draft-ietf-perc-private-media-framework-01.txt		draft-ietf-perc-private-media-framework-02.txt
	Network Working Group P. Jones		Network Working Group P. Jones
	Internet-Draft D. Benham		Internet-Draft D. Benham
	Intended status: Standards Track Cisco		Intended status: Standards Track Cisco
	Expires: January 9, 2017 C. Groves		Expires: May 4, 2017 C. Groves
	Huawei		Huawei
	July 8, 2016		October 31, 2016
	A Solution Framework for Private Media in Privacy Enhanced RTP		A Solution Framework for Private Media in Privacy Enhanced RTP
	Conferencing		Conferencing
	draft-ietf-perc-private-media-framework-01		draft-ietf-perc-private-media-framework-02
	Abstract		Abstract
	This document describes a solution framework for ensuring that media		This document describes a solution framework for ensuring that media
	confidentiality and integrity are maintained end-to-end within the		confidentiality and integrity are maintained end-to-end within the
	context of a switched conferencing environment where media		context of a switched conferencing environment where media
	distribution devices are not trusted with the end-to-end media		distribution devices are not trusted with the end-to-end media
	encryption keys. The solution aims to build upon existing security		encryption keys. The solution aims to build upon existing security
	mechanisms defined for the real-time transport protocol (RTP).		mechanisms defined for the real-time transport protocol (RTP).
	skipping to change at page 1, line 38 ¶		skipping to change at page 1, line 38 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on January 9, 2017.		This Internet-Draft will expire on May 4, 2017.
	Copyright Notice		Copyright Notice
	Copyright (c) 2016 IETF Trust and the persons identified as the		Copyright (c) 2016 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 31 ¶		skipping to change at page 2, line 31 ¶
	4.1. End-to-End and Hop-by-Hop Authenticated Encryption . . . 7		4.1. End-to-End and Hop-by-Hop Authenticated Encryption . . . 7
	4.2. E2E Key Confidentiality . . . . . . . . . . . . . . . . . 8		4.2. E2E Key Confidentiality . . . . . . . . . . . . . . . . . 8
	4.3. E2E Keys and Endpoint Operations . . . . . . . . . . . . 9		4.3. E2E Keys and Endpoint Operations . . . . . . . . . . . . 9
	4.4. HBH Keys and Hop Operations . . . . . . . . . . . . . . . 9		4.4. HBH Keys and Hop Operations . . . . . . . . . . . . . . . 9
	4.5. Key Exchange . . . . . . . . . . . . . . . . . . . . . . 10		4.5. Key Exchange . . . . . . . . . . . . . . . . . . . . . . 10
	4.5.1. Initial Key Exchange and Key Distributor . . . . . . 10		4.5.1. Initial Key Exchange and Key Distributor . . . . . . 10
	4.5.2. Key Exchange during a Conference . . . . . . . . . . 11		4.5.2. Key Exchange during a Conference . . . . . . . . . . 11
	5. Entity Trust . . . . . . . . . . . . . . . . . . . . . . . . 12		5. Entity Trust . . . . . . . . . . . . . . . . . . . . . . . . 12
	5.1. Identity Assertions . . . . . . . . . . . . . . . . . . . 12		5.1. Identity Assertions . . . . . . . . . . . . . . . . . . . 12
	5.2. Certificate Fingerprints in Session Signaling . . . . . . 12		5.2. Certificate Fingerprints in Session Signaling . . . . . . 12
	6. Attacks on Privacy Enhanced RTP Conferencing . . . . . . . . 13		5.3. Conferences Identification . . . . . . . . . . . . . . . 13
			6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
	6.1. Third Party Attacks . . . . . . . . . . . . . . . . . . . 13		6.1. Third Party Attacks . . . . . . . . . . . . . . . . . . . 13
	6.2. Media Distributor Attacks . . . . . . . . . . . . . . . . 14		6.2. Media Distributor Attacks . . . . . . . . . . . . . . . . 14
	6.2.1. Denial of service . . . . . . . . . . . . . . . . . . 14		6.2.1. Denial of service . . . . . . . . . . . . . . . . . . 14
	6.2.2. Replay Attack . . . . . . . . . . . . . . . . . . . . 14		6.2.2. Replay Attack . . . . . . . . . . . . . . . . . . . . 15
	6.2.3. Delayed Playout Attack . . . . . . . . . . . . . . . 15		6.2.3. Delayed Playout Attack . . . . . . . . . . . . . . . 15
	6.2.4. Splicing Attack . . . . . . . . . . . . . . . . . . . 15		6.2.4. Splicing Attack . . . . . . . . . . . . . . . . . . . 15
	7. To-Do List . . . . . . . . . . . . . . . . . . . . . . . . . 15		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16		8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 16		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
	10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16		9.1. Normative References . . . . . . . . . . . . . . . . . . 16
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16		9.2. Informative References . . . . . . . . . . . . . . . . . 17
	11.1. Normative References . . . . . . . . . . . . . . . . . . 16
	11.2. Informative References . . . . . . . . . . . . . . . . . 17
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
	1. Introduction		1. Introduction
	Switched conferencing is an increasingly popular model for multimedia		Switched conferencing is an increasingly popular model for multimedia
	conferences with multiple participants using a combination of audio,		conferences with multiple participants using a combination of audio,
	video, text, and other media types. With this model, real-time media		video, text, and other media types. With this model, real-time media
	flows from conference participants are not mixed, transcoded,		flows from conference participants are not mixed, transcoded,
	transrated, recomposed, or otherwise manipulated by a Media		transrated, recomposed, or otherwise manipulated by a Media
	Distributor, as might be the case with a traditional media server or		Distributor, as might be the case with a traditional media server or
	skipping to change at page 4, line 21 ¶		skipping to change at page 4, line 18 ¶
	Hop-by-Hop (HBH): Communications between an endpoint and a Media		Hop-by-Hop (HBH): Communications between an endpoint and a Media
	Distribution Device or between Media Distribution Devices.		Distribution Device or between Media Distribution Devices.
	Endpoint: An RTP flow terminating entity that has possession of E2E		Endpoint: An RTP flow terminating entity that has possession of E2E
	media encryption keys and terminates E2E encryption. This may		media encryption keys and terminates E2E encryption. This may
	include embedded user conferencing equipment or browsers on		include embedded user conferencing equipment or browsers on
	computers, media gateways, MCUs, media recording device and more that		computers, media gateways, MCUs, media recording device and more that
	are in the trusted domain for a given deployment.		are in the trusted domain for a given deployment.
	Media Distributor (MD): An RTP middlebox that is not allowed to to		Media Distributor (MD): An RTP middlebox that is not allowed to to
	have access to E2E encryption keys. It may operate according to any		have access to E2E encryption keys. It operates according to the
	of the RTP topologies [I-D.ietf-avtcore-rtp-topologies-update] per		Selective Forwarding Middlebox RTP topologies
	the constraints defined by the PERC system, which includes, but not		[I-D.ietf-avtcore-rtp-topologies-update] per the constraints defined
	limited to, having no access to RTP media unencrypted and having		by the PERC system, which includes, but not limited to, having no
	limits on what RTP header field it can alter.		access to RTP media unencrypted and having limits on what RTP header
			field it can alter.
	Key Distributor: An entity that is a logical function which passes		Key Distributor: An entity that is a logical function which passes
	keying material and related information to endpoints and Media		keying material and related information to endpoints and Media
	Distributor(s) that is appropriate for each. The Key Distributor		Distributor(s) that is appropriate for each. The Key Distributor
	might be co-resident with another entity trusted with E2E keying		might be co-resident with another entity trusted with E2E keying
	material.		material.
	Conference: Two or more participants communicating via trusted		Conference: Two or more participants communicating via trusted
	endpoints to exchange RTP flows through one or more Media		endpoints to exchange RTP flows through one or more Media
	Distributor.		Distributor.
	skipping to change at page 7, line 17 ¶		skipping to change at page 7, line 14 ¶
	3.2.2. Key Distributor		3.2.2. Key Distributor
	The Key Distributor, which may be collocated with an endpoint or		The Key Distributor, which may be collocated with an endpoint or
	exist standalone, is responsible for providing key information to		exist standalone, is responsible for providing key information to
	endpoints for both end-to-end and hop-by-hop security and for		endpoints for both end-to-end and hop-by-hop security and for
	providing key information to Media Distributors for the hop-by-hop		providing key information to Media Distributors for the hop-by-hop
	security.		security.
	Interaction between the Key Distributor and the call processing		Interaction between the Key Distributor and the call processing
	function may be necessary to for proper conference-to-endpoint		function is necessary to for proper conference-to-endpoint mappings.
	mappings, which may or may not be satisfied by getting information		This is described in Section 5.3.
	directly from the endpoints or via some other means. See Section 7
	for a related item in the To Do list.
	The Key Distributor needs to be secured and managed in a way to		The Key Distributor needs to be secured and managed in a way to
	prevent exploitation by an adversary, as any kind of compromise of		prevent exploitation by an adversary, as any kind of compromise of
	the Key Distributor puts the security of the conference at risk.		the Key Distributor puts the security of the conference at risk.
	4. Framework for PERC		4. Framework for PERC
	The purpose for this framework is to define a means through which		The purpose for this framework is to define a means through which
	media privacy can be ensured when communicating within a conferencing		media privacy can be ensured when communicating within a conferencing
	environment consisting of one or more Media Distributors that only		environment consisting of one or more Media Distributors that only
	switch, hence not terminate, media. It does not otherwise attempt to		switch, hence not terminate, media. It does not otherwise attempt to
	hide the fact that a conference between endpoints is taking place.		hide the fact that a conference between endpoints is taking place.
	This framework reuses several specified RTP security technologies,		This framework reuses several specified RTP security technologies,
	including SRTP [RFC3711], PERC EKT [I-D.ietf-perc-srtp-ekt-diet], and		including SRTP [RFC3711], PERC EKT [I-D.ietf-perc-srtp-ekt-diet], and
	DTLS-SRTP [RFC5764].		DTLS-SRTP [RFC5764].
	4.1. End-to-End and Hop-by-Hop Authenticated Encryption		4.1. End-to-End and Hop-by-Hop Authenticated Encryption
	This solution framework focuses on the end-to-end privacy and		This solution framework focuses on the end-to-end privacy and
	integrity of the participant's media by limiting access to end-to-end		integrity of the participant's media by limiting access of the end-
	key information to trusted entities. However, this framework does		to-end key information to trusted entities. However, this framework
	give a Media Distributor access to RTP headers and all or most header		does give a Media Distributor access to RTP headers and all or most
	extensions, as well as the ability to modify a certain subset of		header extensions, as well as the ability to modify a certain subset
	those headers and to add header extensions. Packets received by a		of those headers and to add header extensions. Packets received by a
	Media Distributor or an endpoint are authenticated hop-by-hop.		Media Distributor or an endpoint are authenticated hop-by-hop.
	To enable all of the above, this framework defines the use of two		To enable all of the above, this framework defines the use of two
	security contexts and two associated encryption keys; an "inner" key		security contexts and two associated encryption keys; an "inner" key
	(E2E Key(i); i={a given endpoint}) for authenticated encryption of		(E2E Key(i); i={a given endpoint}) for authenticated encryption of
	RTP media between endpoints and an "outer" key (HBH Key(j); j={a		RTP media between endpoints and an "outer" key (HBH Key(j); j={a
	given hop}) for the hop between an endpoint and a Media Distributor		given hop}) for the hop between an endpoint and a Media Distributor
	or between Media Distributor. Reference the following figure.		or between Media Distributor. Reference the following figure.
	+-------------+ +-------------+		+-------------+ +-------------+
	skipping to change at page 8, line 48 ¶		skipping to change at page 8, line 46 ¶
	framework introduces no additional step for RTCP authenticated		framework introduces no additional step for RTCP authenticated
	encryption, so the procedures needed are specified in [RFC3711] and		encryption, so the procedures needed are specified in [RFC3711] and
	use the same outer, hop-by-hop cryptographic context chosen in the		use the same outer, hop-by-hop cryptographic context chosen in the
	Double operation described above.		Double operation described above.
	4.2. E2E Key Confidentiality		4.2. E2E Key Confidentiality
	To ensure the confidentiality of E2E keys shared between endpoints,		To ensure the confidentiality of E2E keys shared between endpoints,
	endpoints will make use of a common Key Encryption Key (KEK) that is		endpoints will make use of a common Key Encryption Key (KEK) that is
	known only by the trusted entities in a conference. That KEK,		known only by the trusted entities in a conference. That KEK,
	defined in the PERC EKT [I-D.ietf-perc-srtp-ekt-diet] as the EKT Key,		defined in the PERC EKT [I-D.ietf-perc-srtp-ekt-diet] as the EKTKey,
	will be used to subsequently encrypt SRTP master keys used for E2E		will be used to subsequently encrypt SRTP master keys used for E2E
	authenticated encryption (E2E Key(i); i={a given endpoint}) of media		authenticated encryption (E2E Key(i); i={a given endpoint}) of media
	sent by a given endpoint.		sent by a given endpoint.
	+---------------------+------------+-------+-------+------------+		+---------------------+------------+-------+-------+------------+
	| Key / Entity | Endpoint A | MD X | MD Y | Endpoint B |		| Key / Entity | Endpoint A | MD X | MD Y | Endpoint B |
	+---------------------+------------+-------+-------+------------+		+---------------------+------------+-------+-------+------------+
	| KEK | Yes | No | No | Yes |		| KEK | Yes | No | No | Yes |
	+---------------------+------------+-------+-------+------------+		+---------------------+------------+-------+-------+------------+
	| E2E Key (i) | Yes | No | No | Yes |		| E2E Key (i) | Yes | No | No | Yes |
	skipping to change at page 9, line 27 ¶		skipping to change at page 9, line 27 ¶
	Figure 2: Keys per Entity		Figure 2: Keys per Entity
	4.3. E2E Keys and Endpoint Operations		4.3. E2E Keys and Endpoint Operations
	Any given RTP media flow can be identified by its SSRC, and endpoints		Any given RTP media flow can be identified by its SSRC, and endpoints
	might send more than one at a time and change the mix of media flows		might send more than one at a time and change the mix of media flows
	transmitted during the life of a conference.		transmitted during the life of a conference.
	Thus, endpoints MUST maintain a list of SSRCs from received RTP flows		Thus, endpoints MUST maintain a list of SSRCs from received RTP flows
	and each SSRC's associated E2E Key(i) information. Following a		and each SSRC's associated E2E Key(i) information. Following a
	change of the KEK (i.e., EKT Key), prior E2E Key(i) information		change of the KEK (i.e., EKTKey), prior E2E Key(i) information SHOULD
	SHOULD be retained for a period long enough to ensure that late-		be retained for a period long enough to ensure that late-arriving or
	arriving or out-of-order packets from other endpoints can be		out-of-order packets from other endpoints can be successfully
	successfully decrypted. The endpoint MUST discard the E2E Key(i) and		decrypted. The endpoint MUST discard the E2E Key(i) and KEK
	KEK information no later than when it leaves the conference.		information no later than when it leaves the conference.
	If there is a need to encrypt one or more RTP header extensions end-		If there is a need to encrypt one or more RTP header extensions end-
	to-end, an encryption key is derived from the end-to-end SRTP master		to-end, an encryption key is derived from the end-to-end SRTP master
	key to encrypt header extensions as per [RFC6904]. The Media		key to encrypt header extensions as per [RFC6904]. The Media
	Distributor will not be able use the information contained in those		Distributor will not be able use the information contained in those
	header extensions encrypted with E2E keys. See Section 7 for a		header extensions encrypted with E2E keys.
	related item in the To Do list.
	4.4. HBH Keys and Hop Operations		4.4. HBH Keys and Hop Operations
	To ensure the integrity of transmitted media packets, this framework		To ensure the integrity of transmitted media packets, this framework
	requires that every packet be authenticated hop-by-hop (HBH) between		requires that every packet be authenticated hop-by-hop (HBH) between
	an endpoint and a Media Distributor, as well between Media		an endpoint and a Media Distributor, as well between Media
	Distributors. The authentication key used for hop-by-hop		Distributors. The authentication key used for hop-by-hop
	authentication is derived from an SRTP master key shared only on the		authentication is derived from an SRTP master key shared only on the
	respective hop (HBH Key(j); j={a given hop}). Each HBH Key(j) is		respective hop (HBH Key(j); j={a given hop}). Each HBH Key(j) is
	distinct per hop and no two hops ever intentionally use the same SRTP		distinct per hop and no two hops ever intentionally use the same SRTP
	skipping to change at page 10, line 28 ¶		skipping to change at page 10, line 28 ¶
	all hops - in the untrusted domain at least - will need to decrypt		all hops - in the untrusted domain at least - will need to decrypt
	and re-encrypt these encrypted header extensions.		and re-encrypt these encrypted header extensions.
	4.5. Key Exchange		4.5. Key Exchange
	To facilitate key exchange required to establish or generate an E2E		To facilitate key exchange required to establish or generate an E2E
	key and a HBH key for an endpoint and the same HBH key for the Media		key and a HBH key for an endpoint and the same HBH key for the Media
	Distributor, this framework utilizes a DTLS-SRTP [RFC5764]		Distributor, this framework utilizes a DTLS-SRTP [RFC5764]
	association between an endpoint and the Key Distributor. To		association between an endpoint and the Key Distributor. To
	establish this association, an endpoint will send DTLS-SRTP messages		establish this association, an endpoint will send DTLS-SRTP messages
	to the Media Distributor which will then forward them to the Media		to the Media Distributor which will then forward them to the Key
	Distributor as defined in [I-D.jones-perc-dtls-tunnel]. The Key		Distributor as defined in [I-D.jones-perc-dtls-tunnel]. The Key
	Encryption Key (KEK) (i.e., EKT Key) is also conveyed by the Key		Encryption Key (KEK) (i.e., EKTKey) is also conveyed by the Key
	Distributor over the DTLS association to endpoints via procedures		Distributor over the DTLS association to endpoints via procedures
	defined in PERC EKT [I-D.ietf-perc-srtp-ekt-diet].		defined in PERC EKT [I-D.ietf-perc-srtp-ekt-diet].
	Media Distributors use DTLS-SRTP [RFC5764] directly with a peer Media		Media Distributors use DTLS-SRTP [RFC5764] directly with a peer Media
	Distributor to establish HBH keys for transmitting RTP and RTCP		Distributor to establish HBH keys for transmitting RTP and RTCP
	packets that peer Media Distributor. The Key Distributor does not		packets to that peer Media Distributor. The Key Distributor does not
	facilitate establishing HBH keys for use between Media Distributors.		facilitate establishing HBH keys for use between Media Distributors.
	4.5.1. Initial Key Exchange and Key Distributor		4.5.1. Initial Key Exchange and Key Distributor
	The procedures defined in DTLS Tunnel for PERC		The procedures defined in DTLS Tunnel for PERC
	[I-D.jones-perc-dtls-tunnel] establish one or more DTLS tunnels		[I-D.jones-perc-dtls-tunnel] establish one or more TLS tunnels
	between the Media Distributor and Key Distributor, making it is		between the Media Distributor and Key Distributor, making it is
	possible for the Media Distributor to facilitate the establishment of		possible for the Media Distributor to facilitate the establishment of
	a secure DTLS association between each endpoint and the Key		a secure DTLS association between each endpoint and the Key
	Distributor as shown the following figure. The DTLS association		Distributor as shown the following figure. The DTLS association
	between endpoints and the Key Distributor will enable each endpoint		between endpoints and the Key Distributor will enable each endpoint
	to receive E2E key information, Key Encryption Key (KEK) information		to receive E2E key information, Key Encryption Key (KEK) information
	(i.e., EKT Key), and HBH key information. At the same time, the Key		(i.e., EKTKey), and HBH key information. At the same time, the Key
	Distributor can securely provide the HBH key information to the Media		Distributor can securely provide the HBH key information to the Media
	Distributor. The key information summarized here may include the		Distributor. The key information summarized here may include the
	SRTP master key, SRTP master salt, and the negotiated cryptographic		SRTP master key, SRTP master salt, and the negotiated cryptographic
	transform.		transform.
	+-----------+		+-----------+
	KEK info | Key | HBH Key info to		KEK info | Key | HBH Key info to
	to Endpoints |Distributor| Endpoints & Media Distributor		to Endpoints |Distributor| Endpoints & Media Distributor
	+-----------+		+-----------+
	# ^ ^ #		# ^ ^ #
	# | | #-DTLS Tunnel		# | | #-TLS Tunnel
	# | | #		# | | #
	+-----------+ +-----------+ +-----------+		+-----------+ +-----------+ +-----------+
	| Endpoint | DTLS | Media | DTLS | Endpoint |		| Endpoint | DTLS | Media | DTLS | Endpoint |
	| KEK |<------------|Distributor|------------>| KEK |		| KEK |<------------|Distributor|------------>| KEK |
	| HBH Key(j)| to Key Dist | HBH Keys | to Key Dist | HBH Key(j)|		| HBH Key(j)| to Key Dist | HBH Keys | to Key Dist | HBH Key(j)|
	+-----------+ +-----------+ +-----------+		+-----------+ +-----------+ +-----------+
	Figure 3: Exchanging Key Information Between Entities		Figure 3: Exchanging Key Information Between Entities
	Endpoints will establish a DTLS-SRTP association over the RTP		Endpoints will establish a DTLS-SRTP association over the RTP
	session's media ports for the purposes of key information exchange		session's media ports for the purposes of key information exchange
	with the Key Distributor. The Media Distributor will not terminate		with the Key Distributor. The Media Distributor will not terminate
	the DTLS signaling, but will instead forward DTLS packets received		the DTLS signaling, but will instead forward DTLS packets received
	from an endpoint on to the Key Distributor (and vice versa) via a		from an endpoint on to the Key Distributor (and vice versa) via a
	tunnel established between Media Distributor and the Key Distributor.		tunnel established between Media Distributor and the Key Distributor.
	This tunnel used to encapsulate the DTLS-SRTP signaling between the		This tunnel is used to encapsulate the DTLS-SRTP signaling between
	Key Distributor and endpoints will also be used to convey HBH key		the Key Distributor and endpoints will also be used to convey HBH key
	information from the Key Distributor to the Media Distributor, so no		information from the Key Distributor to the Media Distributor, so no
	additional protocol or interface is required.		additional protocol or interface is required.
	4.5.2. Key Exchange during a Conference		4.5.2. Key Exchange during a Conference
	Following the initial key information exchange with the Key		Following the initial key information exchange with the Key
	Distributor, endpoints will be able to encrypt media end-to-end with		Distributor, endpoints will be able to encrypt media end-to-end with
	their E2E Key(i), sending that E2E Key(i) to other endpoints		their E2E Key(i), sending that E2E Key(i) to other endpoints
	encrypted with KEK, and will be able to encrypt and authenticate RTP		encrypted with KEK, and will be able to encrypt and authenticate RTP
	packets using local HBH Key(j). The procedures defined do not allow		packets using local HBH Key(j). The procedures defined do not allow
	the Media Distributor to gain access to the KEK information,		the Media Distributor to gain access to the KEK information,
	preventing it from gaining access to any endpoint's E2E key and		preventing it from gaining access to any endpoint's E2E key and
	subsequently decrypting media.		subsequently decrypting media.
	The KEK (i.e., EKT Key) may need to change from time-to-time during		The KEK (i.e., EKTKey) may need to change from time-to-time during
	the life of a conference, such as when a new participant joins or		the life of a conference, such as when a new participant joins or
	leaves a conference. Dictating if, when or how often a conference is		leaves a conference. Dictating if, when or how often a conference is
	to be re-keyed is outside the scope of this document, but this		to be re-keyed is outside the scope of this document, but this
	framework does accommodate re-keying during the life of a conference.		framework does accommodate re-keying during the life of a conference.
	When a Key Distributor decides to rekey a conference, it transmits a		When a Key Distributor decides to rekey a conference, it transmits a
	specific message defined in PERC EKT [I-D.ietf-perc-srtp-ekt-diet] to		specific message defined in PERC EKT [I-D.ietf-perc-srtp-ekt-diet] to
	each of the conference participants. The endpoint MUST create a new		each of the conference participants. The endpoint MUST create a new
	SRTP master key and prepare to send that key inside a Full EKT Field		SRTP master key and prepare to send that key inside a Full EKT Field
	using the new EKT Key. Since it may take some time for all of the		using the new EKTKey. Since it may take some time for all of the
	endpoints in conference to finish re-keying, senders MUST delay a		endpoints in conference to finish re-keying, senders MUST delay a
	short period of time before sending media encrypted with the new		short period of time before sending media encrypted with the new
	master key, but it MUST be prepared to make use of the information		master key, but it MUST be prepared to make use of the information
	from a new inbound EKT Key immediately. See Section 2.2.2 of		from a new inbound EKTKey immediately. See Section 2.2.2 of
	[I-D.ietf-perc-srtp-ekt-diet].		[I-D.ietf-perc-srtp-ekt-diet].
	5. Entity Trust		5. Entity Trust
	It is important to this solution framework that the entities can		It is important to this solution framework that the entities can
	trust and validate the authenticity of other entities, especially the		trust and validate the authenticity of other entities, especially the
	Key Distributor and endpoints. The details of this are outside the		Key Distributor and endpoints. The details of this are outside the
	scope of specification but a few possibilities are discussed in the		scope of specification but a few possibilities are discussed in the
	following sections. The key requirements is that endpoints can		following sections. The key requirements is that endpoints can
	verify they are connected to the correct Key Distributor for the		verify they are connected to the correct Key Distributor for the
	conference and the Key Distributor can verify the endpoints are the		conference and the Key Distributor can verify the endpoints are the
	correct endpoints for the conference.		correct endpoints for the conference.
	Two possible approaches to solve this are Identity Assertions and		Two possible approaches to solve this are Identity Assertions and
	Certificate Fingerprints.		Certificate Fingerprints.
	5.1. Identity Assertions		5.1. Identity Assertions
	WebRTC Identity assertion (EDITOR NOTE: add I-D reference) can be		WebRTC Identity assertion [I-D.ietf-rtcweb-security-arch] can be used
	used to bind the identity of the user of the endpoint to the		to bind the identity of the user of the endpoint to the fingerprint
	fingerprint of the DTLS-SRTP certificate used for the call. This		of the DTLS-SRTP certificate used for the call. This certificate is
	certificate is unique for a given call and a conference. This allows		unique for a given call and a conference. This allows the Key
	the Key Distributor to ensure that only authorized users participate		Distributor to ensure that only authorized users participate in the
	in the conference. Similarly the Key Distributor can create a WeBRTC		conference. Similarly the Key Distributor can create a WebRTC
	Identity assertion bound the fingerprint of the unique certificate		Identity assertion to bind the fingerprint of the unique certificate
	used by the Key Distributor for this conference so that the endpoint		used by the Key Distributor for this conference so that the endpoint
	can validate it is talking to the correct Key Distributor.		can validate it is talking to the correct Key Distributor. Such a
			setup requires an Identity Provider (Idp) trusted by the endpoints
			and the Key Distributor.
	5.2. Certificate Fingerprints in Session Signaling		5.2. Certificate Fingerprints in Session Signaling
	Entities managing session signaling are generally assumed to be		Entities managing session signaling are generally assumed to be
	untrusted in the PERC framework. However, there are some deployment		untrusted in the PERC framework. However, there are some deployment
	scenarios where parts of the session signaling may be assumed		scenarios where parts of the session signaling may be assumed
	trustworthy for the purposes of exchanging, in a manner that can be		trustworthy for the purposes of exchanging, in a manner that can be
	authenticated, the fingerprint of an entity's certificate.		authenticated, the fingerprint of an entity's certificate.
	As a concrete example, SIP [RFC3261] and SDP [RFC4566] can be used to		As a concrete example, SIP [RFC3261] and SDP [RFC4566] can be used to
	skipping to change at page 13, line 18 ¶		skipping to change at page 13, line 22 ¶
	connections to find the identity of the far end of the DTLS-SRTP		connections to find the identity of the far end of the DTLS-SRTP
	connection and check that is the authorized entity.		connection and check that is the authorized entity.
	Ultimately, if using session signaling, an endpoint's certificate		Ultimately, if using session signaling, an endpoint's certificate
	fingerprint would need to be securely mapped to a user and conveyed		fingerprint would need to be securely mapped to a user and conveyed
	to the Key Distributor so that it can check that that user is		to the Key Distributor so that it can check that that user is
	authorized. Similarly, the Key Distributor's certificate fingerprint		authorized. Similarly, the Key Distributor's certificate fingerprint
	can be conveyed to endpoint in a manner that can be authenticated as		can be conveyed to endpoint in a manner that can be authenticated as
	being an authorized Key Distributor for this conference.		being an authorized Key Distributor for this conference.
	6. Attacks on Privacy Enhanced RTP Conferencing		5.3. Conferences Identification
			The Key Distributor is responsible for knowing what endpoints are
			allowed in a given conference. Thus, the Key Distributor and the
			Media Distributor will need to know endpoint-to-conference mappings,
			which is enabled by exchanging a conference-specific unique
			identifier as defined in [I-D.jones-perc-dtls-tunnel]. How this
			unique identifier is assigned is outside the scope of this document.
			6. Security Considerations
	This framework, and the individual protocols defined to support it,		This framework, and the individual protocols defined to support it,
	must take care to not increase the exposure to Denial of Service		must take care to not increase the exposure to Denial of Service
	(DoS) attacks by untrusted or third-party entities and should take		(DoS) attacks by untrusted or third-party entities and should take
	measures to mitigate, where possible, more serious DoS attacks from		measures to mitigate, where possible, more serious DoS attacks from
	on-path and off-path attackers.		on-path and off-path attackers.
	The following section enumerates the kind of attacks that will be		The following section enumerates the kind of attacks that will be
	considered in the development of this framework's solution.		considered in the development of this framework's solution.
	skipping to change at page 15, line 36 ¶		skipping to change at page 15, line 47 ¶
	The splicing attack is an attack where a Media Distributor receiving		The splicing attack is an attack where a Media Distributor receiving
	multiple media sources splices one media stream into the other. If		multiple media sources splices one media stream into the other. If
	the Media Distributor is able to change the SSRC without the receiver		the Media Distributor is able to change the SSRC without the receiver
	having any method for verifying the original source ID, then the		having any method for verifying the original source ID, then the
	Media Distributor could first deliver stream A and then later forward		Media Distributor could first deliver stream A and then later forward
	stream B under the same SSRC as stream A was previously using. Not		stream B under the same SSRC as stream A was previously using. Not
	allowing the Media Distributor to change the SSRC mitigates this		allowing the Media Distributor to change the SSRC mitigates this
	attack.		attack.
	7. To-Do List		7. IANA Considerations
	o The mapping of endpoints-to-conference identifiers may need to be
	conveyed in the framework. Need Revisit this text after a design
	choice is made between alternatives.
	o Consider adding a list of RTP header extensions that should/must
	not be E2E encrypted.
	o Endpoints, Key Distributor and Media Distributor provider must
	securely convey their respective certificate information directly
	or indirectly via some means, such as via an identity service
	provider.
	o If as in "Double" draft, the ROC value is no longer in the clear
	and associated with the "outer" protection scheme, we may need to
	require that the Media Distributor maintain a separate ROC value
	for each SSRC sent to each endpoint. This ROC value should start
	at 0 regardless of the sequence number in that first packet sent
	to an endpoint.
	o Investigate adding ability to enable the transmission of one-way
	media from a non-trusted device (e.g., announcements). One
	possible solution is to have the Key Distributor send an "ekt_key"
	message that is explicitly labeled for receive-only and giving
	that to announcement servers. A possible approach would be to
	define EKT Keys with a SPI > 32000, for example, for this purpose
	and endpoints should only use those EKT Keys to decrypt Full EKT
	Fields received from such transmitters. Endpoints would never
	send media with EKT Keys with those SPI values.
	8. IANA Considerations
	There are no IANA considerations for this document.		There are no IANA considerations for this document.
	9. Security Considerations		8. Acknowledgments
	[TBD]
	10. Acknowledgments
	The authors would like to thank Mo Zanaty and Christian Oien for		The authors would like to thank Mo Zanaty and Christian Oien for
	invaluable input on this document. Also, we would like to		invaluable input on this document. Also, we would like to
	acknowledge Nermeen Ismail for serving on the initial versions of		acknowledge Nermeen Ismail for serving on the initial versions of
	this document as a co-author.		this document as a co-author.
	11. References		9. References
	11.1. Normative References		9.1. Normative References
	[I-D.ietf-perc-double]		[I-D.ietf-perc-double]
	Jennings, C., Jones, P., and A. Roach, "SRTP Double		Jennings, C., Jones, P., and A. Roach, "SRTP Double
	Encryption Procedures", draft-ietf-perc-double-00 (work in		Encryption Procedures", draft-ietf-perc-double-01 (work in
	progress), May 2016.		progress), July 2016.
	[I-D.ietf-perc-srtp-ekt-diet]		[I-D.ietf-perc-srtp-ekt-diet]
	Mattsson, J., McGrew, D., Wing, D., and C. Jennings,		Mattsson, J., McGrew, D., Wing, D., and C. Jennings,
	"Encrypted Key Transport for Secure RTP", draft-ietf-perc-		"Encrypted Key Transport for Secure RTP", draft-ietf-perc-
	srtp-ekt-diet-00 (work in progress), May 2016.		srtp-ekt-diet-01 (work in progress), July 2016.
	[I-D.jones-perc-dtls-tunnel]		[I-D.jones-perc-dtls-tunnel]
	Jones, P., "DTLS Tunnel between Media Distribution Device		Jones, P., "A DTLS Tunnel between Media Distributor and
	and Key Management Function to Facilitate Key Exchange",		Key Distributor to Facilitate Key Exchange", draft-jones-
	draft-jones-perc-dtls-tunnel-03 (work in progress), July		perc-dtls-tunnel-03 (work in progress), July 2016.
	2016.
	[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, DOI 10.17487/		Requirement Levels", BCP 14, RFC 2119,
	RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<http://www.rfc-editor.org/info/rfc2119>.		<http://www.rfc-editor.org/info/rfc2119>.
	[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.		[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
	Jacobson, "RTP: A Transport Protocol for Real-Time		Jacobson, "RTP: A Transport Protocol for Real-Time
	Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,		Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
	July 2003, <http://www.rfc-editor.org/info/rfc3550>.		July 2003, <http://www.rfc-editor.org/info/rfc3550>.
	[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.		[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
	Norrman, "The Secure Real-time Transport Protocol (SRTP)",		Norrman, "The Secure Real-time Transport Protocol (SRTP)",
	RFC 3711, DOI 10.17487/RFC3711, March 2004,		RFC 3711, DOI 10.17487/RFC3711, March 2004,
	<http://www.rfc-editor.org/info/rfc3711>.		<http://www.rfc-editor.org/info/rfc3711>.
	[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer		[RFC5764] McGrew, D. and E. Rescorla, "Datagram Transport Layer
	Security (DTLS) Extension to Establish Keys for the Secure		Security (DTLS) Extension to Establish Keys for the Secure
	Real-time Transport Protocol (SRTP)", RFC 5764, DOI		Real-time Transport Protocol (SRTP)", RFC 5764,
	10.17487/RFC5764, May 2010,		DOI 10.17487/RFC5764, May 2010,
	<http://www.rfc-editor.org/info/rfc5764>.		<http://www.rfc-editor.org/info/rfc5764>.
	[RFC6904] Lennox, J., "Encryption of Header Extensions in the Secure		[RFC6904] Lennox, J., "Encryption of Header Extensions in the Secure
	Real-time Transport Protocol (SRTP)", RFC 6904, DOI		Real-time Transport Protocol (SRTP)", RFC 6904,
	10.17487/RFC6904, April 2013,		DOI 10.17487/RFC6904, April 2013,
	<http://www.rfc-editor.org/info/rfc6904>.		<http://www.rfc-editor.org/info/rfc6904>.
	11.2. Informative References		9.2. Informative References
	[I-D.ietf-avtcore-rtp-topologies-update]		[I-D.ietf-avtcore-rtp-topologies-update]
	Westerlund, M. and S. Wenger, "RTP Topologies", draft-		Westerlund, M. and S. Wenger, "RTP Topologies", draft-
	ietf-avtcore-rtp-topologies-update-10 (work in progress),		ietf-avtcore-rtp-topologies-update-10 (work in progress),
	July 2015.		July 2015.
			[I-D.ietf-rtcweb-security-arch]
			Rescorla, E., "WebRTC Security Architecture", draft-ietf-
			rtcweb-security-arch-12 (work in progress), June 2016.
	[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,		[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
	A., Peterson, J., Sparks, R., Handley, M., and E.		A., Peterson, J., Sparks, R., Handley, M., and E.
	Schooler, "SIP: Session Initiation Protocol", RFC 3261,		Schooler, "SIP: Session Initiation Protocol", RFC 3261,
	DOI 10.17487/RFC3261, June 2002,		DOI 10.17487/RFC3261, June 2002,
	<http://www.rfc-editor.org/info/rfc3261>.		<http://www.rfc-editor.org/info/rfc3261>.
	[RFC4474] Peterson, J. and C. Jennings, "Enhancements for		[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
	Authenticated Identity Management in the Session		Authenticated Identity Management in the Session
	Initiation Protocol (SIP)", RFC 4474, DOI 10.17487/		Initiation Protocol (SIP)", RFC 4474,
	RFC4474, August 2006,		DOI 10.17487/RFC4474, August 2006,
	<http://www.rfc-editor.org/info/rfc4474>.		<http://www.rfc-editor.org/info/rfc4474>.
	[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session		[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
	Description Protocol", RFC 4566, DOI 10.17487/RFC4566,		Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
	July 2006, <http://www.rfc-editor.org/info/rfc4566>.		July 2006, <http://www.rfc-editor.org/info/rfc4566>.
	[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework		[RFC5763] Fischl, J., Tschofenig, H., and E. Rescorla, "Framework
	for Establishing a Secure Real-time Transport Protocol		for Establishing a Secure Real-time Transport Protocol
	(SRTP) Security Context Using Datagram Transport Layer		(SRTP) Security Context Using Datagram Transport Layer
	Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May		Security (DTLS)", RFC 5763, DOI 10.17487/RFC5763, May
	2010, <http://www.rfc-editor.org/info/rfc5763>.		2010, <http://www.rfc-editor.org/info/rfc5763>.
	[RFC6464] Lennox, J., Ed., Ivov, E., and E. Marocco, "A Real-time		[RFC6464] Lennox, J., Ed., Ivov, E., and E. Marocco, "A Real-time
	Transport Protocol (RTP) Header Extension for Client-to-		Transport Protocol (RTP) Header Extension for Client-to-
	Mixer Audio Level Indication", RFC 6464, DOI 10.17487/		Mixer Audio Level Indication", RFC 6464,
	RFC6464, December 2011,		DOI 10.17487/RFC6464, December 2011,
	<http://www.rfc-editor.org/info/rfc6464>.		<http://www.rfc-editor.org/info/rfc6464>.
	Authors' Addresses		Authors' Addresses
	Paul E. Jones		Paul E. Jones
	Cisco		Cisco
	7025 Kit Creek Rd.		7025 Kit Creek Rd.
	Research Triangle Park, North Carolina 27709		Research Triangle Park, North Carolina 27709
	USA		USA
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