draft-ietf-dkim-implementation-report-00.txt   draft-ietf-dkim-implementation-report-01.txt 
DKIM Working Group M. Kucherawy DKIM Working Group M. Kucherawy
Internet-Draft Cloudmark Internet-Draft Cloudmark
Intended status: Informational August 17, 2010 Intended status: Informational September 29, 2010
Expires: February 18, 2011 Expires: April 2, 2011
RFC4871 Implementation Report RFC4871 Implementation Report
draft-ietf-dkim-implementation-report-00 draft-ietf-dkim-implementation-report-01
Abstract Abstract
This document contains an implementation report for the IESG covering This document contains an implementation report for the IESG covering
DKIM in support of the advancement of that specification along the DKIM in support of the advancement of that specification along the
Standards Track. Standards Track.
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 18, 2011. This Internet-Draft will expire on April 2, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. DKIM Interoperability Event . . . . . . . . . . . . . . . . . 5 3. DKIM Interoperability Event . . . . . . . . . . . . . . . . . 5
3.1. Participants . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Participants . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Testing Methodology . . . . . . . . . . . . . . . . . . . 5 3.2. Testing Methodology . . . . . . . . . . . . . . . . . . . 5
3.3. Observations . . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Observations . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.4. Results . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Collected DKIM Interoperability and Use Data . . . . . . . . . 7 4. Collected DKIM Interoperability and Use Data . . . . . . . . . 7
4.1. The OpenDKIM Project . . . . . . . . . . . . . . . . . . . 7 4.1. The OpenDKIM Project . . . . . . . . . . . . . . . . . . . 7
4.1.1. Details . . . . . . . . . . . . . . . . . . . . . . . 7 4.1.1. Details . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.2. Results . . . . . . . . . . . . . . . . . . . . . . . 7 4.1.2. Results . . . . . . . . . . . . . . . . . . . . . . . 7
4.1.3. Conclusions . . . . . . . . . . . . . . . . . . . . . 8 4.1.3. Conclusions . . . . . . . . . . . . . . . . . . . . . 9
4.2. Other Collected Data . . . . . . . . . . . . . . . . . . . 9 4.2. AOL Data . . . . . . . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 6. Informative References . . . . . . . . . . . . . . . . . . . . 12
6.1. Normative References . . . . . . . . . . . . . . . . . . . 11 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 13
6.2. Informative References . . . . . . . . . . . . . . . . . . 11 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
[DKIM], published in May 2007, has reached a level of maturity [DKIM], published in May 2007, has reached a level of maturity
sufficient to consider its advancement along the standards track. sufficient to consider its advancement along the standards track.
Enclosed is a summary of collected interoperability data provided Enclosed is a summary of collected interoperability data provided
from sources that are aggregating such information as well as from a from sources that are aggregating such information as well as from a
more formal DKIM interoperability event that took place in October more formal DKIM interoperability event that took place in October
2007. 2007.
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In October 2007, Alt-N Technologies of Dallas, Texas hosted an In October 2007, Alt-N Technologies of Dallas, Texas hosted an
interoperability and testing event at their headquarters. Twenty interoperability and testing event at their headquarters. Twenty
organizations sent engineers and their various DKIM implementations organizations sent engineers and their various DKIM implementations
to connect to a private internal network and exchange test messages to connect to a private internal network and exchange test messages
and tabulate observed results. and tabulate observed results.
3.1. Participants 3.1. Participants
The interoperability event included participants from all of the The interoperability event included participants from all of the
following organizations: Alt-N Technologies, AOL, AT&T Inc., Bizanga following organizations: Alt-N Technologies, AOL, AT&T Laboratories,
Ltd., Brandenburg InternetWorking, Brandmail Solutions, ColdSpark, Bizanga Ltd., Brandenburg InternetWorking, Brandmail Solutions,
Constant Contact, Inc., DKIMproxy, Domain Assurance Council, Google ColdSpark, Constant Contact, Inc., DKIMproxy, Domain Assurance
Inc., ICONIX Inc., Internet Initiative Japan (IIJ), Ironport Systems, Council, Google Inc., ICONIX Inc., Internet Initiative Japan (IIJ),
Message Systems, Port25 Solutions, Postfix, Sendmail, Inc., Ironport Systems, Message Systems, Port25 Solutions, Postfix,
StrongMail Systems, and Yahoo! Inc. Most of the participants Sendmail, Inc., StrongMail Systems, and Yahoo! Inc. Most of the
traveled to Dallas and participated in person, but a few operated participants traveled to Dallas and participated in person, but a few
remotely. operated remotely.
Nearly all of the implementations were based on disjoint code Nearly all of the implementations were based on disjoint code
development projects. A few were based on a common open source base development projects. A few were based on a common open source base
project. project.
3.2. Testing Methodology 3.2. Testing Methodology
Participants were encouraged before the event to craft a set of test Participants were encouraged before the event to craft a set of test
messages meant to exercise their own implementations as well as those messages meant to exercise their own implementations as well as those
of the other participants, both in terms of successful verifications of the other participants, both in terms of successful verifications
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development team as part of this interoperability report work. The development team as part of this interoperability report work. The
data can be anonymized to conceal the sending domain and client IP data can be anonymized to conceal the sending domain and client IP
addresses, though these data are passed through a one-way hash to addresses, though these data are passed through a one-way hash to
enable collation of data from common sources. enable collation of data from common sources.
4.1.2. Results 4.1.2. Results
At the time of writing of this document, the results of this effort At the time of writing of this document, the results of this effort
are as follows: are as follows:
Reporting Hosts: 11 individual MTAs representing seven distinct Reporting Hosts: six individual MTAs representing four distinct
ADMDs ADMDs
Total Messages: 111101 Total Messages: 416393
Signatures: 80984 messages (72.9%) were not signed; 29663 (26.7%) Signatures: 304801 messages (73.2%) were not signed; 109367 (26.2%)
had one signature; 419 (0.3%) had two signatures; the remainder had one signature; 2198 (0.5%) had two signatures; the remainder
(less than 0.04%) had more (less than 0.01%) had more.
Signing Algorithms: 58.5% of signatures used "rsa-sha1", while the Signing Algorithms: 48.7% of signatures used "rsa-sha1", while the
balance used "rsa-sha256" balance used "rsa-sha256".
Header Canonicalization Algorithms: 31.3% of signatures used Header Canonicalization Algorithms: 13.7% of signatures used
"simple", while the balance used "relaxed" "simple", while the balance used "relaxed"; when grouped by
domains, the percentages were similar.
Body Canonicalization Algorithms: 38.6% of signatures used "simple", Body Canonicalization Algorithms: 25.4% of signatures used "simple",
while the balance used "relaxed" while the balance used "relaxed"; when grouped by domains, the
percentages were similar.
Keys in Test Mode: 46% of keys retrieved from the DNS were tagged as Keys in Test Mode: 55.8% of keys retrieved from the DNS were tagged
being in test mode as being in test mode.
Keys with Syntax Errors: 0.1% of keys retrieved from the DNS had Keys with Specific Granularity: Four keys were retrieved that had
syntax errors specific names in their "g=" tags.
Missing Keys: 1.4% of signatures received referenced keys that were Keys with Syntax Errors: Less than 0.1% of keys retrieved from the
DNS had syntax errors.
DomainKeys Compatibility: 1.4% of the retrieved keys appeared to be
intended for use with the older DomainKeys proposal rather than
DKIM
Missing Keys: 2% of signatures received referenced keys that were
not found in the DNS not found in the DNS
Optional Signature Tags: Of the optional signature tags supported by Optional Signature Tags: Of the optional signature tags supported by
the base specification, "t=" was seen 45.7% of the time (0.4% of the base specification, "t=" was seen 46.4% of the time (1% of
which included timestamps in the future, even after forgiving some 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% clock drift); "x=" was seen 4.4% of the time; "l=" was seen 4.6%
of the time; "z=" was seen 3.0% of the time. of the time; "z=" was seen 4.8% of the time.
Body Length Limits: Of the signatures for which "l=" was used, 76.1% Body Length Limits: Of the signatures for which "l=" was used, 6.4%
of them had the body extended after signing. of them signed none of the body, and 100% of the rest had the body
extended after signing.
Signature Pass Rates: Overall, 72.7% of observed signatures were Signature Pass Rates: Overall, 89.9% of observed signatures were
successfully verified. successfully verified.
Pass Rates for Non-List Mail: Where "list mail" is defined as any 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 mail not bearing one of the header fields defined in [LIST-ID] or
in [LIST-URLS], or a "Precedence: list" field, selecting only for in [LIST-URLS], or a "Precedence: list" field, selecting only for
mail that is not list mail revealed a successful verification rate mail that is not list mail revealed a successful verification rate
of 92.5%; selecting only for list mail produced a 54.3% success of 93.6%; selecting only for list mail produced a 84.7% success
rate. rate.
Author vs. Third-Party: 75.2% of the signatures observed were author Author vs. Third-Party: 73% of the signatures observed were author
signatures, meaning the "d=" value in the signature matched the signatures, meaning the "d=" value in the signature matched the
domain found in the From: header field. The remainder, therefore, domain found in the From: header field. The remainder, therefore,
were third-party signatures. were third-party signatures.
DNSSEC: Only one reporting site is currently checking for DNSSEC on
keys retrieved from the DNS. It found no signed keys.
Common errors: The top five verification errors observed: Key not
found in DNS (18.7%), key granularity mismatch (13%), DNS
retrieval failure such as timeouts (2%), key revoked (1.9%),
unknown key type (1.8%).
Detected Header Field Changes: A subset of the reporting sites are
capable of reporting header fields known to have been changed in
transit (e.g. when "z=" tags were used by the signer). In such
cases, changes to the "To:" field were more common than any other
by a factor of four or more.
Most Commonly Signed Fields: From: (100%), To: (95.5%), Subject:
(93.7%), Date: (92.3%), MIME-Version: (88.8%), Content-Type:
(80%), Message-Id: (75.9%), Received: (59.7%). All others are
below 50%.
Multiple-use Signing Domains: 9512 unique signing domains were
observed. Of these, 42.7% of them sent a single signed message in
the sample period, 18.6% sent two and 8.6% sent three.
4.1.3. Conclusions 4.1.3. Conclusions
The results of the OpenDKIM work are updated constantly as more data The results of the OpenDKIM work are updated constantly as more data
feeds come online and more data are reported. Based on the data feeds come online and more data are reported. Based on the data
available at the time of writing, some conclusions are possible. available at the time of writing, some conclusions are possible.
At least some implementations of all of the optional signature At least some implementations of all of the optional signature
features, all of the canonicalization combinations and all of the features, all of the canonicalization combinations and all of the
signing algorithms are in general use. None of the features had zero signing algorithms are in general use. None of the features had zero
use counts. use counts.
The current collection implementation did not collect data about Overall signature pass rates are generally quite high. The impact of
optional features of keys that are in use. A future version will signature survivability when correlated against MLM activity is
address this. surprisingly low based on observed data. More research into this is
recommended. The DKIM Working Group is already working on an
Informational draft to discuss those issues.
Overall signature pass rates are generally quite high, except for That the "To" field is the one most often associated with
cases where the mail passes through a mailing list. In that case verification failures suggests some MTAs handling the message are
almost half of the signatures are invalidated. (Earlier snapshots of correcting cases where the field is improperly formed. A common case
data in this effort showed this figure to be even higher.) It is failing to quote the comment portion of that field when required
follows that for DKIM to be successful, increased co-operation with to do so by [MAIL]. Such corrections cause signatures to become
MLMs is desirable. The working group has already started work on an invalid.
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 The counts of low-use signing domains suggest that spammers, who
typically rotate domain names with high frequency, have adopted DKIM
as a tool to try to get through message filters.
[Summaries of data collected and reported by other sources can go 4.2. AOL Data
here.]
A one-day summary of observed traffic from America Online reports the
following:
Ratio of DKIM-signed mail: 42%
Properly formed signatures: 1.4 billion
Malformed signatures: 3000
Unique signing domains: 50,000-90,000
Key retrieval errors: 14 million
Signature refers to nonexistent domain: 10 million
Signature refers to nonexistent key: 36 million
Signature refers to revoked key: 138,000
Originator signatures: 1.2 billion
Third-party signatures: 184 million
Verified signatures: 1.2 billion
Failed signatures (body changed): 78 million
Failed signatures (other): 34 million
Expired signatures: less than 1 million
5. Security Considerations 5. Security Considerations
This document is an implementation report and thus has no security This document is an implementation report and thus has no security
considerations. considerations.
6. References 6. Informative References
6.1. Normative References [ABNF] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 5234, January 2008.
[DKIM] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton, [DKIM] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton,
J., and M. Thomas, "DomainKeys Identified Mail (DKIM) J., and M. Thomas, "DomainKeys Identified Mail (DKIM)
Signatures", RFC 4871, May 2007. 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] [EMAIL-ARCH]
Crocker, D., "Internet Mail Architecture", RFC 5598, Crocker, D., "Internet Mail Architecture", RFC 5598,
July 2009. July 2009.
[LIST-ID] Chandhok, R. and G. Wenger, "List-Id: A Structured Field [LIST-ID] Chandhok, R. and G. Wenger, "List-Id: A Structured Field
and Namespace for the Identification of Mailing Lists", and Namespace for the Identification of Mailing Lists",
RFC 2919, March 2001. RFC 2919, March 2001.
[LIST-URLS] [LIST-URLS]
Neufeld, G. and J. Baer, "The Use of URLs as Meta-Syntax Neufeld, G. and J. Baer, "The Use of URLs as Meta-Syntax
for Core Mail List Commands and their Transport through for Core Mail List Commands and their Transport through
Message Header Fields", RFC 2369, July 1998. Message Header Fields", RFC 2369, July 1998.
[MAIL] Resnick, P., "Internet Message Format", RFC 5322,
October 2008.
Appendix A. Acknowledgements Appendix A. Acknowledgements
The author wishes to acknowledge the following for their review and The author wishes to acknowledge the following for their review and
constructive criticism of this document: [names] constructive criticism of this document: Tony Hansen
The working group expresses its thanks to Alt-N Technologies for The working group expresses its thanks to Alt-N Technologies for
graciously hosting the 2007 DKIM interoperability event. graciously hosting the 2007 DKIM interoperability event.
Author's Address Author's Address
Murray S. Kucherawy Murray S. Kucherawy
Cloudmark Cloudmark
128 King St., 2nd Floor 128 King St., 2nd Floor
San Francisco, CA 94107 San Francisco, CA 94107
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