Re: A89: rom checksum


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Re: A89: rom checksum




As far as I have understand it, the MD5 checksum is cryptaded useing the private
key that ti has. Thats why you cant sign it yourself. the key in the rom is the
public, and can only be used to decrypt the checksum.

//Olle

Robin Kirkman wrote:
> The calculator uses MD5 to compute the ROM checksum when it recieves a
> ROM, right?
> The general opinion is that it uses RSA, but has TI verified this?
> There -are- MD5 romcalls, though...
> 
> Well... MD5 is not a public/private key algorythm.
> MD5 is a hashing algorythm.
> With a single key. (Not public/private)
> Guess what that means...
> 
> s
> 
> p
> 
> o
> 
> i
> 
> l
> 
> e
> 
> r
> 
> s
> 
> p
> 
> a
> 
> c
> 
> e
> 
> It means the key is in the ROM already!
> You just have to step through it, find the routine in the boot loader
> that does the actual MD5 hashing, and the key will be there too!
> Hehe, this means free app signing... ;)
> 
> A bit for the crypto nuts:
> MD5 produces a 128bit checksum, whereas the 89 is rumored to have a 512
> bit one.
> Well, what's to stop TI from having FOUR 128bit checksums? That comes
> out to 512.
> Sneaky, eh?


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