ENUM WG R. Mahy Internet-Draft Plantronics Intended status: Standards Track March 10, 2008 Expires: September 11, 2008 A Telephone Number Mapping (ENUM) Service Registration for Internet Calendaring Services draft-ietf-enum-calendar-service-04.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 11, 2008. Copyright Notice Copyright (C) The IETF Trust (2008). Abstract 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. Mahy Expires September 11, 2008 [Page 1] Internet-Draft IM Enumservice March 2008 1. Introduction ENUM (E.164 Number Mapping, RFC 3761 [1]) is a system that uses DNS (Domain Name Service, RFC 1034 [2]) to translate telephone numbers, such as '+12025550100', into URIs (Uniform Resource Identifiers, RFC 3986 [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] [Transport-Independent Interoperability Protocol] describes a way to use the iCalendar language to do scheduling. iMIP [6] [Message-Based Interoperability Protocol] describes how to do iTIP scheduling via e-mail." Recently another standard track protocol for calendar and scheduling access has appeared. CalDAV [7] (Calendaring Extensions to WebDAV) is a WebDAV [8] (Web-based Distributed Authoring and Versioning) 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. 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 an enumservice for advertising internet calendaring information associated with an E.164 number, using the 'mailto:', 'http:', or 'https:' schemes. 2. ENUM Service Registration - ical As defined in RFC 3761 [1], the following is a template covering information needed for the registration of the enumservice specified in this document: Enumservice Name: Mahy Expires September 11, 2008 [Page 2] Internet-Draft IM Enumservice March 2008 "ical" Enumservice Type: "ical" Enumservice Subtypes: sched URI scheme(s): "mailto:", "http:", "https:" Functional Specification: 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 [6] protocol, and 'http:' or 'https:' URIs for a planned scheduling extension [15] to the CalDAV [7] protocol. Security considerations: See section 3. Intended usage: COMMON Author: Rohan Mahy (rohan@ekabal.com) Enumservice Name: "ical" Enumservice Type: "ical" Enumservice Subtypes: access URI scheme(s): "http:", "https:" Functional Specification: 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 [7] protocol. Security considerations: See section 3. Intended usage: COMMON Author: Rohan Mahy (rohan@ekabal.com) 3. Example of Usage Below is a set of sample resource records for this enumservice. Mahy Expires September 11, 2008 [Page 3] Internet-Draft IM Enumservice March 2008 $ORIGIN 3.2.1.0.5.5.5.2.1.2.1.e164.arpa. @ NAPTR 10 100 "u" "E2U+ical:access" "!^.*$!http://cal.example.com/home/alice/calendars/!" . $ORIGIN 3.2.1.0.5.5.5.2.1.2.1.e164.arpa. @ NAPTR 10 100 "u" "E2U+ical:sched" "!^.*$!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. 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 [14]. Many of these problems are prevented when the resolver verifies the authenticity of answers to its ENUM queries via DNSSEC [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 [13] (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 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 Mahy Expires September 11, 2008 [Page 4] Internet-Draft IM Enumservice March 2008 reveal an unprotected calendaring resource is unlikely in practice. 5. IANA Considerations This document requests registration of the "iCal" Enumservice 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. [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. Mahy Expires September 11, 2008 [Page 5] Internet-Draft IM Enumservice March 2008 6.2. Informational 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 1.1", RFC 4346, April 2006. [14] Atkins, D. and R. Austein, "Threat Analysis of the Domain Name System (DNS)", RFC 3833, August 2004. [15] Daboo, C., Desruisseaux, B., and L. Dusseault, "CalDAV Scheduling Extensions to WebDAV", draft-desruisseaux-caldav-sched-04 (work in progress), November 2007. Appendix A. Acknowlegments Thanks to Lisa Dusseault and Alexander Mayrhofer for reviewing this document. Author's Address Rohan Mahy Plantronics Email: rohan@ekabal.com Mahy Expires September 11, 2008 [Page 6] Internet-Draft IM Enumservice March 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 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