[Servercert-wg] Ballot SC31 Browser Alignment - CRL and OCSP profiles

[Ryan Sleevi]

Corey,

Could you see if https://github.com/sleevi/cabforum-docs/pull/30 makes this
clearer? I appreciate your careful review, as it did reveal a small gap
here in handling existing certificates that were issued for "hybrid"
issuing CAs.

That is, if a single Issuing CA was issuing, say, smartcard certs NOT
subject to the BRs, and TLS certs subject to the BRs, then the Issuing CA
was also subject to the BRs, and would not be able to suspend the smartcard
certificates. The above PR tries to resolve that, by having CAs transition
to separate issuing intermediates, which is also covered within this SC31.

On Thu, Jun 25, 2020 at 12:40 PM Ryan Sleevi <sleevi at google.com> wrote:

>
>
> On Thu, Jun 25, 2020 at 12:12 PM Corey Bonnell via Servercert-wg <
> servercert-wg at cabforum.org> wrote:
>
>> In giving another pass on the SC31 ballot text, I have the following
>> questions/comments:
>>
>>
>>
>> From 7.2.2 (
>> https://github.com/cabforum/documents/pull/195/files#diff-7f6d14a20e7f3beb696b45e1bf8196f2R1986
>> ):
>>
>> > The `CRLReason` indicated MUST NOT be unspecified (0), MUST NOT be
>> certificateHold (6), and MUST indicate the most appropriate reason for
>> revocation of the certificate.
>>
>>
>>
>> 1. Does this requirement apply to end-entity certificate CRL entries? The
>> formatting makes it appear that it does, but the Root Program requirement
>> where this is derived from only is for CA certificates.
>>
>
> So there's two parts to unpack:
> A)  Is the reason code required
> B) If the reason code is present, what's expected
>
> The attempt to answer A is
>
> https://github.com/cabforum/documents/pull/195/files#diff-7f6d14a20e7f3beb696b45e1bf8196f2R1990-R1994
>
> It MUST be present for Intermediates. This comes from Microsoft.
> It SHOULD be present for end-entities. This comes from browsers consuming
> CRLs and acting on them (Apple, Google, Mozilla), and those that prioritize
> reason status (Google).
>
> The answer for B is
>
> https://github.com/cabforum/documents/pull/195/files#diff-7f6d14a20e7f3beb696b45e1bf8196f2R1995-R1997
>
> This is profiling a SHOULD of the relevant RFCs into a MUST, and is
> effectively saying "Use the smallest possible encoding". If a Subscriber
> certificate is revoked for an unspecified reason, the "minimal encoding" is
> actually to omit the CRLReason entirely. It has the same semantics, but
> saves twelve bytes.
>
> Here, this applies to *all* entries in the CRL. The prohibition on
> certificateHold reflects the prohibition on certificate suspension.
>
> 2. Given that the semantics of the X.509 reasonCodes are not well defined
>> [1], do Root Programs have guidance on what each allowed reasonCode means
>> and when it is most appropriate to use? Absent this, I think the “MUST”
>> requirement should be relaxed to a “SHOULD” (or eliminated entirely) until
>> there are commonly agreed-upon semantics for the allowed set of reasonCodes.
>>
>
> The intent here is that the CA defines this, and what they define, they
> follow. I agree that there's an opportunity to improve the consistency
> across CAs, but I think similar to SC30, or past work (e.g. CAA), the first
> step is to permit CAs to work through their policies as to what most
> appropriate means, based on the criteria they define and the guidance
> within RFC 5280 and, where appropriate, ITU-T X.509.
>
>
>>
>>
>> From 7.3 (
>> https://github.com/cabforum/documents/pull/195/files#diff-7f6d14a20e7f3beb696b45e1bf8196f2R1998
>> ):
>>
>> > The `CRLReason` used SHALL contain a value permitted for CRLs, as
>> specified in Section 7.2.2.
>>
>>
>>
>> Similar to question #1 above, does this apply to OCSP responses for
>> end-entity certificates?
>>
>
>  If present, yes.
>
> Similar to answer A, this is optional for end-entity certificates to be
> present, but when it is present, it should follow a consistent form as the
> CRL, since OCSP and CRLs are meant to be interchangeable to an extent.
>
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