draft-ietf-acme-email-tls-02.txt   draft-ietf-acme-email-tls-03.txt 
Network Working Group A. Melnikov Network Working Group A. Melnikov
Internet-Draft Isode Ltd Internet-Draft Isode Ltd
Intended status: Informational November 11, 2017 Intended status: Informational March 4, 2018
Expires: May 15, 2018 Expires: September 5, 2018
Extensions to Automatic Certificate Management Environment for email TLS Extensions to Automatic Certificate Management Environment for email TLS
draft-ietf-acme-email-tls-02 draft-ietf-acme-email-tls-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 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-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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 15, 2018. This Internet-Draft will expire on September 5, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 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
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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names-port-numbers.xhtml>. names-port-numbers.xhtml>.
ACME servers compliant with this specification MUST support [RFC7817] ACME servers compliant with this specification MUST support [RFC7817]
(in particular see Section 4 of that document). (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. ACME server MAY check that the
TCP port corresponds to the requested "service", for example that the
port is the assigned default port for the service.
[[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. [[TODO: Make sure that both service name and port number are
into the hash?]] incorporated into the hash]]
3.4. CAPABILITY challenge for email services 3.4. CAPABILITY challenge for email services
For "capability-smtp-00" challenge, ACME client (== SMTP server) For "capability-smtp-00" challenge, ACME client (== SMTP server)
constructs a key authorization from the "token" value provided in the constructs a key authorization from the "token" value provided in the
challenge and the client's account key. The client then computes the challenge and the client's account key. The client then computes the
SHA-256 digest [FIPS180-4] of the key authorization. SMTP server SHA-256 digest [FIPS180-4] of the key authorization. SMTP server
than returns the base64url encoding of this digest as a value of the than returns the base64url encoding of this digest as a value of the
"ACME" EHLO capability. For example: "ACME" EHLO capability. For example:
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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]]
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?) certificate a restriction imposed by this document?) Maybe if
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
running? (How can this be done reliably?) Many email servers
don't allow different certificates to be configured for different
ports they are listening on.
2. Add support for LMTP (RFC 2033)? 2. Add support for LMTP (RFC 2033)?
3. One possible alternative for issuing TLS certificates for email
services is to define a new Identifier Type that specifies
service@domain. The current version of the document just reuses
"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
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