[trill] Eric Rescorla's Discuss on draft-ietf-trill-over-ip-15: (with DISCUSS and COMMENT)

Eric Rescorla <ekr@rtfm.com> Sun, 18 March 2018 08:56 UTC

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From: Eric Rescorla <ekr@rtfm.com>
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Date: Sun, 18 Mar 2018 01:56:05 -0700
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Subject: [trill] Eric Rescorla's Discuss on draft-ietf-trill-over-ip-15: (with DISCUSS and COMMENT)
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Eric Rescorla has entered the following ballot position for
draft-ietf-trill-over-ip-15: Discuss

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DISCUSS:
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Hopefully this is easy to resolve. In the best case, you will be
able to demonstrate that this is not a problem in practice and
document that. If not, the actual fix is straightforward, though
incompatible.

S 7.1.1.
I am concerned about the use of the IS-IS key in this way. First, on
general principles, you should not use a single key both as input to a
KDF and directly as a working key. Specifically, however, RFC 5310
defines the use of HMAC authentication with IS-IS-key as the HMAC
key, and HKDF-Expand is really just SHA-256. Thus, if an attacker
was able to observe (or cause to be created) an IS-IS packet that
happened to have the same contents as the HKDF Info value you
provide would then know the IKE PSK.

The correct practice here is to separately expand both the IS-IS
key *and* the IKE PSK from the same original value. If you cannot
do that, you should at least generate an Info value which is
guaranteed to not be the input to any RFC 5310 MAC.

   When IS-IS security is in use, IKEv2 SHOULD use a pre-shared key that
   incorporates the IS-IS shared key in order to bind the TRILL data
   session to the IS-IS session.  The pre-shared key that will be used

The technique you provide does not guarantee a binding between the
sessions. It merely ensures (modulo the caveat above) that both sides
know the IS-IS Key. It's easy to see this by noting that you could
move IS-IS traffic from one IPsec association to another. If you
actually want to bind these sessions, you must do something different.


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COMMENT:
----------------------------------------------------------------------

I see that native encapsulation is incompatible with NATs (S 8).
That's probably worth stating upfront to minimize confusion.

S 5.4.2.

      f. No middleboxes are allowed in the TRILL over IP transport link
         because middlebox support is beyond the scope of this document.

How would you know if no middleboxes were in the link?

S 5.5.
Can you use VXLAN with IPsec?

S 5.6.
What security mechanism do you expect to use for TCP? IPsec again?

   the timing and implementation details may be such that P! and P2 each

Nit: P1, right?