DMARC Working Group K. Andersen
Internet-Draft LinkedIn
Intended status: Experimental B. Long, Ed.
Expires: October 25, 2018 Google
S. Jones, Ed.
TDP
S. Blank, Ed.
Valimail
M. Kucherawy, Ed.
TDP
April 23, 2018
Authenticated Received Chain (ARC) Protocol
draft-ietf-dmarc-arc-protocol-14
Abstract
The Authenticated Received Chain (ARC) protocol creates a mechanism
whereby a series of handlers of an email message can conduct
authentication of the email message as it passes among them on the
way to its destination, and create an attached, authenticated record
of the status at each step along the handling path, for use by the
final recipient in making choices about the disposition of the
message. Changes in the message that might break existing
authentication mechanisms can be identified through the ARC Set of
header fields.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 25, 2018.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. General Concepts . . . . . . . . . . . . . . . . . . . . 5
1.2. Differences Between ARC and DKIM . . . . . . . . . . . . 5
1.3. Definitions and Terminology . . . . . . . . . . . . . . . 6
1.3.1. Terms defined and used in this document . . . . . . . 6
1.3.2. Referenced Definitions . . . . . . . . . . . . . . . 7
2. Protocol Elements and Features . . . . . . . . . . . . . . . 7
2.1. The "ARC Set" of Header Fields . . . . . . . . . . . . . 8
2.1.1. Instance Tags . . . . . . . . . . . . . . . . . . . . 9
2.2. Chain Validation Status . . . . . . . . . . . . . . . . . 9
2.3. Trace Information . . . . . . . . . . . . . . . . . . . . 9
2.4. Key Management . . . . . . . . . . . . . . . . . . . . . 9
2.5. All Failures are Permanent . . . . . . . . . . . . . . . 10
2.6. Chain of Custody . . . . . . . . . . . . . . . . . . . . 10
2.7. Optional Participation . . . . . . . . . . . . . . . . . 10
2.8. Broad Responsibility to Seal . . . . . . . . . . . . . . 10
2.9. One Chain to Rule Them All . . . . . . . . . . . . . . . 11
2.10. Sealing is Always Safe . . . . . . . . . . . . . . . . . 11
3. The ARC Header Fields . . . . . . . . . . . . . . . . . . . . 11
3.1. Instance ('i=') Tag . . . . . . . . . . . . . . . . . . . 11
3.2. ARC-Authentication-Results (AAR) . . . . . . . . . . . . 12
3.3. ARC-Message-Signature (AMS) . . . . . . . . . . . . . . . 12
3.4. ARC-Seal (AS) . . . . . . . . . . . . . . . . . . . . . . 13
3.4.1. Covered Header Fields . . . . . . . . . . . . . . . . 13
3.4.2. The 'cv' Tag . . . . . . . . . . . . . . . . . . . . 14
4. Verifier Actions . . . . . . . . . . . . . . . . . . . . . . 14
4.1. Authentication-Results Information . . . . . . . . . . . 15
4.2. Handling DNS Problems While Validating ARC . . . . . . . 16
4.3. Responding to ARC Validity Violations During the SMTP
Transaction . . . . . . . . . . . . . . . . . . . . . . . 16
5. Sealer Actions . . . . . . . . . . . . . . . . . . . . . . . 16
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5.1. Marking and Sealing "cv=fail" (Invalid) Chains . . . . . 17
6. Recording and Reporting the Results of ARC Evaluation . . . . 17
6.1. Information from an ARC Evaluation . . . . . . . . . . . 17
6.2. Recording (local) ARC Evaluation Results . . . . . . . . 17
6.3. DMARC Reporting of ARC Findings - Interim . . . . . . . . 18
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8.1. Authentication-Results Method Registry Update . . . . . . 19
8.2. Email Authentication Result Names Registry Update . . . . 19
8.3. Definitions of the ARC header fields . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20
9.1. Header Size . . . . . . . . . . . . . . . . . . . . . . . 20
9.2. DNS Operations . . . . . . . . . . . . . . . . . . . . . 20
9.3. Message Content Suspicion . . . . . . . . . . . . . . . . 21
10. Evaluating the Efficacy of the ARC Protocol (Experimental
Considerations) . . . . . . . . . . . . . . . . . . . . . . . 21
10.1. Success Consideration . . . . . . . . . . . . . . . . . 21
10.2. Failure Considerations . . . . . . . . . . . . . . . . . 22
10.3. Open Questions . . . . . . . . . . . . . . . . . . . . . 22
10.3.1. Value of the ARC-Seal (AS) Header . . . . . . . . . 22
10.3.2. DNS Overhead . . . . . . . . . . . . . . . . . . . . 22
10.3.3. Distinguishing Valuable from Worthless Trace
Information . . . . . . . . . . . . . . . . . . . . 22
11. Implementation Status . . . . . . . . . . . . . . . . . . . . 23
11.1. GMail test reflector and incoming validation . . . . . . 24
11.2. AOL test reflector and internal tagging . . . . . . . . 24
11.3. dkimpy . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.4. OpenARC . . . . . . . . . . . . . . . . . . . . . . . . 25
11.5. Mailman 3.2 patch . . . . . . . . . . . . . . . . . . . 25
11.6. Copernica/MailerQ web-based validation . . . . . . . . . 25
11.7. Rspamd . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.8. PERL MAIL::DKIM module . . . . . . . . . . . . . . . . . 26
11.9. PERL Mail::Milter::Authentication module . . . . . . . . 27
11.10. Sympa List Manager . . . . . . . . . . . . . . . . . . . 27
11.11. Oracle Messaging Server . . . . . . . . . . . . . . . . 27
11.12. MessageSystems Momentum and PowerMTA platforms . . . . . 28
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
12.1. Normative References . . . . . . . . . . . . . . . . . . 28
12.2. Informative References . . . . . . . . . . . . . . . . . 29
12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Appendix A. Appendix A - Design Requirements . . . . . . . . . . 31
A.1. Primary Design Criteria . . . . . . . . . . . . . . . . . 31
A.2. Out of Scope . . . . . . . . . . . . . . . . . . . . . . 31
Appendix B. Appendix B - Example Usage . . . . . . . . . . . . . 31
B.1. Example 1: Simple mailing list . . . . . . . . . . . . . 31
B.1.1. Here's the message as it exits the Origin: . . . . . 31
B.1.2. Message is then received at example.org . . . . . . . 32
B.1.3. Example 1: Message received by Recipient . . . . . . 34
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B.2. Example 2: Mailing list to forwarded mailbox . . . . . . 35
B.2.1. Here's the message as it exits the Origin: . . . . . 35
B.2.2. Message is then received at example.org . . . . . . . 36
B.2.3. Example 2: Message received by Recipient . . . . . . 40
B.3. Example 3: Mailing list to forwarded mailbox with source 42
B.3.1. Here's the message as it exits the Origin: . . . . . 42
B.3.2. Message is then received at example.org . . . . . . . 43
B.3.3. Example 3: Message received by Recipient . . . . . . 48
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 50
Appendix D. Comments and Feedback . . . . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
1. Introduction
Modern email authentication techniques such as the Sender Policy
Framework (SPF) [RFC7208] and DomainKeys Identified Mail (DKIM)
[RFC6376] have become common. However, their end-to-end utility is
limited by the effects of intermediaries along the transmission path,
which either are not listed (for SPF) or which break digital
signatures (for DKIM). These issues are described in substantial
detail in those protocols' defining documents as well as in [RFC6377]
and [RFC7960].
Technologies that build upon the use of SPF and DKIM can reduce the
success of fraudulent email campaigns. To this end, Domain-based
Mail Authentication, Reporting and Conformance (DMARC) [RFC7489],
validates the domain of the RFC5322.From header field. However its
use along email transmission paths that have independent
intermediaries, such as some forwarders and essentially all mailing
list services, produces false positive rejections that are
problematic, both for the message authors, the intermediary
service(s), and for those they are interacting with.
[RFC7960] documented the need for a mechanism which would survive
legitimate alteration of a message, in spite of breaking the
associated SPF and DKIM information so that the end receiver
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
sequence for a message, especially the points where alterations of
the content might have occurred. Equipped with this more complete
information, the recipient system(s) can make a more informed
handling choice, reducing or eliminating the rejections that would
occur with the use of DKIM and/or SPF alone.
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1.1. General Concepts
ARC provides a "chain of custody" for a message, allowing each entity
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
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.
When the message reaches final delivery, the decision to accept and
deliver the message, or, alternatively, to reject, discard, or
quarantine it, can take the chain of custody into account, applying
local policy in addition to policies advertised by the (purported)
sending domain. Consider, for example, this scenario:
1. A sender from mysender.example posts a message to a mailing list
hosted at listmania.example;
2. The mailing list modifies the message by prepending the list name
to the subject line, then sends it to the subscribers;
3. One of the subscribers is alice@mail.service.example, which
receives the message from listmania.example.
Assuming the original message was DKIM-signed and mysender.example
published an SPF record, the handling by the mailing list will break
the DKIM signature because of the message modification, and the
forwarding will cause the SPF check to fail in the next step. But
listmania.example can add ARC headers to the message to add itself to
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
also see that both of these succeeded when they were checked by
listmania.example, and can verify listmania's assertion.
As part of its evaluation of the message for delivery,
mail.service.example can see that mysender.example publishes a DMARC
policy asking that unauthenticated messages be rejected. But is can
also see the assertion by listmania.example that the message was
correctly authenticated when the message arrived there, and if it
accepts that assertion, it can accept the message for further
processing, rather than reject it, based on the additional
information that ARC has provided.
1.2. Differences Between ARC and DKIM
In DKIM, every participating signing agent attaches a signature that
is based on some of the content of the message, local policy, and the
domain name of the signing agent's Administrative Management Domain
(ADMD). Any verifier can process such a signature; a verified
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signature means that the domain referenced in the signature's "d="
parameter has some responsibility for handling the message. An
artifact of using digital signature technology for this means that
verification also ensures that the portion of the message that was
"covered" by the signature has not been altered since the signature
was applied. The signatures themselves are generally independent of
one another.
In contrast, a validated ARC Set conveys the following pieces of
information:
1. An assertion that, at the time that the intermediary ADMD
processed the message, the various assertions (such as SPF, DKIM-
Signature(s) and/or ARC Chain) already attached to the message by
other ADMDs were or were not valid;
2. As with DKIM, an assertion that, for a validated ARC signature,
the domain name in the signature takes some responsibility for
handling of the message and that the covered content of the
message is unchanged since that signature was applied;
3. A further assertion that binds the ARC evaluation results into
the ARC Chain sequence.
1.3. Definitions and Terminology
This section defines terms used in the rest of the document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP14 ([RFC2119][RFC8174]).
Because many of the core concepts and definitions are found in
[RFC5598], readers should to be familiar with the contents of
[RFC5598], and in particular, the potential roles of intermediaries
in the delivery of email.
Syntax descriptions use Augmented BNF (ABNF) [RFC5234].
1.3.1. Terms defined and used in this document
o "ARC-Authentication-Results" (AAR) - an ARC header field described
in Section 3.2.
o "ARC-Message-Signature" (AMS) - an ARC header field described in
Section 3.3.
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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
Section 2.1 is called an "ARC Set".
o "ARC Chain" - the complete sequence of ARC Sets for a message.
The ARC Chain represents a "chain of custody" for the message,
recording its authentication status at each ARC-participating ADMD
that handled the message.
1.3.2. Referenced Definitions
The following terms are defined in other RFCs. Those definitions can
be found as follows:
o ADMD - [RFC5598], Section 2.3
o MTA - [RFC5598], Section 4.3.2
o MSA - [RFC5598], Section 4.3.1
o MDA - [RFC5598], Section 4.3.3
The three header fields that are part of this specification borrow
heavily from existing specifications. Rather than repeating all of
the formal definitions that are being reused in ARC, this document
only describes and specifies changes in syntax and semantics.
Language, syntax, and other details are imported from DKIM [RFC6376].
Specific references can be found below.
2. Protocol Elements and Features
As with other domain authentication technologies (such as SPF, DKIM,
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
Final Receiver is able to ascertain:
o all (participating) domains that claim responsibility for handling
(and possibly modifying) the email message in transit;
o trace information, including:
* the [RFC7601] Authentication-Results each participating ADMD
saw; and
* additional data needed to compile a DMARC report for the
sending domain.
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Given this information, each receiver is able to make a more informed
local policy decision regarding message processing and, ultimately,
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
and Final Receiver, is both an ARC Validator (when receiving) and
then an ARC Sealer (when sending a message onward).
_INFORMATIONAL_: It is important to understand that validating and
then immediately sealing a message leaves no room for message
modification, and many early implementations of ARC did not initially
work because both operations were performed in a single pass over the
message.
The following protocol features are functional parts and design
decisions related the protocol that are not specific to either
Validators or Sealers, but ensure that the ARC Chain conveys this
information to a Final Receiver.
2.1. The "ARC Set" of Header Fields
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
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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.
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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
message, signed by each handler of the message. Each link in the
chain (AMS) is designed to be brittle, insofar as it survives only
until the next modification of the message. However, the sequence of
intermediaries in the handling chain (AS) is designed to remain
intact over the entirety of the chain.
The ARC Chain can be conceptualized through an analogy with the chain
of custody for legal evidence. The material evidence itself is
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
evidence container (AAR) and signs for the evidence on a chain of
custody report form (AS). As with all analogies, this one should not
be taken to interpretive extremes, but primarily used as a conceptual
framework.
An ARC Chain that is valid and passing has the attributes listed
above in Section 2.
2.7. Optional Participation
Validating an existing chain and then adding your own ARC Set to a
message allows you to claim responsibility for handling the message
and modifications, if any, done by your ADMD to benefit message
delivery downstream. However, no ADMD is obligated to perform these
actions.
2.8. Broad Responsibility to Seal
Any mediator ([RFC5598], section 5) that modifies a message may seal
its own changes. ARC is not solely intended for perimeter MTAs.
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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
chain of custody is no longer valid and responsibility for the
message has been lost. For further discussion of this topic and the
designed restriction which prevents chain continuation or re-
establishment, see [ARC-USAGE].
2.10. Sealing is Always Safe
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:
o properly adding an ARC Set to a message does not damage or
invalidate an existing chain,
o sealing a chain when you did not modify a message does not
negatively affect the chain, and
o validating a message exposes no new threat vectors (see
Section 9).
_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.
For complex or nested ADMD relationships such as found in some hosted
mail solutions, this "inbound seal" can be used to facilitate
traversal of internal boundaries as well as properly conveying
incoming state to any egress MTAs that may need to assert a seal upon
exit from the ADMD. Since these internal relationships are highly
implementation dependent, this protocol definition can not usefully
explore such usage except to note that it is intentionally allowed
within the scope of this specification.
3. The ARC Header Fields
3.1. Instance ('i=') Tag
The header fields comprising a single ARC Set are identified by a
common "instance" tag value. The instance tag is a string in each
header field value that complies with the "tag-spec" ABNF found in
Section 3.2 of [RFC6376]. The tag-name is "i" and the value is the
text representation of a positive integer, indicating the position in
the ARC sequence this set occupies, where the first ARC Set is
numbered 1. In ABNF terms:
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position = 1*2DIGIT ; 1 - 50
instance = [FWS] %x69 [FWS] "=" [FWS] position [FWS] ";"
Valid ARC Sets MUST have exactly one instance of each header field
(of three) for a given instance value and signing algorithm.
(_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).
ARC Chains longer than the defined maximum count MUST be marked as
failed.
_INFORMATIONAL_: 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.
3.2. ARC-Authentication-Results (AAR)
The ARC-Authentication-Results header field is syntactically and
semantically identical, except for the header field name itself and
its instance tag, to an Authentication-Results header field (defined
in Section 2.2 of [I-D-7601bis]).
Formally, the header field is specified as follows using ABNF
[RFC5234]:
arc-info = instance [CFWS] ";" authres-payload
arc-authres-header = "ARC-Authentication-Results:" [CFWS] arc-info
The AAR MUST contain all Authentication-Results from within the
participating ADMD, regardless of how many Authentication-Results
headers are on the message.
3.3. ARC-Message-Signature (AMS)
The ARC-Message-Signature header field is simplified version of a
DKIM-Signature header field [RFC6376], with the following
modifications:
o There is an "i" tag, as described in Section 3.1.
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o There is no "v" tag defined for the AMS header. As required for
undefined tags (in [RFC6376]), if seen, it MUST be ignored.
ARC-related header fields (ARC-Seal, ARC-Message-Signture, ARC-
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
present on the message in the header fields covered by this
signature.
Authentication-Results header fields MUST NOT be included since they
are likely to be deleted by downstream ADMDs (per Section 5 of
[RFC7601]), thereby breaking the AMS signature.
3.4. ARC-Seal (AS)
The ARC-Seal header field is syntactically and semantically similar
to a DKIM-Signature field, with the following exceptions:
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
only covers specific header fields as defined below:
Section 3.4.1. No body canonicalization is done.
o Only "relaxed" header canonicalization (Section 3.4.2 of
[RFC6376]) is used.
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].
o An additional tag, "cv" is defined in Section 3.4.2
3.4.1. Covered Header Fields
The ARC-Seal signs a specific canonicalized form of the ARC Set
header values. The ARC set header values are compiled in increasing
instance order, starting at 1, and include the set being added at the
time of sealing the message.
Within a set, the header fields are listed in the following order:
1. ARC-Authentication-Results
2. ARC-Message-Signature
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3. ARC-Seal
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
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
situation where a chain has failed validation (see Section 5.1).
3.4.2. The 'cv' Tag
A new tag "cv" (chain validation) indicates the outcome of evaluating
the existing ARC Chain upon arrival at the ADMD that is adding this
header field. The values are defined per Section Section 2.2.
In ABNF terms:
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.
2. Check the morphology of the ARC Chain. If any of these
conditions are not met, the chain state is "fail" and the
algorithm stops here:
1. Each ARC Set must be complete (e.g., contains exactly one of
each of the three ARC-specific header fields);
2. The instance values must form a continuous sequence from 1..N
with no gaps or repeats;
3. The cv value for all ARC-Seal(s) must be non-failing:
1. For i > 1, the value must be "pass";
2. For i = 1, the value must be "none".
3. For each ARC-Message-Signature from the "N"th instance to the
first, validate the AMS:
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1. If the "N"th instance (most recent) signature fails, then the
chain state is "fail" and the algorithm stops here.
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
be lost in transit when messages are handled by intermediaries. For
example, failing DKIM signatures are sometimes removed by MTAs, and
most DKIM signatures on messages modified by intermediaries will
fail. Recording the following information in the Authentication-
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.
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The ptypes and properties defined in this section SHOULD be recorded
in the Authentication-Results:
o smtp.client-ip - The connecting client IP address from which the
message is received;
o header.oldest-pass - The instance number of the oldest AMS that
still validates, or 0 if all pass.
4.2. Handling DNS Problems While Validating ARC
DNS-based failures to verify a chain are treated no differently than
any other ARC violation. They result in a "cv=fail" verdict.
4.3. Responding to ARC Validity Violations During the SMTP Transaction
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
[RFC3463] "message integrity failure" [ENHANCED-STATUS] and
corresponding SMTP response code.
5. Sealer Actions
An ARC sealer MUST take the following actions when presented with a
message:
1. Before creating an ARC signature, perform any other, normal
authentication and/or signing, so that the ARC signature can
cover those results.
2. Build and attach the new ARC Set:
1. If an ARC Chain exists on the message, then set "N" equal to
the highest instance number found on the chain (i=);
otherwise set "N" equal to zero for the following steps.
2. Generate and attach to the message an ARC-Authentication-
Results header field as defined in Section Section 3.2, using
instance number N+1 and the same content from the previous
step.
3. Generate and attach to the message an ARC-Message-Signature
header field as defined in Section 3.3 above, using instance
number N+1.
4. Generate and attach to the message an ARC-Seal header field
using the general algorithm described in Section 3.4 above,
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the chain validation status as determined in Section 4, and
instance number N+1.
5.1. Marking and Sealing "cv=fail" (Invalid) Chains
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
by the MTA which detected the malformed chain, as if this newest ARC
Set was the only set present.
_INFORMATIONAL:_ In the case of a malformed or otherwise invalid
chain there is no way to generate a deterministic set of AS header
fields ({#implicit_as_h}) so this approach is mandated.
6. Recording and Reporting the Results of ARC Evaluation
The evaluation of an ARC Chain provides information which will be
useful to both the receiver (or intermediary) and to the initial
sender of the message. This information should be preserved and
reported as follows.
6.1. Information from an ARC Evaluation
The evaluation of an ARC Chain produces a list of domain names for
participating intermediaries which handled the message, to wit:
o A list of the "d=" domains found in the validated ARC-Seal header
fields
o The "d=" domain found in the most recent (highest instance number)
AMS header field (since that is the only one necessarily
validated)
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
terminal ARC Set.
6.2. Recording (local) ARC Evaluation Results
Receivers who process an attached ARC Chain SHOULD add an
"arc=[pass|fail|policy]" method annotation into a locally-affixed
Authentication-Results [RFC7601] header field along with any salient
comment(s).
Details of the ARC Chain which was evaluated should be included in
the Authentication-Results and AAR headers per Section Section 4.1.
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6.3. DMARC Reporting of ARC Findings - Interim
Receivers SHOULD indicate situations in which ARC evaluation
influenced the results of their local policy determination. DMARC
reporting of ARC-informed decisions can be accomplished by adding a
local_policy comment explanation containing the list of data
discovered in the ARC evaluation, which at a minimum SHOULD include:
* the Chain Validation status, * the domain and selector for each AS,
* the IP addresses of the mail originating ADMD:
<policy_evaluated>
<disposition>none</disposition>
<dkim>fail</dkim>
<spf>fail</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 client-ip[1]=10.10.10.13</comment>
</reason>
</policy_evaluated>
In the sample above, d2.example is the sealing domain for ARC[2] and
d1.example is the sealing domain for ARC[1].
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.
7. Privacy Considerations
The ARC Chain provides a verifiable record of the handlers for a
message. Anonymous remailers will probably not find this compatible
with their operating goals.
8. IANA Considerations
[[ Note to the RFC Editors: Some of these fields are defined both
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.
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8.1. Authentication-Results Method Registry Update
This draft adds one item to the IANA "Email Authentication Methods"
registry:
o Method : arc
Defined: [I-D.ARC]
ptype: header
Property: chain evaluation result
Value: chain evaluation result status (see Section 3.4)
Status: active
8.2. Email Authentication Result Names Registry Update
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:
o Auth Method : arc
Code: "none", "pass", "fail"
Specification: [I-D.ARC] Section 3.4.2 Status: active
o Method : spf
Defined: [I-D.ARC]
ptype: smtp
Property: client-ip
Value: the connecting client IP address from which the message is
received
Status: active
o Method : arc
Defined: [I-D.ARC]
ptype: header
Property: oldest-pass
Value: the oldest instance with a still validating AMS signature
Status: active
8.3. Definitions of the ARC header fields
This specification adds three new header fields to the "Permanent
Message Header Field Registry", as follows:
o Header field name: ARC-Seal
Applicable protocol: mail
Status: draft
Author/Change controller: IETF
Specification document(s): [I-D.ARC]
Related information: [RFC6376]
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o Header field name: ARC-Message-Signature
Applicable protocol: mail
Status: draft
Author/Change controller: IETF
Specification document(s): [I-D.ARC]
Related information: [RFC6376]
o Header field name: ARC-Authentication-Results
Applicable protocol: mail
Status: standard
Author/Change controller: IETF
Specification document(s): [I-D.ARC]
Related information: [RFC7601]
9. Security Considerations
The Security Considerations of [RFC6376] and [RFC7601] apply directly
to this specification.
9.1. Header Size
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
greater size of the header.
9.2. DNS Operations
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
mechanisms which can increase the lookups for a given target value).
This has at least two effects:
1. An attacker can send a message to an ARC participant with a
concocted sequence of ARC Sets bearing the domains of intended
victims, and all of them will be queried by the participant until
a failure is discovered. The difficulty of forging the signature
values should limit the extent of this load to domains under
control of the attacker.
2. DKIM only does one DNS check per signature, while this one can do
many (per chain). Absent caching, slow DNS responses can cause
SMTP timeouts; and backlogged delivery queues on mediating
systems. This could be exploited as a DoS attack.
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9.3. Message Content Suspicion
Recipients are cautioned to treat messages bearing ARC Sets with the
same suspicion that they apply to all other email messages. This
includes appropriate content scanning and other checks for
potentially malicious content. The handlers which are identified
within the ARC Chain may be used to provide input to local policy
engines in cases where DMARC validation fails (due to mediation
impacting SPF attribution, DKIM validity or alignment).
Note that a passing ARC Chain may not adequately mean that the
message is safe because:
1. You have to trust all signatories; and
2. Even trusted systems may have become compromised or may not
properly authenticate messages, so even with a chain of trusted
participants, the message might still never have authenticated in
the first place (which is why you have the AAR to inspect) or
could have been subject to unintended modifications.
10. Evaluating the Efficacy of the ARC Protocol (Experimental
Considerations)
The ARC protocol is designed to mitigate some of the most common
failure conditions for email which transits intermediary handlers en
route to the final recipient. Some of these problems have happened
due to the adoption of the DMARC protocol [RFC7489] and are listed in
[RFC6377] and [RFC7960].
As the ARC protocol becomes standardized and implemented amongst
intermediary handlers, the following aspects should be evaluated in
order to determine the success of the protocol in accomplishing the
intended benefits.
NOTE: Terminology within this section does NOT follow [RFC2119]
interpretation. This section represents the current thoughts of the
working group regarding unanswered questions related to the protocol.
Wider deployment will inform these topics and probably expand them.
10.1. Success Consideration
Currently, many receivers have heuristically determined overrides in
order to rescue mail from intermediary-caused failures. Many of
those overrides rely on inferrence rather than direct evidence.
ARC will be a success if, for ARC sealed messages, receivers are able
to implment ARC-based algorithmic decisions based on the direct
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evidence found within the ARC Chain. This is especially relevant for
DMARC processing when the DKIM d= value is aligned with the
rfc5322.From author domain.
10.2. Failure Considerations
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 9) then
this protocol will be a failure. Note that weaknesses inherent in
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
this specification.
10.3. Open Questions
The following open questions are academic and have no clear answer at
the time of the development of the protocol. However, wide-spread
deployment should be able to gather the necessary data to answer some
or all of them.
10.3.1. Value of the ARC-Seal (AS) Header
Data should be collected to show if the ARC-Seal (AS) provides value
beyond the ARC Message Signature (AMS) for either making delivery
decisions or catching malicious actors trying to craft or replay
malicious chains.
10.3.2. DNS Overhead
Longer ARC Chains will require more queries to retrieve the keys for
validating the chain. While this is not believed to be a security
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
query load concerns which were debated at the time of the DKIM
specification development.
Data should be collected to better understand usable length and
distribution of lengths found in valid ARC Chains along with the the
DNS impact of processing ARC Chains.
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
make the difference between message delivery or rejection. For
example, if there is a well known mailing list that ARC seals but
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doesn't do its own initial DMARC enforcement, a Final Receiver with
this knowledge could make a delivery decision based upon the
authentication information it sees in the corresponding AAR header.
Certain trace information in the AAR is useful/necessary in the
construction of DMARC reports. It would be beneficial to identify
the value-add of having intermediary-handled mail flow information
added into the DMARC reports going back to senders.
Certain receivers believe the entire set of trace information would
be valuable to feed into machine learning systems to identify fraud
and/or provide other signals related to message delivery.
It is unclear what trace information will be valuable for all
receivers, regardless of size.
Data should be collected on what trace information receivers are
using that provides useful signals that affect deliverability, and
what portions of the trace data are left untouched or provide no
useful information.
Since many such systems are intentionally proprietary or confidential
to prevent gaming by abusers, it may not be viable to reliably answer
this particular question. The evolving nature of attacks can also
shift the landscape of "useful" information over time.
11. Implementation Status
[[ Note to the RFC Editor: Please remove this section before
publication along with the reference to [RFC6982]. ]]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC6982].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
This information is known to be correct as of the seventh
interoperability test event which was held on 2017-07-15 & 16 at
IETF99.
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For a few of the implementations, later status information was
available as of December 2017.
11.1. GMail test reflector and incoming validation
Organization: Google
Description: Internal production implementation with both debug
analysis and validating + sealing pass-through function
Status of Operation: Production - Incoming Validation
Coverage: Full spec implemented as of [ARC-DRAFT-06]
Licensing: Proprietary - Internal only
Implementation Notes:
o Full functionality was demonstrated during the interop testing on
2017-07-15.
Contact Info: arc-discuss@dmarc.org [2]
11.2. AOL test reflector and internal tagging
Organization: AOL
Description: Internal prototype implementation with both debug
analysis and validating + sealing pass-through function
Status of Operation: Beta
Coverage: ARC Chain validity status checking is operational, but only
applied to email addresses enrolled in the test program.
This system conforms to [ARC-DRAFT-06]
Licensing: Proprietary - Internal only
Implementation Notes:
o 2017-07-15: Full functionality verified during the interop
testing.
Contact Info: arc-discuss@dmarc.org [3]
11.3. dkimpy
Organization: dkimpy developers/Scott Kitterman
Description: Python DKIM package
Status of Operation: Production
Coverage:
o 2017-07-15: The internal test suite is incomplete, but the command
line developmental version of validator was demonstrated to
interoperate with the Google and AOL implementations during the
interop on 2017-07-15 and the released version passes the tests in
[ARC-TEST] arc_test_suite [4] with both python and python3.
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Licensing: Open/Other (same as dkimpy package = BCD version 2)
Contact Info: https://launchpad.net/dkimpy
11.4. OpenARC
Organization: TDP/Murray Kucherawy
Description: Implemention of milter functionality related to the
OpenDKIM and OpenDMARC packages
Status of Operation: Beta
Coverage: Built to support [ARC-DRAFT-10]
Licensing: Open/Other (same as OpenDKIM and OpenDMARC packages)
Implementation Notes:
o The build is FreeBSD oriented but some packages have been built
for easier deployment on RedHat-based Linux platforms.
o Some issues still exist when deploying in a chained milter
arrangement (such as OpenSPF -> OpenDKIM -> OpenDMARC -> OpenARC)
with coordination between the stages. When deployed in a
"sandwich" configuration around an MLM, there is no effective
mechanism to convey trust from the ingress (validator) to egress
(signer) instances. (_NOTE_: this is expected to resolved with a
new release of OpenDMARC expected in January 2018.)
Contact Info: arc-discuss@dmarc.org [5]
11.5. Mailman 3.2 patch
Organization: Mailman development team
Description: Integrated ARC capabilities within the Mailman 3.2
package
Status of Operation: Patch submitted
Coverage: Based on OpenARC
Licensing: Same as mailman package - GPL
Implementation Notes:
o Appears to work properly in at least one beta deployment, but
waiting on acceptance of the pull request into the mainline of
mailman development
Contact Info: https://www.gnu.org/software/mailman/contact.html
11.6. Copernica/MailerQ web-based validation
Organization: Copernica
Description: Web-based validation of ARC-signed messages
Status of Operation: Beta
Coverage: Built to support [ARC-DRAFT-05]
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Licensing: On-line usage only
Implementation Notes:
o Released 2016-10-24
o Requires full message content to be pasted into a web form found
at http://arc.mailerq.com/ (warning - https is not supported).
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.
o 2017-07-15: Testing shows that results match the other
implementations listed in this section.
Contact Info: https://www.copernica.com/
11.7. Rspamd
Organization: Rspamd community
Description: ARC signing and verification module
Status of Operation: Production, though deployment usage is unknown
Coverage: Built to support [ARC-DRAFT-06]
Licensing: Open source
Implementation Notes:
o 2017-06-12: Released with version 1.6.0
o 2017-07-15: Testing during the interop showed that the validation
functionality interoperated with the Google, AOL, dkimpy and
MailerQ implementations
Contact Info: https://rspamd.com/doc/modules/arc.html and
https://github.com/vstakhov/rspamd
11.8. PERL MAIL::DKIM module
Organization: FastMail
Description: Email domain authentication (sign and/or verify) module,
previously included SPF / DKIM / DMARC, now has ARC added
Status of Operation: Production, deployment usage unknown
Coverage: Built to support [ARC-DRAFT-10]
Licensing: Open Source
Implementation Notes:
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/
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11.9. PERL Mail::Milter::Authentication module
Organization: FastMail
Description: Email domain authentication milter, uses MAIL::DKIM (see
above)
Status of Operation: Intial validation completed during IETF99
hackathon with some follow-on work during the week
Coverage: Built to support [I-D.ARC]
Licensing: Open Source
Implementation Notes:
o 2017-07-15: Validation functionality which interoperates with
Gmail, AOL, dkimpy was demonstrated; later in the week of IETF99,
the signing functionality was reported to be working
o 2017-07-20: ARC functionality has not yet been pushed back to the
github repo but should be showing up soon
Contact Info: https://github.com/fastmail/authentication_milter
11.10. Sympa List Manager
Organization: Sympa Dev Community
Description: Work in progress
Status of Operation: Work in progress
Coverage: unknown
Licensing: open source
Implementation Notes:
o 2018-01-05: Tracked as https://github.com/sympa-community/sympa/
issues/153
Contact Info: https://github.com/sympa-community
11.11. Oracle Messaging Server
Organization: Oracle
Description:
Status of Operation: Intial development work during IETF99 hackathon.
Status since then unknown.
Coverage: Work in progress
Licensing: Unknown
Implementation Notes:
o 2018-03: Protocol handling components are completed, but crypto is
not yet functional.
Contact Info: Chris Newman
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11.12. MessageSystems Momentum and PowerMTA platforms
Organization: MessageSystems/SparkPost
Description: OpenARC integration into the LUA-enabled Momentum
processing space
Status of Operation: Beta
Coverage: Built to support [ARC-DRAFT-10]
Licensing: Unknown
Implementation Notes:
o Initial deployments for validation expected in mid-2018.
Contact Info:
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3463] Vaudreuil, G., "Enhanced Mail System Status Codes",
RFC 3463, DOI 10.17487/RFC3463, January 2003,
<https://www.rfc-editor.org/info/rfc3463>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<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,
DOI 10.17487/RFC5598, July 2009,
<https://www.rfc-editor.org/info/rfc5598>.
[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, DOI 10.17487/RFC6376, September 2011,
<https://www.rfc-editor.org/info/rfc6376>.
[RFC6377] Kucherawy, M., "DomainKeys Identified Mail (DKIM) and
Mailing Lists", BCP 167, RFC 6377, DOI 10.17487/RFC6377,
September 2011, <https://www.rfc-editor.org/info/rfc6377>.
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[RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for
Authorizing Use of Domains in Email, Version 1", RFC 7208,
DOI 10.17487/RFC7208, April 2014,
<https://www.rfc-editor.org/info/rfc7208>.
[RFC7601] Kucherawy, M., "Message Header Field for Indicating
Message Authentication Status", RFC 7601,
DOI 10.17487/RFC7601, August 2015,
<https://www.rfc-editor.org/info/rfc7601>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
12.2. Informative References
[ARC-DRAFT-05]
Andersen, K., "Authenticated Received Chain (ARC) Protocol
(I-D-05)", n.d., <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-protocol-05>.
[ARC-DRAFT-06]
Andersen, K., "Authenticated Received Chain (ARC) Protocol
(I-D-06)", n.d., <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-protocol-06>.
[ARC-DRAFT-10]
Andersen, K., "Authenticated Received Chain (ARC) Protocol
(I-D-10)", n.d., <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-protocol-10>.
[ARC-MULTI]
Andersen, K., "Using Multiple Signing Algorithms with
ARC", January 2018, <https://tools.ietf.org/html/
draft-ietf-dmarc-arc-multi-01>.
[ARC-TEST]
Blank, S., "ARC Test Suite", January 2017,
<https://github.com/Valimail/arc_test_suite>.
[ARC-USAGE]
Jones, S., Adams, T., Rae-Grant, J., and K. Andersen,
"Recommended Usage of the ARC Headers", December 2017,
<https://tools.ietf.org/html/
draft-ietf-dmarc-arc-usage-01>.
Andersen, et al. Expires October 25, 2018 [Page 29]
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[ENHANCED-STATUS]
"IANA SMTP Enhanced Status Codes", n.d.,
<http://www.iana.org/assignments/smtp-enhanced-status-
codes/smtp-enhanced-status-codes.xhtml>.
[I-D-7601bis]
Kucherawy, M., "Message Header Field for Indicating
Message Authentication Status", February 2018,
<https://datatracker.ietf.org/doc/
draft-ietf-dmarc-rfc7601bis/>.
[RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", RFC 6982,
DOI 10.17487/RFC6982, July 2013,
<https://www.rfc-editor.org/info/rfc6982>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<https://www.rfc-editor.org/info/rfc7489>.
[RFC7960] Martin, F., Ed., Lear, E., Ed., Draegen. Ed., T., Zwicky,
E., Ed., and K. Andersen, Ed., "Interoperability Issues
between Domain-based Message Authentication, Reporting,
and Conformance (DMARC) and Indirect Email Flows",
RFC 7960, DOI 10.17487/RFC7960, September 2016,
<https://www.rfc-editor.org/info/rfc7960>.
12.3. URIs
[1] https://datatracker.ietf.org/wg/dcrup/about/
[2] mailto:arc-discuss@dmarc.org
[3] mailto:arc-discuss@dmarc.org
[4] https://github.com/Valimail/arc_test_suite
[5] mailto:arc-discuss@dmarc.org
[6] https://trac.ietf.org/trac/dmarc/ticket/17
[7] mailto:dmarc@ietf.org
[8] mailto:arc-discuss@dmarc.org
Andersen, et al. Expires October 25, 2018 [Page 30]
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Appendix A. Appendix A - Design Requirements
(This section is re-inserted for background information from
[ARC-DRAFT-06] and earlier versions.)
The specification of the ARC framework is driven by the following
high-level goals, security considerations, and practical operational
requirements.
A.1. Primary Design Criteria
o Provide a verifiable "chain of custody" for email messages;
o Not require changes for originators of email;
o Support the verification of the ARC header field set by each hop
in the handling chain;
o Work at Internet scale; and
o Provide a trustable mechanism for the communication of
Authentication-Results across trust boundaries.
A.2. Out of Scope
ARC is not a trust framework. Users of the ARC header fields are
cautioned against making unsubstantiated conclusions when
encountering a "broken" ARC sequence.
Appendix B. Appendix B - Example Usage
[[ Note: The following examples were mocked up early in the
definition process for the spec. They no longer reflect the current
definition and need various updates which will be included in a
future draft. Issue 17 [6] ]]
(Obsolete but retained for illustrative purposes)
B.1. Example 1: Simple mailing list
B.1.1. Here's the message as it exits the Origin:
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Return-Path: <jqd@d1.example>
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijrvQw
bv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4Gd3TRJl
gotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@dmarc.org
Subject: Example 1
Hey gang,
This is a test message.
--J.
B.1.2. Message is then received at example.org
B.1.2.1. Example 1, Step A: Message forwarded to list members
Processing at example.org:
o example.org performs authentication checks
o No previous Authentication-Results or ARC-Seal headers are present
o example.org adds ARC-Authentication-Results header
o example.org adds Received: header
o example.org adds a ARC-Seal header
Here's the message as it exits example.org:
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Return-Path: <jqd@d1.example>
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=seal2015; d=example.org; cv=none;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=example.org; s=clochette; t=1421363105;
bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
h=List-Id:List-Unsubscribe:List-Archive:List-Post:
List-Help:List-Subscribe:Reply-To:DKIM-Signature;
b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF1F5
vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3A+m4bw
a6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
spf=pass smtp.mfrom=jqd@d1.example;
dkim=pass (1024-bit key) header.i=@d1.example;
dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
Hey gang,
This is a test message.
--J.
Andersen, et al. Expires October 25, 2018 [Page 33]
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B.1.3. Example 1: Message received by Recipient
Let's say that the Recipient is example.com
Processing at example.com:
o example.com performs usual authentication checks
o example.com adds Authentication-Results: header, Received header
o Determines that message fails DMARC
o Checks for ARC-Seal: header; finds one
o Validates the signature in the ARC-Seal: header, which covers the
ARC-Authentication-Results: header
o example.com can use the ARC-Authentication-Results values or
verify the DKIM-Signature from lists.example.org
Here's what the message looks like at this point:
Return-Path: <jqd@d1.example>
Received: from example.org (example.org [208.69.40.157])
by clothilde.example.com with ESMTP id
d200mr22663000ykb.93.1421363207
for <fmartin@example.com>; Thu, 14 Jan 2015 15:02:40 -0800 (PST)
Authentication-Results: clothilde.example.com; spf=fail
smtp.from=jqd@d1.example; dkim=pass (1024-bit key)
header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=seal2015; d=example.org; cv=none;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=example.org; s=clochette; t=1421363105;
bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
h=List-Id:List-Unsubscribe:List-Archive:List-Post:
List-Help:List-Subscribe:Reply-To:DKIM-Signature;
b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
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spf=pass smtp.mfrom=jqd@d1.example;
dkim=pass (1024-bit key) header.i=@d1.example;
dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijrvQw
bv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4Gd3TRJl
gotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
Hey gang,
This is a test message.
--J.
B.2. Example 2: Mailing list to forwarded mailbox
B.2.1. Here's the message as it exits the Origin:
Andersen, et al. Expires October 25, 2018 [Page 35]
Internet-Draft ARC-Protocol April 2018
Return-Path: <jqd@d1.example>
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijrvQw
bv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4Gd3TRJl
gotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: Example 1
Hey gang,
This is a test message.
--J.
B.2.2. Message is then received at example.org
B.2.2.1. Example 2, Step A: Message forwarded to list members
Processing at example.org:
o example.org performs authentication checks
o example.org applies standard DKIM signature
o No previous Authentication-Results or ARC-Seal headers are present
o example.org adds ARC-Authentication-Results header
o example.org adds usual Received: header
o example.org adds a ARC-Seal header
Here's the message as it exits Step A:
Andersen, et al. Expires October 25, 2018 [Page 36]
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Return-Path: <jqd@d1.example>
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=seal2015; d=example.org; cv=none;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=example.org; s=clochette; t=1421363105;
bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
h=List-Id:List-Unsubscribe:List-Archive:List-Post:
List-Help:List-Subscribe:Reply-To:DKIM-Signature;
b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
spf=pass smtp.mfrom=jqd@d1.example;
dkim=pass (1024-bit key) header.i=@d1.example;
dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
Hey gang,
This is a test message.
--J.
Andersen, et al. Expires October 25, 2018 [Page 37]
Internet-Draft ARC-Protocol April 2018
B.2.2.2. Example 2, Step B: Message from list forwarded
The message is delivered to a mailbox at gmail.com
Processing at gmail.com:
o gmail.com performs usual authentication checks
o gmail.com adds Authentication-Results: and Received: header
o Determines that message fails DMARC
o Checks for ARC-Seal: header; finds one
o Validates the signature in the ARC-Seal: header, which covers the
ARC-Authentication-Results: header
o Uses the ARC-Authentication-Results: values, but:
o Instead of delivering message, prepares to forward message per
user settings
o Applies usual DKIM signature
o gmail.com adds it's own ARC-Seal: header, contents of which are
* version
* sequence number ("i=2")
* hash algorithm (SHA256 as example)
* timestamp ("t=")
* selector for key ("s=notary01")
* domain for key ("d=gmail.com")
* headers included in hash ("h=ARC-Authentication-Results:ARC-
Seal")
* Note: algorithm requires only ARC-Seals with lower sequence #
be included, in ascending order
* signature of the header hash
Here's what the message looks like at this point:
Return-Path: <jqd@d1.example>
Andersen, et al. Expires October 25, 2018 [Page 38]
Internet-Draft ARC-Protocol April 2018
ARC-Seal: i=2; a=rsa-sha256; t=1421363253;
s=notary01; d=gmail.com; cv=pass;
b=sjHDMriRZ0Mui5eVEOGscRHWbQHcy97lvrduHQ8h+f2CfIrxUiKOE44x3LQwDWR
YbDjf5fcM9MdcIahC+cP59BQ9Y9DHwMDzwRTnM7NVb4kY+tSaVnLoIOaP9lF/sut
txO+RRNr0fCFw==
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
d=gmail.com; s=20120806;
h=mime-version:content-type:x-original-sender:
x-original-authentication-results:precedence:mailing-list:
list-id:list-post:list-help:list-archive:sender:reply-to:
list-unsubscribe:DKIM-Signature;
bh=2+gZwZhUK2V7JbpoO2MTrU19WvhcA4JnjiohFm9ZZ/g=;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0Ab8Oi1ebYV/hIBmfhS
LF1E80hMPcMijONfTQB6g5Hoh/kE6N2fgp6aSngL/WA3+g3Id8ElhXHvIGcJRFeM
KdJqiW5cxdqPTRW+BnR5ee6Tzg06kr265NTDIAU8p8fQNuLfZj49MMA+QwDBJtXw
bQoZyRtb6X6q0mYaszUB8kw==
Received: by mail-yk0-f179.google.com with SMTP id 19so2728865ykq.10
for <mailbox@gmail.com>; Thu, 14 Jan 2015 15:02:45 -0800 (PST)
Authentication-Results: i=2; gmail.com; spf=fail
smtp.from=jqd@d1.example; dkim=pass (1024-bit key)
header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=seal2015; d=example.org; cv=none:
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=example.org; s=clochette; t=1421363105;
bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
h=List-Id:List-Unsubscribe:List-Archive:List-Post:
List-Help:List-Subscribe:Reply-To:DKIM-Signature;
b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
spf=pass smtp.mfrom=jqd@d1.example;
dkim=pass (1024-bit key) header.i=@d1.example;
dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
Andersen, et al. Expires October 25, 2018 [Page 39]
Internet-Draft ARC-Protocol April 2018
(envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
Hey gang,
This is a test message.
--J.
B.2.3. Example 2: Message received by Recipient
Let's say that the Recipient is example.com
Processing at example.com:
o example.com performs usual authentication checks
o example.com adds Authentication-Results: header, Received header
o Determines that message fails DMARC
o Checks for ARC-Seal: header; finds two
o Validates the signature in the highest numbered ("i=2") ARC-Seal:
header, which covers all previous ARC-Seal: and ARC-
Authentication-Results: headers
o Validates the other ARC-Seal header ("i=1"), which covers the ARC-
Authentication-Results: header
o example.com uses the ARC-Authentication-Results: values
Here's what the message looks like at this point:
Return-Path: <jqd@d1.example>
Received: from mail-ob0-f188.google.com (mail-ob0-f188.google.com
[208.69.40.157]) by clothilde.example.com with ESMTP id
d200mr22663000ykb.93.1421363268
for <fmartin@example.com>; Thu, 14 Jan 2015 15:03:15 -0800 (PST)
Andersen, et al. Expires October 25, 2018 [Page 40]
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Authentication-Results: clothilde.example.com; spf=fail
smtp.from=jqd@d1.example; dkim=pass (1024-bit key)
header.i=@gmail.com; dmarc=fail; arc=pass
ARC-Seal: i=2; a=rsa-sha256; t=1421363253;
s=notary01; d=gmail.com; cv=pass;
b=sjHDMriRZ0Mui5eVEOGscRHWbQHcy97lvrduHQ8h+f2CfIrxUiKOE44x3LQwDWR
YbDjf5fcM9MdcIahC+cP59BQ9Y9DHwMDzwRTnM7NVb4kY+tSaVnLoIOaP9lF/sut
txO+RRNr0fCFw==
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
d=gmail.com; s=20120806;
h=mime-version:content-type:x-original-sender:
x-original-authentication-results:precedence:mailing-list:
list-id:list-post:list-help:list-archive:sender:reply-to:
:list-unsubscribe:DKIM-Signature;
bh=2+gZwZhUK2V7JbpoO2MTrU19WvhcA4JnjiohFm9ZZ/g=;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0Ab8Oi1ebYV/hIBmfhS
LF1E80hMPcMijONfTQB6g5Hoh/kE6N2fgp6aSngL/WA3+g3Id8ElhXHvIGcJRFeM
KdJqiW5cxdqPTRW+BnR5ee6Tzg06kr265NTDIAU8p8fQNuLfZj49MMA+QwDBJtXw
bQoZyRtb6X6q0mYaszUB8kw==
Received: by mail-yk0-f179.google.com with SMTP id 19so2728865ykq.10
for <mailbox@gmail.com>; Thu, 14 Jan 2015 15:02:45 -0800 (PST)
Authentication-Results: i=2; gmail.com; spf=fail
smtp.from=jqd@d1.example; dkim=pass (1024-bit key)
header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=seal2015; d=example.org; cv=none;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=example.org; s=clochette; t=1421363105;
bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
h=List-Id:List-Unsubscribe:List-Archive:List-Post:
List-Help:List-Subscribe:Reply-To:DKIM-Signature;
b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Authentication-Results: i=1; lists.example.org;
spf=pass smtp.mfrom=jqd@d1.example;
dkim=pass (1024-bit key) header.i=@d1.example;
dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
Andersen, et al. Expires October 25, 2018 [Page 41]
Internet-Draft ARC-Protocol April 2018
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=d1.example;
s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=Message-ID:Date:From:MIME-Version:To:CC:Subject:Content-Type:
Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
Hey gang,
This is a test message.
--J.
B.3. Example 3: Mailing list to forwarded mailbox with source
B.3.1. Here's the message as it exits the Origin:
Andersen, et al. Expires October 25, 2018 [Page 42]
Internet-Draft ARC-Protocol April 2018
Return-Path: <jqd@d1.example>
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=origin2015; d=d1.example; cv=none;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61T
X6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69EU
8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=d1.example; s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=MIME-Version:CC:Content-Type:Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijrv
Qwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4Gd3
TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: Example 1
Hey gang,
This is a test message.
--J.
B.3.2. Message is then received at example.org
B.3.2.1. Example 3, Step A: Message forwarded to list members with
source
Processing at example.org:
o example.org performs authentication checks
o example.org applies standard DKIM signature
o Checks for ARC-Seal: header; finds one (i=1)
o Validates the signature in the ARC-Seal (i=1): header, which
covers the d1.example ARC-Message-Signature: header
o example.org adds ARC-Authentication-Results header
o example.org adds usual Received: header
Andersen, et al. Expires October 25, 2018 [Page 43]
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o example.org adds a DKIM-Signature
o example.org adds a ARC-Seal header, contents of which are
* sequence number ("i=2")
* hash algorithm (SHA256 as example)
* timestamp ("t=")
* chain validity ("cv=")
* selector for key ("s=seal2015")
* domain for key ("d=example.org")
* signature ("b=")
Here's the message as it exits Step A:
Andersen, et al. Expires October 25, 2018 [Page 44]
Internet-Draft ARC-Protocol April 2018
Return-Path: <jqd@d1.example>
ARC-Seal: i=2; a=rsa-sha256; t=1421363107;
s=seal2015; d=example.org; cv=pass;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
d=example.org; s=clochette; t=1421363105;
bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
h=List-Id:List-Unsubscribe:List-Archive:List-Post:
List-Help:List-Subscribe:From:Reply-To:DKIM-Signature;
b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF
1F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3
A+m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Authentication-Results: i=2; lists.example.org;
spf=pass smtp.mfrom=jqd@d1.example;
dkim=pass (1024-bit key) header.i=@d1.example;
dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=origin2015; d=d1.example; cv=none;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=d1.example; s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=MIME-Version:CC:Content-Type:Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
Hey gang,
This is a test message.
--J.
Andersen, et al. Expires October 25, 2018 [Page 45]
Internet-Draft ARC-Protocol April 2018
B.3.2.2. Example 3, Step B: Message from list forwarded with source
The message is delivered to a mailbox at gmail.com
Processing at gmail.com:
o gmail.com performs usual authentication checks
o gmail.com adds Authentication-Results: and Received: header
o Determines that message fails DMARC
o Checks for ARC-Seal: header; finds two
o Validates the signature in the ARC-Seal (i=2): header, which
covers the ARC-Authentication-Results: header
o Validates the signature in the ARC-Seal (i=1): header, which
covers the d1.example ARC-Message-Signature: header
o Uses the ARC-Authentication-Results: values, but:
o Instead of delivering message, prepares to forward message per
user settings
o Applies usual DKIM signature
o gmail.com adds it's own ARC-Seal: header, contents of which are
* version
* sequence number ("i=2")
* hash algorithm (SHA256 as example)
* timestamp ("t=")
* selector for key ("s=notary01")
* domain for key ("d=gmail.com")
* Note: algorithm requires only ARC-Seals with lower sequence #
be included, in ascending order
* signature of the chain
Here's what the message looks like at this point:
Return-Path: <jqd@d1.example>
Andersen, et al. Expires October 25, 2018 [Page 46]
Internet-Draft ARC-Protocol April 2018
ARC-Seal: i=3; a=rsa-sha256; t=1421363253;
s=notary01; d=gmail.com; cv=pass;
b=sjHDMriRZ0Mui5eVEOGscRHWbQHcy97lvrduHQ8h+f2CfIrxUiKOE44x3LQwD
WRYbDjf5fcM9MdcIahC+cP59BQ9Y9DHwMDzwRTnM7NVb4kY+tSaVnLoIOaP9lF
/suttxO+RRNr0fCFw==
ARC-Message-Signature: i=3; a=rsa-sha256; c=relaxed/relaxed;
d=gmail.com; s=20120806;
h=mime-version:content-type:x-original-sender
:x-original-authentication-results:precedence:mailing-list
:list-id:list-post:list-help:list-archive:sender
:list-unsubscribe:reply-to;
bh=2+gZwZhUK2V7JbpoO2MTrU19WvhcA4JnjiohFm9ZZ/g=;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0Ab8Oi1ebYV/hIBm
fhSLF1E80hMPcMijONfTQB6g5Hoh/kE6N2fgp6aSngL/WA3+g3Id8ElhXHvIGcJ
RFeMKdJqiW5cxdqPTRW+BnR5ee6Tzg06kr265NTDIAU8p8fQNuLfZj49MMA+QwD
BJtXwbQoZyRtb6X6q0mYaszUB8kw==
Received: by mail-yk0-f179.google.com with SMTP id 19so2728865ykq.10
for <mailbox@gmail.com>; Thu, 14 Jan 2015 15:02:45 -0800 (PST)
Authentication-Results: i=3; gmail.com; spf=fail
smtp.from=jqd@d1.example; dkim=pass (1024-bit key)
header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=2; a=rsa-sha256; t=1421363107;
s=seal2015; d=example.org; cv=pass;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
d=example.org; s=clochette; t=1421363105;
bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
h=List-Id:List-Unsubscribe:List-Archive:List-Post:
List-Help:List-Subscribe:Reply-To:DKIM-Signature;
b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF1
F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3A+
m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Authentication-Results: i=2; lists.example.org;
spf=pass smtp.mfrom=jqd@d1.example;
dkim=pass (1024-bit key) header.i=@d1.example;
dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
Andersen, et al. Expires October 25, 2018 [Page 47]
Internet-Draft ARC-Protocol April 2018
(envelope-from jqd@d1.example)
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=origin2015; d=d1.example; cv=none;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=d1.example; s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=MIME-Version:CC:Content-Type:Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYij
rvQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD
4Gd3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
Hey gang,
This is a test message.
--J.
B.3.3. Example 3: Message received by Recipient
Let's say that the Recipient is example.com
Processing at example.com:
o example.com performs usual authentication checks
o example.com adds Authentication-Results: header, Received header
o Determines that message fails DMARC
o Checks for ARC-Seal: header; finds three
o Validates the signature in the highest numbered ("i=2") ARC-Seal:
header, which covers all previous ARC-Seal: and ARC-
Authentication-Results: headers
o Validates the other ARC-Seal header ("i=2"), which covers the ARC-
Authentication-Results: header
o Validates the other ARC-Seal header ("i=1"), which covers the
d1.example ARC-Message-Signature: header
o example.com uses the ARC-Authentication-Results: values
Andersen, et al. Expires October 25, 2018 [Page 48]
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Here's what the message looks like at this point:
Return-Path: <jqd@d1.example>
Received: from mail-ob0-f188.google.com (mail-ob0-f188.google.com
[208.69.40.157]) by clothilde.example.com with ESMTP id
d200mr22663000ykb.93.1421363268
for <fmartin@example.com>; Thu, 14 Jan 2015 15:03:15 -0800 (PST)
Authentication-Results: clothilde.example.com; spf=fail
smtp.from=jqd@d1.example; dkim=pass (1024-bit key)
header.i=@gmail.com; dmarc=fail; arc=pass
ARC-Seal: i=3; a=rsa-sha256; t=1421363253;
s=notary01; d=gmail.com; cv=pass;
b=sjHDMriRZ0Mui5eVEOGscRHWbQHcy97lvrduHQ8h+f2CfIrxUiKOE44x3LQwDW
RYbDjf5fcM9MdcIahC+cP59BQ9Y9DHwMDzwRTnM7NVb4kY+tSaVnLoIOaP9lF/s
uttxO+RRNr0fCFw==
ARC-Message-Signature: i=3; a=rsa-sha256; c=relaxed/relaxed;
d=gmail.com; s=20120806;
h=mime-version:content-type:x-original-sender
:x-original-authentication-results:precedence
:mailing-list:list-id:list-post:list-help:list-archive:sender
:list-unsubscribe:reply-to;
bh=2+gZwZhUK2V7JbpoO2MTrU19WvhcA4JnjiohFm9ZZ/g=;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0Ab8Oi1ebYV/hIBm
fhSLF1E80hMPcMijONfTQB6g5Hoh/kE6N2fgp6aSngL/WA3+g3Id8ElhXHvIGcJ
RFeMKdJqiW5cxdqPTRW+BnR5ee6Tzg06kr265NTDIAU8p8fQNuLfZj49MMA+QwD
BJtXwbQoZyRtb6X6q0mYaszUB8kw==
Received: by mail-yk0-f179.google.com with SMTP id 19so2728865ykq.10
for <mailbox@gmail.com>; Thu, 14 Jan 2015 15:02:45 -0800 (PST)
Authentication-Results: i=3; gmail.com; spf=fail
smtp.from=jqd@d1.example; dkim=pass (1024-bit key)
header.i=@example.org; dmarc=fail; arc=pass
ARC-Seal: i=2; a=rsa-sha256; t=1421363107;
s=seal2015; d=example.org; cv=pass;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz6
1TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L
69EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=2; a=rsa-sha256; c=relaxed/relaxed;
d=example.org; s=clochette; t=1421363105;
bh=FjQYm3HhXStuzauzV4Uc02o55EzATNfL4uBvEoy7k3s=;
h=List-Id:List-Unsubscribe:List-Archive:List-Post:
List-Help:List-Subscribe:Reply-To:DKIM-Signature;
b=Wb4EiVANwAX8obWwrRWpmlhxmdIvj0dv0psIkiaGOOug32iTAcc74/iWvlPXpF1
F5vYVF0mw5cmKOa824tKkUOOE3yinTAekqnly7GJuFCDeSA1fQHhStVV7BzAr3A+
m4bwa6RIDgr3rOPJil678dZTHfztFWyjwIUxB5Ajxj/M=
Received: from segv.d1.example (segv.d1.example [72.52.75.15])
by lists.example.org (8.14.5/8.14.5) with ESMTP id t0EKaNU9010123
Andersen, et al. Expires October 25, 2018 [Page 49]
Internet-Draft ARC-Protocol April 2018
for <arc@example.org>; Thu, 14 Jan 2015 15:01:30 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Authentication-Results: i=2; lists.example.org;
spf=pass smtp.mfrom=jqd@d1.example;
dkim=pass (1024-bit key) header.i=@d1.example;
dmarc=pass
Received: from [10.10.10.131] (w-x-y-z.dsl.static.isp.com [w.x.y.z])
(authenticated bits=0)
by segv.d1.example with ESMTP id t0FN4a8O084569;
Thu, 14 Jan 2015 15:00:01 -0800 (PST)
(envelope-from jqd@d1.example)
ARC-Seal: i=1; a=rsa-sha256; t=1421363107;
s=origin2015; d=d1.example; cv=none;
b=pCw3Qxgfs9E1qnyNZ+cTTF3KHgAjWwZz++Rju0BceSiuwIg0Pkk+3RZH/kaiz61
TX6RVT6E4gs49Sstp41K7muj1OR5R6Q6llahLlQJZ/YfDZ3NImCU52gFWLUD7L69
EU8TzypfkUhscqXjOJgDwjIceBNNOfh3Jy+V8hQZrVFCw0A=
ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed;
d=d1.example; s=20130426; t=1421363082;
bh=EoJqaaRvhrngQxmQ3VnRIIMRBgecuKf1pdkxtfGyWaU=;
h=MIME-Version:To:CC:Subject:Content-Type:Content-Transfer-Encoding;
b=HxsvPubDE+R96v9dM9Y7V3dJUXvajd6rvF5ec5BPe/vpVBRJnD4I2weEIyYijr
vQwbv9uUA1t94kMN0Q+haFo6hiQPnkuDxku5+oxyZWOqtNH7CTMgcBWWTp4QD4G
d3TRJlgotsX4RkbNcUhlfnoQ0p+CywWjieI8aR6eof6WDQ=
Message-ID: <54B84785.1060301@d1.example>
Date: Thu, 14 Jan 2015 15:00:01 -0800
From: John Q Doe <jqd@d1.example>
To: arc@example.org
Subject: [Lists] Example 1
Hey gang,
This is a test message.
--J.
Appendix C. Acknowledgements
This draft originated with the work of OAR-Dev Group.
The authors thank all of the OAR-Dev group for the ongoing help and
though-provoking discussions from all the participants, especially:
Alex Brotman, Brandon Long, Dave Crocker, Elizabeth Zwicky, Franck
Martin, Greg Colburn, J. Trent Adams, John Rae-Grant, Mike Hammer,
Mike Jones, Steve Jones, Terry Zink, Tim Draegen.
Grateful appreciation is extended to the people who provided feedback
through the discuss mailing list.
Andersen, et al. Expires October 25, 2018 [Page 50]
Internet-Draft ARC-Protocol April 2018
Appendix D. Comments and Feedback
Please address all comments, discussions, and questions to
dmarc@ietf.org [7]. Earlier discussions can be found at arc-
discuss@dmarc.org [8].
Authors' Addresses
Kurt Andersen
LinkedIn
1000 West Maude Ave
Sunnyvale, California 94085
USA
Email: kurta@linkedin.com
Brandon Long (editor)
Google
Email: blong@google.com
Steven Jones (editor)
TDP
Email: smj@crash.com
Seth Blank (editor)
Valimail
Email: seth@valimail.com
Murray Kucherawy (editor)
TDP
Email: superuser@gmail.com
Andersen, et al. Expires October 25, 2018 [Page 51]
