--- 1/draft-ietf-dkim-ssp-08.txt 2009-02-06 01:12:05.000000000 +0100 +++ 2/draft-ietf-dkim-ssp-09.txt 2009-02-06 01:12:05.000000000 +0100 @@ -1,48 +1,58 @@ Network Working Group E. Allman Internet-Draft Sendmail, Inc. Intended status: Standards Track J. Fenton -Expires: June 20, 2009 Cisco Systems, Inc. +Expires: August 9, 2009 Cisco Systems, Inc. M. Delany Yahoo! Inc. J. Levine Taughannock Networks - December 17, 2008 + February 5, 2009 DomainKeys Identified Mail (DKIM) Author Domain Signing Practices (ADSP) - draft-ietf-dkim-ssp-08 + draft-ietf-dkim-ssp-09 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. + This Internet-Draft is submitted to IETF in full conformance with the + provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months 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 June 20, 2009. + This Internet-Draft will expire on August 9, 2009. + +Copyright Notice + + Copyright (c) 2009 IETF Trust and the persons identified as the + document authors. All rights reserved. + + This document is subject to BCP 78 and the IETF Trust's Legal + Provisions Relating to IETF Documents + (http://trustee.ietf.org/license-info) in effect on the date of + publication of this document. Please review these documents + carefully, as they describe your rights and restrictions with respect + to this document. 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. @@ -53,62 +63,62 @@ 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 + 3.2. ADSP Usage . . . . . . . . . . . . . . . . . . . . . . . . 7 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 + 4.3. ADSP Lookup Procedure . . . . . . . . . . . . . . . . . . 9 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5.1. ADSP Specification Tag Registry . . . . . . . . . . . . . 10 - 5.2. ADSP Outbound Signing Practices Registry . . . . . . . . . 10 + 5.2. ADSP Outbound Signing Practices Registry . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6.1. ADSP Threat Model . . . . . . . . . . . . . . . . . . . . 11 6.2. DNS Considerations . . . . . . . . . . . . . . . . . . . . 12 6.3. DNS Wildcards . . . . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. References - Normative . . . . . . . . . . . . . . . . . . 13 7.2. References - Informative . . . . . . . . . . . . . . . . . 13 - Appendix A. Lookup Examples . . . . . . . . . . . . . . . . . . . 13 + Appendix A. Lookup Examples . . . . . . . . . . . . . . . . . . . 14 A.1. Domain and ADSP exist . . . . . . . . . . . . . . . . . . 14 A.2. Domain exists, ADSP does not exist . . . . . . . . . . . . 14 - A.3. Domain does not exist . . . . . . . . . . . . . . . . . . 14 + A.3. Domain does not exist . . . . . . . . . . . . . . . . . . 15 Appendix B. Usage Examples . . . . . . . . . . . . . . . . . . . 15 B.1. Single Location Domains . . . . . . . . . . . . . . . . . 15 B.2. Bulk Mailing Domains . . . . . . . . . . . . . . . . . . . 15 B.3. Bulk Mailing Domains with Discardable Mail . . . . . . . . 16 B.4. Third Party Senders . . . . . . . . . . . . . . . . . . . 16 - B.5. Domains with Independent Users and Liberal Use Policies . 16 - B.6. Non-email Domains . . . . . . . . . . . . . . . . . . . . 16 + B.5. Domains with Independent Users and Liberal Use Policies . 17 + B.6. Non-email Domains . . . . . . . . . . . . . . . . . . . . 17 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 17 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 17 - D.1. Changes since -ietf-dkim-07 . . . . . . . . . . . . . . . 17 - D.2. Changes since -ietf-dkim-06 . . . . . . . . . . . . . . . 17 - D.3. Changes since -ietf-dkim-05 . . . . . . . . . . . . . . . 17 - D.4. Changes since -ietf-dkim-04 . . . . . . . . . . . . . . . 17 - D.5. Changes since -ietf-dkim-03 . . . . . . . . . . . . . . . 18 - D.6. Changes since -ietf-dkim-02 . . . . . . . . . . . . . . . 19 - D.7. Changes since -ietf-dkim-ssp-01 . . . . . . . . . . . . . 19 - D.8. Changes since -ietf-dkim-ssp-00 . . . . . . . . . . . . . 20 - D.9. Changes since -allman-ssp-02 . . . . . . . . . . . . . . . 21 - D.10. Changes since -allman-ssp-01 . . . . . . . . . . . . . . . 21 - D.11. Changes since -allman-ssp-00 . . . . . . . . . . . . . . . 21 + D.1. Changes since -ietf-dkim-08 . . . . . . . . . . . . . . . 17 + D.2. Changes since -ietf-dkim-07 . . . . . . . . . . . . . . . 17 + D.3. Changes since -ietf-dkim-06 . . . . . . . . . . . . . . . 18 + D.4. Changes since -ietf-dkim-05 . . . . . . . . . . . . . . . 18 + D.5. Changes since -ietf-dkim-04 . . . . . . . . . . . . . . . 18 + D.6. Changes since -ietf-dkim-03 . . . . . . . . . . . . . . . 18 + D.7. Changes since -ietf-dkim-02 . . . . . . . . . . . . . . . 19 + D.8. Changes since -ietf-dkim-ssp-01 . . . . . . . . . . . . . 20 + D.9. Changes since -ietf-dkim-ssp-00 . . . . . . . . . . . . . 21 + D.10. Changes since -allman-ssp-02 . . . . . . . . . . . . . . . 21 + D.11. Changes since -allman-ssp-01 . . . . . . . . . . . . . . . 22 + D.12. Changes since -allman-ssp-00 . . . . . . . . . . . . . . . 22 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22 - Intellectual Property and Copyright Statements . . . . . . . . . . 23 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. @@ -174,43 +184,45 @@ 2.6. Author Domain Signing Practices "Author Domain Signing Practices" (or just "practices") consist of a machine-readable record published by the domain of an Alleged Author which includes statements about the domain's practices with respect to mail it sends with its domain in the From: line. 2.7. Author Signature - 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 "i=" tag or its default value from the "d=" tag) matches an - Author Address in the message. When the identity of the user or - agent includes a Local-part, the identities match if the Local-parts - are the same string, and the domains are the same string. Otherwise, - the identities match if the domains are the same string. Following + An "author signature" is a Valid Signature that has the same domain + name in the DKIM signing identity as the domain name in the Author + Address. If the DKIM signing identity has a Local-part, it is be + identical to the Local-part in the Author Address. Following [RFC5321], Local-part comparisons are case sensitive, but domain comparisons are case insensitive. For example, if a message has a Valid Signature, with the DKIM- Signature field containing "i=a@domain.example", then domain.example is asserting that it takes responsibility for the message. If the - message's From: field contains the address "b@domain.example" and an - ADSP query produces a "dkim=all" or "dkim=discardable" result, that + message's From: field contains the address "b@domain.example", that would mean that the message does not have a valid Author Signature. - Even though the message is signed by the same domain, it fails to - satisfy ADSP. + Even though the message is signed by the same domain, it will not + satisfy ADSP that specifies "dkim=all" or "dkim=discardable". + + Note: ADSP is incompatible with valid DKIM usage in which a signer + uses "i=" with values that are not the same as addresses in mail + headers. In that case, a possible workaround could be to add a + second DKIM signature a "d=" value that matches the Author + Address, but no "i=". 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. + Domain owners 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 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, @@ -223,59 +235,65 @@ scope of ADSP. ADSP applies to specific domains, not domain subtrees. If, for example, an Author Address were user@domain.example, the Author Domain would be domain.example, and the applicable ADSP record would be at _adsp._domainkey.domain.example. An Author Address in a subdomain such as user@sub.domain.example would have a different ADSP record at _adsp._domainkey.sub.domain.example. ADSP makes no connection between a domain and its parent or child domains. + Note: If an organization wants to publish Author Domain Signing + Practices for all the subdomains it uses, such as host names of + servers within the domain, it does so by creating ADSP records for + every _adsp._domainkey..domain.example. Wildcards cannot be + used (see Section 6.3.); however, suitable DNS management tools + could automate creation of the ADSP records. + 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 checker 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 recipient gets varying amounts of useful information from each ADSP lookup. o If a message has no Valid Signature, the ADSP result is directly relevant to the message. - o If a message has a Valid Signature from an Author Domain, ADSP - provides no benefit relative to that domain since the message is - already known to be compliant with any possible ADSP for that - domain. + o If a message has an Author Signature, ADSP provides no benefit + relative to that domain since the message is already known to be + compliant with any possible ADSP for that domain. - 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 - ADSP result in its evaluation of the message. + o If a message has a Valid Signature other than an Author Signature, + the receiver can use both the Signature and the ADSP result in its + evaluation of the message. 3.3. ADSP Results An ADSP lookup for an Author Address produces one of four possible 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 ADSP record is found. - o All messages from this domain are signed. + o All messages from this domain are signed with an Author Signature. - o All messages from this domain are signed and discardable, i.e., if - a message arrives without a valid Author Signature, the domain - encourages the recipient(s) to discard it. + o All messages from this domain are signed with an Author Signature + and discardable, i.e., if a message arrives without a valid Author + Signature, the domain encourages the recipient(s) to discard it. o This domain is out of scope, i.e., the domain does not exist in the DNS. An ADSP lookup could terminate without producing any result if a DNS lookup results in a temporary failure. 4. Detailed Description 4.1. DNS Representation @@ -355,45 +373,45 @@ 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 is that the Author domain does not exist in the DNS (often called - an "NXDOMAIN" error, rcode=3 in [RFC1035]), the algorithm MUST + an NXDOMAIN error, rcode=3 in [RFC1035]), the algorithm MUST terminate with an error indicating that the domain is out of scope. Note that a result with rcode=0 but no records (often - called "NODATA") is not the same as NXDOMAIN. + called NODATA) is not the same as NXDOMAIN. 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 + 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 [RFC5321]. 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 (rcode=0 in + If the result of this query is a NOERROR response (rcode=0 in [RFC1035]) with an answer which is a single record that is a valid ADSP record, use that record, and the algorithm terminates. If the result of the query is NXDOMAIN or NOERROR with zero records, there is no ADSP record. If the result of the query contains more than one record, or a record that is not a valid ADSP record, the ADSP result is undefined. If a query results in a "SERVFAIL" error response (rcode=2 in [RFC1035]), the algorithm terminates without returning a result; @@ -709,33 +728,46 @@ B.6. 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 C. Acknowledgements This document greatly benefited from comments by Steve Atkins, Jon - Callas, Dave Crocker, JD Falk, Arvel Hathcock, Ellen Siegel, Michael - Thomas, and Wietse Venema. + Callas, Dave Crocker, Pasi Eronen, JD Falk, Arvel Hathcock, Ellen + Siegel, Michael Thomas, and Wietse Venema. Appendix D. Change Log *NOTE TO RFC EDITOR: This section may be removed upon publication of this document as an RFC.* -D.1. Changes since -ietf-dkim-07 +D.1. Changes since -ietf-dkim-08 + + o Simplify and clarify interpretation of d= and i=. + + o Add note pointing out that i= usage conflicts with normal usage, + and suggest workaround. + + o Add note pointing out that you can mechanically add ADSP records + for all the subdomains you use. + + o in Section 3.2 fix text to say that only an Author Signature + counts. + +D.2. Changes since -ietf-dkim-07 Clarify that ADSP records use WSP rather than FWS in 4.1 and 4.2.1. -D.2. Changes since -ietf-dkim-06 +D.3. Changes since -ietf-dkim-06 Minor editorial changes suggested by AD: o expand DKIM in title o clarify that there's no subdomain matching in Section 3.1 o ADSP lookup can terminate without a result if the DNS lookup fails o random dkim= values are treated as unknown @@ -743,40 +775,41 @@ o in 4.2 note WSP not FWS o in 4.3 note that NODATA is not NXDOMAIN o add new Appendix A with lookup examples Also address Tony's nits in http://mipassoc.org/pipermail/ietf-dkim/2008q3/010720.html. Make the examples consistently use the .example domain. -D.3. Changes since -ietf-dkim-05 +D.4. 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. -D.4. Changes since -ietf-dkim-04 +D.5. 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. -D.5. Changes since -ietf-dkim-03 +D.6. 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. @@ -798,21 +831,21 @@ 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. -D.6. Changes since -ietf-dkim-02 +D.7. 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. @@ -820,21 +853,21 @@ 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 -D.7. Changes since -ietf-dkim-ssp-01 +D.8. 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). @@ -868,21 +901,21 @@ 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). -D.8. Changes since -ietf-dkim-ssp-00 +D.9. 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. @@ -897,56 +930,56 @@ 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. -D.9. Changes since -allman-ssp-02 +D.10. 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. -D.10. Changes since -allman-ssp-01 +D.11. 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. -D.11. Changes since -allman-ssp-00 +D.12. 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. @@ -979,50 +1011,10 @@ Email: markd+dkim@yahoo-inc.com John Levine Taughannock Networks PO Box 727 Trumansburg, NY 14886 Phone: +1 831 480 2300 Email: standards@taugh.com URI: http://www.taugh.com - -Full Copyright Statement - - Copyright (C) The IETF Trust (2008). - - This document is subject to the rights, licenses and restrictions - contained in BCP 78, and except as set forth therein, the authors - retain all their rights. - - This document and the information contained herein are provided on an - "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS - OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND - THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS - OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF - THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED - WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - -Intellectual Property - - The IETF takes no position regarding the validity or scope of any - Intellectual Property Rights or other rights that might be claimed to - pertain to the implementation or use of the technology described in - this document or the extent to which any license under such rights - might or might not be available; nor does it represent that it has - made any independent effort to identify any such rights. Information - on the procedures with respect to rights in RFC documents can be - found in BCP 78 and BCP 79. - - Copies of IPR disclosures made to the IETF Secretariat and any - assurances of licenses to be made available, or the result of an - attempt made to obtain a general license or permission for the use of - such proprietary rights by implementers or users of this - specification can be obtained from the IETF on-line IPR repository at - http://www.ietf.org/ipr. - - The IETF invites any interested party to bring to its attention any - copyrights, patents or patent applications, or other proprietary - rights that may cover technology that may be required to implement - this standard. Please address the information to the IETF at - ietf-ipr@ietf.org.