SMTP Security via Opportunistic DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS)
RFC 7672
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Type |
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RFC - Proposed Standard
(October 2015; No errata)
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Last updated |
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2015-10-14
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Stream |
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IETF
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plain text
pdf
html
bibtex
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WG state
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Submitted to IESG for Publication
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Document shepherd |
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Ólafur Guðmundsson
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Shepherd write-up |
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Show
(last changed 2015-03-23)
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| IESG |
IESG state |
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RFC 7672 (Proposed Standard)
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Consensus Boilerplate |
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Yes
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Telechat date |
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Responsible AD |
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Stephen Farrell
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Send notices to |
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(None)
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| IANA |
IANA review state |
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Version Changed - Review Needed
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IANA action state |
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No IC
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Internet Engineering Task Force (IETF) V. Dukhovni
Request for Comments: 7672 Two Sigma
Category: Standards Track W. Hardaker
ISSN: 2070-1721 Parsons
October 2015
SMTP Security via Opportunistic DNS-Based Authentication of Named
Entities (DANE) Transport Layer Security (TLS)
Abstract
This memo describes a downgrade-resistant protocol for SMTP transport
security between Message Transfer Agents (MTAs), based on the DNS-
Based Authentication of Named Entities (DANE) TLSA DNS record.
Adoption of this protocol enables an incremental transition of the
Internet email backbone to one using encrypted and authenticated
Transport Layer Security (TLS).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7672.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Dukhovni & Hardaker Standards Track [Page 1]
RFC 7672 SMTP Security via Opportunistic DANE TLS October 2015
Table of Contents
1. Introduction ....................................................3
1.1. Terminology ................................................4
1.2. Background .................................................6
1.3. SMTP Channel Security ......................................6
1.3.1. STARTTLS Downgrade Attack ...........................7
1.3.2. Insecure Server Name without DNSSEC .................7
1.3.3. Sender Policy Does Not Scale ........................8
1.3.4. Too Many Certification Authorities ..................9
2. Identifying Applicable TLSA Records .............................9
2.1. DNS Considerations .........................................9
2.1.1. DNS Errors, "Bogus" Responses, and
"Indeterminate" Responses ...........................9
2.1.2. DNS Error Handling .................................11
2.1.3. Stub Resolver Considerations .......................12
2.2. TLS Discovery .............................................13
2.2.1. MX Resolution ......................................14
2.2.2. Non-MX Destinations ................................16
2.2.3. TLSA Record Lookup .................................18
3. DANE Authentication ............................................20
3.1. TLSA Certificate Usages ...................................20
3.1.1. Certificate Usage DANE-EE(3) .......................21
3.1.2. Certificate Usage DANE-TA(2) .......................22
3.1.3. Certificate Usages PKIX-TA(0) and PKIX-EE(1) .......23
3.2. Certificate Matching ......................................24
3.2.1. DANE-EE(3) Name Checks .............................24
3.2.2. DANE-TA(2) Name Checks .............................24
3.2.3. Reference Identifier Matching ......................25
4. Server Key Management ..........................................26
5. Digest Algorithm Agility .......................................27
6. Mandatory TLS Security .........................................27
7. Note on DANE for Message User Agents ...........................28
8. Interoperability Considerations ................................28
8.1. SNI Support ...............................................28
8.2. Anonymous TLS Cipher Suites ...............................29
9. Operational Considerations .....................................29
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