Internet DRAFT - draft-melnikov-acme-email-smime
draft-melnikov-acme-email-smime
Network Working Group A. Melnikov
Internet-Draft Isode Ltd
Intended status: Informational June 7, 2017
Expires: December 9, 2017
Extensions to Automatic Certificate Management Environment for end user
S/MIME certificates
draft-melnikov-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
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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 email
services. 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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