Skip to content

RFC 5333: IANA Registration of Enumservices for Internet Calendaring

  • R. Mahy,  
  • B. Hoeneisen
Proposed Standard
This RFC was updated, see 
Network Working Group                                            R. Mahy
Request for Comments: 5333                                  Unaffiliated
Category: Standards Track                                   B. Hoeneisen
                                                                Swisscom
                                                            October 2009


       IANA Registration of Enumservices for Internet Calendaring

Abstract

   This document registers Enumservices for Internet calendaring.
   Specifically, this document focuses on Enumservices for scheduling
   with iMIP (iCalendar Message-Based Interoperability Protocol) and for
   accessing Internet calendaring information with CalDAV (Calendaring
   Extensions to WebDAV).

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 and License Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
   modifications of such material outside the IETF Standards Process.
   Without obtaining an adequate license from the person(s) controlling
   the copyright in such materials, this document may not be modified
   outside the IETF Standards Process, and derivative works of it may



Mahy & Hoeneisen            Standards Track                     [Page 1]

           Internet Calendaring Enumservices        October 2009


   not be created outside the IETF Standards Process, except to format
   it for publication as an RFC or to translate it into languages other
   than English.

1.  Introduction

   ENUM (E.164 Number Mapping,  [1]) is a system that uses DNS
   (Domain Name System,  [2]) to translate telephone numbers,
   such as '+12025550100', into URIs (Uniform Resource Identifiers, 
    [3]), 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 [10] describes the relationship
   between various Internet calendaring specifications like this:
   "iCalendar [4] is the language used to describe calendar objects.
   iTIP [5] [iCalendar Transport-Independent Interoperability Protocol]
   describes a way to use the iCalendar language to do scheduling.  iMIP
   [6] [iCalendar 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) [7] is a WebDAV (Web-based Distributed Authoring and
   Versioning) [8] based mechanism for manipulating Internet calendars,
   viewing free/busy lists, and via a planned scheduling extension [15],
   could be used for proposing calendar events as well in the future.

   The existing 'mailto:' URI scheme (defined in  [3]) is
   already used to address iMIP compatible Calendar Services.  Likewise,
   the existing 'http:' and 'https:' URI schemes (defined in 
   [11] and  [12]) are already used to address CalDAV compatible
   Calendar Services.

   This document registers Enumservices for scheduling and accessing
   Internet calendaring information associated with an E.164 number.












Mahy & Hoeneisen            Standards Track                     [Page 2]

           Internet Calendaring Enumservices        October 2009


2.  Enumservice Registrations

   As defined in  [1], the following templates cover the
   information needed for the registration of the Enumservices specified
   in this document:

   Enumservice Name:
      "ical-sched"
   Enumservice Type:
      "ical-sched"
   Enumservice Subtypes:
      "mailto"
   URI scheme(s):
      'mailto:'
   Functional Specification:
      This Enumservice indicates that the resource identified can be
      addressed by the associated URI used for scheduling using Internet
      calendaring via Internet mail with the iMIP [6] protocol.
   Security considerations:
      See Section 4.
   Intended usage:
      COMMON
   Author:
      Rohan Mahy (rohan@ekabal.com)

   Enumservice Name:
      "ical-access"
   Enumservice Type:
      "ical-access"
   Enumservice Subtypes:
      "http"
   URI scheme(s):
      'http:'
   Functional Specification:
      This Enumservice indicates that the resource identified can be
      addressed by the associated URI in order to access a user's
      calendar (for example free/busy status) using the CalDAV [7]
      protocol for Internet calendaring.
   Security considerations:
      See Section 4.
   Intended usage:
      COMMON
   Author:
      Rohan Mahy (rohan@ekabal.com)







Mahy & Hoeneisen            Standards Track                     [Page 3]

           Internet Calendaring Enumservices        October 2009


   Enumservice Name:
      "ical-access"
   Enumservice Type:
      "ical-access"
   Enumservice Subtypes:
      "https"
   URI scheme(s):
      'https:'
   Functional Specification:
      This Enumservice indicates that the resource identified can be
      addressed by the associated URI in order to access a user's
      calendar (for example free/busy status) using the CalDAV [7]
      protocol for Internet calendaring.
   Security considerations:
      See Section 4.
   Intended usage:
      COMMON
   Author:
      Rohan Mahy (rohan@ekabal.com)

   Note: These Enumservices use a dash "-" in the Type strings.  To
   allow for hierarchical concepts (as required in this case), some kind
   of boundary needs to be in place.  Neither  [1] nor its
   intended successor [17] foresee the concept of sub-subtyping.  The
   natural solution to address this requirement is the usage of dash "-"
   in Type strings, which is slightly contradictory to  [1].
   However, its intended successors [16] [17] clearly allow a dash "-"
   in Type strings, so that using "-" is seen as a practical way
   forward.

3.  Examples

   $ORIGIN 3.2.1.0.5.5.5.2.1.2.1.e164.arpa.
   @ NAPTR 10 100 "u" "E2U+ical-access:https" \
      "!^.*$!https://cal.example.com/home/alice/calendars/!" .

   $ORIGIN 3.2.1.0.5.5.5.2.1.2.1.e164.arpa.
   @ NAPTR 20 100 "u" "E2U+ical-sched:mailto" \
      "!^.*$!mailto:alice@example.com!" .

4.  Security Considerations

   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.



Mahy & Hoeneisen            Standards Track                     [Page 4]

           Internet Calendaring Enumservices        October 2009


   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  [1], and a
   thorough analysis of threats to the DNS itself is covered in 
   [14].  Many of these problems are prevented when the resolver
   verifies the authenticity of answers to its ENUM queries via DNSSEC
   (DNS Security,  [9]) 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  [5]) 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,  [13]) 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.

5.  IANA Considerations

   This document requests registration of the "ical-sched" and "ical-
   access" Enumservices according to the definitions in Section 2 of
   this document and  [1].

6.  References

6.1.  Normative References

   [1]   Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource
         Identifiers (URI) Dynamic Delegation Discovery System (DDDS)
         Application (ENUM)", , April 2004.

   [2]   Mockapetris, P., "Domain names - concepts and facilities",
         STD 13, , November 1987.



Mahy & Hoeneisen            Standards Track                     [Page 5]

           Internet Calendaring Enumservices        October 2009


   [3]   Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
         Resource Identifier (URI): Generic Syntax", STD 66, ,
         January 2005.

   [4]   Dawson, F. and Stenerson, D., "Internet Calendaring and
         Scheduling Core Object Specification (iCalendar)", ,
         November 1998.

   [5]   Silverberg, S., Mansour, S., Dawson, F., and R. Hopson,
         "iCalendar Transport-Independent Interoperability Protocol
         (iTIP) Scheduling Events, BusyTime, To-dos and Journal
         Entries", , November 1998.

   [6]   Dawson, F., Mansour, S., and S. Silverberg, "iCalendar
         Message-Based Interoperability Protocol (iMIP)", ,
         November 1998.

   [7]   Daboo, C., Desruisseaux, B., and L. Dusseault, "Calendaring
         Extensions to WebDAV (CalDAV)", , March 2007.

   [8]   Dusseault, L., "HTTP Extensions for Web Distributed Authoring
         and Versioning (WebDAV)", , June 2007.

   [9]   Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
         "Protocol Modifications for the DNS Security Extensions",
         , March 2005.

6.2.  Informative References

   [10]  Mahoney, B., Babics, G., and A. Taler, "Guide to Internet
         Calendaring", , June 2002.

   [11]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
         Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
         HTTP/1.1", , June 1999.

   [12]  Rescorla, E., "HTTP Over TLS", , May 2000.

   [13]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
         Protocol Version 1.2", , August 2008.

   [14]  Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
         System (DNS)", , August 2004.

   [15]  Daboo, C. and B. Desruisseaux, "CalDAV Scheduling Extensions to
         WebDAV", Work in Progress, August 2009.





Mahy & Hoeneisen            Standards Track                     [Page 6]

           Internet Calendaring Enumservices        October 2009


   [16]  Bradner, S., Conroy, L., and K. Fujiwara, "The E.164 to Uniform
         Resource Identifiers (URI) Dynamic Delegation Discovery System
         (DDDS) Application (ENUM)", Work in Progress, May 2009.

   [17]  Hoeneisen, B., Mayrhofer, A., and J. Livingood, "IANA
         Registration of Enumservices: Guide, Template and IANA
         Considerations", Work in Progress, September 2009.












































Mahy & Hoeneisen            Standards Track                     [Page 7]

           Internet Calendaring Enumservices        October 2009


Appendix A.  Acknowledgments

   Thanks to Lisa Dusseault and Alexander Mayrhofer for reviewing this
   document.

Authors' Addresses

   Rohan Mahy
   Unaffiliated

   EMail: rohan@ekabal.com


   Bernie Hoeneisen
   Swisscom
   CH-8000 Zuerich
   Switzerland

   EMail: bernie@ietf.hoeneisen.ch (bernhard.hoeneisen@swisscom.com)
   URI:   http://www.swisscom.com/































Mahy & Hoeneisen            Standards Track                     [Page 8]

RFC 5333: IANA Registration of Enumservices for Internet Calendaring

Proposed Standard