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<span style="font-size: 12pt;">Do I understand you correctly that in your opinion domain name owners should not have the ability to restrict all certificate issuance with a single record?</span><br>
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I don't think we can expect that a domain name owner would add CAA records for every ecosystem (if they even know about there existence) because these ecosystems want to be independent.</div>
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If you have a link to the relevant discussion on MDSP that would be great!</div>
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<div id="divRplyFwdMsg"><strong>From:</strong> Tim Hollebeek <tim.hollebeek@digicert.com><br>
<strong>Sent:</strong> Friday, 29 January 2021, 19:18<br>
<strong>To:</strong> Paul van Brouwershaven; Neil Dunbar; SMIME Certificate Working Group<br>
<strong>Cc:</strong> Kirk Hall<br>
<strong>Subject:</strong> [EXTERNAL] RE: [Smcwg-public] CAA and S/MIME<br>
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<p class="MsoNormal">Paul,</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">You might want to review the previous discussions of this issue on MDSP, where it was made pretty clear, including by the author of the RFC, that the “issue” tag was intended to be specific to the web. CAA for certificate type has also
been discussed quite a bit here at the Forum recently (it was an idea we introduced about three years ago and were pushing), so you might want to review the long discussion of those proposals and why they didn’t move forward.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">It’s not clear why you think there are problems with having both ‘issue’ and ‘issueesmime’, especially since your analysis seems to assume that if they’re both there, they interact in some way. They should not, and that seems to be the
source of the problems you’re trying to highlight.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">What one wants is to be able to clearly state the policy for each ecosystem, without interactions. Interactions between different certificate ecosystems are the cause of most of PKIs problems, and we should be looking to eliminate cross-PKI
interactions, not introduce new ones.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">It’s pretty straightforward to do that with a new tag. No additional properties or semantics are required. And the process of adding a new tag is something this group has already successfully done once (“CAA CONTACT”).</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">-Tim</p>
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<p class="MsoNormal"><b>From:</b> Paul van Brouwershaven <Paul.vanBrouwershaven@entrust.com>
<br>
<b>Sent:</b> Friday, January 29, 2021 11:13 AM<br>
<b>To:</b> Neil Dunbar <ndunbar@trustcorsystems.com>; SMIME Certificate Working Group <smcwg-public@cabforum.org>; Tim Hollebeek <tim.hollebeek@digicert.com><br>
<b>Cc:</b> Kirk Hall <Kirk.Hall@entrust.com><br>
<b>Subject:</b> Re: [Smcwg-public] CAA and S/MIME</p>
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<p class="MsoNormal"> </p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">While the BR only specifies how CAA must be implemented/used for TLS certificates the CAA RFC is not limited to just TLS certificates, the RFC 8659 (and previously RFC 6844) begins with:</span></p>
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<blockquote>
<pre style="background:white"><span style="color:black">The Certification Authority Authorization (CAA) DNS Resource Record</span></pre>
<pre style="background:white"><span style="color:black"> allows a DNS domain name holder to specify one or more Certification</span></pre>
<pre style="background:white"><span style="color:black"> Authorities (CAs) authorized to issue certificates for that domain</span></pre>
<pre style="background:white"><span style="color:black"> name.</span></pre>
</blockquote>
<p class="MsoNormal" style="background:white"><span style="font-size:11.5pt; font-family:"Segoe UI",sans-serif; color:black"> </span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">This does make sense as this would create a `deny all, except` principle where you need to give explicit permission like as in a good firewall configuration. But I agree that there should be a
possibility to change permission per certificate type and to drop restrictions where needed (such as for S/MIME with shared mail providers).</span></p>
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<p class="MsoNormal"> </p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">I'm currently not in favor of having a new S/MIME specific property, and one for client certs, document signing, etc. as where does it stop. It would also not allow to have separate `iodef` settings
for example (or only enable them for TLS).</span></p>
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<p class="MsoNormal"> </p>
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<p class="MsoNormal"><span style="color:black">We could define one new parameter to define the certificate type, the standard already has a reversed policy property which was used in the draft RFC to limit issuance on policy OID. </span><span style="font-size:12.0pt; color:black">Rob
pointed me at the draft CAA specification that had a policy property value instead of a CA domain name.</span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black"><a href="https://datatracker.ietf.org/doc/html/draft-hallambaker-donotissue-04#section-3.1.2">https://datatracker.ietf.org/doc/html/draft-hallambaker-donotissue-04#section-3.1.2</a></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black"> </span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">This could work with cabforum defined OID's, the advantage from using OID's is that it would support an OID prefix, and it would be easier for CAs to enforce. But it's not very user friendly..?</span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black"> </span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">This would allow:
</span></p>
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<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> $ORIGIN example.com</span><span style="color:black"></span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca1.example.net; policy=2.23.140.1" // Only cabforum</span><span style="color:black"></span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca2.example.net; policy=2.23.140.1.5" // SMIME</span><span style="color:black"></span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca3.example.net; policy=2.23.140.1.2" // DV, OV, IV</span><span style="color:black"></span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca4.example.net; policy=2.23.140.1.1" // EV</span><span style="color:black"></span></pre>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black"> </span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black"> </span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">For <span style="background:white">
user </span>friendliness, we could define a new parameter such as `type` with the same intention but based on a name value:</span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black"> </span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">This would allow:</span></p>
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<p class="MsoNormal"> </p>
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<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> $ORIGIN example.com</span></pre>
<pre><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca1.example.net"</span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca2.example.net; type=smime"</span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca3.example.net; type=tls"</span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca4.example.net; type=tls-ev"</span></pre>
<pre><span style="font-family:"Calibri",sans-serif; color:#201F1E; background:white"> </span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">Where:</span></pre>
<pre style="margin-left:.5in; text-indent:-.25in; mso-list:l0 level1 lfo1; break-before:page"><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">ca1 could issue any type of certificate not explicitly specified (so no S/MIME, or TLS certificates in this example)</span></pre>
<pre style="margin-left:.5in; text-indent:-.25in; mso-list:l0 level1 lfo1"><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">ca2 could issue only smime certificates</span></pre>
<pre style="margin-left:.5in; text-indent:-.25in; mso-list:l0 level1 lfo1; break-before:page"><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">ca3 could issue any type of TLS certificate except for EV</span></pre>
<pre style="margin-left:.5in; text-indent:-.25in; mso-list:l0 level1 lfo1; break-before:page"><span style="font-family:Symbol"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman""> </span></span></span><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">ca4 could issue only EV TLS certificates</span></pre>
<pre style="break-before:page"> </pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">Alternatively, we could define two parameters, one for the certificate type and one for the assurance level, this would give:</span></pre>
<pre style="break-before:page"> </pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> $ORIGIN example.com</span></pre>
<pre style="background:white"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca1.example.net"</span><span style="font-size:10.5pt; color:black"></span></pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca2.example.net; type=smime"</span><span style="color:black"></span></pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca3.example.net; type=tls"</span><span style="color:black"></span></pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca4.example.net; type=tls; level=ev;"</span><span style="color:black"></span></pre>
<p class="MsoNormal"> </p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">The challenge for all these methods is how do we drop CAA limitations, as we want something like:</span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black"> </span></p>
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<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> $ORIGIN example.com</span></pre>
<pre style="background:white"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca1.example.net"</span><span style="font-size:10.5pt; font-family:"Calibri",sans-serif; color:black"></span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black; background:white"> . CAA 0 issue "*; type=smime"</span><span style="color:black; background:white"></span></pre>
<pre style="background:white; break-before:page"><span style="font-size:10.5pt; font-family:"Calibri",sans-serif; color:black"> </span></pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">But that is not allowed by the RFC.</span></pre>
<pre style="break-before:page"> </pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">If we would define a separate property per certificate type but follow the RFC and honoring the inheritance, we would still have the same challenge of stopping the inheritance .</span></pre>
<pre style="break-before:page"> </pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> $ORIGIN example.com</span></pre>
<pre style="background:white"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca1.example.net"</span><span style="font-size:10.5pt; color:black"></span></pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issuesmime "ca2.example.net"</span><span style="color:black"></span></pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issuetls "ca3.example.net"</span><span style="color:black"></span></pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issuetlsev "ca4.example.net"</span><span style="color:black"></span></pre>
<pre> </pre>
<pre style="break-before:page"><span style="font-size:12.0pt; font-family:"Calibri",sans-serif; color:black">Maybe we could simply create an 'unrestricted' parameter to overrule the RFC?:</span></pre>
<pre style="break-before:page"> </pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> $ORIGIN example.com</span></pre>
<pre style="background:white"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "ca1.example.net"</span><span style="font-size:10.5pt; color:black"></span></pre>
<pre style="background:white; break-before:page"><span style="font-size:12.0pt; font-family:Consolas; color:black"> . CAA 0 issue "; type=smime; unrestricted=true"</span><span style="color:black"></span></pre>
<pre> </pre>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black">Paul</span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt; color:black"> </span></p>
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<p class="MsoNormal"><b><span style="color:black">From:</span></b><span style="color:black"> Smcwg-public <<a href="mailto:smcwg-public-bounces@cabforum.org">smcwg-public-bounces@cabforum.org</a>> on behalf of Tim Hollebeek via Smcwg-public <<a href="mailto:smcwg-public@cabforum.org">smcwg-public@cabforum.org</a>><br>
<b>Sent:</b> Monday, October 26, 2020 15:25<br>
<b>To:</b> Neil Dunbar <<a href="mailto:ndunbar@trustcorsystems.com">ndunbar@trustcorsystems.com</a>>; SMIME Certificate Working Group <<a href="mailto:smcwg-public@cabforum.org">smcwg-public@cabforum.org</a>><br>
<b>Subject:</b> [EXTERNAL]Re: [Smcwg-public] CAA and S/MIME</span> </p>
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<p class="MsoNormal"> </p>
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<p class="xmsonormal">This is how I feel about the issue. CAA is potentially an interesting improvement to the S/MIME ecosystem, but the current tags and implementation were meant for TLS, and shouldn’t be reused.</p>
<p class="xmsonormal"> </p>
<p class="xmsonormal">The RFC has an extension mechanism which can easily be used to add new tags for S/MIME issuance, and issuance of other kinds of non-TLS certificates.</p>
<p class="xmsonormal"> </p>
<p class="xmsonormal">-Tim</p>
<p class="xmsonormal"> </p>
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<p class="xmsonormal"><b>From:</b> Smcwg-public <<a href="mailto:smcwg-public-bounces@cabforum.org">smcwg-public-bounces@cabforum.org</a>>
<b>On Behalf Of </b>Neil Dunbar via Smcwg-public<br>
<b>Sent:</b> Monday, October 26, 2020 6:03 AM<br>
<b>To:</b> <a href="mailto:smcwg-public@cabforum.org">smcwg-public@cabforum.org</a><br>
<b>Subject:</b> Re: [Smcwg-public] CAA and S/MIME</p>
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<p class="xmsonormal"> </p>
<p> </p>
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<p class="xmsonormal">On 24/10/2020 16:21, Stephen Davidson via Smcwg-public wrote:</p>
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<blockquote style="margin-top:5.0pt; margin-bottom:5.0pt">
<p class="xmsonormal">Hello:</p>
<p class="xmsonormal"> </p>
<p class="xmsonormal">The topic of Certification Authority Authorisation (CAA) has arisen a number of times in relation to the evolving S/MIME Baseline.</p>
<p class="xmsonormal">I highlight a discussion on that subject related to the Mozilla policy:
<a href="https://github.com/mozilla/pkipolicy/issues/135">https://github.com/mozilla/pkipolicy/issues/135</a></p>
<p class="xmsonormal">A significant number of email providers – such as gmail.com, outlook.com, protonmail.com, and others – have CAA records.</p>
<p class="xmsonormal"><br>
Questions for us to address later in our discussions:</p>
<p class="xmsonormal"> </p>
<ul type="disc" style="margin-top:0in">
<li class="xmsolistparagraph" style="margin-top:0in; margin-bottom:0in; mso-list:l1 level1 lfo2">
Is CAA a desired requirement of the S/MIME Baseline?</li><li class="xmsolistparagraph" style="margin-top:0in; margin-bottom:0in; mso-list:l1 level1 lfo2">
Should the S/MIME Baseline rely upon the existing requirements stated in the TLS BR, or is the S/MIME use case sufficiently different to merit a separate CAA tag?</li></ul>
<p class="xmsonormal" style="margin-bottom:12.0pt"> </p>
</blockquote>
<p>Generally, I'm a fan of allowing organisations (however defined) to specify their policy requirements for publicly trusted certificates via CAA records; so I would say "yes", it is a desired requirement of the S/MIME baseline. I would certainly expect it
to make its way into the root program requirements at some point, and having a pan-root program consensus on those requirements beats having overlapping or potentially conflicting requirements.</p>
<p>That said, I'm not a fan of ninja semantics (changing the meaning of a deployed resource where the deployer might not have considered its eventual full scope) - it seems to me that the "issue" and "issuewild" tags were framed with TLS certificates in mind[*],
and I think extending "issue" to cover S/MIME could have effects on domain owners which were not expected. In other words, we would be saying to them that all certificates are hereby covered, without them having any means of expressing the policy "I want CA
X to issue TLS certificates, but any CA could issue S/MIME certificates"; so I'm less of a fan of reducing the expressive potential of domain owners.</p>
<p>To that extent, I think that I'd prefer tags like "issue-tls", "issue-tls-wildcard", "issue-email", and so on, with similar semantics which work over "issue" and "issuewild" right now. Once those are in effect, then you could extend the "issue" tag to mean
"all certificates" as a shorthand, while leaving finer detailed policy expressions. However, that goes further than anything the S/MIME WG could reasonably pronounce upon. But "issue-email" to cover S/MIME certs falls within its charter and seems to have a
clearer scope. There's even an opportunity to allow domain owners to specify the validation methods permissible for issuance, but that's a whole different discussion.</p>
<p>Just my opinion, of course.</p>
<p>Neil</p>
<p>[*] Genuine question: would "issuewild" have any meaning outside of TLS certificates?</p>
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