Using DNSSEC and DANE as a Prooftype for XMPP Delegation
draft-miller-xmpp-dnssec-prooftype-01

Network Working Group                                          M. Miller
Internet-Draft                                            P. Saint-Andre
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: December 10, 2012                                  June 8, 2012

        Using DNSSEC and DANE as a Prooftype for XMPP Delegation
                 draft-miller-xmpp-dnssec-prooftype-01

Abstract

   This document specifies how to use DNSSEC and DANE to securely
   delegate an XMPP service identified by a domain to a host associated
   with a different domain.

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   This Internet-Draft will expire on December 10, 2012.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Requirements  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Use of DNSSEC . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Use of DANE . . . . . . . . . . . . . . . . . . . . . . . . . . 4
     5.1.  No Service Records  . . . . . . . . . . . . . . . . . . . . 4
     5.2.  Insecure Delegation . . . . . . . . . . . . . . . . . . . . 5
     5.3.  Secure Delegation . . . . . . . . . . . . . . . . . . . . . 5
   6.  Internationalization Considerations . . . . . . . . . . . . . . 5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

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1.  Introduction

   In the core XMPP specification [RFC6120], the domain to which an XMPP
   initiating entity wants to connect is asserted via the 'to' attribute
   of the <stream:stream> header, and the TLS certificate offered by the
   receiving server is required to match this source domain (e.g.,
   "im.example.com").  However, this model can cause problems if the
   source domain is delegated (via DNS SRV records [RFC2782]) to a host
   associated with a different domain that is derived via SRV (e.g.,
   "hosting.example.net"), since the derived domain might also be the
   delegate for a number of other source domains and, for operational
   and security reasons, a hosting server is rarely able to present a
   certificate that matches the source domain.

   Absent the use of DNS Security [RFC4033], delegation via SRV does not
   provide a strong basis for checking the derived domain rather than
   the source domain.  This document describes how the use of DNSSEC
   with SRV results in more secure delegation, such that the initiating
   XMPP server can legitimately check the derived domain rather than the
   source domain.  This document also describes how to utilize [DANE] to
   verify TLS certificates of domains, delegated or otherwise.

2.  Terminology

   This document inherits XMPP-related terminology from [RFC6120], DNS-
   related terminology from [RFC1034], [RFC1035], [RFC2782] and
   [RFC4033], and security-related terminology from [RFC4949] and
   [RFC5280].  The terms "source domain" and "derived domain" are used
   as defined in the "CertID" specification [RFC6125].

   This document is applicable to connections made from an XMPP client
   to an XMPP server ("_xmpp-client._tcp") or between XMPP servers
   ("_xmpp-server._tcp").  In both cases, the XMPP initiating entity
   acts as a TLS client and the XMPP receiving entity acts as a TLS
   server.  Therefore, to simplify discussion this document uses "_xmpp-
   client._tcp" to describe to both cases, unless otherwise indicated.

   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.  Requirements

   An XMPP initiating entity (TLS client) that wishes to use this
   prooftype MUST do so before exchanging stanzas addressed to the

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   source domain.  In general, this means the prooftype MUST be
   completed before the XMPP stream is restarted following STARTTLS
   negotiation (as specified in [RFC6120]).  However, connections
   between XMPP servers MAY also use this prooftype to verify
   delegations of additional source domains onto an existing connection,
   such as multiplexing via [XEP-0220].

4.  Use of DNSSEC

   An XMPP initiating entity (TLS client) that wishes to use this
   prooftype performs the following actions:
   1.  Query for the appropriate SRV resource record for the source
       domain (e.g. "_xmpp-client._tcp.im.example.com").

   2.  If there is no SRV resource record, pursue the fallback methods
       described in [RFC6120].

   3.  If there is an SRV resource record, validate that the SRV record
       answer is secure according to [RFC4033].  If the answer is
       insecure, then delegation to the derived domain (as indicated by
       the "target host" field) is insecure and the TLS client MUST
       verify the certificate against the source domain as described in
       [RFC6120]; if the answer is bogus, the TLS client MUST abort.

   4.  The TLS client SHOULD consider a connection to that derived
       domain as securely delegated; when verifying the certificate (as
       described in [RFC6125]), the TLS client MUST allow the derived
       domain or the source domain.

5.  Use of DANE

   [DANE] provides additional tools to verify the keys used in TLS
   connections.  A TLS client MAY use [DANE] for TLS certificate
   verification; its use depends on the delegation status of the source
   domain, as described in the following sections.

5.1.  No Service Records

   If no SRV records are found for the source domain, then the TLS
   client MUST query for a TLSA resource record as described in [DANE],
   where the prepared domain name MUST contain the source domain and the
   IANA-registered port 5222 for client-to-server streams (e.g.
   "_5222._tcp.im.example.com") or the IANA-registered port 5269 for
   server-to-server streams (e.g. "_5269._tcp.im.example.com").

   In this case, the TLS client MUST perform certificate verification

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   against the source domain as described in [RFC6120].

5.2.  Insecure Delegation

   If the delegation of a source domain to a derived domain is not
   secure, then the TLS client MUST NOT make a TLSA record query to the
   derived domain as described in [DANE].  Instead, the TLS client MUST
   perform certificate verification against the source domain as
   described in [RFC6120], and MUST NOT use [DANE].

5.3.  Secure Delegation

   If the source domain has been delegated to a derived domain in a
   secure manner as described under Section 4, then the TLS client MUST
   query for a TLSA resource record as described in [DANE], where the
   prepared domain name MUST contain the derived domain and a port
   obtained from the SRV record (e.g. or "_5555._tcp/
   hosting.example.net" for an SRV record such as "_xmpp-
   client._tcp.im.example.com IN TLSA 1 1 5555 hosting.example.net").

   If no TLSA resource records exist for the specified service, then the
   TLA client MUST perform certificate verification as described in
   Section 4.

   If TLSA resource records exist for the specified service, then the
   TLS client MUST perform certificate verification against the derived
   domain, using the information from the TLSA answer as the basis for
   verification as described in [DANE].

6.  Internationalization Considerations

   If the SRV, A/AAAA, and TLSA record queries are for an
   internationalized domain name, then they need to use the A-label form
   as defined in [RFC5890].

7.  Security Considerations

   This document supplements but does not supersede the security
   considerations provided in [RFC4033], [RFC6120], [RFC6125], and
   [DANE].

8.  IANA Considerations

   This document has no actions for the IANA.

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9.  Normative References

   [DANE]     Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
              of Named Entities (DANE) Transport Layer Security (TLS)
              Protocol: TLSA", draft-ietf-dane-protocol-21 (work in
              progress), May 2012.

   [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2782]  Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
              specifying the location of services (DNS SRV)", RFC 2782,
              February 2000.

   [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and S.
              Rose, "DNS Security Introduction and Requirements",
              RFC 4033, May 2005.

   [RFC4949]  Shirey, R., "Internet Security Glossary, Version 2",
              RFC 4949, August 2007.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5890]  Klensin, J., "Internationalized Domain Names for
              Applications (IDNA): Definitions and Document Framework",
              RFC 5890, August 2010.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              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.

   [XEP-0220]
              Miller, J., Saint-Andre, P., and P. Hancke, "Server
              Dialback", XSF XEP 0220, August 2011.

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Authors' Addresses

   Matthew Miller
   Cisco Systems, Inc.
   1899 Wynkoop Street, Suite 600
   Denver, CO  80202
   USA

   Email: mamille2@cisco.com

   Peter Saint-Andre
   Cisco Systems, Inc.
   1899 Wynkoop Street, Suite 600
   Denver, CO  80202
   USA

   Email: psaintan@cisco.com

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