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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group P. Hoffman 3 Internet-Draft VPN Consortium 4 Intended status: Standards Track J. Schlyter 5 Expires: February 23, 2012 Kirei AB 6 August 22, 2011 8 Using Secure DNS to Associate Certificates with Domain Names For S/MIME 9 draft-hoffman-dane-smime-01 11 Abstract 13 S/MIME uses certificates for authenticating and encrypting messages. 14 Users want their mail user agents to securely associate a certificate 15 with the sender of an encrypted and/or signed message. DNSSEC 16 provides a mechanism for a zone operator to sign DNS information 17 directly. This way, bindings of certificates to users within a 18 domain are asserted not by external entities, but by the entities 19 that operate the DNS. This document describes how to use secure DNS 20 to associate an S/MIME user's certificate with the intended domain 21 name. 23 IMPORTANT NOTE: This draft is intentionally sketchy. It is meant as 24 a possible starting point for the DANE WG if it wants to consider 25 making a protocol similar to TLSA, as described in 26 draft-ietf-dane-protocol, but that applies to S/MIME. The WG may or 27 may not want to adopt such work, or if it does, may want to use a 28 very different scheme from the one described here. 30 Status of this Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on February 23, 2012. 47 Copyright Notice 48 Copyright (c) 2011 IETF Trust and the persons identified as the 49 document authors. All rights reserved. 51 This document is subject to BCP 78 and the IETF Trust's Legal 52 Provisions Relating to IETF Documents 53 (http://trustee.ietf.org/license-info) in effect on the date of 54 publication of this document. Please review these documents 55 carefully, as they describe your rights and restrictions with respect 56 to this document. Code Components extracted from this document must 57 include Simplified BSD License text as described in Section 4.e of 58 the Trust Legal Provisions and are provided without warranty as 59 described in the Simplified BSD License. 61 Table of Contents 63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 1.1. Certificate Associations . . . . . . . . . . . . . . . . . 3 65 1.2. Securing Certificate Associations . . . . . . . . . . . . . 3 66 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 67 2. The SMIMEA Resource Record . . . . . . . . . . . . . . . . . . 3 68 3. Domain Names for S/MIME Certificate Associations . . . . . . . 4 69 4. Use of S/MIME Certificate Associations in S/MIME . . . . . . . 4 70 5. Mandatory-to-Implement Algorithms . . . . . . . . . . . . . . . 4 71 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 4 72 7. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 73 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 74 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 75 9.1. Normative References . . . . . . . . . . . . . . . . . . . 5 76 9.2. Informative References . . . . . . . . . . . . . . . . . . 5 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 5 79 1. Introduction 81 S/MIME [RFC5751] messages often contain a certificate. This 82 certificate assists in authenticating the sender of the message and 83 can be used for encrypting messages that will be sent in reply. In 84 order for the S/MIME receiver to authenticate that a message is from 85 the sender whom is identified in the message the receiver's mail user 86 agent (MUA) must validate that this certificate is associated with 87 the purported sender. Currently, the MUA must trust a trust anchor 88 upon which the sender's certificate is rooted, and must successfully 89 validate the certificate. 91 Some people want a different way to authenticate the association of 92 the sender's certificate with the sender without trusting a CA. 93 Given that the DNS administrator for a domain name is authorized to 94 give identifying information about the zone, it makes sense to allow 95 that administrator to also make an authoritative binding between 96 email messages purporting to come from the domain name and a 97 certificate that might be used by someone authorized to send mail 98 from those servers. The easiest way to do this is to use the DNS. 100 [[ More here about additional uses, such as CMS that is not S/MIME 101 where the certificates have email addresses for the subject name. ]] 103 1.1. Certificate Associations 105 [[ Will mostly duplicate the text from Section 1.1 of 106 draft-ietf-dane-protocol ]] 108 1.2. Securing Certificate Associations 110 [[ Will mostly duplicate the text from Section 1.2 of 111 draft-ietf-dane-protocol ]] 113 1.3. Terminology 115 [[ Will mostly duplicate the text from Section 1.3 of 116 draft-ietf-dane-protocol ]] 118 2. The SMIMEA Resource Record 120 [[ Will mostly duplicate the text from Section 2 of 121 draft-ietf-dane-protocol, but will define "SMIMEA" instead of "TLSA". 122 ]] 124 3. Domain Names for S/MIME Certificate Associations 126 Domain names are prepared for requests in the following manner. 128 1. The user name (the "left-hand side" of the email address, called 129 the "local-part" in RFC 2822 [RFC2822]) becomes the left-most 130 label in the prepared domain name. This does not include the "@" 131 character that separates the left and right sides of the email 132 address. 134 2. The string "_smimecert" becomes the second left-most label in the 135 prepared domain name. 137 3. The domain name (the "right-hand side" of the email address, 138 called the "domain" in RFC 2822) is appended to the result of 139 step 2 to complete the prepared domain name. 141 For example, to request a SMIMEA resource record for a user whose 142 address is "chris@example.com", you would use 143 "chris._smimecert.example.com" in the request. 145 [[ Need to discuss back-quoting, such as for chris.smith@example.com 146 becoming chris\.smith._smimecert.example.com ]] 148 4. Use of S/MIME Certificate Associations in S/MIME 150 [[ Stuff here that sounds like TLSA but is actually about S/MIME 151 senders and receivers. Lots of text lifted from 152 draft-ietf-dane-protocol. ]] 154 5. Mandatory-to-Implement Algorithms 156 [[ Mostly copied from draft-ietf-dane-protocol. ]] 158 6. IANA Considerations 160 [[ Mostly copied from draft-ietf-dane-protocol but using "SMIMEA" 161 instead. ]] 163 7. Security Considerations 165 [[ Mostly copied from draft-ietf-dane-protocol but is actually about 166 S/MIME senders and receivers. ]] 168 8. Acknowledgements 170 [[ Mostly copied from draft-ietf-dane-protocol ]] 172 9. References 174 9.1. Normative References 176 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 177 Requirement Levels", BCP 14, RFC 2119, March 1997. 179 [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. 180 Rose, "DNS Security Introduction and Requirements", 181 RFC 4033, March 2005. 183 [RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S. 184 Rose, "Resource Records for the DNS Security Extensions", 185 RFC 4034, March 2005. 187 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 188 Rose, "Protocol Modifications for the DNS Security 189 Extensions", RFC 4035, March 2005. 191 [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., 192 Housley, R., and W. Polk, "Internet X.509 Public Key 193 Infrastructure Certificate and Certificate Revocation List 194 (CRL) Profile", RFC 5280, May 2008. 196 [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet 197 Mail Extensions (S/MIME) Version 3.2 Message 198 Specification", RFC 5751, January 2010. 200 9.2. Informative References 202 [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, 203 April 2001. 205 Authors' Addresses 207 Paul Hoffman 208 VPN Consortium 210 Email: paul.hoffman@vpnc.org 211 Jakob Schlyter 212 Kirei AB 214 Email: jakob@kirei.se