draft-ietf-acme-email-tls-01.txt   draft-ietf-acme-email-tls-02.txt 
Network Working Group A. Melnikov Network Working Group A. Melnikov
Internet-Draft Isode Ltd Internet-Draft Isode Ltd
Intended status: Informational October 28, 2017 Intended status: Informational November 11, 2017
Expires: May 1, 2018 Expires: May 15, 2018
Extensions to Automatic Certificate Management Environment for email TLS Extensions to Automatic Certificate Management Environment for email TLS
draft-ietf-acme-email-tls-01 draft-ietf-acme-email-tls-02
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
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 1, 2018. This Internet-Draft will expire on May 15, 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.
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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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 use by TLS-protected SMTP and IMAP services . 2 3. Use of ACME for use by TLS-protected SMTP and IMAP services . 2
3.1. "service" JWS header parameter . . . . . . . . . . . . . 3 3.1. "service" JWS header parameter . . . . . . . . . . . . . 3
3.2. "port" JWS header parameter . . . . . . . . . . . . . . . 3 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 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 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,
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new challenge types specific to SMTP and IMAP. new challenge types specific to SMTP and IMAP.
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 MUST (SHOULD?) be included. See 2. "port" JWS header parameter SHOULD be included. See Section 3.2
Section 3.2 for more details. for more details.
For example, if the client were to respond to the "dns-email-00" For example, if the ACME client were to respond to the "dns-email-00"
challenge, it would send the following request: challenge, it would send the following request:
POST /acme/authz/asdf/0 HTTP/1.1 POST /acme/authz/asdf/0 HTTP/1.1
Host: example.com Host: example.com
Content-Type: application/jose+json Content-Type: application/jose+json
{ {
"protected": base64url({ "protected": base64url({
"alg": "ES256", "alg": "ES256",
"kid": "https://example.com/acme/acct/1", "kid": "https://example.com/acme/acct/1",
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} }
Figure 1 Figure 1
3.1. "service" JWS header parameter 3.1. "service" JWS header parameter
The "service" JWS header parameter specifies the service for which The "service" JWS header parameter specifies the service for which
TLS server certificate should be issued. Valid values come from TLS server certificate should be issued. Valid values come from
"Service Names and Transport Protocol Port Numbers" IANA registry "Service Names and Transport Protocol Port Numbers" IANA registry
<https://www.iana.org/assignments/service-names-port-numbers/service- <https://www.iana.org/assignments/service-names-port-numbers/service-
names-port-numbers.xhtml>. ACME server MAY include SRV-ID [RFC6125] names-port-numbers.xhtml>.
subjectAltNames in issued certificates.
ACME servers compliant with this specification MUST support [RFC7817]
(in particular see Section 4 of that document).
[[This parameter might have applicability beyond email services.]] [[This parameter might have applicability beyond email services.]]
3.2. "port" JWS header parameter 3.2. "port" JWS header parameter
The "port" JWS header parameter specifies the TCP port number where The "port" JWS header parameter specifies the TCP port number where
the corresponding service is running. the corresponding service is running.
[[This parameter might have applicability beyond email services.]] [[This parameter might have applicability beyond email services.]]
3.3. DNS challenge for email services 3.3. DNS challenge for email services
"dns-email-00" is very similar to "dns-01" defined in Section 8.4 of "dns-email-00" is very similar to "dns-01" defined in Section 8.4 of
[I-D.ietf-acme-acme]. [I-D.ietf-acme-acme].
The difference between processing of "dns-email-00" and "dns-01" are The difference between processing of "dns-email-00" and "dns-01" are
listed below: listed below:
1. The TXT record used to validate this challenge is 1. The TXT record used to validate this challenge is
_<port>._<service>_acme-challenge.<domain>. For example, for _<port>._<service>._acme-challenge.<domain>. For example, for
domain "example.com" and IMAP service running on port 993, the domain "example.com" and IMAP service running on port 993, the
TXT record name is _993._imaps._acme-challenge.example.com. For TXT record name is _993._imaps._acme-challenge.example.com. For
domain "example.net" and IMAP service running on port 143, the domain "example.net" and IMAP service running on port 143, the
TXT record name is _143._imap._acme-challenge.example.next. TXT record name is _143._imap._acme-challenge.example.next.
2. [[OPEN ISSUE: Should service name and port number be incorporated 2. [[OPEN ISSUE: Should service name and port number be incorporated
into the hash?]] into the hash?]]
3.4. CAPABILITY challenge for email services 3.4. CAPABILITY challenge for email services
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250-HELP 250-HELP
250-DSN 250-DSN
250-CHUNKING 250-CHUNKING
250-AUTH SCRAM-SHA-1 250-AUTH SCRAM-SHA-1
250-AUTH=SCRAM-SHA-1 250-AUTH=SCRAM-SHA-1
250-STARTTLS 250-STARTTLS
250-ACME gfj9Xq...Rg85nM 250-ACME gfj9Xq...Rg85nM
250-MT-PRIORITY 250-MT-PRIORITY
250 ENHANCEDSTATUSCODES 250 ENHANCEDSTATUSCODES
Note that in the above example only presence of the ACME and possibly Note that in the above example only presence of the ACME is relevant
STARTTLS capabilities is relevant as far as this document is as far as this document is concerned.
concerned.
Figure 2 Figure 2
Similarly, "capability-imap-00" challenge, ACME client (== IMAP Similarly, "capability-imap-00" challenge, ACME client (== IMAP
server) constructs a key authorization from the "token" value server) constructs a key authorization from the "token" value
provided in the challenge and the client's account key. The client provided in the challenge and the client's account key. The client
then computes the SHA-256 digest [FIPS180-4] of the key then computes the SHA-256 digest [FIPS180-4] of the key
authorization. SMTP server than returns the base64url encoding of authorization. IMAP server than returns the base64url encoding of
this digest as a value of the "ACME" capability: this digest as a value of the "ACME" capability:
* OK [CAPABILITY IMAP4rev1 LOGINDISABLED LITERAL+ ENABLE STARTTLS ACME=gfj9Xq...Rg85nM] Example IMAP4rev1 server ready * OK [CAPABILITY IMAP4rev1 LOGINDISABLED LITERAL+ ENABLE STARTTLS ACME=gfj9Xq...Rg85nM] Example IMAP4rev1 server ready
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 and possibly Note that in the above example only presence of the ACME capability
STARTTLS capabilities is relevant as far as this document is token is relevant as far as this document is concerned.
concerned.
Figure 3 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? (143) and IMAPS (993) ports? (These ports have different service
names associated with them. Is 1 service/port per ACME
2. Add support for LMTP? certificate a restriction imposed by this document?)
2. Add support for LMTP (RFC 2033)?
3. One possible alternative for issuing TLS certificates for email 3. One possible alternative for issuing TLS certificates for email
services is to define a new Identifier Type that specifies services is to define a new Identifier Type that specifies
service@domain. The current version of the document just reuses service@domain. The current version of the document just reuses
"dns". "dns".
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 and "capability-imap". The reference for all of them is this
document. 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.
[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>.
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2011, <https://www.rfc-editor.org/info/rfc6125>. 2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6409] Gellens, R. and J. Klensin, "Message Submission for Mail", [RFC6409] Gellens, R. and J. Klensin, "Message Submission for Mail",
STD 72, RFC 6409, DOI 10.17487/RFC6409, November 2011, STD 72, RFC 6409, DOI 10.17487/RFC6409, November 2011,
<https://www.rfc-editor.org/info/rfc6409>. <https://www.rfc-editor.org/info/rfc6409>.
[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, <https://www.rfc-editor.org/info/rfc7515>. 2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7817] Melnikov, A., "Updated Transport Layer Security (TLS)
Server Identity Check Procedure for Email-Related
Protocols", RFC 7817, DOI 10.17487/RFC7817, March 2016,
<https://www.rfc-editor.org/info/rfc7817>.
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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