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Short Range Agent Communication

In the espionage trade, Short Range Agent Communication (SRAC) is method for delivering and collecting information by means of short range radio. It is in fact the electronic variant of the so-called dead letter box, which is why it is also known as electronic dead drop (EDD) or electronic dead letter box (EDLB) [1]. It is a practicle implementation of Near Field Communication (NFC).

The first use of SRAC dates back to the Cold War in the early 1960s, and was exploited by both sides. It usually involved small electronic devices that were capable of making burst transmissions in the VHF radio band, sometimes even with data encryption. The devices were used for delivering messages at an electronic dead letter box (EDLB).

An early example of an SCRAC device is the VHF FM transmitter that is shown in the image on the right. It was used by the Czechoslovakian secret services in many espionage operations, and used an UHER tape recorder as the storage device.
UHER 206 EDLB transmitter - interior

In this case, the tape recorder was used to play back a verbal message at the highest possible speed, but there are also examples of (Western) devices that were as small as a pack of cigarettes and that were able to record and playback encrypted digital messages at very high speed (burst).

One example is a US-made set, known as CDS-501, that was reportedly captured in Cuba [1] and in the former USSR [2]. These devices are also thought to have been used in Central and Eastern Europe [2]. It operates in the VHF-H band and sends bursts of data, encrypted with a CK-42 device, from an agent to a receiving station located in a Western diplomatic facility (embassy) in the hosting country. Other known sets are the RT-517, the RT-519, the CDR-701 (RX only), and the RS-804, with the latter being the long-range variant of the CDS-501, that works via satellite.

SRAC devices on this website
Czech UHER-based one-way electronic dead letter box
Infra-red transceiver (Lichtsprechgerät) JO-4.03 developed in the DDR
Modular infra-red transceiver (Lichtsprechgerät) developed in the DDR
Wanted item: American short-range agent transmitter
RS-804 satellite message burst transmitter (long-range variant of CDS-501)
Miniature encryptor for burst messages
Known SRAC devices
  1. Long range variant of the CDS-501.

  1. Wikipedia, Short-range agent communications
    Retrieved September 2015.

  2. Jan Bury, Project Kalina: The Lotos Operation Conundrum
    Cryptologia 36:2, April 2012, pp. 119-128.
Further information
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© Crypto Museum. Created: Thursday 04 October 2018. Last changed: Thursday, 25 November 2021 - 20:57 CET.
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