Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  merge_ready
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:  ahf   |Sponsor:
--+-
Changes (by ahf):

 * status:  needs_review => merge_ready


Comment:

 The code also looks good to me. The uTLS library is neat and I love the
 idea of profiles. Didn't look at the wire part of the uTLS library, but I
 assume others have looked at that?

 Let's get the code in.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:  ahf   |Sponsor:
--+--

Comment (by dcf):

 Replying to [comment:22 cohosh]:
 > Hey a did a quick look, here are some comments:
 >
 > - meek-client now requires go version 1.11 or later because of utls. I
 looked but didn't find in the documentation or READMEs the required go
 version for building the client. It's possible I missed it, just wanted to
 point out the required version update.

 Thank you for reviewing.

 Yes, it's a bit of a bummer to require such a recent go... I think it's
 because uTLS is a copy of the stdlib crypto/tls with changes applied on
 top, and the stdlib is not shy about requiring a recent compiler.
 Unfortunately uTLS will put us on more of an update and maintenance
 treadmill. Not only will we have to keep an eye on uTLS to pick up new
 fingerprints, but uTLS will have to stay on top of crypto/tls updates
 ([https://github.com/refraction-networking/utls/pull/12 like this]).
 There's a fair amount of uncertainty yet, I feel.

 > {{{
 > +// otherwise, create an internal http.Transport. In either case, set
 DialTLS on
 > +// the created Transport do a function that dials using uTLS As a
 special case,
 > }}}
 > do-->to
 > uTLS-->uTLS.

 Thanks, fixed these in [https://gitweb.torproject.org/pluggable-
 
transports/meek.git/commit/?h=utls_3&id=dd26d797b15b8a05262209e07846f7204420e81a
 dd26d797b15b8a05262209e07846f7204420e81a].

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:  ahf   |Sponsor:
--+--

Comment (by cohosh):

 Hey a did a quick look, here are some comments:

 - meek-client now requires go version 1.11 or later because of utls. I
 looked but didn't find in the documentation or READMEs the required go
 version for building the client. It's possible I missed it, just wanted to
 point out the required version update.

 Otherwise, I only have some minor copy edit notes for one of the comments:

 in meek-client/utls.go:
 {{{
 +// otherwise, create an internal http.Transport. In either case, set
 DialTLS on
 +// the created Transport do a function that dials using uTLS As a special
 case,
 }}}
 do-->to
 uTLS-->uTLS.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:  ahf   |Sponsor:
--+--
Changes (by ahf):

 * reviewer:   => ahf


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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--

Comment (by dcf):

 * https://gitweb.torproject.org/pluggable-
 transports/meek.git/log/?h=utls_3&id=21abea57d28abe614887135ab380bfb4355de9fc

 Here's another merge candidate, rebased and cleaned up. It's the same
 utls_2 from comment:12, except for squashed commits, more tests, and fixes
 for two small bugs I found through testing: when the `utls.Config` doesn't
 have a `ServerName` set, take the SNI from the dial address; and if
 someone happens to make an http request using `UTLSRoundTripper`, honor
 the proxy setting on the `UTLSRoundTripper`.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--

Comment (by yawning):

 I have changed meek_lite to use `Firefox_Auto` and a forked version of
 utls that adds a number of compatibility fixes.  Additionally I believe
 that the Firefox fingerprint is unchanged in 65.  There was one
 ciphersuite difference between FF 65 as packaged and ran on Fedora and
 that produced by utls, but that is due to Fedora disabling 3DES.

 There's one more feature I want to add to meek_lite before tagging, but
 unless anything comes up, this is close to what I'm currently leaning
 towards tagging as 0.0.9.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--

Comment (by yawning):

 I'm convinced (after wasting an afternoon trying to get it to work) that
 `HelloChrome_Auto` is an acceptable default assuming the front is not on
 Google infrastructure.  At some point in the future when more servers use
 BoringSSL with multiple draft and or non-standard extensions, that stance
 will need to be revisited.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--

Comment (by yawning):

 > Making the library support the NIST curves is trivial, and would fix
 this problem.

 {{{
 arnhem :: Documents/Development/utls-test % ./fuck --utls
 HelloFirefox_Auto https://www.google.com
 utls: &{Firefox 63}
  0 HTTP/2.0 200 OK
  1 HTTP/2.0 200 OK
  2 HTTP/2.0 200 OK
  3 HTTP/2.0 200 OK
 }}}

 Not sure if I want to make the fork public yet.  The test suite doesn't
 pass with my changes applied, and while I think I know why, I haven't dug
 into it enough to prove it to my satisfaction.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--

Comment (by yawning):

 > This sounds like a good design. I think for at least the next release
 I'll leave no utls meaning native TLS, and then a future release can
 compatibly upgrade it to mean some sensible uTLS configuration by default.

 Ok, I'll let you know if behavior there changes, though I don't anticipate
 much beyond potentially changing which fingerprint `meek_lite` will use as
 a "sensible default".

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--

Comment (by dcf):

 * https://gitweb.torproject.org/pluggable-
 transports/meek.git/log/?h=utls_2&id=e4bc7b1c3aae41252f64b3affc8c08e525831e08
  * https://gitweb.torproject.org/pluggable-
 
transports/meek.git/diff/?h=utls_2&id=e4bc7b1c3aae41252f64b3affc8c08e525831e08&id2=cb2d7d1a6f0c8ada45d22f49ed0524bbc689b1b1

 Here's a merge candidate for the utls_2 branch. Changes since comment:12:
  * Support for socks5, http, and https proxies. (The same proxy types
 net/http supports.)
  * `utls=none` and `utls=HelloGolang` mean "no uTLS".
  * Copying default `http.Transport` timeouts and other settings.
  * Rudimentary integration tests for the http and https proxies.

 Replying to [comment:13 yawning]:
 > Note that I treat not specifying the argument as "use a sensible
 default", and have `none` special cased as "use the built in TLS stack",
 under the rationale that once the code is solid the only reason to not use
 utls is if something breaks, and "Add `utls=none`" is a easier interim
 workaround to convey to the unwashed masses than "Edit an existing
 argument".

 This sounds like a good design. I think for at least the next release I'll
 leave no `utls` meaning native TLS, and then a future release can
 compatibly upgrade it to mean some sensible uTLS configuration by default.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--
Changes (by yawning):

 * cc: yawning (added)


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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--

Comment (by yawning):

 > Here is a new candidate

 Looks ok at a first glance.  I guess I should add the timeout values to
 meek_lite too.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+--
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  needs_review
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+--
Changes (by dcf):

 * status:  new => needs_review


Comment:

 Here is a new candidate: meek branch [https://gitweb.torproject.org
 /pluggable-
 transports/meek.git/log/?h=utls_2&id=6c2cad6ce0e1d0d23ec88edb7942362de2552b0e
 utls_2]

 This is a rewrite using the obfs4proxy-inspired technique (comment:4),
 with a few implementation differences. Instead of `dialTLS` being attached
 to the `RoundTripper` wrapper with a distinguised error code, use a
 standalone `dialUTLS` function. Store the state for the dynamically
 created `Transport` in a closure rather than in the parent struct. Raise
 an error if the ALPN changes.

 You control which fingerprint to use with a SOCKS arg, like
 `utls=HelloChrome_Auto`. With the SOCKS arg, it uses the stdlib net/http
 as before. Using `utls=` with `--helper` is an error.

 Currently this breaks proxy support, because previously we were using the
 built-in proxy support of net/http, and we can't do that anymore with
 uTLS; we'll have to make our own proxy connections. I'll restore proxy
 support separately.

 I've removed HelloRandomized and HelloGolang from the table of allowed TLS
 fingerprints. HelloRandomized because
 [https://lists.torproject.org/pipermail/tor-dev/2019-January/013639.html
 it can negotiate different ALPN], and HelloGolang because that's ideally
 equivalent to omitting the `utls=` arg. I'm open to having it recognize
 `utls=HelloGolang` as an alias for omitting the `utls=` arg, because
 compatibility with meek_lite is the most important thing here.

 When creating the internal `http.Transport`, I think I'd like to make it
 have the same default settings as `http.DefaultTransport` with respect to
 timeouts, idle connections, etc. So I'm thinking of cloning the public
 fields of `http.DefaultTransport` using the reflection trick from
 comment:11:ticket:12208. Unfortunately `http2.Transport`
 [https://github.com/golang/go/issues/16581 doesn't expose configuration
 options] in the same way. Maybe it doesn't matter much? My main concern
 here is not having infinite timeouts.

 I tested the TLS fingerprint with a few different configurations.
 ||=configuration =||=fingerprint =||=  seen (all time)=||
 ||no camouflage ||[https://tlsfingerprint.io/id/c4b0fe116abff001
 c4b0fe116abff001]
 
[https://web.archive.org/web/20190125221734/https://tlsfingerprint.io/id/c4b0fe116abff001
 archive] ||  0.01%||
 ||`--helper` (Tor Browser 8.0.4 / Firefox 60.4.0esr)
 ||[https://tlsfingerprint.io/id/bb94e801f7aee52b bb94e801f7aee52b]
 
[https://web.archive.org/web/20190125221851/https://tlsfingerprint.io/id/bb94e801f7aee52b
 archive] ||  0.58%||
 ||`utls=HelloChrome_70` ||[https://tlsfingerprint.io/id/bc4c7e42f4961cd7
 bc4c7e42f4961cd7]
 
[https://web.archive.org/web/20190125222100/https://tlsfingerprint.io/id/bc4c7e42f4961cd7
 archive] ||  3.54%||
 ||`utls=HelloFirefox_63` ||[https://tlsfingerprint.io/id/6bfedc5d5c740d58
 6bfedc5d5c740d58]
 
[https://web.archive.org/web/20190125222153/https://tlsfingerprint.io/id/6bfedc5d5c740d58
 archive] ||  1.66%||

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by dcf):

 Replying to [comment:10 yawning]:
 > Making the library support the NIST curves is trivial, and would fix
 this problem.

 Okay; maybe it's better to have that discussion on the utls tracker?

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by yawning):

 >  100% of the failures used a fingerprint with TLSv1.3, while only 28% of
 the successes did. I haven't dug deeper to see what the difference between
 the success and failure TLSv1.3 handshakes is.

 The kludges inherited from `crypto/tls` only apply when TLS 1.3 is
 requested.

  * https://github.com/refraction-
 networking/utls/blob/master/handshake_client.go#L121
  * https://github.com/refraction-
 networking/utls/blob/master/handshake_client_tls13.go#L300
  * https://github.com/refraction-
 networking/utls/blob/master/handshake_client_tls13.go#L215

 Making the library support the NIST curves is trivial, and would fix this
 problem.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by watt):

 Replying to [comment:6 dcf]:
 > what the difference between the success and failure TLSv1.3 handshakes
 is.
 draft vs final TLSv1.3?

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by dcf):

 Replying to [comment:7 watt]:
 > Replying to [comment:6 dcf]:
 > > TLSv1.3 (which `Firefox_60` always does).
 > `Firefox_60` doesn't support TLSv1.3.

 My bad, I actually meant `HelloFirefox_63`. You can see where the
 fingerprint specifies TLSv1.3 [https://github.com/refraction-
 networking/utls/blob/fd72b83e043e8ed28e5ce8cdca84a1080927c208/u_parrots.go#L195
 here]. `HelloFirefox_Auto` currently means `HelloFirefox_63`.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by watt):

 Replying to [comment:6 dcf]:
 > TLSv1.3 (which `Firefox_60` always does).
 `Firefox_60` doesn't support TLSv1.3.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by dcf):

 Yeah I did some tests today with `HelloRandomizedNoALPN`, 400 trials
 against each of 3 servers.
 =**ajax.aspnetcdn.com** =||
 ||  284||no error ||
 ||   80||remote error: tls: handshake failure ||
 ||   36||tls: server selected unsupported group ||
 =**golang.org** =||
 ||  335||no error ||
 ||   65||remote error: tls: handshake failure ||
 =**www.cloudflare.com** =||
 ||  400||no error ||

 `HelloRandomizedNoALPN` [https://github.com/refraction-
 
networking/utls/blob/a89e7e6da482a5a0db02578fc606ace9ccfbea62/u_parrots.go#L557-L564
 unconditionally includes] sec256r1 and sec384r1, but it doesn't seem to
 cause a problem unless it also happens to choose TLSv1.3 (which
 `Firefox_60` always does). 100% of the failures used a fingerprint with
 TLSv1.3, while only 28% of the successes did. I haven't dug deeper to see
 what the difference between the success and failure TLSv1.3 handshakes is.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by yawning):

 Replying to [comment:1 dcf]:
 > (b) causes the server to select a feature that the client advertised in
 its fake fingerprint but doesn't actually support. When this happens, you
 get an error in the meek-client log like
 > {{{
 > error in handling request: tls: server selected unsupported group
 > }}}

 Probably old news, but since this happens with the `Firefox_Auto` preset
 on the Azure bridge, I looked into it a bit, and it is primarily caused by
 `utls`'s support for curves other than X25519 being non-existent in
 certain cases.

 This is code inherited from `crypto/tls`, and the issue arises from the
 assumption that the server will always negotiate X25519
 (ajax.aspnetcdn.com will pick `secp256r1`) if it is present in the
 ClientHello's Supported Curves extension.

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by yawning):

 
https://gitlab.com/yawning/obfs4/commit/4d453dab2120082b00bf6e63ab4aaeeda6b8d8a3

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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-
Changes (by gk):

 * cc: gk (added)


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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-
Changes (by dcf):

 * cc: sf (added)


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Re: [tor-bugs] #29077 [Obfuscation/meek]: uTLS for meek-client camouflage

[Tor Bug Tracker & Wiki]

#29077: uTLS for meek-client camouflage
--+-
 Reporter:  dcf   |  Owner:  dcf
 Type:  enhancement   | Status:  new
 Priority:  Medium|  Milestone:
Component:  Obfuscation/meek  |Version:
 Severity:  Normal| Resolution:
 Keywords:  moat utls |  Actual Points:
Parent ID:| Points:
 Reviewer:|Sponsor:
--+-

Comment (by dcf):

 I started trying this out in
  * meek branch [https://gitweb.torproject.org/pluggable-
 transports/meek.git/log/?h=utls&id=90d82c205c0269b87de5a6956e485225f8a9a2cb
 utls]
  * tor-browser-build branch [https://gitweb.torproject.org/user/dcf/tor-
 browser-build.git/log/?h=meek-client-
 utls&id=1758a67bc2f366a8af2730d924b80a5c4133eec4 meek-client-utls]

 I built a browser with these changes. It works, but not well. It hangs and
 stalls frequently, and Moat often throws errors. There are two primary
 causes for these problems.

  1. utls's interaction with Go's built-in HTTPS is awkward. In meek-client
 we use an [https://golang.org/pkg/net/http/#Transport http.Transport] to
 enable connection reuse, manage idle timeouts, etc. To hook into utls, I'm
 [https://gitweb.torproject.org/pluggable-
 transports/meek.git/commit/?h=utls&id=5a98c4447e8d3cb14e53b9ef15d6faa812aed226
 setting the DialTLS callback]--but setting DialTLS has the side effect of
 disabling automatic HTTP/2 support on the client. This wouldn't be a
 problem, except for the fact that with e.g. the `HelloFirefox_63` and
 `HelloChrome_70` fingerprint, utls sends a Client Hello with an ALPN that
 negotiates HTTP/2. The server starts speaking HTTP/2 while the net/http
 client, oblivious to what utls has done, continues speaking HTTP/1.1, and
 you get an error. There are more details on this problem on
 [https://github.com/refraction-networking/utls/issues/16 GitHub ticket
 #16].

 As a workaround for the ALPN mismatch issue, I tried specifying the
 `HelloRandomizedNoALPN` client. Randomized means it picks fingerprint
 features randomly, and NoALPN means it won't negotiate HTTP/2. The loss of
 HTTP/2 is a bummer, but the bigger problem is

  2. The randomized fingerprint is re-randomized for every new TLS
 connection, and occasionally it generates a Client Hello that either (a)
 the server rejects or (b) causes the server to select a feature that the
 client advertised in its fake fingerprint but doesn't actually support.
 When this happens, you get an error in the meek-client log like
 {{{
 error in handling request: tls: server selected unsupported group
 }}}
 At the tor level, you get a stall until tor decides to try the bridge
 again. With Moat, you get an error dialog like "Unable to obtain a bridge
 from BridgeDB. NS_ERROR_NET_INTERRUPT", unless you are lucky that none of
 the TLS connections for the duration of the Moat session had the
 randomization error. The re-randomization of fingerprints normally
 wouldn't a severe problem because of connection reuse, but the combination
 of DialTLS and the lack of HTTP/2 means that connections are reused less
 than normal.

 In summary: the static fingerprints fail completely because of an ALPN
 mismatch; the randomized fingerprints fail sometimes because of server
 feature mismatches.

 There is a partial workaround. Using
 [https://godoc.org/golang.org/x/net/http2#Transport http2.Transport] in
 place of http.Transport seemingly solves all the above problems--with the
 caveat that it doesn't work with servers that don't support HTTP/2.
 [https://github.com/refraction-
 networking/utls/issues/16#issuecomment-453697993 Details here.] So what
 I'm planning to do next is add `utls` and `http2` controls to the PT
 configuration. `utls` would allow you to choose a utls fingerprint (with
 knowledge of the errors described above). `http2` would let meek-client
 assume that the front server always supports HTTP/2, solving the errors
 described above as long as the server actually does support HTTP/2.

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