< draft-ietf-dprive-bcp-op-01.txt		draft-ietf-dprive-bcp-op-02.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: June 21, 2019 R. van Rijswijk-Deij		Expires: September 12, 2019 R. van Rijswijk-Deij
	NLnet Labs		NLnet Labs
	A. Mankin		A. Mankin
	Salesforce		Salesforce
	December 18, 2018		March 11, 2019
	Recommendations for DNS Privacy Service Operators		Recommendations for DNS Privacy Service Operators
	draft-ietf-dprive-bcp-op-01		draft-ietf-dprive-bcp-op-02
	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 operators who choose to offer DNS Privacy
	services. With these recommendations, the operator can make		services. With these recommendations, the operator can make
	deliberate decisions regarding which services to provide, and how the		deliberate decisions regarding which services to provide, and how the
	decisions and alternatives impact the privacy of users.		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 DNS
	skipping to change at page 1, line 36 ¶		skipping to change at page 1, line 36 ¶
	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 https://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 June 21, 2019.		This Internet-Draft will expire on September 12, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 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
	(https://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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4		2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Privacy related documents . . . . . . . . . . . . . . . . . . 5		3. Privacy related documents . . . . . . . . . . . . . . . . . . 5
	4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5		4. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
	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 . . . . . . . 7		5.1.2. Authentication of DNS privacy services . . . . . . . 7
	5.1.3. Protocol recommendations . . . . . . . . . . . . . . 9		5.1.3. Protocol recommendations . . . . . . . . . . . . . . 9
	5.1.4. Availability . . . . . . . . . . . . . . . . . . . . 11		5.1.4. Availability . . . . . . . . . . . . . . . . . . . . 10
	5.1.5. Service options . . . . . . . . . . . . . . . . . . . 11		5.1.5. Service options . . . . . . . . . . . . . . . . . . . 11
	5.1.6. Impact on Operators . . . . . . . . . . . . . . . . . 11		5.1.6. Impact on Operators . . . . . . . . . . . . . . . . . 11
	5.1.7. Limitations of using a pure TLS proxy . . . . . . . . 11		5.1.7. Limitations of using a pure TLS proxy . . . . . . . . 12
	5.2. Data at rest on the server . . . . . . . . . . . . . . . 12		5.2. Data at rest on the server . . . . . . . . . . . . . . . 12
	5.2.1. Data handling . . . . . . . . . . . . . . . . . . . . 12		5.2.1. Data handling . . . . . . . . . . . . . . . . . . . . 12
	5.2.2. Data minimization of network traffic . . . . . . . . 13		5.2.2. Data minimization of network traffic . . . . . . . . 13
	5.2.3. IP address pseudonymization and anonymization methods 14		5.2.3. IP address pseudonymization and anonymization methods 14
	5.2.4. Pseudonymization, anonymization or discarding of		5.2.4. Pseudonymization, anonymization or discarding of
	other correlation data . . . . . . . . . . . . . . . 15		other correlation data . . . . . . . . . . . . . . . 15
	5.2.5. Cache snooping . . . . . . . . . . . . . . . . . . . 15		5.2.5. Cache snooping . . . . . . . . . . . . . . . . . . . 16
	5.3. Data sent onwards from the server . . . . . . . . . . . . 16		5.3. Data sent onwards from the server . . . . . . . . . . . . 16
	5.3.1. Protocol recommendations . . . . . . . . . . . . . . 16		5.3.1. Protocol recommendations . . . . . . . . . . . . . . 16
	5.3.2. Client query obfuscation . . . . . . . . . . . . . . 17		5.3.2. Client query obfuscation . . . . . . . . . . . . . . 17
	5.3.3. Data sharing . . . . . . . . . . . . . . . . . . . . 17		5.3.3. Data sharing . . . . . . . . . . . . . . . . . . . . 18
	6. DNS privacy policy and practice statement . . . . . . . . . . 18		6. DNS privacy policy and practice statement . . . . . . . . . . 19
	6.1. Recommended contents of a DPPPS . . . . . . . . . . . . . 18		6.1. Recommended contents of a DPPPS . . . . . . . . . . . . . 19
	6.1.1. Policy . . . . . . . . . . . . . . . . . . . . . . . 18		6.1.1. Policy . . . . . . . . . . . . . . . . . . . . . . . 19
	6.1.2. Practice. . . . . . . . . . . . . . . . . . . . . . . 19		6.1.2. Practice . . . . . . . . . . . . . . . . . . . . . . 20
	6.2. Current policy and privacy statements . . . . . . . . . . 20		6.2. Current policy and privacy statements . . . . . . . . . . 21
	6.3. Enforcement/accountability . . . . . . . . . . . . . . . 21		6.3. Enforcement/accountability . . . . . . . . . . . . . . . 21
	7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 21		7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 22
	8. Security considerations . . . . . . . . . . . . . . . . . . . 21		8. Security considerations . . . . . . . . . . . . . . . . . . . 22
	9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
	10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22		10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 22
	11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 22		11. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 22
	12. References . . . . . . . . . . . . . . . . . . . . . . . . . 23		12. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
	12.1. Normative References . . . . . . . . . . . . . . . . . . 23		12.1. Normative References . . . . . . . . . . . . . . . . . . 24
	12.2. Informative References . . . . . . . . . . . . . . . . . 25		12.2. Informative References . . . . . . . . . . . . . . . . . 26
	12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 26		12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 27
	Appendix A. Documents . . . . . . . . . . . . . . . . . . . . . 27		Appendix A. Documents . . . . . . . . . . . . . . . . . . . . . 29
	A.1. Potential increases in DNS privacy . . . . . . . . . . . 27		A.1. Potential increases in DNS privacy . . . . . . . . . . . 29
	A.2. Potential decreases in DNS privacy . . . . . . . . . . . 28		A.2. Potential decreases in DNS privacy . . . . . . . . . . . 29
	A.3. Related operational documents . . . . . . . . . . . . . . 28		A.3. Related operational documents . . . . . . . . . . . . . . 30
	Appendix B. Encryption and DNSSEC . . . . . . . . . . . . . . . 29		Appendix B. Encryption and DNSSEC . . . . . . . . . . . . . . . 30
	Appendix C. IP address techniques . . . . . . . . . . . . . . . 29		Appendix C. IP address techniques . . . . . . . . . . . . . . . 30
	C.1. Google Analytics non-prefix filtering . . . . . . . . . . 30		C.1. Google Analytics non-prefix filtering . . . . . . . . . . 31
	C.2. dnswasher . . . . . . . . . . . . . . . . . . . . . . . . 30		C.2. dnswasher . . . . . . . . . . . . . . . . . . . . . . . . 32
	C.3. Prefix-preserving map . . . . . . . . . . . . . . . . . . 31		C.3. Prefix-preserving map . . . . . . . . . . . . . . . . . . 32
	C.4. Cryptographic Prefix-Preserving Pseudonymisation . . . . 31		C.4. Cryptographic Prefix-Preserving Pseudonymisation . . . . 32
	C.5. Top-hash Subtree-replicated Anonymisation . . . . . . . . 31		C.5. Top-hash Subtree-replicated Anonymisation . . . . . . . . 33
	C.6. ipcipher . . . . . . . . . . . . . . . . . . . . . . . . 32		C.6. ipcipher . . . . . . . . . . . . . . . . . . . . . . . . 33
	C.7. Bloom filters . . . . . . . . . . . . . . . . . . . . . . 32		C.7. Bloom filters . . . . . . . . . . . . . . . . . . . . . . 33
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
	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 "open resolvers" [I-D.ietf-dnsop-terminology-bis] which users may		of "public resolvers" [I-D.ietf-dnsop-terminology-bis] which users
	prefer to use instead of the default network resolver because they		may prefer to use instead of the default network resolver because
	offer a specific feature (e.g. good reachability, encrypted		they offer a specific feature (e.g. good reachability, encrypted
	transport, strong privacy policy, filtering (or lack of), etc.).		transport, strong privacy policy, filtering (or lack of), etc.).
	These open resolvers have tended to be at the forefront of adoption		These open resolvers have tended to be at the forefront of adoption
	of privacy related enhancements but it is anticipated that operators		of privacy related enhancements but it is anticipated that operators
	of other resolver services will follow.		of other resolver services will 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
	skipping to change at page 4, line 12 ¶		skipping to change at page 4, line 12 ¶
	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.
	It should also be noted that the choice of a user to configure a		It should also be noted that the choice of a user to configure a
	single resolver (or a fixed set of resolvers) and an encrypted		single resolver (or a fixed set of resolvers) and an encrypted
	transport to use in all network environments has both advantages and		transport to use in all network environments has both advantages and
	disadvantages. For example the user has a clear expectation of which		disadvantages. For example the user has a clear expectation of which
	resolvers have visibility of their query data however this resolver/		resolvers have visibility of their query data however this resolver/
	transport selection may provide an added mechanism to track them as		transport selection may provide an added mechanism to track them as
	they move across network environments. Commitments from operators to		they move across network environments. Commitments from operators to
	minimize such tracking are also likely to play a role in users		minimize such tracking are also likely to play a role in user
	selection of resolver.		selection of resolvers.
	More recently the global legislative landscape with regard to		More recently the global legislative landscape with regard to
	personal data collection, retention, and pseudonymization has seen		personal data collection, retention, and pseudonymization has seen
	significant activity. It is an untested area that simply using a DNS		significant activity. It is an untested area that simply using a DNS
	resolution service constitutes consent from the user for the operator		resolution service constitutes consent from the user for the operator
	to process their query data. The impact of recent legislative		to process their query data. The impact of recent legislative
	changes on data pertaining to the users of both Internet Service		changes on data pertaining to the users of both Internet Service
	Providers and DNS open resolvers is not fully understood at the time		Providers and public DNS resolvers is not fully understood at the
	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 Privacy Policy and Practice Statement (DPPPS)
	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		DPPPS is a document that an operator can publish outlining their
	skipping to change at page 6, line 20 ¶		skipping to change at page 6, line 20 ¶
	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 DPPPS.
	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 are		* 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].
	o DNS Privacy Threats		o DNS Privacy Threats
	* These are threats to the users and operators of DNS privacy		* These are threats to the users and operators of DNS privacy
	services that are not directly covered by [RFC6973]. These may		services that are not directly covered by [RFC6973]. These may
	be more operational in nature such as certificate management or		be more operational in nature such as certificate management or
	service availability issues.		service availability issues.
	We describe three classes of actions that operators of DNS privacy		We describe three classes of actions that operators of DNS privacy
	skipping to change at page 7, line 39 ¶		skipping to change at page 7, line 39 ¶
	o DoH [RFC8484]		o DoH [RFC8484]
	It is noted that a DNS privacy service can also be provided over DNS-		It is noted that a DNS privacy service can also be provided over DNS-
	over-DTLS [RFC8094], however this is an Experimental specification		over-DTLS [RFC8094], however this is an Experimental specification
	and there are no known implementations at the time of writing.		and there are no known implementations at the time of writing.
	It is also noted that DNS privacy service might be provided over		It is also noted that DNS privacy service might be provided over
	IPSec, DNSCrypt or VPNs. However, use of these transports for DNS		IPSec, DNSCrypt or VPNs. However, use of these transports for DNS
	are not standardized and any discussion of best practice for		are not standardized and any discussion of best practice for
	providing such service is out of scope for this document.		providing such a service is out of scope for this document.
	Whilst encryption of DNS traffic can protect against active injection		Whilst encryption of DNS traffic can protect against active injection
	this does not diminish the need for DNSSEC, see Appendix B.		this does not diminish the need for DNSSEC, see Appendix B.
	5.1.2. Authentication of DNS privacy services		5.1.2. Authentication of DNS privacy services
	[RFC6973] Threats:		[RFC6973] Threats:
	o Surveillance:		o Surveillance:
	skipping to change at page 8, line 15 ¶		skipping to change at page 8, line 15 ¶
	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, SPKI		provide credentials in the form of either X.509 certificates or SPKI
	pinsets or TLSA records.		pinsets.
	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		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		draft has been removed as it is no longer considered an active TLS WG
	document.		document.
	Optimizations:		Optimizations:
	skipping to change at page 10, line 23 ¶		skipping to change at page 10, line 23 ¶
	[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 [I-D.ietf-dnsop-session-signal]
	o Offer a separate service that uses only TLS 1.3 [RFC8446]
	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 [2]
	o Potential for client tracking via transport identifiers		o Potential for client tracking via transport identifiers
	Mitigations:		Mitigations:
	o Clients should not be required to use HTTP Cookies [RFC6265].		o Clients must be able to forego the use of HTTP Cookies [RFC6265]
			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. (Some		absolute minimum to obtain service from a DoH server. (See
	initial work in this area has been proposed		Section 6.1 of [I-D.ietf-httpbis-bcp56bis].)
	[I-D.dickinson-doh-dohpe] but there are no clear guidelines for
	HTTP header privacy, more work on this topic is required.)
	Optimizations:
	o Offer a separate service that uses only TLS 1.3 [RFC8446]
	5.1.4. Availability		5.1.4. Availability
	DNS Privacy Threats:		DNS Privacy Threats:
	o A failed DNS privacy service could force the user to switch		o A failed DNS privacy service 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 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.		motivation for users to switch services. See, for example
			Section IV-C of Passive Observations of a Large DNS Service: 2.5
	TODO: Add reference to ongoing research on this topic.		Years in the Life of Google [3].
	5.1.5. Service options		5.1.5. 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		to the services available. This could force the user to switch
	the services available. providers, fallback to cleartext or accept		providers, fallback to cleartext or accept no DNS service for the
	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 of), DNSSEC validation, etc.		filtering (or lack thereof), DNSSEC validation, etc.
	5.1.6. Impact on Operators		5.1.6. Impact on 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
			nature of this traffic and work by intercepting traffic on the wire,
			either using a separate view on the connection between clients and
			the resolver, or as a separate process on the resolver system that
			inspects network traffic. Such solutions will no longer function
			when traffic between clients and resolvers is encrypted. There are,
			however, legitimate reasons for operators to inspect DNS traffic,
			e.g. to monitor for network security threats. Operators may
			therefore need to invest in alternative means of monitoring that
			relies on either the resolver software directly, or exporting DNS
			traffic from the resolver using e.g. dnstap [4].
			Optimization:
			When implementing alternative means for traffic monitoring, operators
			of a DNS privacy service should consider using privacy conscious
			means to do so (see, for example, the discussion on the use of Bloom
			Filters in the #documents appendix in this document).
	5.1.7. Limitations of using a pure TLS proxy		5.1.7. Limitations of using a pure TLS proxy
	DNS Privacy Threats:		DNS Privacy Threats:
	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
			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 [3], haproxy [4] or stunnel [5]) in front of a DNS		(e.g. nginx [5], haproxy [6] or stunnel [7]) 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.		Operators may choose to use a DNS aware proxy such as dnsdist [8]
			which offer custom options (similar to that proposed in
			[I-D.bellis-dnsop-xpf]) to add source information to packets to
			address this shortcoming. It should be noted that such options
			potentially significantly increase the leaked information in the
			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
	[RFC6973] Threats:		[RFC6973] Threats:
	o Surveillance		o Surveillance
	o Stored data compromise		o Stored data compromise
	skipping to change at page 12, line 28 ¶		skipping to change at page 13, line 4 ¶
	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
	[RFC6973] Threats:		[RFC6973] Threats:
	o Surveillance		o Surveillance
	o Stored data compromise		o Stored data compromise
	o Correlation		o Correlation
	o Identification		o Identification
	o Secondary use		o Secondary use
	o Disclosure		o Disclosure
	Other Treats		Other Threats
	o Contravention of legal requirements not to process user data?		o Contravention of legal requirements not to process user data?
	Mitigations:		Mitigations:
	The following are common activities for DNS service operators and in		The following are common activities for DNS service operators and in
	all cases should be minimized or completely avoided if possible for		all cases should be minimized or completely avoided if possible for
	DNS privacy services. If data is retained it should be encrypted and		DNS privacy services. If data is retained it should be encrypted and
	either aggregated, pseudonymized or anonymized whenever possible. In		either aggregated, pseudonymized or anonymized whenever possible. In
	general the principle of data minimization described in [RFC6973]		general the principle of data minimization described in [RFC6973]
	skipping to change at page 14, line 8 ¶		skipping to change at page 14, line 30 ¶
	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. [6]		from van Dijkhuizen et al. [9]
	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.
	skipping to change at page 14, line 35 ¶		skipping to change at page 15, line 9 ¶
	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. This following table presents a high level		unencumbered by patents. The following table presents a high level
	comparison of various techniques employed or under development today		comparison of various techniques employed or under development today
	and classifies them according to categorization of technique and		and classifies them according to categorization of technique and
	other properties. The list of techniques includes the main		other properties. The list of techniques includes the main
	techniques in current use, but does not claim to be comprehensive.		techniques in current use, but does not claim to be comprehensive.
	Appendix C provides a more detailed survey of these techniques and		Appendix C 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.
	Figure showing comparison of IP address techniques (SVG) [7]		Figure showing comparison of IP address techniques (SVG) [10]
	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
	[I-D.ietf-dnsop-dns-capture-format] that can be used as input to		[I-D.ietf-dnsop-dns-capture-format] that can be used as input to
	existing analysis tools. In that case, use of a Format-preserving		existing analysis tools. In that case, use of a format-preserving
	technique is essential. This, though, is not cost-free - several		technique is essential. This, though, is not cost-free - several
	authors (e.g. Brenker & Arnes [8]) have observed that, as the		authors (e.g. Brenker & Arnes [11]) have observed that, as the
	entropy in a IPv4 address is limited, given a de-identified log from		entropy in an IPv4 address is limited, given a de-identified log from
	a target, if an attacker is capable of ensuring packets are captured		a target, if an attacker is capable of ensuring packets are captured
	by the target and the attacker can send forged traffic with arbitrary		by the target and the attacker can send forged traffic with arbitrary
	source and destination addresses to that target, any format-		source and destination addresses to that target, any format-
	preserving pseudonymization is vulnerable to an attack along the		preserving pseudonymization is vulnerable to 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:
	skipping to change at page 15, line 45 ¶		skipping to change at page 16, line 19 ¶
	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 [9] for an example		o See ISC Knowledge database on cache snooping [12] for an example
	discussion on defending against cache snooping		discussion on defending against cache snooping
	TODO: Describe other techniques to defend against cache snooping		TODO: Describe other techniques to defend 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
	skipping to change at page 18, line 4 ¶		skipping to change at page 18, line 21 ¶
	o Surveillance		o Surveillance
	o Stored data compromise		o Stored data compromise
	o Correlation		o Correlation
	o Identification		o Identification
	o Secondary use		o Secondary use
	o Disclosure		o Disclosure
	DNS Privacy Threats:		DNS Privacy Threats:
	o Contravention of legal requirements not to process user data?		o Contravention of legal requirements not to process user data?
	Mitigations:		Mitigations:
	Operators should not provide identifiable data to third-parties		Operators should not provide identifiable data to third-parties
	without explicit consent from clients (we take the stance here that		without explicit consent from clients (we take the stance here that
	simply using the resolution service itself does not constitute		simply using the resolution service itself does not constitute
	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.		purposes, within or outside of their own organization. See SURFnet's
			policy [13] on data sharing for research as an example.
	TODO: More on data for research vs operations... how to still		TODO: More on data for research vs operations... how to still
	motivate operators to share anonymized data?		motivate operators to share anonymized data?
	TODO: Guidelines for when consent is granted?		TODO: Guidelines for when consent is granted?
	TODO: Applies to server data handling too.. could operators offer		TODO: Applies to server data handling too.. could operators offer
	alternatives services one that implies consent for data processing,		alternatives services one that implies consent for data processing,
	one that doesn't?		one that doesn't?
	skipping to change at page 18, line 45 ¶		skipping to change at page 19, line 16 ¶
	6.1. Recommended contents of a DPPPS		6.1. Recommended contents of a DPPPS
	6.1.1. Policy		6.1.1. Policy
	1. Make an explicit statement that IP addressses are treated as PII		1. Make an explicit statement that IP addressses are treated as PII
	2. State if IP addresses are being logged		2. State if IP addresses are being logged
	3. Specify clearly what data (including whether it is aggregated,		3. Specify clearly what data (including whether it is aggregated,
	pseudonymized or anonymized) is:		pseudonymized or anonymized and the conditions of data transfer)
			is:
	* Collected and retained by the operator (and for how long)		* Collected and retained by the operator, and for what period it
			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		4. Specify any exceptions to the above, for example technically
	malicious or anomalous behavior		malicious or anomalous behavior
	5. Declare any partners, third-party affiliations or sources of		5. Declare any partners, third-party affiliations or sources of
	funding		funding
	skipping to change at page 19, line 38 ¶		skipping to change at page 20, line 12 ¶
	mandatory legal reasons, due to applicable legislation or		mandatory legal reasons, due to applicable legislation or
	binding orders by courts and other public authorities		binding orders by courts and other public authorities
	* Specify if any replies are being filtered out or altered for		* Specify if any replies are being filtered out or altered for
	voluntary legal reasons, due to an internal policy by the		voluntary legal reasons, due to an internal policy by the
	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. Specify any temporary or permanent deviations from the policy for
	operational reasons		operational reasons
	2. With reference to section Section 5 provide specific details of		2. With reference to section Section 5 provide specific details of
	which capabilities are provided on which client facing address		which capabilities are provided on which client facing addresses
	and ports		and ports
	3. Specify the authentication name to be used (if any) and if TLSA		3. Specify the authentication name to be used (if any) and if TLSA
	records are published (including options used in the TLSA		records are published (including options used in the TLSA
	records)		records)
	4. Specify the SPKI pinsets to be used (if any) and policy for		4. Specify the SPKI pinsets to be used (if any) and policy for
	rolling keys		rolling keys
	5. Provide contact/support information for the service		5. Provide contact/support information for the service
	skipping to change at page 20, line 42 ¶		skipping to change at page 21, line 17 ¶
	dealing with security and intelligence, to give them access to		dealing with security and intelligence, to give them access to
	the servers and/or to the data		the servers and/or to the data
	7. Describe how consent is obtained from the user of the DNS privacy		7. Describe how consent is obtained from the user of the DNS privacy
	service differentiating		service differentiating
	* Uninformed users for whom this trust relationship is implicit		* Uninformed users for whom this trust relationship is implicit
	* Privacy-conscious users, that make an explicit trust choice		* Privacy-conscious users, that make an explicit trust choice
	this may prove relevant in the context of e.g. the GDPR as it relates		(this may prove relevant in the context of e.g. the GDPR as it
	to consent.		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 on the proposed DPPPS
	structure can be found on dnsprivacy.org [10].		structure can be found on dnsprivacy.org [14].
	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.
	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
	skipping to change at page 21, line 23 ¶		skipping to change at page 21, line 47 ¶
	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 [11] or Internet.nl [12].		that are currently available e.g. SSL Labs [15] or Internet.nl [16].
	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 DPPPS.
	7. IANA considerations		7. IANA considerations
	None		None
	8. Security considerations		8. Security considerations
	skipping to change at page 22, line 25 ¶		skipping to change at page 22, line 48 ¶
	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-02
			o Change 'open resolver' for 'public resolver'
			o Minor editorial changes
			o Remove recommendation to run a separate TLS 1.3 service
			o Move TLSA to purely a optimisation in Section 5.2.1
			o Update reference on minimal DoH headers.
			o Add reference on user switching provider after service issues in
			Section 5.1.4
			o Add text in Section 5.1.6 on impact on operators.
			o Add text on additional threat to TLS proxy use (Section 5.1.7)
			o Add reference in Section 5.3.1 on example policies.
	draft-ietf-dprive-bcp-op-01		draft-ietf-dprive-bcp-op-01
	o Many minor editorial fixes		o Many minor editorial fixes
	o Update DoH reference to RFC8484 and add more text on DoH		o Update DoH reference to RFC8484 and add more text on DoH
	o Split threat descriptions into ones directly referencing RFC6973		o Split threat descriptions into ones directly referencing RFC6973
	and other DNS Privacy threats		and other DNS Privacy threats
	o Improve threat descriptions throughout		o Improve threat descriptions throughout
	skipping to change at page 23, line 4 ¶		skipping to change at page 23, line 45 ¶
	o Re-structure the DPPPS, add Result filtering section.		o Re-structure the DPPPS, add Result filtering section.
	o Remove the direct inclusion of privacy policy comparison, now just		o Remove the direct inclusion of privacy policy comparison, now just
	reference dnsprivacy.org and an example of such work.		reference dnsprivacy.org and an example of such work.
	o Add an appendix briefly discussing DNSSEC		o Add an appendix briefly discussing DNSSEC
	o Update affiliation of 1 author		o Update affiliation of 1 author
	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]		[I-D.ietf-dnsop-session-signal]
	Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,		Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
	Lemon, T., and T. Pusateri, "DNS Stateful Operations",		Lemon, T., and T. Pusateri, "DNS Stateful Operations",
	draft-ietf-dnsop-session-signal-20 (work in progress),		draft-ietf-dnsop-session-signal-20 (work in progress),
	December 2018.		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,		DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
	<https://www.rfc-editor.org/info/rfc2119>.		editor.org/info/rfc2119>.
	[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,		[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
	"Transport Layer Security (TLS) Session Resumption without		"Transport Layer Security (TLS) Session Resumption without
	Server-Side State", RFC 5077, DOI 10.17487/RFC5077,		Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
	January 2008, <https://www.rfc-editor.org/info/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,		DOI 10.17487/RFC6265, April 2011, <https://www.rfc-
	<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,		DOI 10.17487/RFC6973, July 2013, <https://www.rfc-
	<https://www.rfc-editor.org/info/rfc6973>.		editor.org/info/rfc6973>.
	[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,		[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
	"Recommendations for Secure Use of Transport Layer		"Recommendations for Secure Use of Transport Layer
	Security (TLS) and Datagram Transport Layer Security		Security (TLS) and Datagram Transport Layer Security
	(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May		(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
	2015, <https://www.rfc-editor.org/info/rfc7525>.		2015, <https://www.rfc-editor.org/info/rfc7525>.
	[RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and		[RFC7766] Dickinson, J., Dickinson, S., Bellis, R., Mankin, A., and
	D. Wessels, "DNS Transport over TCP - Implementation		D. Wessels, "DNS Transport over TCP - Implementation
	Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,		Requirements", RFC 7766, DOI 10.17487/RFC7766, March 2016,
	<https://www.rfc-editor.org/info/rfc7766>.		<https://www.rfc-editor.org/info/rfc7766>.
	[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve		[RFC7816] Bortzmeyer, S., "DNS Query Name Minimisation to Improve
	Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,		Privacy", RFC 7816, DOI 10.17487/RFC7816, March 2016,
	<https://www.rfc-editor.org/info/rfc7816>.		<https://www.rfc-editor.org/info/rfc7816>.
	[RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The		[RFC7828] Wouters, P., Abley, J., Dickinson, S., and R. Bellis, "The
	edns-tcp-keepalive EDNS0 Option", RFC 7828,		edns-tcp-keepalive EDNS0 Option", RFC 7828,
	DOI 10.17487/RFC7828, April 2016,		DOI 10.17487/RFC7828, April 2016, <https://www.rfc-
	<https://www.rfc-editor.org/info/rfc7828>.		editor.org/info/rfc7828>.
	[RFC7830] Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,		[RFC7830] Mayrhofer, A., "The EDNS(0) Padding Option", RFC 7830,
	DOI 10.17487/RFC7830, May 2016,		DOI 10.17487/RFC7830, May 2016, <https://www.rfc-
	<https://www.rfc-editor.org/info/rfc7830>.		editor.org/info/rfc7830>.
	[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,		[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
	and P. Hoffman, "Specification for DNS over Transport		and P. Hoffman, "Specification for DNS over Transport
	Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May		Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
	2016, <https://www.rfc-editor.org/info/rfc7858>.		2016, <https://www.rfc-editor.org/info/rfc7858>.
	[RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W.		[RFC7871] Contavalli, C., van der Gaast, W., Lawrence, D., and W.
	Kumari, "Client Subnet in DNS Queries", RFC 7871,		Kumari, "Client Subnet in DNS Queries", RFC 7871,
	DOI 10.17487/RFC7871, May 2016,		DOI 10.17487/RFC7871, May 2016, <https://www.rfc-
	<https://www.rfc-editor.org/info/rfc7871>.		editor.org/info/rfc7871>.
	[RFC7873] Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS)		[RFC7873] Eastlake 3rd, D. and M. Andrews, "Domain Name System (DNS)
	Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016,		Cookies", RFC 7873, DOI 10.17487/RFC7873, May 2016,
	<https://www.rfc-editor.org/info/rfc7873>.		<https://www.rfc-editor.org/info/rfc7873>.
	[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles		[RFC8310] Dickinson, S., Gillmor, D., and T. Reddy, "Usage Profiles
	for DNS over TLS and DNS over DTLS", RFC 8310,		for DNS over TLS and DNS over DTLS", RFC 8310,
	DOI 10.17487/RFC8310, March 2018,		DOI 10.17487/RFC8310, March 2018, <https://www.rfc-
	<https://www.rfc-editor.org/info/rfc8310>.		editor.org/info/rfc8310>.
	[RFC8404] Moriarty, K., Ed. and A. Morton, Ed., "Effects of		[RFC8404] Moriarty, K., Ed. and A. Morton, Ed., "Effects of
	Pervasive Encryption on Operators", RFC 8404,		Pervasive Encryption on Operators", RFC 8404,
	DOI 10.17487/RFC8404, July 2018,		DOI 10.17487/RFC8404, July 2018, <https://www.rfc-
	<https://www.rfc-editor.org/info/rfc8404>.		editor.org/info/rfc8404>.
	[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
	Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
	<https://www.rfc-editor.org/info/rfc8446>.
	[RFC8467] Mayrhofer, A., "Padding Policies for Extension Mechanisms		[RFC8467] Mayrhofer, A., "Padding Policies for Extension Mechanisms
	for DNS (EDNS(0))", RFC 8467, DOI 10.17487/RFC8467,		for DNS (EDNS(0))", RFC 8467, DOI 10.17487/RFC8467,
	October 2018, <https://www.rfc-editor.org/info/rfc8467>.		October 2018, <https://www.rfc-editor.org/info/rfc8467>.
	[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS		[RFC8484] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
	(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,		(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
	<https://www.rfc-editor.org/info/rfc8484>.		<https://www.rfc-editor.org/info/rfc8484>.
	12.2. Informative References		12.2. Informative References
			[I-D.bellis-dnsop-xpf]
			Bellis, R., Dijk, P., and R. Gacogne, "DNS X-Proxied-For",
			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-01		Considerations", draft-bortzmeyer-dprive-rfc7626-bis-02
	(work in progress), July 2018.		(work in progress), January 2019.
	[I-D.dickinson-doh-dohpe]
	Dickinson, S. and W. Toorop, "DoHPE: DoH with Privacy
	Enhancements", draft-dickinson-doh-dohpe-00 (work in
	progress), July 2018.
	[I-D.ietf-dnsop-dns-capture-format]		[I-D.ietf-dnsop-dns-capture-format]
	Dickinson, J., Hague, J., Dickinson, S., Manderson, T.,		Dickinson, J., Hague, J., Dickinson, S., Manderson, T.,
	and J. Bond, "C-DNS: A DNS Packet Capture Format", draft-		and J. Bond, "C-DNS: A DNS Packet Capture Format", draft-
	ietf-dnsop-dns-capture-format-10 (work in progress),		ietf-dnsop-dns-capture-format-10 (work in progress),
	December 2018.		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-02 (work in progress), May 2018.		requirements-03 (work in progress), January 2019.
	[I-D.ietf-dnsop-terminology-bis]		[I-D.ietf-dnsop-terminology-bis]
	Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS		Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
	Terminology", draft-ietf-dnsop-terminology-bis-14 (work in		Terminology", draft-ietf-dnsop-terminology-bis-14 (work in
	progress), September 2018.		progress), September 2018.
			[I-D.ietf-httpbis-bcp56bis]
			Nottingham, M., "Building Protocols with HTTP", draft-
			ietf-httpbis-bcp56bis-08 (work in progress), November
			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://www.ietf.org/mail-archive/web/
	dns-privacy/current/pdfWqAIUmEl47.pdf>.		dns-privacy/current/pdfWqAIUmEl47.pdf>.
	[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,
	skipping to change at page 26, line 16 ¶		skipping to change at page 27, line 21 ¶
	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
	Servers by Running One on Loopback", RFC 7706,		Servers by Running One on Loopback", RFC 7706,
	DOI 10.17487/RFC7706, November 2015,		DOI 10.17487/RFC7706, November 2015, <https://www.rfc-
	<https://www.rfc-editor.org/info/rfc7706>.		editor.org/info/rfc7706>.
	[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,		DOI 10.17487/RFC8094, February 2017, <https://www.rfc-
	<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		12.3. URIs
	[1] https://www.ietf.org/mail-archive/web/dns-privacy/current/		[1] https://www.ietf.org/mail-archive/web/dns-privacy/current/
	pdfWqAIUmEl47.pdf		pdfWqAIUmEl47.pdf
	[2] https://petsymposium.org/2018/files/hotpets/4-siby.pdf		[2] https://petsymposium.org/2018/files/hotpets/4-siby.pdf
	[3] https://nginx.org/		[3] http://tma.ifip.org/2018/wp-content/uploads/sites/3/2018/06/
			tma2018_paper30.pdf
	[4] https://www.haproxy.org/		[4] http://dnstap.info
	[5] https://kb.isc.org/article/AA-01386/0/DNS-over-TLS.html		[5] https://nginx.org/
	[6] https://doi.org/10.1145/3182660		[6] https://www.haproxy.org/
	[7] https://github.com/Sinodun/draft-dprive-bcp-op/blob/master/draft-		[7] https://kb.isc.org/article/AA-01386/0/DNS-over-TLS.html
	00/ip_techniques_table.svg
	[8] https://pdfs.semanticscholar.org/7b34/12c951cebe71cd2cddac5fda164		[8] https://dnsdist.org
	fb2138a44.pdf
	[9] https://kb.isc.org/docs/aa-00482		[9] https://doi.org/10.1145/3182660
	[10] https://dnsprivacy.org/wiki/display/DP/		[10] https://github.com/Sinodun/draft-dprive-bcp-op/blob/master/
			draft-00/ip_techniques_table.svg
			[11] https://pdfs.semanticscholar.org/7b34/12c951cebe71cd2cddac5fda16
			4fb2138a44.pdf
			[12] https://kb.isc.org/docs/aa-00482
			[13] https://surf.nl/datasharing
			[14] https://dnsprivacy.org/wiki/display/DP/
	Comparison+of+policy+and+privacy+statements		Comparison+of+policy+and+privacy+statements
	[11] https://www.ssllabs.com/ssltest/		[15] https://www.ssllabs.com/ssltest/
	[12] https://internet.nl		[16] https://internet.nl
	[13] https://support.google.com/analytics/answer/2763052?hl=en		[17] https://support.google.com/analytics/answer/2763052?hl=en
	[14] https://www.conversionworks.co.uk/blog/2017/05/19/anonymize-ip-		[18] https://www.conversionworks.co.uk/blog/2017/05/19/anonymize-ip-
	geo-impact-test/		geo-impact-test/
	[15] https://github.com/edmonds/pdns/blob/master/pdns/dnswasher.cc		[19] https://github.com/edmonds/pdns/blob/master/pdns/dnswasher.cc
	[16] http://ita.ee.lbl.gov/html/contrib/tcpdpriv.html		[20] http://ita.ee.lbl.gov/html/contrib/tcpdpriv.html
	[17] http://an.kaist.ac.kr/~sbmoon/paper/intl-journal/2004-cn-		[21] http://an.kaist.ac.kr/~sbmoon/paper/intl-journal/2004-cn-
	anon.pdf		anon.pdf
	[18] https://www.cc.gatech.edu/computing/Telecomm/projects/cryptopan/		[22] https://www.cc.gatech.edu/computing/Telecomm/projects/cryptopan/
	[19] http://mharvan.net/talks/noms-ip_anon.pdf		[23] http://mharvan.net/talks/noms-ip_anon.pdf
	[20] http://www.ecs.umass.edu/ece/wolf/pubs/ton2007.pdf		[24] http://www.ecs.umass.edu/ece/wolf/pubs/ton2007.pdf
	[21] https://medium.com/@bert.hubert/on-ip-address-encryption-		[25] https://medium.com/@bert.hubert/on-ip-address-encryption-
	security-analysis-with-respect-for-privacy-dabe1201b476		security-analysis-with-respect-for-privacy-dabe1201b476
	[22] https://github.com/PowerDNS/ipcipher		[26] https://github.com/PowerDNS/ipcipher
	[23] https://github.com/veorq/ipcrypt		[27] https://github.com/veorq/ipcrypt
	[24] https://www.ietf.org/mail-archive/web/cfrg/current/msg09494.html		[28] https://www.ietf.org/mail-archive/web/cfrg/current/msg09494.html
	[25] https://tnc18.geant.org/core/presentation/127		[29] https://tnc18.geant.org/core/presentation/127
	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 30, line 30 ¶		skipping to change at page 31, line 43 ¶
	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.
	C.1. Google Analytics non-prefix filtering		C.1. Google Analytics non-prefix filtering
	Since May 2010, Google Analytics has provided a facility [13] that		Since May 2010, Google Analytics has provided a facility [17] 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 [14] which suggest that the impact of		There are some analysis results [18] 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).
	C.2. dnswasher		C.2. dnswasher
	Since 2006, PowerDNS have included a de-identification tool dnswasher		Since 2006, PowerDNS have included a de-identification tool dnswasher
	[15] with their PowerDNS product. This is a PCAP filter that		[19] 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.
	C.3. Prefix-preserving map		C.3. Prefix-preserving map
	Used in TCPdpriv [16], this algorithm stores a set of original and		Used in TCPdpriv [20], 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).
	C.4. Cryptographic Prefix-Preserving Pseudonymisation		C.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. [17] and implemented in the		in TCPdpriv, described in Xu et al. [21] and implemented in the
	Crypto-PAn tool [18]. Crypto-PAn is now frequently used as an		Crypto-PAn tool [22]. 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 [19] and implemented in snmpdump. This uses a		Schoenwaelder [23] 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).
	C.5. Top-hash Subtree-replicated Anonymisation		C.5. Top-hash Subtree-replicated Anonymisation
	Proposed in Ramaswamy & Wolf [20], Top-hash Subtree-replicated		Proposed in Ramaswamy & Wolf [24], 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).
	C.6. ipcipher		C.6. ipcipher
	A recently-released proposal from PowerDNS [21], ipcipher [22] is a		A recently-released proposal from PowerDNS [25], ipcipher [26] 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 [23]		encrypted, but using a recently proposed encryption ipcrypt [27]
	suitable for 32bit block lengths. However, the author of ipcrypt has		suitable for 32bit block lengths. However, the author of ipcrypt has
	since indicated [24] that it has low security, and further analysis		since indicated [28] 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.
	C.7. Bloom filters		C.7. Bloom filters
	van Rijswijk-Deij et al. [25] have recently described work using		van Rijswijk-Deij et al. [29] 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
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