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Network Working Group                                            R. MahyRequest for Comments: 5333                                  UnaffiliatedCategory: Standards Track                                   B. Hoeneisen                                                                Swisscom                                                            October 2009IANA Registration of Enumservices for Internet CalendaringAbstract   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 toBCP 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 mayMahy & Hoeneisen            Standards Track                     [Page 1]

RFC 5333           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,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,RFC3986 [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 inRFC 3986 [3]) is   already used to address iMIP compatible Calendar Services.  Likewise,   the existing 'http:' and 'https:' URI schemes (defined inRFC 2616   [11] andRFC 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.Mahy & Hoeneisen            Standards Track                     [Page 2]

RFC 5333           Internet Calendaring Enumservices        October 20092.  Enumservice Registrations   As defined inRFC 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:      SeeSection 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:      SeeSection 4.   Intended usage:      COMMON   Author:      Rohan Mahy (rohan@ekabal.com)Mahy & Hoeneisen            Standards Track                     [Page 3]

RFC 5333           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:      SeeSection 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.  NeitherRFC 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 toRFC 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: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]

RFC 5333           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 inRFC 3761 [1], and a   thorough analysis of threats to the DNS itself is covered inRFC 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 inRFC 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 inSection 2 of   this document andRFC 3761 [1].6.  References6.1.  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.Mahy & Hoeneisen            Standards Track                     [Page 5]

RFC 5333           Internet Calendaring Enumservices        October 2009   [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.Mahy & Hoeneisen            Standards Track                     [Page 6]

RFC 5333           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]

RFC 5333           Internet Calendaring Enumservices        October 2009Appendix 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]