[Cryptography] 'The intelligence coup of the century'

[Henry Baker]

At 10:03 PM 2/14/2020, Bill Stewart wrote:
>Back in the 486 or early Pentium years, I was visiting my parents and noticed that my laptop's screen was showing up, shrunken and slightly out of phase, on their TV set. We were guessing that it was the VGA port on the back leaking signal, but it was certainly fun from a TEMPEST perspective - why bother decoding the CPU's signals when you can receive the screen's output directly?

The NSA came to MIT to recruit computer science people in the early 1970's,
and they brought a van and parked it at the base of the 9-story building
at 545 Tech Square.  Supposedly (I didn't go inside the van, but was told
by others) that the van was showing -- in real time -- the contents of the
video screens on the 9th floor in the computer room.

Since I wasn't there, and didn't see the complete setup, I couldn't
tell from the story whether they were simply receiving the video signals
from the video monitors, or whether they had hacked into the computers.
The video signals would be relatively easy to capture, but then how
could they separate out one particular screen from 50-100 *other screens*
operating in various floors of this building in real time?