[langsec-discuss] Is computation half the story?

Sashank Dara krishna.sashank at gmail.com
Fri Mar 27 11:41:35 UTC 2015

Interesting read. Have come across "Emergent Behavior in Cyber Security"

Not sure if that would help you in some way. But it is an important area of


On Fri, Mar 27, 2015 at 5:52 AM, Taylor Hornby <havoc at defuse.ca> wrote:

> I wrote a blog post...
> https://defuse.ca/how-do-we-model-this-robot.htm
> ...wherein I make the distinction between a machine's computational
> abilities (i.e. which languages can it decide?) and a machine's
> "informational" abilities (i.e. how can the machine influence the
> outside world? what APIs is it allowed to call?).
> I chose the the term "informational" for lack of a better word because
> it is about information entering and exiting the machine, or moving
> between "parts" of the machine.
> I concluded the post by claiming computer science has no general theory*
> of this property. We understand computation well from computability and
> complexity theory, but "informational" capabilities are only understood
> through limited models like ACLs, Bell-LaPaudula, noninterference, etc.
> Those models are properties systems should have in order to be called
> secure. I'm thinking more along the lines of starting with a given
> system then quantifying its its "power" and proving theorems about what
> it can and can't do. Most importantly, relating the power of one given
> system to another given system.
> The models we have lack completeness and generality. There is no
> equivalent to the Church-Turing thesis for informational capabilities.
> There are no theorems about what happens when we "nest" systems. (Think
> about questions like: If System B is a process running on System A, is
> System A free of covert channels if-and-only-if System B is?).
> So: Am I right about this? Are we really missing half of the picture? Or
> do the models we have satisfy our needs? Has it been proven that no such
> theory can exist, or if it did it couldn't be useful?
> I would appreciate references to the literature.
> If what I am saying makes any sense at all, I propose we stop thinking
> of "access control"-type notions as part of information security.
> Instead, they should be studied as a fundamental part of computer
> science, in complete generality (not an easy task!).
> Thanks,
> - Taylor
> * By "theory" I mean a general system of knowledge and understanding.
> Think "theory of evolution", not "theorems."
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