Re: [pkix] How do we differentiate authentic servers from proxies performing TLS interception?

Jeffrey Walton <> Mon, 16 November 2015 03:54 UTC

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Date: Sun, 15 Nov 2015 22:54:03 -0500
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From: Jeffrey Walton <>
To: "Miller, Timothy J." <>
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Subject: Re: [pkix] How do we differentiate authentic servers from proxies performing TLS interception?
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> No certificate marking is needed, though.  Clients could invoke alternative certificate processing when a certificate name match fails but the certificate chains to a trust anchor marked as "trusted for proxy."
You will have to forgive my ignorance... For user agents and other
software that conforms to RFC 7469 and provides the overrides, how are
they supposed to know when to break a known good pinset if its not
signaled? That is, how do they differentiate between the "good" bad
guys and the "bad" bad guys.


  Corporate DLP - ACME, LLC sets Proxy key usage for subordinate
      and server certificate. User agent allows an override to the Pinset
      in accordance with RFC 7469 because they declared the intent and
      confirmed with the user.

  Diginotar - Bad guy starts minting server certificates. Proxy is
      not set in subordinate CA or server certificate. The user agent
      refuses to break the known good pinset according to RFC 7469.

And RFC's 7469 {SHOULD NOT|MUST NOT} logging requirement can be lifted
or refined so the failures can be reported instead of making user
agents complicit in the cover-up.

RFC 7469's overrides opened a can of worms, but its probably best in
the big picture. This stuff has always been going on and allowed to
fester behind the scenes in a "don't ask don't tell" fashion. Now that
its been brought to the fore-front, it can be dealt with accordingly.