GEOPRIV H. Schulzrinne
Internet-Draft Columbia U.
Expires: April 5, 2005 J. Morris
CDT
H. Tschofenig
J. Cuellar
Siemens
J. Polk
Cisco
J. Rosenberg
DynamicSoft
October 5, 2004
A Document Format for Expressing Privacy Preferences
draft-ietf-geopriv-common-policy-02.txt
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Abstract
This document defines a framework for authorization policies
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controling access to application specific data. This framework
combines common location- and SIP-presence-specific authorization
aspects. An XML schema specifies the language in which common policy
rules are represented. The common policy framework can be extended
to other application domains.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Modes of Operation . . . . . . . . . . . . . . . . . . . . . 6
3.1 Passive Request-Response - PS as Server (Responder) . . . 6
3.2 Active Request-Response - PS as Client (Initiator) . . . . 6
3.3 Event Notification . . . . . . . . . . . . . . . . . . . . 6
4. Goals and Assumptions . . . . . . . . . . . . . . . . . . . 8
5. Non-Goals . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Basic Data Model and Processing . . . . . . . . . . . . . . 11
6.1 Identification of Rules . . . . . . . . . . . . . . . . . 12
6.2 Extensions . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Conditions . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1 Identity . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.2 Sphere . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.3 Validity . . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Actions . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9. Transformations . . . . . . . . . . . . . . . . . . . . . . 17
10. Procedure for Combining Permissions . . . . . . . . . . . . 18
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . 18
10.2 Algorithm . . . . . . . . . . . . . . . . . . . . . . . 18
10.3 Example . . . . . . . . . . . . . . . . . . . . . . . . 19
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 Common Policy Schema Registration . . . . . . . . . . . 29
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
16.1 Normative References . . . . . . . . . . . . . . . . . . . 30
16.2 Informative References . . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 30
A. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 32
B. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 33
Intellectual Property and Copyright Statements . . . . . . . 34
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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 applications
domains.
The general framework defined in this document is intended to be
accompanied and enhanced by application-specific policies specified
elsewhere. Using the 'Location-specific Policy' and the
'Presence-specific Policy' documents [both are currently under
development - references to be included here], figureFigure 1
illustrates the relationship between the 'Common Policy' framework
defined in this document and application-specific enhancements of
this framework.
+-----------------+
| |
| Common |
| Policy |
| |
+---+---------+---+
/|\ /|\
| |
+-------------------+ | | +-------------------+
| | | enhance | | |
| Location-specific | | | | Presence-specific |
| Policy |----+ +----| Policy |
| | | |
+-------------------+ +-------------------+
Figure 1: Common Policy Enhancements
This document starts with an introduction to the terminology
inSection 2, an illustration of basic modes of operation inSection 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
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Section 6. The structure of a rule, namely conditions, actions and
transformations, are described in Section 7, in Section 8 and in
Section 9. The procedure for combining permissions is explained in
Section 10 and used when more than one rule fires. An example is
provided in Section 12. The XML schema will be discussed in Section
13. IANA considerations in Section 15 follow security considerations
Section 14.
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2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT","RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [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
interchangeable.
The terms 'authorization policy rule', 'policy rule' and 'rule' are
used interchangeable.
The term 'using protocol' is defined in[RFC3693]. 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 result is returned to the WR, possibly modified
by transformation policies.
A single PS may authorize access to data items in more than one mode.
Rather than having different rule sets for different modes all three
modes are supported with a one rule set schema. Specific instances
of the rule set can omit elements that are only applicable to the
subscription model. The three different modes are explained below.
3.1 Passive Request-Response - PS as Server (Responder)
In a passive request-response scenario, the WR queries the PS for
data items about the PT. Examples of protocols following this mode
of operation include HTTP, FTP, LDAP, finger or various RPC
protocols, including Sun RPC, DCE, DCOM, Corba and SOAP. The PS uses
the ruleset to 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
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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.
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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 will be
covered in future versions of the document.
Protocol-independent: The rule set supports constraints on both
notifications or queries as well as subscriptions for event-based
systems such as presence systems.
No false assurance: It appears more dangerous to give the user the
impression that the system will prevent disclosure automatically,
but fail to do so with a significant probability of operator error
or misunderstanding, than to force the user to explicitly invoke
simpler rules. For example, rules based on weekday and
time-of-day ranges seem particularly subject to misinterpretation
and false assumptions on part of the RM. (For example, a
non-technical RM would probably assume that the rules are based on
the timezone of his current location, which may not be known to
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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 work.
No repeat times: Repeat times are difficult to make work correctly,
due to the different time zones that PT, WR, PS and RM may occupy.
It appears that suggestions for including time intervals are often
based on supporting work/non-work distinctions, which
unfortunately are difficult to capture by time alone.
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6. Basic Data Model and Processing
A rule set (or synonymously, a policy) consists of zero or more
rules. The ordering of these rules is 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 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. The combination <PT identity, RM
identity, rule identity> uniquely identifies a rule.
6.2 Extensions
The authorization policy framework defined in this document is meant
to be extensible towards specific application domains. Such an
extension is accomplished by defining conditions, actions and
transformations that are specific to the desired application domain.
Each extension MUST define its own namespace and indicate its version
number.
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7. Conditions
The access to data items needs to be matched with the rule set stored
at the PS. Each instance of a request has different attributes
(e.g., the identity of the requestor) which are used for
authorization. A rule in a rule set might have a number of
conditions which need to be verified before executing the remaining
parts of a rule (i.e., actions and transformations). Details about
rule matching are described inSection 10. This document specifies
only a few conditions (namely identity, sphere, and validity). Other
conditions are left for extensions of this document.
7.1 Identity
The policy framework specified in this document supports the usage of
authenticated identities as input to access authorization decision
processes. This framework, however, abstracts from the
particularities of concrete authentication mechanisms employed by
different using protocols and is therefore unable to specify
explicitly the details of identity relevant information. Documents
that enhance this framework should describe how a particular using
protocol is able to provide identity information in a meaningful way.
Such an enhancement needs to map the identity used by the
authentication protocol employed in the using protocol to an identity
used in the authorization policy. It is necessary to clearly define
a mapping between the authenticated identity of the user (and the
domain of the user) and the identities used in the authorization
policies. This mapping needs to consider the large number of
possible identities used in various authentication protocols and also
to consider identities in using protocols. Furthermore, it is
important to designate an identifier that denotes an 'anonymous
user', i.e., a user that has not authenticated itself to the PS. The
authors suggest to treat anonymous users by omitting this attribute
in the rule which causes a 'NULL' value to be created in the ruleset
table of a relational database. Any request for a data item (for a
given PT) would match with respect to this attribute in a rule.
Furthermore, pseudonyms need to be addressed as part of this mapping
process.
This specification provides an <identity> element which belongs to
the group of condition elements. It can have either the <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.
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<identity>
<id>jack@example.com</id>
</identity>
It is allowed to list more than one identity within a single rule as
described in the following example. If multiple identities are
provided in a single rule than the rule matches if one of the listed
identities in a rule matches the authenticated identity of the entity
requesting access to a resource. For the given example the rule
matches if the entity requesting access to a resource is either
alice@example.com or bob@example.com.
<identity>
<id>alice@example.com</id>
<id>bob@example.com</id>
</identity>
The next example shows how exceptions are implemented. A request
MUST match the domain part and all three exceptions parts in an
atomic fashion to be a successful match.
<identity>
<domain>example.com</domain>
<except>joe</except>
<except>tony</except>
<except>mike</except>
</identity>
7.2 Sphere
The <sphere> element belongs to the group of condition elements. It
can be used to indicate a state (e.g., 'work', 'home', 'meeting',
'travel') the PT is currently in. A sphere condition matches only if
the PT is currently in the state indicated. The state may be
conveyed by manual configuration or by some protocol. For example,
RPID [RFC3863] provides the ability to inform the PS of its current
sphere. Switching from one sphere to another causes to switch
between different modes of visibility. As a result different subsets
of rules might be applicable. An example of a rule fragment is shown
below:
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<rule id="f3g44r1">
<conditions>
<sphere>work</sphere>
<identity>
<id>andrew@example.com</id>
</identity>
</conditions>
</rule>
<rule id="y6y55r2">
<conditions>
<sphere>home</sphere>
<identity>
<id>allison@example.com</id>
</identity>
</conditions>
</rule>
The code snippet 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
dateTime format. Expressing the lifetime of a rule implements a
garbage collection mechanism. A rule maker might not have always
access to the PS to remove some rules which grant permissions. Hence
this mechanisms allows to remove or invalidate granted permissions
automatically without further interaction between the rule maker and
the PS.
An example of a rule fragment is shown below:
<validity>
<from>2003-08-15T10:20:00.000-05:00</from>
<to>2003-09-15T10:20:00.000-05:00</to>
</validity>
The <identity>, the <sphere> and the <validity> element MUST NOT
appear more than one 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. This document does not define any actions. 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 by location information. This document does not
define any transformations since they depend on the application
domain.
A simple transformation example is provided in Section 10.
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10. Procedure for Combining Permissions
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 a value of a
certain data type or it is not equipped with a value. In the latter
case the value of this attribute is undefined. 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. 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.
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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
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 the algorithm might not
be capable of producing the 'intuitively expected' result. The
combining permissions algorithm is based set theory and protocol
designers and users should be aware of the limitations.
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> 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
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nothing. This permission might be related to location information or
other presence attributes like mood. Internally we use the data type
Integer for computing the permission of this attribute.
Conditions Actions/Transformations
+--------------------------------+---------------------+
| Id WR-ID sphere from to | X Y Z |
+--------------------------------+---------------------+
| 1 bob home A1 A2 | TRUE 10 o |
| 2 alice work A1 A2 | FALSE 5 + |
| 3 bob work A1 A2 | TRUE 3 - |
| 4 tom work A1 A2 | TRUE 5 + |
| 5 bob work A1 A3 | undef 12 o |
| 6 bob work B1 B2 | FALSE 10 - |
+--------------------------------+---------------------+
Again for editorial reasons, we use the following abbreviations for
the two <validity> attributes 'from' and 'to':
A1=2003-12-24T17:00:00+01:00
A2=2003-12-24T21:00:00+01:00
A3=2003-12-24T23:30:00+01:00
B1=2003-12-22T17:00:00+01:00
B2=2003-12-23T17:00:00+01:00
The entity 'bob' acts as a WR and requests data items. The policy P
consists of the six rules shown in the table and identified by the
values 1 to 6 in the 'Id' column. The PS receives the query at
2003-12-24T17:15:00+01:00. The value of the attribute with name
'sphere' indicating the state the PT is 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:
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Actions/Transformations
+-----------------------+
| X Y Z |
+-----------------------+
| TRUE 3 - |
| undef 12 o |
+-----------------------+
The results of the permission combining algorithm is shown below.
The combined value V(X) regarding the permission with name X equals
TRUE according to the first combining rule listed above. The maximum
of 3 and 12 is 12, so that V(Y)=12. For the attribute Z in this
example the maximum between 'o' and '-' (i.e., between 2 and 3) is
'-'.
Actions/Transformations
+-----------------------+
| X Y Z |
+-----------------------+
| TRUE 12 - |
+-----------------------+
Documents that extend the authorization policy framework defined here
by introducing application specific actions and transformation MUST
NOT define permissions whose values are of data type other than
Boolean, Integer, Set, and Undef. Furthermore, permissions and the
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.
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... 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.
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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 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
information).
<?xml version="1.0" encoding="UTF-8"?>
<ruleset xmlns="urn:ietf:params:xml:ns:common-policy">
<rule id="f3g44r1">
<conditions>
<identity>
<uri>bob@example.com</uri>
</identity>
<validity>
<from>2003-12-24T17:00:00+01:00</from>
<to>2003-12-24T19:00:00+01:00</to>
</validity>
</conditions>
<actions></actions>
</rule>
</ruleset>
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13. XML Schema Definition
This section provides the XML schema definition for the common policy
markup language described in this document.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema
targetNamespace="urn:ietf:params:xml:ns:common-policy"
xmlns:cp="urn:ietf:params:xml:ns:common-policy"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<xs:element name="ruleset">
<xs:complexType>
<xs:sequence>
<xs:element name="rule" type="cp:ruleType"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:complexType name="ruleType">
<xs:sequence>
<xs:element name="conditions" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element ref="cp:condition"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="actions" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element ref="cp:action"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name="transformations" minOccurs="0">
<xs:complexType>
<xs:sequence>
<xs:element ref="cp:transformation"
minOccurs="0" maxOccurs="unbounded"/>
</xs:sequence>
</xs:complexType>
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</xs:element>
</xs:sequence>
<xs:attribute name="id" type="xs:string" use="required"/>
</xs:complexType>
<xs:element name="condition" abstract="true"/>
<xs:element name="action" abstract="true"/>
<xs:element name="transformation" abstract="true"/>
<xs:element name="validity" substitutionGroup="cp:condition">
<xs:complexType>
<xs:all>
<xs:element name="from" type="xs:dateTime"/>
<xs:element name="to" type="xs:dateTime"/>
</xs:all>
</xs:complexType>
</xs:element>
<xs:element name="sphere" type="xs:string"
substitutionGroup="cp:condition"/>
<xs:element name="identity" substitutionGroup="cp:condition">
<xs:complexType>
<xs:choice>
<xs:element name="id" type="xs:string"
maxOccurs="unbounded"/>
<xs:sequence>
<xs:element name="domain" type="xs:string"/>
<xs:sequence minOccurs="0">
<xs:element name="except" type="xs:string"
maxOccurs="unbounded"/>
</xs:sequence>
</xs:sequence>
</xs:choice>
</xs:complexType>
</xs:element>
</xs:schema>
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.
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XML schemas that extend this common policy schema by introducing new
conditions, actions, and transformations MUST declare to which of
these three substitution group the respective attribute belongs.
These new attribute elements can then be used as immediate child
elements of the <conditions>, <actions>, and <transformations>
elements, depending on to which substitution group they belong.
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14. Security Considerations
This document describes a framework for authorization policy rules.
This framework is intended to be enhanced elsewhere towards
application domain specific data. Security considerations are to a
great extent application data dependent, and 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 and a new XML schema with
IANA.
15.1 Common Policy Namespace Registration
URI: urn:ietf:params:xml:ns:common-policy
Registrant Contact: IETF Geopriv Working Group, Henning Schulzrinne
(hgs+geopriv@cs.columbia.edu).
XML:
BEGIN
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
"http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="content-type"
content="text/html;charset=iso-8859-1"/>
<title>Common Policy Namespace</title>
</head>
<body>
<h1>Namespace for Common Authorization Policies</h1>
<h2>urn:ietf:params:xml:ns:common-policy</h2>
<p>See <a href="[[[URL of published RFC]]]">RFCXXXX</a>.</p>
</body>
</html>
END
15.2 Common Policy Schema Registration
URI: Please assign.
Registrant Contact: IETF Geopriv Working Group, Henning Schulzrinne
(hgs+geopriv@cs.columbia.edu).
XML: The XML schema to be registered is contained in Section 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
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
16.2 Informative References
[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
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
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Hannes Tschofenig
Siemens
Otto-Hahn-Ring 6
Munich, Bayern 81739
Germany
EMail: Hannes.Tschofenig@siemens.com
URI: http://www.tschofenig.com
Jorge R. Cuellar
Siemens
Otto-Hahn-Ring 6
Munich, Bayern 81739
Germany
EMail: Jorge.Cuellar@siemens.com
James Polk
Cisco
2200 East President George Bush Turnpike
Richardson, Texas 75082
USA
EMail: jmpolk@cisco.com
Jonathan Rosenberg
DynamicSoft
600 Lanidex Plaza
Parsippany, New York 07054
USA
EMail: jdrosen@dynamicsoft.com
URI: http://www.jdrosen.net
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Appendix A. Contributors
We would like to thank Christian Guenther for his help with this
document.
Christian Guenther
Siemens AG
Corporate Technology
81730 Munich
Email: christian.guenther@siemens.com
Germany
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Appendix B. Acknowledgments
This document is partially based on the discussions within the IETF
GEOPRIV working group. Discussions at the Geopriv Interim Meeting
2003 in Washington, D.C., helped the working group to make progress
on the authorization policies based on the discussions among the
participants.
We particularly want to thank Allison Mankin <mankin@psg.com>,
Randall Gellens <rg+ietf@qualcomm.com>, Andrew Newton
<anewton@ecotroph.net>, Ted Hardie <hardie@qualcomm.com>, Jon
Peterson <jon.peterson@neustar.biz> for discussing a number of
details with us. They helped us to improve the quality of this
document.
Furthermore, we would like to thank the IETF SIMPLE working group for
their discussions of J. Rosenberg's draft on XCAP authorization
policies. We thank Stefan Berg, Christian Schmidt, Markus Isomaki
and Eva Maria Leppanen for their comments.
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