draft-ietf-uta-email-tls-certs-02.txt   draft-ietf-uta-email-tls-certs-03.txt 
Network Working Group A. Melnikov Network Working Group A. Melnikov
Internet-Draft Isode Ltd Internet-Draft Isode Ltd
Updates: 2595, 3207, 3501, 5804 (if March 23, 2015 Updates: 2595, 3207, 3501, 5804 (if June 17, 2015
approved) approved)
Intended status: Standards Track Intended status: Standards Track
Expires: September 24, 2015 Expires: December 19, 2015
Updated TLS Server Identity Check Procedure for Email Related Protocols Updated TLS Server Identity Check Procedure for Email Related Protocols
draft-ietf-uta-email-tls-certs-02 draft-ietf-uta-email-tls-certs-03
Abstract Abstract
This document describes TLS server identity verification procedure This document describes TLS server identity verification procedure
for SMTP Submission, IMAP, POP and ManageSieve clients. It replaces for SMTP Submission, IMAP, POP and ManageSieve clients. It replaces
Section 2.4 of RFC 2595. Section 2.4 of RFC 2595.
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 24, 2015. This Internet-Draft will expire on December 19, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://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. Email Server Certificate Verification Rules . . . . . . . . . 3 3. Email Server Certificate Verification Rules . . . . . . . . . 3
4. Compliance Checklist for Certificate Authorities . . . . . . 4 4. Compliance Checklist for Certification Authorities . . . . . 4
5. Compliance Checklist for Mail Service Providers and 5. Compliance Checklist for Mail Service Providers and
Certificate Signing Request generation tools . . . . . . . . 4 Certificate Signing Request generation tools . . . . . . . . 4
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5 8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6 9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 6 9.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 7
Appendix B. Changes since draft-ietf-uta-email-tls-certs-00 . . 7 Appendix B. Changes since draft-ietf-uta-email-tls-certs-00 . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
Use of TLS by SMTP Submission, IMAP, POP and ManageSieve clients is Use of TLS by SMTP Submission, IMAP, POP and ManageSieve clients is
described in [RFC3207], [RFC3501], [RFC2595] and [RFC5804] described in [RFC3207], [RFC3501], [RFC2595] and [RFC5804]
respectively. Each of the documents describes slightly different respectively. Each of the documents describes slightly different
rules for server certificate identity verification (or doesn't define rules for server certificate identity verification (or doesn't define
any rules at all). In reality, email client and server developers any rules at all). In reality, email client and server developers
implement many of these protocols at the same time, so it would be implement many of these protocols at the same time, so it would be
good to define modern and consistent rules for verifying email server good to define modern and consistent rules for verifying email server
identities using TLS. identities using TLS.
This document describes the updated TLS server identity verification This document describes the updated TLS server identity verification
procedure for SMTP Submission [RFC4409] [RFC3207], IMAP [RFC3501], procedure for SMTP Submission [RFC6409] [RFC3207], IMAP [RFC3501],
POP [RFC1939] and ManageSieve [RFC5804] clients. It replaces POP [RFC1939] and ManageSieve [RFC5804] clients. It replaces
Section 2.4 of RFC 2595. Section 2.4 of RFC 2595.
Note that this document doesn't apply to use of TLS in MTA-to-MTA Note that this document doesn't apply to use of TLS in MTA-to-MTA
SMTP. SMTP.
The main goal of the document is to provide consistent TLS server The main goal of the document is to provide consistent TLS server
identity verification procedure across multiple email related identity verification procedure across multiple email related
protocols. This should make it easier for Certificate Authorities protocols. This should make it easier for Certification Authorities
and ISPs to deploy TLS for email use, and would enable email client and ISPs to deploy TLS for email use, and would enable email client
developers to write more secure code. developers to write more secure code.
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. Email Server Certificate Verification Rules 3. Email Server Certificate Verification Rules
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5. Email protocols allow use of certain wilcards in identifiers 5. Email protocols allow use of certain wilcards in identifiers
presented by email servers. The "*" wildcard character MAY be presented by email servers. The "*" wildcard character MAY be
used as the left-most name component of DNS-ID or CN-ID in the used as the left-most name component of DNS-ID or CN-ID in the
certificate. For example, a DNS-ID of *.example.com would match certificate. For example, a DNS-ID of *.example.com would match
a.example.com, foo.example.com, etc. but would not match a.example.com, foo.example.com, etc. but would not match
example.com. Note that the wildcard character MUST NOT be used example.com. Note that the wildcard character MUST NOT be used
as a fragment of the left-most name component (e.g., as a fragment of the left-most name component (e.g.,
*oo.example.com, f*o.example.com, or foo*.example.com). *oo.example.com, f*o.example.com, or foo*.example.com).
4. Compliance Checklist for Certificate Authorities 4. Compliance Checklist for Certification Authorities
1. CA MUST support issuance of server certificates with DNS-ID 1. CA MUST support issuance of server certificates with DNS-ID
identifier type (subjectAltName of dNSName type [RFC5280]). identifier type (subjectAltName of dNSName type [RFC5280]).
2. CA MUST support issuance of server certificates with SRV-ID 2. CA MUST support issuance of server certificates with SRV-ID
identifier type (subjectAltName of SRVName type [RFC4985]) for identifier type (subjectAltName of SRVName type [RFC4985]) for
each type of email service. each type of email service.
3. For backward compatibility with deployed client base, CA MUST 3. For backward compatibility with deployed client base, CA MUST
support issuance of server certificates with CN-ID identifier support issuance of server certificates with CN-ID identifier
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DNS-ID or CN-ID in Certificate Signing Requests. DNS-ID or CN-ID in Certificate Signing Requests.
6. Examples 6. Examples
Consider an IMAP-accessible email server which supports both IMAP and Consider an IMAP-accessible email server which supports both IMAP and
IMAPS (IMAP-over-TLS) at the host "mail.example.net" servicing email IMAPS (IMAP-over-TLS) at the host "mail.example.net" servicing email
addresses of the form "user@example.net" and discoverable via DNS SRV addresses of the form "user@example.net" and discoverable via DNS SRV
lookups in domain "example.net" (DNS SRV records lookups in domain "example.net" (DNS SRV records
"_imap._tcp.example.net" and "_imaps._tcp.example.net"). A "_imap._tcp.example.net" and "_imaps._tcp.example.net"). A
certificate for this service needs to include SRV-IDs of certificate for this service needs to include SRV-IDs of
"_imap.example.net" and "_imaps.example.net" (see [RFC6186]. Note "_imap.example.net" (when STARTTLS is used on the IMAP port) and
that unlike DNS SRV there is no "_tcp" component in SRV-IDs) along "_imaps.example.net" (when TLS is used on IMAPS port). See [RFC6186]
with DNS-IDs of "example.net" and "mail.example.net". It might also for more details. (Note that unlike DNS SRV there is no "_tcp"
include CN-IDs of "mail.example.net" for backward compatibility with component in SRV-IDs) along with DNS-IDs of "example.net" and
deployed infrastructure. "mail.example.net". It might also include CN-IDs of
"mail.example.net" for backward compatibility with deployed
infrastructure.
Consider an SMTP Submission server at the host "submit.example.net" Consider an SMTP Submission server at the host "submit.example.net"
servicing email addresses of the form "user@example.net" and servicing email addresses of the form "user@example.net" and
discoverable via DNS SRV lookups in domain "example.net" (DNS SRV discoverable via DNS SRV lookups in domain "example.net" (DNS SRV
records "_submission._tcp.example.net"). A certificate for this records "_submission._tcp.example.net"). A certificate for this
service needs to include SRV-IDs of "_submission.example.net" (see service needs to include SRV-IDs of "_submission.example.net" (see
[RFC6186]) along with DNS-IDs of "example.net" and [RFC6186]) along with DNS-IDs of "example.net" and
"submit.example.net". It might also include CN-IDs of "submit.example.net". It might also include CN-IDs of
"submit.example.net" for backward compatibility with deployed "submit.example.net" for backward compatibility with deployed
infrastructure. infrastructure.
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7. IANA Considerations 7. IANA Considerations
This document doesn't require any action from IANA. This document doesn't require any action from IANA.
8. Security Considerations 8. Security Considerations
The goal of this document is to improve interoperability and thus The goal of this document is to improve interoperability and thus
security of email clients wishing to access email servers over TLS security of email clients wishing to access email servers over TLS
protected email protocols, by specifying a consistent set of rules protected email protocols, by specifying a consistent set of rules
that email service providers, email client writers and certificate that email service providers, email client writers and Certification
authorities can use when creating server certificates. Authorities can use when creating server certificates.
9. References 9. References
9.1. Normative References 9.1. Normative References
[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, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
October 2008. October 2008.
[RFC4409] Gellens, R. and J. Klensin, "Message Submission for Mail", [RFC6409] Gellens, R. and J. Klensin, "Message Submission for Mail",
RFC 4409, April 2006. STD 72, RFC 6409, November 2011.
[RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over [RFC3207] Hoffman, P., "SMTP Service Extension for Secure SMTP over
Transport Layer Security", RFC 3207, February 2002. Transport Layer Security", RFC 3207, February 2002.
[RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION [RFC3501] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION
4rev1", RFC 3501, March 2003. 4rev1", RFC 3501, March 2003.
[RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3", [RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3",
STD 53, RFC 1939, May 1996. STD 53, RFC 1939, May 1996.
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9.2. Informative References 9.2. Informative References
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC [RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", RFC
2595, June 1999. 2595, June 1999.
[RFC6186] Daboo, C., "Use of SRV Records for Locating Email [RFC6186] Daboo, C., "Use of SRV Records for Locating Email
Submission/Access Services", RFC 6186, March 2011. Submission/Access Services", RFC 6186, March 2011.
Appendix A. Acknowledgements Appendix A. Acknowledgements
Thank you to Chris Newman for comments on this document. Thank you to Chris Newman and Sean Turner for comments on this
document.
The editor of this document copied lots of text from RFC 2595 and RFC The editor of this document copied lots of text from RFC 2595 and RFC
6125, so the hard work of editors of these document is appreciated. 6125, so the hard work of editors of these document is appreciated.
Appendix B. Changes since draft-ietf-uta-email-tls-certs-00 Appendix B. Changes since draft-ietf-uta-email-tls-certs-00
[[Note to RFC Editor: Please delete this section before publication]] [[Note to RFC Editor: Please delete this section before publication]]
Added another example, clarified that subjectAltName and DNS SRV are Added another example, clarified that subjectAltName and DNS SRV are
using slightly different syntax. using slightly different syntax.
 End of changes. 14 change blocks. 
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