Subject: [dnsext] [Errata Verified] RFC4034 (4552)

From: RFC Errata System <[email-masked]>
Date: Mon, 14 Dec 2015 07:08:51 -0800 (PST)

The following errata report has been verified for RFC4034,
"Resource Records for the DNS Security Extensions". 

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You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=4034&eid=4552

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Status: Verified
Type: Technical

Reported by: Ben Laurie <[email-masked]>
Date Reported: 2015-12-04
Verified by: Brian Haberman (IESG)

Section: Appendix B

Original Text
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These groups are then added together, ignoring any carry bits.

Corrected Text
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These groups are then added together with at least 32-bit precision,
retaining any carry bits.
The carry bits are then added to the result, and finally, only the lower
16 bits of the result are used as the key tag. Note that this means any
carries generated during the addition of the carry bits are ignored.
This, in turn, means that the keytag calculation is often the same as
reduction modulo 65535, but not always.

Notes
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Errata 2681 already proposes a fix to Appendix B, however the proposed fix is not quite clear. The first part of the corrected text is from 2681.

Its worth pointing this out because a naive analysis says in fact the keytag is exactly the same as reduction modulo 65535, and this has already wasted a fair amount of time.

It is also worth pointing out, perhaps, that this is a poor choice of algorithm for this particular application as it interacts badly with the properties of keys.

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RFC4034 (draft-ietf-dnsext-dnssec-records-11)
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Title               : Resource Records for the DNS Security Extensions
Publication Date    : March 2005
Author(s)           : R. Arends, R. Austein, M. Larson, D. Massey, S. Rose
Category            : PROPOSED STANDARD
Source              : DNS Extensions
Area                : Internet
Stream              : IETF
Verifying Party     : IESG