Re: OpenID/Debian PRNG/DNS Cache poisoning advisory

["Stefan Kanthak" <stefan.kanthak () nexgo de>]

Dan Kaminsky wrote:
> Eric Rescorla wrote:
> > At Fri, 8 Aug 2008 17:31:15 +0100,
> > Dave Korn wrote:
> >   
> > > Eric Rescorla wrote on 08 August 2008 16:06:
> > >
> > >     
> > > > At Fri, 8 Aug 2008 11:50:59 +0100,
> > > > Ben Laurie wrote:
> > > >       
> > > > > However, since the CRLs will almost certainly not be checked, this
> > > > > means the site will still be vulnerable to attack for the lifetime of
> > > > > the certificate (and perhaps beyond, depending on user
> > > > > behaviour). Note that shutting down the site DOES NOT prevent the attack.
> > > > >
> > > > > Therefore mitigation falls to other parties.
> > > > >
> > > > > 1. Browsers must check CRLs by default.
> > > > >         
> > > > Isn't this a good argument for blacklisting the keys on the client
> > > > side?
> > > >       
> > >   Isn't that exactly what "Browsers must check CRLs" means in this context
> > > anyway?  What alternative client-side blacklisting mechanism do you suggest?
> > >     
> >
> > It's easy to compute all the public keys that will be generated
> > by the broken PRNG. The clients could embed that list and refuse
> > to accept any certificate containing one of them. So, this
> > is distinct from CRLs in that it doesn't require knowing 
> > which servers have which cert...
> Funnily enough I was just working on this -- and found that we'd end up 
> adding a couple megabytes to every browser.

At least for the weak keys kudos to Debian's OpenSSL maintainer
there exists an extension to Firefox which checks the keys, see <http://codefromthe70s.org/sslblacklist.asp>, as well 
as c't's
SSLguardian for the Windows Crypto API, see
<http://www.heise-online.co.uk/security/features/111039/0> and
<http://www.heise-online.co.uk/security/features/111039/1>

Stefan