GEOPRIV WG M. Thomson
Internet-Draft J. Winterbottom
Expires: December 30, 2005 Nortel
June 28, 2005
Domain Authorization for PIDF-LO
draft-thomson-domain-auth-01.txt
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Copyright (C) The Internet Society (2005).
Abstract
This document describes a standard method for digitally signing
Presence Information Data Format Location Object (PIDF-LO) documents
using a subset of the XML Digital Signature specification. A digital
signature enables the user of a signed PIDF-LO document to attribute
that information to an authorized source within the domain of the
target entity. A schema is defined for including a domain
authorization element in the PIDF-LO and a set of XML Path Language
(XPath) filters for selecting the correct elements for signing.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Conventions used in this document . . . . . . . . . . . . 3
2. The Domain Authorization Element . . . . . . . . . . . . . . . 5
2.1 'expires' attribute . . . . . . . . . . . . . . . . . . . 5
3. Signature Elements . . . . . . . . . . . . . . . . . . . . . . 6
3.1 PIDF-LO Document Transform . . . . . . . . . . . . . . . . 6
3.2 Algorithms . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3 Signature Key Data . . . . . . . . . . . . . . . . . . . . 7
4. XML Definitions . . . . . . . . . . . . . . . . . . . . . . . 9
4.1 XML Schema . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2 XPath Filter . . . . . . . . . . . . . . . . . . . . . . . 10
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 16
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
7.1 URN Sub-Namespace Registration for
urn:ietf:params:xml:ns:pidf:geopriv10:domain-auth . . . . 17
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . 19
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1. Introduction
Users of location information may desire to be able to attribute this
information to an authorized entity. This entity may not have
provided the information, but they must be able to vouch for its
accuracy. In most cases this will mean that the trusted entity
resides within the same domain, or access network, as the target
entity.
This specification describes a means by which a domain authority may
assume responsibility for the validity of the location information
provided in a Presence Information Data Format Location Object
(PIDF-LO [I-D.ietf-geopriv-pidf-lo]). A standard form is described
whereby a domain authority may digitally sign the PIDF-LO document.
This signature ensures that a user of the PIDF-LO can verify that the
presentity identified is at the described location within certain
time bounds.
Only selected data are signed within a PIDF, allowing a user freedom
to change other parts of the document without affecting the
signature. A signature only applies to a single tuple element,
allowing separate tuples to be unsigned, or to be signed separately.
Elements such as notes, contact information and the privacy
preferences described in [I-D.ietf-geopriv-pidf-lo] are not signed to
allow for modification. The signed elements are restricted to:
the presentity identifier: the entity attribute of the _presence_
element.
timestamp: the timestamp associated with the location information
location-info: the actual location information
expires: the time at which the signature expires, this datum is added
by this specification
1.1 Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The term _presentity_ is used as defined in RFC 2778 [RFC2778].
The term _location user_ is used to refer to the entity that is
consuming location information. In the context of RFC 2778
[RFC2778], the location user may be a watcher.
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The term _domain authority_ is used to refer to the entity that
assumes responsibility for the accuracy of the information provided
in the PIDF-LO.
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2. The Domain Authorization Element
This specification describes a new namespace for a domain
authorization element. This element contains the digital signature
described in RFC 3275 [RFC3275] and an expiry time for the signature.
The "domain-auth" element is added to the "tuple" element that
contains the "geopriv" element. Separate "tuple" elements are signed
separately. The XML Schema definition for the "domain-auth" element
is included in Section 4.1.
The digital signature signs the PIDF-LO document that includes only
the "tuple" element that the "domain-auth" element is included
within. Section 3.1 describes the specific means by which the
correct elements are selected.
2.1 'expires' attribute
The "expires" attribute defines the expiry time for the domain
authorization provided. A user of the PIDF-LO document MUST consider
the document to be unsigned beyond the expiry time.
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3. Signature Elements
The XML Signature specification [RFC3275] describes a means to sign
XML documents. The "Signature" element consists of three major
parts:
1. a description of the signed elements, which may be an entire
document, or selected parts of a document
2. a digital signature
3. information on the key used to sign the document
3.1 PIDF-LO Document Transform
Since the content of XML documents is indeterminate based on similar
data sets, RFC 3275 [RFC3275] describes a set of transforms that may
be applied to a document before applying a digital signature.
The input PIDF-LO document MUST be canonicalized using either
Canonical XML ("http://www.w3.org/TR/2001/REC-xml-c14n-20010315") or
Exclusive Canonical XML
("http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/") [W3C.REC-
xml-exc-c14n-20020718]. Note that both of these canonicalization
methods remove comments from the source document.
The signature form selected for this document is an enveloped
signature. Therefore the enveloped signature transform
("http://www.w3.org/2000/09/xmldsig#enveloped-signature") MUST be
applied to the document.
A filter is applied to the input document in order to select the
correct elements for signing. It is RECOMMENDED that the transformed
document is also a valid PIDF-LO. In addition, the transform should
exclude "tuple" elements other than the element that is directly
signed. This ensures that other content may be included in other
"tuple" elements, including other digital signatures.
The following elements MUST be selected:
o the "presence" element, which includes the "entity" attribute
o the "location-info" element and all of its contents
o the "timestamp" element associated with the signed "tuple" element
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o the "domain-auth" element
The minimum set of elements required to ensure that the signed
document is a valid PIDF-LO SHOULD also be included.
The XML Path Language (XPath) filter defined in Section 4.2 meets the
above criteria. For convenience, and to reduce the size of a signed
PIDF-LO document, this transform may be identified by the URN
"urn:ietf:params:xml:ns:pidf:geopriv10:domain-auth#PIDF-LO".
Note that any elements from other namespaces included within the
"domain-auth" element are selected by this XPath filter. This
ensures that additions to this element are covered by the digital
signature.
3.2 Algorithms
As recommended in RFC 3275 [RFC3275], implementations of this
specification MUST provide the following algorithms:
digest algorithm: The SHA1 digest, as identified by the URN
"http://www.w3.org/2000/09/xmldsig#sha1".
signature algorithm: DSA with SHA1, as identified by the URN
"http://www.w3.org/2000/09/xmldsig#dsa-sha1".
canonicalization method: Canonical XML [RFC3076], as identified by
the URN "http://www.w3.org/TR/2001/REC-xml-c14n-20010315".
transforms: The enveloped signature transform, as identified by the
URN "http://www.w3.org/2000/09/xmldsig#enveloped-signature"; and
the transform defined in Section 4.2, as identified by the URN
"urn:ietf:params:xml:ns:pidf:geopriv10:domain-auth#PIDF-LO".
It is also RECOMMENDED that the following are also supported:
signature algorithm: PKCS1 (RSA-SHA1) signature algorithm, as
idenfied by "http://www.w3.org/2000/09/xmldsig#rsa-sha1".
canonicalization method: Exclusive Canonical XML, as identified by
the URN "http://www.w3.org/TR/2002/REC-xml-exc-c14n-20020718/"
[W3C.REC-xml-exc-c14n-20020718].
3.3 Signature Key Data
RFC 3275 [RFC3275] describes a number of methods for describing the
key used to sign the document. For this specification, the "KeyInfo"
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element MUST be provided in the "Signature" element.
The domain authority MUST also describe a means to retrieve an X.509
certificate that includes the key used to sign the document. This
can be either by including an "X509Certificate" element, or by
referencing another certificate.
A reference to a certificate within the same document may be made
using the "X509SubjectName" element or a fragment identifier URI. A
fragment identifier URI might be applicable where multiple signatures
are applied to different parts of the document. External certificate
sources SHOULD be described by URI only in the "RetrievalMethod"
element. It is RECOMMENDED that the scheme for the RetrievalMethod
URI indicates a secure protocol, such as HTTPS.
The domain authority MAY include additional information in the
"KeyInfo" element that could assist the location user in validating
the certificate. For example a certificate chain and certificate
revocation list may be added. However, this specification does not
specify how the location user validates the certificate.
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4. XML Definitions
4.1 XML Schema
The following XML schema describes the "domain-auth" element. This
schema defines a new namespace:
"urn:ietf:params:xml:ns:pidf:geopriv10:domain-auth".
See RFCXXXX.
END 8. References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2778] Day, M., Rosenberg, J., and H. Sugano, "A Model for Presence and Instant Messaging", RFC 2778, February 2000. [RFC3076] Boyer, J., "Canonical XML Version 1.0", RFC 3076, March 2001. [RFC3275] Eastlake, D., Reagle, J., and D. Solo, "(Extensible Markup Language) XML-Signature Syntax and Processing", RFC 3275, March 2002. [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, January 2004. Thomson & Winterbottom Expires December 30, 2005 [Page 17] Internet-Draft Domain Auth. June 2005 [I-D.ietf-geopriv-pidf-lo] Peterson, J., "A Presence-based GEOPRIV Location Object Format", draft-ietf-geopriv-pidf-lo-03 (work in progress), September 2004. [W3C.REC-xml-exc-c14n-20020718] 3rd, D., Boyer, J., and J. Reagle, "Exclusive XML Canonicalization Version 1.0", W3C REC REC-xml-exc-c14n- 20020718, July 2002. Authors' Addresses Martin Thomson Nortel PO Box U87 University of Wollongong, NSW 2500 AU Phone: +61 2 4254 7515 Email: martin.thomson@nortel.com URI: http://www.nortel.com/ James Winterbottom Nortel PO Box U87 University of Wollongong, NSW 2500 AU Phone: +61 2 4223 3038 Email: winterb@nortel.com URI: http://www.nortel.com/ Thomson & Winterbottom Expires December 30, 2005 [Page 18] Internet-Draft Domain Auth. June 2005 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. The IETF has been notified of intellectual property rights claimed in regard to some or all of the specification contained in this document. For more information consult the online list of claimed rights. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Thomson & Winterbottom Expires December 30, 2005 [Page 19] Internet-Draft Domain Auth. June 2005 Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Thomson & Winterbottom Expires December 30, 2005 [Page 20]