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Re: Design principles and ethics

From: Bas Wijnen
Subject: Re: Design principles and ethics
Date: Mon, 1 May 2006 23:20:23 +0200
User-agent: Mutt/1.5.11+cvs20060403

On Mon, May 01, 2006 at 11:31:56AM -0400, Jonathan S. Shapiro wrote:
> > > In order to guarantee confinement (and encapsulation, as you define it
> > > below),
> > > A. The instantiator must know that there is no unauthorized outward
> > >    communication.  Unauthorized by the instantiator, that is.
> > > B. The parent must know that information cannot be extracted from the
> > >    program without the parent's consent.
> > > 
> > > Now the question is: are these requirements fulfilled for the case of
> > > "trivial confinement".  Indeed they are, because in that case the parent
> > > and the instantiator are the same process, which leads to an implicit
> > > trust of each other.
> > 
> > But trivial confinement adds an additional, perhaps unwanted,
> > requirement:
> > 
> > C. The child cannot have any capability that the parent couldn't gain
> > access to.

This is correct, but it isn't an extra requirement.  Just like in the
constructor, the child cannot receive a capability that neither the parent
nor the instantiator possess.

> I think that this is correct, but it would be more precise to say: "the
> child cannot have any *initial* capability that the parent couldn't gain
> access to.
> Subsequent interaction may lead to the process acquiring more
> capabilities.

Yes, but the parent could also have received these without spawning the child.
Trivial confinement does not lead to rights for any party, that they couldn't
get without starting a new process.  It can only be used to protect the parent
from a potentially malicous and/or buggy child, due to the confinement and


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