[cryptography] really sub-CAs for MitM deep packet inspectors? (Re: Auditable CAs)

Peter Gutmann pgut001 at cs.auckland.ac.nz
Wed Nov 30 23:02:42 EST 2011

Adam Back <adam at cypherspace.org> writes:

>Are there really any CAs which issue sub-CA for "deep packet inspection" aka
>doing MitM and issue certs on the fly for everything going through them:
>gmail, hotmail, online banking etc.
>Do blue coat and other MitM proxies mentioned on this list recently actually
>support on the fly cert generation and putting a CA cert in there?

It's a documented feature of a number of products that support this, see e.g.

  In the Client DPI-SSL scenario, the SonicWALL UTM appliance typically does
  not own the certificates and private keys for the content it is inspecting.
  After the appliance performs DPI-SSL inspection, it re-writes the
  certificate sent by the remote server and signs this newly generated
  certificate with the certificate specified in the Client DPI-SSL
  configuration. By default, this is the SonicWALL certificate authority (CA)
  certificate, or a different certificate can be specified.

See my earlier message about my interest in getting samples of these MITM cert
chains when they're signed by CAs that chain up to public roots.  With the
SonicWall boxes you don't get that (unless you install your own CA cert in
there), but possibly someone like Boingo does it.

(Oh, and this also answers my earlier question of how they get the cert
details for the remote system if they don't know the FQDN that was used to
access it, all they need to do is pull them out of the genuine cert).


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