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DNS privacy considerations

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7626.
Author Stéphane Bortzmeyer
Last updated 2015-06-11 (Latest revision 2015-05-23)
Replaces draft-bortzmeyer-dnsop-dns-privacy
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Warren "Ace" Kumari
Shepherd write-up Show Last changed 2015-03-23
IESG IESG state Became RFC 7626 (Informational)
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Terry Manderson
Send notices to "Warren Kumari" <>
IANA IANA review state IANA OK - No Actions Needed
DNS PRIVate Exchange (dprive) Working Group                S. Bortzmeyer
Internet-Draft                                                     AFNIC
Intended status: Informational                              May 23, 2015
Expires: November 24, 2015

                       DNS privacy considerations


   This document describes the privacy issues associated with the use of
   the DNS by Internet users.  It is intended to be an analysis of the
   present situation and does not prescribe solutions.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 24, 2015.

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   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Risks . . . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  The alleged public nature of DNS data . . . . . . . . . .   5
     2.2.  Data in the DNS request . . . . . . . . . . . . . . . . .   5
     2.3.  Cache snooping  . . . . . . . . . . . . . . . . . . . . .   6
     2.4.  On the wire . . . . . . . . . . . . . . . . . . . . . . .   7
     2.5.  In the servers  . . . . . . . . . . . . . . . . . . . . .   8
       2.5.1.  In the recursive resolvers  . . . . . . . . . . . . .   9
       2.5.2.  In the authoritative name servers . . . . . . . . . .   9
       2.5.3.  Rogue servers . . . . . . . . . . . . . . . . . . . .  10
     2.6.  Re-identification and other inferences  . . . . . . . . .  11
   3.  Actual "attacks"  . . . . . . . . . . . . . . . . . . . . . .  11
   4.  Legalities  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Security considerations . . . . . . . . . . . . . . . . . . .  12
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   7.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13
     8.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  17
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  17

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] and
   many later RFCs, which have never been consolidated.  It is one of
   the most important infrastructure components of the Internet and
   often ignored or misunderstood by Internet users (and even by many
   professionals).  Almost every activity on the Internet starts with a
   DNS query (and often several).  Its use has many privacy implications
   and this is an attempt at a comprehensive and accurate list.

   Let us begin with a simplified reminder of how the DNS works.  (See
   also [I-D.ietf-dnsop-dns-terminology].)  A client, the stub resolver,
   issues a DNS query to a server, called the recursive resolver (also
   called caching resolver or full resolver or recursive name server).
   Let's use the query "What are the AAAA records for"
   as an example.  AAAA is the QTYPE (Query Type), and
   is the QNAME (Query Name).  (The description which follows assume a
   cold cache, for instance because the server just started.)  The
   recursive resolver will first query the root nameservers.  In most
   cases, the root nameservers will send a referral.  In this example,
   the referral will be to the .com nameservers.  The resolver repeats

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   the query to one of the .com nameservers.  The .com nameservers, in
   turn, will refer to the nameservers.  The
   nameserver will then return the answer.  The root name servers, the
   name servers of .com and the name servers of are called
   authoritative name servers.  It is important, when analyzing the
   privacy issues, to remember that the question asked to all these name
   servers is always the original question, not a derived question.  The
   question sent to the root name servers is "What are the AAAA records
   for", 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 DNS relies on caching heavily, the algorithm described just
   above is actually a bit more complicated, and not all questions are
   sent to the authoritative name servers.  If a few seconds later the
   stub resolver asks to the recursive resolver, "What are the SRV
   records of", the recursive resolver
   will remember that it knows the name servers of and will
   just query them, bypassing the root and .com.  Because there is
   typically no caching in the stub resolver, the recursive resolver,
   unlike the authoritative servers, sees all the DNS traffic.
   (Applications, like Web browsers, may have some form of caching which
   do not follow DNS rules, for instance because it may ignore the TTL.
   So, the recursive resolver does not see all the name resolution

   It should be noted that DNS recursive resolvers sometimes forward
   requests to other recursive resolvers, typically bigger machines,
   with a larger and more shared cache (and the query hierarchy can be
   even deeper, with more than two levels of recursive resolvers).  From
   the point of view of privacy, these forwarders are like resolvers,
   except that they do not see all of the requests being made (due to
   caching in the first resolver).

   Almost all this DNS traffic is currently sent in clear (unencrypted).
   There are a few cases where there is some channel encryption, for
   instance in an IPsec VPN, at least between the stub resolver and the

   Today, almost all DNS queries are sent over UDP [thomas-ditl-tcp].
   This has practical consequences when considering encryption of the
   traffic as a possible privacy technique.  Some encryption solutions
   are only designed for TCP, not UDP.

   Another important point to keep in mind when analyzing the privacy
   issues of DNS is the fact that DNS requests received by a server were
   triggered by different reasons.  Let's assume an eavesdropper wants

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   to know which Web page is viewed by a user.  For a typical Web page,
   there are three sorts of DNS requests being issued:

      Primary request: this is the domain name in the URL that the user
      typed, selected from a bookmark or chose by clicking on an
      hyperlink.  Presumably, this is what is of interest for the

      Secondary requests: these are the additional requests performed by
      the user agent (here, the Web browser) without any direct
      involvement or knowledge of the user.  For the Web, they are
      triggered by embedded content, CSS sheets, JavaScript code,
      embedded images, etc.  In some cases, there can be dozens of
      domain names in different contexts on a single Web page.

      Tertiary requests: these are the additional requests performed by
      the DNS system itself.  For instance, if the answer to a query is
      a referral to a set of name servers, and the glue records are not
      returned, the resolver will have to do additional requests to turn
      name 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 than stricly necessary are sent, for instance to
   prefetch resources that the user may query later, or when
   autocompleting the URL in the address bar.  It is a big privacy
   concern since it may leak information even about non-explicit
   actions.  For instance, just reading a local HTML page, even without
   selecting the hyperlinks, may trigger DNS requests.

   For privacy-related terms, we will use here the terminology of

2.  Risks

   This document focuses mostly on the study of privacy risks for the
   end-user (the one performing DNS requests).  We consider the risks of
   pervasive surveillance ([RFC7258]) as well as risks coming from a
   more focused surveillance.  Privacy risks for the holder of a zone
   (the risk that someone gets the data) are discussed in [RFC5936] and
   [RFC5155].  Non-privacy risks (such as cache poisoning) are out of

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2.1.  The alleged public nature of DNS data

   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
   are multiple facets to the data and metadata involved that deserve a
   more detailed look.  First, access control lists and private
   namespaces nonwithstanding, the DNS operates under the assumption
   that public facing authoritative name servers will respond to "usual"
   DNS queries for any zone they are authoritative for without further
   authentication or authorization of the client (resolver).  Due to the
   lack of search capabilities, only a given QNAME will reveal the
   resource records associated with that name (or that name's non-
   existence).  In other words: one needs to know what to ask for, in
   order to receive a response.  The zone transfer QTYPE [RFC5936] is
   often blocked or restricted to authenticated/authorized access to
   enforce this difference (and maybe for other, more dubious reasons).

   Another differentiation to be considered is between the DNS data
   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
   described above, and may not have any confidentiality requirements.
   However, the same is not true of a single transaction or sequence of
   transactions; that transaction is not/should not be public.  A
   typical example from outside the DNS world is: the Web site of
   Alcoholics Anonymous is public; the fact that you visit it should not

2.2.  Data in the DNS request

   The DNS request includes many fields but two of them seem
   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 + maybe source port", because the port is also in
   the request and can be used to differentiate between several users
   sharing an IP address (behind a CGN for instance [RFC6269]).

   The QNAME is the full name sent by the user.  It gives information
   about what the user does ("What are the MX records of"
   means he probably wants to send email to someone at,
   which may be a domain used by only a few persons and therefore very
   revealing about communication relationships).  Some QNAMEs are more
   sensitive than others.  For instance, querying the A record of a
   well-known Web statistics domain reveals very little (everybody
   visits Web sites which use this analytics service) but querying the A
   record of www.verybad.example where verybad.example is the domain of
   an organization that some people find offensive or objectionable, may
   create more problems for the user.  Also, sometimes, the QNAME embeds
   the software one uses, which could be a privacy issue.  For instance,

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   There are also some BitTorrent clients that query a SRV record for

   Another important thing about the privacy of the QNAME is the future
   usages.  Today, the lack of privacy is an obstacle to putting
   potentially sensitive or personally identifiable data in the DNS.  At
   the moment your DNS traffic might reveal that you are doing email but
   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.
   And email is just an example; there would be other really interesting
   uses for a more privacy-friendly DNS.

   For the communication between the stub resolver and the recursive
   resolver, the source IP address is the address of the user's machine.
   Therefore, all the issues and warnings about collection of IP
   addresses apply here.  For the communication between the recursive
   resolver and the authoritative name servers, the source IP address
   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
   recursive resolver which, in a way "hides" the real user.  However,
   hiding does not always work.  Sometimes
   [I-D.ietf-dnsop-edns-client-subnet] is used (see its privacy 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 [sidn-entrada].

   A note about IP addresses: there is currently no IETF document which
   describes in detail all the privacy issues around IP addressing.  In
   the meantime, the discussion here is intended to include both IPv4
   and IPv6 source addresses.  For a number of reasons their assignment
   and utilization characteristics are different, which may have
   implications for details of information leakage associated with the
   collection of source addresses.  (For example, a specific IPv6 source
   address seen on the public Internet is less likely than an IPv4
   address to originate behind a CGN or other NAT.)  However, for both
   IPv4 and IPv6 addresses, it's important to note that source addresses
   are propagated with queries and comprise metadata about the host,
   user, or application that originated them.

2.3.  Cache snooping

   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
   with RD=0 to inspect cache content, particularly looking at the DNS
   TTLs [grangeia.snooping].  Since this also is a reconnaissance

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   technique for subsequent cache poisoning attacks, some counter
   measures have already been developed and deployed.

2.4.  On the wire

   DNS traffic can be seen by an eavesdropper like any other traffic.
   It is typically not encrypted.  (DNSSEC, specified in [RFC4033]
   explicitly excludes confidentiality from its goals.)  So, if an
   initiator starts a HTTPS communication with a recipient, while the
   HTTP traffic will be encrypted, the DNS exchange prior to it will not
   be.  When other protocols will become more and more privacy-aware and
   secured against surveillance, the DNS may become "the weakest link"
   in privacy.

   An important specificity of the DNS traffic is that it may take a
   different path than the communication between the initiator and the
   recipient.  For instance, an eavesdropper may be unable to tap the
   wire between the initiator and the recipient but may have access to
   the wire going to the recursive resolver, or to the authoritative
   name servers.

   The best place to tap, from an eavesdropper's point of view, is
   clearly between the stub resolvers and the recursive resolvers,
   because traffic is not limited by DNS caching.

   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
   configured.  By order of increasing attack surface:

      The recursive resolver can be on the end user's computer.  In
      (currently) a small number of cases, individuals may choose to
      operate their own DNS resolver on their local machine.  In this
      case the attack surface for the connection between the stub
      resolver and the caching resolver is limited to that single

      The recursive resolver may be at the local network edge.  For
      many/most enterprise networks and for some residential users the
      caching 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 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 enterprise network.  In this case the enterprise
      network could be thought of as similar to the IAP network
      referenced below.

      The recursive resolver can be in the IAP (Internet Access
      Provider) premises.  For most residential users and potentially

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      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 recursive resolvers 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 recursive resolvers.

      The recursive resolver can be a public DNS service.  Some machines
      may be configured to use public DNS resolvers such as those
      operated today 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

   Using the terminology of [RFC6973], the DNS servers (recursive
   resolvers and authoritative servers) are enablers: they facilitate
   communication between an initiator and a recipient without being
   directly in the communications path.  As a result, they are often
   forgotten in risk analysis.  But, to quote again [RFC6973], "Although
   [...] enablers may not generally be considered as attackers, they may
   all pose privacy threats (depending on the context) because they are
   able to observe, collect, process, and transfer privacy-relevant
   data."  In [RFC6973] parlance, enablers become observers when they
   start collecting data.

   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
   sophisticated programs like PacketQ [packetq] and DNSmezzo
   [dnsmezzo].  The organization managing the DNS server can use these
   data itself or it can be part of a surveillance program like PRISM
   [prism] and pass data to an outside observer.

   Sometimes, these data are kept for a long time and/or distributed to
   third parties, for research purposes [ditl] [day-at-root], for
   security analysis, or for surveillance tasks.  These uses are
   sometimes under some sort of contract, with various limitations, for
   instance on redistribution, giving the sensitive nature of the data.
   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]").

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2.5.1.  In the recursive resolvers

   Recursive Resolvers see all the traffic since there is typically no
   caching before them.  To summarize: your recursive resolver knows a
   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
   the data collected by reading the privacy policy of a big public
   resolver [1].

2.5.2.  In the authoritative name servers

   Unlike what happens for recursive resolvers, observation capabilities
   of authoritative name servers are limited by caching; they see only
   the requests for which the answer was not in the cache.  For
   aggregated statistics ("What is the percentage of LOC queries?"),
   this is sufficient; but it prevents an observer from seeing
   everything.  Still, the authoritative name servers see a part of the
   traffic, and this subset may be sufficient to violate some privacy

   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
   given public resolver), while having no control and perhaps no
   awareness of the role of the authoritative name servers and their
   observation abilities.

   As noted before, using a local resolver or a resolver close to the
   machine decreases the attack surface for an on-the-wire eavesdropper.
   But it may decrease privacy against an observer located on an
   authoritative name server.  This authoritative name server will see
   the IP address of the end client, instead of the address of a big
   recursive resolver shared by many users.

   This "protection", when using a large resolver with many clients, is
   no longer present if [I-D.ietf-dnsop-edns-client-subnet] is used
   because, in this case, the authoritative name server sees the
   original IP address (or prefix, depending on the setup).

   As of today, all the instances of one root name server, L-root,
   receive together around 50,000 queries per second.  While most of it
   is "junk" (errors on the TLD name), it gives an idea of the amount of
   big data which pours into name servers.

   Many domains, including TLDs, are partially hosted by third-party
   servers, sometimes in a different country.  The contracts between the
   domain manager and these servers may or may not take privacy into
   account.  Whatever the contract, the third-party hoster may be honest
   or not but, in any case, it will have to follow its local laws.  So,

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   requests to a given ccTLD may go to servers managed by organizations
   outside of the ccTLD's country.  End-users may not anticipate that,
   when doing a security analysis.

   Also, it seems [aeris-dns] that there is a strong concentration of
   authoritative name servers among "popular" domains (such as the Alexa
   Top N list).  For instance, among the Alexa Top 100k, one DNS
   provider hosts today 10 % of the domains.  The ten most important DNS
   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

   The previous paragraphs discussed DNS privacy, assuming that all the
   traffic was directed to the intended servers, and that the potential
   attacker was purely passive.  But, in reality, we can have active
   attackers, redirecting the traffic, not for changing it but just to
   observe it.

   For instance, a rogue DHCP server, or a trusted DHCP server that has
   had its configuration altered by malicious parties, can direct you to
   a rogue recursive resolver.  Most of the time, it seems to be done to
   divert traffic, by providing lies for some domain names.  But it
   could be used just to capture the traffic and gather information
   about you.  Other attacks, besides using DHCP, are possible.  The
   traffic from a DNS client to a DNS server can be intercepted along
   its way from originator to intended source; for instance by
   transparent DNS proxies in the network that will divert the traffic
   intended for a legitimate DNS server.  This rogue server can
   masquerade as the intended server and respond with data to the
   client.  (Rogue servers that inject malicious data are possible, but
   is a separate problem not relevant to privacy.)  A rogue server may
   respond correctly for a long period of time, thereby foregoing
   detection.  This may be done for what could be claimed to be good
   reasons, such as optimization or caching, but it leads to a reduction
   of privacy compared to if there were no attacker present.  Also,
   malware like DNSchanger [dnschanger] can change the recursive
   resolver in the machine's configuration, or the routing itself can be
   subverted (for instance [turkey-googledns]).

   A practical consequence of this section is that solutions for DNS
   privacy may have to address authentication of the server, not just
   passive sniffing.

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2.6.  Re-identification and other inferences

   An observer has access not only to the data he/she directly collects
   but also to the results of various inferences about these data.

   For instance, a user can be re-identified via DNS queries.  If the
   adversary knows a user's identity and can watch their DNS queries for
   a period, then that same adversary may be able to re-identify the
   user solely based on their pattern of DNS queries later on regardless
   of the location from which the user makes those queries.  For
   example, one study [herrmann-reidentification] found that such re-
   identification is possible so that "73.1% of all day-to-day links
   were correctly established, i.e.  user u was either re-identified
   unambiguously (1) or the classifier correctly reported that u was not
   present on day t+1 any more (2)".  While that study related to web
   browsing behaviour, equally characteristic patterns may be produced
   even in machine-to-machine communications or without a user taking
   specific actions, e.g. at reboot time if a characteristic set of
   services are accessed by the device.

   The IAB privacy and security programme also have a work in progress
   [I-D.iab-privsec-confidentiality-threat] that considers such
   inference based attacks in a more general framework.

3.  Actual "attacks"

   A very quick examination of DNS traffic may lead to the false
   conclusion that extracting the needle from the haystack is difficult.
   "Interesting" primary DNS requests are mixed with useless (for the
   eavesdropper) secondary and tertiary requests (see the terminology in
   Section 1).  But, in this time of "big data" processing, powerful
   techniques now exist to get from the raw data to what the
   eavesdropper is actually interested in.

   Many research papers about malware detection use DNS traffic to
   detect "abnormal" behaviour that can be traced back to the activity
   of malware on infected machines.  Yes, this research was done for the
   good; but, technically, it is a privacy attack and it demonstrates
   the power of the observation of DNS traffic.  See [dns-footprint],
   [dagon-malware] and [darkreading-dns].

   Passive DNS systems [passive-dns] allow reconstruction of the data of
   sometimes an entire zone.  They are used for many reasons, some good,
   some bad.  Well-known passive DNS systems keep only the DNS
   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.

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   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 surreptitiously gather
   information about the users, is another good example showing that the
   lack of privacy protections in the DNS is actively exploited.

4.  Legalities

   To our knowledge, there are no specific privacy laws for DNS data, in
   any country.  Interpreting general privacy laws like
   [data-protection-directive] (European Union) in the context of DNS
   traffic data is not an easy task and it seems there is no court
   precedent here.  An interesting analysis is [sidn-entrada].

5.  Security considerations

   This document is entirely about security, more precisely privacy.  It
   just lays out the problem, it does not try to set requirements (with
   the choices and compromises they imply), much less to define
   solutions.  A possible document on requirments for DNS privacy is
   [I-D.hallambaker-dnse].  Possible solutions to the issues described
   here are discussed in other documents (currently too many to all be
   mentioned), see for instance [I-D.ietf-dnsop-qname-minimisation] for
   the minimisation of data, or [I-D.hzhwm-start-tls-for-dns] about

6.  Acknowledgments

   Thanks to Nathalie Boulvard and to the CENTR members for the original
   work which leaded to this document.  Thanks to Ondrej Sury for the
   interesting discussions.  Thanks to Mohsen Souissi and John Heidemann
   for proofreading, to Paul Hoffman, Matthijs Mekking, Marcos Sanz, Tim
   Wicinski, Francis Dupont, Allison Mankin and Warren Kumari for
   proofreading, technical remarks, and many readability improvements.
   Thanks to Dan York, Suzanne Woolf, Tony Finch, Stephen Farrell, Peter
   Koch, Simon Josefsson and Frank Denis for good written contributions.

7.  IANA considerations

   This document has no actions for IANA.

8.  References

8.1.  Normative References

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

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   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973, July

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, May 2014.

8.2.  Informative References

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements", RFC
              4033, March 2005.

   [RFC5155]  Laurie, B., Sisson, G., Arends, R., and D. Blacka, "DNS
              Security (DNSSEC) Hashed Authenticated Denial of
              Existence", RFC 5155, March 2008.

   [RFC5936]  Lewis, E. and A. Hoenes, "DNS Zone Transfer Protocol
              (AXFR)", RFC 5936, June 2010.

   [RFC6269]  Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
              Roberts, "Issues with IP Address Sharing", RFC 6269, June

              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.

              Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
              Trammell, B., Huitema, C., and D. Borkmann,
              "Confidentiality in the Face of Pervasive Surveillance: A
              Threat Model and Problem Statement", draft-iab-privsec-
              confidentiality-threat-06 (work in progress), May 2015.

              Hallam-Baker, P., "DNS Privacy and Censorship: Use Cases
              and Requirements.", draft-hallambaker-dnse-02 (work in
              progress), November 2014.

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              Wouters, P., "Using DANE to Associate OpenPGP public keys
              with email addresses", draft-wouters-dane-openpgp-02 (work
              in progress), February 2014.

              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.

              Bortzmeyer, S., "DNS query name minimisation to improve
              privacy", draft-ietf-dnsop-qname-minimisation-02 (work in
              progress), March 2015.

              Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
              Terminology", draft-ietf-dnsop-dns-terminology-01 (work in
              progress), April 2015.

   [dprive]   IETF, DPRIVE., "The DPRIVE working group", March 2014,

              Denis, F., "Security and privacy issues of edns-client-
              subnet", August 2013, <

              Dagon, D., "Corrupted DNS Resolution Paths: The Rise of a
              Malicious Resolution Authority", 2007, <https://www.dns-

              Stoner, E., "DNS footprint of malware", October 2010,

              Grothoff, C., Wachs, M., Ermert, M., and J. Appelbaum,
              "NSA's MORECOWBELL: Knell for DNS", January 2015,

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              Lemos, R., "Got Malware? Three Signs Revealed In DNS
              Traffic", May 2013,

              Wikipedia, , "DNSchanger", November 2011,

   [packetq]  Dot SE, , "PacketQ, a simple tool to make SQL-queries
              against PCAP-files", 2011,

              Bortzmeyer, S., "DNSmezzo", 2009,

   [prism]    NSA, , "PRISM", 2007, <

              Grangeia, L., "DNS Cache Snooping or Snooping the Cache
              for Fun and Profit", 2004,

   [ditl]     CAIDA, , "A Day in the Life of the Internet (DITL)", 2002,

              Castro, S., Wessels, D., Fomenkov, M., and K. Claffy, "A
              Day at the Root of the Internet", 2008,

              Bortzmeyer, S., "Hijacking of public DNS servers in
              Turkey, through routing", 2014,

              Europe, , "European directive 95/46/EC on the protection
              of individuals with regard to the processing of personal
              data and on the free movement of such data", November
              1995, <

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              Weimer, F., "Passive DNS Replication", April 2005,

              Tor, , "DNS leaks in Tor", 2013,

              Yanbin, L. and G. Tsudik, "Towards Plugging Privacy Leaks
              in the Domain Name System", 2009,

              Castillo-Perez, S. and J. Garcia-Alfaro, "Anonymous
              Resolution of DNS Queries", 2008,

              Fangming, , Hori, Y., and K. Sakurai, "Analysis of Privacy
              Disclosure in DNS Query", 2007,

              Thomas, M. and D. Wessels, "An Analysis of TCP Traffic in
              Root Server DITL Data"", 2014, <https://indico.dns-

              Federrath, H., Fuchs, K., Herrmann, D., and C. Piosecny,
              "Privacy-Preserving DNS: Analysis of Broadcast, Range
              Queries and Mix-Based Protection Methods", 2011,

              Vinot, N., "[In French] Vie privee : et le DNS alors ?",
              2015, <

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              Herrmann, D., Gerber, C., Banse, C., and H. Federrath,
              "Analyzing characteristic host access patterns for re-
              identification of web user sessions", 2012,

              Hesselman, C., Jansen, J., Wullink, M., Vink, K., and M.
              Simon, "A privacy framework for 'DNS big data'
              applications", 2014,

8.3.  URIs


Author's Address

   Stephane Bortzmeyer
   1, rue Stephenson
   Montigny-le-Bretonneux  78180

   Phone: +33 1 39 30 83 46

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