[130163] in cryptography@c2.net mail archive
RE: OpenID/Debian PRNG/DNS Cache poisoning advisory
daemon@ATHENA.MIT.EDU (Dave Korn)
Fri Aug 8 13:57:56 2008
From: "Dave Korn" <dave.korn@artimi.com>
To: "'Eric Rescorla'" <ekr@networkresonance.com>
Cc: "'Ben Laurie'" <benl@google.com>,
<bugtraq@securityfocus.com>,
<security@openid.net>,
"'OpenID List'" <general@openid.net>,
<cryptography@metzdowd.com>,
<full-disclosure@lists.grok.org.uk>
Date: Fri, 8 Aug 2008 18:08:03 +0100
In-Reply-To: <20080808165730.7761450846@romeo.rtfm.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....
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