[Pearg] About hiding in crowds

Christian Huitema <huitema@huitema.net> Mon, 10 August 2020 23:25 UTC

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From: Christian Huitema <huitema@huitema.net>
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Date: Mon, 10 Aug 2020 16:24:32 -0700
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Subject: [Pearg] About hiding in crowds
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A lot of the privacy extensions recently developed amount to "hiding in
crowds". For example, SNI encryption assumes that multiple servers are
accessible through the same IP address. If the SNI is hidden, outside
observers won't know which one was accessed. DNS encryption makes the
same assumption in an indirect way. It assumes that we gain privacy by
hiding the DNS exchange that maps www.example.com to an IP address. This
is fine, except for the fact that most servers have their own IP
address. You can hide the DNS exchange, you can hide the SNI, but
outside observers will still be able to understand which servers you are
accessing by simply looking at the address header. If we want real
privacy, we will need something else!

How do I know? I started with the Majestic Million list of domain names,
and resolved 25,000 of these names, and found out that on average a
given IP address was shared by about 1.21 names, as explained in:
https://huitema.wordpress.com/2020/08/09/can-internet-services-hide-in-crowds/).
And then I resolved the next 25000 names to be more sure of the results.
The average increased slightly, from 1.21 to 1.22, which does not change
the results much. 74.6% of domains use an address that is unique to
them, 8.7% use an address shared by 2 domains, and only 8% use an
address shared by 10 or more servers. DNS encryption and SNI encryption
do bring privacy for a minority of connection, for which it may well be
important. But they do not improve privacy in 75% of the cases.

I understand that privacy-warriors can use VPN, proxies or Tor. But
these tools are far from perfect -- see the recent Sybil attacks against
Tor, or the outveiling of shady business practices by many VPNs. In any
case, these tools at best provide "privacy for a few active users". But
that leaves aside the bulk of Internet users. Thus my question for this
program: how would we provide privacy for the masses?

-- Christian Huitema