< draft-ietf-dprive-padding-policy-03.txt		draft-ietf-dprive-padding-policy-04.txt >
	Network Working Group A. Mayrhofer		Network Working Group A. Mayrhofer
	Internet-Draft nic.at GmbH		Internet-Draft nic.at GmbH
	Intended status: Experimental January 17, 2018		Intended status: Experimental February 6, 2018
	Expires: July 21, 2018		Expires: August 10, 2018
	Padding Policy for EDNS(0)		Padding Policy for EDNS(0)
	draft-ietf-dprive-padding-policy-03		draft-ietf-dprive-padding-policy-04
	Abstract		Abstract
	RFC 7830 specifies the EDNS(0) 'Padding' option, but does not specify		RFC 7830 specifies the EDNS(0) 'Padding' option, but does not specify
	the actual padding length for specific applications. This memo lists		the actual padding length for specific applications. This memo lists
	the possible options ("Padding Policies"), discusses implications of		the possible options ("Padding Policies"), discusses implications of
	each of these options, and provides a recommended (experimental)		each of these options, and provides a recommended (experimental)
	option.		option.
	Status of This Memo		Status of This Memo
	skipping to change at page 1, line 34 ¶		skipping to change at page 1, line 34 ¶
	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 https://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 July 21, 2018.		This Internet-Draft will expire on August 10, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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		(https://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 . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. General Guidance . . . . . . . . . . . . . . . . . . . . . . 3		3. General Guidance . . . . . . . . . . . . . . . . . . . . . . 3
	4. Padding Strategies . . . . . . . . . . . . . . . . . . . . . 3		4. Padding Strategies . . . . . . . . . . . . . . . . . . . . . 3
	4.1. No Padding . . . . . . . . . . . . . . . . . . . . . . . 3		4.1. Block Length Padding . . . . . . . . . . . . . . . . . . 3
	4.2. Fixed Length Padding . . . . . . . . . . . . . . . . . . 4		4.2. Maximal Length Padding ('The Full Monty') . . . . . . . . 4
	4.3. Block Length Padding . . . . . . . . . . . . . . . . . . 4		4.3. Random Length Padding . . . . . . . . . . . . . . . . . . 4
	4.4. Maximal Length Padding ('The Full Monty') . . . . . . . . 5		4.4. Random Block Length Padding . . . . . . . . . . . . . . . 5
	4.5. Random Length Padding . . . . . . . . . . . . . . . . . . 5		5. Recommended Strategy . . . . . . . . . . . . . . . . . . . . 5
	4.6. Random Block Length Padding . . . . . . . . . . . . . . . 6		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
	5. Recommended Strategy . . . . . . . . . . . . . . . . . . . . 6		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7		8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	9. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 7		9. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
	9.1. draft-ietf-dprive-padding-policy-03 . . . . . . . . . . . 8		9.1. draft-ietf-dprive-padding-policy-04 . . . . . . . . . . . 7
	9.2. draft-ietf-dprive-padding-policy-02 . . . . . . . . . . . 8		9.2. draft-ietf-dprive-padding-policy-03 . . . . . . . . . . . 7
	9.3. draft-ietf-dprive-padding-policy-01 . . . . . . . . . . . 8		9.3. draft-ietf-dprive-padding-policy-02 . . . . . . . . . . . 7
	9.4. draft-ietf-dprive-padding-policy-00 . . . . . . . . . . . 8		9.4. draft-ietf-dprive-padding-policy-01 . . . . . . . . . . . 7
	9.5. draft-mayrhofer-dprive-padding-profiles-00 . . . . . . . 8		9.5. draft-ietf-dprive-padding-policy-00 . . . . . . . . . . . 7
	10. Normative References . . . . . . . . . . . . . . . . . . . . 8		9.6. draft-mayrhofer-dprive-padding-profiles-00 . . . . . . . 8
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8		10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
			10.1. Normative References . . . . . . . . . . . . . . . . . . 8
			10.2. Informative References . . . . . . . . . . . . . . . . . 8
			Appendix A. Non-sensible Padding Policies . . . . . . . . . . . 8
			A.1. No Padding . . . . . . . . . . . . . . . . . . . . . . . 8
			A.2. Fixed Length Padding . . . . . . . . . . . . . . . . . . 9
			Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
	1. Introduction		1. Introduction
	[RFC7830] specifies the Extensions Mechanisms for DNS (EDNS(0))		[RFC7830] specifies the Extensions Mechanisms for DNS (EDNS(0))
	"Padding" option, which allows DNS clients and servers to		"Padding" option, which allows DNS clients and servers to
	artificially increase the size of a DNS message by a variable number		artificially increase the size of a DNS message by a variable number
	of bytes, hampering size-based correlation of encrypted DNS messages.		of bytes, hampering size-based correlation of encrypted DNS messages.
	However, RFC 7830 deliberately does not specify the actual length of		However, RFC 7830 deliberately does not specify the actual length of
	padding to be used. This memo discusses options regarding the actual		padding to be used. This memo discusses options regarding the actual
	size of padding, lists advantages and disadvantages of each of these		size of padding, lists advantages and disadvantages of each of these
	"Padding Strategies", and provides a recommended (experimental)		"Padding Strategies", and provides a recommended (experimental)
	strategy.		strategy.
			Padding DNS messages is useful only when transport is encrypted,
			using protocols such as DNS over Transport Layer Security [RFC7858],
			DNS over Datagram Transport Layer Security [RFC8094] or other
			encrypted DNS transports specified in the future.
	2. Terminology		2. 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		"OPTIONAL" in this document are to be interpreted as described in
	[RFC2119].		[RFC2119].
	3. General Guidance		3. General Guidance
	EDNS(0) options space: The maximum message length as dictated by		EDNS(0) options space: The maximum message length as dictated by
	skipping to change at page 3, line 35 ¶		skipping to change at page 3, line 42 ¶
	a "Block Length" padding strategy with a block length of 32 octets,		a "Block Length" padding strategy with a block length of 32 octets,
	and a DNS message with a size of 59 octets, the message would be		and a DNS message with a size of 59 octets, the message would be
	padded to 64 octets when transported over UDP. If that same message		padded to 64 octets when transported over UDP. If that same message
	was transported over TCP, and the padding strategy would consider the		was transported over TCP, and the padding strategy would consider the
	extra 2 octects of the length field (61 octets in total), the padded		extra 2 octects of the length field (61 octets in total), the padded
	message would be 96 octets long (as the minimum length of the Padding		message would be 96 octets long (as the minimum length of the Padding
	option is 4 octets).		option is 4 octets).
	4. Padding Strategies		4. Padding Strategies
	This section is a non-exhaustive list of possible strategies in		This section is a non-exhaustive list of sensible strategies in
	choosing padding length.		choosing padding length. Note that, for completeness, Appendix A
			contains two more (non-sensible) strategies.
	4.1. No Padding
	In the "No Padding" policy, the EDNS(0) Padding option is not used,
	and the size of the final (actually, "non-padded") message obviously
	exactly matches the size of the unpadded message. Even though this
	"non-policy" seems redundant in this list, its properties must be
	considered for cases where just one of the parties (client or server)
	applies padding.
	Also, this "policy" is required when the remaining message size of
	the unpadded message does not allow for the Padding option to be
	included (less than 4 octets left).
	Advantages: This "policy" requires no additional resources on client,
	server and network side.
	Disadvantages: The original size of the message remains unchanged,
	hence this approach provides no additional confidentiality.
	"No Padding" MUST NOT be used unless message size disallows the use
	of Padding.
	4.2. Fixed Length Padding
	In fixed length padding, a sender chooses to pad each message with a
	padding of constant length.
	Options: Actual length of padding
	Advantages: Since the padding is constant in length, this policy is
	very easy to implement, and at least ensures that the message length
	diverges from the length of the original packet (even only by a fixed
	value).
	Disadvantage: Obviously, the amount of padding is easily discoverable
	from a single unencrypted message, or by observing message patterns.
	When a public DNS server applies this policy, the length of the
	padding must be assumed to be public knowledge. Therefore, this
	policy is (almost) as useless as the "No Padding" option described
	above.
	"Fixed Length Padding" MUST NOT be used except for experimental
	applications.
	4.3. Block Length Padding		4.1. Block Length Padding
	In Block Length Padding, a sender pads each message so that its		In Block Length Padding, a sender pads each message so that its
	padded length is a multiple of a chosen block length. This creates a		padded length is a multiple of a chosen block length. This creates a
	greatly reduced variety of message lengths. An implementor needs to		greatly reduced variety of message lengths. An implementor needs to
	consider that even the zero-length EDNS(0) Padding Option increases		consider that even the zero-length EDNS(0) Padding Option increases
	the length of the packet by 4 octets.		the length of the packet by 4 octets.
	Options: Block Length - values between 16 and 128 octets for the		Options: Block Length - values between 16 and 128 octets for the
	queries seem reasonable, responses will require larger block sizes		queries seem reasonable, responses will require larger block sizes
	(see [dkg-padding-ndss] and Section 5 for a discussion).		(see [dkg-padding-ndss] and Section 5 for a discussion).
	Very large block lengths will have confidentiality properties similar		Very large block lengths will have confidentiality properties similar
	to the "Maximum Length Padding" strategy (Section 4.4), since almost		to the "Maximum Length Padding" strategy (Section 4.2), since almost
	all messages will fit into a single block. In that case, reasonable		all messages will fit into a single block. In that case, reasonable
	values may be 288 bytes for the query (the maximum size of a one-		values may be 288 bytes for the query (the maximum size of a one-
	question query over TCP, without any EDNS(0) options), and the		question query over TCP, without any EDNS(0) options), and the
	EDNS(0) buffer size of the server for the responses.		EDNS(0) buffer size of the server for the responses.
	Advantages: This policy is reasonably easy to implement, reduces the		Advantages: This policy is reasonably easy to implement, reduces the
	variety of message ("fingerprint") sizes significantly, and does not		variety of message ("fingerprint") sizes significantly, and does not
	require a source of (pseudo) random numbers, since the padding length		require a source of (pseudo) random numbers, since the padding length
	required can be derived from the actual (unpadded) message.		required can be derived from the actual (unpadded) message.
	Disadvantage: Given an unpadded message and the block size of the		Disadvantage: Given an unpadded message and the block size of the
	padding (which is assumed to be public knowledge once a server is		padding (which is assumed to be public knowledge once a server is
	reachable), the size of a padded message can be predicted.		reachable), the size of a padded message can be predicted.
	Therefore, minimum and maximum length of the unpadded message are		Therefore, minimum and maximum length of the unpadded message are
	known.		known.
	Block Length Padding is the currently RECOMMENDED strategy (see		Block Length Padding is the currently RECOMMENDED strategy (see
	Section 5).		Section 5).
	4.4. Maximal Length Padding ('The Full Monty')		4.2. Maximal Length Padding ('The Full Monty')
	In Maximal Length Padding the sender pads every message to the		In Maximal Length Padding the sender pads every message to the
	maximum size as allowed by protocol negotiations.		maximum size as allowed by protocol negotiations.
	Advantages: Maximal Length Padding, when combined with encrypted		Advantages: Maximal Length Padding, when combined with encrypted
	transport, provides the highest possible level of message size		transport, provides the highest possible level of message size
	confidentiality.		confidentiality.
	Disadvantages: Maximal Length Padding is wasteful, and requires		Disadvantages: Maximal Length Padding is wasteful, and requires
	resources on the client, all intervening network and equipment, and		resources on the client, all intervening network and equipment, and
	the server.		the server.
	Maximal Length Padding is NOT RECOMMENDED.		Maximal Length Padding is NOT RECOMMENDED.
	4.5. Random Length Padding		4.3. Random Length Padding
	When using Random Length Padding, a sender pads each message with a		When using Random Length Padding, a sender pads each message with a
	random amount of padding. Due to the size of the EDNS(0) Padding		random amount of padding. Due to the size of the EDNS(0) Padding
	Option itself, each message size is hence increased by at least 4		Option itself, each message size is hence increased by at least 4
	octets. The upper limit for pading is the maximum message size.		octets. The upper limit for pading is the maximum message size.
	However, a client or server may choose to impose a lower maximum		However, a client or server may choose to impose a lower maximum
	padding length.		padding length.
	Options: Maximum and minimum padding length.		Options: Maximum and minimum padding length.
	Advantages: Theoretically, this policy should create a natural		Advantages: Theoretically, this policy should create a natural
	"distribution" of message sizes.		"distribution" of message sizes.
	Disadvantage: This policy requires a good source of (pseudo) which		Disadvantage: This policy requires a good source of (pseudo) which
	can keep up with the required message rates. Especially on busy		can keep up with the required message rates. Especially on busy
	servers, this may be a significant hindrance.		servers, this may be a hindrance.
	TODO: Recommendation - this is (at first glance) the best policy, but		According to the limited empirical data available, Random Length
	requires significant effort		Padding performs slightly worse than Block Length Padding.
	4.6. Random Block Length Padding		4.4. Random Block Length Padding
	This policy combines Block Length Padding with a random component.		This policy combines Block Length Padding with a random component.
	Specifically, a sender randomly chooses between a few block length		Specifically, a sender randomly chooses between a few block length
	values and then applies Block Length Padding based on the chosen		values and then applies Block Length Padding based on the chosen
	block length. The random selection of block length might even be		block length. The random selection of block length might even be
	reasonably based on a "weak" source of randomness, such as the		reasonably based on a "weak" source of randomness, such as the
	transction ID of the message.		transction ID of the message.
	Options: Number of and the values for the set of Block Lengths,		Options: Number of and the values for the set of Block Lengths,
	source of "randomness"		source of "randomness"
	skipping to change at page 6, line 34 ¶		skipping to change at page 5, line 43 ¶
	Disadvantage: Requires more implementation effort compared to simple		Disadvantage: Requires more implementation effort compared to simple
	Block Length Padding		Block Length Padding
	Random Block Length Padding (as other combinations of padding		Random Block Length Padding (as other combinations of padding
	strategies) requires further empirical study.		strategies) requires further empirical study.
	5. Recommended Strategy		5. Recommended Strategy
	Based on empirical research performed by Daniel K. Gillmor		Based on empirical research performed by Daniel K. Gillmor
	[dkg-padding-ndss], EDNS(0) Padding SHOULD be performed as follows:		[dkg-padding-ndss], EDNS Padding SHOULD be performed as follows:
	(1) Clients SHOULD pad queries to the closest multiple of 128		(1) Clients SHOULD pad queries to the closest multiple of 128
	octets.		octets.
	(2) If a Server receives a query that includes the EDNS(0) Padding		(2) If a Server receives a query that includes the EDNS(0) Padding
	Option, it MUST pad the corresponding response (See Section 4 of		Option, it MUST pad the corresponding response (See Section 4 of
	[RFC7830]) and SHOULD pad the response to a multiple of 468		RFC7830) and SHOULD pad the corresponding response to a multiple
	octects.		of 468 octects.
			Note that the recommendation above does apply only if DNS transport
			is encrypted (See Section 6 of RFC 7830).
	The empirical research cited above performed a simulation of padding,		The empirical research cited above performed a simulation of padding,
	based on real-world DNS traffic captured on busy recursive resolvers		based on real-world DNS traffic captured on busy recursive resolvers
	of a research network. The evaluation of the performance of		of a research network. The evaluation of the performance of
	individual padding policies was based on a "cost to attacker" and		individual padding policies was based on a "cost to attacker" and
	"cost to defender" function, where the "cost to attacker" was defined		"cost to defender" function, where the "cost to attacker" was defined
	as the percentage of query/response pairs falling into the same size		as the percentage of query/response pairs falling into the same size
	bucket, and "cost to defender" as the size factor between padded and		bucket, and "cost to defender" as the size factor between padded and
	unpadded messages. Padding with a block size of 128 bytes on the		unpadded messages. Padding with a block size of 128 bytes on the
	query side, and 468 bytes on the response side was considered the		query side, and 468 bytes on the response side was considered the
	skipping to change at page 7, line 28 ¶		skipping to change at page 6, line 41 ¶
	7. IANA Considerations		7. IANA Considerations
	This document has no considerations for IANA.		This document has no considerations for IANA.
	8. Security Considerations		8. Security Considerations
	The choice of the right padding policy (and the right parameters for		The choice of the right padding policy (and the right parameters for
	the chosen policy) has a significant impact on the resilience of		the chosen policy) has a significant impact on the resilience of
	encrypted DNS against size-based correlation attacks. Therefore, any		encrypted DNS against size-based correlation attacks. Therefore, any
	implementor of EDNS(0) Padding must carefully consider the chosen		implementor of EDNS(0) Padding must carefully consider which policies
	policy and its parameters.		to implement, the default policy chosen, which parameters to make
			configurable, and the default parameter values.
	No matter how carefully a client selects their Padding policy, this		No matter how carefully a client selects their Padding policy, this
	effort can be jeopardized if the server chooses to apply an		effort can be jeopardized if the server chooses to apply an
	inffective Padding policy to the corresponding response packets.		inffective Padding policy to the corresponding response packets.
	Therefore, a client applying Padding may want to choose a DNS server		Therefore, a client applying Padding may want to choose a DNS server
	which does apply at least an equally effective Padding policy on		which does apply at least an equally effective Padding policy on
	responses.		responses.
	Note that even with encryption and padding, it might be trivial to		Note that even with encryption and padding, it might be trivial to
	identify that the observed traffic is DNS. Also, padding does not		identify that the observed traffic is DNS. Also, padding does not
	prevent information leak via other side channels (particularly timing		prevent information leak via other side channels (particularly timing
	information).		information and number of query/response pairs). Counter-measures
			against such other side channels could include injecting artificial
			"cover traffic" into the stream of DNS messages, or delaying DNS
			responses by a certain amount of jitter. Such strategies are out of
			scope of this document. Additionally, there is neither enough
			theoretic analysis nor experimental data available to recommend any
			such countermeasures.
	9. Changes		9. Changes
	[Note to RFC Editors: This whole section is to be removed before		[Note to RFC Editors: This whole section is to be removed before
	publication]		publication]
	9.1. draft-ietf-dprive-padding-policy-03		9.1. draft-ietf-dprive-padding-policy-04
			Changes based on WGLC: Changed implementor consideration text in
			Security Con section (Sara), moved "No Padding" and "Fixed Length
			Padding" to appendix (Stephane, Paul), Changed TODO in Random Padding
			to info from empirical study (Stephen), Added note to pad only if
			transport encrypted (Stephen), added intro text referencing to
			DNSoTLS and DNSoDTLS (Stephane), added text about timing/jitter to
			security considerations.
			9.2. draft-ietf-dprive-padding-policy-03
	Editorial changes in various spots. Added text about excluding TCP		Editorial changes in various spots. Added text about excluding TCP
	length field, more security considerations, addressing Sara's other		length field, more security considerations, addressing Sara's other
	feedback to -02.		feedback to -02.
	9.2. draft-ietf-dprive-padding-policy-02		9.3. draft-ietf-dprive-padding-policy-02
	Changed Document Status to Experimental, added "maximum length"		Changed Document Status to Experimental, added "maximum length"
	padding policy, reworded "block length" policy, some editorial		padding policy, reworded "block length" policy, some editorial
	changes.		changes.
	9.3. draft-ietf-dprive-padding-policy-01		9.4. draft-ietf-dprive-padding-policy-01
	Some (mostly editorial) changes to text. Added "Recommendation"		Some (mostly editorial) changes to text. Added "Recommendation"
	section based on dkg's research.		section based on dkg's research.
	9.4. draft-ietf-dprive-padding-policy-00		9.5. draft-ietf-dprive-padding-policy-00
	Initial (mostly unmodified) WG version. Changed "Profile" to		Initial (mostly unmodified) WG version. Changed "Profile" to
	"Policy" to avoid confusion with the (D)TLS profiles document.		"Policy" to avoid confusion with the (D)TLS profiles document.
	9.5. draft-mayrhofer-dprive-padding-profiles-00		9.6. draft-mayrhofer-dprive-padding-profiles-00
	Initial version		Initial version
	10. Normative References		10. References
			10.1. Normative References
	[dkg-padding-ndss]		[dkg-padding-ndss]
	Gillmor, D., "Empirical DNS Padding Policy", March 2017,		Gillmor, D., "Empirical DNS Padding Policy", March 2017,
	<https://dns.cmrg.net/		<https://dns.cmrg.net/
	ndss2017-dprive-empirical-DNS-traffic-size.pdf>.		ndss2017-dprive-empirical-DNS-traffic-size.pdf>.
	[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-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[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-editor.org/info/rfc7830>.		<https://www.rfc-editor.org/info/rfc7830>.
			10.2. Informative References
			[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
			and P. Hoffman, "Specification for DNS over Transport
			Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
			2016, <https://www.rfc-editor.org/info/rfc7858>.
			[RFC8094] Reddy, T., Wing, D., and P. Patil, "DNS over Datagram
			Transport Layer Security (DTLS)", RFC 8094,
			DOI 10.17487/RFC8094, February 2017,
			<https://www.rfc-editor.org/info/rfc8094>.
			Appendix A. Non-sensible Padding Policies
			A.1. No Padding
			In the "No Padding" policy, the EDNS0 Padding option is not used, and
			the size of the final (actually, "non-padded") message obviously
			exactly matches the size of the unpadded message. Even though this
			"non-policy" seems redundant in this list, its properties must be
			considered for cases where just one of the parties (client or server)
			applies padding.
			Also, this "policy" is required when the remaining message size of
			the unpadded message does not allow for the Padding option to be
			included (less than 4 octets left).
			Advantages: This "policy" requires no additional resources on client,
			server and network side.
			Disadvantages: The original size of the message remains unchanged,
			hence this approach provides no additional confidentiality.
			"No Padding" MUST NOT be used unless message size disallows the use
			of Padding.
			A.2. Fixed Length Padding
			In fixed length padding, a sender chooses to pad each message with a
			padding of constant length.
			Options: Actual length of padding
			Advantages: Since the padding is constant in length, this policy is
			very easy to implement, and at least ensures that the message length
			diverges from the length of the original packet (even only by a fixed
			value)
			Disadvantage: Obviously, the amount of padding easily discoverable
			from a single unencrypted message, or by observing message patterns.
			When a public DNS server applies this policy, the length of the
			padding hence must be assumed to be public knowledge. Therefore,
			this policy is (almost) as useless as the "No Padding" option
			described above.
			"Fixed Length Padding" MUST NOT be used except for experimental
			applications.
	Author's Address		Author's Address
	Alexander Mayrhofer		Alexander Mayrhofer
	nic.at GmbH		nic.at GmbH
	Karlsplatz 1/2/9		Karlsplatz 1/2/9
	Vienna 1010		Vienna 1010
	Austria		Austria
	Email: alex.mayrhofer.ietf@gmail.com		Email: alex.mayrhofer.ietf@gmail.com
			URI: http://edns0-padding.org/
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