Re: Cisco IOS Shellcode Presentation

[Valdis.Kletnieks () vt edu]

On Fri, 29 Jul 2005 15:02:51 -1000, Jason Coombs said:

> There are any number of technical solutions that one could use to 
> redesign, fundamentally, the turing machine so that before each 
> operation is performed a verification step is employed to ensure that 
> the operation is the correct one in the correct sequence given prior 
> configuration settings loaded into memory at the time the device was 
> activated.

Ahem. No.  You *can't* "ensure" it (although you *can* do things like bounds
checking to *minimize* issues).

It's called the Turing Halting Problem, and in fact, the 'Turing machine' was
invented specifically to (a) show the problem for that simple architecture, and
then (b) show that all Turing-equivalent systems have the exact same problem.

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