<div><div dir="auto">This is a really good point Aaron. Thank you. </div><div dir="auto"><br></div><div dir="auto">I also wanted to ask in general, why does WHOIS based validation not fall under the same rules as a delegated third party for domain validation?</div></div><div><div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Sep 23, 2024 at 18:03 Aaron Gable via Servercert-wg <<a href="mailto:servercert-wg@cabforum.org" target="_blank">servercert-wg@cabforum.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)"><div dir="ltr">While I agree with Andrew's points about how the ACME validation methods can be MITM'd, I disagree with the conclusion that this makes them equivalent to WHOIS-based methods.<div><br></div><div>When an adversary MITMs one of the ACME validation methods, they are taking control of the domain in question. By manipulating the structure of the internet (usually via BGP hijacking) they are exerting control over the content seen at that domain name by a whole section of the internet -- a section that just so happens to include the CA performing validation. However briefly, they did in fact demonstrate control over that domain.</div><div><br></div><div>When an adversary MITMs a CA's WHOIS query, the domain being validated remains untouched. The adversary has not shown any control over the domain in question, only over the CA, or over a largely-unrelated third party.</div><div><br></div><div>This is the fundamental weakness of all secret-token based methods. All that is required is that the adversary take control of <i>something other than the domain in question</i> so that they can get the secret delivered to them. If I had my personal druthers, I would limit domain control validation to only methods where the token being public knowledge is not considered a weakness of the validation protocol.</div></div><div dir="ltr"><div><br></div><div>Aaron</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Sep 20, 2024 at 10:47 AM Dimitris Zacharopoulos (HARICA) via Servercert-wg <<a href="mailto:servercert-wg@cabforum.org" target="_blank">servercert-wg@cabforum.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)"><u></u>
<div>
Hi Mike,<br>
<br>
<div>On 19/9/2024 5:22 μ.μ., Mike Shaver via
Servercert-wg wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Hi Dimitris,</div>
<div><br>
</div>
<div>I've been thinking about your email all night, and I want
to figure out where our reasoning about the integrity of DCV
via WHOIS-1932 or HTTP-nonce (3.2.2.5.1) diverge. I was quite
surprised by your statements about the properties of internet
security, the responsibility of TLS and SCWG, and the
limitations that should be accepted in performing DCV. I'm
hoping that your new responsibilities as Chair
(congratulations!) will still leave you a bit of time to point
out where my reasoning doesn't connect. :)<br>
</div>
</div>
</blockquote>
<br>
Thank you for that :) New officers will start their duties on
2024-12-01 but I believe Member's contributions to the Forum are a
lot more important when we're having these discussions, working on
ballots and continuously improving the standards! Officers mainly
have to do the "administrative" work and make sure the WG Charter
and Bylaws are followed. <br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div><br>
</div>
<div>Because I'm not sure where we diverge, I'm going to walk
through my understanding of the principles underlying the DCV
methods used historically by CA/BF (and CAs in the dark days
of private deals with individual browsers), and the direction
towards which the SCWG and root programs seem to be headed in
terms of those principles. Please, *please* do not take this
as me implying that you don't know these things: I'm not
trying to lecture, but to be as explicit as reasonable in
explaining my thinking, so that it's easiest for yourself or
others to help me correct error in it. I would be quite
grateful for such generosity, honestly! I also apologize in
advance for the length of this message. I lack the wisdom to
make it smaller, perhaps.<br>
</div>
<div><br>
</div>
<div>(Some of this is entangled with "what is this even for?"
sorts of discussion about who the web PKI should ultimately
benefit, but I've tried to keep that separate.)<br>
</div>
<div><br>
</div>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, Sep 18, 2024 at
12:18 PM Dimitris Zacharopoulos (HARICA) <<a href="mailto:dzacharo@harica.gr" target="_blank">dzacharo@harica.gr</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
<div>We don't need Domain Name Registrars to go through
WebTrust or ETSI audits suitable for Trust Service
Providers. These Registrars are the source of truth for
the DNS on which all Internet connections, and the WebPKI
relies on. It's so fundamental to the ecosystem that IMO
it doesn't make sense to ask ourselves how this Forum can
make them better. Other authorities should be working on
that.<br>
</div>
</blockquote>
<div><br>
</div>
<div>A recurring theme throughout web PKI operations has been
that a participant in the ecosystem thinks that they are
doing a good job, and perhaps indeed are doing a good job of
some kind, but are not providing the guarantees or
protections that others are assuming are in place. I don't
mean "good job" in the sense of competence or ethics, but
rather "meeting the requirements through actions". The
farther that the participant is from the core of the web PKI
ecosystem, which is to say the less likely they are to
evaluate all their actions by the effects of those actions
on the trustworthiness of web certificates and server
authentication. This means, IMO, that this group and other
stewards of the PKI should be very conservative, and very
explicit, when depending on another participant of the
ecosystem to maintain certain properties. Otherwise, those
dependency-bearing organizations may not even know what is
being expected of them.<br>
</div>
<div><br>
</div>
<div>I am not suggesting that CA/BF in any way place
requirements on what an organization must do in order to be
a domain registrar, and reporter of that registry. As you
say, that is beyond both the scope and the expertise of this
group, and this group has plenty to keep it busy! I am,
rather, suggesting that SCWG should establish criteria
against which it will determine if a registrar's publication
of domain information should be considered to be reliable
enough to accomplish DCV. Similarly, the group does not put
any requirements forcing public DNS servers to strictly
check DNSSEC, but if a CA is going to use a DNS server for
checking CAA records or doing 3.2.2.4.7 "DNS Change"
validation, then that's only acceptable if the DNS server
enforces DNSSEC in the presence of a validation chain. (I
think that might only be in Bugzilla and not yet captured in
the BRs, but it's well-enough understood that failure to
adhere to it has required reissuance.)<br>
</div>
</div>
</div>
</blockquote>
<br>
I see your point. In general, as you say, it is difficult for a
group like the CA/B Forum to enforce rules and expectations placed
upon another industry group (Domain Name Registrars/TLD Operators)
if those other industry groups do not participate or don't even have
knowledge about those expectations. I would be very concerned if the
SCWG or the Forum at large, would create a set of "expectations from
a Registrar/TLD Operator to be considered good-enough for the WebPKI
to rely upon". I think this group would be heavily criticized for
doing that.<br>
<br>
If we believe this area is so security-critical for the WebPKI, the
best think we could do is to have members of this Forum engage with
IANA or other ccTLD-coordinating venues to promote ideas for
improved security, external monitoring and transparency. It feels
similar to what Members of this Forum have done in the past when we
bring up ideas for improving the security of our ecosystem, and
bring those ideas to IETF (LAMPS WG or other similar venues) to
standardize.<br>
<br>
I'm not opposed to adding requirements that prohibit the use of
external information in egregious failure cases, but it's not easy
to find the right language in a standard for this.<br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div><br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
<div> If a ".cookoo" TLD operator is not functioning
properly, then the entire TLD is in jeopardy and every
Domain owner under that TLD is at risk. Certificates are
the least of people's problems when relying parties
connect to websites operated under that unsafe TLD
operator.<br>
</div>
</blockquote>
<div><br>
</div>
<div>As above, this depends very much on exactly what form
"not functioning properly" takes. If their systems are
broken such that it's impossible to make changes to
registrations, or to look up registrations, I think we would
all agree that the TLD operator is not functioning properly,
but that would not have as much risk to the integrity of the
web PKI as those systems being broken such that *anyone* can
change any TLD.</div>
<div><br>
</div>
<div>For CAs to rely on email address information from
registrars for issuance of certificates, I think it's only
appropriate that they ensure that the information is "fit
for purpose" and that it's managed (and accessed) in a way
consistent with the level of trust placed in it.</div>
<div><br>
</div>
<div>This means making sure that the integrity of the response
is maintained, which is a role that WHOIS-3912 simply cannot
perform.<br>
</div>
<div> <br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
No, the SCWG and TLS is not here to solve the unencrypted
nature of the DNS protocol. IETF and DNSSEC is. There is a
great number of Domain Names in the DNS without DNSSEC,
and there is still heavy reliance on the unencrypted DNS
protocol in almost EVERY Domain Validation under 3.2.2.4.<br>
</blockquote>
<div><br>
</div>
<div>DNS being unencrypted is not a problem, and indeed even
DNSSEC doesn't encrypt traffic. DNS results being
*unauthenticated* is a problem for clients who wish to be
certain that they have been given an authorized address in
response to their lookup, but even with DNSSEC that leaves
the issue of ensuring that the unauthenticated IP layer
reached the "real" home of that address (thus DANE).<br>
</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
Even the Agreed-upon change to website method, 3.2.2.4.18,
relies on "Authorized Ports that are offered via
non-encrypted channels (ports 80, 25, 22).<br>
</blockquote>
<div><br>
</div>
<div>Again, encryption during validation is not necessary
for there to be a reliable chain of trust from the browser
to the site certificate, via CA-operated root
certificates. We need authentication, but only
authentication, of every step of the delegation of trust.<br>
</div>
<div> </div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
I would go as far as to say that even the ACME methods
connecting to https URLs are untrusted, because the
endpoints are not protected by publicly trusted
certificates and anyone could launch a MiTM attack.</blockquote>
</div>
<div><br>
</div>
<div> This is a part that really got stuck in my head. Are you
saying that ALPN-1 is vulnerable to a MITM attack during
validation? That would be a pretty shocking situation, in my
opinion!</div>
<div><br>
</div>
<div>How would the attacker get access to the key material
needed to complete the challenge? It never leaves the
subscriber machine from what I can tell. Similarly, the ACME
account key is used in HTTP-01 to render MITM attacks
ineffective.<br>
</div>
<div><br>
</div>
<div>This is how the trust in that connection is bootstrapped
based on the trust in the connection between subscriber and
CA when the certificate is requested. Presumably
publicly-trusted certificates are used when the subscriber
connects to the CA's server to make that request and obtain
the account key!<br>
</div>
<div><br>
</div>
<div>This transitivity of trust goes to the issue with WHOIS.
Even if the registrar is maximally diligent in their key
ceremonies and internal processes and generating
certificates correctly, WHOIS-3912 puts a *maximum*
trustworthiness on the entire operation, which is that of
unauthenticated TCP. In my opinion, that is not appropriate
for web PKI, and is a relic of a time before this community
took technical registration-time attacks as seriously as we
do now.<br>
</div>
</div>
</div>
</blockquote>
<br>
I consider Andrew's <a href="https://lists.cabforum.org/pipermail/servercert-wg/2024-September/004883.html" target="_blank">response</a>
a lot clearer than mine. I believe it answers your questions and how
to MiTM the ACME TLS-ALPN-01 challenge.<br>
<br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div><br>
</div>
<div>
<blockquote> In order for the SCWG measures to be
proportionate, we should not blame the entire WHOIS
protocol but work on additional controls to minimize the
risk of CAs using those problematic WHOIS libraries.<br>
<br>
</blockquote>
Could you describe how a non-problematic WHOIS-3912 library
could provide assurance of the validity of the data
returned, equivalent to the integrity of the results from
HTTP-01/DNS-01/ALPN-01?<br>
</div>
</div>
</div>
</blockquote>
<br>
Assuming no MiTM, it's no different than any of those methods. The
CA "trusts" that the information is coming from an authoritative
source or from a source that demonstrated control of the
Authorization Domain Name. In the HTTP-01 case, it retrieves a
random value or request token from a designated URL that contains
the FQDN to-be-included in the Certificate. In the WHOIS case, it
retrieves the email address of a tech or admin contact associated
with the registration of that Base Domain Name.<br>
<br>
The .mobi issue, in my understanding, is that some CAs were (still
are?) using WHOIS libraries that were not looking for the currently
authoritative Registrar of that TLD. If the SCWG could identify
those insecure libraries, or if criteria were added to use libraries
that check for the most recent authoritative source for each Base
Domain Name Registrar, it would be a good emergency mitigation.<br>
<br>
We had a similar discussion when discussing the linting tools. At
some point we need to add rules for continuous updates, taking into
account proper testing and change management procedures.<br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
<div> Instead, we could focus on requiring
immediate/emergency measures for CAs to use the
WHOIS protocol securely</div>
</blockquote>
<div><br>
</div>
</div>
</div>
</blockquote>
<div dir="ltr">
<div class="gmail_quote">
<div>This is definitely one place that our reasoning
diverges: I don't see a way to use WHOIS-3912
securely, where by "securely" I mean "in such a way as
to not weaken the DCV guarantees that the web PKI
wishes to make".<br>
</div>
</div>
</div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div> </div>
I disagree. We are trying to move from "http" to a
"trustworthy https" (note: "trustworthy https" in the
sense that it doesn't use untrusted certificates). At
some point, CAs need to rely on unencrypted
communication to achieve that.</div>
<div class="gmail_quote"><br>
</div>
</div>
</blockquote>
<div dir="ltr">
<div class="gmail_quote">Why do CAs need to rely on
unauthenticated communication to achieve that? If we
were establishing the very first root, someone would
have to carry the key physically to the browser
developer as a form of IRL authentication, but we have
sufficient systems in place now to inductively create a
completely authenticated chain of validation if we
should want to.</div>
<div class="gmail_quote"><br>
</div>
<div class="gmail_quote">Where is that chain impossible to
authenticate, in your opinion?<br>
</div>
</div>
</div>
</div>
</div>
</blockquote>
<br>
Andrew's answer covers this very clearly IMO. This is just how it
works. There is no single source of truth or "one key to rule them
all" that everyone trusts. The closest we have is the DNS.<br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div><br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">
I'm confused by this statement. Is this a plea to the CAs
to stop using what you think is an insecure method?</blockquote>
</div>
<div><br>
</div>
<div>Yes, it is exactly that. I don't know how anyone can
seriously claim that WHOIS-3912 is a secure method,
regardless of how high quality the data on the other side
is.<br>
</div>
</div>
</div>
</blockquote>
<br>
Then the second sentence of my snipped quoted statement applies:<br>
<br>
"Everyone is entitled to an opinion but that's why we are having
these discussions publicly so that the SCWG members can find
"substantial consensus" as mandated in the Bylaws. I'm sure some CAs
are already working, or have already stopped using WHOIS,
proactively, until this discussion comes to an end."<br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-style:solid;padding-left:1ex;border-left-color:rgb(204,204,204)">Domain
Registries for validation of domain contacts: domain
registry information should, IMO, only be used at
*all*, independent of protocol, if the SCWG can be
confident that IANA or another trusted body will be
able to ensure that all those registries, for all
domains present and future, will meet the SCWG's
requirements for reliability.<br>
</blockquote>
</div>
</div>
</blockquote>
<blockquote> This is like saying that the Registrars, the
main stewards assigned to run the DNS which is fundamental
for how the Internet works and practically the World Wide
Web, need to meet the SCWG requirements for reliability.</blockquote>
</div>
<div><br>
</div>
<div>As above, domain registrars do not need to meet any SCWG
requirements. CAs need to meet the SCWG requirements, and I
think that those requirements should include minimum
properties that must hold of a registrar's data management
practices, and the means of accessing it, if such data is to
be used as authoritative proof of domain control.<br>
</div>
<div><br>
</div>
<div>An example: do registrars inform registrants that anyone
who can receive email at the listed contact address can be
issued a certificate for their domain? I think that the
significance of that address as used for DCV is not
well-understood by most registrants, and that many will send
that email to ticket/CS lists composed of people who are
*not* authorized to make changes to DNS, and are not assumed
to have the same authority for requesting certificates.
Similarly, I don't think that registrants understand that
someone popping a domain-privacy provider not only gets
their email and contact information, but could plausibly
also silently have certificates issued against their domain.</div>
<div><br>
</div>
<div>If these participants in the ecosystem (registrar and
registrants) don't regard the email contact field as having
such immense security significance, then it is unlikely that
they will manage it with appropriate care. Given that, as
you correctly point out, the SCWG is in no position to put
requirements on registrars or registrants, all that we can
do is say that CAs must not use registrar data unless it is
managed to an appropriate standard, and accessed in an
appropriate way. That is *well* within the mandate of the
SCWG, and consistent with all of its other activities in
defining validation standards.<br>
</div>
</div>
</div>
</blockquote>
<br>
This is a very tough sell because there is no stop to this line of
arguments. Should CAs also monitor the behavior of Internet Service
Providers responsible of the Internet connectivity? Should they
monitor Telecommunication Providers for how they run the SMS GSM
networks used by CAs to contact Applicants? Should they monitor the
Postal Services when sending letters to Applicants?<br>
<br>
The publicly-trusted ecosystem (WebPKI in the SCWG) needs to rely on
some fundamental services offered by entities outside the scope of
the CA/Browser Forum, that are governed by their own policies and
practices. The CABF cannot police or directly intervene with these
fundamental services at a global level.<br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div> </div>
<div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div> </div>
I believe the WHOIS deprecation could follow a similar
pattern but for sure the SCWG should urgently focus on
requiring CAs to use WHOIS libraries that query the
proper Registrar endpoints, IF they are using the
WHOIS method to query Domain Contact information</div>
<div class="gmail_quote"><br>
</div>
</div>
</blockquote>
<div dir="ltr">
<div class="gmail_quote">If CAs are going to continue to
use WHOIS-3912, I think that the SCWG should require
that the traffic be carried over an authenticated TLS
channel, or that the response be signed. Anything less
doesn't address the fundamental insecurity of the
*access protocol*, whatever the truth of the data
returned in the request. Do you feel that
unauthenticated requests over the public internet really
have a place in DCV?<br>
</div>
</div>
</div>
</div>
</div>
</blockquote>
<br>
Based on Andrew's and my answers, I hope you can see that this point
just doesn't apply.<br>
<br>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_quote">
<div>
<div dir="ltr">
<div class="gmail_quote"> </div>
<div class="gmail_quote"><br>
</div>
<div class="gmail_quote">Saying that the internet is
fundamentally insecure is like saying that electricity
is fundamentally insecure, to me. The base protocols of
the internet, like IP, don't provide sufficient security
properties given the importance of the modern web. But
just as TCP provides in-order delivery over un-ordered
IP, and TLS provides privacy and integrity over TCP
(which features neither of those, save a trivial attempt
at integrity aimed at signalling errors and not
malicious interception), the web PKI can provide
authentication of domain ownership and connection
validity by layering appropriate protocols (computer and
human) atop the less-capable lower layers. That to me is
the essence of the mandate of the SCWG. We are to TLS
what ICANN is to DNS: ICANN doesn't say that you can't
return arbitrary nonsense in a DNS response from your
server on a private network, but it *does* say that if
you want to operate a DNS server on behalf of a gTLD,
you need to meet certain requirements or ICANN simply
won't point traffic at you. We should "stop pointing
traffic" at certificates that were validated using
WHOIS-3912 DCV, and I wish I'd pushed to do so multiple
decades ago.</div>
</div>
</div>
</div>
</div>
</blockquote>
<br>
Apologies for oversimplifying, but I just want to clarify what I
meant. The Internet was built on some principles. These principles
included anonymity and clear-text communication. Encryption and
authentication came later, but they were built on top of the
anonymous/clear-text layers.<br>
<br>
What does "secure the Internet" mean? There are various answers to
that statement but one answer is "the assurance that communication
between two points (point-to-point) is authenticated and encrypted".
For this you need cryptography but you need to solve the key
distribution problem. One solution is the WebPKI. There are other
solutions (DANE, VPN, etc).<br>
<br>
In order to validate a Domain Name and verify a binding between a
key and a name, a CA must use some parts of the
unauthenticated/unencrypted Internet in order to get assurance that
it is interacting/communicating/contacting the proper and authorized
recipient. I don't think there is a way around that.<br>
<br>
Dimitris.<br>
</div>
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