The first publicly documented use of the CK-42 dates back to 1980,
when the CIA
reportedly smuggled the first CDS-501 radio set into Cuba for use
by their agents in or near Havana .
The device measures only 100 x 68 x 18 mm and weights just 160 grams,
extemely small for its age, making it very easy to hide the device.
It has a memory capacity of 1579 characters that are encrypted with
a 19-character key. All text is entered on the keyboard by means of a
stylus. Including the message preamble, the longest message
that can be sent is 1596 characters.
The device is connected to an external battery or a transmitter, via
a connector at the top.
Once a message is stored in the device's internal memory, and the device
is connected to a transmitter, it can send the message
as a high-speed data burst that takes 4 to 21 seconds,
depending on the length of the message.
The device was first used with the
CDS-501 line-of-sight (LoS) transmitter
and shortly afterwards also with the
RS-804 satellite communicator.
Although the CK-42 unit is labelled as COMSEC Controlled Item, many of
them are known to have fallen into enemy hands.
The CK-42 was introduced around 1980, but it took several years before
the radio sets that were supplied with it, were reliable enough for field
The device is known to have been used in the Soviet Union (USSR),
Cuba, Poland and East-Germany (DDR), right until the end of the
In CIA nomenclature, CK = Coder/keyer.
The diagram below shows the control panel of the CK-42. The device
connects to the transmitter via a wide connector at the top. Messages
are entered via the 32-button keypad that should be operated with a sharp
object like a stylus. There is no optical feedback of the entered data.
For a full description of its operation, please refer to the desciption
of the CDS-501
or RS-804 radios.
Before entering a message, a 19-character encryption KEY is entered.
The keys were supplied on a separate sheet and a new key was used for each
message. According to [1 p.29], the keys were supplied to Cuban agents printed on
plastic tape. Each tape was suitable for 135 messages.
The CK-42 was compromised in several cases, along with the associated radio sets.
There are documented cases of captures of this equipment in Cuba in 1983
and in Russia, also in 1983 .
Furthermore, it is suggested in  that the
Cubans were able to capture quite a few of these devices. The same device were
also captured by the Russians in Afghanistan at late as 1988.
➤ More information about the Cuban capture
➤ More information about the Russian capture
Although the CK-42 and the accompanying CDS-501 and RS-805 radio sets
are mentioned and described in several publications ,
there is very little detailed information about these devices
in the public domain.
At present we have no better pictures than the ones shown above
and the encryption algorithm is still unknown. As the devices are no longer
in use and many of them have
fallen into the hands of 'hostile' countries
during the 1980s, there can be no good reasons to withhold such information.
If you have any further information, please contact us.
- José Luis Morera et al., The CIA's War Against Cuba
Havana, 1988. Published by the Cuban National Information Service
in cooperation with the Ministry of the Interior of the Republic of Cuba.
- Jan Bury, Project Kalina: The Lotos Operation Conundrum
Cryptologia 36:2, April 2012, pp. 119-128.
- Robert Wallace & H. Keith Melton, Spycraft: The secret story of the CIA's Spytechs...
2008. ISBN 978-0593062043.
- Archives of the Polish Institute of National Remembrance (IPN)
Information on the PHOBOS agent radio communications device from the First
Secretary of the US Embassy in Moscow R. Osborne on 7 March 1983.
Warsaw 1983. 1
Available at the Archives of the Polish Insitute of National Remembrance.
File # IPN BU 01304/953.
Original text: Informacja dotyczaca agenturalnej aparatury
lacznosci radiowej 'FOBOS' zatrzymanej u pierwszego sekretarza ambasady
USA w Moskwie R. Osborne'a w dniu 07.03.1983 r. Warszawa 1983.
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© Crypto Museum. Created: Monday 07 September 2015. Last changed: Sunday, 25 February 2018 - 14:49 CET.