--- 1/draft-ietf-dkim-ssp-05.txt 2008-09-20 00:12:15.000000000 +0200 +++ 2/draft-ietf-dkim-ssp-06.txt 2008-09-20 00:12:15.000000000 +0200 @@ -1,23 +1,23 @@ Network Working Group E. Allman Internet-Draft Sendmail, Inc. Intended status: Standards Track J. Fenton -Expires: February 6, 2009 Cisco Systems, Inc. +Expires: March 23, 2009 Cisco Systems, Inc. M. Delany Yahoo! Inc. J. Levine Taughannock Networks - August 5, 2008 + September 19, 2008 DKIM Author Domain Signing Practices (ADSP) - draft-ietf-dkim-ssp-05 + draft-ietf-dkim-ssp-06 Status of this Memo By submitting this Internet-Draft, each author represents that any 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 aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that @@ -28,80 +28,81 @@ and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. - This Internet-Draft will expire on February 6, 2009. + This Internet-Draft will expire on March 23, 2009. Abstract DomainKeys Identified Mail (DKIM) defines a domain-level authentication framework for email to permit verification of the source and contents of messages. This document specifies an adjunct mechanism to aid in assessing messages that do not contain a DKIM signature for the domain used in the author's address. It defines a record that can advertise whether a domain signs its outgoing mail, and how other hosts can access that record. Table of Contents - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 2. Language and Terminology . . . . . . . . . . . . . . . . . . . 3 - 2.1. Terms Imported from DKIM Signatures Specification . . . . 3 - 2.2. Valid Signature . . . . . . . . . . . . . . . . . . . . . 4 - 2.3. Author Address . . . . . . . . . . . . . . . . . . . . . . 4 - 2.4. Author Domain . . . . . . . . . . . . . . . . . . . . . . 4 - 2.5. Alleged Author . . . . . . . . . . . . . . . . . . . . . . 4 - 2.6. Author Domain Signing Practices . . . . . . . . . . . . . 4 - 2.7. Author Signature . . . . . . . . . . . . . . . . . . . . . 4 - 3. Operation Overview . . . . . . . . . . . . . . . . . . . . . . 5 - 3.1. ADSP Applicability . . . . . . . . . . . . . . . . . . . . 5 - 3.2. ADSP Usage . . . . . . . . . . . . . . . . . . . . . . . . 5 - 3.3. ADSP Results . . . . . . . . . . . . . . . . . . . . . . . 6 - 4. Detailed Description . . . . . . . . . . . . . . . . . . . . . 6 - 4.1. DNS Representation . . . . . . . . . . . . . . . . . . . . 6 - 4.2. Publication of ADSP Records . . . . . . . . . . . . . . . 7 - 4.3. ADSP Lookup Procedure . . . . . . . . . . . . . . . . . . 7 - 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 - 5.1. ADSP Specification Tag Registry . . . . . . . . . . . . . 9 - 5.2. ADSP Outbound Signing Practices Registry . . . . . . . . . 9 - 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 - 6.1. ADSP Threat Model . . . . . . . . . . . . . . . . . . . . 10 - 6.2. DNS Attacks . . . . . . . . . . . . . . . . . . . . . . . 10 - 6.3. DNS Wildcards . . . . . . . . . . . . . . . . . . . . . . 11 - 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 7.1. References - Normative . . . . . . . . . . . . . . . . . . 11 - 7.2. References - Informative . . . . . . . . . . . . . . . . . 12 - Appendix A. Usage Examples . . . . . . . . . . . . . . . . . . . 12 - A.1. Single Location Domains . . . . . . . . . . . . . . . . . 12 - A.2. Bulk Mailing Domains . . . . . . . . . . . . . . . . . . . 13 - A.3. Bulk Mailing Domains with Discardable Mail . . . . . . . . 13 - A.4. Third Party Senders . . . . . . . . . . . . . . . . . . . 13 - A.5. Domains with Independent Users and Liberal Use Policies . 14 - A.6. Non-email Domains . . . . . . . . . . . . . . . . . . . . 14 - Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 14 - Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 14 - C.1. Changes since -ietf-dkim-04 . . . . . . . . . . . . . . . 14 - C.2. Changes since -ietf-dkim-03 . . . . . . . . . . . . . . . 14 - C.3. Changes since -ietf-dkim-02 . . . . . . . . . . . . . . . 15 - C.4. Changes since -ietf-dkim-ssp-01 . . . . . . . . . . . . . 16 - C.5. Changes since -ietf-dkim-ssp-00 . . . . . . . . . . . . . 17 - C.6. Changes since -allman-ssp-02 . . . . . . . . . . . . . . . 17 - C.7. Changes since -allman-ssp-01 . . . . . . . . . . . . . . . 18 - C.8. Changes since -allman-ssp-00 . . . . . . . . . . . . . . . 18 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 - Intellectual Property and Copyright Statements . . . . . . . . . . 20 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 + 2. Language and Terminology . . . . . . . . . . . . . . . . . . . 4 + 2.1. Terms Imported from DKIM Signatures Specification . . . . 4 + 2.2. Valid Signature . . . . . . . . . . . . . . . . . . . . . 5 + 2.3. Author Address . . . . . . . . . . . . . . . . . . . . . . 5 + 2.4. Author Domain . . . . . . . . . . . . . . . . . . . . . . 5 + 2.5. Alleged Author . . . . . . . . . . . . . . . . . . . . . . 5 + 2.6. Author Domain Signing Practices . . . . . . . . . . . . . 5 + 2.7. Author Signature . . . . . . . . . . . . . . . . . . . . . 5 + 3. Operation Overview . . . . . . . . . . . . . . . . . . . . . . 6 + 3.1. ADSP Applicability . . . . . . . . . . . . . . . . . . . . 6 + 3.2. ADSP Usage . . . . . . . . . . . . . . . . . . . . . . . . 6 + 3.3. ADSP Results . . . . . . . . . . . . . . . . . . . . . . . 7 + 4. Detailed Description . . . . . . . . . . . . . . . . . . . . . 7 + 4.1. DNS Representation . . . . . . . . . . . . . . . . . . . . 7 + 4.2. Publication of ADSP Records . . . . . . . . . . . . . . . 8 + 4.3. ADSP Lookup Procedure . . . . . . . . . . . . . . . . . . 8 + 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 + 5.1. ADSP Specification Tag Registry . . . . . . . . . . . . . 10 + 5.2. ADSP Outbound Signing Practices Registry . . . . . . . . . 10 + 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 + 6.1. ADSP Threat Model . . . . . . . . . . . . . . . . . . . . 11 + 6.2. DNS Attacks . . . . . . . . . . . . . . . . . . . . . . . 11 + 6.3. DNS Wildcards . . . . . . . . . . . . . . . . . . . . . . 12 + 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 + 7.1. References - Normative . . . . . . . . . . . . . . . . . . 12 + 7.2. References - Informative . . . . . . . . . . . . . . . . . 13 + Appendix A. Usage Examples . . . . . . . . . . . . . . . . . . . 13 + A.1. Single Location Domains . . . . . . . . . . . . . . . . . 13 + A.2. Bulk Mailing Domains . . . . . . . . . . . . . . . . . . . 14 + A.3. Bulk Mailing Domains with Discardable Mail . . . . . . . . 14 + A.4. Third Party Senders . . . . . . . . . . . . . . . . . . . 14 + A.5. Domains with Independent Users and Liberal Use Policies . 15 + A.6. Non-email Domains . . . . . . . . . . . . . . . . . . . . 15 + Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 15 + Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 15 + C.1. Changes since -ietf-dkim-05 . . . . . . . . . . . . . . . 15 + C.2. Changes since -ietf-dkim-04 . . . . . . . . . . . . . . . 15 + C.3. Changes since -ietf-dkim-03 . . . . . . . . . . . . . . . 16 + C.4. Changes since -ietf-dkim-02 . . . . . . . . . . . . . . . 16 + C.5. Changes since -ietf-dkim-ssp-01 . . . . . . . . . . . . . 17 + C.6. Changes since -ietf-dkim-ssp-00 . . . . . . . . . . . . . 18 + C.7. Changes since -allman-ssp-02 . . . . . . . . . . . . . . . 19 + C.8. Changes since -allman-ssp-01 . . . . . . . . . . . . . . . 19 + C.9. Changes since -allman-ssp-00 . . . . . . . . . . . . . . . 19 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 + Intellectual Property and Copyright Statements . . . . . . . . . . 21 1. Introduction DomainKeys Identified Mail (DKIM) defines a mechanism by which email messages can be cryptographically signed, permitting a signing domain to claim responsibility for the introduction of a message into the mail stream. Message recipients can verify the signature by querying the signer's domain directly to retrieve the appropriate public key, and thereby confirm that the message was attested to by a party in possession of the private key for the signing domain. @@ -194,21 +195,21 @@ satisfy ADSP. 3. Operation Overview Domain owners can publish ADSP information via a query mechanism such as the Domain Name System; specific details are given in Section 4.1. Hosts can look up the ADSP information of the domain(s) specified by the Author Address(es) as described in Section 4.3. If a message has multiple Author Addresses the ADSP lookups SHOULD be performed - independently on each address. This standard does not address the + independently on each address. This document does not address the process a host might use to combine the lookup results. 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 checker implementation @@ -246,21 +247,21 @@ results: o Messages from this domain might or might not have an author signature. This is the default if the domain exists in the DNS but no record is found. o All messages from this domain are signed. o All messages from this domain are signed and discardable. - o The domain is not a valid mail domain. + o This domain is out of scope. 4. Detailed Description 4.1. DNS Representation ADSP records are published using the DNS TXT resource record type. The RDATA for ADSP resource records is textual in format, with specific syntax and semantics relating to their role in describing ADSP. The "Tag=Value List" syntax described in section 3.2 of @@ -324,71 +325,73 @@ 4.3. ADSP Lookup Procedure Hosts doing an ADSP lookup MUST produce a result that is semantically equivalent to applying the following steps in the order listed below. In practice, these steps can be performed in parallel in order to improve performance. However, implementations SHOULD avoid doing unnecessary DNS lookups. For the purposes of this section a "valid ADSP record" is one that is both syntactically and semantically correct; in particular, it - matches the ABNF for a "tag-list" and includes a valid "dkim" tag. + matches the ABNF for a "tag-list" and starts with a valid "dkim" tag. Check Domain Scope: An ADSP checker implementation MUST determine whether a given Author Domain is within scope for ADSP. Given the background in Section 3.1 the checker MUST decide which degree of approximation is acceptable. The checker MUST return an appropriate error result for Author Domains that are outside the scope of ADSP. 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 + 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. + an "NXDOMAIN" error, rcode=3 in [RFC1035]), the algorithm MUST + terminate with an error indicating that the domain is out of + scope. NON-NORMATIVE DISCUSSION: Any resource record type could be used for this query since the existence of a resource record of any type will prevent an "NXDOMAIN" error. MX is a reasonable choice for this purpose because this record type is thought to be the most common for domains used in e-mail, and will therefore produce a result which can be more readily cached than a negative result. If the domain does exist, the checker MAY make more extensive checks to verify the existence of the domain, such as the ones described in Section 5 of [RFC2821]. If those checks indicate that the Author domain does not exist for mail, e.g., the domain has no MX, A, or AAAA record, the checker SHOULD terminate with an error indicating that the domain is out of scope. Fetch Named ADSP Record: The host MUST query DNS for a TXT record corresponding to the Author Domain prefixed by "_adsp._domainkey." (note the trailing dot). - 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. + If the result of this query is a "NOERROR" response (rcode=0 in + [RFC1035]) with an answer which is a valid ADSP record, use that + record, and the algorithm terminates. - If a query results in a "SERVFAIL" error response, the algorithm - terminates without returning a result; possible actions include - queuing the message or returning an SMTP error indicating a - temporary failure. + If a query results in a "SERVFAIL" error response (rcode=2 in + [RFC1035]), the algorithm terminates without returning a result; + possible actions include queuing the message or returning an SMTP + error indicating a temporary failure. 5. IANA Considerations 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 [RFC5226]. + documented in a published RFC after IETF Review as specified in + [RFC5226]. 5.1. ADSP Specification Tag Registry 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 | @@ -491,20 +494,23 @@ the "_adsp._domainkey." prefix on ADSP records does not allow publication of wildcard records that cover ADSP records without also covering non-ADSP records, nor of wildcard records that cover non- ADSP records without also covering ADSP records. Hence a domain MUST NOT publish wildcard ADSP records. 7. References 7.1. References - Normative + [RFC1035] Mockapetris, P., "Domain names - implementation and + specification", STD 13, RFC 1035, November 1987. + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April 2001. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005. @@ -633,37 +639,44 @@ This document greatly benefited from comments by Steve Atkins, Jon Callas, Dave Crocker, JD Falk, Arvel Hathcock, Ellen Siegel, Michael Thomas, and Wietse Venema. Appendix C. Change Log *NOTE TO RFC EDITOR: This section may be removed upon publication of this document as an RFC.* -C.1. Changes since -ietf-dkim-04 +C.1. Changes since -ietf-dkim-05 + + Minor editorial nits: define NOERROR, SERVFAIL, NXDOMAIN as rfc1035 + rcodes, change some punctuation, IANA section change IETF Consensus + to the new IETF Review. + +C.2. Changes since -ietf-dkim-04 o Require dkim at the front of each record. o Disparage wildcard records. o Changed ABNF use of whitespace from FWS back to WSP, dkim-base is wrong. o RFC 2434 -> 5226, make ref to 4686 informational since it's not standards track. o Improve examples with material from Ellen. -C.2. Changes since -ietf-dkim-03 +C.3. Changes since -ietf-dkim-03 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. @@ -682,21 +695,21 @@ 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.3. Changes since -ietf-dkim-02 +C.4. Changes since -ietf-dkim-02 o Merge in more text from ADSP draft. o Phrase actions as host's rather than checker. o Explanatory description of i= matching. o Lookup procedure consistently refers to one ADSP record per lookup. @@ -704,21 +717,21 @@ o Simplify imports of terms from other RFCs, add Local-part, 4234 -> 5234. o Add usage example appendix. o Add IANA considerations. o Update authors list -C.4. Changes since -ietf-dkim-ssp-01 +C.5. Changes since -ietf-dkim-ssp-01 o Reworded introduction for clarity. o Various definition clarifications. o Changed names of practices to unknown, all, and discardable. o Removed normative language mandating use of SSP in particular situations (issue 1538). @@ -752,21 +765,21 @@ o Introduced the concepts of "SSP Checker" and "Evaluator". o Multiple author case now handled my separate invocations of SSP checker by Evaluator (issue 1525). o Removed check to avoid querying top-level domains. o Changed ABNF use of whitespace from [FWS] to *WSP (partially addresses issue 1543). -C.5. Changes since -ietf-dkim-ssp-00 +C.6. Changes since -ietf-dkim-ssp-00 o Clarified Operation Overview and eliminated use of Legitimate as the counterpart of Suspicious since the words have different meanings. o Improved discussion (courtesy of Arvel Hathcock) of the use of TXT records in DNS vs. a new RR type. o Clarified publication rules for multilevel names. @@ -781,56 +794,56 @@ o Added "handling" tag to express alleged sending domain's preference about handling of Suspicious messages. o Clarified handling of SERVFAIL error in SSP check. o Replaced "entity" with "domain", since with the removal of user- granularity SSP, the only entities having sender signing policies are domains. -C.6. Changes since -allman-ssp-02 +C.7. Changes since -allman-ssp-02 o Removed user-granularity SSP and u= tag. o Replaced DKIMP resource record with a TXT record. o Changed name of the primary tag from "p" to "dkim". o Replaced lookup algorithm with one which traverses upward at most one level. o Added description of records to be published, and effect of wildcard records within the domain, on SSP. -C.7. Changes since -allman-ssp-01 +C.8. Changes since -allman-ssp-01 o Changed term "Sender Signing Policy" to "Sender Signing Practices". o Changed query methodology to use a separate DNS resource record type, DKIMP. o Changed tag values from SPF-like symbols to words. o User level policies now default to that of the domain if not specified. o Removed the "Compliance" section since we're still not clear on what goes here. o Changed the "parent domain" policy to only search up one level (assumes that subdomains will publish SSP records if appropriate). o Added detailed description of SSP check procedure. -C.8. Changes since -allman-ssp-00 +C.9. Changes since -allman-ssp-00 From a "diff" perspective, the changes are extensive. Semantically, the changes are: o Added section on "Third-Party Signatures and Mailing Lists" o Added "Compliance" (transferred from -base document). I'm not clear on what needs to be done here. o Extensive restructuring.