E.164 Number Mapping (ENUM)  uses the Domain Name System (DNS) 
to refer from E.164 numbers  to Uniform Resource Identifiers
(URIs) . The registration process for Enumservices is described
in Section 3 of RFC 3761.
"vCard"  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.
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 .
3. Enumservice Registration - vCard
Enumservice Name: "vCard"
Enumservice Type: "vcard"
Enumservice Subtype: n/a
URI Schemes: "http", "https"
This Enumservice indicates that the resource identified is a plain
vCard, according to RFC 2426, which may be accessed using HTTP/
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 <firstname.lastname@example.org>
An example ENUM entry referencing to a vCard could look like:
@ IN NAPTR 100 10 "u" "E2U+vcard" \
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
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:
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  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 ) 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.
ENUM deployments using this Enumservice together with DNS Security
Extensions (DNSSEC)  should consider using Minimally Covering
NSEC Records  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 .
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
8.1. Normative References
 Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
Application (ENUM)", RFC 3761, April 2004.
 Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
 ITU-T, "The international public telecommunication numbering
plan", Recommendation E.164 (02/05), Feb 2005.
 Dawson, F. and T. Howes, "vCard MIME Directory Profile",
RFC 2426, September 1998.
 Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
 Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
 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.
 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.
 Kristol, D. and L. Montulli, "HTTP State Management Mechanism",
RFC 2965, October 2000.
 Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
"DNS Security Introduction and Requirements", RFC 4033,
 Weiler, S. and J. Ihren, "Minimally Covering NSEC Records and
DNSSEC On-line Signing", RFC 4470, April 2006.
Phone: +43 1 5056416 34
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