Using Early Data in DNS over TLS
draft-ghedini-dprive-early-data-00

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Network Working Group                                         A. Ghedini
Internet-Draft                                          Cloudflare, Inc.
Intended status: Standards Track                          March 25, 2019
Expires: September 26, 2019

                    Using Early Data in DNS over TLS
                   draft-ghedini-dprive-early-data-00

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 September 26, 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
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   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
     4.4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . .   4
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .   4
     5.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   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 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, and it can be useful 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

   TODO: talk more about 0-RTT vs. 1-RTT security properties.

   A server can signal to clients whether it is willing to accept early
   data in future connections by providing the "early_data" TLS
   extension as part of a TLS session ticket, as well as limit the
   amount of early data it is willing to accept using the
   "max_early_data_size" field of the "early_data" extension.
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