I've been digging into DNS and TLS lately. Given the way ACME works (essentially using DNS to verify you own a domain before giving you a cert), what's the reason you can't just put your public key in a DNS record? I'm assuming it has something to do with security issues at the DNS level, but don't really know.
DANE assumes that DNSSEC is in place, so that the DNS records are authenticated. This allows the DNS records to be used to deliver TLS trust information in a way that is still ultimately rooted in a certificate authority (whoever operates DNSSEC for the TLD).
Adoption has been limited, mostly because adoption of DNSSEC itself has been limited, arguably because DNSSEC is overcomplicated and high-maintenance, but also just due to a lack of motivation. Similarly, users couldn't care less about how TLS trust is delivered and DANE has never really gotten a big corporate champion to push for it, so there just hasn't been the drive. Industry seems to have chosen DNS-over-HTTPS as the long-term solution to many of DNS's problems, and it clashes somewhat with DANE - I'm sure you could make them work together but it would definitely become awkward
However, even with DNSSEC, bob could obtain domain.tld's keys and then use them to MITM alice's DNS requests, getting her browser to show a malicious site for domain.tld complete with a trusted certificate. Furthermore, bob can do this for alice and only alice, decreasing the odds of detection by a large margin.
With LE you gain:
- Targeted attacks harder to pull off, since you would need to successfully attack the LE servers/networks first and then your actual target.
- LE participates in the certificate transparency initiative, meaning every time a certificated is emitted for a domain it gets recorded.
These things are particularly relevant when you consider that in most cases the DNS is either directly or indirectly controlled by state actors at their root. With DNS-only, they could pull off such targeted attacks without anybody noticing. With LE, they can still pull off these attacks, but there would be a papertrail when that happened.
- active (injecting/tampering with content), which is what DNSSEC protects against.
- passive (eavesdropping), which is what DNS over TLS protects against.
Am I missing something?
DNS over HTTPS, DNS over TLS and DNSCurve are intended to protect against this type of interception/tampering and should be used along side DNSSEC.
For a MITM attack to work in this scenario, the attacker would have to first get fake keys for the root domain (that normally come with the OS) into your computer, at which point not even DNS over anything would work because they should be able to install TLS certs too.
As far as I know, all these DNS-over-TLS flavors' advantage is that they prevent eavesdropping, not spoofed traffic (because DNSSEC can do that too as per my explanation above).
It's not an academic concern, because the two most common modes of deployment for DNS are "with ISP DNS servers", in which case one of your most important and active DNS adversaries is on-path, and "with services like 8.8.8.8", in which case the whole Internet is between you and the thing that validated DNSSEC for you.
It's not a good system, and it's true that DoH does a better job at addressing this problem.
But without DNSSEC a middlebox still gets to tamper anyway, since there's no authenticity of the answers you receive, you're just moving your trustworthy source of these potentially bogus answers for whatever that's worth.
Thomas believes your ISP is "one of your most important and active DNS adversaries" and yet astonishingly he trusts them to provide you with authentic DNS answers.
If you do local validation, which you're free to, DNSSEC solves the problem.
If you do remote validation but you trust the remote DNS server to do that on your behalf correctly, DNSSEC solves the problem and then any DPRIVE protocol brings those correct answers home intact.
If you believe there are certainly authentic answers where Google is (I have a lot of used iron available, central Paris area, it's in the form of a big tower so you can't miss it, buyer collects) then just DPRIVE lets you get their authentic answers. Notice that Google does not warrant that this is true, and "where Google is" might mean a data centre controlled by your country's censors.
Same way upgrading from HTTP to HTTPS doesn't prevent you getting misinformation from Conservapedia. The answers on the site are bad, so ensuring nobody "tampers" with those bad answers doesn't really help you.
DPRIVE is good stuff, and one of the things that great about it is that it unsticks the deployability problem for DNSSEC client validation, but I'm guessing that's not the part you're keen on.
As to "not using ISP DNS servers in the first place" I guess you do not consider Comcast to be an ISP?
Or perhaps you didn't hear. Both Chrome and Firefox will automatically give Comcast's customers Comcast DNS over HTTPS. Mozilla secured a TRR agreement from Comcast in exchange, and presumably Google feels that this agreement plus any undisclosed paperwork from Comcast that they were shown as part of their onboarding process is enough to likewise trust it automatically in Chrome. We expect to see more ISPs doing this over the next few years. If you cannot beat them, join them, eh?
There's a working group that hopes to own everything on the Internet, but DoH happened outside that process, and was deployed (thankfully) over the objections of people involved in the group.
There's actually a pretty big contingent on HN that wanted this, they see the alternatives as either my DNS query goes to the ISP I've already chosen and contracted with, or to Google/ Cloudflare/ OpenDNS who I maybe don't like and don't deal with otherwise - and they'd prefer the former.
The "point" of DoH is actually that it sidesteps ossification. One of the big differences from Mozilla's user privacy focused TRR is that Google's programme cuts to the chase immediately. Your DoH service must work for well formed queries you don't understand, in particular HTTPSSRV. Why? Because the "point" is to get to a world where we can actually use technologies like QUIC and ECH and we can't deploy those technologies at scale in a world where your 1990s ad-tech DNS server responds to anything other than an A query with confused silence.
One of the things DoH allowed them to throw in is a way to express "I won't tell you the answer because censorship" as distinct from just giving bogus answers. Again Google's programme is specific that it's fine to censor stuff, but Comcast are obliged to use this mechanism so that Chrome can tell users "No, you aren't allowed to look at Porn Hub" rather than "Huh, Porn Hub doesn't exist". And again, even though I'd guess you're like me and don't want censorship lots of people do so defeating censorship is not "the point" either.
[Edited to fix quote]
Edit: I should clarify, I think the issue stems from DNS being a potential attack vector itself. You can't blindly trust what DNS tells you. This is precisely the problem that certificate chains (issued by a trusted third party) purport to resolve-- one of trust.
Then there is Certificate Transparency logs. It will be passive action at this point, but it's an action regardless.
Let's Encrypt checks DNS validation and DNS CAA from multiple PoPs, but I don't think it's enforced by CA/B requirements to do so (happy to be corrected).