draft-ietf-uta-email-tls-certs-05.txt   draft-ietf-uta-email-tls-certs-06.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 September 20, 2015 Updates: 2595, 3207, 3501, 5804 (if December 4, 2015
approved) approved)
Intended status: Standards Track Intended status: Standards Track
Expires: March 23, 2016 Expires: June 6, 2016
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-05 draft-ietf-uta-email-tls-certs-06
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, updates Section 4.1 of RFC 3207, updates Section 2.4 of RFC 2595, updates Section 4.1 of RFC 3207, updates
Section 11.1 of RFC 3501, updates Section 2.2.1 of RFC 5804. Section 11.1 of RFC 3501, updates Section 2.2.1 of RFC 5804.
Status of This Memo Status of This Memo
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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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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 March 23, 2016. This Internet-Draft will expire on June 6, 2016.
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.
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Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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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 . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Email Server Certificate Verification Rules . . . . . . . . . 3 3. Email Server Certificate Verification Rules . . . . . . . . . 3
4. Compliance Checklist for Certification Authorities . . . . . 4 4. Compliance Checklist for Certification Authorities . . . . . 5
4.1. Notes on handling of SRV-ID by Certificate Authorities . 5
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 . . . . . . . . 5
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.1. Notes on hosted domains . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 6 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 9 9.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix B. Changes since draft-ietf-uta-email-tls-certs-00 . . 9 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9 Appendix B. Changes since draft-ietf-uta-email-tls-certs-00 . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
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 [RFC6409] [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 This document provides a consistent TLS server identity verification
identity verification procedure across multiple email related procedure across multiple email related protocols. This should make
protocols. This should make it easier for Certification Authorities it easier for Certification Authorities and ISPs to deploy TLS for
and ISPs to deploy TLS for email use, and would enable email client email use, and would enable email client developers to write more
developers to write more secure code. 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].
The following terms or concepts are used through the document: The following terms or concepts are used through the document:
reference identifier: (as defined in [RFC6125]) One of the domain reference identifier: (as defined in [RFC6125]) One of the domain
names associated by the email (i.e., an SMTP, IMAP, POP3 or names associated by the email (i.e., an SMTP, IMAP, POP3 or
ManageSieve) client with the destination email server and ManageSieve) client with the target email server and optionally an
optionally an application service type for performing name checks application service type for performing name checks on the server
on the server certificate. When name checks are applicable, at certificate. When name checks are applicable, at least one of the
least one of the reference identifiers MUST match an [RFC6125] reference identifiers MUST match an [RFC6125] DNS-ID or SRV-ID (or
DNS-ID or SRV-ID (or if none are present the [RFC6125] CN-ID) of if none are present the [RFC6125] CN-ID) of the server
the server certificate. certificate.
CN-ID, DNS-ID, SRV-ID and URI-ID are identifier types (see [RFC6125]
for details). For convenience, their short definitions from
[RFC6125] are listed below:
CN-ID = a Relative Distinguished Name (RDN) in the certificate
subject field that contains one and only one attribute-type-and-
value pair of type Common Name (CN), where the value matches the
overall form of a domain name (informally, dot- separated letter-
digit-hyphen labels).
DNS-ID = a subjectAltName entry of type dNSName
SRV-ID = a subjectAltName entry of type otherName whose name form
is SRVName
URI-ID = a subjectAltName entry of type uniformResourceIdentifier
whose value includes both (i) a "scheme" and (ii) a "host"
component (or its equivalent) that matches the "reg-name" rule
(where the quoted terms represent the associated [RFC5234]
productions from [RFC3986]).
3. Email Server Certificate Verification Rules 3. Email Server Certificate Verification Rules
During a TLS negotiation, an email client (i.e., an SMTP, IMAP, POP3 During a TLS negotiation, an email client (i.e., an SMTP, IMAP, POP3
or ManageSieve client) MUST check its understanding of the server or ManageSieve client) MUST check its understanding of the server
hostname against the server's identity as presented in the server hostname against the server's identity as presented in the server
Certificate message, in order to prevent man-in-the-middle attacks. Certificate message, in order to prevent man-in-the-middle attacks.
This check is only performed after the server certificate passes
certification path validation as described in Section 6 of [RFC5280].
Matching is performed according to the rules specified in Section 6 Matching is performed according to the rules specified in Section 6
of [RFC6125], including "certificate pinning" and the procedure on of [RFC6125], including "certificate pinning" and the procedure on
failure to match. The following inputs are used by the verification failure to match. The following inputs are used by the verification
procedure used in [RFC6125]: procedure used in [RFC6125]:
1. For DNS-ID and CN-ID identifier types the client MUST use one or 1. For DNS-ID and CN-ID identifier types the client MUST use one or
more of the following as "reference identifiers": (a) the right more of the following as "reference identifiers": (a) the domain
hand side of the email address, (b) the hostname it used to open portion of the user's email address, (b) the hostname it used to
the connection (without CNAME canonicalization). The client MAY open the connection (without CNAME canonicalization). The client
also use (c) a value securely derived from (a) or (b), such as MAY also use (c) a value securely derived from (a) or (b), such
using "secure" DNSSEC validated lookup. as using "secure" DNSSEC validated lookup.
2. When using email service discovery procedure specified in 2. When using email service discovery procedure specified in
[RFC6186] the client MUST also use the right hand side of the [RFC6186] the client MUST also use the domain portion of the
email address as another "reference identifier" to compare user's email address as another "reference identifier" to compare
against SRV-ID identifier in the server certificate. against SRV-ID identifier in the server certificate.
The rules and guidelines defined in [RFC6125] apply to an email The rules and guidelines defined in [RFC6125] apply to an email
server certificates, with the following supplemental rules: server certificate, with the following supplemental rules:
1. Support for the DNS-ID identifier type (subjectAltName of dNSName 1. Support for the DNS-ID identifier type (subjectAltName of dNSName
type [RFC5280]) is REQUIRED in Email client software type [RFC5280]) is REQUIRED in Email client software
implementations. implementations.
2. Support for the SRV-ID identifier type (subjectAltName of SRVName 2. Support for the SRV-ID identifier type (subjectAltName of SRVName
type [RFC4985]) is REQUIRED for email client software type [RFC4985]) is REQUIRED for email client software
implementations that support [RFC6186]. List of SRV-ID types for implementations that support [RFC6186]. List of SRV-ID types for
email services is specified in [RFC6186]. For the ManageSieve email services is specified in [RFC6186]. For the ManageSieve
protocol the service name "sieve" is used. protocol the service name "sieve" is used.
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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 Certification 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. See Section 4.1 for more discussion
on what this means for Certification Authorities.
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
type (CN attribute from the subject name, see [RFC6125]). type (CN attribute from the subject name, see [RFC6125]).
4. CA MAY allow "*" (wildcard) as the left-most name component of 4. CA MAY allow "*" (wildcard) as the left-most name component of
DNS-ID or CN-ID in server certificates it issues. DNS-ID or CN-ID in server certificates it issues.
4.1. Notes on handling of SRV-ID by Certificate Authorities
TBD. List some possible recommendations and limitations of different
approaches.
5. Compliance Checklist for Mail Service Providers and Certificate 5. Compliance Checklist for Mail Service Providers and Certificate
Signing Request generation tools Signing Request generation tools
1. SHOULD include the DNS-ID identifier type (subjectAltName of 1. MUST include the DNS-ID identifier type in Certificate Signing
dNSName type [RFC5280]) in Certificate Signing Requests for both Requests for the host name(s) where the email server(s) are
the right hand side of served email addresses, as well as for the running. SHOULD include the DNS-ID identifier type in
host name where the email server(s) are running. Certificate Signing Requests for the domain portion of served
email addresses.
2. If the email services provided are discoverable using DNS SRV as 2. If the email services provided are discoverable using DNS SRV as
specified in [RFC6186], the Mail Service Provider MUST include specified in [RFC6186], the Mail Service Provider MUST include
the SRV-ID identifier type (subjectAltName of SRVName type the SRV-ID identifier type for each type of email service in
[RFC4985]) for each type of email service in Certificate Signing Certificate Signing Requests.
Requests.
3. SHOULD include CN-ID identifier type (CN attribute from the 3. SHOULD include CN-ID identifier type for the host name where the
subject name, see [RFC6125]) for the host name where the email email server(s) is running in Certificate Signing Requests for
server(s) is running in Certificate Signing Requests for backward backward compatibility with deployed email clients. (Note, a
compatibility with deployed email clients. (Note, a certificate certificate can only include a single CN-ID, so if a mail service
can only include a single CN-ID, so if a mail service is running is running on multiple hosts, either each host has to use
on multiple hosts, either each host has to use different different certificate with its own CN-ID, a single certificate
certificate with its own CN-ID, a single certificate with with multiple DNS-IDs, or a single certificate with wildcard in
multiple DNS-IDs, or a single certificate with wildcard in CN-ID CN-ID can be used).
can be used).
4. MAY include "*" (wildcard) as the left-most name component of 4. MAY include "*" (wildcard) as the left-most name component of
DNS-ID or CN-ID in Certificate Signing Requests. DNS-ID or CN-ID in Certificate Signing Requests.
5.1. Notes on hosted domains
TBD. Compare one certificate that contains all hosted domains versa
use of SNI or separate IPs for each hosted domain with its own
certificate.
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". A certificate for this addresses of the form "user@example.net". A certificate for this
service needs to include DNS-IDs of "example.net" (because it is the service needs to include DNS-IDs of "example.net" (because it is the
right hand side of emails) and "mail.example.net" (this is what a domain portion of emails) and "mail.example.net" (this is what a user
user of this server enters manually, if not using [RFC6186]). It of this server enters manually, if not using [RFC6186]). It might
might also include CN-IDs of "mail.example.net" for backward also include CN-ID of "mail.example.net" for backward compatibility
compatibility with deployed infrastructure. with deployed infrastructure.
Consider the IMAP-accessible email server from the previous paragraph Consider the IMAP-accessible email server from the previous paragraph
which is additionally discoverable via DNS SRV lookups in domain which is additionally discoverable via DNS SRV lookups in domain
"example.net" (DNS SRV records "_imap._tcp.example.net" and "example.net" (DNS SRV records "_imap._tcp.example.net" and
"_imaps._tcp.example.net"). In addition to DNS-ID/CN-ID identity "_imaps._tcp.example.net"). In addition to DNS-ID/CN-ID identity
types specified above, a certificate for this service also needs to types specified above, a certificate for this service also needs to
include SRV-IDs of "_imap.example.net" (when STARTTLS is used on the include SRV-IDs of "_imap.example.net" (when STARTTLS is used on the
IMAP port) and "_imaps.example.net" (when TLS is used on IMAPS port). IMAP port) and "_imaps.example.net" (when TLS is used on IMAPS port).
See [RFC6186] for more details. (Note that unlike DNS SRV there is See [RFC6186] for more details. (Note that unlike DNS SRV there is
no "_tcp" component in SRV-IDs). no "_tcp" component in SRV-IDs).
Consider the IMAP-accessible email server from the first paragraph
which is running on a host also known as "mycompany.example.com". In
addition to DNS-ID identity types specified above, a certificate for
this service also needs to include DNS-ID of "mycompany.example.com"
(this is what a user of this server enters manually, if not using
[RFC6186]). It might also include CN-ID of "mycompany.example.com"
instead of the CN-ID "mail.example.net" for backward compatibility
with deployed infrastructure. (This is so, because a certificate can
only include a single CN-ID)
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-ID of
"submit.example.net" for backward compatibility with deployed "submit.example.net" for backward compatibility with deployed
infrastructure. infrastructure.
Consider a host "mail.example.net" servicing email addresses of the Consider a host "mail.example.net" servicing email addresses of the
form "user@example.net" and discoverable via DNS SRV lookups in form "user@example.net" and discoverable via DNS SRV lookups in
domain "example.net", which runs SMTP Submission, IMAPS and POP3S domain "example.net", which runs SMTP Submission, IMAPS and POP3S
(POP3-over-TLS) and ManageSieve services. Each of the servers can (POP3-over-TLS) and ManageSieve services. Each of the servers can
use their own certificate specific to their service (see examples use their own certificate specific to their service (see examples
above). Alternatively they can all share a single certificate that above). Alternatively they can all share a single certificate that
would include SRV-IDs of "_submission.example.net", would include SRV-IDs of "_submission.example.net",
"_imaps.example.net", "_pop3s.example.net" and "_sieve.example.net" "_imaps.example.net", "_pop3s.example.net" and "_sieve.example.net"
along with DNS-IDs of "example.net" and "mail.example.net". It might along with DNS-IDs of "example.net" and "mail.example.net". It might
also include CN-IDs of "mail.example.net" for backward compatibility also include CN-ID of "mail.example.net" for backward compatibility
with deployed infrastructure. with deployed infrastructure.
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
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if they are a target of a DNS SRV lookup) or derived using a secure if they are a target of a DNS SRV lookup) or derived using a secure
third party service (e.g. DNSSEC-protected SRV records which are third party service (e.g. DNSSEC-protected SRV records which are
verified by the client or trusted local resolver). Future work in verified by the client or trusted local resolver). Future work in
this area might benefit from integration with DANE [RFC6698], but it this area might benefit from integration with DANE [RFC6698], but it
is not covered by this document. is not covered by this document.
9. References 9. References
9.1. Normative References 9.1. Normative References
[RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3",
STD 53, RFC 1939, DOI 10.17487/RFC1939, May 1996,
<http://www.rfc-editor.org/info/rfc1939>.
[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,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC6409] Gellens, R. and J. Klensin, "Message Submission for Mail",
STD 72, RFC 6409, DOI 10.17487/RFC6409, November 2011,
<http://www.rfc-editor.org/info/rfc6409>.
[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, DOI 10.17487/RFC3207, Transport Layer Security", RFC 3207, DOI 10.17487/RFC3207,
February 2002, <http://www.rfc-editor.org/info/rfc3207>. February 2002, <http://www.rfc-editor.org/info/rfc3207>.
[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,
<http://www.rfc-editor.org/info/rfc3501>. <http://www.rfc-editor.org/info/rfc3501>.
[RFC1939] Myers, J. and M. Rose, "Post Office Protocol - Version 3", [RFC4985] Santesson, S., "Internet X.509 Public Key Infrastructure
STD 53, RFC 1939, DOI 10.17487/RFC1939, May 1996, Subject Alternative Name for Expression of Service Name",
<http://www.rfc-editor.org/info/rfc1939>. RFC 4985, DOI 10.17487/RFC4985, August 2007,
<http://www.rfc-editor.org/info/rfc4985>.
[RFC5804] Melnikov, A., Ed. and T. Martin, "A Protocol for Remotely [RFC5804] Melnikov, A., Ed. and T. Martin, "A Protocol for Remotely
Managing Sieve Scripts", RFC 5804, DOI 10.17487/RFC5804, Managing Sieve Scripts", RFC 5804, DOI 10.17487/RFC5804,
July 2010, <http://www.rfc-editor.org/info/rfc5804>. July 2010, <http://www.rfc-editor.org/info/rfc5804>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <http://www.rfc-editor.org/info/rfc6125>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<http://www.rfc-editor.org/info/rfc5280>. <http://www.rfc-editor.org/info/rfc5280>.
[RFC4985] Santesson, S., "Internet X.509 Public Key Infrastructure [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Subject Alternative Name for Expression of Service Name", Verification of Domain-Based Application Service Identity
RFC 4985, DOI 10.17487/RFC4985, August 2007, within Internet Public Key Infrastructure Using X.509
<http://www.rfc-editor.org/info/rfc4985>. (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <http://www.rfc-editor.org/info/rfc6125>.
[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, Submission/Access Services", RFC 6186,
DOI 10.17487/RFC6186, March 2011, DOI 10.17487/RFC6186, March 2011,
<http://www.rfc-editor.org/info/rfc6186>. <http://www.rfc-editor.org/info/rfc6186>.
[RFC6409] Gellens, R. and J. Klensin, "Message Submission for Mail",
STD 72, RFC 6409, DOI 10.17487/RFC6409, November 2011,
<http://www.rfc-editor.org/info/rfc6409>.
9.2. Informative References 9.2. Informative References
[RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP", [RFC2595] Newman, C., "Using TLS with IMAP, POP3 and ACAP",
RFC 2595, DOI 10.17487/RFC2595, June 1999, RFC 2595, DOI 10.17487/RFC2595, June 1999,
<http://www.rfc-editor.org/info/rfc2595>. <http://www.rfc-editor.org/info/rfc2595>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication [RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS) of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <http://www.rfc-editor.org/info/rfc6698>. 2012, <http://www.rfc-editor.org/info/rfc6698>.
Appendix A. Acknowledgements Appendix A. Acknowledgements
Thank you to Chris Newman, Viktor Dukhovni and Sean Turner for Thank you to Chris Newman, Viktor Dukhovni, Sean Turner, Russ Housley
comments on this document. and Alessandro Vesely 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. 30 change blocks. 
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