[Servercert-wg] Discussion Period Begins - Ballot SC-067 V2: "Require domain validation and CAA checks to be performed from multiple Network Perspectives"

Roman Fischer roman.fischer at swisssign.com
Tue Jul 2 04:53:16 UTC 2024 

Dear Chris,

Sorry that I wasn't aware of that previous discussion ☹. And since it's a MAY, I guess I'm good with how it's formulated right now.

Rgds
Roman

From: Chris Clements <cclements at google.com>
Sent: Montag, 1. Juli 2024 20:39
To: Aaron Gable <aaron at letsencrypt.org>; CA/B Forum Server Certificate WG Public Discussion List <servercert-wg at cabforum.org>
Cc: Roman Fischer <roman.fischer at swisssign.com>
Subject: Re: [Servercert-wg] Discussion Period Begins - Ballot SC-067 V2: "Require domain validation and CAA checks to be performed from multiple Network Perspectives"


Hi Roman, Aaron,


The existing ballot text was intended to offer flexibility to adopters and was in response to community feedback on earlier drafts of the ballot (e.g., here<https://lists.cabforum.org/pipermail/validation/2023-June/001904.html>).


While we agree with your perspective re: simplicity, we equally believe CA Owners should be able to evaluate and adopt implementations that work best for them while also achieving the stated security objectives of the ballot.


Thanks

-Chris


On Fri, Jun 28, 2024 at 10:34 AM Aaron Gable via Servercert-wg <servercert-wg at cabforum.org<mailto:servercert-wg at cabforum.org>> wrote:
Let's Encrypt already implements MPIC, including doing CAA checks from all of our perspectives. Obviously our experience is not universal, but we made the decision to treat remote CAA checks the exact same as primary ones: valid for at most 8 hours. Although this does increase the number of remote CAA checks we perform, it keeps us much more confident in our code and compliance.

While I understand the motivation behind allowing remote CAA results to be cached for an extended period, I personally don't think that the motivation is strong enough to actually overcome the extra complications that it brings. I would prefer that all remote results have the same lifetimes as primary validation data.

Aaron

On Fri, Jun 28, 2024, 01:33 Roman Fischer via Servercert-wg <servercert-wg at cabforum.org<mailto:servercert-wg at cabforum.org>> wrote:
Thanks to both Doug and Chris for these examples.

That makes me wonder: Wouldn't it be simpler (and thus less error-prone) to remove the CAA caching and just do the CAA check with each domain validation?

Rgds
Roman

From: Servercert-wg <servercert-wg-bounces at cabforum.org<mailto:servercert-wg-bounces at cabforum.org>> On Behalf Of Chris Clements via Servercert-wg
Sent: Donnerstag, 27. Juni 2024 15:36
To: Doug Beattie <doug.beattie at globalsign.com<mailto:doug.beattie at globalsign.com>>
Cc: CA/B Forum Server Certificate WG Public Discussion List <servercert-wg at cabforum.org<mailto:servercert-wg at cabforum.org>>
Subject: Re: [Servercert-wg] Discussion Period Begins - Ballot SC-067 V2: "Require domain validation and CAA checks to be performed from multiple Network Perspectives"


Hi Doug,


Working through your examples - and adding one additional, below.


Note: these examples strictly assume the to-be-issued certificates only contain the subject dnsName being described (i.e., if www.example.com<http://www.example.com/> is the named subject, we do not assume the certificate will also include a dnsName of example.com<http://example.com/>).


  *   Day 1: CA performs MPIC for www.example.com<http://www.example.com/>

     *   Corroborating DCV: This includes observing a domain validation random token from [N] perspectives, as required by quorum expectations.
     *   Corroborating CAA: This includes observing permission to issue when checking CAA from [N] perspectives, as required by quorum expectations.


  *   Day 100: A certificate request is made for shop.example.com<http://shop.example.com/> from the same applicant

     *   Corroborating DCV: This includes observing a domain validation random token from [N] perspectives, as required by quorum expectations.
     *   Corroborating CAA: This MAY NOT be skipped given the certificate issued to the customer on Day 1 was for www.example.com<http://www.example.com/> and shop.example.com<http://shop.example.com/> is not a subdomain of www.example.com<http://www.example.com/>. The process must be completed as it is described in the “Day 1" example.


  *   Day 150: A certificate request is made for x1.www.example.com<http://www.x1.example.com/> from the same applicant

     *   Corroborating DCV: This includes observing a domain validation random token from [N] perspectives, as required by quorum expectations.
     *   Corroborating CAA: This MAY be skipped given the MPIC CAA event on Day 1 for www.example.com<http://www.example.com/> and the described 398-day reuse period because x1.www.example.com<http://x1.www.example.com/> is a subdomain of www.example.com<http://www.example.com/>.


  *   Day 400: A certificate request is made for x2.www.example.com<http://www.x1.example.com/>

     *   Corroborating DCV: This includes observing a domain validation random token from [N] perspectives, as required by quorum expectations.
     *   Corroborating CAA: Prior reuse cache for www.example.com<http://www.example.com/> (Day 1) is now expired. The CA must observe permission to issue when checking CAA from [N] perspectives, as required by quorum expectations.


Hopefully this helps clarify, but let us know if you have any questions.

-Chris

P.S., this response has also been copied to the same doc<https://docs.google.com/document/d/11V43IrkwGbDvL69hxm2smukJfgZH9Qs0md4CPNdbViw/edit> we referenced in response to Christophe in case of any formatting issues conveyed through the list.

On Tue, Jun 25, 2024 at 2:17 PM Doug Beattie <doug.beattie at globalsign.com<mailto:doug.beattie at globalsign.com>> wrote:
Hi Chris,

I was taking a closer look at the ballot and specifically this section on caching the remote node CAA checks:

A CA MAY reuse corroborating evidence for CAA record quorum compliance for a maximum of 398 days. After issuing a Certificate to a domain, remote Network Perspectives MAY omit retrieving and processing CAA records for the same domain or its subdomains in subsequent Certificate requests from the same Applicant for up to a maximum of 398 days.

I think understand the first sentence – if you do a full check on a FQDN (the value that you will put into the SAN field), then you only need to do the normal CAA check for that FQDN from the primary node for 398 days.

I don’t understand the references to domain and subdomains in the second sentence.  Can you explain how this should work?

  *   You do a full MIC  check on www.example.com<http://www.example.com/> on day 1
  *   You find CAA records with permission to issue on example.com<http://example.com/> on primary and remote nodes so you issue
  *   Day 100, customer wants to issue to shop.example.com<http://shop.example.com/>

     *   This is a subdomain of example.com<http://example.com/> where we found the records permitting issuance on day 1.
     *   What checks do we need to do for this request?

  *   Day 150, Applicant wants to issue to x1.www.example.com<http://x1.www.example.com/> (a subdomain of www.example.com<http://www.example.com/> we issued on day 1):

     *   What checks would be required here?

Maybe I’m reading too much into this…

Thanks!

Doug

From: Servercert-wg <servercert-wg-bounces at cabforum.org<mailto:servercert-wg-bounces at cabforum.org>> On Behalf Of Chris Clements via Servercert-wg
Sent: Friday, April 26, 2024 1:01 PM
To: CA/B Forum Server Certificate WG Public Discussion List <servercert-wg at cabforum.org<mailto:servercert-wg at cabforum.org>>
Subject: [Servercert-wg] Discussion Period Begins - Ballot SC-067 V2: "Require domain validation and CAA checks to be performed from multiple Network Perspectives"


Purpose of Ballot SC-067 V2:



This Ballot proposes updates to the Baseline Requirements for the Issuance and Management of Publicly-Trusted TLS Server Certificates (i.e., TLS BRs) related to “Multi-Perspective Issuance Corroboration” (“MPIC”).



Background:



- MPIC refers to performing domain validation and CAA checks from multiple Network Perspectives before certificate issuance, as described within the Ballot for the applicable validation methods in TLS BR Sections 3.2.2.4 and 3.2.2.5.

- Not all methods described in TLS BR Sections 3.2.2.4 and 3.2.2.5 will require using MPIC.

- This work was most recently motivated by research presented at Face-to-Face 58 [1] by Princeton University, but has been discussed for years prior as well.

- The goal of this proposal is to make it more difficult for adversaries to successfully launch equally-specific prefix attacks against the domain validation processes described in the TLS BRs.

- Additional background information can be found in an update shared at Face-to-Face 60 [2].



Benefits of Adoption:



- Recent publicly-documented attacks have used BGP hijacks to fool domain control validation and obtain malicious certificates, which led to the impersonation of HTTPS websites [3][4].

- Routing security defenses (e.g., RPKI) can mitigate the risk of global BGP attacks, but localized, equally-specific BGP attacks still pose a significant threat to the Web PKI [5][6].

- Corroborating domain control validation checks from multiple network perspectives (i.e., MPIC) spread across the Internet substantially reduces the threat posed by equally-specific BGP attacks, ensuring the integrity of domain validation and issuance decisions [5][7][8].

- Existing deployments of MPIC at the scale of millions of certificates a day demonstrate the feasibility of this technique at Internet scale [7][9].



Intellectual Property (IP) Disclosure:



- While not a Server Certificate Working Group Member, researchers from Princeton University presented at Face-to-Face 58, provided academic expertise, and highlighted publicly-available peer-reviewed research to support Members in drafting this ballot.

- The Princeton University researchers indicate that they have not filed for any patents relating to their MPIC work and do not plan to do so in the future.

- Princeton University has indicated that it is unable to agree to the CA/Browser Forum IPR agreement because it could encumber inventions invented by researchers not involved in the development of MPIC or with the CA/B Forum.

- Princeton University has instead provided the attached IPR statement. Pursuant to the IPR statement, Princeton University has granted a worldwide royalty free license to the intellectual property in MPIC developed by the researchers and has made representations regarding its lack of knowledge of any other Princeton intellectual property needed to implement MPIC.

- The attached IPR statement has not changed since disclosed in Discussion Round 1.

- For clarity, Princeton University’s IPR statement is NOT intended to replace the Forum’s IPR agreement or allow Princeton to participate in the Forum in any capacity.

- Members seeking legal advice regarding this ballot should consult their own counsel.



Proposal Revision History:



- Pre-Ballot Release #1 (work team artifacts and broader Validation Subcommittee collaboration) [10]

- Pre-Ballot Release #2 [11]



Previous versions of this Ballot:

 - Ballot Release #1 [12] (comparing Version 2 to Version 1) [13]. Note, some of the changes represented in the comparison are updates made by other ballots that have since passed (e.g., SC-069).



References:

[1] https://cabforum.org/wp-content/uploads/13-CAB-Forum-face-to-face-multiple-vantage-points.pdf

[2] https://drive.google.com/file/d/1LTwtAwHXcSaPVSsqKQztNJrV2ozHJ7ZL/view?usp=drive_link

[3] https://medium.com/s2wblog/post-mortem-of-klayswap-incident-through-bgp-hijacking-en-3ed7e33de600

[4] https://www.coinbase.com/blog/celer-bridge-incident-analysis

[5] https://www.usenix.org/conference/usenixsecurity23/presentation/cimaszewski

[6] https://www.blackhat.com/docs/us-15/materials/us-15-Gavrichenkov-Breaking-HTTPS-With-BGP-Hijacking-wp.pdf

[7] https://www.usenix.org/conference/usenixsecurity21/presentation/birge-lee

[8] https://www.usenix.org/conference/usenixsecurity18/presentation/birge-lee

[9] https://security.googleblog.com/2023/05/google-trust-services-acme-api_0503894189.html

[10] https://github.com/ryancdickson/staging/pull/6

[11] https://github.com/ryancdickson/staging/pull/8

[12] https://github.com/cabforum/servercert/pull/487

[13] https://github.com/cabforum/servercert/compare/6d10abda8980c6eb941987d3fc26e753e62858c0..5224983ef0a6f94c18808ea3469e7a5ae35746e5



The following motion has been proposed by Chris Clements and Ryan Dickson of Google (Chrome Root Program) and endorsed by Aaron Gable (ISRG / Let’s Encrypt) and Wayne Thayer (Fastly).



— Motion Begins —



This ballot modifies the “Baseline Requirements for the Issuance and Management of Publicly-Trusted TLS Server Certificates” (“Baseline Requirements”), based on Version 2.0.4.



MODIFY the Baseline Requirements as specified in the following Redline:

https://github.com/cabforum/servercert/compare/c4a34fe2292022e0a04ba66b5a85df75907ac2a2..5224983ef0a6f94c18808ea3469e7a5ae35746e5



— Motion Ends —



This ballot proposes a Final Maintenance Guideline. The procedure for approval of this ballot is as follows:



Discussion (at least 14 days)

- Start: 2024-04-26 17:00:00 UTC

- End no earlier than: 2024-05-10 17:00:00 UTC



Vote for approval (7 days)

- Start: TBD

- End: TBD

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