idea, which means that we are on the right path. So we started making our own vocoder. And just before the war, we already had a prototype of it working. True, while he still "spoke" poorly in a "trembling voice".