< draft-saintandre-xmpp-tls-05.txt		draft-saintandre-xmpp-tls-06.txt >
	Network Working Group P. Saint-Andre		Network Working Group P. Saint-Andre
	Internet-Draft &yet		Internet-Draft &yet
	Updates: 6120 (if approved) T. Alkemade		Updates: 6120 (if approved) T. Alkemade
	Intended status: Standards Track		Intended status: Standards Track
	Expires: August 17, 2014 February 13, 2014		Expires: September 5, 2014 March 4, 2014
	Use of Transport Layer Security (TLS) in the Extensible Messaging and		Use of Transport Layer Security (TLS) in the Extensible Messaging and
	Presence Protocol (XMPP)		Presence Protocol (XMPP)
	draft-saintandre-xmpp-tls-05		draft-saintandre-xmpp-tls-06
	Abstract		Abstract
	This document provides recommendations for the use of Transport Layer		This document provides recommendations for the use of Transport Layer
	Security (TLS) in the Extensible Messaging and Presence Protocol		Security (TLS) in the Extensible Messaging and Presence Protocol
	(XMPP). This document updates RFC 6120.		(XMPP). This document updates RFC 6120.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
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	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on August 17, 2014.		This Internet-Draft will expire on September 5, 2014.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 IETF Trust and the persons identified as the		Copyright (c) 2014 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
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	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
	3. Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 3		3. Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 3
	4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3		4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
	4.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3		4.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3
	4.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3		4.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3
	4.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 3		4.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 3
	4.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 3		4.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 3
	4.5. Certificate Validation . . . . . . . . . . . . . . . . . 3		4.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 3
	4.6. Unauthenticated Connections . . . . . . . . . . . . . . . 4		4.6. Session Resumption . . . . . . . . . . . . . . . . . . . 4
	4.7. Server Name Indication . . . . . . . . . . . . . . . . . 4		4.7. Authenticated Connections . . . . . . . . . . . . . . . . 4
	4.8. Session Resumption . . . . . . . . . . . . . . . . . . . 4		4.8. Unauthenticated Connections . . . . . . . . . . . . . . . 4
	4.9. Compression . . . . . . . . . . . . . . . . . . . . . . . 4		4.9. Server Name Indication . . . . . . . . . . . . . . . . . 4
	4.10. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5		4.10. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5
	5. Implementation Notes . . . . . . . . . . . . . . . . . . . . 5		5. Implementation Notes . . . . . . . . . . . . . . . . . . . . 5
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 5		7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6		8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
	8.1. Normative References . . . . . . . . . . . . . . . . . . 6		8.1. Normative References . . . . . . . . . . . . . . . . . . 6
	8.2. Informative References . . . . . . . . . . . . . . . . . 6		8.2. Informative References . . . . . . . . . . . . . . . . . 6
	8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7		8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
	Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8		Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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	supports TLS), the initiating entity MUST NOT proceed with the stream		supports TLS), the initiating entity MUST NOT proceed with the stream
	negotiation and MUST instead abort the connection attempt. Although		negotiation and MUST instead abort the connection attempt. Although
	XMPP servers SHOULD include the <required/> child element to indicate		XMPP servers SHOULD include the <required/> child element to indicate
	that negotiation of TLS is mandatory, clients and peer servers MUST		that negotiation of TLS is mandatory, clients and peer servers MUST
	NOT depend on receiving the <required/> flag in determining whether		NOT depend on receiving the <required/> flag in determining whether
	TLS will be enforced for the stream.		TLS will be enforced for the stream.
	4.2. Protocol Versions		4.2. Protocol Versions
	Implementations MUST follow the recommendations in		Implementations MUST follow the recommendations in
	[I-D.sheffer-tls-bcp].		[I-D.sheffer-tls-bcp] as to supporting various TLS versions and
			avoiding fallback to SSL.
	4.3. Cipher Suites		4.3. Cipher Suites
	Implementations MUST follow the recommendations in		Implementations MUST follow the recommendations in
	[I-D.sheffer-tls-bcp].		[I-D.sheffer-tls-bcp].
	4.4. Public Key Length		4.4. Public Key Length
	Implementations MUST follow the recommendations in		Implementations MUST follow the recommendations in
	[I-D.sheffer-tls-bcp].		[I-D.sheffer-tls-bcp].
	4.5. Certificate Validation		4.5. Compression
			Implementations MUST follow the recommendations in
			[I-D.sheffer-tls-bcp].
			XMPP supports an application-layer compression technology [XEP-0138],
			which might have slightly stronger security properties than TLS (at
			least because it is enabled after SASL authentication, as described
			in [XEP-0170]).
			4.6. Session Resumption
			Implementations MUST follow the recommendations in
			[I-D.sheffer-tls-bcp].
			Use of session IDs [RFC5246] is RECOMMENDED instead of session
			tickets [RFC5077], since XMPP does not in general use state
			management technologies such as tickets or "cookies" [RFC6265].
			Note that, in XMPP, TLS session resumption can be used in concert
			with the XMPP Stream Management extension; see [XEP-0198] for further
			details.
			4.7. Authenticated Connections
	Both the core XMPP specification [RFC6120] and the "CertID"		Both the core XMPP specification [RFC6120] and the "CertID"
	specification [RFC6125] provide recommendations and requirements for		specification [RFC6125] provide recommendations and requirements for
	certificate checking. This document does not supersede those		certificate validation in the context of authenticated connections.
	specifications.		This document does not supersede those specifications. Wherever
			possible, it is best to prefer authenticated connections (along with
			SASL [RFC4422]), as already stated in the core XMPP specification
			[RFC6120]. In particular, clients MUST authenticate servers.
	4.6. Unauthenticated Connections		4.8. Unauthenticated Connections
	The core XMPP specification [RFC6120] states a preference for the use		Given the pervasiveness of passive eavesdropping, even an
	of TLS for encryption along with SASL [RFC4422] for authentication.		unauthenticated connection might be better than an unencrypted
	In general, it is preferable for a connection to be authenticated,		connection (this is similar to the "better than nothing security"
	including proper identity checking as defined by the "CertID"		approach for IPsec [RFC5386]). In particular, because of current
	specification [RFC6125]. However, given the pervasiveness of passive		deployment challenges for authenticated connections between XMPP
	eavesdropping, even an unauthenticated connection might be better		servers (see [I-D.ietf-xmpp-dna] for details), it might be reasonable
	than an unencrypted connection (this is similar to the "better than		for XMPP server implementations to accept unauthenticated connections
	nothing security" approach for IPsec [RFC5386]). In particular,		when the Server Dialback protocol [XEP-0220] is used for weak
	given current deployment challenges for authenticated connections		identity verification; this will at least enable encryption of
	between XMPP servers (see [I-D.ietf-xmpp-dna] for details), it might		server-to-server connections. Unauthenticated connections include
	be reasonable for XMPP server implementations to accept		connections negotiated using anonymous Diffie-Hellman algorithms or
	unauthenticated connections when the Server Dialback protocol		using self-signed certificates, among other scenarios.
	[XEP-0220] is used for weak identity verification; this will at least
	enable encryption of server-to-server connections. Unauthenticated
	connections include connections negotiated using anonymous Diffie-
	Hellman algorithms or using self-signed certificates, among other
	scenarios.
	4.7. Server Name Indication		4.9. Server Name Indication
	Although there is no harm in supporting the TLS Server Name		Although there is no harm in supporting the TLS Server Name
	Indication (SNI) extension [RFC6066], this is not necessary since the		Indication (SNI) extension [RFC6066], this is not necessary since the
	same function is served in XMPP by the 'to' address of the initial		same function is served in XMPP by the 'to' address of the initial
	stream header as explained in Section 4.7.2 of [RFC6120].		stream header as explained in Section 4.7.2 of [RFC6120].
	4.8. Session Resumption
	If TLS session resumption is used (e.g., in concert with the XMPP
	Stream Management extension [XEP-0198]), care ought to be taken to do
	so safely. In particular, the resumption information (either session
	IDs [RFC5246] or session tickets [RFC5077]) needs to be authenticated
	and encrypted to prevent modification or eavesdropping by an
	attacker.
	Use of session IDs [RFC5246] is RECOMMENDED instead of session
	tickets [RFC5077], since XMPP does not in general use state
	management technologies such as tickets or "cookies" [RFC6265].
	4.9. Compression
	XMPP is not generally subject to attacks based on TLS-layer
	compression (e.g., the "CRIME" attack), since it is not typically
	used to communicate static strings of the kind communicated over
	HTTP, such as "cookies" [RFC6265]. However, because XMPP also
	supports an application-layer compression technology [XEP-0138],
	implementers might wish to prefer XMPP compression over TLS
	compression in order to avoid any potential security issues with TLS-
	layer compression. (See [I-D.sheffer-tls-bcp] for related
	discussion.)
	4.10. Human Factors		4.10. Human Factors
	It is RECOMMENDED that XMPP clients provide ways for end users (and		It is RECOMMENDED that XMPP clients provide ways for end users (and
	that XMPP servers provide ways for administators) to complete the		that XMPP servers provide ways for administators) to complete the
	following tasks:		following tasks:
	o Determine if a client-to-server or server-to-server connection is		o Determine if a client-to-server or server-to-server connection is
	encrypted and authenticated.		encrypted and authenticated.
	o Determine the version of TLS used for a client-to-server or		o Determine the version of TLS used for a client-to-server or
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	"metadata" that might leak.		"metadata" that might leak.
	It is possible that XMPP servers themselves might be compromised. In		It is possible that XMPP servers themselves might be compromised. In
	that case, per-hop encryption would not protect XMPP communications,		that case, per-hop encryption would not protect XMPP communications,
	and even end-to-end encryption of (parts of) XMPP stanza payloads		and even end-to-end encryption of (parts of) XMPP stanza payloads
	would leave addressing information and XMPP roster data in the clear.		would leave addressing information and XMPP roster data in the clear.
	By the same token, it is possible that XMPP clients (or the end-user		By the same token, it is possible that XMPP clients (or the end-user
	devices on which such clients are installed) could also be		devices on which such clients are installed) could also be
	compromised, leaving users utterly at the mercy of an adversary.		compromised, leaving users utterly at the mercy of an adversary.
	This document, along with actions currently being taken to improve		This document, along with actions currently being taken to strenthen
	the security of the XMPP network, do not assume widespread compromise		the security of the XMPP network, do not assume widespread compromise
	of XMPP servers and clients or their underlying operating systems or		of XMPP servers and clients or their underlying operating systems or
	hardware. Thus it is assumed that ubiquitous use of per-hop TLS		hardware. Thus it is assumed that ubiquitous use of per-hop TLS
	channel encryption and more significant deployment of end-to-end		channel encryption and more significant deployment of end-to-end
	object encryption technologies will serve to protect XMPP		object encryption technologies will serve to protect XMPP
	communications to a measurable degree, compared to the alternatives.		communications to a measurable degree, compared to the alternatives.
	8. References		8. References
	8.1. Normative References		8.1. Normative References
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	[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:		[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
	Extension Definitions", RFC 6066, January 2011.		Extension Definitions", RFC 6066, January 2011.
	[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,		[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
	April 2011.		April 2011.
	[XEP-0138]		[XEP-0138]
	Hildebrand, J. and P. Saint-Andre, "Stream Compression",		Hildebrand, J. and P. Saint-Andre, "Stream Compression",
	XSF XEP 0138, May 2009.		XSF XEP 0138, May 2009.
			[XEP-0170]
			Saint-Andre, P., "Recommended Order of Stream Feature
			Negotiation", XSF XEP 0170, January 2007.
	[XEP-0198]		[XEP-0198]
	Karneges, J., Saint-Andre, P., Hildebrand, J., Forno, F.,		Karneges, J., Saint-Andre, P., Hildebrand, J., Forno, F.,
	Cridland, D., and M. Wild, "Stream Management", XSF XEP		Cridland, D., and M. Wild, "Stream Management", XSF XEP
	0198, June 2011.		0198, June 2011.
	[XEP-0220]		[XEP-0220]
	Miller, J., Saint-Andre, P., and P. Hancke, "Server		Miller, J., Saint-Andre, P., and P. Hancke, "Server
	Dialback", XSF XEP 0220, September 2013.		Dialback", XSF XEP 0220, September 2013.
	8.3. URIs		8.3. URIs
	[1] https://www.ietf.org/mailman/listinfo/xmpp		[1] https://www.ietf.org/mailman/listinfo/xmpp
	[2] https://www.ietf.org/mailman/listinfo/uta		[2] https://www.ietf.org/mailman/listinfo/uta
	Appendix A. Acknowledgements		Appendix A. Acknowledgements
	Thanks to the following individuals for their input: Thijs Alkemade,		Thanks to the following individuals for their input: Dave Cridland,
	Dave Cridland, Philipp Hancke, Olle Johansson, Steve Kille, Tobias		Philipp Hancke, Olle Johansson, Steve Kille, Tobias Markmann, Matt
	Markmann, Matt Miller, and Rene Treffer.		Miller, and Rene Treffer.
	Authors' Addresses		Authors' Addresses
	Peter Saint-Andre		Peter Saint-Andre
	&yet		&yet
	Email: ietf@stpeter.im		Email: ietf@stpeter.im
	Thijs Alkemade		Thijs Alkemade
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