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GEOPRIV                                                   H. Schulzrinne
Internet-Draft                                               Columbia U.
Expires: January 19, 2006                                      J. Morris
                                                                     CDT
                                                           H. Tschofenig
                                                              J. Cuellar
                                                                 Siemens
                                                                 J. Polk
                                                                   Cisco
                                                            J. Rosenberg
                                                             DynamicSoft
                                                           July 18, 2005


          A Document Format for Expressing Privacy Preferences
                draft-ietf-geopriv-common-policy-05.txt

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Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract




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   This document defines a framework for authorization policies
   controling access to application specific data.  This framework
   combines common location- and 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 . . . . . . . . . . . . . . . . . . . . . . . . . .  17
     7.3  Validity . . . . . . . . . . . . . . . . . . . . . . . . .  18
   8.   Actions  . . . . . . . . . . . . . . . . . . . . . . . . . .  20
   9.   Transformations  . . . . . . . . . . . . . . . . . . . . . .  21
   10.  Procedure for Combining Permissions  . . . . . . . . . . . .  22
     10.1   Introduction . . . . . . . . . . . . . . . . . . . . . .  22
     10.2   Algorithm  . . . . . . . . . . . . . . . . . . . . . . .  22
     10.3   Example  . . . . . . . . . . . . . . . . . . . . . . . .  23
   11.  Meta Policies  . . . . . . . . . . . . . . . . . . . . . . .  26
   12.  Example  . . . . . . . . . . . . . . . . . . . . . . . . . .  27
   13.  XML Schema Definition  . . . . . . . . . . . . . . . . . . .  28
   14.  Security Considerations  . . . . . . . . . . . . . . . . . .  32
   15.  IANA Considerations  . . . . . . . . . . . . . . . . . . . .  33
     15.1   Common Policy Namespace Registration . . . . . . . . . .  33
     15.2   Content-type registration for
            'application/auth-policy+xml'  . . . . . . . . . . . . .  33
     15.3   Common Policy Schema Registration  . . . . . . . . . . .  35
   16.  References . . . . . . . . . . . . . . . . . . . . . . . . .  36
     16.1   Normative References . . . . . . . . . . . . . . . . . .  36
     16.2   Informative References . . . . . . . . . . . . . . . . .  36
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  37
   A.   Contributors . . . . . . . . . . . . . . . . . . . . . . . .  39
   B.   Acknowledgments  . . . . . . . . . . . . . . . . . . . . . .  40
        Intellectual Property and Copyright Statements . . . . . . .  41





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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 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 application
   domains.

   The general framework defined in this document is intended to be
   accompanied and enhanced by application-specific policies specified
   elsewhere.  The common policy framework described here is enhanced by
   domain-speific policy documents, including presence [5] and
   location[6].  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 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)
   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



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   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.















































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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
   interchangeably.

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

   The term 'using protocol' is defined in [7].  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 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 combined rules are applied to the application
   data, resulting in the application of privacy based on the
   transformation policies.  The resulting application data is returned
   to the WR.

   Three different modes of operation can be distinguished:

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

   In a passive request-response 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



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   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.












































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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 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 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 is outside the 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.




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   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.)







































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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 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.









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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 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 (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



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   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.

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.

   Extensions cannot change the schema defined in this document, and
   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.
















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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 met 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 authorization policy framework specified in this document
   supports the usage of identities as input to access authorization
   decision processes.  This document, 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.  Hence, we
   only assume that an identity has a structure with a username and a
   domain part.  Documents that enhance the schema defined in this
   document should, if possible, 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
   identities used in the authorization policies.  This mapping needs to
   consider the large number of possible identities used in various
   authentication protocols.

   In this document we distinguish between three different identities:

   Authenticated Identities:

      The WR was authenticated by the PS.  The authenticated identity is
      used as input to the rule matching procedure.

   Unauthenticated Identities:

      The WR was not authenticated by the PS and thus any identity
      provided by the WR might be spoofed.







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   Asserted Identities:

      The WR was not directly authenticated by the PS.  Instead the WR
      was authenticated by an asserting party that provides an assurance
      to the PS about the authentication of the WR.  It is assumed that
      the PS and the asserting party have some relationship with each
      other and that there is a certain degree of trust that the
      asserting party does not misbehave (such as lying about a non-
      existing authentication of the WR and by making an incorrect
      assertion).  An example of this approach can be found in [8].

   These three identities are used for the rule matching algorithms
   whereby no differentiation is made between an authenicated and an
   asserted identity in this document.  However, there is another
   identity, the anonymous identity, that plays a role in this context.
   Most using protocols also designate an identifier that denotes an
   'anonymous user'.  The WR, as such, is not authenticated by the PS
   nor does an assertion exist that provides the PS with information
   about the authenticated identity.  In order to provide an
   authorization decision non-identity based (or trait-based
   authorization) might be applicable.  This might be accomplished by an
   assertion provided by a third party that hides the identity but
   offers attributes about the WR that are used as the foundation for an
   access control decision.  Ensuring authorization for anonymous users
   is outside the scope of this document.

   The following guidelines apply when performing rule matching (related
   to the identity element in the conditions part of a rule):

   1.  A rule with no conditions matches any subscription irrelevant
       whether an authenticated or an unauthenticated was used by the WR
       to access resources.

   2.  A rule with an <identity> element assumes that there are either
       <id> or <domain> elements as child elements.  Unauthenticated
       identities never match the values of the <id> element(s) or the
       <domain> element(s).

       1.  If the <identity> element contains one or multiple <id>
           element(s) then the authenticated identities (as provided by
           the security protocol used by the using protocol) MUST be
           used for an equality match.

       2.  If the <identity> element contains the <domain> element
           consisting of one or more <except> element(s) then the domain
           part of the authenticated identity MUST be used for an
           equality match.  This allows implementing a simple blacklist
           mechanism.  The <except> element contains the identity



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           without the domain part (i.e., the username part) since it
           equals the domain of the <domain> element.  Only
           authenticated identities MUST be matched with the username
           part of the values of the <except> element(s).

   3.  The <any-identity> condition that matches authenticated and
       unauthenticated identities.  The <any-identity> MAY contain one
       or multiple <except-domain> elements and MAY contain one or
       multiple <domain> elements.

       1.  If the <any-identity> element does not contain child elements
           then the rule matches with any authenticated or
           unauthenticated identity.

       2.  If the <any-identity> element contains one or multiple
           <domain> elements then the domain part of the authenticated
           or unauthenticated identity MUST be matched against the
           values of the <domain> element(s).

       3.  If the <any-identity> element contains one or multiple
           <except-domain> element(s) then the domain part of the
           authenticated or unauthenticated identity MUST be matched
           against the values of the <except-domain> element(s).

   Regarding string comparison the following rules apply:

   1.  The <id> elements of the <identity> condition part of the rule
       matches, if the 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.

   2.  The identity of the WR matches a <domain> (either listed in the
       <identity> or the <any-identity> element) when the domain part of
       the identity matches, based on case insensitive string
       comparison, the value of the <domain> element, and the user part
       matches none of the <except> element values, based on case
       sensitive string comparison.  The values of a <domain> element
       MUST be matched with the domain part of the provided identity
       using an equality match.  No wildcarding is provided.

   Next, we list a few examples.  The following example illustrates
   conditions based on an identity.








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   Authenticated Identities


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

     <rule id="f3g44r2">
       <conditions>
         <identity>
           <id entity="alice@example.com"/>
           <id entity="bob@example.com"/>
         </identity>
       </conditions>
     </rule>
   </ruleset>

                 Figure 2: Matching authenticated identities


      The example shown in Figure 2 shows a rule that matches if the
      authenticated identity of the WR is either alice@example.com or
      bob@example.com.

   Exceptions within the Identity Element:

      The example in Figure 3 shows how exceptions are implemented.  For
      the given example the rule matches if the authenticated identity
      of the WR is from the example.com domain but the user identity of
      the WR is neither joe@example.com, toni@example.com nor
      mike@example.com.

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

     <rule id="f3g44r2">
       <conditions>
         <identity>
           <domain domain="example.com"/>
           <except entity="joe"/>
           <except entity="tony"/>
           <except entity="mike"/>
         </identity>
       </conditions>
     </rule>
   </ruleset>

                  Figure 3: Using the Domain/Except Elements




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      If a WR with the identity john@foo.example.com requests access to
      a resource the above-shown rule is not applied since the case
      insensitive equality match between the domain part of the WR
      identity (namely 'foo.example.com') does not match the value in
      the domain part of the rule (namely 'example.com').

   Any Identity

      The following example matches any authenticated and any
      unauthenticated identity.

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

     <rule id="f3g44r2">
       <conditions>
         <any-identity/>
       </conditions>
     </rule>
   </ruleset>

                      Figure 4: The Any-Identity Element

      The following rule fires for any authenticated and any
      unauthenticated identity except for WR's from the example.com and
      the foo.com domain.  The rule would therefore fire for
      joe@foo.bar.com but not for alice@foo.com.

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

     <rule id="f3g44r2">
       <conditions>
         <any-identity>
           <except-domain domain="example.com"/>
           <except-domain domain="foo.com"/>
         </any-identity>
       </conditions>
     </rule>
   </ruleset>

          Figure 5: Any-Identity combined with Except-Domain Element


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',



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   '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 [9] 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="f3g44r2">
       <conditions>
         <sphere value="work"/>
         <identity>
           <id entity="andrew@example.com"/>
         </identity>
       </conditions>
       <actions/>
       <transformations/>
     </rule>

     <rule id="y6y55r2">
       <conditions>
         <sphere value="home"/>
         <identity>
           <id entity="allison@example.com"/>
         </identity>
       </conditions>
       <actions/>
       <transformations/>
     </rule>

   </ruleset>

   The rule example above illustrates that the rule with the entity
   andrew@example.com matches if the sphere is been set to 'work'.  In
   the second rule with the entity allison@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



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   dateTime format.A rule maker might not have always access to the PS
   to invalidate some rules which grant permissions.  Hence this
   mechanisms allows to 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
   up.

   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">
       <conditions>
           <validity>
               <from>2003-08-15T10:20:00.000-05:00</from>
               <until>2003-09-15T10:20:00.000-05:00</until>
           </validity>
       </conditions>
       <actions/>
       <transformations/>
     </rule>
   </ruleset>

   The <identity>, the <sphere> and the <validity> element MUST NOT
   appear more than 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.






















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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.  Actions are defined by application specific
   usages of this framework.  The reader is referred to the
   corresponding extensions to see examples of such elements.
































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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 for location privacy.  Transformations are defined
   by application specific usages of this framework.

   A simple transformation example is provided in Section 10.








































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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 has a name,
   has a certain data type.  A value may be assigned to an attribute or
   it may be undefined, in case it does not have a value 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'.  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.

10.2  Algorithm

   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



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   to the resulting value V(n) are the following:

   CR 1: If d(r,n)=Boolean 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 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 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.

   The combining operation will result in the largest value for an
   Integral type, the Or operation for boolean, and union for set.

   As a result, applications should define values such that, for
   integers, the 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 <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.











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         Conditions                  Actions/Transformations
     +---------------------------------+---------------------+
     | Id  WR-ID    sphere  from until |  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 'until':


     A1=2003-12-24T17:00:00+01:00
     A2=2003-12-24T21:00:00+01:00
     A3=2003-12-24T23:30:00+01:00
     B1=2003-12-22T17:00:00+01:00
     B2=2003-12-23T17:00:00+01:00

   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:


             Actions/Transformations
     +-----+-----------------------+
     | Id  |  X       Y      Z     |
     +-----+-----------------------+
     |  3  |  TRUE     3     -     |
     |  5  |  undef   12     o     |



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     +-----+-----------------------+

   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
     +-----+-----------------------+
     | Id  |  X       Y      Z     |
     +-----+-----------------------+
     |  5  |  TRUE    12     -     |
     +-----+-----------------------+



































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








































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12.  Example

   This section gives an 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
   information).

   Below a rule is shown with a condition that matches for a given
   authenticated identity (bob@example.com) and within a given time
   period.  Additionally, the rule matches only if the target has set
   its sphere to 'work'.

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

     <rule id="f3g44r1">

       <conditions>
         <identity>
           <id entity="bob@example.com"/>
         </identity>
         <sphere value="work"/>
         <validity>
           <from>2003-12-24T17:00:00+01:00</from>
           <until>2003-12-24T19:00:00+01:00</until>
         </validity>
       </conditions>

       <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">

     <!-- Rule Set -->

     <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>

     <!-- Rule -->

     <xs:complexType name="ruleType">

       <xs:sequence>

         <!-- Conditions -->

         <xs:element name="conditions" minOccurs="0">
           <xs:complexType>
             <xs:sequence>

               <xs:element name="validity" minOccurs="0">
                 <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="identity" minOccurs="0">
                 <xs:complexType>



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                   <xs:choice>

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

                     <xs:sequence>
                       <xs:element name="domain"
                         minOccurs="0" maxOccurs="unbounded">
                         <xs:complexType>
                           <xs:attribute name="domain"
                             type="xs:string" use="required"/>
                         </xs:complexType>
                       </xs:element>
                       <xs:element name="except"
                         minOccurs="0" maxOccurs="unbounded">
                         <xs:complexType>
                           <xs:attribute name="entity"
                             type="xs:string" use="required"/>
                         </xs:complexType>
                       </xs:element>
                     </xs:sequence>



                     <xs:element name="any-identity">
                       <xs:complexType>
                         <xs:sequence>

                           <xs:element name="domain"
                             minOccurs="0" maxOccurs="unbounded">
                             <xs:complexType>
                               <xs:attribute name="domain"
                                 type="xs:string" use="required"/>
                             </xs:complexType>
                           </xs:element>

                           <xs:element name="except-domain"
                             minOccurs="0" maxOccurs="unbounded">
                             <xs:complexType>
                               <xs:attribute name="domain"
                                 type="xs:string" use="required"/>
                             </xs:complexType>
                           </xs:element>




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                         </xs:sequence>
                       </xs:complexType>
                     </xs:element>

                   </xs:choice>
                 </xs:complexType>
               </xs:element>

               <xs:element name="sphere"
                 minOccurs="0" maxOccurs="unbounded">
                 <xs:complexType>
                   <xs:attribute name="value"
                     type="xs:string" use="required"/>
                 </xs:complexType>
               </xs:element>

               <xs:any namespace="##other" processContents="lax"
                 minOccurs="0" maxOccurs="unbounded"/>

             </xs:sequence>
           </xs:complexType>
         </xs:element>

         <!-- Actions -->

         <xs:element name="actions" minOccurs="0">
           <xs:complexType>
             <xs:sequence>
               <xs:any namespace="##other" processContents="lax"
                 minOccurs="0" maxOccurs="unbounded"/>
             </xs:sequence>
           </xs:complexType>
         </xs:element>

         <!-- Transformations -->

         <xs:element name="transformations" minOccurs="0">
           <xs:complexType>
             <xs:sequence>
               <xs:any namespace="##other" processContents="lax"
                 minOccurs="0" maxOccurs="unbounded" />
             </xs:sequence>
           </xs:complexType>
         </xs:element>

       </xs:sequence>

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



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     </xs:complexType>

   </xs:schema>
















































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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 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.







































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15.  IANA Considerations

   This section registers a new XML namespace, a new XML schema and a
   new MIME-type.  This section registers a new XML namespace per the
   procedures in [2].

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
       [NOTE TO IANA/RFC-EDITOR:
        Please replace XXXX with the RFC number of this
       specification.]</a>.</p>
   </body>
   </html>
   END


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 [3] and guidelines in RFC
   3023 [4].

   MIME media type name: application







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   MIME subtype name: auth-policy+xml


   Mandatory parameters: none


   Optional parameters: charset

      Indicates the character encoding of enclosed XML.  Default is
      UTF-8.


   Encoding considerations:

      Uses XML, which can employ 8-bit characters, depending on the
      character encoding used.  See RFC 3023 [4], 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
      information.


   Interoperability considerations: none


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


   Applications which use this media type:

      Presence- and location-based systems


   Additional information:

      Magic Number: None







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      File Extension: .xml


      Macintosh file type code: 'TEXT'


   Personal and email address for further information: Hannes
      Tschofenig, Hannes.Tschofenig@siemens.com


   Intended usage: LIMITED USE


   Author/Change controller:

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


15.3  Common Policy Schema Registration

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

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

   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

   </xs:schema>

















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16.  References

16.1  Normative References

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

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

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

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

16.2  Informative References

   [5]  Rosenberg, J., "Presence Authorization Rules",
        draft-ietf-simple-presence-rules-02 (work in progress),
        February 2005.

   [6]  Schulzrinne, H., "A Document Format for Expressing Privacy
        Preferences for Location Information",
        draft-ietf-geopriv-policy-05 (work in progress), November 2004.

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

   [8]  Jennings, C., Peterson, J., and M. Watson, "Private Extensions
        to the Session Initiation Protocol (SIP) for Asserted Identity
        within Trusted Networks", RFC 3325, November 2002.

   [9]  Schulzrinne, H., "RPID: Rich Presence Extensions to the Presence
        Information Data Format (PIDF)", draft-ietf-simple-rpid-07 (work
        in progress), June 2005.














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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


   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, Bavaria  81739
   Germany

   Email: Hannes.Tschofenig@siemens.com
   URI:   http://www.tschofenig.com


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

   Email: Jorge.Cuellar@siemens.com










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   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.  We thank Stefan Berg, Christian Schmidt, Markus Isomaki,
   Aki Niemi and Eva Maria Leppanen for their comments.
































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