[Servercert-wg] Discussion Period Begins - Ballot SC-067 V3: "Require domain validation and CAA checks to be performed from multiple Network Perspectives"

Thu May 30 09:55:02 UTC 2024

Hi Chris, all,

I’d like to discuss a few interpretations related to the scope of corroboration.

Case 1: DNS TXT with correct expected TXT value but different other TXT values present on remote perspective

Suppose the following responses from:

*	Primary perspective: TXT with 2 records: a=1; c=2
*	Remote perspective: TXT with 2 records: a=1; c=3

If the expected random value is a=1, is the corroboration limited to only the “a” TXT record, and not impacted by a difference to the “c” record? 

Our understanding is yes due to the statement “can corroborate the outcomes determined by the Primary Network Perspective”, where that outcome would be “was the primary perspective able to retrieve a TXT record a=1”.

Case 2: DNS TXT with corroboration between remote perspectives only

Suppose the following responses from:

*	Primary perspective: no TXT records
*	Remote perspective 1: TXT with expected value
*	Remote perspective 2: TXT with expected value

Suppose the # of allowed non-corroborations is 1 (the primary perspective being the non-corroborating instance). Is our understanding correct that “corroboration” is intended to confirm the value of the primary perspective, meaning that if there was no success obtaining the value on the primary perspective, it can not be corroborated? This is based on the statement “To count as corroborating, a Network Perspective MUST observe the same challenge information (i.e. Random Value or Request Token) as the Primary Network Perspective.”

Or is the intention to consider the 3 nodes as the quorum and since remote perspective 1 and 2 corroborate, the expected value is verified successfully? In other words, is the quorum including all network perspectives, including the primary, or only the remote perspectives?

Case 3: CAA returns valid but different Issuer Domain Names from different subdomains

Suppose the following responses from:

*	Primary perspective: a.b.c.domain.com returns ca.com for CAA
*	Remote perspective 1: b.c.domain.com returns ca.net for CAA

And both ca.com and ca.net are defined by the CA as Issuer Domain Names.

Is the intention of corroboration to only confirm if all network perspectives return a “permission to issue”? Would corroboration also require the contents of the CAA values to match (so ca.com and ca.net would not corroborate)? Would the difference in path building (primary perspective obtains the result from a.b.c, remote perspective obtains from b.c) result in a non-corroboration result? The statement “regardless of whether the responses from both Perspectives are byte-for-byte identical.” Seems to hint at the contents of the CAA values, but maybe this is not intentional.

Christophe

From: Servercert-wg <servercert-wg-bounces at cabforum.org> On Behalf Of Chris Clements via Servercert-wg
Sent: Monday, May 20, 2024 4:30 PM
To: CA/B Forum Server Certificate WG Public Discussion List <servercert-wg at cabforum.org>
Subject: [Servercert-wg] Discussion Period Begins - Ballot SC-067 V3: "Require domain validation and CAA checks to be performed from multiple Network Perspectives"

Purpose of Ballot SC-067 V3:

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).

- Ballot Release #2 [14] (comparing Version 3 to Version 2) [15]. Note, some of the changes represented in the comparison are updates made by other ballots that have since passed (e.g., SC-072).

References:

[1]  <https://cabforum.org/wp-content/uploads/13-CAB-Forum-face-to-face-multiple-vantage-points.pdf> 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> 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> https://medium.com/s2wblog/post-mortem-of-klayswap-incident-through-bgp-hijacking-en-3ed7e33de600 

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

[5]  <https://www.usenix.org/conference/usenixsecurity23/presentation/cimaszewski> 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> 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> https://www.usenix.org/conference/usenixsecurity21/presentation/birge-lee 

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

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

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

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

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

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

[14]  <https://github.com/cabforum/servercert/pull/507> https://github.com/cabforum/servercert/pull/507 

[15]  <https://github.com/cabforum/servercert/compare/5224983ef0a6f94c18808ea3469e7a5ae35746e5..2dcf1a8fe5fc7b6a864b5767ab1db718bc447463> https://github.com/cabforum/servercert/compare/5224983ef0a6f94c18808ea3469e7a5ae35746e5..2dcf1a8fe5fc7b6a864b5767ab1db718bc447463 

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..2dcf1a8fe5fc7b6a864b5767ab1db718bc447463> https://github.com/cabforum/servercert/compare/c4a34fe2292022e0a04ba66b5a85df75907ac2a2..2dcf1a8fe5fc7b6a864b5767ab1db718bc447463 

— Motion Ends —

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

Discussion (at least 11 days)

- Start: 2024-05-20 14:30:00 UTC

- End no earlier than: 2024-05-31 14:30:00 UTC

Vote for approval (7 days)

- Start: TBD

- End: TBD

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