SMTP Security via Opportunistic DNS-Based Authentication of Named Entities (DANE) Transport Layer Security (TLS)
RFC 7672
Document | Type | RFC - Proposed Standard (October 2015; Errata) | |
---|---|---|---|
Authors | Viktor Dukhovni , Wes Hardaker | ||
Last updated | 2020-01-21 | ||
Stream | IETF | ||
Formats | plain text html pdf htmlized with errata bibtex | ||
Reviews | |||
Stream | WG state | Submitted to IESG for Publication | |
Document shepherd | Ólafur Guðmundsson | ||
Shepherd write-up | Show (last changed 2015-03-23) | ||
IESG | IESG state | RFC 7672 (Proposed Standard) | |
Action Holders |
(None)
|
||
Consensus Boilerplate | Yes | ||
Telechat date | |||
Responsible AD | Stephen Farrell | ||
Send notices to | (None) | ||
IANA | IANA review state | Version Changed - Review Needed | |
IANA action state | No IANA Actions |
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 9.1. Client Operational Considerations .........................29 9.2. Publisher Operational Considerations ......................30Show full document text