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rfc:rfc4969

Network Working Group A. Mayrhofer Request for Comments: 4969 enum.at Category: Standards Track August 2007

              IANA Registration for vCard Enumservice

Status of This Memo

 This document specifies an Internet standards track protocol for the
 Internet community, and requests discussion and suggestions for
 improvements.  Please refer to the current edition of the "Internet
 Official Protocol Standards" (STD 1) for the standardization state
 and status of this protocol.  Distribution of this memo is unlimited.

Copyright Notice

 Copyright (C) The IETF Trust (2007).

Abstract

 This memo registers the Enumservice "vCard" using the URI schemes
 "http" and "https".  This Enumservice is to be used to refer from an
 ENUM domain name to a vCard instance describing the user of the
 respective E.164 number.
 Information gathered from those vCards could be used before, during,
 or after inbound or outbound communication takes place.  For example,
 a callee might be presented with the name and association of the
 caller before picking up the call.

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 3.  Enumservice Registration - vCard  . . . . . . . . . . . . . . . 2
 4.  Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
 5.  Security and Privacy Considerations . . . . . . . . . . . . . . 3
   5.1.  The ENUM Record Itself  . . . . . . . . . . . . . . . . . . 3
   5.2.  The Resource Identified . . . . . . . . . . . . . . . . . . 4
 6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
 7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
 8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
   8.2.  Informative References  . . . . . . . . . . . . . . . . . . 5

Mayrhofer Standards Track [Page 1] RFC 4969 vCard Enumservice August 2007

1. Introduction

 E.164 Number Mapping (ENUM) [1] uses the Domain Name System (DNS) [2]
 to refer from E.164 numbers [3] to Uniform Resource Identifiers
 (URIs) [6].  The registration process for Enumservices is described
 in Section 3 of RFC 3761.
 "vCard" [4] is a transport-independent data format for the exchange
 of information about an individual.  For the purpose of this
 document, the term "vCard" refers to a specific instance of this data
 format -- an "electronic business card". vCards are exchanged via
 several protocols; most commonly, they are distributed as electronic
 mail attachments or published on web servers.  Most popular personal
 information manager applications are capable of reading and writing
 vCards.
 The Enumservice specified in this document deals with the relation
 between an E.164 number and vCards.  An ENUM record using this
 Enumservice identifies a resource from where a vCard corresponding to
 the respective E.164 number could be fetched.
 Clients could use those resources to, e.g., automatically update
 local address books (a Voice over IP phone could try to fetch vCards
 for all outbound and inbound calls taking place on that phone and
 display them together with the call journal).  In a more integrated
 scenario, information gathered from those vCards could even be
 automatically incorporated into the personal information manager
 application of the respective user.

2. Terminology

 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 RFC 2119 [5].

3. Enumservice Registration - vCard

 Enumservice Name: "vCard"
 Enumservice Type: "vcard"
 Enumservice Subtype: n/a
 URI Schemes: "http", "https"

Mayrhofer Standards Track [Page 2] RFC 4969 vCard Enumservice August 2007

 Functional Specification:
    This Enumservice indicates that the resource identified is a plain
    vCard, according to RFC 2426, which may be accessed using HTTP/
    HTTPS [7].
    Clients fetching the vCard from the resource indicated should
    expect access to be restricted.  Additionally, the comprehension
    of the data provided may vary depending on the client's identity.
 Security Considerations: see Section 5
 Intended Usage: COMMON
 Author: Alexander Mayrhofer <alexander.mayrhofer@enum.at>

4. Example

 An example ENUM entry referencing to a vCard could look like:
    $ORIGIN 6.4.9.0.6.4.9.7.0.2.4.4.e164.arpa.
    @  IN NAPTR 100 10 "u" "E2U+vcard" \
    "!^.*$!http://example.net/vcard.vcf!" .

5. Security and Privacy Considerations

 As with any Enumservice, the security considerations of ENUM itself
 (Section 6 of RFC 3761) apply.

5.1. The ENUM Record Itself

 Since ENUM uses DNS -- a publicly available database -- any
 information contained in records provisioned in ENUM domains must be
 considered public as well.  Even after revoking the DNS entry and
 removing the referred resource, copies of the information could still
 be available.
 Information published in ENUM records could reveal associations
 between E.164 numbers and their owners - especially if URIs contain
 personal identifiers or domain names for which ownership information
 can be obtained easily.  For example, the following URI makes it easy
 to guess the owner of an E.164 number, as well as his location and
 association, by just examining the result from the ENUM lookup:
    http://sandiego.company.example.com/joe-william-user.vcf

Mayrhofer Standards Track [Page 3] RFC 4969 vCard Enumservice August 2007

 However, it is important to note that the ENUM record itself does not
 need to contain any personal information.  It just points to a
 location where access to personal information could be granted.  For
 example, the following URI only reveals the service provider hosting
 the vCard (who probably even provides anonymous hosting):
    http://anonhoster.example.org/file_adfa001.vcf
 ENUM records pointing to third-party resources can easily be
 provisioned on purpose by the ENUM domain owner - so any assumption
 about the association between a number and an entity could therefore
 be completely bogus unless some kind of identity verification is in
 place.  This verification is out of scope for this memo.

5.2. The Resource Identified

 In most cases, vCards provide information about individuals.  Linking
 telephone numbers to such Personally Identifiable Information (PII)
 is a very sensitive topic, because it provides a "reverse lookup"
 from the number to its owner.  Publication of such PII is covered by
 data-protection law in many legislations.  In most cases, the
 explicit consent of the affected individual is required.
 Users MUST therefore carefully consider information they provide in
 the resource identified by the ENUM record as well as in the record
 itself.  Considerations SHOULD include serving information only to
 entities of the user's choice and/or limiting the comprehension of
 the information provided based on the identity of the requestor.
 The use of HTTP in this Enumservice allows using built-in
 authentication, authorization, and session control mechanisms to be
 used to maintain access controls on vCards.  Most notable, Digest
 Authentication [8] could be used to challenge requestors, and even
 synthesize vCards based on the client's identity (or refuse access
 entirely).  This could especially be useful in private ENUM
 deployments (like within enterprises), where clients would more
 likely have a valid credential to access the indicated resource.
 Even public deployments could synthesize vCards based on the identity
 of the client.  Social network sites, for example, could (based on
 HTTP session data like cookies [9]) provide more comprehensive vCards
 to their members than to anonymous clients.
 If access restrictions on the vCard resource are deployed, standard
 HTTP authentication, authorization, and state management mechanisms
 (as described in RFCs 2617 and 2695) MUST be used to enforce those
 restrictions.  HTTPS SHOULD be preferred if the deployed mechanisms
 are prone to eavesdropping and replay attacks.

Mayrhofer Standards Track [Page 4] RFC 4969 vCard Enumservice August 2007

 ENUM deployments using this Enumservice together with DNS Security
 Extensions (DNSSEC) [10] should consider using Minimally Covering
 NSEC Records [11] to prevent zone walking, as the PII data contained
 in vCards constitutes a rich target for such attempts.

6. IANA Considerations

 This memo requests registration of the "vCard" Enumservice according
 to the template in Section 3 of this document and the definitions in
 RFC 3761 [1].

7. Acknowledgements

 The author wishes to thank David Lindner for his contributions during
 the early stages of this document.  In addition, Klaus Nieminen, Jon
 Peterson, Ondrej Sury, and Ted Hardie provided very helpful
 suggestions.

8. References

8.1. Normative References

 [1]   Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
       Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
       Application (ENUM)", RFC 3761, April 2004.
 [2]   Mockapetris, P., "Domain names - implementation and
       specification", STD 13, RFC 1035, November 1987.
 [3]   ITU-T, "The international public telecommunication numbering
       plan", Recommendation E.164 (02/05), Feb 2005.
 [4]   Dawson, F. and T. Howes, "vCard MIME Directory Profile",
       RFC 2426, September 1998.
 [5]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.

8.2. Informative References

 [6]   Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
       Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
       January 2005.
 [7]   Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
       Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
       HTTP/1.1", RFC 2616, June 1999.

Mayrhofer Standards Track [Page 5] RFC 4969 vCard Enumservice August 2007

 [8]   Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
       Leach, P., Luotonen, A., and L. Stewart, "HTTP Authentication:
       Basic and Digest Access Authentication", RFC 2617, June 1999.
 [9]   Kristol, D. and L. Montulli, "HTTP State Management Mechanism",
       RFC 2965, October 2000.
 [10]  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
       "DNS Security Introduction and Requirements", RFC 4033,
       March 2005.
 [11]  Weiler, S. and J. Ihren, "Minimally Covering NSEC Records and
       DNSSEC On-line Signing", RFC 4470, April 2006.

Author's Address

 Alexander Mayrhofer
 enum.at GmbH
 Karlsplatz 1/2/9
 Wien  A-1010
 Austria
 Phone: +43 1 5056416 34
 EMail: alexander.mayrhofer@enum.at
 URI:   http://www.enum.at/

Mayrhofer Standards Track [Page 6] RFC 4969 vCard Enumservice August 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 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.
 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, THE IETF TRUST 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.

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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Mayrhofer Standards Track [Page 7]

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