[Cscwg-public] CRL Revocation Date Clarification Pre-Ballot

Wed Sep 22 15:38:38 UTC 2021

I prefer the former, since it doesn’t appear that any Certificate Consumer
has any plans to consume the Invalidity Date, even in the future.  And
“substantial portion” is just going to cause arguments … it’s better to
remain silent the issue until there’s a concrete consumer with actual plans
to implement.

Bruce, what’s the concern with having the requirement that the invalidity
date, if present, must be the same date?  Certificates with two different
dates are going to confuse a lot of people, and it seems completely
unnecessary to allow them, unless I’m missing a use case, which I very well
could be.

-Tim

From: Cscwg-public <cscwg-public-bounces at cabforum.org> On Behalf Of Rob
Stradling via Cscwg-public
Sent: Tuesday, September 21, 2021 11:49 AM
To: Corey Bonnell <Corey.Bonnell at digicert.com>; cscwg-public at cabforum.org;
Bruce Morton <bruce.morton at entrust.com>
Subject: Re: [Cscwg-public] CRL Revocation Date Clarification Pre-Ballot

I think it's valuable for CABForum documents to explicitly call out
deviations from RFC5280, but I'd take a different approach to Bruce's
suggestion...

In the Server Certificate BRs, "Application of RFC 5280" describes a
scenario (Precertificates) where RFC5280 does not apply at all; whereas what
I think we're trying to do here is specify that RFC5280 does apply (to CRLs)
except for one required deviation (i.e., "revocationDate" MUST match the
RFC5280 semantics for Invalidity Date, rather than necessarily be "The date
on which the revocation occurred").  Deviation is not "Application", in my
view.

I think the most similar concept in the Server Certificate BRs is the
language about non-critical Name Constraints:

"Non‐critical Name Constraints are an exception to RFC 5280 (4.2.1.10),
however, they MAY be used until

the Name Constraints extension is supported by Application Software
Suppliers whose software is used by

a substantial portion of Relying Parties worldwide."

The effect of this text is that RFC5280 does apply (to the Name Constraints
extension) except for one required deviation (i.e., we permit the extension
to be non-critical, at least for now).

How about adding this language to the ballot...

'Permitting the "revocationDate" to be set earlier than the date on which
the revocation occurred is an exception to RFC 5280 (5.1.2.6)."

Or, if we're hoping that this RFC5280 deviation will be temporary, how
about...

'Permitting the "revocationDate" to be set earlier than the date on which
the revocation occurred is an exception to RFC 5280 (5.1.2.6); however, this
MAY be done until the Invalidity Date extension is supported by Application
Software Suppliers whose software is used by a substantial portion of
Relying Parties worldwide."

WDYT?

  _____

From: Cscwg-public <cscwg-public-bounces at cabforum.org
<mailto:cscwg-public-bounces at cabforum.org> > on behalf of Bruce Morton via
Cscwg-public <cscwg-public at cabforum.org <mailto:cscwg-public at cabforum.org> >
Sent: 21 September 2021 16:04
To: Corey Bonnell <Corey.Bonnell at digicert.com
<mailto:Corey.Bonnell at digicert.com> >; cscwg-public at cabforum.org
<mailto:cscwg-public at cabforum.org>  <cscwg-public at cabforum.org
<mailto:cscwg-public at cabforum.org> >
Subject: Re: [Cscwg-public] CRL Revocation Date Clarification Pre-Ballot

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Hi Corey,

I was thinking that we would create a section similar to the BRs called
“Application of RFC 5280.” We could have text that says, “For the
purposes of clarification, the revocationDate MAY be set the same as the
invalidityDate, which would mean that the revocationDate may precede the
date of issue of earlier CRLs.”

I don’t think that we need to address or change the requirements for
invalidityDate as this date is not used by Windows; however, it may be used
by other applications per RFC 5280.

Bruce.

From: Corey Bonnell <Corey.Bonnell at digicert.com
<mailto:Corey.Bonnell at digicert.com> >
Sent: Tuesday, September 21, 2021 8:45 AM
To: Bruce Morton <Bruce.Morton at entrust.com <mailto:Bruce.Morton at entrust.com>
>; cscwg-public at cabforum.org <mailto:cscwg-public at cabforum.org>
Subject: [EXTERNAL] RE: CRL Revocation Date Clarification Pre-Ballot

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  _____

Hi Bruce,

I interpreted Ian’s message from last week [1] as guidance that all CAs
should be using the revocationDate to denote when the Code Signing
Certificate is first invalid. Since Windows (Authenticode) does not consume
the invalidityDate extension value when making trust decisions, there is a
negative security impact when CAs set the invalidityDate and revocationDate
in the manner described in RFC 5280. This ballot codifies the guidance Ian
shared so that the revocationDate is set uniformly across all CAs.

Thanks,

Corey

[1] https://lists.cabforum.org/pipermail/cscwg-public/2021-September/000532.
html
<https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.cab
forum.org%2Fpipermail%2Fcscwg-public%2F2021-September%2F000532.html&data=04%
7C01%7Crob%40sectigo.com%7C0d12b84938cc4d7ed05208d97d1118a7%7C0e9c48946caa46
5d96604b6968b49fb7%7C0%7C0%7C637678334657724301%7CUnknown%7CTWFpbGZsb3d8eyJW
IjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=
0y8EPWbaEx8JjusdPkaCY%2F6AZTmk3mzEJxeQuPv5yhk%3D&reserved=0>

From: Bruce Morton <Bruce.Morton at entrust.com
<mailto:Bruce.Morton at entrust.com> >
Sent: Monday, September 20, 2021 2:31 PM
To: Corey Bonnell <Corey.Bonnell at digicert.com
<mailto:Corey.Bonnell at digicert.com> >; cscwg-public at cabforum.org
<mailto:cscwg-public at cabforum.org>
Subject: RE: CRL Revocation Date Clarification Pre-Ballot

Hi Corey,

Is there a reason that we cannot allow CAs to continue to use Revocation
date and Invalidity date as per RFC 5280?

My assumption is that we were going to allow the Revocation date to be a
date earlier than the time the certificate was revoked. I am not seeing how
this change would impact the Invalidity date.

Bruce.

From: Cscwg-public <cscwg-public-bounces at cabforum.org
<mailto:cscwg-public-bounces at cabforum.org> > On Behalf Of Corey Bonnell via
Cscwg-public
Sent: Monday, September 20, 2021 12:52 PM
To: cscwg-public at cabforum.org <mailto:cscwg-public at cabforum.org>
Subject: [EXTERNAL] [Cscwg-public] CRL Revocation Date Clarification
Pre-Ballot

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  _____

Hello,

As discussed last week, it would be valuable to ensure that there is clarity
regarding how revocation/invalidity dates are encoded in CRLs so that
relying party software can make the correct trust decisions regarding
compromised code. Attached is a small change to 13.2.1 to reflect that the
revocationDate CRL entry field shall be used to denote when a certificate is
invalid. The proposed language allows for the Invalidity Date CRL entry
extension to continue to appear, but the time encoded in it must be the same
as the revocationDate for the entry. I don’t believe this causes issues
with Windows CRL processing, please let me know if it does and I’ll remove
the provision.

For reference, here are the two proposed paragraphs to be added to 13.2.1:

If a Code Signing Certificate is revoked, and the CA later becomes aware of
a more appropriate revocation date, then the CA MAY use that revocation date
in subsequent CRL entries and OCSP responses for that Code Signing
Certificate.

Effective 2022-02-01, if the CA includes the Invalidity Date CRL entry
extension in a CRL entry for a Code Signing Certificate, then the time
encoded in the Invalidity Date CRL extension SHALL be equal to the time
encoded in the revocationDate field of the CRL entry.

Given that the revocation date is potentially security sensitive, I think
it’s worthwhile to get this clarified prior to the RFC 3647/Pandoc effort.
In addition to comments/questions on the proposed language, we’re looking
for two endorsers.

Thanks,

Corey

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