A mighty fortress is our PKI, Part II

[Ben Laurie]

On 28/07/2010 09:57, Peter Gutmann wrote:
> Ben Laurie <ben at links.org> writes:
>> On 24/07/2010 18:55, Peter Gutmann wrote:
>>> - PKI dogma doesn't even consider availability issues but expects the
>>>   straightforward execution of the condition "problem -> revoke cert".  For a
>>>   situation like this, particularly if the cert was used to sign 64-bit
>>>   drivers, I wouldn't have revoked because the global damage caused by that is
>>>   potentially much larger than the relatively small-scale damage caused by the
>>>   malware.  So alongside "too big to fail" we now have "too widely-used to
>>>   revoke".  Is anyone running x64 Windows with revocation checking enabled and
>>>   drivers signed by the Realtek or JMicron certs?
>>
>> One way to mitigate this would be to revoke a cert on a date, and only reject 
>> signatures on files you received after that date.
> 
> This wouldn't make any difference, except for the special case of x64, 
> signatures are only verified on install, so existing installed code isn't 
> affected and anything new that's being installed is, with either form of 
> sig-checking.

Obviously if you are going to change revocation you can also change when
signatures are checked. This hardly seems like a show-stopper.

> In any case though the whole thing is really a moot point given the sucking 
> void that is revocation-handling, the Realtek certificate was revoked on the 
> 16th but one of my spies has informed me that as of yesterday it was still 
> regarded as valid by Windows.  Previous experience with revoked certs has been 
> that they remain valid more or less indefinitely (which would be really great 
> if CAs offered something like domain-tasting for certs, you could get as many 
> free certs as you wanted).

Again, citing the failure to use revocation correctly right now does not
tell us anything much about the possibility of using it correctly in the
future.

> The way to revoke a cert for signed malware is to wait 0-12 hours for the 
> malware signature to be added to AV databases, not to actually expect PKI to 
> work.

At which time they release another version? Doesn't sound like the
optimal answer to me.

I find your response strange. You ask how we might fix the problems,
then you respond that since the world doesn't work that way right now,
the fixes won't work. Is this just an exercise in one-upmanship? You
know more ways the world is broken than I do?

Cheers,

Ben.

-- 
http://www.apache-ssl.org/ben.html           http://www.links.org/

"There is no limit to what a man can do or how far he can go if he
doesn't mind who gets the credit." - Robert Woodruff

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