Yes, your summary of the status is correct. I’ve had no bandwidth to deal with CABF stuff since Aug 17th, and will not until after the holiday weekend.
Thanks for making concrete suggestions. I hope to have time to review and incorporate your and Corey’s feedback on Tuesday. Hopefully we can get this wrapped up soon. -Tim From: Ryan Sleevi <[email protected]> Sent: Thursday, August 30, 2018 9:32 PM To: Tim Hollebeek <[email protected]> Cc: [email protected]; Corey Bonnell <[email protected]>; CABFPub <[email protected]> Subject: Re: [Servercert-wg] Ballot SC4 - email and CAA CONTACT I'm understanding that https://github.com/cabforum/documents/compare/Ballot-SC4---CAA-CONTACT-email?diff=unified <https://github.com/cabforum/documents/compare/Ballot-SC4---CAA-CONTACT-email?diff=unified&expand=1> &expand=1 remains the current state, with the last update on August 17. Is there a newer version? It sounds like you plan on incorporating Corey's feedback at some point in the future, but that isn't done yet? In addition to that concrete feedback pending incorporation, there are a number of issues. 1) The terminology seems to interchangably use "email to DNS domain name holder" and "DNS contact email address". It seems aligning this terminology within the text itself is good. 2) The structure of the requirements within the first paragraph of each reads ambiguously. That is, item (i) states "sending an email to a DNS domain name holder", while the following sentence describes how that email address is obtained. - This can be read as suggesting these are distinct emails. That is, that you send the e-mail to "a DNS domain name holder" (determined at the CAs discretion) AND the email address specified through the given means. The terminology alignment can help here, as well as rewording the second sentence to indicate that "The CA SHALL determine the DNS contact email address using the procedure specified in ..." or some equivalent. - Alternatively, the ordering of steps can be restructured in such a way that the determination is the first step, followed by the subsequent step of sending the email (that is, (i) becomes (ii), and the second sentence is reworded and becomes (i)). 3) Format wise, as previously suggested, we've seen ambiguity issues arise when ordered list of steps are attempted to naturally flow in to sentences. As depressing as it seems, but certainly after incorporating the above feedback, separating out (i) - (iii) onto distinct lines seems to provide greater clarity about the necessary combined steps. 4) The issue of mixing TXT and CAA records is still present, through the ambiguity of "DNS contact email address" being reused between .13 and .14. It seems simpler and clearer, not to mention consistent with other methods, to ensure that unambiguously, if you determine an email using .14, that doesn't mean you can combine with .13 (or .2). This can be resolved by changing the language from "provided that the email address used has been obtained using this method" or some sort. 5) I again reiterate the value of separating out the TXT and CAA discussions, so that we can unblock the CAA work from proceeding and separately address the TXT. This would equally unblock the method regarding phone validation and CAA, which seems valuable and useful for impacted CAs. That is, treat these as two separate ballots. With respect to the TXT method 1) "an email address found in the DNS TXT record of the Authorization Domain Name in the format defined in Appendix B" is ambiguous. This implies a TXT record on the ADN, while the stated intent of this is to be a grandchild label of the ADN. This can be resolved through greater specificity as to how that email address is determined, in line with the above feedback for restructuring the list steps and the method of determining the e-mail. 2) The language still remarks on its similarity to the iodef tag, except in this current revision, there is no similarity to the iodef tag. 3) With respect to the contactemail property, "or it cannot be used" leaves some ambiguity for CAs that will no doubt result in questions, similar to the recent discussions around "invalid" domains for CAA. Consider, for example, if a CAA record for child.example.com <http://child.example.com> contains "[email protected] <mailto:[email protected]> " (note, trailing padding), and example.com <http://example.com> contains "[email protected] <mailto:[email protected]> " (note, well-formed). Can the CA dispatch an email to [email protected] <mailto:[email protected]> on the basis that it cannot use the CAA record for child.example.com <http://child.example.com> ? The answer presumably is "NO", but the current language leaves this ambiguous. If there's consensus on this, then we can restructure the process/algorithm for determining the email by defining it in terms of CAA RRSets - that is, that there first is a concrete step to 'gather' the matching RRSets, a second step to 'validate' the RRSets, and the output of such an algorithm is one or more e-mail addresses that can be used. 4) However, this problem - the competition between the CAA algorithm and the use of ADN - creates new issues. Am I permitted, in the course of issuing for child.example.com <http://child.example.com> , to examine the CAA record for example.com <http://example.com> ? As currently specified in the CAA section, this is ambiguous, due to CAA's prohibition on tree walking once you run into a child. However, this is exacerbated by the TXT record, since its use on authorization domain names suggests that I can ignore "_caa_contact_email.child.example.com <http://caa_contact_email.child.example.com> " and use "_caa_contact_email.example.com <http://caa_contact_email.example.com> ". This is because the TXT section uses "domain" without clarifying whether we're speaking about the ADN or the FQDN, and the method invoking this algorithm (.14) uses ADN. To resolve this, it's best to specify concretely what you want to happen, and we can find text that tries to accomplish this. I would encourage you trying to describe in prose / plain text in this thread what you want, rather than trying to invoke spec text and try to capture that on the first go. 5) The issue with TXT and security still exists, in a way that does not manifest for CAA. I appreciate that you've collapsed from grandchild to child in the latest revision (specifically, the use of "_caa_contact_email"), but as noted, domain holders now need to take steps to ensure that such a domain is fully protected. This is an existing issue with .7 that the VWG identified, and our options here are "introduce something known-weak and ope to fix it later" or "prevent new methods from being weak". Given the incentive structures for correcting the weaknesses are misaligned, it's better to prevent its inclusion to begin with, so that we can resolve how best to solve these - the same as if introducing new blessed emails for 3.2.2.4.4. As previously proposed, one method of resolution is to improve the transparency of the reliance on this method, much as Microsoft has done for "deprecated but still widely used" technologies, such as SMB1 ( https://blogs.technet.microsoft.com/filecab/2017/06/01/smb1-product-clearinghouse/ ). I've not received a clear response as to your position on this. On Wed, Aug 29, 2018 at 11:36 AM Tim Hollebeek <[email protected] <mailto:[email protected]> > wrote: I’ve been on vacation for a week. If you have specific improvements to offer, please do. -Tim From: Ryan Sleevi <[email protected] <mailto:[email protected]> > Sent: Monday, August 27, 2018 5:52 PM To: Tim Hollebeek <[email protected] <mailto:[email protected]> >; [email protected] <mailto:[email protected]> Cc: Corey Bonnell <[email protected] <mailto:[email protected]> >; CABFPub <[email protected] <mailto:[email protected]> > Subject: Re: [Servercert-wg] Ballot SC4 - email and CAA CONTACT Tim, Has there been an update to the ballot? Similarly, has there been any effort to address the TXT deprecation, or the use of multiple layers of subdomains? On Thu, Aug 16, 2018 at 10:35 AM Tim Hollebeek via Servercert-wg <[email protected] <mailto:[email protected]> > wrote: Thanks Corey. This is very helpful. I’ll update the ballot. -Tim From: Corey Bonnell <[email protected] <mailto:[email protected]> > Sent: Thursday, August 9, 2018 11:04 AM To: Tim Hollebeek <[email protected] <mailto:[email protected]> >; CA/B Forum Server Certificate WG Public Discussion List <[email protected] <mailto:[email protected]> >; CA/Browser Forum Public Discussion List <[email protected] <mailto:[email protected]> > Subject: Re: [Servercert-wg] Ballot SC4 - email and CAA CONTACT Tim, There are additional concerns, namely regarding the character set encoding (as in UTF-8, UTF-16, Shift-JIS, etc.). A TXT record could conceivably contain a Shift-JIS-encoded (or some other character set) email address which may be treated as “valid” by a CA (who then sends an email to the Shift-JIS-encoded email address). However, when the TXT record RDATA is interpreted as UTF-8 by another CA, this will yield another email address, allowing an attacker to setup a mailbox to receive the DV email. Given this, I do not believe I am being overly pedantic in asking that we more concretely define what “valid” means. Given that I’ve seen at least one certificate in CT that had various Subject RDN values be encoded in UTF-16 (where UTF-16 isn’t even allowed), I believe this scenario is very likely to occur. Explicitly specifying what “valid” means by referencing RFC 6532 section 3.2 will provide guidance to the ecosystem to mitigate this risk. My suggested wording is to change “valid email address, with no additional padding or structure” to “valid email address as defined in RFC 6532 section 3.2, with no additional padding or structure”. That being said, I think there’s significant value in aligning the syntax of the CAA and TXT record. Specifying a single syntax makes it less cumbersome for Applicants, CA engineers and support personnel, and DNS providers who will likely author tools to generate these records. I agree with you that using the proposed TXT “valid email address” (with the addition of a reference to RFC 6532 to define “valid”) is preferable over mailto: for the reasons that you mentioned, provided that it’s used for both the CAA record (whose property tag would probably need to be renamed to “contactemail” or something similar) and TXT record. Thanks, Corey From: Tim Hollebeek <[email protected] <mailto:[email protected]> > Date: Tuesday, August 7, 2018 at 7:29 PM To: Corey Bonnell <[email protected] <mailto:[email protected]> >, CA/B Forum Server Certificate WG Public Discussion List <[email protected] <mailto:[email protected]> >, CA/Browser Forum Public Discussion List <[email protected] <mailto:[email protected]> > Subject: RE: [Servercert-wg] Ballot SC4 - email and CAA CONTACT No, I don’t think that scheme-based encodings and representations outside of a URI scheme is a reasonable interpretation of the text as written. The draft text specifically states that the contents must be a valid email address. That means it must be represented in the standard way, without alternative encodings or other silliness. I can put in the RFC 6532 reference to make that even more clear than it already is. But I don’t want to have another Ballot 219 where we’re doing a lot of work to add text specifically to rule out unreasonable interpretations. There’s an infinite amount of work down that road. -Tim From: Corey Bonnell <[email protected] <mailto:[email protected]> > Sent: Tuesday, August 7, 2018 3:32 PM To: Tim Hollebeek <[email protected] <mailto:[email protected]> >; CA/B Forum Server Certificate WG Public Discussion List <[email protected] <mailto:[email protected]> >; CA/Browser Forum Public Discussion List <[email protected] <mailto:[email protected]> > Subject: Re: [Servercert-wg] Ballot SC4 - email and CAA CONTACT Tim, If Internationalized Email Address support is desired, then for completeness, “valid” should be more concretely defined. The reason why I think merely stating “valid” is insufficient is that there are multiple ways to encode an email address, and inconsistent handling of these values across CA implementations may create vulnerabilities where attackers can obtain certificates for domains that they don’t control. As an example, a “valid” email address could be interpreted as the scheme-specific part of a mailto: URL (eg, the [email protected] <mailto:[email protected]> in mailto:[email protected]). The CAA “contact” property tag specifies a mailto: URL, so it reasonable to think that the TXT record does as well. URI-encoding of the scheme-specific part (see RFC 6068, section 2 https://tools.ietf.org/html/rfc6068#section-2 <https://scanmail.trustwave.com/?c=4062&d=vavq28pjHFI2ph_WoO8TpMTD8JkSCWk7cxp_KdSnIA&s=5&u=https%3a%2f%2ftools%2eietf%2eorg%2fhtml%2frfc6068%23section-2> ) differs from an email address encoded as specified in RFC 6532, section 3.2 (https://tools.ietf.org/html/rfc6532#section-3.2 <https://scanmail.trustwave.com/?c=4062&d=vavq28pjHFI2ph_WoO8TpMTD8JkSCWk7cxwletXyeg&s=5&u=https%3a%2f%2ftools%2eietf%2eorg%2fhtml%2frfc6532%23section-3%2e2> ). Given the differences between these encodings, it would be possible for an attacker to find a CA that uses a different encoding than the CA that the domain owner used and setup a mailbox such that they receive the DV email when requesting a certificate for the victim domain from the other CA. For this reason, I think that explicitly mandating “a RFC 6532-compliant email address” would be prudent. Or alternatively, change the TXT record to specify a mailto: URL so that it is consistent with the CAA syntax. Thanks, Corey From: Tim Hollebeek <[email protected] <mailto:[email protected]> > Date: Tuesday, August 7, 2018 at 10:59 AM To: Corey Bonnell <[email protected] <mailto:[email protected]> >, CA/B Forum Server Certificate WG Public Discussion List <[email protected] <mailto:[email protected]> >, CA/Browser Forum Public Discussion List <[email protected] <mailto:[email protected]> > Subject: RE: [Servercert-wg] Ballot SC4 - email and CAA CONTACT I’d like not to make it more complicated than necessary, but if there are useful clarifications you can suggest about how better to define “valid”, I’m all ears. For the particular concern you mentioned, it seems clear to me that an Internationalized Email Address is in fact a valid email address for method 14 (assuming it is not invalid for some other reason). -Tim From: Corey Bonnell <[email protected] <mailto:[email protected]> > Sent: Tuesday, August 7, 2018 10:35 AM To: Tim Hollebeek <[email protected] <mailto:[email protected]> >; CA/B Forum Server Certificate WG Public Discussion List <[email protected] <mailto:[email protected]> >; CA/Browser Forum Public Discussion List <[email protected] <mailto:[email protected]> > Subject: Re: [Servercert-wg] Ballot SC4 - email and CAA CONTACT Hi Tim, I think this updated text is fine (with one caveat about raw addresses; see below), pending changing “domain being validated” to “Authorization Domain Name” to be consistent with other changes of this usage in the ballot. If the TXT record data is merely the raw email address (as opposed to a mailto: URL), it would be good to specify more concretely what “valid” means. This is especially relevant in regard to Internationalized Email Addresses (and the potential can of worms that entails) and whether or not they’re considered “valid” for method 14. Thanks, Corey From: Tim Hollebeek < <mailto:[email protected]> [email protected]> Date: Friday, August 3, 2018 at 4:57 PM To: Corey Bonnell < <mailto:[email protected]> [email protected]>, CA/B Forum Server Certificate WG Public Discussion List < <mailto:[email protected]> [email protected]>, CA/Browser Forum Public Discussion List < <mailto:[email protected]> [email protected]> Subject: RE: [Servercert-wg] Ballot SC4 - email and CAA CONTACT Corey, Upon further review, I believe the domain-authorization-email is a relic of a previous proposal, and could be safely removed. The DNS TXT record MUST be placed on the "_caa_contact_email" subdomain of the domain being validated. The entire RDATA value of the "_caa_contact_email" record MUST be a valid email address, with no additional padding or structure, or it cannot be used. ? -Tim From: Corey Bonnell <[email protected] <mailto:[email protected]> > Sent: Friday, August 3, 2018 1:44 PM To: Tim Hollebeek <[email protected] <mailto:[email protected]> >; CA/B Forum Server Certificate WG Public Discussion List <[email protected] <mailto:[email protected]> >; CA/Browser Forum Public Discussion List <[email protected] <mailto:[email protected]> > Subject: Re: [Servercert-wg] Ballot SC4 - email and CAA CONTACT Given that the entire RDATA is the email address, I don’t see how “The DNS record MUST be named "domain-authorization-email"” is applicable here, as there is nowhere in the RDATA to specify the name. Also, is the RDATA a mailto: URL (as in the CAA record), or is it a plain email address? I’d imagine the former would be preferable for parity with the CAA syntax as well as reuse of the “_caa_contact” attribute leaf for phone numbers. Thanks, Corey From: Tim Hollebeek < <mailto:[email protected]> [email protected]> Date: Friday, August 3, 2018 at 12:19 PM To: Corey Bonnell < <mailto:[email protected]> [email protected]>, CA/B Forum Server Certificate WG Public Discussion List < <mailto:[email protected]> [email protected]>, CA/Browser Forum Public Discussion List < <mailto:[email protected]> [email protected]> Subject: RE: [Servercert-wg] Ballot SC4 - email and CAA CONTACT I expect the email address would be the entirety of the RDATA for the RR, with no additional formatting. I can make that explicit if you think it would be helpful. -Tim From: Corey Bonnell <[email protected] <mailto:[email protected]> > Sent: Friday, August 3, 2018 12:04 PM To: Tim Hollebeek <[email protected] <mailto:[email protected]> >; CA/B Forum Server Certificate WG Public Discussion List <[email protected] <mailto:[email protected]> >; CA/Browser Forum Public Discussion List <[email protected] <mailto:[email protected]> > Subject: Re: [Servercert-wg] Ballot SC4 - email and CAA CONTACT Hi Tim, Can you provide an example of how a TXT record would be formatted to convey the email address (as was done for the CAA records)? It’s not clear to me based on the description given. Thanks, Corey Bonnell Senior Software Engineer Trustwave | SMART SECURITY ON DEMAND <http://www.trustwave.com/> https://www.trustwave.com From: Servercert-wg < <mailto:[email protected]> [email protected]> on behalf of Tim Hollebeek via Servercert-wg < <mailto:[email protected]> [email protected]> Reply-To: Tim Hollebeek < <mailto:[email protected]> [email protected]>, CA/B Forum Server Certificate WG Public Discussion List < <mailto:[email protected]> [email protected]> Date: Friday, August 3, 2018 at 11:50 AM To: CA/Browser Forum Public Discussion List < <mailto:[email protected]> [email protected]>, " <mailto:[email protected]> [email protected]" < <mailto:[email protected]> [email protected]> Subject: [Servercert-wg] Ballot SC4 - email and CAA CONTACT Ballot SC4: CAA Contact Property and Associated E-mail Validation Methods Purpose of Ballot: Increasingly, contact information is not available in WHOIS due to concerns about potential GDPR violations. This ballot specifies a method by which domain holders can publish their contact information via DNS, and how CAs can use that information for validating domain control. The following motion has been proposed by Tim Hollebeek of DigiCert and endorsed by Bruce Morton of Entrust and Doug Beattie of GlobalSign. --- MOTION BEGINS --- This ballot modifies the “Baseline Requirements for the Issuance and Management of Publicly-Trusted Certificates” as follows, based on Version 1.6.0: Add Section 3.2.2.4.13: Domain Owner Email in CAA Confirm the Applicant's control over the FQDN by (i) sending an email to a DNS domain name holder, (ii) including a Random Value in the email, and (iii) receiving a confirming response utilizing the Random Value. The CA MUST send the email to an email address found in the CAA Contact property record of the Authorization Domain Name as defined in Appendix B. Each email MAY confirm control of multiple FQDNs, provided the email address used is a DNS contact email address for each ADN being validated. The Random Value SHALL be unique in each email. The email MAY be re-sent in its entirety, including the re-use of the Random Value, provided that its entire contents and recipient SHALL remain unchanged. The Random Value SHALL remain valid for use in a confirming response for no more than 30 days from its creation. The CPS MAY specify a shorter validity period for Random Values. Note: Once the FQDN has been validated using this method, the CA MAY also issue Certificates for other FQDNs that end with all the labels of the validated FQDN. This method is suitable for validating Wildcard Domain Names. Add Section 3.2.2.4.14: Domain Owner Email published in TXT record Confirm the Applicant's control over the FQDN by (i) sending an email to a DNS domain name holder, (ii) including a Random Value in the email, and (iii) receiving a confirming response utilizing the Random Value. The CA MUST send the email to an email address found in the DNS TXT record of the Authorization Domain Name in the format defined in Appendix B. Each email MAY confirm control of multiple FQDNs, provided the email address used is a DNS contact email address for each ADN being validated. The Random Value SHALL be unique in each email. The email MAY be re-sent in its entirety, including the re-use of the Random Value, provided that its entire contents and recipient SHALL remain unchanged. The Random Value SHALL remain valid for use in a confirming response for no more than 30 days from its creation. The CPS MAY specify a shorter validity period for Random Values. Note: Once the FQDN has been validated using this method, the CA MAY also issue Certificates for other FQDNs that end with all the labels of the validated FQDN. This method is suitable for validating Wildcard Domain Names. Add Appendix B: CAA Contact Tag The syntax for the contact property is similar to the iodef property. It allows domain owners to publish contact information in DNS in addition to WHOIS for the purpose of validating domain control. CAA contact Property contact <URL> : The contact property entry specifies the authorized means of contacting the holder of the domain or another party who is authorized to approve issuance of certificates for the domain. The contact property specifies a means of contacting the domain holder, or another party that is authorized to approve issuance of certificates for the domain in question. The contact property takes a URL as its parameter. The following URL scheme type SHOULD be implemented: mailto: An SMTP email address where the domain holder or other authorized party can be contacted. Schemes other than "mailto:"; MUST NOT be used. The following is an example where the holder of the domain specified the contact property using an email address. $ORIGIN example.com <http://scanmail.trustwave.com/?c=4062&d=vavq28pjHFI2ph_WoO8TpMTD8JkSCWk7c08pedHzeg&s=5&u=http%3a%2f%2fexample%2ecom> . CAA 0 issue “ca.example.net <http://ca.example.net> ” . CAA 0 contact “mailto:[email protected]” Support for Legacy Systems Some systems still do not have sufficient support for CAA records. To allow users of those systems to specify contact information, a legacy format using text records is allowed. The DNS TXT record MUST be placed on the "_caa_contact" subdomain of the domain being validated. The DNS record MUST be named "domain-authorization-email". The value of "domain-authorization-email" MUST contain a valid email address, or it cannot be used. --- MOTION ENDS --- *** WARNING ***: USE AT YOUR OWN RISK. THE REDLINE BELOW IS NOT THE OFFICIAL VERSION OF THE CHANGES (CABF Bylaws, Section 2.4(a)): A comparison of the changes can be found at: https://github.com/cabforum/documents/compare/Ballot-SC4---CAA-CONTACT-email?diff=unified <https://scanmail.trustwave.com/?c=4062&d=vavq28pjHFI2ph_WoO8TpMTD8JkSCWk7cxwlc4T2fA&s=5&u=https%3a%2f%2fgithub%2ecom%2fcabforum%2fdocuments%2fcompare%2fBallot-SC4---CAA-CONTACT-email%3fdiff%3dunified%26amp%3bexpand%3d1> &expand=1 The procedure for approval of this ballot is as follows: Discussion (7+ days) Start Time: 2018-08-03 11:50 Eastern End Time: Not before 2018-08-10 11:50 Eastern Vote for approval (7 days) Start Time: TBD End Time: TBD _______________________________________________ Servercert-wg mailing list [email protected] <mailto:[email protected]> http://cabforum.org/mailman/listinfo/servercert-wg
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