Friday, January 09, 2009


I just happened across an interesting page on signals intelligence. Signals intelligence is about finding out what the enemy is doing by intercepting radio and other electromagnetic signals. There is a lot of information at the link but let me focus on one small part to give you a flavor of the page.

Monitoring friendly communications

More a part of communications security than true intelligence collection, SIGINT units still may have the responsibility of monitoring one's own communications or other electronic emissions, to avoid providing intelligence to the enemy. For example, a security monitor may hear an individual transmitting inappropriate information over an unencrypted radio network, or simply one that is not authorized for the type of information being given. If immediately calling attention to the violation would not create an even greater security risk, the monitor will call out one of the BEADWINDOW codes[9] used by Australia, Canada, New Zealand, the United Kingdom, the United States, and other nations working under their procedures. Standard BEADWINDOW codes (e.g., "BEADWINDOW 2") include:
I'm just going to give a couple of the BREADWINDOW codes and an example of how they can lead to an adverse impact during war time.
5. Friendly or enemy key personnel: "Movement or identity of friendly or enemy officers, visitors, commanders; movement of key maintenance personnel indicating equipment limitations."
7. Wrong circuit: "Inappropriate transmission. Information requested, transmitted or about to be transmitted which should not be passed on the subject circuit because it either requires greater security protection or it is not appropriate to the purpose for which the circuit is provided."
Leading to:
In WWII, for example, the Japanese Navy made possible the interception and death of the Combined Fleet commander, Admiral Isoroku Yamamoto, by BEADWINDOW 5 and 7 violations. They identified a key person's movement over a low-security cryptosystem.
The study of crypto and communications intelligence is one of my hobbies. If it interests you the link is provided.

Cross Posted at Classical Values

1 comment:

Anonymous said...

In WWII the Germans knew that it was, in theory, possible to break enigma with a known plaintext attack, but didn't believe that anyone would put out the effort needed to do so.

The British build COLOSSUS and broke Enigma, the Germans didn't know until AFTER the war that for most of it the Allies were reading their supposedly secure messages.

(The known plaintext bit came from the standard header type information that was pretty easy to guess at (message recipient, dates etc))

Actually the usual Enigma machines were pretty easy and they were cracking them without bothering to do a known plaintext attack, the naval version of Enigma was stronger and it took longer for them to break it.

They also went to great lengths to keep the Germans from suspecting that Enigma was broken (spreading rumours about how they knew things, mythical new radars etc, sometimes they let the Germans succeed in attacks they knew were coming but took steps to lessen the impact, eg fewer ships in a convoy)