[Cryptography] 'The intelligence coup of the century'

Bill Stewart billstewart at pobox.com
Sat Feb 15 01:03:30 EST 2020


On 2/14/2020 9:15 AM, Whitfield Diffie wrote:
>>> BTW, IBM mainframes had powerful radio side-channels: in the early
>>> 1960's, one of the programmers that worked with me used to put an
>>> ordinary portable radio on top of the IBM CPU so that he could
>>> "listen" to his program go through its paces.  Any change in the
>>> audio would indicate a problem with the software.

> 
>> Is this a TEMPEST tool, perhaps long used, even now? Ross Anderson aware of it?
> 
>      Listening to CPUs with radios was common.  I haven't tried it in
> years but I recall being surprised that when I had a TEMPEST-shielded
> Sun workstation in the '90s, it could be heard on the radio.  I don't
> recall much about what is sounded like.  With the PDP-6, I recall that
> you could hear the different phases of a radix sort.

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 TEMPEST-shielded room we had in the mid-late 80s was good to about 
120dB at 450MHz.  Since the VAX ran at 10 MHz, this wasn't too much of a 
risk, though the early Sun Sparc machines were probably 100 MHz and may 
have leaked some harmonics.


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