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Internet Engineering Task Force (IETF)                     L. Velvindron
Request for Comments: 8997                                 cyberstorm.mu
Updates: 8314                                                 S. Farrell
Category: Standards Track                         Trinity College Dublin
ISSN: 2070-1721                                               March 2021

Deprecation of TLS 1.1 for Email Submission and Access

Abstract

This specification updates the current recommendation for the use of the Transport Layer Security (TLS) protocol to provide confidentiality of email between a Mail User Agent (MUA) and a Mail Submission Server or Mail Access Server. This document updates RFC 8314.

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 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8997.

Copyright Notice

Copyright © 2021 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 (https://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.

Table of Contents

   1.  Introduction
   2.  Conventions Used in This Document
   3.  Updates to RFC 8314
   4.  IANA Considerations
   5.  Security Considerations
   6.  References
     6.1.  Normative References
     6.2.  Informative References
   Acknowledgements
   Authors' Addresses

1. Introduction

[RFC8314] defines the minimum recommended version of TLS as version 1.1. Due to the deprecation of TLS 1.1 in [RFC8996], this recommendation is no longer valid. Therefore, this document updates [RFC8314] so that the minimum version for TLS is TLS 1.2.

2. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Updates to RFC 8314

OLD: 

   |  4.1.  Deprecation of Services Using Cleartext and TLS Versions
   |  Less Than 1.1

NEW: 

   |  4.1.  Deprecation of Services Using Cleartext and TLS Versions
   |  Less Than 1.2

OLD: 

   |  As soon as practicable, MSPs currently supporting Secure Sockets
   |  Layer (SSL) 2.x, SSL 3.0, or TLS 1.0 SHOULD transition their users
   |  to TLS 1.1 or later and discontinue support for those earlier
   |  versions of SSL and TLS.

NEW: 

   |  As soon as practicable, MSPs currently supporting Secure Sockets
   |  Layer (SSL) 2.x, SSL 3.0, TLS 1.0, or TLS 1.1 SHOULD transition
   |  their users to TLS 1.2 or later and discontinue support for those
   |  earlier versions of SSL and TLS.

In Section 4.1 of [RFC8314], the text should be revised from:

OLD: 

   |  One way is for the server to refuse a ClientHello message from any
   |  client sending a ClientHello.version field corresponding to any
   |  version of SSL or TLS 1.0.

NEW: 

   |  One way is for the server to refuse a ClientHello message from any
   |  client sending a ClientHello.version field corresponding to any
   |  version of SSL or TLS earlier than TLS 1.2.

OLD: 

   |  It is RECOMMENDED that new users be required to use TLS version
   |  1.1 or greater from the start.  However, an MSP may find it
   |  necessary to make exceptions to accommodate some legacy systems
   |  that support only earlier versions of TLS or only cleartext.

NEW: 

   |  It is RECOMMENDED that new users be required to use TLS version
   |  1.2 or greater from the start.  However, an MSP may find it
   |  necessary to make exceptions to accommodate some legacy systems
   |  that support only earlier versions of TLS or only cleartext.

OLD: 

   |  If, however, an MUA provides such an indication, it MUST NOT
   |  indicate confidentiality for any connection that does not at least
   |  use TLS 1.1 with certificate verification and also meet the
   |  minimum confidentiality requirements associated with that account.

NEW: 

   |  If, however, an MUA provides such an indication, it MUST NOT
   |  indicate confidentiality for any connection that does not at least
   |  use TLS 1.2 with certificate verification and also meet the
   |  minimum confidentiality requirements associated with that account.
   
   OLD
   
   |  MUAs MUST implement TLS 1.2 [RFC5246] or later.  Earlier TLS and
   |  SSL versions MAY also be supported, so long as the MUA requires at
   |  least TLS 1.1 [RFC4346] when accessing accounts that are
   |  configured to impose minimum confidentiality requirements.

NEW: 

   |  MUAs MUST implement TLS 1.2 [RFC5246] or later, e.g., TLS 1.3
   |  [RFC8446].  Earlier TLS and SSL versions MAY also be supported, so
   |  long as the MUA requires at least TLS 1.2 [RFC5246] when accessing
   |  accounts that are configured to impose minimum confidentiality
   |  requirements.

OLD: 

   |  The default minimum expected level of confidentiality for all new
   |  accounts MUST require successful validation of the server's
   |  certificate and SHOULD require negotiation of TLS version 1.1 or
   |  greater.  (Future revisions to this specification may raise these
   |  requirements or impose additional requirements to address newly
   |  discovered weaknesses in protocols or cryptographic algorithms.)

NEW: 

   |  The default minimum expected level of confidentiality for all new
   |  accounts MUST require successful validation of the server's
   |  certificate and SHOULD require negotiation of TLS version 1.2 or
   |  greater.  (Future revisions to this specification may raise these
   |  requirements or impose additional requirements to address newly
   |  discovered weaknesses in protocols or cryptographic algorithms.)

4. IANA Considerations

This document has no IANA actions.

5. Security Considerations

The purpose of this document is to document updated recommendations for using TLS with email services. Those recommendations are based on [RFC8996].

6. References

6.1. Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.
   
   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.
   
   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.
   
   [RFC8314]  Moore, K. and C. Newman, "Cleartext Considered Obsolete:
              Use of Transport Layer Security (TLS) for Email Submission
              and Access", RFC 8314, DOI 10.17487/RFC8314, January 2018,
              <https://www.rfc-editor.org/info/rfc8314>.
   
   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.
   
   [RFC8996]  Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
              1.1", RFC 8996, DOI 10.17487/RFC8996, March 2021,
              <https://www.rfc-editor.org/info/rfc8996>.

6.2. Informative References

   [RFC4346]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.1", RFC 4346,
              DOI 10.17487/RFC4346, April 2006,
              <https://www.rfc-editor.org/info/rfc4346>.

Acknowledgements

The authors would like to thank Vittorio Bertola and Viktor Dukhovni for their feedback.

Authors' Addresses

Loganaden Velvindron
cyberstorm.mu
88 Avenue De Plevitz Roches Brunes
71259
Rose Hill
Mauritius 

   Phone: +230 59762817
   Email: logan@cyberstorm.mu

Stephen Farrell
Trinity College Dublin
Dublin
2
Ireland 

   Phone: +353-1-896-2354
   Email: stephen.farrell@cs.tcd.ie