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2 Network Working Group P. Saint-Andre
3 Internet-Draft &yet
4 Updates: 6120 (if approved) T. Alkemade
5 Intended status: Standards Track
6 Expires: May 30, 2015 November 26, 2014
8 Use of Transport Layer Security (TLS) in the Extensible Messaging and
9 Presence Protocol (XMPP)
10 draft-ietf-uta-xmpp-04
12 Abstract
14 This document provides recommendations for the use of Transport Layer
15 Security (TLS) in the Extensible Messaging and Presence Protocol
16 (XMPP). This document updates RFC 6120.
18 Status of This Memo
20 This Internet-Draft is submitted in full conformance with the
21 provisions of BCP 78 and BCP 79.
23 Internet-Drafts are working documents of the Internet Engineering
24 Task Force (IETF). Note that other groups may also distribute
25 working documents as Internet-Drafts. The list of current Internet-
26 Drafts is at http://datatracker.ietf.org/drafts/current/.
28 Internet-Drafts are draft documents valid for a maximum of six months
29 and may be updated, replaced, or obsoleted by other documents at any
30 time. It is inappropriate to use Internet-Drafts as reference
31 material or to cite them other than as "work in progress."
33 This Internet-Draft will expire on May 30, 2015.
35 Copyright Notice
37 Copyright (c) 2014 IETF Trust and the persons identified as the
38 document authors. All rights reserved.
40 This document is subject to BCP 78 and the IETF Trust's Legal
41 Provisions Relating to IETF Documents
42 (http://trustee.ietf.org/license-info) in effect on the date of
43 publication of this document. Please review these documents
44 carefully, as they describe your rights and restrictions with respect
45 to this document. Code Components extracted from this document must
46 include Simplified BSD License text as described in Section 4.e of
47 the Trust Legal Provisions and are provided without warranty as
48 described in the Simplified BSD License.
50 Table of Contents
52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
54 3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
55 3.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3
56 3.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 3
57 3.3. Session Resumption . . . . . . . . . . . . . . . . . . . 3
58 3.4. Authenticated Connections . . . . . . . . . . . . . . . . 3
59 3.5. Unauthenticated Connections . . . . . . . . . . . . . . . 4
60 3.6. Server Name Indication . . . . . . . . . . . . . . . . . 4
61 3.7. Human Factors . . . . . . . . . . . . . . . . . . . . . . 4
62 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
63 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
64 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
65 6.1. Normative References . . . . . . . . . . . . . . . . . . 5
66 6.2. Informative References . . . . . . . . . . . . . . . . . 6
67 Appendix A. Implementation Notes . . . . . . . . . . . . . . . . 7
68 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 7
69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
71 1. Introduction
73 The Extensible Messaging and Presence Protocol (XMPP) [RFC6120]
74 (along with its precursor, the so-called "Jabber protocol") has used
75 Transport Layer Security (TLS) [RFC5246] (along with its precursor,
76 Secure Sockets Layer or SSL) since 1999. Both [RFC6120] and its
77 predecessor [RFC3920] provided recommendations regarding the use of
78 TLS in XMPP. In order to address the evolving threat model on the
79 Internet today, this document provides stronger recommendations.
81 NOTE: Unless explicitly noted otherwise, all of the
82 recommendations specified in [I-D.ietf-uta-tls-bcp] apply to XMPP.
83 In the main, this document merely provides supplementary
84 information; those who implement and deploy XMPP technologies are
85 expected to follow the recommendations of [I-D.ietf-uta-tls-bcp].
87 This document updates [RFC6120].
89 2. Terminology
91 Various security-related terms are to be understood in the sense
92 defined in [RFC4949].
94 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
95 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
96 "OPTIONAL" in this document are to be interpreted as described in
97 [RFC2119].
99 3. Recommendations
101 3.1. Support for TLS
103 Support for TLS (specifically, the XMPP profile of STARTTLS) is
104 mandatory for XMPP implementations, as already specified in [RFC6120]
105 and its predecessor [RFC3920].
107 The server (i.e., the XMPP receiving entity) to which a client or
108 peer server (i.e., the XMPP initiating entity) connects might not
109 offer a stream feature of . Although in general this stream feature indicates that
111 the server supports XMPP 1.0 and therefore supports TLS, it is
112 possible that this stream feature might be stripped out by an
113 attacker (see Section 2.1 of [I-D.ietf-uta-tls-attacks]). Therefore,
114 the initiating entity SHOULD proceed with the stream negotiation even
115 if the receiving entity does not advertise support for TLS.
116 Similarly, although a receiving entity SHOULD include the
117 child element to indicate that negotiation of TLS is mandatory, an
118 initiating entity MUST NOT depend on receiving the flag
119 in determining whether TLS will be enforced for the stream.
121 3.2. Compression
123 XMPP supports an application-layer compression technology [XEP-0138].
124 Although this XMPP extension might have slightly stronger security
125 properties than TLS-layer compression (since it is enabled after SASL
126 authentication, as described in [XEP-0170]), this document neither
127 encourages nor discourages use of XMPP-layer compression.
129 3.3. Session Resumption
131 In XMPP, TLS session resumption can be used in concert with the XMPP
132 Stream Management extension; see [XEP-0198] for further details.
134 3.4. Authenticated Connections
136 Both the core XMPP specification [RFC6120] and the "CertID"
137 specification [RFC6125] provide recommendations and requirements for
138 certificate validation in the context of authenticated connections.
139 This document does not supersede those specifications. Wherever
140 possible, it is best to prefer authenticated connections (along with
141 SASL [RFC4422]), as already stated in the core XMPP specification
142 [RFC6120]. In particular, clients MUST authenticate servers.
143 Because this document does not mandate that servers need to
144 authenticate peer servers, unauthenticated server-to-server
145 connections are allowed (consistent with current practice on the XMPP
146 network).
148 This document does not modify the recommendations in [RFC6120]
149 regarding the Subject Alternative Names (or other certificate
150 details) that need to be supported for authentication of XMPP
151 connections.
153 3.5. Unauthenticated Connections
155 Given the pervasiveness of passive eavesdropping, even an
156 unauthenticated connection might be better than an unencrypted
157 connection (this is similar to the "better than nothing security"
158 approach for IPsec [RFC5386]). In particular, because of current
159 deployment challenges for authenticated connections between XMPP
160 servers (see [I-D.ietf-xmpp-dna] and [I-D.ietf-xmpp-posh] for
161 details), it can be reasonable for XMPP server implementations to
162 accept unauthenticated connections when the Server Dialback protocol
163 [XEP-0220] is used for weak identity verification; this will at least
164 enable encryption of server-to-server connections. Unauthenticated
165 connections include connections negotiated using anonymous Diffie-
166 Hellman algorithms or using self-signed certificates, among other
167 scenarios.
169 3.6. Server Name Indication
171 Although there is no harm in supporting the TLS Server Name
172 Indication (SNI) extension [RFC6066], this is not necessary since the
173 same function is served in XMPP by the 'to' address of the initial
174 stream header as explained in Section 4.7.2 of [RFC6120].
176 3.7. Human Factors
178 It is strongly encouraged that XMPP clients provide ways for end
179 users (and that XMPP servers provide ways for administrators) to
180 complete the following tasks:
182 o Determine if a client-to-server or server-to-server connection is
183 encrypted and authenticated.
185 o Determine the version of TLS used for a client-to-server or
186 server-to-server connection.
188 o Inspect the certificate offered by an XMPP server.
190 o Determine the cipher suite used to encrypt a connection.
192 o Be warned if the certificate changes for a given server.
194 4. IANA Considerations
196 This document requests no actions of the IANA.
198 5. Security Considerations
200 The use of TLS can help limit the information available for
201 correlation to the network and transport layer headers as opposed to
202 the application layer. As typically deployed, XMPP technologies do
203 not leave application-layer routing data (such as XMPP 'to' and
204 'from' addresses) at rest on intermediate systems, since there is
205 only one hop between any two given XMPP servers. As a result,
206 encrypting all hops (sending client to sender's server, sender's
207 server to recipient's server, recipient's server to recipient's
208 client) can help to limit the amount of "metadata" that might leak.
210 It is possible that XMPP servers themselves might be compromised. In
211 that case, per-hop encryption would not protect XMPP communications,
212 and even end-to-end encryption of (parts of) XMPP stanza payloads
213 would leave addressing information and XMPP roster data in the clear.
214 By the same token, it is possible that XMPP clients (or the end-user
215 devices on which such clients are installed) could also be
216 compromised, leaving users utterly at the mercy of an adversary.
218 This document and related actions to strengthen the security of the
219 XMPP network are based on the assumption that XMPP servers and
220 clients have not been subject to widespread compromise. If this
221 assumption is valid, then ubiquitous use of per-hop TLS channel
222 encryption and more significant deployment of end-to-end object
223 encryption technologies will serve to protect XMPP communications to
224 a measurable degree, compared to the alternatives.
226 6. References
228 6.1. Normative References
230 [I-D.ietf-uta-tls-bcp]
231 Sheffer, Y., Holz, R., and P. Saint-Andre,
232 "Recommendations for Secure Use of TLS and DTLS", draft-
233 ietf-uta-tls-bcp-07 (work in progress), November 2014.
235 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
236 Requirement Levels", BCP 14, RFC 2119, March 1997.
238 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
239 4949, August 2007.
241 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
242 (TLS) Protocol Version 1.2", RFC 5246, August 2008.
244 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
245 Protocol (XMPP): Core", RFC 6120, March 2011.
247 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
248 Verification of Domain-Based Application Service Identity
249 within Internet Public Key Infrastructure Using X.509
250 (PKIX) Certificates in the Context of Transport Layer
251 Security (TLS)", RFC 6125, March 2011.
253 6.2. Informative References
255 [I-D.ietf-uta-tls-attacks]
256 Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing
257 Current Attacks on TLS and DTLS", draft-ietf-uta-tls-
258 attacks-05 (work in progress), October 2014.
260 [I-D.ietf-xmpp-dna]
261 Saint-Andre, P. and M. Miller, "Domain Name Associations
262 (DNA) in the Extensible Messaging and Presence Protocol
263 (XMPP)", draft-ietf-xmpp-dna-08 (work in progress),
264 October 2014.
266 [I-D.ietf-xmpp-posh]
267 Miller, M. and P. Saint-Andre, "PKIX over Secure HTTP
268 (POSH)", draft-ietf-xmpp-posh-02 (work in progress),
269 October 2014.
271 [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
272 Protocol (XMPP): Core", RFC 3920, October 2004.
274 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
275 Security Layer (SASL)", RFC 4422, June 2006.
277 [RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing
278 Security: An Unauthenticated Mode of IPsec", RFC 5386,
279 November 2008.
281 [RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
282 Extension Definitions", RFC 6066, January 2011.
284 [XEP-0138]
285 Hildebrand, J. and P. Saint-Andre, "Stream Compression",
286 XSF XEP 0138, May 2009.
288 [XEP-0170]
289 Saint-Andre, P., "Recommended Order of Stream Feature
290 Negotiation", XSF XEP 0170, January 2007.
292 [XEP-0198]
293 Karneges, J., Saint-Andre, P., Hildebrand, J., Forno, F.,
294 Cridland, D., and M. Wild, "Stream Management", XSF XEP
295 0198, June 2011.
297 [XEP-0220]
298 Miller, J., Saint-Andre, P., and P. Hancke, "Server
299 Dialback", XSF XEP 0220, September 2013.
301 Appendix A. Implementation Notes
303 Some governments enforce legislation prohibiting the export of strong
304 cryptographic technologies. Nothing in this document ought to be
305 taken as advice to violate such prohibitions.
307 Appendix B. Acknowledgements
309 The authors would like to thank the following individuals for their
310 input: Dave Cridland, Philipp Hancke, Olle Johansson, Steve Kille,
311 Tobias Markmann, Matt Miller, and Rene Treffer.
313 Authors' Addresses
315 Peter Saint-Andre
316 &yet
318 Email: peter@andyet.com
319 URI: https://andyet.com/
321 Thijs Alkemade
323 Email: me@thijsalkema.de