Review of: DKIM is Harmful as Specified
I-D: draft-otis-dkim-harmful-00
Reviewed by: D. Crocker
Review Date: 12 May 2013
Summary:
DKIM is in wide use for email operations today; it is currently at
Draft Standard and has been submitted for elevation to full Internet
Standard. The nature and purpose of DKIM is described in the opening
lines of the Abstract for its core specification (RFC 6376):
DomainKeys Identified Mail (DKIM) permits a person, role, or
organization that owns the signing domain to claim some
responsibility for a message by associating the domain with the
message. This can be an author's organization, an operational relay,
or one of their agents. DKIM separates the question of the identity
of the Signer of the message from the purported author of the
message. Assertion of responsibility is validated through a
cryptographic signature and by querying the Signer's domain directly
to retrieve the appropriate public key.
The current document expresses concerns about DKIM's limitations and
its use, and it re-raises issues that were extensively discussed and
rejected in the original DKIM working group. The document essentially
criticizes DKIM's performance for message validation, rather than for
its stated purpose of affixing a domain name to the message. The
document also cites some exploits that are not prevented/detected by
DKIM, in spite of their being entirely of the scope of the DKIM
specification. The document seems to be basing its justification for
this criticism on the fact there there are some unspecified people or
organizations that misunderstand DKIM functions.
Much of the text in this document is factually incorrect, confused
and/or confusing, including architectural layer confusion; some of it
is simply irrelevant to the stated purpose of the document.
Given DKIM's 6+ years of extensive production experience, flaws as
deep as this document claims exist should be more widely perceived by
now.
Detailed Comments:
Abstract
Currently, email lacks conventions ensuring SMTP clients can be
identified by an authenticated domain. Unfortunately many hope to
use DKIM as an alternative, but it is independent of intended
DKIM is associated with the message object; in technical terms, it is
independent of the message channel, such as SMTP client. (As a handling
agent, an SMTP client might affix a DKIM signature, but the associated
identifier does not carry any explicit or implicit statement of the
handling role.) Hence, the opening sentence is misguided or, at least,
misleading.
Also, who are the 'many' and what is the evidence of the claimed
confusion? DKIM has been in production deployment since 2006. If the
dangers and damages threatened in this document were as real and serious
as claimed, surely we'd have heard of them from others in the community.
recipients and domains accountable for sending the message. This
DKIM is explicitly defined to be affixed by domains declaring 'some'
responsibility for the message; this may include domains that send the
message. Hence, the assertion here is wrong.
means DKIM is poorly suited for establishing abuse assessments for
unsolicited messaging of commercial email otherwise known as SPAM,
Actually, DKIM is for making trust assessments, not abuse assessments,
as acknowledged a bit farther down in the text...
nor was this initially DKIM's intent. DKIM lacks message context
essential to ensure fair assessment and to ensure this assessment is
not poisoned.
I don't know what "message context" means here.
Taken on its own, this sentence sounds portentous but it has no obvious
meaning or substantiation.
DKIM was instead intended to establish increased levels of trust
Exactly.
based upon valid DKIM signatures controlling acceptance and what a
user sees within the FROM header field. But DKIM failed to guard
The identifier used by DKIM is independent of the rfc5322.From field and
the specification is explicit that it carries no relationship to it.
Hence this sentence is wrong.
against pre-pended header fields where any acceptance based on valid
DKIM signatures is sure to exclude header field spoofing, especially
It's true that DKIM does not protect against all possible attacks...
that of the FROM. This weakness allows malefactors to exploit DKIM
signature acceptance established by high-volume DKIM domains to spoof
ANY other domain, even when prohibited within the Signer's network.
It's true that attacks through vectors not covered by DKIM will not be
prevented or detected by DKIM use...
It's also true that none of these limitations have been noted as
problems by the DKIM operations community.
1. Introduction
Currently, IPv4 address reputation provides the primary basis for
defending SMTP open services. Use of IP addresses in this role
I do not understand what "SMTP open services" means here.
completely breaks down when dealing with IPv6 [RFC2460]. There are
That's a prediction, not yet an observable fact.
Although the prediction is reasonable, it's not appropriate to assert it
as fact. For example there have been some analyses which suggest that
adaptation of IPv4-based mechanisms might still prove useful.
currently 18,209,237,415,985,168 /64 equivalent IPv6 prefixes routed.
[v6-BGP-Rpts]. In comparison, for IPv4 there are 2,614,711,792 IP
addresses routed. While IPv4 is reaching its maximum, IPv6 has about
0.1% of the available /64 prefix routed and this continues to grow
rapidly. Unlike IPv4, there is no practical means to scan reverse
DNS namespace within IPv6 since each /64 prefix may contain any
number of PTR records ranging up to 184,000,000,000,000,000,000.
A technique commonly employed to automate IPv4 address categorization
of suitable hosts is to check whether reverse PTR records appear to
represent valid hostnames. Those that represent 4 decimal numbers
are often considered unacceptable, for example. Our processing of
reverse DNS namespace in cooperation with network providers now
excludes about 38%, or about 1,000,000,000 IPv4 addresses. Comparing
IPv6 /64 prefixes with the remainder of routable IPv4 addresses shows
there are 11.3 million times more IPv6 /64 prefixes needing
categorization. In addition, there is no practical means to
facilitate this effort.
Some also suggest there will not be a significant increase in the
number of servers running over IPv6 and since their overall number
should be comparable, email should still be dealing with a similar
number of IP addresses. Unlike IPv4, IPv6 does not constrain the
number of IP addresses assigned to a network interface. This feature
allows each connection from a server to originate from a different IP
address over the entire life of its operation while also having an
ability to effortlessly change /64 prefixes. The potential increase
allowed by IPv6 may prove explosive.
All three of the above paragraphs are essentially irrelevant to a
critique of DKIM...
Many now hope DKIM will be able to offer a domain identity to provide
a basis for acceptance to replace that of the IP address used by SMTP
awkward sentence construction...
clients. With a lack of uptake by commercial reputation services,
there are proposals within the IETF aimed at establishing DKIM as a
Both claims in this sentence are false.
basis for reputation schemes in the Repute WG. When such an ill-
considered effort is combined with DKIM's inability to detect invalid
prefixed header fields, the results can prove highly harmful.
The 'ill-considered' apparently refers to the Repute working group, but
there's no explanation of its flaws. Since this is offered as the basis
for harm, it undermines the entire document.
It's also not clear how reference to the Repute WG is relevant to a
criticism of DKIM.
2. Maintaining Trust
Not every subsystem or protocol layer should be expected to repeat
previous security checks, however critical checks should not be
assumed, especially those that involve a trivial amount of effort.
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With high levels of abuse resulting from email's open nature,
delegating checks in a structured manner better conserves essential
resources. However, email's highly distributed store and forward
protocol could not function if rigid message structures were enforced
by the transport. New authentication or presentation requirements
may involve small structural adjustments. For example,
internationalization introduced a format negotiation not assured to
survive beyond the next hop.
I do not understand the applicability of the text in this section to to
the premise of the document, and especially not to the title of the section.
3. Responding to Defects and Exploitation
With the advent of aviation, the world marveled at the skill and
intellect taking us to ever greater heights. With aviation, faults
threatening security, that when found, demanded our attention and
diligence to effect repair. As with aviation, the success of email
has risen to great heights. Email has become an integral component
Email does not travel via airplanes, except for those few passengers
using their laptops, connected during flight. But perhaps I'm confused
about the meaning and relevance of this section...
in general commerce and the maintenance of security such as reporting
system failures, break-in attempts, and facilitating account access
recovery.
Reporting or predicting failure should not be viewed as exhibiting a
lack of respect for achieved accomplishments. Noting and repairing
faults only signify the importance of email's prominent role. As
with most security related protocols, responding to noted defects is
fairly common. Not responding to discovered defects in a security
related protocol would be shocking.
I do not understand the applicability of the text in this section to to
the premise of the document.
4. SMTP Can't
SMTP [RFC5321] recommends against rejecting messages based upon
perceived defects in the message structure. This liberal acceptance
permits evolutionary changes in message specifications starting at
[RFC0822] that was based on [RFC0733] replaced by [RFC2822] and again
by [RFC5322], [RFC6152], [RFC6532], and [RFC6854]; the second to last
paragraph in section 3 of [RFC5321] provides a definitive statement
Section 3.3, not Section 3.
messages should not be rejected due to perceived defects in the
[RFC0822] message structure. The initial reference to [RFC0822] in
this paragraph offers two foot notes with the second referencing the
latest version of [RFC0822] which is [RFC5322] which itself has
recently been updated. The impact of initially removing text
specifically indicating which header fields are not to repeat is
I do not understand what 'removing' is meant here.
unknown. This information was implied within the then-new ABNF
ABNF was new in 1977, not 1982...
notation. Clarifying text for this requirement did not return until
the [RFC0822] revision 19 years later which also indicates this
specification's success at providing a foundation that allowed email
to flourish.
I do not understand the point of the text here. It seems to be irrelevant.
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There are many SMTP servers that have been in operation for decades
with years passing between security patches. Such an accomplishment
is most remarkable considering the volume of traffic being handled,
often from highly malicious sources. This amazing stability and
scalability with high levels of security would not have been possible
if SMTP had been expected to validate message formats.
Expecting SMTP to validate message formats to protect against
vulnerabilities pertaining to protocols such as DKIM does not scale.
DKIM has essentially nothing to do with SMTP. As such, all of the above
text is irrelevant to a critique of DKIM.
The general use of DKIM permits signature checks subsequent to
acceptance where only the status of signatures determines internal
placement. As such, it becomes critical to ensure a valid signature
is never declared having malformed header field stacks. To
I can't parse this "As such" sentence.
accomplish this, the DKIM specification must change.
5. DKIM Vulnerability
DKIM permits a vulnerability by not checking the message header field
stack for invalid repeats when signing or verifying a signature. The
DKIM does not "validate" a message. It associates a domain name with the
message. The difference is fundamental and essential. Again, there are
many attacks DKIM does not protect against, since it isn't trying to
protect against them...
DKIM signature process must walk both down and then up the header
No, it is not required to; alternative approaches are viable and permitted.
field stack while selecting the header fields to be included in the
hash process of the signature. The DKIM process will even ignore
prefixed FROM header fields which is the only header field always
included.
The WG concluded that "listing non-existent header fields as signed"
hack added in non-normative language together with opinions that
FWIW, this also had AD support...
checking for invalid repeated header fields is not to be considered
DKIM's problem. See section 8.15 of [RFC6376] where this issue was
expressed as not an attack against the trust DKIM intends to convey,
and thus not a concern for DKIM. Nevertheless, improperly formed
messages may display only the first of multiple header fields that,
as a result of erroneous assumptions of there being no invalid
repeated header fields, the prefixed header fields are likely to be
displayed in lieu of those signed while not impacting DKIM's
signature validity.
This text appears to be irrelevant to DKIM's functions, if only because
DKIM does not cover displays to users.
DKIM incorrectly assumed the header field stack's starting condition,
which DKIM itself is best able to determine, and is an option in the
I don't understand what this sentence is trying to say.
OpenDKIM implementation. This is likely to astonish most recipients
that DKIM failed to make a robust effort to maintain the trust it is
attempting to convey. Three members of the WG authored proposed
Small nit: IETF working group have participants, not 'members'...
changes aimed specifically at addressing this issue [DKIM-MH-Attack].
At the time, some expressed concerns about whether this might set
This appears to be an attempt to re-raise an issue that was considered
and rejected by the working group. How is that productive?
back DKIM's standardization process. As such, DKIM Signers may sign
malformed messages (e.g., violate [RFC5322]) and be in compliance
DKIM's RFC 6376, Section 3.8:
Accordingly, DKIM's design is predicated on valid input.
So the assertion being made here appears to be incorrect.
with DKIM specifications. In addition, receivers may verify these
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messages as having valid signatures despite multiple instances of a
header field only permitted to occur once and also be in compliance
with DKIM specifications. See addendum for examples.
Use of DKIM on such messages exposes a vulnerability in the
evaluation process. Rather than ensuring essential checks are made
prior to producing a result, a wasteful hack was later suggested
where extra non-existent header fields could be included in the list
of signed header fields. Any pre-pended header field added after
signing would thereby change resulting hashes and invalidate the
signature. Not all domains are attempting to achieve the same level
of trust and may be more sensitive to incurring incremental storage
requirements. Some domains may even inadvertently sign invalid
repeated header fields because this check had not been required in
the DKIM process. These same DKIM domains are also likely to
establish themselves as being Too Big To Block. These TBTB domains
can then be used to spoof other domains that may have otherwise
established a high level of trust by implementing the hack where, due
to this defect in DKIM, can still do nothing in their defense from
the perspective of now deceived recipients.
This vulnerability in DKIM represents an exploit allowing serious
attacks caused by erroneous assumptions made in DKIM's signature
process. There is also a header field, which because of its label,
may potentially mislead recipients into believing it contains valid
"Authentication-Results" [RFC5451]. Common phrases such as
"Authentication-Results", "pass", and "fail", rather than use of
result codes belies introductory claims this header is not intended
for direct human consumption.
6. Barriers to an Authenticated Domain
Some advocate use of DKIM as a means to obtain domain references
I do not understand what "a means to obtain domain references" means here?
based on the increased prevalence of this protocol. DKIM is
independent of the domain actually sending the message and the
exactly.
recipient by design. Unfortunately, DKIM also does not attempt to
protect against likely abuses that are also beyond the control of the
signing domain in which DKIM signature validity conveys no assurance
pre-fixed header fields have not changed what recipients see. As
It's true that there are many abuses that DKIM does not protect against
and does not attempt to protect against.
such, DKIM signing domains can not be held accountable for incidents
of abuse appearing to violate subscription policies or that spoof
other domains.
Because of DKIM's vulnerability to header field spoofing, it would
never be safe to express positive reputations either. Any such
assurance could be exploited by malefactors to deceive those trusting
DKIM results. In short, a DKIM signed domain as currently defined,
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can never be safely used in any context, other than the most rigid
exclusion of any unsigned content which is well beyond any existing
implementation. It can never be used for email reputation as
currently defined.
7. Domains as a Basis for Managing Traffic
A manageable basis for assessments can leverage a smaller number of
related domains, compared to IPv6 or even IPv4 addresses. Although
I do not understand what "a smaller number of related domains" means
here, nor especially how being 'related' is relevant.
technically the domain name space can be larger than the massively
large IPv6 address space, in practice it is not. One hundred
thousand domains control 90% of Internet traffic out of approximately
100 million domains active each month. The top 150 domains control
50% of the traffic, and the top 2,500 domains control 75%. This
level of domain consolidation permits effective fast-path white-
listing. Improvements achieved using domains to consolidate the
threat landscape can easily justify added cryptographic
authentication burdens. Even APL resource records [RFC3123] can
authenticate EHLO using a single DNS transaction, but this would not
allow IPv6 email to be more easily managed, which cryptographic
technology can offer.
8. XMPP Shows the Way Forward
In addition to SMTP [RFC5321] using StartTLS [RFC3207] XMPP [RFC6122]
uses StartTLS [RFC6120] over a different port with many of the
features used by web servers such as [RFC2560] as one means to
increase scalability. It seems plausible that by defining SMTP
access over a different port is where a new authentication and
international requirements can be resolved together. Of course, port
25 can be used, where it might require StartTLS in the case of IPv6
connections.
This appears to be proposing a channel-based, one-hop authentication
mechanism. One problem is that TLS is rarely used for authentication of
the client...
In any event, this section is irrelevant to the stated topic of the
document, namely DKIM 'harm'.
Many administrators overlook a serious problem made much worse by
chatty protocols that impose processing delays. Examining server
logs will not reveal any problem either, because the limited resource
being consumed is the number of outstanding connections TCP is able
to support. Reaching this limit will prevent new connections from
being instantiated but this is not logged as an event. Over time
administrators may hear complaints email is not being delivered or
just see an ever growing percentage of spam.
9. IANA Considerations
This document requires no IANA consideration.
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10. Security Considerations
This draft intends to describe serious security concerns raised with
use of DKIM exacerbated with IPv6 email. The contained
recommendations are expected to reduce the security concerns. To
ensure security, the DKIM specification must change.
11. References - Informative
[DKIM-MH-Attack]
http://trac.tools.ietf.org/wg/dkim/trac/ticket/24,
"Multiple-header-attack alternative proposal", April 2011.
[RFC0733] Crocker, D., Vittal, J., Pogran, K., and D. Henderson,
"Standard for the format of ARPA network text messages",
RFC 733, November 1977.
[RFC0822] Crocker, D., "Standard for the format of ARPA Internet
text messages", STD 11, RFC 822, August 1982.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2560] Myers, M., Ankney, R., Malpani, A., Galperin, S., and C.
Adams, "X.509 Internet Public Key Infrastructure Online
Certificate Status Protocol - OCSP", RFC 2560, June 1999.
[RFC2822] Resnick, P., "Internet Message Format", RFC 2822,
April 2001.
[RFC3123] Koch, P., "A DNS RR Type for Lists of Address Prefixes
(APL RR)", RFC 3123, June 2001.
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
[RFC4408] Wong, M. and W. Schlitt, "Sender Policy Framework (SPF)
for Authorizing Use of Domains in E-Mail, Version 1",
RFC 4408, April 2006.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
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Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, September 2007.
[RFC4954] Siemborski, R. and A. Melnikov, "SMTP Service Extension
for Authentication", RFC 4954, July 2007.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
October 2008.
[RFC5451] Kucherawy, M., "Message Header Field for Indicating
Message Authentication Status", RFC 5451, April 2009.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
[RFC6122] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Address Format", RFC 6122, March 2011.
[RFC6152] Klensin, J., Freed, N., Rose, M., and D. Crocker, "SMTP
Service Extension for 8-bit MIME Transport", STD 71,
RFC 6152, March 2011.
[RFC6376] Crocker, D., Hansen, T., and M. Kucherawy, "DomainKeys
Identified Mail (DKIM) Signatures", RFC 6376,
September 2011.
[RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized
Email Headers", RFC 6532, February 2012.
[RFC6854] Leiba, B., "Update to Internet Message Format to Allow
Group Syntax in the "From:" and "Sender:" Header Fields",
RFC 6854, March 2013.
[v6-BGP-Rpts]
http://bgp.potaroo.net/v6/as6447/, "BGP Routing Table
Analysis Reports/IPv6/AS6447 views", May 2013.
Appendix A. DKIM Examples
From Random User Tue Mar 12 12:07:37 2013
X-Apparently-To: just4spamdlr(_at_)yahoo(_dot_)com via 72.30.237.8; Tue, 12 Mar
2013 12:08:37 -0700
Return-Path: <Fake(_dot_)user(_at_)gmail(_dot_)com>
Received-SPF: neutral (192.83.249.65 is neither permitted nor denied by domain
of gmail.com)
A3RleHQvcGxhaW4DAzACA3RleHQvaHRtbAMDMQ--
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Internet-Draft DKIM-HARMFUL May 2013
X-YMailISG: Po8J_9cWLDuz5QIo_tChc7OagZYPBIscsK7APx8FMj835hEX
clyJxoQr6Ojy40ccEugqmkym_ayJu65fKm.KJY73k6aprxb9s7Bj6P32lpml
6yGzxWFYdNXCwcxHtFGdhKe3v7Tjh8x051jkxjIqfuS0vo8J5rZOr.Z__6vD
4wiGFDUwFHNUWAwuz_pwp7pZ5HCivuuuyszYVvH0eIFsrQ9crR.rrk_3EQU2
Xkv_fInlGDFR8fafFPMOgQ7QOrHhy0zQUbptDEFGdh1QVOyLwIpjwEC7264k
4MqxUH7zz_M5JOQzj6dJslH0.iz5y9Sgp6y6kTUHAVP2f_t1hMeRvf3F7WJ6
1yY2rZJALIME1CtiNKQJoDctzgGFRnh_5mo415MvUcEIH7qqS5RFgWtXEQpd
JIpyYlECDXVUcuASoLmzbuGSiCEVLq7f4EiBTAsaMwXJ07OgXBR.QYDw3VfA
Z0AcfnFrUVHNLZtLaFukQKzdk9c6SpHFHSuCAsvLPuZeRy4Ij5ndXd7viyCS
IkAHsnhG_u3.nZr3zUDFOrqw8sEKphobj6ZJ8KEXtuhr_tx.94abE1JRJYi5
fukj2h8y9s.K10ZxoTClaw41_DD8fxESbyfyTRPytiEXUdK1WEjgS3rAZ0TA
WPJPDr063xLYk20UY0V.N5J15lBCtqZcde_9pdXwxVySyXo1KEQOaH3TNRBZ
AKMFuCC7NF56aklkiUgk2EWm8iYoHsFez5_HtOz1zmc1dv4mNFOPTaNrXF2X
qjFiwfdUipupIlAEc6pIdv0_le.xvz1jnaewEOyxo4dKd2XLVvybLfsLY16U
FzLS9MJJ1wC0Cmf3G2SbOmT4ZiAvPjyv8QnHzbSDDDy3hqg8F0uEE03sJ5dm
on5FxOHZZ1wCH7DL1QAXpZYxYWKV.h3q69dKQMl6HbnmfT_WZQY4X8uKXqkZ
o34v.YmvJxHSRCSmhFpug1EstpJ4gHVitl_eJzT_n6xYQwhNAuMZ9uRjN2xE
1Lf7NpgzRf9bFvOpJAlyLoK5Xvxbx711cMgEUfGIha_JtL1P7hyfncRszHDv
txgUYzcsVvRyAyVvwDAM.TEBsFhAtqqwOibqo2l5xCBj2yXRbKJ0EOC1JDMs
HA--
X-Originating-IP: [192.83.249.65]
Authentication-Results: mta1225.mail.bf1.yahoo.com from=gmail.com;
domainkeys=neutral (no sig);
from=gmail.com; dkim=pass (ok)
Received: from 127.0.0.1 (EHLO rdaver.bungi.com) (192.83.249.65)
by mta1225.mail.bf1.yahoo.com with SMTP; Tue, 12 Mar 2013 12:08:36 -0700
Received: by rdaver.bungi.com
via smail with stdio
id <m1UFUYr-00KeXPC(_at_)rdaver(_dot_)bungi(_dot_)com>
for Just4spamdlr(_at_)yahoo(_dot_)com; Tue, 12 Mar 2013 12:08:33 -0700
(PDT)
(Smail-3.2.0.94 1997-Apr-22 #591 built 2011-Feb-5)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
d=gmail.com; s=20120113;
h=mime-version:x-received:date:message-id:subject:from:to
:content-type;
bh=PS9xMxYwwTGwWXbCd8bjBBm2rwb79wVOSDLhmp+k4b4=;
b=qnYVUccLSAi2DGJdUgDDIP9A3uPk3PaxgqhYLBn6xU382MsCi/ICFgKAoFPuwM7BvL
AuSuqL6P54cIJ3Pn36h2xmXy+ucNr5r5OqIY63rtvj6Apjr4uW1PzG47J7BGEiP9iwDZ
PLTzl9ZLpZXvZZpTCJOXUQP2HF8q6aivCblYZIQcCdVRCftG+A4z0+dEyTHbxoAMx9U3
GFISRRHcZ7k7GAyYmLrSr3fUTjvpa1YWoNK+IcSALC2tKVSW5FP1IQAT07f1e8+bOgHh
JleaQIw8b1Vjlzhs4hFKLdedmjQqjDJXVP/K3J+t/ggfYn4H547fu6Pb5syKZIiuPf1e
yJqA==
MIME-Version: 1.0
X-Received: by 10.220.221.143 with SMTP id ic15mr6773333vcb.32.1363115257152;
Tue, 12 Mar 2013 12:07:37 -0700 (PDT)
Received: by 10.52.70.169 with HTTP; Tue, 12 Mar 2013 12:07:37 -0700 (PDT)
Date: Tue, 12 Mar 2013 09:07:37 -1000
Message-ID:
<CA+VnpPKv0s-p2nKkAkNHS4V2SxZehw_6S9QF5p1p2ji+FMof=Q(_at_)mail(_dot_)gmail(_dot_)com>
Otis & Rand Expires November 13, 2013 [Page 11]
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Subject: An example signed message
From: Random User <random(_dot_)j(_dot_)user(_dot_)994(_at_)gmail(_dot_)com>
To: just4spamdlr(_at_)yahoo(_dot_)com
Content-Type: multipart/alternative; boundary=14dae9cdc33bb0ff5204d7bf00ff
Content-Length: 280
reporting valid signature
From Fake User Tue Mar 12 12:07:37 2013
X-Apparently-To: just4spamdlr(_at_)yahoo(_dot_)com via 72.30.237.8; Tue, 12 Mar
2013 12:09:01 -0700
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A3RleHQvcGxhaW4DAzACA3RleHQvaHRtbAMDMQ--
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Otis & Rand Expires November 13, 2013 [Page 12]
Internet-Draft DKIM-HARMFUL May 2013
:content-type;
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Date: Tue, 12 Mar 2013 09:07:37 -1000
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Subject: An example signed message
From: Random User <random(_dot_)j(_dot_)user(_dot_)994(_at_)gmail(_dot_)com>
To: just4spamdlr(_at_)yahoo(_dot_)com
Content-Type: multipart/alternative; boundary=14dae9cdc33bb0ff5204d7bf00ff
Content-Length: 280
spoofed DKIM with valid signature
Appendix B. Stats
Total spams: 9438
DKIM pass: 688 (about 25% relayed from large ESPs)
DKIM fail: 189
DKIM pass w/multiple from: 28 (about 2% on average)
Unsigned: 8561
Looking at a few minutes of spam.
Authors' Addresses
Douglas Otis
Trend Micro
10101 N. De Anza Blvd
Cupertino, CA 95014
USA
Phone: +1.408.257-1500
Email: doug_otis(_at_)trendmicro(_dot_)com
Otis & Rand Expires November 13, 2013 [Page 13]
Internet-Draft DKIM-HARMFUL May 2013
Dave Rand
Trend Micro
10101 N. De Anza Blvd
Cupertino, CA 95014
USA
Phone: +1.408.257-1500
Email: dave_rand(_at_)trendmicro(_dot_)com
Otis & Rand Expires November 13, 2013 [Page 14]
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net