CRL Issuance Frequency for non-published CRLs

[Aaron Gable]

Hi MDSP,

Section 4.9.7 of the Baseline Requirements says (emphasis added):

> If the CA publishes a CRL, then the CA SHALL update and reissue CRLs at least once every seven days, and the value of the nextUpdate field MUST NOT be more than ten days beyond the value of the thisUpdate field.

Let's Encrypt is currently in the final stages of standing up infrastructure to issue and publish CRLs, in compliance with the upcoming Apple and Mozilla root program requirements that go into effect on October 1st.

As with many systems, we would like to test this as thoroughly as possible prior to making it fully available. Of course we're already running it in our non-production environment with an untrusted hierarchy of issuers. But there's a risk that, if we were to run the new infrastructure in our production environment and discover some sort of fault, we would not be able to turn it off again due to the reissuance and update requirements.

It is our interpretation of the above-quoted text from Section 4.9.7 that this risk does not actually exist. As long as we do not publish the CRLs, they are not required to be updated on specific timetables.

Does anyone disagree with this interpretation? Are there other requirements that I'm missing that would prevent us from turning the new infrastructure off?

Thanks,

Aaron

[Corey Bonnell]

Hi Aaron,

 

> As long as we do not publish the CRLs, they are not required to be updated on specific timetables.

 

My understanding is that absent the inclusion of a URI in a CRLDP extension of a Certificate that is subject to the BRs or some other Root Program requirement, there is no obligation by the CA to publish and update CRL-based revocation information on any specific cadence.

 

Given this, I believe that it’s compliant to not publish CRLs that are signed by the CA.

 

Thanks,

Corey

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[Ben Wilson]

All,

Mozilla's position is that adding CRL URLs to the CCADB (as required effective Oct. 1, 2022, by MRSP section 4.1) will be considered "publishing" them because we will be relying on that information in the CCADB to operate CRLite. I have added Issue #251 to GitHub to address this issue more precisely in the next version of the Mozilla Root Store Policy. For this, we will use the timeframes from section 4.9.7 of the Baseline Requirements, "the CA SHALL update and reissue CRLs at least once every seven days ...." (In the future, we might want to see that time frame shortened.) 

Thanks,

Ben Wilson

Mozilla Root Store Program

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[Aaron Gable]

Thanks, Corey and Ben!

We'll start creating CRLs from our production hierarchy very soon, but will ensure that we don't add those URLs to CCADB until we're confident that the infrastructure can run continuously.

Aaron

[Christophe Bonjean]

Hi Ben,

 

There’s a few CA and CRL lifecycle events linked to this change:

1. T= 0 : CA creation
2. T= 0 + a: CRL URL assignment (not yet publishing CRLs)
3. T = max 7 days: CA disclosure in CCADB (section 5.3.2)
4. T = 7 days + b: CRL disclosure in CCADB (section 4.1)
5. T = 7 days + c: First CRL published
6. T = d: First certificate issued from CA (with CRL in certificate profile)

 

The proposed change to section 4.1 means that CRLs need to be published as soon as they are being disclosed in CCADB.

 

In some cases, CAs are generated a while before they are used, for example TLS CAs that we rotate on a quarterly basis. In that case, CRLs will only be published close to the when the CA becomes operational.

 

It seems the timeline to populate the CRL information in CCADB is currently flexible and supports this approach (i.e. populating and publishing the CRL a while after the CA is disclosed).

 

Is this the correct understanding? If there’s a different interpretation or intention to restrict this timeline in the future, we would like to further discuss.

 

Thanks

 

Christophe

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[Ben Wilson]

Hi Christophe,

We do want to maintain some flexibility here and to mirror current practices without creating new unnecessary requirements.  We could modify MRSP section 4.1 to more clearly indicate when full CRLs need to be added to the CCADB.  For discussion, the language could be something like, "Full CRL URLs MUST be provided in the CCADB before the CA signs certificates, or if it is already signing certificates, then within 7 days of disclosing the CA certificate in the CCADB."

Thoughts?

Ben

[Clint Wilson]

Hi all,

FWIW, the below language also matches the intent of the similar Apple Root Program requirement.

Thanks,

-Clint

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[Christophe Bonjean]

Hi Ben,

 

The proposed phrasing sounds like a more flexible approach of CRL publishing, which seems to still meet the intention of the requirement.

 

This would allow for the use cases we highlighted.

 

Christophe