I suppose that would work for us but wouldn't there be the same concern with _pki and wildcard domains.
Why not permit both validation methods? -----Original Message----- From: Peter Bowen [mailto:[email protected]] Sent: Thursday, September 8, 2016 11:39 AM To: Jeremy Rowley <[email protected]> Cc: Kane York <[email protected]>; [email protected]; Ryan Sleevi <[email protected]> Subject: Re: [cabfpub] CNAME-based validation Yes, that is the suggestion. > On Sep 8, 2016, at 9:37 AM, Jeremy Rowley <[email protected]> wrote: > > Are you suggesting _pki.shop.example.com CNAME <rnd>.cnameauth.digicert.com > would be used to validate shop.example.com? > > From: Kane York [mailto:[email protected]] > Sent: Thursday, September 8, 2016 8:32 AM > To: Jeremy Rowley <[email protected]>; Peter Bowen > <[email protected]> > Cc: [email protected]; Ryan Sleevi <[email protected]> > Subject: Re: [cabfpub] CNAME-based validation > > I think it would be more secure, but without compromising functionality, to > point > _pki.shop.example.com CNAME <Random Value>.cnameauth.digicert.com > > ... , just like how a TXT record validation sets the text to a Random Value. > > (Using the BR's definition of Random Value here.) > > > On Wed, Sep 7, 2016, 10:20 PM Jeremy Rowley <[email protected]> > wrote: > Not really. No one wants to point their site to a different domain. I'm > hoping we can do something where there's a set process for showing control > over the domain (such as by creating sub-domains) to validate certificate > issuance. > > Pointing <rnd>.shop.example.com to digicert.com is a whole lot better for > customers than pointing shop.example.com. > > -----Original Message----- > From: Peter Bowen [mailto:[email protected]] > Sent: Wednesday, September 7, 2016 12:51 PM > To: Jeremy Rowley <[email protected]> > Cc: Ryan Sleevi <[email protected]>; [email protected] > Subject: Re: [cabfpub] CNAME-based validation > > Jeremy, > > It seems that there are two different discussions here that are getting > conflated. > > The first is allowing someone to confirm control of a standard domain by > using a CNAME record instead of a TXT record. The process would be very > similar: prepend a defined string to the domain and set the canonical name to > something containing a random value. > > The second is authentication with one level of indirection. I think that is > already mostly covered as the Authorization Domain Name can be the result of > dereferencing a CNAME pointer. So if you have: > > shop.example.com IN CNAME webstorehosting.webpki.com. > > You can run the validation for webstorehosting.webpki.com using constructed > email to domain contact, agreed-upon change to a website, DNS change, test > certificate or TLS using random number. If this passes, then > shop.example.com is validated. > > Does that not solve your issue? > > Thansk, > Peter > > > > On Sep 6, 2016, at 5:07 PM, Jeremy Rowley <[email protected]> > > wrote: > > > > Hi Ryan, > > > > Pardon my DNS ignorance, but how does the server know which CNAME record to > > use in this case? If shop.domain.comCNAMEs to digicert.com and *.domain.com > > CNAMEs to google.com, then how do you know which will resolve? There isn’t > > a weight/ordering preference for CNAME like there is TXT records. > > > > As for how to resolve this, what if the CA generated two random numbers, > > holding one of the numbers in reserve. Immediately after verifying that > > <rnd1>.domain.com CNAME points to a validated domain, the CA can then check > > <rnd2>.domain.com to see if it resolves. If it resolves successfully, a > > wildcard DNS is in place and the domain is not validated. If the domain > > does not resolve, a wildcard DNS is not present and the domain is > > considered validated. Does this resolve your concern? > > > > Jeremy > > > > From: Ryan Sleevi [mailto:[email protected]] > > Sent: Friday, September 2, 2016 7:40 PM > > To: Jeremy Rowley <[email protected]> > > Cc: Peter Bowen <[email protected]>; [email protected] > > Subject: Re: [cabfpub] CNAME-based validation > > > > Hi Jeremy, > > > > I'm afraid you may have misread my example. > > > > shop.example.com is a CNAME to paymentprovider.example.org (curse > > our lack of distinct TLDs). It does not resolve to example.net > > > > On Fri, Sep 2, 2016 at 6:29 PM, Jeremy Rowley <[email protected]> > > wrote: > > Here’s the steps: > > 1) CA verifies example.net using any one of the methods permitted > > > > 2) CA receives request for shop.example.com > > > > 3) CA retrieves CNAME for shop.example.com (permitted under > > Authorization Domain Name definition: “The CA may use the FQDN returned > > from a DNS CNAME lookup as the FQDN for the purposes of domain validation”) > > > > 4) CNAME causes resolution to example.net. > > > > 5) Example.net is verified under step 1, permitting issuance of the > > certificate > > > > > > > > > > > > > > From: Ryan Sleevi [mailto:[email protected]] > > Sent: Friday, September 2, 2016 5:12 PM > > To: Jeremy Rowley <[email protected]> > > Cc: Peter Bowen <[email protected]>; [email protected] > > > > Subject: Re: [cabfpub] CNAME-based validation > > > > Right, and I'm not sure that (2) sufficiently establishes that example.com > > is authorizing the request, given wildcards. > > > > I think this would be a similar concern with, say, following HTTP open > > redirects and saying a "200 OK" code authorizes the request - wellllll, not > > really. > > > > I'm curious if you could expand more why you believe other methods would > > permit a cert to be issued in the presence of this Wildcard DNS. > > > > As a concrete example: > > example.com A [my host] > > *.example.com CNAME example.net > > shop.example.com CNAME paymentprovider.example.org > > > > Under this scenario, could you explain what ways that the > > [<rnd>.example.com] would be able to issue a cert for either example.com or > > shop.example.com ? Perhaps I'm just missing the implications of the > > existing validation methods. > > > > > > > > > > On Fri, Sep 2, 2016 at 3:33 PM, Jeremy Rowley <[email protected]> > > wrote: > > Yes. Those are the two steps I am proposing. > > > > -----Original Message----- > > From: Peter Bowen [mailto:[email protected]] > > Sent: Friday, September 2, 2016 4:31 PM > > To: Jeremy Rowley <[email protected]> > > Cc: Ryan Sleevi <[email protected]>; [email protected] > > Subject: Re: [cabfpub] CNAME-based validation > > > > I think you are talking about two different things. > > > > Ryan is concerned that a customer has an existing record that is > > “*.example.com CNAME vanityblogs.example.net”. If you say “if you can make > > a record show up at _309654fddb59444d8efd6d2cc98881d5.example.com you are > > validated” that is bad. Instead, you are proposing a two prong validation > > test: > > > > 1) Confirm control of vanityblogs.example.net. > > 2) Make _309654fddb59444d8efd6d2cc98881d5.example.com point to > > vanityblogs.example.net. > > > > You are proposing that passing these both would confirm control of > > example.com, right? And this would allow getting a certificate for > > shop.example.com, correct? > > > > Thanks, > > Peter > > > > > On Sep 2, 2016, at 3:25 PM, Jeremy Rowley <[email protected]> > > > wrote: > > > > > > We are talking about the same thing (wildcard DNS records). > > > > > > Examples: > > > > > > sleevi.example.com CNAME vdomain.com *.example.com CNAME > > > vdomain.com <rnd>.example.com CNAME vdomain.com > > > > > > The BRs permit verification of each of these by establishing control over > > > vdomain.com (under the definition of authorization domain name). > > > > > > If *.example.com can be verified this way, what is different between > > > verifying *.example.com and <rnd>.example.com to verify all sub domains > > > of example.com? All the RND does is make it so the website doesn’t have > > > to point to vdomain.com. > > > > > > Jeremy > > > > > > From: [email protected] > > > [mailto:[email protected]] > > > On Behalf Of Ryan Sleevi > > > Sent: Friday, September 2, 2016 4:05 PM > > > To: Jeremy Rowley <[email protected]> > > > Cc: [email protected] > > > Subject: Re: [cabfpub] CNAME-based validation > > > > > > Jeremy, > > > > > > Perhaps it wasn't clear, I wasn't speaking of wildcard certificates, but > > > wildcard DNS rules, in which all requests for a given subdomain return a > > > preconfigured record type. While for TXT and CAA records this is quite > > > uncommon, it's exceedingly common to have CNAME records. > > > > > > That is, both <rnd>.example.com and sleevi.example.com may both CNAME to > > > example.com, by virtue of of the host putting a rule of "*.example.com > > > 3600 CNAME example.com" > > > > > > I am attempting to assert that placing the <rnd> in the subdomain is > > > insufficient proof of authorization, and is meaningfully and tangibly > > > different than the proof of control demonstrated in 3.2.2.4.7. > > > > > > As I read your wording, it suggests the following: > > > CA looks up <rnd>.example.com > > > <rnd>.example.com points to example.com CA sees it previously > > > issued a certificate for example.com using one of the other > > > methods CA issues certificate for <rnd>.example.com > > > > > > That concerns me. > > > > > > Peter's rewording suggests the inverse: > > > CA looks up _certvalidation.example.com > > > _certvalidation.example.com points (CNAMEs) to > > > <rnd>.validation.[nameofca].com CA issues certificate for > > > example.com > > > > > > This is much less concerning. > > > > > > Could you help clarify which you intend, and for what names/purposes? > > > > > > > > > On Fri, Sep 2, 2016 at 2:52 PM, Jeremy Rowley > > > <[email protected]> wrote: > > > Wildcard domains are already allowed. We can verify Wildcard DNS because > > > a CNAME for *.domain.com is pointing to a record previously verified. > > > This verification method is permitted under the definition of > > > Authorization Domain Name (where the FQDN returned by a CNAME lookup can > > > be used to verify the requested FQDN). Although <rnd>.domain.com isn’t > > > necessarily distinguishable from *.domain.com, the validation ends up > > > being the same because either its considered an Authorized Domain Name > > > (under the definition) or it was validated as a random value in this new > > > method. > > > > > > For example: > > > > > > *.domain.com -> dcv.example.com (validated under the Authorized > > > Domain Name section) <rnd>.domain.com ->validation.example.com > > > (validated under this new section) > > > > > > Because each is validated properly, tracking which exact section was used > > > in the validation isn’t necessary. > > > > > > Jeremy > > > > > > From: Ryan Sleevi [mailto:[email protected]] > > > Sent: Friday, September 2, 2016 3:28 PM > > > To: Jeremy Rowley <[email protected]> > > > Cc: [email protected] > > > Subject: Re: [cabfpub] CNAME-based validation > > > > > > > > > _______________________________________________ > > > Public mailing list > > > [email protected] > > > https://cabforum.org/mailman/listinfo/public > > > > _______________________________________________ > Public mailing list > [email protected] > https://cabforum.org/mailman/listinfo/public
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