I am cutting off all I have responded to in v 14 & 15.
I have posted ver 16.
there is one outstanding issue about the proper octet encoding, see
below. I am open to what to use for that.
Otherwise, I believe I have addressed all of Roman's comments either
with changes to the draft of explanations in my email responses.
On 3/6/20 9:21 AM, Robert Moskowitz wrote:
On 3/4/20 1:28 PM, Roman Danyliw via Datatracker wrote:
Roman Danyliw has entered the following ballot position for
draft-ietf-hip-dex-13: Discuss
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DISCUSS:
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(initial ballot now that this draft is deferred)
** 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()?
Will research this and see if more text is needed and how.
KEYMAT is used for both the Master Key and Pair-wise Key.
The key derivation for the Master Key SA employs always both the
Extract and Expand phases. The Pair-wise Key SA needs only the
Extract phase when the key is smaller or equal to 128 bits, but
otherwise requires also the Expand phase.
So there are 2 IKMs:
IKM Input keying material
the Diffie-Hellman derived key, concatenated with the
random I_NONCE value for the Master Key SA
the Diffie-Hellman derived key, concatenated with the
random values of the ENCRYPTED_KEY parameters in
the same order as the HITs with sort(HIT-I | HIT-R)
for the Pair-wise Key SA
If you want the IKM better explained, I will expand the text somehow.
This is in an artwork block right now.
And yes, Kij is used in both places. This is the result of extensive
discussions with Hugo Krawczyk and Lily Chen on how to safely use CMAC.
Or as safe as possible and within the bounds of this application. Those
discussions are somewhere back in my archives...
-- 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?
Will check this too.
This approach I have historically seen a lot in standards. The
character string is supplied with the instruction to use the octet
equiv. You make a very valid point. In fact NIST SP800-185 is very
explicit in supplying the text string and then the bit representation.
Using an online text to octet converter
(https://www.browserling.com/tools/text-to-octal) I got:
103 113 104 106 55 105 170 164 162 141 143 164
So WHAT IS the proper value? Can an Implementer jump in here? I will
specify whatever binary is agreed on...
** 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).
Good point. Will do.
Done. See sec 9.3
** 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.
I thought I did. Grumble. Will take care of this too.
Done. Sec 6.7 step 4 and 6.8 step 5.
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.”
I did not want this, if I recall correctly. It was something of a
standard wording back when this was first done. At this point, I will
pull this. It is not uncommon that a standard goes out and then some
years later deployment teaches us things about what SHOULD and what MUST.
I have pulled this para.
-- 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?
Actually this is another area that can be pulled now. Rene did
testing on the difficulty and I believe we captured his experiences.
I will look at this and clarify.
I have dropped this paragraph. The proper behavior, based on testing,
is described in sec 7. This was old text that should have been pulled
versions ago.
** 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?
In the workgroup I was asked to keep it in? To /harmonize/ with other
areas of constrained security? This is some years back though, and it
is another area where by this time, we have enough to drop it? I am
willing to, but I should ask on the HIPSEC list and see what private
replies I get.
I have removed SECP160R1. I have kept the text as comments in the XML
if there is later pushback for including it.
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COMMENT:
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** 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?
This text is lifted right out of sec 3 of rfc7401. ESP SPIs are a
stated example further in that paragraph.
** 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.
A case of lifting text from 7401 where it needs to be adjusted a bit.
I will make the change.
Change made.
** 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?
Some packet that has enough information for the receiver to deduce
that an I1 COULD have been sent and to then respond with an R1 to see
if the sender supports HIP.
None have been defined. This actually goes back to 5201. More of a
placeholder to allow others to make adjustments in their implementation.
** 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?
Again, nothing has been specified, but in a closed environment it was
thought that an ACL or other data store would contain enough
information, like the supported DH Groups to successfully trigger an
R1 without receiving an I1. This is more a placeholder for any
developer that is working on an alternative to using the I1 to note
all that must be done if something other than an I1 is used.
"If you are going to try and optimize this protocol, remember all that
you have to include" kind of thing.
** 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?
IIRC, the implementers want this in. It goes back to 5201, sec 6.6.
Perhaps one that is still around (hint, Jeff or Tom) can comment.
I am leaving this as is. I am open to changes, if someone provides me
with actual numbers.
** 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?
A MUST costs a round trip. It is possible that the Initiator, based
on local policy, can make a decision to go with the received R1 rather
than restart the exchange. Thus we chose SHOULD here over MUST.
** 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?
Seems reasonable request. But this text goes back to 5201. Perhaps
some of the HIPv1 and/or v2 implementors can tell want they do here.
** 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?
When we did IEEE 802.11i, we actually had an annex giving pseudo code
for gathering entropy by listening to the radio noise or how to build
an ring-occilator on your chip.
Is there any good IETF RFC recommendation on a good RND for
constrained devices? I would be happy to include copied text or a
reference.
Additional text has been added.
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