draft-ietf-dprive-problem-statement-00.txt   draft-ietf-dprive-problem-statement-01.txt 
Network Working Group S. Bortzmeyer DNS PRIVate Exchange (dprive) Working Group S. Bortzmeyer
Internet-Draft AFNIC Internet-Draft AFNIC
Intended status: Informational October 26, 2014 Intended status: Informational January 7, 2015
Expires: April 29, 2015 Expires: July 11, 2015
DNS privacy considerations DNS privacy considerations
draft-ietf-dprive-problem-statement-00 draft-ietf-dprive-problem-statement-01
Abstract Abstract
This document describes the privacy issues associated with the use of This document describes the privacy issues associated with the use of
the DNS by Internet users. It is intended to be mostly an analysis the DNS by Internet users. It is intended to be mostly an analysis
of the present situation, in the spirit of section 8 of [RFC6973] and of the present situation, in the spirit of section 8 of [RFC6973] and
it does not prescribe solutions. it does not prescribe solutions.
Discussions of the document should take place on the DPRIVE working Discussions of the document should take place on the DPRIVE working
group mailing list [dprive]. group mailing list [dprive].
skipping to change at page 1, line 36 skipping to change at page 1, line 36
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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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 April 29, 2015. This Internet-Draft will expire on July 11, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 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 . . . . . . . . . . 4 2.1. The alleged public nature of DNS data . . . . . . . . . . 4
2.2. Data in the DNS request . . . . . . . . . . . . . . . . . 4 2.2. Data in the DNS request . . . . . . . . . . . . . . . . . 5
2.3. Cache snooping . . . . . . . . . . . . . . . . . . . . . 6 2.3. Cache snooping . . . . . . . . . . . . . . . . . . . . . 6
2.4. On the wire . . . . . . . . . . . . . . . . . . . . . . . 6 2.4. On the wire . . . . . . . . . . . . . . . . . . . . . . . 6
2.5. In the servers . . . . . . . . . . . . . . . . . . . . . 7 2.5. In the servers . . . . . . . . . . . . . . . . . . . . . 7
2.5.1. In the resolvers . . . . . . . . . . . . . . . . . . 7 2.5.1. In the recursive resolvers . . . . . . . . . . . . . 8
2.5.2. In the authoritative name servers . . . . . . . . . . 8 2.5.2. In the authoritative name servers . . . . . . . . . . 8
2.5.3. Rogue servers . . . . . . . . . . . . . . . . . . . . 9 2.5.3. Rogue servers . . . . . . . . . . . . . . . . . . . . 9
3. Actual "attacks" . . . . . . . . . . . . . . . . . . . . . . 9 3. Actual "attacks" . . . . . . . . . . . . . . . . . . . . . . 10
4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 9 4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Security considerations . . . . . . . . . . . . . . . . . . . 9 5. Security considerations . . . . . . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 10 7.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 10 7.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13 7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
The Domain Name System is specified in [RFC1034] and [RFC1035]. It The Domain Name System is specified in [RFC1034] and [RFC1035]. It
is one of the most important infrastructure components of the is one of the most important infrastructure components of the
Internet and one of the most often ignored or misunderstood. Almost Internet and one of the most often ignored or misunderstood. Almost
every activity on the Internet starts with a DNS query (and often every activity on the Internet starts with a DNS query (and often
several). Its use has many privacy implications and we try to give several). Its use has many privacy implications and we try to give
here a comprehensive and accurate list. here a comprehensive and accurate list.
Let us begin with a simplified reminder of how the DNS works. A Let us begin with a simplified reminder of how the DNS works.
client, the stub resolver, issues a DNS query to a server, the (REMOVE BEFORE PUBLICATION: We hope that the document
resolver (also called caching resolver or full resolver or recursive [I-D.hoffman-dns-terminology] will be published as a RFC so most of
name server). Let's use the query "What are the AAAA records for this section could be replaced by a reference to it.) A client, the
www.example.com?" as an example. AAAA is the qtype (Query type), and stub resolver, issues a DNS query to a server, the recursive resolver
www.example.com is the qname (Query Name). The resolver will first (also called caching resolver or full resolver or simply resolver
query the root nameservers. In most cases, the root nameservers will recursive name server). Let's use the query "What are the AAAA
send a referral. In this example, the referral will be to .com records for www.example.com?" as an example. AAAA is the qtype
nameservers. The .com nameserver, in turn, will refer to the (Query type), and www.example.com is the qname (Query Name). The
example.com nameservers. The example.com nameserver will then return recursive resolver will first query the root nameservers. In most
the answer. The root name servers, the name servers of .com and cases, the root nameservers will send a referral. In this example,
those of example.com are called authoritative name servers. It is the referral will be to .com nameservers. The resolver repeats the
important, when analyzing the privacy issues, to remember that the query to one of the .com nameservers. The .com nameserver, in turn,
question asked to all these name servers is always the original will refer to the example.com nameservers. The example.com
question, not a derived question. Unlike what many "DNS for dummies" nameserver will then return the answer. The root name servers, the
articles say, the question sent to the root name servers is "What are name servers of .com and those of example.com are called
the AAAA records for www.example.com?", not "What are the name authoritative name servers. It is important, when analyzing the
servers of .com?". By repeating the full question, instead of just privacy issues, to remember that the question asked to all these name
the relevant part of the question to the next in line, the DNS servers is always the original question, not a derived question.
provides more information than necessary to the nameserver. Unlike what many "DNS for dummies" articles say, the 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
repeating the full question, instead of just the relevant part of the
question to the next in line, the DNS provides more information than
necessary to the nameserver.
Because the DNS uses caching heavily, not all questions are sent to Because the DNS uses caching heavily, not all questions are sent to
the authoritative name servers. If the stub resolver, a few seconds the authoritative name servers. If the stub resolver, a few seconds
later, asks to the resolver "What are the SRV records of _xmpp- later, asks to the recursive resolver "What are the SRV records of
server._tcp.example.com?", the resolver will remember that it knows _xmpp-server._tcp.example.com?", the recursive resolver will remember
the name servers of example.com and will just query them, bypassing that it knows the name servers of example.com and will just query
the root and .com. Because there is typically no caching in the stub them, bypassing the root and .com. Because there is typically no
resolver, the resolver, unlike the authoritative servers, sees caching in the stub resolver, the recursive resolver, unlike the
everything. authoritative servers, sees everything.
Today, almost all DNS queries are sent over UDP. This has practical It should be noted that DNS recursive resolvers sometimes forward
consequences, when considering the encryption of this traffic: some requests to bigger machines, with a larger and more shared cache, the
encryption solutions are only designed for TCP, not UDP. forwarders (and the query hierarchy can be even deeper, with more
than two levels of recursive resolvers). From the point of view of
privacy, forwarders are like resolvers, except that the caching in
the recursive resolvers before them decreases the amount of data they
can see.
It should be noted that DNS resolvers sometimes forward requests to All this DNS traffic is today sent in clear (unencryted), except a
bigger machines, with a larger and more shared cache, the forwarders. few cases when the IP traffic is protected, for instance in an IPsec
From the point of view of privacy, forwarders are like resolvers, VPN.
except that the caching in the resolver before them decreases the
amount of data they can see. Today, almost all DNS queries are sent over UDP. This has practical
consequences, when considering a possible privacy technique,
encryption of the traffic: some encryption solutions 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 mix of many sort of DNS requests received by a issues of DNS is the mix of many sort of DNS requests received by a
server. Let's assume the eavesdropper want to know which Web page is server. Let's assume the eavesdropper wants to know which Web page
visited by a user. For a typical Web page displayed by the user, is viewed by an user. For a typical Web page displayed by the user,
there are three sorts of DNS requests: there are three sorts of DNS requests being issued:
Primary request: this is the domain name that the user typed or Primary request: this is the domain name in the URL that the user
selected from a bookmark or choosed by clicking on an hyperklink. typed or selected from a bookmark or choose by clicking on an
Presumably, this is what is of interest for the eavesdropper. hyperlink. Presumably, this is what is of interest for the
eavesdropper.
Secondary requests: these are the requests performed by the user Secondary requests: these are the additional requests performed by
agent (here, the Web browser) without any direct involvement or the user agent (here, the Web browser) without any direct
knowledge of the user. For the Web, they are triggered by involvement or knowledge of the user. For the Web, they are
included content, CSS sheets, JavaScript code, embedded images, triggered by embedded content, CSS sheets, JavaScript code,
etc. In some cases, there can be dozens of domain names in a embedded images, etc. In some cases, there can be dozens of
single page. domain names in different contexts on a single Web page.
Tertiary requests: these are the requests performed by the DNS Tertiary requests: these are the additional requests performed by
system itself. For instance, if the answer to a query is a the DNS system itself. For instance, if the answer to a query is
referral to a set of name servers, and the glue is not returned, a referral to a set of name servers, and the glue is not returned,
the resolver will have to do tertiary requests to turn name the resolver will have to do tertiary requests to turn name
servers' named into IP addresses. servers' names into IP addresses. Similarly, even if glue records
are returned, a careful recursive server will do 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
DNS requests are sent, for instance to prefetch resources that the
user may query later, or when autocompleting the URL in the address
bar (which obviously is a big privacy concern).
For privacy-related terms, we will use here the terminology of For privacy-related terms, we will use here the terminology of
[RFC6973]. [RFC6973].
2. Risks 2. Risks
This draft focuses mostly on the study of privacy risks for the end- This document focuses mostly on the study of privacy risks for the
user (the one performing DNS requests). Privacy risks for the holder end-user (the one performing DNS requests). We consider the risks of
of a zone (the risk that someone gets the data) are discussed in pervasive surveillance ([RFC7258]) and also risks coming from a more
[RFC5936]. Non-privacy risks (such as cache poisoning) are out of focused surveillance. Privacy risks for the holder of a zone (the
scope. risk that someone gets the data) are discussed in [RFC5936]. Non-
privacy risks (such as cache poisoning) are out of 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 data and meta data that deserve a more are multiple facets to the data and metadata involved that deserve a
detailed look. First, access control lists and private name spaces more detailed look. First, access control lists and private
nonwithstanding, the DNS operates under the assumption that public namespaces nonwithstanding, the DNS operates under the assumption
facing authoritative name servers will respond to "usual" DNS queries that public facing authoritative name servers will respond to "usual"
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, more dubious reasons). enforce this difference (and maybe for other, more dubious 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 sequence of
transactions; that data is not/should not be public. A typical transactions; that transaction is not/should not be public. A
example from outside the DNS world is: the Web site of Alcoholics typical example from outside the DNS world is: the Web site of
Anonymous is public; the fact that you visit it should not be. Alcoholics Anonymous is public; the fact that you visit it should not
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 + may be 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 sort out several users sharing an IP the request and can be used to sort out several users sharing an IP
address (CGN for instance). address (behind a CGN for instance).
The qname is the full name sent by the original user. It gives The qname is the full name sent by the user. It gives information
information about what the user does ("What are the MX records of about what the user does ("What are the MX records of example.net?"
example.net?" means he probably wants to send email to someone at means he probably wants to send email to someone at example.net,
example.net, which may be a domain used by only a few persons and which may be a domain used by only a few persons and therefore very
therefore very revealing). Some qnames are more sensitive than revealing about communication relationships). Some qnames are more
others. For instance, querying the A record of google-analytics.com sensitive than others. For instance, querying the A record of
reveals very little (everybody visits Web sites which use Google google-analytics.com reveals very little (everybody visits Web sites
Analytics) but querying the A record of www.verybad.example where which use Google Analytics) but querying the A record of
verybad.example is the domain of an illegal or very offensive www.verybad.example where verybad.example is the domain of an illegal
organization may create more problems for the user. Another example or very offensive organization may create more problems for the user.
is when the qname embeds the software one uses. For instance, Also, sometimes, the qname embeds the software one uses, which could
_ldap._tcp.Default-First-Site-Name._sites.gc._msdcs.example.org. Or be a privacy issue. For instance, _ldap._tcp.Default-First-Site-
some BitTorrent clients that query a SRV record for _bittorrent- Name._sites.gc._msdcs.example.org. There are also some BitTorrent
clients that query a SRV record for _bittorrent-
tracker._tcp.domain.example. 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 but
not who with. If your MUA starts looking up PGP keys in the DNS not with whom. If your MUA starts looking up PGP keys in the DNS
[I-D.wouters-dane-openpgp] then privacy becomes a lot more important. [I-D.wouters-dane-openpgp] then privacy becomes a lot more important.
And email is just an example; there will be other really interesting And email is just an example; there would be other really interesting
uses for a more privacy-friendly DNS. uses for a more privacy-friendly DNS.
For the communication between the stub resolver and the resolver, the For the communication between the stub resolver and the recursive
source IP address is the address of the user's machine. Therefore, resolver, the source IP address is the address of the user's machine.
all the issues and warnings about collection of IP addresses apply Therefore, all the issues and warnings about collection of IP
here. For the communication between the resolver and the addresses apply here. For the communication between the recursive
authoritative name servers, the source IP address has a different resolver and the authoritative name servers, the source IP address
meaning; it does not have the same status as the source address in a has a different meaning; it does not have the same status as the
HTTP connection. It is now the IP address of the resolver which, in source address in a HTTP connection. It is now the IP address of the
a way "hides" the real user. However, it does not always work. recursive resolver which, in a way "hides" the real user. However,
Sometimes [I-D.vandergaast-edns-client-subnet] is used (see its hiding does not always work. Sometimes
privacy analysis in [denis-edns-client-subnet]). Sometimes the end [I-D.vandergaast-edns-client-subnet] is used (see its privacy
user has a personal resolver on her machine. In that case, the IP analysis in [denis-edns-client-subnet]). Sometimes the end user has
a personal recursive resolver on her machine. In both cases, the IP
address is as sensitive as it is for HTTP. address is as sensitive as it is for HTTP.
A note about IP addresses: there is currently no IETF document which A note about IP addresses: there is currently no IETF document which
describes in detail the privacy issues of IP addressing. In the mean describes in detail the privacy issues of IP addressing. In the
time, the discussion here is intended to include both IPv4 and IPv6 meantime, the discussion here is intended to include both IPv4 and
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 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 resolvers can reveal data about the clients using it. The content of recursive resolvers' caches can reveal data about the
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. Since this also is a reconnaissance technique for subsequent TTLs. Since this also is a reconnaissance technique for subsequent
cache poisoning attacks, some counter measures have already been cache poisoning attacks, some counter measures have already been
developed and deployed. 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]
explicitely 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 a 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 the other protocols will become more or more privacy-aware be. When other protocols will become more and more privacy-aware and
and secured against surveillance, the DNS risks to become "the secured against surveillance, the DNS risks to become "the weakest
weakest link" in privacy. link" in privacy.
What also makes the DNS traffic different 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 resolver, or to the authoritative name servers. the wire going to the recursive resolver, or to the authoritative
name servers.
The best place, from an eavesdropper's point of view, is clearly The best place to tap, from an eavesdropper's point of view, is
between the stub resolvers and the resolvers, because he is not clearly between the stub resolvers and the recursive resolvers,
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 resolver can be on the end user's computer. In (currently) a The recursive resolver can be on the end user's computer. In
small number of cases, individuals may choose to operate their own (currently) a small number of cases, individuals may choose to
DNS resolver on their local machine. In this case the attack surface operate their own DNS resolver on their local machine. In this case
for the stub resolver to caching resolver connection is limited to the attack surface for the connection between the stub resolver and
that single machine. the caching resolver is limited to that single machine.
The resolver can be in the IAP (Internet Access Provider) premises.
For most residential users and potentially other networks the typical
case is for the end user's computer to be configured (typically
automatically through DHCP) with the addresses of the DNS resolver at
the IAP. The attack surface for on-the-wire attacks is therefore
from the end user system across the local network and across the IAP
network to the IAP's resolvers.
The resolver may also be at the local network edge. For many/most The recursive resolver may be at the local network edge. For many/
enterprise networks and for some residential users the caching most enterprise networks and for some residential users the caching
resolver may exist on a server at the edge of the local network. In resolver may exist on a server at the edge of the local network. In
this case the attack surface is the local network. Note that in this case the attack surface is the local network. Note that in
large enterprise networks the DNS resolver may not be located at the large enterprise networks the DNS resolver may not be located at the
edge of the local network but rather at the edge of the overall edge of the local network but rather at the edge of the overall
enterprise network. In this case the enterprise network could be enterprise network. In this case the enterprise network could be
thought of as similar to the IAP network referenced above. thought of as similar to the IAP network referenced below.
The resolver can be a public DNS service. Some end users may be The recursive resolver can be in the IAP (Internet Access Provider)
configured to use public DNS resolvers such as those operated by premises. For most residential users and potentially other networks
Google Public DNS or OpenDNS. The end user may have configured their the typical case is for the end user's computer to be configured
machine to use these DNS resolvers themselves - or their IAP may (typically automatically through DHCP) with the addresses of the DNS
choose to use the public DNS resolvers rather than operating their recursive resolvers at the IAP. The attack surface for on-the-wire
own resolvers. In this case the attack surface is the entire public attacks is therefore from the end user system across the local
Internet between the end user's connection and the public DNS network and across the IAP network to the IAP's recursive resolvers.
service.
The recursive resolver can be a public DNS service. Some machines
may be configured to use public DNS resolvers such as those operated
by Google Public DNS or OpenDNS. The end user may have configured
their machine to use these DNS recursive resolvers themselves - or
their IAP may have chosen to use the public DNS resolvers rather than
operating their own resolvers. In this case the attack surface is
the entire public Internet between the 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 (resolvers and Using the terminology of [RFC6973], the DNS servers (recursive
authoritative servers) are enablers: they facilitate communication resolvers and authoritative servers) are enablers: they facilitate
between an initiator and a recipient without being directly in the communication between an initiator and a recipient without being
communications path. As a result, they are often forgotten in risk directly in the communications path. As a result, they are often
analysis. But, to quote again [RFC6973], "Although [...] enablers forgotten in risk analysis. But, to quote again [RFC6973], "Although
may not generally be considered as attackers, they may all pose [...] enablers may not generally be considered as attackers, they may
privacy threats (depending on the context) because they are able to all pose privacy threats (depending on the context) because they are
observe, collect, process, and transfer privacy-relevant data." In able to observe, collect, process, and transfer privacy-relevant
[RFC6973] parlance, enablers become observers when they start data." In [RFC6973] parlance, enablers become observers when they
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] and DNSmezzo
[dnsmezzo]. The organization managing the DNS server can use this [dnsmezzo]. The organization managing the DNS server can use these
data itself or it can be part of a surveillance program like PRISM data itself or it can be part of a surveillance program like PRISM
[prism] and pass data to an outside attacker. [prism] and pass data to an outside observer.
Sometimes, these data are kept for a long time and/or distributed to Sometimes, these data are kept for a long time and/or distributed to
third parties, for research purposes [ditl], for security analysis, third parties, for research purposes [ditl], for security analysis,
or for surveillance tasks. Also, there are observation points in the or for surveillance tasks. Also, there are observation points in the
network which gather DNS data and then make it accessible to third- network which gather DNS data and then make it accessible to third-
parties for research or security purposes ("passive DNS parties for research or security purposes ("passive DNS
[passive-dns]"). [passive-dns]").
2.5.1. In the resolvers 2.5.1. In the recursive resolvers
Resolvers see all the traffic since there is typically no caching
before them. They are, therefore, well situated to observe the Recursive Resolvers see all the traffic since there is typically no
traffic. To summarize: your resolver knows a lot about you. The caching before them. To summarize: your recursive resolver knows a
resolver of a large IAP, or a large public resolver can collect data lot about you. The resolver of a large IAP, or a large public
from many users. You may get an idea of the data collected by resolver can collect data from many users. You may get an idea of
reading the privacy policy of a big public resolver [1]. the data collected by reading the privacy policy of a big public
resolver [1].
2.5.2. In the authoritative name servers 2.5.2. In the authoritative name servers
Unlike resolvers, authoritative name servers are limited by caching; Unlike what happens for recursive resolvers, observation capabilities
they see only a part of the requests. For aggregated statistics of authoritative name servers are limited by caching; they see only
("What is the percentage of LOC queries?"), this is sufficient; but the requests for which the answer was not in the cache. For
it may prevent an observer from seeing everything. Still, the aggregated statistics ("What is the percentage of LOC queries?"),
authoritative name servers see a part of the traffic, and this subset this is sufficient; but it prevents an observer from seeing
may be sufficient to violate some privacy expectations. everything. Still, the authoritative name servers see a part of the
traffic, and this subset may be sufficient to violate some privacy
expectations.
Also, the end user has typically some legal/contractual link with the Also, the end user has typically some legal/contractual link with the
resolver (he has chosen the IAP, or he has chosen to use a given recursive resolver (he has chosen the IAP, or he has chosen to use a
public resolver), while he is often not even aware of the role of the given public resolver), while having no control and perhaps no
authoritative name servers and their observation abilities. awareness of the role of the authoritative name servers and their
observation abilities.
It is an interesting question whether the privacy issues are bigger It is an interesting question whether the privacy issues are bigger
in the root or in a large TLD. The root sees the traffic for all the in the root or in a large TLD. The root sees the traffic for all the
TLDs (and the huge amount of traffic for non-existing TLD), but a TLDs (and the huge amount of traffic for non-existing TLDs), but a
large TLD has less caching before it. large TLDs has less caching before it.
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
resolver shared by many users. A possible solution is to have a recursive resolver shared by many users.
local resolver and to forward the cache misses to a big resolver.
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.vandergaast-edns-client-subnet] is used no longer present if [I-D.vandergaast-edns-client-subnet] is used
because, in this case, the authoritative name server sees the because, in this case, the authoritative name server sees the
original IP address (or prefix, depending on the setup). original IP address (or 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 20,000 queries per second. While most of it receive together around 20,000 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 TLD name), it gives an idea of the amount of
big data which pours into name servers. big data which pours into name servers.
Many domains, including TLD, 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. It or not but, in any case, it will have to follow its local laws. It
may be surprising for an end-user that requests to a given ccTLD may may be surprising for an end-user that requests to a given ccTLD may
go to servers managed by organisations outside of the country. go to servers managed by organisations outside of the country.
Also, it seems (TODO: actual numbers requested) that there is a
strong concentration of authoritative name servers among "popular"
domains (such as the Alexa Top N list). With the control (or the
ability to sniff the traffic) of a few name servers, you can gather a
lot of information.
2.5.3. Rogue servers 2.5.3. Rogue servers
A rogue DHCP server can direct you to a rogue resolver. Most of the A rogue DHCP server, or a trusted DHCP server that has had its
times, it seems to be done to divert traffic, by providing lies for configuration altered by malicious parties, can direct you to a rogue
some domain names. But it could be used just to capture the traffic recursive resolver. Most of the times, it seems to be done to divert
and gather information about you. Same thing for malwares like traffic, by providing lies for some domain names. But it could be
DNSchanger[dnschanger] which changes the resolver in the machine's used just to capture the traffic and gather information about you.
configuration. Same thing for malware like DNSchanger[dnschanger] which changes the
recursive resolver in the machine's configuration, or with
transparent DNS proxies in the network that will divert the traffic
intended for a legitimate DNS server (for instance
[turkey-googledns]).
3. Actual "attacks" 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) second and tertiary requests (see the terminology in eavesdropper) second 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 you're actually techniques now exist to get from the raw data to what you're actually
interested in. 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" behaviour that can be traced back to the activity
of malware on infected machines. Yes, this research was done for the of malware on infected machines. Yes, this research was done for the
good but, technically, it is a privacy attack and it demonstrates the good but, technically, it is a privacy attack and it demonstrates the
power of the observation of DNS traffic. See [dns-footprint], power of the observation of DNS traffic. See [dns-footprint],
[dagon-malware] and [darkreading-dns]. [dagon-malware] and [darkreading-dns].
Passive DNS systems [passive-dns] allow reconstruction of the data of Passive DNS systems [passive-dns] allow reconstruction of the data of
sometimes an entire zone. It is used for many reasons, some good, sometimes an entire zone. It is used for many reasons, some good,
some bad. It is an example of privacy issue even when no source IP some bad. It is an example of a privacy issue even when no source IP
address is kept. address is kept.
4. Legalities 4. Legalities
To our knowledge, there are no specific privacy laws for DNS data. To our knowledge, there are no specific privacy laws for DNS data.
Interpreting general privacy laws like [data-protection-directive] Interpreting general privacy laws like [data-protection-directive]
(European Union) in the context of DNS traffic data is not an easy (European Union) in the context of DNS traffic data is not an easy
task and it seems there is no court precedent here. task and it seems there is no court precedent here.
5. Security considerations 5. Security considerations
This document is entirely about security, more precisely privacy. A This document is entirely about security, more precisely privacy. It
document on requirments for DNS privacy is [I-D.hallambaker-dnse]. just lays down the problem, it does not try to set requirments (with
Possible solutions to the issues described here are discussed in the choices and compromises they imply), much less to define
[I-D.ietf-dnsop-qname-minimisation] (qname minimization), in solutions. A document on requirments for DNS privacy is
[I-D.hallambaker-dnse]. Possible solutions to the issues described
[I-D.bortzmeyer-dnsop-privacy-sol] (local caching resolvers, here are discussed in other documents (currently too many to be
gratuitous queries), [I-D.hzhwm-start-tls-for-dns] (encryption of listed here).
traffic), in [I-D.wijngaards-dnsop-confidentialdns] (encryption also)
or in many other documents (there are many proposals to encrypt the
DNS). Attempts have been made to encrypt the resource record data
[I-D.timms-encrypt-naptr].
6. Acknowledgments 6. 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 which leaded to this draft. Thanks to Ondrej Sury for the work which leaded to this document. Thanks to Ondrej Sury for the
interesting discussions. Thanks to Mohsen Souissi for proofreading interesting discussions. Thanks to Mohsen Souissi and John Heidemann
and to Warren Kumari for proofreading and many readability for proofreading, to Paul Hoffman, Marcos Sanz and Warren Kumari for
improvements. Thanks to Dan York, Suzanne Woolf, Tony Finch, Peter proofreading, technical remarks, and many readability improvements.
Koch and Frank Denis for good written contributions. Thanks to Dan York, Suzanne Woolf, Tony Finch, Peter Koch and Frank
Denis for good written contributions.
7. References 7. References
7.1. Normative References 7.1. 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, November 1987.
[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, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[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, July
2013. 2013.
7.2. Informative References [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
Attack", BCP 188, RFC 7258, May 2014.
[RFC2181] Elz, R. and R. Bush, "Clarifications to the DNS 7.2. Informative References
Specification", RFC 2181, July 1997.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC Rose, "DNS Security Introduction and Requirements", RFC
4033, March 2005. 4033, March 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC5936] Lewis, E. and A. Hoenes, "DNS Zone Transfer Protocol [RFC5936] Lewis, E. and A. Hoenes, "DNS Zone Transfer Protocol
(AXFR)", RFC 5936, June 2010. (AXFR)", RFC 5936, June 2010.
[I-D.vandergaast-edns-client-subnet] [I-D.vandergaast-edns-client-subnet]
Contavalli, C., Gaast, W., Leach, S., and E. Lewis, Contavalli, C., Gaast, W., Leach, S., and E. Lewis,
"Client Subnet in DNS Requests", draft-vandergaast-edns- "Client Subnet in DNS Requests", draft-vandergaast-edns-
client-subnet-02 (work in progress), July 2013. client-subnet-02 (work in progress), July 2013.
[I-D.bortzmeyer-dnsop-privacy-sol]
Bortzmeyer, S., "Possible solutions to DNS privacy
issues", draft-bortzmeyer-dnsop-privacy-sol-00 (work in
progress), December 2013.
[I-D.ietf-dnsop-qname-minimisation]
Bortzmeyer, S., "DNS query name minimisation to improve
privacy", draft-ietf-dnsop-qname-minimisation-00 (work in
progress), October 2014.
[I-D.wijngaards-dnsop-confidentialdns]
Wijngaards, W. and G. Wiley, "Confidential DNS", draft-
wijngaards-dnsop-confidentialdns-01 (work in progress),
March 2014.
[I-D.timms-encrypt-naptr]
Timms, B., Reid, J., and J. Schlyter, "IANA Registration
for Encrypted ENUM", draft-timms-encrypt-naptr-01 (work in
progress), July 2008.
[I-D.hzhwm-start-tls-for-dns]
Zi, Z., Zhu, L., Heidemann, J., Mankin, A., and D.
Wessels, "Starting TLS over DNS", draft-hzhwm-start-tls-
for-dns-00 (work in progress), February 2014.
[I-D.hallambaker-dnse] [I-D.hallambaker-dnse]
Hallam-Baker, P., "DNS Privacy and Censorship: Use Cases Hallam-Baker, P., "DNS Privacy and Censorship: Use Cases
and Requirements.", draft-hallambaker-dnse-01 (work in and Requirements.", draft-hallambaker-dnse-01 (work in
progress), May 2014. progress), May 2014.
[I-D.wouters-dane-openpgp] [I-D.wouters-dane-openpgp]
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", draft-wouters-dane-openpgp-02 (work
in progress), February 2014. in progress), February 2014.
[dprive] IETF, ., "The DPRIVE working group", March 2014, [I-D.hoffman-dns-terminology]
<http://www.ietf.org/mail-archive/web/dns-privacy/>. Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", draft-hoffman-dns-terminology-00 (work in
progress), November 2014.
[dnsop] IETF, ., "The DNSOP working group", October 2013, [dprive] IETF, DPRIVE., "The DPRIVE working group", March 2014,
<http://www.ietf.org/mail-archive/web/dnsop/>. <http://www.ietf.org/mail-archive/web/dns-privacy/>.
[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/edns-
client-subnet/>. client-subnet/>.
[dagon-malware] [dagon-malware]
Dagon, D., "Corrupted DNS Resolution Paths: The Rise of a Dagon, D., "Corrupted DNS Resolution Paths: The Rise of a
Malicious Resolution Authority", 2007, <https://www.dns- Malicious Resolution Authority", 2007, <https://www.dns-
oarc.net/files/workshop-2007/Dagon-Resolution- oarc.net/files/workshop-2007/Dagon-Resolution-
corruption.pdf>. corruption.pdf>.
[dns-footprint] [dns-footprint]
Stoner, E., "DNS footprint of malware", October 2010, Stoner, E., "DNS footprint of malware", October 2010,
<https://www.dns-oarc.net/files/workshop-201010/OARC- <https://www.dns-oarc.net/files/workshop-201010/OARC-ers-
ers-20101012.pdf>. 20101012.pdf>.
[darkreading-dns] [darkreading-dns]
Lemos, R., "Got Malware? Three Signs Revealed In DNS Lemos, R., "Got Malware? Three Signs Revealed In DNS
Traffic", May 2013, <http://www.darkreading.com/monitoring Traffic", May 2013,
/got-malware-three-signs-revealed-in-dns/240154181>. <http://www.darkreading.com/monitoring/
got-malware-three-signs-revealed-in-dns/240154181>.
[dnschanger] [dnschanger]
Wikipedia, ., "DNSchanger", November 2011, Wikipedia, , "DNSchanger", November 2011,
<http://en.wikipedia.org/wiki/DNSChanger>. <http://en.wikipedia.org/wiki/DNSChanger>.
[dnscrypt] [packetq] Dot SE, , "PacketQ, a simple tool to make SQL-queries
Denis, F., "DNSCrypt", , <http://dnscrypt.org/>. against PCAP-files", 2011,
<https://github.com/dotse/packetq/wiki>.
[dnscurve]
Bernstein, D., "DNScurve", , <http://dnscurve.org/>.
[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/ [prism] NSA, , "PRISM", 2007, <http://en.wikipedia.org/wiki/
PRISM_%28surveillance_program%29>. PRISM_%28surveillance_program%29>.
[crime] Rizzo, J. and T. Dong, "The CRIME attack against TLS", [ditl] CAIDA, , "A Day in the Life of the Internet (DITL)", 2002,
2012, <http://www.caida.org/projects/ditl/>.
<http://en.wikipedia.org/wiki/CRIME_(security_exploit)>.
[ditl] CAIDA, ., "A Day in the Life of the Internet (DITL)", [turkey-googledns]
2002, <http://www.caida.org/projects/ditl/>. Bortzmeyer, S., "Hijacking of public DNS servers in
Turkey, through routing", 2014,
<http://www.bortzmeyer.org/
dns-routing-hijack-turkey.html>.
[data-protection-directive] [data-protection-directive]
Europe, ., "European directive 95/46/EC on the protection Europe, , "European directive 95/46/EC on the protection
of individuals with regard to the processing of personal of individuals with regard to the processing of personal
data and on the free movement of such data", November data and on the free movement of such data", November
1995, <http://eur-lex.europa.eu/LexUriServ/ 1995, <http://eur-lex.europa.eu/LexUriServ/
LexUriServ.do?uri=CELEX:31995L0046:EN:HTML>. 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] [tor-leak]
Tor, ., "DNS leaks in Tor", 2013, <https:// Tor, , "DNS leaks in Tor", 2013,
trac.torproject.org/projects/tor/wiki/doc/TorFAQ#Ikeepseei <https://trac.torproject.org/projects/tor/wiki/doc/TorFAQ#
ngthesewarningsaboutSOCKSandDNSandinformationleaks.ShouldI IkeepseeingthesewarningsaboutSOCKSandDNSandinformationleak
worry>. s.ShouldIworry>.
[yanbin-tsudik]
Yanbin, L. and G. Tsudik, "Towards Plugging Privacy Leaks
in the Domain Name System", 2009,
<http://arxiv.org/abs/0910.2472>.
[castillo-garcia]
Castillo-Perez, S. and J. Garcia-Alfaro, "Anonymous
Resolution of DNS Queries", 2008,
<http://deic.uab.es/~joaquin/papers/is08.pdf>.
[fangming-hori-sakurai]
Fangming, , Hori, Y., and K. Sakurai, "Analysis of Privacy
Disclosure in DNS Query", 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", 2011,
<https://svs.informatik.uni-hamburg.de/publications/2011/2
011-09-14_FFHP_PrivacyPreservingDNS_ESORICS2011.pdf>.
7.3. URIs
[1] https://developers.google.com/speed/public-dns/privacy
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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