Re: OpenID/Debian PRNG/DNS Cache poisoning advisory
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