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Versions: 00 01                                                         
Internet Engineering Task Force                     J. Stracke
INTERNET DRAFT                                            eCal
draft-stracke-calsch-crisp-00.txt                  August 2000
                                        Expires: February 2001

           CAP Realtime iTIP-based Scheduling Profile (CRISP)

1.  Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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 docu-
   ments 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

   The list of Internet-Draft Shadow Directories can be accessed at

   Distribution of this document is unlimited. Please send comments to
   francis@ecal.com or to the ietf-calendar@imc.org discussion list
   (subscription address ietf-calendar-request@imc.org; "SUBSCRIBE" or
   "UNSUBSCRIBE" in the body).

2.  Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

3.  Abstract

   This document sets forth a restricted profile of [CAP], one which
   supports no operations beyond the scheduling functionality of [iTIP].
   The motivation is to permit use of CAP's real-time iTIP functionality
   without exposing the calendar access functionality (which may require
   stricter security controls than iTIP).

Stracke                                                         [Page 1]

CRISP                                                           May 2000

4.  Introduction

   [iTIP] defines a scheduling protocol based on exchanging specially
   formatted [iCalendar] messages.  iTIP is defined to be independent of
   transport protocol.  At present, there is one standard binding of
   iTIP to a transport protocol, [iMIP], which carries iTIP messages in
   email.  This is a useful base level capability (email can reach vir-
   tually any user on the Net), but can involve considerable latencies.
   A real-time binding for iTIP would be useful; it would permit appli-
   cation developers to give users better feedback on the progress of
   the iTIP operations.

   Since CAP includes full iTIP functionality, one option would be to
   permit full access to CAP; to schedule an event with a remote user,
   one would then make a CAP connection to their CS.  The problem is
   that such a connection may be considered a security risk in some
   organizations; even though the CS has ACLs to prevent the client from
   performing non-iTIP operations, it would be better if client simply
   could not attempt such operations.  (It's as if mail administrators
   were told that an SMTP server outside the firewall had to include
   IMAP functionality as well.)  Thus, this document defines a profile
   of CAP, a subset which does not support non-iTIP operations.

5.  Profile Definition

   A CRISP server is a CAP server with the following capabilities:

      * ITIPVERSION=1.0
      * CAPVERSION=1.0
      * CAR=NONE

   In addition, various AUTH capabilities are expected.  Other capabili-
   ties which apply to iTIP operations may be specified; e.g., MAXDATE

   Note that NONE is not a legal value for CAR or QUERYLEVEL in the cur-
   rent draft of CAP.  This will have to be resolved.

   A CRISP server MUST NOT accept any iCalendar component which is not a
   valid iTIP component.

6.  Firewall Application

   Clearly, it would be undesirable for an organization with a CAP
   server to have a CRISP server implemented completely separately, but

Stracke                                                         [Page 2]

CRISP                                                           May 2000

   having access to the same database.  Such duplication would increase
   development costs, maintenance costs, and security exposure.  On the
   other hand, it would be possible to build a CRISP server which han-
   dles all operations by proxying them to the CAP server.  Such a proxy
   could be placed in the "no-man's-land" common in firewalls; the fire-
   wall would permit CAP connections from the outside to the proxy, and
   from the proxy to the internal CAP server.  The proxy would review
   all incoming iCalendar components and validate that they were legiti-
   mate iTIP operations; no non-iTIP components would be forwarded to
   the CAP server.  Similarly, if necessary, the proxy might censor the
   iTIP replies coming from the CAP server.

7.  Security Considerations

   The protocol defined in this document is a subset of [CAP], and
   accordingly inherits all of CAP's security analysis.  However, new
   analysis does need to be done for the subset, especially since the
   whole point of the subset is to address security concerns.

8.  Author's Address:

   John Stracke
   Chief Scientist
   eCal Corp.
   Email: francis@ecal.com

9.  References

   [iTIP] Silverberg, Mansour, Dawson, Hopson, "iCalendar Transport-
   Independent Interoperability Protocol (iTIP)", RFC 2446, November

   [iMIP] Dawson, Mansour, Silverberg, "iCalendar Message-Based Interop-
   erability Protocol (iMIP)", RFC 2445, November 1998

   [CAP] Mansour, Dawson, Royer, Taler, Hill, "Calendar Access Protocol
   (CAP)", draft-ietf-calsch-cap-03.txt, July 2000.  Work in progress.

   [iCAL] Dawson, Stenerson, "Internet Calendaring and Scheduling Core
   Object Specification (iCalendar)", RFC 2445, November 1998

Stracke                                                         [Page 3]