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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 RFC 4745

GEOPRIV                                                   H. Schulzrinne
Internet-Draft                                               Columbia U.
Expires: August 9, 2004                                        J. Morris
                                                                     CDT
                                                           H. Tschofenig
                                                              J. Cuellar
                                                                 Siemens
                                                                 J. Polk
                                                                   Cisco
                                                            J. Rosenberg
                                                             DynamicSoft
                                                        February 9, 2004


                             Common Policy
                  draft-ietf-geopriv-common-policy-00

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
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   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 9, 2004.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

   This document defines a framework for authorization policies
   controling access to application specific data. This framework
   combines common location- and SIP-presence-specific authorization
   aspects. An XML schema specifies the language in which common policy



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   rules are represented. The common policy framework can be extended to
   other application domains.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Terminology  . . . . . . . . . . . . . . . . . . . . . . . .   5
   3.   Modes of Operation . . . . . . . . . . . . . . . . . . . . .   6
   3.1  Passive Request-Response - PS as Server (Responder)  . . . .   6
   3.2  Active Request-Response - PS as Client (Initiator) . . . . .   6
   3.3  Event Notification . . . . . . . . . . . . . . . . . . . . .   6
   4.   Goals and Assumptions  . . . . . . . . . . . . . . . . . . .   8
   5.   Non-Goals  . . . . . . . . . . . . . . . . . . . . . . . . .  10
   6.   Basic Data Model and Processing  . . . . . . . . . . . . . .  11
   6.1  Identification of Rules  . . . . . . . . . . . . . . . . . .  12
   6.2  Extensions . . . . . . . . . . . . . . . . . . . . . . . . .  12
   7.   Conditions . . . . . . . . . . . . . . . . . . . . . . . . .  13
   7.1  Identity . . . . . . . . . . . . . . . . . . . . . . . . . .  13
   7.2  Sphere . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   7.3  Validity . . . . . . . . . . . . . . . . . . . . . . . . . .  15
   8.   Actions  . . . . . . . . . . . . . . . . . . . . . . . . . .  16
   9.   Transformations  . . . . . . . . . . . . . . . . . . . . . .  17
   10.  Procedure for Combining Permissions  . . . . . . . . . . . .  18
   11.  Meta Policies  . . . . . . . . . . . . . . . . . . . . . . .  22
   12.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . .  23
   13.  XML Schema Definition  . . . . . . . . . . . . . . . . . . .  24
   14.  Security Considerations  . . . . . . . . . . . . . . . . . .  27
   15.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  28
   15.1 Common Policy Namespace Registration . . . . . . . . . . . .  28
   15.2 Common Policy Schema Registration  . . . . . . . . . . . . .  28
        Normative References . . . . . . . . . . . . . . . . . . . .  30
        Informative References . . . . . . . . . . . . . . . . . . .  31
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  31
   A.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  33
   B.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  34
        Intellectual Property and Copyright Statements . . . . . . .  35















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1. Introduction

   This document defines a framework for creating authorization policies
   for access to application specific data. This framework is the result
   of finding the common aspects of single authorization systems that
   more specifically control access to presence [2] and location
   information [7] and that previously had been developed separately.
   The benefit of combining these two authorization systems is two-fold.
   First, it allows to build a system which enhances the value of
   presences with location information in a natural way and reuses the
   same underlying authorization mechanism. Second, it encourages a more
   generic authorization framework with mechanisms for extensibility.
   The applicability of the framework specified in this document is not
   limited to policies controling access to presence and location
   information data, but can be extended to other applications domains.

   The general framework defined in this document is intended to be
   accompanied and enhanced by application-specific policies specified
   elsewhere. Using the 'Location-specific Policy' and the
   'Presence-specific Policy' documents [both are currently under
   development - references to be included here], figure Figure 1
   illustrates the relationship between the 'Common Policy' framework
   defined in this document and application-specific enhancements of
   this framework.


                           +-----------------+
                           |                 |
                           |     Common      |
                           |     Policy      |
                           |                 |
                           +---+---------+---+
                              /|\       /|\
                               |         |
      +-------------------+    |         |    +-------------------+
      |                   |    | enhance |    |                   |
      | Location-specific |    |         |    | Presence-specific |
      |      Policy       |----+         +----|      Policy       |
      |                   |                   |                   |
      +-------------------+                   +-------------------+



                  Figure 1: Common Policy Enhancements

   This document starts with an introduction to the terminology in
   Section 2, an illustration of basic modes of operation in Section 3,
   a description of goals (see Section 4) and non-goals (see Section 5)



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   of the authorization policy framework, followed by the data model in
   Section 6. The structure of a rule, namely conditions, actions and
   transformations, are described in Section 7, in Section 8 and in
   Section 9. The procedure for combining permissions is explained in
   Section 10 and used when more than one rule fires. An example is
   provided in Section 12. The XML schema will be discussed in Section
   13. IANA considerations in Section 15 follow security considerations
   Section 14.











































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2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT","RECOMMENDED",  "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [1].

   This document introduces the following terms:

   PT - Presentity / Target: The PT is the entity about whom information
      has been requested.

   RM - Rule Maker: RM is an entity which creates the authorization
      rules which restrict access to data items.

   PS - (Authorization) Policy Server: This entity has access to both
      the authorization policies and to the data items. In
      location-specific applications, the entity PS is labeled as
      location server (LS).

   WR - Watcher / Recipient: This entity requests access to data items
      of the PT. An access operation might be either be a read, write or
      any other operation. In case of access to location information it
      might be a read operation.

   An 'authorization policy' is given by a 'rule set'. A 'rule set'
   contains an unordered list of 'rules'. A 'rule' has a 'conditions',
   an 'actions' and a 'transformations' part.

   The term 'permission' indicates the action and transformation
   components of a 'rule'.

   The terms 'authorization policy', 'policy' and 'rule set' are used
   interchangable.

   The terms 'authorization policy rule', 'policy rule' and 'rule' are
   used interchangable.

   The term 'using protocol' is defined in [4]. It refers to the
   protocol which is used to request access to and to return privacy
   sensitive data items.











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3. Modes of Operation

   The abstract sequence of operations can roughly be described as
   follows. The PS receives either a query for data items for a
   particular PT, via the using protocol. The using protocol provides
   the identity of the requestor (or more precisely the authentication
   protocol), either at the time of the query or at the subscription
   time. The authenticated identity of the WR, together with other
   information provided by the using protocol or generally available to
   the server, is then used for searching through the rule set. All
   matching rules are combined according to a permission combining
   algorithm described in Section 10. The result is returned to the WR,
   possibly modified by transformation policies.

   A single PS may authorize access to data items in more than one mode.
   Rather than having different rule sets for different modes all three
   modes are supported with a one rule set schema. Specific instances of
   the rule set can omit elements that are only applicable to the
   subscription model. The three different modes are explained below.

3.1 Passive Request-Response - PS as Server (Responder)

   In a passive request-response scenario, the WR queries the PS for
   data items about the PT. Examples of protocols following this mode of
   operation include HTTP, FTP, LDAP, finger or various RPC protocols,
   including Sun RPC, DCE, DCOM, Corba and SOAP. The PS uses the ruleset
   to prevent the transmission of information to the WR by refusing the
   request. Furthermore, the PS might filter information by removing
   elements or by reducing the resolution of elements.

3.2 Active Request-Response - PS as Client (Initiator)

   Alternatively, the PS may contact the WR and convey data items.
   Examples include HTTP, SIP session setup (INVITE request), H.323
   session setup or SMTP.

3.3 Event Notification

   Event notification adds a subscription phase to the "PS as client"
   mode of operation. A watcher or subscriber asks to be added to the
   notification list for a particular presentity or event. When the
   presentity changes state or the event occurs, the PS sends a message
   to the WR containing the updated state. (Presence is a special case
   of event notification; thus, we often use the term interchangeably.)

   In addition, the subscriber may itself add a filter to the
   subscription, limiting the rate or content of the notifications. If
   an event, after filtering by the rulemaker-provided rules and by the



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   subscriber-provided rules, only produces the same notification
   content that was sent previously, no event notification is sent.

















































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4. Goals and Assumptions

   Below, we summarize our design goals and constraints.

   Table representation: Each rule must be representable as a row in a
      relational database. This design goal should allow efficient
      policy rule implementation by utilizing standard database
      optimization techniques.

   Permit only: Rules only provide permissions rather than denying them.
      Allowing both 'permit' and 'deny' actions would require some rule
      ordering which had implications on the update operations executed
      on these rules. Additionally it would make distributed rule sets
      more complicated. Hence, only 'permit' actions are allowed which
      result in more efficient rule processing. This also implies that
      rule ordering is not important. Consequently, to make a policy
      decision requires processing all policy rules.

   Additive permissions: A query for access to data items is matched
      against the rules in the rule database. If several rules match,
      then the overall permissions granted to the WR are the union of
      those permissions. A more detailed discussion is provided in
      Section 10.

   Upgradeable: It should be possible to add additional rules later,
      without breaking PSs that have not been upgraded. Any such
      upgrades must not degrade privacy constraints, but PSs not yet
      upgraded may reveal less information than the rulemaker would have
      chosen.

   Versioning support: In addition to the previous goal, a RM should be
      able to determine which types of rules are supported by the PS.
      The mechanism used to determine the capability of a PS will be
      covered in future versions of the document.

   Protocol-independent: The rule set supports constraints on both
      notifications or queries as well as subscriptions for event-based
      systems such as presence systems.

   No false assurance: It appears more dangerous to give the user the
      impression that the system will prevent disclosure automatically,
      but fail to do so with a significant probability of operator error
      or misunderstanding, than to force the user to explicitly invoke
      simpler rules. For example, rules based on weekday and time-of-day
      ranges seem particularly subject to misinterpretation and false
      assumptions on part of the RM. (For example, a non-technical RM
      would probably assume that the rules are based on the timezone of
      his current location, which may not be known to other components



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      of the system.)


















































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5. Non-Goals

   We explicitly decided that a number of possibly worthwhile
   capabilities are beyond the scope of this first version. Future
   versions may include these capabilities, using the extension
   mechanism described in this document. Non-goals include:

   No external references: Attributes within specific rules cannot refer
      to external rule sets, databases, directories or other network
      elements. Any such external reference would make simple database
      implementation difficult and hence they are not supported in this
      version.

   No regular expression or wildcard matching: Conditions are matched on
      equality or 'greater-than'-style comparisons, not regular
      expressions, partial matches such as the SQL LIKE operator (e.g.,
      LIKE "%foo%") or glob-style matches ("*@example.com"). Most of
      these are better expressed as explicit elements.

   No all-except conditions: It is not possible to express exclusion
      conditions based on identities such as "everybody except Alice".
      However, this restriction does not prevent all forms of
      blacklisting. It is still possible to express an authorization
      rule like 'I allow access to my location information for everyone
      of domain example.com except for John'. See the example in section
      Section 7.1 describing how exceptions can be made work.

   No repeat times: Repeat times are difficult to make work correctly,
      due to the different time zones that PT, WR, PS and RM may occupy.
      It appears that suggestions for including time intervals are often
      based on supporting work/non-work distinctions, which
      unfortunately are difficult to capture by time alone.



















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6. Basic Data Model and Processing

   A rule set (or synonymously, a policy) consists of zero or more
   rules. The ordering of these rules is immaterial. The rule set can be
   stored at the PS and conveyed from RM to PS as a single document, in
   subsets or as individual rules. A rule consists of three parts -
   conditions (see section Section 7), actions (see Section 8), and
   transformations (see Section 9).

   The conditions part is a set of expressions, each of which evaluates
   to either TRUE or FALSE, i.e., each of which is equipped with a value
   of either TRUE or FALSE by the PS. When a WR asks for information
   about a PT, the PS goes through each rule in the rule set. For each
   rule, it evaluates the expressions in the conditions part. If all of
   the expressions evaluate to TRUE, then the rule is applicable to this
   request. Generally, each expression specifies a condition based on
   some variable that is associated with the context of the request.
   These variables can include the identity of the WR, the domain of the
   WR, the time of day, or even external variables, such as the
   temperature or the mood of the PT.

   Assuming that the rule is applicable to the request, the actions and
   transformations (commonly referred to as permissions) in the rule
   specify how the PS is supposed to handle this request. If the request
   is to view the location of the PT, or to view its presence, the
   typical action is "permit", which allows the request to proceed.

   Assuming the action allows the request to proceed, the
   transformations part of the rule specifies how the information about
   the PT - their location information, their presence, etc. - is
   modified before being presented to the WR. These transformations are
   in the form of positive permissions. That is, they always specify a
   piece of information which is allowed to be seen by the WR. When a PS
   processes a request, it takes the transformations specified across
   all rules that match, and creates the union of them. The means for
   computing this union depend on the data type - Integer, Boolean, Set,
   or the Undef data type - and are described in more detail in section
   Section 10. The resulting union effectively represents a "mask" - it
   defines what information is exposed to the WR. This mask is applied
   to the actual location or presence data for the PT, and the data
   which is permitted by the mask is shown to the WR. If the WR request
   a subset of information only (such as city-level civil location data
   only, instead of the full civil location information), the
   information delivered to the WR SHOULD be the intersection of the
   permissions granted to the WR and the data requested by the WR.

   In accordance to this document, rules are encoded in XML. To this
   end, section Section 13 contains an XML schema defining the Common



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   Policy Markup Language. This, however, is purely an exchange format
   between RM and PS. The format does not imply that the RM or the PS
   use this format internally, e.g., in matching a query with the policy
   rules. The rules are designed so that a PS may translate the rules
   into a relational database table, with each rule represented by one
   row in the database. The database representation is by no means
   mandatory; we will use it as a convenient and widely-understood
   example of an internal representation. The database model has the
   advantage that operations on rows have tightly defined meanings. In
   addition, it appears plausible that larger-scale implementations will
   employ a backend database to store and query rules, as they can then
   benefit from existing optimized indexing, access control, scaling and
   integrity constraint mechanisms. Smaller-scale implementations may
   well choose different implementations, e.g., a simple traversal of
   the set of rules.

6.1 Identification of Rules

   Each rule is equipped with a parameter that identifies the rule. This
   rule identifier is an opaque token chosen by the RM. A RM MUST NOT
   use the same identifier for two rules that are available to the PS at
   the same time for a given PT. The combination <PT identity, RM
   identity, rule identity> uniquely identifies a rule.

6.2 Extensions

   The authorization policy framework defined in this document is meant
   to be extensible towards specific application domains. Such an
   extension is accomplished by defining conditions, actions and
   transformations that are specific to the desired application domain.
   Each extension MUST define its own namespace and indicate its version
   number.



















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7. Conditions

   The access to data items needs to be matched with the rule set stored
   at the PS. Each instance of a request has different attributes (e.g.,
   the identity of the requestor) which are used for authorization. A
   rule in a rule set might have a number of conditions which need to be
   verified before executing the remaining parts of a rule (i.e.,
   actions and transformations). Details about rule matching are
   described in Section 10. This document specifies only a few
   conditions (namely identity, sphere, and validity). Other conditions
   are left for extensions of this document.

7.1 Identity

   The policy framework specified in this document supports the usage of
   authenticated identities as input to access authorization decision
   processes. This framework, however, abstracts from the
   particularities of concrete authentication mechanisms employed by
   different using protocols and is therefore unable to specify
   explicitly the details of identity relevant information. Documents
   that enhance this framework should describe how a particular using
   protocol is able to provide identity information in a meaningful way.

   Such an enhancement needs to map the identity used by the
   authentication protocol employed in the using protocol to an identity
   used in the authorization policy. It is necessary to clearly define a
   mapping between the authenticated identity of the user (and the
   domain of the user) and the identities used in the authorization
   policies. This mapping needs to consider the large number of possible
   identities used in various authentication protocols and also to
   consider identities in using protocols. Furthermore, it is important
   to designate an identifier that denotes an 'anonymous user', i.e., a
   user that has not authenticated itself to the PS. The authors suggest
   to treat anonymous users by omitting this attribute in the rule which
   causes a 'NULL' value to be created in the ruleset table of a
   relational database. Any request for a data item (for a given PT)
   would match with respect to this attribute in a rule. Furthermore,
   pseudonyms need to be addressed as part of this mapping process.

   This specification provides an <identity> element which belongs to
   the group of condition elements. It can have either the <uri> or the
   <domain> element as child elements. The <domain> element contains a
   list of <except> elements and allows to implement a simple blacklist
   mechanism. The domain value of the <domain> element MUST match the
   value in the domain part of the URI in the <except> element. The
   following example illustrates conditions based on an identity.





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   <identity>
     <uri>jack@example.com</uri>
   </identity>

   The next example shows how exceptions are implemented. A request MUST
   match the domain part and all three exceptions parts in an atomic
   fashion to be a successful match.


   <identity>
     <domain>example.com</domain>
     <except>joe@example.com</except>
     <except>tony@example.com</except>
     <except>mike@example.com</except>
   </identity>


7.2 Sphere

   The <sphere> element belongs to the group of condition elements. It
   can be used to indicate a state (e.g., 'work', 'home', 'meeting',
   'travel') the PT is currently in. A sphere condition matches only if
   the PT is currently in the state indicated. The state may be conveyed
   by manual configuration or by some protocol. For example, RPID [5]
   provides the ability to inform the PS of its current sphere.
   Switching from one sphere to another causes to switch between
   different modes of visibility. As a result different subsets of rules
   might be applicable. An example of a rule fragment is shown below:



     <rule id="f3g44r1">
       <conditions>
         <sphere>work</sphere>
         <identity>
           <uri>bob@example.com</uri>
         </identity>
       </conditions>
     </rule>

     <rule id="y6y55r2">
       <conditions>
         <sphere>home</sphere>
         <identity>
           <uri>alice@example.com</uri>
         </identity>
       </conditions>
     </rule>



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   The code snippet above illustrates that the rule with the entity
   bob@example.com matches if the sphere is been set to 'work'. In the
   second rule with the entity alice@example.com matches if the sphere
   is set to 'home'.

7.3 Validity

   The <validity> element is the third condition element specified in
   this document. It expresses the rule validity period by two
   attributes, a starting and a ending time. Times are expressed in XML
   dateTime format. Expressing the lifetime of a rule implements a
   garbage collection mechanism. A rule maker might not have always
   access to the PS to remove some rules which grant permissions. Hence
   this mechanisms allows to remove or invalidate granted permissions
   automatically without further interaction between the rule maker and
   the PS.

   An example of a rule fragment is shown below:


   <validity>
     <from>2003-08-15T10:20:00.000-05:00</from>
     <to>2003-09-15T10:20:00.000-05:00</to>
   </validity>



























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8. Actions

   While conditions are the 'if'-part of rules, actions and
   transformations build the 'then'-part of them. The actions and
   transformations parts of a rule determine which operations the PS
   MUST execute after having received from a WR a data access request
   that matches all conditions of this rule. Actions and transformations
   only permit certain operations; there is no 'deny' functionality.
   Transformations exclusively specify PS-side operations that lead to a
   modification of the data items requested by the WR. Regarding
   location data items, for instance, a transformation could force the
   PS to lower the precision of the location information which is
   returned to the WR.

   Actions, on the other hand, specify all remaining types of operations
   the PS is obliged to execute, i.e., all operations that are not of
   transformation type. For example, this document introduces the
   'confirmation' action for using protocols that follow the
   subscription model. To this end, the common policy markup language
   contains the <confirmation> element of boolean type. If it is set to
   'true', the PS MUST bring in a subscription approval or disapproval
   from the PT and grant subscription to the requesting WR only in case
   of an approval. In case of 'false' or if this element is omitted, the
   PS SHOULD NOT ask the PT for subscription approval or disapproval.

   The subscription is marked as 'pending' while the PS waits for the PT
   to decide. The approval mechanism depends on the using protocol and
   is beyond the scope of this document. As an example, SIP defines a
   mechanism where the presentity is notified of a subscription attempt
   [3] and then either allows or refuses the subscription.





















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9. Transformations

   Two sub-parts follow the conditions part of a rule: transformations
   and actions. As defined in section Section 8, transformations specify
   operations that the PS MUST execute and that modify the result which
   is returned to the WR. This functionality is particularly helpful in
   reducing the granularity of information provided to the WR, as for
   example required by location information. This document does not
   define any transformations since they depend on the application
   domain.

   A simple transformation example is provided in Section 10.







































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10. Procedure for Combining Permissions

   We use the following terminology (which in parts has already been
   introduced in previous sections): The term 'permission' stands for an
   action or a transformation. The notion 'attribute' terms a condition,
   an action, or a transformation. An attribute MUST specify its name.
   An attribute MUST either be equipped with a value of a certain data
   type or it is not equipped with a value. In the latter case the value
   of this attribute automatically equals 'undef' of data type 'Undef'.
   For example, the name of the <sphere> attribute discussed in section
   Section 7 is 'sphere', its data type is 'string', and its value may
   be set to 'home'. The values of attributes of the same name MUST all
   be of the same data type or of the Undef data type. To evaluate a
   condition means to associate either TRUE or FALSE to the condition. A
   rule matches if all conditions contained in the conditions part of a
   rule evaluate to TRUE.

   When the PS receives a request for access to privacy-sensitive data
   then it needs to be matched against a rule set. The conditions part
   of each individual rule is evaluated and as a result one or more
   rules might match. If only a single rule matches then the result is
   determined by executing the actions and the transformations part
   following the conditions part of a rule. However, it can also be the
   case that two or more matching rules contain a permission of the same
   name (e.g., two rules contain a permission named 'precision of
   geospatial location information'), but do not specify the same value
   for that permission (e.g., the two rule might specify values of '10
   km' and '200 km', respectively, for the permission named 'precision
   of geospatial location information'). This section describes the
   procedure for combining permissions in such cases. The values of
   permissions MUST be of either Boolean, Integer, Set, or Undef data
   type. Attributes with values of data type Integer can also be used
   for enumerations. For example, you can enumerate different levels of
   civil location information precision (e.g., level 0 "country, city,
   street" vs. level 1 "country, city") by associating integers to these
   levels.

   The combining rules are simple and depend on the data types of the
   values of permissions: Let P be a policy. Let M be the subset of P
   consisting of rules r in P that match with respect to a given
   request. Let n be a name of a permission contained in a rule r in M,
   and let M(n) be the subset of M consisting of rules r in M that have
   a permission of name n. For each rule r in M(n), let v(r,n) and
   d(r,n) be the value and the data type, respectively, of the attribute
   of r with name n. Finally, let V(n) be the combined value of all the
   permissions values v(r,n), r in M(n). The combining rules that lead
   to the resulting value V(n) are the following:




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   CR 1: If d(r,n)=Boolean or d(r,n)=Undef for all r in M(n),  then V(n)
   is given as follows: If there is a r in M(n) with v(r,n)=TRUE, then
      V(n)=TRUE. Otherwise, V(n)=FALSE.

   CR 2: If d(r,n)=Integer or d(r,n)=Undef for all r in M(n),  then V(n)
   is given as follows: If v(r,n)=undef for all r in M(n), then V(n) is
      not specified by this specification. Otherwise, V(n)=max{v(r,n) |
      r in M(n)}.

   CR 3: If d(r,n)=Set or d(r,n)=Undef for all r in M(n),  then V(n) is
   given as follows: V(n)=intersection of all v(r,n), the intersection
      to be computed over all r in M(n) with v(r,n)!=undef.

   In the following example we illustrate the process of combining
   permissions. We will consider three conditions for our purpose,
   namely those of name identity, sphere, and validity. For editorial
   reasons the rule set in this example is represented in a table.
   Furthermore, the domain part of the identity of the WR is omitted.
   For actions we use two permissions with names X and Y. The values of
   X and Y are of data types Boolean and Integer, respectively.
   Permission X might, for example, represent the <confirmation> action.
   For transformations we use the attribute with the name Z whose value
   can be set either to '+'(or 1), 'o' (or 2) or '-' (or 3). Permission
   Z allows us to show the granularity reduction whereby a value of '+'
   shows the corresponding information unrestricted and '-' shows
   nothing. This permission might be related to location information or
   other presence attributes like mood. Internally we use the data type
   Integer for computing the permission of this attribute.


   Conditions                       Actions/Transformations
   +--------------------------------+---------------------+
   | Id  WR-ID    sphere  from  to  |  X       Y     Z    |
   +--------------------------------+---------------------+
   |  1   bob      home    A1    A2 |  TRUE    10    o    |
   |  2   alice    work    A1    A2 |  FALSE   5     +    |
   |  3   bob      work    A1    A2 |  TRUE    3     -    |
   |  4   tom      work    A1    A2 |  TRUE    5     +    |
   |  5   bob      work    A1    A3 |  undef   12    o    |
   |  6   bob      work    B1    B2 |  FALSE   10    -    |
   +--------------------------------+---------------------+

   Again for editorial reasons, we use the following abbreviations for
   the two <validity> attributes 'from' and 'to':


   A1=2003-12-24T17:00:00+01:00
   A2=2003-12-24T21:00:00+01:00



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   A3=2003-12-24T23:30:00+01:00
   B1=2003-12-22T17:00:00+01:00
   B2=2003-12-23T17:00:00+01:00

   The entity 'bob' acts as a WR and requests data items. The policy P
   consists of the six rules shown in the table and identified by the
   values 1 to 6 in the 'Id' column. The PS receives the query at
   2003-12-24T17:15:00+01:00. The value of the attribute with name
   'sphere' indicating the state the PT is curretnly in is set to
   'work'.

   Rule 1 does not match since the sphere condition does not match. Rule
   2 does not match as the identity of the WR (here 'alice') does not
   equal 'bob'. Rule 3 matches since all conditions evaluate to TRUE.
   Rule 4 does not match as the identity of the WR (here 'tom') does not
   equal 'bob'. Rule 5 matches. Rule 6 does not match since the rule is
   not valid anymore. Therefore, the set M of matching rules consists of
   the rules 3 and 5. These two rules are used to compute the combined
   permission V(X), V(Y), and V(Z) for each of the permissions X, Y, and
   Z:


     Actions/Transformations
   +-----------------------+
   |  X       Y      Z     |
   +-----------------------+
   |  TRUE     3     -     |
   |  undef   12     o     |
   +-----------------------+

   The results of the permission combining algorithm is shown below. The
   combined value V(X) regarding the permission with name X equals TRUE
   according to the first combining rule listed above. The maximum of 3
   and 12 is 12, so that V(Y)=12. For the attribute Z in this example
   the maximum between 'o' and '-' (i.e., between 2 and 3) is '-'.


     Actions/Transformations
   +-----------------------+
   |  X       Y      Z     |
   +-----------------------+
   |  TRUE    12     -     |
   +-----------------------+

   Documents that extend the authorization policy framework defined here
   by introducing application specific actions and transformation MUST
   NOT define permissions whose values are of data type other than
   Boolean, Integer, Set, and Undef. Furthermore, permissions and the



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   meaning of their values MUST be defined in such a way that the usage
   of the combining rules CR 1, CR2, and CR 3 always preserves or
   increases the level of privacy protection for the PT. In other words,
   the definition of new permissions MUST respect the way in which CR 1,
   CR 2, and CF 3 have been formulated in order to guarantee an
   appropriate level of privacy protection.

   Explicitly, it is not allowed to introduce a new permission whose
   value is of data type ...

      ... Boolean and the PS-side operation corresponding to the
      permission value TRUE has a lower privacy protection level than
      that operation that corresponds to the value FALSE.

      ... Integer and for any two permission values v1 and v2, v1 > v2,
      the PS-side operation corresponding to the value v1 has a lower
      privacy protection level than that operation that corresponds to
      the value v2.

      ... Set and for any two permission values s1 and s2, the PS-side
      operation corresponding to the intersection of s1 and s2 has a
      lower privacy protection level than those operations that
      correspond to s1 or s2.




























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11. Meta Policies

   Meta policies authorize a rulemaker to insert, update or delete a
   particular rule or an entire rule set. Some authorization policies
   are required to prevent unauthorized modification of rule sets. Meta
   policies are outside the scope of this document.

   A simple implementation could restrict access to the rule set only to
   the PT but more sophisticated mechanisms are useful. Hence, in this
   case the rule maker is the PT.









































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12. Example

   This section gives a basic example of an XML document valid with
   respect to the XML schema defined in Section 13. More useful examples
   can be found in documents which extend this schema with application
   domain specific data (e.g., location information).


   <?xml version="1.0" encoding="UTF-8"?>
   <ruleset xmlns="urn:ietf:params:xml:ns:common-policy">

     <rule id="f3g44r1">

       <conditions>
         <identity>
           <uri>bob@example.com</uri>
         </identity>
         <validity>
           <from>2003-12-24T17:00:00+01:00</from>
           <to>2003-12-24T19:00:00+01:00</to>
         </validity>
       </conditions>

       <actions>
         <confirmation>true</confirmation>
       </actions>

     </rule>

   </ruleset>





















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13. XML Schema Definition

   This section provides the XML schema definition for the common policy
   markup language described in this document.


   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema
     targetNamespace="urn:ietf:params:xml:ns:common-policy"
     xmlns:cp="urn:ietf:params:xml:ns:common-policy"
     xmlns:xs="http://www.w3.org/2001/XMLSchema"
     elementFormDefault="qualified"
     attributeFormDefault="unqualified">

     <xs:element name="ruleset">
       <xs:complexType>
         <xs:sequence>
           <xs:element name="rule" type="cp:ruleType"
             minOccurs="0" maxOccurs="unbounded"/>
         </xs:sequence>
       </xs:complexType>
     </xs:element>

     <xs:complexType name="ruleType">
       <xs:sequence>
         <xs:element name="conditions" minOccurs="0">
           <xs:complexType>
             <xs:sequence>
               <xs:element ref="cp:condition"
                 minOccurs="0" maxOccurs="unbounded"/>
             </xs:sequence>
           </xs:complexType>
         </xs:element>
         <xs:element name="actions" minOccurs="0">
           <xs:complexType>
             <xs:sequence>
               <xs:element ref="cp:action"
                 minOccurs="0" maxOccurs="unbounded"/>
             </xs:sequence>
           </xs:complexType>
         </xs:element>
         <xs:element name="transformations" minOccurs="0">
           <xs:complexType>
             <xs:sequence>
               <xs:element ref="cp:transformation"
                 minOccurs="0" maxOccurs="unbounded"/>
             </xs:sequence>
           </xs:complexType>



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         </xs:element>
       </xs:sequence>
       <xs:attribute name="id" type="xs:string" use="required"/>
     </xs:complexType>

     <xs:element name="condition" abstract="true"/>
     <xs:element name="action" abstract="true"/>
     <xs:element name="transformation" abstract="true"/>

     <xs:element name="validity" substitutionGroup="cp:condition">
       <xs:complexType>
         <xs:all>
           <xs:element name="from" type="xs:dateTime"/>
           <xs:element name="to" type="xs:dateTime"/>
         </xs:all>
       </xs:complexType>
     </xs:element>

     <xs:element name="sphere" type="xs:string"
       substitutionGroup="cp:condition"/>

     <xs:element name="identity" substitutionGroup="cp:condition">
       <xs:complexType>
         <xs:choice>
           <xs:element name="uri" type="xs:anyURI"/>
           <xs:sequence>
             <xs:element name="domain" type="xs:string"/>
             <xs:sequence minOccurs="0">
               <xs:element name="except" type="xs:anyURI"
                 maxOccurs="unbounded"/>
             </xs:sequence>
           </xs:sequence>
         </xs:choice>
       </xs:complexType>
     </xs:element>

     <xs:element name="confirmation" type="xs:boolean"
       substitutionGroup="cp:action"/>

   </xs:schema>

   Although the XML schema does not require detailed explanations the
   following issues are worth to be mentioned: Each of the <conditions>,
   <actions>, and <transformations> (plural!) elements consists of zero
   or more child elements that belong to the substitution groups
   'condition', 'action', and 'transformation', respectively. The
   respective heads of these substitution groups are the elements
   <condition>, <action>, and <transformation> (singular!). These



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   elements cannot be used directly in an instance document since they
   are labeled as abstract.

   XML schemas that extend this common policy schema by introducing new
   conditions, actions, and transformations MUST declare to which of
   these three substitution group the respective attribute belongs.
   These new attribute elements can then be used as immediate child
   elements of the <conditions>, <actions>, and <transformations>
   elements, depending on to which substitution group they belong.










































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14. Security Considerations

   This document describes a framework for authorization policy rules.
   This framework is intended to be enhanced elsewhere towards
   application domain specific data. Security considerations are to a
   great extent application data dependent, and need therefore to be
   covered by documents that extend the framework defined in this
   specification. However, new action and transformation permissions
   along with their allowed values must be defined in a way so that the
   usage of the permissions combining rules of section Section 10 does
   not lower the level of privacy protection. See section Section 10 for
   more details on this privacy issue.







































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15. IANA Considerations

   This section registers a new XML namespace and a new XML schema with
   IANA.

15.1 Common Policy Namespace Registration

   URI: urn:ietf:params:xml:ns:common-policy

   Registrant Contact: IETF Geopriv Working Group, Henning Schulzrinne
      (hgs+geopriv@cs.columbia.edu).

   XML:


   BEGIN
   <?xml version="1.0"?>
   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
     "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
   <html xmlns="http://www.w3.org/1999/xhtml">
   <head>
     <meta http-equiv="content-type"
           content="text/html;charset=iso-8859-1"/>
     <title>Common Policy Namespace</title>
   </head>
   <body>
     <h1>Namespace for Common Authorization Policies</h1>
     <h2>urn:ietf:params:xml:ns:common-policy</h2>
     <p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
   </body>
   </html>
   END


15.2 Common Policy Schema Registration

   URI: Please assign.

   Registrant Contact: IETF Geopriv Working Group, Henning Schulzrinne
      (hgs+geopriv@cs.columbia.edu).

   XML: The XML schema to be registered is contained in section Section
      13. Its first line is


   <?xml version="1.0" encoding="UTF-8"?>





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       and its last line is


   </xs:schema>















































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Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", March 1997.















































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Informative References

   [2]  Rosenberg, J., "Extensible Markup Language (XML) Configuration
        Access Protocol (XCAP)  Usages for Setting Presence
        Authorization", draft-ietf-simple-xcap-auth-usage-01 (work in
        progress), October 2003.

   [3]  Rosenberg, J., "A Watcher Information Event Template-Package for
        the Session Initiation  Protocol (SIP)",
        draft-ietf-simple-winfo-package-05 (work in progress), January
        2003.

   [4]  Cuellar, J., Morris, J., Mulligan, D., Peterson, J. and J. Polk,
        "Geopriv Requirements", draft-ietf-geopriv-reqs-04 (work in
        progress), October 2003.

   [5]  Sugano, H., Fujimoto, S. and J. Peterson, "Presence Information
        Data Format (PIDF)", draft-ietf-impp-cpim-pidf-08 (work in
        progress), May 2003.

   [6]  Schulzrinne, H., Morris, J., Tschofenig, H. and J. Polk,
        "Geopriv Authorization Rules", draft-ietf-geopriv-rules-00 (work
        in progress), January 2004.

   [7]  Tschofenig, H., Morris, J., Cuellar, J., Polk, J. and H.
        Schulzrinne, "Policy Rules for Disclosure and Modification of
        Geographic Information", draft-ietf-geopriv-policy-00 (work in
        progress), October 2003.


Authors' Addresses

   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   450 Computer Science Building
   New York, NY  10027
   USA

   Phone: +1 212 939 7042
   EMail: schulzrinne@cs.columbia.edu
   URI:   http://www.cs.columbia.edu/~hgs









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   John B. Morris, Jr.
   Center for Democracy and Technology
   1634 I Street NW, Suite 1100
   Washington, DC  20006
   USA

   EMail: jmorris@cdt.org
   URI:   http://www.cdt.org


   Hannes Tschofenig
   Siemens
   Otto-Hahn-Ring 6
   Munich, Bayern  81739
   Germany

   EMail: Hannes.Tschofenig@siemens.com


   Jorge R. Cuellar
   Siemens
   Otto-Hahn-Ring 6
   Munich, Bayern  81739
   Germany

   EMail: Jorge.Cuellar@siemens.com


   James Polk
   Cisco
   2200 East President George Bush Turnpike
   Richardson, Texas  75082
   USA

   EMail: jmpolk@cisco.com


   Jonathan Rosenberg
   DynamicSoft
   600 Lanidex Plaza
   Parsippany, New York  07054
   USA

   EMail: jdrosen@dynamicsoft.com
   URI:   http://www.jdrosen.net






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Appendix A. Contributors

   We would like to thank Christian Guenther for his help with this
   document.


   Christian Guenther
   Siemens AG
   Corporate Technology
   81730 Munich
   Email: christian.guenther@siemens.com
   Germany







































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Appendix B. Acknowledgments

   This document is partially based on the discussions within the IETF
   GEOPRIV working group.  Discussions at the Geopriv Interim Meeting
   2003 in Washington, D.C., helped the working group to make progress
   on the authorization policies based on the discussions among the
   participants.

   We particularly want to thank Allison Mankin <mankin@psg.com>,
   Randall Gellens <rg+ietf@qualcomm.com>, Andrew Newton
   <anewton@ecotroph.net>, Ted Hardie <hardie@qualcomm.com>, Jon
   Peterson <jon.peterson@neustar.biz> for discussing a number of
   details with us. They helped us to improve the quality of this
   document.

   Furthermore, we would like to thank the IETF SIMPLE working group for
   their discussions of J. Rosenberg's draft on XCAP authorization
   policies.

































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Intellectual Property Statement

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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































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