< draft-ietf-dprive-rfc7626-bis-04.txt   draft-ietf-dprive-rfc7626-bis-05.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: July 19, 2020 January 16, 2020 Expires: November 5, 2020 May 4, 2020
DNS Privacy Considerations DNS Privacy Considerations
draft-ietf-dprive-rfc7626-bis-04 draft-ietf-dprive-rfc7626-bis-05
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 July 19, 2020. This Internet-Draft will expire on November 5, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 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
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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. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3. Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. The Alleged Public Nature of DNS Data . . . . . . . . . . 5 4. Risks in the DNS Data . . . . . . . . . . . . . . . . . . . . 6
3.2. Data in the DNS Request . . . . . . . . . . . . . . . . . 6 4.1. The Alleged Public Nature of DNS Data . . . . . . . . . . 6
3.2.1. Data in the DNS payload . . . . . . . . . . . . . . . 7 4.2. Data in the DNS Request . . . . . . . . . . . . . . . . . 6
3.3. Cache Snooping . . . . . . . . . . . . . . . . . . . . . 8 4.2.1. Data in the DNS Payload . . . . . . . . . . . . . . . 8
3.4. On the Wire . . . . . . . . . . . . . . . . . . . . . . . 8 4.3. Cache Snooping . . . . . . . . . . . . . . . . . . . . . 8
3.4.1. Unencrypted Transports . . . . . . . . . . . . . . . 8 5. Risks On the Wire . . . . . . . . . . . . . . . . . . . . . . 8
3.4.2. Encrypted Transports . . . . . . . . . . . . . . . . 10 5.1. Unencrypted Transports . . . . . . . . . . . . . . . . . 8
3.5. In the Servers . . . . . . . . . . . . . . . . . . . . . 11 5.2. Encrypted Transports . . . . . . . . . . . . . . . . . . 10
3.5.1. In the Recursive Resolvers . . . . . . . . . . . . . 11 6. Risks in the Servers . . . . . . . . . . . . . . . . . . . . 11
3.5.2. In the Authoritative Name Servers . . . . . . . . . . 15 6.1. In the Recursive Resolvers . . . . . . . . . . . . . . . 12
3.6. Re-identification and Other Inferences . . . . . . . . . 16 6.1.1. Resolver Selection . . . . . . . . . . . . . . . . . 12
3.7. More Information . . . . . . . . . . . . . . . . . . . . 17 6.1.2. Active Attacks on Resolver Configuration . . . . . . 14
4. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 17 6.1.3. Blocking of User Selected DNS Resolution Services . . 15
5. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 18 6.1.4. Encrypted Transports and Recursive Resolvers . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18 6.2. In the Authoritative Name Servers . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 7. Other risks . . . . . . . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 7.1. Re-identification and Other Inferences . . . . . . . . . 17
9. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 19 7.2. More Information . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 8. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . 21 9. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 19
10.2. Informative References . . . . . . . . . . . . . . . . . 21 10. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 27 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
13. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 20
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
14.1. Normative References . . . . . . . . . . . . . . . . . . 22
14.2. Informative References . . . . . . . . . . . . . . . . . 22
14.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
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 (DNS) is specified in [RFC1034], [RFC1035], The Domain Name System (DNS) is specified in [RFC1034], [RFC1035],
and many later RFCs, which have never been consolidated. It is one and many later RFCs, which have never been consolidated. It is one
of the most important infrastructure components of the Internet and of the most important infrastructure components of the Internet and
often ignored or misunderstood by Internet users (and even by many often ignored or misunderstood by Internet users (and even by many
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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. In this simplified description, necessary to the name server. In this simplified description,
recursive resolvers do not implement QNAME minimization as described recursive resolvers do not implement QNAME minimization as described
in [RFC7816], which will only send the relevant part of the question in [RFC7816], which will only send the relevant part of the question
to the upstream name server. to the upstream name server.
Because DNS relies on caching heavily, the algorithm described above DNS relies on caching heavily, so the algorithm described above is
is actually a bit more complicated, and not all questions are sent to actually a bit more complicated, and not all questions are sent to
the authoritative name servers. If a few seconds later the stub the authoritative name servers. If a few seconds later the stub
resolver asks the recursive resolver, "What are the SRV records of resolver asks the recursive resolver, "What are the SRV records of
_xmpp-server._tcp.example.com?", the recursive resolver will remember _xmpp-server._tcp.example.com?", the recursive resolver will remember
that it knows the name servers of example.com and will just query that it knows the name servers of example.com and will just query
them, bypassing the root and .com. Because there is typically no them, bypassing the root and .com. Because there is typically no
caching in the stub resolver, the recursive resolver, unlike the 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
web browsers, may have some form of caching that does not follow DNS web browsers, may have some form of caching that does not follow DNS
rules, for instance, because it may ignore the TTL. So, the rules, for instance, because it may ignore the TTL. So, the
recursive resolver does not see all the name resolution activity.) recursive resolver does not see all the name resolution activity.)
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namespaces or blocklists are out of scope for this document. namespaces or blocklists are out of scope for this document.
Non-privacy risks (e.g security related considerations such as cache Non-privacy risks (e.g security related considerations such as cache
poisoning) are also out of scope. poisoning) are also out of scope.
The privacy risks associated with the use of other protocols that The privacy risks associated with the use of other protocols that
make use of DNS information are not considered here. make use of DNS information are not considered here.
3. Risks 3. Risks
This section outlines the privacy considerations associated with The following four sections outline the privacy considerations
different aspects of the DNS for the end user. When reading this associated with different aspects of the DNS for the end user. When
section it needs to be kept in mind that many of the considerations reading these sections it needs to be kept in mind that many of the
(for example, recursive resolver and transport protocol) can be considerations (for example, recursive resolver and transport
specific to the network context that a device is using at a given protocol) can be specific to the network context that a device is
point in time. A user may have many devices and each device might using at a given point in time. A user may have many devices and
utilize many different networks (e.g. home, work, public or cellular) each device might utilize many different networks (e.g. home, work,
over a period of time or even concurrently. An exhaustive analysis public or cellular) over a period of time or even concurrently. An
of the privacy considerations for an individual user would need to exhaustive analysis of the privacy considerations for an individual
take into account the set of devices used and the multiple dynamic user would need to take into account the set of devices used and the
contexts of each device. This document does not attempt such a multiple dynamic contexts of each device. This document does not
complex analysis, instead it presents an overview of the various attempt such a complex analysis, instead it presents an overview of
considerations that could form the basis of such an analysis. the various considerations that could form the basis of such an
analysis.
3.1. The Alleged Public Nature of DNS Data 4. Risks in the DNS Data
4.1. 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 (ACLs) and private more detailed look. First, access control lists (ACLs) 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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existence). In other words: one needs to know what to ask for, in existence). In other words: one needs to know what to ask for, in
order to receive a response. The zone transfer QTYPE [RFC5936] is order to receive a response. The zone transfer QTYPE [RFC5936] is
often blocked or restricted to authenticated/authorized access to often blocked or restricted to authenticated/authorized access to
enforce this difference (and maybe for other reasons). enforce this difference (and maybe for other reasons).
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; those transaction are not / should not be public. A
typical example from outside the DNS world is: the web site of single transactions reveals both the originator of the query and the
Alcoholics Anonymous is public; the fact that you visit it should not query contents which potentially leaks sensitive information about a
be. specific user. A typical example from outside the DNS world is: the
web site of Alcoholics Anonymous is public; the fact that you visit
it should not be. Furthermore, the ability to link queries reveals
information about individual use patterns.
3.2. Data in the DNS Request 4.2. 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 number", because the port "source IP address + maybe source port number", because the port
number is also in the request and can be used to differentiate number is also in the request and can be used to differentiate
between several users sharing an IP address (behind a Carrier-Grade between several users sharing an IP address (behind a Carrier-Grade
NAT (CGN), for instance [RFC6269]). NAT (CGN), for instance [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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resolver, the source IP address is the address of the user's machine. resolver, the source IP address is the address of the user's machine.
Therefore, all the issues and warnings about collection of IP Therefore, all the issues and warnings about collection of IP
addresses apply here. For the communication between the recursive addresses apply here. For the communication between the recursive
resolver and the authoritative name servers, the source IP address resolver and the authoritative name servers, the source IP address
has a different meaning; it does not have the same status as the has a different meaning; it does not have the same status as the
source address in an HTTP connection. It is typically the IP address source address in an HTTP connection. It is typically the IP address
of the recursive resolver that, in a way, "hides" the real user. of the recursive resolver that, in a way, "hides" the real user.
However, hiding does not always work. Sometimes EDNS(0) Client However, hiding does not always work. Sometimes EDNS(0) Client
subnet [RFC7871] is used (see its privacy analysis in subnet [RFC7871] is used (see its privacy analysis in
[denis-edns-client-subnet]). Sometimes the end user has a personal [denis-edns-client-subnet]). Sometimes the end user has a personal
recursive resolver on her machine. In both cases, the IP address is recursive resolver on her machine. In both cases, the IP address
as sensitive as it is for HTTP [sidn-entrada]. originating queries to the authoritative server is as sensitive as it
is for HTTP [sidn-entrada].
A note about IP addresses: there is currently no IETF document that A note about IP addresses: there is currently no IETF document that
describes in detail all the privacy issues around IP addressing in describes in detail all the privacy issues around IP addressing in
general, although [RFC7721] does discuss privacy considerations for general, although [RFC7721] does discuss privacy considerations for
IPv6 address generation mechanisms. In the meantime, the discussion IPv6 address generation mechanisms. In the meantime, the discussion
here is intended to include both IPv4 and IPv6 source addresses. For here is intended to include both IPv4 and IPv6 source addresses. For
a number of reasons, their assignment and utilization characteristics a number of reasons, their assignment and utilization characteristics
are different, which may have implications for details of information are different, which may have implications for details of information
leakage associated with the collection of source addresses. (For leakage associated with the collection of source addresses. (For
example, a specific IPv6 source address seen on the public Internet example, a specific IPv6 source address seen on the public Internet
is less likely than an IPv4 address to originate behind an address is less likely than an IPv4 address to originate behind an address
sharing scheme.) However, for both IPv4 and IPv6 addresses, it is sharing scheme.) However, for both IPv4 and IPv6 addresses, it is
important to note that source addresses are propagated with queries important to note that source addresses are propagated with queries
and comprise metadata about the host, user, or application that and comprise metadata about the host, user, or application that
originated them. originated them.
3.2.1. Data in the DNS payload 4.2.1. 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 [RFC6891] for stub to
communications to support proprietary functionality implemented at resolver communications to support proprietary functionality
the resolver (e.g., parental filtering). implemented at the resolver (e.g., parental filtering).
3.3. Cache Snooping 4.3. 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
[cache-snooping-defence].
3.4. On the Wire 5. Risks On the Wire
3.4.1. Unencrypted Transports 5.1. 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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o The recursive resolver can be in the IAP network. For most o The recursive resolver can be in the IAP network. For most
residential users and potentially other networks, the typical case residential users and potentially other networks, the typical case
is for the end user's device to be configured (typically is for the end user's device to be configured (typically
automatically through DHCP or RA options) with the addresses of automatically through DHCP or RA options) with the addresses of
the DNS proxy in the CPE, which in turns points to the DNS the DNS proxy in the CPE, which in turns points to the DNS
recursive resolvers at the IAP. The attack surface for on-the- recursive resolvers at the IAP. The attack surface for on-the-
wire attacks is therefore from the end user system across the wire attacks is therefore from the end user system across the
local network and across the IAP network to the IAP's recursive local network and across the IAP network to the IAP's recursive
resolvers. resolvers.
o The recursive resolver can be a public DNS service. Some machines o The recursive resolver can be a public DNS service (or a privately
run DNS resolver hosted on the public internet). 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 by Google Public DNS or OpenDNS. The end user may have operated by Google Public DNS or OpenDNS. The end user may have
configured their machine to use these DNS recursive resolvers 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. It can be noted
that if the user selects a single resolver with a small client
population (even when using an encrypted transport) it can
actually serve to aid tracking of that user as they move across
network environment.
It is also noted that typically a device connected _only_ to a modern It is also noted that typically a device connected _only_ to a modern
cellular network is cellular network is
o directly configured with only the recursive resolvers of the IAP o directly configured with only the recursive resolvers of the IAP
and and
o afforded some level of protection against some types of o afforded some level of protection against some types of
eavesdropping for all traffic (including DNS traffic) due to the eavesdropping for all traffic (including DNS traffic) due to the
cellular network link-layer encryption. cellular network link-layer encryption.
The attack surface for this specific scenario is not considered here. The attack surface for this specific scenario is not considered here.
3.4.2. Encrypted Transports 5.2. 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. This section enumerates the residual privacy risks attacks possible. This section enumerates the residual privacy risks
to an end user when an attacker can passively monitor encrypted DNS to an end user when an attacker can passively monitor encrypted DNS
traffic flows on the wire. 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 IPv4 TTL, IPv6 Hop Limit, or TCP Window sizes os- highlighted that IPv4 TTL, IPv6 Hop Limit, or TCP Window sizes os-
fingerprint [2] values can be used to fingerprint client OS's or that fingerprint [2] values can be used to fingerprint client OS's or that
various techniques can be used to de-NAT DNS queries dns-de-nat [3]. various techniques can be used to de-NAT DNS queries dns-de-nat [3].
Note that even when using encrypted transports the use of clear text Note that even when using encrypted transports the use of clear text
transport options to decrease latency can provide correlation of a transport options to decrease latency can provide correlation of a
users' connections e.g. using TCP Fast Open [RFC7413] with TLS 1.2. users' connections e.g. using TCP Fast Open [RFC7413].
More specifically, (since the deployment of encrypted transports is
not widespread at the time of writing) users wishing to use encrypted
transports for DNS may in practice be limited in the resolver
services available. Given this, the choice of a user to configure a
single resolver (or a fixed set of resolvers) and an encrypted
transport to use in all network environments can actually serve to
identify the user as one that desires privacy and can provide an
added mechanism to track them as they move across network
environments.
Implementations that support encrypted transports also commonly re- Implementations that support encrypted transports also commonly re-
use sessions for multiple DNS queries to optimize performance (e.g. use connections for multiple DNS queries to optimize performance
via DNS pipelining or HTTPS multiplexing). Default configuration (e.g. via DNS pipelining or HTTPS multiplexing). Default
options for encrypted transports could in principle fingerprint a configuration options for encrypted transports could in principle
specific client application. For example: fingerprint a specific client application. For example:
o TLS version or cipher suite selection o TLS version or cipher suite selection
o session resumption o session resumption
o the maximum number of messages to send or o the maximum number of messages to send or
o a maximum connection time before closing a connections and re- o a maximum connection time before closing a connections and re-
opening. opening.
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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 the development of TLS 1.3 recent recommendations [RFC7525] and the development of TLS 1.3
[RFC8446] largely mitigate those. [RFC8446] largely mitigate those.
Traffic analysis of unpadded encrypted traffic is also possible Traffic analysis of unpadded encrypted traffic is also possible
[pitfalls-of-dns-encryption] because the sizes and timing of [pitfalls-of-dns-encryption] because the sizes and timing of
encrypted DNS requests and responses can be correlated to unencrypted encrypted DNS requests and responses can be correlated to unencrypted
DNS requests upstream of a recursive resolver. DNS requests upstream of a recursive resolver.
3.5. In the Servers 6. Risks 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
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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]).
3.5.1. In the Recursive Resolvers 6.1. 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. resolver, can collect data from many users.
3.5.1.1. Resolver Selection 6.1.1. Resolver Selection
Given all the above considerations, the choice of recursive resolver Given all the above considerations, the choice of recursive resolver
has direct privacy considerations for end users. Historically, end has direct privacy considerations for end users. Historically, end
user devices have used the DHCP-provided local network recursive user devices have used the DHCP-provided local network recursive
resolver, which may have strong, medium, or weak privacy policies resolver. The choice by a user to join a particular network (e.g. by
depending on the network. Privacy policies for these servers may or physically plugging in a cable or selecting a network in a OS
may not be available and users need to be aware that privacy dialogue) typically updates a number of system resources - these can
guarantees will vary with network. include IP addresses, availability of IPv4/IPv6, DHCP server, and DNS
resolver. These individual changes, including the change in DNS
resolver, are not normally communicated directly to the user by the
OS when the network is joined. The choice of network has
historically determined the default system DNS resolver selection;
the two are directly coupled in this model.
The vast majority of users do not change their default system DNS
settings and so implicitly accept the network settings for DNS. The
network resolvers have therefore historically been the sole
destination for all of the DNS queries from a device. These
resolvers 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.
All major OS's expose the system DNS settings and allow users to
manually override them if desired.
More recently, some networks and end users have actively chosen to More recently, some networks and end users have actively chosen to
use a large public resolver, e.g., Google Public DNS [4], Cloudflare use a large public resolver, e.g., Google Public DNS [4], Cloudflare
[5], or Quad9 [6]. There can be many reasons: cost considerations [5], or Quad9 [6]. There can be many reasons: cost considerations
for network operators, better reliability or anti-censorship for network operators, better reliability or anti-censorship
considerations are just a few. Such services typically do provide a 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 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 by such operators by reading one e.g., Google Public DNS - Your
Privacy [7]. Privacy [7].
In general, as with many other protocols, issues around In general, as with many other protocols, issues around
centralization also arise with DNS. The picture is fluid with centralization also arise with DNS. The picture is fluid with
several competing factors contributing which can also vary by several competing factors contributing which can also vary by
geographic region. These include: geographic region. These include:
o ISP outsourcing, including to third party and public resolvers o ISP outsourcing, including to third party and public resolvers
o regional market domination by one or only a few ISPs o regional market domination by one or only a few ISPs
o popular applications directing DNS traffic by default to specific
dominant resolvers, see Section 6.1.1.2
An increased proportion of the global DNS resolution traffic being An increased proportion of the global DNS resolution traffic being
served by only a few entities means that the privacy considerations served by only a few entities means that the privacy considerations
for end users are highly dependent on the privacy policies and for end users are additionally highly dependent on the privacy
practices of those entities. Many of the issues around policies and practices of those entities. Many of the issues around
centralization are discussed in centralization are discussed in
[centralisation-and-data-sovereignty]. [centralisation-and-data-sovereignty].
3.5.1.1.1. Dynamic Discovery of DoH and Strict DoT 6.1.1.1. Dynamic Discovery of DoH and Strict DoT
Whilst support for opportunistic DoT can be determined by probing a Whilst support for opportunistic DoT can be determined by probing a
resolver on port 853, there is currently no standardized discovery resolver on port 853, there is currently no standardized discovery
mechanism for DoH and Strict DoT servers. mechanism for DoH and Strict DoT servers.
This means that clients which might want to dynamically discover such This means that clients which might want to dynamically discover such
encrypted services, and where users are willing to trust such encrypted services, and where users are willing to trust such
services, are not able to do so. At the time of writing, efforts to services, are not able to do so. At the time of writing, efforts to
provide standardized signaling mechanisms to discover the services provide standardized signaling mechanisms to discover the services
offered by local resolvers are in progress offered by local resolvers are in progress
[I-D.ietf-dnsop-resolver-information]. Note that an increasing [I-D.ietf-dnsop-resolver-information]. Note that an increasing
numbers of ISPs are deploying encrypted DNS and publishing DNS numbers of ISPs are deploying encrypted DNS, for example see the
privacy polices, for example see the Encrypted DNS Deployment Encrypted DNS Deployment Initiative [EDDI].
Initiative [EDDI].
3.5.1.1.2. Application-specific Resolver Selection 6.1.1.2. Application-specific Resolver Selection
An increasing number of applications are offering application- An increasing number of applications are offering application-
specific encrypted DNS resolution settings, rather than defaulting to specific encrypted DNS resolution settings, rather than defaulting to
using only the system resolver. A variety of heuristics and using only the system resolver. A variety of heuristics and
resolvers are available in different applications including hard- resolvers are available in different applications including hard-
coded lists of recognized DoH/DoT servers. coded lists of recognized DoH/DoT servers.
Users will only be aware of and have the ability to control such For users to have the ability to manage the DNS resolver settings for
settings if applications provide the following functions: each individual application in a similar fashion to the OS DNS
settings, each application would need to expose the default settings
to the user, provide a configuration interface to change them, and
support configuration of user specified resolvers.
o communicate clearly the change in default to users The system resolver resolution path is sometimes used to configure
additional DNS controls e.g. query logging, domain based query re-
direction or filtering. If all of the applications used on a given
device can be configured to use the system resolver, such controls
need only be configured on the system resolver resolution path.
However if applications offer neither the option to use the system
resolver nor equivalent application-specific DNS controls then users
should take note that for queries generated by such an application
they may not be able to
o provide configuration options to change the default o directly inspect the DNS queries (e.g. if they are encrypted), or
o provide configuration options to always use the system resolver o manage them to set DNS controls across the device which are
consistent with the system resolver controls.
Note that if a client device is compromised by a malicious
application, the attacker can use application-specific DNS resolvers,
transport and controls of its own choosing.
Application-specific changes to default destinations for users' DNS Application-specific changes to default destinations for users' DNS
queries might increase or decrease user privacy - it is highly queries might increase or decrease user privacy - it is highly
dependent on the network context and the application-specific dependent on the network context and the application-specific
default. This is an area of active debate and the IETF is working on default. This is an area of active debate and the IETF is working on
a number of issues related to application-specific DNS settings. a number of issues related to application-specific DNS settings.
3.5.1.2. Active Attacks on Resolver Configuration 6.1.2. Active Attacks on Resolver Configuration
The previous section discussed DNS privacy, assuming that all the The previous section discussed DNS privacy, assuming that all the
traffic was directed to the intended servers (i.e those that would be 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 used in the absence of an active attack) and that the potential
attacker was purely passive. But, in reality, we can have active attacker was purely passive. But, in reality, we can have active
attackers in the network. attackers in the network.
The Internet Threat model, as described in [RFC3552], assumes that The Internet Threat model, as described in [RFC3552], assumes that
the attacker controls the network. Such an attacker can completely the attacker controls the network. Such an attacker can completely
control any insecure DNS resolution, both passively monitoring the control any insecure DNS resolution, both passively monitoring the
queries and responses and substituting their own responses. Even if queries and responses and substituting their own responses. Even if
encrypted DNS such as DoH or DoT is used, unless the client has been encrypted DNS such as DoH or DoT is used, unless the client has been
configured in a secure way with the server identity, an active configured in a secure way with the server identity, an active
attacker can impersonate the server. This implies that opportunistic attacker can impersonate the server. This implies that opportunistic
modes of DoH/DoT as well as modes where the client learns of the DoH/ modes of DoH/DoT as well as modes where the client learns of the DoH/
DoT server via in-network mechanisms such as DHCP are vulnerable to DoT server via in-network mechanisms such as DHCP are vulnerable to
attack. In addition, if the client is compromised, the attacker can attack. In addition, if the client is compromised, the attacker can
replace the DNS configuration with one of its own choosing. replace the DNS configuration with one of its own choosing.
3.5.1.3. Blocking of User Selected DNS Resolution Services 6.1.3. Blocking of User Selected DNS Resolution Services
User privacy can also be at risk if there is blocking (by local User privacy can also be at risk if there is blocking (by local
network operators or more general mechanisms) of access to remote network operators or more general mechanisms) of access to remote
recursive servers that offer encrypted transports when the local recursive servers that offer encrypted transports when the local
resolver does not offer encryption and/or has very poor privacy resolver does not offer encryption and/or has very poor privacy
policies. For example, active blocking of port 853 for DoT or of policies. For example, active blocking of port 853 for DoT or of
specific IP addresses could restrict the resolvers available to the specific IP addresses could restrict the resolvers available to the
user. The extent of the risk to end user privacy is highly dependent user. The extent of the risk to end user privacy is highly dependent
on the specific network and user context; a user on a network that is 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 known to perform surveillance would be compromised if they could not
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This is a form of Rendezvous-Based Blocking as described in This is a form of Rendezvous-Based Blocking as described in
Section 4.3 of [RFC7754]. Such blocklists often include servers know Section 4.3 of [RFC7754]. Such blocklists often include servers know
to be used for malware, bots or other security risks. In order to to be used for malware, bots or other security risks. In order to
prevent circumvention of their blocking policies, some networks also prevent circumvention of their blocking policies, some networks also
block access to resolvers with incompatible policies. block access to resolvers with incompatible policies.
It is also noted that attacks on remote resolver services, e.g., DDoS It is also noted that attacks on remote resolver services, e.g., DDoS
could force users to switch to other services that do not offer could force users to switch to other services that do not offer
encrypted transports for DNS. encrypted transports for DNS.
3.5.1.4. Encrypted Transports and Recursive Resolvers 6.1.4. Encrypted Transports and Recursive Resolvers
3.5.1.4.1. DoT and DoH 6.1.4.1. 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 described in Section 3.4.2 information about users to operators. As described in Section 5.2
use of session based encrypted transports (TCP/TLS) can expose use of session based encrypted transports (TCP/TLS) can expose
correlation data about users. correlation data about users.
3.5.1.4.2. DoH Specific Considerations 6.1.4.2. DoH Specific Considerations
DoH inherits the full privacy properties of the HTTPS stack and as a DoH inherits the full privacy properties of the HTTPS stack and as a
consequence introduces new privacy considerations when compared with consequence introduces new privacy considerations when compared with
DNS over UDP, TCP or TLS [RFC7858]. Section 8.2 of [RFC8484] DNS over UDP, TCP or TLS [RFC7858]. Section 8.2 of [RFC8484]
describes the privacy consideration in the server of the DoH describes the privacy consideration in the server of the DoH
protocol. protocol.
A brief summary of some of the issues includes: A brief summary of some of the issues includes:
o HTTPS presents new considerations for correlation, such as o HTTPS presents new considerations for correlation, such as
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o Implementations are advised to expose the minimal set of data o Implementations are advised to expose the minimal set of data
needed to achieve the desired feature set. needed to achieve the desired feature set.
[RFC8484] specifically makes selection of HTTPS functionality vs [RFC8484] specifically makes selection of HTTPS functionality vs
privacy an implementation choice. At the extremes, there may be privacy an implementation choice. At the extremes, there may be
implementations that attempt to achieve parity with DoT from a implementations that attempt to achieve parity with DoT from a
privacy perspective at the cost of using no identifiable HTTP privacy perspective at the cost of using no identifiable HTTP
headers, there might be others that provide feature rich data flows headers, there might be others that provide feature rich data flows
where the low-level origin of the DNS query is easily identifiable. where the low-level origin of the DNS query is easily identifiable.
Some implementations have, in fact, chosen restrict the use of the Some implementations have, in fact, chosen to restrict the use of the
'User-Agent' header so that resolver operators cannot identify the 'User-Agent' header so that resolver operators cannot identify the
specific application that is originating the DNS queries. specific application that is originating the DNS queries.
Privacy focused users should be aware of the potential for additional Privacy focused users should be aware of the potential for additional
client identifiers in DoH compared to DoT and may want to only use client identifiers in DoH compared to DoT and may want to only use
DoH client implementations that provide clear guidance on what DoH client implementations that provide clear guidance on what
identifiers they add. identifiers they add.
3.5.2. In the Authoritative Name Servers 6.2. 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. Similarly the increasing deployment of QNAME everything. Similarly the increasing deployment of QNAME
minimisation [ripe-qname-measurements] reduces the data visible at minimisation [ripe-qname-measurements] reduces the data visible at
the authoritative name server. Still, the authoritative name servers the authoritative name server. Still, the authoritative name servers
see a part of the traffic, and this subset may be sufficient to see a part of the traffic, and this subset may be sufficient to
violate some privacy expectations. violate some privacy expectations.
Also, the end user typically has some legal/contractual link with the Also, the end user often 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
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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 [8], one DNS provider hosts today 10% of the among the Alexa Top 100K [8], 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.
3.6. Re-identification and Other Inferences 7. Other risks
7.1. 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. The 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 term 'observer' here is used very generally, it might be one that is
passively observing cleartext DNS traffic, one in the network that is passively observing cleartext DNS traffic, one in the network that is
actively attacking the user by re-directing DNS resolution, or it actively attacking the user by re-directing DNS resolution, or it
might be a local or remote resolver operator. 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
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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.
3.7. More Information 7.2. 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].
4. Actual "Attacks" 8. 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
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from the National Security Agency (NSA) provide evidence of the use from the National Security Agency (NSA) provide evidence of the use
of the DNS in mass surveillance operations [morecowbell]. For of the DNS in mass surveillance operations [morecowbell]. For
example the MORECOWBELL surveillance program, which uses a dedicated example the MORECOWBELL surveillance program, which uses a dedicated
covert monitoring infrastructure to actively query DNS servers and covert monitoring infrastructure to actively query DNS servers and
perform HTTP requests to obtain meta information about services and perform HTTP requests to obtain meta information about services and
to check their availability. Also the QUANTUMTHEORY [9] project to check their availability. Also the QUANTUMTHEORY [9] project
which includes detecting lookups for certain addresses and injecting which includes detecting lookups for certain addresses and injecting
bogus replies is another good example showing that the lack of bogus replies is another good example showing that the lack of
privacy protections in the DNS is actively exploited. privacy protections in the DNS is actively exploited.
5. Legalities 9. 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 [10] applicable in the European [data-protection-directive] or GDPR [10] 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].
6. Security Considerations 10. 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].
7. IANA Considerations 11. IANA Considerations
This document makes no requests of the IANA. This document makes no requests of the IANA.
8. Acknowledgments 12. 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. Thanks to Vittorio Bertola and for good written contributions. Thanks to Vittorio Bertola and
Mohamed Boucadair for a detailed review of the -bis. And thanks to Mohamed Boucadair for a detailed review of the -bis. And thanks to
the IESG members for the last remarks. the IESG members for the last remarks.
9. Changelog 13. Changelog
draft-ietf-dprive-rfc7626-bis-05
o Editorial updates from second IESG last call
o Section renumbering as suggested by Vittorio Bertola
draft-ietf-dprive-rfc7626-bis-04 draft-ietf-dprive-rfc7626-bis-04
o Tsvart review: Add reference to DNS-over-QUIC, fix typo. o Tsvart review: Add reference to DNS-over-QUIC, fix typo.
o Secdir review: Add text in Section 3 on devices using many o Secdir review: Add text in Section 3 on devices using many
networks. Update bullet in 3.4.1 on cellular encryption. networks. Update bullet in 3.4.1 on cellular encryption.
o Section 3.5.1.1 - re-work the section to try to address multiple o Section 3.5.1.1 - re-work the section to try to address multiple
comments. comments.
skipping to change at page 21, line 4 skipping to change at page 22, line 12
Initial commit. Differences to RFC7626: Initial commit. Differences to RFC7626:
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
10. References 14. References
10.1. Normative References 14.1. 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>.
10.2. Informative References 14.2. 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>.
[cache-snooping-defence]
ISC, , "ISC Knowledge Database: DNS Cache snooping -
should I be concerned?", 2018, <https://kb.isc.org/docs/
aa-00482>.
[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>.
[centralisation-and-data-sovereignty] [centralisation-and-data-sovereignty]
De Filippi, P. and S. McCarthy, "Cloud Computing: De Filippi, P. and S. McCarthy, "Cloud Computing:
Centralization and Data Sovereignty", October 2012, Centralization and Data Sovereignty", October 2012,
<https://papers.ssrn.com/sol3/ <https://papers.ssrn.com/sol3/
papers.cfm?abstract_id=2167372>. papers.cfm?abstract_id=2167372>.
skipping to change at page 23, line 48 skipping to change at page 25, line 8
[I-D.huitema-quic-dnsoquic] [I-D.huitema-quic-dnsoquic]
Huitema, C., Shore, M., Mankin, A., Dickinson, S., and J. Huitema, C., Shore, M., Mankin, A., Dickinson, S., and J.
Iyengar, "Specification of DNS over Dedicated QUIC Iyengar, "Specification of DNS over Dedicated QUIC
Connections", draft-huitema-quic-dnsoquic-07 (work in Connections", draft-huitema-quic-dnsoquic-07 (work in
progress), September 2019. progress), September 2019.
[I-D.ietf-dnsop-resolver-information] [I-D.ietf-dnsop-resolver-information]
Sood, P., Arends, R., and P. Hoffman, "DNS Resolver Sood, P., Arends, R., and P. Hoffman, "DNS Resolver
Information Self-publication", draft-ietf-dnsop-resolver- Information Self-publication", draft-ietf-dnsop-resolver-
information-00 (work in progress), August 2019. information-01 (work in progress), February 2020.
[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-07 (work in Operators", draft-ietf-dprive-bcp-op-08 (work in
progress), December 2019. progress), January 2020.
[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-24 (work and Secure Transport", draft-ietf-quic-transport-27 (work
in progress), November 2019. in progress), February 2020.
[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-09 SNI Encryption in TLS", draft-ietf-tls-sni-encryption-09
(work in progress), October 2019. (work in progress), October 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://pdfs.semanticscholar.org/2610/2b99bdd6a258a 2015, <https://pdfs.semanticscholar.org/2610/2b99bdd6a258a
skipping to change at page 25, line 19 skipping to change at page 26, line 24
[RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
(AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010, (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
<https://www.rfc-editor.org/info/rfc5936>. <https://www.rfc-editor.org/info/rfc5936>.
[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and [RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
P. Roberts, "Issues with IP Address Sharing", RFC 6269, P. Roberts, "Issues with IP Address Sharing", RFC 6269,
DOI 10.17487/RFC6269, June 2011, <https://www.rfc- DOI 10.17487/RFC6269, June 2011, <https://www.rfc-
editor.org/info/rfc6269>. editor.org/info/rfc6269>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013, <https://www.rfc-
editor.org/info/rfc6891>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>. <https://www.rfc-editor.org/info/rfc7413>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre, [RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer "Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May (DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>. 2015, <https://www.rfc-editor.org/info/rfc7525>.
skipping to change at page 27, line 22 skipping to change at page 28, line 30
[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>.
10.3. URIs 14.3. 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/014143.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://developers.google.com/speed/public-dns [4] https://developers.google.com/speed/public-dns
[5] https://developers.cloudflare.com/1.1.1.1/setting-up-1.1.1.1/ [5] https://developers.cloudflare.com/1.1.1.1/setting-up-1.1.1.1/
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