A Flags Extension for TLS 1.3
draft-nir-tls-tlsflags-01

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TLS                                                               Y. Nir
Internet-Draft                                                   DellEMC
Intended status: Standards Track                          March 27, 2019
Expires: September 28, 2019

                     A Flags Extension for TLS 1.3
                       draft-nir-tls-tlsflags-01

Abstract

   A number of extensions are proposed in the TLS working group that
   carry no interesting information except the 1-bit indication that a
   certain optional feature is supported.  Such extensions take 4 octets
   each.  This document defines a flags extension that can provide such
   indications at an average cost of 1.5 bits each.  More precisely, it
   provides up to 64 such indications in a fixed-size, 12-octet
   extension.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on September 28, 2019.

Copyright Notice

   Copyright (c) 2019 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

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements and Other Notation . . . . . . . . . . . . .   2
   2.  The tls_flags Extension . . . . . . . . . . . . . . . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   4
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     6.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   Since the publication of TLS 1.3 ([RFC8446]) there have been several
   proposal for extensions to this protocol, where the presence of the
   content-free extension in both the ClientHello and either the
   ServerHello or EncryptedExtensions indicates nothing except either
   support for the optional feature or an intent to use the optional
   feature.  Examples:

   o  An extension that allows the server to tell the client that cross-
      SNI resumption is allowed: [I-D.sy-tls-resumption-group].

   o  An extension that is used to negotiate support for authentication
      using both certificates and external PSKs:
      [I-D.ietf-tls-tls13-cert-with-extern-psk].

   This document proposes a single extension called tls_flags that can
   enumerate such flag extensions and allowing both client and server to
   indicate support for optional features in a concise way.

1.1.  Requirements and Other Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD 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.

   The term "flag extension" is used to denote an extension where the
   extension_data field is zero-length in all cases and the presence of

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   the extension denotes either support for some feature or the intent
   to use that feature.

   The term "flag-type feature" denotes an options TLS 1.3 feature the
   support for which is negotiated using a flag extension, whether that
   flag extension is its own extension or a value in the extension
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