RFC4969: IANA Registration for vCard Enumservice

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Related keywords:  (E.164) (enum)

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).


   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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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

   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",
   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:

      @  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:


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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):


   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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   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

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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   [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

   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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