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rfc:rfc6651

Internet Engineering Task Force (IETF) M. Kucherawy Request for Comments: 6651 Cloudmark Category: Standards Track June 2012 ISSN: 2070-1721

Extensions to DomainKeys Identified Mail (DKIM) for Failure Reporting

Abstract

 This document presents extensions to the DomainKeys Identified Mail
 (DKIM) specification to allow for detailed reporting of message
 authentication failures in an on-demand fashion.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6651.

Copyright Notice

 Copyright (c) 2012 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
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Kucherawy Standards Track [Page 1] RFC 6651 DKIM Reporting Extensions June 2012

Table of Contents

 1. Introduction ....................................................3
 2. Definitions .....................................................3
    2.1. Key Words ..................................................3
    2.2. Notation ...................................................3
    2.3. Imported Definitions .......................................3
    2.4. Other Definitions ..........................................3
 3. Optional Reporting for DKIM .....................................4
    3.1. Extension DKIM Signature Tag ...............................4
    3.2. DKIM Reporting TXT Record ..................................4
    3.3. DKIM Reporting Algorithm ...................................6
 4. Optional Reporting Address for DKIM ADSP ........................8
 5. Requested Reports ...............................................9
    5.1. Requested Reports for DKIM Failures .......................10
    5.2. Requested Reports for DKIM ADSP Failures ..................10
 6. Report Generation ..............................................11
    6.1. Report Format .............................................11
    6.2. Other Guidance ............................................11
 7. IANA Considerations ............................................11
    7.1. DKIM Signature Tag Registration ...........................11
    7.2. DKIM ADSP Tag Registration ................................12
    7.3. DKIM Reporting Tag Registry ...............................12
 8. Security Considerations ........................................13
    8.1. Inherited Considerations ..................................13
    8.2. Report Volume .............................................13
    8.3. Deliberate Misuse .........................................13
    8.4. Unreported Fraud ..........................................14
 9. References .....................................................14
    9.1. Normative References ......................................14
    9.2. Informative References ....................................15
 Appendix A. Acknowledgements ......................................16
 Appendix B. Examples ..............................................16
    B.1. Example Use of DKIM Signature Extension Tag ...............16
    B.2. Example DKIM Reporting TXT Record .........................17
    B.3. Example Use of DKIM ADSP Extension Tags ...................17

Kucherawy Standards Track [Page 2] RFC 6651 DKIM Reporting Extensions June 2012

1. Introduction

 DomainKeys Identified Mail [DKIM] introduced a mechanism for message
 signing and authentication.  It uses digital signing to associate a
 domain name with a message in a reliable manner.  The verified domain
 name can then be evaluated (e.g., checking advertised sender policy,
 comparison to a known-good list, submission to a reputation service,
 etc.).
 Deployers of message authentication technologies are increasingly
 seeking visibility into DKIM verification failures and conformance
 failures involving the published signing practices (e.g., Author
 Domain Signing Practices [ADSP]) of an ADministrative Management
 Domain (ADMD; see [EMAIL-ARCH]).
 This document extends [DKIM] and [ADSP] to add an optional reporting
 address and some reporting parameters.  Reports are generated using
 the format defined in [ARF-AUTHFAIL].

2. Definitions

2.1. Key Words

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [KEYWORDS].

2.2. Notation

 Certain properties of email messages described in this document are
 referenced using notation found in [EMAIL-ARCH] (e.g.,
 "RFC5322.From").

2.3. Imported Definitions

 Numerous DKIM-specific terms used here are defined in [DKIM].
 The definitions of the [ABNF] tokens "domain-name" and
 "dkim-quoted-printable" can also be found there.

2.4. Other Definitions

 report generator:  A report generator is an entity that generates and
    sends reports.  For the scope of this document, the term refers to
    Verifiers, as defined in Section 2.2 of [DKIM], with the added
    capability to generate authentication failure reports according to
    this specification.

Kucherawy Standards Track [Page 3] RFC 6651 DKIM Reporting Extensions June 2012

3. Optional Reporting for DKIM

 A domain name owner employing [DKIM] for email signing and
 authentication might want to know when signatures that ought to be
 verifiable are not successfully verifying.  Currently, there is no
 such mechanism defined.
 This section adds optional "tags" (as defined in [DKIM]) to the
 DKIM-Signature header field and the DKIM key record in the DNS, using
 the formats defined in that specification.

3.1. Extension DKIM Signature Tag

 The following tag is added to DKIM-Signature header fields when a
 Signer wishes to request that reports of failed verifications be
 generated by a Verifier:
 r=  Reporting Requested (plain-text; OPTIONAL; no default).  If
     present, this tag indicates that the Signer requests that
     Verifiers generate a report when verification of the DKIM
     signature fails.  At present, the only legal value is the single
     character "y".  A complete description and illustration of how
     this is applied can be found in Section 3.3.
    ABNF:
    sig-r-tag = %x72 *WSP "=" *WSP %x79
              ; "r=y" (lower-case only)

3.2. DKIM Reporting TXT Record

 When a Signer wishes to advertise that it wants to receive failed
 verification reports, it places in the DNS a TXT Resource Record
 (RR).  The RR contains a sequence of tag-value objects in a format
 similar to DKIM key records (see Section 3.6.1 of [DKIM]), but it is
 entirely independent of those key records and is found at a different
 name.  The tag-value objects in this case comprise the parameters to
 be used when generating the reports.  A report generator will request
 the content of this record when it sees an "r=" tag in a
 DKIM-Signature header field.
 Section 3.6.2.2 of [DKIM] provides guidance with respect to the
 handling of a TXT RR that comprises multiple distinct strings
 ("character-strings" in the parlance of [DNS]).  The same process
 MUST be applied here.

Kucherawy Standards Track [Page 4] RFC 6651 DKIM Reporting Extensions June 2012

 Implementations MUST support all tags defined in this document, and
 any other tag found in the content of the record that is not
 recognized by an implementation MUST be ignored.  See Section 7.3 for
 details about finding or registering extension tags.
 The initial list of tags supported for the reporting TXT record is as
 follows:
 ra=  Reporting Address (plain-text; OPTIONAL).  A
      dkim-quoted-printable string (see Section 2.11 of [DKIM])
      containing the local-part of an email address to which a report
      SHOULD be sent when mail fails DKIM verification for one of the
      reasons enumerated below.  The value MUST be interpreted as a
      local-part only.  To construct the actual address to which the
      report is sent, the Verifier simply appends to this value an "@"
      followed by the domain name found in the "d=" tag of the
      DKIM-Signature header field.  Therefore, a Signer making use of
      this specification MUST ensure that an email address thus
      constructed can receive reports generated as described in
      Section 6.
    ABNF:
    rep-ra-tag = %x72.61 *WSP "=" *WSP dkim-quoted-printable
               ; "ra=..." (lower-case only for the tag name)
 rp=  Requested Report Percentage (plain-text; OPTIONAL; default is
      "100").  The value is an integer from 0 to 100 inclusive that
      indicates what percentage of incidents of signature
      authentication failures, selected at random, are to cause
      reports to be generated.  The report generator SHOULD NOT issue
      reports for more than the requested percentage of incidents.
      Report generators MAY make use of the "Incidents:" field in
      [ARF] to indicate that there are more reportable incidents than
      there are reports.
    ABNF:
    rep-rp-tag = %x72.70 *WSP "=" *WSP 1*3DIGIT
               ; "rp=..." (lower-case only)

Kucherawy Standards Track [Page 5] RFC 6651 DKIM Reporting Extensions June 2012

 rr=  Requested Reports (plain-text; OPTIONAL; default is "all").  The
      value MUST be a colon-separated list of tokens representing
      those conditions under which a report is desired.  See
      Section 5.1 for a list of valid tokens.
    ABNF:
    rep-rr-type = ( "all" / "d" / "o" / "p" / "s" / "u" / "v" / "x" )
    rep-rr-tag = %x72.72 *WSP "=" *WSP rep-rr-type
                 *WSP *( ":" *WSP rep-rr-type )
               ; "rr=..." (lower-case only for the tag name)
 rs=  Requested SMTP Error String (plain-text; OPTIONAL; no default).
      The value is a dkim-quoted-printable string that the publishing
      ADMD requests be included in [SMTP] error strings if messages
      are rejected during the delivery SMTP session.
    ABNF:
    rep-rs-tag = %x72.73 *WSP "=" dkim-quoted-printable
               ; "rs=..." (lower-case only for the tag name)
 In the absence of an "ra=" tag, the "rp=" and "rr=" tags MUST be
 ignored, and the report generator MUST NOT issue a report.

3.3. DKIM Reporting Algorithm

 Report generators MUST apply the following algorithm, or one
 semantically equivalent to it, for each DKIM-Signature header field
 whose verification fails for some reason.  Note that this processing
 is done as a reporting extension only; the outcome of the specified
 DKIM evaluation MUST be otherwise unaffected.
 1.  If the DKIM-Signature field did not contain a valid "r=" tag,
     terminate.
 2.  Issue a [DNS] TXT query to the name that results from appending
     the value of the "d=" tag in the DKIM-Signature field to the
     string "_report._domainkey.".  For example, if the DKIM-Signature
     header field contains "d=example.com", issue a DNS TXT query to
     "_report._domainkey.example.com".
 3.  If the DNS query returns anything other than RCODE 0 (NOERROR),
     or if multiple TXT records are returned, terminate.
 4.  If the resultant TXT is in several string fragments, concatenate
     them as described in Section 3.6.2.2 of [DKIM].

Kucherawy Standards Track [Page 6] RFC 6651 DKIM Reporting Extensions June 2012

 5.  If the TXT content is syntactically invalid (see Section 3.2),
     terminate.
 6.  If the reason for the signature evaluation failure does not match
     one of the report requests found in the "rr=" tag (or its default
     value), terminate.
 7.  If a report percentage ("rp=") tag was present, select a random
     number between 0 and 99, inclusive; if the selected number is not
     lower than the tag's value, terminate.
 8.  If no "ra=" tag was present, skip this step and the next one.
     Otherwise, determine the reporting address by extracting the
     value of the "ra=" tag and appending to it an "@" followed by the
     domain name found in the "d=" tag of the DKIM-Signature header
     field.
 9.  Construct and send a report in compliance with Section 6 of this
     document that includes as its intended recipient the address
     constructed in the previous step.
 10. If the [SMTP] session during which the DKIM signature was
     evaluated is still active and the SMTP server has not already
     given its response to the DATA command that relayed the message,
     and an "rs=" tag was present in the TXT record, the SMTP server
     SHOULD include the decoded string found in the "rs=" tag in its
     SMTP reply to the DATA command.
 In order to thwart attacks that seek to convert report generators
 into unwitting denial-of-service attack participants, a report
 generator SHOULD NOT issue more than one report to any given domain
 as a result of a single message.  Further, a report generator SHOULD
 establish an upper bound on the number of reports a single message
 can generate overall.  For example, a message with three invalid
 signatures, two from example.com and one from example.net, would
 generate at most one report to each of those domains.
 This algorithm has the following advantages over previous
 pre-standardization implementations, such as early versions of
 [OPENDKIM]:
 a.  If the DKIM signature fails to verify, no additional DNS check is
     made to see if reporting is requested; the request is active in
     that it is included in the DKIM-Signature header field.
     (Previous implementations included the reporting address in the
     DKIM key record, which is not queried for certain failure cases.
     This meant, for full reporting, that the key record had to be
     retrieved even when it was not otherwise necessary.)

Kucherawy Standards Track [Page 7] RFC 6651 DKIM Reporting Extensions June 2012

 b.  The request is confirmed by the presence of a corresponding TXT
     record in the DNS, since the Signer thus provides the parameters
     required to construct and send the report.  This means a
     malicious Signer cannot falsely assert that someone else wants
     failure reports and cause unwanted mail to be generated.  It can
     cause additional DNS traffic against the domain listed in the
     "d=" signature tag, but negative caching of the requested DNS
     record will help to mitigate this issue.
 c.  It is not possible for a Signer to direct reports to an email
     address outside of its own domain, preventing distributed email-
     based denial-of-service attacks.
 See Section 8.4 for some considerations regarding limitations of this
 mechanism.

4. Optional Reporting Address for DKIM ADSP

 A domain name owner employing Author Domain Signing Practices [ADSP]
 may also want to know when messages are received without valid author
 domain signatures.  Currently, there is no such mechanism defined.
 This section adds the following optional "tags" (as defined in
 [ADSP]) to the DKIM ADSP records, using the form defined in that
 specification:
 ra=  Reporting Address (plain-text; OPTIONAL; no default).  The value
      MUST be a dkim-quoted-printable string containing the local-part
      of an email address to which a report SHOULD be sent when mail
      claiming to be from this domain failed the verification
      algorithm described in [ADSP], in particular because a message
      arrived without a signature that validates, which contradicts
      what the ADSP record claims.  The value MUST be interpreted as a
      local-part only.  To construct the actual address to which the
      report is sent, the Verifier simply appends to this value an "@"
      followed by the domain whose policy was queried in order to
      evaluate the sender's ADSP, i.e., the RFC5322.From domain of the
      message under evaluation.  Therefore, a Signer making use of
      this extension tag MUST ensure that an email address thus
      constructed can receive reports generated as described in
      Section 6.
    ABNF:
    adsp-ra-tag = %x72.61 *WSP "=" dkim-quoted-printable
                ; "ra=..." (lower-case only for the tag name)

Kucherawy Standards Track [Page 8] RFC 6651 DKIM Reporting Extensions June 2012

 rp=  Requested Report Percentage (plain-text; OPTIONAL; default is
      "100").  The value is a single integer from 0 to 100 inclusive
      that indicates what percentage of incidents of ADSP evaluation
      failures, selected at random, are to cause reports to be
      generated.  The report generator SHOULD NOT issue reports for
      more than the requested percentage of incidents.  An exception
      to this might be some out-of-band arrangement between two
      parties to override it with some mutually agreed value.  Report
      generators MAY make use of the "Incidents:" field in [ARF] to
      indicate that there are more reportable incidents than there are
      reports.
    ABNF:
    adsp-rp-tag = %x72.70 *WSP "=" *WSP 1*3DIGIT
                ; "rp=..." (lower-case only)
 rr=  Requested Reports (plain-text; OPTIONAL; default is "all").  The
      value MUST be a colon-separated list of tokens representing
      those conditions under which a report is desired.  See
      Section 5.2 for a list of valid tokens.
    ABNF:
    adsp-rr-type = ( "all" / "o" / "p" / "s" / "u" )
    adsp-rr-tag = %x72.72 *WSP "=" *WSP adsp-rr-type
                  *WSP *( ":" *WSP adsp-rr-type )
                ; "rr=..." (lower-case only for the tag name)
 rs=  Requested SMTP Error String (plain-text; OPTIONAL; no default).
      The value is a string the signing domain requests be included in
      [SMTP] error strings when messages are rejected during a single
      SMTP session.
    ABNF:
    adsp-rs-tag = %x72.73 *WSP "=" dkim-quoted-printable
                ; "rs=..." (lower-case only for the tag name)
 In the absence of an "ra=" tag, the "rp=" and "rr=" tags MUST be
 ignored, and the report generator MUST NOT issue a report.

5. Requested Reports

 The "rr" tags defined above allow a Signer to specify the types of
 errors about which it is interested in receiving reports.  This
 section defines the error types and corresponding token values.

Kucherawy Standards Track [Page 9] RFC 6651 DKIM Reporting Extensions June 2012

 Verifiers MUST NOT generate reports for incidents that do not match a
 requested report and MUST ignore requests for reports not included in
 this list.

5.1. Requested Reports for DKIM Failures

 The following report requests are defined for DKIM keys:
 all  All reports are requested.
 d    Reports are requested for signature evaluation errors that
      resulted from DNS issues (e.g., key retrieval problems).
 o    Reports are requested for any reason related to DKIM signature
      evaluation not covered by other report requests listed here.
 p    Reports are requested for signatures that are rejected for local
      policy reasons at the Verifier that are related to DKIM
      signature evaluation.
 s    Reports are requested for signature or key syntax errors.
 u    Reports are requested for signatures that include unknown tags
      in the signature field.
 v    Reports are requested for signature verification failures or
      body hash mismatches.
 x    Reports are requested for signatures rejected by the Verifier
      because the expiration time has passed.

5.2. Requested Reports for DKIM ADSP Failures

 The following report requests are defined for ADSP records:
 all  All reports are requested.
 o    Reports are requested for any [ADSP]-related failure reason not
      covered by other report requests listed here.
 p    Reports are requested for messages that are rejected for local
      policy reasons at the Verifier that are related to [ADSP].
 s    Reports are requested for messages that have a valid [DKIM]
      signature but do not match the published [ADSP] policy.
 u    Reports are requested for messages that have no valid [DKIM]
      signature and do not match the published [ADSP] policy.

Kucherawy Standards Track [Page 10] RFC 6651 DKIM Reporting Extensions June 2012

6. Report Generation

 This section describes the process for generating and sending reports
 in accordance with the request of the Signer and/or sender as
 described above.

6.1. Report Format

 All reports generated as a result of requests contained in these
 extension parameters MUST be generated in compliance with [ARF] and
 its extension specific to this work, [ARF-AUTHFAIL].  Moreover,
 because abuse reports from unverified sources might be handled with
 some skepticism, report generators are strongly advised to use [DKIM]
 to sign reports they generate.

6.2. Other Guidance

 Additional guidance about the generation of these reports can be
 found in [ARF-AS], especially in Section 6.

7. IANA Considerations

 As required by [IANA-CONS], this section contains registry
 information for the new [DKIM] signature tags and for the new [ADSP]
 tags.  It also creates a DKIM reporting tag registry.

7.1. DKIM Signature Tag Registration

 IANA has added the following item to the DKIM Signature Tag
 Specifications registry:
               +------+-----------------+--------+
               | TYPE | REFERENCE       | STATUS |
               +------+-----------------+--------+
               | r    | (this document) | active |
               +------+-----------------+--------+

Kucherawy Standards Track [Page 11] RFC 6651 DKIM Reporting Extensions June 2012

7.2. DKIM ADSP Tag Registration

 IANA has added the following items to the DKIM ADSP Specification
 Tags registry:
               +------+-----------------+
               | TYPE | REFERENCE       |
               +------+-----------------+
               | ra   | (this document) |
               | rp   | (this document) |
               | rr   | (this document) |
               | rs   | (this document) |
               +------+-----------------+

7.3. DKIM Reporting Tag Registry

 IANA has created a sub-registry of the DKIM Parameters registry
 called "DKIM Reporting Tag Registry".  Additions to this registry
 follow the "Specification Required" rules, with the following columns
 required for all registrations:
 Tag:  The name of the tag being used in reporting records
 Reference:  The document that specifies the tag being defined
 Status:  The status of the tag's current use -- either "active"
    indicating active use, or "historic" indicating discontinued or
    deprecated use
 The initial registry entries are as follows:
               +-----+-----------------+--------+
               | TAG | REFERENCE       | STATUS |
               +-----+-----------------+--------+
               | ra  | (this document) | active |
               | rp  | (this document) | active |
               | rr  | (this document) | active |
               | rs  | (this document) | active |
               +-----+-----------------+--------+

Kucherawy Standards Track [Page 12] RFC 6651 DKIM Reporting Extensions June 2012

8. Security Considerations

 Security issues with respect to these reports are similar to those
 found in [DSN].

8.1. Inherited Considerations

 Implementers are advised to consider the Security Considerations
 sections of [DKIM], [ADSP], [ARF-AS], and [ARF-AUTHFAIL].  Many
 security issues related to this document are already covered in those
 documents.

8.2. Report Volume

 It is impossible to predict the volume of reports this facility will
 generate when enabled by a report receiver.  An implementer ought to
 anticipate substantial volume, since the amount of abuse occurring at
 receivers cannot be known ahead of time, and may vary rapidly and
 unpredictably.

8.3. Deliberate Misuse

 Some threats caused by deliberate misuse of this error-reporting
 mechanism are discussed in Section 3.3, but they warrant further
 discussion here.
 The presence of the DNS record that indicates willingness to accept
 reports opens the recipient to abuse.  In particular, it is possible
 for an attacker to attempt to cause a flood of reports toward the
 domain identified in a signature's "d=" tag in one of these ways:
 1.  Alter existing DKIM-Signature header fields by adding an "r=y"
     tag (and possibly altering the "d=" tag to point at the target
     domain);
 2.  Add a new but bogus signature bearing an "r=y" tag and a "d=" tag
     pointing at the target domain;
 3.  Generate a completely new message bearing an "r=y" tag and a "d="
     tag pointing at the target domain.
 Consider, for example, the situation where an attacker sends out a
 multi-million-message spam run and includes in the messages a fake
 DKIM signature containing "d=example.com; r=y".  It won't matter that
 those signatures couldn't possibly be real: each will fail
 verification, and any implementations that support this specification
 will report those failures, in the millions and in short order, to
 example.com.

Kucherawy Standards Track [Page 13] RFC 6651 DKIM Reporting Extensions June 2012

 Implementers are therefore strongly advised not to advertise the DNS
 record specified in this document except when failure reports are
 desired.  Upon doing so, unexpected traffic volumes and attacks
 should be anticipated.
 Negative caching offers some protection against this pattern of
 abuse, although it will work only as long as the negative time-to-
 live on the relevant SOA record in the DNS.
 Positive caching of this DNS reply also means that turning off the
 flow of reports by removing the record is not likely to have an
 immediate effect.  A low time-to-live on the record needs to be
 considered.

8.4. Unreported Fraud

 An attacker can craft fraudulent DKIM-Signature fields on messages,
 without using "r=" tags, and avoid having these reported.  The
 procedure described in Section 3.3 does not permit the detection and
 reporting of such cases.
 It might be useful to some Signers to receive such reports, but the
 mechanism does not support it.  To offer such support, a Verifier
 would have to violate the first step in the procedure and continue
 even in the absence of an "r=" tag.  Although that would enable the
 desired report, it would also create a possible denial-of-service
 attack: such Verifiers would always look for the reporting TXT
 record, so a generator of fraudulent messages could simply send a
 large volume of messages without an "r=" tag to a number of
 destinations.  To avoid that outcome, reports of fraudulent
 DKIM-Signature header fields are not possible using the published
 mechanism.

9. References

9.1. Normative References

 [ABNF]     Crocker, D., Ed., and P. Overell, "Augmented BNF for
            Syntax Specifications: ABNF", RFC 5234, January 2008.
 [ADSP]     Allman, E., Fenton, J., Delany, M., and J. Levine,
            "DomainKeys Identified Mail (DKIM) Author Domain Signing
            Practices (ADSP)", RFC 5617, August 2009.
 [ARF]      Shafranovich, Y., Levine, J., and M. Kucherawy, "An
            Extensible Format for Email Feedback Reports", RFC 5965,
            August 2010.

Kucherawy Standards Track [Page 14] RFC 6651 DKIM Reporting Extensions June 2012

 [ARF-AS]   Falk, J. and M. Kucherawy, Ed., "Creation and Use of Email
            Feedback Reports: An Applicability Statement for the Abuse
            Reporting Format (ARF)", RFC 6650, June 2012.
 [ARF-AUTHFAIL]
            Fontana, H., "Authentication Failure Reporting Using the
            Abuse Reporting Format", RFC 6591, April 2012.
 [DKIM]     Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
            "DomainKeys Identified Mail (DKIM) Signatures", RFC 6376,
            September 2011.
 [DNS]      Mockapetris, P., "Domain names - implementation and
            specification", STD 13, RFC 1035, November 1987.
 [EMAIL-ARCH]
            Crocker, D., "Internet Mail Architecture", RFC 5598,
            July 2009.
 [IANA-CONS]
            Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 5226,
            May 2008.
 [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [SMTP]     Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
            October 2008.

9.2. Informative References

 [DSN]      Moore, K. and G. Vaudreuil, "An Extensible Message Format
            for Delivery Status Notifications", RFC 3464,
            January 2003.
 [OPENDKIM] Kucherawy, M., "OpenDKIM -- Open Source DKIM Library and
            Filter", August 2009, <http://www.opendkim.org>.

Kucherawy Standards Track [Page 15] RFC 6651 DKIM Reporting Extensions June 2012

Appendix A. Acknowledgements

 The author wishes to acknowledge the following for their review and
 constructive criticism of this proposal: Steve Atkins, Monica Chew,
 Dave Crocker, Tim Draegen, Frank Ellermann, J.D. Falk, John Levine,
 Scott Kitterman, and Andrew Sullivan.

Appendix B. Examples

 This section contains examples of the use of each of the extensions
 defined by this document.

B.1. Example Use of DKIM Signature Extension Tag

 This example shows a DKIM-Signature field using the extension tag
 defined by this document:
     DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple;
             d=example.com; s=jan2012; r=y;
             h=from:to:subject:date:message-id;
             bh=YJAYwiNdc3wMh6TD8FjVhtmxaHYHo7Z/06kHQYvQ4tQ=;
             b=jHF3tpgqr6nH/icHKIqFK2IJPtCLF0CRJaz2Hj1Y8yNwTJ
               IMYIZtLccho3ymGF2GYqvTl2nP/cn4dH+55rH5pqkWNnuJ
               R9z54CFcanoKKcl9wOZzK9i5KxM0DTzfs0r8
         Example 1: DKIM-Signature Field Using This Extension
 This example DKIM-Signature field contains the "r=" tag that
 indicates reports are requested on verification failure.
 Assuming the public key retrieved from the DNS and processed
 according to [DKIM] would determine that the signature is invalid, a
 TXT query will be sent to "_report._domainkey.example.com" to
 retrieve a reporting address and other report parameters as described
 in Section 3.3.

Kucherawy Standards Track [Page 16] RFC 6651 DKIM Reporting Extensions June 2012

B.2. Example DKIM Reporting TXT Record

 An example DKIM Reporting TXT record as defined by this document is
 as follows:
     ra=dkim-errors; rp=100; rr=v:x
            Example 2: Example DKIM Reporting TXT Record
 This example, continuing from the previous one, shows a message that
 might be found at "_report._domainkey.example.com" in a TXT record.
 It makes the following requests:
 o  Reports about signature evaluation failures should be sent to the
    address "dkim-errors" at the Signer's domain;
 o  All incidents (100%) should be reported;
 o  Only reports about signature verification failures and expired
    signatures should be generated.

B.3. Example Use of DKIM ADSP Extension Tags

 This example shows a DKIM ADSP record using the extensions defined by
 this document:
     dkim=all; ra=dkim-adsp-errors; rr=u
          Example 3: DKIM ADSP Record Using These Extensions
 This example ADSP record makes the following assertions:
 o  The sending domain (i.e., the one that is advertising this policy)
    signs all mail it sends;
 o  Reports about ADSP evaluation failures should be sent to the
    address "dkim-adsp-errors" at the Author's domain;
 o  Only reports about unsigned messages should be generated.

Kucherawy Standards Track [Page 17] RFC 6651 DKIM Reporting Extensions June 2012

Author's Address

 Murray S. Kucherawy
 Cloudmark
 128 King St., 2nd Floor
 San Francisco, CA  94107
 US
 Phone: +1 415 946 3800
 EMail: superuser@gmail.com

Kucherawy Standards Track [Page 18]

/data/webs/external/dokuwiki/data/pages/rfc/rfc6651.txt · Last modified: 2012/06/25 17:02 by 127.0.0.1

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