draft-ietf-acme-email-smime-00.txt   draft-ietf-acme-email-smime-01.txt 
Network Working Group A. Melnikov Network Working Group A. Melnikov
Internet-Draft Isode Ltd Internet-Draft Isode Ltd
Intended status: Informational June 18, 2017 Intended status: Informational October 29, 2017
Expires: December 20, 2017 Expires: May 2, 2018
Extensions to Automatic Certificate Management Environment for end user Extensions to Automatic Certificate Management Environment for end user
S/MIME certificates S/MIME certificates
draft-ietf-acme-email-smime-00 draft-ietf-acme-email-smime-01
Abstract Abstract
This document specifies identifiers and challenges required to enable This document specifies identifiers and challenges required to enable
the Automated Certificate Management Environment (ACME) to issue the Automated Certificate Management Environment (ACME) to issue
certificates for use for email recipients that want to use S/MIME. certificates for use by email users that want to use S/MIME.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 20, 2017. This Internet-Draft will expire on May 2, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
skipping to change at page 2, line 42 skipping to change at page 2, line 42
3. Use of ACME for issuing end user S/MIME certificates 3. Use of ACME for issuing end user S/MIME certificates
[I-D.ietf-acme-acme] defines "dns" Identifier Type that is used to [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 verify that a particular entity has control over a domain or specific
service associated with the domain. In order to be able to issue service associated with the domain. In order to be able to issue
end-user S/MIME certificates, ACME needs a new Identifier Type that end-user S/MIME certificates, ACME needs a new Identifier Type that
proves ownership of an email address. proves ownership of an email address.
This document defines a new Identifier Type "email" which corresponds This document defines a new Identifier Type "email" which corresponds
to an (all ASCII) email address [RFC5321]. This can be used with to an (all ASCII) email address [RFC5321] or Internationalized Email
S/MIME or other similar service that requires posession of a addresses [RFC6531]. This can be used with S/MIME or other similar
certificate tied to an email address. service that requires posession of a certificate tied to an email
address.
A new challenge type "email-reply-00" is used with "email" Identifier A new challenge type "email-reply-00" is used with "email" Identifier
Type, which provides proof that an ACME client has control over an Type, which provides proof that an ACME client has control over an
email address: [[Very rough outline follows]] email address: [[Very rough outline follows]]
1. ACME server generates an email message with the subject 1. ACME server generates a "challenge" email message with the
containing "ACME <token-part1>", where <token-part1> is the subject "ACME: <token-part1>", where <token-part1> is the
base64url encoded first part of the token, which contains at base64url encoded first part of the token, which contains at
least 64 bit of entropy. The second part of the token (token- least 64 bit of entropy. The challenge email message MUST have a
part2, which also contains at least 64 bit of entropy) is single text/plain MIME body part [RFC2045]. The second part of
returned over HTTPS to the ACME client. ACME client concatenates the token (token-part2, which also contains at least 64 bit of
"token-part1" and "token-part2" to create "token", calculates entropy) is returned over HTTPS to the ACME client. ACME client
key-authz (as per Section 8.1 of [I-D.ietf-acme-acme]), then concatenates "token-part1" and "token-part2" to create "token",
included the base64url encoded SHA-256 digest [FIPS180-4] of the calculates key-authz (as per Section 8.1 of
key authorization in a response email message. The response [I-D.ietf-acme-acme]), then includes the base64url encoded
email message has a single text/plain MIME body part. [[Do we SHA-256 digest [FIPS180-4] of the key authorization in the body
need to handle text/html or multipart/alternative? Simplicity of a response email message containing a single text/plain MIME
suggests "no".]] body part [RFC2045].
[[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 4. Open Issues
[[This section should be empty before publication]] [[This section should be empty before publication]]
1. Do we need to handle text/html or multipart/alternative in email
challenge? Simplicity suggests "no".
2. Do we need a proof that ACME client can submit email on behalf of
the user, not just read the challenge using IMAP? Alexey:
probably yes, because intercepting somebody's email is easier
than generating email on the user's behalf.
5. IANA Considerations 5. IANA Considerations
IANA is requested to register a new Identifier Type "email" which IANA is requested to register a new Identifier Type "email" which
corresponds to an (all ASCII) email address [RFC5321]. corresponds to an (all ASCII) email address [RFC5321].
And finally, IANA is requested to register the following ACME And finally, IANA is requested to register the following ACME
challenge types that are used with Identifier Type "email": "email- challenge types that are used with Identifier Type "email": "email-
reply". The reference for it is this document. reply". The reference for it is this document.
6. Security Considerations 6. Security Considerations
TBD. TBD.
7. Normative References 7. Normative References
[FIPS180-4]
National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-4, August 2015,
<https://csrc.nist.gov/publications/detail/fips/180/4/
final>.
[I-D.ietf-acme-acme] [I-D.ietf-acme-acme]
Barnes, R., Hoffman-Andrews, J., and J. Kasten, "Automatic Barnes, R., Hoffman-Andrews, J., and J. Kasten, "Automatic
Certificate Management Environment (ACME)", draft-ietf- Certificate Management Environment (ACME)", draft-ietf-
acme-acme-06 (work in progress), March 2017. acme-acme-06 (work in progress), March 2017.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008, DOI 10.17487/RFC5321, October 2008,
<http://www.rfc-editor.org/info/rfc5321>. <https://www.rfc-editor.org/info/rfc5321>.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, DOI 10.17487/RFC5751, January Specification", RFC 5751, DOI 10.17487/RFC5751, January
2010, <http://www.rfc-editor.org/info/rfc5751>. 2010, <https://www.rfc-editor.org/info/rfc5751>.
[RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized
Email", RFC 6531, DOI 10.17487/RFC6531, February 2012,
<https://www.rfc-editor.org/info/rfc6531>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <http://www.rfc-editor.org/info/rfc7515>. 2015, <https://www.rfc-editor.org/info/rfc7515>.
Author's Address Author's Address
Alexey Melnikov Alexey Melnikov
Isode Ltd Isode Ltd
14 Castle Mews 14 Castle Mews
Hampton, Middlesex TW12 2NP Hampton, Middlesex TW12 2NP
UK UK
EMail: Alexey.Melnikov@isode.com EMail: Alexey.Melnikov@isode.com
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