Re: [SystemSafety] Statistical Assessment of SW ......

From: David MENTRÉ < >
Date: Wed, 28 Jan 2015 21:27:41 +0100


Hello Mr. Ladkin,

Le 2015-01-23 07:42, Peter Bernard Ladkin a écrit :
> Suppose you have a piece of SW S which is deterministic.

Therefore you assume your software is free of uninitialized variables and similar internal sources of non-determinism. This can be proven but is not regularly applied as far as I know.

> And S reverts to an initial state with no
> memory of its previous behavior each time it produces its output.

Is it a valid assumption, except for the most basic software (e.g. "emergency button handler")? Most safety critical software I know of have modes, memory of current mode and so on.

> Suppose the distribution of inputs to S has a stochastic character.

As others have pointed out, I'm skeptical about that point. Besides hardware failure and other unexpected inputs to the software, you need also to consider an attacker that would systematically use the weakest point of your software (e.g. the special input sequence in your example).

Sincerely yours,
D. Mentré



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