    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

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    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"

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       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

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       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.

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    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.

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    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/

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    RFC 4969                   vCard Enumservice                 August 2007

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       Copyright (C) The IETF Trust (2007).

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