RE: OpenID/Debian PRNG/DNS Cache poisoning advisory

["Dave Korn" <dave.korn () artimi com>]

Eric Rescorla wrote on 08 August 2008 17:58:

> 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...

<scurries off to read CRL format in RFC>

  Oh, you can't specify them solely by key, you have to have all the
associated metadata.  That's annoying, yes, I understand your point now.

  IIRC various of the vendors' sshd updates released in the immediate wake
of the Debian catastrophe do indeed block all the weak keys.


    cheers,
      DaveK
-- 
Can't think of a witty .sigline today....