Re: OpenID/Debian PRNG/DNS Cache poisoning advisory

From: Ben Laurie <benl@google.com>
To: Eric Rescorla <ekr@networkresonance.com>
Cc: Dave Korn <dave.korn@artimi.com>,bugtraq@securityfocus.com,security@openid.net,OpenID List <general@openid.net>,cryptography@metzdowd.com,full-disclosure@lists.grok.org.uk
Subject: Re: OpenID/Debian PRNG/DNS Cache poisoning advisory
Date:


On Fri, Aug 8, 2008 at 5:57 PM, Eric Rescorla <ekr@networkresonance.com> 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...

It also only fixes this single type of key compromise. Surely it is
time to stop ignoring CRLs before something more serious goes wrong?





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