Re: [fw-wiz] The Mathematics of Relative Security

From: Chris Pugrud (chris_at_pugrud.net)
Date: 09/21/04

  • Next message: ArkanoiD: "Re: [fw-wiz] LDAP and Kerberos?" 
    To: Crispin Cowan <crispin@immunix.com>, Chris Pugrud <chris@pugrud.net>
Date: Tue, 21 Sep 2004 12:28:15 -0700 (PDT)

    --- Crispin Cowan <crispin@immunix.com> wrote:
    > More succinctly, if you ask the question "am I secure?" in a highly
    > rigorous fashion, the likely answer is "Hell no" :)

    This is distinctly the intuitively obvious answer. The more rigourous answer
    is that only insecurity can be proven, testing security reduces to the halting
    problem.

    1. Test security
    2. If you find a problem, stop, the system is insecure
    3. If you run out of tests, get more, you obviously missed something
    4. return to 1

    I'm wondering more if the problem can be reduced to a simple enough model that
    it is both rigorous and meaningful.

    It is easy to prove the relative security of networks that are air-gapped.
    They enjoy absolute relative security because there is no connection between
    them.

    TCP also introduces a wrinkle that is not easily covered by the set theory I
    have learned, or I'm missing something - the concept of one-way membership. If
    a "firewall" sits bewteen A and B and enforces the rule that says A can
    initiate to B, but B can not initiate to A, then A is relatively secure with
    respect to B while B is fully exposed to A. Now expand this to include C, the
    DMZ that sits between them (exercise left to the reader to save space). You
    start to learn more about why DMZ's work and why they fail (or really fail when
    violated). I know that the concepts are obvious to reasonable

    Once this is fleshed out you land into the rather thorny issue of highly
    restricted but not absolute boundaries. What effect does opening up another
    port on the firewall have? I think it's silly to walk down this road until the
    simplest model is rigorously fleshed out. What is intuitively obvious, the
    relative security when the interactions of three domains is analyzed, is much
    harder to analyze when you are talking about complex compartmentalized systems
    that have many domains and non-intuitive boundaries.

    Good reading, thank you for the links,

    Chris

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  • Next message: ArkanoiD: "Re: [fw-wiz] LDAP and Kerberos?"

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