draft-ietf-uta-smtp-tlsrpt-11.txt   draft-ietf-uta-smtp-tlsrpt-12.txt 
Using TLS in Applications D. Margolis Using TLS in Applications D. Margolis
Internet-Draft Google, Inc Internet-Draft Google, Inc
Intended status: Standards Track A. Brotman Intended status: Standards Track A. Brotman
Expires: May 12, 2018 Comcast, Inc Expires: June 7, 2018 Comcast, Inc
B. Ramakrishnan B. Ramakrishnan
Yahoo!, Inc Yahoo!, Inc
J. Jones J. Jones
Microsoft, Inc Microsoft, Inc
M. Risher M. Risher
Google, Inc Google, Inc
November 8, 2017 December 4, 2017
SMTP TLS Reporting SMTP TLS Reporting
draft-ietf-uta-smtp-tlsrpt-11 draft-ietf-uta-smtp-tlsrpt-12
Abstract Abstract
A number of protocols exist for establishing encrypted channels A number of protocols exist for establishing encrypted channels
between SMTP Mail Transfer Agents, including STARTTLS, DANE TLSA, and between SMTP Mail Transfer Agents, including STARTTLS, DANE TLSA, and
MTA-STS. These protocols can fail due to misconfiguration or active MTA-STS. These protocols can fail due to misconfiguration or active
attack, leading to undelivered messages or delivery over unencrypted attack, leading to undelivered messages or delivery over unencrypted
or unauthenticated channels. This document describes a reporting or unauthenticated channels. This document describes a reporting
mechanism and format by which sending systems can share statistics mechanism and format by which sending systems can share statistics
and specific information about potential failures with recipient and specific information about potential failures with recipient
skipping to change at page 1, line 39 skipping to change at page 1, line 39
misconfigurations. misconfigurations.
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
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 http://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 12, 2018. This Internet-Draft will expire on June 7, 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
(http://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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
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5.4. HTTPS Transport . . . . . . . . . . . . . . . . . . . . . 15 5.4. HTTPS Transport . . . . . . . . . . . . . . . . . . . . . 15
5.5. Delivery Retry . . . . . . . . . . . . . . . . . . . . . 16 5.5. Delivery Retry . . . . . . . . . . . . . . . . . . . . . 16
5.6. Metadata Variances . . . . . . . . . . . . . . . . . . . 16 5.6. Metadata Variances . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
6.1. Message headers . . . . . . . . . . . . . . . . . . . . . 16 6.1. Message headers . . . . . . . . . . . . . . . . . . . . . 16
6.2. Report Type . . . . . . . . . . . . . . . . . . . . . . . 17 6.2. Report Type . . . . . . . . . . . . . . . . . . . . . . . 17
6.3. application/tlsrpt+json Media Type . . . . . . . . . . . 17 6.3. application/tlsrpt+json Media Type . . . . . . . . . . . 17
6.4. application/tlsrpt+gzip Media Type . . . . . . . . . . . 18 6.4. application/tlsrpt+gzip Media Type . . . . . . . . . . . 18
6.5. STARTTLS Validation Result Types . . . . . . . . . . . . 19 6.5. STARTTLS Validation Result Types . . . . . . . . . . . . 19
7. Security Considerations . . . . . . . . . . . . . . . . . . . 19 7. Security Considerations . . . . . . . . . . . . . . . . . . . 19
8. Appendix 1: Example Reporting Policy . . . . . . . . . . . . 21 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Report using MAILTO . . . . . . . . . . . . . . . . . . . 21 8.1. Normative References . . . . . . . . . . . . . . . . . . 21
8.2. Report using HTTPS . . . . . . . . . . . . . . . . . . . 21 8.2. Informative References . . . . . . . . . . . . . . . . . 23
9. Appendix 2: Example JSON Report . . . . . . . . . . . . . . . 21 Appendix A. Example Reporting Policy . . . . . . . . . . . . . . 23
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 A.1. Report using MAILTO . . . . . . . . . . . . . . . . . . . 23
10.1. Normative References . . . . . . . . . . . . . . . . . . 23 A.2. Report using HTTPS . . . . . . . . . . . . . . . . . . . 23
10.2. Informative References . . . . . . . . . . . . . . . . . 25 Appendix B. Example JSON Report . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
The STARTTLS extension to SMTP [RFC3207] allows SMTP clients and The STARTTLS extension to SMTP [RFC3207] allows SMTP clients and
hosts to establish secure SMTP sessions over TLS. The protocol hosts to establish secure SMTP sessions over TLS. The protocol
design is based on "Opportunistic Security" (OS) [RFC7435], which design is based on "Opportunistic Security" (OS) [RFC7435], which
maintains interoperability with clients that do not support STARTTLS maintains interoperability with clients that do not support STARTTLS
but means that any attacker who can delete parts of the SMTP session but means that any attacker who can delete parts of the SMTP session
(such as the "250 STARTTLS" response) or redirect the entire SMTP (such as the "250 STARTTLS" response) or redirect the entire SMTP
session (perhaps by overwriting the resolved MX record of the session (perhaps by overwriting the resolved MX record of the
delivery domain) can perform a downgrade or interception attack. delivery domain) can perform a downgrade or interception attack.
Because such "downgrade attacks" are not necessarily apparent to the Because such "downgrade attacks" are not necessarily apparent to the
receiving MTA, this document defines a mechanism for sending domains receiving MTA, this document defines a mechanism for sending domains
to report on failures at multiple stages of the MTA-to-MTA to report on failures at multiple stages of the MTA-to-MTA
conversation. conversation.
Recipient domains may also use the mechanisms defined by MTA-STS Recipient domains may also use the mechanisms defined by MTA-STS
(TODO: Add ref) or DANE [RFC6698] to publish additional encryption [I-D.ietf-uta-mta-sts] or DANE [RFC6698] to publish additional
and authentication requirements; this document defines a mechanism encryption and authentication requirements; this document defines a
for sending domains that are compatible with MTA-STS or DANE to share mechanism for sending domains that are compatible with MTA-STS or
success and failure statistics with recipient domains. DANE to share success and failure statistics with recipient domains.
Specifically, this document defines a reporting schema that covers Specifically, this document defines a reporting schema that covers
failures in routing, STARTTLS negotiation, and both DANE [RFC6698] failures in routing, STARTTLS negotiation, and both DANE [RFC6698]
and MTA-STS (TODO: Add ref) policy validation errors, and a standard and MTA-STS [I-D.ietf-uta-mta-sts] policy validation errors, and a
TXT record that recipient domains can use to indicate where reports standard TXT record that recipient domains can use to indicate where
in this format should be sent. reports in this format should be sent.
This document is intended as a companion to the specification for This document is intended as a companion to the specification for
SMTP MTA Strict Transport Security (MTA-STS, TODO: Add ref). SMTP MTA Strict Transport Security [I-D.ietf-uta-mta-sts].
1.1. Terminology 1.1. Terminology
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].
We also define the following terms for further use in this document: We also define the following terms for further use in this document:
o MTA-STS Policy: A definition of the expected TLS availability, o MTA-STS Policy: A definition of the expected TLS availability,
behavior, and desired actions for a given domain when a sending behavior, and desired actions for a given domain when a sending
MTA encounters problems in negotiating a secure channel. MTA-STS MTA encounters problems in negotiating a secure channel. MTA-STS
is defined in [TODO] is defined in [I-D.ietf-uta-mta-sts].
o DANE Policy: A mechanism by which administrators can supply a o DANE Policy: A mechanism by which administrators can supply a
record that can be used to validate the certificate presented by record that can be used to validate the certificate presented by
an MTA. DANE is defined in [RFC6698]. an MTA. DANE is defined in [RFC6698].
o TLSRPT Policy: A policy specifying the endpoint to which sending o TLSRPT Policy: A policy specifying the endpoint to which sending
MTAs should deliver reports. MTAs should deliver reports.
o Policy Domain: The domain against which an MTA-STS or DANE Policy o Policy Domain: The domain against which an MTA-STS or DANE Policy
is defined. is defined.
o Sending MTA: The MTA initiating the delivery of an email message. o Sending MTA: The MTA initiating the delivery of an email message.
2. Related Technologies 2. Related Technologies
o This document is intended as a companion to the specification for o This document is intended as a companion to the specification for
SMTP MTA Strict Transport Security (MTA-STS, TODO: Add RFC ref). SMTP MTA Strict Transport Security [I-D.ietf-uta-mta-sts].
o SMTP-TLSRPT defines a mechanism for sending domains that are o SMTP-TLSRPT defines a mechanism for sending domains that are
compatible with MTA-STS or DANE to share success and failure compatible with MTA-STS or DANE to share success and failure
statistics with recipient domains. DANE is defined in [RFC6698] statistics with recipient domains. DANE is defined in [RFC6698]
and MTA-STS is defined in [TODO : Add RFC ref] and MTA-STS is defined in [I-D.ietf-uta-mta-sts].
3. Reporting Policy 3. Reporting Policy
A domain publishes a record to its DNS indicating that it wishes to A domain publishes a record to its DNS indicating that it wishes to
receive reports. These SMTP TLSRPT policies are distributed via DNS receive reports. These SMTP TLSRPT policies are distributed via DNS
from the Policy Domain's zone, as TXT records (similar to DMARC from the Policy Domain's zone, as TXT records (similar to DMARC
policies) under the name "_smtp-tlsrpt". For example, for the Policy policies) under the name "_smtp-tlsrpt". For example, for the Policy
Domain "example.com", the recipient's TLSRPT policy can be retrieved Domain "example.com", the recipient's TLSRPT policy can be retrieved
from "_smtp-tlsrpt.example.com". from "_smtp-tlsrpt.example.com".
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[RFC7489], the policy domain can specify a comma-separated list of [RFC7489], the policy domain can specify a comma-separated list of
URIs. URIs.
o In the case of "https", reports should be submitted via POST o In the case of "https", reports should be submitted via POST
([RFC7231]) to the specified URI. Report submitters MAY ignore ([RFC7231]) to the specified URI. Report submitters MAY ignore
certificate validation errors when submitting reports via https. certificate validation errors when submitting reports via https.
o In the case of "mailto", reports should be submitted to the o In the case of "mailto", reports should be submitted to the
specified email address ([RFC6068]). When sending failure reports specified email address ([RFC6068]). When sending failure reports
via SMTP, sending MTAs MUST deliver reports despite any TLS- via SMTP, sending MTAs MUST deliver reports despite any TLS-
related failuresand SHOULD NOT include this SMTP session in the related failures and SHOULD NOT include this SMTP session in the
next report. This may mean that the reports are delivered in the next report. This may mean that the reports are delivered in the
clear. Additionally, reports sent via SMTP MUST contain a valid clear. Additionally, reports sent via SMTP MUST contain a valid
DKIM [RFC6376] signature by the reporting domain. Reports lacking DKIM [RFC6376] signature by the reporting domain. Reports lacking
such a signature MUST be ignored by the recipient. DKIM such a signature MUST be ignored by the recipient. DKIM
signatures must not use the "l=" attribute to limit the body signatures must not use the "l=" attribute to limit the body
length used in the signature. length used in the signature.
The formal definition of the "_smtp-tlsrpt" TXT record, defined using The formal definition of the "_smtp-tlsrpt" TXT record, defined using
[RFC5234] & [RFC7405], is as follows: [RFC5234] & [RFC7405], is as follows:
tlsrpt-record = tlsrpt-version 1*(field-delim tlsrpt-field) tlsrpt-record = tlsrpt-version 1*(field-delim tlsrpt-field)
[field-delim] [field-delim]
field-delim = *WSP ";" *WSP field-delim = *WSP ";" *WSP
tlsrpt-field = tlsrpt-rua / ; Note that the tlsrpt-rua tlsrpt-field = tlsrpt-rua / ; Note that the
tlsrpt-extension ; record is required. tlsrpt-extension ; tlsrpt-rua record is
; required.
tlsrpt-version = %s"v=TLSRPTv1" tlsrpt-version = %s"v=TLSRPTv1"
tlsrpt-rua = %s"rua=" tlsrpt-rua = %s"rua="
tlsrpt-uri *(*WSP "," *WSP tlsrpt-uri) tlsrpt-uri *(*WSP "," *WSP tlsrpt-uri)
tlsrpt-uri = URI tlsrpt-uri = URI
; "URI" is imported from [@!RFC3986]; commas (ASCII ; "URI" is imported from [@!RFC3986];
; 0x2C) and exclamation points (ASCII 0x21) ; commas (ASCII 0x2C) and exclamation
; MUST be encoded ; points (ASCII 0x21) MUST be encoded
tlsrpt-extension = tlsrpt-ext-name "=" tlsrpt-ext-value tlsrpt-extension = tlsrpt-ext-name "=" tlsrpt-ext-value
tlsrpt-ext-name = (ALPHA / DIGIT) *31(ALPHA / DIGIT / "_" / "-" / ".") tlsrpt-ext-name = (ALPHA / DIGIT) *31(ALPHA /
DIGIT / "_" / "-" / ".")
tlsrpt-ext-value = 1*(%x21-3A / %x3C / %x3E-7E) ; chars excluding tlsrpt-ext-value = 1*(%x21-3A / %x3C / %x3E-7E)
; "=", ";", SP, and ; chars excluding "=", ";", SP, and control
; control chars ; chars
If multiple TXT records for "_smtp-tlsrpt" are returned by the If multiple TXT records for "_smtp-tlsrpt" are returned by the
resolver, records which do not begin with "v=TLSRPTv1;" are resolver, records which do not begin with "v=TLSRPTv1;" are
discarded. If the number of resulting records is not one, senders discarded. If the number of resulting records is not one, senders
MUST assume the recipient domain does not implement TLSRPT. If the MUST assume the recipient domain does not implement TLSRPT. If the
resulting TXT record contains multiple strings, then the record MUST resulting TXT record contains multiple strings, then the record MUST
be treated as if those strings are concatenated together without be treated as if those strings are concatenated together without
adding spaces. adding spaces.
Parsers MUST accept TXT records which are syntactically valid (i.e. Parsers MUST accept TXT records which are syntactically valid (i.e.
valid key-value pairs separated by semi-colons) and implementing a valid key-value pairs separated by semi-colons) and implementing a
superset of this specification, in which case unknown fields SHALL be superset of this specification, in which case unknown fields SHALL be
ignored. ignored.
3.1. Example Reporting Policy 3.1. Example Reporting Policy
3.1.1. Report using MAILTO 3.1.1. Report using MAILTO
_smtp-tlsrpt.example.com. IN TXT \ _smtp-tlsrpt.example.com. IN TXT \
"v=TLSRPTv1;rua=mailto:reports@example.com" "v=TLSRPTv1;rua=mailto:reports@example.com"
3.1.2. Report using HTTPS 3.1.2. Report using HTTPS
_smtp-tlsrpt.example.com. IN TXT \ _smtp-tlsrpt.example.com. IN TXT \
"v=TLSRPTv1; \ "v=TLSRPTv1; \
rua=https://reporting.example.com/v1/tlsrpt" rua=https://reporting.example.com/v1/tlsrpt"
4. Reporting Schema 4. Reporting Schema
The report is composed as a plain text file encoded in the I-JSON The report is composed as a plain text file encoded in the I-JSON
format ([RFC7493]). format ([RFC7493]).
Aggregate reports contain the following fields: Aggregate reports contain the following fields:
o Report metadata: o Report metadata:
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The extension MUST be "json" for a plain JSON file, or "json.gz" for The extension MUST be "json" for a plain JSON file, or "json.gz" for
a JSON file compressed using GZIP. a JSON file compressed using GZIP.
"unique-id" allows an optional unique ID generated by the Sending MTA "unique-id" allows an optional unique ID generated by the Sending MTA
to distinguish among multiple reports generated simultaneously by to distinguish among multiple reports generated simultaneously by
different sources within the same Policy Domain. For example, this different sources within the same Policy Domain. For example, this
is a possible filename for the gzip file of a report to the Policy is a possible filename for the gzip file of a report to the Policy
Domain "example.net" from the Sending MTA "mail.sender.example.com": Domain "example.net" from the Sending MTA "mail.sender.example.com":
`mail.sender.example.com!example.net!1470013207!1470186007!001.json.gz` "mail.sender.example.com!example.net!1470013207!1470186007!001.json.g
z"
5.2. Compression 5.2. Compression
The report SHOULD be subjected to GZIP compression for both email and The report SHOULD be subjected to GZIP compression for both email and
HTTPS transport. Declining to apply compression can cause the report HTTPS transport. Declining to apply compression can cause the report
to be too large for a receiver to process (a commonly observed to be too large for a receiver to process (a commonly observed
receiver limit is ten megabytes); compressing the file increases the receiver limit is ten megabytes); compressing the file increases the
chances of acceptance of the report at some compute cost. chances of acceptance of the report at some compute cost.
5.3. Email Transport 5.3. Email Transport
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HTTPS transport. Declining to apply compression can cause the report HTTPS transport. Declining to apply compression can cause the report
to be too large for a receiver to process (a commonly observed to be too large for a receiver to process (a commonly observed
receiver limit is ten megabytes); compressing the file increases the receiver limit is ten megabytes); compressing the file increases the
chances of acceptance of the report at some compute cost. chances of acceptance of the report at some compute cost.
5.3. Email Transport 5.3. Email Transport
The report MAY be delivered by email. To make the reports machine- The report MAY be delivered by email. To make the reports machine-
parsable for the receivers, we define a top-level media type parsable for the receivers, we define a top-level media type
"multipart/report" with a new parameter "report-type="tlsrpt"". "multipart/report" with a new parameter "report-type="tlsrpt"".
Inside it, there are two parts: The first part is human readable, Inside it, there are two parts: The first part is human readable,
typically "text/plain", and the second part is machine readable with typically "text/plain", and the second part is machine readable with
a new media type defined called "application/tlsrpt+json". If a new media type defined called "application/tlsrpt+json". If
compressed, the report should use the media type "application/ compressed, the report should use the media type "application/
tlsrpt+gzip". tlsrpt+gzip".
In addition, the following two new top level message header fields In addition, the following two new top level message header fields
are defined: are defined:
TLS-Report-Domain: Receiver-Domain "TLS-Report-Domain: Receiver-Domain TLS-Report-Submitter: Sender-
TLS-Report-Submitter: Sender-Domain Domain" The "TLS-Report-Submitter" value MUST match the value found
in the filename and the [RFC5321] domain from the "contact-info" from
The "TLS-Report-Submitter" value MUST match the value found in the the report body. These message headers MUST be included and should
filename and the [RFC5321] domain from the "contact-info" from the allow for easy searching for all reports submitted by a report domain
report body. These message headers MUST be included and should allow or a particular submitter, for example in IMAP [RFC3501]:
for easy searching for all reports submitted by a report domain or a
particular submitter, for example in IMAP [RFC3501]:
"s SEARCH HEADER "TLS-Report-Domain" "example.com"" "s SEARCH HEADER "TLS-Report-Domain" "example.com""
It is presumed that the aggregate reporting address will be equipped It is presumed that the aggregate reporting address will be equipped
to process new message header fields and extract MIME parts with the to process new message header fields and extract MIME parts with the
prescribed media type and filename, and ignore the rest. These prescribed media type and filename, and ignore the rest. These
additional headers SHOULD be included in the DKIM [RFC6376] signature additional headers SHOULD be included in the DKIM [RFC6376] signature
for the message. for the message.
The [RFC5322].Subject field for report submissions SHOULD conform to The [RFC5322].Subject field for report submissions SHOULD conform to
the following ABNF: the following ABNF:
tlsrpt-subject = %s"Report" FWS ; "Report" tlsrpt-subject = %s"Report" FWS ; "Report"
%s"Domain:" FWS ; "Domain:" %s"Domain:" FWS ; "Domain:"
domain-name FWS ; per RFC6376 domain-name FWS ; per RFC6376
%s"Submitter:" FWS ; "Submitter:" %s"Submitter:" FWS ; "Submitter:"
domain-name FWS ; per RFC6376 domain-name FWS ; per RFC6376
%s"Report-ID:" FWS ; "Report-ID: %s"Report-ID:" FWS ; "Report-ID:
"<" id-left "@" id-right ">" ; per RFC5322 "<" id-left "@" id-right ">" ; per RFC5322
[CFWS] ; per RFC5322 (as with FWS) [CFWS] ; per RFC5322
; (as with FWS)
The first domain-name indicates the DNS domain name about which the The first domain-name indicates the DNS domain name about which the
report was generated. The second domain-name indicates the DNS report was generated. The second domain-name indicates the DNS
domain name representing the Sending MTA generating the report. The domain name representing the Sending MTA generating the report. The
purpose of the Report-ID: portion of the field is to enable the purpose of the Report-ID: portion of the field is to enable the
Policy Domain to identify and ignore duplicate reports that might be Policy Domain to identify and ignore duplicate reports that might be
sent by a Sending MTA. sent by a Sending MTA.
For instance, this is a possible Subject field for a report to the For instance, this is a possible Subject field for a report to the
Policy Domain "example.net" from the Sending MTA Policy Domain "example.net" from the Sending MTA
"mail.sender.example.com". It is line-wrapped as allowed by "mail.sender.example.com". It is line-wrapped as allowed by
[RFC5322]: Subject: Report Domain: example.net
Submitter: mail.sender.example.com
Subject: Report Domain: example.net Report-ID: <735ff.e317+bf22029@mailexample.net>
Submitter: mail.sender.example.com
Report-ID: <735ff.e317+bf22029@mailexample.net>
5.3.1. Example Report 5.3.1. Example Report
From: tlsrpt@mail.sender.example.com From: tlsrpt@mail.sender.example.com
Date: Fri, May 09 2017 16:54:30 -0800 Date: Fri, May 09 2017 16:54:30 -0800
To: mts-sts-tlsrpt@example.net To: mts-sts-tlsrpt@example.net
Subject: Report Domain: example.net Subject: Report Domain: example.net
Submitter: mail.sender.example.com Submitter: mail.sender.example.com
Report-ID: <735ff.e317+bf22029@example.net> Report-ID: <735ff.e317+bf22029@example.net>
TLS-Report-Domain: example.net TLS-Report-Domain: example.net
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including attacks designed to thwart negotiation of encrypted including attacks designed to thwart negotiation of encrypted
connections (by downgrading opportunistic encryption or, in the case connections (by downgrading opportunistic encryption or, in the case
of MTA-STS, preventing discovery of a new MTA-STS policy), we must of MTA-STS, preventing discovery of a new MTA-STS policy), we must
also consider the risk that an adversary who can induce such a also consider the risk that an adversary who can induce such a
downgrade attack can also prevent discovery of the TLSRPT TXT record downgrade attack can also prevent discovery of the TLSRPT TXT record
(and thus prevent discovery of the successful downgrade attack). (and thus prevent discovery of the successful downgrade attack).
Administrators are thus encouraged to deploy TLSRPT TXT records with Administrators are thus encouraged to deploy TLSRPT TXT records with
a large TTL (reducing the window for successful attacks against DNS a large TTL (reducing the window for successful attacks against DNS
resolution of the record) or to deploy DNSSEC on the deploying zone. resolution of the record) or to deploy DNSSEC on the deploying zone.
8. Appendix 1: Example Reporting Policy 8. References
8.1. Report using MAILTO
_smtp-tlsrpt.mail.example.com. IN TXT \
"v=TLSRPTv1;rua=mailto:reports@example.com"
8.2. Report using HTTPS
_smtp-tlsrpt.mail.example.com. IN TXT \
"v=TLSRPTv1; \
rua=https://reporting.example.com/v1/tlsrpt"
9. Appendix 2: Example JSON Report
{
"organization-name": "Company-X",
"date-range": {
"start-datetime": "2016-04-01T00:00:00Z",
"end-datetime": "2016-04-01T23:59:59Z"
},
"contact-info": "sts-reporting@company-x.com",
"report-id": "5065427c-23d3-47ca-b6e0-946ea0e8c4be",
"policies": [{
"policy": {
"policy-type": "sts",
"policy-string": "version: STSv1\r\nmode: report\r\nmx: .mail.company-y.com\r\nmax_age: 86400",
"policy-domain": "company-y.com",
"mx-host": ".mail.company-y.com"
},
"summary": {
"total-successful-session-count": 5326,
"total-failure-session-count": 303
},
"failure-details": [{
"result-type": "certificate-expired",
"sending-mta-ip": "98.136.216.25",
"receiving-mx-hostname": "mx1.mail.company-y.com",
"failed-session-count": 100
}, {
"result-type": "starttls-not-supported",
"sending-mta-ip": "98.22.33.99",
"receiving-mx-hostname": "mx2.mail.company-y.com",
"failed-session-count": 200,
"additional-information": "https://reports.company-x.com/
report_info ? id = 5065427 c - 23 d3# StarttlsNotSupported "
}, {
"result-type": "validation-failure",
"sending-mta-ip": "47.97.15.2",
"receiving-mx-hostname": "mx-backup.mail.company-y.com",
"failed-session-count": 3,
"failure-error-code": "X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED"
}]
}]
}
Figure: Example JSON report for a messages from Company-X to
Company-Y, where 100 sessions were attempted to Company Y servers
with an expired certificate and 200 sessions were attempted to
Company Y servers that did not successfully respond to the "STARTTLS"
command. Additionally 3 sessions failed due to
"X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED".
10. References 8.1. Normative References
10.1. Normative References [I-D.ietf-uta-mta-sts]
Margolis, D., Risher, M., Ramakrishnan, B., Brotman, A.,
and J. Jones, "SMTP MTA Strict Transport Security (MTA-
STS)", draft-ietf-uta-mta-sts-11 (work in progress),
November 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, DOI 10.17487/ Requirement Levels", BCP 14, RFC 2119,
RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet: [RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002, Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<http://www.rfc-editor.org/info/rfc3339>. <https://www.rfc-editor.org/info/rfc3339>.
[RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode [RFC3492] Costello, A., "Punycode: A Bootstring encoding of Unicode
for Internationalized Domain Names in Applications for Internationalized Domain Names in Applications
(IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003, (IDNA)", RFC 3492, DOI 10.17487/RFC3492, March 2003,
<http://www.rfc-editor.org/info/rfc3492>. <https://www.rfc-editor.org/info/rfc3492>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC Resource Identifier (URI): Generic Syntax", STD 66,
3986, DOI 10.17487/RFC3986, January 2005, RFC 3986, DOI 10.17487/RFC3986, January 2005,
<http://www.rfc-editor.org/info/rfc3986>. <https://www.rfc-editor.org/info/rfc3986>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/ Specifications: ABNF", STD 68, RFC 5234,
RFC5234, January 2008, DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>. <https://www.rfc-editor.org/info/rfc5234>.
[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>. <https://www.rfc-editor.org/info/rfc5280>.
[RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321, [RFC5321] Klensin, J., "Simple Mail Transfer Protocol", RFC 5321,
DOI 10.17487/RFC5321, October 2008, DOI 10.17487/RFC5321, October 2008,
<http://www.rfc-editor.org/info/rfc5321>. <https://www.rfc-editor.org/info/rfc5321>.
[RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322, DOI [RFC5322] Resnick, P., Ed., "Internet Message Format", RFC 5322,
10.17487/RFC5322, October 2008, DOI 10.17487/RFC5322, October 2008,
<http://www.rfc-editor.org/info/rfc5322>. <https://www.rfc-editor.org/info/rfc5322>.
[RFC5891] Klensin, J., "Internationalized Domain Names in [RFC5891] Klensin, J., "Internationalized Domain Names in
Applications (IDNA): Protocol", RFC 5891, DOI 10.17487/ Applications (IDNA): Protocol", RFC 5891,
RFC5891, August 2010, DOI 10.17487/RFC5891, August 2010,
<http://www.rfc-editor.org/info/rfc5891>. <https://www.rfc-editor.org/info/rfc5891>.
[RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
Address Text Representation", RFC 5952, DOI 10.17487/ Address Text Representation", RFC 5952,
RFC5952, August 2010, DOI 10.17487/RFC5952, August 2010,
<http://www.rfc-editor.org/info/rfc5952>. <https://www.rfc-editor.org/info/rfc5952>.
[RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto' [RFC6068] Duerst, M., Masinter, L., and J. Zawinski, "The 'mailto'
URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010, URI Scheme", RFC 6068, DOI 10.17487/RFC6068, October 2010,
<http://www.rfc-editor.org/info/rfc6068>. <https://www.rfc-editor.org/info/rfc6068>.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March Security (TLS)", RFC 6125, DOI 10.17487/RFC6125, March
2011, <http://www.rfc-editor.org/info/rfc6125>. 2011, <https://www.rfc-editor.org/info/rfc6125>.
[RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed., [RFC6376] Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
"DomainKeys Identified Mail (DKIM) Signatures", STD 76, "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
RFC 6376, DOI 10.17487/RFC6376, September 2011, RFC 6376, DOI 10.17487/RFC6376, September 2011,
<http://www.rfc-editor.org/info/rfc6376>. <https://www.rfc-editor.org/info/rfc6376>.
[RFC6522] Kucherawy, M., Ed., "The Multipart/Report Media Type for [RFC6522] Kucherawy, M., Ed., "The Multipart/Report Media Type for
the Reporting of Mail System Administrative Messages", STD the Reporting of Mail System Administrative Messages",
73, RFC 6522, DOI 10.17487/RFC6522, January 2012, STD 73, RFC 6522, DOI 10.17487/RFC6522, January 2012,
<http://www.rfc-editor.org/info/rfc6522>. <https://www.rfc-editor.org/info/rfc6522>.
[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, <https://www.rfc-editor.org/info/rfc6698>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
10.17487/RFC7231, June 2014, <https://www.rfc-editor.org/ DOI 10.17487/RFC7231, June 2014,
info/rfc7231>. <https://www.rfc-editor.org/info/rfc7231>.
[RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF", RFC [RFC7405] Kyzivat, P., "Case-Sensitive String Support in ABNF",
7405, DOI 10.17487/RFC7405, December 2014, RFC 7405, DOI 10.17487/RFC7405, December 2014,
<http://www.rfc-editor.org/info/rfc7405>. <https://www.rfc-editor.org/info/rfc7405>.
[RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493, DOI [RFC7493] Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
10.17487/RFC7493, March 2015, DOI 10.17487/RFC7493, March 2015,
<http://www.rfc-editor.org/info/rfc7493>. <https://www.rfc-editor.org/info/rfc7493>.
10.2. Informative References 8.2. Informative References
[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, <https://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>. <https://www.rfc-editor.org/info/rfc3501>.
[RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
Procedures for Message Header Fields", BCP 90, RFC 3864, Procedures for Message Header Fields", BCP 90, RFC 3864,
DOI 10.17487/RFC3864, September 2004, DOI 10.17487/RFC3864, September 2004,
<http://www.rfc-editor.org/info/rfc3864>. <https://www.rfc-editor.org/info/rfc3864>.
[RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection [RFC7435] Dukhovni, V., "Opportunistic Security: Some Protection
Most of the Time", RFC 7435, DOI 10.17487/RFC7435, Most of the Time", RFC 7435, DOI 10.17487/RFC7435,
December 2014, <http://www.rfc-editor.org/info/rfc7435>. December 2014, <https://www.rfc-editor.org/info/rfc7435>.
[RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning [RFC7469] Evans, C., Palmer, C., and R. Sleevi, "Public Key Pinning
Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April Extension for HTTP", RFC 7469, DOI 10.17487/RFC7469, April
2015, <http://www.rfc-editor.org/info/rfc7469>. 2015, <https://www.rfc-editor.org/info/rfc7469>.
[RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based [RFC7489] Kucherawy, M., Ed. and E. Zwicky, Ed., "Domain-based
Message Authentication, Reporting, and Conformance Message Authentication, Reporting, and Conformance
(DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015, (DMARC)", RFC 7489, DOI 10.17487/RFC7489, March 2015,
<http://www.rfc-editor.org/info/rfc7489>. <https://www.rfc-editor.org/info/rfc7489>.
Appendix A. Example Reporting Policy
A.1. Report using MAILTO
_smtp-tlsrpt.mail.example.com. IN TXT \
"v=TLSRPTv1;rua=mailto:reports@example.com"
A.2. Report using HTTPS
_smtp-tlsrpt.mail.example.com. IN TXT \
"v=TLSRPTv1; \
rua=https://reporting.example.com/v1/tlsrpt"
Appendix B. Example JSON Report
{
"organization-name": "Company-X",
"date-range": {
"start-datetime": "2016-04-01T00:00:00Z",
"end-datetime": "2016-04-01T23:59:59Z"
},
"contact-info": "sts-reporting@company-x.example",
"report-id": "5065427c-23d3-47ca-b6e0-946ea0e8c4be",
"policies": [{
"policy": {
"policy-type": "sts",
"policy-string": "version: STSv1\r\nmode: report\r\n
mx: .mail.company-y.example\r\nmax_age: 86400",
"policy-domain": "company-y.example",
"mx-host": ".mail.company-y.example"
},
"summary": {
"total-successful-session-count": 5326,
"total-failure-session-count": 303
},
"failure-details": [{
"result-type": "certificate-expired",
"sending-mta-ip": "98.136.216.25",
"receiving-mx-hostname": "mx1.mail.company-y.example",
"failed-session-count": 100
}, {
"result-type": "starttls-not-supported",
"sending-mta-ip": "98.22.33.99",
"receiving-mx-hostname": "mx2.mail.company-y.example",
"failed-session-count": 200,
"additional-information": "https://reports.company-x.example/
report_info ? id = 5065427 c - 23 d3# StarttlsNotSupported "
}, {
"result-type": "validation-failure",
"sending-mta-ip": "47.97.15.2",
"receiving-mx-hostname": "mx-backup.mail.company-y.example",
"failed-session-count": 3,
"failure-error-code": "X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED"
}]
}]
}
Figure: Example JSON report for a messages from Company-X to Company-
Y, where 100 sessions were attempted to Company Y servers with an
expired certificate and 200 sessions were attempted to Company Y
servers that did not successfully respond to the "STARTTLS" command.
Additionally 3 sessions failed due to
"X509_V_ERR_PROXY_PATH_LENGTH_EXCEEDED".
Authors' Addresses Authors' Addresses
Daniel Margolis Daniel Margolis
Google, Inc Google, Inc
Email: dmargolis (at) google.com Email: dmargolis (at) google (dot com)
Alexander Brotman Alexander Brotman
Comcast, Inc Comcast, Inc
Email: alex_brotman (at) comcast.com Email: alex_brotman (at) comcast (dot com)
Binu Ramakrishnan Binu Ramakrishnan
Yahoo!, Inc Yahoo!, Inc
Email: rbinu (at) yahoo-inc (dot com) Email: rbinu (at) yahoo-inc (dot com)
Janet Jones Janet Jones
Microsoft, Inc Microsoft, Inc
Email: janet.jones (at) microsoft (dot com) Email: janet.jones (at) microsoft (dot com)
Mark Risher Mark Risher
Google, Inc Google, Inc
Email: risher (at) google (dot com) Email: risher (at) google (dot com)
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