draft-ietf-dprive-rfc7626-bis-06.txt   draft-ietf-dprive-rfc7626-bis-07.txt 
dprive T. Wicinski, Ed. dprive T. Wicinski, Ed.
Internet-Draft September 22, 2020 Internet-Draft October 7, 2020
Obsoletes: 7626 (if approved) Obsoletes: 7626 (if approved)
Intended status: Informational Intended status: Informational
Expires: March 26, 2021 Expires: April 10, 2021
DNS Privacy Considerations DNS Privacy Considerations
draft-ietf-dprive-rfc7626-bis-06 draft-ietf-dprive-rfc7626-bis-07
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 https://datatracker.ietf.org/drafts/current/. Drafts is at https://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 March 26, 2021. This Internet-Draft will expire on April 10, 2021.
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
(https://trustee.ietf.org/license-info) in effect on the date of (https://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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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
4. Risks in the DNS Data . . . . . . . . . . . . . . . . . . . . 6 4. Risks in the DNS Data . . . . . . . . . . . . . . . . . . . . 6
4.1. The Alleged Public Nature of DNS Data . . . . . . . . . . 6 4.1. The Public Nature of DNS Data . . . . . . . . . . . . . . 6
4.2. Data in the DNS Request . . . . . . . . . . . . . . . . . 6 4.2. Data in the DNS Request . . . . . . . . . . . . . . . . . 6
4.2.1. Data in the DNS Payload . . . . . . . . . . . . . . . 8 4.2.1. Data in the DNS Payload . . . . . . . . . . . . . . . 8
4.3. Cache Snooping . . . . . . . . . . . . . . . . . . . . . 8 4.3. Cache Snooping . . . . . . . . . . . . . . . . . . . . . 8
5. Risks On the Wire . . . . . . . . . . . . . . . . . . . . . . 8 5. Risks On the Wire . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Unencrypted Transports . . . . . . . . . . . . . . . . . 8 5.1. Unencrypted Transports . . . . . . . . . . . . . . . . . 8
5.2. Encrypted Transports . . . . . . . . . . . . . . . . . . 10 5.2. Encrypted Transports . . . . . . . . . . . . . . . . . . 10
6. Risks in the Servers . . . . . . . . . . . . . . . . . . . . 11 6. Risks in the Servers . . . . . . . . . . . . . . . . . . . . 11
6.1. In the Recursive Resolvers . . . . . . . . . . . . . . . 12 6.1. In the Recursive Resolvers . . . . . . . . . . . . . . . 12
6.1.1. Resolver Selection . . . . . . . . . . . . . . . . . 12 6.1.1. Resolver Selection . . . . . . . . . . . . . . . . . 12
6.1.2. Active Attacks on Resolver Configuration . . . . . . 14 6.1.2. Active Attacks on Resolver Configuration . . . . . . 14
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6.2. In the Authoritative Name Servers . . . . . . . . . . . . 16 6.2. In the Authoritative Name Servers . . . . . . . . . . . . 16
7. Other risks . . . . . . . . . . . . . . . . . . . . . . . . . 17 7. Other risks . . . . . . . . . . . . . . . . . . . . . . . . . 17
7.1. Re-identification and Other Inferences . . . . . . . . . 17 7.1. Re-identification and Other Inferences . . . . . . . . . 17
7.2. More Information . . . . . . . . . . . . . . . . . . . . 18 7.2. More Information . . . . . . . . . . . . . . . . . . . . 18
8. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 18 8. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 18
9. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 19 9. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 19
10. Security Considerations . . . . . . . . . . . . . . . . . . . 19 10. Security Considerations . . . . . . . . . . . . . . . . . . . 19
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
12. Contributions . . . . . . . . . . . . . . . . . . . . . . . . 19 12. Contributions . . . . . . . . . . . . . . . . . . . . . . . . 19
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
14. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 19 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 22 14.1. Normative References . . . . . . . . . . . . . . . . . . 20
15.1. Normative References . . . . . . . . . . . . . . . . . . 22 14.2. Informative References . . . . . . . . . . . . . . . . . 20
15.2. Informative References . . . . . . . . . . . . . . . . . 22 14.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 26
15.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 28 Appendix A. Updates since RFC7626 . . . . . . . . . . . . . . . 27
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 28 Appendix B. Changelog . . . . . . . . . . . . . . . . . . . . . 27
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 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
professionals). Almost every activity on the Internet starts with a professionals). Almost every activity on the Internet starts with a
DNS query (and often several). Its use has many privacy implications DNS query (and often several). Its use has many privacy implications
and this document is an attempt at a comprehensive and accurate list. and this document is an attempt at a comprehensive and accurate list.
Let us begin with a simplified reminder of how the DNS works (See Lets begin with a simplified reminder of how the DNS works (See also
also [RFC8499]). A client, the stub resolver, issues a DNS query to [RFC8499]). A client, the stub resolver, issues a DNS query to a
a server, called the recursive resolver (also called caching resolver server, called the recursive resolver (also called caching resolver
or full resolver or recursive name server). Let's use the query or full resolver or recursive name server). Let's use the query
"What are the AAAA records for www.example.com?" as an example. AAAA "What are the AAAA records for www.example.com?" as an example. AAAA
is the QTYPE (Query Type), and www.example.com is the QNAME (Query is the QTYPE (Query Type), and www.example.com is the QNAME (Query
Name). (The description that follows assumes a cold cache, for Name). (The description that follows assumes a cold cache, for
instance, because the server just started.) The recursive resolver instance, because the server just started.) The recursive resolver
will first query the root name servers. In most cases, the root name will first query the root name servers. In most cases, the root name
servers will send a referral. In this example, the referral will be servers will send a referral. In this example, the referral will be
to the .com name servers. The resolver repeats the query to one of to the .com name servers. The resolver repeats the query to one of
the .com name servers. The .com name servers, in turn, will refer to the .com name servers. The .com name servers, in turn, will refer to
the example.com name servers. The example.com name server will then the example.com name servers. The example.com name server will then
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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.
DNS relies on caching heavily, so the algorithm described above is DNS relies heavily on caching, so the algorithm described above 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
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It should be noted that DNS recursive resolvers sometimes forward It should be noted that DNS recursive resolvers sometimes forward
requests to other recursive resolvers, typically bigger machines, requests to other recursive resolvers, typically bigger machines,
with a larger and more shared cache (and the query hierarchy can be with a larger and more shared cache (and the query hierarchy can be
even deeper, with more than two levels of recursive resolvers). From even deeper, with more than two levels of recursive resolvers). From
the point of view of privacy, these forwarders are like resolvers, the point of view of privacy, these forwarders are like resolvers,
except that they do not see all of the requests being made (due to except that they do not see all of the requests being made (due to
caching in the first resolver). caching in the first resolver).
At the time of writing, almost all this DNS traffic is currently sent At the time of writing, almost all this DNS traffic is currently sent
in clear (i.e., unencrypted). However there is increasing deployment unencrypted. However, there is increasing deployment of DNS-over-TLS
of DNS-over-TLS (DoT) [RFC7858] and DNS-over-HTTPS (DoH) [RFC8484], (DoT) [RFC7858] and DNS-over-HTTPS (DoH) [RFC8484], particularly in
particularly in mobile devices, browsers, and by providers of anycast mobile devices, browsers, and by providers of anycast recursive DNS
recursive DNS resolution services. There are a few cases where there resolution services. There are a few cases where there is some
is some alternative channel encryption, for instance, in an IPsec VPN alternative channel encryption, for instance, in an IPsec VPN tunnel,
tunnel, at least between the stub resolver and the resolver. 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 and new solutions are still are only designed for TCP, not UDP, and new solutions are still
emerging [I-D.ietf-quic-transport] [I-D.huitema-quic-dnsoquic]. emerging [I-D.ietf-quic-transport] [I-D.ietf-dprive-dnsoquic].
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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page. page.
o Tertiary requests: these are the additional requests performed by o Tertiary requests: these are the additional requests performed by
the DNS system itself. For instance, if the answer to a query is the DNS system itself. For instance, if the answer to a query is
a referral to a set of name servers, and the glue records are not a referral to a set of name servers, and the glue records are not
returned, the resolver will have to do additional requests to turn returned, the resolver will have to do additional requests to turn
the name servers' names into IP addresses. Similarly, even if the name servers' names into IP addresses. Similarly, even if
glue records are returned, a careful recursive server will do glue records are returned, a careful recursive server will do
tertiary requests to verify the IP addresses of those records. tertiary requests to verify the IP addresses of those records.
It can be noted also that, in the case of a typical web browser, more It can also be noted that, in the case of a typical web browser, more
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 significant
concern since they may leak information even about non-explicit privacy concern since they may leak information even about non-
actions. For instance, just reading a local HTML page, even without explicit actions. For instance, just reading a local HTML page, even
selecting the hyperlinks, may trigger DNS requests. without selecting the hyperlinks, may trigger DNS requests.
For privacy-related terms, we will use the terminology from For privacy-related terms, the terminology is from [RFC6973].
[RFC6973].
2. Scope 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). The risks of pervasive
pervasive surveillance [RFC7258] as well as risks coming from a more surveillance [RFC7258] are considered as well as risks coming from a
focused surveillance. more focused surveillance.
This document does not attempt a comparison of specific privacy This document does not attempt a comparison of specific privacy
protections provided by individual networks or organizations, it protections provided by individual networks or organizations, it
makes only general observations about typical current practices. makes only general observations about typical current practices.
Privacy risks for the holder of a zone (the risk that someone gets Privacy risks for the holder of a zone (the risk that someone gets
the data) are discussed in [RFC5936] and [RFC5155]. the data) are discussed in [RFC5936] and [RFC5155].
Privacy risks for recursive operators (including access providers and Privacy risks for recursive operators (including access providers and
operators in enterprise networks) such as leakage of private operators in enterprise networks) such as leakage of private
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associated with different aspects of the DNS for the end user. When associated with different aspects of the DNS for the end user. When
reading these sections it needs to be kept in mind that many of the reading these sections it needs to be kept in mind that many of the
considerations (for example, recursive resolver and transport considerations (for example, recursive resolver and transport
protocol) can be specific to the network context that a device is protocol) can be specific to the network context that a device is
using at a given point in time. A user may have many devices and using at a given point in time. A user may have many devices and
each device might utilize many different networks (e.g. home, work, each device might utilize many different networks (e.g. home, work,
public or cellular) over a period of time or even concurrently. An public or cellular) over a period of time or even concurrently. An
exhaustive analysis of the privacy considerations for an individual exhaustive analysis of the privacy considerations for an individual
user would need to take into account the set of devices used and the user would need to take into account the set of devices used and the
multiple dynamic contexts of each device. This document does not multiple dynamic contexts of each device. This document does not
attempt such a complex analysis, instead it presents an overview of attempt such a complex analysis, but instead it presents an overview
the various considerations that could form the basis of such an of the various considerations that could form the basis of such an
analysis. analysis.
4. Risks in the DNS Data 4. Risks in the DNS Data
4.1. The Alleged Public Nature of DNS Data 4.1. The Public Nature of DNS Data
It has long been claimed that "the data in the DNS is public". While It is often stated that "the data in the DNS is public". This
this sentence makes sense for an Internet-wide lookup system, there sentence makes sense for an Internet-wide lookup system, and 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
resource records associated with that name (or that name's non- resource records associated with that name (or that name's non-
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. There are many ways in which supposed
often blocked or restricted to authenticated/authorized access to "private" resources currently leak. A few examples are DNSSEC NSEC
enforce this difference (and maybe for other reasons). zone walking[RFC4470]; passive-DNS services[passive-dns]; etc. The
zone transfer QTYPE [RFC5936] is often blocked or restricted to
authenticated/authorized access to 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; those transaction are not / should not be public. A of transactions; those transactions are not / should not be public.
single transactions reveals both the originator of the query and the A single transactions reveals both the originator of the query and
query contents which potentially leaks sensitive information about a the query contents which potentially leaks sensitive information
specific user. A typical example from outside the DNS world is: the about a specific user. A typical example from outside the DNS world
web site of Alcoholics Anonymous is public; the fact that you visit is: the web site of Alcoholics Anonymous is public; the fact that you
it should not be. Furthermore, the ability to link queries reveals visit it should not be. Furthermore, the ability to link queries
information about individual use patterns. reveals information about individual use patterns.
4.2. 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]).
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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), but 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 [RFC6891] for stub to being inserted in non-standard EDNS(0) options [RFC6891] for stub to
resolver communications to support proprietary functionality resolver communications to support proprietary functionality
implemented at the resolver (e.g., parental filtering). implemented at the resolver (e.g., parental filtering).
4.3. 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
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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
time of writing there is on-going work attempting to encrypt the SNI time of writing there is on-going work attempting to encrypt the SNI
in the TLS handshake [I-D.ietf-tls-sni-encryption]. in the TLS handshake [RFC8744].
An important specificity of the DNS traffic is that it may take a An important specificity of the DNS traffic is that it may take a
different path than the communication between the initiator and the different path than the communication between the initiator and the
recipient. For instance, an eavesdropper may be unable to tap the recipient. For instance, an eavesdropper may be unable to tap the
wire between the initiator and the recipient but may have access to wire between the initiator and the recipient but may have access to
the wire going to the recursive resolver, or to the authoritative the wire going to the recursive resolver, or to the authoritative
name servers. name servers.
The best place to tap, from an eavesdropper's point of view, is The best place to tap, from an eavesdropper's point of view, is
clearly between the stub resolvers and the recursive resolvers, clearly between the stub resolvers and the recursive resolvers,
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Note that in large enterprise networks, the DNS resolver may not Note that in large enterprise networks, the DNS resolver may not
be located at the edge of the local network but rather at the edge be located at the edge of the local network but rather at the edge
of the overall enterprise network. In this case, the enterprise of the overall enterprise network. In this case, the enterprise
network could be thought of as similar to the Internet Access network could be thought of as similar to the Internet Access
Provider (IAP) network referenced below. Provider (IAP) network referenced below.
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 Customer Premise Equipment (CPE), which in
recursive resolvers at the IAP. The attack surface for on-the- turns points to the DNS recursive resolvers at the IAP. The
wire attacks is therefore from the end user system across the attack surface for on-the-wire attacks is therefore from the end
local network and across the IAP network to the IAP's recursive user system across the local network and across the IAP network to
resolvers. the IAP's recursive resolvers.
o The recursive resolver can be a public DNS service (or a privately o The recursive resolver can be a public DNS service (or a privately
run DNS resolver hosted on the public internet). Some machines 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. It can be noted 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 that if the user selects a single resolver with a small client
population (even when using an encrypted transport) it can population (even when using an encrypted transport) it can
actually serve to aid tracking of that user as they move across actually serve to aid tracking of that user as they move across
network environment. network environments.
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.
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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].
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]. users' connections, e.g. using TCP Fast Open [RFC7413].
Implementations that support encrypted transports also commonly re- Implementations that support encrypted transports also commonly re-
use connections for multiple DNS queries to optimize performance use connections for multiple DNS queries to optimize performance
(e.g. via DNS pipelining or HTTPS multiplexing). Default (e.g. via DNS pipelining or HTTPS multiplexing). Default
configuration options for encrypted transports could in principle configuration options for encrypted transports could in principle
fingerprint a 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
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resolver. These individual changes, including the change in DNS resolver. These individual changes, including the change in DNS
resolver, are not normally communicated directly to the user by the resolver, are not normally communicated directly to the user by the
OS when the network is joined. The choice of network has OS when the network is joined. The choice of network has
historically determined the default system DNS resolver selection; historically determined the default system DNS resolver selection;
the two are directly coupled in this model. the two are directly coupled in this model.
The vast majority of users do not change their default system DNS The vast majority of users do not change their default system DNS
settings and so implicitly accept the network settings for DNS. The settings and so implicitly accept the network settings for DNS. The
network resolvers have therefore historically been the sole network resolvers have therefore historically been the sole
destination for all of the DNS queries from a device. These destination for all of the DNS queries from a device. These
resolvers may have strong, medium, or weak privacy policies depending resolvers may have may have varied privacy policies depending on the
on the network. Privacy policies for these servers may or may not be network. Privacy policies for these servers may or may not be
available and users need to be aware that privacy guarantees will available and users need to be aware that privacy guarantees will
vary with network. vary with network.
All major OS's expose the system DNS settings and allow users to All major OS's expose the system DNS settings and allow users to
manually override them if desired. 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 [3], Cloudflare
[5], or Quad9 [6]. There can be many reasons: cost considerations [4], or Quad9 [5]. 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 [6].
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 applications directing DNS traffic by default to limited subset of o applications directing DNS traffic by default to a limited subset
resolvers, see Section 6.1.1.2 of 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 additionally highly dependent on the privacy for end users are highly dependent on the privacy policies and
policies and practices of those entities. Many of the issues around 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].
6.1.1.1. 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
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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.
6.1.2. 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, there can be 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.
6.1.3. 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 of access to
network operators or more general mechanisms) of access to remote remote recursive servers that offer encrypted transports when the
recursive servers that offer encrypted transports when the local 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
access such services, whereas a user on a trusted network might have access such services, whereas a user on a trusted network might have
no privacy motivation to do so. no privacy motivation to do so.
As a matter of policy, some recursive resolvers use their position in As a matter of policy, some recursive resolvers use their position in
the query path to selectively block access to certain DNS records. the query path to selectively block access to certain DNS records.
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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
access such services, whereas a user on a trusted network might have access such services, whereas a user on a trusted network might have
no privacy motivation to do so. no privacy motivation to do so.
As a matter of policy, some recursive resolvers use their position in As a matter of policy, some recursive resolvers use their position in
the query path to selectively block access to certain DNS records. the query path to selectively block access to certain DNS records.
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
to be used for malware, bots or other security risks. In order to known to be used for malware, bots or other security risks. In order
prevent circumvention of their blocking policies, some networks also to prevent circumvention of their blocking policies, some networks
block access to resolvers with incompatible policies. also 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.,
could force users to switch to other services that do not offer DDoS, could force users to switch to other services that do not offer
encrypted transports for DNS. encrypted transports for DNS.
6.1.4. Encrypted Transports and Recursive Resolvers 6.1.4. Encrypted Transports and Recursive Resolvers
6.1.4.1. 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 5.2 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
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domain manager and these servers may or may not take privacy into domain manager and these servers may or may not take privacy into
account. Whatever the contract, the third-party hoster may be honest account. Whatever the contract, the third-party hoster may be honest
or not but, in any case, it will have to follow its local laws. So, or not but, in any case, it will have to follow its local laws. So,
requests to a given ccTLD may go to servers managed by organizations requests to a given ccTLD may go to servers managed by organizations
outside of the ccTLD's country. End users may not anticipate that, outside of the ccTLD's country. End users may not anticipate that,
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 [7], 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.
7. Other risks 7. Other risks
7.1. Re-identification and Other Inferences 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
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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
detect "abnormal" behavior that can be traced back to the activity of detect "abnormal" behavior that can be traced back to the activity of
malware on infected machines. Yes, this research was done for the malware on infected machines. Yes, this research was done for the
good, but technically it is a privacy attack and it demonstrates the good, but technically it is a privacy attack and it demonstrates the
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. Well-known passive DNS systems keep only
good, some bad. Well-known passive DNS systems keep only the DNS the DNS responses, and not the source IP address of the client,
responses, and not the source IP address of the client, precisely for precisely for privacy reasons. Other passive DNS systems may not be
privacy reasons. Other passive DNS systems may not be so careful. so careful. And there is still the potential problems with revealing
And there is still the potential problems with revealing QNAMEs. 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) 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 [8] 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.
9. 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 [9] 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
do not know a court precedent here. See an interesting analysis in there is no known court precedent. See an interesting analysis in
[sidn-entrada]. [sidn-entrada].
10. 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].
11. IANA Considerations 11. IANA Considerations
This document makes no requests of the IANA. This document makes no requests of the IANA.
12. Contributions 12. Contributions
Sara Dickinson and Stephane Bortzmeyer were the original authors on Sara Dickinson and Stephane Bortzmeyer were the original authors on
the document, and their contribution on the initial version is the document, and their contribution on the initial version is
greatly apprecriated. greatly appreciated.
13. Acknowledgments 13. 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.
14. Changelog 14. References
14.1. Normative References
draft-ietf-dprive-rfc7626-bis-06
o Removed Sara and Stephane as editors, made chairs as Editor.
o Replaced the text in 6.1.1.2 with the text from the -04 version.
o Clarified text about resolver selection in 6.1.1.
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
o Tsvart review: Add reference to DNS-over-QUIC, fix typo.
o Secdir review: Add text in Section 3 on devices using many
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
comments.
o Section 3.5.1.4 - remove this section as now covered by 3.5.1.1.
o Section 3.5.1.5.2 - Remove several paragraphs and more directly
reference RFC8484 by including bullet points quoting text from
Section 8.2 of RFC8484. Retain the last 2 paragraphs as they are
information for users, not implementors.
o Section 3.4.2 - some minor updates made based on specific
comments.
draft-ietf-dprive-rfc7626-bis-03
o Address 2 minor nits (typo in section 3.4.1 and adding an IANA
section)
o Minor updates from AD review
draft-ietf-dprive-rfc7626-bis-02
o Numerous editorial corrections thanks to Mohamed Boucadair and
* Minor additions to Scope section
* New text on cellular network DNS
o Additional text from Vittorio Bertola on blocking and security
draft-ietf-dprive-rfc7626-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-rfc7626-bis-00
o Rename after WG adoption
o Use DoT acronym throughout
o Minor updates to status of deployment and other drafts
draft-bortzmeyer-dprive-rfc7626-bis-02
o Update various references and fix some nits.
draft-bortzmeyer-dprive-rfc7626-bis-01
o Update reference for dickinson-bcp-op to draft-dickinson-dprive-
bcp-op
draft-borztmeyer-dprive-rfc7626-bis-00:
Initial commit. Differences to RFC7626:
o Update many references
o Add discussions of encrypted transports including DoT and DoH
o Add section on DNS payload
o Add section on authentication of servers
o Add section on blocking of services
15. References
15.1. 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, DOI 10.17487/RFC6973, July 2013,
<https://www.rfc-editor.org/info/rfc6973>. <https://www.rfc-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>.
15.2. 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, 2015,
<https://blog.imirhil.fr/vie-privee-et-le-dns-alors.html>. <https://blog.imirhil.fr/vie-privee-et-le-dns-alors.html>.
[cache-snooping-defence] [cache-snooping-defence]
ISC, "ISC Knowledge Database: DNS Cache snooping - should ISC, "ISC Knowledge Database: DNS Cache snooping - should
I be concerned?", 2018, I be concerned?", 2018,
<https://kb.isc.org/docs/aa-00482>. <https://kb.isc.org/docs/aa-00482>.
skipping to change at page 24, line 42 skipping to change at page 22, line 39
Snooping-the-Cache-for-Fun-and- Snooping-the-Cache-for-Fun-and-
1-Grangeia/9b22f606e10b3609eafbdcbfc9090b63be8778c3>. 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.huitema-quic-dnsoquic]
Huitema, C., Shore, M., Mankin, A., Dickinson, S., and J.
Iyengar, "Specification of DNS over Dedicated QUIC
Connections", draft-huitema-quic-dnsoquic-07 (work in
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-01 (work in progress), February 2020. 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-14 (work in Operators", draft-ietf-dprive-bcp-op-14 (work in
progress), July 2020. progress), July 2020.
[I-D.ietf-dprive-dnsoquic]
Huitema, C., Mankin, A., and S. Dickinson, "Specification
of DNS over Dedicated QUIC Connections", draft-ietf-
dprive-dnsoquic-00 (work in progress), April 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-30 (work and Secure Transport", draft-ietf-quic-transport-31 (work
in progress), September 2020. in progress), September 2020.
[I-D.ietf-tls-sni-encryption]
Huitema, C. and E. Rescorla, "Issues and Requirements for
SNI Encryption in TLS", draft-ietf-tls-sni-encryption-09
(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
98740af8217ba8da8a1e4fa.pdf>. 98740af8217ba8da8a1e4fa.pdf>.
[packetq] DNS-OARC, "PacketQ, a simple tool to make SQL-queries [packetq] DNS-OARC, "PacketQ, a simple tool to make SQL-queries
against PCAP-files", 2011, against PCAP-files", 2011,
<https://github.com/DNS-OARC/PacketQ>. <https://github.com/DNS-OARC/PacketQ>.
skipping to change at page 26, line 5 skipping to change at page 23, line 48
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC [RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552, Text on Security Considerations", BCP 72, RFC 3552,
DOI 10.17487/RFC3552, July 2003, DOI 10.17487/RFC3552, July 2003,
<https://www.rfc-editor.org/info/rfc3552>. <https://www.rfc-editor.org/info/rfc3552>.
[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>.
[RFC4470] Weiler, S. and J. Ihren, "Minimally Covering NSEC Records
and DNSSEC On-line Signing", RFC 4470,
DOI 10.17487/RFC4470, April 2006,
<https://www.rfc-editor.org/info/rfc4470>.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008, Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
<https://www.rfc-editor.org/info/rfc5155>. <https://www.rfc-editor.org/info/rfc5155>.
[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
skipping to change at page 27, line 40 skipping to change at page 25, line 40
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS [RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>. <https://www.rfc-editor.org/info/rfc8484>.
[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>.
[RFC8744] Huitema, C., "Issues and Requirements for Server Name
Identification (SNI) Encryption in TLS", RFC 8744,
DOI 10.17487/RFC8744, July 2020,
<https://www.rfc-editor.org/info/rfc8744>.
[ripe-qname-measurements] [ripe-qname-measurements]
Vries, W., "Making the DNS More Private with QNAME Vries, W., "Making the DNS More Private with QNAME
Minimisation", April 2019, Minimisation", April 2019,
<https://labs.ripe.net/Members/wouter_de_vries/make-dns-a- <https://labs.ripe.net/Members/wouter_de_vries/make-dns-a-
bit-more-private-with-qname-minimisation>. 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,
skipping to change at page 28, line 22 skipping to change at page 26, 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>.
15.3. URIs 14.3. URIs
[1] https://lists.dns-oarc.net/pipermail/dns- [1] https://lists.dns-oarc.net/pipermail/dns-
operations/2016-January/014143.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://developers.google.com/speed/public-dns
based_De-NAT_Scheme
[4] https://developers.google.com/speed/public-dns
[5] https://developers.cloudflare.com/1.1.1.1/setting-up-1.1.1.1/ [4] https://developers.cloudflare.com/1.1.1.1/setting-up-1.1.1.1/
[6] https://www.quad9.net [5] https://www.quad9.net
[7] https://developers.google.com/speed/public-dns/privacy [6] https://developers.google.com/speed/public-dns/privacy
[8] https://www.alexa.com/topsites [7] https://www.alexa.com/topsites
[9] https://theintercept.com/document/2014/03/12/nsa-gchqs- [8] https://theintercept.com/document/2014/03/12/nsa-gchqs-
quantumtheory-hacking-tactics/ quantumtheory-hacking-tactics/
[10] https://www.eugdpr.org/the-regulation.html [9] https://www.eugdpr.org/the-regulation.html
Appendix A. Updates since RFC7626
Update many references; Add discussions of encrypted transports
including DoT and DoH; Added section on DNS payload; Add section on
authentication of servers; Add section on blocking of services. With
the publishing of RFC7816 on QNAME minimisation, text, references,
and initial attempts to measure deployment were added to reflect
this. The text and references on the Snowden revelations were
updated.
The "Risks overview" section was changed to "Scope" to help clarify
the risks being considered. Text was adding on cellular network DNS,
blocking and security
o Collect considerations for recursive resolvers together
o Re-work several sections here to clarify their context (e.g.,
'Rogue servers' becomes 'Active attacks on resolver
configuration')
o Add discussion of resolver selection
Appendix B. Changelog
draft-ietf-dprive-rfc7626-bis-06
o Removed Sara and Stephane as editors, made chairs as Editor.
o Replaced the text in 6.1.1.2 with the text from the -04 version.
o Clarified text about resolver selection in 6.1.1.
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
o Tsvart review: Add reference to DNS-over-QUIC, fix typo.
o Secdir review: Add text in Section 3 on devices using many
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
comments.
o Section 3.5.1.4 - remove this section as now covered by 3.5.1.1.
o Section 3.5.1.5.2 - Remove several paragraphs and more directly
reference RFC8484 by including bullet points quoting text from
Section 8.2 of RFC8484. Retain the last 2 paragraphs as they are
information for users, not implementors.
o Section 3.4.2 - some minor updates made based on specific
comments.
draft-ietf-dprive-rfc7626-bis-03
o Address 2 minor nits (typo in section 3.4.1 and adding an IANA
section)
o Minor updates from AD review
draft-ietf-dprive-rfc7626-bis-02
o Numerous editorial corrections thanks to Mohamed Boucadair and
* Minor additions to Scope section
* New text on cellular network DNS
o Additional text from Vittorio Bertola on blocking and security
draft-ietf-dprive-rfc7626-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-rfc7626-bis-00
o Rename after WG adoption
o Use DoT acronym throughout
o Minor updates to status of deployment and other drafts
draft-bortzmeyer-dprive-rfc7626-bis-02
o Update various references and fix some nits.
draft-bortzmeyer-dprive-rfc7626-bis-01
o Update reference for dickinson-bcp-op to draft-dickinson-dprive-
bcp-op
draft-borztmeyer-dprive-rfc7626-bis-00:
Initial commit. Differences to RFC7626:
o Update many references
o Add discussions of encrypted transports including DoT and DoH
o Add section on DNS payload
o Add section on authentication of servers
o Add section on blocking of services
Author's Address Author's Address
Tim Wicinski (editor) Tim Wicinski (editor)
Elkins, WV 26241 Elkins, WV 26241
USA USA
Email: tjw.ietf@gmail.com Email: tjw.ietf@gmail.com
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