draft-ietf-dprive-bcp-op-03.txt   draft-ietf-dprive-bcp-op-04.txt 
dprive S. Dickinson dprive S. Dickinson
Internet-Draft Sinodun IT Internet-Draft Sinodun IT
Intended status: Best Current Practice B. Overeinder Intended status: Best Current Practice B. Overeinder
Expires: January 9, 2020 R. van Rijswijk-Deij Expires: April 6, 2020 R. van Rijswijk-Deij
NLnet Labs NLnet Labs
A. Mankin A. Mankin
Salesforce Salesforce
July 8, 2019 October 4, 2019
Recommendations for DNS Privacy Service Operators Recommendations for DNS Privacy Service Operators
draft-ietf-dprive-bcp-op-03 draft-ietf-dprive-bcp-op-04
Abstract Abstract
This document presents operational, policy and security This document presents operational, policy and security
considerations for DNS operators who choose to offer DNS Privacy considerations for DNS recursive resolver operators who choose to
services. With these recommendations, the operator can make offer DNS Privacy services. With these recommendations, the operator
deliberate decisions regarding which services to provide, and how the can make deliberate decisions regarding which services to provide,
decisions and alternatives impact the privacy of users. and how the decisions and alternatives impact the privacy of users.
This document also presents a framework to assist writers of DNS This document also presents a framework to assist writers of a DNS
Privacy Policy and Practices Statements (analogous to DNS Security Recursive Operator Privacy Statement (analogous to DNS Security
Extensions (DNSSEC) Policies and DNSSEC Practice Statements described Extensions (DNSSEC) Policies and DNSSEC Practice Statements described
in [RFC6841]). in RFC6841).
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2020. This Internet-Draft will expire on April 6, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 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
skipping to change at page 2, line 20 skipping to change at page 2, line 20
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Privacy related documents . . . . . . . . . . . . . . . . . . 5 3. Privacy related documents . . . . . . . . . . . . . . . . . . 5
4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Recommendations for DNS privacy services . . . . . . . . . . 6 5. Recommendations for DNS privacy services . . . . . . . . . . 6
5.1. On the wire between client and server . . . . . . . . . . 7 5.1. On the wire between client and server . . . . . . . . . . 7
5.1.1. Transport recommendations . . . . . . . . . . . . . . 7 5.1.1. Transport recommendations . . . . . . . . . . . . . . 7
5.1.2. Authentication of DNS privacy services . . . . . . . 8 5.1.2. Authentication of DNS privacy services . . . . . . . 8
5.1.3. Protocol recommendations . . . . . . . . . . . . . . 9 5.1.3. Protocol recommendations . . . . . . . . . . . . . . 9
5.1.4. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 11 5.1.4. DNSSEC . . . . . . . . . . . . . . . . . . . . . . . 11
5.1.5. Availability . . . . . . . . . . . . . . . . . . . . 11 5.1.5. Availability . . . . . . . . . . . . . . . . . . . . 12
5.1.6. Service options . . . . . . . . . . . . . . . . . . . 12 5.1.6. Service options . . . . . . . . . . . . . . . . . . . 12
5.1.7. Impact on Operators . . . . . . . . . . . . . . . . . 12 5.1.7. Impact on DNS Privacy Service Operators . . . . . . . 12
5.1.8. Limitations of using a pure TLS proxy . . . . . . . . 13 5.1.8. Limitations of using a pure TLS proxy . . . . . . . . 13
5.2. Data at rest on the server . . . . . . . . . . . . . . . 13 5.2. Data at rest on the server . . . . . . . . . . . . . . . 14
5.2.1. Data handling . . . . . . . . . . . . . . . . . . . . 13 5.2.1. Data handling . . . . . . . . . . . . . . . . . . . . 14
5.2.2. Data minimization of network traffic . . . . . . . . 14 5.2.2. Data minimization of network traffic . . . . . . . . 15
5.2.3. IP address pseudonymization and anonymization methods 15 5.2.3. IP address pseudonymization and anonymization methods 16
5.2.4. Pseudonymization, anonymization or discarding of 5.2.4. Pseudonymization, anonymization or discarding of
other correlation data . . . . . . . . . . . . . . . 16 other correlation data . . . . . . . . . . . . . . . 17
5.2.5. Cache snooping . . . . . . . . . . . . . . . . . . . 17 5.2.5. Cache snooping . . . . . . . . . . . . . . . . . . . 18
5.3. Data sent onwards from the server . . . . . . . . . . . . 17 5.3. Data sent onwards from the server . . . . . . . . . . . . 18
5.3.1. Protocol recommendations . . . . . . . . . . . . . . 17 5.3.1. Protocol recommendations . . . . . . . . . . . . . . 18
5.3.2. Client query obfuscation . . . . . . . . . . . . . . 18 5.3.2. Client query obfuscation . . . . . . . . . . . . . . 19
5.3.3. Data sharing . . . . . . . . . . . . . . . . . . . . 19 5.3.3. Data sharing . . . . . . . . . . . . . . . . . . . . 20
6. DNS privacy policy and practice statement . . . . . . . . . . 19 6. DNS Recursive Operator Privacy (DROP) statement . . . . . . . 21
6.1. Recommended contents of a DPPPS . . . . . . . . . . . . . 20 6.1. Recommended contents of a DROP statement . . . . . . . . 21
6.1.1. Policy . . . . . . . . . . . . . . . . . . . . . . . 20 6.1.1. Policy . . . . . . . . . . . . . . . . . . . . . . . 21
6.1.2. Practice . . . . . . . . . . . . . . . . . . . . . . 21 6.1.2. Practice . . . . . . . . . . . . . . . . . . . . . . 22
6.2. Current policy and privacy statements . . . . . . . . . . 22 6.2. Current policy and privacy statements . . . . . . . . . . 23
6.3. Enforcement/accountability . . . . . . . . . . . . . . . 22 6.3. Enforcement/accountability . . . . . . . . . . . . . . . 24
7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 23 7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 24
8. Security considerations . . . . . . . . . . . . . . . . . . . 23 8. Security considerations . . . . . . . . . . . . . . . . . . . 24
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 23 10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 23 11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 25
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
12.1. Normative References . . . . . . . . . . . . . . . . . . 25 12.1. Normative References . . . . . . . . . . . . . . . . . . 27
12.2. Informative References . . . . . . . . . . . . . . . . . 27 12.2. Informative References . . . . . . . . . . . . . . . . . 28
12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 28 12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Appendix A. Documents . . . . . . . . . . . . . . . . . . . . . 30 Appendix A. Documents . . . . . . . . . . . . . . . . . . . . . 31
A.1. Potential increases in DNS privacy . . . . . . . . . . . 30 A.1. Potential increases in DNS privacy . . . . . . . . . . . 32
A.2. Potential decreases in DNS privacy . . . . . . . . . . . 30 A.2. Potential decreases in DNS privacy . . . . . . . . . . . 32
A.3. Related operational documents . . . . . . . . . . . . . . 31 A.3. Related operational documents . . . . . . . . . . . . . . 33
Appendix B. IP address techniques . . . . . . . . . . . . . . . 31 Appendix B. IP address techniques . . . . . . . . . . . . . . . 33
B.1. Google Analytics non-prefix filtering . . . . . . . . . . 32 B.1. Google Analytics non-prefix filtering . . . . . . . . . . 34
B.2. dnswasher . . . . . . . . . . . . . . . . . . . . . . . . 33 B.2. dnswasher . . . . . . . . . . . . . . . . . . . . . . . . 34
B.3. Prefix-preserving map . . . . . . . . . . . . . . . . . . 33 B.3. Prefix-preserving map . . . . . . . . . . . . . . . . . . 35
B.4. Cryptographic Prefix-Preserving Pseudonymisation . . . . 33 B.4. Cryptographic Prefix-Preserving Pseudonymisation . . . . 35
B.5. Top-hash Subtree-replicated Anonymisation . . . . . . . . 34 B.5. Top-hash Subtree-replicated Anonymisation . . . . . . . . 35
B.6. ipcipher . . . . . . . . . . . . . . . . . . . . . . . . 34 B.6. ipcipher . . . . . . . . . . . . . . . . . . . . . . . . 36
B.7. Bloom filters . . . . . . . . . . . . . . . . . . . . . . 34 B.7. Bloom filters . . . . . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 Appendix C. Example DROP statement . . . . . . . . . . . . . . . 36
C.1. Policy . . . . . . . . . . . . . . . . . . . . . . . . . 37
C.2. Practice . . . . . . . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
1. Introduction 1. Introduction
The Domain Name System (DNS) is at the core of the Internet; almost The Domain Name System (DNS) is at the core of the Internet; almost
every activity on the Internet starts with a DNS query (and often every activity on the Internet starts with a DNS query (and often
several). However the DNS was not originally designed with strong several). However the DNS was not originally designed with strong
security or privacy mechanisms. A number of developments have taken security or privacy mechanisms. A number of developments have taken
place in recent years which aim to increase the privacy of the DNS place in recent years which aim to increase the privacy of the DNS
system and these are now seeing some deployment. This latest system and these are now seeing some deployment. This latest
evolution of the DNS presents new challenges to operators and this evolution of the DNS presents new challenges to operators and this
document attempts to provide an overview of considerations for document attempts to provide an overview of considerations for
privacy focused DNS services. privacy focused DNS services.
In recent years there has also been an increase in the availability In recent years there has also been an increase in the availability
of "public resolvers" [I-D.ietf-dnsop-terminology-bis] which users of "public resolvers" [RFC8499] which users may prefer to use instead
may prefer to use instead of the default network resolver because of the default network resolver because they offer a specific feature
they offer a specific feature (e.g. good reachability, encrypted (e.g. good reachability, encrypted transport, strong privacy policy,
transport, strong privacy policy, filtering (or lack of), etc.). filtering (or lack of), etc.). These open resolvers have tended to
These open resolvers have tended to be at the forefront of adoption be at the forefront of adoption of privacy related enhancements but
of privacy related enhancements but it is anticipated that operators it is anticipated that operators of other resolver services will
of other resolver services will follow. follow.
Whilst protocols that encrypt DNS messages on the wire provide Whilst protocols that encrypt DNS messages on the wire provide
protection against certain attacks, the resolver operator still has protection against certain attacks, the resolver operator still has
(in principle) full visibility of the query data and transport (in principle) full visibility of the query data and transport
identifiers for each user. Therefore, a trust relationship exists. identifiers for each user. Therefore, a trust relationship exists.
The ability of the operator to provide a transparent, well The ability of the operator to provide a transparent, well
documented, and secure privacy service will likely serve as a major documented, and secure privacy service will likely serve as a major
differentiating factor for privacy conscious users if they make an differentiating factor for privacy conscious users if they make an
active selection of which resolver to use. active selection of which resolver to use.
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changes on data pertaining to the users of both Internet Service changes on data pertaining to the users of both Internet Service
Providers and public DNS resolvers is not fully understood at the Providers and public DNS resolvers is not fully understood at the
time of writing. time of writing.
This document has two main goals: This document has two main goals:
o To provide operational and policy guidance related to DNS over o To provide operational and policy guidance related to DNS over
encrypted transports and to outline recommendations for data encrypted transports and to outline recommendations for data
handling for operators of DNS privacy services. handling for operators of DNS privacy services.
o To introduce the DNS Privacy Policy and Practice Statement (DPPPS) o To introduce the DNS Recursive Operator Privacy (DROP) statement
and present a framework to assist writers of this document. A and present a framework to assist writers of this document. A
DPPPS is a document that an operator can publish outlining their DROP statement is a document that an operator can publish
operational practices and commitments with regard to privacy outlining their operational practices and commitments with regard
thereby providing a means for clients to evaluate the privacy to privacy thereby providing a means for clients to evaluate the
properties of a given DNS privacy service. In particular, the privacy properties of a given DNS privacy service. In particular,
framework identifies the elements that should be considered in the framework identifies the elements that should be considered in
formulating a DPPPS. This document does not, however, define a formulating a DROP statement. This document does not, however,
particular Policy or Practice Statement, nor does it seek to define a particular Privacy statement, nor does it seek to provide
provide legal advice or recommendations as to the contents. legal advice or recommendations as to the contents.
A desired operational impact is that all operators (both those A desired operational impact is that all operators (both those
providing resolvers within networks and those operating large anycast providing resolvers within networks and those operating large anycast
services) can demonstrate their commitment to user privacy thereby services) can demonstrate their commitment to user privacy thereby
driving all DNS resolution services to a more equitable footing. driving all DNS resolution services to a more equitable footing.
Choices for users would (in this ideal world) be driven by other Choices for users would (in this ideal world) be driven by other
factors e.g. differing security policies or minor difference in factors e.g. differing security policies or minor difference in
operator policy rather than gross disparities in privacy concerns. operator policy rather than gross disparities in privacy concerns.
Community insight [or judgment?] about operational practices can Community insight [or judgment?] about operational practices can
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Appendix A for reference. Appendix A for reference.
4. Terminology 4. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] and [RFC8174] when, and only when, they appear in all 14 [RFC2119] and [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
DNS terminology is as described in [I-D.ietf-dnsop-terminology-bis] DNS terminology is as described in [RFC8499] with one modification:
with one modification: we restate the clause in the original we restate the clause in the original definition of Privacy-enabling
definition of Privacy-enabling DNS server in [RFC8310] to include the DNS server in [RFC8310] to include the requirement that a DNS over
requirement that a DNS over (D)TLS server should also offer at least (D)TLS server should also offer at least one of the credentials
one of the credentials described in Section 8 and implement the described in Section 8 and implement the (D)TLS profile described in
(D)TLS profile described in Section 9 of [RFC8310]. Section 9 of [RFC8310].
Other Terms: Other Terms:
o DPPPS: DNS Privacy Policy and Practice Statement, see Section 6. o DROP: DNS Recursive Operator Privacy statement, see Section 6.
o DNS privacy service: The service that is offered via a privacy- o DNS privacy service: The service that is offered via a privacy-
enabling DNS server and is documented either in an informal enabling DNS server and is documented either in an informal
statement of policy and practice with regard to users privacy or a statement of policy and practice with regard to users privacy or a
formal DPPPS. formal DROP statement.
5. Recommendations for DNS privacy services 5. Recommendations for DNS privacy services
We describe two classes of threats: We describe two classes of threats:
o 'Privacy Considerations for Internet Protocols' [RFC6973] Threats o 'Privacy Considerations for Internet Protocols' [RFC6973] Threats
* Privacy terminology, threats to privacy and mitigations as * Privacy terminology, threats to privacy and mitigations as
described in Sections 3, 5 and 6 of [RFC6973]. described in Sections 3, 5 and 6 of [RFC6973].
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Mitigations: Mitigations:
DNS privacy services should ensure clients can authenticate the DNS privacy services should ensure clients can authenticate the
server. Note that this, in effect, commits the DNS privacy service server. Note that this, in effect, commits the DNS privacy service
to a public identity users will trust. to a public identity users will trust.
When using DNS-over-TLS clients that select a 'Strict Privacy' usage When using DNS-over-TLS clients that select a 'Strict Privacy' usage
profile [RFC8310] (to mitigate the threat of active attack on the profile [RFC8310] (to mitigate the threat of active attack on the
client) require the ability to authenticate the DNS server. To client) require the ability to authenticate the DNS server. To
enable this, DNS privacy services that offer DNS-over-TLS should enable this, DNS privacy services that offer DNS-over-TLS should
provide credentials in the form of either X.509 certificates or SPKI provide credentials in the form of either X.509 certificates
pinsets. [RFC5280] or SPKI pin sets [RFC8310].
When offering DoH [RFC8484], HTTPS requires authentication of the When offering DoH [RFC8484], HTTPS requires authentication of the
server as part of the protocol. server as part of the protocol.
NOTE: At this time the reference to the TLS DNSSEC chain extension
draft has been removed as it is no longer considered an active TLS WG
document.
Optimizations: Optimizations:
DNS privacy services can also consider the following capabilities/ DNS privacy services can also consider the following capabilities/
options: options:
o As recommended in [RFC8310] providing DANE TLSA records for the o As recommended in [RFC8310] providing DANE TLSA records for the
nameserver nameserver
* In particular, the service could provide TLSA records such that * In particular, the service could provide TLSA records such that
authenticating solely via the PKIX infrastructure can be authenticating solely via the PKIX infrastructure can be
avoided. avoided.
5.1.2.1. Certificate management 5.1.2.1. Certificate management
Anecdotal evidence to date highlights the management of certificates Anecdotal evidence to date highlights the management of certificates
as one of the more challenging aspects for operators of traditional as one of the more challenging aspects for operators of traditional
DNS resolvers that choose to additionally provide a DNS privacy DNS resolvers that choose to additionally provide a DNS privacy
service as management of such credentials is new to those DNS service as management of such credentials is new to those DNS
operators. operators.
It is noted that SPKI pinset management is described in [RFC7858] but It is noted that SPKI pin set management is described in [RFC7858]
that key pinning mechanisms in general have fallen out of favor but that key pinning mechanisms in general have fallen out of favor
operationally for various reasons such as the logistical overhead of operationally for various reasons such as the logistical overhead of
rolling keys. rolling keys.
DNS Privacy Threats: DNS Privacy Threats:
o Invalid certificates, resulting in an unavailable service. o Invalid certificates, resulting in an unavailable service.
o Mis-identification of a server by a client e.g. typos in URLs or o Mis-identification of a server by a client e.g. typos in URLs or
authentication domain names authentication domain names
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certificates certificates
5.1.3. Protocol recommendations 5.1.3. Protocol recommendations
5.1.3.1. DNS-over-TLS 5.1.3.1. DNS-over-TLS
DNS Privacy Threats: DNS Privacy Threats:
o Known attacks on TLS such as those described in [RFC7457] o Known attacks on TLS such as those described in [RFC7457]
o Traffic analysis, for example: Pitfalls of DNS Encryption [1] o Traffic analysis, for example: [Pitfalls-of-DNS-Encryption]
o Potential for client tracking via transport identifiers o Potential for client tracking via transport identifiers
o Blocking of well known ports (e.g. 853 for DNS-over-TLS) o Blocking of well known ports (e.g. 853 for DNS-over-TLS)
Mitigations: Mitigations:
In the case of DNS-over-TLS, TLS profiles from Section 9 and the In the case of DNS-over-TLS, TLS profiles from Section 9 and the
Countermeasures to DNS Traffic Analysis from section 11.1 of Countermeasures to DNS Traffic Analysis from section 11.1 of
[RFC8310] provide strong mitigations. This includes but is not [RFC8310] provide strong mitigations. This includes but is not
limited to: limited to:
o Adhering to [RFC7525] o Adhering to [RFC7525]
o Implementing only (D)TLS 1.2 or later as specified in [RFC8310] o Implementing only (D)TLS 1.2 or later as specified in [RFC8310]
o Implementing EDNS(0) Padding [RFC7830] using the guidelines in o Implementing EDNS(0) Padding [RFC7830] using the guidelines in
[RFC8467] [RFC8467] or a successor specification.
o Clients should not be required to use TLS session resumption o Clients should not be required to use TLS session resumption
[RFC5077] or Domain Name System (DNS) Cookies [RFC7873]. [RFC5077] with TLS 1.2 or Domain Name System (DNS) Cookies
[RFC7873].
o A DNS-over-TLS privacy service on both port 853 and 443. This o A DNS-over-TLS privacy service on both port 853 and 443. This
practice may not be possible if e.g. the operator deploys DoH on practice may not be possible if e.g. the operator deploys DoH on
the same IP address. the same IP address.
Optimizations: Optimizations:
o Concurrent processing of pipelined queries, returning responses as o Concurrent processing of pipelined queries, returning responses as
soon as available, potentially out of order as specified in soon as available, potentially out of order as specified in
[RFC7766]. This is often called 'OOOR' - out-of-order responses. [RFC7766]. This is often called 'OOOR' - out-of-order responses.
(Providing processing performance similar to HTTP multiplexing) (Providing processing performance similar to HTTP multiplexing)
o Management of TLS connections to optimize performance for clients o Management of TLS connections to optimize performance for clients
using either using either
* [RFC7766] and EDNS(0) Keepalive [RFC7828] and/or * [RFC7766] and EDNS(0) Keepalive [RFC7828] and/or
* DNS Stateful Operations [I-D.ietf-dnsop-session-signal] * DNS Stateful Operations [RFC8490]
Additional options that providers may consider: Additional options that providers may consider:
o Offer a .onion [RFC7686] service endpoint o Offer a .onion [RFC7686] service endpoint
5.1.3.2. DoH 5.1.3.2. DoH
DNS Privacy Threats: DNS Privacy Threats:
o Known attacks on TLS such as those described in [RFC7457] o Known attacks on TLS such as those described in [RFC7457]
o Traffic analysis, for example: DNS Privacy not so private: the o Traffic analysis, for example: DNS Privacy not so private: the
traffic analysis perspective [2] traffic analysis perspective [1]
o Potential for client tracking via transport identifiers o Potential for client tracking via transport identifiers
Mitigations: Mitigations:
o Clients must be able to forego the use of HTTP Cookies [RFC6265] o Clients must be able to forego the use of HTTP Cookies [RFC6265]
and still use the service and still use the service
o Clients should not be required to include any headers beyond the o Clients should not be required to include any headers beyond the
absolute minimum to obtain service from a DoH server. (See absolute minimum to obtain service from a DoH server. (See
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outage. outage.
Mitigations: Mitigations:
A DNS privacy service must be engineered for high availability. A DNS privacy service must be engineered for high availability.
Particular care should to be taken to protect DNS privacy services Particular care should to be taken to protect DNS privacy services
against denial-of-service attacks, as experience has shown that against denial-of-service attacks, as experience has shown that
unavailability of DNS resolving because of attacks is a significant unavailability of DNS resolving because of attacks is a significant
motivation for users to switch services. See, for example motivation for users to switch services. See, for example
Section IV-C of Passive Observations of a Large DNS Service: 2.5 Section IV-C of Passive Observations of a Large DNS Service: 2.5
Years in the Life of Google [3]. Years in the Life of Google [2].
Techniques such as those described in Section 10 of [RFC7766] can be Techniques such as those described in Section 10 of [RFC7766] can be
of use to operators to defend against such attacks. of use to operators to defend against such attacks.
5.1.6. Service options 5.1.6. Service options
DNS Privacy Threats: DNS Privacy Threats:
o Unfairly disadvantaging users of the privacy service with respect o Unfairly disadvantaging users of the privacy service with respect
to the services available. This could force the user to switch to the services available. This could force the user to switch
providers, fallback to cleartext or accept no DNS service for the providers, fallback to cleartext or accept no DNS service for the
outage. outage.
Mitigations: Mitigations:
A DNS privacy service should deliver the same level of service as A DNS privacy service should deliver the same level of service as
offered on un-encrypted channels in terms of such options as offered on un-encrypted channels in terms of such options as
filtering (or lack thereof), DNSSEC validation, etc. filtering (or lack thereof), DNSSEC validation, etc.
5.1.7. Impact on Operators 5.1.7. Impact on DNS Privacy Service Operators
DNS Privacy Threats: DNS Privacy Threats:
o Increased use of encryption impacts operator ability to manage o Increased use of encryption impacts operator ability to manage
their network [RFC8404] their network [RFC8404]
Many monitoring solutions for DNS traffic rely on the plain text Many monitoring solutions for DNS traffic rely on the plain text
nature of this traffic and work by intercepting traffic on the wire, nature of this traffic and work by intercepting traffic on the wire,
either using a separate view on the connection between clients and either using a separate view on the connection between clients and
the resolver, or as a separate process on the resolver system that the resolver, or as a separate process on the resolver system that
inspects network traffic. Such solutions will no longer function inspects network traffic. Such solutions will no longer function
when traffic between clients and resolvers is encrypted. There are, when traffic between clients and resolvers is encrypted. There are,
however, legitimate reasons for operators to inspect DNS traffic, however, legitimate reasons for operators to inspect DNS traffic,
e.g. to monitor for network security threats. Operators may e.g. to monitor for network security threats. Operators may
therefore need to invest in alternative means of monitoring that therefore need to invest in alternative means of monitoring that
relies on either the resolver software directly, or exporting DNS relies on either the resolver software directly, or exporting DNS
traffic from the resolver using e.g. dnstap [4]. traffic from the resolver using e.g. dnstap [3].
Optimization: Optimization:
When implementing alternative means for traffic monitoring, operators When implementing alternative means for traffic monitoring, operators
of a DNS privacy service should consider using privacy conscious of a DNS privacy service should consider using privacy conscious
means to do so (see, for example, the discussion on the use of Bloom means to do so (see, for example, the discussion on the use of Bloom
Filters in the #documents appendix in this document). Filters in the #documents appendix in this document).
5.1.8. Limitations of using a pure TLS proxy 5.1.8. Limitations of using a pure TLS proxy
skipping to change at page 13, line 23 skipping to change at page 13, line 31
o Limited ability to manage or monitor incoming connections using o Limited ability to manage or monitor incoming connections using
DNS specific techniques DNS specific techniques
o Misconfiguration of the target server could lead to data leakage o Misconfiguration of the target server could lead to data leakage
if the proxy to target server path is not encrypted. if the proxy to target server path is not encrypted.
Optimization: Optimization:
Some operators may choose to implement DNS-over-TLS using a TLS proxy Some operators may choose to implement DNS-over-TLS using a TLS proxy
(e.g. nginx [5], haproxy [6] or stunnel [7]) in front of a DNS (e.g. nginx [4], haproxy [5] or stunnel [6]) in front of a DNS
nameserver because of proven robustness and capacity when handling nameserver because of proven robustness and capacity when handling
large numbers of client connections, load balancing capabilities and large numbers of client connections, load balancing capabilities and
good tooling. Currently, however, because such proxies typically good tooling. Currently, however, because such proxies typically
have no specific handling of DNS as a protocol over TLS or DTLS using have no specific handling of DNS as a protocol over TLS or DTLS using
them can restrict traffic management at the proxy layer and at the them can restrict traffic management at the proxy layer and at the
DNS server. For example, all traffic received by a nameserver behind DNS server. For example, all traffic received by a nameserver behind
such a proxy will appear to originate from the proxy and DNS such a proxy will appear to originate from the proxy and DNS
techniques such as ACLs, RRL or DNS64 will be hard or impossible to techniques such as ACLs, RRL or DNS64 will be hard or impossible to
implement in the nameserver. implement in the nameserver.
Operators may choose to use a DNS aware proxy such as dnsdist [8] Operators may choose to use a DNS aware proxy such as dnsdist [7]
which offer custom options (similar to that proposed in which offer custom options (similar to that proposed in
[I-D.bellis-dnsop-xpf]) to add source information to packets to [I-D.bellis-dnsop-xpf]) to add source information to packets to
address this shortcoming. It should be noted that such options address this shortcoming. It should be noted that such options
potentially significantly increase the leaked information in the potentially significantly increase the leaked information in the
event of a misconfiguration. event of a misconfiguration.
5.2. Data at rest on the server 5.2. Data at rest on the server
5.2.1. Data handling 5.2.1. Data handling
skipping to change at page 14, line 37 skipping to change at page 14, line 50
o The retention period of DNS traffic logs should be only those o The retention period of DNS traffic logs should be only those
required to sustain operation of the service and, to the extent required to sustain operation of the service and, to the extent
that such exists, meet regulatory requirements. that such exists, meet regulatory requirements.
o DNS privacy services should not track users except for the o DNS privacy services should not track users except for the
particular purpose of detecting and remedying technically particular purpose of detecting and remedying technically
malicious (e.g. DoS) or anomalous use of the service. malicious (e.g. DoS) or anomalous use of the service.
o Data access should be minimized to only those personnel who o Data access should be minimized to only those personnel who
require access to perform operational duties. require access to perform operational duties. It should also be
limited to anonymized or pseudonymized data were operationally
feasible, with access to full logs (if any are held) only
permitted when necessary.
Optimizations: Optimizations:
o Consider use of full disk encryption for logs and data capture o Consider use of full disk encryption for logs and data capture
storage. storage.
5.2.2. Data minimization of network traffic 5.2.2. Data minimization of network traffic
Data minimization refers to collecting, using, disclosing, and Data minimization refers to collecting, using, disclosing, and
storing the minimal data necessary to perform a task, and this can be storing the minimal data necessary to perform a task, and this can be
skipping to change at page 15, line 29 skipping to change at page 15, line 44
the decade. Developments over the last decade have been both a the decade. Developments over the last decade have been both a
blessing and a curse; the large increase in size between an IPv4 and blessing and a curse; the large increase in size between an IPv4 and
an IPv6 address, for example, renders some techniques impractical, an IPv6 address, for example, renders some techniques impractical,
but also makes available a much larger amount of input entropy, the but also makes available a much larger amount of input entropy, the
better to resist brute force re-identification attacks that have better to resist brute force re-identification attacks that have
grown in practicality over the period. grown in practicality over the period.
Techniques employed may be broadly categorized as either Techniques employed may be broadly categorized as either
anonymization or pseudonymization. The following discussion uses the anonymization or pseudonymization. The following discussion uses the
definitions from [RFC6973] Section 3, with additional observations definitions from [RFC6973] Section 3, with additional observations
from van Dijkhuizen et al. [9] from van Dijkhuizen et al. [8]
o Anonymization. To enable anonymity of an individual, there must o Anonymization. To enable anonymity of an individual, there must
exist a set of individuals that appear to have the same exist a set of individuals that appear to have the same
attribute(s) as the individual. To the attacker or the observer, attribute(s) as the individual. To the attacker or the observer,
these individuals must appear indistinguishable from each other. these individuals must appear indistinguishable from each other.
o Pseudonymization. The true identity is deterministically replaced o Pseudonymization. The true identity is deterministically replaced
with an alternate identity (a pseudonym). When the with an alternate identity (a pseudonym). When the
pseudonymization schema is known, the process can be reversed, so pseudonymization schema is known, the process can be reversed, so
the original identity becomes known again. the original identity becomes known again.
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5.2.3. IP address pseudonymization and anonymization methods 5.2.3. IP address pseudonymization and anonymization methods
As [I-D.bortzmeyer-dprive-rfc7626-bis] makes clear, the big privacy As [I-D.bortzmeyer-dprive-rfc7626-bis] makes clear, the big privacy
risk in DNS is connecting DNS queries to an individual and the major risk in DNS is connecting DNS queries to an individual and the major
vector for this in DNS traffic is the client IP address. vector for this in DNS traffic is the client IP address.
There is active discussion in the space of effective pseudonymization There is active discussion in the space of effective pseudonymization
of IP addresses in DNS traffic logs, however there seems to be no of IP addresses in DNS traffic logs, however there seems to be no
single solution that is widely recognized as suitable for all or most single solution that is widely recognized as suitable for all or most
use cases. There are also as yet no standards for this that are use cases. There are also as yet no standards for this that are
unencumbered by patents. The following table presents a high level unencumbered by patents.
comparison of various techniques employed or under development today
and classifies them according to categorization of technique and The following table presents a high level comparison of various
other properties. The list of techniques includes the main techniques employed or under development today and classifies them
techniques in current use, but does not claim to be comprehensive. according to categorization of technique and other properties.
Appendix B provides a more detailed survey of these techniques and Appendix B provides a more detailed survey of these techniques and
definitions for the categories and properties listed below. definitions for the categories and properties listed below. The list
of techniques includes the main techniques in current use, but does
not claim to be comprehensive.
Figure showing comparison of IP address techniques (SVG) [10] +---------------------------+----+---+----+---+----+---+---+
| Categorisation/Property | GA | d | TC | C | TS | i | B |
+---------------------------+----+---+----+---+----+---+---+
| Anonymisation | X | X | X | | | | X |
| Pseudoanonymisation | | | | X | X | X | |
| Format preserving | X | X | X | X | X | X | |
| Prefix preserving | | | X | X | X | | |
| Replacement | | | X | | | | |
| Filtering | X | | | | | | |
| Generalisation | | | | | | | X |
| Enumeration | | X | | | | | |
| Reordering/Shuffling | | | X | | | | |
| Random substitution | | | X | | | | |
| Crytpographic permutation | | | | X | X | X | |
| IPv6 issues | | | | | X | | |
| CPU intensive | | | | X | | | |
| Memory intensive | | | X | | | | |
| Security concerns | | | | | | X | |
+---------------------------+----+---+----+---+----+---+---+
Table 1: Classification of techniques
GA = Google Analytics, d = dnswasher, TC = TCPdpriv, C = CryptoPAn,
TS = TSA, i = ipcipher, B = Bloom filter
The choice of which method to use for a particular application will The choice of which method to use for a particular application will
depend on the requirements of that application and consideration of depend on the requirements of that application and consideration of
the threat analysis of the particular situation. the threat analysis of the particular situation.
For example, a common goal is that distributed packet captures must For example, a common goal is that distributed packet captures must
be in an existing data format such as PCAP [pcap] or C-DNS be in an existing data format such as PCAP [pcap] or C-DNS [RFC8618]
[I-D.ietf-dnsop-dns-capture-format] that can be used as input to that can be used as input to existing analysis tools. In that case,
existing analysis tools. In that case, use of a format-preserving use of a format-preserving technique is essential. This, though, is
technique is essential. This, though, is not cost-free - several not cost-free - several authors (e.g. Brenker & Arnes [9]) have
authors (e.g. Brenker & Arnes [11]) have observed that, as the observed that, as the entropy in an IPv4 address is limited, given a
entropy in an IPv4 address is limited, given a de-identified log from de-identified log from a target, if an attacker is capable of
a target, if an attacker is capable of ensuring packets are captured ensuring packets are captured by the target and the attacker can send
by the target and the attacker can send forged traffic with arbitrary forged traffic with arbitrary source and destination addresses to
source and destination addresses to that target, any format- that target, any format-preserving pseudonymization is vulnerable to
preserving pseudonymization is vulnerable to an attack along the an attack along the lines of a cryptographic chosen plaintext attack.
lines of a cryptographic chosen plaintext attack.
5.2.4. Pseudonymization, anonymization or discarding of other 5.2.4. Pseudonymization, anonymization or discarding of other
correlation data correlation data
DNS Privacy Threats: DNS Privacy Threats:
o IP TTL/Hoplimit can be used to fingerprint client OS o IP TTL/Hoplimit can be used to fingerprint client OS
o TLS version/Cipher suite combinations can be used to fingerprint o TLS version/Cipher suite combinations can be used to fingerprint
the client application or TLS library the client application or TLS library
o Tracking of TCP sessions o Tracking of TCP sessions
o Tracking of TLS sessions and session resumption mechanisms o Tracking of TLS sessions and session resumption mechanisms
o Resolvers _might_ receive client identifiers e.g. MAC addresses o Resolvers _might_ receive client identifiers e.g. MAC addresses
in EDNS(0) options - some CPE devices are known to add them. in EDNS(0) options - some CPE devices are known to add them.
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5.2.5. Cache snooping 5.2.5. Cache snooping
[RFC6973] Threats: [RFC6973] Threats:
o Surveillance: o Surveillance:
* Profiling of client queries by malicious third parties * Profiling of client queries by malicious third parties
Mitigations: Mitigations:
o See ISC Knowledge database on cache snooping [12] for an example o See ISC Knowledge database on cache snooping [10] for an example
discussion on defending against cache snooping discussion on defending against cache snooping
5.3. Data sent onwards from the server 5.3. Data sent onwards from the server
In this section we consider both data sent on the wire in upstream In this section we consider both data sent on the wire in upstream
queries and data shared with third parties. queries and data shared with third parties.
5.3.1. Protocol recommendations 5.3.1. Protocol recommendations
[RFC6973] Threats: [RFC6973] Threats:
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o Surveillance: o Surveillance:
* Transmission of identifying data upstream. * Transmission of identifying data upstream.
Mitigations: Mitigations:
As specified in [RFC8310] for DNS-over-TLS but applicable to any DNS As specified in [RFC8310] for DNS-over-TLS but applicable to any DNS
Privacy services the server should: Privacy services the server should:
o Implement QNAME minimization [RFC7816] o Implement QNAME minimization [RFC7816]
o Honor a SOURCE PREFIX-LENGTH set to 0 in a query containing the o Honor a SOURCE PREFIX-LENGTH set to 0 in a query containing the
EDNS(0) Client Subnet (ECS) option and not send an ECS option in EDNS(0) Client Subnet (ECS) option and not send an ECS option in
upstream queries. upstream queries.
Optimizations: Optimizations:
o The server should either o The server should either
* not use the ECS option in upstream queries at all, or * not use the ECS option in upstream queries at all, or
* offer alternative services, one that sends ECS and one that * offer alternative services, one that sends ECS and one that
does not. does not.
If operators do offer a service that sends the ECS options upstream If operators do offer a service that sends the ECS options upstream
they should use the shortest prefix that is operationally feasible they should use the shortest prefix that is operationally feasible
(NOTE: the authors believe they will be able to add a reference for and ideally use a policy of whitelisting upstream servers to send ECS
advice here soon) and ideally use a policy of whitelisting upstream to in order to minimize data leakage. Operators should make clear in
servers to send ECS to in order to minimize data leakage. Operators any policy statement what prefix length they actually send and the
should make clear in any policy statement what prefix length they specific policy used.
actually send and the specific policy used.
Whitelisting has the benefit that not only does the operator know Whitelisting has the benefit that not only does the operator know
which upstream servers can use ECS but also allows the operator to which upstream servers can use ECS but also allows the operator to
decide which upstream servers apply privacy policies that the decide which upstream servers apply privacy policies that the
operator is happy with. However some operators consider whitelisting operator is happy with. However some operators consider whitelisting
to incur significant operational overhead compared to dynamic to incur significant operational overhead compared to dynamic
detection of ECS on authoritative servers. detection of ECS on authoritative servers.
Additional options: Additional options:
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consent). consent).
Even when consent is granted operators should employ data Even when consent is granted operators should employ data
minimization techniques such as those described in Section 5.2.1 if minimization techniques such as those described in Section 5.2.1 if
data is shared with third-parties. data is shared with third-parties.
Operators should consider including specific guidelines for the Operators should consider including specific guidelines for the
collection of aggregated and/or anonymized data for research collection of aggregated and/or anonymized data for research
purposes, within or outside of their own organization. This can purposes, within or outside of their own organization. This can
benefit not only the operator (through inclusion in novel research) benefit not only the operator (through inclusion in novel research)
but also the wider Internet community. See SURFnet's policy [13] on but also the wider Internet community. See SURFnet's policy [11] on
data sharing for research as an example. data sharing for research as an example.
6. DNS privacy policy and practice statement 6. DNS Recursive Operator Privacy (DROP) statement
6.1. Recommended contents of a DPPPS
6.1.1. Policy The following section outlines the recommended contents of a DROP
statement an operator might choose to publish. An example statement
for a specific scenario is provided for guidance only in Appendix C.
1. Make an explicit statement that IP addressses are treated as PII 6.1. Recommended contents of a DROP statement
2. State if IP addresses are being logged 6.1.1. Policy
3. Specify clearly what data (including whether it is aggregated, 1. Treatment of IP addresses. Make an explicit statement that IP
pseudonymized or anonymized and the conditions of data transfer) addresses are treated as PII.
is:
2. Data collection and sharing. Specify clearly what data
(including IP addresses) is:
* Collected and retained by the operator, and for what period it * Collected and retained by the operator, and for what period it
is retained is retained
* Shared with partners * Shared with partners
* Shared, sold or rented to third-parties * Shared, sold or rented to third-parties
4. Specify any exceptions to the above, for example technically and in each case whether it is aggregated, pseudonymized or
malicious or anomalous behavior anonymized and the conditions of data transfer.
5. Declare any partners, third-party affiliations or sources of 3. Exceptions. Specify any exceptions to the above, for example
funding technically malicious or anomalous behavior.
6. Whether user DNS data is correlated or combined with any other 4. Associated entities. Declare any partners, third-party
personal information held by the operator affiliations or sources of funding.
7. Result filtering. This section should explain whether the 5. Correlation. Whether user DNS data is correlated or combined
with any other personal information held by the operator.
6. Result filtering. This section should explain whether the
operator filters, edits or alters in any way the replies that it operator filters, edits or alters in any way the replies that it
receives from the authoritative servers for each DNS zone, before receives from the authoritative servers for each DNS zone, before
forwarding them to the clients. For each category listed below, forwarding them to the clients. For each category listed below,
the operator should also specify how the filtering lists are the operator should also specify how the filtering lists are
created and managed, whether it employs any third-party sources created and managed, whether it employs any third-party sources
for such lists, and which ones. for such lists, and which ones.
* Specify if any replies are being filtered out or altered for * Specify if any replies are being filtered out or altered for
network and computer security reasons (e.g. preventing network and computer security reasons (e.g. preventing
connections to malware-spreading websites or botnet control connections to malware-spreading websites or botnet control
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operator aiming at reducing potential legal risks operator aiming at reducing potential legal risks
* Specify if any replies are being filtered out or altered for * Specify if any replies are being filtered out or altered for
any other reason, including commercial ones any other reason, including commercial ones
6.1.2. Practice 6.1.2. Practice
This section should explain the current operational practices of the This section should explain the current operational practices of the
service. service.
1. Specify any temporary or permanent deviations from the policy for 1. Deviations. Specify any temporary or permanent deviations from
operational reasons the policy for operational reasons.
2. With reference to section Section 5 provide specific details of 2. Client facing capabilities. With reference to section Section 5
which capabilities are provided on which client facing addresses provide specific details of which capabilities are provided on
and ports which client facing addresses and ports:
3. Specify the authentication name to be used (if any) and if TLSA 1. For DoT, specify the authentication name to be used (if any)
records are published (including options used in the TLSA and if TLSA records are published (including options used in
records) the TLSA records)
4. Specify the SPKI pinsets to be used (if any) and policy for 2. For DoT, specify the SPKI pin sets to be used (if any) and
rolling keys policy for rolling keys
5. Provide contact/support information for the service 3. Upstream capabilities. With reference to section Section 5.3
provide specific details of which capabilities are provided
upstream for data sent to authoritative servers.
6. Jurisdiction. This section should communicate the applicable 4. Support. Provide contact/support information for the service.
5. Jurisdiction. This section should communicate the applicable
jurisdictions and law enforcement regimes under which the service jurisdictions and law enforcement regimes under which the service
is being provided. is being provided.
* Specify the entity or entities that will control the data and 1. Specify the operator entity or entities that will control the
be responsible for their treatment, and their legal place of data and be responsible for their treatment, and their legal
business place of business.
* Specify, either directly or by pointing to the applicable
privacy policy, the relevant privacy laws that apply to the
treatment of the data, the rights that users enjoy in regard
to their own personal information that is treated by the
service, and how they can contact the operator to enforce them
* Specify the countries in which the servers handling the DNS
requests and the data are located (if the operator applies a
geolocation policy so that requests from certain countries are
only served by certain servers, this should be specified as
well)
* Specify whether the operator has any agreement in place with
law enforcement agencies, or other public and private parties
dealing with security and intelligence, to give them access to
the servers and/or to the data
7. Describe how consent is obtained from the user of the DNS privacy 2. Specify, either directly or by pointing to the applicable
service differentiating privacy policy, the relevant privacy laws that apply to the
treatment of the data, the rights that users enjoy in regard
to their own personal information that is treated by the
service, and how they can contact the operator to enforce
them.
* Uninformed users for whom this trust relationship is implicit 3. Additionally specify the countries in which the servers
handling the DNS requests and the data are located (if the
operator applies a geolocation policy so that requests from
certain countries are only served by certain servers, this
should be specified as well).
* Privacy-conscious users, that make an explicit trust choice 4. Specify whether the operator has any agreement in place with
law enforcement agencies, or other public and private parties
dealing with security and intelligence, to give them access
to the servers and/or to the data.
(this may prove relevant in the context of e.g. the GDPR as it 6. Consent. For any activity which is documented in this statement
relates to consent) as 'requiring consent' before being performed, describe the full
process of what you as an operator consider 'obtaining consent',
distinguishing clearly between any implicit and explicit consent
models. Additionally, state if these processes are considered by
you the operator to conform to any relevant legislation (this may
prove relevant in the context of e.g. the GDPR as it relates to
consent).
6.2. Current policy and privacy statements 6.2. Current policy and privacy statements
A tabular comparison of existing policy and privacy statements from A tabular comparison of existing policy and privacy statements from
various DNS Privacy service operators based on the proposed DPPPS various DNS Privacy service operators based loosely on the proposed
structure can be found on dnsprivacy.org [14]. DROP structure can be found on dnsprivacy.org [12].
We note that the existing set of policies vary widely in style, We note that the existing set of policies vary widely in style,
content and detail and it is not uncommon for the full text for a content and detail and it is not uncommon for the full text for a
given operator to equate to more than 10 pages of moderate font sized given operator to equate to more than 10 pages of moderate font sized
A4 text. It is a non-trivial task today for a user to extract a A4 text. It is a non-trivial task today for a user to extract a
meaningful overview of the different services on offer. meaningful overview of the different services on offer.
It is also noted that Mozilla have published a Security/DoH-resolver It is also noted that Mozilla have published a Security/DoH-resolver
policy [15], which describes the minimum set of policy requirements policy [13], which describes the minimum set of policy requirements
that a party must satisfy to be considered as a potential partner for that a party must satisfy to be considered as a potential partner for
Mozilla's Trusted Recursive Resolver (TRR) program. Mozilla's Trusted Recursive Resolver (TRR) program.
6.3. Enforcement/accountability 6.3. Enforcement/accountability
Transparency reports may help with building user trust that operators Transparency reports may help with building user trust that operators
adhere to their policies and practices. adhere to their policies and practices.
Independent monitoring or analysis could be performed where possible Independent monitoring or analysis could be performed where possible
of: of:
o ECS, QNAME minimization, EDNS(0) padding, etc. o ECS, QNAME minimization, EDNS(0) padding, etc.
o Filtering o Filtering
o Uptime o Uptime
This is by analogy with e.g. several TLS or website analysis tools This is by analogy with e.g. several TLS or website analysis tools
that are currently available e.g. SSL Labs [16] or Internet.nl [17]. that are currently available e.g. SSL Labs [14] or Internet.nl [15].
Additionally operators could choose to engage the services of a third Additionally operators could choose to engage the services of a third
party auditor to verify their compliance with their published DPPPS. party auditor to verify their compliance with their published DROP
statement.
7. IANA considerations 7. IANA considerations
None None
8. Security considerations 8. Security considerations
Security considerations for DNS-over-TCP are given in [RFC7766], many Security considerations for DNS-over-TCP are given in [RFC7766], many
of which are generally applicable to session based DNS. of which are generally applicable to session based DNS.
TODO: e.g. New issues for DoS defence, server admin policies
9. Acknowledgements 9. Acknowledgements
Many thanks to Amelia Andersdotter for a very thorough review of the Many thanks to Amelia Andersdotter for a very thorough review of the
first draft of this document. Thanks to John Todd for discussions on first draft of this document and Stephen Farrell for a thorough
this topic, and to Stephane Bortzmeyer, Puneet Sood and Vittorio review at WGLC and for suggesting the inclusion of an example DROP
Bertola for review. Thanks to Daniel Kahn Gillmor, Barry Green, Paul statement. Thanks to John Todd for discussions on this topic, and to
Hoffman, Dan York, John Reed, Lorenzo Colitti for comments at the Stephane Bortzmeyer, Puneet Sood and Vittorio Bertola for review.
mic. Thanks to Loganaden Velvindron for useful updates to the text. Thanks to Daniel Kahn Gillmor, Barry Green, Paul Hoffman, Dan York,
John Reed, Lorenzo Colitti for comments at the mic. Thanks to
Loganaden Velvindron for useful updates to the text.
Sara Dickinson thanks the Open Technology Fund for a grant to support Sara Dickinson thanks the Open Technology Fund for a grant to support
the work on this document. the work on this document.
10. Contributors 10. Contributors
The below individuals contributed significantly to the document: The below individuals contributed significantly to the document:
John Dickinson John Dickinson
Sinodun Internet Technologies Sinodun Internet Technologies
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Jim Hague Jim Hague
Sinodun Internet Technologies Sinodun Internet Technologies
Magdalen Centre Magdalen Centre
Oxford Science Park Oxford Science Park
Oxford OX4 4GA Oxford OX4 4GA
United Kingdom United Kingdom
11. Changelog 11. Changelog
draft-ietf-dprive-bcp-op-04
o Change DPPPS to DROP (DNS Recursive Operator Privacy) statement
o Update structure of DROP slightly
o Add example DROP statement
o Add text about restricting access to full logs
o Move table in section 5.2.3 from SVG to inline table
o Fix many editorial and reference nits
draft-ietf-dprive-bcp-op-03 draft-ietf-dprive-bcp-op-03
o Add paragraph about operational impact o Add paragraph about operational impact
o Move DNSSEC requirement out of the Appendix into main text as a o Move DNSSEC requirement out of the Appendix into main text as a
privacy threat that should be mitigated privacy threat that should be mitigated
o Add TLS version/Cipher suite as tracking threat o Add TLS version/Cipher suite as tracking threat
o Add reference to Mozilla TRR policy o Add reference to Mozilla TRR policy
o Remove several TODOs and QUESTIONS. o Remove several TODOs and QUESTIONS.
draft-ietf-dprive-bcp-op-02 draft-ietf-dprive-bcp-op-02
skipping to change at page 25, line 21 skipping to change at page 27, line 9
draft-ietf-dprive-bcp-op-00 draft-ietf-dprive-bcp-op-00
o Initial commit of re-named document after adoption to replace o Initial commit of re-named document after adoption to replace
draft-dickinson-dprive-bcp-op-01 draft-dickinson-dprive-bcp-op-01
12. References 12. References
12.1. Normative References 12.1. Normative References
[I-D.ietf-dnsop-session-signal]
Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
Lemon, T., and T. Pusateri, "DNS Stateful Operations",
draft-ietf-dnsop-session-signal-20 (work in progress),
December 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>. editor.org/info/rfc2119>.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <https://www.rfc-editor.org/info/rfc5077>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011, <https://www.rfc- DOI 10.17487/RFC6265, April 2011, <https://www.rfc-
editor.org/info/rfc6265>. editor.org/info/rfc6265>.
[RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
Morris, J., Hansen, M., and R. Smith, "Privacy Morris, J., Hansen, M., and R. Smith, "Privacy
Considerations for Internet Protocols", RFC 6973, Considerations for Internet Protocols", RFC 6973,
DOI 10.17487/RFC6973, July 2013, <https://www.rfc- DOI 10.17487/RFC6973, July 2013, <https://www.rfc-
editor.org/info/rfc6973>. editor.org/info/rfc6973>.
skipping to change at page 27, line 24 skipping to change at page 28, line 47
[I-D.bellis-dnsop-xpf] [I-D.bellis-dnsop-xpf]
Bellis, R., Dijk, P., and R. Gacogne, "DNS X-Proxied-For", Bellis, R., Dijk, P., and R. Gacogne, "DNS X-Proxied-For",
draft-bellis-dnsop-xpf-04 (work in progress), March 2018. draft-bellis-dnsop-xpf-04 (work in progress), March 2018.
[I-D.bortzmeyer-dprive-rfc7626-bis] [I-D.bortzmeyer-dprive-rfc7626-bis]
Bortzmeyer, S. and S. Dickinson, "DNS Privacy Bortzmeyer, S. and S. Dickinson, "DNS Privacy
Considerations", draft-bortzmeyer-dprive-rfc7626-bis-02 Considerations", draft-bortzmeyer-dprive-rfc7626-bis-02
(work in progress), January 2019. (work in progress), January 2019.
[I-D.ietf-dnsop-dns-capture-format]
Dickinson, J., Hague, J., Dickinson, S., Manderson, T.,
and J. Bond, "C-DNS: A DNS Packet Capture Format", draft-
ietf-dnsop-dns-capture-format-10 (work in progress),
December 2018.
[I-D.ietf-dnsop-dns-tcp-requirements] [I-D.ietf-dnsop-dns-tcp-requirements]
Kristoff, J. and D. Wessels, "DNS Transport over TCP - Kristoff, J. and D. Wessels, "DNS Transport over TCP -
Operational Requirements", draft-ietf-dnsop-dns-tcp- Operational Requirements", draft-ietf-dnsop-dns-tcp-
requirements-04 (work in progress), June 2019. requirements-04 (work in progress), June 2019.
[I-D.ietf-dnsop-terminology-bis]
Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", draft-ietf-dnsop-terminology-bis-14 (work in
progress), September 2018.
[I-D.ietf-httpbis-bcp56bis] [I-D.ietf-httpbis-bcp56bis]
Nottingham, M., "Building Protocols with HTTP", draft- Nottingham, M., "Building Protocols with HTTP", draft-
ietf-httpbis-bcp56bis-08 (work in progress), November ietf-httpbis-bcp56bis-08 (work in progress), November
2018. 2018.
[pcap] tcpdump.org, "PCAP", 2016, <http://www.tcpdump.org/>. [pcap] tcpdump.org, "PCAP", 2016, <http://www.tcpdump.org/>.
[Pitfalls-of-DNS-Encryption] [Pitfalls-of-DNS-Encryption]
Shulman, H., "Pretty Bad Privacy: Pitfalls of DNS Shulman, H., "Pretty Bad Privacy: Pitfalls of DNS
Encryption", 2014, <https://www.ietf.org/mail-archive/web/ Encryption", 2014, <https://dl.acm.org/
dns-privacy/current/pdfWqAIUmEl47.pdf>. citation.cfm?id=2665959>.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005, RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>. <https://www.rfc-editor.org/info/rfc4033>.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <https://www.rfc-editor.org/info/rfc5077>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC6235] Boschi, E. and B. Trammell, "IP Flow Anonymization [RFC6235] Boschi, E. and B. Trammell, "IP Flow Anonymization
Support", RFC 6235, DOI 10.17487/RFC6235, May 2011, Support", RFC 6235, DOI 10.17487/RFC6235, May 2011,
<https://www.rfc-editor.org/info/rfc6235>. <https://www.rfc-editor.org/info/rfc6235>.
[RFC6841] Ljunggren, F., Eklund Lowinder, AM., and T. Okubo, "A
Framework for DNSSEC Policies and DNSSEC Practice
Statements", RFC 6841, DOI 10.17487/RFC6841, January 2013,
<https://www.rfc-editor.org/info/rfc6841>.
[RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing [RFC7457] Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
Known Attacks on Transport Layer Security (TLS) and Known Attacks on Transport Layer Security (TLS) and
Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457, Datagram TLS (DTLS)", RFC 7457, DOI 10.17487/RFC7457,
February 2015, <https://www.rfc-editor.org/info/rfc7457>. February 2015, <https://www.rfc-editor.org/info/rfc7457>.
[RFC7686] Appelbaum, J. and A. Muffett, "The ".onion" Special-Use [RFC7686] Appelbaum, J. and A. Muffett, "The ".onion" Special-Use
Domain Name", RFC 7686, DOI 10.17487/RFC7686, October Domain Name", RFC 7686, DOI 10.17487/RFC7686, October
2015, <https://www.rfc-editor.org/info/rfc7686>. 2015, <https://www.rfc-editor.org/info/rfc7686>.
[RFC7706] Kumari, W. and P. Hoffman, "Decreasing Access Time to Root [RFC7706] Kumari, W. and P. Hoffman, "Decreasing Access Time to Root
skipping to change at page 28, line 42 skipping to change at page 30, line 14
[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram [RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
Transport Layer Security (DTLS)", RFC 8094, Transport Layer Security (DTLS)", RFC 8094,
DOI 10.17487/RFC8094, February 2017, <https://www.rfc- DOI 10.17487/RFC8094, February 2017, <https://www.rfc-
editor.org/info/rfc8094>. editor.org/info/rfc8094>.
[RFC8198] Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of [RFC8198] Fujiwara, K., Kato, A., and W. Kumari, "Aggressive Use of
DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198, DNSSEC-Validated Cache", RFC 8198, DOI 10.17487/RFC8198,
July 2017, <https://www.rfc-editor.org/info/rfc8198>. July 2017, <https://www.rfc-editor.org/info/rfc8198>.
12.3. URIs [RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
Lemon, T., and T. Pusateri, "DNS Stateful Operations",
RFC 8490, DOI 10.17487/RFC8490, March 2019,
<https://www.rfc-editor.org/info/rfc8490>.
[1] https://www.ietf.org/mail-archive/web/dns-privacy/current/ [RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
pdfWqAIUmEl47.pdf Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/info/rfc8499>.
[2] https://petsymposium.org/2018/files/hotpets/4-siby.pdf [RFC8618] Dickinson, J., Hague, J., Dickinson, S., Manderson, T.,
and J. Bond, "Compacted-DNS (C-DNS): A Format for DNS
Packet Capture", RFC 8618, DOI 10.17487/RFC8618, September
2019, <https://www.rfc-editor.org/info/rfc8618>.
[3] http://tma.ifip.org/2018/wp-content/uploads/sites/3/2018/06/ 12.3. URIs
tma2018_paper30.pdf
[4] http://dnstap.info [1] https://petsymposium.org/2018/files/hotpets/4-siby.pdf
[5] https://nginx.org/ [2] http://tma.ifip.org/2018/wp-content/uploads/sites/3/2018/06/
tma2018_paper30.pdf
[6] https://www.haproxy.org/ [3] http://dnstap.info
[7] https://kb.isc.org/article/AA-01386/0/DNS-over-TLS.html [4] https://nginx.org/
[8] https://dnsdist.org [5] https://www.haproxy.org/
[9] https://doi.org/10.1145/3182660 [6] https://kb.isc.org/article/AA-01386/0/DNS-over-TLS.html
[10] https://github.com/Sinodun/draft-dprive-bcp-op/blob/master/ [7] https://dnsdist.org
draft-00/ip_techniques_table.svg
[11] https://pdfs.semanticscholar.org/7b34/12c951cebe71cd2cddac5fda16 [8] https://doi.org/10.1145/3182660
4fb2138a44.pdf
[12] https://kb.isc.org/docs/aa-00482 [9] https://pdfs.semanticscholar.org/7b34/12c951cebe71cd2cddac5fda164
fb2138a44.pdf
[13] https://surf.nl/datasharing [10] https://kb.isc.org/docs/aa-00482
[14] https://dnsprivacy.org/wiki/display/DP/ [11] https://surf.nl/datasharing
[12] https://dnsprivacy.org/wiki/display/DP/
Comparison+of+policy+and+privacy+statements Comparison+of+policy+and+privacy+statements
[15] https://wiki.mozilla.org/Security/DOH-resolver-policy [13] https://wiki.mozilla.org/Security/DOH-resolver-policy
[16] https://www.ssllabs.com/ssltest/ [14] https://www.ssllabs.com/ssltest/
[17] https://internet.nl [15] https://internet.nl
[18] https://support.google.com/analytics/answer/2763052?hl=en [16] https://support.google.com/analytics/answer/2763052?hl=en
[19] https://www.conversionworks.co.uk/blog/2017/05/19/anonymize-ip- [17] https://www.conversionworks.co.uk/blog/2017/05/19/anonymize-ip-
geo-impact-test/ geo-impact-test/
[20] https://github.com/edmonds/pdns/blob/master/pdns/dnswasher.cc [18] https://github.com/edmonds/pdns/blob/master/pdns/dnswasher.cc
[21] http://ita.ee.lbl.gov/html/contrib/tcpdpriv.html [19] http://ita.ee.lbl.gov/html/contrib/tcpdpriv.html
[22] http://an.kaist.ac.kr/~sbmoon/paper/intl-journal/2004-cn- [20] http://an.kaist.ac.kr/~sbmoon/paper/intl-journal/2004-cn-
anon.pdf anon.pdf
[23] https://www.cc.gatech.edu/computing/Telecomm/projects/cryptopan/ [21] https://www.cc.gatech.edu/computing/Telecomm/projects/cryptopan/
[24] http://mharvan.net/talks/noms-ip_anon.pdf [22] http://mharvan.net/talks/noms-ip_anon.pdf
[25] http://www.ecs.umass.edu/ece/wolf/pubs/ton2007.pdf [23] http://www.ecs.umass.edu/ece/wolf/pubs/ton2007.pdf
[26] https://medium.com/@bert.hubert/on-ip-address-encryption- [24] https://medium.com/@bert.hubert/on-ip-address-encryption-
security-analysis-with-respect-for-privacy-dabe1201b476 security-analysis-with-respect-for-privacy-dabe1201b476
[27] https://github.com/PowerDNS/ipcipher [25] https://github.com/PowerDNS/ipcipher
[28] https://github.com/veorq/ipcrypt [26] https://github.com/veorq/ipcrypt
[29] https://www.ietf.org/mail-archive/web/cfrg/current/msg09494.html [27] https://www.ietf.org/mail-archive/web/cfrg/current/msg09494.html
[30] http://dl.ifip.org/db/conf/im/im2019/189282.pdf [28] http://dl.ifip.org/db/conf/im/im2019/189282.pdf
Appendix A. Documents Appendix A. Documents
This section provides an overview of some DNS privacy related This section provides an overview of some DNS privacy related
documents, however, this is neither an exhaustive list nor a documents, however, this is neither an exhaustive list nor a
definitive statement on the characteristic of the document. definitive statement on the characteristic of the document.
A.1. Potential increases in DNS privacy A.1. Potential increases in DNS privacy
These documents are limited in scope to communications between stub These documents are limited in scope to communications between stub
skipping to change at page 31, line 4 skipping to change at page 32, line 36
o 'DNS Query Name minimization to Improve Privacy' [RFC7816] o 'DNS Query Name minimization to Improve Privacy' [RFC7816]
referred to here as 'QNAME minimization' referred to here as 'QNAME minimization'
A.2. Potential decreases in DNS privacy A.2. Potential decreases in DNS privacy
These documents relate to functionality that could provide increased These documents relate to functionality that could provide increased
tracking of user activity as a side effect: tracking of user activity as a side effect:
o 'Client Subnet in DNS Queries' [RFC7871] o 'Client Subnet in DNS Queries' [RFC7871]
o 'Domain Name System (DNS) Cookies' [RFC7873]) o 'Domain Name System (DNS) Cookies' [RFC7873])
o 'Transport Layer Security (TLS) Session Resumption without Server- o 'Transport Layer Security (TLS) Session Resumption without Server-
Side State' [RFC5077] referred to here as simply TLS session Side State' [RFC5077] referred to here as simply TLS session
resumption. resumption.
o 'A DNS Packet Capture Format' [I-D.ietf-dnsop-dns-capture-format] o 'A DNS Packet Capture Format' [RFC8618]
o Passive DNS [I-D.ietf-dnsop-terminology-bis] o Passive DNS [RFC8499]
Note that depending on the specifics of the implementation [RFC8484] Note that depending on the specifics of the implementation [RFC8484]
may also provide increased tracking. may also provide increased tracking.
A.3. Related operational documents A.3. Related operational documents
o 'DNS Transport over TCP - Implementation Requirements' [RFC7766] o 'DNS Transport over TCP - Implementation Requirements' [RFC7766]
o 'Operational requirements for DNS-over-TCP' o 'Operational requirements for DNS-over-TCP'
[I-D.ietf-dnsop-dns-tcp-requirements] [I-D.ietf-dnsop-dns-tcp-requirements]
o 'The edns-tcp-keepalive EDNS0 Option' [RFC7828] o 'The edns-tcp-keepalive EDNS0 Option' [RFC7828]
o 'DNS Stateful Operations' [I-D.ietf-dnsop-session-signal] o 'DNS Stateful Operations' [RFC8490]
Appendix B. IP address techniques Appendix B. IP address techniques
Data minimization methods may be categorized by the processing used Data minimization methods may be categorized by the processing used
and the properties of their outputs. The following builds on the and the properties of their outputs. The following builds on the
categorization employed in [RFC6235]: categorization employed in [RFC6235]:
o Format-preserving. Normally when encrypting, the original data o Format-preserving. Normally when encrypting, the original data
length and patterns in the data should be hidden from an attacker. length and patterns in the data should be hidden from an attacker.
Some applications of de-identification, such as network capture Some applications of de-identification, such as network capture
skipping to change at page 32, line 37 skipping to change at page 34, line 23
o Random substitution. As replacement, but using randomly generated o Random substitution. As replacement, but using randomly generated
replacement values. replacement values.
o Cryptographic permutation. Using a permutation function, such as o Cryptographic permutation. Using a permutation function, such as
a hash function or cryptographic block cipher, to generate a a hash function or cryptographic block cipher, to generate a
replacement de-identified value. replacement de-identified value.
B.1. Google Analytics non-prefix filtering B.1. Google Analytics non-prefix filtering
Since May 2010, Google Analytics has provided a facility [18] that Since May 2010, Google Analytics has provided a facility [16] that
allows website owners to request that all their users IP addresses allows website owners to request that all their users IP addresses
are anonymized within Google Analytics processing. This very basic are anonymized within Google Analytics processing. This very basic
anonymization simply sets to zero the least significant 8 bits of anonymization simply sets to zero the least significant 8 bits of
IPv4 addresses, and the least significant 80 bits of IPv6 addresses. IPv4 addresses, and the least significant 80 bits of IPv6 addresses.
The level of anonymization this produces is perhaps questionable. The level of anonymization this produces is perhaps questionable.
There are some analysis results [19] which suggest that the impact of There are some analysis results [17] which suggest that the impact of
this on reducing the accuracy of determining the user's location from this on reducing the accuracy of determining the user's location from
their IP address is less than might be hoped; the average discrepancy their IP address is less than might be hoped; the average discrepancy
in identification of the user city for UK users is no more than 17%. in identification of the user city for UK users is no more than 17%.
Anonymization: Format-preserving, Filtering (grey marking). Anonymization: Format-preserving, Filtering (grey marking).
B.2. dnswasher B.2. dnswasher
Since 2006, PowerDNS have included a de-identification tool dnswasher Since 2006, PowerDNS have included a de-identification tool dnswasher
[20] with their PowerDNS product. This is a PCAP filter that [18] with their PowerDNS product. This is a PCAP filter that
performs a one-to-one mapping of end user IP addresses with an performs a one-to-one mapping of end user IP addresses with an
anonymized address. A table of user IP addresses and their de- anonymized address. A table of user IP addresses and their de-
identified counterparts is kept; the first IPv4 user addresses is identified counterparts is kept; the first IPv4 user addresses is
translated to 0.0.0.1, the second to 0.0.0.2 and so on. The de- translated to 0.0.0.1, the second to 0.0.0.2 and so on. The de-
identified address therefore depends on the order that addresses identified address therefore depends on the order that addresses
arrive in the input, and running over a large amount of data the arrive in the input, and running over a large amount of data the
address translation tables can grow to a significant size. address translation tables can grow to a significant size.
Anonymization: Format-preserving, Enumeration. Anonymization: Format-preserving, Enumeration.
B.3. Prefix-preserving map B.3. Prefix-preserving map
Used in TCPdpriv [21], this algorithm stores a set of original and Used in TCPdpriv [19], this algorithm stores a set of original and
anonymised IP address pairs. When a new IP address arrives, it is anonymised IP address pairs. When a new IP address arrives, it is
compared with previous addresses to determine the longest prefix compared with previous addresses to determine the longest prefix
match. The new address is anonymized by using the same prefix, with match. The new address is anonymized by using the same prefix, with
the remainder of the address anonymized with a random value. The use the remainder of the address anonymized with a random value. The use
of a random value means that TCPdrpiv is not deterministic; different of a random value means that TCPdrpiv is not deterministic; different
anonymized values will be generated on each run. The need to store anonymized values will be generated on each run. The need to store
previous addresses means that TCPdpriv has significant and unbounded previous addresses means that TCPdpriv has significant and unbounded
memory requirements, and because of the need to allocated anonymized memory requirements, and because of the need to allocated anonymized
addresses sequentially cannot be used in parallel processing. addresses sequentially cannot be used in parallel processing.
Anonymization: Format-preserving, prefix preservation (general). Anonymization: Format-preserving, prefix preservation (general).
B.4. Cryptographic Prefix-Preserving Pseudonymisation B.4. Cryptographic Prefix-Preserving Pseudonymisation
Cryptographic prefix-preserving pseudonymisation was originally Cryptographic prefix-preserving pseudonymisation was originally
proposed as an improvement to the prefix-preserving map implemented proposed as an improvement to the prefix-preserving map implemented
in TCPdpriv, described in Xu et al. [22] and implemented in the in TCPdpriv, described in Xu et al. [20] and implemented in the
Crypto-PAn tool [23]. Crypto-PAn is now frequently used as an Crypto-PAn tool [21]. Crypto-PAn is now frequently used as an
acronym for the algorithm. Initially it was described for IPv4 acronym for the algorithm. Initially it was described for IPv4
addresses only; extension for IPv6 addresses was proposed in Harvan & addresses only; extension for IPv6 addresses was proposed in Harvan &
Schoenwaelder [24] and implemented in snmpdump. This uses a Schoenwaelder [22] and implemented in snmpdump. This uses a
cryptographic algorithm rather than a random value, and thus cryptographic algorithm rather than a random value, and thus
pseudonymity is determined uniquely by the encryption key, and is pseudonymity is determined uniquely by the encryption key, and is
deterministic. It requires a separate AES encryption for each output deterministic. It requires a separate AES encryption for each output
bit, so has a non-trivial calculation overhead. This can be bit, so has a non-trivial calculation overhead. This can be
mitigated to some extent (for IPv4, at least) by pre-calculating mitigated to some extent (for IPv4, at least) by pre-calculating
results for some number of prefix bits. results for some number of prefix bits.
Pseudonymization: Format-preserving, prefix preservation (general). Pseudonymization: Format-preserving, prefix preservation (general).
B.5. Top-hash Subtree-replicated Anonymisation B.5. Top-hash Subtree-replicated Anonymisation
Proposed in Ramaswamy & Wolf [25], Top-hash Subtree-replicated Proposed in Ramaswamy & Wolf [23], Top-hash Subtree-replicated
Anonymisation (TSA) originated in response to the requirement for Anonymisation (TSA) originated in response to the requirement for
faster processing than Crypto-PAn. It used hashing for the most faster processing than Crypto-PAn. It used hashing for the most
significant byte of an IPv4 address, and a pre-calculated binary tree significant byte of an IPv4 address, and a pre-calculated binary tree
structure for the remainder of the address. To save memory space, structure for the remainder of the address. To save memory space,
replication is used within the tree structure, reducing the size of replication is used within the tree structure, reducing the size of
the pre-calculated structures to a few Mb for IPv4 addresses. the pre-calculated structures to a few Mb for IPv4 addresses.
Address pseudonymization is done via hash and table lookup, and so Address pseudonymization is done via hash and table lookup, and so
requires minimal computation. However, due to the much increased requires minimal computation. However, due to the much increased
address space for IPv6, TSA is not memory efficient for IPv6. address space for IPv6, TSA is not memory efficient for IPv6.
Pseudonymization: Format-preserving, prefix preservation (general). Pseudonymization: Format-preserving, prefix preservation (general).
B.6. ipcipher B.6. ipcipher
A recently-released proposal from PowerDNS [26], ipcipher [27] is a A recently-released proposal from PowerDNS [24], ipcipher [25] is a
simple pseudonymization technique for IPv4 and IPv6 addresses. IPv6 simple pseudonymization technique for IPv4 and IPv6 addresses. IPv6
addresses are encrypted directly with AES-128 using a key (which may addresses are encrypted directly with AES-128 using a key (which may
be derived from a passphrase). IPv4 addresses are similarly be derived from a passphrase). IPv4 addresses are similarly
encrypted, but using a recently proposed encryption ipcrypt [28] encrypted, but using a recently proposed encryption ipcrypt [26]
suitable for 32bit block lengths. However, the author of ipcrypt has suitable for 32bit block lengths. However, the author of ipcrypt has
since indicated [29] that it has low security, and further analysis since indicated [27] that it has low security, and further analysis
has revealed it is vulnerable to attack. has revealed it is vulnerable to attack.
Pseudonymization: Format-preserving, cryptographic permutation. Pseudonymization: Format-preserving, cryptographic permutation.
B.7. Bloom filters B.7. Bloom filters
van Rijswijk-Deij et al. [30] have recently described work using van Rijswijk-Deij et al. [28] have recently described work using
Bloom filters to categorize query traffic and record the traffic as Bloom filters to categorize query traffic and record the traffic as
the state of multiple filters. The goal of this work is to allow the state of multiple filters. The goal of this work is to allow
operators to identify so-called Indicators of Compromise (IOCs) operators to identify so-called Indicators of Compromise (IOCs)
originating from specific subnets without storing information about, originating from specific subnets without storing information about,
or be able to monitor the DNS queries of an individual user. By or be able to monitor the DNS queries of an individual user. By
using a Bloom filter, it is possible to determine with a high using a Bloom filter, it is possible to determine with a high
probability if, for example, a particular query was made, but the set probability if, for example, a particular query was made, but the set
of queries made cannot be recovered from the filter. Similarly, by of queries made cannot be recovered from the filter. Similarly, by
mixing queries from a sufficient number of users in a single filter, mixing queries from a sufficient number of users in a single filter,
it becomes practically impossible to determine if a particular user it becomes practically impossible to determine if a particular user
performed a particular query. Large numbers of queries can be performed a particular query. Large numbers of queries can be
tracked in a memory-efficient way. As filter status is stored, this tracked in a memory-efficient way. As filter status is stored, this
approach cannot be used to regenerate traffic, and so cannot be used approach cannot be used to regenerate traffic, and so cannot be used
with tools used to process live traffic. with tools used to process live traffic.
Anonymized: Generalization. Anonymized: Generalization.
Appendix C. Example DROP statement
The following example DROP statement is very loosely based on some
elements of published privacy statements for some public resolvers,
with additional fields populated to illustrate the what the full
contents of a DROP statement might look like. This should not be
interpreted as
o having been reviewed or approved by any operator in any way
o having any legal standing or validity at all
o being complete or exhaustive
This is a purely hypothetical example of a DROP statement to outline
example contents - in this case for a public resolver operator
providing a basic DNS Privacy service via one IP address and one DoH
URI with security based filtering. It does aim to meet minimal
compliance as specified in Section 5.
C.1. Policy
1. Treatment of IP addresses. Many nations classify IP addresses as
Personally-Identifiable Information (PII), and we take a
conservative approach in treating IP addresses as PII in all
jurisdictions in which our systems reside.
2. Data collection and sharing.
1. IP addresses. Our normal course of data management does not
have any IP address information or other PII logged to disk
or transmitted out of the location in which the query was
received. We may aggregate certain counters to larger
network block levels for statistical collection purposes, but
those counters do not maintain specific IP address data nor
is the format or model of data stored capable of being
reverse-engineered to ascertain what specific IP addresses
made what queries.
2. Data collected in logs. We do keep some generalized location
information (at the city/metropolitan area level) so that we
can conduct debugging and analyze abuse phenomena. We also
use the collected information for the creation and sharing of
telemetry (timestamp, geolocation, number of hits, first
seen, last seen) for contributors, public publishing of
general statistics of use of system (protections, threat
types, counts, etc.) When you use our DNS Services, here is
the full list of items that are
included in our logs:
+ Request domain name, e.g. example.net
+ Record type of requested domain, e.g. A, AAAA, NS, MX,
TXT, etc.
+ Transport protocol on which the request arrived, i.e. UDP,
TCP, DoT,
DoH
+ Origin IP general geolocation information: i.e. geocode,
region ID, city ID, and metro code
+ IP protocol version - IPv4 or IPv6
+ Response code sent, e.g. SUCCESS, SERVFAIL, NXDOMAIN,
etc.
+ Absolute arrival time
+ Name of the specific instance that processed this request
+ IP address of the specific instance to which this request
was addressed (no relation to the requestor's IP address)
We may keep the following data as summary information,
including all the above EXCEPT for data about the DNS record
requested:
+ Currently-advertised BGP-summarized IP prefix/netmask of
apparent client origin
+ Autonomous system number (BGP ASN) of apparent client
origin
All the above data may be kept in full or partial form in
permanent archives.
3. Sharing of data. Except as described in this document, we do
not intentionally share, sell, or rent individual personal
information associated with the requestor (i.e. source IP
address or any other information that can positively identify
the client using our infrastructure) with anyone without your
consent. We generate and share high level anonymized
aggregate statistics including threat metrics on threat type,
geolocation, and if available, sector, as well as other
vertical metrics including performance metrics on our DNS
Services (i.e. number of threats blocked, infrastructure
uptime) when available with the our threat intelligence (TI)
partners, academic researchers, or the public. Our DNS
Services share anonymized data on specific domains queried
(records such as domain, timestamp, geolocation, number of
hits, first seen, last seen) with its threat intelligence
partners. Our DNS Services also builds, stores, and may
share certain DNS data streams which store high level
information about domain resolved, query types, result codes,
and timestamp. These streams do not contain IP address
information of requestor and cannot be correlated to IP
address or other PII. We do not and never will share any of
its data with marketers, nor will it use this data for
demographic analysis.
3. Exceptions. There are exceptions to this storage model: In the
event of events or observed behaviors which we deem malicious or
anomalous, we may utilize more detailed logging to collect more
specific IP address data in the process of normal network defence
and mitigation. This collection and transmission off-site will
be limited to IP addresses that we determine are involved in the
event.
4. Associated entities. Details of our Threat Intelligence partners
can be found at our website page (insert link).
5. Correlation of Data. We do not correlate or combine information
from our logs with any personal information that you have
provided us for other services, or with your specific IP address.
6. Result filtering.
1. Filtering. We utilise cyber threat intelligence about
malicious domains from a variety of public and private
sources and blocks access to those malicious domains when
your system attempts to contact them. An NXDOMAIN is
returned for blocked sites.
1. Censorship. We will not provide a censoring component
and will limit our actions solely to the blocking of
malicious domains around phishing, malware, and exploit
kit domains.
2. Accidental blocking. We implement whitelisting
algorithms to make sure legitimate domains are not
blocked by accident. However, in the rare case of
blocking a legitimate domain, we work with the users to
quickly whitelist that domain. Please use our support
form (insert link) if you believe we are blocking a
domain in error.
C.2. Practice
1. Deviations from Policy. None currently in place.
2. Client facing capabilities.
1. We offer UDP and TCP DNS on port 53 on (insert IP address)
2. We offer DNS-over-TLS as specified in RFC7858 on (insert IP
address). It is available on port 853 and port 443. We also
implement RFC7766.
1. The DoT authentication name used is (insert domain name).
No TLSA records are available for this domain name.
2. We do not publish SPKI pin sets.
3. We offer DNS-over-HTTPS as specified in RFC8484 on (insert
URI template). Both POST and GET are supported.
4. Both services offer TLS 1.2 and TLS 1.3.
5. Both services pad DNS responses according to RFC8467.
6. Both services provide DNSSEC validation.
3. Upstream capabilities.
1. Our servers implement QNAME minimisation.
2. Our servers do not send ECS upstream.
4. Support. Support information for this service is available at
(insert link).
5. Jurisdiction.
1. We operate as the legal entity (insert entity) registered in
(insert country) as (insert company identifier e.g Company
Number). Our Headquarters are located at (insert address).
2. As such we operate under (insert country) law. For details
of our company privacy policy see (insert link). For
questions on this policy and enforcement contact our Data
Protection Officer on (insert email address).
3. We operate servers in the following countries (insert list).
4. We have no agreements in place with law enforcement agencies
to give them access to the data. Apart from as stated in the
Policy section of this document with regard to cyber threat
intelligence, we have no agreements in place with other
public and private parties dealing with security and
intelligence, to give them access to the servers and/or to
the data.
6. Consent. As described, we do not intentionally share, sell, or
rent individual personal information associated with the
requestor with anyone without your consent. In order to provide
consent you must have a user account for our service - this can
be set up via our support page (insert link). We may contact
existing users with accounts to enquire if you would be willing
to provide consent for specific situations. Users can then
provide explicit consent by choosing to enable certain account
options which are disabled by default.
Authors' Addresses Authors' Addresses
Sara Dickinson Sara Dickinson
Sinodun IT Sinodun IT
Magdalen Centre Magdalen Centre
Oxford Science Park Oxford Science Park
Oxford OX4 4GA Oxford OX4 4GA
United Kingdom United Kingdom
Email: sara@sinodun.com Email: sara@sinodun.com
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