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



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  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, RFC 3761 [1]) is a system that uses DNS
  (Domain Name System, RFC 1034 [2]) to translate telephone numbers,
  such as '+12025550100', into URIs (Uniform Resource Identifiers, RFC
  3986 [3]), such as 'mailto:[email protected]'.  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 RFC 3986 [3]) is
  already used to address iMIP compatible Calendar Services.  Likewise,
  the existing 'http:' and 'https:' URI schemes (defined in RFC 2616
  [11] and RFC 2818 [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.












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2.  Enumservice Registrations

  As defined in RFC 3761 [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 ([email protected])

  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 ([email protected])







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  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 ([email protected])

  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 RFC 3761 [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 RFC 3761 [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:[email protected]!" .

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.



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  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 [1], and a
  thorough analysis of threats to the DNS itself is covered in RFC 3833
  [14].  Many of these problems are prevented when the resolver
  verifies the authenticity of answers to its ENUM queries via DNSSEC
  (DNS Security, RFC 4035 [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 RFC 2446 [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, RFC 5246 [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 RFC 3761 [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)", RFC 3761, April 2004.

  [2]   Mockapetris, P., "Domain names - concepts and facilities",
        STD 13, RFC 1034, November 1987.



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  [3]   Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
        Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986,
        January 2005.

  [4]   Dawson, F. and Stenerson, D., "Internet Calendaring and
        Scheduling Core Object Specification (iCalendar)", RFC 2445,
        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", RFC 2446, November 1998.

  [6]   Dawson, F., Mansour, S., and S. Silverberg, "iCalendar
        Message-Based Interoperability Protocol (iMIP)", RFC 2447,
        November 1998.

  [7]   Daboo, C., Desruisseaux, B., and L. Dusseault, "Calendaring
        Extensions to WebDAV (CalDAV)", RFC 4791, March 2007.

  [8]   Dusseault, L., "HTTP Extensions for Web Distributed Authoring
        and Versioning (WebDAV)", RFC 4918, June 2007.

  [9]   Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose,
        "Protocol Modifications for the DNS Security Extensions",
        RFC 4035, March 2005.

6.2.  Informative References

  [10]  Mahoney, B., Babics, G., and A. Taler, "Guide to Internet
        Calendaring", RFC 3283, 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", RFC 2616, June 1999.

  [12]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

  [13]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
        Protocol Version 1.2", RFC 5246, August 2008.

  [14]  Atkins, D. and R. Austein, "Threat Analysis of the Domain Name
        System (DNS)", RFC 3833, August 2004.

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





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  [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.












































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Appendix A.  Acknowledgments

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

Authors' Addresses

  Rohan Mahy
  Unaffiliated

  EMail: [email protected]


  Bernie Hoeneisen
  Swisscom
  CH-8000 Zuerich
  Switzerland

  EMail: [email protected] ([email protected])
  URI:   http://www.swisscom.com/































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