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Versions: (draft-melnikov-acme-email-smime) 00

Network Working Group                                        A. Melnikov
Internet-Draft                                                 Isode Ltd
Intended status: Informational                             June 18, 2017
Expires: December 20, 2017


Extensions to Automatic Certificate Management Environment for end user
                          S/MIME certificates
                     draft-ietf-acme-email-smime-00

Abstract

   This document specifies identifiers and challenges required to enable
   the Automated Certificate Management Environment (ACME) to issue
   certificates for use for email recipients that want to use S/MIME.

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 December 20, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  Use of ACME for issuing end user S/MIME certificates  . . . .   2
   4.  Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   3
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   [I-D.ietf-acme-acme] is a mechanism for automating certificate
   management on the Internet.  It enables administrative entities to
   prove effective control over resources like domain names, and
   automates the process of generating and issuing certificates.

   This document describes an extension to ACME for use by S/MIME.
   Section 3 defines extensions for issuing end user S/MIME [RFC5751]
   certificates.

2.  Conventions Used in This Document

   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].

3.  Use of ACME for issuing end user S/MIME certificates

   [I-D.ietf-acme-acme] defines "dns" Identifier Type that is used to
   verify that a particular entity has control over a domain or specific
   service associated with the domain.  In order to be able to issue
   end-user S/MIME certificates, ACME needs a new Identifier Type that
   proves ownership of an email address.

   This document defines a new Identifier Type "email" which corresponds
   to an (all ASCII) email address [RFC5321].  This can be used with
   S/MIME or other similar service that requires posession of a
   certificate tied to an email address.

   A new challenge type "email-reply-00" is used with "email" Identifier
   Type, which provides proof that an ACME client has control over an
   email address: [[Very rough outline follows]]

   1.  ACME server generates an email message with the subject
       containing "ACME <token-part1>", where <token-part1> is the
       base64url encoded first part of the token, which contains at



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       least 64 bit of entropy.  The second part of the token (token-
       part2, which also contains at least 64 bit of entropy) is
       returned over HTTPS to the ACME client.  ACME client concatenates
       "token-part1" and "token-part2" to create "token", calculates
       key-authz (as per Section 8.1 of [I-D.ietf-acme-acme]), then
       included the base64url encoded SHA-256 digest [FIPS180-4] of the
       key authorization in a response email message.  The response
       email message has a single text/plain MIME body part.  [[Do we
       need to handle text/html or multipart/alternative?  Simplicity
       suggests "no".]]

   [[Do we need a proof that ACME client can submit email on behalf of
   the user, not just read the challenge using IMAP?]]

4.  Open Issues

   [[This section should be empty before publication]]

5.  IANA Considerations

   IANA is requested to register a new Identifier Type "email" which
   corresponds to an (all ASCII) email address [RFC5321].

   And finally, IANA is requested to register the following ACME
   challenge types that are used with Identifier Type "email": "email-
   reply".  The reference for it is this document.

6.  Security Considerations

   TBD.

7.  Normative References

   [I-D.ietf-acme-acme]
              Barnes, R., Hoffman-Andrews, J., and J. Kasten, "Automatic
              Certificate Management Environment (ACME)", draft-ietf-
              acme-acme-06 (work in progress), March 2017.

   [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>.

   [RFC5321]  Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
              DOI 10.17487/RFC5321, October 2008,
              <http://www.rfc-editor.org/info/rfc5321>.





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   [RFC5751]  Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, DOI 10.17487/RFC5751, January
              2010, <http://www.rfc-editor.org/info/rfc5751>.

   [RFC7515]  Jones, M., Bradley, J., and N. Sakimura, "JSON Web
              Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
              2015, <http://www.rfc-editor.org/info/rfc7515>.

Author's Address

   Alexey Melnikov
   Isode Ltd
   14 Castle Mews
   Hampton, Middlesex  TW12 2NP
   UK

   EMail: Alexey.Melnikov@isode.com

































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