User:Anewcharliega/KO-6

The KO-6 was the workhorse of Secret and Top Secret military communications in the late 1950s and early 1960s. It was capable of encrypting Teletype, Fax and Voice, but did very poorly with voice and somewhat worse with Fax. It was magic with Teletype signals, though. It could encrypt five channels of Teletype signals (between two stations) simultaneously with a very low error rate, all five channels operating at full speed of 100 wpm (words per minute)in full duplex. Ordinarily, four of the five channels were used for regular communications, the fifth channel was reserved by the Crypto operations for essential communications to maintain the encrypted link between the stations.

The machine was the size of three refrigerators [1]and somewhat the same configuration in gray steel cases. Each of the refrigerator-size bays was made of two units, one atop the other. The bays on the right and left were identical and were dedicated separately to transmission and reception. The middle bay was the same size as the other two but was dedicated to power and control. All bays were firmly attached together. On top of the machine sat an oscilloscope and some other electronic test equipment. The electronics in the bays was on wired chassis with glides, essentially drawers. Well over a thousand vacuum tubes controlled the switching. Except for the few special purpose tubes in the central bay, all the tubes were dual-triodes and each was configured into a bistable multivibrator (aka "flip-flop) the common circuit of a computer. Each of the drawers had attached near the front corner a “pin straightener” for correcting bent pins on the tubes. There was a simple tube tester in the middle bay for checking suspected tubes. Troubleshooting the machine was reminiscent of finding the burned out bulb in a 1940s vintage string of series-wired Christmas tree lights. A known-good tube replaced the tube in the first socket in a suspected drawer. If that did not solve the problem the tube that was removed was deemed to be working and it replaced the tube in the second socket, and so forth until the bad tube was discovered. Of course, a great deal of theoretical understanding was required before one could begin to guess which tube to replace. So many vacuum tubes in a confined space was an invitation to failure, and the majority of failures resulted from burned out vacuum tubes.

The encryption algorithm was based on a pseudorandom string of numbers, much the same as present-day algorithms are. The generation of that string of numbers differed greatly from present day techniques, though. The string was generated in real time and had to be duplicated on both terminals of the communications link simultaneously. The actual generation was accomplished electromechanically. Steel disks with notches around their perimeter were rotated in a magnetic field, and the changed magnetic fields around the notches were picked up by coils much like the pickups in an electric guitar. Essentially, each notch generated an electrical pulse which was fed into the system. There were six disks on each side of the system (transmission and reception) and each disk had a unique diameter and a unique rotation speed. The hubs which drove the disks were arranged around a central drive gear, each hub having a driven gear with a different number of cogs thus giving the different rotational speeds of each disk. Complicated enough already, each of the six disks was replaceable, and each was one of a set of several (maybe ten) disks of the same diameter with different patterns of notches around the perimeter. Each of these disks were marked for identification, and were packaged in identical sets which were distributed with the KO-6 machines around the world. Not only could the six disks be replaced, but each one could be indexed, that is, rotated independently of the other five, to a pre-determined start position.

In operation, clear (un-encrypted) communications were required. In one form, those communications were printed lists of each of the six disks and the index numbers for each one. These lists were distributed by the National Security Agency (NSA) initially, and later by secure teletype over the very lines that were encrypted by the KO-6. The only real-time communication needed was an agreement as to page and line number in the list for a start. To simplify a simultaneous start, one machine was “slave” to the “master” which transmitted a start signal. The “clear” communications for this took the form of letters in an international phonetic alphabet and some numbers (golf, tango, five, oscar, papa, delta) . The pre-determined understanding was something to the effect that, “You are master, we are slave, we are ready, we acknowledge that you are ready, let’s go” At this point both machines were idle, six disks on the transmit side of each machine were matched and indexed the same as the receive side on the other machine, and the operators at both ends of the link were hopeful that everything would go well. Then the “master” started both machines and the operators watched the oscilloscopes. Starts were never simultaneous, but nearly so, and a phase shifter on the “master” machine would slightly shift the rotation of the central drive gear which was turning all six code disks. Normally this resulted in a flat-line signal on the oscilloscope, indicated that the two machines were synchronized. Occasionally the synchronized start failed and protocol required a new index position for the disks. Three failures required replacing all twenty-four disks on both machines. Although the pseudorandom chain of pulses was said to be able to run for years or decades without repetition, the whole system was shut down every eight hours and re-started with different disks at different index positions.

Security for the equipment and its operation was executed by locating the machines in the most secure areas of the various military installations where they were installed. Often this was underground, possibly several stories below ground level, and always behind several guarded checkpoints. The room which housed the KO-6 was always a vault with a minimum four-place combination lock. Operators and maintenance technicians were cleared for Top Secret access with a Crypto endorsement on their clearance. No one without that endorsement was ever admitted to the crypto vault. Additionally, all the equipment including the code disks was fitted with thermite explosive charges designed to reduce it to molten metal in the event that it was in imminent danger of being captured by an enemy force.

Secure communications through KO-6 required that a KO-6 be installed at each terminal of the network. Locations of KO-6 machines in 1960 included but not necessarily limited to: Pentagon, Washington, DC, HQ SAC, Omaha, NE, HQ NORAD, Boulder CO, HQ Eighth Air Force, Vandenberg AFB, CA. Hickam AFB, HA, High Wycam (sp) AFB, UK, Weisbaden, DE, Thule AFB, Greenland.