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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: Stefan Kanthak <stefan.kanthak_at_nospam>
Date: Fri Aug 08 2008 - 22:29:52 GMT
To: "Dan Kaminsky" <dan@doxpara.com>, "Eric Rescorla" <ekr@networkresonance.com>


Dan Kaminsky wrote: > > > Eric Rescorla 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...

> Funnily enough I was just working on this -- and found that we'd end up > adding a couple megabytes to every browser.

At least for the weak keys kudos to Debian's OpenSSL maintainer there exists an extension to Firefox which checks the keys, see <http://codefromthe70s.org/sslblacklist.asp>, as well as c't's SSLguardian for the Windows Crypto API, see <http://www.heise-online.co.uk/security/features/111039/0> and <http://www.heise-online.co.uk/security/features/111039/1>

Stefan



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