[A83] Re: DS Thread Extended onto this list


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[A83] Re: DS Thread Extended onto this list



> At 03:28 PM 12/11/2002 -0800, you wrote:
> >(Lurk mode off :)
> >
> >>(See, to  emulate the restriction, you'd have to know how to check for 
> >>it, thus how to break it . . . )
> >
> >Not necesarrily.  Actually checing to see if the os image is valid is 
> >probably pretty easy.  I assume the TI-83 does it in software, which
> means 
> >both that VTI already checks the images (by vitrue of emulating the 
> >calculator), and also anyone clever as disassembly could figure out how
> it 
> >works.  It's actually signing an OS image that's a bitch.
> >
> >I assume (though I'm not sure) that the signing system is a variation of 
> >very well known and understood public-key encryption.  TI signes their OS
> 
> >with a secret, private-key.  The OS can then be verified using a 
> >public-key that can be stored in the TI-83 ROM.  Because of some very 
> >complicated math having to do with number theory, the public key can be 
> >calculated using the private key, but not the other way around.  This is 
> >the way most digital content is securely signed these days.
> >
> >Thus, even though you can check to see if data is correctly signed, you 
> >have no way of actually creating signed data yourself (without years of 
> >CPU time spend brute-forcing the crypto).
> 
> VTI doesn't emulate the os check.  Just see by changing a string in a ROM 
> image.  I wonder, though.  What if you load a hacked os in VTI, then use 
> the Send Product Code feature of said OS to transmit to a real calc via
> the 
> virtual link? 

Did you mean the SendSW (<OS1.14?) or the SendOS (>=OS1.14) option? Don't
bother, I tried it.

-- 
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    Ronald Teune @School
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