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List:       cryptography
Subject:    Re: [Cryptography] shielding
From:       John Denker <jsd () av8n ! com>
Date:       2017-02-28 22:04:16
Message-ID: dd6518cc-e902-31e2-4a5d-127d9a163057 () av8n ! com
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On 02/28/2017 02:28 PM, Tom Mitchell wrote:

> Quantifying the level of shielding deployed or needed is hard.
> It is almost easy to build a shielded room or home inadvertently.

I disagree.

Let me call attention to Murphy's Law.  One of the corollaries is:
 -- If you want the signal to be strong, it will fade.
 -- If you want the signal to be contained, it will leak.

Murphy's law is sometimes stated in facetious terms, but it has
a solid foundation in engineering principles.  The situation is
very asymmetric:
 -- When a wireless widget is supposed to work, you expect it
  to work everywhere in the home / office / whatever.  So you
  care about the weakest signal.
 -- The attacker, Eve, does not need to succeed everywhere; she
  only needs to succeed somewhere.  So she cares about the
  strongest leak.

Security is hard, and will always be hard.  It requires tremendous
attention to detail.

On 02/28/2017 08:05 AM, Henry Baker wrote:
> When I lived in Los Angeles in the early 1980's, I met someone whose
> business was building Faraday Cage rooms for several million dollars
> a pop.

Try building one sometime.  One that works when there is a strong
source on one side and a delicate receiver on the other side.  One
that works across a wide range of frequencies.

Most people have no idea how to begin.  Even if you know, it's still
a lot of work.

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