The EDNS(0) Padding Option
RFC 7830

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Internet Engineering Task Force (IETF)                      A. Mayrhofer
Request for Comments: 7830                                   nic.at GmbH
Category: Standards Track                                       May 2016
ISSN: 2070-1721

                       The EDNS(0) Padding Option

Abstract

   This document specifies the EDNS(0) "Padding" option, which allows
   DNS clients and servers to pad request and response messages by a
   variable number of octets.

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 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/rfc7830.

Copyright Notice

   Copyright (c) 2016 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.

Mayrhofer                    Standards Track                    [Page 1]
RFC 7830                     EDNS(0) Padding                    May 2016

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  The "Padding" Option  . . . . . . . . . . . . . . . . . . . .   3
   4.  Usage Considerations  . . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The Domain Name System (DNS) [RFC1035] was specified to transport DNS
   messages in cleartext form.  Since this can expose significant
   amounts of information about the Internet activities of an end user,
   the IETF has undertaken work to provide confidentiality to DNS
   transactions (see the DPRIVE working group).  Encrypting the DNS
   transport is considered one of the options to improve the situation.

   However, even if both DNS query and response messages were encrypted,
   metadata could still be used to correlate such messages with well-
   known unencrypted messages, hence jeopardizing some of the
   confidentiality gained by encryption.  One such property is the
   message size.

   This document specifies the Extensions Mechanisms for DNS (EDNS(0))
   "Padding" option, which allows DNS clients and servers to
   artificially increase the size of a DNS message by a variable number
   of bytes, hampering size-based correlation of the encrypted message.

2.  Terminology

   The terms "Requestor" and "Responder" are to be interpreted as
   specified in [RFC6891].

   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
   [RFC2119].

Mayrhofer                    Standards Track                    [Page 2]
RFC 7830                     EDNS(0) Padding                    May 2016

3.  The "Padding" Option

   The EDNS(0) [RFC6891] specifies a mechanism to include new options in
   DNS packets, contained in the RDATA of the OPT meta-RR.  This
   document specifies the "Padding" option in order to allow clients and
   servers to pad DNS packets by a variable number of bytes.  The
   "Padding" option MUST occur at most, once per OPT meta-RR (and hence,
   at most once per message).

   The figure below specifies the structure of the option in the RDATA
   of the OPT RR:

                0                       8                      16
                +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                |                  OPTION-CODE                  |
                +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
                |                 OPTION-LENGTH                 |