Re: SCADA

On Wed, 15 Apr 2009, Marcus J. Ranum wrote:

> A reliable system is one that does what it is designed to do,
> no less. And certainly no more. An "insecure" system is one
> that does quite a bit more than it was designed to do - namely
> it hosts hostile activity. When discussing "normal" system

1.  I'm not sure "no more" fits in the definition- for instance a system 
that's designed to send company email can also send personal email- how 
does that make the system less reliable?

2.  An "insecure" system _can_ host hostile activity, but that doesn't 
mean it does.

> That's not exactly true. A system that does exactly what it
> is supposed to - no more, no less - is achievable. It's not

I'm not sure it's achievable.  General purpose systems are too flexible to 
be completely locked down.  I can use my "Shift" key to play the Monty 
Python theme, certainly not a design goal...

> Where we get into problems is when the requirements are not
> anything that can actually be accomplished. As Tom Ptacek once
> pointed out, in a fit of brilliance, the problem is that we
> have general-purpose computers that are designed to be
> programmable to do anything; and we want to restrict what
> they can do.

I'd already typed the GP computer comment, so I'm leaving it in.

> If I had a dollar - just one dollar - for every time I've
> heard that, I'd be retired and I wouldn't care if the power
> grid I rely on melts down.

If I had one beer for every time I've heard that, you'd be out of beer!  
Again! :)

Paul
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