GEOPRIV                                                   H. Schulzrinne
Internet-Draft                                               Columbia U.
Expires: April 5, 24, 2005                                        J. Morris
                                                           H. Tschofenig
                                                              J. Cuellar
                                                                 J. Polk
                                                            J. Rosenberg
                                                        October 5, 24, 2004

          A Document Format for Expressing Privacy Preferences

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, I certify each
   author represents that any applicable patent or other IPR claims of
   which I am he or she is aware have been or will be disclosed, and any of
   which I he or she become aware will be disclosed, in accordance with
   RFC 3668.

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Copyright Notice

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

   This document defines a framework for authorization policies
   controling access to application specific data.  This framework
   combines common location- and SIP-presence-specific presence-specific authorization
   aspects.  An XML schema specifies the language in which common policy
   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  17
   9.   Transformations  . . . . . . . . . . . . . . . . . . . . . .  17  18
   10.  Procedure for Combining Permissions  . . . . . . . . . . . .  18  19
     10.1   Introduction . . . . . . . . . . . . . . . . . . . . . .  18  19
     10.2   Algorithm  . . . . . . . . . . . . . . . . . . . . . . .  18  19
     10.3   Example  . . . . . . . . . . . . . . . . . . . . . . . .  19  20
   11.  Meta Policies  . . . . . . . . . . . . . . . . . . . . . . .  23
   12.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . .  24
   13.  XML Schema Definition  . . . . . . . . . . . . . . . . . . .  25
   14.  Security Considerations  . . . . . . . . . . . . . . . . . .  28
   15.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  29
     15.1   Common Policy Namespace Registration . . . . . . . . . .  29
     15.2   Content-type registration for
            'application/auth-policy+xml'  . . . . . . . . . . . . .  29
     15.3   Common Policy Schema Registration  . . . . . . . . . . .  29  31
   16.  References . . . . . . . . . . . . . . . . . . . . . . . . .  30  32
   16.1   Normative References . . . . . . . . . . . . . . . . . . .  30  32
   16.2   Informative References . . . . . . . . . . . . . . . . . .  30  32
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  30  33
   A.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  32  35
   B.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  33  36
        Intellectual Property and Copyright Statements . . . . . . .  34  37

1.  Introduction

   This document defines a framework for creating authorization policies
   for access to application specific data.  This framework is the
   result of combining the common aspects of single authorization
   systems that more specifically control access to presence and
   location information 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 application

   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], figureFigure 1
   illustrates the relationship between the 'Common Policy'  The common policy framework
   defined in this document described here is enhanced by
   domain-speific policy documents, including presence
   [I-D.ietf-simple-presence-rules] and application-specific enhancements of
   this framework.
   location[I-D.ietf-geopriv-policy].  This relationship is shown
   inFigure 1.

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

                  Figure 1: Common Policy Enhancements

   This document starts with an introduction to the terminology
   inSection in
   Section 2, an illustration of basic modes of operation inSection in Section 3,
   a description of goals (see Section 4) and non-goals (see Section 5)
   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.  A short
   description of meta policies is given in Section 11.  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.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

   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

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

   The term 'using protocol' is defined in[RFC3693]. in [RFC3693].  It refers to the
   protocol which is used to request access to and to return privacy
   sensitive data items.

3.  Modes of Operation

   The abstract sequence of operations can roughly be described as
   follows.  The PS receives 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 combined rules are applied to the WR, possibly modified
   by transformation policies.

   A single PS may authorize access to data items application
   data, resulting 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 the application of privacy based on the rule set can omit elements that are only applicable
   transformation policies.  The resulting application data is returned
   to the
   subscription model.  The three WR.

   Three different modes are explained below. of operation can be distinguished:

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

   In a passive request-response scenario, mode, 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 determine whether the WR is authorized to access the PTs
   information, refusing the request if necessary.  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
   subscriber-provided rules, only produces the same notification
   content that was sent previously, no event notification is sent.

   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.

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
      inSection 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

   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 is outside
      the document. scope of this specification.

   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 of the system.)

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

   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 ("*").  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 except for John'.  See the example in
      Section 7.1 describing how exceptions can be made to work.  The
      reason for this choice is the ease with which identities can be
      manufactured, and the implication that all-except types of rules
      are easily subverted.

   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.

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 irrelevant.  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 (seeSection (see 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
   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 13 contains an XML schema defining the Common 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 namespace.

   Extensions cannot change the schema defined in this document, and indicate its version
   this schema is not expected to change excepting a revision to this
   specification.  and that no versioning procedures for this schema or
   namespace are therfore provided.

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 met before executing the remaining parts
   of a rule (i.e., actions and transformations).  Details about rule
   matching are described inSection 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.  This
   document only assumes that the identity has a username part and a
   domain part.  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

   This specification provides an <identity> element which belongs to
   the group of condition elements.  It can have either the <id> 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 <except> element contains the identity without the
   domain part since it equals the domain of the <domain> element.  The
   following example illustrates conditions based on an identity.


   It is allowed to list more than one

   The identity within a single condition part of the rule as
   described in matches, if the following example. identity of
   the WR matches, based on case sensitive string comparison, the user
   part of the <id>, and the domain part of the of the <id>, based on
   case insensitive string comparison.

   A single <identity> element can contain multiple <id> elements.  If
   multiple identities are provided in a single rule than then the rule
   matches if at least one of the listed identities in a rule matches
   the authenticated identity of the entity
   requesting access to a resource. WR.

   For the given example the rule matches if the entity requesting access to a resource WR is either or


   The next example shows how exceptions are implemented.  A request
   MUST match  The identity
   of the WR matches a <domain> when the domain part of the identity
   matches, based on case insensitive string comparison, the value of
   the domain element, and all three exceptions parts in an
   atomic fashion to be a successful match. the user part matches none of the <except>
   element values, based on case sensitive string comparison.


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 [RFC3863] [I-D.ietf-simple-rpid] provides the ability to inform the PS of
   its current sphere.  The application domain needs to describe in more
   detail how the sphere state is determined.  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:

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

     <rule id="f3g44r1"> id="f3g44r2">

     <rule id="y6y55r2">


   The code snippet rule example above illustrates that the rule with the entity matches if the sphere is been set to 'work'.  In
   the second rule with the entity 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 format.A rule maker might not have always access to the PS
   to remove invalidate 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.  The
   PS does not remove the rules instead the rule maker has to clean them

   An example of a rule fragment is shown below:

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

     <rule id="f3g44r3">

   The <identity>, the <sphere> and the <validity> element MUST NOT
   appear more than one once in the conditions part of a single rule.  The
   <id> element on the other hand may appear more than once as described
   in this section.

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.  This document does not define any actions.  Actions are defined by application specific
   usages of this framework.  The reader is referred to the
   corresponding extensions to see examples of such elements.

9.  Transformations

   Two sub-parts follow the conditions part of a rule: transformations
   and actions.  As defined in 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 for location information.  This document does not
   define any transformations since they depend on the privacy.  Transformations are defined
   by application
   domain. specific usages of this framework.

   A simple transformation example is provided in Section 10.

10.  Procedure for Combining Permissions

10.1  Introduction

   This section describes the mechanism to evaluate the final result of
   a rule evaluation.  The result is reflected in the action and
   transformation part of a rule.  This procedure is sometimes referred
   as conflict resolution.

   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 has a value of name,
   has a certain data type type.  A value may be assigned to an attribute or
   it is may be undefined, in case it does not equipped with have a value.  In the latter
   case the value of this attribute is undefined. associated with
   the attribute.  For example, the name of the <sphere> attribute
   discussed in 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.  To evaluate a condition means to
   associate either TRUE or FALSE to the condition.  Please note that
   the <identity> element is a condition whereas the <id> element is a
   parameter of that 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
   attributes MUST be of either Boolean, Integer, Set or undefined.  The
   value is undefined if no value is given for a particular attribute.
   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.

10.2  Algorithm

   This section describes the algorithm in a more formal fashion.

   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:

   CR 1: If d(r,n)=Boolean or d(r,n)=Undefined 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)=Undefined for all r in M(n), then V(n) is given as
   follows: If v(r,n)=undefined 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)=Undefined for all r in M(n), then V(n) is given as follows:
      V(n)=union of all v(r,n), the union to be computed over all r in
      M(n) with v(r,n)!=undefined.

   It is important to note that documents enhancing this concept (and
   therefore using this algorithm) should make sure that output of the

   The combining permissions algorithm is privacy safe.  It is desirable to
   reveal less than more information.  Furthermore, the algorithm
   considers each individual attribute independently.  If there is a
   dependency between different attributes then operation will result in the algorithm might not
   be capable of producing largest value for an
   Integral type, the 'intuitively expected' result.  The
   combining permissions algorithm is based set theory and protocol
   designers Or operation for boolean, and users union for set.

   As a result, applications should be aware of define values such that, for
   integers, the limitations. lowest value corresponds to the most privacy, for
   booleans, false corresponds to the most privacy, and for sets, the
   empty set corresponds to the most privacy.  More

10.3  Example

   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> <sub-handling> 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':


    Note that B1 < B2 < A1 < A2 < A3.

   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 which falls between A1 and A2.  The value
   of the attribute with name 'sphere' indicating the state the PT is
   currently 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:

     | Id  |  X       Y      Z     |
     |  3  |  TRUE     3     -     |
     |  5  |  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

     | Id  |  X       Y      Z     |
     |  5  |  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
   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 union of s1 and s2 has a lower
      privacy protection level than those operations that correspond to
      s1 or s2.

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 could be useful.  As an
   example of such policies one could think of parents configuring the
   policies for their children.

12.  Example

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

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

     <rule id="f3g44r1">






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

     <xs:complexType name="ruleType">
         <xs:element name="conditions" minOccurs="0">
               <xs:element ref="cp:condition"
                 minOccurs="0" maxOccurs="unbounded"/>
         <xs:element name="actions" minOccurs="0">
               <xs:element ref="cp:action"
                 minOccurs="0" maxOccurs="unbounded"/>
         <xs:element name="transformations" minOccurs="0">
               <xs:element ref="cp:transformation"
                 minOccurs="0" maxOccurs="unbounded"/>
       <xs:attribute name="id" type="xs:string" use="required"/>

     <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:element name="from" type="xs:dateTime"/>
           <xs:element name="to" type="xs:dateTime"/>

     <xs:element name="sphere" type="xs:string"

     <xs:element name="identity" substitutionGroup="cp:condition">
           <xs:element name="id" type="xs:string"
             <xs:element name="domain" type="xs:string"/>
             <xs:sequence minOccurs="0">
               <xs:element name="except" type="xs:string"


   Although the XML schema does not require detailed explanations the
   following issues are worth mentioning: 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
   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.

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 therefore need 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 10 does not lower
   the level of privacy protection.  See Section 10 for more details on
   this privacy issue.

15.  IANA Considerations

   This section registers a new XML namespace and namespace, a new XML schema with
   IANA. and a
   new MIME-type.  This section registers a new XML namespace per the
   procedures in [RFC3688].

15.1  Common Policy Namespace Registration

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

   Registrant Contact: IETF Geopriv Working Group, Henning Schulzrinne


   <?xml version="1.0"?>
   <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
   <html xmlns="">
     <meta http-equiv="content-type"
     <title>Common Policy Namespace</title>
     <h1>Namespace for Common Authorization Policies</h1>
   <p>See <a href="[[[URL href="[URL of published RFC]]]">RFCXXXX</a>.</p> RFC]">RFCXXXX
        Please replace XXXX with the RFC number of this

15.2  Content-type registration for 'application/auth-policy+xml'

   This specification requests the registration of a new MIME type
   according to the procedures of RFC 2048 [RFC2048] and guidelines in
   RFC 3023 [RFC3023].

   MIME media type name: application
   MIME subtype name: auth-policy+xml

   Mandatory parameters: none

   Optional parameters: charset

      Indicates the character encoding of enclosed XML.  Default is

   Encoding considerations:

      Uses XML, which can employ 8-bit characters, depending on the
      character encoding used.  See RFC 3023 [RFC3023], Section 3.2.

   Security considerations:

      This content type is designed to carry authorization policies.
      Appropriate precautions should be adopted to limit disclosure of
      this information.  Please refer to RFCXXXX [NOTE TO IANA/
      RFC-EDITOR: Please replace XXXX with the RFC number of this
      specification.] security considerations section for more

   Interoperability considerations: none

   Published specification: RFCXXXX [NOTE TO IANA/RFC-EDITOR: Please
      replace XXXX with the RFC number of this specification.] this

   Applications which use this media type:

      Presence- and location-based systems

   Additional information:

      Magic Number: None
      File Extension: .xml

      Macintosh file type code: 'TEXT'

   Personal and email address for further information: Hannes

   Intended usage: LIMITED USE

   Author/Change controller:

      This specification is a work item of the IETF GEOPRIV working
      group, with mailing list address <>.

15.3  Common Policy Schema Registration

   URI: Please assign. urn:ietf:params:xml:schema:common-policy

   Registrant Contact: IETF Geopriv Working Group, Henning Schulzrinne

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

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

       and its last line is


16.  References

16.1  Normative References

   [RFC2048]  Freed, N., Klensin, J. and J. Postel, "Multipurpose
              Internet Mail Extensions (MIME) Part Four: Registration
              Procedures", BCP 13, RFC 2048, November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", March 1997.

   [RFC3023]  Murata, M., St. Laurent, S. and D. Kohn, "XML Media
              Types", RFC 3023, January 2001.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

16.2  Informative References

              Schulzrinne, H., "A Document Format for Expressing Privacy
              Preferences for Location  Information",
              draft-ietf-geopriv-policy-03 (work in progress), October

              Rosenberg, J., "Presence Authorization Rules",
              draft-ietf-simple-presence-rules-00 (work in progress),
              May 2004.

              Schulzrinne, H., Gurbani, V., Kyzivat, P. and J.
              Rosenberg, "RPID: Rich Presence: Extensions to the
              Presence Information Data Format  (PIDF)",
              draft-ietf-simple-rpid-03 (work in progress), March 2004.

   [RFC3693]  Cuellar, J., Morris, J., Mulligan, D., Peterson, J. and J.
              Polk, "Geopriv Requirements", RFC 3693, February 2004.

   [RFC3863]  Sugano, H., Fujimoto, S., Klyne, G., Bateman, A., Carr, W.
              and J. Peterson, "Presence Information Data Format
              (PIDF)", RFC 3863, August 2004.

Authors' Addresses

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

   Phone: +1 212 939 7042

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


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


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

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


   Jonathan Rosenberg
   600 Lanidex Plaza
   Parsippany, New York  07054


Appendix A.  Contributors

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

   Christian Guenther
   Siemens AG
   Corporate Technology
   81730 Munich

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

   We particularly want to thank Allison Mankin <>,
   Randall Gellens <>, Andrew Newton
   <>, Ted Hardie <>, Jon
   Peterson <> for discussing a number of
   details with us.  They helped us to improve the quality of this

   Furthermore, we would like to thank the IETF SIMPLE working group for
   their discussions of J.  Rosenberg's draft on XCAP authorization
   policies.  We thank Stefan Berg, Christian Schmidt, Markus Isomaki
   and Eva Maria Leppanen for their comments.

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