[Cryptography] 'The intelligence coup of the century'

[Whitfield Diffie]

> >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.

> >I would guess that this radio technique would have been sufficient
> >to enable a person listening to pick out the individual bits in a
> >modular exponentiation, as those computers weren't all that fast.

> >We didn't have a name for it, but in retrospect we should have
> >called it 'ADB' -- 'Audio Debugging Bridge'.

> >I never tested the *range* of these radio signals, but I suspect
> >that they could easily have been heard outside the building
> >where the computer was located.

> 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.

                           Whit