draft-ietf-dprive-problem-statement-06.txt   rfc7626.txt 
DNS PRIVate Exchange (dprive) Working Group S. Bortzmeyer Internet Engineering Task Force (IETF) S. Bortzmeyer
Internet-Draft AFNIC Request for Comments: 7626 AFNIC
Intended status: Informational June 15, 2015 Category: Informational August 2015
Expires: December 17, 2015 ISSN: 2070-1721
DNS privacy considerations DNS Privacy Considerations
draft-ietf-dprive-problem-statement-06
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. present situation and does not prescribe solutions.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for informational purposes.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
This Internet-Draft will expire on December 17, 2015. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7626.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. The alleged public nature of DNS data . . . . . . . . . . 5 2.1. The Alleged Public Nature of DNS Data . . . . . . . . . . 4
2.2. Data in the DNS request . . . . . . . . . . . . . . . . . 5 2.2. Data in the DNS Request . . . . . . . . . . . . . . . . . 5
2.3. Cache snooping . . . . . . . . . . . . . . . . . . . . . 6 2.3. Cache Snooping . . . . . . . . . . . . . . . . . . . . . 6
2.4. On the wire . . . . . . . . . . . . . . . . . . . . . . . 7 2.4. On the Wire . . . . . . . . . . . . . . . . . . . . . . . 7
2.5. In the servers . . . . . . . . . . . . . . . . . . . . . 8 2.5. In the Servers . . . . . . . . . . . . . . . . . . . . . 8
2.5.1. In the recursive resolvers . . . . . . . . . . . . . 9 2.5.1. In the Recursive Resolvers . . . . . . . . . . . . . 8
2.5.2. In the authoritative name servers . . . . . . . . . . 9 2.5.2. In the Authoritative Name Servers . . . . . . . . . . 9
2.5.3. Rogue servers . . . . . . . . . . . . . . . . . . . . 10 2.5.3. Rogue Servers . . . . . . . . . . . . . . . . . . . . 10
2.6. Re-identification and other inferences . . . . . . . . . 11 2.6. Re-identification and Other Inferences . . . . . . . . . 11
3. Actual "attacks" . . . . . . . . . . . . . . . . . . . . . . 11 2.7. More Information . . . . . . . . . . . . . . . . . . . . 11
3. Actual "Attacks" . . . . . . . . . . . . . . . . . . . . . . 11
4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 12
5. Security considerations . . . . . . . . . . . . . . . . . . . 12 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 12 6.1. Normative References . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.2. Informative References . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2. Informative References . . . . . . . . . . . . . . . . . 13
8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17
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] and [RFC1035] and The Domain Name System is specified in [RFC1034], [RFC1035], and many
many later RFCs, which have never been consolidated. It is one of later RFCs, which have never been consolidated. It is one of the
the most important infrastructure components of the Internet and most important infrastructure components of the Internet and often
often ignored or misunderstood by Internet users (and even by many 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 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 [I-D.ietf-dnsop-dns-terminology].) A client, the stub resolver, also [DNS-TERMS].) A client, the stub resolver, issues a DNS query
issues a DNS query to a server, called the recursive resolver (also to a server, called the recursive resolver (also called caching
called caching resolver or full resolver or recursive name server). resolver or full resolver or recursive name server). Let's use the
Let's use the query "What are the AAAA records for www.example.com?" query "What are the AAAA records for www.example.com?" as an example.
as an example. AAAA is the QTYPE (Query Type), and www.example.com AAAA is the QTYPE (Query Type), and www.example.com is the QNAME
is the QNAME (Query Name). (The description which follows assumes a (Query Name). (The description that follows assumes a cold cache,
cold cache, for instance because the server just started.) The for instance, because the server just started.) The recursive
recursive resolver will first query the root nameservers. In most resolver will first query the root name servers. In most cases, the
cases, the root nameservers will send a referral. In this example, root name servers will send a referral. In this example, the
the referral will be to the .com nameservers. The resolver repeats referral will be to the .com name servers. The resolver repeats the
the query to one of the .com nameservers. The .com nameservers, in query to one of the .com name servers. The .com name servers, in
turn, will refer to the example.com nameservers. The example.com turn, will refer to the example.com name servers. The example.com
nameserver will then return the answer. The root name servers, the name server will then return the answer. The root name servers, the
name servers of .com and the name servers of example.com are called name servers of .com, and the name servers of example.com are called
authoritative name servers. It is important, when analyzing the authoritative name servers. It is important, when analyzing the
privacy issues, to remember that the question asked to all these name privacy issues, to remember that the question asked to all these name
servers is always the original question, not a derived question. The servers is always the original question, not a derived question. The
question sent to the root name servers is "What are the AAAA records question sent to the root name servers is "What are the AAAA records
for www.example.com?", not "What are the name servers of .com?". By for 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 nameserver. necessary to the name server.
Because DNS relies on caching heavily, the algorithm described just Because DNS relies on caching heavily, the algorithm described just
above is actually a bit more complicated, and not all questions are above is actually a bit more complicated, and not all questions are
sent to the authoritative name servers. If a few seconds later the sent to the authoritative name servers. If a few seconds later the
stub resolver asks to the recursive resolver, "What are the SRV stub resolver asks the recursive resolver, "What are the SRV records
records of _xmpp-server._tcp.example.com?", the recursive resolver of _xmpp-server._tcp.example.com?", the recursive resolver will
will remember that it knows the name servers of example.com and will remember that it knows the name servers of example.com and will just
just query them, bypassing the root and .com. Because there is query them, bypassing the root and .com. Because there is typically
typically no caching in the stub resolver, the recursive resolver, no caching in the stub resolver, the recursive resolver, unlike the
unlike the authoritative servers, sees all the DNS traffic. authoritative servers, sees all the DNS traffic. (Applications, like
(Applications, like Web browsers, may have some form of caching which web browsers, may have some form of caching that does not follow DNS
do not follow DNS rules, for instance because it may ignore the TTL. rules, for instance, because it may ignore the TTL. So, the
So, the recursive resolver does not see all the name resolution recursive resolver does not see all the name resolution activity.)
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).
Almost all this DNS traffic is currently sent in clear (unencrypted). Almost all this DNS traffic is currently sent in clear (unencrypted).
There are a few cases where there is some channel encryption, for There are a few cases where there is some channel encryption, for
instance in an IPsec VPN, at least between the stub resolver and the instance, in an IPsec VPN, at least between the stub resolver and the
resolver. resolver.
Today, almost all DNS queries are sent over UDP [thomas-ditl-tcp]. Today, almost all DNS queries are sent over UDP [thomas-ditl-tcp].
This has practical consequences when considering encryption of the This has practical consequences when considering encryption of the
traffic as a possible privacy technique. Some encryption solutions traffic as a possible privacy technique. Some encryption solutions
are only designed for TCP, not UDP. are only designed for TCP, not UDP.
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 were 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:
Primary request: this is the domain name in the URL that the user 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
eavesdropper. eavesdropper.
Secondary requests: these are the additional requests performed by Secondary requests: these are the additional requests performed by
the user agent (here, the Web browser) without any direct the user agent (here, the web browser) without any direct
involvement or knowledge of the user. For the Web, they are involvement or knowledge of the user. For the Web, they are
triggered by embedded content, CSS sheets, JavaScript code, triggered by embedded content, Cascading Style Sheets (CSS),
embedded images, etc. In some cases, there can be dozens of JavaScript code, embedded images, etc. In some cases, there can
domain names in different contexts on a single Web page. be dozens of domain names in different contexts on a single web
page.
Tertiary requests: these are the additional requests performed by 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
name servers' names into IP addresses. Similarly, even if glue the name servers' names into IP addresses. Similarly, even if
records are returned, a careful recursive server will do tertiary glue records are returned, a careful recursive server will do
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 be noted also that, in the case of a typical web browser, more
DNS requests than stricly necessary are sent, for instance to DNS requests than strictly necessary are sent, for instance, to
prefetch resources that the user may query later, or when prefetch resources that the user may query later or when
autocompleting the URL in the address bar. Both are a big privacy autocompleting the URL in the address bar. Both are a big privacy
concern since they may leak information even about non-explicit concern since they may leak information even about non-explicit
actions. For instance, just reading a local HTML page, even without actions. For instance, just reading a local HTML page, even without
selecting the hyperlinks, may trigger DNS requests. selecting the hyperlinks, may trigger DNS requests.
For privacy-related terms, we will use here the terminology of For privacy-related terms, we will use the terminology from
[RFC6973]. [RFC6973].
2. Risks 2. Risks
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 pervasive surveillance [RFC7258] as well as risks coming from a more
more focused surveillance. Privacy risks for the holder of a zone focused surveillance. Privacy risks for the holder of a zone (the
(the risk that someone gets the data) are discussed in [RFC5936] and risk that someone gets the data) are discussed in [RFC5936] and
[RFC5155]. Non-privacy risks (such as cache poisoning) are out of [RFC5155]. Non-privacy risks (such as cache poisoning) are out of
scope. scope.
2.1. The alleged public nature of DNS data 2.1. The Alleged Public Nature of DNS Data
It has long been claimed that "the data in the DNS is public". While It has long been claimed that "the data in the DNS is public". While
this sentence makes sense for an Internet-wide lookup system, there this sentence makes sense for an Internet-wide lookup system, there
are multiple facets to the data and metadata involved that deserve a are multiple facets to the data and metadata involved that deserve a
more detailed look. First, access control lists and private more detailed look. First, access control lists and private
namespaces nonwithstanding, 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).
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 sequence of However, the same is not true of a single transaction or a sequence
transactions; that transaction is not/should not be public. A of transactions; that transaction is not / should not be public. A
typical example from outside the DNS world is: the Web site of typical example from outside the DNS world is: the web site of
Alcoholics Anonymous is public; the fact that you visit it should not Alcoholics Anonymous is public; the fact that you visit it should not
be. be.
2.2. Data in the DNS request 2.2. Data in the DNS Request
The DNS request includes many fields but two of them seem The DNS request includes many fields, but two of them seem
particularly relevant for the privacy issues: the QNAME and the particularly relevant for the privacy issues: the QNAME and the
source IP address. "source IP address" is used in a loose sense of source IP address. "source IP address" is used in a loose sense of
"source IP address + maybe source port", because the port is also in "source IP address + maybe source port", because the port is also in
the request and can be used to differentiate between several users the request and can be used to differentiate between several users
sharing an IP address (behind a CGN for instance [RFC6269]). sharing an IP address (behind a Carrier-Grade NAT (CGN), for instance
[RFC6269]).
The QNAME is the full name sent by the user. It gives information The QNAME is the full name sent by the user. It gives information
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 therefore very which may be a domain used by only a few persons and is therefore
revealing about communication relationships). Some QNAMEs are more very revealing about communication relationships). Some QNAMEs are
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 which 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
an organization that some people find offensive or objectionable, may an organization that some people find offensive or objectionable may
create more problems for the user. Also, sometimes, the QNAME embeds create more problems for the user. Also, sometimes, the QNAME embeds
the software one uses, which could be a privacy issue. For instance, the software one uses, which could be a privacy issue. For instance,
_ldap._tcp.Default-First-Site-Name._sites.gc._msdcs.example.org. _ldap._tcp.Default-First-Site-Name._sites.gc._msdcs.example.org.
There are also some BitTorrent clients that query a 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 but the moment, your DNS traffic might reveal that you are doing email
not with whom. If your MUA starts looking up PGP keys in the DNS but not with whom. If your Mail User Agent (MUA) starts looking up
[I-D.wouters-dane-openpgp] then privacy becomes a lot more important. Pretty Good Privacy (PGP) keys in the DNS [DANE-OPENPGPKEY], then
And email is just an example; there would be other really interesting privacy becomes a lot more important. And email is just an example;
uses for a more privacy-friendly DNS. there would be other really interesting uses for a more privacy-
friendly 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 a HTTP connection. It is now the IP address of the source address in an HTTP connection. It is now the IP address of
recursive resolver which, in a way "hides" the real user. However, the recursive resolver that, in a way, "hides" the real user.
hiding does not always work. Sometimes However, hiding does not always work. Sometimes [CLIENT-SUBNET] is
[I-D.ietf-dnsop-edns-client-subnet] is used (see its privacy analysis used (see its privacy analysis in [denis-edns-client-subnet]).
in [denis-edns-client-subnet]). Sometimes the end user has a Sometimes the end user has a personal recursive resolver on her
personal recursive resolver on her machine. In both cases, the IP machine. In both cases, the IP address is as sensitive as it is for
address is as sensitive as it is for HTTP [sidn-entrada]. HTTP [sidn-entrada].
A note about IP addresses: there is currently no IETF document which 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 a CGN or other NAT.) However, for both
IPv4 and IPv6 addresses, it's important to note that source addresses IPv4 and IPv6 addresses, it's important to note that source addresses
are propagated with queries and comprise metadata about the host, are propagated with queries and comprise metadata about the host,
user, or application that originated them. user, or application that originated them.
2.3. Cache snooping 2.3. Cache Snooping
The content of recursive resolvers' caches can reveal data about the The content of recursive resolvers' caches can reveal data about the
clients using it (the privacy risks depend on the number of clients). clients using it (the privacy risks depend on the number of clients).
This information can sometimes be examined by sending DNS queries This information can sometimes be examined by sending DNS queries
with RD=0 to inspect cache content, particularly looking at the DNS with RD=0 to inspect cache content, particularly looking at the DNS
TTLs [grangeia.snooping]. Since this also is a reconnaissance TTLs [grangeia.snooping]. Since this also is a reconnaissance
technique for subsequent cache poisoning attacks, some counter technique for subsequent cache poisoning attacks, some counter
measures have already been developed and deployed. measures have already been developed and deployed.
2.4. On the wire 2.4. On the Wire
DNS traffic can be seen by an eavesdropper like any other traffic. DNS traffic can be seen by an eavesdropper like any other traffic.
It is typically not encrypted. (DNSSEC, specified in [RFC4033] It is typically not encrypted. (DNSSEC, specified in [RFC4033],
explicitly excludes confidentiality from its goals.) So, if an explicitly excludes confidentiality from its goals.) So, if an
initiator starts a HTTPS communication with a recipient, while the initiator starts an HTTPS communication with a recipient, while the
HTTP traffic will be encrypted, the DNS exchange prior to it will not HTTP traffic will be encrypted, the DNS exchange prior to it will not
be. When other protocols will become more and more privacy-aware and be. When other protocols will become more and more privacy-aware and
secured against surveillance, the DNS may become "the weakest link" secured against surveillance, the DNS may become "the weakest link"
in privacy. in privacy.
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
skipping to change at page 7, line 36 skipping to change at page 7, line 34
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 computer 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 The recursive resolver can be on the end user's computer. 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 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 be Note that in large enterprise networks, the DNS resolver may not
located at the edge of the local network but rather at the edge of be located at the edge of the local network but rather at the edge
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 IAP (Internet Access network could be thought of as similar to the Internet Access
Provider) network referenced below. Provider (IAP) network referenced below.
The recursive resolver can be in the IAP (Internet Access The recursive resolver can be in the IAP premises. For most
Provider) premises. For most residential users and potentially residential users and potentially other networks, the typical case
other networks the typical case is for the end user's computer to is for the end user's computer to be configured (typically
be configured (typically automatically through DHCP) with the automatically through DHCP) with the addresses of the DNS
addresses of the DNS recursive resolvers at the IAP. The attack recursive resolvers at the IAP. The attack surface for on-the-
surface for on-the-wire attacks is therefore from the end user wire attacks is therefore from the end-user system across the
system across the local network and across the IAP network to the local network and across the IAP network to the IAP's recursive
IAP's recursive resolvers. resolvers.
The recursive resolver can be a public DNS service. Some machines The recursive resolver can be a public DNS service. Some machines
may be configured to use public DNS resolvers such as those may be configured to use public DNS resolvers such as those
operated today by Google Public DNS or OpenDNS. The end user may operated today by Google Public DNS or OpenDNS. The end user may
have configured their machine to use these DNS recursive resolvers have configured their machine to use these DNS recursive resolvers
themselves - or their IAP may have chosen to use the public DNS themselves -- or their IAP may have chosen to use the public DNS
resolvers rather than operating their own resolvers. In this case resolvers rather than operating their own resolvers. In this
the attack surface is the entire public Internet between the end case, the attack surface is the entire public Internet between the
user's connection and the public DNS service. end user's connection and the public DNS service.
2.5. In the servers 2.5. In the Servers
Using the terminology of [RFC6973], the DNS servers (recursive Using the terminology of [RFC6973], the DNS servers (recursive
resolvers and authoritative servers) are enablers: they facilitate resolvers and authoritative servers) are enablers: they facilitate
communication between an initiator and a recipient without being communication between an initiator and a recipient without being
directly in the communications path. As a result, they are often directly in the communications path. As a result, they are often
forgotten in risk analysis. But, to quote again [RFC6973], "Although forgotten in risk analysis. But, to quote again [RFC6973], "Although
[...] enablers may not generally be considered as attackers, they may [...] enablers may not generally be considered as attackers, they may
all pose privacy threats (depending on the context) because they are all pose privacy threats (depending on the context) because they are
able to observe, collect, process, and transfer privacy-relevant able to observe, collect, process, and transfer privacy-relevant
data." In [RFC6973] parlance, enablers become observers when they data." In [RFC6973] parlance, enablers become observers when they
start collecting data. start collecting data.
Many programs exist to collect and analyze DNS data at the servers. Many programs exist to collect and analyze DNS data at the servers --
From the "query log" of some programs like BIND, to tcpdump and more from the "query log" of some programs like BIND to tcpdump and more
sophisticated programs like PacketQ [packetq] and DNSmezzo sophisticated programs like PacketQ [packetq] [packetq-list] and
[dnsmezzo]. The organization managing the DNS server can use these DNSmezzo [dnsmezzo]. The organization managing the DNS server can
data itself or it can be part of a surveillance program like PRISM use this data itself, or it can be part of a surveillance program
[prism] and pass data to an outside observer. like PRISM [prism] and pass data to an outside observer.
Sometimes, these data are kept for a long time and/or distributed to Sometimes, this data is kept for a long time and/or distributed to
third parties, for research purposes [ditl] [day-at-root], for third parties for research purposes [ditl] [day-at-root], security
security analysis, or for surveillance tasks. These uses are analysis, or surveillance tasks. These uses are sometimes under some
sometimes under some sort of contract, with various limitations, for sort of contract, with various limitations, for instance, on
instance on redistribution, giving the sensitive nature of the data. redistribution, given the sensitive nature of the data. Also, there
Also, there are observation points in the network which gather DNS are observation points in the network that gather DNS data and then
data and then make it accessible to third-parties for research or make it accessible to third parties for research or security purposes
security purposes ("passive DNS [passive-dns]"). ("passive DNS" [passive-dns]).
2.5.1. In the recursive resolvers 2.5.1. In the Recursive Resolvers
Recursive Resolvers see all the traffic since there is typically no Recursive Resolvers see all the traffic since there is typically no
caching before them. To summarize: your recursive resolver knows a caching before them. To summarize: your recursive resolver knows a
lot about you. The resolver of a large IAP, or a large public lot about you. The resolver of a large IAP, or a large public
resolver can collect data from many users. You may get an idea of resolver, can collect data from many users. You may get an idea of
the data collected by reading the privacy policy of a big public the data collected by reading the privacy policy of a big public
resolver [1]. resolver, e.g., <https://developers.google.com/speed/public-dns/
privacy>.
2.5.2. In the authoritative name servers 2.5.2. In the Authoritative Name Servers
Unlike what happens for recursive resolvers, observation capabilities Unlike what happens for recursive resolvers, observation capabilities
of authoritative name servers are limited by caching; they see only of authoritative name servers are limited by caching; they see only
the requests for which the answer was not in the cache. For the requests for which the answer was not in the cache. For
aggregated statistics ("What is the percentage of LOC queries?"), aggregated statistics ("What is the percentage of LOC queries?"),
this is sufficient; but it prevents an observer from seeing this is sufficient, but it prevents an observer from seeing
everything. Still, the authoritative name servers see a part of the everything. Still, the authoritative name servers see a part of the
traffic, and this subset may be sufficient to violate some privacy traffic, and this subset may be sufficient to violate some privacy
expectations. expectations.
Also, the end user has typically some legal/contractual link with the Also, the end user typically has some legal/contractual link with the
recursive resolver (he has chosen the IAP, or he has chosen to use a recursive resolver (he has chosen the IAP, or he has chosen to use a
given public resolver), while having no control and perhaps no given public resolver), while having no control and perhaps no
awareness of the role of the authoritative name servers and their awareness of the role of the authoritative name servers and their
observation abilities. observation abilities.
As noted before, using a local resolver or a resolver close to the As noted before, using a local resolver or a resolver close to the
machine decreases the attack surface for an on-the-wire eavesdropper. machine decreases the attack surface for an on-the-wire eavesdropper.
But it may decrease privacy against an observer located on an But it may decrease privacy against an observer located on an
authoritative name server. This authoritative name server will see authoritative name server. This authoritative name server will see
the IP address of the end client, instead of the address of a big the IP address of the end client instead of the address of a big
recursive resolver shared by many users. recursive resolver shared by many users.
This "protection", when using a large resolver with many clients, is This "protection", when using a large resolver with many clients, is
no longer present if [I-D.ietf-dnsop-edns-client-subnet] is used no longer present if [CLIENT-SUBNET] is used because, in this case,
because, in this case, the authoritative name server sees the the authoritative name server sees the original IP address (or
original IP address (or prefix, depending on the setup). prefix, depending on the setup).
As of today, all the instances of one root name server, L-root, As of today, all the instances of one root name server, L-root,
receive together around 50,000 queries per second. While most of it receive together around 50,000 queries per second. While most of it
is "junk" (errors on the TLD name), it gives an idea of the amount of is "junk" (errors on the Top-Level Domain (TLD) name), it gives an
big data which pours into name servers. (And even "junk" can leak idea of the amount of big data that pours into name servers. (And
information, for instance if there is a typing error in the TLD, the even "junk" can leak information; for instance, if there is a typing
user will send data to a TLD which is not the usual one.) error in the TLD, the user will send data to a TLD that is not the
usual one.)
Many domains, including TLDs, are partially hosted by third-party Many domains, including TLDs, are partially hosted by third-party
servers, sometimes in a different country. The contracts between the servers, sometimes in a different country. The contracts between the
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 [aeris-dns] that there is a strong concentration of Also, it seems (see the survey described in [aeris-dns]) that there
authoritative name servers among "popular" domains (such as the Alexa is a strong concentration of authoritative name servers among
Top N list). For instance, among the Alexa Top 100k, one DNS "popular" domains (such as the Alexa Top N list). For instance,
provider hosts today 10 % of the domains. The ten most important DNS among the Alexa Top 100K, one DNS provider hosts today 10% of the
providers host together one third of the domains. With the control domains. The ten most important DNS providers host together one
(or the ability to sniff the traffic) of a few name servers, you can third of the domains. With the control (or the ability to sniff the
gather a lot of information. traffic) of a few name servers, you can gather a lot of information.
2.5.3. Rogue servers 2.5.3. Rogue Servers
The previous paragraphs discussed DNS privacy, assuming that all the The previous paragraphs discussed DNS privacy, assuming that all the
traffic was directed to the intended servers, and that the potential traffic was directed to the intended servers 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, redirecting the traffic, not for changing it but just to attackers redirecting the traffic, not to change it but just to
observe it. observe it.
For instance, a rogue DHCP server, or a trusted DHCP server that has For instance, a rogue DHCP server, or a trusted DHCP server that has
had its configuration altered by malicious parties, can direct you to had its configuration altered by malicious parties, can direct you to
a rogue recursive resolver. Most of the time, it seems to be done to a rogue recursive resolver. Most of the time, it seems to be done to
divert traffic, by providing lies for some domain names. But it divert traffic by providing lies for some domain names. But it could
could be used just to capture the traffic and gather information be used just to capture the traffic and gather information about you.
about you. Other attacks, besides using DHCP, are possible. The Other attacks, besides using DHCP, are possible. The traffic from a
traffic from a DNS client to a DNS server can be intercepted along DNS client to a DNS server can be intercepted along its way from
its way from originator to intended source; for instance by originator to intended source, for instance, by transparent DNS
transparent DNS proxies in the network that will divert the traffic proxies in the network that will divert the traffic intended for a
intended for a legitimate DNS server. This rogue server can legitimate DNS server. This rogue server can masquerade as the
masquerade as the intended server and respond with data to the intended server and respond with data to the client. (Rogue servers
client. (Rogue servers that inject malicious data are possible, but that inject malicious data are possible, but it is a separate problem
is a separate problem not relevant to privacy.) A rogue server may not relevant to privacy.) A rogue server may respond correctly for a
respond correctly for a long period of time, thereby foregoing long period of time, thereby foregoing detection. This may be done
detection. This may be done for what could be claimed to be good for what could be claimed to be good reasons, such as optimization or
reasons, such as optimization or caching, but it leads to a reduction caching, but it leads to a reduction of privacy compared to if there
of privacy compared to if there were no attacker present. Also, was no attacker present. Also, malware like DNSchanger [dnschanger]
malware like DNSchanger [dnschanger] can change the recursive can change the recursive resolver in the machine's configuration, or
resolver in the machine's configuration, or the routing itself can be the routing itself can be subverted (for instance,
subverted (for instance [turkey-googledns]). [ripe-atlas-turkey]).
A practical consequence of this section is that solutions for DNS A practical consequence of this section is that solutions for DNS
privacy may have to address authentication of the server, not just privacy may have to address authentication of the server, not just
passive sniffing. passive sniffing.
2.6. Re-identification and other inferences 2.6. Re-identification and Other Inferences
An observer has access not only to the data he/she directly collects An observer has access not only to the data he/she directly collects
but also to the results of various inferences about these data. but also to the results of various inferences about this data.
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 behaviour, 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, for an intelligence agency to For instance, one could imagine that an intelligence agency
identify people going to a site by putting in a very long DNS name identifies people going to a site by putting in a very long DNS name
and looking for queries of a specific length. Such traffic analysis and looking for queries of a specific length. Such traffic analysis
could weaken some privacy solutions. could weaken some privacy solutions.
The IAB privacy and security programme also have a work in progress The IAB privacy and security program also have a work in progress
[I-D.iab-privsec-confidentiality-threat] that considers such [RFC7624] that considers such inference-based attacks in a more
inference based attacks in a more general framework. general framework.
3. Actual "attacks" 2.7. More Information
Useful background information can also be found in [tor-leak] (about
the risk of privacy leak through DNS) and in a few academic papers:
[yanbin-tsudik], [castillo-garcia], [fangming-hori-sakurai], and
[federrath-fuchs-herrmann-piosecny].
3. Actual "Attacks"
A very quick examination of DNS traffic may lead to the false A very quick examination of DNS traffic may lead to the false
conclusion that extracting the needle from the haystack is difficult. conclusion that extracting the needle from the haystack is difficult.
"Interesting" primary DNS requests are mixed with useless (for the "Interesting" primary DNS requests are mixed with useless (for the
eavesdropper) secondary and tertiary requests (see the terminology in eavesdropper) secondary and tertiary requests (see the terminology in
Section 1). But, in this time of "big data" processing, powerful Section 1). But, in this time of "big data" processing, powerful
techniques now exist to get from the raw data to what the techniques now exist to get from the raw data to what the
eavesdropper is actually interested in. eavesdropper is actually interested in.
Many research papers about malware detection use DNS traffic to Many research papers about malware detection use DNS traffic to
detect "abnormal" behaviour that can be traced back to the activity detect "abnormal" behavior that can be traced back to the activity of
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 good, but technically it is a privacy attack and it demonstrates the
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 good, sometimes an entire zone. They are used for many reasons -- some
some bad. Well-known passive DNS systems keep only the DNS good, some bad. Well-known passive DNS systems keep only the DNS
responses, and not the source IP address of the client, precisely for responses, and not the source IP address of the client, precisely for
privacy reasons. Other passive DNS systems may not be so careful. privacy reasons. Other passive DNS systems may not be so careful.
And there is still the potential problems with revealing QNAMEs. And there is still the potential problems with revealing QNAMEs.
The revelations (from the Edward Snowden documents, leaked from the The revelations (from the Edward Snowden documents, which were leaked
NSA) of the MORECOWBELL surveillance program [morecowbell], which from the National Security Agency (NSA)) of the MORECOWBELL
uses the DNS, both passively and actively, to surreptitiously gather surveillance program [morecowbell], which uses the DNS, both
information about the users, is another good example showing that the passively and actively, to surreptitiously gather information about
lack of privacy protections in the DNS is actively exploited. the users, is another good example showing that the lack of privacy
protections in the DNS is actively exploited.
4. Legalities 4. 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] (European Union) in the context of DNS [data-protection-directive] (European Union) in the context of DNS
traffic data is not an easy task and we do not know a court precedent traffic data is not an easy task, and we do not know a court
here. An interesting analysis is [sidn-entrada]. precedent here. See an interesting analysis in [sidn-entrada].
5. Security considerations 5. 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 to define the choices and compromises they imply), much less define solutions.
solutions. Possible solutions to the issues described here are Possible solutions to the issues described here are discussed in
discussed in other documents (currently too many to all be other documents (currently too many to all be mentioned); see, for
mentioned), see for instance [I-D.ietf-dnsop-qname-minimisation] for instance, [QNAME-MINIMIZATION] for the minimization of data or
the minimisation of data, or [I-D.ietf-dprive-start-tls-for-dns] [TLS-FOR-DNS] about encryption.
about encryption.
6. Acknowledgments
Thanks to Nathalie Boulvard and to the CENTR members for the original
work which leaded to this document. Thanks to Ondrej Sury for the
interesting discussions. Thanks to Mohsen Souissi and John Heidemann
for proofreading, to Paul Hoffman, Matthijs Mekking, Marcos Sanz, Tim
Wicinski, Francis Dupont, Allison Mankin and Warren Kumari for
proofreading, technical remarks, and many readability improvements.
Thanks to Dan York, Suzanne Woolf, Tony Finch, Stephen Farrell, Peter
Koch, Simon Josefsson and Frank Denis for good written contributions.
And thanks to the IESG members for the last remarks.
7. IANA considerations
This document has no actions for IANA.
8. References 6. References
8.1. Normative References 6.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<http://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, November 1987. specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <http://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, July Considerations for Internet Protocols", RFC 6973,
2013. DOI 10.17487/RFC6973, July 2013,
<http://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, May 2014. Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
2014, <http://www.rfc-editor.org/info/rfc7258>.
8.2. Informative References
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS 6.2. Informative References
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, March 2008.
[RFC5936] Lewis, E. and A. Hoenes, "DNS Zone Transfer Protocol [aeris-dns]
(AXFR)", RFC 5936, June 2010. Vinot, N., "Vie privee: et le DNS alors?", (In French),
2015,
<https://blog.imirhil.fr/vie-privee-et-le-dns-alors.html>.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P. [castillo-garcia]
Roberts, "Issues with IP Address Sharing", RFC 6269, June Castillo-Perez, S. and J. Garcia-Alfaro, "Anonymous
2011. Resolution of DNS Queries", 2008,
<http://deic.uab.es/~joaquin/papers/is08.pdf>.
[I-D.ietf-dnsop-edns-client-subnet] [CLIENT-SUBNET]
Contavalli, C., Gaast, W., Lawrence, D., and W. Kumari, Contavalli, C., Gaast, W., Lawrence, D., and W. Kumari,
"Client Subnet in DNS Querys", draft-ietf-dnsop-edns- "Client Subnet in DNS Queries", Work in Progress,
client-subnet-01 (work in progress), May 2015. draft-ietf-dnsop-edns-client-subnet-02, July 2015.
[I-D.iab-privsec-confidentiality-threat] [dagon-malware]
Barnes, R., Schneier, B., Jennings, C., Hardie, T., Dagon, D., "Corrupted DNS Resolution Paths: The Rise of a
Trammell, B., Huitema, C., and D. Borkmann, Malicious Resolution Authority", ISC/OARC Workshop, 2007,
"Confidentiality in the Face of Pervasive Surveillance: A <https://www.dns-oarc.net/files/workshop-2007/
Threat Model and Problem Statement", draft-iab-privsec- Dagon-Resolution-corruption.pdf>.
confidentiality-threat-07 (work in progress), May 2015.
[I-D.wouters-dane-openpgp] [DANE-OPENPGPKEY]
Wouters, P., "Using DANE to Associate OpenPGP public keys Wouters, P., "Using DANE to Associate OpenPGP public keys
with email addresses", draft-wouters-dane-openpgp-02 (work with email addresses", Work in Progress,
in progress), February 2014. draft-ietf-dane-openpgpkey-03, April 2015.
[I-D.ietf-dprive-start-tls-for-dns] [darkreading-dns]
Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., Lemos, R., "Got Malware? Three Signs Revealed In DNS
and P. Hoffman, "TLS for DNS: Initiation and Performance Traffic", InformationWeek Dark Reading, May 2013,
Considerations", draft-ietf-dprive-start-tls-for-dns-00 <http://www.darkreading.com/analytics/security-monitoring/
(work in progress), May 2015. got-malware-three-signs-revealed-in-dns-traffic/d/
d-id/1139680>.
[I-D.ietf-dnsop-qname-minimisation] [data-protection-directive]
Bortzmeyer, S., "DNS query name minimisation to improve European Parliament, "Directive 95/46/EC of the European
privacy", draft-ietf-dnsop-qname-minimisation-03 (work in Pariament and of the council on the protection of
progress), June 2015. individuals with regard to the processing of personal data
and on the free movement of such data", Official Journal L
281, pp. 0031 - 0050, November 1995,
<http://eur-lex.europa.eu/LexUriServ/
LexUriServ.do?uri=CELEX:31995L0046:EN:HTML>.
[I-D.ietf-dnsop-dns-terminology] [day-at-root]
Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Castro, S., Wessels, D., Fomenkov, M., and K. Claffy, "A
Terminology", draft-ietf-dnsop-dns-terminology-02 (work in Day at the Root of the Internet", ACM SIGCOMM Computer
progress), May 2015. Communication Review, Vol. 38, Number 5, DOI
10.1145/1452335.1452341, October 2008,
<http://www.sigcomm.org/sites/default/files/ccr/
papers/2008/October/1452335-1452341.pdf>.
[denis-edns-client-subnet] [denis-edns-client-subnet]
Denis, F., "Security and privacy issues of edns-client- Denis, F., "Security and privacy issues of edns-client-
subnet", August 2013, <https://00f.net/2013/08/07/edns- subnet", August 2013, <https://00f.net/2013/08/07/
client-subnet/>. edns-client-subnet/>.
[dagon-malware] [ditl] CAIDA, "A Day in the Life of the Internet (DITL)", 2002,
Dagon, D., "Corrupted DNS Resolution Paths: The Rise of a <http://www.caida.org/projects/ditl/>.
Malicious Resolution Authority", 2007, <https://www.dns-
oarc.net/files/workshop-2007/Dagon-Resolution-
corruption.pdf>.
[dns-footprint] [dns-footprint]
Stoner, E., "DNS footprint of malware", October 2010, Stoner, E., "DNS Footprint of Malware", OARC Workshop,
<https://www.dns-oarc.net/files/workshop-201010/OARC-ers- October 2010, <https://www.dns-oarc.net/files/
20101012.pdf>. workshop-201010/OARC-ers-20101012.pdf>.
[morecowbell]
Grothoff, C., Wachs, M., Ermert, M., and J. Appelbaum,
"NSA's MORECOWBELL: Knell for DNS", January 2015,
<https://gnunet.org/morecowbell>.
[darkreading-dns] [DNS-TERMS]
Lemos, R., "Got Malware? Three Signs Revealed In DNS Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Traffic", May 2013, Terminology", Work in Progress,
<http://www.darkreading.com/monitoring/ draft-ietf-dnsop-dns-terminology-03, June 2015.
got-malware-three-signs-revealed-in-dns/240154181>.
[dnschanger] [dnschanger]
Wikipedia, , "DNSchanger", November 2011, Wikipedia, "DNSChanger", October 2013,
<http://en.wikipedia.org/wiki/DNSChanger>. <https://en.wikipedia.org/w/
index.php?title=DNSChanger&oldid=578749672>.
[packetq] Dot SE, , "PacketQ, a simple tool to make SQL-queries
against PCAP-files", 2011,
<https://github.com/dotse/packetq/wiki>.
[dnsmezzo] [dnsmezzo] Bortzmeyer, S., "DNSmezzo", 2009,
Bortzmeyer, S., "DNSmezzo", 2009,
<http://www.dnsmezzo.net/>. <http://www.dnsmezzo.net/>.
[prism] NSA, , "PRISM", 2007, <http://en.wikipedia.org/wiki/ [fangming-hori-sakurai]
PRISM_%28surveillance_program%29>. Fangming, Z., Hori, Y., and K. Sakurai, "Analysis of
Privacy Disclosure in DNS Query", 2007 International
Conference on Multimedia and Ubiquitous Engineering (MUE
2007), Seoul, Korea, ISBN: 0-7695-2777-9, pp. 952-957,
DOI 10.1109/MUE.2007.84, April 2007,
<http://dl.acm.org/citation.cfm?id=1262690.1262986>.
[federrath-fuchs-herrmann-piosecny]
Federrath, H., Fuchs, K., Herrmann, D., and C. Piosecny,
"Privacy-Preserving DNS: Analysis of Broadcast, Range
Queries and Mix-based Protection Methods", Computer
Security ESORICS 2011, Springer, page(s) 665-683, ISBN
978-3-642-23821-5, 2011,
<https://svs.informatik.uni-hamburg.de/publications/2011/
2011-09-14_FFHP_PrivacyPreservingDNS_ESORICS2011.pdf>.
[grangeia.snooping] [grangeia.snooping]
Grangeia, L., "DNS Cache Snooping or Snooping the Cache Grangeia, L., "DNS Cache Snooping or Snooping the Cache
for Fun and Profit", 2004, for Fun and Profit", February 2004,
<http://www.msit2005.mut.ac.th/msit_media/1_2551/nete4630/ <http://www.msit2005.mut.ac.th/msit_media/1_2551/nete4630/
materials/20080718130017Hc.pdf>. materials/20080718130017Hc.pdf>.
[ditl] CAIDA, , "A Day in the Life of the Internet (DITL)", 2002, [herrmann-reidentification]
<http://www.caida.org/projects/ditl/>. Herrmann, D., Gerber, C., Banse, C., and H. Federrath,
"Analyzing Characteristic Host Access Patterns for
Re-Identification of Web User Sessions",
DOI 10.1007/978-3-642-27937-9_10, 2012,
<http://epub.uni-regensburg.de/21103/1/
Paper_PUL_nordsec_published.pdf>.
[day-at-root] [morecowbell]
Castro, S., Wessels, D., Fomenkov, M., and K. Claffy, "A Grothoff, C., Wachs, M., Ermert, M., and J. Appelbaum,
Day at the Root of the Internet", 2008, "NSA's MORECOWBELL: Knell for DNS", GNUnet e.V., January
<http://www.sigcomm.org/sites/default/files/ccr/ 2015, <https://gnunet.org/morecowbell>.
papers/2008/October/1452335-1452341.pdf>.
[turkey-googledns] [packetq] Dot SE, "PacketQ, a simple tool to make SQL-queries
Bortzmeyer, S., "Hijacking of public DNS servers in against PCAP-files", 2011,
Turkey, through routing", 2014, <https://github.com/dotse/packetq/wiki>.
<http://www.bortzmeyer.org/
dns-routing-hijack-turkey.html>.
[data-protection-directive] [packetq-list]
Europe, , "European directive 95/46/EC on the protection PacketQ, "PacketQ Mailing List",
of individuals with regard to the processing of personal <http://lists.iis.se/mailman/listinfo/packetq>.
data and on the free movement of such data", November
1995, <http://eur-lex.europa.eu/LexUriServ/
LexUriServ.do?uri=CELEX:31995L0046:EN:HTML>.
[passive-dns] [passive-dns]
Weimer, F., "Passive DNS Replication", April 2005, Weimer, F., "Passive DNS Replication", April 2005,
<http://www.enyo.de/fw/software/dnslogger/#2>. <http://www.enyo.de/fw/software/dnslogger/#2>.
[tor-leak] [prism] Wikipedia, "PRISM (surveillance program)", July 2015,
Tor, , "DNS leaks in Tor", 2013, <https://en.wikipedia.org/w/index.php?title=PRISM_
<https://trac.torproject.org/projects/tor/wiki/doc/TorFAQ# (surveillance_program)&oldid=673789455>.
IkeepseeingthesewarningsaboutSOCKSandDNSandinformationleak
s.ShouldIworry>.
[yanbin-tsudik] [QNAME-MINIMIZATION]
Yanbin, L. and G. Tsudik, "Towards Plugging Privacy Leaks Bortzmeyer, S., "DNS query name minimisation to improve
in the Domain Name System", 2009, privacy", Work in Progress,
<http://arxiv.org/abs/0910.2472>. draft-ietf-dnsop-qname-minimisation-04, June 2015.
[castillo-garcia] [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Castillo-Perez, S. and J. Garcia-Alfaro, "Anonymous Rose, "DNS Security Introduction and Requirements",
Resolution of DNS Queries", 2008, RFC 4033, DOI 10.17487/RFC4033, March 2005,
<http://deic.uab.es/~joaquin/papers/is08.pdf>. <http://www.rfc-editor.org/info/rfc4033>.
[fangming-hori-sakurai] [RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Fangming, , Hori, Y., and K. Sakurai, "Analysis of Privacy Security (DNSSEC) Hashed Authenticated Denial of
Disclosure in DNS Query", 2007, Existence", RFC 5155, DOI 10.17487/RFC5155, March 2008,
<http://dl.acm.org/citation.cfm?id=1262690.1262986>. <http://www.rfc-editor.org/info/rfc5155>.
[thomas-ditl-tcp] [RFC5936] Lewis, E. and A. Hoenes, Ed., "DNS Zone Transfer Protocol
Thomas, M. and D. Wessels, "An Analysis of TCP Traffic in (AXFR)", RFC 5936, DOI 10.17487/RFC5936, June 2010,
Root Server DITL Data"", 2014, <https://indico.dns- <http://www.rfc-editor.org/info/rfc5936>.
oarc.net/event/20/session/2/contribution/15/material/
slides/1.pdf>.
[federrath-fuchs-herrmann-piosecny] [RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
Federrath, H., Fuchs, K., Herrmann, D., and C. Piosecny, P. Roberts, "Issues with IP Address Sharing", RFC 6269,
"Privacy-Preserving DNS: Analysis of Broadcast, Range DOI 10.17487/RFC6269, June 2011,
Queries and Mix-Based Protection Methods", 2011, <http://www.rfc-editor.org/info/rfc6269>.
<https://svs.informatik.uni-hamburg.de/publications/2011/2
011-09-14_FFHP_PrivacyPreservingDNS_ESORICS2011.pdf>.
[aeris-dns] [RFC7624] Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Vinot, N., "[In French] Vie privee : et le DNS alors ?", Trammell, B., Huitema, C., and D. Borkmann,
2015, <https://blog.imirhil.fr/vie-privee-et-le-dns- "Confidentiality in the Face of Pervasive Surveillance: A
alors.html>. Threat Model and Problem Statement", RFC 7624,
DOI 10.17487/RFC7624, August 2015,
<http://www.rfc-editor.org/info/rfc7624>.
[herrmann-reidentification] [ripe-atlas-turkey]
Herrmann, D., Gerber, C., Banse, C., and H. Federrath, Aben, E., "A RIPE Atlas View of Internet Meddling in
"Analyzing characteristic host access patterns for re- Turkey", March 2014,
identification of web user sessions", 2012, <https://labs.ripe.net/Members/emileaben/
<http://epub.uni-regensburg.de/21103/1/ a-ripe-atlas-view-of-internet-meddling-in-turkey>.
Paper_PUL_nordsec_published.pdf>.
[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", 2014, applications", November 2014,
<https://www.sidnlabs.nl/uploads/tx_sidnpublications/ <https://www.sidnlabs.nl/uploads/tx_sidnpublications/
SIDN_Labs_Privacyraamwerk_Position_Paper_V1.4_ENG.pdf>. SIDN_Labs_Privacyraamwerk_Position_Paper_V1.4_ENG.pdf>.
8.3. URIs [thomas-ditl-tcp]
Thomas, M. and D. Wessels, "An Analysis of TCP Traffic in
Root Server DITL Data", DNS-OARC 2014 Fall Workshop,
October 2014, <https://indico.dns-oarc.net/event/20/
session/2/contribution/15/material/slides/1.pdf>.
[1] https://developers.google.com/speed/public-dns/privacy [TLS-FOR-DNS]
Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "TLS for DNS: Initiation and Performance
Considerations", Work in Progress, draft-ietf-dprive-
start-tls-for-dns-01, July 2015.
[tor-leak] Tor, "DNS leaks in Tor", 2013,
<https://www.torproject.org/docs/
faq.html.en#WarningsAboutSOCKSandDNSInformationLeaks>.
[yanbin-tsudik]
Yanbin, L. and G. Tsudik, "Towards Plugging Privacy Leaks
in the Domain Name System", October 2009,
<http://arxiv.org/abs/0910.2472>.
Acknowledgments
Thanks to Nathalie Boulvard and to the CENTR members for the original
work that led to this document. Thanks to Ondrej Sury for the
interesting discussions. Thanks to Mohsen Souissi and John Heidemann
for proofreading and to Paul Hoffman, Matthijs Mekking, Marcos Sanz,
Tim Wicinski, Francis Dupont, Allison Mankin, and Warren Kumari for
proofreading, providing technical remarks, and making many
readability improvements. Thanks to Dan York, Suzanne Woolf, Tony
Finch, Stephen Farrell, Peter Koch, Simon Josefsson, and Frank Denis
for good written contributions. And thanks to the IESG members for
the last remarks.
Author's Address Author's Address
Stephane Bortzmeyer Stephane Bortzmeyer
AFNIC AFNIC
1, rue Stephenson 1, rue Stephenson
Montigny-le-Bretonneux 78180 Montigny-le-Bretonneux 78180
France France
Phone: +33 1 39 30 83 46 Phone: +33 1 39 30 83 46
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