draft-ietf-dprive-rfc7626-bis-00.txt   draft-ietf-dprive-rfc7626-bis-01.txt 
dprive S. Bortzmeyer dprive S. Bortzmeyer
Internet-Draft AFNIC Internet-Draft AFNIC
Obsoletes: 7626 (if approved) S. Dickinson Obsoletes: 7626 (if approved) S. Dickinson
Intended status: Informational Sinodun IT Intended status: Informational Sinodun IT
Expires: January 9, 2020 July 8, 2019 Expires: March 30, 2020 September 27, 2019
DNS Privacy Considerations DNS Privacy Considerations
draft-ietf-dprive-rfc7626-bis-00 draft-ietf-dprive-rfc7626-bis-01
Abstract Abstract
This document describes the privacy issues associated with the use of This document describes the privacy issues associated with the use of
the DNS by Internet users. It is intended to be an analysis of the the DNS by Internet users. It is intended to be an analysis of the
present situation and does not prescribe solutions. This document present situation and does not prescribe solutions. This document
obsoletes RFC 7626. obsoletes RFC 7626.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2020. This Internet-Draft will expire on March 30, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. The Alleged Public Nature of DNS Data . . . . . . . . . . 5 3. Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2. Data in the DNS Request . . . . . . . . . . . . . . . . . 5 3.1. The Alleged Public Nature of DNS Data . . . . . . . . . . 5
2.2.1. Data in the DNS payload . . . . . . . . . . . . . . . 7 3.2. Data in the DNS Request . . . . . . . . . . . . . . . . . 6
2.3. Cache Snooping . . . . . . . . . . . . . . . . . . . . . 7 3.2.1. Data in the DNS payload . . . . . . . . . . . . . . . 7
2.4. On the Wire . . . . . . . . . . . . . . . . . . . . . . . 7 3.3. Cache Snooping . . . . . . . . . . . . . . . . . . . . . 7
2.4.1. Unencrypted Transports . . . . . . . . . . . . . . . 7 3.4. On the Wire . . . . . . . . . . . . . . . . . . . . . . . 8
2.4.2. Encrypted Transports . . . . . . . . . . . . . . . . 9 3.4.1. Unencrypted Transports . . . . . . . . . . . . . . . 8
2.5. In the Servers . . . . . . . . . . . . . . . . . . . . . 10 3.4.2. Encrypted Transports . . . . . . . . . . . . . . . . 9
2.5.1. In the Recursive Resolvers . . . . . . . . . . . . . 10 3.5. In the Servers . . . . . . . . . . . . . . . . . . . . . 10
2.5.2. In the Authoritative Name Servers . . . . . . . . . . 12 3.5.1. In the Recursive Resolvers . . . . . . . . . . . . . 11
2.5.3. Rogue Servers . . . . . . . . . . . . . . . . . . . . 13 3.5.2. In the Authoritative Name Servers . . . . . . . . . . 15
2.5.4. Authentication of servers . . . . . . . . . . . . . . 13 3.6. Re-identification and Other Inferences . . . . . . . . . 16
2.5.5. Blocking of services . . . . . . . . . . . . . . . . 14 3.7. More Information . . . . . . . . . . . . . . . . . . . . 17
2.6. Re-identification and Other Inferences . . . . . . . . . 14 4. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 17
2.7. More Information . . . . . . . . . . . . . . . . . . . . 15 5. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 18
3. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 15 6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 15 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
5. Security Considerations . . . . . . . . . . . . . . . . . . . 16 8. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 19
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
7. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.1. Normative References . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 17 9.2. Informative References . . . . . . . . . . . . . . . . . 20
8.1. Normative References . . . . . . . . . . . . . . . . . . 17 9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.2. Informative References . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction 1. Introduction
This document is an analysis of the DNS privacy issues, in the spirit This document is an analysis of the DNS privacy issues, in the spirit
of Section 8 of [RFC6973]. of Section 8 of [RFC6973].
The Domain Name System is specified in [RFC1034], [RFC1035], and many The Domain Name System is specified in [RFC1034], [RFC1035], and many
later RFCs, which have never been consolidated. It is one of the later RFCs, which have never been consolidated. It is one of the
most important infrastructure components of the Internet and often most important infrastructure components of the Internet and often
ignored or misunderstood by Internet users (and even by many ignored or misunderstood by Internet users (and even by many
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the example.com name servers. The example.com name server will then the example.com name servers. The example.com name server will then
return the answer. The root name servers, the name servers of .com, return the answer. The root name servers, the name servers of .com,
and the name servers of example.com are called authoritative name and the name servers of example.com are called authoritative name
servers. It is important, when analyzing the privacy issues, to servers. It is important, when analyzing the privacy issues, to
remember that the question asked to all these name servers is always remember that the question asked to all these name servers is always
the original question, not a derived question. The question sent to the original question, not a derived question. The question sent to
the root name servers is "What are the AAAA records for the root name servers is "What are the AAAA records for
www.example.com?", not "What are the name servers of .com?". By www.example.com?", not "What are the name servers of .com?". By
repeating the full question, instead of just the relevant part of the repeating the full question, instead of just the relevant part of the
question to the next in line, the DNS provides more information than question to the next in line, the DNS provides more information than
necessary to the name server. necessary to the name server. In this simplified description,
recursive resolvers do not implement QNAME minimization as described
in [RFC7816], which will only send the relevant part of the question
to the upstream name server.
Because DNS relies on caching heavily, the algorithm described just Because DNS relies on caching heavily, the algorithm described just
above is actually a bit more complicated, and not all questions are above is actually a bit more complicated, and not all questions are
sent to the authoritative name servers. If a few seconds later the sent to the authoritative name servers. If a few seconds later the
stub resolver asks the recursive resolver, "What are the SRV records stub resolver asks the recursive resolver, "What are the SRV records
of _xmpp-server._tcp.example.com?", the recursive resolver will of _xmpp-server._tcp.example.com?", the recursive resolver will
remember that it knows the name servers of example.com and will just remember that it knows the name servers of example.com and will just
query them, bypassing the root and .com. Because there is typically query them, bypassing the root and .com. Because there is typically
no caching in the stub resolver, the recursive resolver, unlike the no caching in the stub resolver, the recursive resolver, unlike the
authoritative servers, sees all the DNS traffic. (Applications, like authoritative servers, sees all the DNS traffic. (Applications, like
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in clear (unencrypted). However there is increasing deployment of in clear (unencrypted). However there is increasing deployment of
DNS-over-TLS (DoT) [RFC7858] and DNS-over-HTTPS (DoH) [RFC8484], DNS-over-TLS (DoT) [RFC7858] and DNS-over-HTTPS (DoH) [RFC8484],
particularly in mobile devices, browsers and by providers of anycast particularly in mobile devices, browsers and by providers of anycast
recursive DNS resolution services. There are a few cases where there recursive DNS resolution services. There are a few cases where there
is some alternative channel encryption, for instance, in an IPsec is some alternative channel encryption, for instance, in an IPsec
VPN, at least between the stub resolver and the resolver. VPN, at least between the stub resolver and the resolver.
Today, almost all DNS queries are sent over UDP [thomas-ditl-tcp]. Today, almost all DNS queries are sent over UDP [thomas-ditl-tcp].
This has practical consequences when considering encryption of the This has practical consequences when considering encryption of the
traffic as a possible privacy technique. Some encryption solutions traffic as a possible privacy technique. Some encryption solutions
are only designed for TCP, not UDP. are only designed for TCP, not UDP and new solutions are still
emerging [I-D.ietf-quic-transport].
Another important point to keep in mind when analyzing the privacy Another important point to keep in mind when analyzing the privacy
issues of DNS is the fact that DNS requests received by a server are issues of DNS is the fact that DNS requests received by a server are
triggered by different reasons. Let's assume an eavesdropper wants triggered by different reasons. Let's assume an eavesdropper wants
to know which web page is viewed by a user. For a typical web page, to know which web page is viewed by a user. For a typical web page,
there are three sorts of DNS requests being issued: there are three sorts of DNS requests being issued:
o Primary request: this is the domain name in the URL that the user o Primary request: this is the domain name in the URL that the user
typed, selected from a bookmark, or chose by clicking on an typed, selected from a bookmark, or chose by clicking on an
hyperlink. Presumably, this is what is of interest for the hyperlink. Presumably, this is what is of interest for the
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DNS requests than strictly necessary are sent, for instance, to DNS requests than strictly necessary are sent, for instance, to
prefetch resources that the user may query later or when prefetch resources that the user may query later or when
autocompleting the URL in the address bar. Both are a big privacy autocompleting the URL in the address bar. Both are a big privacy
concern since they may leak information even about non-explicit concern since they may leak information even about non-explicit
actions. For instance, just reading a local HTML page, even without actions. For instance, just reading a local HTML page, even without
selecting the hyperlinks, may trigger DNS requests. selecting the hyperlinks, may trigger DNS requests.
For privacy-related terms, we will use the terminology from For privacy-related terms, we will use the terminology from
[RFC6973]. [RFC6973].
2. Risks 2. Scope
This document focuses mostly on the study of privacy risks for the This document focuses mostly on the study of privacy risks for the
end user (the one performing DNS requests). We consider the risks of end user (the one performing DNS requests). We consider the risks of
pervasive surveillance [RFC7258] as well as risks coming from a more pervasive surveillance [RFC7258] as well as risks coming from a more
focused surveillance. Privacy risks for the holder of a zone (the focused surveillance.
risk that someone gets the data) are discussed in [RFC5936] and
[RFC5155]. Non-privacy risks (such as cache poisoning) are out of
scope.
2.1. The Alleged Public Nature of DNS Data Privacy risks for the holder of a zone (the risk that someone gets
the data) are discussed in [RFC5936] and [RFC5155].
Privacy risks for recursive operators such as leakage of private
namespaces or blocklists are out of scope for this document.
Non-privacy risks (e.g security related concerns such as cache
poisoning) are also out of scope.
3. Risks
3.1. The Alleged Public Nature of DNS Data
It has long been claimed that "the data in the DNS is public". While It has long been claimed that "the data in the DNS is public". While
this sentence makes sense for an Internet-wide lookup system, there this sentence makes sense for an Internet-wide lookup system, there
are multiple facets to the data and metadata involved that deserve a are multiple facets to the data and metadata involved that deserve a
more detailed look. First, access control lists and private more detailed look. First, access control lists and private
namespaces notwithstanding, the DNS operates under the assumption namespaces notwithstanding, the DNS operates under the assumption
that public-facing authoritative name servers will respond to "usual" that public-facing authoritative name servers will respond to "usual"
DNS queries for any zone they are authoritative for without further DNS queries for any zone they are authoritative for without further
authentication or authorization of the client (resolver). Due to the authentication or authorization of the client (resolver). Due to the
lack of search capabilities, only a given QNAME will reveal the lack of search capabilities, only a given QNAME will reveal the
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Another differentiation to be considered is between the DNS data Another differentiation to be considered is between the DNS data
itself and a particular transaction (i.e., a DNS name lookup). DNS itself and a particular transaction (i.e., a DNS name lookup). DNS
data and the results of a DNS query are public, within the boundaries data and the results of a DNS query are public, within the boundaries
described above, and may not have any confidentiality requirements. described above, and may not have any confidentiality requirements.
However, the same is not true of a single transaction or a sequence However, the same is not true of a single transaction or a sequence
of transactions; that transaction is not / should not be public. A of transactions; that transaction is not / should not be public. A
typical example from outside the DNS world is: the web site of typical example from outside the DNS world is: the web site of
Alcoholics Anonymous is public; the fact that you visit it should not Alcoholics Anonymous is public; the fact that you visit it should not
be. be.
2.2. Data in the DNS Request 3.2. Data in the DNS Request
The DNS request includes many fields, but two of them seem The DNS request includes many fields, but two of them seem
particularly relevant for the privacy issues: the QNAME and the particularly relevant for the privacy issues: the QNAME and the
source IP address. "source IP address" is used in a loose sense of source IP address. "source IP address" is used in a loose sense of
"source IP address + maybe source port", because the port is also in "source IP address + maybe source port", because the port is also in
the request and can be used to differentiate between several users the request and can be used to differentiate between several users
sharing an IP address (behind a Carrier-Grade NAT (CGN), for instance sharing an IP address (behind a Carrier-Grade NAT (CGN), for instance
[RFC6269]). [RFC6269]).
The QNAME is the full name sent by the user. It gives information The QNAME is the full name sent by the user. It gives information
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and IPv6 source addresses. For a number of reasons, their assignment and IPv6 source addresses. For a number of reasons, their assignment
and utilization characteristics are different, which may have and utilization characteristics are different, which may have
implications for details of information leakage associated with the implications for details of information leakage associated with the
collection of source addresses. (For example, a specific IPv6 source collection of source addresses. (For example, a specific IPv6 source
address seen on the public Internet is less likely than an IPv4 address seen on the public Internet is less likely than an IPv4
address to originate behind a CGN or other NAT.) However, for both address to originate behind a CGN or other NAT.) However, for both
IPv4 and IPv6 addresses, it's important to note that source addresses IPv4 and IPv6 addresses, it's important to note that source addresses
are propagated with queries and comprise metadata about the host, are propagated with queries and comprise metadata about the host,
user, or application that originated them. user, or application that originated them.
2.2.1. Data in the DNS payload 3.2.1. Data in the DNS payload
At the time of writing there are no standardized client identifiers At the time of writing there are no standardized client identifiers
contained in the DNS payload itself (ECS [RFC7871] while widely used contained in the DNS payload itself (ECS [RFC7871] while widely used
is only of Category Informational). is only of Category Informational).
DNS Cookies [RFC7873] are a lightweight DNS transaction security DNS Cookies [RFC7873] are a lightweight DNS transaction security
mechanism that provides limited protection against a variety of mechanism that provides limited protection against a variety of
increasingly common denial-of-service and amplification/forgery or increasingly common denial-of-service and amplification/forgery or
cache poisoning attacks by off-path attackers. It is noted, however, cache poisoning attacks by off-path attackers. It is noted, however,
that they are designed to just verify IP addresses (and should change that they are designed to just verify IP addresses (and should change
once a client's IP address changes), they are not designed to once a client's IP address changes), they are not designed to
actively track users (like HTTP cookies). actively track users (like HTTP cookies).
There are anecdotal accounts of MAC addresses [1] and even user names There are anecdotal accounts of MAC addresses [1] and even user names
being inserted in non-standard EDNS(0) options for stub to resolver being inserted in non-standard EDNS(0) options for stub to resolver
communications to support proprietary functionality implemented at communications to support proprietary functionality implemented at
the resolver (e.g. parental filtering). the resolver (e.g. parental filtering).
2.3. Cache Snooping 3.3. Cache Snooping
The content of recursive resolvers' caches can reveal data about the The content of recursive resolvers' caches can reveal data about the
clients using it (the privacy risks depend on the number of clients). clients using it (the privacy risks depend on the number of clients).
This information can sometimes be examined by sending DNS queries This information can sometimes be examined by sending DNS queries
with RD=0 to inspect cache content, particularly looking at the DNS with RD=0 to inspect cache content, particularly looking at the DNS
TTLs [grangeia.snooping]. Since this also is a reconnaissance TTLs [grangeia.snooping]. Since this also is a reconnaissance
technique for subsequent cache poisoning attacks, some counter technique for subsequent cache poisoning attacks, some counter
measures have already been developed and deployed. measures have already been developed and deployed.
2.4. On the Wire 3.4. On the Wire
2.4.1. Unencrypted Transports 3.4.1. Unencrypted Transports
For unencrypted transports, DNS traffic can be seen by an For unencrypted transports, DNS traffic can be seen by an
eavesdropper like any other traffic. (DNSSEC, specified in eavesdropper like any other traffic. (DNSSEC, specified in
[RFC4033], explicitly excludes confidentiality from its goals.) So, [RFC4033], explicitly excludes confidentiality from its goals.) So,
if an initiator starts an HTTPS communication with a recipient, while if an initiator starts an HTTPS communication with a recipient, while
the HTTP traffic will be encrypted, the DNS exchange prior to it will the HTTP traffic will be encrypted, the DNS exchange prior to it will
not be. When other protocols will become more and more privacy-aware not be. When other protocols will become more and more privacy-aware
and secured against surveillance (e.g. [RFC8446], and secured against surveillance (e.g. [RFC8446],
[I-D.ietf-quic-transport]), the use of unencrypted transports for DNS [I-D.ietf-quic-transport]), the use of unencrypted transports for DNS
may become "the weakest link" in privacy. It is noted that at the may become "the weakest link" in privacy. It is noted that at the
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The recursive resolver can be a public DNS service. Some machines The recursive resolver can be a public DNS service. Some machines
may be configured to use public DNS resolvers such as those may be configured to use public DNS resolvers such as those
operated today by Google Public DNS or OpenDNS. The end user may operated today by Google Public DNS or OpenDNS. The end user may
have configured their machine to use these DNS recursive resolvers have configured their machine to use these DNS recursive resolvers
themselves -- or their IAP may have chosen to use the public DNS themselves -- or their IAP may have chosen to use the public DNS
resolvers rather than operating their own resolvers. In this resolvers rather than operating their own resolvers. In this
case, the attack surface is the entire public Internet between the case, the attack surface is the entire public Internet between the
end user's connection and the public DNS service. end user's connection and the public DNS service.
2.4.2. Encrypted Transports 3.4.2. Encrypted Transports
The use of encrypted transports directly mitigates passive The use of encrypted transports directly mitigates passive
surveillance of the DNS payload, however there are still some privacy surveillance of the DNS payload, however there are still some privacy
attacks possible. attacks possible. This section enumerates the residual privacy risks
to an end user when an attacker can passively monitor encrypted DNS
traffic flows on the wire.
These are cases where user identification, fingerprinting or These are cases where user identification, fingerprinting or
correlations may be possible due to the use of certain transport correlations may be possible due to the use of certain transport
layers or clear text/observable features. These issues are not layers or clear text/observable features. These issues are not
specific to DNS, but DNS traffic is susceptible to these attacks when specific to DNS, but DNS traffic is susceptible to these attacks when
using specific transports. using specific transports.
There are some general examples, for example, certain studies have There are some general examples, for example, certain studies have
highlighted that IP TTL or TCP Window sizes os-fingerprint [2] values highlighted that IP TTL or TCP Window sizes os-fingerprint [2] values
can be used to fingerprint client OS's or that various techniques can can be used to fingerprint client OS's or that various techniques can
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services available. Given this, the choice of a user to configure a services available. Given this, the choice of a user to configure a
single resolver (or a fixed set of resolvers) and an encrypted single resolver (or a fixed set of resolvers) and an encrypted
transport to use in all network environments can actually serve to transport to use in all network environments can actually serve to
identify the user as one that desires privacy and can provide an identify the user as one that desires privacy and can provide an
added mechanism to track them as they move across network added mechanism to track them as they move across network
environments. environments.
Users of encrypted transports are also highly likely to re-use Users of encrypted transports are also highly likely to re-use
sessions for multiple DNS queries to optimize performance (e.g. via sessions for multiple DNS queries to optimize performance (e.g. via
DNS pipelining or HTTPS multiplexing). Certain configuration options DNS pipelining or HTTPS multiplexing). Certain configuration options
for encrypted transports could also in principle fingerprint a user, for encrypted transports could also in principle fingerprint a user
for example session resumption, the maximum number of messages to or client application. For example:
send or a maximum connection time before closing a connections and
re-opening. o TLS version or cipher suite selection
o session resumption
o the maximum number of messages to send or
o a maximum connection time before closing a connections and re-
opening.
Whilst there are known attacks on older versions of TLS the most Whilst there are known attacks on older versions of TLS the most
recent recommendations [RFC7525] and developments [RFC8446] in this recent recommendations [RFC7525] and developments [RFC8446] in this
area largely mitigate those. area largely mitigate those.
Traffic analysis of unpadded encrypted traffic is also possible Traffic analysis of unpadded encrypted traffic is also possible
[pitfalls-of-dns-encrption] because the sizes and timing of encrypted [pitfalls-of-dns-encrption] because the sizes and timing of encrypted
DNS requests and responses can be correlated to unencrypted DNS DNS requests and responses can be correlated to unencrypted DNS
requests upstream of a recursive resolver. requests upstream of a recursive resolver.
2.5. In the Servers 3.5. In the Servers
Using the terminology of [RFC6973], the DNS servers (recursive Using the terminology of [RFC6973], the DNS servers (recursive
resolvers and authoritative servers) are enablers: they facilitate resolvers and authoritative servers) are enablers: they facilitate
communication between an initiator and a recipient without being communication between an initiator and a recipient without being
directly in the communications path. As a result, they are often directly in the communications path. As a result, they are often
forgotten in risk analysis. But, to quote again [RFC6973], "Although forgotten in risk analysis. But, to quote again [RFC6973], "Although
[...] enablers may not generally be considered as attackers, they may [...] enablers may not generally be considered as attackers, they may
all pose privacy threats (depending on the context) because they are all pose privacy threats (depending on the context) because they are
able to observe, collect, process, and transfer privacy-relevant able to observe, collect, process, and transfer privacy-relevant
data." In [RFC6973] parlance, enablers become observers when they data." In [RFC6973] parlance, enablers become observers when they
start collecting data. start collecting data.
Many programs exist to collect and analyze DNS data at the servers -- Many programs exist to collect and analyze DNS data at the servers --
from the "query log" of some programs like BIND to tcpdump and more from the "query log" of some programs like BIND to tcpdump and more
sophisticated programs like PacketQ [packetq] [packetq-list] and sophisticated programs like PacketQ [packetq] and DNSmezzo
DNSmezzo [dnsmezzo]. The organization managing the DNS server can [dnsmezzo]. The organization managing the DNS server can use this
use this data itself, or it can be part of a surveillance program data itself, or it can be part of a surveillance program like PRISM
like PRISM [prism] and pass data to an outside observer. [prism] and pass data to an outside observer.
Sometimes, this data is kept for a long time and/or distributed to Sometimes, this data is kept for a long time and/or distributed to
third parties for research purposes [ditl] [day-at-root], security third parties for research purposes [ditl] [day-at-root], security
analysis, or surveillance tasks. These uses are sometimes under some analysis, or surveillance tasks. These uses are sometimes under some
sort of contract, with various limitations, for instance, on sort of contract, with various limitations, for instance, on
redistribution, given the sensitive nature of the data. Also, there redistribution, given the sensitive nature of the data. Also, there
are observation points in the network that gather DNS data and then are observation points in the network that gather DNS data and then
make it accessible to third parties for research or security purposes make it accessible to third parties for research or security purposes
("passive DNS" [passive-dns]). ("passive DNS" [passive-dns]).
2.5.1. In the Recursive Resolvers 3.5.1. In the Recursive Resolvers
Recursive Resolvers see all the traffic since there is typically no Recursive Resolvers see all the traffic since there is typically no
caching before them. To summarize: your recursive resolver knows a caching before them. To summarize: your recursive resolver knows a
lot about you. The resolver of a large IAP, or a large public lot about you. The resolver of a large IAP, or a large public
resolver, can collect data from many users. You may get an idea of resolver, can collect data from many users.
the data collected by reading the privacy policy of a big public
resolver, e.g., <https://developers.google.com/speed/public-dns/
privacy>.
2.5.1.1. Encrypted transports 3.5.1.1. Resolver selection
Given all the above considerations the choice of recursive resolver
has direct privacy considerations for end users. Historically end
user devices have used the DHCP provided local network recursive
resolver which may have strong, medium or weak privacy policies
depending on the network. Privacy policies for these servers may or
may not be available and users need to be aware that privacy
guarantees will vary with network.
More recently some networks and end users have actively chosen to use
a large public resolver instead e.g. Google Public DNS, Cloudflare
or Quad9 (need refs). There can be many reasons: cost considerations
for network operators, better reliability or anti-censorship
considerations are just a few. Such services typically do provide a
privacy policy and the end user can get an idea of the data collected
by such operators by reading one e.g., Google Public DNS - Your
Privacy [4].
Even more recently some applications have announced plans to deploy
application specific DNS settings which might be enabled by default.
For example current proposals by Firefox [firefox] revolve around a
default based on geographic region using a pre-configured list of
large public resolver services which offer DoH, combined with non-
standard probing and signalling mechanism to disable DoH in
particular networks. Whereas Chrome [chrome] is experimenting with
using DoH to the DHCP provided resolver if it is on a list of DoH-
compatible providers. At the time of writing efforts to provide
standardized signalling mechanisms for applications to discover the
services offered by local resolvers are in progress
[I-D.ietf-dnsop-resolver-information].
If applications enable application specific DNS settings without
properly informing the user of the change (or do not provide an
option for user configuration of the application recursive resolver)
there is a potential privacy issue; depending on the network context
and the application default the application might use a recursive
server that provides less privacy protection than the default network
provided server without the users full knowledge. Users that are
fully aware of an application specific DNS setting may want to
actively override any default in favour of their chosen recursive
resolver.
There are also concerns that should the trend towards using large
public resolvers increase, this will itself provide a privacy concern
due to a small number of operators having visibility of the majority
of DNS requests globally and the potential for aggregating data
across services about a user. Additionally the operating
organisation of the resolver may be in a different legal jurisdiction
to the user which creates further privacy concerns around legal
protections of and access to the data collected by the operator.
At the time of writing the deployment models for DNS are evolving,
their implications are complex and extend beyond the scope of this
document. They are the subject of much other work including
[I-D.livingood-doh-implementation-risks-issues], the IETF ADD mailing
list [5] and the Encrypted DNS Deployment Initiative [6].
3.5.1.2. Active attacks on resolver configuration
The previous paragraphs discussed DNS privacy, assuming that all the
traffic was directed to the intended servers (i.e those that would be
used in the absence of an active attack) and that the potential
attacker was purely passive. But, in reality, we can have active
attackers in the network redirecting the traffic, not just to observe
it but also potentially change it.
For instance, a DHCP server controlled by an attacker can direct you
to a recursive resolver also controlled by that attacker. Most of
the time, it seems to be done to divert traffic in order to also
direct the user to a web server controlled by the attacker. However
it could be used just to capture the traffic and gather information
about you.
Other attacks, besides using DHCP, are possible. The cleartext
traffic from a DNS client to a DNS server can be intercepted along
its way from originator to intended source, for instance, by
transparent attacker controlled DNS proxies in the network that will
divert the traffic intended for a legitimate DNS server. This server
can masquerade as the intended server and respond with data to the
client. (Attacker controlled servers that inject malicious data are
possible, but it is a separate problem not relevant to privacy.) A
server controlled by an attacker may respond correctly for a long
period of time, thereby foregoing detection.
Also, malware like DNSchanger [dnschanger] can change the recursive
resolver in the machine's configuration, or the routing itself can be
subverted (for instance, [ripe-atlas-turkey]).
3.5.1.3. Blocking of user selected services
User privacy can also be at risk if there is blocking (by local
network operators or more general mechanisms) of access to remote
recursive servers that offer encrypted transports when the local
resolver does not offer encryption and/or has very poor privacy
policies. For example active blocking of port 853 for DoT or of
specific IP addresses (e.g. 1.1.1.1 or 2606:4700:4700::1111) could
restrict the resolvers available to the user. The extent of the risk
to end user privacy is highly dependant on the specific network and
user context; a user on a network that is known to perform
surveillance would be compromised if they could not access such
services whereas a user on a trusted network might have no privacy
motivation to do so.
Similarly attacks on such services e.g. DDoS could force users to
switch to other services that do not offer encrypted transports for
DNS.
3.5.1.4. Authentication of Servers
Both DoH and Strict mode for DoT require authentication of the server
and therefore as long as the authentication credentials are obtained
over a secure channel then using either of these transports defeats
the attack of re-directing traffic to rogue servers. Of course
attacks on these secure channels are also possible, but out of the
scope of this document.
3.5.1.5. Encrypted Transports
3.5.1.5.1. DoT and DoH
Use of encrypted transports does not reduce the data available in the Use of encrypted transports does not reduce the data available in the
recursive resolver and ironically can actually expose more recursive resolver and ironically can actually expose more
information about users to operators. As mentioned in Section 2.4 information about users to operators. As mentioned in Section 3.4
use of session based encrypted transports (TCP/TLS) can expose use of session based encrypted transports (TCP/TLS) can expose
correlation data about users. Such concerns in the TCP/TLS layers correlation data about users. Such concerns in the TCP/TLS layers
apply equally to DoT and DoH which both use TLS as the underlying apply equally to DoT and DoH which both use TLS as the underlying
transport. transport, some examples are:
2.5.1.2. DoH vs DoT o fingerprinting based on TLS version and/or cipher suite selection
o user tracking via session resumption in TLS 1.2
3.5.1.5.2. DoH Specific Considerations
The proposed specification for DoH [RFC8484] includes a Privacy The proposed specification for DoH [RFC8484] includes a Privacy
Considerations section which highlights some of the differences Considerations section which highlights some of the differences
between HTTP and DNS. As a deliberate design choice DoH inherits the between HTTP and DNS. As a deliberate design choice DoH inherits the
privacy properties of the HTTPS stack and as a consequence introduces privacy properties of the HTTPS stack and as a consequence introduces
new privacy concerns when compared with DNS over UDP, TCP or TLS new privacy concerns when compared with DNS over UDP, TCP or TLS
[RFC7858]. The rationale for this decision is that retaining the [RFC7858]. The rationale for this decision is that retaining the
ability to leverage the full functionality of the HTTP ecosystem is ability to leverage the full functionality of the HTTP ecosystem is
more important than placing specific constraints on this new protocol more important than placing specific constraints on this new protocol
based on privacy considerations (modulo limiting the use of HTTP based on privacy considerations (modulo limiting the use of HTTP
skipping to change at page 12, line 9 skipping to change at page 15, line 28
depending on the DoH use case and implementation. depending on the DoH use case and implementation.
At the extremes, there may be implementations that attempt to achieve At the extremes, there may be implementations that attempt to achieve
parity with DoT from a privacy perspective at the cost of using no parity with DoT from a privacy perspective at the cost of using no
identifiable headers, there might be others that provide feature rich identifiable headers, there might be others that provide feature rich
data flows where the low-level origin of the DNS query is easily data flows where the low-level origin of the DNS query is easily
identifiable. identifiable.
Privacy focussed users should be aware of the potential for Privacy focussed users should be aware of the potential for
additional client identifiers in DoH compared to DoT and may want to additional client identifiers in DoH compared to DoT and may want to
only use DoH implementations that provide clear guidance on what only use DoH client implementations that provide clear guidance on
identifiers they add. what identifiers they add.
2.5.2. In the Authoritative Name Servers 3.5.2. In the Authoritative Name Servers
Unlike what happens for recursive resolvers, observation capabilities Unlike what happens for recursive resolvers, observation capabilities
of authoritative name servers are limited by caching; they see only of authoritative name servers are limited by caching; they see only
the requests for which the answer was not in the cache. For the requests for which the answer was not in the cache. For
aggregated statistics ("What is the percentage of LOC queries?"), aggregated statistics ("What is the percentage of LOC queries?"),
this is sufficient, but it prevents an observer from seeing this is sufficient, but it prevents an observer from seeing
everything. Still, the authoritative name servers see a part of the everything. Similarly the increasing deployment of QNAME
traffic, and this subset may be sufficient to violate some privacy minimisation [ripe-qname-measurements] reduces the data visible at
expectations. the authoritative name server. Still, the authoritative name servers
see a part of the traffic, and this subset may be sufficient to
violate some privacy expectations.
Also, the end user typically has some legal/contractual link with the Also, the end user typically has some legal/contractual link with the
recursive resolver (he has chosen the IAP, or he has chosen to use a recursive resolver (he has chosen the IAP, or he has chosen to use a
given public resolver), while having no control and perhaps no given public resolver), while having no control and perhaps no
awareness of the role of the authoritative name servers and their awareness of the role of the authoritative name servers and their
observation abilities. observation abilities.
As noted before, using a local resolver or a resolver close to the As noted before, using a local resolver or a resolver close to the
machine decreases the attack surface for an on-the-wire eavesdropper. machine decreases the attack surface for an on-the-wire eavesdropper.
But it may decrease privacy against an observer located on an But it may decrease privacy against an observer located on an
authoritative name server. This authoritative name server will see authoritative name server. This authoritative name server will see
the IP address of the end client instead of the address of a big the IP address of the end client instead of the address of a big
recursive resolver shared by many users. recursive resolver shared by many users.
This "protection", when using a large resolver with many clients, is This "protection", when using a large resolver with many clients, is
no longer present if ECS [RFC7871] is used because, in this case, the no longer present if ECS [RFC7871] is used because, in this case, the
authoritative name server sees the original IP address (or prefix, authoritative name server sees the original IP address (or prefix,
depending on the setup). depending on the setup).
skipping to change at page 13, line 18 skipping to change at page 16, line 40
when doing a security analysis. when doing a security analysis.
Also, it seems (see the survey described in [aeris-dns]) that there Also, it seems (see the survey described in [aeris-dns]) that there
is a strong concentration of authoritative name servers among is a strong concentration of authoritative name servers among
"popular" domains (such as the Alexa Top N list). For instance, "popular" domains (such as the Alexa Top N list). For instance,
among the Alexa Top 100K, one DNS provider hosts today 10% of the among the Alexa Top 100K, one DNS provider hosts today 10% of the
domains. The ten most important DNS providers host together one domains. The ten most important DNS providers host together one
third of the domains. With the control (or the ability to sniff the third of the domains. With the control (or the ability to sniff the
traffic) of a few name servers, you can gather a lot of information. traffic) of a few name servers, you can gather a lot of information.
2.5.3. Rogue Servers 3.6. Re-identification and Other Inferences
The previous paragraphs discussed DNS privacy, assuming that all the
traffic was directed to the intended servers and that the potential
attacker was purely passive. But, in reality, we can have active
attackers redirecting the traffic, not to change it but just to
observe it.
For instance, a rogue DHCP server, or a trusted DHCP server that has
had its configuration altered by malicious parties, can direct you to
a rogue recursive resolver. Most of the time, it seems to be done to
divert traffic by providing lies for some domain names. But it could
be used just to capture the traffic and gather information about you.
Other attacks, besides using DHCP, are possible. The traffic from a
DNS client to a DNS server can be intercepted along its way from
originator to intended source, for instance, by transparent DNS
proxies in the network that will divert the traffic intended for a
legitimate DNS server. This rogue server can masquerade as the
intended server and respond with data to the client. (Rogue servers
that inject malicious data are possible, but it is a separate problem
not relevant to privacy.) A rogue server may respond correctly for a
long period of time, thereby foregoing detection. This may be done
for what could be claimed to be good reasons, such as optimization or
caching, but it leads to a reduction of privacy compared to if there
was no attacker present. Also, malware like DNSchanger [dnschanger]
can change the recursive resolver in the machine's configuration, or
the routing itself can be subverted (for instance,
[ripe-atlas-turkey]).
2.5.4. Authentication of servers
Both DoH and Strict mode for DoT require authentication of the server
and therefore as long as the authentication credentials are obtained
over a secure channel then using either of these transports defeats
the attack of re-directing traffic to rogue servers. Of course
attacks on these secure channels are also possible, but out of the
scope of this document.
2.5.5. Blocking of services
User privacy can also be at risk if there is blocking (by local
network operators or more general mechanisms) of access to recursive
servers that offer encrypted transports. For example active blocking
of port 853 for DoT or of specific IP addresses (e.g. 1.1.1.1 or
2606:4700:4700::1111) could restrict the resolvers available to the
client. Similarly attacks on such services e.g. DDoS could force
users to switch to other services that do not offer encrypted
transports for DNS.
2.6. Re-identification and Other Inferences
An observer has access not only to the data he/she directly collects An observer has access not only to the data he/she directly collects
but also to the results of various inferences about this data. but also to the results of various inferences about this data. The
term 'observer' here is used very generally, it might be one that is
passively observing cleartext DNS traffic, one in the network that is
actively attacking the user by re-directing DNS resolution, or it
might be a local or remote resolver operator.
For instance, a user can be re-identified via DNS queries. If the For instance, a user can be re-identified via DNS queries. If the
adversary knows a user's identity and can watch their DNS queries for adversary knows a user's identity and can watch their DNS queries for
a period, then that same adversary may be able to re-identify the a period, then that same adversary may be able to re-identify the
user solely based on their pattern of DNS queries later on regardless user solely based on their pattern of DNS queries later on regardless
of the location from which the user makes those queries. For of the location from which the user makes those queries. For
example, one study [herrmann-reidentification] found that such re- example, one study [herrmann-reidentification] found that such re-
identification is possible so that "73.1% of all day-to-day links identification is possible so that "73.1% of all day-to-day links
were correctly established, i.e. user u was either re-identified were correctly established, i.e. user u was either re-identified
unambiguously (1) or the classifier correctly reported that u was not unambiguously (1) or the classifier correctly reported that u was not
skipping to change at page 15, line 5 skipping to change at page 17, line 24
For instance, one could imagine that an intelligence agency For instance, one could imagine that an intelligence agency
identifies people going to a site by putting in a very long DNS name identifies people going to a site by putting in a very long DNS name
and looking for queries of a specific length. Such traffic analysis and looking for queries of a specific length. Such traffic analysis
could weaken some privacy solutions. could weaken some privacy solutions.
The IAB privacy and security program also have a work in progress The IAB privacy and security program also have a work in progress
[RFC7624] that considers such inference-based attacks in a more [RFC7624] that considers such inference-based attacks in a more
general framework. general framework.
2.7. More Information 3.7. More Information
Useful background information can also be found in [tor-leak] (about Useful background information can also be found in [tor-leak] (about
the risk of privacy leak through DNS) and in a few academic papers: the risk of privacy leak through DNS) and in a few academic papers:
[yanbin-tsudik], [castillo-garcia], [fangming-hori-sakurai], and [yanbin-tsudik], [castillo-garcia], [fangming-hori-sakurai], and
[federrath-fuchs-herrmann-piosecny]. [federrath-fuchs-herrmann-piosecny].
3. Actual "Attacks" 4. Actual "Attacks"
A very quick examination of DNS traffic may lead to the false A very quick examination of DNS traffic may lead to the false
conclusion that extracting the needle from the haystack is difficult. conclusion that extracting the needle from the haystack is difficult.
"Interesting" primary DNS requests are mixed with useless (for the "Interesting" primary DNS requests are mixed with useless (for the
eavesdropper) secondary and tertiary requests (see the terminology in eavesdropper) secondary and tertiary requests (see the terminology in
Section 1). But, in this time of "big data" processing, powerful Section 1). But, in this time of "big data" processing, powerful
techniques now exist to get from the raw data to what the techniques now exist to get from the raw data to what the
eavesdropper is actually interested in. eavesdropper is actually interested in.
Many research papers about malware detection use DNS traffic to Many research papers about malware detection use DNS traffic to
skipping to change at page 15, line 36 skipping to change at page 18, line 7
power of the observation of DNS traffic. See [dns-footprint], power of the observation of DNS traffic. See [dns-footprint],
[dagon-malware], and [darkreading-dns]. [dagon-malware], and [darkreading-dns].
Passive DNS systems [passive-dns] allow reconstruction of the data of Passive DNS systems [passive-dns] allow reconstruction of the data of
sometimes an entire zone. They are used for many reasons -- some sometimes an entire zone. They are used for many reasons -- some
good, some bad. Well-known passive DNS systems keep only the DNS good, some bad. Well-known passive DNS systems keep only the DNS
responses, and not the source IP address of the client, precisely for responses, and not the source IP address of the client, precisely for
privacy reasons. Other passive DNS systems may not be so careful. privacy reasons. Other passive DNS systems may not be so careful.
And there is still the potential problems with revealing QNAMEs. And there is still the potential problems with revealing QNAMEs.
The revelations (from the Edward Snowden documents, which were leaked The revelations from the Edward Snowden documents, which were leaked
from the National Security Agency (NSA)) of the MORECOWBELL from the National Security Agency (NSA) provide evidence of the use
surveillance program [morecowbell], which uses the DNS, both of the DNS in mass surveillance operations [morecowbell]. For
passively and actively, to surreptitiously gather information about example the MORECOWBELL surveillance program, which uses a dedicated
the users, is another good example showing that the lack of privacy covert monitoring infrastructure to actively query DNS servers and
perform HTTP requests to obtain meta information about services and
to check their availability. Also the QUANTUMTHEORY project which
includes detecting lookups for certain addresses and injecting bogus
replies is another good example showing that the lack of privacy
protections in the DNS is actively exploited. protections in the DNS is actively exploited.
4. Legalities 5. Legalities
To our knowledge, there are no specific privacy laws for DNS data, in To our knowledge, there are no specific privacy laws for DNS data, in
any country. Interpreting general privacy laws like any country. Interpreting general privacy laws like
[data-protection-directive] or GDPR [4] applicable in the European [data-protection-directive] or GDPR [7] applicable in the European
Union in the context of DNS traffic data is not an easy task, and we Union in the context of DNS traffic data is not an easy task, and we
do not know a court precedent here. See an interesting analysis in do not know a court precedent here. See an interesting analysis in
[sidn-entrada]. [sidn-entrada].
5. Security Considerations 6. Security Considerations
This document is entirely about security, more precisely privacy. It This document is entirely about security, more precisely privacy. It
just lays out the problem; it does not try to set requirements (with just lays out the problem; it does not try to set requirements (with
the choices and compromises they imply), much less define solutions. the choices and compromises they imply), much less define solutions.
Possible solutions to the issues described here are discussed in Possible solutions to the issues described here are discussed in
other documents (currently too many to all be mentioned); see, for other documents (currently too many to all be mentioned); see, for
instance, 'Recommendations for DNS Privacy Operators' instance, 'Recommendations for DNS Privacy Operators'
[I-D.ietf-dprive-bcp-op]. [I-D.ietf-dprive-bcp-op].
6. Acknowledgments 7. Acknowledgments
Thanks to Nathalie Boulvard and to the CENTR members for the original Thanks to Nathalie Boulvard and to the CENTR members for the original
work that led to this document. Thanks to Ondrej Sury for the work that led to this document. Thanks to Ondrej Sury for the
interesting discussions. Thanks to Mohsen Souissi and John Heidemann interesting discussions. Thanks to Mohsen Souissi and John Heidemann
for proofreading and to Paul Hoffman, Matthijs Mekking, Marcos Sanz, for proofreading and to Paul Hoffman, Matthijs Mekking, Marcos Sanz,
Tim Wicinski, Francis Dupont, Allison Mankin, and Warren Kumari for Tim Wicinski, Francis Dupont, Allison Mankin, and Warren Kumari for
proofreading, providing technical remarks, and making many proofreading, providing technical remarks, and making many
readability improvements. Thanks to Dan York, Suzanne Woolf, Tony readability improvements. Thanks to Dan York, Suzanne Woolf, Tony
Finch, Stephen Farrell, Peter Koch, Simon Josefsson, and Frank Denis Finch, Stephen Farrell, Peter Koch, Simon Josefsson, and Frank Denis
for good written contributions. And thanks to the IESG members for for good written contributions. And thanks to the IESG members for
the last remarks. the last remarks.
7. Changelog 8. Changelog
draft-ietf-dprive-rfc7627-bis-01
o Re-structure section 3.5 (was 2.5)
* Collect considerations for recursive resolvers together
* Re-work several sections here to clarify their context (e.g.
'Rogue servers' becomes 'Active attacks on resolver
configuration')
* Add discussion of resolver selection
o Update text and old reference on Snowdon revelations.
o Add text on and references to QNAME minimisation RFC and
deployment measurements
o Correct outdated references
o Clarify scope by adding a Scope section (was Risks overview)
o Clarify what risks are considered in section 3.4.2
draft-ietf-dprive-rfc7627-bis-00 draft-ietf-dprive-rfc7627-bis-00
o Rename after WG adoption o Rename after WG adoption
o Use DoT acronym throughout o Use DoT acronym throughout
o Minor updates to status of deployment and other drafts o Minor updates to status of deployment and other drafts
draft-bortzmeyer-dprive-rfc7626-bis-02 draft-bortzmeyer-dprive-rfc7626-bis-02
skipping to change at page 17, line 12 skipping to change at page 20, line 12
o Update many references o Update many references
o Add discussions of encrypted transports including DoT and DoH o Add discussions of encrypted transports including DoT and DoH
o Add section on DNS payload o Add section on DNS payload
o Add section on authentication of servers o Add section on authentication of servers
o Add section on blocking of services o Add section on blocking of services
8. References 9. References
8.1. Normative References 9.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>. <https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and [RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>. November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013, <https://www.rfc- DOI 10.17487/RFC6973, July 2013, <https://www.rfc-
editor.org/info/rfc6973>. editor.org/info/rfc6973>.
[RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <https://www.rfc-editor.org/info/rfc7258>. 2014, <https://www.rfc-editor.org/info/rfc7258>.
8.2. Informative References [RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.
9.2. Informative References
[aeris-dns] [aeris-dns]
Vinot, N., "Vie privee: et le DNS alors?", (In French), Vinot, N., "Vie privee: et le DNS alors?", (In French),
2015, <https://blog.imirhil.fr/vie-privee-et-le-dns- 2015, <https://blog.imirhil.fr/vie-privee-et-le-dns-
alors.html>. alors.html>.
[castillo-garcia] [castillo-garcia]
Castillo-Perez, S. and J. Garcia-Alfaro, "Anonymous Castillo-Perez, S. and J. Garcia-Alfaro, "Anonymous
Resolution of DNS Queries", 2008, Resolution of DNS Queries", 2008,
<http://deic.uab.es/~joaquin/papers/is08.pdf>. <http://deic.uab.es/~joaquin/papers/is08.pdf>.
[chrome] Baheux, , "Experimenting with same-provider DNS-over-HTTPS
upgrade", September 2019,
<https://blog.chromium.org/2019/09/experimenting-with-
same-provider-dns.html>.
[dagon-malware] [dagon-malware]
Dagon, D., "Corrupted DNS Resolution Paths: The Rise of a Dagon, D., "Corrupted DNS Resolution Paths: The Rise of a
Malicious Resolution Authority", ISC/OARC Workshop, 2007, Malicious Resolution Authority", ISC/OARC Workshop, 2007,
<https://www.dns-oarc.net/files/workshop-2007/Dagon- <https://www.dns-oarc.net/files/workshop-2007/Dagon-
Resolution-corruption.pdf>. Resolution-corruption.pdf>.
[darkreading-dns] [darkreading-dns]
Lemos, R., "Got Malware? Three Signs Revealed In DNS Lemos, R., "Got Malware? Three Signs Revealed In DNS
Traffic", InformationWeek Dark Reading, May 2013, Traffic", InformationWeek Dark Reading, May 2013,
<http://www.darkreading.com/analytics/security-monitoring/ <http://www.darkreading.com/analytics/security-monitoring/
skipping to change at page 19, line 22 skipping to change at page 22, line 31
[federrath-fuchs-herrmann-piosecny] [federrath-fuchs-herrmann-piosecny]
Federrath, H., Fuchs, K., Herrmann, D., and C. Piosecny, Federrath, H., Fuchs, K., Herrmann, D., and C. Piosecny,
"Privacy-Preserving DNS: Analysis of Broadcast, Range "Privacy-Preserving DNS: Analysis of Broadcast, Range
Queries and Mix-based Protection Methods", Computer Queries and Mix-based Protection Methods", Computer
Security ESORICS 2011, Springer, page(s) 665-683, Security ESORICS 2011, Springer, page(s) 665-683,
ISBN 978-3-642-23821-5, 2011, <https://svs.informatik.uni- ISBN 978-3-642-23821-5, 2011, <https://svs.informatik.uni-
hamburg.de/publications/2011/2011-09-14_FFHP_PrivacyPreser hamburg.de/publications/2011/2011-09-14_FFHP_PrivacyPreser
vingDNS_ESORICS2011.pdf>. vingDNS_ESORICS2011.pdf>.
[firefox] Deckelmann, , "What's next in making Encrypted DNS-over-
HTTPS the Default", September 2019,
<https://blog.mozilla.org/futurereleases/2019/09/06/whats-
next-in-making-dns-over-https-the-default/>.
[grangeia.snooping] [grangeia.snooping]
Grangeia, L., "DNS Cache Snooping or Snooping the Cache Grangeia, L., "DNS Cache Snooping or Snooping the Cache
for Fun and Profit", February 2004, for Fun and Profit", 2005,
<http://www.msit2005.mut.ac.th/msit_media/1_2551/nete4630/ <https://www.semanticscholar.org/paper/Cache-Snooping-or-
materials/20080718130017Hc.pdf>. Snooping-the-Cache-for-Fun-and-
1-Grangeia/9b22f606e10b3609eafbdcbfc9090b63be8778c3>.
[herrmann-reidentification] [herrmann-reidentification]
Herrmann, D., Gerber, C., Banse, C., and H. Federrath, Herrmann, D., Gerber, C., Banse, C., and H. Federrath,
"Analyzing Characteristic Host Access Patterns for Re- "Analyzing Characteristic Host Access Patterns for Re-
Identification of Web User Sessions", Identification of Web User Sessions",
DOI 10.1007/978-3-642-27937-9_10, 2012, <http://epub.uni- DOI 10.1007/978-3-642-27937-9_10, 2012, <http://epub.uni-
regensburg.de/21103/1/Paper_PUL_nordsec_published.pdf>. regensburg.de/21103/1/Paper_PUL_nordsec_published.pdf>.
[I-D.ietf-dnsop-resolver-information]
Sood, P., Arends, R., and P. Hoffman, "DNS Resolver
Information Self-publication", draft-ietf-dnsop-resolver-
information-00 (work in progress), August 2019.
[I-D.ietf-dprive-bcp-op] [I-D.ietf-dprive-bcp-op]
Dickinson, S., Overeinder, B., Rijswijk-Deij, R., and A. Dickinson, S., Overeinder, B., Rijswijk-Deij, R., and A.
Mankin, "Recommendations for DNS Privacy Service Mankin, "Recommendations for DNS Privacy Service
Operators", draft-ietf-dprive-bcp-op-02 (work in Operators", draft-ietf-dprive-bcp-op-03 (work in
progress), March 2019. progress), July 2019.
[I-D.ietf-quic-transport] [I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-20 (work and Secure Transport", draft-ietf-quic-transport-23 (work
in progress), April 2019. in progress), September 2019.
[I-D.ietf-tls-sni-encryption] [I-D.ietf-tls-sni-encryption]
Huitema, C. and E. Rescorla, "Issues and Requirements for Huitema, C. and E. Rescorla, "Issues and Requirements for
SNI Encryption in TLS", draft-ietf-tls-sni-encryption-04 SNI Encryption in TLS", draft-ietf-tls-sni-encryption-06
(work in progress), November 2018. (work in progress), September 2019.
[I-D.livingood-doh-implementation-risks-issues]
Livingood, J., Antonakakis, M., Sleigh, B., and A.
Winfield, "Centralized DNS over HTTPS (DoH) Implementation
Issues and Risks", draft-livingood-doh-implementation-
risks-issues-04 (work in progress), September 2019.
[morecowbell] [morecowbell]
Grothoff, C., Wachs, M., Ermert, M., and J. Appelbaum, Grothoff, C., Wachs, M., Ermert, M., and J. Appelbaum,
"NSA's MORECOWBELL: Knell for DNS", GNUnet e.V., January "NSA's MORECOWBELL: Knell for DNS", GNUnet e.V., January
2015, <https://gnunet.org/morecowbell>. 2015, <https://pdfs.semanticscholar.org/2610/2b99bdd6a258a
98740af8217ba8da8a1e4fa.pdf>.
[packetq] Dot SE, "PacketQ, a simple tool to make SQL-queries
against PCAP-files", 2011,
<https://github.com/dotse/packetq/wiki>.
[packetq-list] [packetq] DNS-OARC, "PacketQ, a simple tool to make SQL-queries
PacketQ, "PacketQ Mailing List", against PCAP-files", 2011, <https://github.com/DNS-OARC/
<http://lists.iis.se/mailman/listinfo/packetq>. PacketQ>.
[passive-dns] [passive-dns]
Weimer, F., "Passive DNS Replication", April 2005, Weimer, F., "Passive DNS Replication", April 2005,
<http://www.enyo.de/fw/software/dnslogger/#2>. <https://www.first.org/conference/2005/papers/florian-
weimer-slides-1.pdf>.
[pitfalls-of-dns-encrption] [pitfalls-of-dns-encrption]
Shulman, H., "Pretty Bad Privacy:Pitfalls of DNS Shulman, H., "Pretty Bad Privacy:Pitfalls of DNS
Encryption", <https://www.ietf.org/mail-archive/web/dns- Encryption", <https://dl.acm.org/citation.cfm?id=2665959>.
privacy/current/pdfWqAIUmEl47.pdf>.
[prism] Wikipedia, "PRISM (surveillance program)", July 2015, [prism] Wikipedia, "PRISM (surveillance program)", July 2015,
<https://en.wikipedia.org/w/index.php?title=PRISM_(surveil <https://en.wikipedia.org/w/index.php?title=PRISM_(surveil
lance_program)&oldid=673789455>. lance_program)&oldid=673789455>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005, RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>. <https://www.rfc-editor.org/info/rfc4033>.
skipping to change at page 22, line 11 skipping to change at page 25, line 37
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499, Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>. January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[ripe-atlas-turkey] [ripe-atlas-turkey]
Aben, E., "A RIPE Atlas View of Internet Meddling in Aben, E., "A RIPE Atlas View of Internet Meddling in
Turkey", March 2014, Turkey", March 2014,
<https://labs.ripe.net/Members/emileaben/a-ripe-atlas- <https://labs.ripe.net/Members/emileaben/a-ripe-atlas-
view-of-internet-meddling-in-turkey>. view-of-internet-meddling-in-turkey>.
[ripe-qname-measurements]
University of Twente, "Making the DNS More Private with
QNAME Minimisation", April 2019,
<https://labs.ripe.net/Members/wouter_de_vries/make-dns-a-
bit-more-private-with-qname-minimisation>.
[sidn-entrada] [sidn-entrada]
Hesselman, C., Jansen, J., Wullink, M., Vink, K., and M. Hesselman, C., Jansen, J., Wullink, M., Vink, K., and M.
Simon, "A privacy framework for 'DNS big data' Simon, "A privacy framework for 'DNS big data'
applications", November 2014, applications", November 2014,
<https://www.sidnlabs.nl/uploads/tx_sidnpublications/ <https://www.sidnlabs.nl/downloads/
yBW6hBoaSZe4m6GJc_0b7w/2211058ab6330c7f3788141ea19d3db7/
SIDN_Labs_Privacyraamwerk_Position_Paper_V1.4_ENG.pdf>. SIDN_Labs_Privacyraamwerk_Position_Paper_V1.4_ENG.pdf>.
[thomas-ditl-tcp] [thomas-ditl-tcp]
Thomas, M. and D. Wessels, "An Analysis of TCP Traffic in Thomas, M. and D. Wessels, "An Analysis of TCP Traffic in
Root Server DITL Data", DNS-OARC 2014 Fall Workshop, Root Server DITL Data", DNS-OARC 2014 Fall Workshop,
October 2014, <https://indico.dns- October 2014, <https://indico.dns-
oarc.net/event/20/session/2/contribution/15/material/ oarc.net/event/20/session/2/contribution/15/material/
slides/1.pdf>. slides/1.pdf>.
[tor-leak] [tor-leak]
Tor, "DNS leaks in Tor", 2013, Tor, "DNS leaks in Tor", 2013,
<https://www.torproject.org/docs/ <https://www.torproject.org/docs/
faq.html.en#WarningsAboutSOCKSandDNSInformationLeaks>. faq.html.en#WarningsAboutSOCKSandDNSInformationLeaks>.
[yanbin-tsudik] [yanbin-tsudik]
Yanbin, L. and G. Tsudik, "Towards Plugging Privacy Leaks Yanbin, L. and G. Tsudik, "Towards Plugging Privacy Leaks
in the Domain Name System", October 2009, in the Domain Name System", October 2009,
<http://arxiv.org/abs/0910.2472>. <http://arxiv.org/abs/0910.2472>.
8.3. URIs 9.3. URIs
[1] https://lists.dns-oarc.net/pipermail/dns- [1] https://lists.dns-oarc.net/pipermail/dns-
operations/2016-January/014141.html operations/2016-January/014141.html
[2] http://netres.ec/?b=11B99BD [2] http://netres.ec/?b=11B99BD
[3] https://www.researchgate.net/publication/320322146_DNS-DNS_DNS- [3] https://www.researchgate.net/publication/320322146_DNS-DNS_DNS-
based_De-NAT_Scheme based_De-NAT_Scheme
[4] https://www.eugdpr.org/the-regulation.html [4] https://developers.google.com/speed/public-dns/privacy
[5] https://mailarchive.ietf.org/arch/browse/static/add
[6] https://www.encrypted-dns.org
[7] https://www.eugdpr.org/the-regulation.html
Authors' Addresses Authors' Addresses
Stephane Bortzmeyer Stephane Bortzmeyer
AFNIC AFNIC
1, rue Stephenson 1, rue Stephenson
Montigny-le-Bretonneux Montigny-le-Bretonneux
France 78180 France 78180
Email: bortzmeyer+ietf@nic.fr Email: bortzmeyer+ietf@nic.fr
Sara Dickinson Sara Dickinson
Sinodun IT Sinodun IT
Magdalen Centre Magdalen Centre
Oxford Science Park Oxford Science Park
Oxford OX4 4GA Oxford OX4 4GA
United Kingdom United Kingdom
Email: sara@sinodun.com Email: sara@sinodun.com
 End of changes. 59 change blocks. 
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