draft-ietf-acme-email-tls-03.txt   draft-ietf-acme-email-tls-04.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 March 20, 2018
Expires: September 5, 2018 Expires: September 21, 2018
Extensions to Automatic Certificate Management Environment for email TLS Extensions to Automatic Certificate Management Environment for email TLS
draft-ietf-acme-email-tls-03 draft-ietf-acme-email-tls-04
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 TLS email services. certificates for use by TLS email services.
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 September 21, 2018.
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.
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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
2. Conventions Used in This Document . . . . . . . . . . . . . . 2 2. Conventions Used in This Document . . . . . . . . . . . . . . 2
3. Use of ACME for use by TLS-protected SMTP and IMAP services . 2 3. Use of ACME for use by TLS-protected SMTP, IMAP and POP3
services . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3.1. "service" JWS header parameter . . . . . . . . . . . . . 3 3.1. "service" JWS header parameter . . . . . . . . . . . . . 3
3.2. "port" JWS header parameter . . . . . . . . . . . . . . . 4 3.2. "port" JWS header parameter . . . . . . . . . . . . . . . 4
3.3. DNS challenge for email services . . . . . . . . . . . . 4 3.3. DNS challenge for email services . . . . . . . . . . . . 4
3.4. CAPABILITY challenge for email services . . . . . . . . . 4 3.4. CAPABILITY challenge for email services . . . . . . . . . 4
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
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 extensions to ACME for use by email services. This document describes extensions to ACME for use by email services.
Section 3 defines extensions for how email services (such as SMTP, Section 3 defines extensions for how email services (such as SMTP,
IMAP) can get certificates for use with TLS. IMAP and POP3) can get certificates for use with TLS.
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 use by TLS-protected SMTP and IMAP services 3. Use of ACME for use by TLS-protected SMTP, IMAP and POP3 services
SMTP [RFC5321] (including SMTP Submission [RFC6409]) and IMAP SMTP [RFC5321] (including SMTP Submission [RFC6409]), IMAP [RFC3501]
[RFC3501] servers use TLS [RFC5246] to provide server identity and POP3 [RFC2449] servers use TLS [RFC5246] to provide server
authentication, data confidentiality and integrity services. Such identity authentication, data confidentiality and integrity services.
TLS protected email services either use STARTTLS command or run on a Such TLS protected email services either use STARTTLS command or run
separate TLS-protected port . on a separate TLS-protected port .
[I-D.ietf-acme-acme] defines several challenge types that can be [I-D.ietf-acme-acme] defines several challenge types that can be
extended for use by email services. This document also defines some extended for use by email services. This document also defines some
new challenge types specific to SMTP and IMAP. new challenge types specific to SMTP, IMAP and POP3.
In order to use these challenges JWS [RFC7515] object used by In order to use these challenges JWS [RFC7515] object used by
[I-D.ietf-acme-acme] is extended. The following extra requirements [I-D.ietf-acme-acme] is extended. The following extra requirements
are in addition to requirements on JWS objects sent in ACME defined are in addition to requirements on JWS objects sent in ACME defined
in Section 6.2 of [I-D.ietf-acme-acme]: in Section 6.2 of [I-D.ietf-acme-acme]:
1. "service" JWS header parameter MUST be included. See Section 3.1 1. "service" JWS header parameter MUST be included. See Section 3.1
for more details. for more details.
2. "port" JWS header parameter SHOULD be included. See Section 3.2 2. "port" JWS header parameter SHOULD be included. See Section 3.2
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or or
* CAPABILITY IMAP4rev1 LOGINDISABLED LITERAL+ ENABLE STARTTLS ACME=gfj9Xq...Rg85nM * CAPABILITY IMAP4rev1 LOGINDISABLED LITERAL+ ENABLE STARTTLS ACME=gfj9Xq...Rg85nM
Note that in the above example only presence of the ACME capability Note that in the above example only presence of the ACME capability
token is relevant as far as this document is concerned. token is relevant as far as this document is concerned.
Figure 3 Figure 3
[[TODO: Add support for POP3 as per John Levine]] Similarly, "capability-pop-00" challenge, ACME client (== POP3
server) constructs a key authorization from the "token" value
provided in the challenge and the client's account key. The client
then computes the SHA-256 digest [FIPS180-4] of the key
authorization. POP3 server than returns the base64url encoding of
this digest as a value of the "ACME" capability in response to CAPA
command [RFC2449]:
C: CAPA
S: +OK Capability list follows
S: TOP
S: SASL CRAM-MD5 KERBEROS_V4
S: UIDL
S: ACME gfj9Xq...Rg85nM
S: IMPLEMENTATION Shlemazle-Plotz-v915
S: .
Note that in the above example only presence of the ACME capability
token is relevant as far as this document is concerned.
Figure 3
4. Open Issues 4. Open Issues
[[This section should be empty before publication]] [[This section should be empty before publication]]
1. Should the same certificate be allowed to be used on both IMAP 1. Should the same certificate be allowed to be used on both IMAP
(143) and IMAPS (993) ports? (These ports have different service (143) and IMAPS (993) ports? (These ports have different service
names associated with them. Is 1 service/port per ACME names associated with them. Is 1 service/port per ACME
certificate a restriction imposed by this document?) Maybe if certificate a restriction imposed by this document?) Maybe if
the ACME server sees a request for port 143 (or 993), it can the ACME server sees a request for port 143 (or 993), it can
include SRV-ID for the other port, if it can verify that both are include SRV-ID for the other port, if it can verify that both are
running? (How can this be done reliably?) Many email servers running? (How can this be done reliably?) Many email servers
don't allow different certificates to be configured for different don't allow different certificates to be configured for different
ports they are listening on. ports they are listening on.
2. Add support for LMTP (RFC 2033)? 2. Add support for LMTP (RFC 2033)?
5. IANA Considerations 5. IANA Considerations
IANA is requested to register the following ACME challenge types that IANA is requested to register the following ACME challenge types that
are used with Identifier Type "dns": "dns-email", "capability-smtp" are used with Identifier Type "dns": "dns-email", "capability-smtp",
and "capability-imap". The reference for all of them is this "capability-imap" and "capability-pop". The reference for all of
document. them 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,
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[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.
[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>.
[RFC2449] Gellens, R., Newman, C., and L. Lundblade, "POP3 Extension
Mechanism", RFC 2449, DOI 10.17487/RFC2449, November 1998,
<https://www.rfc-editor.org/info/rfc2449>.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003, 4rev1", RFC 3501, DOI 10.17487/RFC3501, March 2003,
<https://www.rfc-editor.org/info/rfc3501>. <https://www.rfc-editor.org/info/rfc3501>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, (TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008, DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>. <https://www.rfc-editor.org/info/rfc5246>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
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