draft-ietf-dkim-ssp-03.txt   draft-ietf-dkim-ssp-04.txt 
Network Working Group E. Allman Network Working Group E. Allman
Internet-Draft Sendmail, Inc. Internet-Draft Sendmail, Inc.
Intended status: Standards Track J. Fenton Intended status: Standards Track J. Fenton
Expires: August 26, 2008 Cisco Systems, Inc. Expires: January 3, 2009 Cisco Systems, Inc.
M. Delany M. Delany
Yahoo! Inc. Yahoo! Inc.
J. Levine J. Levine
Taughannock Networks Taughannock Networks
February 23, 2008 July 2, 2008
DKIM Author Signing Practices (ASP) DKIM Author Domain Signing Practices (ADSP)
draft-ietf-dkim-ssp-03 draft-ietf-dkim-ssp-04
Status of this Memo Status of this Memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
skipping to change at page 1, line 39 skipping to change at page 1, line 39
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
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This Internet-Draft will expire on August 26, 2008. This Internet-Draft will expire on January 3, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract Abstract
DomainKeys Identified Mail (DKIM) defines a domain-level DomainKeys Identified Mail (DKIM) defines a domain-level
authentication framework for email using public-key cryptography and authentication framework for email to permit verification of the
key server technology to permit verification of the source and source and contents of messages. This document specifies an adjunct
contents of messages by either Mail Transport Agents (MTAs) or Mail mechanism to aid in assessing messages that do not contain a DKIM
User Agents (MUAs). The primary DKIM protocol is described in signature for the domain used in the author's address. It defines a
[RFC4871]. This document describes the records that authors' domains record that can advertise whether they sign their outgoing mail, and
can use to advertise their practices for signing their outgoing mail, how other hosts can access those records.
and how other hosts can access those records.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Language and Terminology . . . . . . . . . . . . . . . . . . . 4 2. Language and Terminology . . . . . . . . . . . . . . . . . . . 3
2.1. Terms Imported from DKIM Signatures Specification . . . . 4 2.1. Terms Imported from DKIM Signatures Specification . . . . 3
2.2. Valid Signature . . . . . . . . . . . . . . . . . . . . . 5 2.2. Valid Signature . . . . . . . . . . . . . . . . . . . . . 4
2.3. Author Address . . . . . . . . . . . . . . . . . . . . . . 5 2.3. Author Address . . . . . . . . . . . . . . . . . . . . . . 4
2.4. Author Domain . . . . . . . . . . . . . . . . . . . . . . 5 2.4. Author Domain . . . . . . . . . . . . . . . . . . . . . . 4
2.5. Alleged Author . . . . . . . . . . . . . . . . . . . . . . 5 2.5. Alleged Author . . . . . . . . . . . . . . . . . . . . . . 4
2.6. Author Signing Practices . . . . . . . . . . . . . . . . . 5 2.6. Author Domain Signing Practices . . . . . . . . . . . . . 4
2.7. Author Signature . . . . . . . . . . . . . . . . . . . . . 5 2.7. Author Signature . . . . . . . . . . . . . . . . . . . . . 4
3. Operation Overview . . . . . . . . . . . . . . . . . . . . . . 6 3. Operation Overview . . . . . . . . . . . . . . . . . . . . . . 5
3.1. ASP Usage . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. ADSP Applicability . . . . . . . . . . . . . . . . . . . . 5
3.2. ASP Results . . . . . . . . . . . . . . . . . . . . . . . 6 3.2. ADSP Usage . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Detailed Description . . . . . . . . . . . . . . . . . . . . . 7 3.3. ADSP Results . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. DNS Representation . . . . . . . . . . . . . . . . . . . . 7 4. Detailed Description . . . . . . . . . . . . . . . . . . . . . 6
4.2. Publication of ASP Records . . . . . . . . . . . . . . . . 7 4.1. DNS Representation . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 4.2. Publication of ADSP Records . . . . . . . . . . . . . . . 6
5.1. ASP Specification Tag Registry . . . . . . . . . . . . . . 10 4.3. ADSP Lookup Procedure . . . . . . . . . . . . . . . . . . 7
5.2. ASP Outbound Signing Practices Registry . . . . . . . . . 10 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.3. ASP Flags Registry . . . . . . . . . . . . . . . . . . . . 11 5.1. ADSP Specification Tag Registry . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5.2. ADSP Outbound Signing Practices Registry . . . . . . . . . 9
6.1. ASP Threat Model . . . . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6.2. DNS Attacks . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. ADSP Threat Model . . . . . . . . . . . . . . . . . . . . 9
6.3. DNS Wildcards . . . . . . . . . . . . . . . . . . . . . . 12 6.2. DNS Attacks . . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.3. DNS Wildcards . . . . . . . . . . . . . . . . . . . . . . 10
7.1. References - Normative . . . . . . . . . . . . . . . . . . 13 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.2. References - Informative . . . . . . . . . . . . . . . . . 13 7.1. References - Normative . . . . . . . . . . . . . . . . . . 11
Appendix A. Usage Examples . . . . . . . . . . . . . . . . . . . 13 7.2. References - Informative . . . . . . . . . . . . . . . . . 11
A.1. Single Location Domains . . . . . . . . . . . . . . . . . 14 Appendix A. Usage Examples . . . . . . . . . . . . . . . . . . . 11
A.2. Bulk Mailing Domains . . . . . . . . . . . . . . . . . . . 14 A.1. Single Location Domains . . . . . . . . . . . . . . . . . 12
A.3. Bulk Mailing Domains with Discardable Mail . . . . . . . . 14 A.2. Bulk Mailing Domains . . . . . . . . . . . . . . . . . . . 12
A.4. Third Party Senders . . . . . . . . . . . . . . . . . . . 15 A.3. Bulk Mailing Domains with Discardable Mail . . . . . . . . 13
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 15 A.4. Third Party Senders . . . . . . . . . . . . . . . . . . . 13
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 15 A.5. Non-email Domains . . . . . . . . . . . . . . . . . . . . 13
C.1. Changes since -ietf-dkim-02 . . . . . . . . . . . . . . . 15 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 13
C.2. Changes since -ietf-dkim-ssp-01 . . . . . . . . . . . . . 16 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 13
C.3. Changes since -ietf-dkim-ssp-00 . . . . . . . . . . . . . 17 C.1. Changes since -ietf-dkim-03 . . . . . . . . . . . . . . . 14
C.4. Changes since -allman-ssp-02 . . . . . . . . . . . . . . . 17 C.2. Changes since -ietf-dkim-02 . . . . . . . . . . . . . . . 14
C.5. Changes since -allman-ssp-01 . . . . . . . . . . . . . . . 18 C.3. Changes since -ietf-dkim-ssp-01 . . . . . . . . . . . . . 15
C.6. Changes since -allman-ssp-00 . . . . . . . . . . . . . . . 18 C.4. Changes since -ietf-dkim-ssp-00 . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 C.5. Changes since -allman-ssp-02 . . . . . . . . . . . . . . . 16
Intellectual Property and Copyright Statements . . . . . . . . . . 20 C.6. Changes since -allman-ssp-01 . . . . . . . . . . . . . . . 17
C.7. Changes since -allman-ssp-00 . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . . . . 19
1. Introduction 1. Introduction
DomainKeys Identified Mail (DKIM) defines a mechanism by which email DomainKeys Identified Mail (DKIM) defines a mechanism by which email
messages can be cryptographically signed, permitting a signing domain messages can be cryptographically signed, permitting a signing domain
to claim responsibility for the introduction of a message into the to claim responsibility for the introduction of a message into the
mail stream. Message recipients can verify the signature by querying mail stream. Message recipients can verify the signature by querying
the signer's domain directly to retrieve the appropriate public key, the signer's domain directly to retrieve the appropriate public key,
and thereby confirm that the message was attested to by a party in and thereby confirm that the message was attested to by a party in
possession of the private key for the signing domain. possession of the private key for the signing domain.
However, the legacy of the Internet is such that not all messages However, the legacy of the Internet is such that not all messages
will be signed, and the absence of a signature on a message is not an will be signed, and the absence of a signature on a message is not an
a priori indication of forgery. In fact, during early phases of a priori indication of forgery. In fact, during early phases of
deployment it is very likely that most messages will remain unsigned. deployment it is very likely that most messages will remain unsigned.
However, some domains might decide to sign all of their outgoing However, some domains might decide to sign all of their outgoing
mail, for example, to protect their brand name. It is desirable for mail, for example, to protect their brand names. It is desirable for
such domains to be able to advertise that fact to other hosts. This such domains to be able to advertise that fact to other hosts. This
is the topic of Author Signing Practices (ASP). is the topic of Author Domain Signing Practices (ADSP).
Hosts implementing this specification can inquire what Author Signing Hosts implementing this specification can inquire what Author Signing
Practices a domain advertises. This inquiry is called an Author Practices a domain advertises. This inquiry is called an Author
Signing Practices check. Signing Practices check.
The detailed requirements for Author Signing Practices are given in The basic requirements for ADSP are given in [RFC5016]. This
[RFC5016]. This document refers extensively to [RFC4871] and assumes document refers extensively to [RFC4871] and assumes the reader is
the reader is familiar with it. familiar with it.
Requirements Notation: The key words "MUST", "MUST NOT", "REQUIRED", Requirements Notation: The key words "MUST", "MUST NOT",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"MAY", and "OPTIONAL" in this document are to be interpreted as "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
described in [RFC2119] interpreted as described in [RFC2119]
2. Language and Terminology 2. Language and Terminology
2.1. Terms Imported from DKIM Signatures Specification 2.1. Terms Imported from DKIM Signatures Specification
Some terminology used herein is derived directly from [RFC4871]. In Some terminology used herein is derived directly from [RFC4871]. In
several cases, references in that document to Sender have been several cases, references in that document to Sender have been
changed to Author here, to emphasize the relationship to the Author changed to Author here, to emphasize the relationship to the Author
address(es) in the From: header field described in [RFC2822]. address(es) in the From: header field described in [RFC2822].
Briefly, Briefly,
o A "Signer" is the agent that signs a message, as defined in o A "Signer" is the agent that signs a message, as defined in
section 2.1 of [RFC4871]. section 2.1 of [RFC4871].
o A "Selector" specifies which of the keys published by a signing o A "Local-part" is the part of an address preceding the @
domain is to be queried, as defined in section 3.1 of [RFC4871]. character, as defined in [RFC2822] and used in [RFC4871].
o A "Local-part" is the part of an address preceding the @ sign, as
defined in [RFC2822] and used in [RFC4871].
2.2. Valid Signature 2.2. Valid Signature
A "Valid Signature" is any signature on a message which correctly A "Valid Signature" is any signature on a message which correctly
verifies using the procedure described in section 6.1 of [RFC4871]. verifies using the procedure described in section 6.1 of [RFC4871].
2.3. Author Address 2.3. Author Address
An "Author Address" is an email address in the From header field of a An "Author Address" is an email address in the From header field of a
message [RFC2822]. If the From header field contains multiple message [RFC2822]. If the From header field contains multiple
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2.4. Author Domain 2.4. Author Domain
An "Author Domain" is everything to the right of the "@" in an Author An "Author Domain" is everything to the right of the "@" in an Author
Address (excluding the "@" itself). Address (excluding the "@" itself).
2.5. Alleged Author 2.5. Alleged Author
An "Alleged Author" is an Author Address of a message; it is An "Alleged Author" is an Author Address of a message; it is
"alleged" because it has not yet been verified. "alleged" because it has not yet been verified.
2.6. Author Signing Practices 2.6. Author Domain Signing Practices
"Author Signing Practices" (or just "practices") consist of a "Author Domain Signing Practices" (or just "practices") consist of a
machine-readable record published by the domain of an Alleged Author machine-readable record published by the domain of an Alleged Author
which includes statements about the domain's practices with respect which includes statements about the domain's practices with respect
to mail it sends with its domain in the From: line. to mail it sends with its domain in the From: line.
2.7. Author Signature 2.7. Author Signature
An "Author Signature" is any Valid Signature where the identity of An "Author Signature" is any Valid Signature where the identity of
the user or agent on behalf of which the message is signed (listed in the user or agent on behalf of which the message is signed (listed in
the ""i="" tag or its default value from the ""d="" tag) matches an the "i=" tag or its default value from the "d=" tag) matches an
Author Address in the message. When the identity of the user or Author Address in the message. When the identity of the user or
agent includes a Local-part, the identities match if the Local-parts agent includes a Local-part, the identities match if the Local-parts
match and the domains match. Otherwise, the identities match if the are the same string, and the domains are the same string. Otherwise,
domains match. the identities match if the domains are the same string. Following
[RFC2821], Local-part comparisons are case sensitive, domain
comparisons are case insensitive.
For example, if a message has a Valid Signature, with the DKIM- For example, if a message has a Valid Signature, with the DKIM-
Signature field containing "i=a@domain.example", then domain.example Signature field containing "i=a@domain.example", then domain.example
is asserting that it takes responsibility for the message. If the is asserting that it takes responsibility for the message. If the
message's From: field contains the address "b@domain.example" and an message's From: field contains the address "b@domain.example" and an
ASP query produces a "dkim=all" or "dkim=discardable" result, that ADSP query produces a "dkim=all" or "dkim=discardable" result, that
would mean that the message does not have a valid Author Signature. would mean that the message does not have a valid Author Signature.
Even though the message is signed by the same domain, its failure to Even though the message is signed by the same domain, it fails to
satisfy ASP could be problematic. satisfy ADSP.
3. Operation Overview 3. Operation Overview
Domain owners can publish Author Signing Practices via a query Domain owners can publish ADSP information via a query mechanism such
mechanism such as the Domain Name System; specific details are given as the Domain Name System; specific details are given in Section 4.1.
in Section 4.1.
Hosts can look up the Author Signing Practices of the domain(s) Hosts can look up the ADSP information of the domain(s) specified by
specified by the Author Address(es) as described in Section 4.2.2. the Author Address(es) as described in Section 4.3. If a message has
If a message has multiple Author Addresses the ASP lookups SHOULD be multiple Author Addresses the ADSP lookups SHOULD be performed
performed independently on each address. This standard does not independently on each address. This standard does not address the
address the process a host might use to combine the lookup results. process a host might use to combine the lookup results.
3.1. ASP Usage 3.1. ADSP Applicability
ADSP as defined in this document is bound to DNS. For this reason,
ADSP is applicable only to Author Domains with appropriate DNS
records (see Note below). The handling of other Author Domains is
outside the scope of this document. However, attackers may use such
domain names in a deliberate attempt to sidestep an organization's
ADSP policy statements. It is up to the ADSP verifier implementation
to return an appropriate error result for Author Domains outside the
scope of ADSP.
Note: The results from DNS queries that are intended to validate a
domain name unavoidably approximate the set of Author Domains that
can appear in legitimate email. For example, a DNS A record could
belong to a device that does not even have an email
implementation. It is up to the verifier to decide what degree of
approximation is acceptable.
3.2. ADSP Usage
Depending on the Author Domain(s) and the signatures in a message, a Depending on the Author Domain(s) and the signatures in a message, a
recipient gets varying amounts of useful information from each ASP recipient gets varying amounts of useful information from each ADSP
lookup. lookup.
o If a message has no Valid Signature, the ASP result is directly o If a message has no Valid Signature, the ADSP result is directly
relevant to the message. relevant to the message.
o If a message has a Valid Signature from an Author Domain, ASP o If a message has a Valid Signature from an Author Domain, ADSP
provides no benefit relative to that domain since the message is provides no benefit relative to that domain since the message is
already known to be compliant with any possible ASP for that already known to be compliant with any possible ADSP for that
domain. domain.
o If a message has a Valid Signature from a domain other than an o If a message has a Valid Signature from a domain other than an
Author Domain, the receiver can use both the Signature and the ASP Author Domain, the receiver can use both the Signature and the
result in its evaluation of the message. ADSP result in its evaluation of the message.
3.2. ASP Results 3.3. ADSP Results
An Author Signing Practices lookup for an Author Address produces one An ADSP lookup for an Author Address produces one of four possible
of four possible results: results:
o Messages from this domain might or might not have an author o Messages from this domain might or might not have an author
signature. This is the default if the domain exists in the DNS signature. This is the default if the domain exists in the DNS
but no record is found. but no record is found.
o All messages from this domain are signed. o All messages from this domain are signed.
o All messages from this domain are signed and discardable. o All messages from this domain are signed and discardable.
o The domain does not exist. o The domain is not a valid mail domain.
4. Detailed Description 4. Detailed Description
4.1. DNS Representation 4.1. DNS Representation
Author Signing Practices records are published using the DNS TXT ADSP records are published using the DNS TXT resource record type.
resource record type.
NON-NORMATIVE DISCUSSION [to be removed before publication]: There
has been considerable discussion on the DKIM WG mailing list
regarding the relative advantages of TXT and a new resource record
(RR) type. Read the archive for details.
The RDATA for ASP resource records is textual in format, with The RDATA for ADSP resource records is textual in format, with
specific syntax and semantics relating to their role in describing specific syntax and semantics relating to their role in describing
Author Signing Practices. The "Tag=Value List" syntax described in ADSP. The "Tag=Value List" syntax described in section 3.2 of
section 3.2 of [RFC4871] is used. Records not in compliance with [RFC4871] is used. Records not in compliance with that syntax or the
that syntax or the syntax of individual tags described in Section 4.3 syntax of individual tags described in Section 4.3 MUST be ignored
MUST be ignored (considered equivalent to a NODATA result) for (considered equivalent to a NODATA result) for purposes of ADSP,
purposes of ASP, although they MAY cause the logging of warning although they MAY cause the logging of warning messages via an
messages via an appropriate system logging mechanism. If the RDATA appropriate system logging mechanism. If the RDATA contains multiple
contains multiple character strings, the strings are logically character strings, the strings are logically concatenated with no
concatenated with no delimiters between the strings. delimiters between the strings.
The ASP record for a domain is published at a location in the The ADSP record for a domain is published at a location in the
domain's DNS hierarchy prefixed by _asp._domainkey.; e.g., the ASP domain's DNS hierarchy prefixed by _adsp._domainkey.; e.g., the ADSP
record for example.com would be a TXT record that is published at record for example.com would be a TXT record that is published at
"_asp._domainkey.example.com". A domain MUST NOT publish more than "_adsp._domainkey.example.com". A domain MUST NOT publish more than
one ASP record; the semantics of an ASP lookup that returns multiple one ADSP record; the semantics of an ADSP lookup that returns
ASP records for a single domain are undefined. (Note that multiple ADSP records for a single domain are undefined. (Note that
example.com and mail.example.com are different domains.) example.com and mail.example.com are different domains.)
4.2. Publication of ASP Records 4.2. Publication of ADSP Records
Author Signing Practices are intended to apply to all mail sent from
the domain of an Alleged Author. In order to ensure that ASP applies
to any hosts within that domain (e.g., www.example.com,
ftp.example.com.) the ASP lookup algorithm looks up one level in the
domain tree. For example, mail signed by www.example.com could be
covered by the ASP record for example.com. This avoids the need to
include an ASP record for every name within a given domain.
Normally, a domain expressing Author Signing Practices will want to ADSP is intended to apply to all mail sent using the domain name
do so for both itself and all of its "descendants" (child domains at string of an Alleged Author.
all lower levels). Domains wishing to do so MUST publish ASP records
for the domain itself and any subdomains.
Wildcards within a domain publishing ASP records pose a particular Wildcards within a domain publishing ADSP records pose a particular
problem. This is discussed in more detail in Section 6.3. problem. This is discussed in more detail in Section 6.3.
4.2.1. Record Syntax 4.2.1. Record Syntax
ASP records use the "tag=value" syntax described in section 3.2 of ADSP records use the "tag=value" syntax described in section 3.2 of
[RFC4871]. [RFC4871].
Tags used in ASP records are described below. Unrecognized tags MUST Tags used in ADSP records are described below. Unrecognized tags
be ignored. In the ABNF below, the WSP token is imported from MUST be ignored. In the ABNF below, the FWS token is imported from
[RFC2822]. The ALPHA and DIGIT tokens are imported from [RFC5234]. [RFC4871]. The ALPHA and DIGIT tokens are imported from [RFC5234].
dkim= Outbound signing practices for the domain (plain-text; dkim= Outbound signing practices for the domain (plain-text;
REQUIRED). Possible values are as follows: REQUIRED). Possible values are as follows:
unknown The domain might sign some or all email. unknown The domain might sign some or all email.
all All mail from the domain is signed with an Author Signature. all All mail from the domain is signed with an Author
Signature.
discardable All mail from the domain is signed with an Author discardable All mail from the domain is signed with an Author
Signature. Furthermore, if a message arrives without a valid Signature. Furthermore, if a message arrives without a valid
Author Signature due to modification in transit, submission via Author Signature due to modification in transit, submission via
a path without access to a signing key, or other reason, the a path without access to a signing key, or other reason, the
domain encourages the recipient(s) to discard it. domain encourages the recipient(s) to discard it.
ABNF: ABNF:
adsp-dkim-tag = %x64.6b.69.6d *FWS "=" *FWS
("unknown" / "all" / "discardable")
asp-dkim-tag = %x64.6b.69.6d *WSP "=" 4.3. ADSP Lookup Procedure
*WSP ("unknown" / "all" / "discardable")
t= Flags, represented as a colon-separated list of names (plain-text;
OPTIONAL, default is that no flags are set). Flag values are:
s The signing practices apply only to the named domain, and not
to subdomains.
ABNF:
asp-t-tag = %x74 *WSP "=" *WSP { asp-t-tag-flag
0*( *WSP ":" *WSP asp-t-tag-flag )
asp-t-tag-flag = "s" / hyphenated-word
; for future extension
hyphenated-word = ALPHA [ *(ALPHA / DIGIT / "-")
(ALPHA / DIGIT) ]
Unrecognized flags MUST be ignored.
4.2.2. Author Signing Practices Lookup Procedure
Hosts doing an ASP lookup MUST produce a result that is semantically Hosts doing an ADSP lookup MUST produce a result that is semantically
equivalent to applying the following steps in the order listed below. equivalent to applying the following steps in the order listed below.
In practice, several of these steps can be performed in parallel in In practice, these steps can be performed in parallel in order to
order to improve performance. However, implementations SHOULD avoid improve performance. However, implementations SHOULD avoid doing
doing unnecessary DNS lookups. For the purposes of this section a unnecessary DNS lookups.
"valid ASP record" is one that is both syntactically and semantically
correct; in particular, it matches the ABNF for a "tag-list" and
includes a defined "dkim=" tag.
1. _Fetch Named ASP Record._ The host MUST query DNS for a TXT For the purposes of this section a "valid ADSP record" is one that is
record corresponding to the Author Domain prefixed by both syntactically and semantically correct; in particular, it
"_asp._domainkey." (note the trailing dot). If the result of matches the ABNF for a "tag-list" and includes a defined "dkim=" tag.
this query is a "NOERROR" response with an answer which is a
valid ASP record, use that record; otherwise, continue to the
next step.
2. _Verify Domain Exists._ The host MUST perform a DNS query for a Verify Domain Scope: An ADSP verifier implementation MUST determine
record corresponding to the Author Domain (with no prefix). The whether a given Author Domain is within scope for ADSP. Given the
type of the query can be of any type, since this step is only to background in Section 3.1 the verifier MUST decide which degree of
determine if the domain itself exists in DNS. This query MAY be over-approximation is acceptable. The verifier MUST return an
done in parallel with the query made in step 2. If the result of appropriate error result for Author Domains that are outside the
this query is an "NXDOMAIN" error, the algorithm MUST terminate scope of ADSP.
with an appropriate error.
The host MUST perform a DNS query for a record corresponding to
the Author Domain (with no prefix). The type of the query can be
of any type, since this step is only to determine if the domain
itself exists in DNS. This query MAY be done in parallel with the
query to fetch the Named ADSP Record. If the result of this query
is that the Author domain does not exist in the DNS (often called
an "NXDOMAIN" error), the algorithm MUST terminate with an error
indicating that the domain is out of scope.
NON-NORMATIVE DISCUSSION: Any resource record type could be NON-NORMATIVE DISCUSSION: Any resource record type could be
used for this query since the existence of a resource record used for this query since the existence of a resource record of
of any type will prevent an "NXDOMAIN" error. MX is a any type will prevent an "NXDOMAIN" error. MX is a reasonable
reasonable choice for this purpose is because this record type choice for this purpose because this record type is thought to
is thought to be the most common for likely domains, and will be the most common for domains used in e-mail, and will
therefore result in a result which can be more readily cached therefore produce a result which can be more readily cached
than a negative result. than a negative result.
3. _Try Parent Domain._ The host MUST query DNS for a TXT record for If the domain does exist, the verifier MAY make more extensive
the immediate parent domain, prefixed with "_asp._domainkey." If checks to verify the existence of the domain, such as the ones
the result of this query is anything other than a "NOERROR" described in Section 5 of [RFC2821]. If those checks indicate
response with a valid ASP record, the algorithm terminates with a that the Author domain does not exist for mail, e.g., the domain
result indicating that no ASP record was present. If the ASP "t" has no MX, A, or AAAA record, the verifier SHOULD terminate with
tag exists in the response and any of the flags is "s" an error indicating that the domain is out of scope.
(indicating it does not apply to a subdomain), the algorithm also
terminates without finding an ASP record. Otherwise, use that
record.
If any of the queries involved in the Author Signing Practices Check Fetch Named ADSP Record: The host MUST query DNS for a TXT record
result in a "SERVFAIL" error response, the algorithm terminates corresponding to the Author Domain prefixed by "_adsp._domainkey."
without returning a result; possible actions include queuing the (note the trailing dot).
message or returning an SMTP error indicating a temporary failure.
5. IANA Considerations If the result of this query is a "NOERROR" response with an answer
which is a valid ADSP record, use that record, and the algorithm
terminates.
ASP introduces some new namespaces that have been registered with If a query results in a "SERVFAIL" error response, the algorithm
IANA. In all cases, new values are assigned only for values that terminates without returning a result; possible actions include
have been documented in a published RFC that has IETF Consensus queuing the message or returning an SMTP error indicating a
[RFC2434]. temporary failure.
INFORMATIVE NOTE [ to be removed before publication ]: RFC 4871 5. IANA Considerations
defines a selector as a sub-domain, importing the term from RFC 2822.
A sub-domain starts with a letter or digit, hence names such as _asp
that start with an underscore cannot collide with valid selectors.
5.1. ASP Specification Tag Registry ADSP adds the following namespaces to the IANA registry. In all
cases, new values are assigned only for values that have been
documented in a published RFC that has IETF Consensus [RFC2434].
An ASP record provides for a list of specification tags. IANA has 5.1. ADSP Specification Tag Registry
established the ASP Specification Tag Registry for specification tags
that can be used in ASP fields.
The initial entries in the registry comprise: An ADSP record provides for a list of specification tags. IANA has
established the ADSP Specification Tag Registry for specification
tags that can be used in ADSP fields.
The initial entry in the registry is:
+------+-----------------+ +------+-----------------+
| TYPE | REFERENCE | | TYPE | REFERENCE |
+------+-----------------+ +------+-----------------+
| dkim | (this document) | | dkim | (this document) |
| t | (this document) |
+------+-----------------+ +------+-----------------+
ADSP Specification Tag Registry Initial Values
ASP Specification Tag Registry Initial Values 5.2. ADSP Outbound Signing Practices Registry
5.2. ASP Outbound Signing Practices Registry
The "dkim=" tag spec, defined in Section 4.2.1, provides for a value The "dkim=" tag spec, defined in Section 4.2.1, provides for a value
specifying Outbound Signing Practices. IANA has established the ASP specifying Outbound Signing Practices. IANA has established the ADSP
Outbound Signing Practices Registry for Outbound Signing Practices. Outbound Signing Practices Registry for Outbound Signing Practices.
The initial entries in the registry comprise: The initial entries in the registry comprise:
+-------------+-----------------+ +-------------+-----------------+
| TYPE | REFERENCE | | TYPE | REFERENCE |
+-------------+-----------------+ +-------------+-----------------+
| unknown | (this document) | | unknown | (this document) |
| all | (this document) | | all | (this document) |
| discardable | (this document) | | discardable | (this document) |
+-------------+-----------------+ +-------------+-----------------+
ADSP Outbound Signing Practices Registry Initial Values
ASP Outbound Signing Practices Registry Initial Values
5.3. ASP Flags Registry
The "t=" tag spec, defined in Section 4.2.1, provides for a value
specifying Flags. IANA has established the ASP Flags Registry for
ASP Flags.
The initial entries in the registry comprise:
+------+-----------------+
| TYPE | REFERENCE |
+------+-----------------+
| s | (this document) |
+------+-----------------+
ASP Flags Registry Initial Values
6. Security Considerations 6. Security Considerations
Security considerations in the Author Signing Practices are mostly Security considerations in the ADSP are mostly related to attempts on
related to attempts on the part of malicious senders to represent the part of malicious senders to represent themselves as authors for
themselves as authors for whom they are not authorized to send mail, whom they are not authorized to send mail, often in an attempt to
often in an attempt to defraud either the recipient or an Alleged defraud either the recipient or an Alleged Author.
Author.
Additional security considerations regarding Author Signing Practices Additional security considerations regarding Author Domain Signing
are found in the DKIM threat analysis [RFC4686]. Practices are found in the DKIM threat analysis [RFC4686].
6.1. ASP Threat Model 6.1. ADSP Threat Model
Email recipients often have a core set of content authors that they Email recipients often have a core set of content authors that they
already trust. Common examples include financial institutions with already trust. Common examples include financial institutions with
which they have an existing relationship and Internet web transaction which they have an existing relationship and Internet web transaction
sites with which they conduct business. sites with which they conduct business.
Email abuse often seeks to exploit the name-recognition that Email abuse often seeks to exploit a legitimate email author's name-
recipients will have, for a legitimate email author, by using its recognition among recipients, by using the author's domain name in
domain name in the From: header field. Especially since many popular the From: header field. Especially since many popular MUAs do not
MUAs do not display the author's email address, there is no empirical display the author's email address, there is no empirical evidence of
evidence of the extent that this particular unauthorized use of a the extent that this particular unauthorized use of a domain name
domain name contributes to recipient deception or that eliminating it contributes to recipient deception or that eliminating it will have
will have significant effect. significant effect.
However, closing this exploit could facilitate some types of However, closing this exploit could facilitate some types of
optimized processing by receive-side message filtering engines, since optimized processing by receive-side message filtering engines, since
it could permit them to maintain higher-confidence assertions about it could permit them to maintain higher-confidence assertions about
From: header field uses of a domain, when the occurrence is From: header field uses of a domain, when the occurrence is
authorized. authorized.
Unauthorized uses of domain names occur elsewhere in messages, as do Unauthorized uses of domain names occur elsewhere in messages, as do
unauthorized uses of organizations' names. These attacks are outside unauthorized uses of organizations' names. These attacks are outside
the scope of this specification. the scope of this specification.
ASP does not provide any benefit--nor, indeed, have any effect at ADSP does not provide any benefit--nor, indeed, have any effect at
all--unless an external system acts upon the verdict, either by all--unless an external system acts upon the verdict, either by
treating the message differently during the delivery process or by treating the message differently during the delivery process or by
showing some indicator to the end recipient. Such a system is out of showing some indicator to the end recipient. Such a system is out of
scope for this specification. scope for this specification.
ASP Checkers perform up to three DNS lookups per Alleged Author ADSP checkers may perform multiple DNS lookups per Alleged Author
Domain. Since these lookups are driven by domain names in email Domain. Since these lookups are driven by domain names in email
message headers of possibly fraudulent email, legitimate ASP Checkers message headers of possibly fraudulent email, legitimate ADSP
can become participants in traffic multiplication attacks. checkers can become participants in traffic multiplication attacks.
6.2. DNS Attacks 6.2. DNS Attacks
An attacker might attack the DNS infrastructure in an attempt to An attacker might attack the DNS infrastructure in an attempt to
impersonate ASP records, in an attempt to influence a receiver's impersonate ADSP records to influence a receiver's decision on how it
decision on how it will handle mail. However, such an attacker is will handle mail. However, such an attacker is more likely to attack
more likely to attack at a higher level, e.g., redirecting A or MX at a higher level, e.g., redirecting A or MX record lookups in order
record lookups in order to capture traffic that was legitimately to capture traffic that was legitimately intended for the target
intended for the target domain. These DNS security issues are domain. These DNS security issues are addressed by DNSSEC [RFC4033].
addressed by DNSSEC [RFC4033].
Because ASP operates within the framework of the legacy e-mail Because ADSP operates within the framework of the legacy e-mail
system, the default result in the absence of an ASP record is that system, the default result in the absence of an ADSP record is that
the domain does not sign all of its messages. It is therefore the domain does not sign all of its messages. It is therefore
important that the ASP clients distinguish a DNS failure such as important that the ADSP clients distinguish a DNS failure such as
"SERVFAIL" from other DNS errors so that appropriate actions can be "SERVFAIL" from other DNS errors so that appropriate actions can be
taken. taken.
6.3. DNS Wildcards 6.3. DNS Wildcards
Wildcards within a domain publishing ASP records, including but not If a domain contains wildcards, then any name that matches the
limited to wildcard MX records, pose a particular problem. While wildcard according to [RFC4592] is potentially a valid mail domain
referencing the immediate parent domain allows the discovery of an eligible for ADSP. It is possible to add a wildcard TXT record
ASP record corresponding to an unintended immediate-child subdomain, alongside a wildcard MX that will provide suitable ADSP records for
wildcard records apply at multiple levels. For example, if there is any domain chosen by an attacker, since if the wildcard synthesizes
a wildcard MX record for "example.com", the domain chosen-name.example.com IN MX, it will then also synthesize
"foo.bar.example.com" can receive mail through the named mail _adsp._domainkey.chosen-name.example.com IN TXT. However multiple
exchanger. Conversely, the existence of the record makes it wildcard TXT records produce an undefined ADSP result, which means
impossible to tell whether "foo.bar.example.com" is a legitimate name you cannot also publish both ADSP records and records for any other
since a query for that name will not return an "NXDOMAIN" error. For TXT-using protocol (such as SPF) for a wildcard domain.
that reason, ASP coverage for subdomains of domains containing a
wildcard record is incomplete.
NON-NORMATIVE NOTE: Complete ASP coverage of domains containing (or
where any parent contains) wildcards generally cannot be provided by
standard DNS servers.
7. References 7. References
7.1. References - Normative 7.1. References - Normative
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an [RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434, IANA Considerations Section in RFCs", BCP 26, RFC 2434,
skipping to change at page 13, line 37 skipping to change at page 11, line 40
[RFC4871] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton, [RFC4871] Allman, E., Callas, J., Delany, M., Libbey, M., Fenton,
J., and M. Thomas, "DomainKeys Identified Mail (DKIM) J., and M. Thomas, "DomainKeys Identified Mail (DKIM)
Signatures", RFC 4871, May 2007. Signatures", RFC 4871, May 2007.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008. Specifications: ABNF", STD 68, RFC 5234, January 2008.
7.2. References - Informative 7.2. References - Informative
[RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821,
April 2001.
[RFC5016] Thomas, M., "Requirements for a DomainKeys Identified Mail [RFC5016] Thomas, M., "Requirements for a DomainKeys Identified Mail
(DKIM) Signing Practices Protocol", RFC 5016, (DKIM) Signing Practices Protocol", RFC 5016,
October 2007. October 2007.
Appendix A. Usage Examples Appendix A. Usage Examples
These examples are intended to illustrate typical uses of ASP. They These examples are intended to illustrate typical uses of ADSP. They
are not intended to be exhaustive, nor to apply to every domain's or are not intended to be exhaustive, nor to apply to every domain's or
mail system's individual situation. mail system's individual situation.
Domain managers are advised to consider the ways that mail processing Domain managers are advised to consider the ways that mail processing
can modify messages in ways that will invalidate an existing DKIM can modify messages in ways that will invalidate an existing DKIM
signature, such as mailing lists, courtesy forwarders, and other signature, such as mailing lists, courtesy forwarders, and other
paths that could add or modify headers, or modify the message body. paths that could add or modify headers, or modify the message body.
In that case, if the modifications invalidate the DKIM signature, In that case, if the modifications invalidate the DKIM signature,
recipient hosts will consider the mail not to have an Author recipient hosts will consider the mail not to have an Author
Signature, even though the signature was present when the mail was Signature, even though the signature was present when the mail was
originally sent. originally sent.
A.1. Single Location Domains A.1. Single Location Domains
A common mail system configuration handles all of a domain's users' A common mail system configuration handles all of a domain's users'
incoming and outgoing mail through a single MTA or group of MTAs. In incoming and outgoing mail through a single MTA or group of MTAs. In
that case, the MTA(s) can be configured to sign outgoing mail with an that case, the MTA(s) can be configured to sign outgoing mail with an
Author Signature. Author Signature.
In this situation it might be appropriate to publish an ASP record In this situation it might be appropriate to publish an ADSP record
for the domain containing "all", depending on whether the users also for the domain containing "all", depending on whether the users also
send mail through other paths that do not apply an Author Signature. send mail through other paths that do not apply an Author Signature.
Such paths could include MTAs at hotels or hotspot networks used by Such paths could include MTAs at hotels or hotspot networks used by
travelling users, or web sites that provide "mail an article" travelling users, or web sites that provide "mail an article"
features. features.
A.2. Bulk Mailing Domains A.2. Bulk Mailing Domains
Another common configuration uses a domain solely for bulk or Another common configuration uses a domain solely for bulk or
broadcast mail, with no individual human users, again typically broadcast mail, with no individual human users, again typically
skipping to change at page 14, line 46 skipping to change at page 13, line 5
bulk mail. In that case, the mailing provider needs access to a bulk mail. In that case, the mailing provider needs access to a
suitable signing key in order to apply an Author Signature. One suitable signing key in order to apply an Author Signature. One
possible route would be for the domain owner to generate the key and possible route would be for the domain owner to generate the key and
give it to the mailing provider. Another would be for the domain to give it to the mailing provider. Another would be for the domain to
delegate a subdomain to the mailing provider, for example, delegate a subdomain to the mailing provider, for example,
bigbank.example might delegate email.bigbank.example to such a bigbank.example might delegate email.bigbank.example to such a
provider. In that case, the provider can generate the keys and DKIM provider. In that case, the provider can generate the keys and DKIM
DNS records itself and use the subdomain in the Author address in the DNS records itself and use the subdomain in the Author address in the
mail. mail.
Regardless of the DNS and key management strategy chosen, whoever
maintains the DKIM records for the domain could also install an ADSP
record containing "all".
A.3. Bulk Mailing Domains with Discardable Mail A.3. Bulk Mailing Domains with Discardable Mail
In some cases, a domain might sign all its outgoing mail with an In some cases, a domain might sign all of its outgoing mail with an
Author Signature, but prefer that recipient systems discard mail Author Signature, but prefer that recipient systems discard mail
without a valid Author Signature to avoid confusion from mail sent without a valid Author Signature to avoid confusion from mail sent
from sources that do not apply an Author Signature. (This latter from sources that do not apply an Author Signature. (This latter
kind of mail is sometimes loosely called "forgeries".) In that case, kind of mail is sometimes loosely called "forgeries".) In that case,
it might be appropriate to publish an ASP record containing it might be appropriate to publish an ADSP record containing
"discardable". Note that a domain SHOULD NOT publish a "discardable" "discardable". Note that a domain SHOULD NOT publish a "discardable"
record if it wishes to maximize the likelihood that mail from the record if it wishes to maximize the likelihood that mail from the
domain is delivered, since it could cause some fraction of the mail domain is delivered, since it could cause some fraction of the mail
the domain sends to be discarded. the domain sends to be discarded.
As a special case, if a domain sends no mail at all, it can safely
publish a "discardable" ASP record, since any mail with an author
address in the domain is a forgery.
A.4. Third Party Senders A.4. Third Party Senders
Another common use case is for a third party to enter into an Another common use case is for a third party to enter into an
agreement whereby that third party will send bulk or other mail on agreement whereby that third party will send bulk or other mail on
behalf of a designated author domain, using that domain in the behalf of a designated author or author domain, using that domain in
RFC2822 From: or other headers. Due to the many and varied the RFC2822 From: or other headers. Due to the many and varied
complexities of such agreements, third party signing is not addressed complexities of such agreements, third party signing is not addressed
in this specification. in this specification.
A.5. Non-email Domains
If a domain sends no mail at all, it can safely publish a
"discardable" ADSP record, since any mail with an author address in
the domain is a forgery.
Appendix B. Acknowledgements Appendix B. Acknowledgements
This document greatly benefited from comments by Steve Atkins, Jon This document greatly benefited from comments by Steve Atkins, Jon
Callas, Dave Crocker, JD Falk, Arvel Hathcock, Ellen Siegel, Michael Callas, Dave Crocker, JD Falk, Arvel Hathcock, Ellen Siegel, Michael
Thomas, and Wietse Venema. Thomas, and Wietse Venema.
Appendix C. Change Log Appendix C. Change Log
*NOTE TO RFC EDITOR: This section may be removed upon publication of *NOTE TO RFC EDITOR: This section may be removed upon publication of
this document as an RFC.* this document as an RFC.*
C.1. Changes since -ietf-dkim-02 C.1. Changes since -ietf-dkim-03
o Merge in more text from ASP draft. o Name change for title and filename, to be ADSP
o String changes throughout, to author Domain signing practices and
to aDsp.
o Added some keywords.
o Clarified comparison of local part and domain in Author Address.
o Streamlined the Abstract.
o Revised text of last bullet in Results list.
o Removed definitions not used in the document.
o Removed all specification details pertaining to sub-domains.
o Moved Lookup Procedure up one document level.
o Revised domain validity specification. Part in ADSP Usage in
Operations section, and part as it as first step in Lookup.
o Fixed xml for figures, including labeling ABNF with new xml2rfc
construct.
o Revised wildcard text.
o Removed 't' tag.
o Removed ADSP Flags Registry section.
o Changed ABNF use of whitespace from WSP back to FWS, for
consistency with dkim-base.
C.2. Changes since -ietf-dkim-02
o Merge in more text from ADSP draft.
o Phrase actions as host's rather than checker. o Phrase actions as host's rather than checker.
o Explanatory description of i= matching. o Explanatory description of i= matching.
o Lookup procedure consistently refers to one ASP record per lookup. o Lookup procedure consistently refers to one ADSP record per
lookup.
o Update security section w/ language from W. Venema o Update security section w/ language from W. Venema
o Simplify imports of terms from other RFCs, add Local-part, 4234 -> o Simplify imports of terms from other RFCs, add Local-part, 4234 ->
5234. 5234.
o Add usage example appendix. o Add usage example appendix.
o Add IANA considerations. o Add IANA considerations.
o Update authors list o Update authors list
C.2. Changes since -ietf-dkim-ssp-01 C.3. Changes since -ietf-dkim-ssp-01
o Reworded introduction for clarity. o Reworded introduction for clarity.
o Various definition clarifications. o Various definition clarifications.
o Changed names of practices to unknown, all, and discardable. o Changed names of practices to unknown, all, and discardable.
o Removed normative language mandating use of SSP in particular o Removed normative language mandating use of SSP in particular
situations (issue 1538). situations (issue 1538).
skipping to change at page 17, line 10 skipping to change at page 16, line 15
o Introduced the concepts of "SSP Checker" and "Evaluator". o Introduced the concepts of "SSP Checker" and "Evaluator".
o Multiple author case now handled my separate invocations of SSP o Multiple author case now handled my separate invocations of SSP
checker by Evaluator (issue 1525). checker by Evaluator (issue 1525).
o Removed check to avoid querying top-level domains. o Removed check to avoid querying top-level domains.
o Changed ABNF use of whitespace from [FWS] to *WSP (partially o Changed ABNF use of whitespace from [FWS] to *WSP (partially
addresses issue 1543). addresses issue 1543).
C.3. Changes since -ietf-dkim-ssp-00 C.4. Changes since -ietf-dkim-ssp-00
o Clarified Operation Overview and eliminated use of Legitimate as o Clarified Operation Overview and eliminated use of Legitimate as
the counterpart of Suspicious since the words have different the counterpart of Suspicious since the words have different
meanings. meanings.
o Improved discussion (courtesy of Arvel Hathcock) of the use of TXT o Improved discussion (courtesy of Arvel Hathcock) of the use of TXT
records in DNS vs. a new RR type. records in DNS vs. a new RR type.
o Clarified publication rules for multilevel names. o Clarified publication rules for multilevel names.
skipping to change at page 17, line 39 skipping to change at page 16, line 44
o Added "handling" tag to express alleged sending domain's o Added "handling" tag to express alleged sending domain's
preference about handling of Suspicious messages. preference about handling of Suspicious messages.
o Clarified handling of SERVFAIL error in SSP check. o Clarified handling of SERVFAIL error in SSP check.
o Replaced "entity" with "domain", since with the removal of user- o Replaced "entity" with "domain", since with the removal of user-
granularity SSP, the only entities having sender signing policies granularity SSP, the only entities having sender signing policies
are domains. are domains.
C.4. Changes since -allman-ssp-02 C.5. Changes since -allman-ssp-02
o Removed user-granularity SSP and u= tag. o Removed user-granularity SSP and u= tag.
o Replaced DKIMP resource record with a TXT record. o Replaced DKIMP resource record with a TXT record.
o Changed name of the primary tag from "p" to "dkim". o Changed name of the primary tag from "p" to "dkim".
o Replaced lookup algorithm with one which traverses upward at most o Replaced lookup algorithm with one which traverses upward at most
one level. one level.
o Added description of records to be published, and effect of o Added description of records to be published, and effect of
wildcard records within the domain, on SSP. wildcard records within the domain, on SSP.
C.5. Changes since -allman-ssp-01 C.6. Changes since -allman-ssp-01
o Changed term "Sender Signing Policy" to "Sender Signing o Changed term "Sender Signing Policy" to "Sender Signing
Practices". Practices".
o Changed query methodology to use a separate DNS resource record o Changed query methodology to use a separate DNS resource record
type, DKIMP. type, DKIMP.
o Changed tag values from SPF-like symbols to words. o Changed tag values from SPF-like symbols to words.
o User level policies now default to that of the domain if not o User level policies now default to that of the domain if not
specified. specified.
o Removed the "Compliance" section since we're still not clear on o Removed the "Compliance" section since we're still not clear on
what goes here. what goes here.
o Changed the "parent domain" policy to only search up one level o Changed the "parent domain" policy to only search up one level
(assumes that subdomains will publish SSP records if appropriate). (assumes that subdomains will publish SSP records if appropriate).
o Added detailed description of SSP check procedure. o Added detailed description of SSP check procedure.
C.6. Changes since -allman-ssp-00 C.7. Changes since -allman-ssp-00
From a "diff" perspective, the changes are extensive. Semantically, From a "diff" perspective, the changes are extensive. Semantically,
the changes are: the changes are:
o Added section on "Third-Party Signatures and Mailing Lists" o Added section on "Third-Party Signatures and Mailing Lists"
o Added "Compliance" (transferred from -base document). I'm not o Added "Compliance" (transferred from -base document). I'm not
clear on what needs to be done here. clear on what needs to be done here.
o Extensive restructuring. o Extensive restructuring.
skipping to change at page 20, line 44 skipping to change at line 871
attempt made to obtain a general license or permission for the use of attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr. http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at this standard. Please address the information to the IETF at
ietf-ipr@ietf.org. ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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