Fundamentally this DANE idea swaps out the problems of a PKI CA hierarchy, the kind your browser is using when you actually log into gmail to read and send your e-mail, with the problems of DNSSEC.
The biggest problems with PKI are that there are too many CAs, who can each go rogue, and that X509 is a horrifically awful format that takes a gigantic TCB to parse. Mitigations include browsers firing CAs and severely impacting their business (so effectively, there is regulation), certificate transparency and more and more testing. Either way you pretty much have to deal with these problems today though, an awful lot of e-mail is sent/received over HTTPS.
The biggest problems with DNSSEC are that DNSSEC doesn't actually protect DNS queries at their most vulnerable points, that you have to trust your TLD provider, and the root operators completely, with no effective means to fire them, and finally that they almost certainly are using embarrassingly stupid crypto that even most ICOs could avoid. This very deck has several 1024-bit RSA keys, right there on a slide with a February 2018 timestamp, as if it's not an incredibly obviously stupid thing to do since the LogJam paper was published, or you know, when everyone stopped using them for TLS years ago.
Actually wait, there's even a 512-bit key on another slide, using alg-5. That's RSA + SHA1!! What's the point of using all of those SHA256 MACs at the TLS Layer if everything depends on utterly breakable RSA plus SHA1 anyway? It's hard to take this seriously.
PS. Yes, this is also my best impression of tptacek
> This instance type has two Intel Xeon E5-2666 v3
processor chips, with 36 vCPUs in a NUMA configuration with 60 GB of RAM
A team built a configuration that could factor a 512-bit RSA in four hours for $75. That was August 2015, so it would clearly cost much less and proceed much more quickly today. As a plus, they call out DNSSEC explicitly in their paper:
Nitpick: I believe you meant to say TLS rather than HTTPS.
The majority of sending indeed takes place over TLS, at least between top-tier senders and ISPs. Google's Safer Email Transparency Report shows how many inbound and outbound connections to/from Gmail are protected by TLS, and the numbers have been climbing steadily in recent years:
Those are problems with XPKI, not with PKI in general. SPKI (RFCs 2692 & 2693) fixed them both — it really should have been picked up. It could be used to ensure that you really are talking to someone authorised to use a particular IP address and host name; it also uses a much lighter format than X.509's ASN.1 (and it's human-readable to boot!).
I encourage anyone building a modern protocol to take a look at SPKI. Some parts of it need to be modernised, but that's easily-enough done.
I'm not so worried about DNSSEC needing to trust TLD & root servers, because with domain-verified certs that's all you get anyway. I contend that domain verification (and IP verification, which to my knowledge no-one does) is good enough for most of what most of us need or want, and the customised SPKI certs could be used for the edge cases.
Beyond that, if I take the insanely bad track record of CAs as a group, and compare to the (as far as I know) complete lack of serious attacks on DNSSEC (including even those with 1024 bit keys), then I would put my money on DNSSEC+DANE.
For DANE you need to do client side validation. But that has been known for quite a while now. And there is code (for example getdns) to do that.
For e-mail there is the additional complexity that DANE seems to be the only way to transition to SMTP over TLS without downgrade attacks.
As for SMTP: the IETF is pursuing STS, which breaks that downgrade attack the same way HSTS does for the web (except far more powerfully, since the most important MTA relationships are far more stable than the web's), with an explicit design goal of not relying on DANE --- which nobody uses.
If you like the security of HSTS, then I guess STS is for you. Personally I'd like something better then just blindly trusting the network the first time you try to connect to something.
It's not a bad idea where the trust model is a little more complex than two parties exchanging keys on a regular schedule. Public implementation leaves a little to be desired, but that doesn't mean the protocol is ill designed.
Unless your real argument is that no one has ever used that in production, anywhere, that should be plenty by way of example.
So, no, you have not actually established that anyone would be endangered were the root KSK private bits published on Pastebin. I suspect, in all seriousness, that the answer to my question is "in reality, nobody would be endangered".
Furthermore, the browsers replace the TLD in who you trust with CAs and in many cases it's practically difficult (or impossible) to "fire" your browser.
I will agree that no one seems to use good crypto with DNSSEC though. The only people I know using it are using 512 bit RSA which is pretty horrifying.
And even a 512-bit RSA key is slightly better than nothing. One needs to remember that DANE in SMTP is a mechanism for downgrade-resistant transition from unauthenticated opportunistic STARTTLS to authenticated required STARTTLS.
Below is the frequency table for RSA key lengths in zone signing keys (primarily 1024-bit RSA keys):
count | bits
8402 | 4096
1135 | 3168
17 | 2432
103 | 2304
20 | 2088
5 | 2064
55927 | 2048
15 | 2024
315 | 1536
17 | 1352
43 | 1304
185095 | 1280
63 | 1152
74 | 1048
291 | 1032
4019966 | 1024
28 | 768
12545 | 512
39715 | 4096
11 | 3248
1149 | 3168
47 | 3072
267 | 2560
25 | 2304
20 | 2088
3051386 | 2048
17 | 1552
180111 | 1536
171 | 1304
1568 | 1280
34 | 1152
1118500 | 1024
11806 | 512
You can reconfigure your trust store, and you can distrust a CA in a few clicks.
Comodo is still around, and Symantec took years to be gradually distrusted. Hell, even the WoSign/StartSSL debacle started in Jan 2015, and they weren't removed before Jan 2017.
An attack against the global public DNSSEC would be much harder to mount undetected, as it is logged and cached by nature of its design.
It's not one of my best arguments against DNSSEC, but it is a valid one: the fact that the people designing and advocating for it don't appear to understand the Internet threat model.
DNSSEC did make one important design decision: Signing is offline. That alone makes the threat model different than with TLS, and makes for some interesting use cases.
I don't know how pure offline signing would have made anything better for DNSSEC (I think it makes a lot of things about it worse), but let's at least be clear that the offline signing design failed.
You didn't really address what I said. My argument, which I think is pretty straightforward, is that it is not in fact harder to carry out pinpoint attacks on DNSSEC than it is to do so on TLS. In fact: it's easier; in many ways, modern browsers act as hundreds of millions of sensors in a distributed CA surveillance system, one that has gotten multiple CAs killed. No DNS software works that way.
Are we talking about the public CA system or TLS in general? The former should be fairly obvious that it is useless in the hards of end users, as Google even had to hard code policy for their own services in their client. The latter argument would depend on what type of attack we're discussing. A wide public attack where you have "hundreds of millions" of clients affected would be impractical to keep undetected in any system. Manipulating a single connection with stolen keys is likely to stay undetected in any case, but where having the information cached at least is a possibility.
Somehow, you claimed, DNSSEC's offline signing design had something to do with how hard it was to conduct pinpoint attacks against DNSSEC.
No, that's not true.
But also: DNSSEC isn't an offline-signing system anymore: the BCP mode of deployment requires online signing; otherwise, dumping all the hosts in a zone is about as hard as cracking a 1990s password file.
You've seen zones where not even that level of protection is employed. Ok? What does that have to do with whether it's easy to launch pinpoint attacks against DNSSEC?
Oh, but pinpoint attacks are possible against TLS. Yes? And? The premise of this subthread is your (false) claim that it's not straightforward to do that against DNSSEC too.
Again: not only is it straightforward to do that, but it's actually easier, because, once again, no end-user DNS resolver also functions as security telemetry surveilling the DNS PKI, unlike the Web PKI where that is in fact the case.
I pointed out that the design for offline signing makes for interesting use cases. You now claim that every real world deployment is online signed, which is not my experience. At least you acknowledge real world deployments.
That has nothing to do with the complexity of pinpointing a connection to break, and nowhere did I make the claim that any attacks are straightforward. I did make the point that it is not easier and that it may very well be more complex. Pinpointing a TLS stream and inserting a false certificate is trivial if you posess a valid CA key, pinpointing the DNS query corresponding to a specific TLS stream is an added complexity (especially where multiple resolvers can be involved, where you also run the risk of being stuck in a cache).
I'm not sure what kind of TLS stack ever delivered telemetry on valid signatures post facto, unless you refer to web browsers on the public Internet which is a different question entirely.
1) Anyone can submit a certificate to the CT logs
2) It will become mandatory that certificates are logged for Chrome to trust them in a matter of weeks (other browsers will follow): https://groups.google.com/a/chromium.org/forum/#!msg/ct-poli...
Nit: Not when the browser developer and CA are part of one entity. Excepting some major change to corporate structure, there are presumably no or very nearly no circumstances under which Chrome will permanently remove the Google CAs. Their behavior is therefore essentially unregulated WRT Chrome users.
That would make it useless if true. Are you talking about trusting an external resolver? I haven't seen any real world deployments like that.
> you have to trust your TLD provider, and the root operators completely
You already have to trust them. They are the authoritative source of who owns a domain. In a perfect world, they could assert that ownership cryptographically.
The bit about weak crypto deployments however are completely correct. That needs to be fixed. Improving the situation takes time, and there are aligned economic and national interests in maintaining the global CA model with its numerous trust points.
Correct. Clients do not validate DNSSEC and clients cannot be made to do so until DNSSEC deployment is universal (at which point you still have several other problems).
Strange if something I've been using for a couple of years cannot exist.
* DV certificate issuance is based on a leap of faith (TOFU) by the CA. It is vulnerable to BGP hijack, DNS cache poisoning, ... as amply illustrated by the "domain control" "proofs" in ACME.
* The CA ecosystem is dying with Let's Encrypt's free certs removing the raison d'etre for most of the other CAs. Actual verification of identity does not scale, and DV "domain control" "verification" does not pay.
* The use of SHA1 in DNSSEC is not subject to collision attacks, only 2nd pre-image resistance is required, and there's no hint of SHA1 (or even MD5!) 2nd pre-images any time soon. While moving to SHA256 makes sense, there's no real problem with SHA1 in DNSSEC, it is adequately secure.
* The domains using 512-bit keys are a tiny minority hosted by a couple of DNS hosting providers (one of them "free", so you get what you pay for).
* Most zones have 2048-bit KSKs, and 1024-bit ZSKs. This can be addressed as more domains deploy ECDSA or 1280-bit and 1536-bit RSA keys (which have an estimated work-factor of 89 and 96 bits respectively, and there is ). The root zone keys are 2048 bits for both KSK and ZSK, and 1 in 3 TLDs has 1280-bit ZSKs, more will do that or switch to EC.
* Logjam researchers estimated the cost for a single widely used DH key (embedded as a constant in software): "The researchers calculated the cost of creating logjam precomputation for one 1024-bit prime at hundreds of millions of USD". This is somewhat specific to DH rather than RSA, and leverages the fact that many users used the same fixed DH groups. ZSKs are not fixed and vary across providers.
* Many estimates of RSA factoring cost ignore memory costs, for a more realistic analysis, see https://pdfs.semanticscholar.org/5f56/b7e3d8423cffa724d8037e...
Finally: the talk is about improving on unauthenticated opportunistic TLS in SMTP. The right comparison is with downgrades to cleartext, not with the latest fashionable crypto in browsers. The browsers moving from 1024-bit RSA directly to 2048-bit RSA is a bit of power-of-two numerology and was overkill (better optics more than better engineering). They did it because signing and verification are still adequately fast, so they can get away with turning it up to 11. That does not mean that more modest key sizes are not effective. Since DNSSEC is used only to authentication, not key agreement, there's no risk from future key compromise once a key is retired, so keys don't need to remain secure for decades, just a few months (for a ZSK) is enough.
Generally, real-world attacks bypass the crypto and attack far weaker defenses. Why break the crypto when you can subpoena the private key material, install malware on the end-systems, break TOFU certificate issuance...
Smug attacks on DNSSEC ignore many deficiencies of the alternatives, and are I suggest a case of letting the perfect be the enemy of the good.
DNSSEC is all-or-nothing. You can publish Ed25519 records (in theory), but for anyone to talk to you, you'll have to publish equivalent RSA records --- more importantly, every parent zone also needs to publish secure records, or else your Ed25519 records are just theater. TLDs still have RSA-1024 keys!
DNSSEC advocates really want DNSSEC's security to asymptotically approach that of TLS, but in fact DNSSEC is far worse.
You can get a ed25519 certificate for your web server today too, but hardly anyone would be able to communicate securely with you. Until deployment reaches critical mass you are in need of a fallback. Sunsetting protocols are even harder, so there's complete equivalency there. The use of TLS is just orders of magnitude more deployed than DNSSEC.
There's also no need to suggest I am an advocate of something when stating basic facts about it. Real world systems are dependent on DNSSEC today, and nothing you or I believe will change that. I will not discuss specifics, but I am sure you recognize its use within well known public protocols such as SMTP and SSH.
ECDSA P-256 and P-384 are widely deployed. New algorithms will take some time to be widely supported by peer resolvers, just as TLS 1.3 will take time to be widely supported by web sites (browsers are more agile, but many websites still don't do forward-secrecy with TLS 1.2).
Algorithm agility is a thorny problem.
Algorithm agility is hard, but it's much harder in DNSSEC than it is in TLS.
It is sufficient to note that every PKI is as secure as its weakest link. If my CA is 512 bit RSA, that is the security I am going to get.
That public DNSSEC infrastructure is neglected in places is not really controversial or what we're discussing here, but the use of a singular trust root in place of hundreds should not be taken as evidence of incompetence from the protocol designer.