A Telephone Number Mapping (ENUM) Service
Registration for Internet Calendaring Servicesrohan@ekabal.com
RAI
ENUM WGENUMiCalThis document may contain material from IETF Documents or IETF
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created outside the IETF Standards Process, except to format it for
publication as an RFC or to translate it into languages other than
English. This document registers a Telephone Number Mapping (ENUM) service for
Internet calendaring services. Specifically, this document focuses on
provisioning 'mailto:' (iMIP) and 'http:' (CalDAV) URIs in ENUM.ENUM (E.164 Number Mapping, RFC 3761)
is a system that uses DNS (Domain Name Service, RFC 1034) to translate telephone numbers, such
as '+12025550100', into URIs (Uniform Resource Identifiers, RFC 3986), such as 'mailto:user@example.com'. ENUM
exists primarily to facilitate the interconnection of systems that rely
on telephone numbers with those that use URIs to identify resources. The ENUM registration here could be used to allow phones, for example, to check the free/busy status of a user in their address book or propose a meeting with him or her from the user's phone number.The Guide to Internet Calendaring describes
the relationship between various Internet calendaring specifications
like this:
"iCalendar is the language used to describe calendar
objects. iTIP [Transport-Independent Interoperability
Protocol] describes a way to use the iCalendar
language to do scheduling. iMIP [Message-Based
Interoperability Protocol] describes how to do iTIP scheduling via e-mail".
Recently, another Standards Track protocol for calendar and
scheduling access has appeared. CalDAV
(Calendaring Extensions to WebDAV) is
a WebDAV (Web-based Distributed
Authoring and Versioning) based mechanism for
manipulating internet calendars, viewing free/busy lists, and
via a
planned scheduling
extension, could be used for proposing calendar events
as well.
The existing 'mailto:' URI scheme (defined in
RFC 3986) is already used to
address iMIP compatible Calendar Services. Likewise, the
existing 'http:' and 'https:' URI schemes (defined in
RFC 2616 and
RFC 2818) are already
used to address CalDAV compatible Calendar Services.
This document registers an
enumservice for advertising Internet calendaring information associated
with an E.164 number, using the 'mailto:', 'http:', or 'https:' schemes.As defined in RFC 3761, the following
is a template covering information needed for the registration of the
enumservice specified in this document:"ical""ical"sched:mail"mailto:"
This Enumservice indicates that the resource identified is a
URI used for scheduling using Internet calendaring via Internet
mail. The supported URI scheme are the 'mailto:' URI for the iMIP protocol.See .COMMONRohan Mahy (rohan@ekabal.com)"ical""ical"sched:web"http:", "https:" This Enumservice
indicates that the resource identified is a URI used for scheduling
using Internet calendaring using CalDAV. Supported URI schemes are
the 'http:' or 'https:' URIs for a
planned scheduling
extension to the CalDAV
protocol.See .COMMONRohan Mahy (rohan@ekabal.com)"ical""ical"sched"mailto:", "http:", "https:"
This Enumservice indicates that the resource identified is a
URI used for scheduling using Internet calendaring. Supported URI schemes are the 'mailto:' URI for the iMIP protocol, and 'http:' or 'https:' URIs for a planned scheduling extension to the CalDAV protocol.See .COMMONRohan Mahy (rohan@ekabal.com)"ical""ical"access"http:", "https:"
This Enumservice indicates that the resource identified is a
URI used for Internet calendaring, which is available to access a user's calendar (for example free/busy status).
Supported URI schemes are 'http:' or 'https:' URIs for the
CalDAV protocol.See .COMMONRohan Mahy (rohan@ekabal.com)Below is a set of sample resource records for this enumservice.Note that an ENUM lookup for "E2U+ical:sched" at this phone number
would return the second record (one match), while a query for "E2U+ical"
would return the first record (of the two matching records, the one with
the lowest order).
The Domain Name System (DNS) does not make policy decisions about
which records it provides to a DNS resolver.
All DNS records must be assumed to be available to all
inquirers at all times. The information provided within an ENUM
record set must therefore be considered open to the public -- which
is a cause for some privacy considerations.
Revealing a calendaring URI by itself is unlikely to introduce many
privacy concerns, although, depending on the structure of the URI, it
might reveal the full name or employer of the target. The use of
anonymous URIs mitigates this risk.
As ENUM uses DNS, which in its current form is an insecure protocol, there is no mechanism for ensuring that the answer returned to a query is authentic. An analysis of threats specific to the dependence of ENUM on the DNS is provided in RFC 3761, and a thorough analysis of threats to the DNS itself is covered in RFC 3833. Many of these problems are prevented when the resolver verifies the authenticity of answers to its ENUM queries via DNSSEC (DNS Security) in zones where it is available.
More serious security concerns are associated with potential attacks against
an underlying calendaring system (for example, unauthorized modification or viewing).
For this reason, iTIP discusses a number of
security requirements (detailed in RFC 2446)
that call for authentication, integrity and confidentiality properties,
and similar measures to prevent such attacks. Any
calendaring protocol used in conjunction with a URI scheme currently meets
these requirements. The use of CalDAV with the 'https:' scheme makes use of
TLS (Transport Layer Security) to provide server authentication, confidentiality, and message integrity.
Unlike a traditional telephone number, the resource identified by an
calendaring URI is often already guessable, and it often requires that
users provide cryptographic credentials
for authentication and authorization before calendar data can be
exchanged. Despite the public availability of ENUM records, the
use of this information to reveal an unprotected calendaring resource
is unlikely in practice.
This document requests registration of the "iCal" Enumservice according
to the definitions in of this document and RFC
3761.CalDAV Scheduling Extensions to WebDAVThanks to Lisa Dusseault and Alexander Mayrhofer for reviewing this document.