[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?
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