Subject: [Gen-art] Gen-ART Telechat review of draft-ietf-hip-rfc4843-bis-06

From: Suresh Krishnan <[email-masked]>
Date: Wed, 25 Jun 2014 00:02:01 +0000

I have been selected as the General Area Review Team (Gen-ART)
reviewerfor this draft (for background on Gen-ART, please see

http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html).

Please wait for direction from your document shepherd or AD before

posting a new version of the draft.

Document: draft-ietf-hip-rfc4843-bis-06.txt

Reviewer: Suresh Krishnan

Review Date: 2014/06/24

IESG Telechat date: 2014/06/26

Summary: This draft is almost ready for publication as a Proposed
Standard but I have a comment you might wish to address.

* Section 2

The Encode_96 function mentions that the output is obtained by
"extracting the middle 96-bit long bitstring" from the argument. This
seems to be in conflct with Appendix E of RFC5201bis where the HIT suite
3 recommends truncation of the hash to 96 bits. Shouldn't this just be a
truncation function?

Thanks

Suresh

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From: Francis Dupont <[email-masked]>
Date: Wed, 25 Jun 2014 08:24:30 +0000

Suresh Krishnan writes:

> seems to be in conflict with Appendix E of RFC5201bis where the HIT suite

=> Encode_96 is a truncation function because it takes a continuous
part of the input, or with other words truncated allows to truncate
one at one end, or twice. I agree it is not the usual/default truncation
function which takes the first bits. So IMHO there is no conflict,
even one can argue RFC5201bis is not enough accurate. (*)

BTW all truncation functions are not really equivalent from a
crypto point of view but in this particular use case it doesn't matter.

To finish the Orchid v1 (RFC4843) uses an Encode_100 with the middle
100 bits.

Regards

Francis Dupont <[email-masked]>

PS (*): RFC5201bis misses the 128 bit Context ID in the hash input
so there is already a conflict.

PPS for Julien: at line 289
OLD
 ORCHID     :=  Prefix | Encode_96( Hash )
NEW
 ORCHID     :=  Prefix | OGA ID | Encode_96( Hash )

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From: Julien Laganier <[email-masked]>
Date: Wed, 25 Jun 2014 08:03:50 -0700

> ORCHID     :=  Prefix | OGA ID | Encode_96( Hash )

Oh! That’s quite a mistake, this has been introduced while rebuilding the XML by hand earlier end of last year… Will need to fix this ASAP. Thanks for catching this, Francis!

—julien

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From: Suresh Krishnan <[email-masked]>
Date: Thu, 26 Jun 2014 04:16:57 +0000

Hi Francis,

> even one can argue RFC5201bis is not enough accurate. (*)

Great. Thanks for the clarification. Glad this issue in RFC5201bis is
identified now :-). I brought up the comment because extracting bits
from the middle of the input was not exactly my first instinctive choice
when I read "truncated to 96 bits" in RFC5201bis.

Thanks
Suresh