DNS PRIVate Exchange (dprive) Working Group                S. BortzmeyerInternet-Draft                                                     AFNICIntended status: Informational                             June 15, 2015Expires: December 17, 2015                       DNS privacy considerations                 draft-ietf-dprive-problem-statement-06Abstract   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   working documents as Internet-Drafts.  The list of current Internet-   Drafts is at http://datatracker.ietf.org/drafts/current/.   Internet-Drafts are draft documents valid for a maximum of six months   and may be updated, replaced, or obsoleted by other documents at any   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 December 17, 2015.Copyright Notice   Copyright (c) 2015 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject to BCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Bortzmeyer              Expires December 17, 2015               [Page 1]Internet-Draft                 DNS privacy                     June 2015Table 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  . . . . . . . . . . . . . . . . . . . . . . . . .  13     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  13     8.2.  Informative References  . . . . . . . . . . . . . . . . .  13     8.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  17   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  171.  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 www.example.com?"   as an example.  AAAA is the QTYPE (Query Type), and www.example.com   is the QNAME (Query Name).  (The description which follows assumes 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 repeatsBortzmeyer              Expires December 17, 2015               [Page 2]Internet-Draft                 DNS privacy                     June 2015   the query to one of the .com nameservers.  The .com nameservers, in   turn, will refer to the example.com nameservers.  The example.com   nameserver will then return the answer.  The root name servers, the   name servers of .com and the name servers of example.com 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 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 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 _xmpp-server._tcp.example.com?", the recursive resolver   will remember that it knows the name servers of example.com 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   activity.)   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   resolver.   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 wantsBortzmeyer              Expires December 17, 2015               [Page 3]Internet-Draft                 DNS privacy                     June 2015   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      eavesdropper.      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.  Both are a big privacy   concern since they 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   [RFC6973].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   scope.Bortzmeyer              Expires December 17, 2015               [Page 4]Internet-Draft                 DNS privacy                     June 20152.1.  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 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   be.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 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   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,Bortzmeyer              Expires December 17, 2015               [Page 5]Internet-Draft                 DNS privacy                     June 2015   _ldap._tcp.Default-First-Site-Name._sites.gc._msdcs.example.org.   There are also some BitTorrent clients that query a SRV record for   _bittorrent-tracker._tcp.domain.example.   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 reconnaissanceBortzmeyer              Expires December 17, 2015               [Page 6]Internet-Draft                 DNS privacy                     June 2015   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      machine.      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 (Internet Access      Provider) network referenced below.      The recursive resolver can be in the IAP (Internet Access      Provider) premises.  For most residential users and potentiallyBortzmeyer              Expires December 17, 2015               [Page 7]Internet-Draft                 DNS privacy                     June 2015      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]").Bortzmeyer              Expires December 17, 2015               [Page 8]Internet-Draft                 DNS privacy                     June 20152.5.1.  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   expectations.   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.  (And even "junk" can leak   information, for instance if there is a typing error in the TLD, the   user will send data to a TLD which is not the usual one.)   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 intoBortzmeyer              Expires December 17, 2015               [Page 9]Internet-Draft                 DNS privacy                     June 2015   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,   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.Bortzmeyer              Expires December 17, 2015              [Page 10]Internet-Draft                 DNS privacy                     June 20152.6.  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.   For instance, one could imagine, for an intelligence agency to   identify people going to a site by putting in a very long DNS name   and looking for queries of a specific length.  Such traffic analysis   could weaken some privacy solutions.   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,Bortzmeyer              Expires December 17, 2015              [Page 11]Internet-Draft                 DNS privacy                     June 2015   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.   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 we do not know a 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.  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.ietf-dprive-start-tls-for-dns]   about encryption.6.  Acknowledgments   Thanks to Nathalie Boulvard and to the CENTR members for the original   work which leaded to this document.  Thanks to Ondrej Sury for the   interesting discussions.  Thanks to Mohsen Souissi and John Heidemann   for proofreading, to Paul Hoffman, Matthijs Mekking, Marcos Sanz, Tim   Wicinski, Francis Dupont, Allison Mankin and Warren Kumari for   proofreading, technical remarks, and many readability improvements.   Thanks to Dan York, Suzanne Woolf, Tony Finch, Stephen Farrell, Peter   Koch, Simon Josefsson and Frank Denis for good written contributions.   And thanks to the IESG members for the last remarks.7.  IANA considerations   This document has no actions for IANA.Bortzmeyer              Expires December 17, 2015              [Page 12]Internet-Draft                 DNS privacy                     June 20158.  References8.1.  Normative References   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",              STD 13, RFC 1034, November 1987.   [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              2013.   [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              2011.   [I-D.ietf-dnsop-edns-client-subnet]              Contavalli, C., Gaast, W., Lawrence, D., and W. Kumari,              "Client Subnet in DNS Querys", draft-ietf-dnsop-edns-              client-subnet-01 (work in progress), May 2015.   [I-D.iab-privsec-confidentiality-threat]              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-07 (work in progress), May 2015.Bortzmeyer              Expires December 17, 2015              [Page 13]Internet-Draft                 DNS privacy                     June 2015   [I-D.wouters-dane-openpgp]              Wouters, P., "Using DANE to Associate OpenPGP public keys              with email addresses", draft-wouters-dane-openpgp-02 (work              in progress), February 2014.   [I-D.ietf-dprive-start-tls-for-dns]              Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,              and P. Hoffman, "TLS for DNS: Initiation and Performance              Considerations", draft-ietf-dprive-start-tls-for-dns-00              (work in progress), May 2015.   [I-D.ietf-dnsop-qname-minimisation]              Bortzmeyer, S., "DNS query name minimisation to improve              privacy", draft-ietf-dnsop-qname-minimisation-03 (work in              progress), June 2015.   [I-D.ietf-dnsop-dns-terminology]              Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS              Terminology", draft-ietf-dnsop-dns-terminology-02 (work in              progress), May 2015.   [denis-edns-client-subnet]              Denis, F., "Security and privacy issues of edns-client-              subnet", August 2013, <https://00f.net/2013/08/07/edns-              client-subnet/>.   [dagon-malware]              Dagon, D., "Corrupted DNS Resolution Paths: The Rise of a              Malicious Resolution Authority", 2007, <https://www.dns-              oarc.net/files/workshop-2007/Dagon-Resolution-              corruption.pdf>.   [dns-footprint]              Stoner, E., "DNS footprint of malware", October 2010,              <https://www.dns-oarc.net/files/workshop-201010/OARC-ers-              20101012.pdf>.   [morecowbell]              Grothoff, C., Wachs, M., Ermert, M., and J. Appelbaum,              "NSA's MORECOWBELL: Knell for DNS", January 2015,              <https://gnunet.org/morecowbell>.   [darkreading-dns]              Lemos, R., "Got Malware? Three Signs Revealed In DNS              Traffic", May 2013,              <http://www.darkreading.com/monitoring/              got-malware-three-signs-revealed-in-dns/240154181>.Bortzmeyer              Expires December 17, 2015              [Page 14]Internet-Draft                 DNS privacy                     June 2015   [dnschanger]              Wikipedia, , "DNSchanger", November 2011,              <http://en.wikipedia.org/wiki/DNSChanger>.   [packetq]  Dot SE, , "PacketQ, a simple tool to make SQL-queries              against PCAP-files", 2011,              <https://github.com/dotse/packetq/wiki>.   [dnsmezzo]              Bortzmeyer, S., "DNSmezzo", 2009,              <http://www.dnsmezzo.net/>.   [prism]    NSA, , "PRISM", 2007, <http://en.wikipedia.org/wiki/              PRISM_%28surveillance_program%29>.   [grangeia.snooping]              Grangeia, L., "DNS Cache Snooping or Snooping the Cache              for Fun and Profit", 2004,              <http://www.msit2005.mut.ac.th/msit_media/1_2551/nete4630/              materials/20080718130017Hc.pdf>.   [ditl]     CAIDA, , "A Day in the Life of the Internet (DITL)", 2002,              <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]              Bortzmeyer, S., "Hijacking of public DNS servers in              Turkey, through routing", 2014,              <http://www.bortzmeyer.org/              dns-routing-hijack-turkey.html>.   [data-protection-directive]              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, <http://eur-lex.europa.eu/LexUriServ/              LexUriServ.do?uri=CELEX:31995L0046:EN:HTML>.   [passive-dns]              Weimer, F., "Passive DNS Replication", April 2005,              <http://www.enyo.de/fw/software/dnslogger/#2>.Bortzmeyer              Expires December 17, 2015              [Page 15]Internet-Draft                 DNS privacy                     June 2015   [tor-leak]              Tor, , "DNS leaks in Tor", 2013,              <https://trac.torproject.org/projects/tor/wiki/doc/TorFAQ#              IkeepseeingthesewarningsaboutSOCKSandDNSandinformationleak              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>.   [thomas-ditl-tcp]              Thomas, M. and D. Wessels, "An Analysis of TCP Traffic in              Root Server DITL Data"", 2014, <https://indico.dns-              oarc.net/event/20/session/2/contribution/15/material/              slides/1.pdf>.   [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>.   [aeris-dns]              Vinot, N., "[In French] Vie privee : et le DNS alors ?",              2015, <https://blog.imirhil.fr/vie-privee-et-le-dns-              alors.html>.   [herrmann-reidentification]              Herrmann, D., Gerber, C., Banse, C., and H. Federrath,              "Analyzing characteristic host access patterns for re-              identification of web user sessions", 2012,              <http://epub.uni-regensburg.de/21103/1/              Paper_PUL_nordsec_published.pdf>.Bortzmeyer              Expires December 17, 2015              [Page 16]Internet-Draft                 DNS privacy                     June 2015   [sidn-entrada]              Hesselman, C., Jansen, J., Wullink, M., Vink, K., and M.              Simon, "A privacy framework for 'DNS big data'              applications", 2014,              <https://www.sidnlabs.nl/uploads/tx_sidnpublications/              SIDN_Labs_Privacyraamwerk_Position_Paper_V1.4_ENG.pdf>.8.3.  URIs   [1] https://developers.google.com/speed/public-dns/privacyAuthor's Address   Stephane Bortzmeyer   AFNIC   1, rue Stephenson   Montigny-le-Bretonneux  78180   France   Phone: +33 1 39 30 83 46   Email: bortzmeyer+ietf@nic.fr   URI:   http://www.afnic.fr/Bortzmeyer              Expires December 17, 2015              [Page 17]