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The KY-28 was an analog, voice
encryption device based on transistor circuitry and was the
shipboard/airborne member of the NESTOR family of equipment.
With reference to the photo, the
KYK-38 (the black box on top of the KY-28) was used to input the
key set. Surrounded by a clamshell cover, it contained rows of
pins corresponding to the rows of small holes on the front of
the KY-28. It was keyed through a small coverplate, that when
opened, exposed a number of holes. A key charging device was
used that was comprised of slide stops on a series of rods and a
cam mechanisim to force the rods out to the distance set by the
slide stops against spring pressure. The rods would penetrate
the holes and set permuter contacts according to the depth of
penetration. It took a lot of pressure to load a key set. A
zeroize pin was activated by closing the cover, such that
opening the cover again would zeroize the permuter settings,
which would also render the equipment incapable of passing an
alarm check and passing to operating mode. For aircraft
operation, the policy was to wire the door shut using safety
wire before the aircraft was cleared for flight.
The charging device was set
according to a distributed and classified key list. The KY-28
equipment was owned by individual services and held the
classification of the keys when loaded.
Caption:
The black block sitting on top of the KY-28 is the
KYK-38 and it plugs into the front of the unit. This
device is on display at the MARCOM Museum in Halifax.
(Photo by Jerry Proc)
The device was also fitted
with a internal shock sensor. If the aircraft crashed,
the resulting 'G' forces would trip this sensor thus
resetting the key. This measure was implemented in order
to prevent a keyed up device from falling into enemy
hands. Sometimes the sensor tripped as a result of a
hard landing. As a further security precaution, the
KYK-38 key plug was left on the ground. The KYK-28 had
two lights as well as a plain/cipher switch. A green
light indicated cipher mode and a red light was used for
plain mode. If the unit was zeroed, the green would not
light up even if the cipher/plain switch was switched to
cipher. It would default to plain mode only.
Control of the KY-28 was
facilitated by mounting a KYK-28 control panel in the
cockpit of the aircraft. The pilot's microphone was
plugged into the KYK-28 control assembly and the
encrypted audio output as well the transmit keying line
was wired directly into the audio and control inputs of
the transmitter of transceiver. Voice quality and
recognition using this crypto device was awful. Even
under optimal conditions, every one sounded like Donald
Duck. The only application where I seen it used was in
FM radio voice communications. The KY-28 system was
replaced in the 1980's by a newer family of equipment
that used a digital encryption scheme.
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