Have they stopped teaching Defense in Depth?

Jay Ashworth jra at baylink.com
Tue Nov 15 15:16:12 CST 2011

----- Original Message -----
> From: "William Herrin" <bill at herrin.us>

> That your computer is not globally addressable ADDS one layer of
> security in a process you hope has enough layers to prevent an attack
> from penetrating.
> And make no mistake: successful security is about layers, about DEPTH.
> You can seek layers from other sources but a shallow security process
> will tend to be easily breached.

This is precisely the point I've been trying to make, and it ties in to my
observations in response in the SCADA thread: not only does the number of
layers matter, so does their "thickness".  Certainly, if you're trying to
"air-gap" a SCADA network to protect it from attack, then you are admitting
a certain degree of vulnerability if your circuit passes through any sort of
transport multiplexer, like a DACS, as that's a place an attacker could
reconfigure to take control of your traffic.

But mounting *that* attack requires insider knowledge of 4 or 5 layers of 
extra information which will be necessary to exploit such an attack.

My estimation is that that makes that layer of your defense in depth "thicker"
than some other layers might be.

Those who think NAT provides no security seem still to be mounting the strawman
that we think it *provides* security, rather than merely contributing some bits

-- jra
Jay R. Ashworth                  Baylink                       jra at baylink.com
Designer                     The Things I Think                       RFC 2100
Ashworth & Associates     http://baylink.pitas.com         2000 Land Rover DII
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