Re: A89: RE: rom checksum
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Re: A89: RE: rom checksum
But who's to say it has to be a 56-bit RSA? Didn't the government just
approve Netscape's 128-bit encryption to be exported outside the U.S.? And
besides, TI has a French unit too. They could do the encryption stuff in
France and ship to the U.S.
Bryan
----- Original Message -----
From: "Robin Kirkman" <misty@drrobin.yi.org>
To: <assembly-89@lists.ticalc.org>
Sent: Thursday, December 09, 1999 9:29 PM
Subject: Re: A89: RE: rom checksum
>
> I was getting my info from _Applied_Cryptography_, by Bruce Schneier.
>
> Anyways... If the calculator used -only- MD5 to create the checksum,
> them it would be easy to generate our own checksums whenever we wanted.
> What TI has done, i think, is to have 4 MD5 checksums (totaling 512
> bits) and then use the RSA algorythm to encrypt them.
>
> Please keep in mind i'm pulling most of this info outta my ass, if
> somebody wants to verify how the ti89 does the checksum, i'd be much
> obliged...
>
> Anyways, RSA has two keys. One of them TI keeps secret, and the other is
> inside the calculator rom. Because of the way the algorythm works, if
> you encrypt something with one key, the only way to decrypt it is with
> the other key. By encrypting the ROM's checksum with their secret
> (private) key, it is now only decryptable with the public key, which is
> inside the ROM. If the calculator decrypts the checksums with the public
> key and it doesn't match a checksum that it calculates itself, then it
> declares the ROM to be crap.
>
> Anyways, what it gets down to is this- there is a VERY large number
> stored in the ROM somewhere that is the product of two very large
> primes. If we could factor this number and find out what the primes are,
> then we could break the encryption. However, that would kinda take a
> while.
>
> Hrm... does anybody here have access to a supercomputer? Like a
> university one, or something? I think 56-bit RSA (The maximum legal
> exportable, i believe) can be broken in a few days with some of the more
> powerfull computers. Although it might take a few weeks to factor that
> number, it would be a whole lot cheaper than paying for signatures :)
>
> Anyways, that's prolly enough rambling for me now...
> --robin
>
> Javier wrote:
> >
> > Where can I find info on RSA, MD5, etc .
> > I would love to know what you are talking about !!
> > Bye
> > Javier
> > PD Why are you so happy, is MD5 easier to hack,why ??
> >
> > -----Mensaje original-----
> > De: Robin Kirkman <misty@drrobin.yi.org>
> > Para: assembly-89@lists.ticalc.org <assembly-89@lists.ticalc.org>
> > Fecha: Miércoles 8 de Diciembre de 1999 21:06 p.m.
> > Asunto: A89: rom checksum
> >
> > >
> > >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?
> > >
> > >Well, i'll be off to go look for code which resembles MD5.
> > >Anybody who wants to join, feel free!
> > >--robin
> > >
>
>
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