[CentOS] Squid and HTTPS interception on CentOS 7 ?

Mon Mar 5 16:04:29 UTC 2018
Valeri Galtsev <galtsev at kicp.uchicago.edu>

On 03/05/18 08:34, Bill Gee wrote:
> On Monday, March 5, 2018 7:23:53 AM CST Leon Fauster wrote:
>> Am 05.03.2018 um 13:04 schrieb Nicolas Kovacs <info at microlinux.fr>:
>>> Le 28/02/2018 à 22:23, Nicolas Kovacs a écrit :
>>>> So far, I've only been able to filter HTTP.
>>>> Do any of you do transparent HTTPS filtering ? Any suggestions,
>>>> advice, caveats, do's and don'ts ?
>>> After a week of trial and error, transparent HTTPS filtering works
>>> perfectly. I wrote a detailed blog article about it.
>>> https://blog.microlinux.fr/squid-https-centos/
>> I wonder if this works with all https enabled sites? Chrome has
>> capabilities hardcoded to check google certificates. Certificate
>> Transparency, HTTP Public Key Pinning, CAA DNS are also supporting
>> the end node to identify MITM. I hope that such setup will be unpractical
>> in the near future.
>> About your legal requirements; Weighing is what courts daily do. So,
>> such requirements are not asking you to destroy the integrity and
>> confidentiality >95% of users activity. Blocking Routing, DNS, IPs,
>> Ports are the way to go.
>> --
>> LF
> Although not really related to CentOS, I do have some thoughts on this.  I
> used to work in the IT department of a public library.  One of the big
> considerations at a library is patron privacy.  We went to great lengths to
> NOT record what web sites were visited by our patrons.  We also deny requests
> from anyone to find out what books a patron has checked out.

I bet, your servers never embedded links to anything external. If it is 
external link, it is requested to open in new browser window. No part of 
the page should need external (not living on our server) content. That 
was the way we did it since forever.

It sounds like I will have to fight soon against "google-analytics" 
glued into each page of our websites. It is amazing that people who have 
no knowledge rule technical aspects of IT in many places...


> The library is required by law to provide web filtering, mainly because we
> have public-use computers which are used by children.  For http this is easy.
> Https is, as this discussion reveals, a different animal.
> We started to set up a filter which would run directly on our router (Juniper
> SRX-series) using EWF software.  It quickly became apparent that any kind of
> https filtering requires a MITM attack.  We were basically decrypting the
> patron's web traffic on our router, then encrypting it again with a different
> cert.
> When we realized what it would take, we had a HUGE internal discussion about
> how to proceed.  Yeah, the lawyers were all over it!  In the end we decided to
> not attempt to filter https traffic except by whatever was not encrypted.
> Basically that means web site names.
> Our test case was the Playboy web site.  They are available on https, but they
> do not automatically redirect http to https.  If you open playboy [dot] com
> with no protocol specified, it goes over http.  Our existing filter blocked
> that.  However, if you open https[colon]// playboy [dot] com, it goes straight
> in.  The traffic never goes over http, so the filter on the router never
> processes it.
> Security by obscurity ...  It was the best we could do without violating our
> own policies on patron privacy.

Valeri Galtsev
Sr System Administrator
Department of Astronomy and Astrophysics
Kavli Institute for Cosmological Physics
University of Chicago
Phone: 773-702-4247