< draft-ietf-dprive-rfc7626-bis-01.txt   draft-ietf-dprive-rfc7626-bis-02.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: March 30, 2020 September 27, 2019 Expires: April 18, 2020 October 16, 2019
DNS Privacy Considerations DNS Privacy Considerations
draft-ietf-dprive-rfc7626-bis-01 draft-ietf-dprive-rfc7626-bis-02
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 March 30, 2020. This Internet-Draft will expire on April 18, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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3.5.2. In the Authoritative Name Servers . . . . . . . . . . 15 3.5.2. In the Authoritative Name Servers . . . . . . . . . . 15
3.6. Re-identification and Other Inferences . . . . . . . . . 16 3.6. Re-identification and Other Inferences . . . . . . . . . 16
3.7. More Information . . . . . . . . . . . . . . . . . . . . 17 3.7. More Information . . . . . . . . . . . . . . . . . . . . 17
4. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 17 4. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 17
5. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 18 5. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18 6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
8. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 19 8. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . 20 9.1. Normative References . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . 20 9.2. Informative References . . . . . . . . . . . . . . . . . 21
9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 26 9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction 1. Introduction
This document is an analysis of the DNS privacy issues, in the spirit This document is an analysis of the DNS privacy issues, in the spirit
of Section 8 of [RFC6973]. of Section 8 of [RFC6973].
The Domain Name System is specified in [RFC1034], [RFC1035], and many The Domain Name System (DNS) is specified in [RFC1034], [RFC1035],
later RFCs, which have never been consolidated. It is one of the and many later RFCs, which have never been consolidated. It is one
most important infrastructure components of the Internet and often of the most important infrastructure components of the Internet and
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 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 Let us begin with a simplified reminder of how the DNS works (See
also [RFC8499]) A client, the stub resolver, issues a DNS query to a also [RFC8499]). A client, the stub resolver, issues a DNS query to
server, called the recursive resolver (also called caching resolver a 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.
Because DNS relies on caching heavily, the algorithm described just Because DNS relies on caching heavily, the algorithm described above
above is actually a bit more complicated, and not all questions are is actually a bit more complicated, and not all questions are sent to
sent to the authoritative name servers. If a few seconds later the the authoritative name servers. If a few seconds later the stub
stub resolver asks the recursive resolver, "What are the SRV records resolver asks the recursive resolver, "What are the SRV records of
of _xmpp-server._tcp.example.com?", the recursive resolver will _xmpp-server._tcp.example.com?", the recursive resolver will remember
remember that it knows the name servers of example.com and will just that it knows the name servers of example.com and will just query
query them, bypassing the root and .com. Because there is typically them, bypassing the root and .com. Because there is typically no
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.)
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 (unencrypted). However there is increasing deployment of in clear (i.e., unencrypted). However there is increasing deployment
DNS-over-TLS (DoT) [RFC7858] and DNS-over-HTTPS (DoH) [RFC8484], of DNS-over-TLS (DoT) [RFC7858] and DNS-over-HTTPS (DoH) [RFC8484],
particularly in mobile devices, browsers and by providers of anycast particularly in mobile devices, browsers, and by providers of anycast
recursive DNS resolution services. There are a few cases where there recursive DNS resolution services. There are a few cases where there
is some alternative channel encryption, for instance, in an IPsec is some alternative channel encryption, for instance, in an IPsec VPN
VPN, at least between the stub resolver and the resolver. tunnel, 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]. emerging [I-D.ietf-quic-transport].
Another important point to keep in mind when analyzing the privacy Another important point to keep in mind when analyzing the privacy
issues of DNS is the fact that DNS requests received by a server are issues of DNS is the fact that DNS requests received by a server are
triggered by different reasons. Let's assume an eavesdropper wants triggered by different reasons. Let's assume an eavesdropper wants
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For privacy-related terms, we will use the terminology from For privacy-related terms, we will use the terminology 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). We consider the risks of
pervasive surveillance [RFC7258] as well as risks coming from a more pervasive surveillance [RFC7258] as well as risks coming from a more
focused surveillance. focused surveillance.
This document does not attempt a comparison of specific privacy
protections provided by individual networks or organisations, it
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 such as leakage of private Privacy risks for recursive operators (including access providers and
operators in enterprise networks) such as leakage of private
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 concerns such as cache Non-privacy risks (e.g security related concerns 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, e.g.,
unencrypted TLS SNI extensions or HTTPS destination IP address
fingerprinting are not considered here.
3. Risks 3. Risks
3.1. The Alleged Public Nature of DNS Data 3.1. The Alleged Public Nature of DNS Data
It has long been claimed that "the data in the DNS is public". While It has long been claimed that "the data in the DNS is public". While
this sentence makes sense for an Internet-wide lookup system, there this sentence makes sense for an Internet-wide lookup system, there
are multiple facets to the data and metadata involved that deserve a are multiple facets to the data and metadata involved that deserve a
more detailed look. First, access control lists and private more detailed look. First, access control lists (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. 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).
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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. 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; that transaction is not / should not be public. A
typical example from outside the DNS world is: the web site of typical example from outside the DNS world is: the web site of
Alcoholics Anonymous is public; the fact that you visit it should not Alcoholics Anonymous is public; the fact that you visit it should not
be. be.
3.2. Data in the DNS Request 3.2. Data in the DNS Request
The DNS request includes many fields, but two of them seem The DNS request includes many fields, but two of them seem
particularly relevant for the privacy issues: the QNAME and the particularly relevant for the privacy issues: the QNAME and the
source IP address. "source IP address" is used in a loose sense of source IP address. "source IP address" is used in a loose sense of
"source IP address + maybe source port", because the port is also in "source IP address + maybe source port number", because the port
the request and can be used to differentiate between several users number is also in the request and can be used to differentiate
sharing an IP address (behind a Carrier-Grade NAT (CGN), for instance between several users sharing an IP address (behind a Carrier-Grade
[RFC6269]). NAT (CGN) or a NPTv6, 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
about what the user does ("What are the MX records of example.net?" about what the user does ("What are the MX records of example.net?"
means he probably wants to send email to someone at example.net, means he probably wants to send email to someone at example.net,
which may be a domain used by only a few persons and is therefore which may be a domain used by only a few persons and is therefore
very revealing about communication relationships). Some QNAMEs are very revealing about communication relationships). Some QNAMEs are
more sensitive than others. For instance, querying the A record of a more sensitive than others. For instance, querying the A record of a
well-known web statistics domain reveals very little (everybody well-known web statistics domain reveals very little (everybody
visits web sites that use this analytics service), but querying the A visits web sites that use this analytics service), but querying the A
record of www.verybad.example where verybad.example is the domain of record of www.verybad.example where verybad.example is the domain of
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There are also some BitTorrent clients that query an SRV record for There are also some BitTorrent clients that query an SRV record for
_bittorrent-tracker._tcp.domain.example. _bittorrent-tracker._tcp.domain.example.
Another important thing about the privacy of the QNAME is the future Another important thing about the privacy of the QNAME is the future
usages. Today, the lack of privacy is an obstacle to putting usages. Today, the lack of privacy is an obstacle to putting
potentially sensitive or personally identifiable data in the DNS. At potentially sensitive or personally identifiable data in the DNS. At
the moment, your DNS traffic might reveal that you are doing email the moment, your DNS traffic might reveal that you are doing email
but not with whom. If your Mail User Agent (MUA) starts looking up but not with whom. If your Mail User Agent (MUA) starts looking up
Pretty Good Privacy (PGP) keys in the DNS [RFC7929], then privacy Pretty Good Privacy (PGP) keys in the DNS [RFC7929], then privacy
becomes a lot more important. And email is just an example; there becomes a lot more important. And email is just an example; there
would be other really interesting uses for a more privacy- friendly would be other really interesting uses for a more privacy-friendly
DNS. DNS.
For the communication between the stub resolver and the recursive For the communication between the stub resolver and the recursive
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 now the IP address of source address in an HTTP connection. It is typically the IP address
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 is
as sensitive as it is for HTTP [sidn-entrada]. 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
the meantime, the discussion here is intended to include both IPv4 the meantime, the discussion here is intended to include both IPv4
and IPv6 source addresses. For a number of reasons, their assignment and IPv6 source addresses. For a number of reasons, their assignment
and utilization characteristics are different, which may have and utilization characteristics are different, which may have
implications for details of information leakage associated with the implications for details of information leakage associated with the
collection of source addresses. (For example, a specific IPv6 source collection of source addresses. (For example, a specific IPv6 source
address seen on the public Internet is less likely than an IPv4 address seen on the public Internet is less likely than an IPv4
address to originate behind a CGN or other NAT.) However, for both address to originate behind an address sharing scheme.) However, for
IPv4 and IPv6 addresses, it's important to note that source addresses both IPv4 and IPv6 addresses, it is important to note that source
are propagated with queries and comprise metadata about the host, addresses are propagated with queries and comprise metadata about the
user, or application that originated them. host, user, or application that originated them.
3.2.1. Data in the DNS payload 3.2.1. Data in the DNS payload
At the time of writing there are no standardized client identifiers At the time of writing there are no standardized client identifiers
contained in the DNS payload itself (ECS [RFC7871] while widely used contained in the DNS payload itself (ECS [RFC7871] while widely used
is only of Category Informational). is only of Category Informational).
DNS Cookies [RFC7873] are a lightweight DNS transaction security DNS Cookies [RFC7873] are a lightweight DNS transaction security
mechanism that provides limited protection against a variety of mechanism that provides limited protection against a variety of
increasingly common denial-of-service and amplification/forgery or increasingly common denial-of-service and amplification/forgery or
cache poisoning attacks by off-path attackers. It is noted, however, cache poisoning attacks by off-path attackers. It is noted, however,
that they are designed to just verify IP addresses (and should change that they are designed to just verify IP addresses (and should change
once a client's IP address changes), they are not designed to once a client's IP address changes), they are not designed to
actively track users (like HTTP cookies). actively track users (like HTTP cookies).
There are anecdotal accounts of MAC addresses [1] and even user names There are anecdotal accounts of MAC addresses [1] and even user names
being inserted in non-standard EDNS(0) options for stub to resolver being inserted in non-standard EDNS(0) options for stub to resolver
communications to support proprietary functionality implemented at communications to support proprietary functionality implemented at
the resolver (e.g. parental filtering). the resolver (e.g., parental filtering).
3.3. Cache Snooping 3.3. Cache Snooping
The content of recursive resolvers' caches can reveal data about the The content of recursive resolvers' caches can reveal data about the
clients using it (the privacy risks depend on the number of clients). clients using it (the privacy risks depend on the number of clients).
This information can sometimes be examined by sending DNS queries This information can sometimes be examined by sending DNS queries
with RD=0 to inspect cache content, particularly looking at the DNS with RD=0 to inspect cache content, particularly looking at the DNS
TTLs [grangeia.snooping]. Since this also is a reconnaissance TTLs [grangeia.snooping]. Since this also is a reconnaissance
technique for subsequent cache poisoning attacks, some counter technique for subsequent cache poisoning attacks, some counter
measures have already been developed and deployed. measures have already been developed and deployed.
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3.4. On the Wire 3.4. On the Wire
3.4.1. Unencrypted Transports 3.4.1. Unencrypted Transports
For unencrypted transports, DNS traffic can be seen by an For unencrypted transports, DNS traffic can be seen by an
eavesdropper like any other traffic. (DNSSEC, specified in eavesdropper like any other traffic. (DNSSEC, specified in
[RFC4033], explicitly excludes confidentiality from its goals.) So, [RFC4033], explicitly excludes confidentiality from its goals.) So,
if an initiator starts an HTTPS communication with a recipient, while if an initiator starts an HTTPS communication with a recipient, while
the HTTP traffic will be encrypted, the DNS exchange prior to it will the HTTP traffic will be encrypted, the DNS exchange prior to it will
not be. When other protocols will become more and more privacy-aware not be. When other protocols will become more and more privacy-aware
and secured against surveillance (e.g. [RFC8446], and secured against surveillance (e.g., [RFC8446],
[I-D.ietf-quic-transport]), the use of unencrypted transports for DNS [I-D.ietf-quic-transport]), the use of unencrypted transports for DNS
may become "the weakest link" in privacy. It is noted that at the may become "the weakest link" in privacy. It is noted that at the
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 [I-D.ietf-tls-sni-encryption].
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,
because traffic is not limited by DNS caching. because traffic is not limited by DNS caching.
The attack surface between the stub resolver and the rest of the The attack surface between the stub resolver and the rest of the
world can vary widely depending upon how the end user's computer is world can vary widely depending upon how the end user's device is
configured. By order of increasing attack surface: configured. By order of increasing attack surface:
The recursive resolver can be on the end user's computer. In o The recursive resolver can be on the end user's device. In
(currently) a small number of cases, individuals may choose to (currently) a small number of cases, individuals may choose to
operate their own DNS resolver on their local machine. In this operate their own DNS resolver on their local machine. In this
case, the attack surface for the connection between the stub case, the attack surface for the connection between the stub
resolver and the caching resolver is limited to that single resolver and the caching resolver is limited to that single
machine. machine.
The recursive resolver may be at the local network edge. For o The recursive resolver may be at the local network edge. For
many/most enterprise networks and for some residential users, the many/most enterprise networks and for some residential users, the
caching resolver may exist on a server at the edge of the local caching resolver may exist on a server at the edge of the local
network. In this case, the attack surface is the local network. network. In this case, the attack surface is the local network.
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.
The recursive resolver can be in the IAP premises. 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 computer to be configured (typically is for the end user's device to be configured (typically
automatically through DHCP) with the addresses of the DNS automatically through DHCP or RA options) with the addresses of
recursive resolvers at the IAP. The attack surface for on-the- the DNS proxy in the CPE, which in turns points to the DNS
wire attacks is therefore from the end-user system across the recursive resolvers at the IAP. The attack surface for on-the-
local network and across the IAP network to the IAP's recursive wire attacks is therefore from the end user system across the
resolvers. local network and across the IAP network to the IAP's recursive
resolvers.
The recursive resolver can be a public DNS service. Some machines o The recursive resolver can be a public DNS service. Some machines
may be configured to use public DNS resolvers such as those may be configured to use public DNS resolvers such as those
operated today by Google Public DNS or OpenDNS. The end user may operated by Google Public DNS or OpenDNS. The end user may have
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 is also noted that typically a device connected _only_ to a modern
cellular network is
o directly configured with only the recursive resolvers of the IAP
and
o all traffic (including DNS) between the device and the cellular
network is encrypted following an encryption profile edited by the
IPv6 for Third Generation Partnership Project (3GPP [2]).
The attack surface for this specific scenario is not considered here.
3.4.2. Encrypted Transports 3.4.2. Encrypted Transports
The use of encrypted transports directly mitigates passive The use of encrypted transports directly mitigates passive
surveillance of the DNS payload, however there are still some privacy surveillance of the DNS payload, however there are still some privacy
attacks possible. 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 IP TTL or TCP Window sizes os-fingerprint [2] values highlighted that IPv4 TTL, IPv6 Hop Limit, or TCP Window sizes os-
can be used to fingerprint client OS's or that various techniques can fingerprint [3] values can be used to fingerprint client OS's or that
be used to de-NAT DNS queries dns-de-nat [3]. various techniques can be used to de-NAT DNS queries dns-de-nat [4].
The use of clear text transport options to decrease latency may also The use of clear text transport options to optimize latency may also
identify a user e.g. using TCP Fast Open [RFC7413]. identify a user, e.g., using TCP Fast Open with TLS 1.2 [RFC7413].
More specifically, (since the deployment of encrypted transports is More specifically, (since the deployment of encrypted transports is
not widespread at the time of writing) users wishing to use encrypted not widespread at the time of writing) users wishing to use encrypted
transports for DNS may in practice be limited in the resolver transports for DNS may in practice be limited in the resolver
services available. Given this, the choice of a user to configure a services available. Given this, the choice of a user to configure a
single resolver (or a fixed set of resolvers) and an encrypted single resolver (or a fixed set of resolvers) and an encrypted
transport to use in all network environments can actually serve to transport to use in all network environments can actually serve to
identify the user as one that desires privacy and can provide an identify the user as one that desires privacy and can provide an
added mechanism to track them as they move across network added mechanism to track them as they move across network
environments. environments.
Users of encrypted transports are also highly likely to re-use Users of encrypted transports are also highly likely to re-use
sessions for multiple DNS queries to optimize performance (e.g. via sessions for multiple DNS queries to optimize performance (e.g., via
DNS pipelining or HTTPS multiplexing). Certain configuration options DNS pipelining or HTTPS multiplexing). Certain configuration options
for encrypted transports could also in principle fingerprint a user for encrypted transports could also in principle fingerprint a user
or client application. For example: or 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
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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 3.5.1. In the Recursive Resolvers
Recursive Resolvers see all the traffic since there is typically no Recursive Resolvers see all the traffic since there is typically no
caching before them. To summarize: your recursive resolver knows a caching before them. To summarize: your recursive resolver knows a
lot about you. The resolver of a large IAP, or a large public lot about you. The resolver of a large IAP, or a large public
resolver, can collect data from many users. resolver, can collect data from many users.
3.5.1.1. Resolver selection 3.5.1.1. 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, which may have strong, medium, or weak privacy policies
depending on the network. Privacy policies for these servers may or depending on the network. Privacy policies for these servers may or
may not be available and users need to be aware that privacy may not be available and users need to be aware that privacy
guarantees will vary with network. guarantees will vary with network.
More recently some networks and end users have actively chosen to use More recently some networks and end users have actively chosen to use
a large public resolver instead e.g. Google Public DNS, Cloudflare a large public resolver instead, e.g., Google Public DNS [5],
or Quad9 (need refs). There can be many reasons: cost considerations Cloudflare [6], or Quad9 [7]. There can be many reasons: cost
for network operators, better reliability or anti-censorship considerations for network operators, better reliability or anti-
considerations are just a few. Such services typically do provide a censorship considerations are just a few. Such services typically do
privacy policy and the end user can get an idea of the data collected provide a privacy policy and the end user can get an idea of the data
by such operators by reading one e.g., Google Public DNS - Your collected by such operators by reading one e.g., Google Public DNS -
Privacy [4]. Your Privacy [8].
Even more recently some applications have announced plans to deploy Even more recently some applications have announced plans to deploy
application specific DNS settings which might be enabled by default. application-specific DNS settings which might be enabled by default.
For example current proposals by Firefox [firefox] revolve around a For example, current proposals by Firefox [firefox] revolve around a
default based on geographic region using a pre-configured list of default based on the geographic region, using a pre-configured list
large public resolver services which offer DoH, combined with non- of large public resolver services which offer DoH, combined with non-
standard probing and signalling mechanism to disable DoH in standard probing and signalling mechanism to disable DoH in
particular networks. Whereas Chrome [chrome] is experimenting with particular networks. Whereas Chrome [chrome] is experimenting with
using DoH to the DHCP provided resolver if it is on a list of DoH- using DoH to the DHCP-provided resolver if it is on a list of DoH-
compatible providers. At the time of writing efforts to provide compatible providers. At the time of writing, efforts to provide
standardized signalling mechanisms for applications to discover the standardized signalling mechanisms for applications to discover the
services offered by local resolvers are in progress services offered by local resolvers are in progress
[I-D.ietf-dnsop-resolver-information]. [I-D.ietf-dnsop-resolver-information].
If applications enable application specific DNS settings without If applications enable application-specific DNS settings without
properly informing the user of the change (or do not provide an properly informing the user of the change (or do not provide an
option for user configuration of the application recursive resolver) option for user configuration of the application's recursive
there is a potential privacy issue; depending on the network context resolver) there is a potential privacy issue; depending on the
and the application default the application might use a recursive network context and the application default, the application might
server that provides less privacy protection than the default network use a recursive server that provides less privacy protection than the
provided server without the users full knowledge. Users that are default network-provided server without the user's full knowledge.
fully aware of an application specific DNS setting may want to Users that are fully aware of an application specific DNS setting may
actively override any default in favour of their chosen recursive want to actively override any default in favour of their chosen
resolver. recursive resolver.
There are also concerns that should the trend towards using large There are also concerns that, should the trend towards using large
public resolvers increase, this will itself provide a privacy concern public resolvers increase, this will itself provide a privacy
due to a small number of operators having visibility of the majority concern, due to a small number of operators having visibility of the
of DNS requests globally and the potential for aggregating data majority of DNS requests globally and the potential for aggregating
across services about a user. Additionally the operating data across services about a user. Additionally the operating
organisation of the resolver may be in a different legal jurisdiction organisation of the resolver may be in a different legal jurisdiction
to the user which creates further privacy concerns around legal than the user, which creates further privacy concerns around legal
protections of and access to the data collected by the operator. protections of and access to the data collected by the operator.
At the time of writing the deployment models for DNS are evolving, At the time of writing the deployment models for DNS are evolving,
their implications are complex and extend beyond the scope of this their implications are complex and extend beyond the scope of this
document. They are the subject of much other work including document. They are the subject of much other work including
[I-D.livingood-doh-implementation-risks-issues], the IETF ADD mailing [I-D.livingood-doh-implementation-risks-issues], the IETF ADD mailing
list [5] and the Encrypted DNS Deployment Initiative [6]. list [9] and the Encrypted DNS Deployment Initiative [10].
3.5.1.2. Active attacks on resolver configuration 3.5.1.2. Active Attacks on Resolver Configuration
The previous paragraphs 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 redirecting the traffic, not just to observe attackers in the network redirecting the traffic, not just to observe
it but also potentially change it. it but also potentially change it.
For instance, a DHCP server controlled by an attacker can direct you For instance, a DHCP server controlled by an attacker can direct you
to a recursive resolver also controlled by that attacker. Most of to a recursive resolver also controlled by that attacker. Most of
the time, it seems to be done to divert traffic in order to also the time, it seems to be done to divert traffic in order to also
direct the user to a web server controlled by the attacker. However direct the user to a web server controlled by the attacker. However
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can masquerade as the intended server and respond with data to the can masquerade as the intended server and respond with data to the
client. (Attacker controlled servers that inject malicious data are client. (Attacker controlled servers that inject malicious data are
possible, but it is a separate problem not relevant to privacy.) A possible, but it is a separate problem not relevant to privacy.) A
server controlled by an attacker may respond correctly for a long server controlled by an attacker may respond correctly for a long
period of time, thereby foregoing detection. period of time, thereby foregoing detection.
Also, malware like DNSchanger [dnschanger] can change the recursive Also, malware like DNSchanger [dnschanger] can change the recursive
resolver in the machine's configuration, or the routing itself can be resolver in the machine's configuration, or the routing itself can be
subverted (for instance, [ripe-atlas-turkey]). subverted (for instance, [ripe-atlas-turkey]).
3.5.1.3. Blocking of user selected services 3.5.1.3. Blocking of User Selected 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 (e.g. 1.1.1.1 or 2606:4700:4700::1111) could specific IP addresses (e.g., 1.1.1.1 or 2606:4700:4700::1111) could
restrict the resolvers available to the user. The extent of the risk restrict the resolvers available to the user. The extent of the risk
to end user privacy is highly dependant on the specific network and to end user privacy is highly dependent on the specific network and
user context; a user on a network that is known to perform user context; a user on a network that is known to perform
surveillance would be compromised if they could not access such surveillance would be compromised if they could not access such
services whereas a user on a trusted network might have no privacy services, whereas a user on a trusted network might have no privacy
motivation to do so. motivation to do so.
Similarly attacks on such services e.g. DDoS could force users to In some cases, networks might block access to remote resolvers for
switch to other services that do not offer encrypted transports for security reasons, for example to cripple malware and bots or to
DNS. prevent data exfiltration methods that use encrypted DNS
communications as transport. In these cases, if the network fully
respects user privacy in other ways (i.e. encrypted DNS and good
data handling policies) the block can serve to further protect user
privacy by ensuring such security precautions.
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
encrypted transports for DNS.
3.5.1.4. Authentication of Servers 3.5.1.4. Authentication of Servers
Both DoH and Strict mode for DoT require authentication of the server Both DoH and Strict mode for DoT [RFC8310] require authentication of
and therefore as long as the authentication credentials are obtained the server and therefore as long as the authentication credentials
over a secure channel then using either of these transports defeats are obtained over a secure channel then using either of these
the attack of re-directing traffic to rogue servers. Of course transports defeats the attack of re-directing traffic to rogue
attacks on these secure channels are also possible, but out of the servers. Of course attacks on these secure channels are also
scope of this document. possible, but out of the scope of this document.
3.5.1.5. Encrypted Transports 3.5.1.5. Encrypted Transports
3.5.1.5.1. DoT and DoH 3.5.1.5.1. DoT and DoH
Use of encrypted transports does not reduce the data available in the Use of encrypted transports does not reduce the data available in the
recursive resolver and ironically can actually expose more recursive resolver and ironically can actually expose more
information about users to operators. As mentioned in Section 3.4 information about users to operators. As mentioned in Section 3.4
use of session based encrypted transports (TCP/TLS) can expose use of session based encrypted transports (TCP/TLS) can expose
correlation data about users. Such concerns in the TCP/TLS layers correlation data about users. Such concerns in the TCP/TLS layers
apply equally to DoT and DoH which both use TLS as the underlying apply equally to DoT and DoH which both use TLS as the underlying
transport, some examples are: transport, some examples are:
o fingerprinting based on TLS version and/or cipher suite selection o fingerprinting based on TLS version and/or cipher suite selection
o user tracking via session resumption in TLS 1.2 o user tracking via session resumption in TLS 1.2
3.5.1.5.2. DoH Specific Considerations 3.5.1.5.2. DoH Specific Considerations
The proposed specification for DoH [RFC8484] includes a Privacy Section 8 of [RFC8484] highlights some of the privacy consideration
Considerations section which highlights some of the differences differences between HTTP and DNS. As a deliberate design choice DoH
between HTTP and DNS. As a deliberate design choice DoH inherits the inherits the privacy properties of the HTTPS stack and as a
privacy properties of the HTTPS stack and as a consequence introduces consequence introduces new privacy concerns when compared with DNS
new privacy concerns when compared with DNS over UDP, TCP or TLS over UDP, TCP or TLS [RFC7858]. The rationale for this decision is
[RFC7858]. The rationale for this decision is that retaining the that retaining the ability to leverage the full functionality of the
ability to leverage the full functionality of the HTTP ecosystem is HTTP ecosystem is more important than placing specific constraints on
more important than placing specific constraints on this new protocol this new protocol based on privacy considerations (modulo limiting
based on privacy considerations (modulo limiting the use of HTTP the use of HTTP cookies).
cookies).
In analyzing the new issues introduced by DoH it is helpful to In analyzing the new issues introduced by DoH it is helpful to
recognize that there exists a natural tension between recognize that there exists a natural tension between
o the wide practice in HTTP to use various headers to optimize HTTP o the wide practice in HTTP to use various headers to optimize HTTP
connections, functionality and behaviour (which can facilitate connections, functionality and behaviour (which can facilitate
user identification and tracking) user identification and tracking)
o and the fact that the DNS payload is currently very tightly o and the fact that the DNS payload is currently very tightly
encoded and contains no standardized user identifiers. encoded and contains no standardized user identifiers.
DoT, for example, would normally contain no client identifiers above DoT, for example, would normally contain no client identifiers above
the TLS layer and a resolver would see only a stream of DNS query the TLS layer and a resolver would see only a stream of DNS query
payloads originating within one or more connections from a client IP payloads originating within one or more connections from a client IP
address. Whereas if DoH clients commonly include several headers in address. Whereas if DoH clients commonly include several headers in
a DNS message (e.g. user-agent and accept-language) this could lead a DNS message (e.g., user-agent and accept-language) this could lead
to the DoH server being able to identify the source of individual DNS to the DoH server being able to identify the source of individual DNS
requests not only to a specific end user device but to a specific requests not only to a specific end user device but to a specific
application. application.
Additionally, depending on the client architecture, isolation of DoH Additionally, depending on the client architecture, isolation of DoH
queries from other HTTP traffic may or may not be feasible or queries from other HTTP traffic may or may not be feasible or
desirable. Depending on the use case, isolation of DoH queries from desirable. Depending on the use case, isolation of DoH queries from
other HTTP traffic may or may not increase privacy. other HTTP traffic may or may not increase privacy.
The picture for privacy considerations and user expectations for DoH The picture for privacy considerations and user expectations for DoH
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HTTPS functionality vs privacy is specifically made an implementation HTTPS functionality vs privacy is specifically made an implementation
choice in DoH and users may well have differing privacy expectations choice in DoH and users may well have differing privacy expectations
depending on the DoH use case and implementation. depending on the DoH use case and implementation.
At the extremes, there may be implementations that attempt to achieve At the extremes, there may be implementations that attempt to achieve
parity with DoT from a privacy perspective at the cost of using no parity with DoT from a privacy perspective at the cost of using no
identifiable headers, there might be others that provide feature rich identifiable headers, there might be others that provide feature rich
data flows where the low-level origin of the DNS query is easily data flows where the low-level origin of the DNS query is easily
identifiable. identifiable.
Privacy focussed users should be aware of the potential for Privacy focused users should be aware of the potential for additional
additional client identifiers in DoH compared to DoT and may want to client identifiers in DoH compared to DoT and may want to only use
only use DoH client implementations that provide clear guidance on DoH client implementations that provide clear guidance on what
what identifiers they add. identifiers they add.
3.5.2. In the Authoritative Name Servers 3.5.2. In the Authoritative Name Servers
Unlike what happens for recursive resolvers, observation capabilities Unlike what happens for recursive resolvers, observation capabilities
of authoritative name servers are limited by caching; they see only of authoritative name servers are limited by caching; they see only
the requests for which the answer was not in the cache. For the requests for which the answer was not in the cache. For
aggregated statistics ("What is the percentage of LOC queries?"), aggregated statistics ("What is the percentage of LOC queries?"),
this is sufficient, but it prevents an observer from seeing this is sufficient, but it prevents an observer from seeing
everything. 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
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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
a period, then that same adversary may be able to re-identify the a period, then that same adversary may be able to re-identify the
user solely based on their pattern of DNS queries later on regardless user solely based on their pattern of DNS queries later on regardless
of the location from which the user makes those queries. For of the location from which the user makes those queries. For
example, one study [herrmann-reidentification] found that such re- example, one study [herrmann-reidentification] found that such re-
identification is possible so that "73.1% of all day-to-day links identification is possible so that "73.1% of all day-to-day links
were correctly established, i.e. user u was either re-identified were correctly established, i.e., user u was either re-identified
unambiguously (1) or the classifier correctly reported that u was not unambiguously (1) or the classifier correctly reported that u was not
present on day t+1 any more (2)." While that study related to web present on day t+1 any more (2)." While that study related to web
browsing behavior, equally characteristic patterns may be produced browsing behavior, equally characteristic patterns may be produced
even in machine-to-machine communications or without a user taking even in machine-to-machine communications or without a user taking
specific actions, e.g., at reboot time if a characteristic set of specific actions, e.g., at reboot time if a characteristic set of
services are accessed by the device. services are accessed by the device.
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
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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 project which to check their availability. Also the QUANTUMTHEORY project which
includes detecting lookups for certain addresses and injecting bogus includes detecting lookups for certain addresses and injecting bogus
replies is another good example showing that the lack of privacy replies is another good example showing that the lack of privacy
protections in the DNS is actively exploited. protections in the DNS is actively exploited.
5. Legalities 5. Legalities
To our knowledge, there are no specific privacy laws for DNS data, in To our knowledge, there are no specific privacy laws for DNS data, in
any country. Interpreting general privacy laws like any country. Interpreting general privacy laws like
[data-protection-directive] or GDPR [7] applicable in the European [data-protection-directive] or GDPR [11] 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 6. Security Considerations
This document is entirely about security, more precisely privacy. It This document is entirely about security, more precisely privacy. It
just lays out the problem; it does not try to set requirements (with just lays out the problem; it does not try to set requirements (with
the choices and compromises they imply), much less define solutions. the choices and compromises they imply), much less define solutions.
Possible solutions to the issues described here are discussed in Possible solutions to the issues described here are discussed in
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7. Acknowledgments 7. Acknowledgments
Thanks to Nathalie Boulvard and to the CENTR members for the original Thanks to Nathalie Boulvard and to the CENTR members for the original
work that led to this document. Thanks to Ondrej Sury for the work that led to this document. Thanks to Ondrej Sury for the
interesting discussions. Thanks to Mohsen Souissi and John Heidemann interesting discussions. Thanks to Mohsen Souissi and John Heidemann
for proofreading and to Paul Hoffman, Matthijs Mekking, Marcos Sanz, for proofreading and to Paul Hoffman, Matthijs Mekking, Marcos Sanz,
Tim Wicinski, Francis Dupont, Allison Mankin, and Warren Kumari for Tim Wicinski, Francis Dupont, Allison Mankin, and Warren Kumari for
proofreading, providing technical remarks, and making many proofreading, providing technical remarks, and making many
readability improvements. Thanks to Dan York, Suzanne Woolf, Tony readability improvements. Thanks to Dan York, Suzanne Woolf, Tony
Finch, Stephen Farrell, Peter Koch, Simon Josefsson, and Frank Denis Finch, Stephen Farrell, Peter Koch, Simon Josefsson, and Frank Denis
for good written contributions. And thanks to the IESG members for for good written contributions. Thanks to Vittorio Bertola and
the last remarks. Mohamed Boucadair for a detailed review of the -bis. And thanks to
the IESG members for the last remarks.
8. Changelog 8. Changelog
draft-ietf-dprive-rfc7627-bis-01 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) o Re-structure section 3.5 (was 2.5)
* Collect considerations for recursive resolvers together * Collect considerations for recursive resolvers together
* Re-work several sections here to clarify their context (e.g. * Re-work several sections here to clarify their context (e.g.,
'Rogue servers' becomes 'Active attacks on resolver 'Rogue servers' becomes 'Active attacks on resolver
configuration') configuration')
* Add discussion of resolver selection * Add discussion of resolver selection
o Update text and old reference on Snowdon revelations. o Update text and old reference on Snowdon revelations.
o Add text on and references to QNAME minimisation RFC and o Add text on and references to QNAME minimisation RFC and
deployment measurements deployment measurements
o Correct outdated references o Correct outdated references
o Clarify scope by adding a Scope section (was Risks overview) o Clarify scope by adding a Scope section (was Risks overview)
o Clarify what risks are considered in section 3.4.2 o Clarify what risks are considered in section 3.4.2
draft-ietf-dprive-rfc7627-bis-00 draft-ietf-dprive-rfc7626-bis-00
o Rename after WG adoption o Rename after WG adoption
o Use DoT acronym throughout o Use DoT acronym throughout
o Minor updates to status of deployment and other drafts o Minor updates to status of deployment and other drafts
draft-bortzmeyer-dprive-rfc7626-bis-02
o Update various references and fix some nits. o Update various references and fix some nits.
draft-bortzmeyer-dprive-rfc7626-bis-01 draft-bortzmeyer-dprive-rfc7626-bis-01
o Update reference for dickinson-bcp-op to draft-dickinson-dprive- o Update reference for dickinson-bcp-op to draft-dickinson-dprive-
bcp-op bcp-op
draft-borztmeyer-dprive-rfc7626-bis-00: draft-borztmeyer-dprive-rfc7626-bis-00:
Initial commit. Differences to RFC7626: Initial commit. Differences to RFC7626:
skipping to change at page 20, line 34 skipping to change at page 21, line 5
[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>.
[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.
9.2. Informative References 9.2. Informative References
[aeris-dns] [aeris-dns]
Vinot, N., "Vie privee: et le DNS alors?", (In French), Vinot, N., "Vie privee: et le DNS alors?", (In French),
2015, <https://blog.imirhil.fr/vie-privee-et-le-dns- 2015, <https://blog.imirhil.fr/vie-privee-et-le-dns-
alors.html>. alors.html>.
[castillo-garcia] [castillo-garcia]
Castillo-Perez, S. and J. Garcia-Alfaro, "Anonymous Castillo-Perez, S. and J. Garcia-Alfaro, "Anonymous
Resolution of DNS Queries", 2008, Resolution of DNS Queries", 2008,
skipping to change at page 23, line 13 skipping to change at page 23, line 27
regensburg.de/21103/1/Paper_PUL_nordsec_published.pdf>. regensburg.de/21103/1/Paper_PUL_nordsec_published.pdf>.
[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-00 (work in progress), August 2019.
[I-D.ietf-dprive-bcp-op] [I-D.ietf-dprive-bcp-op]
Dickinson, S., Overeinder, B., Rijswijk-Deij, R., and A. Dickinson, S., Overeinder, B., Rijswijk-Deij, R., and A.
Mankin, "Recommendations for DNS Privacy Service Mankin, "Recommendations for DNS Privacy Service
Operators", draft-ietf-dprive-bcp-op-03 (work in Operators", draft-ietf-dprive-bcp-op-04 (work in
progress), July 2019. progress), October 2019.
[I-D.ietf-quic-transport] [I-D.ietf-quic-transport]
Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
and Secure Transport", draft-ietf-quic-transport-23 (work and Secure Transport", draft-ietf-quic-transport-23 (work
in progress), September 2019. in progress), September 2019.
[I-D.ietf-tls-sni-encryption] [I-D.ietf-tls-sni-encryption]
Huitema, C. and E. Rescorla, "Issues and Requirements for Huitema, C. and E. Rescorla, "Issues and Requirements for
SNI Encryption in TLS", draft-ietf-tls-sni-encryption-06 SNI Encryption in TLS", draft-ietf-tls-sni-encryption-08
(work in progress), September 2019. (work in progress), October 2019.
[I-D.livingood-doh-implementation-risks-issues] [I-D.livingood-doh-implementation-risks-issues]
Livingood, J., Antonakakis, M., Sleigh, B., and A. Livingood, J., Antonakakis, M., Sleigh, B., and A.
Winfield, "Centralized DNS over HTTPS (DoH) Implementation Winfield, "Centralized DNS over HTTPS (DoH) Implementation
Issues and Risks", draft-livingood-doh-implementation- Issues and Risks", draft-livingood-doh-implementation-
risks-issues-04 (work in progress), September 2019. risks-issues-04 (work in progress), September 2019.
[morecowbell] [morecowbell]
Grothoff, C., Wachs, M., Ermert, M., and J. Appelbaum, Grothoff, C., Wachs, M., Ermert, M., and J. Appelbaum,
"NSA's MORECOWBELL: Knell for DNS", GNUnet e.V., January "NSA's MORECOWBELL: Knell for DNS", GNUnet e.V., January
skipping to change at page 24, line 45 skipping to change at page 25, line 12
(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>.
[RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T., [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann, Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A "Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", RFC 7624, Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015, <https://www.rfc- DOI 10.17487/RFC7624, August 2015, <https://www.rfc-
editor.org/info/rfc7624>. editor.org/info/rfc7624>.
[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
<https://www.rfc-editor.org/info/rfc7816>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., [RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>. 2016, <https://www.rfc-editor.org/info/rfc7858>.
[RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W. [RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W.
Kumari, "Client Subnet in DNS Queries", RFC 7871, Kumari, "Client Subnet in DNS Queries", RFC 7871,
DOI 10.17487/RFC7871, May 2016, <https://www.rfc- DOI 10.17487/RFC7871, May 2016, <https://www.rfc-
editor.org/info/rfc7871>. editor.org/info/rfc7871>.
[RFC7873] Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS) [RFC7873] Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS)
Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016, Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016,
<https://www.rfc-editor.org/info/rfc7873>. <https://www.rfc-editor.org/info/rfc7873>.
[RFC7929] Wouters, P., "DNS-Based Authentication of Named Entities [RFC7929] Wouters, P., "DNS-Based Authentication of Named Entities
(DANE) Bindings for OpenPGP", RFC 7929, (DANE) Bindings for OpenPGP", RFC 7929,
DOI 10.17487/RFC7929, August 2016, <https://www.rfc- DOI 10.17487/RFC7929, August 2016, <https://www.rfc-
editor.org/info/rfc7929>. editor.org/info/rfc7929>.
[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
for DNS over TLS and DNS over DTLS", RFC 8310,
DOI 10.17487/RFC8310, March 2018, <https://www.rfc-
editor.org/info/rfc8310>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<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,
skipping to change at page 26, line 27 skipping to change at page 26, line 47
[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>.
9.3. URIs 9.3. URIs
[1] https://lists.dns-oarc.net/pipermail/dns- [1] https://lists.dns-oarc.net/pipermail/dns-
operations/2016-January/014141.html operations/2016-January/014141.html
[2] http://netres.ec/?b=11B99BD [2] https://www.3gpp.org
[3] https://www.researchgate.net/publication/320322146_DNS-DNS_DNS- [3] http://netres.ec/?b=11B99BD
[4] 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/privacy [5] https://developers.google.com/speed/public-dns
[5] https://mailarchive.ietf.org/arch/browse/static/add [6] https://developers.cloudflare.com/1.1.1.1/setting-up-1.1.1.1/
[6] https://www.encrypted-dns.org [7] https://www.quad9.net
[7] https://www.eugdpr.org/the-regulation.html [8] https://developers.google.com/speed/public-dns/privacy
[9] https://mailarchive.ietf.org/arch/browse/static/add
[10] https://www.encrypted-dns.org
[11] https://www.eugdpr.org/the-regulation.html
Authors' Addresses Authors' Addresses
Stephane Bortzmeyer Stephane Bortzmeyer
AFNIC AFNIC
1, rue Stephenson 1, rue Stephenson
Montigny-le-Bretonneux Montigny-le-Bretonneux
France 78180 France 78180
Email: bortzmeyer+ietf@nic.fr Email: bortzmeyer+ietf@nic.fr
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