How to implement the "extensionEncryptedClientHello (boringssl) (65037)," extended

[xiaoweigege]

How to implement the "extensionEncryptedClientHello (boringssl) (65037)," extended

[jjsaunier]

You can take a look at cloudflare/go@9ea1834 and then

• https://draft-13.esni.defo.ie:11413/
• https://draft-13.esni.defo.ie:10413/

[xiaoweigege]

There doesn't seem to be a corresponding implementation

[jjsaunier]

"extensionEncryptedClientHello (boringssl) (65037)," extended

cloudflare/go@9ea1834#diff-f93ae351e135c874558cc63997db12a4c2c4d220f3bb2be84ecf6c808b2b9599R126

0xfe0d is 65037 in decimal, and ECH is the abbreviation of EncryptedClientHello, why are you saying it does not correspond?

[xiaoweigege]

Thank you, I see! Does adding this extension allow for faster validation of akamai waf?

[jjsaunier]

Probably not; I don't know a browser that has implemented it yet (if it does, it's behind a feature flag), and the RFC is still in draft, so I doubt they use it as a signal or give a faster validation since 99% of traffic do not have it

[gaukas]

a browser that has implemented it yet

the latest Firefox is said to be shipped with ECH enable iff DNS-over-HTTPS is correctly configured.

[gaukas]

But yeah it is probably a great idea to implement ECH for uTLS. PR is welcome.

[xiaoweigege]

Can be like "FakeDelegatedCredentialsExtension", implement a placeholder. It is not clear how ECH is implemented

[gaukas]

how ECH is implemented

I believe that the cloudflare/go actually have it implemented in full. If interested someone may just port it. The License should be compatible.

[xiaoweigege]

Can you transplant him? I am not familiar with golang at the moment

[gaukas]

In case you are asking if I (or anyone from the refraction team) will port this feature from cloudflare, the answer is no, currently we are all at capacity and adding an optional feature is not prioritized.

But if anyone from the community would like to open a pull request on that, I will be happy to review it.

[jjsaunier]

Cloudflare make a blog post about it

https://blog.cloudflare.com/announcing-encrypted-client-hello/ with browser support upcoming

• Chrome https://chromestatus.com/feature/6196703843581952
• FF https://groups.google.com/a/mozilla.org/g/dev-platform/c/uv7PNrHUagA/m/BNA4G8fOAAAJ

[gaukas]

It might be a good time to start discussing how significant is it for uTLS to support ECH and what does a sense-making configurable interface look like in uTLS for ECH.

[pitagoras530]

hi, is there any update to this extension? Most sites do cause issues, if you do not provide the extension

[gaukas]

Most sites do cause issues, if you do not provide the extension.

Would you like to elaborate? Which sites cause issues and what kinds of issue.

My impression is that none of the TLS extensions should be mandatory. Especially a draft extension in no case should be required in anyways.

So far the work on this extension is not prioritized, given that it is not yet generically available, plus it is not yet solidified into an IETF standard.
But again, we are open to pull requests adding new extensions.

[gaukas]

And here's my 2 cents on implementing extensionEncryptedClientHello:

I still believe there are good reason to hold onto this feature even though cloudflare might already have a readily available implementation, until ECH is fairly popular among TLS servers (instead of just the top 2 web browsers, which are considered TLS clients).

Once uTLS, or any popular circumvention tool started exploiting ECH to circumvent DPI-based blocking, censors may respond by blocking/disabling it completely with little to no collateral damage.

---

Btw we already saw reports showing some strong censors blocking the DNS-over-HTTPS, which is usually considered a prerequisite of successful ECH bootstrapping.

[gaukas]

And I am open to merging changes from the hard fork on cloudflare/go by cloudflare , maybe with necessary modification/changes. The LICENSE looks compatible to me (BSD-3-Clause) and their implementation has a fairly assured quality.

I haven't looked into how much additional work will be required on uTLS to support ECH, but it shouldn't be too bad comparing to supporting PSK and post-quantum key share (kyber768-ed25519) in uTLS, which has been handled with a satisfactory standard thanks to the community.

[pitagoras530]

And I am open to merging changes from the hard fork on cloudflare/go by cloudflare , maybe with necessary modification/changes. The LICENSE looks compatible to me (BSD-3-Clause) and their implementation has a fairly assured quality.

I haven't looked into how much additional work will be required on uTLS to support ECH, but it shouldn't be too bad comparing to supporting PSK and post-quantum key share (kyber768-ed25519) in uTLS, which has been handled with a satisfactory standard thanks to the community.

In order to replicate the Ja3 of google chrome, you need the ECH extension else most cloudflare sites block you based on that.

[gaukas]

you need the ECH extension else most cloudflare sites block you based on that

If I understand correctly: when you advertise your support of ECH using the GenericExtension, cloudflare will not be able to complete the handshake correctly. It is pretty much expected. But are there any compelling reason to not just simply give up advertising it? i.e., why do you want to parrot this version of Google Chrome.

The "needs for parrot" again leads to my concern: how popular is the ECH extension on TLS clients and how popular is ECH support on TLS servers? Without an assuring answer, I am afraid implementing ECH too soon in circumvention community will lead to the minimal collateral damage when trivially blocking ECH. The best bet is for us to we wait until ECH become a default behavior for the vast majority of benign TLS clients/servers, so it doesn't become a strong fingerprintable feature.

[biaosheng]

Currently, Google Chrome 120 version has added ECH

[gaukas]

Currently, Google Chrome 120 version has added ECH

Could you please double check if Chrome 120 sends a greased ECH extension if prerequisite for ECH is not met? i.e., if no DoH configured, if target domain is not configured to support ECH, etc.

[gaukas]

So as the first step, today we merged #266 to add the GREASE ECH extension. For pure parroting purposes, this should suffice.

We will keep holding onto the full ECH implementation until fully ECH is fairly common...

Now available in v1.6.0, cheers🥂

[biaosheng]

So as the first step, today we merged #266 to add the GREASE ECH extension. For pure parroting purposes, this should suffice.

We will keep holding onto the full ECH implementation until fully ECH is fairly common...

Now available in v1.6.0, cheers🥂

Wow, you are so great!