Re: Integrity checking NANOBSD images

At 04:45 PM 11/07/2006, R. B. Riddick wrote:
>--- Poul-Henning Kamp <phk@phk.freebsd.dk> wrote:
> > Arming a trojan to just do 'sleep 145 ; echo "sha256 = 0248482..."'
> > when you thing you're running sha256 would be trivia.
> >
>But what if the trojan copies its files to the RAM disc and waits for this
>sha256 binary showing up? And then, when it is there, it removes its 
>changes on
>the hard disc  (those changes certainly must be in unused (formerly zeroed)
>areas of the hard disc or in the (zeroed) end of certain shell 
>scripts... Or do
>I miss something?

Yes, sounds possible.  Between checks, "undo" the trojan.  However, 
the binary would have to live somewhere on the flash or it would not 
survive reboots and you would have to tinker with the bootup process 
to load the trojan at boot time.

>Wasn't is usual some years ago to switch the boot disc hardware to "read only"
>mode? I dont know how to do that, but my source seemed to be trustworthy
>(although I never saw him - I just heard his voice...)... ;-))
>
>A switch like on those 1.44'' floppy discs would be good...
>But then software/OS updates would require physical access to the box...

For this app, the problem is that there might indeed be physical 
tampering with the box despite some reasonable efforts to lock it up. 

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