SSL Certificate Question

Alan DeKok aland at
Wed Jul 9 01:36:01 CEST 2014

Charles Plater wrote:
> Many moons ago, i set up a FreeRadius server as part of our 802.1x / WPA project. At that time, I asked this list about using a commercially signed SSL certificate as opposed to a self signed certificate. I’m not sure I understood all of the reasons, but I was advised by another member of this list to use a self signed certificate. Fast forward 6 years to today, and our management is convinced that problems we are seeing w/ clients having problems connecting are related to the self signed SSL certificate.

  It would help to describe *what* problems you're seeing.

> Could someone please describe to me the reasoning behind using a self signed certificate with on with FreeRadius? What kinds of problems / vulnerabilities will we be exposed to if we use a commercially signed (DigiCert) SSL certificate?

  Let's start off by talking about HTTPS.  When your browser connects to
an HTTPS web site, it has (largely) three pieces of information.  (1)
the domain name it's connecting to.  (2) the certificate of the site in
question.  And (3) the rest of the certificates to the CA root.

  (1) is where you want to go.  But you don't know if the place you
ended up is "really" the web site in question.

  (2) is a certificate which contains the domain name from (1).  This
lets you know you're connected to a site which is claiming to be (1).

  (3) lets you know that everyone ELSE agrees that the site in (1) and
the certificate in (2) really are the same thing.

  In WiFi, there is domain name, because you don't have network access
yet.  You have an SSID.  But the certificate being presented isn't
checked against the SSID.  This is because you may be roaming, which
means that multiple SSIDs may end up at the same server + certificate.

  If you use a "well known" cert from a CA root, all you know is that
the CA handed out the cert to... someone.  You can't check it against
the SSID as with (1) above.  You can't check that the certificate has
the "domain" information as with (2) above.  So the certificate gives
*no* information about the identity of the server.

  It might *look*  like it's giving you information about the server.
But you can't trust the certificate, because you can't verify it against
anything else.  And because the certificate is signed by a "well known"
CA, then *anyone* on the planet can claim to be a server, and you have
no idea who they really are.

  Using a self-signed certificate is more problematic to set up for the
end-users.  They have to get the CA cert, etc. onto their machines.  But
it's MUCH more secure.  When the end user connects to a system present a
certificate signed by that CA, you're sure that YOU are the only person
the planet capable of creating such a certificate.

  Which means the end user is sure that they're connecting to YOUR site,
and not to some random strangers site.

  Alan DeKok.

More information about the Freeradius-Users mailing list