Re: [Gen-art] Genart last call review of draft-ietf-perc-double-10

Richard Barnes <rlb@ipv.sx> Wed, 19 December 2018 16:46 UTC

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From: Richard Barnes <rlb@ipv.sx>
Date: Wed, 19 Dec 2018 11:46:12 -0500
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To: Russ Housley <housley@vigilsec.com>
Cc: gen-art@ietf.org, perc@ietf.org, IETF discussion list <ietf@ietf.org>, draft-ietf-perc-double.all@ietf.org
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Subject: Re: [Gen-art] Genart last call review of draft-ietf-perc-double-10
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Thanks for the review, Russ.  Comments below (nothing major); pull request
here for your review:

https://github.com/ietf/perc-wg/pull/163

On Sat, Oct 20, 2018 at 4:24 AM Russ Housley <housley@vigilsec.com>; wrote:

> Reviewer: Russ Housley
> Review result: Almost Ready
>
> I am the assigned Gen-ART reviewer for this draft. The General Area
> Review Team (Gen-ART) reviews all IETF documents being processed
> by the IESG for the IETF Chair.  Please treat these comments just
> like any other last call comments.
>
> For more information, please see the FAQ at
> <http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>;.
>
> Document: draft-ietf-perc-double-10
> Reviewer: Russ Housley
> Review Date: 2018-10-20
> IETF LC End Date: 2018-11-01
> IESG Telechat date: unknown
>
> Summary: Almost Ready
>
>
> Major Concerns:
>
> Section 10: Doesn't the IANA registry needs to specify the PRF to be
> used with the ciphersuite as well?
>

I don't think so.  I don't see a slot in the relevant registry for that,
and the tabular summary in the IANA considerations section is really just a
courtesy.

https://www.iana.org/assignments/srtp-protection/srtp-protection.xhtml#srtp-protection-1


>
> Minor Concerns:
>
> Section 3: It would be useful to explain the Master Key before the
> reader gets to Section 3.1.
>

Note that the "master key" concept comes from SRTP.  I've added a bit of
text to clarify.



> Section 3.1: It is unclear what assistance is provided by the
> additional level of indirection:
>
>          PRF_double_n(k_master,x) = PRF_inner_(n/2)(k_master,x) ||
>                                     PRF_outer_(n/2)(k_master,x)
>
>          PRF_inner_n(k_master,x)  = PRF_n(inner(k_master),x)
>          PRF_outer_n(k_master,x)  = PRF_n(outer(k_master),x)
>
> It could just say:
>
>          PRF_double_n(k_master,x) = PRF_(n/2)(inner(k_master),x) ||
>                                     PRF_(n/2)(outer(k_master),x)
>

👍

Not sure what I was thinking.



> Section 4: I suggest:
>
>         If the marker bit is not present, then B MUST be set to zero.
>

👍


> Section 5, 1st paragraph: and endpoint cannot verify confidentiality.
>

Well, it can verify that the packet was encrypted with a key known only to
the endpoints.  But OK.


>
> Nits:
>
> The document uses "encryption" and "confidentiality" interchanagably.
> Encryption is a mechanism or algorithm.  Confidentiality is a security
> service.  While I do not think that the reader will be confused by the
> current wording, it would be better to use the terms properly.  In
> addition, it is misleading to say:
>
>    ... the receiving endpoint that can encrypt and authenticate ...
>
> because the sending endpoint encrypts, and the recieving endpoints
> decrypts.  Also, the receiving endpoints check the authentication tag.
>

That's actually just some bad grammar.  Reworded.



> Abstract: s/authenticated encryption with associated data/
>            /authenticated encryption with associated data (AEAD)/
>
> Abstract: s/scheme/algorithm/
>
> Section 5.2: s/GCM/AES-GCM/
>
> Section 7: s/HBH/hop-by-hop/
>
> Section 7: s/E2E/end-to-end/
>
> Section 7.1: s/HBH/hop-by-hop/
>
> Section 7.2: The text is redundant.  I suggest "etc" be dropped from
> "such as SSRC, SEQ, CSRC, etc"
>
> Section 7.2: s/non primary/non-primary/
>
> Section 7.3: s/HBH/hop-by-hop/
>

Implemented all of the above...


> Appendix A: s/HBH/hop-by-hop/
>
> Appendix A: s/E2E/end-to-end/
>

... but I'm going to leave these last two as-is, for brevity.