[cabfpub] [therightkey] Updated Certificate Transparency + Extended Validation plan

[Ben Laurie]

On 6 February 2014 19:05, Adam Langley <agl at chromium.org> wrote:
> On Thu, Feb 6, 2014 at 1:51 PM, Rick Andrews <Rick_Andrews at symantec.com> 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.