draft-ietf-acme-email-tls-04.txt   draft-ietf-acme-email-tls-05.txt 
Network Working Group A. Melnikov Network Working Group A. Melnikov
Internet-Draft Isode Ltd Internet-Draft Isode Ltd
Intended status: Informational March 20, 2018 Intended status: Informational July 25, 2018
Expires: September 21, 2018 Expires: January 26, 2019
Extensions to Automatic Certificate Management Environment for email TLS Extensions to Automatic Certificate Management Environment for email TLS
draft-ietf-acme-email-tls-04 draft-ietf-acme-email-tls-05
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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working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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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 September 21, 2018. This Internet-Draft will expire on January 26, 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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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, IMAP and POP3 3. Use of ACME for use by TLS-protected SMTP, IMAP and POP3
services . . . . . . . . . . . . . . . . . . . . . . . . . . 2 services . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3.1. "service" JWS header parameter . . . . . . . . . . . . . 3 3.1. "service" field in JSON payload . . . . . . . . . . . . . 3
3.2. "port" JWS header parameter . . . . . . . . . . . . . . . 4 3.2. "port" field in JSON payload . . . . . . . . . . . . . . 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
3.4.1. Registration of the ACME SMTP extension . . . . . . . 6
4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Normative References . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 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.
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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, IMAP and POP3 services 3. Use of ACME for use by TLS-protected SMTP, IMAP and POP3 services
SMTP [RFC5321] (including SMTP Submission [RFC6409]), IMAP [RFC3501] SMTP [RFC5321] (including SMTP Submission [RFC6409]), IMAP [RFC3501]
and POP3 [RFC2449] servers use TLS [RFC5246] to provide server and POP3 [RFC2449] servers use TLS [RFC5246] to provide server
identity authentication, data confidentiality and integrity services. identity authentication, data confidentiality and integrity services.
Such TLS protected email services either use STARTTLS command or run Such TLS protected email services either use STARTTLS command or run
on a separate TLS-protected port . on a separate TLS-protected port [RFC8314].
[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, IMAP and POP3. 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
for more details. for more details. If this JWS header parameter is not included,
the default assigned IANA port for the corresponding "service" is
assumed.
For example, if the ACME 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",
"nonce": "Q_s3MWoqT05TrdkM2MTDcw", "nonce": "Q_s3MWoqT05TrdkM2MTDcw",
"url": "https://example.com/acme/authz/asdf/0", "url": "https://example.com/acme/authz/asdf/0"
"service": "smtp",
"port": 25
}), }),
"payload": base64url({ "payload": base64url({
"type": "dns-email-00", "type": "dns-email-00",
"service": "smtp",
"port": 25,
"keyAuthorization": "IlirfxKKXA...vb29HhjjLPSggQiE" "keyAuthorization": "IlirfxKKXA...vb29HhjjLPSggQiE"
}), }),
"signature": "7cbg5JO1Gf5YLjjF...SpkUfcdPai9uVYYU" "signature": "7cbg5JO1Gf5YLjjF...SpkUfcdPai9uVYYU"
} }
Figure 1 Figure 1
3.1. "service" JWS header parameter 3.1. "service" field in JSON payload
The "service" JWS header parameter specifies the service for which The "service" field in JSON payload 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>. 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" field in JSON payload
The "port" JWS header parameter specifies the TCP port number where The "port" field in JSON payload specifies the TCP port number where
the corresponding service is running. ACME server MAY check that the the corresponding service is running. ACME server MAY check that the
TCP port corresponds to the requested "service", for example that the TCP port corresponds to the requested "service", for example that the
port is the assigned default port for the service. port is the assigned default IANA 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 IMAPS 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. [[TODO: Make sure that both service name and port number are
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:
250-smtp.example.com 250-smtp.example.com
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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 is relevant Note that in the above example only presence of the ACME is relevant
as far as this document is concerned. as far as this document is concerned.
Figure 2 Figure 2
The ACME SMTP extension is formerly defined in Section 3.4.1.
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. IMAP 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
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S: UIDL S: UIDL
S: ACME gfj9Xq...Rg85nM S: ACME gfj9Xq...Rg85nM
S: IMPLEMENTATION Shlemazle-Plotz-v915 S: IMPLEMENTATION Shlemazle-Plotz-v915
S: . S: .
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
3.4.1. Registration of the ACME SMTP extension
The ACME SMTP service extension is defined as follows:
1. The textual name of this extension is "ACME for SMTP".
2. The EHLO keyword value associated with this extension is "ACME".
3. The EHLO keyword has a single required parameter which is a
base64url encoded SHA-256 hash, which is 44 octets in length.
4. This extension doesn't define any new SMTP verbs.
5. This extension doesn't add any new parameters to MAIL FROM or
RCPT TO commands.
6. The ACME extension is valid for the submission service [RFC6409]
(default port number 587) or its version running directly over
TLS [RFC8314] ("submissions" service, default port number 465) .
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. The cleanest way is to change
"service" to "services", change "port" to "ports" and make both
of them arrays.
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",
"capability-imap" and "capability-pop". The reference for all of "capability-imap" and "capability-pop". The reference for all of
them is this document. them is this document.
6. Security Considerations 6. Security Considerations
TBD. Security Considerations from [I-D.ietf-acme-acme] relevant to the DNS
challenge type are also relevant to "dns-email".
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., McCarney, D., and J.
Certificate Management Environment (ACME)", draft-ietf- Kasten, "Automatic Certificate Management Environment
acme-acme-06 (work in progress), March 2017. (ACME)", draft-ietf-acme-acme-12 (work in progress), April
2018.
[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 [RFC2449] Gellens, R., Newman, C., and L. Lundblade, "POP3 Extension
Mechanism", RFC 2449, DOI 10.17487/RFC2449, November 1998, Mechanism", RFC 2449, DOI 10.17487/RFC2449, November 1998,
<https://www.rfc-editor.org/info/rfc2449>. <https://www.rfc-editor.org/info/rfc2449>.
skipping to change at page 8, line 5 skipping to change at page 8, line 29
[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) [RFC7817] Melnikov, A., "Updated Transport Layer Security (TLS)
Server Identity Check Procedure for Email-Related Server Identity Check Procedure for Email-Related
Protocols", RFC 7817, DOI 10.17487/RFC7817, March 2016, Protocols", RFC 7817, DOI 10.17487/RFC7817, March 2016,
<https://www.rfc-editor.org/info/rfc7817>. <https://www.rfc-editor.org/info/rfc7817>.
[RFC8314] Moore, K. and C. Newman, "Cleartext Considered Obsolete:
Use of Transport Layer Security (TLS) for Email Submission
and Access", RFC 8314, DOI 10.17487/RFC8314, January 2018,
<https://www.rfc-editor.org/info/rfc8314>.
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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