draft-ietf-dprive-problem-statement-01.txt   draft-ietf-dprive-problem-statement-02.txt 
DNS PRIVate Exchange (dprive) Working Group S. Bortzmeyer DNS PRIVate Exchange (dprive) Working Group S. Bortzmeyer
Internet-Draft AFNIC Internet-Draft AFNIC
Intended status: Informational January 7, 2015 Intended status: Informational February 19, 2015
Expires: July 11, 2015 Expires: August 23, 2015
DNS privacy considerations DNS privacy considerations
draft-ietf-dprive-problem-statement-01 draft-ietf-dprive-problem-statement-02
Abstract Abstract
This document describes the privacy issues associated with the use of This document describes the privacy issues associated with the use of
the DNS by Internet users. It is intended to be mostly an analysis the DNS by Internet users. It is intended to be an analysis of the
of the present situation, in the spirit of section 8 of [RFC6973] and present situation and 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].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 11, 2015. This Internet-Draft will expire on August 23, 2015.
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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. 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 . . . . . . . . . . . . . . . . . 5 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 . . . . . . . . . . . . . . . . . . . . . 8
2.5.1. In the recursive resolvers . . . . . . . . . . . . . 8 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 . . . . . . . . . . . . . . . . . . . . 10
3. Actual "attacks" . . . . . . . . . . . . . . . . . . . . . . 10 3. Actual "attacks" . . . . . . . . . . . . . . . . . . . . . . 10
4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 10 4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Security considerations . . . . . . . . . . . . . . . . . . . 10 5. Security considerations . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 11 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . 11 8.1. Normative References . . . . . . . . . . . . . . . . . . 11
7.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 14 8.2. Informative References . . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 14 8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
This document is an analysis of the DNS privacy issues, in the spirit
of section 8 of [RFC6973].
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 often ignored or misunderstood. Almost every activity
every activity on the Internet starts with a DNS query (and often on the Internet starts with a DNS query (and often several). Its use
several). Its use has many privacy implications and we try to give has many privacy implications and this is an attempt at a
here a comprehensive and accurate list. comprehensive and accurate list.
Let us begin with a simplified reminder of how the DNS works. Let us begin with a simplified reminder of how the DNS works.
(REMOVE BEFORE PUBLICATION: We hope that the document (REMOVE BEFORE PUBLICATION: We hope that the document
[I-D.hoffman-dns-terminology] will be published as a RFC so most of [I-D.hoffman-dns-terminology] will be published as a RFC so most of
this section could be replaced by a reference to it.) A client, the this section could be replaced by a reference to it.) A client, the
stub resolver, issues a DNS query to a server, the recursive resolver stub resolver, issues a DNS query to a server, called the recursive
(also called caching resolver or full resolver or simply resolver resolver (also called caching resolver or full resolver or recursive
recursive name server). Let's use the query "What are the AAAA name server). Let's use the query "What are the AAAA records for
records for www.example.com?" as an example. AAAA is the qtype www.example.com?" as an example. AAAA is the qtype (Query Type), and
(Query type), and www.example.com is the qname (Query Name). The www.example.com is the qname (Query Name). The recursive resolver
recursive resolver will first query the root nameservers. In most will first query the root nameservers. In most cases, the root
cases, the root nameservers will send a referral. In this example, nameservers will send a referral. In this example, the referral will
the referral will be to .com nameservers. The resolver repeats the be to the .com nameservers. The resolver repeats the query to one of
query to one of the .com nameservers. The .com nameserver, in turn, the .com nameservers. The .com nameservers, in turn, will refer to
will refer to the example.com nameservers. The example.com the example.com nameservers. The example.com nameserver will then
nameserver will then return the answer. The root name servers, the return the answer. The root name servers, the name servers of .com
name servers of .com and those of example.com are called and the name servers of example.com are called authoritative name
authoritative name servers. It is important, when analyzing the servers. It is important, when analyzing the privacy issues, to
privacy issues, to remember that the question asked to all these name remember that the question asked to all these name servers is always
servers is always the original question, not a derived question. the original question, not a derived question. The question sent to
Unlike what many "DNS for dummies" articles say, the question sent to
the root name servers is "What are the AAAA records for the root name servers is "What are the AAAA records for
www.example.com?", not "What are the name servers of .com?". By www.example.com?", not "What are the name servers of .com?". By
repeating the full question, instead of just the relevant part of the repeating the full question, instead of just the relevant part of the
question to the next in line, the DNS provides more information than question to the next in line, the DNS provides more information than
necessary to the nameserver. necessary to the nameserver.
Because the DNS uses caching heavily, not all questions are sent to Because DNS relies on caching heavily, not all questions are sent to
the authoritative name servers. If the stub resolver, a few seconds the authoritative name servers. If a few seconds later the stub
later, asks to the recursive resolver "What are the SRV records of resolver asks to the recursive resolver, "What are the SRV records of
_xmpp-server._tcp.example.com?", the recursive resolver will remember _xmpp-server._tcp.example.com?", the recursive resolver will remember
that it knows the name servers of example.com and will just query that it knows the name servers of example.com and will just query
them, bypassing the root and .com. Because there is typically no them, bypassing the root and .com. Because there is typically no
caching in the stub resolver, the recursive resolver, unlike the caching in the stub resolver, the recursive resolver, unlike the
authoritative servers, sees everything. authoritative servers, sees all the DNS traffic. (Applications, like
Web browsers, may have some form of caching, which do not follow DNS
rules. So, the recursive resolver does not see all the name
resolution activity.)
It should be noted that DNS recursive resolvers sometimes forward It should be noted that DNS recursive resolvers sometimes forward
requests to bigger machines, with a larger and more shared cache, the requests to other recursive resolvers, typically bigger machines,
forwarders (and the query hierarchy can be even deeper, with more with a larger and more shared cache (and the query hierarchy can be
than two levels of recursive resolvers). From the point of view of even deeper, with more than two levels of recursive resolvers). From
privacy, forwarders are like resolvers, except that the caching in the point of view of privacy, these forwarders are like resolvers,
the recursive resolvers before them decreases the amount of data they except that they do not see all of the requests being made (due to
can see. caching in the first resolver).
All this DNS traffic is today sent in clear (unencryted), except a All this DNS traffic is currently sent in clear (unencryted), except
few cases when the IP traffic is protected, for instance in an IPsec a few cases when the IP traffic is protected, for instance in an
VPN. IPsec VPN.
Today, almost all DNS queries are sent over UDP. This has practical Today, almost all DNS queries are sent over UDP. This has practical
consequences, when considering a possible privacy technique, consequences when considering encryption of the traffic as a possible
encryption of the traffic: some encryption solutions are only privacy technique. Some encryption solutions are only designed for
designed for TCP, not UDP. 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 wants to know which Web page server. Let's assume an eavesdropper wants to know which Web page is
is viewed by an user. For a typical Web page displayed by the user, viewed by an user. For a typical Web page, there are three sorts of
there are three sorts of DNS requests being issued: 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 or selected from a bookmark or choose 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, CSS sheets, JavaScript code,
embedded images, etc. In some cases, there can be dozens of embedded images, etc. In some cases, there can be dozens of
domain names in different contexts on a single Web page. 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 is not returned, a referral to a set of name servers, and the glue records are not
the resolver will have to do tertiary requests to turn name returned, the resolver will have to do additional requests to turn
servers' names into IP addresses. Similarly, even if glue records name servers' names into IP addresses. Similarly, even if glue
are returned, a careful recursive server will do tertiary requests records are returned, a careful recursive server will do tertiary
to verify the IP addresses of those records. 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 are sent, for instance to prefetch resources that the DNS requests are sent, for instance to prefetch resources that the
user may query later, or when autocompleting the URL in the address user may query later, or when autocompleting the URL in the address
bar (which obviously is a big privacy concern). 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 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]) and also risks coming from a more pervasive surveillance ([RFC7258]) as well as risks coming from a
focused surveillance. Privacy risks for the holder of a zone (the more focused surveillance. Privacy risks for the holder of a zone
risk that someone gets the data) are discussed in [RFC5936]. Non- (the risk that someone gets the data) are discussed in [RFC5936] and
privacy risks (such as cache poisoning) are out of scope. [RFC5155]. 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 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 nonwithstanding, 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
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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 transaction is not/should not be public. A 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 sort out several users sharing an IP the request and can be used to sort out several users sharing an IP
address (behind a CGN for instance). address (behind a 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 therefore very
revealing about communication relationships). Some qnames are more revealing about communication relationships). Some qnames are more
sensitive than others. For instance, querying the A record of sensitive than others. For instance, querying the A record of
google-analytics.com reveals very little (everybody visits Web sites google-analytics.com reveals very little (everybody visits Web sites
which use Google Analytics) but querying the A record of which use Google Analytics) but querying the A record of
www.verybad.example where verybad.example is the domain of an illegal www.verybad.example where verybad.example is the domain of an illegal
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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 a HTTP connection. It is now the IP address of the
recursive resolver which, in a way "hides" the real user. However, recursive resolver which, in a way "hides" the real user. However,
hiding does not always work. Sometimes hiding does not always work. Sometimes
[I-D.vandergaast-edns-client-subnet] is used (see its privacy [I-D.ietf-dnsop-edns-client-subnet] is used (see its privacy analysis
analysis in [denis-edns-client-subnet]). Sometimes the end user has in [denis-edns-client-subnet]). Sometimes the end user has a
a personal recursive resolver on her machine. In both cases, the IP 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 describes in detail all the privacy issues around IP addressing. In
meantime, the discussion here is intended to include both IPv4 and the meantime, the discussion here is intended to include both IPv4
IPv6 source addresses. For a number of reasons their assignment and and IPv6 source addresses. For a number of reasons their assignment
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
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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] and DNSmezzo
[dnsmezzo]. The organization managing the DNS server can use these [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 observer. [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] [day-at-root], for
or for surveillance tasks. Also, there are observation points in the security analysis, or for surveillance tasks. These uses are
network which gather DNS data and then make it accessible to third- sometimes under some sort of contract, with various limitations, for
parties for research or security purposes ("passive DNS instance on redistribution, giving the sensitive nature of the data.
[passive-dns]"). Also, there are observation points in the network which gather DNS
data and then make it accessible to third-parties for research or
security purposes ("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 [1].
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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 has typically 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.
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
TLDs (and the huge amount of traffic for non-existing TLDs), but a
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
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.vandergaast-edns-client-subnet] is used no longer present if [I-D.ietf-dnsop-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 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. 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 Also, it seems [aeris-dns] that there is a strong concentration of
strong concentration of authoritative name servers among "popular" authoritative name servers among "popular" domains (such as the Alexa
domains (such as the Alexa Top N list). With the control (or the Top N list). For instance, among the Alexa Top 100k, one DNS
ability to sniff the traffic) of a few name servers, you can gather a provider hosts today 10 % of the domains. The ten most important DNS
lot of information. providers host together one third of the domains. With the control
(or the ability to sniff the traffic) of a few name servers, you can
gather a lot of information.
2.5.3. Rogue servers 2.5.3. Rogue servers
A rogue DHCP server, or a trusted DHCP server that has had its A rogue DHCP server, or a trusted DHCP server that has had its
configuration altered by malicious parties, can direct you to a rogue configuration altered by malicious parties, can direct you to a rogue
recursive resolver. Most of the times, it seems to be done to divert recursive resolver. Most of the time, it seems to be done to divert
traffic, by providing lies for some domain names. But it could be traffic, by providing lies for some domain names. But it could be
used just to capture the traffic and gather information about you. used just to capture the traffic and gather information about you.
Same thing for malware like DNSchanger[dnschanger] which changes the Same thing for malware like DNSchanger[dnschanger] which changes the
recursive resolver in the machine's configuration, or with recursive resolver in the machine's configuration, or with
transparent DNS proxies in the network that will divert the traffic transparent DNS proxies in the network that will divert the traffic
intended for a legitimate DNS server (for instance intended for a legitimate DNS server (for instance
[turkey-googledns]). [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) 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 you're actually techniques now exist to get from the raw data to what the
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" 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
power of the observation of DNS traffic. See [dns-footprint], the 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. They are used for many reasons, some good,
some bad. It is an example of a privacy issue even when no source IP some bad. Well-known passive DNS systems keep only the DNS
address is kept. responses, and not the source IP address of the client, precisely for
privacy reasons. Other passive DNS systems may not be so careful.
And there is still the potential problems with revealing qnames.
The revelations (from the Edward Snowden documents, leaked from the
NSA) of the MORECOWBELL surveillance program [morecowbell], which
uses the DNS, both passively and actively, to gather surreptitiously
information about the users, is another good example 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. 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. It This document is entirely about security, more precisely privacy. It
just lays down the problem, it does not try to set requirments (with just lays out the problem, it does not try to set requirments (with
the choices and compromises they imply), much less to define the choices and compromises they imply), much less to define
solutions. A document on requirments for DNS privacy is solutions. A possible document on requirments for DNS privacy is
[I-D.hallambaker-dnse]. Possible solutions to the issues described [I-D.hallambaker-dnse]. Possible solutions to the issues described
here are discussed in other documents (currently too many to be here are discussed in other documents (currently too many to all be
listed here). mentioned), see for instance [I-D.ietf-dnsop-qname-minimisation] for
the minimisation of data, or [I-D.hzhwm-start-tls-for-dns] about
encryption.
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 document. Thanks to Ondrej Sury for the work which leaded to this document. Thanks to Ondrej Sury for the
interesting discussions. Thanks to Mohsen Souissi and John Heidemann interesting discussions. Thanks to Mohsen Souissi and John Heidemann
for proofreading, to Paul Hoffman, Marcos Sanz and Warren Kumari for for proofreading, to Paul Hoffman, Marcos Sanz, Tim Wicinski, Allison
proofreading, technical remarks, and many readability improvements. Mankin and Warren Kumari for proofreading, technical remarks, and
Thanks to Dan York, Suzanne Woolf, Tony Finch, Peter Koch and Frank many readability improvements. Thanks to Dan York, Suzanne Woolf,
Denis for good written contributions. Tony Finch, Peter Koch and Frank Denis for good written
contributions.
7. References 7. IANA considerations
7.1. Normative References This document has no actions for IANA.
8. References
8.1. 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
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.
[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, May 2014.
7.2. Informative References 8.2. Informative References
[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.
[RFC5155] Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
Security (DNSSEC) Hashed Authenticated Denial of
Existence", RFC 5155, March 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] [RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Contavalli, C., Gaast, W., Leach, S., and E. Lewis, Roberts, "Issues with IP Address Sharing", RFC 6269, June
"Client Subnet in DNS Requests", draft-vandergaast-edns- 2011.
client-subnet-02 (work in progress), July 2013.
[I-D.ietf-dnsop-edns-client-subnet]
Contavalli, C., Gaast, W., Lawrence, D., and W. Kumari,
"Client Subnet in DNS Requests", draft-ietf-dnsop-edns-
client-subnet-00 (work in progress), November 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-02 (work in
progress), May 2014. progress), November 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.
[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-01 (work in progress), July 2014.
[I-D.ietf-dnsop-qname-minimisation]
Bortzmeyer, S., "DNS query name minimisation to improve
privacy", draft-ietf-dnsop-qname-minimisation-01 (work in
progress), February 2015.
[I-D.hoffman-dns-terminology] [I-D.hoffman-dns-terminology]
Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", draft-hoffman-dns-terminology-00 (work in Terminology", draft-hoffman-dns-terminology-01 (work in
progress), November 2014. progress), January 2015.
[dprive] IETF, DPRIVE., "The DPRIVE working group", March 2014, [dprive] IETF, DPRIVE., "The DPRIVE working group", March 2014,
<http://www.ietf.org/mail-archive/web/dns-privacy/>. <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-ers- <https://www.dns-oarc.net/files/workshop-201010/OARC-ers-
20101012.pdf>. 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] [darkreading-dns]
Lemos, R., "Got Malware? Three Signs Revealed In DNS Lemos, R., "Got Malware? Three Signs Revealed In DNS
Traffic", May 2013, Traffic", May 2013,
<http://www.darkreading.com/monitoring/ <http://www.darkreading.com/monitoring/
got-malware-three-signs-revealed-in-dns/240154181>. 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>.
skipping to change at page 13, line 5 skipping to change at page 14, line 5
[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>.
[ditl] CAIDA, , "A Day in the Life of the Internet (DITL)", 2002, [ditl] CAIDA, , "A Day in the Life of the Internet (DITL)", 2002,
<http://www.caida.org/projects/ditl/>. <http://www.caida.org/projects/ditl/>.
[day-at-root]
Castro, S., Wessels, D., Fomenkov, M., and K. Claffy, "A
Day at the Root of the Internet", 2008,
<http://www.sigcomm.org/sites/default/files/ccr/
papers/2008/October/1452335-1452341.pdf>.
[turkey-googledns] [turkey-googledns]
Bortzmeyer, S., "Hijacking of public DNS servers in Bortzmeyer, S., "Hijacking of public DNS servers in
Turkey, through routing", 2014, Turkey, through routing", 2014,
<http://www.bortzmeyer.org/ <http://www.bortzmeyer.org/
dns-routing-hijack-turkey.html>. 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
skipping to change at page 14, line 5 skipping to change at page 15, line 12
Disclosure in DNS Query", 2007, Disclosure in DNS Query", 2007,
<http://dl.acm.org/citation.cfm?id=1262690.1262986>. <http://dl.acm.org/citation.cfm?id=1262690.1262986>.
[federrath-fuchs-herrmann-piosecny] [federrath-fuchs-herrmann-piosecny]
Federrath, H., Fuchs, K., Herrmann, D., and C. Piosecny, Federrath, H., Fuchs, K., Herrmann, D., and C. Piosecny,
"Privacy-Preserving DNS: Analysis of Broadcast, Range "Privacy-Preserving DNS: Analysis of Broadcast, Range
Queries and Mix-Based Protection Methods", 2011, Queries and Mix-Based Protection Methods", 2011,
<https://svs.informatik.uni-hamburg.de/publications/2011/2 <https://svs.informatik.uni-hamburg.de/publications/2011/2
011-09-14_FFHP_PrivacyPreservingDNS_ESORICS2011.pdf>. 011-09-14_FFHP_PrivacyPreservingDNS_ESORICS2011.pdf>.
7.3. URIs [aeris-dns]
Vinot, N., "[In French] Vie privee : et le DNS alors ?",
2015, <https://blog.imirhil.fr/vie-privee-et-le-dns-
alors.html>.
8.3. URIs
[1] https://developers.google.com/speed/public-dns/privacy [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
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