The KG-24 was a secure video unit used for the encryption of TV signals between the Pentagon and any site which needed to be secured. With the requirement for encrypting TV signals, the problem of generating keys at extremely high speed had to be solved. Work proceeded and eventually the device was packaged to fit into a single cabinet. There were six Version 1 units built and seven Version 2's. The main hindrance for further development had to do with the high unit cost.
"A History of U.S. Communications Security (Volumes I and II); the David G. Boak Lectures, National Security Agency (NSA), 1973” says this about the KG-24:
Specialized Systems. — There are two other types of systems now in the inventory beyond those I have described that I want to touch on briefly. I have left them till last because they are among the most specialized and have as yet seen relatively little use in comparison with the big Systems we have talked about. The first of these is the KG-24, designed for the encryption of TV signals — civision we call it. With the requirement for encrypting TV signals, we found ourselves faced with the problem of generating key at extremely high speeds, even by computer standards. So far, the fastest system I have described to you was the old AFSAY-816 with a bit-rate of 320 KHz-but this took six bays of equipment and had security, operational, and maintenance problems almost from the outlet. Among the modem systems, the KG-3/13, with bit rates up to 100 kilobits was the fastest. But. aa you know, with your home TV set, you tune to megahertz instead of kilohertz and it takes millions of bits each second to describe and transmit these TV signals.. The KG-24 does it, and in one fairly large cabinet. During the development. radiation reared its ugly head again, and much of the cost and delay in getting this equipment could be attributed to the efforts that went into suppression of these compromising emanations. When I cover the radiation problem I'll show why there are special difficulties when very high speed signals are generated and show you the solution that was chosen in the particular case of the KG-24. The KG-24 uses the Fibonacci principle and works alright. But there are only 6 (V-1) and 7 (V-2) models in existence, and further procurement is not planned. The main thing wrong with it is simply that it costs much too much.
Aandy Turner relates his experiences with the KG-24." I was one of the first to work on the KG-24. I completed 240 hours of training on the machine at Andrews AFB in 1969 and was part of the evaluation and testing team. Two KG-24s were set up between Andrews and the Pentagon to test functionality and system security. The original concept was a one way secured transmission for the use of the President to alert multiple sites of something very important. This was the Cold War era, so you can imagine what the President would have to say. Back then there was the fear of spoofing encrypted data, but encrypted video took care of that so this was a major breakthrough.
During the test period, we had to physically monitor the system for several weeks. The testing required a continuous live video and audio feed, so they decided to use a major TV network as the source of data. The only interesting event that came from the monitoring was a TEMPEST failure. They detected what we were watching outside of the vault. Three screws were inadvertently left out of a panel on the A/D converter. Once the screws were in place we were back in the black. There were two refrigerator size cabinets at each end, with an analog to digital convertor and the KG-24. I guess you can say that this was the first digital TV.
Unfortunately, I do not remember the bit rate but it was wide enough to handle NTSC at 30 frames per second. The testing was completed in late 1969 and as far as I know the system was never deployed. My next assignment was NORAD which I think would have been one of the remote sites, I can safely say now that it did not make it that far. I always wonder what would happen to the equipment after we packed it up. There were only a handful of people at that time that knew it existed. We weren't allowed to talk about it but I could tell my wife what I saw on the soap opera "General Hospital". It is interesting that the only evidence that it did exist is in the “A History of U.S. Communications Security”. Today high speed encrypted video is old news but back in the 1960’s it was a different story. I wish I could remember more".
KG-24 all buttoned up.The cabinet is about 6 feet tall and the Key Generator is top the cabinet. . Part of the KG-24 control panel Lower section of KG-24 cabinet KG-24 nameplate All phots in this table by the National Cryptologic Museum
Contributorss and Credits:
1) David Brooks <brook61(at)bellsouth.net>
2) http://www.governmentattic.org/2docs/Hist_US_COMSEC_Boak_NSA_1973.pdf Pg 65 from the lecture series of David Boak
3) Andy Turner [batwings(at)comcast.net]
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