rohan@ekabal.com

RAI ENUM WG ENUM iCal 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 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. 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 . COMMON Rohan 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 . COMMON Rohan 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 . COMMON Rohan 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 . COMMON Rohan Mahy (rohan@ekabal.com)

Below is a set of sample resource records for this enumservice.

$ORIGIN 3.2.1.0.5.5.5.2.1.2.1.e164.arpa. @ NAPTR 10 100 "u" "E2U+ical:access" "!^.*$!http://cal.example.com/home/alice/calendars/!" . $ORIGIN 3.2.1.0.5.5.5.2.1.2.1.e164.arpa. @ NAPTR 20 100 "u" "E2U+ical:sched:mail" "!^.*$!mailto:alice@example.com!" .

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.

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