Network Working Group M. Miller
Internet-Draft P. Saint-Andre
Intended status: Standards Track Cisco Systems, Inc.
Expires: December 13, 2012 June 6, 2012
Using DNSSEC and DANE as a Prooftype for XMPP Delegation
draft-miller-xmpp-dnssec-prooftype-00
Abstract
This document defines a model for securely delegating an XMPP service
for a domain to a host associated with a different domain.
Status of this Memo
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This Internet-Draft will expire on December 13, 2012.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 2
4. Use of DNSSEC . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Use of DANE . . . . . . . . . . . . . . . . . . . . . . . . . 3
5.1. No Delegation . . . . . . . . . . . . . . . . . . . . . . 3
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5.2. Insecure Delegation . . . . . . . . . . . . . . . . . . . 4
5.3. Secure Delegation . . . . . . . . . . . . . . . . . . . . 4
5.4. TLSA Certificate Usage 3 Considerations . . . . . . . . . 4
6. Internationalization Considerations . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 4
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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.
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
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An XMPP initiating entity (TLS client) that wishes to use this
prooftype MUST do so before exchanging stanzas addressed to the
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 or bogus, 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].
4. If there is an SRV record, for each derived domain from the SRV
record answer (e.g. "hosting.example.net"), query for the "A"
and/or "AAAA" resource records as described in [RFC6120].
5. For each derived domain, validate that the address record answers
are provably secure according to [RFC4033]
6. If any answer is insecure or bogus, then the TLS client MUST NOT
consider a connection to that derived domain as securely
delegated from the source domain; when verifying the certificate,
the TLS client MUST do so against the source domain as described
in [RFC6120].
7. For each address record answer that is a provably secure, 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 SHOULD do so against the derived
domain but MAY also verify the certificate against the source
domain.
5. Use of DANE
[DANE] provides additional tools to verify the keys used in TLS
connections. Whether it is appropriate to use [DANE] for TLS
certificate verification depends on the delegation status of the
source domain, as described in the following sections.
5.1. No Delegation
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If the source domain has not been delegated to a derived domain,
i.e., if the source domain and the derived domain are identical
(e.g., "im.example.com"), then the TLS client MAY query for a TLSA
resource record as described in [DANE], where the prepared domain
name MUST contain the source domain and a port of 5222 for client-to-
server streams (e.g. "_5222._tcp.im.example.com") or 5269 for
server-to-server streams (e.g. "_5269._tcp.im.example.com").
In this case, the TLS client MUST perform certificate verification
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 MAY make a TLSA query against the source
domain.
5.3. Secure Delegation
If the source domain has been delegated to a derived domain in a
secure manner as described under [protocol], then the TLS client
SHOULD query for a TLSA resource record as described in [DANE], where
the prepared domain name MUST contain the derived domain and a port
of 5222 for client-to-server streams or 5269 for server-to-server
streams (e.g. "_5222._tcp.hosting.example.net").
If no TLSA resource records exist for the specified service, then the
TLA client MUST perform certificate verification against the source
domain as described in [RFC6120].
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].
5.4. TLSA Certificate Usage 3 Considerations
If a TLSA resource record specifies certificate usage 3 (also known
as "domain-issued certificate"), verification MUST NOT consider the
source or derived domain. Instead, the target certificate MUST match
the TLSA record, as specified in [DANE]. If matched, the TLS
connection MUST considered valid for the source domain regardless of
the target certificate's information.
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
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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.
9. References
[DANE] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", Internet-Draft draft-ietf-dane-
protocol-21, 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]
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Miller, J, Saint-Andre, P and P Hancke, "Server Dialback",
XSF XEP 0220, August 2011.
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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