Subject: [Hipsec] Roman Danyliw's Discuss on draft-ietf-hip-dex-13: (with DISCUSS and COMMENT)

From: Roman Danyliw via Datatracker <[email-masked]>
Date: Wed, 04 Mar 2020 10:28:46 -0800

Roman Danyliw has entered the following ballot position for
draft-ietf-hip-dex-13: Discuss

When responding, please keep the subject line intact and reply to all
email addresses included in the To and CC lines. (Feel free to cut this
introductory paragraph, however.)

Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
for more information about IESG DISCUSS and COMMENT positions.

The document, along with other ballot positions, can be found here:
https://datatracker.ietf.org/doc/draft-ietf-hip-dex/

----------------------------------------------------------------------
DISCUSS:
----------------------------------------------------------------------

(initial ballot now that this draft is deferred)

** Section 1.2.  Thanks for the scoping provided by this applicability
statement.  Given the reduced security that DEX will provide, IMO it needs a
bit more precision (and caution).

OLD
   HIP DEX MUST  only be used in communicating with such constrained
   devices (e.g., class 0 and 1 devices as defined in section 3 in
   [RFC7228]).

NEW

HIP DEX MUST only be used when one of the peers is a class 0 or 1 constrained
device as defined in Section 3 of [RFC7228].  HIP DEX MUST NOT be used if both
peers are class 2 constrained devices or have greater capability.

** Section 3.2.1, Per “Since collision-resistance is not possible with the
tools at hand, any reasonable function (e.g.  FOLD) that takes the full value
of the HI into generating the HIT can be used, provided that collision
detection is part of the HIP-DEX deployment design.  This is achieved here
through either an ACL or some other lookup process that externally binds the
HIT and HI.”, when exactly should this ACL lookup occur?  Please provide
guidance in an explicit step in the appropriate packet processing section
(i.e., in Section 6.*) on when this should be.

** Section 5.2.1 – Is this list of DH Group IDs intended to be a subset of the
HIP Group ID sub-registry?  If so, Curve25519 and Curve448 don’t appear to be
in the
https://www.iana.org/assignments/hip-parameters/hip-parameters.xhtml#hip-parameters-5?
 Should they be registered?

** Section 6.3.  Per “Some payload protection mechanisms have their own Key
Derivation Function, and if so this mechanism SHOULD be used.”, if the payload
protection mechanisms have their own KDF, how would their security properties
be trusted if their KDF is NOT used?  Why is this SHOULD not a MUST?

** Section 6.3.  The input to CKDR-Extract seems underspecified:
-- Per the definition of IKM, when should these different inputs be used (at
least two appear to be specified)?  References to Kij are made in this section
and in other parts of the document, but they aren’t input for CKDR-Extract()?

-- Per “where ‘CKDF-Extract’ is an octet string “ in the definition of “info”
in CKDR-Extract(), what encoding should be used to convert that into an octet
string?  Is it ASCII, as in 067 075 068 070 045 069 120 116 114 097 099 116?

** Section 9.  Please add language to the effect that “production deployments
of this specification MUST NOT use the NULL-ENCRYPT HIP_CIPHER” (to mirror the
language already stated in Section 5.2.2 on the topic).

** Section 9.2.  This mandatory guidance to validate public keys is helpful. 
Please provide guidance in an explicit step in the appropriate packet
processing section (i.e., in Section 6.*) on when this should be done.

Two “discuss discuss”-es with the caveat that I didn’t follow the WG
discussions.

** The following seems to indicate we don’t have everything we need to publish
a standards track document: -- Section 6.  “It should be noted that many of the
packet processing rules are denoted here with "SHOULD" but may be updated to
"MUST" when further implementation experience provides better guidance.”

-- Section 9.  “o  The puzzle mechanism using CMAC explained in Section 4.1.1
may need further study regarding the level of difficulty in order to establish
best practices with current generation of  constrained devices.”

If there isn’t sufficient implementation experience, why isn’t this document
experimental?  What is the plan for getting better guidance?  Is there a risk
in not having this clarity?

** Section 9.1.  Thanks for this section.  However, I’m not convinced that
SECP160R1 is needed.  DEX is already selectively profiling RFC7401 (i.e., its
already choosing to exclude certain things) and there are “no production”
implementation of DEX.  What is the rationale for keeping it?

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

** Section 3.0.  Per “Thus, it is not expected that these parameters are
carried in every packet, but other methods are used to map the data packets to
the corresponding His”, what are these other methods?

** Section 3.1.  Per “There are two advantages of using a hashed encoding  over
the actual variable-sized public key in protocols.”, perhaps as a reminder is
in order that in this document the HIT isn’t a hashed encoding but a compressed.

** Section 4.1.  Per “Note that in some cases it may be possible to replace
this trigger packet by some  other form of a trigger, in which case the
protocol starts with the Responder sending the R1 packet.”, how does this
additional trigger occur?

** Section 4.1. Per “In such cases, another mechanism to convey the Initiator's
supported DH Groups (e.g., by using a default group) must be specified.”,
where/how would it be specified?

** Section 4.1.2.1. Per “This strategy is based on a timeout that is set to a
value larger than the worst-case anticipated round-trip time (RTT ).”, how is
the worst case RTT computed?

** Section 5.3.2.  Per “Responder sets the source HIT in the R2 packet based on
the destination HIT from the I1 packet”, shouldn’t this say “Responder sets the
source HIT in the _R1_ packet …”?

** Section 5.3.2.  Per “Based on the deviating DH group ID in the HOST_ID
parameter, the Initiator then SHOULD abort …”, why not MUST abort?

** Section 6.8. Step 5.  Per “5.  If any of the checks above fail, there is a
high probability of an ongoing man-in-the-middle or other security attack.  The
system SHOULD act accordingly, based on its local policy.”, this guidance seems
underspecified.  Could the text at least provide a recommendation of aborting
and logging?

** Section 9.  Per “The strength of the keys for the Pair-wise Key SA is based
on the quality of the random keying material.  As either peer may be a sensor
or an actuator device, there is a natural concern about the quality of its
random number generator.”, this is helpful caution. What guidance can be given
to ameliorate the concern?

** Editorial
-- Section 1.2.  The sentence “Also, it is often the case that HIP DEX …” is
repeated twice.

-- Section 4.1. s/the the/the/

-- Section 6.3.  Typo.
s/The HIP DEX KEYMAT process is based on the is the/
The HIP DEX KEYMAT process is based on the/

-- Section 9.2.  Editorial.  Per “With the curves specified here, there is a
straightforward key extraction attack, which is a very serious problem the use
of static keys in HIP-DEX”, there appears to be some missing words – perhaps “…
with the use of static keys by HIP-DEX”.