Network Working Group K. Fujiwara
Internet-Draft JPRS
Intended status: Informational 13 July 2021
Expires: 14 January 2022
DNS over HTTPS via HTTP proxies
draft-fujiwara-dprive-doh-via-httpproxy-00
Abstract
DNS queries over HTTPS (DoH) hides DNS query information by (HTTPS)
encryption. However, DoH providers know both query source IP
addresses and DNS queries, and it is a privacy issue of DoH. It is
possible to hide query source IP addresses from DoH providers by
existing protocol (HTTP) and implementations (HTTP proxy software).
This document proposes the use of DoH via HTTP proxy services.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Idea to hide query source IP addresses . . . . . . . . . . . 3
3.1. DoH over Carrier Grade NAT (CGN) . . . . . . . . . . . . 3
3.2. DoH over public NAT64 services . . . . . . . . . . . . . 3
3.3. DoH via HTTP proxies . . . . . . . . . . . . . . . . . . 4
4. Proposal: Use of open HTTP proxy services for DoH . . . . . . 4
4.1. Details of DNS over HTTPS via HTTP proxy . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Example Squid configuration . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
DNS clients (stub resolvers) send end users' DNS queries to full-
service resolvers.
The queries between stub resolvers and full-service resolvers are not
encrypted on traditional DNS [RFC1034,RFC1035]. DNS over TLS (DoT)
[RFC7858] and DNS queries over HTTPS (DoH) [RFC8484] provide the
encrypted transport (TLS or HTTPS) between stub resolvers and full-
service resolvers.
Sensitive data of personal privacy in DNS is a combination of the
query time, the query source IP address, and the DNS query itself
(query name, query type, query class). The dataset indicates when
(timestamp) and who (IP address) is trying to access the specified
host (query name).
DoH providers have the ability to collect the dataset. Many DNS/DoH
providers offer decent privacy policies and they usually don't
actively use privacy information. However, it is important to
provide a way to protect personal privacy for self-defense.
To meet the demand, several methods have been proposed to protect
personal privacy by hiding query source IP addresses. One is DNS
over Tor and the other is Oblivious DNS / DoH
[I-D.pauly-dprive-oblivious-doh]. However, it is possible to hide
query source IP addresses from DoH providers by a more simple way
existing protocols.
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This document describes some idea to hide the query source IP
addresses and proposes the use of DoH via HTTP [RFC7231] proxy
services.
If multiple providers offer specialized HTTP proxies that relays DoH
queries to multiple DoH providers, users can hide their query source
IP addresses from DoH providers.
2. Terminology
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
BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Many of the specialized terms used in this document are defined in
DNS Terminology [RFC8499].
3. Idea to hide query source IP addresses
The IP Network Address Translation (NAT) [RFC3022] is a way to hide
stub resolvers' IP addresses. However, NAT public IP address may
disclose some part of end users' information. Therefore, additional
element is required to hide the IP address.
3.1. DoH over Carrier Grade NAT (CGN)
There are many low-priced Mobile Virtual Network Operator (MVNO)
services. Many of them uses Carrier Grade NAT (CGN) [RFC6888], and
multiple users share one IPv4 global address.
If users buy the MVNO services and use them exclusively for name
resolution, it provides to hide their original IP address from DoH
providers.
Pros: people can hide their IP addresses from DoH providers.
Cons: This idea requires MVNO's costs.
3.2. DoH over public NAT64 services
[RFC6146] specified Stateful NAT64: Network Address and Protocol
Translation from IPv6 Clients to IPv4 Servers.
Some operators provide public NAT64 services. NAT64 service rewrites
query source IPv6 addresses to shared IPv4 addresses.
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If DoH clients connect to DoH servers' IPv4 addresses via the NAT64
services, The DoH providers can only know the NAT64 providers' public
IPv4 addresses.
Pros: DoH clients can hide their IPv6 addresses from DoH providers.
Users can use multiple DoH providers and multiple NAT64 prefixes/
services to increase personal privacy.
Cons: Public NAT64 service providers are limited.
3.3. DoH via HTTP proxies
DNS over HTTPS (DoH) is a simple HTTP protocol. Therefore, DoH via
HTTP proxies is also possible.
HTTP proxies cannot know the DoH queries because HTTP proxies act as
TCP relay and DNS queries between DoH clients and DoH providers are
encrypted by HTTPS. And DoH providers cannot know the original query
source IP addresses.
Pros: No need to develop new protocols.
Cons: Public HTTP proxies may be abused.
4. Proposal: Use of open HTTP proxy services for DoH
Prepare open HTTP proxies that relays DoH queries to well-known DoH
providers only.
DoH clients send DoH queries to DoH providers via the open HTTP
proxies.
User's privacy can be improved by using multiple DoH proxies and
multiple DoH providers for each query.
+----------+ +-------+ +---------+
|DoH client| | HTTP | | DoH |
| +--(DoH via proxy)---+ proxy +--(DoH)---+ Provider|
| | 1: CONNECT DoH:443 | | | |
+----------+ HTTP/1.1 +-------+ +---------+
2: (HTTPS setup)
3: GET/PUT DoH protocol
4.1. Details of DNS over HTTPS via HTTP proxy
1. A DoH client (that would like to use HTTP proxy) connects to a
specified HTTP proxy.
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2. The DoH client sends "CONNECT doH-server-name:443 HTTP/1.1" to
the HTTP proxy.
3. Then, the HTTP proxy relays TCP connection to the "doh-server-
name" port 443.
4. The DoH client communicate queries by DNS over HTTPS with "doh-
server-name" via the HTTP proxy.
5. IANA Considerations
This document has no IANA actions.
6. Security Considerations
HTTP proxies may be abused.
To reduce abusive use of open HTTP proxies, limit destination port to
443 and destination host names to popular DoH providers.
The frequency of connections from each IP address should be limited.
DoH providers can track end-users' privacy information by using TLS
session information. Privacy information may be leaked if
optimizations such as TLS pinning is used.
Disconnecting the TCP/TLS session every time may improve privacy,
however it increases DoH query latency.
7. Acknowledgments
The author would like to specifically thank DNS over Tor and
Oblivious DNS / DoH [I-D.pauly-dprive-oblivious-doh].
8. References
8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
DOI 10.17487/RFC3022, January 2001,
<https://www.rfc-editor.org/info/rfc3022>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<https://www.rfc-editor.org/info/rfc7231>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
8.2. Informative References
[I-D.pauly-dprive-oblivious-doh]
Kinnear, E., McManus, P., Pauly, T., Verma, T., and C. A.
Wood, "Oblivious DNS Over HTTPS", Work in Progress,
Internet-Draft, draft-pauly-dprive-oblivious-doh-06, 8
March 2021, <https://www.ietf.org/archive/id/draft-pauly-
dprive-oblivious-doh-06.txt>.
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[RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
A., and H. Ashida, "Common Requirements for Carrier-Grade
NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
April 2013, <https://www.rfc-editor.org/info/rfc6888>.
[SQUID] "Squid: Optimising Web Delivery", n.d.,
<http://www.squid-cache.org/>.
Appendix A. Example Squid configuration
Squid: Optimising Web Delivery [SQUID] is a well-used open source
caching proxy software for the Web.
An example squid configuration example that can only connect to some
DoH servers is here.
acl SSL_ports port 443
acl CONNECT method CONNECT
acl doh dstdomain dns.google
acl doh dstdomain cloudflare-dns.com
acl doh dstdomain doh.opendns.com
acl doh dstdomain dns.quad9.net
acl doh dstdomain public.dns.iij.jp
http_access allow doh CONNECT SSL_ports
http_access deny all
Author's Address
Kazunori Fujiwara
Japan Registry Services Co., Ltd.
Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda, Chiyoda-ku, Tokyo
101-0065
Japan
Phone: +81 3 5215 8451
Email: fujiwara@jprs.co.jp
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