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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: September 5, 2014 March 4, 2014
8 Use of Transport Layer Security (TLS) in the Extensible Messaging and
9 Presence Protocol (XMPP)
10 draft-saintandre-xmpp-tls-06
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 September 5, 2014.
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. Discussion Venue . . . . . . . . . . . . . . . . . . . . . . 3
55 4. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3
56 4.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3
57 4.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3
58 4.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 3
59 4.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 3
60 4.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 3
61 4.6. Session Resumption . . . . . . . . . . . . . . . . . . . 4
62 4.7. Authenticated Connections . . . . . . . . . . . . . . . . 4
63 4.8. Unauthenticated Connections . . . . . . . . . . . . . . . 4
64 4.9. Server Name Indication . . . . . . . . . . . . . . . . . 4
65 4.10. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5
66 5. Implementation Notes . . . . . . . . . . . . . . . . . . . . 5
67 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
68 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
69 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
70 8.1. Normative References . . . . . . . . . . . . . . . . . . 6
71 8.2. Informative References . . . . . . . . . . . . . . . . . 6
72 8.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 7
73 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8
74 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
76 1. Introduction
78 The Extensible Messaging and Presence Protocol (XMPP) [RFC6120]
79 (along with its precursor, the so-called "Jabber protocol") has used
80 Transport Layer Security (TLS) [RFC5246] (along with its precursor,
81 Secure Sockets Layer or SSL) since 1999. Both [RFC6120] and its
82 predecessor [RFC3920] provided recommendations regarding the use of
83 TLS in XMPP. In order to address the evolving threat model on the
84 Internet today (see, for example, [I-D.trammell-perpass-ppa]), this
85 document provides stronger recommendations (see also
86 [I-D.sheffer-tls-bcp]). This document updates [RFC6120].
88 2. Terminology
90 Various security-related terms are to be understood in the sense
91 defined in [RFC4949].
93 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
94 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
95 "OPTIONAL" in this document are to be interpreted as described in
96 [RFC2119].
98 3. Discussion Venue
100 The discussion venue for this document is the mailing list of the
101 XMPP Working Group, for which archives and subscription information
102 can be found at [1]. Discussion might also occur on the mailing list
103 of the UTA Working Group, for which archives and subscription
104 information can be found at [2].
106 4. Recommendations
108 4.1. Support for TLS
110 Support for TLS (specifically, the XMPP profile of STARTTLS) is
111 mandatory for XMPP implementations, as already specified in [RFC6120]
112 and its predecessor [RFC3920].
114 If the server to which an XMPP client or peer server connects does
115 not offer a stream feature of (thus indicating that it is an XMPP 1.0 server that
117 supports TLS), the initiating entity MUST NOT proceed with the stream
118 negotiation and MUST instead abort the connection attempt. Although
119 XMPP servers SHOULD include the child element to indicate
120 that negotiation of TLS is mandatory, clients and peer servers MUST
121 NOT depend on receiving the flag in determining whether
122 TLS will be enforced for the stream.
124 4.2. Protocol Versions
126 Implementations MUST follow the recommendations in
127 [I-D.sheffer-tls-bcp] as to supporting various TLS versions and
128 avoiding fallback to SSL.
130 4.3. Cipher Suites
132 Implementations MUST follow the recommendations in
133 [I-D.sheffer-tls-bcp].
135 4.4. Public Key Length
137 Implementations MUST follow the recommendations in
138 [I-D.sheffer-tls-bcp].
140 4.5. Compression
142 Implementations MUST follow the recommendations in
143 [I-D.sheffer-tls-bcp].
145 XMPP supports an application-layer compression technology [XEP-0138],
146 which might have slightly stronger security properties than TLS (at
147 least because it is enabled after SASL authentication, as described
148 in [XEP-0170]).
150 4.6. Session Resumption
152 Implementations MUST follow the recommendations in
153 [I-D.sheffer-tls-bcp].
155 Use of session IDs [RFC5246] is RECOMMENDED instead of session
156 tickets [RFC5077], since XMPP does not in general use state
157 management technologies such as tickets or "cookies" [RFC6265].
159 Note that, in XMPP, TLS session resumption can be used in concert
160 with the XMPP Stream Management extension; see [XEP-0198] for further
161 details.
163 4.7. Authenticated Connections
165 Both the core XMPP specification [RFC6120] and the "CertID"
166 specification [RFC6125] provide recommendations and requirements for
167 certificate validation in the context of authenticated connections.
168 This document does not supersede those specifications. Wherever
169 possible, it is best to prefer authenticated connections (along with
170 SASL [RFC4422]), as already stated in the core XMPP specification
171 [RFC6120]. In particular, clients MUST authenticate servers.
173 4.8. Unauthenticated Connections
175 Given the pervasiveness of passive eavesdropping, even an
176 unauthenticated connection might be better than an unencrypted
177 connection (this is similar to the "better than nothing security"
178 approach for IPsec [RFC5386]). In particular, because of current
179 deployment challenges for authenticated connections between XMPP
180 servers (see [I-D.ietf-xmpp-dna] for details), it might be reasonable
181 for XMPP server implementations to accept unauthenticated connections
182 when the Server Dialback protocol [XEP-0220] is used for weak
183 identity verification; this will at least enable encryption of
184 server-to-server connections. Unauthenticated connections include
185 connections negotiated using anonymous Diffie-Hellman algorithms or
186 using self-signed certificates, among other scenarios.
188 4.9. Server Name Indication
190 Although there is no harm in supporting the TLS Server Name
191 Indication (SNI) extension [RFC6066], this is not necessary since the
192 same function is served in XMPP by the 'to' address of the initial
193 stream header as explained in Section 4.7.2 of [RFC6120].
195 4.10. Human Factors
197 It is RECOMMENDED that XMPP clients provide ways for end users (and
198 that XMPP servers provide ways for administators) to complete the
199 following tasks:
201 o Determine if a client-to-server or server-to-server connection is
202 encrypted and authenticated.
204 o Determine the version of TLS used for a client-to-server or
205 server-to-server connection.
207 o Inspect the certificate offered by an XMPP server.
209 o Determine the cipher suite used to encrypt a connection.
211 o Be warned if the certificate changes for a given server.
213 5. Implementation Notes
215 Some governments enforce legislation prohibiting the export of strong
216 cryptographic technologies. Nothing in this document ought to be
217 taken as advice to violate such prohibitions.
219 6. IANA Considerations
221 This document requests no actions of the IANA.
223 7. Security Considerations
225 As noted in "A Threat Model for Pervasive Passive Surveillance"
226 [I-D.trammell-perpass-ppa]), the use of TLS can help limit the
227 information available for correlation to the network and transport
228 layer headers as opposed to the application layer. As typically
229 deployed, XMPP technologies do not leave application-layer routing
230 data (such as XMPP 'to' and 'from' addresses) at rest on intermediate
231 systems, since there is only one hop between any two given XMPP
232 servers. As a result, encrypting all hops (sending client to
233 sender's server, sender's server to recipient's server, recipient's
234 server to recipient's client) can help to limit the amount of
235 "metadata" that might leak.
237 It is possible that XMPP servers themselves might be compromised. In
238 that case, per-hop encryption would not protect XMPP communications,
239 and even end-to-end encryption of (parts of) XMPP stanza payloads
240 would leave addressing information and XMPP roster data in the clear.
241 By the same token, it is possible that XMPP clients (or the end-user
242 devices on which such clients are installed) could also be
243 compromised, leaving users utterly at the mercy of an adversary.
245 This document, along with actions currently being taken to strenthen
246 the security of the XMPP network, do not assume widespread compromise
247 of XMPP servers and clients or their underlying operating systems or
248 hardware. Thus it is assumed that ubiquitous use of per-hop TLS
249 channel encryption and more significant deployment of end-to-end
250 object encryption technologies will serve to protect XMPP
251 communications to a measurable degree, compared to the alternatives.
253 8. References
255 8.1. Normative References
257 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
258 Requirement Levels", BCP 14, RFC 2119, March 1997.
260 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
261 4949, August 2007.
263 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
264 "Transport Layer Security (TLS) Session Resumption without
265 Server-Side State", RFC 5077, January 2008.
267 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
268 (TLS) Protocol Version 1.2", RFC 5246, August 2008.
270 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
271 Protocol (XMPP): Core", RFC 6120, March 2011.
273 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and
274 Verification of Domain-Based Application Service Identity
275 within Internet Public Key Infrastructure Using X.509
276 (PKIX) Certificates in the Context of Transport Layer
277 Security (TLS)", RFC 6125, March 2011.
279 8.2. Informative References
281 [I-D.ietf-xmpp-dna]
282 Saint-Andre, P. and M. Miller, "Domain Name Associations
283 (DNA) in the Extensible Messaging and Presence Protocol
284 (XMPP)", draft-ietf-xmpp-dna-05 (work in progress),
285 February 2014.
287 [I-D.sheffer-tls-bcp]
288 Sheffer, Y., Holz, R., and P. Saint-Andre,
289 "Recommendations for Secure Use of TLS and DTLS", draft-
290 sheffer-tls-bcp-02 (work in progress), February 2014.
292 [I-D.trammell-perpass-ppa]
293 Trammell, B., Borkmann, D., and C. Huitema, "A Threat
294 Model for Pervasive Passive Surveillance", draft-trammell-
295 perpass-ppa-01 (work in progress), November 2013.
297 [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence
298 Protocol (XMPP): Core", RFC 3920, October 2004.
300 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and
301 Security Layer (SASL)", RFC 4422, June 2006.
303 [RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing
304 Security: An Unauthenticated Mode of IPsec", RFC 5386,
305 November 2008.
307 [RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
308 Extension Definitions", RFC 6066, January 2011.
310 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
311 April 2011.
313 [XEP-0138]
314 Hildebrand, J. and P. Saint-Andre, "Stream Compression",
315 XSF XEP 0138, May 2009.
317 [XEP-0170]
318 Saint-Andre, P., "Recommended Order of Stream Feature
319 Negotiation", XSF XEP 0170, January 2007.
321 [XEP-0198]
322 Karneges, J., Saint-Andre, P., Hildebrand, J., Forno, F.,
323 Cridland, D., and M. Wild, "Stream Management", XSF XEP
324 0198, June 2011.
326 [XEP-0220]
327 Miller, J., Saint-Andre, P., and P. Hancke, "Server
328 Dialback", XSF XEP 0220, September 2013.
330 8.3. URIs
332 [1] https://www.ietf.org/mailman/listinfo/xmpp
334 [2] https://www.ietf.org/mailman/listinfo/uta
336 Appendix A. Acknowledgements
338 Thanks to the following individuals for their input: Dave Cridland,
339 Philipp Hancke, Olle Johansson, Steve Kille, Tobias Markmann, Matt
340 Miller, and Rene Treffer.
342 Authors' Addresses
344 Peter Saint-Andre
345 &yet
347 Email: ietf@stpeter.im
349 Thijs Alkemade
351 Email: me@thijsalkema.de