Re: A89: Re: faking a rom

To: assembly-89@lists.ticalc.org
Subject: Re: A89: Re: faking a rom
From: Jimmy Baker <ashbar83@yahoo.com>
Date: Mon, 5 Jun 2000 07:10:18 -0700 (PDT)
Reply-To: assembly-89@lists.ticalc.org

Talk to Wormhole....

--- Juan Corral <juancorral@lvcm.com> wrote:
> 
> Just one question, why are "we" all of sudden
> assuming that the key is
> 512-bits?  I think it's a far, more reasonable
> number (*hint*) something
> like 24-64-bit.  But I'm probably wrong...
> 
> Juan
> TI-Net @ http://www.tinews.net
> 
> ----- Original Message -----
> From: "Robin Kirkman" <misty@drrobin.yi.org>
> To: <assembly-89@lists.ticalc.org>
> Sent: Saturday, June 03, 2000 3:04 PM
> Subject: A89: faking a rom
> 
> 
> >
> > i just thought of a way to reduce the amount of
> brute forcing for
> generationg
> > your own ROM from 2^512 to 2^68...
> >
> > I make the assumption that the 512bit checksum is
> really just 8 RC5
> checksums
> > (64bits each), that was then encrypted w/ RSA.
> >
> > I also make the assumption that the checksums are
> sequential, eg:
> >
> > There is 1mb of FlashRom.
> > There are 8 checksums.
> > the 1st 128kb are used for checksum 1
> > the 2nd 128kb are used for checksum 2
> > the 3rd 128kb are used for checksum 3
> > etc..
> >
> > rather than trying to brute force the RC5, which
> has not only a big key
> size,
> > but is slow, instead focus on the rc5.
> > essentially, i can change that first 128kb of
> flashrom any way i like,
> provided
> > that the rc5 checksum for it is the same as the
> rc5 checksum for the
> original.
> > since an rc5 checksum is 64 bits, and each bit of
> the input is equally
> likely to
> > change any bit on the output...
> > leave 8 bytes (64 bits) that you are going to
> brute force with. run the
> rc5 on
> > that 1st 128kb with different values for those
> 64bits, and eventually, you
> will
> > get an rc5 checksum that matches the original!
> >
> > on average, brute forcing one of the rc5 checksums
> will take 2^63
> operations.
> > on average, brute forcing all 8 will take 2^66
> tries.
> >
> > this is within the limits of modern day computing!
> > if we can write our own rom image with correct
> checksums, we can, for
> example,
> > modify it to not check the checksums on
> applications... thereby removing
> the
> > necessity to purchase TI's SDK.
> >
> > anyone else got ideas for this?
> > --robin
> >
> 
> 


__________________________________________________
Do You Yahoo!?
Yahoo! Photos -- now, 100 FREE prints!
http://photos.yahoo.com