On Sep 24, 2009, at 3:13 PM, M.B.Jr. wrote:
On Thu, Sep 24, 2009 at 2:21 PM, David Shaw <ds...@jabberwocky.com>
wrote:
On Sep 24, 2009, at 12:30 PM, M.B.Jr. wrote:
Hi David,
about the first "tidbit":
On Tue, Sep 22, 2009 at 6:08 PM, David Shaw
<ds...@jabberwocky.com> wrote:
First of all, someone has factored a 512-bit RSA key (the one
used to
protect a TI programmable calculator, it seems). It took 73 days
on a
dual-core 1900Mhz Athlon64. It took just under 5 gigs of storage
and
around
2.5 gigs of RAM. In other words: not much at all. It's not some
big
distributed project - rather it's a single guy who wanted to
factor it
and
just left it running in the background for 2 and a half months.
(This is
actually a month old - forgot to send it before now).
http://www.unitedti.org/index.php?showtopic=8888
dummy question:
by factoring a public key integer, one can get somehow to its
corresponding private key?
Yes, that's exactly what happens. If you factor the public key,
you can
derive the private key.
Is this a generic asymmetric premise?
I mean: is it valid both to the (computational) Mathematics behind
OpenPGP's and X.509's public keys' integers?
Factoring is an attack against RSA. It applies to wherever RSA keys
are used, whether OpenPGP, X.509, or whatever you like.
This idea is not specific to RSA though: there are other, similar (in
general concept, though not in the specific math of course) attacks
against other asymmetric systems. The goal is to make it hard (for
whatever definition of "hard" works for your particular environment)
to derive anything non-public from the public key.
Keep in mind that nobody has used a 512-bit key in many years (they're
too small, as this result makes clear). It seems TI's mistake here
was in choosing a 512-bit key in the (around) 1999-2001 time frame,
and not realizing that less than a decade later, that key length would
be small enough for someone to factor in their spare time. It's a
little surprising, as it was well known around that time that 512 bits
were not sufficient. I wonder if the memory size and CPU capability
of what is essentially a pocket calculator influenced that decision.
David
_______________________________________________
Gnupg-users mailing list
Gnupg-users@gnupg.org
http://lists.gnupg.org/mailman/listinfo/gnupg-users
