[GreenKeys] Declassified NSA Document Reveals the Secret History of TEMPEST

[Bryan Brodie]

great story @ wired.com about reading electrical signals from an
unshielded teletype:

"Bell Telephone faced a dilemma. They had sold the equipment to the
military with the assurance that it was secure, but it wasn't. The
only thing they could do was to tell the [U.S. Army] Signal Corps
about it, which they did. There they met the charter members of a club
of skeptics who could not believe that these tiny pips could really be
exploited under practical field conditions. They are alleged to have
said something like: "Don't you realize there's a war on? We can't
bring our cryptographic operations to a screeching halt based on a
dubious and esoteric laboratory phenomenon. If this is really
dangerous, prove it."

So the Bell engineers were place in a building on Varick Street in New
York. Across the street and 80 feet away was Signal Corps Varick
Street cryptocenter. The engineers recorded signals for about an hour.
Three or four hours later, they produced about 75% of the plain text
that was being processed--a fast performance, by the way, that has
been rarely equaled."

story: http://blog.wired.com/27bstroke6/2008/04/nsa-releases-se.html

declassified document: http://www.nsa.gov/public/pdf/tempest.pdf