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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Downref: Normative reference to an Informational RFC: RFC 7489 Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Levine 3 Internet-Draft Taughannock Networks 4 Intended status: Standards Track July 4, 2015 5 Expires: January 5, 2016 7 E-mail Authentication for Internationalized Mail 8 draft-levine-appsarea-eaiauth-00 10 Abstract 12 SPF, DKIM, and DMARC enable a domain owner to publish e-mail 13 authentication and policy information in the DNS. In 14 internationalized e-mail, domain names can occur both as U-labels and 15 A-labels. This specification clarifies when to use which form of a 16 domain names when using SPF, DKIM, and DMARC. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at http://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on January 5, 2016. 35 Copyright Notice 37 Copyright (c) 2015 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (http://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2 54 3. SPF and internationalized mail . . . . . . . . . . . . . . . 3 55 4. DKIM and internationalized mail . . . . . . . . . . . . . . . 3 56 5. DMARC and internationalized mail . . . . . . . . . . . . . . 3 57 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 58 7. Security Considerations . . . . . . . . . . . . . . . . . . . 4 59 8. Normative References . . . . . . . . . . . . . . . . . . . . 4 60 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 62 1. Introduction 64 SPF, DKIM, and DMARC enable a domain owner to publish e-mail 65 authentication and policy information in the DNS. SPF primarily 66 publishes information about what host addresses are authorized to 67 send mail for a domain. DKIM places cryptographic signatures on 68 e-mail messages, with the validation keys published in the DNS. 69 DMARC publishes policy information related to the domain in the From: 70 header of e-mail messages. 72 In conventional e-mail, all domain names are ASCII in all contexts so 73 there is no question about the representation of the domain names. 74 All internationalized domain names are represented as A-labels 75 [RFC5890] in message bodies, in SMTP sessions, and in the DNS. 76 Internationalized mail [RFC6530] allows U-labels in SMTP sessions 77 [RFC6531] and in message headers [RFC6532]. 79 Every U-label is equivalent to an A-label, so in principle the choice 80 of label format should not cause any ambiguities. But in practice, 81 consistent use of label formats will make it more likely that mail 82 senders' and receivers' code interoperates. 84 2. Definitions 86 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 87 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 88 document are to be interpreted as described in [RFC2119]. 90 The term IDN, for Internationalized Domain Name, refers to either a 91 U-label or an A-label. 93 Since DMARC is not currently a standards track protocol, this 94 specification offers advice rather than requirements for DMARC. 96 3. SPF and internationalized mail 98 SPF [RFC7208] uses two identities from the SMTP session, the host 99 name in the EHLO command, and the domain in the address in the MAIL 100 FROM command. Since the EHLO command precedes the server response 101 that identifies the SMTPUTF8 extension, an IDN domain name argument 102 SHOULD be represented as an A-label. An IDN domain name in MAIL FROM 103 can be either a U-label or an A-label. 105 All U-labels MUST be converted to A-labels before being used for an 106 SPF validation. This includes both the original DNS lookup, 107 described in Section 3 of [RFC7208] and the macro expansion of 108 domain-spec described in section 7. Section 4.3 of [RFC7208] states 109 that all IDNs in an SPF DNS record MUST be A-labels; this rule is 110 unchanged since any SPF record may be used to authorize either 111 internationalized or conventional mail. 113 4. DKIM and internationalized mail 115 DKIM [RFC6376] specifies a message header that contains a 116 cryptographic message signature and a DNS record that contains the 117 validation key. 119 Section 3.5 of [RFC6376] states that IDNs in the d=, i=, and s= tags 120 of a DKIM-Signature header MUST be encoded as A-labels. This rule is 121 relaxed only for headers in internationalized messages [RFC6532] so 122 IDNs MAY be represented either as A-labels or U-labels. This 123 provides improved consistency with other headers, particularly since 124 the local-part of the i= tag is likely to be UTF-8 rather than ASCII. 125 When computing or verifying the hash used a DKIM signature as 126 described in section 3.7, the hash MUST use the domain name in the 127 format it occurs in the header. When retrieving or processing a DKIM 128 key record from the DNS, all U-labels must first be converted into 129 A-labels before creating the domain name to be looked up. 131 DKIM key records, described in section 3.6.1, do not contain domain 132 names, so there is no change to their specification. 134 5. DMARC and internationalized mail 136 DMARC [RFC7489] defines a policy language that domain owners can 137 specify for the domain of the address in a RFC5322.From header. 139 Section 6.6.1 specifies, somewhat imprecisely, how IDNs in the 140 RFC5322.From address domain are to be handled. That section is 141 updated to say that all U-labels in the domain are converted to 142 A-labels before further processing. Sections 6.7 and 7.1 are 143 similarly updated to say that all U-labels in domains being handled 144 are converted to A-labels before further processing. 146 DMARC policy records, described in section 6.3, can contain e-mail 147 addresses in the rua and ruf tags. Since a policy record can be used 148 for both internationalized and conventional mail, those addresses 149 have to be conventional addresses, not internationalized addresses. 151 6. IANA Considerations 153 This document makes no request of IANA. 155 7. Security Considerations 157 Nothing new. 159 8. Normative References 161 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 162 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 163 RFC2119, March 1997, 164 . 166 [RFC5890] Klensin, J., "Internationalized Domain Names for 167 Applications (IDNA): Definitions and Document Framework", 168 RFC 5890, DOI 10.17487/RFC5890, August 2010, 169 . 171 [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., 172 "DomainKeys Identified Mail (DKIM) Signatures", STD 76, 173 RFC 6376, DOI 10.17487/RFC6376, September 2011, 174 . 176 [RFC6530] Klensin, J. and Y. Ko, "Overview and Framework for 177 Internationalized Email", RFC 6530, DOI 10.17487/RFC6530, 178 February 2012, . 180 [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized 181 Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, 182 . 184 [RFC6532] Yang, A., Steele, S., and N. Freed, "Internationalized 185 Email Headers", RFC 6532, DOI 10.17487/RFC6532, February 186 2012, . 188 [RFC7208] Kitterman, S., "Sender Policy Framework (SPF) for 189 Authorizing Use of Domains in Email, Version 1", RFC 7208, 190 DOI 10.17487/RFC7208, April 2014, 191 . 193 [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based 194 Message Authentication, Reporting, and Conformance 195 (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, 196 . 198 Author's Address 200 John Levine 201 Taughannock Networks 202 PO Box 727 203 Trumansburg, NY 14886 205 Phone: +1 831 480 2300 206 Email: standards@taugh.com 207 URI: http://jl.ly