draft-ietf-uta-xmpp-00.txt   draft-ietf-uta-xmpp-01.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: September 28, 2014 March 27, 2014 Expires: March 15, 2015 September 11, 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-ietf-uta-xmpp-00 draft-ietf-uta-xmpp-01
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
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
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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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 September 28, 2014. This Internet-Draft will expire on March 15, 2015.
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.
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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. Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 3 3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3
4.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3 3.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3
4.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3 3.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 3
4.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 3 3.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 3
4.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 3 3.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 3
4.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 3 3.6. Session Resumption . . . . . . . . . . . . . . . . . . . 4
4.6. Session Resumption . . . . . . . . . . . . . . . . . . . 4 3.7. Authenticated Connections . . . . . . . . . . . . . . . . 4
4.7. Authenticated Connections . . . . . . . . . . . . . . . . 4 3.8. Unauthenticated Connections . . . . . . . . . . . . . . . 4
4.8. Unauthenticated Connections . . . . . . . . . . . . . . . 4 3.9. Server Name Indication . . . . . . . . . . . . . . . . . 4
4.9. Server Name Indication . . . . . . . . . . . . . . . . . 4 3.10. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5
4.10. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Implementation Notes . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6.1. Normative References . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 6.2. Informative References . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6 Appendix A. Implementation Notes . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 6 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 7
8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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 (see, for example, [I-D.trammell-perpass-ppa]), this Internet today, this document provides stronger recommendations based
document provides stronger recommendations (see also on [I-D.ietf-uta-tls-bcp]. This document updates [RFC6120].
[I-D.ietf-uta-tls-bcp]). This document updates [RFC6120].
2. Terminology 2. Terminology
Various security-related terms are to be understood in the sense Various security-related terms are to be understood in the sense
defined in [RFC4949]. defined in [RFC4949].
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. Discussion Venue 3. Recommendations
The discussion venue for this document is the mailing list of the
XMPP Working Group, for which archives and subscription information
can be found at [1]. Discussion might also occur on the mailing list
of the UTA Working Group, for which archives and subscription
information can be found at [2].
4. Recommendations
4.1. Support for TLS 3.1. Support for TLS
Support for TLS (specifically, the XMPP profile of STARTTLS) is Support for TLS (specifically, the XMPP profile of STARTTLS) is
mandatory for XMPP implementations, as already specified in [RFC6120] mandatory for XMPP implementations, as already specified in [RFC6120]
and its predecessor [RFC3920]. and its predecessor [RFC3920].
If the server to which an XMPP client or peer server connects does If the server to which a client or peer server connects does not
not offer a stream feature of <starttls xmlns='urn:ietf:params:xml:ns offer a stream feature of <starttls xmlns='urn:ietf:params:xml:ns
:xmpp-tls'/> (thus indicating that it is an XMPP 1.0 server that :xmpp-tls'/> (thus indicating that it is an XMPP 1.0 server that
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 3.2. Protocol Versions
Implementations MUST follow the recommendations in Implementations MUST follow the recommendations in
[I-D.ietf-uta-tls-bcp] as to supporting various TLS versions and [I-D.ietf-uta-tls-bcp] as to supporting various TLS versions and
avoiding fallback to SSL. avoiding fallback to SSL.
4.3. Cipher Suites 3.3. Cipher Suites
Implementations MUST follow the recommendations in Implementations MUST follow the recommendations in
[I-D.ietf-uta-tls-bcp]. [I-D.ietf-uta-tls-bcp].
4.4. Public Key Length 3.4. Public Key Length
Implementations MUST follow the recommendations in Implementations MUST follow the recommendations in
[I-D.ietf-uta-tls-bcp]. [I-D.ietf-uta-tls-bcp].
4.5. Compression 3.5. Compression
Implementations MUST follow the recommendations in Implementations MUST follow the recommendations in
[I-D.ietf-uta-tls-bcp]. [I-D.ietf-uta-tls-bcp].
XMPP supports an application-layer compression technology [XEP-0138], XMPP supports an application-layer compression technology [XEP-0138],
which might have slightly stronger security properties than TLS (at which might have slightly stronger security properties than TLS (at
least because it is enabled after SASL authentication, as described least because it is enabled after SASL authentication, as described
in [XEP-0170]). in [XEP-0170]).
4.6. Session Resumption 3.6. Session Resumption
Implementations MUST follow the recommendations in Implementations MUST follow the recommendations in
[I-D.ietf-uta-tls-bcp]. [I-D.ietf-uta-tls-bcp].
Use of session IDs [RFC5246] is RECOMMENDED instead of session Use of session IDs [RFC5246] is RECOMMENDED instead of session
tickets [RFC5077], since XMPP does not in general use state tickets [RFC5077], since XMPP does not in general use state
management technologies such as tickets or "cookies" [RFC6265]. management technologies such as tickets or "cookies" [RFC6265].
Note that, in XMPP, TLS session resumption can be used in concert In XMPP, TLS session resumption can be used in concert with the XMPP
with the XMPP Stream Management extension; see [XEP-0198] for further Stream Management extension; see [XEP-0198] for further details.
details.
4.7. Authenticated Connections 3.7. 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 validation in the context of authenticated connections. certificate validation in the context of authenticated connections.
This document does not supersede those specifications. Wherever This document does not supersede those specifications. Wherever
possible, it is best to prefer authenticated connections (along with possible, it is best to prefer authenticated connections (along with
SASL [RFC4422]), as already stated in the core XMPP specification SASL [RFC4422]), as already stated in the core XMPP specification
[RFC6120]. In particular, clients MUST authenticate servers. [RFC6120]. In particular, clients MUST authenticate servers.
4.8. Unauthenticated Connections 3.8. Unauthenticated Connections
Given the pervasiveness of passive eavesdropping, even an Given the pervasiveness of passive eavesdropping, even an
unauthenticated connection might be better than an unencrypted unauthenticated connection might be better than an unencrypted
connection (this is similar to the "better than nothing security" connection (this is similar to the "better than nothing security"
approach for IPsec [RFC5386]). In particular, because of current approach for IPsec [RFC5386]). In particular, because of current
deployment challenges for authenticated connections between XMPP deployment challenges for authenticated connections between XMPP
servers (see [I-D.ietf-xmpp-dna] for details), it might be reasonable servers (see [I-D.ietf-xmpp-dna] for details), it might be reasonable
for XMPP server implementations to accept unauthenticated connections for XMPP server implementations to accept unauthenticated connections
when the Server Dialback protocol [XEP-0220] is used for weak when the Server Dialback protocol [XEP-0220] is used for weak
identity verification; this will at least enable encryption of identity verification; this will at least enable encryption of
server-to-server connections. Unauthenticated connections include server-to-server connections. Unauthenticated connections include
connections negotiated using anonymous Diffie-Hellman algorithms or connections negotiated using anonymous Diffie-Hellman algorithms or
using self-signed certificates, among other scenarios. using self-signed certificates, among other scenarios.
4.9. Server Name Indication 3.9. 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].
4.10. Human Factors 3.10. 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 administrators) 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
server-to-server connection. server-to-server connection.
o Inspect the certificate offered by an XMPP server. o Inspect the certificate offered by an XMPP server.
o Determine the cipher suite used to encrypt a connection. o Determine the cipher suite used to encrypt a connection.
o Be warned if the certificate changes for a given server. o Be warned if the certificate changes for a given server.
5. Implementation Notes 4. IANA Considerations
Some governments enforce legislation prohibiting the export of strong
cryptographic technologies. Nothing in this document ought to be
taken as advice to violate such prohibitions.
6. IANA Considerations
This document requests no actions of the IANA. This document requests no actions of the IANA.
7. Security Considerations 5. Security Considerations
As noted in "A Threat Model for Pervasive Passive Surveillance" The use of TLS can help limit the information available for
[I-D.trammell-perpass-ppa]), the use of TLS can help limit the correlation to the network and transport layer headers as opposed to
information available for correlation to the network and transport the application layer. As typically deployed, XMPP technologies do
layer headers as opposed to the application layer. As typically not leave application-layer routing data (such as XMPP 'to' and
deployed, XMPP technologies do not leave application-layer routing 'from' addresses) at rest on intermediate systems, since there is
data (such as XMPP 'to' and 'from' addresses) at rest on intermediate only one hop between any two given XMPP servers. As a result,
systems, since there is only one hop between any two given XMPP encrypting all hops (sending client to sender's server, sender's
servers. As a result, encrypting all hops (sending client to server to recipient's server, recipient's server to recipient's
sender's server, sender's server to recipient's server, recipient's client) can help to limit the amount of "metadata" that might leak.
server to 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, along with actions currently being taken to strenthen This document and related actions to strengthen the security of the
the security of the XMPP network, do not assume widespread compromise XMPP network are based on the assumption that XMPP servers and
of XMPP servers and clients or their underlying operating systems or clients have not been subject to widespread compromise. If this
hardware. Thus it is assumed that ubiquitous use of per-hop TLS assumption is valid, then ubiquitous use of per-hop TLS channel
channel encryption and more significant deployment of end-to-end encryption and more significant deployment of end-to-end object
object encryption technologies will serve to protect XMPP encryption technologies will serve to protect XMPP communications to
communications to a measurable degree, compared to the alternatives. a measurable degree, compared to the alternatives.
8. References 6. References
8.1. Normative References 6.1. Normative References
[I-D.ietf-uta-tls-bcp]
Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of TLS and DTLS", draft-
ietf-uta-tls-bcp-02 (work in progress), August 2014.
[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, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
4949, August 2007. 4949, August 2007.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without "Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, January 2008. Server-Side State", RFC 5077, January 2008.
skipping to change at page 6, line 43 skipping to change at page 6, line 38
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011. Protocol (XMPP): Core", RFC 6120, March 2011.
[RFC6125] Saint-Andre, P. and J. Hodges, "Representation and [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
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.
8.2. Informative References 6.2. Informative References
[I-D.ietf-uta-tls-bcp]
Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of TLS and DTLS", draft-
ietf-uta-tls-bcp-00 (work in progress), March 2014.
[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
(DNA) in the Extensible Messaging and Presence Protocol (DNA) in the Extensible Messaging and Presence Protocol
(XMPP)", draft-ietf-xmpp-dna-05 (work in progress), (XMPP)", draft-ietf-xmpp-dna-06 (work in progress), June
February 2014. 2014.
[I-D.trammell-perpass-ppa]
Trammell, B., Borkmann, D., and C. Huitema, "A Threat
Model for Pervasive Passive Surveillance", draft-trammell-
perpass-ppa-01 (work in progress), November 2013.
[RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 3920, October 2004. Protocol (XMPP): Core", RFC 3920, October 2004.
[RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
Security Layer (SASL)", RFC 4422, June 2006. Security Layer (SASL)", RFC 4422, June 2006.
[RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing [RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing
Security: An Unauthenticated Mode of IPsec", RFC 5386, Security: An Unauthenticated Mode of IPsec", RFC 5386,
November 2008. November 2008.
skipping to change at page 8, line 5 skipping to change at page 7, line 32
[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 Appendix A. Implementation Notes
[1] https://www.ietf.org/mailman/listinfo/xmpp
[2] https://www.ietf.org/mailman/listinfo/uta Some governments enforce legislation prohibiting the export of strong
cryptographic technologies. Nothing in this document ought to be
taken as advice to violate such prohibitions.
Appendix A. Acknowledgements Appendix B. Acknowledgements
Thanks to the following individuals for their input: Dave Cridland, Thanks to the following individuals for their input: Dave Cridland,
Philipp Hancke, Olle Johansson, Steve Kille, Tobias Markmann, Matt Philipp Hancke, Olle Johansson, Steve Kille, Tobias Markmann, Matt
Miller, and Rene Treffer. Miller, and Rene Treffer.
Authors' Addresses Authors' Addresses
Peter Saint-Andre Peter Saint-Andre
&yet &yet
P.O. Box 787
Parker, CO 80134
USA
Email: ietf@stpeter.im Email: peter@andyet.net
Thijs Alkemade Thijs Alkemade
Email: me@thijsalkema.de Email: me@thijsalkema.de
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