draft-ietf-acme-email-smime-02.txt   draft-ietf-acme-email-smime-03.txt 
Network Working Group A. Melnikov Network Working Group A. Melnikov
Internet-Draft Isode Ltd Internet-Draft Isode Ltd
Intended status: Informational March 4, 2018 Intended status: Informational September 1, 2018
Expires: September 5, 2018 Expires: March 5, 2019
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-02 draft-ietf-acme-email-smime-03
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 by email users 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
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on September 5, 2018. This Internet-Draft will expire on March 5, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 2 2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. Use of ACME for issuing end user S/MIME certificates . . . . 2 3. Use of ACME for issuing end user S/MIME certificates . . . . 2
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. ACME challenge email . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 3.2. ACME response email . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 3 4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 3 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
[I-D.ietf-acme-acme] is a mechanism for automating certificate [I-D.ietf-acme-acme] is a mechanism for automating certificate
management on the Internet. It enables administrative entities to management on the Internet. It enables administrative entities to
prove effective control over resources like domain names, and prove effective control over resources like domain names, and
automates the process of generating and issuing certificates. automates the process of generating and issuing certificates.
This document describes an extension to ACME for use by S/MIME. This document describes an extension to ACME for use by S/MIME.
Section 3 defines extensions for issuing end user S/MIME [RFC5751] Section 3 defines extensions for issuing end user S/MIME [RFC5750]
certificates. certificates.
2. Conventions Used in This Document 2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Use of ACME for issuing end user S/MIME certificates 3. Use of ACME for issuing end user S/MIME certificates
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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] or Internationalized Email to an (all ASCII) email address [RFC5321] or Internationalized Email
addresses [RFC6531]. This can be used with S/MIME or other similar addresses [RFC6531]. This can be used with S/MIME or other similar
service that requires posession of a certificate tied to an email service that requires posession of a certificate tied to an email
address. address.
Any identifier of type "email" in a new-order request MUST NOT have a
wildcard ("*") character in its value.
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: email address:
1. ACME server generates a "challenge" email message with the 1. ACME server generates a "challenge" email message with the
subject "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 challenge email message MUST have a least 64 bit of entropy. The challenge email message structure
single text/plain MIME body part [RFC2045]. The second part of is described in more details in Section 3.1. The second part of
the token (token-part2, which also contains at least 64 bit of the token (token-part2, which also contains at least 64 bit of
entropy) is returned over HTTPS to the ACME client. ACME client entropy) is returned over HTTPS [RFC2818] to the ACME client.
concatenates "token-part1" and "token-part2" to create "token",
calculates key-authz (as per Section 8.1 of 2. 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 includes the base64url encoded [I-D.ietf-acme-acme]), then includes the base64url encoded
SHA-256 digest [FIPS180-4] of the key authorization in the body SHA-256 digest [FIPS180-4] of the key authorization in the body
of a response email message containing a single text/plain MIME of a response email message containing a single text/plain MIME
body part [RFC2045]. body part [RFC2045]. The response email message structure is
described in more details in Section 3.2
For an identifier of type "email", CSR MUST contain the request email
address in an extensionRequest attribute [RFC2985] requesting a
subjectAltName extension. (These identifiers may appear in any sort
order.)
3.1. ACME challenge email
A "challenge" email message MUST have the following structure:
1. The message Subject header field has the following syntax: "ACME:
<token-part1>", where the prefix "ACME:" is followed by at least
one SP or TAB character. <token-part1> is the base64url encoded
first part of the ACME token.
2. The message MUST include the "Auto-Submitted: auto-generated"
header field [RFC3834]. It MAY include optional parameters as
allowed by syntax of Auto-Submitted header field.
3. The message MUST have a single text/plain MIME body part
[RFC2045], that contains human readable explanation of the
purpose of the message.
Example ACME "challenge" email
Auto-Submitted: auto-generated
Date: Sat, 1 Sep 2018 10:08:55 +0100
Message-ID: <A2299BB.FF7788@example.org>
From: acme-generator@example.org
To: alexey@example.com
Subject: ACME: <base64url-encoded-token-with-64-octets-of-entropy>
Content-Type: text/plain
This is an automatically generated ACME challenge for email address
&lt;alexey@example.com&gt;. If you haven't requested an S/MIME
certificate generation for this email address, be very afraid.
If you did request it, your email client might be able to process
this request automatically, or you might have to paste the first
token part into an external program.
Figure 1
3.2. ACME response email
A "response" email message MUST have the following structure:
1. The message Subject header field has the following syntax: "Re:
ACME: <token-part1>", where the prefix "ACME:" is followed by at
least one SP or TAB character. <token-part1> is the base64url
encoded first part of the ACME token.
2. The To: header field of the response contains the value from the
From: header field of the challenge email.
3. The message MUST have a single text/plain MIME body part
[RFC2045], containing base64url encoded SHA-256 digest
[FIPS180-4] of the key authorization. Note that due to historic
line length limitations in email, line endings (CRLFs) can be
freely inserted in the middle of the encoded digest, so they need
to be ignored when processing it.
Example ACME "response" email
Date: Sat, 1 Sep 2018 11:12:00 +0100
Message-ID: <111-22222-3333333@example.com>
From: alexey@example.com
To: acme-generator@example.org
Subject: Re: ACME: <base64url-encoded-token-with-64-octets-of-entropy>
Content-Type: text/plain
LoqXcYV8q5ONbJQxbmR7SCTNo3tiAXDfowy
jxAjEuX0.9jg46WB3rR_AHD-EBXdN7cBkH1WOu0tA3M9
fm21mqTI
Figure 2
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 1. Do we need to handle text/html or multipart/alternative in email
challenge? Simplicity suggests "no". challenge? Simplicity suggests "no". However, for automated
processing it might be better to use at least multipart/mixed
with a special MIME type.
2. Define a new parameter to "Auto-Submitted: auto-generated", so
that it is easier to figure out that a particilar message is an
ACME challenge message?
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] or
Internationalized Email addresses [RFC6531].
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] [FIPS180-4]
National Institute of Standards and Technology, "Secure National Institute of Standards and Technology, "Secure
Hash Standard (SHS)", FIPS PUB 180-4, August 2015, Hash Standard (SHS)", FIPS PUB 180-4, August 2015,
<https://csrc.nist.gov/publications/detail/fips/180/4/ <https://csrc.nist.gov/publications/detail/fips/180/4/
final>. 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-14 (work in progress), August 2018.
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail [RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996, Bodies", RFC 2045, DOI 10.17487/RFC2045, November 1996,
<https://www.rfc-editor.org/info/rfc2045>. <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,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<https://www.rfc-editor.org/info/rfc2818>.
[RFC2985] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
Classes and Attribute Types Version 2.0", RFC 2985,
DOI 10.17487/RFC2985, November 2000,
<https://www.rfc-editor.org/info/rfc2985>.
[RFC3834] Moore, K., "Recommendations for Automatic Responses to
Electronic Mail", RFC 3834, DOI 10.17487/RFC3834, August
2004, <https://www.rfc-editor.org/info/rfc3834>.
[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,
<https://www.rfc-editor.org/info/rfc5321>. <https://www.rfc-editor.org/info/rfc5321>.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet [RFC5750] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message Mail Extensions (S/MIME) Version 3.2 Certificate
Specification", RFC 5751, DOI 10.17487/RFC5751, January Handling", RFC 5750, DOI 10.17487/RFC5750, January 2010,
2010, <https://www.rfc-editor.org/info/rfc5751>. <https://www.rfc-editor.org/info/rfc5750>.
[RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized [RFC6531] Yao, J. and W. Mao, "SMTP Extension for Internationalized
Email", RFC 6531, DOI 10.17487/RFC6531, February 2012, Email", RFC 6531, DOI 10.17487/RFC6531, February 2012,
<https://www.rfc-editor.org/info/rfc6531>. <https://www.rfc-editor.org/info/rfc6531>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
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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