Internet Engineering Task Force SIMPLE WG
Internet Draft J. Rosenberg
dynamicsoft
M. Isomaki
Nokia
draft-ietf-simple-data-req-00.txt
October 9, 2002
Expires: April 2003
Requirements for Manipulation of Data Elements in SIMPLE Systems
STATUS OF THIS MEMO
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Abstract
In an instant messaging and presence application, it is frequently
necessary for the user to configure a number of pieces of
information. Users will need to manipulate their presentity list,
adding and removing presentities, and manipulate their authorization
lists, which specify the set of users that can subscribe to their
presence. In this document, we provide a framework and requirements
for such data manipulations.
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Table of Contents
1 Introduction ........................................ 3
2 Terminology ......................................... 3
3 Framework ........................................... 4
4 Presentity Collection Manipulation Requirements ..... 7
5 Authorization Policy Manipulation ................... 9
5.1 Acceptance Policy Requirements ...................... 9
5.2 Notification Requirements ........................... 11
5.3 Content Requirements ................................ 12
5.4 General Requirements ................................ 12
6 Possible Solutions .................................. 13
7 Security Considerations ............................. 13
8 Acknowledgements .................................... 14
9 Authors Addresses ................................... 14
10 Normative References ................................ 15
11 Informative References .............................. 15
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1 Introduction
Consumer-based instant messaging and presence applications typically
provide a rich set of features. In addition to being able to
subscribe to, and get notified of, changes in presence, users can
also configure the operation of the application.
Most systems allow the user to add or remove users from their "buddy
list", which we refer to here as a presentity collection. The
presentity collection is the set of presentities [1] that a user is
subscribed to. This list is frequently stored on the server, allowing
the user to generate a single subscription to the entire list. The
server then "fans out" that subscription too all the presentities on
the list. Subscription to presentity collections is supported through
the presence collection event package defined for SIMPLE [2].
However, no automated means is currently defined to create these
lists, add users to them, remove users from them, or query for the
set of users on the list.
Similarly, most systems support user-defined authorization policies.
A user can specify which watchers are (or are not) allowed to
subscribe to their presence, and furthermore, what aspects of their
presence a watcher is able to see. While SIMPLE [3] systems can
support such authorization policies, besides human-driven techniques,
such as web or voice response, there is no automated way to specify
these policies.
In this document, we propose a framework and a set of requirements
for manipulation of presentity collections and authorization
policies.
2 Terminology
This document uses the following terminology:
Presentity Collection: A presentity collection is a set of
presentities, each of which is identified by a URI. The
collection itself is identified by a URI (for example,
sip:myfriends@example.com). Using the presence list package
[2], a watcher can subscribe to the presentity collection
and learn about the presence state of all the presentities
in the set.
Presence Authorization Policy: Presence authorization policy
refers to the set of directives given to a presence agent
on what subscriptions to accept, when to generate
notifications for a subscription, and what information
should be placed in those notifications.
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Acceptance Policy: The component of presence authorization
policy that determines whether or not to accept a
subscription from a watcher.
Notification Policy: The component of presence authorization
policy that determines when a notification should be sent
to a watcher.
Content Policy: The component of presence authorization that
determines the content of the information provided to a
watcher in a notification.
SIMPLE Data Elements: SIMPLE data elements are user specified
data that determine the behavior of a presence agent. This
includes presentity collections and presence authorization
policy.
Data Manipulation Client: A data manipulation client is a
protocol agent that reads, writes, and receives
notifications of changes in SIMPLE data elements.
Data Manipulation Server: A data manipulation server is a
protocol agent that receives reads, writes, and sends
notifications of changes in SIMPLE data elements. The
server is responsible for the storage of the SIMPLE data
elements.
3 Framework
The framework for the the usage and manipulation of SIMPLE data
elements is shown in Figure 1.
The data manipulation client (just referred to as the client) uses
some protocol, whose requirements are specified here, to interact
with the data manipulation server. Those interactions include
requests to read a SIMPLE data element, write one, or receive
notifications in changes to one. The data manipulation server (just
referred to as the server) mananges a persistent store of the SIMPLE
data elements, and interacts with the client.
When a Presence Agent (PA) receives a SIP SUBSCRIBE request [3], it
may require access to SIMPLE data elements in order to process the
request. For example, if the subscription is for a presentity
collection, the PA will need to determine that this is the case, and
secondly, "expand" the collection, obtaining the list of URIs for
that collection.
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SUBSCRIBE +--------+
--------------->| | Read
| PA |<--+ //----\\
<---------------| | | || ||
NOTIFY +--------+ +--- \\----//|
| |
| Storage|
| |
+--------+ | |
| Server |------> | |
| | Write \ /
| | \------/
+--------+
^ |
| |
| | BL/Auth
| | Manipulations
| |
| |
| V
+--------+
| Client |
| |
| |
+--------+
Figure 1: Framework for Data Manipulation
If the SUBSCRIBE request is for a presentity, the PA will need to
obtain the presence authorization policy of that presentity in order
to process the SUBSCRIBE request.
In both cases, the PA requires only read access to the data. As a
result, it obtains it directly from the data store, rather than
interacting with the server. This, of course, is just a model of the
system; a real implementation might involve interaction with the
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server before reading the data.
Between the presentity collection and presence authorization policy,
the presence authorization policy is a far more complicated piece of
data. The authorization policy can be reasonably split into three
separate pieces. The first, which we call the acceptance policy,
determines whether or not to grant a subscription to the subscriber.
This policy results in a binary decision. The second piece, which we
call the notification policy, determines when that particular
subscriber should receive notifications. For example, a subscriber
might only be permitted to see when I log in or log out of IM, but
not receive notifications when my phone goes on hook. This is closely
related to the third piece, which we call the content policy. This
policy specifies the content of the information present in a
notification that is sent to a subscriber.
Generally, there are two aspects to each of these policy components.
One is the logic that guides the policy, and the other is the data
(such as lists of users) accessed by that logic. As an example, the
logic of the acceptance policy might dictate that a watcher is
checked against an explicit deny list, and if present, their
subscription is denied. If they are not on the deny list, they are
checked against an explicit allow list, and if present, their
subscription is accepted. If they are on neither list, they are
marked as pending. This logic makes use of two lists, which represent
the data.
In this model, the logic can be represented by a script, similar to
the operation of a Call Processing Language (CPL) [4] script. The
primitives of the scripting language would allow for access to the
lists that represent the data. For example, a CPL-like script
representing the policy example of the previous paragraph might look
like:
<cpl>
<subscription>
<lookup source="sip:denylist@example.com">
<success>
<reject status="denied"/>
</success>
<notfound>
<lookup source="sip:allowlist@example.com">
<success>
<accept/>
</success>
<notfound>
<pending/>
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</notfound>
</lookup>
</notfound>
</lookup>
</subscription>
</cpl>
The deny and allow lists are, in this example, represented by SIP
URIs. The script itself can also be represented by a URI. In order to
activate a policy, a particular script is bound to the authorization
function that executes at the PA.
4 Presentity Collection Manipulation Requirements
The following are the set of requirements for the protocol between
the client and the server for the purposes of manipulation presentity
collections.
REQ 1: It MUST be possible for the client to create a presentity
collection and associate it with a URI.
REQ 2: It MUST be possible for the user to specify the URI for
the presentity collection when one is created. If the name
cannot be allocated (because it already exists, for
example), it MUST be possible to inform the client of the
failure, and the reason for it.
REQ 3: It SHOULD be possible for the server to provide the
client a URI for the list when one is created, in the case
where the client does not provide it.
REQ 4: It MUST be possible to add an entry to the presentity
collection. Each entry MUST consist of at least a URI, and
MAY include a display name. It MUST be possible for the
entry to be any URI that is meaningful in the context of a
presentity collection. Examples would include a SIP URI or
pres URI [5].
REQ 5: It MUST be possible for a presentity collection to
contain entries which are themselves presentity
collections.
REQ 6: It MUST be possible to remove an entry from the
presentity collection, by providing the URI for the
specific entry to be removed. If the entry does not exist,
it MUST be possible for the server to inform the client of
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this fact.
REQ 7: It SHOULD be possible to clear all entries from a
presentity collection.
REQ 8: It MUST be possible to delete a presentity collection. In
this context, deleted means that the name of the presentity
collection is no longer defined, so that subscriptions to
the list would fail.
REQ 9: It MUST be possible to query for the set of URIs in a
particular presentity collection, by providing the URI for
the presentity collection.
REQ 10: It MUST be possible for the presentity collection to be
associated with a list of authorized users. Those
authorized users are the only ones permitted to manipulate
the presentity collection.
REQ 11: It MUST be possible for a client to store a cached copy
of the list. This implies that it MUST be possible for the
server to notify the client of a change in the list. It
MUST be possible for the client to manipulate the local
cached copy even when there is no connectivity to the
server. It MUST be possible to synchronize the cached copy
with the master copy on the server, when connectivity is
re-established.
This particular requirement is crucial for wireless
systems, where a copy of the list resides ont he handset.
Without this requirement, a user would not be able to view
the list, or add a user to it, when they go out of
coverage.
REQ 12: It MUST be possible for there to be multiple clients
with cached copies of the list.
REQ 13: Manipulations of the presentity collection MUST exhibit
the ACID property; that is, they MUST be atomic, be
consistent, durable, and operate independently.
REQ 14: It MAY be possible for the client to batch multiple
operations (add a presentity, remove a presentity) into a
single request that is processed atomically.
REQ 15: It MUST be possible for the server to authenticate the
client.
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REQ 16: It MUST be possible for the client to authenticate the
server.
REQ 17: It MUST be possible for message integrity to be insured
between the client and the server.
REQ 18: It MUST be possible for privacy to be insured between
the client and server. As a motivating example, an
eavesdropper on the protocol could ascertain the set of
people in my presentity collection, resulting in divulging
private information.
REQ 19: It MUST be possible for the protocol to operate through
an intermediary, such as a proxy.
REQ 20: It MUST be possible to modify an entry in the presentity
collection.
5 Authorization Policy Manipulation
The following are the set of requirements for the protocol between
the client and the server for the purposes of manipulating presence
authorization policy. The requirements are divided between acceptance
policy, notification policy, and content policy.
5.1 Acceptance Policy Requirements
REQ 1: It MUST be possible for the acceptance policy to support
rejection of the subscription if the watcher is present on
a specified list of "blocked watchers". When a list is
checked in this fashion, its referred to as a blocked list.
This is effectively a requirement on the scripting
language.
REQ 2: It MUST be possible for the acceptance policy to support
rejection of the subscription if the watcher is not present
on a specified list of "allowed watchers". When a list is
checked in this fashion, its referred to as an allowed
list.
REQ 3: It MUST be possible for the acceptance policy to check
multiple blocked and allowed lists.
REQ 4: It MUST be possible for the acceptance policy to support
rejection of the subscription based on filter information
provided in the subscription.
REQ 4.1: It MUST be possible for the policy to be based on the
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status types (for example, the basic status type as defined
in PIDF [6] requested in the filter.
REQ 4.2: It MUST be possible for the policy to be based on the
status values requested in the filter.
REQ 4.3: It MUST be possible for the policy to be based on
whether the subscriber has requested, using the filter, to
receive contact addresses.
REQ 5: It SHOULD be possible for the policy to be based on the
time of day.
REQ 6: It SHOULD be possible for the policy to be based on the
means by which the authenticated identity of the watcher
was determined.
REQ 7: It MUST be possible for the user to manipulate any lists
that are checked by by the authorization policy (for
example, the allowed and denied lists).
REQ 7.1: It MUST be possible for the user to add URIs to the
lists.
REQ 7.2: It MUST be possible for the user to remove URIs from
the lists.
REQ 7.3: It MUST be possible for the user to modify URIs in the
lists.
REQ 7.4: It MUST be possible for the user to obtain the contents
of a list.
REQ 7.5: It MUST be possible for the user to create new lists.
REQ 7.6: It MUST be possible for the user to delete lists.
REQ 7.7: It MUST be possible for the user to clear all URIs on a
list.
REQ 7.8: It MUST be possible for the user to assign a URI that
identifies the list.
REQ 7.9: It MUST be possible for the server to assign a URI that
identifies a list created by the user.
REQ 8: It MUST be possible to bind a script defining the logic
for processing to a particular authorization function.
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REQ 9: It MUST be possible for the client to determine the set
of supported scripting languages.
REQ 10: It MUST be possible for the server to reject the script
because it is malformed, too complex, or not acceptable for
some other reason.
REQ 11: It MUST be possible for the client to fetch the current
script.
REQ 12: It MUST be possible for the client to indicate what
script languages it supports when it fetches the script. In
this way, a server could conceivably translate it to a
format supported by the client.
REQ 13: When a list referenced by script is deleted, the user
MUST either be alerted or prevented from doing so.
5.2 Notification Requirements
REQ 1: It MUST be possible for the user to specify that
notifications are to be sent only when the value of a
particular status type changes.
REQ 2: It MUST be possible for the user to specify that the
notifications are to be sent only when a particular status
type changes to a specified value or set of values.
REQ 3: It MUST be possible for the user to specify that the
notifications are to be sent only when a particular status
type changes from a specified value to a specified value
(i.e., from open to closed).
REQ 4: It MUST be possible for the user to specify that the
notifications are to be sent no more frequently than a
specified minimum rate.
REQ 5: It MUST be possible for the user to specify that the
notifications are to be sent only when the value of the
contact address changes.
OPEN ISSUE: Does this even make sense?
REQ 6: It SHOULD be possible for the user to specify that the
notifications are not to be sent on changes in the state of
the subscription (as opposed to the state of the
presentity).
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REQ 7: It SHOULD be possible for the user to specify that the
notifications are to be sent based on the filter policy
present in the SUBSCRIBE request. In that case, the overall
filter policy would be the composition of the requested
filter and the filters explicitly specified by the
presentity.
5.3 Content Requirements
REQ 1: It MUST be possible for the user to specify that the
notification should or should not contain a contact
address.
REQ 2: It MUST be possible for the user to specify that the
notification should contain only specific status types
(such as basic).
REQ 3: The user MUST be able to specify the specific values of a
specific status type that the notification should or should
not contain. Values not permitted must be omitted from the
status in notifications. If all status is omitted, the
tuple must be omitted as well. As an example, a user can
specify that the notification should include tuples with
OPEN status, but suppress those with only CLOSED status.
REQ 4: The user MUST be able to specify that the notification
should only contain information for particular tuples.
OPEN ISSUE: Its not clear how to meaningfully identify
the tuples.
REQ 5: It SHOULD be possible for the user to specify that the
notifications are to be sent based on the filter policy
present in the SUBSCRIBE request. In that case, the overall
filter policy would be the composition of the requested
filter and the filters explicitly specified by the
presentity.
5.4 General Requirements
These requirements apply to all of the three components of the
authorization policy.
REQ 1: It SHOULD be possible for a client to store a cached copy
of the policies and any related data (the lists, for
example). This implies that it MUST be possible for the
server to notify the client of a change in these data. It
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MUST be possible for the client to manipulate the local
cached copy even when there is no connectivity to the
server. It MUST be possible to synchronize the cached copy
with the master copy on the server, when connectivity is
re-established.
REQ 2: It MUST be possible for there to be multiple clients with
cached copies of the data.
REQ 3: Manipulations of the data MUST exhibit the ACID property;
that is, they MUST be atomic, be consistent, durable, and
operate independently.
REQ 4: It MAY be possible for the client to batch multiple
operations (add a user to a list, change the script) into a
single request that is processed atomically.
REQ 5: It MUST be possible for the server to authenticate the
client.
REQ 6: It MUST be possible for the client to authenticate the
server.
REQ 7: It MUST be possible for message integrity to be insured
between the client and the server.
REQ 8: It MUST be possible for privacy to be insured between the
client and server. As a motivating example, an eavesdropper
on the protocol could ascertain the set of people in my
allowed list collection, resulting in divulging private
information.
REQ 9: It MUST be possible for the protocol to operate through
an intermediary, such as a proxy.
6 Possible Solutions
This document is primarily a requirements document, and does not aim
to provide a protocol for meeting the requirements defined here.
However, there are several protocols already in existence which
appear close to meeting the requirements described. One of these is
ACAP [7]. Since the protocol is primarily a client-server RPC type of
operation, it seems like HTTP and SOAP might also serve as a basis,
with a suitably defined set of WSDL. SIP could operate alongside
SOAP, to provide the notification aspects of the requirements. SNMP
is another possibility for the protocol.
7 Security Considerations
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There are many security considerations associated with the protocol
whose requirements are defined here.
The protocol is used to manipulate data that has a signficiant impact
on the operation of a service provided to a user. In particular, if
the data is manipulated by an attacker, the attacker can:
o convey information to subscribers that the presentity wishes
to keep private;
o launch denial of service attacks by flooding a subscriber with
more presence information than they expected;
o deny service to subscribers or to presentities.
To prevent these attacks, the protocol has to ensure than only
authorized users can manipulate the data. Requirements for
authentication and authorization are defined above.
Information conveyed in the protocol represents sensitive data. It
can include the content of presentity collections and lists of
blocked users, both of which reveal personal preferences of a user
that they do not wish to convey. As a result, it is necessary that
the client authenticate the server, to be sure it is passing this
information to a trusted entity. It is also necessary for the
protocol to provide encryption services, so that eavesdroppers cannot
inspect the data as it passes by.
8 Acknowledgements
The authors would like to thank Paul Kyzivat for his input.
9 Authors Addresses
Jonathan Rosenberg
dynamicsoft
72 Eagle Rock Avenue
First Floor
East Hanover, NJ 07936
email: jdrosen@dynamicsoft.com
Markus Isomaki
Nokia
Nokia House
Keilalahti, Espoo
Finland
email: markus.isomaki@nokia.com
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10 Normative References
11 Informative References
[1] M. Day, J. Rosenberg, and H. Sugano, "A model for presence and
instant messaging," RFC 2778, Internet Engineering Task Force, Feb.
2000.
[2] J. Rosenberg and B. Campbell, "A SIP event package for list
presence," Internet Draft, Internet Engineering Task Force, June
2002. Work in progress.
[3] J. Rosenberg, "Session initiation protocol (SIP) extensions for
presence," Internet Draft, Internet Engineering Task Force, May 2002.
Work in progress.
[4] J. Lennox and H. Schulzrinne, "Call processing language framework
and requirements," RFC 2824, Internet Engineering Task Force, May
2000.
[5] D. Crocker et al. , "Common presence and instant messaging
(CPIM)," Internet Draft, Internet Engineering Task Force, Aug. 2002.
Work in progress.
[6] H. Sugano, S. Fujimoto, et al. , "Common presence and instant
messaging (CPIM)presence information data format," Internet Draft,
Internet Engineering Task Force, May 2002. Work in progress.
[7] C. Newman and J. G. Myers, "ACAP -- application configuration
access protocol," RFC 2244, Internet Engineering Task Force, Nov.
1997.
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