Re: Checksums on ftp
Peter Cordes wrote:
> that has the same hash as the file you're trying to spoof. (you don't get
> the advantage of the "birthday paradox" (29 people in a room -> 50% chance
> at least one pair has the same birthday) because the other member of the
> pair is already picked: it is the md5 hash of the original file.
a) I seem to recall it's 23 people. FWIW. Can't be bothered to check,
though.
b) The other member of the pair is not necessarily already picked; you
might be
happy to match any one of a given number of base "nasty" files you had
with any one of
the signed packages that someone might want to download. Not sure that
this would
help significantly enough though ;)
> Besides, I'm almost certain that no system cracker would bother to get the
> md5 digests the same on all the files they changed, since most people don't
> check. I'd say you would be able to find changed files > 99% of the time,
> and either you wouldn't find any changed, which would mean a _very_
> sophisticated cracker, or you would find every file she changed. (the
> chance of one changed file randomly staying unchanged is 1/(2^128))
In this case only one file needs to be changed - the .deb for a package
(*any* package
will do - I'm sure the preinst could do sufficiently nasty stuff before
you realised
it wasn't the package you'd thought - or even without you ever
realising).
I'm not saying it's necessarily feasible, just that there are a few
invalid assumptions
flying around.
Cheers,
Nick
Reply to: