draft-ietf-dprive-problem-statement-05.txt   draft-ietf-dprive-problem-statement-06.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 May 23, 2015 Intended status: Informational June 15, 2015
Expires: November 24, 2015 Expires: December 17, 2015
DNS privacy considerations DNS privacy considerations
draft-ietf-dprive-problem-statement-05 draft-ietf-dprive-problem-statement-06
Abstract Abstract
This document describes the privacy issues associated with the use of This document describes the privacy issues associated with the use of
the DNS by Internet users. It is intended to be an analysis of the the DNS by Internet users. It is intended to be an analysis of the
present situation and does not prescribe solutions. present situation and does not prescribe solutions.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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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 November 24, 2015. This Internet-Draft will expire on December 17, 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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2.5. In the servers . . . . . . . . . . . . . . . . . . . . . 8 2.5. In the servers . . . . . . . . . . . . . . . . . . . . . 8
2.5.1. In the recursive resolvers . . . . . . . . . . . . . 9 2.5.1. In the recursive resolvers . . . . . . . . . . . . . 9
2.5.2. In the authoritative name servers . . . . . . . . . . 9 2.5.2. In the authoritative name servers . . . . . . . . . . 9
2.5.3. Rogue servers . . . . . . . . . . . . . . . . . . . . 10 2.5.3. Rogue servers . . . . . . . . . . . . . . . . . . . . 10
2.6. Re-identification and other inferences . . . . . . . . . 11 2.6. Re-identification and other inferences . . . . . . . . . 11
3. Actual "attacks" . . . . . . . . . . . . . . . . . . . . . . 11 3. Actual "attacks" . . . . . . . . . . . . . . . . . . . . . . 11
4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 12 4. Legalities . . . . . . . . . . . . . . . . . . . . . . . . . 12
5. Security considerations . . . . . . . . . . . . . . . . . . . 12 5. Security considerations . . . . . . . . . . . . . . . . . . . 12
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 12 7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . 13
8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 17 8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction 1. Introduction
This document is an analysis of the DNS privacy issues, in the spirit This document is an analysis of the DNS privacy issues, in the spirit
of section 8 of [RFC6973]. of section 8 of [RFC6973].
The Domain Name System is specified in [RFC1034] and [RFC1035] and The Domain Name System is specified in [RFC1034] and [RFC1035] and
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professionals). Almost every activity on the Internet starts with a professionals). Almost every activity on the Internet starts with a
DNS query (and often several). Its use has many privacy implications DNS query (and often several). Its use has many privacy implications
and this is an attempt at a comprehensive and accurate list. and this is an attempt at a comprehensive and accurate list.
Let us begin with a simplified reminder of how the DNS works. (See Let us begin with a simplified reminder of how the DNS works. (See
also [I-D.ietf-dnsop-dns-terminology].) A client, the stub resolver, also [I-D.ietf-dnsop-dns-terminology].) A client, the stub resolver,
issues a DNS query to a server, called the recursive resolver (also issues a DNS query to a server, called the recursive resolver (also
called caching resolver or full resolver or recursive name server). called caching resolver or full resolver or recursive name server).
Let's use the query "What are the AAAA records for www.example.com?" 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 as an example. AAAA is the QTYPE (Query Type), and www.example.com
is the QNAME (Query Name). (The description which follows assume a is the QNAME (Query Name). (The description which follows assumes a
cold cache, for instance because the server just started.) The cold cache, for instance because the server just started.) The
recursive resolver will first query the root nameservers. In most recursive resolver will first query the root nameservers. In most
cases, the root nameservers will send a referral. In this example, cases, the root nameservers will send a referral. In this example,
the referral will be to the .com nameservers. The resolver repeats the referral will be to the .com nameservers. The resolver repeats
the query to one of the .com nameservers. The .com nameservers, in the query to one of the .com nameservers. The .com nameservers, in
turn, will refer to the example.com nameservers. The example.com turn, will refer to the example.com nameservers. The example.com
nameserver will then return the answer. The root name servers, the nameserver will then return the answer. The root name servers, the
name servers of .com and the name servers of example.com are called name servers of .com and the name servers of example.com are called
authoritative name servers. It is important, when analyzing the authoritative name servers. It is important, when analyzing the
privacy issues, to remember that the question asked to all these name privacy issues, to remember that the question asked to all these name
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the DNS system itself. For instance, if the answer to a query is the DNS system itself. For instance, if the answer to a query is
a referral to a set of name servers, and the glue records are not a referral to a set of name servers, and the glue records are not
returned, the resolver will have to do additional requests to turn returned, the resolver will have to do additional requests to turn
name servers' names into IP addresses. Similarly, even if glue name servers' names into IP addresses. Similarly, even if glue
records are returned, a careful recursive server will do tertiary records are returned, a careful recursive server will do tertiary
requests 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 than stricly necessary are sent, for instance to DNS requests than stricly necessary are sent, for instance to
prefetch resources that the user may query later, or when prefetch resources that the user may query later, or when
autocompleting the URL in the address bar. It is a big privacy autocompleting the URL in the address bar. Both are a big privacy
concern since it may leak information even about non-explicit concern since they may leak information even about non-explicit
actions. For instance, just reading a local HTML page, even without actions. For instance, just reading a local HTML page, even without
selecting the hyperlinks, may trigger DNS requests. selecting the hyperlinks, may trigger DNS requests.
For privacy-related terms, we will use here the terminology of For privacy-related terms, we will use 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
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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
authentication or authorization of the client (resolver). Due to the authentication or authorization of the client (resolver). Due to the
lack of search capabilities, only a given QNAME will reveal the lack of search capabilities, only a given QNAME will reveal the
resource records associated with that name (or that name's non- resource records associated with that name (or that name's non-
existence). In other words: one needs to know what to ask for, in existence). In other words: one needs to know what to ask for, in
order to receive a response. The zone transfer QTYPE [RFC5936] is order to receive a response. The zone transfer QTYPE [RFC5936] is
often blocked or restricted to authenticated/authorized access to often blocked or restricted to authenticated/authorized access to
enforce this difference (and maybe for other, more dubious reasons). enforce this difference (and maybe for other reasons).
Another differentiation to be considered is between the DNS data Another differentiation to be considered is between the DNS data
itself and a particular transaction (i.e., a DNS name lookup). DNS itself and a particular transaction (i.e., a DNS name lookup). DNS
data and the results of a DNS query are public, within the boundaries data and the results of a DNS query are public, within the boundaries
described above, and may not have any confidentiality requirements. described above, and may not have any confidentiality requirements.
However, the same is not true of a single transaction or sequence of However, the same is not true of a single transaction or sequence of
transactions; that 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.
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resolver and the caching resolver is limited to that single resolver and the caching resolver is limited to that single
machine. machine.
The recursive resolver may be at the local network edge. For The recursive resolver may be at the local network edge. For
many/most enterprise networks and for some residential users the many/most enterprise networks and for some residential users the
caching resolver may exist on a server at the edge of the local caching resolver may exist on a server at the edge of the local
network. In this case the attack surface is the local network. network. In this case the attack surface is the local network.
Note that in large enterprise networks the DNS resolver may not be Note that in large enterprise networks the DNS resolver may not be
located at the edge of the local network but rather at the edge of located at the edge of the local network but rather at the edge of
the overall enterprise network. In this case the enterprise the overall enterprise network. In this case the enterprise
network could be thought of as similar to the IAP network network could be thought of as similar to the IAP (Internet Access
referenced below. Provider) network referenced below.
The recursive resolver can be in the IAP (Internet Access The recursive resolver can be in the IAP (Internet Access
Provider) premises. For most residential users and potentially Provider) premises. For most residential users and potentially
other networks the typical case is for the end user's computer to other networks the typical case is for the end user's computer to
be configured (typically automatically through DHCP) with the be configured (typically automatically through DHCP) with the
addresses of the DNS recursive resolvers at the IAP. The attack addresses of the DNS recursive resolvers at the IAP. The attack
surface for on-the-wire attacks is therefore from the end user surface for on-the-wire attacks is therefore from the end user
system across the local network and across the IAP network to the system across the local network and across the IAP network to the
IAP's recursive resolvers. IAP's recursive resolvers.
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recursive resolver shared by many users. recursive resolver shared by many users.
This "protection", when using a large resolver with many clients, is This "protection", when using a large resolver with many clients, is
no longer present if [I-D.ietf-dnsop-edns-client-subnet] is used no longer present if [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 50,000 queries per second. While most of it receive together around 50,000 queries per second. While most of it
is "junk" (errors on the TLD name), it gives an idea of the amount of is "junk" (errors on the TLD name), it gives an idea of the amount of
big data which pours into name servers. 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 Many domains, including TLDs, are partially hosted by third-party
servers, sometimes in a different country. The contracts between the servers, sometimes in a different country. The contracts between the
domain manager and these servers may or may not take privacy into domain manager and these servers may or may not take privacy into
account. Whatever the contract, the third-party hoster may be honest account. Whatever the contract, the third-party hoster may be honest
or not but, in any case, it will have to follow its local laws. So, or not but, in any case, it will have to follow its local laws. So,
requests to a given ccTLD may go to servers managed by organizations requests to a given ccTLD may go to servers managed by organizations
outside of the ccTLD's country. End-users may not anticipate that, outside of the ccTLD's country. End-users may not anticipate that,
when doing a security analysis. when doing a security analysis.
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example, one study [herrmann-reidentification] found that such re- example, one study [herrmann-reidentification] found that such re-
identification is possible so that "73.1% of all day-to-day links identification is possible so that "73.1% of all day-to-day links
were correctly established, i.e. user u was either re-identified were correctly established, i.e. user u was either re-identified
unambiguously (1) or the classifier correctly reported that u was not unambiguously (1) or the classifier correctly reported that u was not
present on day t+1 any more (2)". While that study related to web present on day t+1 any more (2)". While that study related to web
browsing behaviour, equally characteristic patterns may be produced browsing behaviour, equally characteristic patterns may be produced
even in machine-to-machine communications or without a user taking even in machine-to-machine communications or without a user taking
specific actions, e.g. at reboot time if a characteristic set of specific actions, e.g. at reboot time if a characteristic set of
services are accessed by the device. services are accessed by the device.
For instance, one could imagine, for an intelligence agency to
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 The IAB privacy and security programme also have a work in progress
[I-D.iab-privsec-confidentiality-threat] that considers such [I-D.iab-privsec-confidentiality-threat] that considers such
inference based attacks in a more general framework. inference based attacks in a more general framework.
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) secondary and tertiary requests (see the terminology in eavesdropper) secondary and tertiary requests (see the terminology in
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NSA) of the MORECOWBELL surveillance program [morecowbell], which NSA) of the MORECOWBELL surveillance program [morecowbell], which
uses the DNS, both passively and actively, to surreptitiously gather uses the DNS, both passively and actively, to surreptitiously gather
information about the users, is another good example showing that the information about the users, is another good example showing that the
lack of privacy protections in the DNS is actively exploited. lack of privacy protections in the DNS is actively exploited.
4. Legalities 4. Legalities
To our knowledge, there are no specific privacy laws for DNS data, in To our knowledge, there are no specific privacy laws for DNS data, in
any country. Interpreting general privacy laws like any country. Interpreting general privacy laws like
[data-protection-directive] (European Union) in the context of DNS [data-protection-directive] (European Union) in the context of DNS
traffic data is not an easy task and it seems there is no court traffic data is not an easy task and we do not know a court precedent
precedent here. An interesting analysis is [sidn-entrada]. here. An interesting analysis is [sidn-entrada].
5. Security considerations 5. Security considerations
This document is entirely about security, more precisely privacy. It This document is entirely about security, more precisely privacy. It
just lays out the problem, it does not try to set requirements (with just lays out the problem, it does not try to set requirements (with
the choices and compromises they imply), much less to define the choices and compromises they imply), much less to define
solutions. A possible document on requirments for DNS privacy is solutions. Possible solutions to the issues described here are
[I-D.hallambaker-dnse]. Possible solutions to the issues described discussed in other documents (currently too many to all be
here are discussed in other documents (currently too many to all be
mentioned), see for instance [I-D.ietf-dnsop-qname-minimisation] for mentioned), see for instance [I-D.ietf-dnsop-qname-minimisation] for
the minimisation of data, or [I-D.hzhwm-start-tls-for-dns] about the minimisation of data, or [I-D.ietf-dprive-start-tls-for-dns]
encryption. 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, Matthijs Mekking, Marcos Sanz, Tim for proofreading, to Paul Hoffman, Matthijs Mekking, Marcos Sanz, Tim
Wicinski, Francis Dupont, Allison Mankin and Warren Kumari for Wicinski, Francis Dupont, Allison Mankin and Warren Kumari for
proofreading, technical remarks, and many readability improvements. proofreading, technical remarks, and many readability improvements.
Thanks to Dan York, Suzanne Woolf, Tony Finch, Stephen Farrell, Peter Thanks to Dan York, Suzanne Woolf, Tony Finch, Stephen Farrell, Peter
Koch, Simon Josefsson and Frank Denis for good written contributions. Koch, Simon Josefsson and Frank Denis for good written contributions.
And thanks to the IESG members for the last remarks.
7. IANA considerations 7. IANA considerations
This document has no actions for IANA. This document has no actions for IANA.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities", [RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
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[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.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P. [RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, June Roberts, "Issues with IP Address Sharing", RFC 6269, June
2011. 2011.
[I-D.ietf-dnsop-edns-client-subnet] [I-D.ietf-dnsop-edns-client-subnet]
Contavalli, C., Gaast, W., Lawrence, D., and W. Kumari, Contavalli, C., Gaast, W., Lawrence, D., and W. Kumari,
"Client Subnet in DNS Requests", draft-ietf-dnsop-edns- "Client Subnet in DNS Querys", draft-ietf-dnsop-edns-
client-subnet-00 (work in progress), November 2014. client-subnet-01 (work in progress), May 2015.
[I-D.iab-privsec-confidentiality-threat] [I-D.iab-privsec-confidentiality-threat]
Barnes, R., Schneier, B., Jennings, C., Hardie, T., Barnes, R., Schneier, B., Jennings, C., Hardie, T.,
Trammell, B., Huitema, C., and D. Borkmann, Trammell, B., Huitema, C., and D. Borkmann,
"Confidentiality in the Face of Pervasive Surveillance: A "Confidentiality in the Face of Pervasive Surveillance: A
Threat Model and Problem Statement", draft-iab-privsec- Threat Model and Problem Statement", draft-iab-privsec-
confidentiality-threat-06 (work in progress), May 2015. confidentiality-threat-07 (work in progress), May 2015.
[I-D.hallambaker-dnse]
Hallam-Baker, P., "DNS Privacy and Censorship: Use Cases
and Requirements.", draft-hallambaker-dnse-02 (work in
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] [I-D.ietf-dprive-start-tls-for-dns]
Zi, Z., Zhu, L., Heidemann, J., Mankin, A., and D. Zi, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
Wessels, "Starting TLS over DNS", draft-hzhwm-start-tls- and P. Hoffman, "TLS for DNS: Initiation and Performance
for-dns-01 (work in progress), July 2014. Considerations", draft-ietf-dprive-start-tls-for-dns-00
(work in progress), May 2015.
[I-D.ietf-dnsop-qname-minimisation] [I-D.ietf-dnsop-qname-minimisation]
Bortzmeyer, S., "DNS query name minimisation to improve Bortzmeyer, S., "DNS query name minimisation to improve
privacy", draft-ietf-dnsop-qname-minimisation-02 (work in privacy", draft-ietf-dnsop-qname-minimisation-03 (work in
progress), March 2015. progress), June 2015.
[I-D.ietf-dnsop-dns-terminology] [I-D.ietf-dnsop-dns-terminology]
Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", draft-ietf-dnsop-dns-terminology-01 (work in Terminology", draft-ietf-dnsop-dns-terminology-02 (work in
progress), April 2015. progress), May 2015.
[dprive] IETF, DPRIVE., "The DPRIVE working group", March 2014,
<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-
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