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: Dave Korn <dave.korn_at_nospam>
Date: Fri Aug 08 2008 - 17:08:03 GMT
To: "'Eric Rescorla'" <ekr@networkresonance.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.... _______________________________________________ Full-Disclosure - We believe in it. Charter: http://lists.grok.org.uk/full-disclosure-charter.html Hosted and sponsored by Secunia - http://secunia.com/