]> LinkedIn

2029 Stierlin Ct. Mountain View California 94043 USA kurta@linkedin.com

Google

johnrg@google.com

Google

blong@google.com

Paypal

trent.adams@paypal.com

TDP

smj@crash.com

art DMARC Working Group Internet-Draft Authenticated Received Chain (ARC) permits an organization which is creating or handling email to indicate its involvement with the handling process. It defines a set of cryptographically signed header fields in a manner analagous to that of DKIM. Assertion of responsibility is validated through a cryptographic signature and by querying the Signer’s domain directly to retrieve the appropriate public key. Changes in the message that might break DKIM can be identified through the ARC set of header fields.

The development of strong domain authentication through Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) has led to the implementation of the DMARC framework which extends the authentication to the author’s “From:” (RFC5322.From) field and permits publishing policies for non-compliant messages. Implicit within the DMARC framework is a requirement that any intermediaries between the source system and ultimate receiver system need to preserve the validity of the DKIM signature; however, there are common legitimate email practices which break the DKIM validation (). This specification defines an Authenticated Received Chain (ARC). ARC addresses the problems with the untrustworthiness of the standard Received header field sequence. Through the information tracked in the ARC series of headers, receivers can develop a more nuanced interpretation to guide any local policies related to messages that arrive with broken domain authentication (DMARC). Forgery of the Received header fields is a common tactic used by bad actors. One of the goals of this specification defines a comparable set of trace header fields which can be relied upon by receivers, assuming all ADministrative Management Domain (ADMD) intermediary handlers of a message participate in ARC. The Authentication-Results (A-R) mechanism permits the output of an email authentication evaluation process to be transmitted from the evaluating agent to a consuming agent that uses the information. On its own, A-R is believable only within a trust domain. ARC provides a protection mechanism for the data, permiting the communication to cross trust domain boundaries.

The specification of the ARC framework is driven by the following high-level goals, security considerations, and practical operational requirements.

Provide a verifiable “chain of custody” for email messages; Not require changes for originators of email; Support the verification of the ARC header field set by each hop in the handling chain; Work at Internet scale; and Provide a trustable mechanism for the communication of Authentication-Results across trust boundaries.

ARC is not a trust framework. Users of the ARC header fields are cautioned against making unsubstantiated conclusions when encountering a “broken” ARC sequence.

The ARC-related set of header fields can be used (when validated) to determine the path that an email message has taken between the originating system and receiver. Subject to the cautions mentioned in , this information can assist in determining any local policy overrides to for violations of origination domain authentication policies.

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”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in . Readers are encouraged to be familiar with the contents of , and in particular, the potential roles of intermediaries in the delivery of email. Syntax descriptions use Augmented BNF (ABNF) .

When an email message is received without a properly validated originating domain, the inability to believe the accuracy of a series of Received header fields prevents receiving systems from having a way to infer anything about the handling of the message by looking at the ADMDs through which the message has traveled. With ARC, participating ADMDs are able to securely register their handling of an email message. If all mediators () participate in the ARC process, receivers will be able to rely upon the chain and make local policy decisions informed by that information. The ARC set of header fields provides a method by which participating intermediaries can indicate the hand-offs for email messages.

This specification defines three new header fields: Header field name: ARC-Seal (abbreviated below as AS) Header field name: ARC-Message-Signature (abbreviated below as AMS) Header field name: ARC-Authentication-Results (abbreviated below as AAR) Collectively, these header fields form a connected set of attribution information by which receivers can identify the handling path for a message. As described below, a distinct set of these fields share a common sequence number, identified in an “i=” tag. Such a correlated group of header fields is referred to as an “ARC set”. Specific references to individual header fields use the header field names to distinguish such references. The ARC sets SHOULD be added at the top of a message header as it transits MTAs that do authentication checks, so some idea of how far away the checks were done can be inferred. They are therefore considered to be a trace field as defined in , and all of the related definitions in that document apply. Relative ordering of different trace header fields (the ARC sets, DKIM, Received, etc.) is unimportant for this specification. In general, trace header fields, such as ARC, SHOULD be added at the top of the email header fields, but receivers MUST be able to process the header fields from wherever they are found in the message header. Ordering amongst the individual ARC header fields and sets is specified below and MUST be followed for proper canonicalized signing and evaluation.

ARC-Seal is a Structured Header Field as defined in Internet Message Format (). All of the related definitions in that document apply. The ARC-Seal makes use of Tag=Value Lists as defined in , Section 3.2. The value of the header field consists of an authentication sequence identifier, and a series of statements and supporting data. The statements indicate relevant data about the signing of the ARC set. The header field can appear more than once in a single message, but each instance MUST have a unique “i=” value. The ARC-Seal header field includes a digital signature of all preceding ARC message header fields on the message.

The following tags are the only supported tags for an ARC-Seal field. All of them MUST be present. Unknown tags MUST be ignored and do not affect the validity of the header. a = hash algorithm; syntax is the same as the “a=” tag defined in Section 3.5 of ; b = digital signature; syntax is the same as the “b=” tag defined in Section 3.5 of ; cv = chain validation status: valid values: ‘none’ = no pre-existing chain; ‘fail’ = the chain as received does not validate; or ‘pass’ = valid chain received. d = domain for key; syntax is the same as the “d=” tag defined in Section 3.5 of ; i = “instance” or sequence number; monotonically increasing at each “sealing” entity, beginning with ‘1’, may not exceed ‘1024’ s = selector for key; syntax is the same as the “s=” tag defined in Section 3.5 of ; t = timestamp; syntax is the same as the “t=” tag defined in Section 3.5 of .

No ‘bh’ value is defined for ARC-Seal, since only message header fields are ever signed by the ARC-Seal. ARC-Seal does not use the ‘h’ tag (the list of signed header fields) that is defined for DKIM-Signatures because the list of applicable header fields is fully determined by the construction rules (see ). ARC-Seal does not use the ‘c’ (canonicalization) tag because only ‘relaxed’ canonicalization is allowed for ARC-Seal header field canonicalization.

In this section, the term “scope” is used to indicate those header fields signed by an ARC-Seal header field. A number in parentheses indicates the instance of that field, starting at 1. The suffix “-no-b” is used with an ARC-Seal field to indicate that its “b” field is empty at the time the signature is computed, as described in Section 3.5 of . “AAR” refers to ARC-Authentication-Results, “AMS” to ARC- Message-Signature, “AS” to ARC-Seal, and “ASB” to an ARC-Seal with an empty “b” tag. Generally, the scope of an ARC set for a message containing “n” ARC sets is the concatenation of the following, for x (instance number) from 1 to n: AAR(x); AMS(x); ASB(x) if x = n, else AS(x) Thus for a message with no seals (i.e., upon injection), the scope of the first ARC set is AAR(1):AMS(1):ASB(1). The ARC set thus generated would produce a first ARC-Seal with a “b” value. The next ARC set would include in its signed content the prior scope, so it would have a scope of AAR(1):AMS(1):AS(1):AAR(2):AMS(2):ASB(2). Note: Typically header field sets appear within the header in descending instance order.

The ARC-Seal generation process mirrors the procedure used for DKIM-Signature fields described in Section 5 of in that it is at first generated with empty “b” field for the purpose of signature generation, and then the “b” value is added just prior to adding the ARC-Seal field to the message. In particular, signing calculation MUST be done in bottom-up order as specified in Section 5.4.2 of and as illustrated above .

In order for a series of ARC sets to be considered valid, the following statements MUST be satisfied: All ARC-Seal header fields MUST validate; All ARC-Seal header fields MUST have a chain value (cv=) status of “pass” (except the first which MUST be “none”); and The newest (highest instance number (i=)) AMS header field MUST validate.

In the algorith below, a “hop” is represented by the ARC set bearing a particular instance number. The number of hops is the same as the highest instance number found in the ARC sets, or 0 (zero) if there are no ARC sets found within the header. “Success” means that the signature found in the referenced header validates when against the content which was signed.

1 and hop.ARC-Seal.cv == "pass") or (hop_num == 1 and hop.ARC-Seal.cv == "none"): if validate(hop.ARC-Seal) == success: next else: return "fail" return "pass" ]]>

The ARC-Message-Signature header field is a special variant of a DKIM-Signature , using only the relaxed header canonicalization rules specified in . The ARC-Message-Signature header field can appear multiple times in a single message but each instance MUST have a unique “i=” value.

Participants may include any other header fields within the scope of the ARC-Message-Signature signature except that they MUST NOT include ARC-Seal headers fields. In particular, including all DKIM-Signature header fields and all ARC-Authentication-Results header fields is RECOMMENDED. The advice regarding headers to include or avoid for ARC-Message-Signature is otherwise identical to that specified in section 5.4 of .

The ARC-Message-Signature header field MUST be created using the header and body canonicalization rules mechanisms in Section 3.4 of . The corresponding “c=” tag value MUST be specified in the AMS header field value.

Contrary to DKIM, the ‘i’ tag for ARC-Message-Signature identifies the sequential instance of the field, thus indicating that it is part of a particular ARC set. That is, an ARC-Message-Signature, ARC-Seal, and ARC-Authentication-Results all bearing an “i=” tag with the same value are part of the same ARC set (see ).

There is no “v” tag for ARC-Message-Signature.

As with DKIM-Signature and ARC-Seal header fields, the “b” tag of the ARC-Message-Signature is empty until the signature is actually computed, and only then is it added to the header field, before affixing the ARC-Message-Signature to the message. As with ARC-Seal and DKIM-Signature header fields, the order of header fields signed MUST be done in bottom-up order.

ARC-Authentication-Results is a direct copy of the Authentication-Results header field created for archival purposes by the each MTA outside of the trust boundary of the originating system which is contributing to the chain of ARC header fields. The corresponding instance (“i=”) tag value MUST be prefixed to the Authentication-Results. The value of the header field (after removing comments) consists of an instance identifier, an authentication identifier, and then a series of statements and supporting data, as described in . The header field can appear multiple times in a single message but each instance MUST have a unique “i=” value.

ARC-Authentication-Results requires inclusion of an “i=” tag before the “authserv-id” which indicates the ARC set to which it belongs as described in the previous section (see ).

The ARC-Seal is built in the same fashion as the analogous DKIM-Signature , using the relaxed header canonicalization rules specified in that document but with a strict ordering component for the header fields covered by the cryptographic signature: The ARC sets MUST be ordered in descending instance (i=) order. The referenced ARC-Message-Signatures (matching i= value) MUST immediately follow the ARC-Seal instance which included the reference. The associated ARC-Authentication-Results header field (matching i= value) MUST be the last item in the list for each set of ARC header fields. Thus, when prefixing ARC header fields to the existing header, the AAR header would be prefixed first; then the AMS would be calculated and prefixed; lastly the AS would be calculated and prefixed. The ARC-Message-Signature field(s) MUST not include any of the ARC-Seal header field(s) (from prior ARC sets) in their signing scope in order maintain a separation of responsibilities. When adding an ARC-Authentication-Results header field, it MUST be added before computing the ARC-Message-Signature. When “sealing” the message, an operator MUST create and attach the ARC-Message-Signature before the ARC-Seal in order to reference it and embed the ARC-Message-Signature within the ARC-Seal signature scope. Each ARC-Seal is connected to its respective ARC-Message-Signature and ARC-Authentication-Results through the common value of the “i=” tag.

When ordering the ARC header field sets, if there are gross violations of this protocol (e.g., such as duplicated instance numbers), such header field set(s) MUST be ordered as follows when analyzing for validity or subsequent signing: Within each set, header fields are sorted as specified in ; then Any ARC sets that are complete duplicates are removed - leaving only one instance of each unique ARC set; then Any remaining order dependencies between sets are be ordered as follows: (First) By descending order of i=; then (Second) By descending order of t= (from the ARC-Seal header field within the set); then (Finally) By ascending US-ASCII sort order for the entire canonicalized header field set The intent of specifying this ordering is to allow downstream message handlers to add their own ARC sets in a deterministic manner and to provide some resiliance against misbehaving downstream MTAs.

The public keys for ARC header fields follow the same requirements and semantics as those for DKIM-Signatures, described in Section 3.6 of . Operators may use distinct selectors for the ARC header fields at their own discretion.

All ARC-related keys are stored in the same namespace as DKIM keys : “_domainkey” specifically by adding the “._domainkey” suffix to the name of the key (the “selector”). For example, given an ARC-Seal (or ARC-Message-Signature) field of a “d=” tag value of “example.com” and an “s=” value of “foo.bar”, the DNS query seeking the public key will a query at the name “foo.bar._domainkey.example.com”.

For a more thorough treatment of the recommended usage of the ARC header fields for both intermediaries and end receivers, please consult .

The inclusion of additional ARC sets is to be done whenever a trust boundary is crossed, and especially when prior DKIM-Signatures might not survive the handling being performed such as some mailing lists that modify the content of messages or some gateway transformations. Note that trust boundaries might or might not exactly correspond with ADMD boundaries. Each participating ADMD MUST validate the preceding ARC set as a part of asserting their own seal. Even if the set is determined to be invalid, a participating ADMD SHOULD apply their own seal because this can help in analysis of breakage points in the chain.

ARC-aware DKIM signers do not DKIM-sign any ARC header fields.

Determining the validity of a chain of ARC sets is defined above in . Validation failures MUST be indicated with a “cv=” tag value of ‘fail’ when attaching a subsequent ARC-Seal header field.

There are a wide variety of ways in which the ARC set of header fields can be broken. 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. This specification is exclusively focused on well-behaved, participating intermediaries that result in a valid chain of ARC-related header fields. The value of such a well-formed, valid chain needs to be interpreted with care since malicious content can be easily introduced by otherwise well-intended senders through machine or account compromises. All normal content-based analysis still needs to be performed on any messages bearing a valid chain of ARC header sets.

If a receiver determines that the ARC set of header fields has is invalid, the receiver MAY signal the breakage through the extended SMTP response code 5.7.7 “message integrity failure” and corresponding SMTP response code.

Receivers MAY add an “arc=pass” or “arc=fail” method annotation into a locally-affixed Authentication-Results header field.

The evaluation of a series of ARC sets results in the following data which MAY be used to inform local-policy decisions: A list of the “d=” domains found in the validated (all) ARC-Seal header fields; The “d=” domain found in the most recent (highest instance number) AMS header field (since that is the only one necessarily validated)

Receivers SHOULD indicate situations in which ARC evaluation influenced the results of their local policy determination. DMARC reporting of ARC-informed decisions is augmented by adding a local_policy comment explanation as follows:

delivered fail fail local_policy arc=pass ams=d1.example d=d1.example,d2.example ]]>

The ARC-Seal chain provides a verifiable record of the handlers for a message. Anonymous remailers will probably not find this to match their operating goals.

This specification adds three new header fields as defined below.

This draft adds one item to the IANA “Email Authentication Methods” registry: Method : arc Defined: &SELF; ptype: header Property: chain evaluation result Value: chain evaluation result status (see ) Status: active Version: 1

This specification adds three new header fields to the “Permanent Message Header Field Registry”, as follows: Header field name: ARC-Seal Applicable protocol: mail Status: draft Author/Change controller: OAR-Dev Group Specification document(s): &SELF; Related information: Header field name: ARC-Message-Signature Applicable protocol: mail Status: draft Author/Change controller: OAR-Dev Group Specification document(s): &SELF; Related information: Header field name: ARC-Authentication-Results Applicable protocol: mail Status: standard Author/Change controller: IETF Specification document(s): &SELF; Related information:

[[ Note to the RFC Editor: Please remove this section before publication along with the reference to . ]] 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 . 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. According to , “this will allow reviewers and working groups to assign due consideration to documents that have the benefit of running code, which may serve as evidence of valuable experimentation and feedback that have made the implemented protocols more mature. It is up to the individual working groups to use this information as they see fit”. This information is known to be correct as of the third interoperability test event which was held on 2016-06-17. GMail test reflector Organization: Google Description: Internal prototype implementation with both debug analysis and validating + sealing pass-through function Status of Operation: Beta Coverage: Full spec implemented as of Licensing: Proprietary - Internal only Implementation Notes: Full functionality was demonstrated during the interop testing on 2016-06-17 Contact Info: arc-discuss@dmarc.org AOL test reflector Organization: AOL Description: Internal prototype implementation with both debug analysis and validating + sealing pass-through function Status of Operation: Alpha Coverage: ARC chain validity status checking is not operational, but otherwise this system conforms to Licensing: Proprietary - Internal only Implementation Notes: Full functionality with the exception of chain validity checking was demonstrated during the interop testing on 2016-06-17 Contact Info: arc-discuss@dmarc.org dkimpy patch Organization: OAR-DEV Description: Patches to the dkimpy (Python DKIM) package [https://launchpad.net/dkimpy] to add ARC functionality Status of Operation: Beta Coverage: The test suite is incomplete, but the command line validator was demonstrated to interoperate with the Google and AOL implementations during the interop on 2016-06-17 Licensing: Open/Other (same as dkimpy package) Implementation Notes: The patch has been submitted to the dkimpy maintainer for inclusion into the official package. Contact Info: arc-discuss@dmarc.org OpenARC Organization: TDP/Murray Kucherawy Description: Implemention of milter functionality related to the OpenDKIM and OpenDMARC packages Status of Operation: Alpha Coverage: Built to support Licensing: Open/Other (same as OpenDKIM and OpenDMARC packages) Implementation Notes: The build is FreeBSD oriented and takes some tweaks to build on RedHat-based Linux platforms. Initial testing during the interop event on 2016-06-17 showed that it can be operational, but the documentation regarding configuration settings is unclear and the generated signature values do not validate when compared to the Google, AOL or dkimpy implementations. Contact Info: arc-discuss@dmarc.org Mailman addition Organization: Mailman development team Description: Integrated ARC capabilities within the Mailman package Status of Operation: Implementation in progress Coverage: Unknown Licensing: Same as mailman package - GPL Implementation Notes: Incomplete at this time Contact Info: [https://www.gnu.org/software/mailman/contact.html]

The Security Considerations of and apply directly to this specification. 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. Operators who receive a message bearing N ARC sets has to complete 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: An attacker can send a message to an ARC partipant 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. DKIM only does one DNS check per signature, while this one can do many. Absent caching, slow DNS responses can cause SMTP timeouts; this could be exploited as a DoS attack.

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-Seal chain may be used to provide input to local policy engines in cases where the sending system’s DKIM-Signature does not validate.

&RFC1345; &RFC5234; &RFC5321; &RFC5322; &RFC3463; &RFC7601; &RFC7208; &RFC6651; &RFC5863; &RFC6377; &RFC5585; &RFC6376; &RFC4686; &RFC5598; &RFC5226; &RFC2142; &RFC2606; &RFC2119; &RFC6982; &RFC7489;

[[ 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. ]]

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 To: arc@dmarc.org Subject: Example 1 Hey gang, This is a test message. --J. ]]>

Processing at example.org: example.org performs authentication checks No previous Auth-Results or ARC-Seal headers are present example.org adds ARC-Auth-Results header example.org adds Received: header example.org adds a ARC-Seal header Here’s the message as it exits example.org:

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 ; 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 To: arc@example.org Subject: [Lists] Example 1 Hey gang, This is a test message. --J. ]]>

Let’s say that the Recipient is example.com Processing at example.com: example.com performs usual authentication checks example.com adds Auth-Results: header, Received header Determines that message fails DMARC Checks for ARC-Seal: header; finds one Validates the signature in the ARC-Seal: header, which covers the ARC-Authentication-Results: header 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:

Received: from example.org (example.org [208.69.40.157]) by clothilde.example.com with ESMTP id d200mr22663000ykb.93.1421363207 for ; 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 ; 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/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 To: arc@example.org Subject: [Lists] Example 1 Hey gang, This is a test message. --J. ]]>

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 To: arc@example.org Subject: Example 1 Hey gang, This is a test message. --J. ]]>

Processing at example.org: example.org performs authentication checks example.org applies standard DKIM signature No previous Auth-Results or ARC-Seal headers are present example.org adds ARC-Auth-Results header example.org adds usual Received: header example.org adds a ARC-Seal header Here’s the message as it exits Step A:

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 ; 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 To: arc@example.org Subject: [Lists] Example 1 Hey gang, This is a test message. --J. ]]>

The message is delivered to a mailbox at gmail.com Processing at gmail.com: gmail.com performs usual authentication checks gmail.com adds Auth-Results: and Received: header Determines that message fails DMARC Checks for ARC-Seal: header; finds one Validates the signature in the ARC-Seal: header, which covers the ARC-Authentication-Results: header Uses the ARC-Auth-Results: values, but: Instead of delivering message, prepares to forward message per user settings Applies usual DKIM signature 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:

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 ; 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 ; 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 To: arc@example.org Subject: [Lists] Example 1 Hey gang, This is a test message. --J. ]]>

 

Let’s say that the Recipient is example.com Processing at example.com: example.com performs usual authentication checks example.com adds Auth-Results: header, Received header Determines that message fails DMARC Checks for ARC-Seal: header; finds two Validates the signature in the highest numbered (“i=2”) ARC-Seal: header, which covers all previous ARC-Seal: and ARC-Authentication-Results: headers Validates the other ARC-Seal header (“i=1”), which covers the ARC-Authentication-Results: header example.com uses the ARC-Authentication-Results: values Here’s what the message looks like at this point:

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 ; 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=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 ; 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 ; 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 To: arc@example.org Subject: [Lists] Example 1 Hey gang, This is a test message. --J. ]]>

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 To: arc@example.org Subject: Example 1 Hey gang, This is a test message. --J. ]]>

 

Processing at example.org: example.org performs authentication checks example.org applies standard DKIM signature Checks for ARC-Seal: header; finds one (i=1) Validates the signature in the ARC-Seal (i=1): header, which covers the d1.example ARC-Message-Signature: header example.org adds ARC-Auth-Results header example.org adds usual Received: header example.org adds a DKIM-Signature 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:

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 ; 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 To: arc@example.org Subject: [Lists] Example 1 Hey gang, This is a test message. --J. ]]>

The message is delivered to a mailbox at gmail.com Processing at gmail.com: gmail.com performs usual authentication checks gmail.com adds Auth-Results: and Received: header Determines that message fails DMARC Checks for ARC-Seal: header; finds two Validates the signature in the ARC-Seal (i=2): header, which covers the ARC-Authentication-Results: header Validates the signature in the ARC-Seal (i=1): header, which covers the d1.example ARC-Message-Signature: header Uses the ARC-Auth-Results: values, but: Instead of delivering message, prepares to forward message per user settings Applies usual DKIM signature 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:

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 ; 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 ; 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/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 To: arc@example.org Subject: [Lists] Example 1 Hey gang, This is a test message. --J. ]]>

Let’s say that the Recipient is example.com Processing at example.com: example.com performs usual authentication checks example.com adds Auth-Results: header, Received header Determines that message fails DMARC Checks for ARC-Seal: header; finds three Validates the signature in the highest numbered (“i=2”) ARC-Seal: header, which covers all previous ARC-Seal: and ARC-Authentication-Results: headers Validates the other ARC-Seal header (“i=2”), which covers the ARC-Authentication-Results: header Validates the other ARC-Seal header (“i=1”), which covers the d1.example ARC-Message-Signature: header example.com uses the ARC-Authentication-Results: values Here’s what the message looks like at this point:

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 ; 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 ; 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 for ; 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 To: arc@example.org Subject: [Lists] Example 1 Hey gang, This is a test message. --J. ]]>

This draft is 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.

Please address all comments, discussions, and questions to dmarc@ietf.org. Earlier discussions can be found at arc-discuss@dmarc.org.