full-disclosure-uk August 2008 archive
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full-disclosure-uk: Re: [Full-disclosure] OpenID/Debian PRNG/DNS

Re: [Full-disclosure] OpenID/Debian PRNG/DNS Cache poisoning advisory

From: Eric Rescorla <ekr_at_nospam>
Date: Fri Aug 08 2008 - 16:57:30 GMT
To: "Dave Korn" <dave.korn@artimi.com>


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...

-Ekr



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