full-disclosure - Re: OpenID/Debian PRNG/DNS Cache poisoning advisory

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Date: Fri, 8 Aug 2008 18:11:42 +0100
From: "Ben Laurie" <benl@...gle.com>
To: "Eric Rescorla" <ekr@...workresonance.com>
Cc: cryptography@...zdowd.com, Dave Korn <dave.korn@...imi.com>,
	full-disclosure@...ts.grok.org.uk, bugtraq@...urityfocus.com,
	OpenID List <general@...nid.net>, security@...nid.net
Subject: Re: OpenID/Debian PRNG/DNS Cache poisoning
	advisory

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