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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 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: March 15, 2015 September 11, 2014 8 Use of Transport Layer Security (TLS) in the Extensible Messaging and 9 Presence Protocol (XMPP) 10 draft-ietf-uta-xmpp-01 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 March 15, 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. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3 57 3.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 3 58 3.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 3 59 3.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 3 60 3.6. Session Resumption . . . . . . . . . . . . . . . . . . . 4 61 3.7. Authenticated Connections . . . . . . . . . . . . . . . . 4 62 3.8. Unauthenticated Connections . . . . . . . . . . . . . . . 4 63 3.9. Server Name Indication . . . . . . . . . . . . . . . . . 4 64 3.10. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5 65 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 66 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 67 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 68 6.1. Normative References . . . . . . . . . . . . . . . . . . 6 69 6.2. Informative References . . . . . . . . . . . . . . . . . 6 70 Appendix A. Implementation Notes . . . . . . . . . . . . . . . . 7 71 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 7 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 74 1. Introduction 76 The Extensible Messaging and Presence Protocol (XMPP) [RFC6120] 77 (along with its precursor, the so-called "Jabber protocol") has used 78 Transport Layer Security (TLS) [RFC5246] (along with its precursor, 79 Secure Sockets Layer or SSL) since 1999. Both [RFC6120] and its 80 predecessor [RFC3920] provided recommendations regarding the use of 81 TLS in XMPP. In order to address the evolving threat model on the 82 Internet today, this document provides stronger recommendations based 83 on [I-D.ietf-uta-tls-bcp]. This document updates [RFC6120]. 85 2. Terminology 87 Various security-related terms are to be understood in the sense 88 defined in [RFC4949]. 90 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 91 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 92 "OPTIONAL" in this document are to be interpreted as described in 93 [RFC2119]. 95 3. Recommendations 97 3.1. Support for TLS 99 Support for TLS (specifically, the XMPP profile of STARTTLS) is 100 mandatory for XMPP implementations, as already specified in [RFC6120] 101 and its predecessor [RFC3920]. 103 If the server to which a client or peer server connects does not 104 offer a stream feature of (thus indicating that it is an XMPP 1.0 server that 106 supports TLS), the initiating entity MUST NOT proceed with the stream 107 negotiation and MUST instead abort the connection attempt. Although 108 XMPP servers SHOULD include the child element to indicate 109 that negotiation of TLS is mandatory, clients and peer servers MUST 110 NOT depend on receiving the flag in determining whether 111 TLS will be enforced for the stream. 113 3.2. Protocol Versions 115 Implementations MUST follow the recommendations in 116 [I-D.ietf-uta-tls-bcp] as to supporting various TLS versions and 117 avoiding fallback to SSL. 119 3.3. Cipher Suites 121 Implementations MUST follow the recommendations in 122 [I-D.ietf-uta-tls-bcp]. 124 3.4. Public Key Length 126 Implementations MUST follow the recommendations in 127 [I-D.ietf-uta-tls-bcp]. 129 3.5. Compression 131 Implementations MUST follow the recommendations in 132 [I-D.ietf-uta-tls-bcp]. 134 XMPP supports an application-layer compression technology [XEP-0138], 135 which might have slightly stronger security properties than TLS (at 136 least because it is enabled after SASL authentication, as described 137 in [XEP-0170]). 139 3.6. Session Resumption 141 Implementations MUST follow the recommendations in 142 [I-D.ietf-uta-tls-bcp]. 144 Use of session IDs [RFC5246] is RECOMMENDED instead of session 145 tickets [RFC5077], since XMPP does not in general use state 146 management technologies such as tickets or "cookies" [RFC6265]. 148 In XMPP, TLS session resumption can be used in concert with the XMPP 149 Stream Management extension; see [XEP-0198] for further details. 151 3.7. Authenticated Connections 153 Both the core XMPP specification [RFC6120] and the "CertID" 154 specification [RFC6125] provide recommendations and requirements for 155 certificate validation in the context of authenticated connections. 156 This document does not supersede those specifications. Wherever 157 possible, it is best to prefer authenticated connections (along with 158 SASL [RFC4422]), as already stated in the core XMPP specification 159 [RFC6120]. In particular, clients MUST authenticate servers. 161 3.8. Unauthenticated Connections 163 Given the pervasiveness of passive eavesdropping, even an 164 unauthenticated connection might be better than an unencrypted 165 connection (this is similar to the "better than nothing security" 166 approach for IPsec [RFC5386]). In particular, because of current 167 deployment challenges for authenticated connections between XMPP 168 servers (see [I-D.ietf-xmpp-dna] for details), it might be reasonable 169 for XMPP server implementations to accept unauthenticated connections 170 when the Server Dialback protocol [XEP-0220] is used for weak 171 identity verification; this will at least enable encryption of 172 server-to-server connections. Unauthenticated connections include 173 connections negotiated using anonymous Diffie-Hellman algorithms or 174 using self-signed certificates, among other scenarios. 176 3.9. Server Name Indication 178 Although there is no harm in supporting the TLS Server Name 179 Indication (SNI) extension [RFC6066], this is not necessary since the 180 same function is served in XMPP by the 'to' address of the initial 181 stream header as explained in Section 4.7.2 of [RFC6120]. 183 3.10. Human Factors 185 It is RECOMMENDED that XMPP clients provide ways for end users (and 186 that XMPP servers provide ways for administrators) to complete the 187 following tasks: 189 o Determine if a client-to-server or server-to-server connection is 190 encrypted and authenticated. 192 o Determine the version of TLS used for a client-to-server or 193 server-to-server connection. 195 o Inspect the certificate offered by an XMPP server. 197 o Determine the cipher suite used to encrypt a connection. 199 o Be warned if the certificate changes for a given server. 201 4. IANA Considerations 203 This document requests no actions of the IANA. 205 5. Security Considerations 207 The use of TLS can help limit the information available for 208 correlation to the network and transport layer headers as opposed to 209 the application layer. As typically deployed, XMPP technologies do 210 not leave application-layer routing data (such as XMPP 'to' and 211 'from' addresses) at rest on intermediate systems, since there is 212 only one hop between any two given XMPP servers. As a result, 213 encrypting all hops (sending client to sender's server, sender's 214 server to recipient's server, recipient's server to recipient's 215 client) can help to limit the amount of "metadata" that might leak. 217 It is possible that XMPP servers themselves might be compromised. In 218 that case, per-hop encryption would not protect XMPP communications, 219 and even end-to-end encryption of (parts of) XMPP stanza payloads 220 would leave addressing information and XMPP roster data in the clear. 221 By the same token, it is possible that XMPP clients (or the end-user 222 devices on which such clients are installed) could also be 223 compromised, leaving users utterly at the mercy of an adversary. 225 This document and related actions to strengthen the security of the 226 XMPP network are based on the assumption that XMPP servers and 227 clients have not been subject to widespread compromise. If this 228 assumption is valid, then ubiquitous use of per-hop TLS channel 229 encryption and more significant deployment of end-to-end object 230 encryption technologies will serve to protect XMPP communications to 231 a measurable degree, compared to the alternatives. 233 6. References 235 6.1. Normative References 237 [I-D.ietf-uta-tls-bcp] 238 Sheffer, Y., Holz, R., and P. Saint-Andre, 239 "Recommendations for Secure Use of TLS and DTLS", draft- 240 ietf-uta-tls-bcp-02 (work in progress), August 2014. 242 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 243 Requirement Levels", BCP 14, RFC 2119, March 1997. 245 [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC 246 4949, August 2007. 248 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 249 "Transport Layer Security (TLS) Session Resumption without 250 Server-Side State", RFC 5077, January 2008. 252 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 253 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 255 [RFC6120] Saint-Andre, P., "Extensible Messaging and Presence 256 Protocol (XMPP): Core", RFC 6120, March 2011. 258 [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and 259 Verification of Domain-Based Application Service Identity 260 within Internet Public Key Infrastructure Using X.509 261 (PKIX) Certificates in the Context of Transport Layer 262 Security (TLS)", RFC 6125, March 2011. 264 6.2. Informative References 266 [I-D.ietf-xmpp-dna] 267 Saint-Andre, P. and M. Miller, "Domain Name Associations 268 (DNA) in the Extensible Messaging and Presence Protocol 269 (XMPP)", draft-ietf-xmpp-dna-06 (work in progress), June 270 2014. 272 [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence 273 Protocol (XMPP): Core", RFC 3920, October 2004. 275 [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and 276 Security Layer (SASL)", RFC 4422, June 2006. 278 [RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing 279 Security: An Unauthenticated Mode of IPsec", RFC 5386, 280 November 2008. 282 [RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions: 283 Extension Definitions", RFC 6066, January 2011. 285 [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, 286 April 2011. 288 [XEP-0138] 289 Hildebrand, J. and P. Saint-Andre, "Stream Compression", 290 XSF XEP 0138, May 2009. 292 [XEP-0170] 293 Saint-Andre, P., "Recommended Order of Stream Feature 294 Negotiation", XSF XEP 0170, January 2007. 296 [XEP-0198] 297 Karneges, J., Saint-Andre, P., Hildebrand, J., Forno, F., 298 Cridland, D., and M. Wild, "Stream Management", XSF XEP 299 0198, June 2011. 301 [XEP-0220] 302 Miller, J., Saint-Andre, P., and P. Hancke, "Server 303 Dialback", XSF XEP 0220, September 2013. 305 Appendix A. Implementation Notes 307 Some governments enforce legislation prohibiting the export of strong 308 cryptographic technologies. Nothing in this document ought to be 309 taken as advice to violate such prohibitions. 311 Appendix B. Acknowledgements 313 Thanks to the following individuals for their input: Dave Cridland, 314 Philipp Hancke, Olle Johansson, Steve Kille, Tobias Markmann, Matt 315 Miller, and Rene Treffer. 317 Authors' Addresses 319 Peter Saint-Andre 320 &yet 321 P.O. Box 787 322 Parker, CO 80134 323 USA 325 Email: peter@andyet.net 326 Thijs Alkemade 328 Email: me@thijsalkema.de