RE: Administrivia: Testing Emergency Virus Filter..

[Dan Stromberg <strombrg () dcs nac uci edu>]

On Wed, 2003-08-20 at 16:56, Nick FitzGerald wrote:

> 2.  I suspect that Mr Turing and a his halting problem will intervene 
> in any attempt to devise a foolproof "this message contains an 
> attachment" mechanism.  The obvious choice to break any such system is 
> steganographic encoding of a binary stream into a text message.  It may 
> be grossly inefficient, but do you think that really matters?

You likely already know this and just thinko'd, but detecting an
attachment isn't equivalent to the halting problem - not with current
protocols/standards at least.  Detecting an attachment with a nasty
payload is equivalent to the halting problem though, which for those who
didn't study theoretical computer science, means "you can't do it very
well, generally speaking".

However, despite nice general-purpose virus/trojan detection being
equivalent to the halting problem, look at all the antivirus companies
making a living doing it anyway.  If it weren't equivalent to the
halting problem, if it were solvable in a reasonable amount of time in
general, then windows (esp.) and mac users wouldn't have to download new
virus signatures all the time.

-- 
Dan Stromberg DCS/NACS/UCI <strombrg () dcs nac uci edu>

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