[Milsurplus] red/black TTY shipboard question

[Mike Andrews]

On Tue, May 08, 2012 at 10:39:42AM -0400, Nick England wrote:
> I apologize for not being very clear - Yes, I am familiar with
> red/black, TEMPEST, etc. - first learned about them 40 years ago when
> I was an engineer for the Naval Electronics Systems Command.
> 
> My question now is how and why this switch/indicator set-up was used -
> Why was TTY gear in a classified space sometimes switched to a black
> (unclassified) circuit - to copy or send what kind of traffic? What
> gear was typically plugged into this switch box? And am I correct in
> my guess as to why it says CAUTION on the UNCLASSIFIED indicator?

Let us suppose that you're getting ready to set up an encrypted circuit. 

You start with the crypto gear switched out of line, so that it's your TTY
to the TTY at the Distant End (DE), with a bunch of other gear in between
that is transparent when (and if) it works.

You verify that you will be using keying material setting X on your
receiver and his transmitter; this is easily and safely done in the clear.
You set up your receiver and tell him to start his transmitter when he is
ready. Now the circuit from him to you is secure, and he tells you to use
keying material setting Y on your transmitter. You ack that, he tells you
he is ready for you to start your transmitter, and you do so. You verify
that the circuit is good both ways in secure mode and turn it back to the
operators.

If the circuit is, say, from Japan to Hawaii over HF, then when the techies
can't find a good freq and the propagation sucks, you can wind up doing
this every 5 to 15 minutes on a bad shift. I have a whole walk-in closet
full of those T-shirts. Shorter-haul microwave circuits are a whole lot
more stable, but we already knew that.

And sometimes you may want to use a spare channel as an cleartext chat
channel for debugging things -- hardware issues or, as I found myself doing
once, personnel issues. I was TDY to ROK, supposedly to fill a critical
personnel shortage. They had me cleaning and adjusting weapons in the
armory, and then mowing the $%^&*( lawns.

This didn't indicate a critical personnel shortage, so I got on a spare
(unencrypted) channel back to my home unit in Japan, got my shop NCOIC on
the other end, and we discussed what was going on. The next day I was in
the comm center, doing what I was sent to do, and someone else was mowing
the $%^&*( lawn.

And yes, I think you are right w.r.t. the "Caution" legend on the UNCLAS
indicator: don't open a BeadWindow, to use more recent terminology.

-- 
Mike Andrews, W5EGO
mikea at mikea.ath.cx
Tired old sysadmin