Re: [RFT] Reed-Solomon

[Colin Watson]

On Tue, Sep 28, 2010 at 11:13:40AM -0400, Phillip Susi wrote:
> On 9/27/2010 7:34 PM, Lennart Sorensen wrote:
> > FlexNet and similar like to write to track 0 sectors (outside partitioned
> > space) to store license info.  This clobbers part of grub potentially.
> > So to make grub more tolerant of such misbehaviour, the idea suggested
> > was to add error correction to grub so it can survive attacks on its code
> > (and even potential disk errors).
> 
> Ahh, neat.  Two sectors of ECC can fix one that is completely destroyed?
>  I was under the impression that you could only fix a few corrupted
> bits, not an entire sector, but I suppose if you add enough ECC...

http://en.wikipedia.org/wiki/Reed-Solomon_error_correction says that t
check symbols can correct up to floor(t/2) symbols.  (ISTR Vladimir said
he had a variant which did better than this, but I haven't looked yet.)

> I take it that someone has already made sure that the misbehaved
> software only uses a single sector?

All the examples I've seen so far are thus.  Of course if you have
multiple infections then you're doomed, but hopefully the probability of
multiple infections goes down fairly sharply ...

-- 
Colin Watson                                       address@hidden