On 6 February 2014 19:05, Adam Langley <[email protected]> wrote:
> On Thu, Feb 6, 2014 at 1:51 PM, Rick Andrews <[email protected]> 
> wrote:
>> Can you clarify something? The SCT delivery options described in the RFC are 
>> options for the web site owner, not for the CA. CAs will need to support all 
>> three options. We will have customers who won’t do stapling and can’t handle 
>> TLS extensions, so they just want the SCTs embedded in the cert. But not all 
>> customers will prefer that option. I believe other customers will want the 
>> SCT-in-the-OCSP-response or TLS extension option, because in those options 
>> you don’t have to transmit the SCTs in every SSL handshake. I suspect some 
>> of our large customers who are obsessed with performance will demand one of 
>> these options.
>>
>> So CAs will need to support all three options, unless you’re so small a CA 
>> that your few EV customers agree on one option. Is that your expectation?
>
> SCTs embedded in the certificate won't be sent for resumption
> handshakes of course.
>
> The TLS extension will be sent in the same cases as SCTs embedded in
> the certificate. (And the TLS extension doesn't need the CA to do
> anything.)
>
> The stapled OCSP response is likely to be sent in the same cases also.
> One could imagine a client that doesn't request a stapled OCSP
> response when it has a cached OCSP response for the certificate that
> it saw from the server last time. But, if the server responds with a
> different certificate it's stuck. So I expect clients to always
> request the OCSP staple.
>
> So a CA only really need worry about the embedded case. Customers who
> are concerned about the performance impact of a few hundred extra
> bytes very likely have much easier avenues to reduce the size, like
> having different certs for different names rather than dozens of SANs.

Just to clarify: if CAs want to use OCSP stapling, then obviously they
need to add CT support to their OCSP responder. But the only thing CAs
really _have_ to do is the embedded case.
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