Hi Yaron,

It's a weak use case, because short-lived certificates do not solve the 
problem.  I'm not saying CDN revocation is weak (actually - I will say that 
next, but I wasn't initially) - I *am* saying that trying to accomplish it with 
short-lived certs isn't sensible; totally the wrong tool for the job.

Not to mention - the idea of your CDN getting beached? - whoever invented that 
as a reason is clutching at improbable straws!  If you need to stop your CDN 
distributing your stuff, go erase your content from them; showing "expired 
certificates" to customers a few days later is totally not going to cut it (nor 
will it stop the distribution for everyone who ignore those warning, which will 
be almost everyone.)
Plus - the main idea of a CDN is for speed; regularly changing certs will slow 
everyone down too.

Kind Regards,
Chris Drake


Friday, July 22, 2016, 10:52:06 PM, you wrote:

YS> On 22/07/16 13:21, Chris Drake wrote:
>> Hi Yaron,
>>
>> Best I can tell, everyone has jumped onto solving a cool problem,
>> without there actually being any reason to solve it?
>>
>> I asked about the use case, and CDN authority revocation was all I got
>> (imho a really *weak* reason).  Maybe I got it wrong?
>>
>> What *exactly* is a use case for short-term certificates? What about
>> HSTS/HPKP?
>> Why would *any* expired short-term certificate be useful?  Practically
>> no ordinary user cares about bad certs - heck - iPhone users don't even
>> have a way to check a cert even if they wanted to.
>>
>> Kind Regards,
>> Chris Drake
>>

YS> Hi Chris,

YS> Can you please explain why CDN authority revocation is a weak use case?

YS> Let me share my preferred use case: I am running a large web property in
YS> the cloud, where TLS connections are terminated on a cloud-based load 
YS> balancer (Amazon ELB, for a concrete example). I would like the cloud 
YS> provider to present my identity (www.example.com), but I want to revoke
YS> this authority as soon as something bad happens, e.g. the cloud provider
YS> is breached.

YS> There may be alternative solutions, but I think short-term certs are a
YS> reasonable solution here. Either the content owner gives the cloud 
YS> provider a new cert every X days (option 1), or the cloud provider can
YS> get the short-term cert directly from the CA (option 2).

YS> A solution that certainly CANNOT work is to give the cloud provider a 
YS> regular 1-year cert and revoke it if a breach occurs. Because we know 
YS> that cert revocation doesn't work.

YS> Thanks,
YS>         Yaron

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