Network Working Group J. Levine Internet-Draft Taughannock Networks Intended status: Standards Track July 4, 2015 Expires: January 5, 2016 E-mail Authentication for Internationalized Mail draft-levine-appsarea-eaiauth-00 Abstract SPF, DKIM, and DMARC enable a domain owner to publish e-mail authentication and policy information in the DNS. In internationalized e-mail, domain names can occur both as U-labels and A-labels. This specification clarifies when to use which form of a domain names when using SPF, DKIM, and DMARC. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on January 5, 2016. Copyright Notice Copyright (c) 2015 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. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Levine Expires January 5, 2016 [Page 1]
Internet-Draft EAI Authentication July 2015 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. SPF and internationalized mail . . . . . . . . . . . . . . . 3 4. DKIM and internationalized mail . . . . . . . . . . . . . . . 3 5. DMARC and internationalized mail . . . . . . . . . . . . . . 3 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 8. Normative References . . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction SPF, DKIM, and DMARC enable a domain owner to publish e-mail authentication and policy information in the DNS. SPF primarily publishes information about what host addresses are authorized to send mail for a domain. DKIM places cryptographic signatures on e-mail messages, with the validation keys published in the DNS. DMARC publishes policy information related to the domain in the From: header of e-mail messages. In conventional e-mail, all domain names are ASCII in all contexts so there is no question about the representation of the domain names. All internationalized domain names are represented as A-labels [RFC5890] in message bodies, in SMTP sessions, and in the DNS. Internationalized mail [RFC6530] allows U-labels in SMTP sessions [RFC6531] and in message headers [RFC6532]. Every U-label is equivalent to an A-label, so in principle the choice of label format should not cause any ambiguities. But in practice, consistent use of label formats will make it more likely that mail senders' and receivers' code interoperates. 2. Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. The term IDN, for Internationalized Domain Name, refers to either a U-label or an A-label. Since DMARC is not currently a standards track protocol, this specification offers advice rather than requirements for DMARC. Levine Expires January 5, 2016 [Page 2]
Internet-Draft EAI Authentication July 2015 3. SPF and internationalized mail SPF [RFC7208] uses two identities from the SMTP session, the host name in the EHLO command, and the domain in the address in the MAIL FROM command. Since the EHLO command precedes the server response that identifies the SMTPUTF8 extension, an IDN domain name argument SHOULD be represented as an A-label. An IDN domain name in MAIL FROM can be either a U-label or an A-label. All U-labels MUST be converted to A-labels before being used for an SPF validation. This includes both the original DNS lookup, described in Section 3 of [RFC7208] and the macro expansion of domain-spec described in section 7. Section 4.3 of [RFC7208] states that all IDNs in an SPF DNS record MUST be A-labels; this rule is unchanged since any SPF record may be used to authorize either internationalized or conventional mail. 4. DKIM and internationalized mail DKIM [RFC6376] specifies a message header that contains a cryptographic message signature and a DNS record that contains the validation key. Section 3.5 of [RFC6376] states that IDNs in the d=, i=, and s= tags of a DKIM-Signature header MUST be encoded as A-labels. This rule is relaxed only for headers in internationalized messages [RFC6532] so IDNs MAY be represented either as A-labels or U-labels. This provides improved consistency with other headers, particularly since the local-part of the i= tag is likely to be UTF-8 rather than ASCII. When computing or verifying the hash used a DKIM signature as described in section 3.7, the hash MUST use the domain name in the format it occurs in the header. When retrieving or processing a DKIM key record from the DNS, all U-labels must first be converted into A-labels before creating the domain name to be looked up. DKIM key records, described in section 3.6.1, do not contain domain names, so there is no change to their specification. 5. DMARC and internationalized mail DMARC [RFC7489] defines a policy language that domain owners can specify for the domain of the address in a RFC5322.From header. Section 6.6.1 specifies, somewhat imprecisely, how IDNs in the RFC5322.From address domain are to be handled. That section is updated to say that all U-labels in the domain are converted to A-labels before further processing. Sections 6.7 and 7.1 are Levine Expires January 5, 2016 [Page 3]
Internet-Draft EAI Authentication July 2015 similarly updated to say that all U-labels in domains being handled are converted to A-labels before further processing. DMARC policy records, described in section 6.3, can contain e-mail addresses in the rua and ruf tags. Since a policy record can be used for both internationalized and conventional mail, those addresses have to be conventional addresses, not internationalized addresses. 6. IANA Considerations This document makes no request of IANA. 7. Security Considerations Nothing new. 8. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ RFC2119, March 1997, <http://www.rfc-editor.org/info/rfc2119>. [RFC5890] Klensin, J., "Internationalized Domain Names for Applications (IDNA): Definitions and Document Framework", RFC 5890, DOI 10.17487/RFC5890, August 2010, <http://www.rfc-editor.org/info/rfc5890>. [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., "DomainKeys Identified Mail (DKIM) Signatures", STD 76, RFC 6376, DOI 10.17487/RFC6376, September 2011, <http://www.rfc-editor.org/info/rfc6376>. [RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for Internationalized Email", RFC 6530, DOI 10.17487/RFC6530, February 2012, <http://www.rfc-editor.org/info/rfc6530>. [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, <http://www.rfc-editor.org/info/rfc6531>. [RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 2012, <http://www.rfc-editor.org/info/rfc6532>. Levine Expires January 5, 2016 [Page 4]
Internet-Draft EAI Authentication July 2015 [RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for Authorizing Use of Domains in Email, Version 1", RFC 7208, DOI 10.17487/RFC7208, April 2014, <http://www.rfc-editor.org/info/rfc7208>. [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based Message Authentication, Reporting, and Conformance (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, <http://www.rfc-editor.org/info/rfc7489>. Author's Address John Levine Taughannock Networks PO Box 727 Trumansburg, NY 14886 Phone: +1 831 480 2300 Email: standards@taugh.com URI: http://jl.ly Levine Expires January 5, 2016 [Page 5]