31 January 2013. Add A2 comment.
30 January 2013
Inadvertent Via Cavity Emanations
This NSA paper raises the question of more general inadvertent via cavity
Based on the research of cavity resonation* -- which transmits non-electronically
inadvertent emanations requiring TEMPEST or other protection -- is there
research on similar threats of cavity emanations of other computer, network
or communication components which might bypass electronic or other shielding
protection built-in to systems?
Answers to cryptome[at]earthlink.net
* One of the most famous cavity resonators was installed in a Russian gift
to the US Moscow embasssy.
this undated one-page paper:
Technology Profile Fact Sheet
Title: Via Construction to Dampen Cavity Modes in Printed Circuit Boards
Technical Challenge: Vias are used extensively in printed circuit board (PCB)
construction to connect signals from the surface to internal layers and to
provide connectivity between layers in the PCB. However, high speed signals
that transit through these vias can launch propagating modes in cavities
that are created within the PCB. There is very little damping present within
the PCB laminate stack to attenuate these modes once they are launched, resulting
in noise coupling with other signals that propagate along the vias. Although
this drawback can be reduced by using buried vias or by increasing the number
of layers for routing, either approach adds considerable expense to the PCB
Description: This invention constitutes a significant addition to known
technology. It modifies the construction of existing vias by addition of
a radio frequency (RF) absorbing layer to the copper metallurgy that is currently
used to connect different layers. By suitable choice of material thickness
and resistivity, these modified vias will absorb RF energy rather than reflecting
it, thereby reducing the level of noise coupling within the PCB.
In conventional PCB processing, the PCB laminates are stacked and cured,
followed by mechanical drilling to define the through vias. The entire assembly
is then immersed into a seed bath, and a uniform layer of copper is plated
everywhere. In the proposed modification, the laminate is stacked and drilled
as before. However, two additional steps are inserted. The first is a selective
deposition of plating of a resistive material, which does not occur on the
copper, but does coat all other surfaces. Second, the insulating layer is
fortified by exposing the material to oxidation. (If the copper oxidizes
also, the copper oxide is easily removed without affecting the insulating
layer.) The process flow then continues as in the traditional method.
Demonstration Capability: Not at this time.
Potential Commercial Application(s): This invention is potentially applicable
to any manufacturer of digital or analog systems that operate at high rates
Patent Status: A patent application filed has been filed with the USPTO.
Reference Number: 1493
Thanks to A, this appears to be the patent, not by NSA but by two individuals,
Kwark; Young Hoon (Chappaqua, NY), Schuster; Christian (Buchholz, Niedersachsen,
I think the embassy bug was a mechanical box that would flex from sound and
could be read via microwaves and the doppler effect on them from the moving
box walls. The description of RF absorbing layers on a PCB would mostly be
of benefit *inside* the closed shielded grounded conductive enclosure you'd
find sensitive electronics in. Ie, for the benefit of other electronics in
the enclosure, NOT for the reduction of ability of eavesdroppers. Sure, PCB
RF-absorbtion might reduce the amount of signal (noise :-) you have to stop
getting out, but its mostly of use for preventing interference within the
system --the enclosure. Its a lot easier to generate whatever you want inside
a chassis and filter the chassis than to do what is described. What is described
is mostly useful for keeping in-chassis electronic noise down. Just my two