Using Secure DNS to Associate Certificates with Domain Names For S/MIME
draft-ietf-dane-smime-16

Document Type Active Internet-Draft (dane WG)
Last updated 2017-03-22 (latest revision 2017-03-16)
Replaces draft-hoffman-dane-smime
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Network Working Group                                         P. Hoffman
Internet-Draft                                                     ICANN
Intended status: Experimental                                J. Schlyter
Expires: September 17, 2017                                     Kirei AB
                                                          March 16, 2017

Using Secure DNS to Associate Certificates with Domain Names For S/MIME
                        draft-ietf-dane-smime-16

Abstract

   This document describes how to use secure DNS to associate an S/MIME
   user's certificate with the intended domain name, similar to the way
   that DNS-Based Authentication of Named Entities (DANE), RFC 6698,
   does for TLS.

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
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   This Internet-Draft will expire on September 17, 2017.

Copyright Notice

   Copyright (c) 2017 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
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Hoffman & Schlyter     Expires September 17, 2017               [Page 1]
Internet-Draft     DNS-Based Authentication for S/MIME        March 2017

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Experiment Goal . . . . . . . . . . . . . . . . . . . . .   3
   2.  The SMIMEA Resource Record  . . . . . . . . . . . . . . . . .   4
   3.  Location of the SMIMEA Record . . . . . . . . . . . . . . . .   4
   4.  Email Address Variants and Internationalization
       Considerations  . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Mandatory-to-Implement Features . . . . . . . . . . . . . . .   6
   6.  Application Use of S/MIME Certificate Associations  . . . . .   6
   7.  Certificate Size and DNS  . . . . . . . . . . . . . . . . . .   6
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
     9.1.  Response Size . . . . . . . . . . . . . . . . . . . . . .   8
     9.2.  Email Address Information Leak  . . . . . . . . . . . . .   8
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   9
     11.2.  Informative References . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   S/MIME [RFC5751] messages often contain a certificate (some messages
   contain more than one certificate).  These certificates assist in
   authenticating the sender of the message and can be used for
   encrypting messages that will be sent in reply.  In order for the S/
   MIME receiver to authenticate that a message is from the sender who
   is identified in the message, the receiver's mail user agent (MUA)
   must validate that this certificate is associated with the purported
   sender.  Currently, the MUA must trust a trust anchor upon which the
   sender's certificate is rooted, and must successfully validate the
   certificate.  There are other requirements on the MUA, such as
   associating the identity in the certificate with that of the message,
   that are out of scope for this document.

   Some people want to authenticate the association of the sender's
   certificate with the sender without trusting a configured trust
   anchor.  Others to want mitigate the difficulty of finding
   certificates from outside the enterprise.  Given that the DNS
   administrator for a domain name is authorized to give identifying
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