--- 1/draft-ietf-uta-xmpp-02.txt 2014-11-11 20:14:53.985304930 -0800 +++ 2/draft-ietf-uta-xmpp-03.txt 2014-11-11 20:14:54.005305437 -0800 @@ -1,20 +1,20 @@ Network Working Group P. Saint-Andre Internet-Draft &yet Updates: 6120 (if approved) T. Alkemade Intended status: Standards Track -Expires: March 26, 2015 September 22, 2014 +Expires: May 15, 2015 November 11, 2014 Use of Transport Layer Security (TLS) in the Extensible Messaging and Presence Protocol (XMPP) - draft-ietf-uta-xmpp-02 + draft-ietf-uta-xmpp-03 Abstract This document provides recommendations for the use of Transport Layer Security (TLS) in the Extensible Messaging and Presence Protocol (XMPP). This document updates RFC 6120. Status of This Memo This Internet-Draft is submitted in full conformance with the @@ -23,21 +23,21 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on March 26, 2015. + This Internet-Draft will expire on May 15, 2015. Copyright Notice Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -46,148 +46,136 @@ include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. Recommendations . . . . . . . . . . . . . . . . . . . . . . . 3 3.1. Support for TLS . . . . . . . . . . . . . . . . . . . . . 3 - 3.2. Protocol Versions . . . . . . . . . . . . . . . . . . . . 3 - 3.3. Cipher Suites . . . . . . . . . . . . . . . . . . . . . . 3 - 3.4. Public Key Length . . . . . . . . . . . . . . . . . . . . 3 - 3.5. Compression . . . . . . . . . . . . . . . . . . . . . . . 3 - 3.6. Session Resumption . . . . . . . . . . . . . . . . . . . 4 - 3.7. Authenticated Connections . . . . . . . . . . . . . . . . 4 - 3.8. Unauthenticated Connections . . . . . . . . . . . . . . . 4 - 3.9. Server Name Indication . . . . . . . . . . . . . . . . . 4 - 3.10. Human Factors . . . . . . . . . . . . . . . . . . . . . . 5 - 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 + 3.2. Compression . . . . . . . . . . . . . . . . . . . . . . . 3 + 3.3. Session Resumption . . . . . . . . . . . . . . . . . . . 3 + 3.4. Authenticated Connections . . . . . . . . . . . . . . . . 3 + 3.5. Unauthenticated Connections . . . . . . . . . . . . . . . 4 + 3.6. Server Name Indication . . . . . . . . . . . . . . . . . 4 + 3.7. Human Factors . . . . . . . . . . . . . . . . . . . . . . 4 + 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 - 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 6.1. Normative References . . . . . . . . . . . . . . . . . . 6 + 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 6.1. Normative References . . . . . . . . . . . . . . . . . . 5 6.2. Informative References . . . . . . . . . . . . . . . . . 6 Appendix A. Implementation Notes . . . . . . . . . . . . . . . . 7 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction The Extensible Messaging and Presence Protocol (XMPP) [RFC6120] (along with its precursor, the so-called "Jabber protocol") has used Transport Layer Security (TLS) [RFC5246] (along with its precursor, Secure Sockets Layer or SSL) since 1999. Both [RFC6120] and its predecessor [RFC3920] provided recommendations regarding the use of TLS in XMPP. In order to address the evolving threat model on the - Internet today, this document provides stronger recommendations based - on [I-D.ietf-uta-tls-bcp]. This document updates [RFC6120]. + Internet today, this document provides stronger recommendations. + + NOTE: Unless explicitly noted otherwise, all of the + recommendations specified in [I-D.ietf-uta-tls-bcp] apply to XMPP. + In the main, this document merely provides supplementary + information; those who implement and deploy XMPP technologies are + expected to follow the recommendations of [I-D.ietf-uta-tls-bcp]. + + This document updates [RFC6120]. 2. Terminology Various security-related terms are to be understood in the sense defined in [RFC4949]. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Recommendations 3.1. Support for TLS Support for TLS (specifically, the XMPP profile of STARTTLS) is mandatory for XMPP implementations, as already specified in [RFC6120] and its predecessor [RFC3920]. - If the server to which a client or peer server connects does not + The server (i.e., the XMPP receiving entity) to which a client or + peer server (i.e., the XMPP initiating entity) connects might not offer a stream feature of (thus indicating that it is an XMPP 1.0 server that - supports TLS), the initiating entity MUST NOT proceed with the stream - negotiation and MUST instead abort the connection attempt. Although - XMPP servers SHOULD include the child element to indicate - that negotiation of TLS is mandatory, clients and peer servers MUST - NOT depend on receiving the flag in determining whether - TLS will be enforced for the stream. - -3.2. Protocol Versions - - Implementations MUST follow the recommendations in Section 4.1 of - [I-D.ietf-uta-tls-bcp] as to supporting various TLS versions and - avoiding fallback to SSL. - -3.3. Cipher Suites - - Implementations MUST follow the recommendations in Section 5 of - [I-D.ietf-uta-tls-bcp]. - -3.4. Public Key Length - - Implementations MUST follow the recommendations in Section 5.4 of - [I-D.ietf-uta-tls-bcp]. - -3.5. Compression - - Implementations MUST follow the recommendations in Section 4.5 of - [I-D.ietf-uta-tls-bcp]. + :xmpp-tls'/>. Although in general this stream feature indicates that + the server supports XMPP 1.0 and therefore supports TLS, it is + possible that this stream feature might be stripped out by an + attacker (see Section 2.1 of [I-D.ietf-uta-tls-attacks]). Therefore, + the initiating entity SHOULD proceed with the stream negotiation even + if the receiving entity does not advertise support for TLS. + Similarly, although a receiving entity SHOULD include the + child element to indicate that negotiation of TLS is mandatory, an + initiating entity MUST NOT depend on receiving the flag + in determining whether TLS will be enforced for the stream. - XMPP supports an application-layer compression technology [XEP-0138], - which might have slightly stronger security properties than TLS (at - least because it is enabled after SASL authentication, as described - in [XEP-0170]). +3.2. Compression -3.6. Session Resumption + XMPP supports an application-layer compression technology [XEP-0138]. + Although this XMPP extension might have slightly stronger security + properties than TLS-layer compression (since it is enabled after SASL + authentication, as described in [XEP-0170]), this document neither + encourages nor discourages use of XMPP-layer compression. - Implementations MUST follow the recommendations in Section 4.6 of - [I-D.ietf-uta-tls-bcp]. +3.3. Session Resumption Use of session IDs [RFC5246] is RECOMMENDED instead of session tickets [RFC5077], since XMPP does not in general use state management technologies such as tickets or "cookies" [RFC6265]. In XMPP, TLS session resumption can be used in concert with the XMPP Stream Management extension; see [XEP-0198] for further details. -3.7. Authenticated Connections +3.4. Authenticated Connections Both the core XMPP specification [RFC6120] and the "CertID" specification [RFC6125] provide recommendations and requirements for certificate validation in the context of authenticated connections. This document does not supersede those specifications. Wherever possible, it is best to prefer authenticated connections (along with SASL [RFC4422]), as already stated in the core XMPP specification [RFC6120]. In particular, clients MUST authenticate servers. -3.8. Unauthenticated Connections +3.5. Unauthenticated Connections Given the pervasiveness of passive eavesdropping, even an unauthenticated connection might be better than an unencrypted connection (this is similar to the "better than nothing security" approach for IPsec [RFC5386]). In particular, because of current deployment challenges for authenticated connections between XMPP - servers (see [I-D.ietf-xmpp-dna] for details), it might be reasonable - for XMPP server implementations to accept unauthenticated connections - when the Server Dialback protocol [XEP-0220] is used for weak - identity verification; this will at least enable encryption of - server-to-server connections. Unauthenticated connections include - connections negotiated using anonymous Diffie-Hellman algorithms or - using self-signed certificates, among other scenarios. + servers (see [I-D.ietf-xmpp-dna] and [I-D.ietf-xmpp-posh] for + details), it might be reasonable for XMPP server implementations to + accept unauthenticated connections when the Server Dialback protocol + [XEP-0220] is used for weak identity verification; this will at least + enable encryption of server-to-server connections. Unauthenticated + connections include connections negotiated using anonymous Diffie- + Hellman algorithms or using self-signed certificates, among other + scenarios. -3.9. Server Name Indication +3.6. Server Name Indication Although there is no harm in supporting the TLS Server Name Indication (SNI) extension [RFC6066], this is not necessary since the same function is served in XMPP by the 'to' address of the initial stream header as explained in Section 4.7.2 of [RFC6120]. -3.10. Human Factors +3.7. Human Factors It is strongly encouraged that XMPP clients provide ways for end users (and that XMPP servers provide ways for administrators) to complete the following tasks: o Determine if a client-to-server or server-to-server connection is encrypted and authenticated. o Determine the version of TLS used for a client-to-server or server-to-server connection. @@ -230,21 +218,21 @@ encryption technologies will serve to protect XMPP communications to a measurable degree, compared to the alternatives. 6. 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-03 (work in progress), September 2014. + ietf-uta-tls-bcp-07 (work in progress), November 2014. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC 4949, August 2007. [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, "Transport Layer Security (TLS) Session Resumption without Server-Side State", RFC 5077, January 2008. @@ -256,25 +244,35 @@ Protocol (XMPP): Core", RFC 6120, March 2011. [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, March 2011. 6.2. Informative References + [I-D.ietf-uta-tls-attacks] + Sheffer, Y., Holz, R., and P. Saint-Andre, "Summarizing + Current Attacks on TLS and DTLS", draft-ietf-uta-tls- + attacks-05 (work in progress), October 2014. + [I-D.ietf-xmpp-dna] Saint-Andre, P. and M. Miller, "Domain Name Associations (DNA) in the Extensible Messaging and Presence Protocol - (XMPP)", draft-ietf-xmpp-dna-06 (work in progress), June - 2014. + (XMPP)", draft-ietf-xmpp-dna-08 (work in progress), + October 2014. + + [I-D.ietf-xmpp-posh] + Miller, M. and P. Saint-Andre, "PKIX over Secure HTTP + (POSH)", draft-ietf-xmpp-posh-02 (work in progress), + October 2014. [RFC3920] Saint-Andre, P., Ed., "Extensible Messaging and Presence Protocol (XMPP): Core", RFC 3920, October 2004. [RFC4422] Melnikov, A. and K. Zeilenga, "Simple Authentication and Security Layer (SASL)", RFC 4422, June 2006. [RFC5386] Williams, N. and M. Richardson, "Better-Than-Nothing Security: An Unauthenticated Mode of IPsec", RFC 5386, November 2008. @@ -303,26 +301,25 @@ Dialback", XSF XEP 0220, September 2013. Appendix A. Implementation Notes 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 B. Acknowledgements - Thanks to the following individuals for their input: Dave Cridland, - Philipp Hancke, Olle Johansson, Steve Kille, Tobias Markmann, Matt - Miller, and Rene Treffer. + The authors would like to thank the following individuals for their + input: Dave Cridland, Philipp Hancke, Olle Johansson, Steve Kille, + Tobias Markmann, Matt Miller, and Rene Treffer. Authors' Addresses Peter Saint-Andre &yet - P.O. Box 787 - Parker, CO 80134 - USA - Email: peter@andyet.net + Email: peter@andyet.com + URI: https://andyet.com/ + Thijs Alkemade Email: me@thijsalkema.de