Tell HN: Domain fronting to be blocked on Azure

Lack of SNI encryption is the Achilles heel of modern web when it comes to oppressive regimes blocking access.

Between encrypted SNI (Or domain name fronting), encrypted DNS and of course HTTPS. The biggest legitimate use case of Tor would vanish.

It will still be possible to correlate IP addresses and hostnames. You can only hope for plausible deniability provided that the site you are visiting share IP address with a bunch of other sites.

While true, I feel this reasoning has been used to delay improving the situation for far too long. There's a big difference between "accessed this CDN IP used by thousands of websites" and "deliberately connected to example.com"

> Between encrypted SNI (Or domain name fronting), encrypted DNS and of course HTTPS. The biggest legitimate use case of Tor would vanish.

Your comment was on point up until this. Just because the Tor use you seemingly most identify with is access from oppressive regimes to the western web, doesn't mean that the rest should be shunned. If you want to make political points about specific other uses of Tor, do it explicitly rather than maligning the whole project.

Is it 'illegitimate' that I read all of my preferred news content and chat on the internet using Tor?

It's not really why I've run a relay for nearly a decade. But it's better than filesharing I suppose.

This seems to be a user-hostile move.

https://en.m.wikipedia.org/wiki/Domain_fronting

”Many large cloud service providers, including Amazon and Google, now actively prohibit domain fronting, which has limited it as a censorship bypass technique. Pressure from censors in Russia and China is thought to have contributed to these prohibitions”

non crappy link:

https://wikipedia.org/wiki/Domain_fronting

Fixed:

"Many large cloud service providers, including Amazon, Microsoft, and Google, actively prohibit domain fronting, which has limited it as a censorship bypass technique."

sure, it was merely a coincedence that they've started doing it after russian minitrue telegram fiasco.

our venerable corporations would never bend to the will of foreign dictators.

Separate of whether the correlation is correct do you or anyone have info on the Telegram minitrue issue? I was unaware and don't really use Telegram.

they've attempted to block it several years ago, likely due to its popularity among dissidents and/or refusal to cooperate with russian Disinformation Governance Board. they've botched it and a lot of unrelated services got blocked as well. they gave up and stopped trying.

They went one step further after that fiasco — it's heavily used these days to spread pro-Kremlin propaganda (definitely automated — very similar messages get posted to thousands of channels pretty much simultaneously⁰). Comment sections on other channels are filled with bots (you can see them a mile away — the nicknames are generated using the same pattern, the names don't feel right if you intimately know how Russian names are supposed to look, and the message style is obvious once you get to know it).

0: https://twitter.com/sobollubov/status/1567152744812740610

Well if they didn't do this the entire Azure would get banned which is even worse.

Banned by whom and why do you think that?

Spanish isps for example. Did you know that in Spain there’s a deal between rightholders and isps to block any domains/IPs they don’t like? See: https://torrentfreak.com/spanish-isps-blocked-869-domains-su...

I’ve personally seen domains on a shared provider banned without notice even though alleged pirate content was taken down within minutes. Very difficult to unban

It is not just used for censorship. When I was working as a pentester and domain fronting was still allowed on AWS, it became our method of choice for establishing C2 because it camouflaged so well with regular organizational outbound that it will bypass any egress filtering and restrictions.

If we were using it on a pentest, you'd best believe there are actors using it for far more nefarious purposes.

It's not possible to block C2 without also helping censorship on the Internet. Whatever mechanism is used to hide one traffic is going to be used by the other one, and reversely.

Morally, the question is which one is the most important?

The question for cloud providers is not which one is morally more important, but which one is better for their shareholders. It seems like creating a situation where organizations move their workloads off your public cloud because they have to blacklist your entire domain to stop an attack would be bad for their shareholders.

Can’t they use almost any read-write service for C2 though?

“Because Security” arguments like this are increasingly used in place of “think of the children”.

How many read-write services can you use to redirect traffic to your C2 infrastructure while almost guaranteeing organizations will allow outbound connections to it and not look too closely at it?

Google Docs/Forms/Sheets/etc, anything with an image proxy, probably Microsoft's Office Online stuff tho I personally haven't used it, webpush connections, the possibilities are endless.

DNS…

Google and now Microsoft are also blocking domain fronting.

The other 'possibilities' are not necessarily guaranteed to be allowed for egress traffic out of an organization. That's why the cloud providers blocking it is a big deal - most orgs WILL allow outbound traffic on more than a few ports to these platforms

Unless corporate firewalls have advanced to the point where they're DNS aware (eg the client queries www.microsoft.com and only then is allowed to contact those IPs), can one not just direct domain-fronting-style traffic to any VPS?

oh well, you could use a document on google suite to implement the communication. I guess google.com is next.

Some of the key people behind ECH (Encrypted Client Hello, work to hide SNI and other potentially sensitive information from the Client Hello in TLS) work for outfits which would be delivering basically the same functionality via ECH, such as Cloud companies and CDNs. Of course it is possible they don't intend to ever deploy this (but then they've wasted months of work which seems strange) or that their employers won't allow it (but then they're wasting some fraction of productive effort by an employee) but it's also possible their explanation is real. Lets see what the difference is between ECH and Domain Fronting:

Consider two clients, Alice and Bob, they are both connecting to some IP 10.20.30.40 using TLS or QUIC.

Alice wants to access naughty.thing.example and Bob wants to access bland.stuff.example. Perhaps Mallory is trying to prevent Alice from accessing naughty.thing.example (but they don't mind bland.stuff.example) or perhaps Alice just doesn't want Eve to know what she's accessing. Mallory and Eve are both on the network, able to interpose between Alice and Bob and 10.20.30.40 and neither Alice nor Bob can easily prevent that.

Under domain fronting, Bob is just honest, he tells the server I want bland.stuff.example, and then he uses bland.stuff.example as usual and everything works. This means for technical operations it's OK if the 10.20.30.40 server cares what Bob said during connection. For example maybe once Bob says bland.stuff.example, the server spins up an IPC to a Python server which only knows about bland.stuff.example and splices Bob's connection to the IPC.

Under domain fronting, Alice's situation is tricky. Alice says she wants bland.stuff.example but she actually uses naughty.thing.example and expects that to work. Technical ops people who've arranged that bland.stuff.example connections get spliced are faced with bug reports - why didn't naughty.thing.example work, 10.20.30.40 was the right server ???

Under ECH, both Alice and Bob are presenting a visible name (which might be bland.stuff.example or some other value entirely) which Mallory and Eve can easily read, but they're also providing an encrypted destination, Alice can encrypt naughty.thing.example while Bob encrypts bland.stuff.example† The 10.20.30.40 server can decrypt the name, and thus it knows which service Alice and Bob actually intend to access.

† If you thought "What about padding? Those names are different lengths" congratulations, you're now at step 1 of a long process which is why this was not trivial to design and implement.

How would this work? How is the name encrypted before the pubkey is known? I've seen that it uses DNS to fetch another pubkey, but there is no encrypted DNS (DNSSEC is signed DNS).

DNS-over-HTTPS is only used in the last-mile --- recursive resolver to client, not NS to NS, so the request is still sent in plain. Besides, DNS-over-HTTPS still requires ... TLS ...

I believe that the new “HTTPS” record in DNS will help with that (and other issues): https://datatracker.ietf.org/doc/draft-ietf-dnsop-svcb-https...

As I understand, the public key that is used for authenticity is not the same as the one being used for encryption — at least since TLS 1.3, before it depends. The scheme is known as forward secrecy. For the encryption, an ephemeral key pair is used on both sides. These pairs are only used for the Diffie-Helman (or similar) key exchange. Therefore an encrypted connection can be established, then SNI can be exchanged over the encrypted connection, and then the remote can provide the signed nonce together with it's PKI public key, with which it establishes trust respective to the SNI.

So the encrypted connection used to exchange SNI isn't authenticated? This hides the SNI from passive eavesdroppers but not from an active MITM, no?

Good point. So there is more to it, which I didn't consider before. As I understand [1], the client uses the public key of the key pair used by the SNI to encrypt the SNI value, additionally to any TLS encryption. Only the actual SNI has the private key to decrypt the SNI value. The client must look up the public key in the DNS (I guess at least if it doesn't know the key already, which it could have in the cache).

This whole thing is still a draft RFC [2] and currently called encrypted client hello.

What I don't get: The client will have to disclose, which public key it used to encrypt the client hello / SNI value. But don't we know "all" the public keys from the certificate transparency logs? Usually a public key is only valid for a limited set of domains, so it would be easy to associate the public key used for encrypting the SNI value with the relevant service. Just look up the public key, read it's SAN or CN, and you pretty much know the SNI value. Or at least the service, which might be good enough. What am I missing?

[1] https://blog.cloudflare.com/encrypted-sni [2] https://www.ietf.org/archive/id/draft-ietf-tls-esni-15.html

> What I don't get: The client will have to disclose, which public key it used to encrypt the client hello / SNI value

Actually, not necessarily, but first...

> But don't we know "all" the public keys from the certificate transparency logs? Usually a public key is only valid for a limited set of domains, so it would be easy to associate the public key used for encrypting the SNI value with the relevant service

The keys used to encrypt ECH are distinct from keys used to prove identity. So, no only are the CT logs irrelevant (they're logs of the identity information which uses separate keys) but also you would usually choose the same keys for all the names hidden behind some particular server.

Suppose I run big.huge.example a hypothetical CDN. We can use the same public key for clown-porn.example, abortion-rights.example, huge-corp.example, government-stuff.example, even though these services may be entirely segmented internally, we're only using that key to keep the names private from everybody else. As big.huge.example we know whether a client uses clown-porn.example or abortion-rights.example, but an on-path adversary doesn't know that and the key used doesn't help them.

Still back to the encryption problem. We don't actually necessarily need to tell people which key was used. So long as the number of possible keys in use is modest they can guess:

Suppose big.huge actually has four keys in use, maybe two sets of customers on different tiers of product, maybe we're switching keys and there's an overlap period of course - we don't need clients to signal necessarily, we can just decrypt with all four keys, incurring a modest 4x decrypt performance penalty and throwing away the 3 which fail in the ordinary case.

How does domain fronting negatively affect microsoft? Why do they care? Is this all just about making peoples lifes worse?

Unfortunately the most common use-case of fronting is phishing and other scams that do make our lives worse. There's a legit anti-censorship angle but it is not the major use-case.

how would domain fronting help with phishing?

your standard user agent (e.g. browser) will not send different values in SNI and HTTP Host header.

this is a deliberate action by the user agent to obscure the actual traffic destination.

this can of course be used both for censorship circumvention but also misleading corporate traffic inspection when TLS is not broken, though it's debatable whether that should work in the first place.

The issue isn't with phishing. The issue is with threat actors using domain fronting as a network masquerading technique when having command and control traffic call back to Cobalt Strike servers. You can use domain fronting look like it's heading back to legitimate sources such as Microsoft, but unless the corporation is doing SSL termination on the endpoints, it's impossible to determine the exact destination.

Azure originally started on this path in 2021: https://www.microsoft.com/en-us/security/blog/2021/03/26/sec...

Working in the pentest/red team field, I've seen various providers ban consulting companies and red teams from using domain fronting -- however, this doesn't stop the threat actors.

Domain fronting leads to collateral damage in terms of blocking. If I really want to block X and X is using domain fronting to blend in with traffic on a given CDN, that CDN is going to get blocked.

CDN customers that are having their stuff blocked because of that are not going to be happy, in general.

The goal is to get people to stop wanting to block X in the first place. Alternatively, make it so they have to block the entire internet along with X.

That's your (and my) goal, not corporate America's or totalitarian regimes', which are both different flavors of authoritarianism.

That doesn’t seem to match up with reality. A lot of legislations don’t care a lot about collateral damage. They just block. And other customers on the shared IP have to deal with it (move to another IP).

I guess that they're afraid for entire Azure to be blocked by Russia or Kazakhstan. They can't afford such losses.

Let's say customer A got a server cert on Azure for bank_example.com and customer B got a cert on Azure for nsfw_example.com

With domain fronting you may get 'nsfw_example.com' content from a TLS connection negotiated with 'bank_example.com'.

This can be a security threat (not able to properly filter outbound traffic) and customer A may be unhappy about Azure allowing nsfw content to be distributed over a channel secured under the name of their bank.

Unfortunately much like every nice thing on the internet, once it is being abused, it gets axed... Domain fronting (having Host header differ to SNI in TLS) is a powerful way a malware author could send payload into organisations.. imagine seeing seemingly legitimate traffic to azure.com but end up with malwaredomain.com/lulz.exe... Unless organisations are peeking into TLS, check Host header, response with MZ file header...There is nothing they can do to stop this.

Security teams should be doing DPI, using a corporate controlled CA to decrypt the traffic and then feed it into a SIEM which should start screaming bloody murder when it detects a mismatch between SNI and the requested host

big corporation with everyone working in a building, 100% achievable but with everyone working from home these days, it's a big challenge to have all users' internet traffic through a single gateway in some sort of VPN is not scalable. Most corp has to support split tunnel to make it work-able...

Lots of IoC base on DNS as well so that is out of the windows since the malicious traffic is inside TLS...:-/

It's more about mismatch between host and SAN. Mismatch between SNI and host is quite common with h2 connection coalescing.

I know alot of people cite "Security Concerns", but I suspect the problem might be simply a technical reason. I personally have been using nginx's ssl_preread module to reverse proxy my connections without SSL termination, domain fronting would break things in my situation. Having the possibility of domain fronting is just too much to consider in your software stack.

Doesn't domain fronting (by definition) not cover all those who reverse proxy (with cache) their S3 bucket and other apps to reduce their egress bills?

The only part of the definition that applies is a subjective part... "for censorship circumvention".

Google removed domain forwarding the day after a certain authoritarian government started blocking their cloud services back in 2018. Amazon removed domain forwarding a couple weeks later.

Much like back in the 1930s, various major corporations are sending a clear signal about how much they value human rights versus making money. Personally, I buy into the whole argument that we can keep capitalism ethical by "voting with our money" and it's up to the people to boycott unethical companies. I seem to be something of a radical though in today's society.

I suddenly understand why Azure has been dragging their feet on implementing TLS v1.3*. They're trying to avoid having to implement encrypted client hello, which would make their CDN products usable again by groups trying to hide information from government censorship and surveillance by mingling it amongst ordinary web pages.

*) Or at least one of the reasons, none of which are good.

For this domain fronting, do you need to control the 'innocuous' domain for this to even work? I can't hide my traffic behind someone else's domain, can I?

The thing about domain fronting, is you have to use a heavyweight corporate entity's domain because for a would-be censor, blocking those domains would be 'overblocking' and their censorship wouldn't really work. It would be like blocking a bunch of Amazon, Cloudflare, Google IPs. The Internet basically would be unusable, so they have to allow these corporate mega-giants in their allowlist.

> will block any HTTP request that exhibits domain fronting behavior.

How does the CDN detect this? The CDN only sees the encrypted domain, correct?

No, CDN is a full MiTM on the traffic.

And it has to be or it’s not a CDN.

This also only really affective with a popular CDN because you’re leveraging the fact that a government won’t want to block an entire CDN. You can just do this yourself because your IP is just your IP and not shared with anyone important.

For anyone else wondering what domain fronting is:

> Domain fronting is a technique for Internet censorship circumvention that uses different domain names in different communication layers of an HTTPS connection to discreetly connect to a different target domain than is discernable to third parties monitoring the requests and connections.

https://en.wikipedia.org/wiki/Domain_fronting

Cool, so we are bowing down further to oppressive regimes now.

That definition is incomplete. Threat actors also abuse this to hide their command and control infrastructure.

Threat actors use knives to stab people - we have to stop selling those.

There's an argument to be made for that. See, the UK.

Sure. Might be hard for people to do certain manual labor jobs without access to sharp objects. I'm sure they'll figure it out.

We'll have to ban rocks next though.

It's pretty hard to stab people with rocks, especially multiple people.

But pretty easy to cause blunt force trauma to the head

Generations of Native Americans beg to differ.

The native-american generations population probably doesn't intersect with the population of teenage knife-wielding attackers in london, which is what we're talking about.

Then again, if you want to argue stone-age semantics: we can't ban anything and should just resort to continuous murder since rule-based society is too hard.

We just need to watch out for teenagers learning flint-knapping.

In the UK if you're under age and you decided to buy a knife you will have a lot of difficulty unless it's a little folding (but non-locking) pocket knife, like the small Swiss Army type utility knives. Indeed legally as old as 17 you can't even buy a steak knife in England although you can in Scotland.

Once you've bought a knife, it will usually be illegal to carry it in public unless you have a good reason, and "self defence" is not a good reason.

Some particular knives, which have no apparent purpose except as weapons, are just illegal automatically except in some cases if you're a museum. In particular almost all swords (if they have a working blade) are in this category, and most things designed as concealed weapons (e.g. blade hidden in an umbrella, combs that are actually knives, push daggers)

I'm not trying to be an asshole, but we don't get much info from UK here besides things like the Queen dying, so I have to ask, Does it work?

I mean, are instances of kids <=17 year olds with knifes down? What about shivs and other things?

The reason I'm asking is because as a kid, if I had been told to not do something, I'd just find a way to do it. Not to use it, but to find loopholes and just say, _so what?, I can do x_

It absolutely does not work. Violence finds a way.

The mind is humanity's most lethal weapon. With the "right" mindset the entire universe can become a weapon. Efforts to reduce violence tend to focus on the presence of concrete weapons (because this is easier to quantify and measure etc) with much less focus on violent ideation and the root causes of the various forms of interpersonal violence.

Reducing violence is a tricky thing because to a large extent it seems to me to be a symptom of broader and nearly intractable societal malaise. Not that it isn't worth removing nuclear weapons from circulation but the returns diminish quicker than most public policy folks seem to want to admit.

Also ever since “driving while black/poor/not liked” became something you couldn’t arrest on they need another excuse.

I don't know enough about when various laws were passed to say whether the introduction of the laws have had an impact. In 2021 the Office for National Statistics published a reasarch breifing on the topic with some top level numbers [1]. I can say I don't walk around expecting people to have a weapon on them, even in some of the higher crime areas of my city (Bristol). But that's just anecdotal and it'll greatly depend on where you live.

[1] https://commonslibrary.parliament.uk/research-briefings/sn04...

Speaking for myself, I own a Buck Hunter knife that I used to carry as a pocket knife. When I learned that it's not street-legal (it's blade locks, and is 1/2" too long) I stopped carrying it. So that's one anecdatum. I'm not particularly unusual; I imagine many people that once carried a locking pocket knife no longer do.

There was a spate of stabbing reports, about a decade ago. That seems to have died down. My guess (and it's only a guess) is that only drug dealers and people bent on mayhem carry guns or knives that aren't street-legal these days; what's the point in getting busted for carrying a penknife?

Incidentally, I don't get the point of the ban on locking knives. If you stab someone with a knife that doesn't lock, then I suppose there's a risk to your own fingers; but the dude you stabbed won't care if it was a locking knife or not. I do get the blade-length restriction though. You don't need a 3" blade to sharpen pencils.

My straight razors are street-legal, though, and I think they're quite a lot more dangerous than a 3" knife that locks. The sharpened edge of a razor is only about 2" long, so I assume it's street-legal; but you could really make a mess of someone's face with a razor (the preferred weapon of Pinky, the gangster from Brighton Rock).

Another piece of anecdatum: a vague friend of mine once had a routine traffic stop by the police as he'd renewed his car insurance on the day it expired and the change hadn't made it onto the database they use yet. The police officer asked something like "just as a routine question, do you have anything on you that you might think you shouldn't have, like knives etc". He was (at the time) a professional chef and had a large roll of huge, high end kitchen knives on the back seat of the car. He also had chef's whites and was driving to work. The policeman said that apparently a few smarter drug dealers had started doing that (keeping them in a roll) as it was more plausible that they'd be cooking with them rather than stabbing their mates. The give away, apparently, was that they'd just have one massive one and not bother with the chef's job and still end up with a few years in prison.

My friend "got" a nice chat, and went on with his day, but did later comment that had he not had the outfit to go with them, and a vast array of obvious kitchen tools, he thought that they'd probably look at it a lot more seriously.

Talk about a strawman. Knives have utiltiy which is a feature. Domain fronting is a bug not a supported feature.

You’re mixing up definition and policy.

If airlines banned knives and someone posted a definition of “knife” that suggested they are only used for eating food, it would be perfectly reasonable for a reply to point out that there are dangerous uses which might have led to the bad, and that it’s disingenuous to suggest that the ban was obviously motivated by a desire to make eating difficult.

It’s still fair to debate the balance of use and the merits of the ban, but IMO it is not reasonable to be upset over a more complete definition and context.

I really enjoyed this explanation

https://hackernoon.com/domain-fronting-101-what-is-domain-fr...

They've been waging this war for a couple years now. I guess they finally got to every cloud provider. Some related reading:

"Amazon and Google bow to Russian censors in Telegram battle"

https://www.fastcompany.com/40568177/amazon-and-google-bow-t...

"U.S. Cloud Providers Face Backlash From China’s Censors"

https://www.wsj.com/articles/u-s-cloud-providers-face-backla...

https://archive.ph/qhFQ5

>China’s Internet censors have strengthened content screening in recent months, creating difficulties for businesses and disrupting more commonly used firewall-circumvention software called virtual private networks, which connect users to the Web through a proxy server overseas. President Xi Jinping has ordered tighter control of online content that may undermine the ruling Communist Party, with bloggers facing jail for spreading what the government says are false rumors.

I still see Cloudflare.

It's been many years, and I am still angry and disappointed by Cloudflare's decision to block domain fronting and drop Lantern as a customer. Lantern was one of the most effective Great Firewall bypass proxies at the time, and Cloudflare was expanding in China. (I was at Cloudflare at the time, but I don't have private information on the deliberation. I strongly considered quitting over it, maybe I should have, but I was junior back then.)

The CEO even came on HN to try to frame it as an abuse mitigation, accusing Lantern of exploiting Cloudflare and arguing that they were not a customer. That was obviously false because you need to have a Cloudflare zone configured for domain fronting to work. They were a customer as much as the targeted hate websites they strenuously defend.

https://news.ycombinator.com/item?id=9234367

Companies show their color in selecting who they will stand up for.

The insinuation is that somehow we had to stop domain fronting because “China”. That’s false.

What actually happened was we started to get reports from customers that we were serving content from unrelated sites under their domains. Wasn’t happening a lot but for a reverse proxy that’s terrifying and about as bad as it can get. And what made it even weirder was that the domain fronting was connecting to other proxy servers outside Cloudflare and so we literally had situation where a Cloudflare customer's website suddenly served up google.com (not a customer).

The issue was domain fronting where SNI didn’t match Host causing us to handle the traffic incorrectly sometimes (infrequently but not zero). Since standard use of the Internet doesn’t need SNI and Host to not match we blocked the use of domain fronting very fast to ensure the integrity of our service. Lantern was domain fronting tickling this bug and causing our customers trouble.

Hence we dropped domain fronting.

I remember this well because I actually debugged it myself and reported the problem in Jira. You weren’t involved and inventing a story about “China” is dead wrong.

As I said above, I was not involved in the deliberation, so I don't know the reason domain fronting was blocked. I clearly remember it being an explicit decision though, not a bug mitigation, and Matthew's explanation on HN makes no mention of a technical issue.

I do remember one terrifying bug that Lantern was tickling which caused responses to cross streams, and I was involved in debugging that, but it was not due to the Host/SNI mismatch. It just happened around the same time that domain fronting was blocked. (I am going to respect my confidentiality agreement here, but if you want I can share what I remember here or in private.)

I clearly remember it being an explicit decision though, not a bug mitigation

To be clear, that's not correct we did do this to mitigate the bug.

We were facing the bug that I described (the cross stream thing) showing up when Lantern was used. It was causing disruption to our service and customers were writing in. We were trying to understand what was happening and needed to stop it. One of the things we did to stop it was disable domain fronting. As we were seeing the customer reports we didn't know if this was an OpenSSL bug, something in NGINX, something in our code, but we did know that Lantern was somehow causing it and they were doing domain fronting which wasn't the standard use of our service and so we dropped it.

Maybe domain fronting was initially disabled as an unsuccessful attempt to fix that bug, that's possible and as I said I was not involved in that decision. Still, if that's the case, there was a policy decision afterwards to leave it disabled, because disabling it did not fix the bug, as you seem to agree. (Again, not elaborating on the bug publicly without permission, but I remember it turned out to have nothing to do with the SNI.)

My point is that disabling domain fronting (or leaving it disabled after finding the bug's root cause) was a policy decision, not something necessary to mitigate the bug or prevent it from re-occurring.

…he says, as his company eagerly does business with Xi in China.

No organization I am part of will ever do business with you if I can stop it.

You fought for Turing but I suppose the Uyghur concentration camps mean nothing to you. They are not British so how could their lives be worth fighting for when there is money to be made (for yourself) without regard to morality or any sense of decency.

But good job doing Cloudflare PR.

Could you not make domain fronting only work when the inside Host contains a specific component like start-frontin.example.com ? Then it will never work for a naive browser wanting to reach www.customer.com, but will work for non-browser clients deliberately trying to front.

Fascinating, Filippo. We stayed silent on it at the time primarily because we were keeping a low profile particularly as more and more Chinese were using Lantern, but there was also back channel pressure through various contacts, to be honest related to the pending Cloudflare expansion in China.

There was also a prelude to all of this that I think made things stickier and bizarrely personal. Prince and I share a mutual friend who introduced us just a few weeks prior. Prince said he supported what we were doing, but asked that I not talk about it publicly, presumably because of the pending China deal. The problem was that literally moments after our friend had introduced us via email, and before he made that request, I had a call with the WSJ where I talked about precisely this. I did everything I could to walk back the article, but Prince didn't buy it and seemed to go ballistic over it. After the WSJ piece, we pulled back from talking more publicly in general.

Oh, I forgot! We also partly stayed silent because they didn't actually shut down what we were doing at all =). They matched the SNI to the Host header, sure, but they missed a little detail: we weren't using SNI. Hehe. Lantern worked for another six months or so, and then, through a similarly bizarre sequence of events, we essentially tipped them/you off to what was happening. We remained a customer throughout, and we're a customer to this day.

Either way, though, Cloudflare does great work, and everyone has their faults, so I'm generally sympathetic over the whole thing with the one caveat that I am truly unclear how much ultimately did relate to China, most clearly in terms of any public support for these internet freedom techniques.

Oh, and I've wanted you to work on Lantern forever btw. Oooh actually if you're not aware of it, the uTLS Go TLS fork is a hugely impactful project that's in widespread use (I would guess maybe 50 million monthly active users rely on it in censored regions via various projects) but needs updating - https://github.com/refraction-networking/utls

Oh, and if you think we were effective in China then, you should see what we're doing in Russia and especially Iran now!

Oh it's also worth noting that Cloudflare is actually more aggressive in blocking domain fronting than almost anyone else. Lots of folks match the SNI to the Host header, but Cloudflare takes it a step further and also makes sure that TLS connections without SNI have a Host header that's scoped to the IP/server they're actually visiting. That means you can't, for example (not that we would ever, ever do this hehehe), scan the whole Cloudflare IP space for IPs to front through without SNI.

We have ECH (previously known as ESNI) now, is that not just domain fronting in a new form?

Only for the legal stuff... so you will still get complaining comments.

No, because with ECH/ESNI the hostname in both layers (the TLS connection and the HTTP Host header) still matches. The only difference is that the hostname on the both layers is no longer visible on the wire, while without ECH/ESNI the hostname on one layer (the HTTP Host header) is hidden but the hostname in the other layer (the TLS connection) is visible. And you could still do domain fronting even with ECH/ESNI (making the hostname on each layer differ), though it would be kind of pointless.

I was wondering that, thanks.

What I'm wondering now is why one should use that instead of a proxy server that maps some.domain.com to something.else.com

Well, that sucks. What's worse is it is wankers in the "infosec" industry that pushed MS to do this (or at least, are taking credit for it).

If you want to hide your domain name you can use eSNI. Keep in mind another name for censorship is moderation, it isn't just signal that uses it bad guys also abuse it and it was not a feature explicitly built to avoid censorship but more like a bug people were abusing.

It’s too late. Whole countries block all eSNI requests, so it’s always going to fail open.

Yeah, I believe China doesn't even allow TLSv1.3

Not allowing TLS 1.3 means nothing (no modern web sites) works. Modern browsers and servers both speak TLS 1.3 and if they can't they give up. Some things don't work in China, but China wouldn't have a thriving economy if nothing was working. So no, they did not block TLS 1.3 although it's interesting how this rumour seems to have self-popularised. China blocks certain popular sites, but it does not block whole protocols or protocol versions.

This is actually a small triumph for the people responsible for RFC 8446. With previous iterations of TLS it was always discovered shortly after release that idiots broke stuff and so a "fallback" was necessary to allow you to speak the previous version. Such fallback is dangerous because an adversary can thus forcibly downgrade you to an older protocol, and thus attack old protocols even if the new protocol is safe.

How is it done? That is, how does TLS 1.3 avoid downgrade attacks?

When a TLS 1.3 server finds itself talking to somebody over TLS 1.2 (for example maybe a rather archaic web browser is connecting) it scribbles over some of the bytes labelled "random" in its Hello message. It scribbles 44 4F 57 4E 47 52 44 01. Which in ASCII spells "DOWNGRD".

Those bytes don't mean anything special in TLS 1.2, they're just a strange coincidence. But if you're a TLS 1.3 client, seeing those bytes means a Downgrade attack was attempted. So you immediately give up, you are being attacked.

So you might think well, a bad guy could just change those bytes blind right? Nope. The "random" field is used by both parties to choose parameters they're going to verify in a moment to check everything is safe. If you can change the bytes the values will be different and the connection fails anyway.

They can ban tls 1.3 internally and do tls1.3 post intercept to the server.

> Some things don't work in China, but China wouldn't have a thriving economy if nothing was working.

Any company who does not want to lose a market of ~18% of global population will make sure it complies (example: Apple).

We need to think about real life here and not just technical implementation

Well then hopefully tech people will soon wrap their head around the fact that political problems are best solved politically. You can't write tech that overrides the authority of governments but you can override or change governments.

> You can't write tech that overrides the authority of governments

Really? Tor springs to mind.

Same. What's your point? VPNs also bypass government blocks. It's a cat and mouse game, they block vpns and guards as they see fit when they have a good reason to. Look at tor, if a country tls decrypts everything and blocks connections that can't be decrypted can it still bypass their blocks? Just because not every government is doing it does not mean Tor can't be blocked. Hell, countries allow-list connections to allowed sites if they want. Breaking their laws may make you feel edgy but that sort of "revolution exporting" many in other countries consider it a form of neo-colonialism where you undermine their sovreignity and self-determination.

You're right; ultimately, if you have total power, you can just block the internet.

> many in other countries consider it a form of neo-colonialism where you undermine their sovreignity and self-determination.

Only if by "their" you mean the ruling class, and by "self-determination" you mean their ability to control others. You can't really say their opinions represent the will of the people, especially when it's the people themselves ultimately choosing to engage in "illegal" activities.

And sure, "the will of the people" bakes in two very western individual/collectivist values. But as I get older I'm learning to not play the relativism card as much. We should certainly be critical of our culture - but to the point of making it better, not handicapping its spread.

Plus there's still a very easy answer for the poor oppressed tyrant who doesn't like freedom of communication - shut down all Internet connections.

The will of the people is relevant only in a democracy. The neocolonialism part is when you force it in a foreign country. There is absolutley nothing superior or special about democracy. If the people of a country through whatever self-determined means acheive democracy then so be it. The thing people like you don't seem to understand is that individualism is a very western thing, this idea that the individual's will is where a government derives its power from is a very new and western experiment(relatively speaking).

Take a look at Iran, they are religious as a nation. Their religion supersedes any individual's will. Or china, the will if the party supersedes individuals' needs. You in your post-colonialist luxury worry about your own will but historically people worry about the well being of their children and society which means not getting killed/raped, having economic and academic opportunities,etc... and beyonf that also, the will of their god being implemented. Which people? The people with weapons just like in a democracy (else the US would still be under a monarchy). They self determined through violence and politics the state they are in. In China the economy is good so the CCP is actually popular, so they self-determined communism (at least by name).

There many countries where the US exported a revolution or a democracy and they are in shambles now (who cares so long as they are under western influence?) name one nation in europe that was did not prosper under a monarch before self-determining democracy? Yet your arrogant presumption robbed many nations of that opportunity. Because the people are unprepared and uninformed, the loudest asshole takes power by deceiving people and saying the right things the he gets super rich until they protest and he flies off with his money until the next asshole. This keeps happening and is your direct responsibility since it is because of your will your politicians are exporting chaos and installing puppet leaders in other countries. Civil war after civil war, genocide after genocide because humans are tribal by nature and there is no peaceful way a ruling tribe (see iraq) would peacefully let go of power.

Keep in mind that if it wasn't for the threat of violence by your own country's military you also would be part taker in the voiolence and chaos you are exporting.

Democracies cannot thrive when people are starving, destitute and uneducated and lack basic infrastructure by which they can be informed enough to critically analyze what their politicians are saying. "Your life sucks because of $tribe" does that sound familiar?

So you organize a revolt over Tor, I guess the other side will also use Tor to organize the civil war or genocide?

> The thing people like you don't seem to understand is that individualism is a very western thing

Read my comment again - I explicitly acknowledged this.

I'd say that most of your comment is attacking a top-down "exporting democracy" whether covertly, led by the State Department, outright invasion, etc. I agree that these things are evil, especially when "democracy" is used as the marketing for the primary concern of implementing USD-denominated markets.

So where we differ is the bottom up emergent behavior of people making their own choices.

> historically people worry about the well being of their children and society which means not getting killed/raped, having economic and academic opportunities,etc... and beyonf that also, the will of their god being implemented.

And yet, those are the same exact people choosing to use technology that provides things like (very imperfect) communications privacy. Your argument implies that their choices are wrong, so what you're really saying is that the larger population needs to be paternalistically protected from themselves. Which brings us to the huge unstated assumption of your comment that for every society we should respect some ambient "values" of the society, with some more powerful in-group protecting those values against the larger population.

I agree that's a descriptive statement about the power structure of basically every society. But I don't agree that it's a prescriptive model with inherent moral value.

And yes, I do know this viewpoint is a very "western" philosophy. I put "western" in quotes because it seems like a strong general attractor, as communications technology enables human-to-human communication unmediated by traditional top-down power structures. I'm also learning not to handicap myself by getting stuck in the doldrums of relativism. To the extent that it may be inherently western, spreading our own culture through arms length communication and voluntary buy in is a hell of a lot more defensible than the traditional ways of spreading culture - violent conquest and subjugation.

>Keep in mind another name for censorship is moderation

No it's not, see https://news.ycombinator.com/item?id=33446064

On most social media sites they're implemented the same way (ie. posts deleted/hidden from other users), but the objectives are totally different.

Let me rephrase then: what one calls censorship another might call moderation. The difference is authority to remove of hide content, if you have it then it is moderation. So, to be controversial for the sake or discussion then, Russia blocking Signal is moderation within the realm of their authority as is Iran blocking content they don't like or the US gov seizing domains. Either way, domain fronting was never an explicit feature anyone supported.

I'd see them being different in terms of moderation acting as an allow list, and censorship acting as a deny list.

They also have different targets - moderation is about a forum, while censorship is about an idea

Could you explain to me how "nibbleshifter" would use the "feature" for good?

What are you losing here "nibbleshifter"?

Why do you put infosec in scare quotes? Why are they "wankers"? Why scare quote and name call a legitimate profession? Because you have qualms?

Evading censorship in less democratic countries, for a start. I've had to do this quite a number of times on my travels - and its even more important for people in the human rights field.

Tor's "meek" pluggable transport uses domain fronting for this purpose.

I work in the so called "infosec" field, and about half the field are myopic wankers who would readily sacrifice privacy wholesale to gain an ounce of so called security. Think: the kind of people who also want to cripple eSNI or DoH in the name of "network monitoring".

> even more important for people in the human rights field.

Historically these people and even journalists are targeted by Nation States utilizing Israeli made offense tools like Pegasus.

Domain fronting would not help in these cases to avoid censorship, maybe but you are attempting to circumvent a Nation State with almost unlimited money and resources the target would never be able to have.

Does it suck that domain fronting is gone? Yes. Is it a good thing it's gone? Yes.

The fact is the people that used domain fronting for your use case is heavily heavily outweighed by malicious actors.

One could argue that domain fronting and guns are the same. Why should I have my gun taken away when I am using it for legal purposes? Just because bad people use a gun for bad things I shouldn't be scrutinized for my legal use. I shouldn't have access taken away due to bad actors leveraging them for ill gotten gains.

They probably threw in some pablum about "fake news" as well.

China is very, very big business for internet companies. They're not going to risk that just to protect political dissidents.

yes

Good. For every benevolent use case there are a thousand spammers and scammers using this technique for junk and phishing.