Re: GnuPG 1.4.16 fixes RSA key extraction via acoustic side channel (CVE-2013-4576)

[mancha <mancha1 () hush com>]

Solar Designer <solar@...> writes:
> Hi,
>
> GnuPG 1.4.16 was released today with a curious security fix:
>
> http://lists.gnupg.org/pipermail/gnupg-devel/2013-December/028102.html
>
>  * Fixed the RSA Key Extraction via Low-Bandwidth Acoustic
>    Cryptanalysis attack as described by Genkin, Shamir, and Tromer.
>    See <http://www.cs.tau.ac.il/~tromer/acoustic/>.  [CVE-2013-4576]
>
> Direct link to paper (8 MB; the website feels very slow at the moment):
>
> http://www.cs.tau.ac.il/~tromer/papers/acoustic-20131218.pdf
>
> Copy on SlideShare:
>
> http://www.slideshare.net/daniel_bilar/acoustic-20131218
>
> Alexander

As the primary fix for CVE-2013-4576, GnuPG 1.x now uses blinding to
mitigate RSA key extraction attacks. This doesn't affect GnuPG 2.x as
libgcrypt does blinding by default.

The acoustic attack leveraged some particulars of GnuPG by zero-padding
input to force modular reductions in GnuPG's RSA implementation. GnuPG
now cripples this lever by normalizing MPIs used as inputs to secret
key functions.

This secondary mitigation measure was introduced in GnuPG 1.4.16 and
libgcrypt 1.6.0 (relevant for vendors shipping GnuPG 2.x).

--mancha