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Re: [TLS] Possible blocking of Encrypted SNI extension in China

Carrick Bartle <cbartle891@icloud.com> Thu, 13 August 2020 20:04 UTC

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From: Carrick Bartle <cbartle891@icloud.com>
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Date: Thu, 13 Aug 2020 13:04:48 -0700
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To: David Fifield <david@bamsoftware.com>
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Subject: Re: [TLS] Possible blocking of Encrypted SNI extension in China
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Weird. Thanks for the update. How are you confirming that it's blocked from inside-out?



> On Aug 13, 2020, at 10:30 AM, David Fifield <david@bamsoftware.com> wrote:
> 
> On Fri, Aug 07, 2020 at 05:56:30PM -0600, David Fifield wrote:
>> Most of the functions of the Great Firewall work bidirectionally, and
>> the ESNI detection and blocking are no exception. Sending an
>> ESNI-containing ClientHello from *outside* of China to a server
>> *inside* results in temporary blocking, just the same as sending one
>> from the inside to the outside. This makes it easy to experiment with,
>> even if you don't control a host in China.
> 
> Triggering blocking from the outside no longer works. ESNI connections
> that originate inside the firewall are still blocked. This was first
> observed by GFW report, who were able to isolate the change from
> bidirectionality to unidirectional to a five-minute window: between
> 06:27 and 06:32 UTC on 2020-08-13. I tried it myself, and I confirm that
> I am not now able to trigger ESNI blocking from outside the firewall.
> https://github.com/net4people/bbs/issues/43#issuecomment-673322409
> 
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