[CentOS] Squid and HTTPS interception on CentOS 7 ?

Mon Mar 5 14:34:23 UTC 2018
Bill Gee <bgee at campercaver.net>

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.  

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 

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.

Bill Gee