Using Early Data in DNS over TLS
draft-ghedini-dprive-early-data-01

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Network Working Group                                         A. Ghedini
Internet-Draft                                          Cloudflare, Inc.
Intended status: Standards Track                           July 06, 2019
Expires: January 7, 2020

                    Using Early Data in DNS over TLS
                   draft-ghedini-dprive-early-data-01

Abstract

   This document illustrates the risks of using TLS 1.3 early data with
   DNS over TLS, and specifies behaviors that can be adopted by clients
   and servers to reduce those risks.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 7, 2020.

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

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Notational Conventions  . . . . . . . . . . . . . . . . . . .   2
   3.  Early Data in DNS over TLS  . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
     4.1.  Information Exposure  . . . . . . . . . . . . . . . . . .   3
     4.2.  Denial of Service . . . . . . . . . . . . . . . . . . . .   4
     4.3.  Privacy . . . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   TLS 1.3 [TLS13] defines a mechanism, called 0-RTT session resumption
   or early data, that allows clients to send data to servers in the
   first round-trip of a resumed connection without having to wait for
   the TLS handshake to complete.

   This can be used to send DNS queries to DNS over TLS [DOT] servers
   without incurring in the cost of the additional round-trip required
   by the TLS handshake.  This can provide significant performance
   improvements in cases where new DNS over TLS connections need to be
   established often such as on mobile clients where the network might
   not be stable, or on resolvers where keeping an open connection to
   many authoritative servers might not be practical.

   However the use of early data allows an attacker to capture and
   replay the encrypted DNS queries carried on the TLS connection.  This
   can have unwanted consequences and help in recovering information
   about those queries.  While [TLS13] describes tecniques to reduce the
   likelihood of a replay attack, they are not perfect and still leave
   some potential for exploitation.

2.  Notational Conventions

   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.

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3.  Early Data in DNS over TLS

   Early data forms a single stream of data along with other application
   data, meaning that one or more DNS queries can either be partially or
   fully contained within early data.  Once the TLS handshake has
   completed, the early data is known to not be a replayed copy of that
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