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DS-102 →
DS-101   EKMS 603
Common fill interface protocol

DS-101 is the current interface standard for electronic transfer devices, or fill units, developed and endorsed by the US National Security Agency. It superceedes the older DS-102 standard and is supported by nearly all modern radio sets and encryption devices, although most equipment is still backward compatible with DS-102. DS-101 is supported by fill devices like the AN/CYZ-10.

DS-101 is described in the EKMS 603 standard, but unfortunately this standard is not publicly available. It is known however, that DS-101 is an asynchronous serial protocol running at 64 kb/s.

The physical interface is commonly implemented as RS-485, but RS-232D versions are known to exist as well, which can be useful for application in Personal Computer (PC) based environments. In most cases, devices that support newer DS101 – with an anynchronous RS485/RS232 interface – still support the older synchronous interface and are therefore backward compatible with DS102.
AN/CYZ-10 in operation

Unlike the DS-102 standard — which can only transfer cryptographic keys and frequency hopping tables — DS-101 can differentiate between various key and data types by using data tagging. As a result, DS-101 can also be used for distributing firmware and cryptographic algorithm updates.

DS-101 fill units on this website
AN/CYZ-10 Data Transfer Device
Thales DTD-II - Data Transfer Device 2
DS-101 compatible devices on this website
Narrow-band Voice and Data Terminal
KG-40A Replenishment
For connection between the FILL unit, and a radio or encryption device, most devices used a standard U-229 connector. In many cases, this connector is shared with the audio functions of a military radio, for example for the connection of a handset. This connector has 5 or 6 spring-loaded contacts, and is available in a male and female variant, as shown in the diagram below.

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Although each variant has its own specific type number, they are often referred to as U-229/U, or simply U-229, after the female 5-pin cable part. The table below shows the pinout of this connector for the DS-102 standard. On encryption devices this connector is commonly used exclusively for the FILL function, but on radio sets it is often shared with the audio functions.

Pin DS-101 Description Note
A GND Ground (common wire)  
B RTS Request to Send  
C RX Data out of radio or crypto device  
D TX Fill data into radio or crypto device  
E CTS Clear to Send  
F - -  
  • Interface
    RS485 and/or RS232D
  • Type
  • Baudrate
    64 kb/s
  • Handshake
  • Protocol
Help wanted
At present, not much is known about DS-101, EKMS-603 and the underlying data structure. You can help us to expand this page by providing additional information about transfer devices that use DS-101, supported radios, supported encryption devices, and the underlying data structure.

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Crypto Museum. Created: Sunday 11 February 2018. Last changed: Wednesday, 24 August 2022 - 20:01 CET.
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