Record Header Extensions for DTLS
draft-fossati-tls-ext-header-01

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Last updated 2018-03-03
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TLS Working Group                                             T. Fossati
Internet-Draft                                                     Nokia
Updates: 5246, 6347 (if approved)                   N. Mavrogiannopoulos
Intended status: Standards Track                                  RedHat
Expires: September 4, 2018                                March 03, 2018

                   Record Header Extensions for DTLS
                    draft-fossati-tls-ext-header-01

Abstract

   This document proposes a mechanism to extend the record header in
   DTLS.  To that aim, the DTLS header is modified as follows: the
   length field is trimmed to 15 bits, and the length's top bit is given
   the "record header extension indicator" semantics, allowing a sender
   to signal that one or more record header extensions have been added
   to this record.  We define the generic format of a record header
   extension and the general rules associated with its handling.  Any
   details regarding syntax, semantics and negotiation of a specific
   record header extension, are left to future documents.

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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   This Internet-Draft will expire on September 4, 2018.

Copyright Notice

   Copyright (c) 2018 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

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   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
   2.  Length Redefined  . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Record Header Extension . . . . . . . . . . . . . . . . . . .   3
     3.1.  Format  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Negotiation . . . . . . . . . . . . . . . . . . . . . . .   4
     3.3.  Backwards Compatibility . . . . . . . . . . . . . . . . .   4
     3.4.  Use with Connection ID  . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   5.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   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 [RFC2119].

2.  Length Redefined

   DTLS ([RFC6347], [I-D.ietf-tls-dtls13]) requires the size of record
   payloads to not exceed 2^14 bytes - plus a small amount that accounts
   for compression or AEAD expansion.  This means that the first bit in
   the length field of the DTLS record header is, in fact, unused.

   The proposal (Figure 1) is to shorten the length field to 15 bits and
   use the top bit (E) to signify the presence / absence of a record
   header extension.

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    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+
   |  ContentType  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        ProtocolVersion        |             epoch             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        sequence_number                        |
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