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

"Miller, Timothy J." <tmiller@mitre.org> Tue, 17 November 2015 04:33 UTC

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From: "Miller, Timothy J." <tmiller@mitre.org>
To: "noloader@gmail.com" <noloader@gmail.com>
Thread-Topic: [pkix] How do we differentiate authentic servers from proxies performing TLS interception?
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Date: Tue, 17 Nov 2015 04:33:08 +0000
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Subject: Re: [pkix] How do we differentiate authentic servers from proxies performing TLS interception?
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> 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.

That would be a user agent problem, solved by user agent configuration.  

E.g., Microsoft has an extensive set of permissions associated with each trust anchor (in the certificates mmc snap-in, drill down to a root cert, right-click Properties, and you'll see them on the General tab).  "Trusted MitM" could be added to that set.  

Should I point out the obvious here--that list is MUCH longer than the list of KUs and EKUs put together, yet MS doesn't come looking for a new extension every time they want to restrict use.

I also find it odd that advocates for this extension are uncomfortable with the idea of any active MitM, but are perfectly OK with a commercial issuer controlling whether or not your client accepts a cert they issue for active MitM purposes.

If you're going to require UA configuration to accept the active MitM, then it's far easier to mark the user agent's trust store than it is to add an optional extension to the certificate *AND* require the user agent to process, track, and add a UI for the user when it's found.

Take the path of least resistance (and smallest code change), people.

-- T