Listening to cuban spies

What are number radio stations

Spoiler: No, this article will not feature James Bond level hacks with death-defying findings. However, it will show you that anyone can peek into the workings of intelligence agency broadcasts with very little equipment.



The principle of number stations is very simple: using a schedule and frequency known to both the agency and agents, encrypted broadcasts are sent from the originating agencies to agents in the field, usually using an automated mechanism. While these can take many forms (for example, Russian stations use digital transmissions), the classic way to send messages is by sending series of numbers that can be decoded using a One-Time Pad given to agents, hence the name "Number station". The use of one-way radio communications is not new and dates back to the early 20th century, peaking around WW2 and declining in use until the beginning of the 21st century. However, many are still around to mystify their listeners with c

A simple blog post wouldn't do justice to all the community work that has been put into finding and cataloguing spy stations, often referred to as "Number stations". For more information on such stations, check out ENIGMA2000's page, a UK group specialized in the monitoring of number stations.

HM01: The cuban connexion

Also known as the "Atencion lady!", HM01 (it's ENIGMA code) is known to use very powerful emitters located in Havana, and thus is very easy to tune in to. It follows a very strict schedule and format on the AM band, with the number-coded message sent first, followed by a digital file transfer using RDFT, a RDFT, a rare differential phase shift keying mode.  You can decode the file transfers using an old and buggy Windows application called DIGTRX written by PY4ZBZ. Of course, the files are encrypted and nobody from the public has spoken out as having been able to decrypt them yet.

PY4ZBZ came up with a pretty complete schedule for the station, which you can find on his site, along with a thorough reverse-engineering of the radio signal.

Tuning in with any SDR that can reach these frequencies, you'll be welcomed by the famous creepy and mysterious sounds of intelligence broadcasts.

Enjoy !



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