Voice encryption unit
- wanted item
The KY-57 was a
wide-band secure voice (WBSV) encryption unit,
developed by the US National Security Agency (NSA)
in the mid-1970s as replacement for the
NESTOR cryptographic products,
such as the KY-38.
It was suitable for use with a wide range of military radios and telehone lines.
As part of the VINSON family of devices, it was the main crypto 'workhorse' of
the US Army during the 1980s. Even today, many radios and voice encryption devices are still backwards compatible with the KY-57.
The device is also known as TSEC/KY-57 and
as NSN 5810-00-434-3644.
The KY-57 uses the GCHQ/NSA-developed
Type-1 SAVILLE cryptographic algorithm.
When used in combination with a radio transceiver, such as the
the KY-57 allows signal fades or losses for up to 12 seconds without losing
The KY-57 was eventually superceeded by the KY-99 that
offers newer - more advanced - cryptographic algorithms, but that was still
backwards compatible with the KY-57.
ICOM radios, such as the RT-1523,
had built-in KY-57 (VINSON) compatibility.
Both voice and data can be encrypted with the KY-57.
Voice data is digitized using Continuous Variable Slope Delta modulation
(CVSD), similar to other voice crypto systems of the same era, such as
the Philips Spendex-10 ,
the Spendex 50
and the Telsy TS-500.
Data from the CVSD modulator is mixed with data from a key stream
generator that is seeded by a Traffic Encryption Key (TEK).
The resulting digital data stream of 16 kbps requires a wide-band
radio channel, making it unsuitable for use on HF radio frequencies.
Rather than the standard 5 kHz (voice only) channel spacing, the KY-57 requires
a 25 kHz channel, which is why it is VHF/UHF only.
The airborne version, with the same characteristics
albeit in a different enclosure, is known as KY-58.
The KY-57 was interoperable with the
British BID/250 (Lamberton).
It was sometimes used in combination with
HAVE QUICK frequency hopping.
Development of the KY-57 started in 1972, with the first devices being
available in 1975. it was widely fielded in the early 1980s and
was in production until 1993, when it was replaced by more advanced
encryption units such as the KY-99 and radios with
integrated COMSEC ,
such as the modern SINCGARS radios.
The KY-57 has room for 6 front panel selectable cryptographic keys.
Keys 1 to 5 are the Traffic Encryption Keys (TEK). They are either loaded
manually, using a key fill device
such as the KYK-13
and the KOI-18,
or by means of Over The Air Rekeying (OTAR).
Key number 6 must always be loaded manually as it is the Key Encryption Key
(KEK) that is used for OTAR.
When loading the keys manually, the MODE selector (S2) should be placed in
the LD-position. When updating keys 1 to 5 remotely, S2 should be set to
RV (Remote Variable).
The HYX-57 wireline adapter allowed two KY-57 units to be interconnected
via a 2- or 4-wire telephone line, up to a distance of 16 km (10 miles).
In case longer distances were required, multiple HYX-57 units could be
➤ More information
All controls of the KY-57 are on the front panel. The three major connectors
are on the front panel as well. The only other connector is the power socket
which is located at the rear panel.
A detailed description of all connectors can be found on
Brooke Clarke's website.
A detailed description of the
U-229 AUDIO/FILL sockets can be found
- S1 - Operation (right)
OFF: Power OFF
ON: Power ON
TD: Power ON with Time Delay enabled (needed for satellite use)
- S2 - MODE (center)
P: Plain voice (pull out knob first)
LD: Load keys manually
RV: Remote key loading (Remote Variable, OTAR)
- S3 - Key (left)
Z 1-5: ZEROIZE keys 1 to 5 (pull out the knob first)
1-5: Selection of the Traffic Encryption Key (TEK)
6: Select the Key Encryption Key (KEK) for OTAR-use
Z ALL: ZEROIZE ALL keys (pull out the knob first)
- R1 - Volume
This is an analog control (potentiometer) that is used for controlling
the audio volume of the unit. Turn right to raise the volume.
- J1 - AUDIO (right)
Standard U-229 6-pin socket for the connection of audio equipment such as
a headset and/or microphone.
- J2 - FILL (center)
Standard U-229 6-pin socket for the connection of a US military DS-102
compatible key fill device such as the KYK-13.
- J3 - RAD (left)
19-pin connection to a suitable radio set,
such as the PRC-77 UHF FM rig.
- J4 - POWER (rear)
Standard US military power connector. Used for the connection of a battery
box or an external power adapter.
Although the KY-57 is a relatively old device, it is still very difficult -
if not impossible - to find a complete and working unit. This is
mainly due to the fact that some KY-57 units might still be in operation with
the US military or their Allies. Furthermore, later cryptographic devices,
such as the KY-99 and some
SINCGARS radios, are
often backwards compatible with the KY-57.
In the late 2000s however, demilitarized versions of the KY-57 sometimes showed
up on auction sites such as Ebay. Although the internal electronics have all
been removed from these devices, they are still cosmetically complete and do
look nice in any cryptographic collection.
The image on the right shows an example of such a demilitarized KY-57 unit.
All PCBs have been removed from their sockets and the flex wiring has been
cut at various places.
With some effort, it would be possible to convert the unit into a demonstrable dummy.
- TM 11-5810-256-OP-2, Technical Manual TSEC/KY-57
Headqarters, Department of the Army, Washington, 1 December 1981. 1
TM 11-5810-256-OP-6, Operating Procedures KY-57 WANTED
Operating Procedures for Communications Security Equipment TSEC/KY-57
(with HYX-57/TSEC) FM Secure Remote Communications.
Headqarters, Department of the Army, Washington, 12 May 1983.
- TM 11-5820-890-10-1, SINCGARS ICOM Ground Combat Net Radio
Headqarters, Department of the Army, Washington, 1 September 1992. 2
- TM 11-5820-890-10-3, SINCGARS NON-ICOM Ground Combat Net Radio
Headqarters, Department of the Army, Washington, 1 September 1991. 2
- TB 11-5820-890-10-3, Operation of Wireline Adapter Cable CX-13310/VRC
Headqarters, Department of the Army, Washington, 1 April 1993. 2
- Jane's Military Communications, 2005-2006, KY-57
p. 509. ISBN 0-710-2699-1.
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© Crypto Museum. Created: Saturday 18 September 2010. Last changed: Tuesday, 07 March 2017 - 21:21 CET.