Mail User Agent Strict Transport Security (MUA-STS)
draft-ietf-uta-email-deep-06

Document Type Active Internet-Draft (uta WG)
Last updated 2017-03-13
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Network Working Group                                           K. Moore
Internet-Draft                                          Network Heretics
Updates: 1939, 2595, 3464, 3501, 5068,                         C. Newman
         6186, 6409 (if approved)                                 Oracle
Intended status: Standards Track                          March 13, 2017
Expires: September 14, 2017

          Mail User Agent Strict Transport Security (MUA-STS)
                      draft-ietf-uta-email-deep-06

Abstract

   This specification defines a set of requirements and facilities
   designed to improve email confidentiality between a mail user agent
   (MUA) and a mail submission or mail access server.  This provides
   mechanisms intended to increase use of already deployed Transport
   Layer Security (TLS) technology and provides a model for a mail user
   agent's confidentiality assurance.  This enables mail service
   providers to advertise strict transport security (STS) policies that
   request MUAs increase confidentiality assurance.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on September 14, 2017.

Copyright Notice

   Copyright (c) 2017 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

Moore & Newman         Expires September 14, 2017               [Page 1]
Internet-Draft                   MUA-STS                      March 2017

   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions and Terminology Used in This Document . . . . . .   4
   3.  Mail Account Confidentiality Assurance Level  . . . . . . . .   4
     3.1.  Confidentiality Assurance Level 1 . . . . . . . . . . . .   6
     3.2.  Confidentiality Assurance Level 0 . . . . . . . . . . . .   7
     3.3.  Other Confidentiality Assurance Levels  . . . . . . . . .   7
   4.  Implicit TLS  . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Implicit TLS for POP  . . . . . . . . . . . . . . . . . .   8
     4.2.  Implicit TLS for IMAP . . . . . . . . . . . . . . . . . .   8
     4.3.  Implicit TLS for SMTP Submission  . . . . . . . . . . . .   8
     4.4.  Implicit TLS Connection Closure for POP, IMAP and SMTP  .   9
   5.  Email Security Upgrading Using Security Directives  . . . . .   9
   6.  Server Strict Transport Security Policy . . . . . . . . . . .  11
   7.  Client Storage of Email Security Directives . . . . . . . . .  11
     7.1.  Security Directive Upgrade Example  . . . . . . . . . . .  12
     7.2.  Security Policy Failures  . . . . . . . . . . . . . . . .  12
   8.  Recording TLS Cipher Suite in Received Header . . . . . . . .  12
   9.  Extensions for STS Policy and Reporting . . . . . . . . . . .  13
     9.1.  IMAP STS Extension  . . . . . . . . . . . . . . . . . . .  13
     9.2.  POP DEEP Extension  . . . . . . . . . . . . . . . . . . .  15
     9.3.  SMTP MSTS Extension . . . . . . . . . . . . . . . . . . .  16
   10. Account Setup Considerations  . . . . . . . . . . . . . . . .  18
     10.1.  Use of SRV records in Establishing Configuration . . . .  18
     10.2.  Certificate Pinning  . . . . . . . . . . . . . . . . . .  19
   11. Implementation Requirements . . . . . . . . . . . . . . . . .  19
     11.1.  All Implementations (Client and Server)  . . . . . . . .  19
       11.1.1.  Client Certificate Authentication  . . . . . . . . .  20
     11.2.  Mail Server Implementation Requirements  . . . . . . . .  21
     11.3.  Mail User Agent Implementation Requirements  . . . . . .  21
     11.4.  Non-configurable MUAs and nonstandard access protocols .  22
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