[A83] Re: DS Thread Extended onto this list
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[A83] Re: DS Thread Extended onto this list
(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).
Stupid like a fox!
Look ma, I'm an artist: http://aaronstj.deviantart.com
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