Using Early Data in DNS over TLS
draft-ietf-dprive-early-data-00
DPRIVE A. Ghedini
Internet-Draft Cloudflare, Inc.
Intended status: Standards Track April 22, 2020
Expires: October 24, 2020
Using Early Data in DNS over TLS
draft-ietf-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.
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This Internet-Draft will expire on October 24, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
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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
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5.1. Registry for DNS Resource Record (RR) TYPEs for TLS Early
Data . . . . . . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
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
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