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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 SINCGARS non-ICOM RT-1439/VRC, the KY-57 allows signal fades or losses for up to 12 seconds without losing synchronization.

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. Later SINCGARS ICOM radios, such as the RT-1523, had built-in KY-57 (VINSON) compatibility.
KY-57 voice encryption unit

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 [1], such as the modern SINCGARS radios.
KY-57 voice encryption unit Front panel with the connectors covered Front panel Radio connector Fill and Audio sockets Tamper switch and notch in the top lid Battery compartment Wiping all keys (ZEROIZE ALL)

Cryptographic Keys
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).
Wiping all keys (ZEROIZE ALL)

Mounting bracket
The image on the right shows a typical mounting bracket that was used to mount the KY-57 inside a vehicle. The bracket is also suitable for devices that are housed in a similar case, such as the KY-99 and the HYX-57 wireline adapter.   
Mounting bracket

Wireline Adapter   HYX-57
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 cascaded.

 More information
HYX-57 Wireline adapter

Mounting bracket Bottom view KY-57 with mounting bracket KY-57 in mounting bracket Cable Cable Cable Cable
Connections and controls
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 here.
  • 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)
    C: Crypto
    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.
Demilitarized interior. Rear view of the controls.

  1. TM 11-5810-256-OP-2, Technical Manual TSEC/KY-57
    Headqarters, Department of the Army, Washington, 1 December 1981. 1

  2. 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.

  3. TM 11-5820-890-10-1, SINCGARS ICOM Ground Combat Net Radio
    Headqarters, Department of the Army, Washington, 1 September 1992. 2

  4. TM 11-5820-890-10-3, SINCGARS NON-ICOM Ground Combat Net Radio
    Headqarters, Department of the Army, Washington, 1 September 1991. 2

  5. TB 11-5820-890-10-3, Operation of Wireline Adapter Cable CX-13310/VRC
    Headqarters, Department of the Army, Washington, 1 April 1993. 2

  1. Scanned by Google.
  2. Provided by Liberated Manuals.

  1. Jane's Military Communications, 2005-2006, KY-57
    p. 509. ISBN 0-710-2699-1.

Further information

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Crypto Museum. Created: Saturday 18 September 2010. Last changed: Saturday, 27 May 2017 - 07:58 CET.
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