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

Tue Sep 21 15:48:39 UTC 2021

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> on behalf of Bruce Morton via Cscwg-public <cscwg-public at cabforum.org>
Sent: 21 September 2021 16:04
To: Corey Bonnell <Corey.Bonnell at digicert.com>; cscwg-public at cabforum.org <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>
Sent: Tuesday, September 21, 2021 8:45 AM
To: Bruce Morton <Bruce.Morton at entrust.com>; 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.cabforum.org%2Fpipermail%2Fcscwg-public%2F2021-September%2F000532.html&data=04%7C01%7Crob%40sectigo.com%7C0d12b84938cc4d7ed05208d97d1118a7%7C0e9c48946caa465d96604b6968b49fb7%7C0%7C0%7C637678334657724301%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%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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