[secdir] Updated secdir review of draft-ietf-emu-chbind-15.txt

Stephen Hanna <shanna@juniper.net> Fri, 18 May 2012 22:10 UTC

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From: Stephen Hanna <shanna@juniper.net>
To: Sam Hartman <hartmans-ietf@mit.edu>, "emu@ietf.org" <emu@ietf.org>
Date: Fri, 18 May 2012 18:10:19 -0400
Thread-Topic: Updated secdir review of draft-ietf-emu-chbind-15.txt
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Subject: [secdir] Updated secdir review of draft-ietf-emu-chbind-15.txt
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The changes in draft-ietf-emu-chbind-15.txt satisfactorily address
almost all of the comments in my April 13, 2012 secdir review. I do
have one remaining substantive comment on this latest draft and two
non-substantive ones.

Substantive Comment

The last paragraph of section 9.1 points out a security problem
with implementing channel bindings using EAP tunnel methods. If
the EAP tunnel method terminates on the authenticator, the channel
bindings can easily be defeated by the authenticator. While that's
true, nobody terminates the EAP tunnel method on the authenticator
today. In the EAP model, the authenticator is not trusted so
terminating the EAP tunnel method on the authenticator is a bad
idea for many reasons. For example, the authenticator would then
have the ability to bypass protected result indications and to
bypass all the cryptographic protections provided by the tunnel.
Sometimes there is value in having the inner and outer methods
terminate on different servers but both servers must be trusted.
The authenticator is not. So there is no big security hole here,
unless you have already opened an enormous security hole. It's
ironic that this document which attempts to close vulnerabilities
caused by malicious authenticators ends up subtly suggesting that
people open a much larger vulnerability!

I would recommend deleting the end of this paragraph, starting
with the sentence that starts "Even when cryptographic binding".
If you choose to keep this strange text, I suggest that you at
least note that terminating an EAP tunnel method on the
authenticator is unusual. For example, you could add a
parenthetical comment like "(rare)" after the clause "if the
outer method tunnel terminates on the authenticator".

Non-Substantive Comments

In the first paragraph of section 3, an extraneous numeral 3 was
somehow added to the end of the second sentence.

T. Charles Clancy's address in the Authors' Addresses section
now reads:

   T. Charles Clancy
   Virginia Tech
   Virginia Tech
   Arlington, VA  22203

The duplication of Virginia Tech should be removed from
this address.

I appreciate the hard work of the document editors to address
my many earlier comments. I hope that these new comments will
also be useful.