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

Rob Sayre <> Tue, 11 August 2020 07:07 UTC

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From: Rob Sayre <>
Date: Tue, 11 Aug 2020 00:06:54 -0700
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To: Christian Huitema <>
Cc: Peter Gutmann <>, Christopher Wood <>, "" <>
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Subject: Re: [TLS] Possible blocking of Encrypted SNI extension in China
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On Mon, Aug 10, 2020 at 11:49 PM Christian Huitema <>

> Defeating fingerprinting is really hard. It has been tried in the past, as
> in "make me look like Skype" or "make me look like wikipedia". The idea is
> to build a target model, then inject enough noise and padding in your
> traffic to match the target model. But that way easier to say than to do!
Some of the techniques do attempt something like that. For example:

"Wright et al. [wright2009traffic] developed traffic morphing, which pads
packets in such a way so as to make the sequence from one page have
characteristics of another (non-monitored or benign) page. This technique
requires application-specific knowledge about benign pages and is therefore
best implemented outside of the transport layer."

What I couldn't figure out is how much the cited training mechanisms rely
on the ClientHello message. I haven't found a source that mentioned this
outside of "packet size and timing", but I haven't read them all.