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| A KG-13 unit. One drawer bears the designation KGD-3/TSEC. The total weight is around 250 pounds. (Photo courtesy Bill Rhoads, BGR101(a)aol.com) |
The KG-13 was controlled by "key cards". These were IBM-like punch cards that determined the starting point of the KG-13 encryption which was done by "koken stages". The key cards were changed daily at HJ time. When the USS Pueblo, with a live KG-13 aboard, was captured by the North Koreans in 1968, the personnel didn't have time to destroy it. As a result, a working model of the KG-13 fell into enemy hands. NSA quickly designed a modification to the koken stage board to alter its operation in order that the enemy didn't have an identical working model.
CARD READER DESCRIPTION
Select this link to see the inside of the card reader. Ronald Coppock, who worked with the KG-13 indicates that it was fitted with a card cutter and also without. "In Ethiopia, I worked at two locations (Stonehouse and Tract C) that had KG13's equipped with the KW26 style card cutters. All the machines at Stonehouse were equipped that way and about 20% at Tract C. At the 7th Radio Research in South East Asia, about 30% of the KG13's had the card cutter style card readers. 13's equipped with the card cutters were operated on very high priority circuits with short cycles to change key material. Some were on 6 hour and others on 12 hour cycles".
The KG-13 did have a major difference in that in its latter years, it was equipped with a Card Reader Insert Board or CRIB.
INTERNAL DESCRIPTION
The KG-13 employed "FLYBALL" modules. These were modules comprised of discrete components set up as logic element circuit groups such as AND gates, OR gates, FLIP FLOPs, Inverters etc. Once tested, the modules were potted in a compound whose colour indicated functionality. The coloured potting compound was extremely hard and any attempt to penetrate it resulted in damage to the internal circuitry.
In a KG-13, the following colours are confirmed: Pink, Yellow, Green, Blue, Red, Orange and Black. Purple and Brown modules were probably used but those colours are unconfirmed as of this time.
Failures usually occurred in the power supplies, buffers, and synchronizers though most problems were quickly resolved. When new, there was a high frequency of failures due to cold solder joints.
One board in the KG-13 had a black module which was a noise generator. Repair depot technicians were told it was the only module which was classified because the noise from a diode was used to generate a random key stream used in the encryption process.
The circuitry inside the module then used the koken chains to create an extremely random key stream. That was why there was no problem in restarting the KG-13 with the same card. The noisy diode ensured that the chances of duplicating the start point was not measurable by any standards known at the time.
Two of the key cards were for the transmitter and the third for the receiver. There were two for the transmitter because it had two key generators. The keystream mixed with the plain text produced the ciphertext. Two key generators generating the same keystream should match bit for bit at the output and a mismatch would cause a crypto alarm and a shutdown of the output. A key generator failure would stop transmission and prevent a compromise. With only a single key generator in the transmitter a failure could produce a trivial keystream (all one's, all zero's or alternations). A receiver key generator failure just produced garble. The KG-3 could be used to transmit or receive since there is a XMIT/RECV switch on in the lower right hand portion of the lowest unit.
In the 1964/65 time frame, crypto techs were taught that it would
take 50,000 years to break the key on a KG-13 using state of the art techniques
which were available at the time. The KG-13 also employed traffic flow
security.
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| An internal view of one of the drawers showing the potted component technique. (Photo courtesy Bill Rhoads, BGR101(a)aol.com) |
Steve Gardner recalls "One of our operations sites which monitored satellites used an item called a "shark" between the teletype and the KG-13. It was a block message transceiver".
The KG-13 device was taken out of service around 1989-90. This was one of the last discrete component crypto machines built. Shortly after this time, integrated circuits started to appear in crypto machine designs.