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Re: [TLS] "Encrypted" SNI

Roland Zink <roland@zinks.de> Wed, 10 May 2017 22:03 UTC

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To: Christian Huitema <huitema@huitema.net>, tls@ietf.org
References: <3768598.32hupQ9b2b@pintsize.usersys.redhat.com> <a6029246-46f6-d698-983f-b668d70e2780@zinks.de> <1be2b15e-2e96-89f4-fe72-7f35a03ae99b@huitema.net>
From: Roland Zink <roland@zinks.de>
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Date: Thu, 11 May 2017 00:03:15 +0200
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Subject: Re: [TLS] "Encrypted" SNI
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Not necessarily as you may for example use the path part of a URL to 
distinguish between services.


Roland




Am 10.05.2017 um 23:50 schrieb Christian Huitema:
>
> On 5/10/2017 2:40 PM, Roland Zink wrote:
>> The SNI extension is optional, so you don't have to send the literal
>> value. Indeed quite some number of apps do not send it. Browsers
>> currently can't know if the SNI is required by the origin servers and
>> usually send this, but there could be some signal to not send it. One
>> example could be a HTTP header to tell the browser that SNI should be
>> send and if it isn't present then no SNI is send. Unfortunately this
>> would break current sites but still it can be done the other way
>> around e.g. send a header to not send SNI.
> Yes. But this is only possible when each service has a separate IP
> address. The privacy gain occurs precisely when several services share
> the same address, but that's exactly when the SNI is required. If the
> SNI was somehow encrypted, adversaries would not be able to use it to
> find which service the user is connecting to.
>
> -- Christian Huitema
>

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