[cabf_validation] [EXTERNAL]Re: Validation methods used for Wildcards/ADNs

Fri Jan 15 20:14:12 UTC 2021

We are in favor of the proposed change, but our issue will be the effectivity date and the reuse of domains which are currently verified.

We have implemented a system which only uses domain validation methods which can be used for Wildcards and ADNs. However, we will still have demand to use Method 18. This will mean that we will need to change our domain verification management system to have 2 types of verified domains: 1) CAN be used for Wildcard/ADNs and 2) CANNOT be used for Wildcard/ADNs. This could be a complex change in our current system. In addition we will want time for customers and integration partners which use Method 18 will need to re-tool, especially if they have verified domains which they think can be reused for up to 825-days. Even if the customer decides that they will no longer use Method 18, they may still need time to change how they will get their domains verified.

Thanks, Bruce.

From: Validation <validation-bounces at cabforum.org> On Behalf Of Ryan Sleevi via Validation
Sent: Thursday, January 14, 2021 11:44 AM
To: Ryan Sleevi <sleevi at google.com>; CA/Browser Forum Validation SC List <validation at cabforum.org>
Subject: [EXTERNAL]Re: [cabf_validation] Validation methods used for Wildcards/ADNs

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Just resurrecting this for the new year, and hoping people have had a chance to look at data.

We'll work on circulating a concrete draft for the next call to accomplish this, but would love to have data to inform the timelines.

On Fri, Dec 18, 2020 at 9:45 AM Ryan Sleevi via Validation <validation at cabforum.org<mailto:validation at cabforum.org>> wrote:
Yes, that is correct in how Authorization Domain Names and Wildcard Domain Names work, and precisely what this proposal sets forward to accomplish. This is because demonstrating the ability to edit a file on the web server is not equivalent to demonstrating you have controlver over DNS, as the other validation methods achieve, and is equivalent more to demonstrating control over an TLS handshake, where we have intentionally limited in the same way.

On Fri, Dec 18, 2020 at 4:55 AM Adriano Santoni via Validation <validation at cabforum.org<mailto:validation at cabforum.org>> wrote:

Ryan,

do I understand correctly that your post below implies the following? (first bullet is just a typical example, of course it would be the same for all subdomains)

  *   if domain validation is passed on (say) domain.tld by the website change method (§3.2.2.4.6), then a certificate containing www.domain.tld<http://www.domain.tld> MUST NOT be issued
  *   if domain validation is passed on (say) domain.tld by the website change method (§3.2.2.4.6), then a certificate containing *.domain.tld MUST NOT be issued

Adriano

Il 03/12/2020 02:31, Ryan Sleevi via Validation ha scritto:
Hey all,

I know we're not quite done with the certificate profile work, and I'm not wanting to distract from that too much. However, one of the long-standing items we had from our Herndon, VA validation summit (from Meeting 43) was in harmonizing the rules around what 3.2.2.4 methods can be used for Authorization Domain Names / Wildcard Domain Names.

I made an initial attempt at https://github.com/cabforum/servercert/compare/main...sleevi:2020-12-01_Wildcard_Rules to capture this. In effect, allowing validation as an ADN is conceptually "the same as" allowing a Wildcard Domain Name, since the ADN can authorize all children/grandchildren/etc of a domain, and a Wildcard is just a cert that works for all children of a domain.

As we've become aware of some CAs having poorly evaluated the security risks in this space, we'd like to try to close this gap. Here's the TL;DR summary

  *   3.2.2.4.6: Agreed-upon Change to Website

     *   Sunset 2020-06-03 for new validations

  *   3.2.2.4.18: Agreed-upon Change to Website v2
  *   3.2.2.4.19: Agreed-upon Change to Website - ACME
(The other bits are just aligning some of the language, so that "MAY NOT" becomes a clearer "MUST NOT", even though we mean the same)

These methods are proposed to *only* authorize a single FQDN, because they only demonstrate control over a specific service/port on a specific FQDN, and not demonstration of control over the whole domain namespace. This aligns with 3.2.2.4.20 (TLS using ALPN), which also only demonstrates control over a single service/port on a single FQDN.

This doesn't touch 3.2.2.4.4 (Constructed Email to Domain Contact), although we identified that one as potentially messy. However, hopefully we'll see that one fully sunset separately, in favor of the improved CAA methods (.13 - .17).

It'd be useful to spend a few minutes on the call discussing folks initial reactions. The big question, as always, is going to be timelines for changes. If folks think more time is needed than "immediately", my request is that they'd share concrete data.

Since Ballot 190 (2017-09-19), CAs have been required to maintain records of the validation methods they use, so this "should" be as easy as scanning all unexpired validations for these three methods and identifying cetrs which have a SAN that doesn't equal the validated FQDN (e.g. a cert with "www.example.com<http://www.example.com>" when the method used was 3.2.2.4.6 for "example.com<http://example.com>"). Just sharing those numbers is useful to understand any challenges CAs might face.

For example:

  *   30% of our certificates used 3.2.2.4.6. Of that 30%:

     *   80% of our certificates had at least one FQDN validated by ADN, with 40% of that being "www.".
     *   Of the 20% that had >1, we saw an average of 7.3 additional FQDNs validated by FDN.

  *   17% of our certificates used 3.2.2.4.18. of that 17% ....

     *   80% of the FQDNs validated by ADNs were for domains that did not resolve (e.g. "internal.corp.foo.example"), and thus would have to switch to a new validation method or expose those services publicly.
This sort of concrete data helps understand the impact to CAs, and their customers, and thus indirectly, our users. It also helps figure out what reasonable time frames to phase in could be, in the unlikely event a phase-in became necessary.

This sunset "should" be fairly simple and uncontroversial, but since there are edge cases (like internal servers), concrete data like the above is useful if folks have concerns.

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