draft-ietf-uta-xmpp-06.txt   draft-ietf-uta-xmpp-07.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: October 16, 2015 April 14, 2015 Expires: October 25, 2015 April 23, 2015
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-ietf-uta-xmpp-06 draft-ietf-uta-xmpp-07
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 October 16, 2015. This Internet-Draft will expire on October 25, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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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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 . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3 3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3 3.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3
3.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 3 3.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 3
3.3. Session Resumption . . . . . . . . . . . . . . . . . . . 3 3.3. Session Resumption . . . . . . . . . . . . . . . . . . . 3
3.4. Authenticated Connections . . . . . . . . . . . . . . . . 3 3.4. Authenticated Connections . . . . . . . . . . . . . . . . 4
3.5. Server Name Indication . . . . . . . . . . . . . . . . . 4 3.5. Server Name Indication . . . . . . . . . . . . . . . . . 5
3.6. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5 3.6. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6 6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informative References . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Implementation Notes . . . . . . . . . . . . . . . . 8 Appendix A. Implementation Notes . . . . . . . . . . . . . . . . 8
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 8 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
The Extensible Messaging and Presence Protocol (XMPP) [RFC6120] The Extensible Messaging and Presence Protocol (XMPP) [RFC6120]
(along with its precursor, the so-called "Jabber protocol") has used (along with its precursor, the so-called "Jabber protocol") has used
Transport Layer Security (TLS) [RFC5246] (along with its precursor, Transport Layer Security (TLS) [RFC5246] (along with its precursor,
Secure Sockets Layer or SSL) since 1999. Both [RFC6120] and its Secure Sockets Layer or SSL) since 1999. Both [RFC6120] and its
predecessor [RFC3920] provided recommendations regarding the use of predecessor [RFC3920] provided recommendations regarding the use of
TLS in XMPP. In order to address the evolving threat model on the TLS in XMPP. In order to address the evolving threat model on the
Internet today, this document provides stronger recommendations. Internet today, this document provides stronger recommendations.
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3.2. Compression 3.2. Compression
XMPP supports an application-layer compression technology [XEP-0138]. XMPP supports an application-layer compression technology [XEP-0138].
Although this XMPP extension might have slightly stronger security Although this XMPP extension might have slightly stronger security
properties than TLS-layer compression (since it is enabled after SASL properties than TLS-layer compression (since it is enabled after SASL
authentication, as described in [XEP-0170]), this document neither authentication, as described in [XEP-0170]), this document neither
encourages nor discourages use of XMPP-layer compression. encourages nor discourages use of XMPP-layer compression.
3.3. Session Resumption 3.3. Session Resumption
In XMPP, TLS session resumption can be used in concert with the XMPP To improve the reliability of communications over XMPP, it is common
Stream Management extension; see [XEP-0198] for further details. practice for clients and servers to implement the stream management
extension [XEP-0198]. Although that specification includes a method
for resumption of XMPP streams at the application layer, also using
session resumption at the TLS layer further optimizes the overall
process of resuming an XMPP session (see [XEP-0198] for detailed
information). Whether or not XEP-0198 is used for application-layer
session resumption, implementations MUST follow the recommendations
provided in [I-D.ietf-uta-tls-bcp] regarding TLS-layer session
resumption.
3.4. Authenticated Connections 3.4. 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 validation in the context of authenticated connections. certificate validation in the context of authenticated connections.
This document does not supersede those specifications (e.g., it does This document does not supersede those specifications (e.g., it does
not modify the recommendations in [RFC6120] regarding the Subject not modify the recommendations in [RFC6120] regarding the Subject
Alternative Names or other certificate details that need to be Alternative Names or other certificate details that need to be
supported for authentication of XMPP connections using PKIX supported for authentication of XMPP connections using PKIX
certificates). certificates).
Wherever possible, it is best to prefer authenticated connections Wherever possible, it is best to prefer authenticated connections
(along with SASL [RFC4422]), as already stated in the core XMPP (along with SASL [RFC4422]), as already stated in the core XMPP
specification [RFC6120]. In particular, clients MUST authenticate specification [RFC6120]. In particular:
servers and servers MUST authenticate clients.
o Clients MUST authenticate servers.
o Servers MUST authenticate clients.
o Servers SHOULD authenticate other servers.
This document does not mandate that servers need to authenticate peer This document does not mandate that servers need to authenticate peer
servers, although such authentication is strongly preferred and servers, although such authentication is strongly preferred.
servers SHOULD authenticate each other. Unfortunately, in multi- Unfortunately, in multi-tenanted environments it can be extremely
tenanted environments it can be extremely difficult to obtain and difficult to obtain and deploy PKIX certificates with the proper
deploy PKIX certificates with the proper Subject Alternative Names Subject Alternative Names (see [I-D.ietf-xmpp-dna] and
(see [I-D.ietf-xmpp-dna] and [I-D.ietf-xmpp-posh] for details). To [I-D.ietf-xmpp-posh] for details). To overcome that difficulty, the
overcome that difficulty, the Domain Name Associations (DNA) Domain Name Associations (DNA) specification [I-D.ietf-xmpp-dna]
specification [I-D.ietf-xmpp-dna] describes a framework for XMPP describes a framework for XMPP server authentication methods, which
server authentication methods, which include not only PKIX but also include not only PKIX but also DNS-Based Authentication of Named
DNS-Based Authentication of Named Entities (DANE) as defined in Entities (DANE) as defined in [I-D.ietf-dane-srv] and PKIX over
[I-D.ietf-dane-srv] and PKIX over Secure HTTP (POSH) as defined in Secure HTTP (POSH) as defined in [I-D.ietf-xmpp-posh]. These methods
[I-D.ietf-xmpp-posh]. These methods can provide a basis for server can provide a basis for server identity verification when appropriate
identity verification when appropriate PKIX certificates cannot be PKIX certificates cannot be obtained and deployed.
obtained and deployed.
Given the pervasiveness of eavesdropping [RFC7258], even an Given the pervasiveness of eavesdropping [RFC7258], even an encrypted
unauthenticated connection might be better than an unencrypted but unauthenticated connection might be better than an unencrypted
connection in these scenarios (this is similar to the "better than connection in these scenarios (this is similar to the "better than
nothing security" approach for IPsec [RFC5386]). Unauthenticated nothing security" approach for IPsec [RFC5386]). Encrypted but
connections include connections negotiated using anonymous Diffie- unauthenticated connections include connections negotiated using
Hellman mechanisms or using self-signed certificates, among others. anonymous Diffie-Hellman mechanisms or using self-signed
In particular for XMPP server-to-server interactions, it can be certificates, among others. In particular for XMPP server-to-server
reasonable for XMPP server implementations to accept unauthenticated interactions, it can be reasonable for XMPP server implementations to
but encrypted connections when Server Dialback keys [XEP-0220] are accept encrypted but unauthenticated connections when Server Dialback
used; such keys on their own provide only weak identity verification keys [XEP-0220] are used; such keys on their own provide only weak
(made stronger through the use of DNSSEC [RFC4033]), but this at identity verification (made stronger through the use of DNSSEC
least enables encryption of server-to-server connections. The DNA [RFC4033]), but this at least enables encryption of server-to-server
prooftypes described above are intended to mitigate the residual need connections. The DNA prooftypes described above are intended to
for unauthenticated connections in these scenarios. mitigate the residual need for encrypted but unauthenticated
connections in these scenarios.
3.5. Server Name Indication 3.5. 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].
3.6. Human Factors 3.6. Human Factors
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o Be warned if the certificate changes for a given server. o Be warned if the certificate changes for a given server.
4. IANA Considerations 4. IANA Considerations
This document requests no actions of the IANA. This document requests no actions of the IANA.
5. Security Considerations 5. Security Considerations
The use of TLS can help limit the information available for The use of TLS can help limit the information available for
correlation to the network and transport layer headers as opposed to correlation between the XMPP application layer and the underlying
the application layer. As typically deployed, XMPP technologies do network and transport layers. As typically deployed, XMPP
not leave application-layer routing data (such as XMPP 'to' and technologies do not leave application-layer routing data (such as
'from' addresses) at rest on intermediate systems, since there is XMPP 'to' and 'from' addresses) at rest on intermediate systems,
only one hop between any two given XMPP servers. As a result, since there is only one hop between any two given XMPP servers. As a
encrypting all hops (sender's client to sender's server, sender's result, encrypting all hops (sender's client to sender's server,
server to recipient's server, recipient's server to recipient's sender's server to recipient's server, recipient's server to
client) can help to limit the amount of "metadata" that might leak. recipient's client) can help to limit the amount of "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 and related actions to strengthen the security of the This document and related actions to strengthen the security of the
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Verification of Domain-Based Application Service Identity Verification of Domain-Based Application Service Identity
within Internet Public Key Infrastructure Using X.509 within Internet Public Key Infrastructure Using X.509
(PKIX) Certificates in the Context of Transport Layer (PKIX) Certificates in the Context of Transport Layer
Security (TLS)", RFC 6125, March 2011. Security (TLS)", RFC 6125, March 2011.
6.2. Informative References 6.2. Informative References
[I-D.ietf-dane-srv] [I-D.ietf-dane-srv]
Finch, T., Miller, M., and P. Saint-Andre, "Using DNS- Finch, T., Miller, M., and P. Saint-Andre, "Using DNS-
Based Authentication of Named Entities (DANE) TLSA records Based Authentication of Named Entities (DANE) TLSA records
with SRV and MX records.", draft-ietf-dane-srv-12 (work in with SRV and MX records.", draft-ietf-dane-srv-13 (work in
progress), March 2015. progress), April 2015.
[I-D.ietf-stox-im] [I-D.ietf-stox-im]
Saint-Andre, P., Houri, A., and J. Hildebrand, Saint-Andre, P., Houri, A., and J. Hildebrand,
"Interworking between the Session Initiation Protocol "Interworking between the Session Initiation Protocol
(SIP) and the Extensible Messaging and Presence Protocol (SIP) and the Extensible Messaging and Presence Protocol
(XMPP): Instant Messaging", draft-ietf-stox-im-13 (work in (XMPP): Instant Messaging", draft-ietf-stox-im-13 (work in
progress), March 2015. progress), March 2015.
[I-D.ietf-xmpp-dna] [I-D.ietf-xmpp-dna]
Saint-Andre, P. and M. Miller, "Domain Name Associations Saint-Andre, P. and M. Miller, "Domain Name Associations
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Appendix B. Acknowledgements Appendix B. Acknowledgements
The authors would like to thank the following individuals for their The authors would like to thank the following individuals for their
input: Dave Cridland, Philipp Hancke, Olle Johansson, Steve Kille, input: Dave Cridland, Philipp Hancke, Olle Johansson, Steve Kille,
Tobias Markmann, Matt Miller, and Rene Treffer. Tobias Markmann, Matt Miller, and Rene Treffer.
Roni Even caught several important issues in his review on behalf of Roni Even caught several important issues in his review on behalf of
the General Area Review Team. the General Area Review Team.
Ben Campbell, Spencer Dawkins, and Barry Leiba provided helpful input
during IESG review.
Thanks to Leif Johansson and Orit Levin as chairs of the UTA WG, Ben Thanks to Leif Johansson and Orit Levin as chairs of the UTA WG, Ben
Campbell and Joe Hildebrand as chairs of the XMPP WG, and Stephen Campbell and Joe Hildebrand as chairs of the XMPP WG, and Stephen
Farrell as the sponsoring Area Director. Farrell as the sponsoring Area Director.
Authors' Addresses Authors' Addresses
Peter Saint-Andre Peter Saint-Andre
&yet &yet
Email: peter@andyet.com Email: peter@andyet.com
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