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← KY-57
Voice and data encryption unit - wanted item

TSEC/KY-99A is an Advanced Narrowband Digital Voice Terminal (ANDVT), developed in 1994 by the US National Security Agency (NSA). It was used for many years by the US Department of Defence (DoD) for secure voice and data communication over narrow band radio channels. It is interoperable with the other members of the ANDVT-family and is backward compatible with the wideband KY-57 (VINSON), which it replaces. It is also known as NSN 5810-01-391-0187.

The image on the right shows a typical KY-99 unit that was built by ITT Industries. The unit measures 140 x 77 x 200 mm and weights approx. 2 kg. It is a stand-alone unit that needs its own battery (connected at the back).

At the front are three sockets. At the top are two standard 6-pin U-229 connectors for AUDIO and DATA respectively. The DATA connector is also used to connect a standard key FILL device such as the KYK-13. The 13-pin high-density connector for the radio is at the bottom left. The volume control/power switch is at the center.

The ANDVT-family was launched in the late-1970s with the introduction of the AN/USC-43 Tactical Terminal (TACTERM). It was based on the NRLs first successful implementation of the LPC-10 vododer in 1973 [1] and uses SAVILLE as one of its algoritms. The KY-99 (MINTERM) is in fact a miniaturized version of the TACTERM. Its design is based on a modular architecure and, compared to TACTERM, its size is much reduced. The KY-99 features full key distribution plus remote key capability (OTAR) and was certified for secure traffic up to TOP SECRET (NSA Type 1).

Development of the KY-99 was started in the early 1990s, with the first training sessions around 1992 [4]. The design was finalized in 1994, when it was assigned an NSN code. It replaced the narrow-band KY-65 (2400 bps, HF) and the wide-band KY-57 (16 kbps, VHF/UHF). By 2006, over 40,000 ANDVT units were in operation at the US Navy, Air Force, Army, Allied Forces and US government agencies. This includes 9363 units that represented a value of US$ 6207 each [2].

KY-99 front panel
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KY-99 front panel

The MODE selector is at the bottom right. There are 5 modes of operation: Plaintext, Ciphertext, Re-key, Off-line and ZEROIZE. Pull the knob to delete all crypto keys instantly. The rest of the operation is via the three push-buttons and the green 8-position alpha-numerical display.

  • Low-power
  • Lightweight
  • Single channel
  • Half-duplex
  • Narrowband, wideband or wireline
  • Secure voice and data (simultaneously)
  • Full key distribution
  • Over-the-air rekeying (OTAR)
  • VINSON (KY-57/58) legacy mode
  • Improved SATCOM performance, improved synchronisation
  • Improved LPC-10 voice coding algorithm (V58), 2400 baud
  • CVSD voice coding, at 12 and 16 kbps (wideband)
The KY-99A is compatible with the other members of the ANDVT-family, such as the KY-100 (AIRTERM). It is also backward compatible with some legacy products, such as the KY-57 (VINSON), in which case it uses wideband CVSD modulation. As far as we currently know, the KY-99 is compatible with:

HYX-57   Wireline Adapter
The HYX-57 wireline adapter allowed two KY-99 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

  1. Naval Research Laboratory,
    Fulfilling the Roosevelts' Vision for American Naval Power (1923-2003)

    30 June 2006 p. 39 (approved for public release)

  2. Naval Research Laboratory,
    Fulfilling the Roosevelts' Vision for American Naval Power (1923-2003)

    30 June 2006 p. 65 (approved for public release)

  3. NRL and the Advanced Narrowband Secure Voice Terminal
    Timeline of the ANDVT development.

  4. Tim Weichel, Experience
    Certificate of the MINTERM full maintenance course. July-August 1992.
    Retrieved November 2009 from
Further information
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Crypto Museum. Created: Thursday 30 August 2012. Last changed: Wednesday, 24 August 2022 - 20:08 CET.
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