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DKIM Working Group                                          M. Kucherawy
Internet-Draft                                                 Cloudmark
Intended status: Informational                           August 17, 2010
Expires: February 18, 2011


                     RFC4871 Implementation Report
                draft-ietf-dkim-implementation-report-00

Abstract

   This document contains an implementation report for the IESG covering
   DKIM in support of the advancement of that specification along the
   Standards Track.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on February 18, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.





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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  DKIM Interoperability Event  . . . . . . . . . . . . . . . . .  5
     3.1.  Participants . . . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Testing Methodology  . . . . . . . . . . . . . . . . . . .  5
     3.3.  Observations . . . . . . . . . . . . . . . . . . . . . . .  5
     3.4.  Results  . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  Collected DKIM Interoperability and Use Data . . . . . . . . .  7
     4.1.  The OpenDKIM Project . . . . . . . . . . . . . . . . . . .  7
       4.1.1.  Details  . . . . . . . . . . . . . . . . . . . . . . .  7
       4.1.2.  Results  . . . . . . . . . . . . . . . . . . . . . . .  7
       4.1.3.  Conclusions  . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Other Collected Data . . . . . . . . . . . . . . . . . . .  9
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 12
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13






























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1.  Introduction

   [DKIM], published in May 2007, has reached a level of maturity
   sufficient to consider its advancement along the standards track.
   Enclosed is a summary of collected interoperability data provided
   from sources that are aggregating such information as well as from a
   more formal DKIM interoperability event that took place in October
   2007.











































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2.  Definitions

   Various terms specific to email are used in this document.  Their
   definitions and further discussion can be found in [EMAIL-ARCH].















































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3.  DKIM Interoperability Event

   In October 2007, Alt-N Technologies of Dallas, Texas hosted an
   interoperability and testing event at their headquarters.  Twenty
   organizations sent engineers and their various DKIM implementations
   to connect to a private internal network and exchange test messages
   and tabulate observed results.

3.1.  Participants

   The interoperability event included participants from all of the
   following organizations: Alt-N Technologies, AOL, AT&T Inc., Bizanga
   Ltd., Brandenburg InternetWorking, Brandmail Solutions, ColdSpark,
   Constant Contact, Inc., DKIMproxy, Domain Assurance Council, Google
   Inc., ICONIX Inc., Internet Initiative Japan (IIJ), Ironport Systems,
   Message Systems, Port25 Solutions, Postfix, Sendmail, Inc.,
   StrongMail Systems, and Yahoo!  Inc. Most of the participants
   traveled to Dallas and participated in person, but a few operated
   remotely.

   Nearly all of the implementations were based on disjoint code
   development projects.  A few were based on a common open source base
   project.

3.2.  Testing Methodology

   Participants were encouraged before the event to craft a set of test
   messages meant to exercise their own implementations as well as those
   of the other participants, both in terms of successful verifications
   as well as some expected to fail.  Some test cases were developed
   with the intent of confounding verifiers that may not have
   implemented the [ABNF] of [DKIM] correctly.

   The participants set up Mail Transfer Agents (MTAs) equipped with
   their own DKIM signing and verifying modules, and their own tools to
   generate mail to be signed along with tools to analyze the results
   post-verification.  They then sent their own batteries of test
   messages, looking for both expected and unexpected failures in
   response.  Some implementations included "auto-responders" that would
   reply with verification results, while others simply collected the
   results that would then be shared manually.

3.3.  Observations

   All of the implementations implemented all of the required portions
   of [DKIM] in terms of both signature and key features.  Most of the
   implementations implemented all of the optional features of both
   signatures and keys.  There were no notable or common exceptions.



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   The interoperability testing was largely successful.  As might be
   expected, there were many verification false negatives or false
   positives that were the result of bugs in corner cases of some of the
   implementations presented for testing.  In such cases the developers
   were able to identify the issue as resulting from their own mis-
   reading of the specification and not an error in the specification
   itself.

   Several of the failures did occur as a result of specification
   ambiguities.  The participants discussed each of these in turn and
   were able to come to consensus on how they believed the specification
   should be changed to resolve them.

3.4.  Results

   The handful of interoperability issues described above that referred
   to weaknesses or ambiguities in [DKIM] resulted in several errata
   being opened via the RFC Editor web site.  These are being addressed
   in an RFC4871bis draft effort that is now starting from within the
   DKIM working group.































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4.  Collected DKIM Interoperability and Use Data

   Several implementations are collecting private data about DKIM use,
   signature survivability, which properties of the base specification
   are observed in public use, etc.  This section includes collection
   methods and summary reports provided by those implementations.

4.1.  The OpenDKIM Project

   The OpenDKIM Project is an open source project providing a DKIM
   support library, an email filter for use with MTAs, and a set of
   tools to assist with deployment of DKIM.

4.1.1.  Details

   Recent releases have included an optional feature to record
   statistics about messages with and without DKIM signatures.  Sites
   enabling this feature can choose to share the data with the project's
   development team as part of this interoperability report work.  The
   data can be anonymized to conceal the sending domain and client IP
   addresses, though these data are passed through a one-way hash to
   enable collation of data from common sources.

4.1.2.  Results

   At the time of writing of this document, the results of this effort
   are as follows:

   Reporting Hosts:  11 individual MTAs representing seven distinct
      ADMDs

   Total Messages:  111101

   Signatures:  80984 messages (72.9%) were not signed; 29663 (26.7%)
      had one signature; 419 (0.3%) had two signatures; the remainder
      (less than 0.04%) had more

   Signing Algorithms:  58.5% of signatures used "rsa-sha1", while the
      balance used "rsa-sha256"

   Header Canonicalization Algorithms:  31.3% of signatures used
      "simple", while the balance used "relaxed"

   Body Canonicalization Algorithms:  38.6% of signatures used "simple",
      while the balance used "relaxed"






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   Keys in Test Mode:  46% of keys retrieved from the DNS were tagged as
      being in test mode

   Keys with Syntax Errors:  0.1% of keys retrieved from the DNS had
      syntax errors

   Missing Keys:  1.4% of signatures received referenced keys that were
      not found in the DNS

   Optional Signature Tags:  Of the optional signature tags supported by
      the base specification, "t=" was seen 45.7% of the time (0.4% of
      which included timestamps in the future, even after forgiving some
      clock drift); "x=" was seen 4.6% of the time; "l=" was seen 3.3%
      of the time; "z=" was seen 3.0% of the time.

   Body Length Limits:  Of the signatures for which "l=" was used, 76.1%
      of them had the body extended after signing.

   Signature Pass Rates:  Overall, 72.7% of observed signatures were
      successfully verified.

   Pass Rates for Non-List Mail:  Where "list mail" is defined as any
      mail not bearing one of the header fields defined in [LIST-ID] or
      in [LIST-URLS], or a "Precedence: list" field, selecting only for
      mail that is not list mail revealed a successful verification rate
      of 92.5%; selecting only for list mail produced a 54.3% success
      rate.

   Author vs. Third-Party:  75.2% of the signatures observed were author
      signatures, meaning the "d=" value in the signature matched the
      domain found in the From: header field.  The remainder, therefore,
      were third-party signatures.

4.1.3.  Conclusions

   The results of the OpenDKIM work are updated constantly as more data
   feeds come online and more data are reported.  Based on the data
   available at the time of writing, some conclusions are possible.

   At least some implementations of all of the optional signature
   features, all of the canonicalization combinations and all of the
   signing algorithms are in general use.  None of the features had zero
   use counts.

   The current collection implementation did not collect data about
   optional features of keys that are in use.  A future version will
   address this.




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   Overall signature pass rates are generally quite high, except for
   cases where the mail passes through a mailing list.  In that case
   almost half of the signatures are invalidated.  (Earlier snapshots of
   data in this effort showed this figure to be even higher.)  It
   follows that for DKIM to be successful, increased co-operation with
   MLMs is desirable.  The working group has already started work on an
   informational draft discussing use of DKIM with respect to MLMs, and
   it would seem these data support the importance of completing that
   work.

4.2.  Other Collected Data

   [Summaries of data collected and reported by other sources can go
   here.]





































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5.  Security Considerations

   This document is an implementation report and thus has no security
   considerations.















































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6.  References

6.1.  Normative References

   [DKIM]     Allman, E., Callas, J., Delany, M., Libbey, M., Fenton,
              J., and M. Thomas, "DomainKeys Identified Mail (DKIM)
              Signatures", RFC 4871, May 2007.

6.2.  Informative References

   [ABNF]     Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", RFC 5234, January 2008.

   [EMAIL-ARCH]
              Crocker, D., "Internet Mail Architecture", RFC 5598,
              July 2009.

   [LIST-ID]  Chandhok, R. and G. Wenger, "List-Id: A Structured Field
              and Namespace for the Identification of Mailing Lists",
              RFC 2919, March 2001.

   [LIST-URLS]
              Neufeld, G. and J. Baer, "The Use of URLs as Meta-Syntax
              for Core Mail List Commands and their Transport through
              Message Header Fields", RFC 2369, July 1998.


























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Appendix A.  Acknowledgements

   The author wishes to acknowledge the following for their review and
   constructive criticism of this document: [names]

   The working group expresses its thanks to Alt-N Technologies for
   graciously hosting the 2007 DKIM interoperability event.












































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Author's Address

   Murray S. Kucherawy
   Cloudmark
   128 King St., 2nd Floor
   San Francisco, CA  94107
   US

   Phone: +1 415 946 3800
   Email: msk@cloudmark.com









































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