draft-ietf-dmarc-arc-protocol-13.txt   draft-ietf-dmarc-arc-protocol-14.txt 
DMARC Working Group K. Andersen DMARC Working Group K. Andersen
Internet-Draft LinkedIn Internet-Draft LinkedIn
Intended status: Experimental B. Long, Ed. Intended status: Experimental B. Long, Ed.
Expires: September 22, 2018 Google Expires: October 25, 2018 Google
S. Jones, Ed. S. Jones, Ed.
TDP TDP
S. Blank, Ed. S. Blank, Ed.
ValiMail Valimail
M. Kucherawy, Ed. M. Kucherawy, Ed.
TDP TDP
March 21, 2018 April 23, 2018
Authenticated Received Chain (ARC) Protocol Authenticated Received Chain (ARC) Protocol
draft-ietf-dmarc-arc-protocol-13 draft-ietf-dmarc-arc-protocol-14
Abstract Abstract
The Authenticated Received Chain (ARC) protocol creates a mechanism The Authenticated Received Chain (ARC) protocol creates a mechanism
whereby a series of handlers of an email message can conduct whereby a series of handlers of an email message can conduct
authentication of the email message as it passes among them on the authentication of the email message as it passes among them on the
way to its destination, and create an attached, authenticated record way to its destination, and create an attached, authenticated record
of the status at each step along the handling path, for use by the of the status at each step along the handling path, for use by the
final recipient in making choices about the disposition of the final recipient in making choices about the disposition of the
message. Changes in the message that might break existing message. Changes in the message that might break existing
authentication mechanisms can be identified through the ARC set of authentication mechanisms can be identified through the ARC Set of
header fields. header fields.
Status of This Memo Status of This Memo
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5 1.1. General Concepts . . . . . . . . . . . . . . . . . . . . 5
1.1.1. High Level Summary . . . . . . . . . . . . . . . . . 5 1.2. Differences Between ARC and DKIM . . . . . . . . . . . . 5
1.1.2. Technical Summary . . . . . . . . . . . . . . . . . . 7 1.3. Definitions and Terminology . . . . . . . . . . . . . . . 6
1.2. Definitions and Terminology . . . . . . . . . . . . . . . 7 1.3.1. Terms defined and used in this document . . . . . . . 6
1.2.1. Terms defined and used in this document . . . . . . . 7 1.3.2. Referenced Definitions . . . . . . . . . . . . . . . 7
1.2.2. Referenced Definitions . . . . . . . . . . . . . . . 8 2. Protocol Elements and Features . . . . . . . . . . . . . . . 7
2. Protocol Elements and Features . . . . . . . . . . . . . . . 8 2.1. The "ARC Set" of Header Fields . . . . . . . . . . . . . 8
2.1. Features of the ARC Protocol . . . . . . . . . . . . . . 9 2.1.1. Instance Tags . . . . . . . . . . . . . . . . . . . . 9
2.1.1. Chain of Custody . . . . . . . . . . . . . . . . . . 9 2.2. Chain Validation Status . . . . . . . . . . . . . . . . . 9
2.1.2. Optional Participation . . . . . . . . . . . . . . . 10 2.3. Trace Information . . . . . . . . . . . . . . . . . . . . 9
2.1.3. Only one ARC Chain (One Chain to Rule Them All) . . . 10 2.4. Key Management . . . . . . . . . . . . . . . . . . . . . 9
2.1.4. All Failures are Permanent . . . . . . . . . . . . . 10 2.5. All Failures are Permanent . . . . . . . . . . . . . . . 10
2.1.5. Benign nature of an ARC Set . . . . . . . . . . . . . 10 2.6. Chain of Custody . . . . . . . . . . . . . . . . . . . . 10
2.1.6. Key Management . . . . . . . . . . . . . . . . . . . 11 2.7. Optional Participation . . . . . . . . . . . . . . . . . 10
2.1.7. Trace Information . . . . . . . . . . . . . . . . . . 11 2.8. Broad Responsibility to Seal . . . . . . . . . . . . . . 10
2.1.8. Instance Tags . . . . . . . . . . . . . . . . . . . . 11 2.9. One Chain to Rule Them All . . . . . . . . . . . . . . . 11
2.1.9. Chain Validation Status . . . . . . . . . . . . . . . 11 2.10. Sealing is Always Safe . . . . . . . . . . . . . . . . . 11
3. The ARC Header Fields . . . . . . . . . . . . . . . . . . . . 11 3. The ARC Header Fields . . . . . . . . . . . . . . . . . . . . 11
3.1. Instance ('i=') Tag . . . . . . . . . . . . . . . . . . . 11 3.1. Instance ('i=') Tag . . . . . . . . . . . . . . . . . . . 11
3.1.1. Valid Range for Instance Tags . . . . . . . . . . . . 12
3.2. ARC-Authentication-Results (AAR) . . . . . . . . . . . . 12 3.2. ARC-Authentication-Results (AAR) . . . . . . . . . . . . 12
3.3. ARC-Message-Signature (AMS) . . . . . . . . . . . . . . . 13 3.3. ARC-Message-Signature (AMS) . . . . . . . . . . . . . . . 12
3.4. ARC-Seal (AS) . . . . . . . . . . . . . . . . . . . . . . 13 3.4. ARC-Seal (AS) . . . . . . . . . . . . . . . . . . . . . . 13
3.4.1. The 'cv' Tag . . . . . . . . . . . . . . . . . . . . 14 3.4.1. Covered Header Fields . . . . . . . . . . . . . . . . 13
3.4.2. Implicit Header Fields . . . . . . . . . . . . . . . 14 3.4.2. The 'cv' Tag . . . . . . . . . . . . . . . . . . . . 14
4. Verifier Actions . . . . . . . . . . . . . . . . . . . . . . 14 4. Verifier Actions . . . . . . . . . . . . . . . . . . . . . . 14
4.1. ARC Authentication-Results Information . . . . . . . . . 16 4.1. Authentication-Results Information . . . . . . . . . . . 15
4.2. Handling DNS Problems While Validating ARC . . . . . . . 16 4.2. Handling DNS Problems While Validating ARC . . . . . . . 16
4.3. Responding to ARC Validity Violations During the SMTP 4.3. Responding to ARC Validity Violations During the SMTP
Transaction . . . . . . . . . . . . . . . . . . . . . . . 17 Transaction . . . . . . . . . . . . . . . . . . . . . . . 16
5. Sealer Actions . . . . . . . . . . . . . . . . . . . . . . . 16
5. Signer Actions . . . . . . . . . . . . . . . . . . . . . . . 17
5.1. Marking and Sealing "cv=fail" (Invalid) Chains . . . . . 17 5.1. Marking and Sealing "cv=fail" (Invalid) Chains . . . . . 17
6. Usage of ARC and Chain Validity . . . . . . . . . . . . . . . 18 6. Recording and Reporting the Results of ARC Evaluation . . . . 17
6.1. Relationship between DKIM-Signature and AMS signing 6.1. Information from an ARC Evaluation . . . . . . . . . . . 17
scopes . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.2. Recording (local) ARC Evaluation Results . . . . . . . . 17
6.2. Assessing Chain Validity Violations . . . . . . . . . . . 18 6.3. DMARC Reporting of ARC Findings - Interim . . . . . . . . 18
7. Recording and Reporting the Results of ARC Evaluation . . . . 18 7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
7.1. Information from an ARC Evaluation . . . . . . . . . . . 18 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7.2. Recording (local) ARC Evaluation Results . . . . . . . . 19 8.1. Authentication-Results Method Registry Update . . . . . . 19
7.3. DMARC Reporting of ARC Findings - Interim . . . . . . . . 19 8.2. Email Authentication Result Names Registry Update . . . . 19
8. Supporting Alternate Signing Algorithms . . . . . . . . . . . 19 8.3. Definitions of the ARC header fields . . . . . . . . . . 19
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 20 9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 9.1. Header Size . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Authentication-Results Method Registry Update . . . . . 20 9.2. DNS Operations . . . . . . . . . . . . . . . . . . . . . 20
10.2. Definitions of the ARC header fields . . . . . . . . . . 21 9.3. Message Content Suspicion . . . . . . . . . . . . . . . . 21
11. Security Considerations . . . . . . . . . . . . . . . . . . . 22 10. Evaluating the Efficacy of the ARC Protocol (Experimental
11.1. Header Size . . . . . . . . . . . . . . . . . . . . . . 22 Considerations) . . . . . . . . . . . . . . . . . . . . . . . 21
11.2. DNS Operations . . . . . . . . . . . . . . . . . . . . . 22 10.1. Success Consideration . . . . . . . . . . . . . . . . . 21
11.3. Message Content Suspicion . . . . . . . . . . . . . . . 22 10.2. Failure Considerations . . . . . . . . . . . . . . . . . 22
12. Evaluating the Efficacy of the ARC Protocol . . . . . . . . . 23 10.3. Open Questions . . . . . . . . . . . . . . . . . . . . . 22
12.1. Success Consideration . . . . . . . . . . . . . . . . . 23 10.3.1. Value of the ARC-Seal (AS) Header . . . . . . . . . 22
12.2. Failure Considerations . . . . . . . . . . . . . . . . . 24 10.3.2. DNS Overhead . . . . . . . . . . . . . . . . . . . . 22
12.3. Open Questions . . . . . . . . . . . . . . . . . . . . . 24 10.3.3. Distinguishing Valuable from Worthless Trace
12.3.1. Value of the ARC-Seal (AS) Header . . . . . . . . . 24 Information . . . . . . . . . . . . . . . . . . . . 22
12.3.2. DNS Overhead . . . . . . . . . . . . . . . . . . . . 24 11. Implementation Status . . . . . . . . . . . . . . . . . . . . 23
12.3.3. Distinguishing Valuable from Worthless Trace 11.1. GMail test reflector and incoming validation . . . . . . 24
Information . . . . . . . . . . . . . . . . . . . . 24 11.2. AOL test reflector and internal tagging . . . . . . . . 24
13. Implementation Status . . . . . . . . . . . . . . . . . . . . 25 11.3. dkimpy . . . . . . . . . . . . . . . . . . . . . . . . . 24
13.1. GMail test reflector and incoming validation . . . . . . 26 11.4. OpenARC . . . . . . . . . . . . . . . . . . . . . . . . 25
13.2. AOL test reflector and internal tagging . . . . . . . . 26 11.5. Mailman 3.2 patch . . . . . . . . . . . . . . . . . . . 25
13.3. dkimpy . . . . . . . . . . . . . . . . . . . . . . . . . 26 11.6. Copernica/MailerQ web-based validation . . . . . . . . . 25
13.4. OpenARC . . . . . . . . . . . . . . . . . . . . . . . . 27 11.7. Rspamd . . . . . . . . . . . . . . . . . . . . . . . . . 26
13.5. Mailman 3.2 patch . . . . . . . . . . . . . . . . . . . 27 11.8. PERL MAIL::DKIM module . . . . . . . . . . . . . . . . . 26
13.6. Copernica/MailerQ web-based validation . . . . . . . . . 28 11.9. PERL Mail::Milter::Authentication module . . . . . . . . 27
13.7. Rspamd . . . . . . . . . . . . . . . . . . . . . . . . . 28 11.10. Sympa List Manager . . . . . . . . . . . . . . . . . . . 27
13.8. PERL MAIL::DKIM module . . . . . . . . . . . . . . . . . 29 11.11. Oracle Messaging Server . . . . . . . . . . . . . . . . 27
13.9. PERL Mail::Milter::Authentication module . . . . . . . . 29 11.12. MessageSystems Momentum and PowerMTA platforms . . . . . 28
13.10. Sympa List Manager . . . . . . . . . . . . . . . . . . . 30 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
13.11. Oracle Messaging Server . . . . . . . . . . . . . . . . 30 12.1. Normative References . . . . . . . . . . . . . . . . . . 28
13.12. MessageSystems Momentum . . . . . . . . . . . . . . . . 31 12.2. Informative References . . . . . . . . . . . . . . . . . 29
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 31 12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 30
14.1. Normative References . . . . . . . . . . . . . . . . . . 31 Appendix A. Appendix A - Design Requirements . . . . . . . . . . 31
14.2. Informative References . . . . . . . . . . . . . . . . . 32 A.1. Primary Design Criteria . . . . . . . . . . . . . . . . . 31
14.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 33 A.2. Out of Scope . . . . . . . . . . . . . . . . . . . . . . 31
Appendix A. Appendix A - Design Requirements . . . . . . . . . . 34 Appendix B. Appendix B - Example Usage . . . . . . . . . . . . . 31
A.1. Primary Design Criteria . . . . . . . . . . . . . . . . . 34 B.1. Example 1: Simple mailing list . . . . . . . . . . . . . 31
A.2. Out of Scope . . . . . . . . . . . . . . . . . . . . . . 35 B.1.1. Here's the message as it exits the Origin: . . . . . 31
Appendix B. Appendix B - Example Usage . . . . . . . . . . . . . 35 B.1.2. Message is then received at example.org . . . . . . . 32
B.1. Example 1: Simple mailing list . . . . . . . . . . . . . 35 B.1.3. Example 1: Message received by Recipient . . . . . . 34
B.1.1. Here's the message as it exits the Origin: . . . . . 35
B.1.2. Message is then received at example.org . . . . . . . 35 B.2. Example 2: Mailing list to forwarded mailbox . . . . . . 35
B.1.3. Example 1: Message received by Recipient . . . . . . 38 B.2.1. Here's the message as it exits the Origin: . . . . . 35
B.2. Example 2: Mailing list to forwarded mailbox . . . . . . 39 B.2.2. Message is then received at example.org . . . . . . . 36
B.2.1. Here's the message as it exits the Origin: . . . . . 39 B.2.3. Example 2: Message received by Recipient . . . . . . 40
B.2.2. Message is then received at example.org . . . . . . . 40 B.3. Example 3: Mailing list to forwarded mailbox with source 42
B.2.3. Example 2: Message received by Recipient . . . . . . 44 B.3.1. Here's the message as it exits the Origin: . . . . . 42
B.3. Example 3: Mailing list to forwarded mailbox with source 46 B.3.2. Message is then received at example.org . . . . . . . 43
B.3.1. Here's the message as it exits the Origin: . . . . . 46 B.3.3. Example 3: Message received by Recipient . . . . . . 48
B.3.2. Message is then received at example.org . . . . . . . 47 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 50
B.3.3. Example 3: Message received by Recipient . . . . . . 52 Appendix D. Comments and Feedback . . . . . . . . . . . . . . . 51
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 54 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
Appendix D. Comments and Feedback . . . . . . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 55
1. Introduction 1. Introduction
Modern email authentication techniques such as the Sender Policy Modern email authentication techniques such as the Sender Policy
Framework (SPF) [RFC7208] and DomainKeys Identified Mail (DKIM) Framework (SPF) [RFC7208] and DomainKeys Identified Mail (DKIM)
[RFC6376] have become common. However, their end-to-end utility is [RFC6376] have become common. However, their end-to-end utility is
limited by the effects of intermediaries along the transmission path, limited by the effects of intermediaries along the transmission path,
which either are not listed (for SPF) or which break digital which either are not listed (for SPF) or which break digital
signatures (for DKIM). These issues are described in substantial signatures (for DKIM). These issues are described in substantial
detail in those protocols' defining documents as well as in [RFC6377] detail in those protocols' defining documents as well as in [RFC6377]
and [RFC7960]. and [RFC7960].
Technologies that build upon the use of SPF and DKIM can reduce the Technologies that build upon the use of SPF and DKIM can reduce the
success of fraudulent email campaigns. To this end, Domain-based success of fraudulent email campaigns. To this end, Domain-based
Mail Authentication, Reporting and Compliance (DMARC) [RFC7489], Mail Authentication, Reporting and Conformance (DMARC) [RFC7489],
validates the domain of the RFC5322.From author header field. validates the domain of the RFC5322.From header field. However its
However its use along email transmission paths that have independent use along email transmission paths that have independent
intermediaries, such as some forwarders and essentially all mailing intermediaries, such as some forwarders and essentially all mailing
list services, produces false positive rejections that are list services, produces false positive rejections that are
problematic, both for the message authors, the intermediary problematic, both for the message authors, the intermediary
service(s), and for those they are interacting with. service(s), and for those they are interacting with.
What is needed is a mechanism by which legitimate alteration of a [RFC7960] documented the need for a mechanism which would survive
message, which invalidates associated SPF and DKIM information, does legitimate alteration of a message, in spite of breaking the
not ultimately result in a rejection of an email message on delivery. associated SPF and DKIM information so that the end receiver
Authenticated Receive Chain (ARC) builds upon DKIM mechanisms to system(s) can avoid those false positive rejections on delivery.
Authenticated Received Chain (ARC) builds upon DKIM mechanisms to
provide a sequence of signatures that provide a view of the handling provide a sequence of signatures that provide a view of the handling
sequence for a message, especially the points where alterations of sequence for a message, especially the points where alterations of
the content might have occurred. Equipped with this more complete the content might have occurred. Equipped with this more complete
information, the recipient system(s) can make a more informed information, the recipient system(s) can make a more informed
handling choice, reducing or eliminating the rejections that would handling choice, reducing or eliminating the rejections that would
occur with the use of DKIM and/or SPF alone. occur with the use of DKIM and/or SPF alone.
1.1. Overview 1.1. General Concepts
ARC provides a "chain of custody" for a message, allowing each entity ARC provides a "chain of custody" for a message, allowing each entity
that handles the message to see what entities handled it before, and that handles the message to see what entities handled it before, and
to see what the authentication status of the message was at each step to see what the authentication status of the message was at each step
in the handling. The handling entity can then put its own entry into in the handling. The handling entity can then put its own entry into
the chain of custody and then relay the message to the next handler. the chain of custody and then relay the message to the next handler.
When the message reaches final delivery, the decision to accept and When the message reaches final delivery, the decision to accept and
deliver the message, or, alternatively, to reject, discard, or deliver the message, or, alternatively, to reject, discard, or
quarantine it, can take the chain of custody into account, applying quarantine it, can take the chain of custody into account, applying
skipping to change at page 5, line 43 skipping to change at page 5, line 43
the document's chain of custody. When mail.service.example sees the the document's chain of custody. When mail.service.example sees the
message, it can see that SPF and DKIM validation fail, but it can message, it can see that SPF and DKIM validation fail, but it can
also see that both of these succeeded when they were checked by also see that both of these succeeded when they were checked by
listmania.example, and can verify listmania's assertion. listmania.example, and can verify listmania's assertion.
As part of its evaluation of the message for delivery, As part of its evaluation of the message for delivery,
mail.service.example can see that mysender.example publishes a DMARC mail.service.example can see that mysender.example publishes a DMARC
policy asking that unauthenticated messages be rejected. But is can policy asking that unauthenticated messages be rejected. But is can
also see the assertion by listmania.example that the message was also see the assertion by listmania.example that the message was
correctly authenticated when the message arrived there, and if it correctly authenticated when the message arrived there, and if it
accepts that assertion and that modifications made were benign, it accepts that assertion, it can accept the message for further
can deliver the message, rather than reject it, based on the processing, rather than reject it, based on the additional
additional information that ARC has provided. information that ARC has provided.
1.1.1. High Level Summary 1.2. Differences Between ARC and DKIM
In DKIM, every participating signing agent attaches a signature that In DKIM, every participating signing agent attaches a signature that
is based on the some of the content of the message, local policy, and is based on some of the content of the message, local policy, and the
the domain name of the signing agent's Administrative Management domain name of the signing agent's Administrative Management Domain
Domain (ADMD). Any verifier can process such a signature; a verified (ADMD). Any verifier can process such a signature; a verified
signature means that the domain referenced in the signature's "d=" signature means that the domain referenced in the signature's "d="
parameter has some responsibility for handling the message. An parameter has some responsibility for handling the message. An
artifact of using digital signature technology for this means that artifact of using digital signature technology for this means that
verification also ensures that the portion of the message that was verification also ensures that the portion of the message that was
"covered" by the signature has not been altered since the signature "covered" by the signature has not been altered since the signature
was applied. The signatures themselves are generally independent of was applied. The signatures themselves are generally independent of
one another. one another.
In contrast, a validated ARC signature conveys the following pieces In contrast, a validated ARC Set conveys the following pieces of
of information: information:
1. An assertion that, at the time that the intermediary ADMD 1. An assertion that, at the time that the intermediary ADMD
processed the message, the various assertions (SPF, DKIM- processed the message, the various assertions (such as SPF, DKIM-
Signature(s) and/or ARC sets) already attached to the message by Signature(s) and/or ARC Chain) already attached to the message by
other ADMDs were or were not valid; other ADMDs were or were not valid;
2. As with DKIM, an assertion that, for a validated ARC signature, 2. As with DKIM, an assertion that, for a validated ARC signature,
the domain name in the signature takes some responsibility for the domain name in the signature takes some responsibility for
handling of the message and that the covered content of message handling of the message and that the covered content of the
is unchanged since that signature was applied; message is unchanged since that signature was applied;
3. A further assertion that binds the ARC evaluation results into 3. A further assertion that binds the ARC evaluation results into
the ARC chain sequence. the ARC Chain sequence.
The ARC protocol accomplishes this by adding an "ARC Set" of three
new header fields to the message as follows:
1. ARC-Authentication-Results (referred to below as "AAR"):
virtually identical in syntax to an Authentication-Results field
[RFC7601], this field records the results of all message
authentication checks done by the recording ADMD at the time the
message arrived. Additional information is placed in this field
compared to a standard Authentication-Results field in order to
support a more complete DMARC report (see Section 3.2);
2. ARC-Message-Signature (referred to below as "AMS"): virtually
identical in syntax to DKIM-Signature, this field contains the
signature about the message header and body as they existed at
the time of handling by the ADMD adding it (including any
modifications made by the sealing ADMD); and
3. ARC-Seal (referred to below as "AS"): highly similar in structure
and format to a DKIM-Signature, this field applies a digital
signature that protects the integrity of all three of these new
fields when they are added by an ADMD, plus all instances of
these fields added by prior ADMDs.
An ARC participant always adds all of these header fields before
relaying a message to the next handling agent _en route_ to its
destination. Moreover, as described in Section 3.1, they each have
an "instance number" that increases with each ADMD in the handling
chain so that their original order can be preserved and the three
related header fields can be processed as a set.
1.1.2. Technical Summary
[[ possibly including a diagram - this may not be needed any more ]]
1.2. Definitions and Terminology 1.3. Definitions and Terminology
This section defines terms used in the rest of the document. This section defines terms used in the rest of the document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP14 ([RFC2119][RFC8174]). BCP14 ([RFC2119][RFC8174]).
Because many of the core concepts and definitions are found in Because many of the core concepts and definitions are found in
[RFC5598], readers should to be familiar with the contents of [RFC5598], readers should to be familiar with the contents of
[RFC5598], and in particular, the potential roles of intermediaries [RFC5598], and in particular, the potential roles of intermediaries
in the delivery of email. in the delivery of email.
Syntax descriptions use Augmented BNF (ABNF) [RFC5234]. Syntax descriptions use Augmented BNF (ABNF) [RFC5234].
1.2.1. Terms defined and used in this document 1.3.1. Terms defined and used in this document
o "ARC-Authentication-Results" (AAR) - an ARC header field described o "ARC-Authentication-Results" (AAR) - an ARC header field described
in Section 3.2. in Section 3.2.
o "ARC-Message-Signature" (AMS) - an ARC header field described in o "ARC-Message-Signature" (AMS) - an ARC header field described in
Section 3.3. Section 3.3.
o "ARC-Seal" (AS) - an ARC header field described in Section 3.4. o "ARC-Seal" (AS) - an ARC header field described in Section 3.4.
o "ARC Set" - A single group of the header fields introduced in o "ARC Set" - A single group of the header fields introduced in
Section 1.1 is called an "ARC Set". Section 2.1 is called an "ARC Set".
o "ARC Chain" - the complete sequence of ARC Sets for a message. o "ARC Chain" - the complete sequence of ARC Sets for a message.
The ARC Chain represents a "chain of custody" for the message, The ARC Chain represents a "chain of custody" for the message,
recording its authentication status at each ARC-compliant ADMD recording its authentication status at each ARC-participating ADMD
that handled the message. that handled the message.
1.2.2. Referenced Definitions 1.3.2. Referenced Definitions
The following terms are defined in other RFCs. Those definitions can The following terms are defined in other RFCs. Those definitions can
be found as follows: be found as follows:
o ADMD - [RFC5598], Section 2.3 o ADMD - [RFC5598], Section 2.3
o MTA - [RFC5598], Section 4.3.2 o MTA - [RFC5598], Section 4.3.2
o MSA - [RFC5598], Section 4.3.1 o MSA - [RFC5598], Section 4.3.1
skipping to change at page 8, line 30 skipping to change at page 7, line 40
the formal definitions that are being reused in ARC, this document the formal definitions that are being reused in ARC, this document
only describes and specifies changes in syntax and semantics. only describes and specifies changes in syntax and semantics.
Language, syntax, and other details are imported from DKIM [RFC6376]. Language, syntax, and other details are imported from DKIM [RFC6376].
Specific references can be found below. Specific references can be found below.
2. Protocol Elements and Features 2. Protocol Elements and Features
As with other domain authentication technologies (such as SPF, DKIM, As with other domain authentication technologies (such as SPF, DKIM,
and DMARC), ARC makes no claims about the contents of the email and DMARC), ARC makes no claims about the contents of the email
message it has sealed. However, for a valid and passing ARC chain, a message it has sealed. However, for a valid and passing ARC Chain, a
Final Receiver is able to ascertain: Final Receiver is able to ascertain:
o all (participating) domains that claim responsibility for handling o all (participating) domains that claim responsibility for handling
(and possibly modifying) the email message in transit; (and possibly modifying) the email message in transit;
o trace information, including: o trace information, including:
* the [RFC7601] authentication results each participating ADMD * the [RFC7601] Authentication-Results each participating ADMD
saw; and saw; and
* additional data needed to compile a DMARC report for the * additional data needed to compile a DMARC report for the
sending domain. sending domain.
Given this information, a Final Receiver is able to make a more- Given this information, each receiver is able to make a more informed
informed local policy decision regarding message delivery to the end local policy decision regarding message processing and, ultimately,
user in spite of an authentication failure. delivery to the end user in spite of authentication failure(s) and to
inform the message orgination system(s) through the DMARC report(s).
Every participant in an ARC chain, except for the originating sender Every participant in an ARC Chain, except for the originating sender
and Final Receiver, is both an ARC Validator (when receiving) and and Final Receiver, is both an ARC Validator (when receiving) and
then an ARC Sealer (when sending a message onward). The validated then an ARC Sealer (when sending a message onward).
chain status as determined at message receipt must be passed to the
sealer function in order for sealing to occur properly; how this is
done is considered ADMD-specific and an implementation detail.
_INFORMATIONAL_: It is important to understand that validating and _INFORMATIONAL_: It is important to understand that validating and
then immediately sealing a message leaves no room for message then immediately sealing a message leaves no room for message
modification, and many early implementations of ARC did not initially modification, and many early implementations of ARC did not initially
work because both operations were performed in a single pass over the work because both operations were performed in a single pass over the
message. message.
2.1. Features of the ARC Protocol
The following protocol features are functional parts and design The following protocol features are functional parts and design
decisions related the protocol that are not specific to either decisions related the protocol that are not specific to either
Validators or Sealers, but ensure the ARC chain conveys this Validators or Sealers, but ensure that the ARC Chain conveys this
information to a Final Receiver. information to a Final Receiver.
2.1.1. Chain of Custody 2.1. The "ARC Set" of Header Fields
At a high level, an ARC chain represents a chain of custody of Each "ARC Set" consists of the following three new header fields:
1. ARC-Authentication-Results (referred to below as "AAR"):
virtually identical in syntax to an Authentication-Results field
[RFC7601], this field records the results of all message
authentication checks done by the recording ADMD at the time the
message arrived. Additional information is placed in this field
compared to a standard Authentication-Results field in order to
support a more complete DMARC report;
2. ARC-Message-Signature (referred to below as "AMS"): virtually
identical in syntax to DKIM-Signature, this field contains the
signature about the message header and body as they existed at
the time of handling by the ADMD adding it (including any
modifications made by the sealing ADMD); and
3. ARC-Seal (referred to below as "AS"): highly similar in structure
and format to a DKIM-Signature, this field applies a digital
signature that protects the integrity of all three of these new
fields when they are added by an ADMD, plus all instances of
these fields added by prior ADMDs.
An ARC participant always adds all of these header fields before
relaying a message to the next handling agent _en route_ to its
destination. Moreover, they each have an "instance number" that
increases with each ARC Set in the handling chain so that their
original order can be preserved and the three related header fields
can be processed as a set.
2.1.1. Instance Tags
ARC includes an indicator in its header fields to show the order in
which the header fields comprising an ARC Chain were added, and the
specific members of each ARC Set. This is known as the "instance",
and the indicator is an "i=" tag/value. That is, the members of the
first ARC Set affixed to a message will all include "i=1". This is
described in detail in section Section 3.1.
2.2. Chain Validation Status
ARC includes a mechanism which denotes the state of the ARC Chain at
each step. The "chain validation status" ("cv" tag/value) is used to
communicate the current chain status within the ARC Chain and also
through Authentication-Results and ARC-Authentication-Results stamps
as well as DMARC reporting.
The chain validation status has one of three possible values:
o none: There was no chain on the message when it arrived for
validation; typically occurs when the message arrives at a Message
Transfer Agent (MTA) or mediator from a Message Submission Agent
(MSA) or when any upstream handlers may not be participating in
ARC handling;
o fail: The message has a chain whose validation failed;
o pass: The message has a chain whose validation succeeded.
2.3. Trace Information
ARC includes trace information encoded in the AAR. While section
Section 3.2 defines what information must be provided, sealing ADMDs
may provide additional information, and validating receivers may use
this trace information as they find it useful.
2.4. Key Management
The public keys for ARC header fields follow the same requirements,
syntax and semantics as those for DKIM signatures, described in
Section 3.6 of [RFC6376]. ARC places no requirements on the
selectors and/or domains used for the ARC header field signatures.
2.5. All Failures are Permanent
Because ARC Chains are transmitted across multiple intermediaries,
all errors, even temporary ones, become unrecoverable and are
considered permanent.
Any error validating or sealing a chain, for whatever reason, MUST
result in a "cv=fail" verdict as documented in Section 3.4.2.
2.6. Chain of Custody
At a high level, an ARC Chain represents a chain of custody of
authentication and other trace information (AAR) related to a authentication and other trace information (AAR) related to a
message, signed by each handler of the message. Each link in the message, signed by each handler of the message. Each link in the
chain (AMS) is designed to be brittle, insofar as it survives only chain (AMS) is designed to be brittle, insofar as it survives only
until the next modification of the message. However, the sequence of until the next modification of the message. However, the sequence of
intermediaries in the handling chain (AS) is designed to remain intermediaries in the handling chain (AS) is designed to remain
intact over the entirety of the chain. intact over the entirety of the chain.
The ARC chain can be conceptualized through an analogy with the chain The ARC Chain can be conceptualized through an analogy with the chain
of custody for legal evidence. The material evidence itself is of custody for legal evidence. The material evidence itself is
sealed within an tamper-proof bag (AMS) each time. When handed to a sealed within an tamper-proof bag (AMS) each time. When handed to a
new party, that party both vouches for the state of the received new party, that party both vouches for the state of the received
evidence container (AAR) and signs for the evidence on a chain of evidence container (AAR) and signs for the evidence on a chain of
custody report form (AS). As with all analogies, this one should not custody report form (AS). As with all analogies, this one should not
be taken to interpretive extremes, but primarily used as a conceptual be taken to interpretive extremes, but primarily used as a conceptual
framework. framework.
An ARC chain that is valid and passing has the attributes listed An ARC Chain that is valid and passing has the attributes listed
above in Section 2. above in Section 2.
Recipients of an ARC chain that is invalid or does not pass SHOULD 2.7. Optional Participation
NOT draw negative conclusions without a good understanding of the
wider handling context. Until ARC usage is widespread,
intermediaries will continue to modify messages without ARC seals.
As with a failing DKIM signature ([RFC6376] Section-6.3), a failing
ARC chain SHOULD be treated the same as a message with no ARC chain.
[[ NOTE TO WORKING GROUP: This paragraph probably is better placed in
Verifier actions. Ref issue 10 [1] ]]
2.1.2. Optional Participation
Validating an existing chain and then adding your own ARC set to a Validating an existing chain and then adding your own ARC Set to a
message allows you to claim responsibility for handling the message message allows you to claim responsibility for handling the message
and modifications, if any, done by your ADMD to benefit message and modifications, if any, done by your ADMD to benefit message
delivery downstream. However, no ADMD is obligated to perform these delivery downstream. However, no ADMD is obligated to perform these
actions. actions.
2.1.3. Only one ARC Chain (One Chain to Rule Them All) 2.8. Broad Responsibility to Seal
A message can have only one ARC chain on it at a time (see Any mediator ([RFC5598], section 5) that modifies a message may seal
its own changes. ARC is not solely intended for perimeter MTAs.
2.9. One Chain to Rule Them All
A message can have only one ARC Chain on it at a time (see
Section 3.1). Once broken, the chain cannot be continued, as the Section 3.1). Once broken, the chain cannot be continued, as the
chain of custody is no longer valid and responsibility for the chain of custody is no longer valid and responsibility for the
message has been lost. For further discussion of this topic and the message has been lost. For further discussion of this topic and the
designed restriction which prevents chain continuation or re- designed restriction which prevents chain continuation or re-
establishment, see [ARC-USAGE]. establishment, see [ARC-USAGE].
2.1.4. All Failures are Permanent 2.10. Sealing is Always Safe
Because ARC chains are transmitted across multiple intermediaries,
all errors, even temporary ones, become unrecoverable and are
considered permanent.
Any error validating or sealing a chain, for whatever reason, MUST
result in a "cv=fail" verdict.
2.1.5. Benign nature of an ARC Set Even when an ARC Chain is valid and passes, its value is limited to
very specific cases. An ARC Chain is specifically designed to
provide additional information to a receiver evaluating message
delivery in the context of an authentication failure and otherwise be
benign. Specifically:
Even when an ARC chain is valid and passes, its value is limited to o properly adding an ARC Set to a message does not damage or
very specific cases. An ARC chain is specifically designed to invalidate an existing chain,
provide value to a Final Receiver evaluating message delivery in the
context of an authentication failure. An ARC chain in general, and
each ARC set in particular, provide additional information, and
otherwise is benign. Specifically:
o properly adding an ARC set to a message does not damage or o sealing a chain when you did not modify a message does not
invalidate an existing chain, and negatively affect the chain, and
o validating a message exposes no new threat vectors (see o validating a message exposes no new threat vectors (see
Section 11). Section 9).
_INFORMATIONAL_: If an ADMD is unsure whether it will be re-emitting _INFORMATIONAL_: If an ADMD is unsure whether it will be re-emitting
and/or modifying a message, it may elect to seal all inbound mail. and/or modifying a message, it may elect to seal all inbound mail.
For complex or nested ADMD relationships such as found in some hosted For complex or nested ADMD relationships such as found in some hosted
mail solutions, this "inbound seal" can be used to facilitate mail solutions, this "inbound seal" can be used to facilitate
traversal of internal boundaries as well as properly conveying traversal of internal boundaries as well as properly conveying
incoming state to any egress MTAs that may need to assert a seal upon incoming state to any egress MTAs that may need to assert a seal upon
exit from the ADMD. Since these internal relationships are highly exit from the ADMD. Since these internal relationships are highly
implementation dependent, this protocol definition can not usefully implementation dependent, this protocol definition can not usefully
explore such usage except to note that it is intentionally allowed explore such usage except to note that it is intentionally allowed
within the scope of this specification. within the scope of this specification.
2.1.6. Key Management
The public keys for ARC header fields follow the same requirements,
syntax and semantics as those for DKIM signatures, described in
Section 3.6 of [RFC6376]. ARC places no requirements on the
selectors and/or domains used for the ARC header field signatures.
2.1.7. Trace Information
ARC includes trace information encoded in the AAR. While section
Section 3.2 defines what information must be provided, sealing ADMDs
may provide additional information, and validating receivers may use
or ignore this trace information as they wish.
2.1.8. Instance Tags
ARC introduces an indicator to its header fields to show the order in
which the header fields comprising an ARC set were added, and the
specific members of an ARC Set. This is known as an "instance", and
the indicator is an "i=". That is, the members of the first ARC set
affixed to a message will all include "i=1". This is described in
detail in section Section 3.1.
2.1.9. Chain Validation Status
ARC introduces a mechanism, also via a new tag, which indicates the
state of the ARC Chain at each step. This is the "chain validation
status". This is described in detail in section Section 3.4.1.
3. The ARC Header Fields 3. The ARC Header Fields
3.1. Instance ('i=') Tag 3.1. Instance ('i=') Tag
The header fields comprising a single ARC set are identified by the The header fields comprising a single ARC Set are identified by a
presence of a string in the value portion of the header field that common "instance" tag value. The instance tag is a string in each
complies with the "tag-spec" ABNF found in Section 3.2 of [RFC6376]. header field value that complies with the "tag-spec" ABNF found in
The tag-name is "i" and the value is the text representation of a Section 3.2 of [RFC6376]. The tag-name is "i" and the value is the
positive integer, indicating the position in the ARC sequence this text representation of a positive integer, indicating the position in
set occupies, where the first ARC set is numbered 1. In ABNF terms: the ARC sequence this set occupies, where the first ARC Set is
numbered 1. In ABNF terms:
instance = [FWS] %x69 [FWS] "=" [FWS] position [FWS] ";"
position = 1*2DIGIT ; 1 - 50 position = 1*2DIGIT ; 1 - 50
instance = [FWS] %x69 [FWS] "=" [FWS] position [FWS] ";"
Valid ARC sets must have exactly one instance of each header field Valid ARC Sets MUST have exactly one instance of each header field
for a given position value and signing algorithm. (Initial (of three) for a given instance value and signing algorithm.
development of ARC is only being done with a single allowed signing
algorithm, but parallel work in the DCRUP working group [2] is
expanding that. For handling multiple signing algorithms, see
[ARC-MULTI].)
Because the AMS and AS header field values are made up of tag-spec
constructs, the i= tag may be found anywhere within the header field
value, but is represented throughout this spec in the initial
position for convenience. Implementers are encouraged to place the
i= tag at the beginning of the field value to facilitate human
inspection of the headers.
3.1.1. Valid Range for Instance Tags (_INFORMATIONAL:_ Initial development of ARC is only being done with
a single allowed signing algorithm, but parallel work in the DCRUP
working group [1] is expanding that. For handling multiple signing
algorithms, see [ARC-MULTI].)
The 'i' tag value can range from 1-50 (inclusive). The 'i' tag value can range from 1-50 (inclusive).
ARC implementations MUST support at least ten (10) ARC sets. ARC Chains longer than the defined maximum count MUST be marked as
failed.
An effective operational maximum will have to be developed through
deployment experience in the field and will be documented within
[ARC-USAGE] once determined.
ARC chains with more than the defined operational maximum count MUST _INFORMATIONAL_: Because the AMS and AS header field values are made
be marked with "cv=fail". up of tag-spec constructs, the i= tag may be found anywhere within
the header field value, but is represented throughout this spec in
the initial position for convenience. Implementers are encouraged to
place the i= tag at the beginning of the field value to facilitate
human inspection of the headers.
3.2. ARC-Authentication-Results (AAR) 3.2. ARC-Authentication-Results (AAR)
The ARC-Authentication-Results header field is syntactically and The ARC-Authentication-Results header field is syntactically and
semantically identical to an Authentication-Results header field semantically identical, except for the header field name itself and
(defined in Section 2.2 of [I-D-7601bis] (A-R)). Note that several its instance tag, to an Authentication-Results header field (defined
optional data fields SHOULD be added (smtp.client-ip, dkim header.s, in Section 2.2 of [I-D-7601bis]).
arc.oldest-pass) to enable completeness for DMARC reporting.
Formally, the header field is specified as follows using ABNF Formally, the header field is specified as follows using ABNF
[RFC5234]: [RFC5234]:
arc-authres-header-prefix = "ARC-Authentication-Results:" [CFWS] arc-info arc-info = instance [CFWS] ";" authres-payload
arc-info = instance *([CFWS] propspec) [CFWS] ";" authres-payload arc-authres-header = "ARC-Authentication-Results:" [CFWS] arc-info
The purpose of this header field is to transmit the results of any
authentication done on the message downstream to participating ADMDs
validating and continuing the chain.
The AAR MUST contain all A-R results from within the participating The AAR MUST contain all Authentication-Results from within the
ADMD, regardless of how many A-R headers are on the message. participating ADMD, regardless of how many Authentication-Results
headers are on the message.
3.3. ARC-Message-Signature (AMS) 3.3. ARC-Message-Signature (AMS)
The ARC-Message-Signature header field is syntactically and The ARC-Message-Signature header field is simplified version of a
semantically identical to a DKIM-Signature header field [RFC6376], DKIM-Signature header field [RFC6376], with the following
with the following exceptions: modifications:
o There is an "i" tag, as described in Section 3.1. o There is an "i" tag, as described in Section 3.1.
o There is no "v" tag defined for the AMS header. As required for o There is no "v" tag defined for the AMS header. As required for
undefined tags, if seen, it MUST be ignored. undefined tags (in [RFC6376]), if seen, it MUST be ignored.
ARC-Seal header fields MUST NOT be included in the content covered by ARC-related header fields (ARC-Seal, ARC-Message-Signture, ARC-
the signature in this header field. Authentication-Results) MUST NOT be included in the content covered
by the signature in the signature in this header field.
The AMS SHOULD include any DKIM-Signature header fields already The AMS SHOULD include any DKIM-Signature header fields already
present on the message in the header fields covered by this present on the message in the header fields covered by this
signature. signature.
The AMS header field SHOULD not include (sign) the AAR header Authentication-Results header fields MUST NOT be included since they
field(s). (Early drafts of this protocol and some older examples are likely to be deleted by downstream ADMDs (per Section 5 of
included the AAR header(s) within the signing scope for the AMS, but
ambiguity regarding which of the potentially multiple AAR headers
(one per ARC set) argues against such practice.)
Authentication-Results header fields SHOULD NOT be included since
they are likely to be deleted by downstream ADMDs (per Section XXX of
[RFC7601]), thereby breaking the AMS signature. [RFC7601]), thereby breaking the AMS signature.
As with a DKIM-Signature, the purpose of this header field is to
allow the ADMD generating it to take some responsibility for handling
this message as it progresses toward delivery.
3.4. ARC-Seal (AS) 3.4. ARC-Seal (AS)
The ARC-Seal header field is syntactically and semantically similar The ARC-Seal header field is syntactically and semantically similar
to a DKIM-Signature field, with the following exceptions: to a DKIM-Signature field, with the following exceptions:
o There is an "i" tag, as described in Section 3.1. o There is an "i" tag, as described in Section 3.1.
o The ARC-Seal covers none of the body content of the message. It o The ARC-Seal covers none of the body content of the message. It
only covers specific header fields. (See below: Section 3.4.2.) only covers specific header fields as defined below:
As a result, no body canonicalization is done. Further, only Section 3.4.1. No body canonicalization is done.
"relaxed" header canonicalization (Section 3.4.2 of [RFC6376]) is
used.
o The only supported tags are "i" (Section 3.1 supercedes the
[RFC6376] definition), and "a", "b", "d, "s", "t". The latter 5
tag definitions are copied from Section 3.5 of [RFC6376].
o An additional tag, "cv" is defined. (See below: Section 3.4.1)
3.4.1. The 'cv' Tag
A new tag "cv" (chain validation) indicates the the outcome of
evaluating the existing ARC chain upon arrival at the ADMD that is
adding this header field. It accepts one of three possible values:
o none: There was no chain on the message when it arrived for
validation; typically occurs when the message arrives at a Message
Transfer Agent (MTA) from a Message Submission Agent (MSA) or when
any upstream MTAs may not be participating in ARC handling;
o fail: The message has a chain whose validation failed;
o pass: The message has a chain whose validation succeeded. o Only "relaxed" header canonicalization (Section 3.4.2 of
[RFC6376]) is used.
In ABNF terms: o The only supported tags are "i" (from Section 3.1 of this
document), and "a", "b", "d, "s", "t" from Section 3.5 of
[RFC6376].
seal-cv-tag = %x63.76 [FWS] "=" [FWS] ("none" / "fail" / "pass") o An additional tag, "cv" is defined in Section 3.4.2
3.4.2. Implicit Header Fields 3.4.1. Covered Header Fields
The ARC-Seal signs a canonicalized form of the ARC set header values. The ARC-Seal signs a specific canonicalized form of the ARC Set
The ARC set header values are compiled in increasing instance order, header values. The ARC set header values are compiled in increasing
starting at 1, and inclue the set being added at the time of sealing instance order, starting at 1, and include the set being added at the
the message. time of sealing the message.
Within a set, the header fields are listed in the following order: Within a set, the header fields are listed in the following order:
1. ARC-Authentication-Results 1. ARC-Authentication-Results
2. ARC-Message-Signature 2. ARC-Message-Signature
3. ARC-Seal 3. ARC-Seal
Where the ARC-Seal is the one being generated, it is input to the Where the ARC-Seal is the one being generated, it is input to the
hash function in its final form except with an empty "b=" value, in hash function in its final form except with an empty "b=" value, in
the same manner by which a DKIM-Signature signs itself. the same manner by which a DKIM-Signature signs itself ([RFC6376],
section 3.7).
Note that the signing scope for the ARC-Seal is modified in the Note that the signing scope for the ARC-Seal is modified in the
situation where a chain has failed validation (see Section 5.1). situation where a chain has failed validation (see Section 5.1).
4. Verifier Actions 3.4.2. The 'cv' Tag
A verifier takes the following steps to determine the state of the A new tag "cv" (chain validation) indicates the outcome of evaluating
ARC chain on a message (cv value). Canonicalization, hash functions, the existing ARC Chain upon arrival at the ADMD that is adding this
and signature validation methods are imported from Section 5 of header field. The values are defined per Section Section 2.2.
[RFC6376].
[[ Note: need markdown flag to have subordinate numbering distinction In ABNF terms:
issue 11 [3] ]]
1. Collect all ARC sets currently on the message. If there were chain-status = ("none" / "fail" / "pass")
seal-cv-tag = %x63.76 [FWS] "=" [FWS] chain-status
4. Verifier Actions
A verifier takes the following steps to validate the ARC Chain.
Canonicalization, hash functions, and signature validation methods
are imported from Section 5 of [RFC6376].
1. Collect all ARC Sets currently on the message. If there were
none, the ARC state is "none" and the algorithm stops here. none, the ARC state is "none" and the algorithm stops here.
2. If the form of any ARC set is invalid (e.g., does not contain 2. Check the morphology of the ARC Chain. If any of these
exactly one of each of the three ARC-specific header fields), conditions are not met, the chain state is "fail" and the
then the chain state is "fail" and the algorithm stops here. a. algorithm stops here:
To avoid the overhead of unnecessary computation and delay from
crypto and DNS operations, the cv value for all ARC-Seal(s) MAY
be checked at this point. If any of the values are "fail", then
the overall state of the chain is "fail" and the algorithm stops
here.
3. Conduct verification of the ARC-Message-Signature header field 1. Each ARC Set must be complete (e.g., contains exactly one of
bearing the highest instance number. If this verification fails, each of the three ARC-specific header fields);
then the chain state is "fail" and the algorithm stops here.
4. For each ARC-Seal from the "N"th instance to the first, apply the 2. The instance values must form a continuous sequence from 1..N
following logic: a. If the value of the "cv" tag on that seal is with no gaps or repeats;
"fail", the chain state is "fail" and the algorithm stops here.
(This step SHOULD be skipped if the earlier step (2.1) was
performed) b. In Boolean nomenclature: if ((i == 1 && cv !=
"none") or (cv == "none" && i != 1)) then the chain state is
"fail" and the algorithm stops here (note that the ordering of
the logic is structured for short-circuit evaluation). c.
Initialize a hash function corresponding to the "a" tag of the
ARC-Seal. d. Compute the canonicalized form of the ARC header
fields, in the order described in Section 3.4.2, using the
"relaxed" header canonicalization defined in Section 3.4.2 of
[RFC6376]. Pass the canonicalized result to the hash function.
e. Retrieve the final digest from the hash function. f.
Retrieve the public key identified by the "s" and "d" tags in the
ARC-Seal, as described in Section 2.1.6. g. Determine whether
the signature portion ("b" tag) of the ARC-Seal and the digest
computed above are valid according to the public key. (See also
Section Section 4.2 for failure case handling) h. If the
signature is not valid, the chain state is "fail" and the
algorithm stops here.
5. If all seals pass validation, then the chain state is "pass", and 3. The cv value for all ARC-Seal(s) must be non-failing:
the algorithm is complete.
6. Results from the determination of this algorithm SHOULD be 1. For i > 1, the value must be "pass";
recorded in the Authentication-Results header
Whatever the end result of the verifier's checks via the algorithm 2. For i = 1, the value must be "none".
specified above, the results MUST be added into the Authentication-
Results header(s) for the ADMD.
[[ See issue 12 [4] regarding the final paragraph ]] 3. For each ARC-Message-Signature from the "N"th instance to the
first, validate the AMS:
The verifier should save the cv state for subsequent use by any 1. If the "N"th instance (most recent) signature fails, then the
sealing which may be done later (potentially after message chain state is "fail" and the algorithm stops here.
modification) within the same trust boundary. The cv state may be
recorded by sealing at the time of verification in an initial ARC set
(for the ADMD) or may be recorded out of band depending on the
architecture of the ADMD.
4.1. ARC Authentication-Results Information 2. If one of the prior AMS signatures fails to validate (for
instance "M"), then set the oldest-pass value to the lowest
AMS instance number which passed (M+1) and go onto the next
step (there is no need to check any other (older) AMS
signatures). This does not affect the validity of the chain.
3. If all AMS signatures verify, set the oldest-pass value to
zero (0).
4. For each ARC-Seal from the "N"th instance to the first, validate
the seal.
1. If any seal is not valid, the chain state is "fail" and the
algorithm stops here.
2. If all seals pass validation, then the chain state is "pass",
and the algorithm is complete.
The end result of the verifier's checks via this algorithm MUST be
added into the Authentication-Results header(s) for the ADMD.
_INFORMATIONAL_: Recipients of an ARC Chain that is invalid or does
not pass SHOULD NOT draw negative conclusions without a good
understanding of the wider handling context. Until ARC usage is
widespread, intermediaries will continue to modify messages without
ARC seals.
As with a failing DKIM signature ([RFC6376] Section-6.3), a message
with a failing ARC Chain MUST be treated the same as a message with
no ARC Chain.
4.1. Authentication-Results Information
Certain information pertinent to ascertaining message disposition can Certain information pertinent to ascertaining message disposition can
be lost in transit when messages are handled by intermediaries. For be lost in transit when messages are handled by intermediaries. For
example, failing DKIM signatures are sometimes removed by MTAs, and example, failing DKIM signatures are sometimes removed by MTAs, and
most DKIM signatures on messages modified by intermediaries will most DKIM signatures on messages modified by intermediaries will
fail. Recording the following information in the A-R provides a fail. Recording the following information in the Authentication-
mechanism for this information to survive transit. Results stamped as part of the ARC evaluation provides a mechanism
for this information to survive transit through a particular ADMD.
Stamped ARC evaluation results is limited to the Chain Validation
status (cv) from Section 2.2.
The ptypes and properties defined in this section SHOULD be recorded The ptypes and properties defined in this section SHOULD be recorded
in the AR: in the Authentication-Results:
o smtp.client-ip - The connecting client IP address from which the o smtp.client-ip - The connecting client IP address from which the
message is received; message is received;
o header.s - Defined in [RFC6376] section 7.2 o header.oldest-pass - The instance number of the oldest AMS that
still validates, or 0 if all pass.
o arc.oldest-pass - The instance number of the oldest AMS that still
validates, or 0 if all pass.
[[ Also see issue 20 [5] for another possible field to be added and
issue 21 [6] re which document should define these for IANA action.
]]
4.2. Handling DNS Problems While Validating ARC 4.2. Handling DNS Problems While Validating ARC
DNS-based failures to verify a chain are treated no differently than DNS-based failures to verify a chain are treated no differently than
any other ARC violation. They result in a "cv=fail" verdict. any other ARC violation. They result in a "cv=fail" verdict.
4.3. Responding to ARC Validity Violations During the SMTP Transaction 4.3. Responding to ARC Validity Violations During the SMTP Transaction
If a receiver determines that the ARC chain has failed, the receiver If a receiver determines that the ARC Chain has failed, the receiver
MAY signal the breakage through the extended SMTP response code 5.7.7 MAY signal the breakage through the extended SMTP response code 5.7.7
[RFC3463] "message integrity failure" [ENHANCED-STATUS] and [RFC3463] "message integrity failure" [ENHANCED-STATUS] and
corresponding SMTP response code. corresponding SMTP response code.
5. Signer Actions 5. Sealer Actions
[[ See issue 13 [7] for critique ]]
This section includes a specification of the actions an ARC signer
takes when presented with a message.
The signer MUST undertake the following steps: An ARC sealer MUST take the following actions when presented with a
message:
1. Before creating an ARC signature, perform any other, normal 1. Before creating an ARC signature, perform any other, normal
authentication and/or signing, so that the ARC signature can authentication and/or signing, so that the ARC signature can
cover those results. cover those results.
2. Build and attach the new ARC set: 2. Build and attach the new ARC Set:
1. If an ARC chain exists on the message, then set "N" equal to 1. If an ARC Chain exists on the message, then set "N" equal to
the highest instance number found on the chain (i=); the highest instance number found on the chain (i=);
otherwise set "N" equal to zero for the following steps. otherwise set "N" equal to zero for the following steps.
2. Generate and attach to the message an ARC-Authentication- 2. Generate and attach to the message an ARC-Authentication-
Results header field using instance number N+1 and the same Results header field as defined in Section Section 3.2, using
content from the previous step. instance number N+1 and the same content from the previous
step.
3. Generate and attach to the message an ARC-Message-Signature 3. Generate and attach to the message an ARC-Message-Signature
header field as defined in Section 3.3 above, using instance header field as defined in Section 3.3 above, using instance
number N+1. number N+1.
4. Generate and attach to the message an ARC-Seal header field 4. Generate and attach to the message an ARC-Seal header field
using the general algorithm described in Section 3.4 above, using the general algorithm described in Section 3.4 above,
the chain validation status as determined in Section 4, and the chain validation status as determined in Section 4, and
instance number N+1. instance number N+1.
5.1. Marking and Sealing "cv=fail" (Invalid) Chains 5.1. Marking and Sealing "cv=fail" (Invalid) Chains
The header fields signed by the AS header field b= value in the case The header fields signed by the AS header field b= value in the case
of a chain failure MUST be only the matching instance headers created of a chain failure MUST be only the matching instance headers created
by the MTA which detected the malformed chain, as if this newest ARC by the MTA which detected the malformed chain, as if this newest ARC
set was the only set present. Set was the only set present.
6. Usage of ARC and Chain Validity
6.1. Relationship between DKIM-Signature and AMS signing scopes
[[ See issue 14 [8] for critique of this section ]]
DKIM-Signatures SHOULD never sign any ARC header fields.
6.2. Assessing Chain Validity Violations
[[ Issue 15 [9] ]]
Email transit can produce broken signatures for a wide variety of
benign reasons. This includes possibly breaking one or more ARC
signatures. Therefore, receivers need to be wary of ascribing motive
to such breakage although patterns of common behaviour may provide
some basis for adjusting local policy decisions.
ARC does not attempt to protect an entire message. There are various _INFORMATIONAL:_ In the case of a malformed or otherwise invalid
ways that a message can still be problematic, in spite of having a chain there is no way to generate a deterministic set of AS header
valid ARC chain. Consequently, all normal, content-based analysis fields ({#implicit_as_h}) so this approach is mandated.
SHOULD still be performed on any message having a valid chain of ARC
header sets.
7. Recording and Reporting the Results of ARC Evaluation 6. Recording and Reporting the Results of ARC Evaluation
The evaluation of an ARC chain provides information which will be The evaluation of an ARC Chain provides information which will be
useful to both the receiver (or intermediary) and to the initial useful to both the receiver (or intermediary) and to the initial
sender of the message. This information should be preserved and sender of the message. This information should be preserved and
reported as follows. reported as follows.
7.1. Information from an ARC Evaluation 6.1. Information from an ARC Evaluation
The evaluation of an ARC chain produces a list of domain names for The evaluation of an ARC Chain produces a list of domain names for
participating intermediaries which handled the message, to wit: participating intermediaries which handled the message, to wit:
o A list of the "d=" domains found in the validated ARC-Seal header o A list of the "d=" domains found in the validated ARC-Seal header
fields fields
o The "d=" domain found in the most recent (highest instance number) o The "d=" domain found in the most recent (highest instance number)
AMS header field (since that is the only one necessarily AMS header field (since that is the only one necessarily
validated) validated)
In the case of a failed chain, only the terminal ARC set is covered In the case of a failed chain, only the terminal ARC Set is covered
by the ARC-Seal so the reporting is limited to the findings in that by the ARC-Seal so the reporting is limited to the findings in that
terminal ARC set. terminal ARC Set.
7.2. Recording (local) ARC Evaluation Results 6.2. Recording (local) ARC Evaluation Results
Receivers MAY add an "arc=[pass|fail|policy]" method annotation into Receivers who process an attached ARC Chain SHOULD add an
a locally-affixed Authentication-Results [RFC7601] header field along "arc=[pass|fail|policy]" method annotation into a locally-affixed
with any salient comment(s). Authentication-Results [RFC7601] header field along with any salient
comment(s).
Details of the ARC chain which was evaluated should be included in Details of the ARC Chain which was evaluated should be included in
the Authentication-Results and AAR headers per Section Section 4.1. the Authentication-Results and AAR headers per Section Section 4.1.
7.3. DMARC Reporting of ARC Findings - Interim 6.3. DMARC Reporting of ARC Findings - Interim
[[ Note: Move to separate document? [10] (see the additional fields
specified in Section 4.1) ]]
Receivers SHOULD indicate situations in which ARC evaluation Receivers SHOULD indicate situations in which ARC evaluation
influenced the results of their local policy determination. DMARC influenced the results of their local policy determination. DMARC
reporting of ARC-informed decisions can be accomplished by adding a reporting of ARC-informed decisions can be accomplished by adding a
local_policy comment explanation containing the list of data local_policy comment explanation containing the list of data
discovered in the ARC evaluation (Section 7.1 and Section 4.1): discovered in the ARC evaluation, which at a minimum SHOULD include:
* the Chain Validation status, * the domain and selector for each AS,
<policy_evaluated> * the IP addresses of the mail originating ADMD:
<disposition>delivered</disposition>
<dkim>fail</dkim>
<spf>fail <comment>source.ip=10.0.0.1</comment></spf>
<reason>
<type>local_policy</type>
<comment>arc=pass ams[2].d=d2.example ams[2].s=s1 as[2].d=d2.example
as[2].s=s2 as[1].d=d1.example as[1].s=s3</comment>
</reason>
</policy_evaluated>
In the suggested sample, d2.example is the sealing domain for ARC[2]
and d1.example is the sealing domain for ARC[1].
Mediators SHOULD generate DMARC reports on messages which transit <policy_evaluated>
their system just like any other message which they receive. This <disposition>none</disposition>
will result in multiple reports for each mediated message as they <dkim>fail</dkim>
transit the series of handlers. DMARC report consumers should be <spf>fail</spf>
aware of this behaviour and make the necessary accommodations. <reason>
<type>local_policy</type>
<comment>arc=pass ams[2].d=d2.example ams[2].s=s1 as[2].d=d2.example
as[2].s=s2 as[1].d=d1.example as[1].s=s3 client-ip[1]=10.10.10.13</comment>
</reason>
</policy_evaluated>
8. Supporting Alternate Signing Algorithms In the sample above, d2.example is the sealing domain for ARC[2] and
d1.example is the sealing domain for ARC[1].
This section has been moved to [ARC-MULTI] Intermediary message handlers SHOULD generate DMARC reports on
messages which transit their system just like any other message which
they receive. This will result in multiple reports for each mediated
message as they transit the series of handlers. DMARC report
consumers should be aware of this behaviour and make the necessary
accommodations.
9. Privacy Considerations 7. Privacy Considerations
The ARC chain provides a verifiable record of the handlers for a The ARC Chain provides a verifiable record of the handlers for a
message. Anonymous remailers will probably not find this compatible message. Anonymous remailers will probably not find this compatible
with their operating goals. with their operating goals.
10. IANA Considerations 8. IANA Considerations
[[ See issue 21 [11] regarding which document should be definitive [[ Note to the RFC Editors: Some of these fields are defined both
for these fields. ]] here and in [I-D-7601bis]. Please delete the overlap from whichever
document goes through the publication process after the other. ]]
This specification adds three new header fields as defined below. This specification adds three new header fields as defined below.
10.1. Authentication-Results Method Registry Update 8.1. Authentication-Results Method Registry Update
This draft adds one item to the IANA "Email Authentication Methods" This draft adds one item to the IANA "Email Authentication Methods"
registry: registry:
o Method : arc o Method : arc
Defined: [I-D.ARC] Defined: [I-D.ARC]
ptype: header ptype: header
Property: chain evaluation result Property: chain evaluation result
Value: chain evaluation result status (see Section 3.4) Value: chain evaluation result status (see Section 3.4)
Status: active Status: active
o Method : dkim 8.2. Email Authentication Result Names Registry Update
Defined: [I-D.ARC]
ptype: header
Property: selector
Value: value of signature "s" tag (see [RFC6376]) This draft updates the Email Authentication Results registry, most
recently defined in [I-D-7601bis], with one new authentication method
and several status codes, all defined by this document:
Status: active o Auth Method : arc
Code: "none", "pass", "fail"
Specification: [I-D.ARC] Section 3.4.2 Status: active
o Method : spf o Method : spf
Defined: [I-D.ARC] Defined: [I-D.ARC]
ptype: smtp ptype: smtp
Property: client-ip Property: client-ip
Value: the connecting client IP address from which the message is Value: the connecting client IP address from which the message is
received received
Status: active Status: active
o Method : arc o Method : arc
Defined: [I-D.ARC] Defined: [I-D.ARC]
ptype: header ptype: header
Property: oldest-pass Property: oldest-pass
Value: the oldest instance with a still validating AMS signature Value: the oldest instance with a still validating AMS signature
Status: active Status: active
10.2. Definitions of the ARC header fields 8.3. Definitions of the ARC header fields
This specification adds three new header fields to the "Permanent This specification adds three new header fields to the "Permanent
Message Header Field Registry", as follows: Message Header Field Registry", as follows:
o Header field name: ARC-Seal o Header field name: ARC-Seal
Applicable protocol: mail Applicable protocol: mail
Status: draft Status: draft
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): [I-D.ARC] Specification document(s): [I-D.ARC]
Related information: [RFC6376] Related information: [RFC6376]
o Header field name: ARC-Message-Signature o Header field name: ARC-Message-Signature
Applicable protocol: mail Applicable protocol: mail
Status: draft Status: draft
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): [I-D.ARC] Specification document(s): [I-D.ARC]
Related information: [RFC6376] Related information: [RFC6376]
o Header field name: ARC-Authentication-Results o Header field name: ARC-Authentication-Results
Applicable protocol: mail Applicable protocol: mail
Status: standard Status: standard
Author/Change controller: IETF Author/Change controller: IETF
Specification document(s): [I-D.ARC] Specification document(s): [I-D.ARC]
Related information: [RFC7601] Related information: [RFC7601]
11. Security Considerations 9. Security Considerations
The Security Considerations of [RFC6376] and [RFC7601] apply directly The Security Considerations of [RFC6376] and [RFC7601] apply directly
to this specification. to this specification.
11.1. Header Size 9.1. Header Size
Inclusion of ARC sets in the header of emails may cause problems for Inclusion of ARC Sets in the header of emails may cause problems for
some older or more constrained MTAs if they are unable to accept the some older or more constrained MTAs if they are unable to accept the
greater size of the header. greater size of the header.
11.2. DNS Operations 9.2. DNS Operations
Operators who receive a message bearing N ARC sets have to complete Operators who receive a message bearing N ARC Sets have to complete
up to N+1 DNS queries to evaluate the chain (barring DNS redirection up to N+1 DNS queries to evaluate the chain (barring DNS redirection
mechanisms which can increase the lookups for a given target value). mechanisms which can increase the lookups for a given target value).
This has at least two effects: This has at least two effects:
1. An attacker can send a message to an ARC partipant with a 1. An attacker can send a message to an ARC participant with a
concocted sequence of ARC sets bearing the domains of intended concocted sequence of ARC Sets bearing the domains of intended
victims, and all of them will be queried by the participant until victims, and all of them will be queried by the participant until
a failure is discovered. The difficulty of forging the signature a failure is discovered. The difficulty of forging the signature
values should limit the extent of this load to domains under values should limit the extent of this load to domains under
control of the attacker. control of the attacker.
2. DKIM only does one DNS check per signature, while this one can do 2. DKIM only does one DNS check per signature, while this one can do
many (per chain). Absent caching, slow DNS responses can cause many (per chain). Absent caching, slow DNS responses can cause
SMTP timeouts; and backlogged delivery queues on mediating SMTP timeouts; and backlogged delivery queues on mediating
systems. This could be exploited as a DoS attack. systems. This could be exploited as a DoS attack.
11.3. Message Content Suspicion 9.3. Message Content Suspicion
Recipients are cautioned to treat messages bearing ARC sets with the Recipients are cautioned to treat messages bearing ARC Sets with the
same suspicion that they apply to all other email messages. This same suspicion that they apply to all other email messages. This
includes appropriate content scanning and other checks for includes appropriate content scanning and other checks for
potentially malicious content. The handlers which are identified potentially malicious content. The handlers which are identified
within the ARC chain may be used to provide input to local policy within the ARC Chain may be used to provide input to local policy
engines in cases where DMARC validation fails (due to mediation engines in cases where DMARC validation fails (due to mediation
impacting SPF attribution, DKIM validity or alignment). impacting SPF attribution, DKIM validity or alignment).
Note that a passing ARC chain may not adequately mean that the Note that a passing ARC Chain may not adequately mean that the
message is safe because: message is safe because:
1. You have to trust all signatories; and 1. You have to trust all signatories; and
2. Even trusted systems may have become compromised or may not 2. Even trusted systems may have become compromised or may not
properly authenticate messages, so even with a chain of trusted properly authenticate messages, so even with a chain of trusted
participants, the message might still never have authenticated in participants, the message might still never have authenticated in
the first place (which is why you have the AAR to inspect) or the first place (which is why you have the AAR to inspect) or
could have been subject to unintended modifications. could have been subject to unintended modifications.
12. Evaluating the Efficacy of the ARC Protocol 10. Evaluating the Efficacy of the ARC Protocol (Experimental
Considerations)
The ARC protocol is designed to mitigate some of the most common The ARC protocol is designed to mitigate some of the most common
failure conditions for email which transits intermediary handlers en failure conditions for email which transits intermediary handlers en
route to the final recipient. Some of these problems have happened route to the final recipient. Some of these problems have happened
due to the adoption of the DMARC protocol [RFC7489] and are listed in due to the adoption of the DMARC protocol [RFC7489] and are listed in
[RFC6377] and [RFC7960]. [RFC6377] and [RFC7960].
As the ARC protocol becomes standardized and implemented amongst As the ARC protocol becomes standardized and implemented amongst
intermediary handlers, the following aspects should be evaluated in intermediary handlers, the following aspects should be evaluated in
order to determine the success of the protocol in accomplishing the order to determine the success of the protocol in accomplishing the
intended benefits. intended benefits.
NOTE: Terminology within this section does NOT follow [RFC2119] NOTE: Terminology within this section does NOT follow [RFC2119]
interpretation. This section represents the current thoughts of the interpretation. This section represents the current thoughts of the
working group regarding unanswered questions related to the protocol. working group regarding unanswered questions related to the protocol.
Wider deployment will inform these topics and probably expand them. Wider deployment will inform these topics and probably expand them.
12.1. Success Consideration 10.1. Success Consideration
Currently, many receivers have heuristically determined overrides in Currently, many receivers have heuristically determined overrides in
order to rescue mail from intermediary-caused failures. Many of order to rescue mail from intermediary-caused failures. Many of
those overrides rely on inferrence rather than direct evidence. those overrides rely on inferrence rather than direct evidence.
ARC will be a success if, for ARC sealed messages, receivers are able ARC will be a success if, for ARC sealed messages, receivers are able
to implment ARC-based algorithmic decisions based on the direct to implment ARC-based algorithmic decisions based on the direct
evidence found within the ARC chain. This is especially relevant for evidence found within the ARC Chain. This is especially relevant for
DMARC processing when the DKIM d= value is aligned with the DMARC processing when the DKIM d= value is aligned with the
rfc5322.From author domain. rfc5322.From author domain.
12.2. Failure Considerations 10.2. Failure Considerations
The intent of ARC is to be at most value-add and at worst benign. If The intent of ARC is to be at most value-add and at worst benign. If
ARC opens up significant new vectors for abuse (see Section 11) then ARC opens up significant new vectors for abuse (see Section 9) then
this protocol will be a failure. Note that weaknesses inherent in this protocol will be a failure. Note that weaknesses inherent in
the mail protocols ARC is built upon (such as DKIM replay attacks and the mail protocols ARC is built upon (such as DKIM replay attacks and
other known issues) are not new vectors which can be attributed to other known issues) are not new vectors which can be attributed to
this specification. this specification.
12.3. Open Questions 10.3. Open Questions
The following open questions are academic and have no clear answer at The following open questions are academic and have no clear answer at
the time of the development of the protocol. However, wide-spread the time of the development of the protocol. However, wide-spread
deployment should be able to gather the necessary data to answer some deployment should be able to gather the necessary data to answer some
or all of them. or all of them.
12.3.1. Value of the ARC-Seal (AS) Header 10.3.1. Value of the ARC-Seal (AS) Header
Data should be collected to show if the ARC-Seal (AS) provides value Data should be collected to show if the ARC-Seal (AS) provides value
beyond the ARC Message Signature (AMS) for either making delivery beyond the ARC Message Signature (AMS) for either making delivery
decisions or catching malicious actors trying to craft or replay decisions or catching malicious actors trying to craft or replay
malicious chains. malicious chains.
12.3.2. DNS Overhead 10.3.2. DNS Overhead
Longer ARC chains will require more queries to retrieve the keys for Longer ARC Chains will require more queries to retrieve the keys for
validating the chain. While this is not believed to be a security validating the chain. While this is not believed to be a security
issue (see Section 11.2), it is unclear how much overhead will truly issue (see Section 9.2), it is unclear how much overhead will truly
be added. This is similar to some of the initial processing and be added. This is similar to some of the initial processing and
query load concerns which were debated at the time of the DKIM query load concerns which were debated at the time of the DKIM
specification development. specification development.
Data should be collected to better understand usable length and Data should be collected to better understand usable length and
distribution of lengths found in valid ARC chains along with the the distribution of lengths found in valid ARC Chains along with the the
DNS impact of processing ARC chains. DNS impact of processing ARC Chains.
12.3.3. Distinguishing Valuable from Worthless Trace Information An effective operational maximum will have to be developed through
deployment experience in the field.
10.3.3. Distinguishing Valuable from Worthless Trace Information
There are several edge cases where the information in the AAR can There are several edge cases where the information in the AAR can
make the difference between message delivery or rejection. For make the difference between message delivery or rejection. For
example, if there is a well known mailing list that ARC seals but example, if there is a well known mailing list that ARC seals but
doesn't do its own initial DMARC enforcement, a Final Receiver with doesn't do its own initial DMARC enforcement, a Final Receiver with
this knowledge could make a delivery decision based upon the this knowledge could make a delivery decision based upon the
authentication information it sees in the corresponding AAR header. authentication information it sees in the corresponding AAR header.
Certain trace information in the AAR is useful/necessary in the Certain trace information in the AAR is useful/necessary in the
construction of DMARC reports. It would be beneficial to identify construction of DMARC reports. It would be beneficial to identify
skipping to change at page 25, line 19 skipping to change at page 23, line 25
and/or provide other signals related to message delivery. and/or provide other signals related to message delivery.
It is unclear what trace information will be valuable for all It is unclear what trace information will be valuable for all
receivers, regardless of size. receivers, regardless of size.
Data should be collected on what trace information receivers are Data should be collected on what trace information receivers are
using that provides useful signals that affect deliverability, and using that provides useful signals that affect deliverability, and
what portions of the trace data are left untouched or provide no what portions of the trace data are left untouched or provide no
useful information. useful information.
Since many such systems are intentionly proprietary or confidential Since many such systems are intentionally proprietary or confidential
to prevent gaming by abusers, it may not be viable to reliably answer to prevent gaming by abusers, it may not be viable to reliably answer
this particular question. The evolving nature of attacks can also this particular question. The evolving nature of attacks can also
shift the landscape of "useful" information over time. shift the landscape of "useful" information over time.
13. Implementation Status 11. Implementation Status
[[ Note to the RFC Editor: Please remove this section before [[ Note to the RFC Editor: Please remove this section before
publication along with the reference to [RFC6982]. ]] publication along with the reference to [RFC6982]. ]]
This section records the status of known implementations of the This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC6982]. Internet-Draft, and is based on a proposal described in [RFC6982].
The description of implementations in this section is intended to The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation RFCs. Please note that the listing of any individual implementation
skipping to change at page 26, line 5 skipping to change at page 24, line 8
features. Readers are advised to note that other implementations may features. Readers are advised to note that other implementations may
exist. exist.
This information is known to be correct as of the seventh This information is known to be correct as of the seventh
interoperability test event which was held on 2017-07-15 & 16 at interoperability test event which was held on 2017-07-15 & 16 at
IETF99. IETF99.
For a few of the implementations, later status information was For a few of the implementations, later status information was
available as of December 2017. available as of December 2017.
13.1. GMail test reflector and incoming validation 11.1. GMail test reflector and incoming validation
Organization: Google Organization: Google
Description: Internal production implementation with both debug Description: Internal production implementation with both debug
analysis and validating + sealing pass-through function analysis and validating + sealing pass-through function
Status of Operation: Production - Incoming Validation Status of Operation: Production - Incoming Validation
Coverage: Full spec implemented as of [ARC-DRAFT-06] Coverage: Full spec implemented as of [ARC-DRAFT-06]
Licensing: Proprietary - Internal only Licensing: Proprietary - Internal only
Implementation Notes: Implementation Notes:
o Full functionality was demonstrated during the interop testing on o Full functionality was demonstrated during the interop testing on
2017-07-15. 2017-07-15.
Contact Info: arc-discuss@dmarc.org [12] Contact Info: arc-discuss@dmarc.org [2]
13.2. AOL test reflector and internal tagging 11.2. AOL test reflector and internal tagging
Organization: AOL Organization: AOL
Description: Internal prototype implementation with both debug Description: Internal prototype implementation with both debug
analysis and validating + sealing pass-through function analysis and validating + sealing pass-through function
Status of Operation: Beta Status of Operation: Beta
Coverage: ARC Chain validity status checking is operational, but only
Coverage: ARC chain validity status checking is operational, but only applied to email addresses enrolled in the test program.
applied to email addresses enrolled in the test program. This system This system conforms to [ARC-DRAFT-06]
conforms to [ARC-DRAFT-06]
Licensing: Proprietary - Internal only Licensing: Proprietary - Internal only
Implementation Notes: Implementation Notes:
o 2017-07-15: Full functionality verified during the interop o 2017-07-15: Full functionality verified during the interop
testing. testing.
Contact Info: arc-discuss@dmarc.org [13] Contact Info: arc-discuss@dmarc.org [3]
13.3. dkimpy 11.3. dkimpy
Organization: dkimpy developers/Scott Kitterman Organization: dkimpy developers/Scott Kitterman
Description: Python DKIM package Description: Python DKIM package
Status of Operation: Production Status of Operation: Production
Coverage: Coverage:
o 2017-07-15: The internal test suite is incomplete, but the command o 2017-07-15: The internal test suite is incomplete, but the command
line developmental version of validator was demonstrated to line developmental version of validator was demonstrated to
interoperate with the Google and AOL implementations during the interoperate with the Google and AOL implementations during the
interop on 2017-07-15 and the released version passes the tests in interop on 2017-07-15 and the released version passes the tests in
[ARC-TEST] arc_test_suite [14] with both python and python3. [ARC-TEST] arc_test_suite [4] with both python and python3.
Licensing: Open/Other (same as dkimpy package = BCD version 2) Licensing: Open/Other (same as dkimpy package = BCD version 2)
Contact Info: https://launchpad.net/dkimpy Contact Info: https://launchpad.net/dkimpy
13.4. OpenARC 11.4. OpenARC
Organization: TDP/Murray Kucherawy Organization: TDP/Murray Kucherawy
Description: Implemention of milter functionality related to the Description: Implemention of milter functionality related to the
OpenDKIM and OpenDMARC packages OpenDKIM and OpenDMARC packages
Status of Operation: Beta Status of Operation: Beta
Coverage: Built to support [ARC-DRAFT-10] Coverage: Built to support [ARC-DRAFT-10]
Licensing: Open/Other (same as OpenDKIM and OpenDMARC packages) Licensing: Open/Other (same as OpenDKIM and OpenDMARC packages)
Implementation Notes: Implementation Notes:
o The build is FreeBSD oriented but some packages have been built o The build is FreeBSD oriented but some packages have been built
for easier deployment on RedHat-based Linux platforms. for easier deployment on RedHat-based Linux platforms.
o Some issues still exist when deploying in a chained milter o Some issues still exist when deploying in a chained milter
arrangement (such as OpenSPF -> OpenDKIM -> OpenDMARC -> OpenARC) arrangement (such as OpenSPF -> OpenDKIM -> OpenDMARC -> OpenARC)
with coordination between the stages. When deployed in a with coordination between the stages. When deployed in a
"sandwich" configuration around an MLM, there is no effective "sandwich" configuration around an MLM, there is no effective
mechanism to convey trust from the ingress (validator) to egress mechanism to convey trust from the ingress (validator) to egress
skipping to change at page 27, line 44 skipping to change at page 25, line 29
for easier deployment on RedHat-based Linux platforms. for easier deployment on RedHat-based Linux platforms.
o Some issues still exist when deploying in a chained milter o Some issues still exist when deploying in a chained milter
arrangement (such as OpenSPF -> OpenDKIM -> OpenDMARC -> OpenARC) arrangement (such as OpenSPF -> OpenDKIM -> OpenDMARC -> OpenARC)
with coordination between the stages. When deployed in a with coordination between the stages. When deployed in a
"sandwich" configuration around an MLM, there is no effective "sandwich" configuration around an MLM, there is no effective
mechanism to convey trust from the ingress (validator) to egress mechanism to convey trust from the ingress (validator) to egress
(signer) instances. (_NOTE_: this is expected to resolved with a (signer) instances. (_NOTE_: this is expected to resolved with a
new release of OpenDMARC expected in January 2018.) new release of OpenDMARC expected in January 2018.)
Contact Info: arc-discuss@dmarc.org [15] Contact Info: arc-discuss@dmarc.org [5]
13.5. Mailman 3.2 patch 11.5. Mailman 3.2 patch
Organization: Mailman development team Organization: Mailman development team
Description: Integrated ARC capabilities within the Mailman 3.2 Description: Integrated ARC capabilities within the Mailman 3.2
package package
Status of Operation: Patch submitted Status of Operation: Patch submitted
Coverage: Based on OpenARC Coverage: Based on OpenARC
Licensing: Same as mailman package - GPL Licensing: Same as mailman package - GPL
Implementation Notes: Implementation Notes:
o Appears to work properly in at least one beta deployment, but o Appears to work properly in at least one beta deployment, but
waiting on acceptance of the pull request into the mainline of waiting on acceptance of the pull request into the mainline of
mailman development mailman development
Contact Info: https://www.gnu.org/software/mailman/contact.html Contact Info: https://www.gnu.org/software/mailman/contact.html
13.6. Copernica/MailerQ web-based validation 11.6. Copernica/MailerQ web-based validation
Organization: Copernica Organization: Copernica
Description: Web-based validation of ARC-signed messages Description: Web-based validation of ARC-signed messages
Status of Operation: Beta Status of Operation: Beta
Coverage: Built to support [ARC-DRAFT-05] Coverage: Built to support [ARC-DRAFT-05]
Licensing: On-line usage only Licensing: On-line usage only
Implementation Notes: Implementation Notes:
o Released 2016-10-24 o Released 2016-10-24
o Requires full message content to be pasted into a web form found o Requires full message content to be pasted into a web form found
at http://arc.mailerq.com/ (warning - https is not supported). at http://arc.mailerq.com/ (warning - https is not supported).
o An additional instance of an ARC signature can be added if one is o An additional instance of an ARC signature can be added if one is
willing to paste a private key into an unsecured web form. willing to paste a private key into an unsecured web form.
skipping to change at page 28, line 45 skipping to change at page 26, line 20
at http://arc.mailerq.com/ (warning - https is not supported). at http://arc.mailerq.com/ (warning - https is not supported).
o An additional instance of an ARC signature can be added if one is o An additional instance of an ARC signature can be added if one is
willing to paste a private key into an unsecured web form. willing to paste a private key into an unsecured web form.
o 2017-07-15: Testing shows that results match the other o 2017-07-15: Testing shows that results match the other
implementations listed in this section. implementations listed in this section.
Contact Info: https://www.copernica.com/ Contact Info: https://www.copernica.com/
13.7. Rspamd 11.7. Rspamd
Organization: Rspamd community Organization: Rspamd community
Description: ARC signing and verification module Description: ARC signing and verification module
Status of Operation: Production, though deployment usage is unknown Status of Operation: Production, though deployment usage is unknown
Coverage: Built to support [ARC-DRAFT-06] Coverage: Built to support [ARC-DRAFT-06]
Licensing: Open source Licensing: Open source
Implementation Notes: Implementation Notes:
o 2017-06-12: Released with version 1.6.0 o 2017-06-12: Released with version 1.6.0
o 2017-07-15: Testing during the interop showed that the validation o 2017-07-15: Testing during the interop showed that the validation
functionality interoperated with the Google, AOL, dkimpy and functionality interoperated with the Google, AOL, dkimpy and
MailerQ implementations MailerQ implementations
Contact Info: https://rspamd.com/doc/modules/arc.html and Contact Info: https://rspamd.com/doc/modules/arc.html and
https://github.com/vstakhov/rspamd https://github.com/vstakhov/rspamd
skipping to change at page 29, line 19 skipping to change at page 26, line 38
o 2017-06-12: Released with version 1.6.0 o 2017-06-12: Released with version 1.6.0
o 2017-07-15: Testing during the interop showed that the validation o 2017-07-15: Testing during the interop showed that the validation
functionality interoperated with the Google, AOL, dkimpy and functionality interoperated with the Google, AOL, dkimpy and
MailerQ implementations MailerQ implementations
Contact Info: https://rspamd.com/doc/modules/arc.html and Contact Info: https://rspamd.com/doc/modules/arc.html and
https://github.com/vstakhov/rspamd https://github.com/vstakhov/rspamd
13.8. PERL MAIL::DKIM module 11.8. PERL MAIL::DKIM module
Organization: FastMail Organization: FastMail
Description: Email domain authentication (sign and/or verify) module, Description: Email domain authentication (sign and/or verify) module,
previously included SPF / DKIM / DMARC, now has ARC added previously included SPF / DKIM / DMARC, now has ARC added
Status of Operation: Production, deployment usage unknown Status of Operation: Production, deployment usage unknown
Coverage: Built to support [ARC-DRAFT-10] Coverage: Built to support [ARC-DRAFT-10]
Licensing: Open Source Licensing: Open Source
Implementation Notes: Implementation Notes:
o 2017-12-15: v0.50 released with full test set passing for ARC o 2017-12-15: v0.50 released with full test set passing for ARC
Contact Info: http://search.cpan.org/~mbradshaw/Mail-DKIM-0.50/ Contact Info: http://search.cpan.org/~mbradshaw/Mail-DKIM-0.50/
13.9. PERL Mail::Milter::Authentication module 11.9. PERL Mail::Milter::Authentication module
Organization: FastMail Organization: FastMail
Description: Email domain authentication milter, uses MAIL::DKIM (see Description: Email domain authentication milter, uses MAIL::DKIM (see
above) above)
Status of Operation: Intial validation completed during IETF99 Status of Operation: Intial validation completed during IETF99
hackathon with some follow-on work during the week hackathon with some follow-on work during the week
Coverage: Built to support [I-D.ARC] Coverage: Built to support [I-D.ARC]
Licensing: Open Source Licensing: Open Source
Implementation Notes: Implementation Notes:
o 2017-07-15: Validation functionality which interoperates with o 2017-07-15: Validation functionality which interoperates with
Gmail, AOL, dkimpy was demonstrated; later in the week of IETF99, Gmail, AOL, dkimpy was demonstrated; later in the week of IETF99,
the signing functionality was reported to be working the signing functionality was reported to be working
o 2017-07-20: ARC functionality has not yet been pushed back to the o 2017-07-20: ARC functionality has not yet been pushed back to the
github repo but should be showing up soon github repo but should be showing up soon
skipping to change at page 30, line 15 skipping to change at page 27, line 25
o 2017-07-15: Validation functionality which interoperates with o 2017-07-15: Validation functionality which interoperates with
Gmail, AOL, dkimpy was demonstrated; later in the week of IETF99, Gmail, AOL, dkimpy was demonstrated; later in the week of IETF99,
the signing functionality was reported to be working the signing functionality was reported to be working
o 2017-07-20: ARC functionality has not yet been pushed back to the o 2017-07-20: ARC functionality has not yet been pushed back to the
github repo but should be showing up soon github repo but should be showing up soon
Contact Info: https://github.com/fastmail/authentication_milter Contact Info: https://github.com/fastmail/authentication_milter
13.10. Sympa List Manager 11.10. Sympa List Manager
Organization: Sympa Dev Community Organization: Sympa Dev Community
Description: Work in progress Description: Work in progress
Status of Operation: Work in progress Status of Operation: Work in progress
Coverage: unknown Coverage: unknown
Licensing: open source Licensing: open source
Implementation Notes: Implementation Notes:
o 2018-01-05: Tracked as https://github.com/sympa-community/sympa/ o 2018-01-05: Tracked as https://github.com/sympa-community/sympa/
issues/153 issues/153
Contact Info: https://github.com/sympa-community Contact Info: https://github.com/sympa-community
13.11. Oracle Messaging Server 11.11. Oracle Messaging Server
Organization: Oracle Organization: Oracle
Description: Description:
Status of Operation: Intial development work during IETF99 hackathon. Status of Operation: Intial development work during IETF99 hackathon.
Status since then unknown. Status since then unknown.
Coverage: Work in progress
Coverage: Built to support [ARC-DRAFT-06]
Licensing: Unknown Licensing: Unknown
Implementation Notes: Implementation Notes:
o 2018-01: Protocol handling components are completed, but crypto is o 2018-03: Protocol handling components are completed, but crypto is
not yet functional. not yet functional.
Contact Info: Chris Newman Contact Info: Chris Newman
13.12. MessageSystems Momentum 11.12. MessageSystems Momentum and PowerMTA platforms
Organization: MessageSystems/SparkPost Organization: MessageSystems/SparkPost
Description: OpenARC integration into the LUA-enabled Momentum Description: OpenARC integration into the LUA-enabled Momentum
processing space processing space
Status of Operation: Beta Status of Operation: Beta
Coverage: Built to support [ARC-DRAFT-10] Coverage: Built to support [ARC-DRAFT-10]
Licensing: Unknown Licensing: Unknown
Implementation Notes: Implementation Notes:
o Initial deployments for validation expected in mid-2018. o Initial deployments for validation expected in mid-2018.
Contact Info: Contact Info:
14. References 12. References
14.1. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes", [RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes",
RFC 3463, DOI 10.17487/RFC3463, January 2003, RFC 3463, DOI 10.17487/RFC3463, January 2003,
<https://www.rfc-editor.org/info/rfc3463>. <https://www.rfc-editor.org/info/rfc3463>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
DOI 10.17487/RFC5322, October 2008,
<https://www.rfc-editor.org/info/rfc5322>.
[RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598, [RFC5598] Crocker, D., "Internet Mail Architecture", RFC 5598,
DOI 10.17487/RFC5598, July 2009, DOI 10.17487/RFC5598, July 2009,
<https://www.rfc-editor.org/info/rfc5598>. <https://www.rfc-editor.org/info/rfc5598>.
[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76, "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, DOI 10.17487/RFC6376, September 2011, RFC 6376, DOI 10.17487/RFC6376, September 2011,
<https://www.rfc-editor.org/info/rfc6376>. <https://www.rfc-editor.org/info/rfc6376>.
[RFC6377] Kucherawy, M., "DomainKeys Identified Mail (DKIM) and [RFC6377] Kucherawy, M., "DomainKeys Identified Mail (DKIM) and
skipping to change at page 32, line 23 skipping to change at page 29, line 19
[RFC7601] Kucherawy, M., "Message Header Field for Indicating [RFC7601] Kucherawy, M., "Message Header Field for Indicating
Message Authentication Status", RFC 7601, Message Authentication Status", RFC 7601,
DOI 10.17487/RFC7601, August 2015, DOI 10.17487/RFC7601, August 2015,
<https://www.rfc-editor.org/info/rfc7601>. <https://www.rfc-editor.org/info/rfc7601>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
14.2. Informative References 12.2. Informative References
[ARC-DRAFT-05] [ARC-DRAFT-05]
Andersen, K., "Authenticated Received Chain (ARC) Protocol Andersen, K., "Authenticated Received Chain (ARC) Protocol
(I-D-05)", n.d., <https://tools.ietf.org/html/ (I-D-05)", n.d., <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-protocol-05>. draft-ietf-dmarc-arc-protocol-05>.
[ARC-DRAFT-06] [ARC-DRAFT-06]
Andersen, K., "Authenticated Received Chain (ARC) Protocol Andersen, K., "Authenticated Received Chain (ARC) Protocol
(I-D-06)", n.d., <https://tools.ietf.org/html/ (I-D-06)", n.d., <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-protocol-06>. draft-ietf-dmarc-arc-protocol-06>.
skipping to change at page 32, line 47 skipping to change at page 29, line 43
(I-D-10)", n.d., <https://tools.ietf.org/html/ (I-D-10)", n.d., <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-protocol-10>. draft-ietf-dmarc-arc-protocol-10>.
[ARC-MULTI] [ARC-MULTI]
Andersen, K., "Using Multiple Signing Algorithms with Andersen, K., "Using Multiple Signing Algorithms with
ARC", January 2018, <https://tools.ietf.org/html/ ARC", January 2018, <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-multi-01>. draft-ietf-dmarc-arc-multi-01>.
[ARC-TEST] [ARC-TEST]
Blank, S., "ARC Test Suite", January 2017, Blank, S., "ARC Test Suite", January 2017,
<https://github.com/ValiMail/arc_test_suite>. <https://github.com/Valimail/arc_test_suite>.
[ARC-USAGE] [ARC-USAGE]
Jones, S., Adams, T., Rae-Grant, J., and K. Andersen, Jones, S., Adams, T., Rae-Grant, J., and K. Andersen,
"Recommended Usage of the ARC Headers", December 2017, "Recommended Usage of the ARC Headers", December 2017,
<https://tools.ietf.org/html/ <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-usage-01>. draft-ietf-dmarc-arc-usage-01>.
[ENHANCED-STATUS] [ENHANCED-STATUS]
"IANA SMTP Enhanced Status Codes", n.d., "IANA SMTP Enhanced Status Codes", n.d.,
<http://www.iana.org/assignments/smtp-enhanced-status- <http://www.iana.org/assignments/smtp-enhanced-status-
skipping to change at page 33, line 39 skipping to change at page 30, line 33
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>. <https://www.rfc-editor.org/info/rfc7489>.
[RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky, [RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky,
E., Ed., and K. Andersen, Ed., "Interoperability Issues E., Ed., and K. Andersen, Ed., "Interoperability Issues
between Domain-based Message Authentication, Reporting, between Domain-based Message Authentication, Reporting,
and Conformance (DMARC) and Indirect Email Flows", and Conformance (DMARC) and Indirect Email Flows",
RFC 7960, DOI 10.17487/RFC7960, September 2016, RFC 7960, DOI 10.17487/RFC7960, September 2016,
<https://www.rfc-editor.org/info/rfc7960>. <https://www.rfc-editor.org/info/rfc7960>.
14.3. URIs 12.3. URIs
[1] https://trac.ietf.org/trac/dmarc/ticket/10
[2] https://datatracker.ietf.org/wg/dcrup/about/
[3] https://trac.ietf.org/trac/dmarc/ticket/11
[4] https://trac.ietf.org/trac/dmarc/ticket/12
[5] https://trac.ietf.org/trac/dmarc/ticket/20
[6] https://trac.ietf.org/trac/dmarc/ticket/21
[7] https://trac.ietf.org/trac/dmarc/ticket/13
[8] https://trac.ietf.org/trac/dmarc/ticket/14
[9] https://trac.ietf.org/trac/dmarc/ticket/15
[10] https://trac.ietf.org/trac/dmarc/ticket/16
[11] https://trac.ietf.org/trac/dmarc/ticket/21 [1] https://datatracker.ietf.org/wg/dcrup/about/
[12] mailto:arc-discuss@dmarc.org [2] mailto:arc-discuss@dmarc.org
[13] mailto:arc-discuss@dmarc.org [3] mailto:arc-discuss@dmarc.org
[14] https://github.com/ValiMail/arc_test_suite [4] https://github.com/Valimail/arc_test_suite
[15] mailto:arc-discuss@dmarc.org [5] mailto:arc-discuss@dmarc.org
[16] https://trac.ietf.org/trac/dmarc/ticket/17 [6] https://trac.ietf.org/trac/dmarc/ticket/17
[17] mailto:dmarc@ietf.org [7] mailto:dmarc@ietf.org
[18] mailto:arc-discuss@dmarc.org [8] mailto:arc-discuss@dmarc.org
Appendix A. Appendix A - Design Requirements Appendix A. Appendix A - Design Requirements
(This section is re-inserted for background information from (This section is re-inserted for background information from
[ARC-DRAFT-06] and earlier versions.) [ARC-DRAFT-06] and earlier versions.)
The specification of the ARC framework is driven by the following The specification of the ARC framework is driven by the following
high-level goals, security considerations, and practical operational high-level goals, security considerations, and practical operational
requirements. requirements.
skipping to change at page 35, line 16 skipping to change at page 31, line 39
ARC is not a trust framework. Users of the ARC header fields are ARC is not a trust framework. Users of the ARC header fields are
cautioned against making unsubstantiated conclusions when cautioned against making unsubstantiated conclusions when
encountering a "broken" ARC sequence. encountering a "broken" ARC sequence.
Appendix B. Appendix B - Example Usage Appendix B. Appendix B - Example Usage
[[ Note: The following examples were mocked up early in the [[ Note: The following examples were mocked up early in the
definition process for the spec. They no longer reflect the current definition process for the spec. They no longer reflect the current
definition and need various updates which will be included in a definition and need various updates which will be included in a
future draft. Issue 17 [16] ]] future draft. Issue 17 [6] ]]
(Obsolete but retained for illustrative purposes) (Obsolete but retained for illustrative purposes)
B.1. Example 1: Simple mailing list B.1. Example 1: Simple mailing list
B.1.1. Here's the message as it exits the Origin: B.1.1. Here's the message as it exits the Origin:
Return-Path: <jqd@d1.example> Return-Path: <jqd@d1.example>
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z]) Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0) (authenticated bits=0)
skipping to change at page 54, line 39 skipping to change at page 50, line 39
From: John Q Doe <jqd@d1.example> From: John Q Doe <jqd@d1.example>
To: arc@example.org To: arc@example.org
Subject: [Lists] Example 1 Subject: [Lists] Example 1
Hey gang, Hey gang,
This is a test message. This is a test message.
--J. --J.
Appendix C. Acknowledgements Appendix C. Acknowledgements
This draft is the work of OAR-Dev Group. This draft originated with the work of OAR-Dev Group.
The authors thank all of the OAR-Dev group for the ongoing help and The authors thank all of the OAR-Dev group for the ongoing help and
though-provoking discussions from all the participants, especially: though-provoking discussions from all the participants, especially:
Alex Brotman, Brandon Long, Dave Crocker, Elizabeth Zwicky, Franck Alex Brotman, Brandon Long, Dave Crocker, Elizabeth Zwicky, Franck
Martin, Greg Colburn, J. Trent Adams, John Rae-Grant, Mike Hammer, Martin, Greg Colburn, J. Trent Adams, John Rae-Grant, Mike Hammer,
Mike Jones, Steve Jones, Terry Zink, Tim Draegen. Mike Jones, Steve Jones, Terry Zink, Tim Draegen.
Grateful appreciation is extended to the people who provided feedback Grateful appreciation is extended to the people who provided feedback
through the discuss mailing list. through the discuss mailing list.
Appendix D. Comments and Feedback Appendix D. Comments and Feedback
Please address all comments, discussions, and questions to Please address all comments, discussions, and questions to
dmarc@ietf.org [17]. Earlier discussions can be found at arc- dmarc@ietf.org [7]. Earlier discussions can be found at arc-
discuss@dmarc.org [18]. discuss@dmarc.org [8].
Authors' Addresses Authors' Addresses
Kurt Andersen Kurt Andersen
LinkedIn LinkedIn
1000 West Maude Ave 1000 West Maude Ave
Sunnyvale, California 94085 Sunnyvale, California 94085
USA USA
Email: kurta@linkedin.com Email: kurta@linkedin.com
skipping to change at page 55, line 32 skipping to change at page 51, line 32
Google Google
Email: blong@google.com Email: blong@google.com
Steven Jones (editor) Steven Jones (editor)
TDP TDP
Email: smj@crash.com Email: smj@crash.com
Seth Blank (editor) Seth Blank (editor)
ValiMail Valimail
Email: seth@valimail.com Email: seth@valimail.com
Murray Kucherawy (editor) Murray Kucherawy (editor)
TDP TDP
Email: superuser@gmail.com Email: superuser@gmail.com
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