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Re: [TLS] "Encrypted" SNI

Ilari Liusvaara <ilariliusvaara@welho.com> Wed, 10 May 2017 19:28 UTC

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Date: Wed, 10 May 2017 22:28:48 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: Hubert Kario <hkario@redhat.com>
Cc: "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] "Encrypted" SNI
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On Wed, May 10, 2017 at 07:28:51PM +0200, Hubert Kario wrote:
> Yes, encrypted SNI was discussed and ultimately rejected.
> 
> But do we really have to send the literal value? Don't we need to just make 
> sure that the client and server agree on the host that the client wants to 
> connect?
> 
> Couldn't we "encrypt" the SNI by hashing the host name with a salt, sending 
> the salt and the resulting hash, making the server calculate the same hash 
> with each of the virtual host names it supports and comparing with the client 
> provided value?

What makes encrypting SNI nasty is replay attacks.

There also was proposal for putting SNI mapping into DNS (which limits the
leakage if DNS lookups are private). However, I came up with a way to use
that to attack HTTPS (the usual "default vhost" attacks).


-Ilari

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