Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
RFC 7525

Document Type RFC - Best Current Practice (May 2015; Errata)
Also known as BCP 195
Last updated 2015-10-14
Replaces draft-sheffer-tls-bcp
Stream IETF
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Stream WG state Submitted to IESG for Publication
Document shepherd Orit Levin
Shepherd write-up Show (last changed 2015-01-12)
IESG IESG state RFC 7525 (Best Current Practice)
Consensus Boilerplate Yes
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Responsible AD Stephen Farrell
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state No IC
Internet Engineering Task Force (IETF)                        Y. Sheffer
Request for Comments: 7525                                        Intuit
BCP: 195                                                         R. Holz
Category: Best Current Practice                                    NICTA
ISSN: 2070-1721                                           P. Saint-Andre
                                                                    &yet
                                                                May 2015

    Recommendations for Secure Use of Transport Layer Security (TLS)
              and Datagram Transport Layer Security (DTLS)

Abstract

   Transport Layer Security (TLS) and Datagram Transport Layer Security
   (DTLS) are widely used to protect data exchanged over application
   protocols such as HTTP, SMTP, IMAP, POP, SIP, and XMPP.  Over the
   last few years, several serious attacks on TLS have emerged,
   including attacks on its most commonly used cipher suites and their
   modes of operation.  This document provides recommendations for
   improving the security of deployed services that use TLS and DTLS.
   The recommendations are applicable to the majority of use cases.

Status of This Memo

   This memo documents an Internet Best Current Practice.

   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
   BCPs 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/rfc7525.

Sheffer, et al.           Best Current Practice                 [Page 1]
RFC 7525                   TLS Recommendations                  May 2015

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.

Sheffer, et al.           Best Current Practice                 [Page 2]
RFC 7525                   TLS Recommendations                  May 2015

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.  General Recommendations . . . . . . . . . . . . . . . . . . .   5
     3.1.  Protocol Versions . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  SSL/TLS Protocol Versions . . . . . . . . . . . . . .   5
       3.1.2.  DTLS Protocol Versions  . . . . . . . . . . . . . . .   6
       3.1.3.  Fallback to Lower Versions  . . . . . . . . . . . . .   7
     3.2.  Strict TLS  . . . . . . . . . . . . . . . . . . . . . . .   7
     3.3.  Compression . . . . . . . . . . . . . . . . . . . . . . .   8
     3.4.  TLS Session Resumption  . . . . . . . . . . . . . . . . .   8
     3.5.  TLS Renegotiation . . . . . . . . . . . . . . . . . . . .   9
     3.6.  Server Name Indication  . . . . . . . . . . . . . . . . .   9
   4.  Recommendations: Cipher Suites  . . . . . . . . . . . . . . .   9
     4.1.  General Guidelines  . . . . . . . . . . . . . . . . . . .   9
     4.2.  Recommended Cipher Suites . . . . . . . . . . . . . . . .  11
       4.2.1.  Implementation Details  . . . . . . . . . . . . . . .  12
     4.3.  Public Key Length . . . . . . . . . . . . . . . . . . . .  12
     4.4.  Modular Exponential vs. Elliptic Curve DH Cipher Suites .  13
     4.5.  Truncated HMAC  . . . . . . . . . . . . . . . . . . . . .  14
   5.  Applicability Statement . . . . . . . . . . . . . . . . . . .  15
     5.1.  Security Services . . . . . . . . . . . . . . . . . . . .  15
     5.2.  Opportunistic Security  . . . . . . . . . . . . . . . . .  16
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
     6.1.  Host Name Validation  . . . . . . . . . . . . . . . . . .  17
     6.2.  AES-GCM . . . . . . . . . . . . . . . . . . . . . . . . .  18
     6.3.  Forward Secrecy . . . . . . . . . . . . . . . . . . . . .  18
     6.4.  Diffie-Hellman Exponent Reuse . . . . . . . . . . . . . .  19
     6.5.  Certificate Revocation  . . . . . . . . . . . . . . . . .  19
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