COS 80011
Web Application Architectures
Lecture 10
Access Control
Outline

What is Access Control?

Access Control Matrix and Access Control List

Role-Based Access Control
 User-Role Assignment
 Role-Permission Assignment

Attribute-Based Access Control

Context-Aware Access Control
 Context-Aware User-Role Assignment
 Context-Aware Role-Permission Assignment
2
© Swinburne University of Technology
Outline

What is Access Control?

Access Control Matrix and Access Control List

Role-Based Access Control
 User-Role Assignment
 Role-Permission Assignment

Attribute-Based Access Control

Context-Aware Access Control
 Context-Aware User-Role Assignment
 Context-Aware Role-Permission Assignment
3
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Access Control (I)
Access control is one of the fundamental security mechanisms

 needed to protect computer resources (and/or services) against
unauthorized access according to a security policy
 policy – is a rule (who can access what)
 verifying whether a subject (user) is allowed to carry out a specific
action (operation) on an object (resource)
 it is a mechanism to determine whether a request from a user to
access resources in a system should be permitted or denied
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Access Control (II)
It has three major components

 subjects – represent the users in a system performing actions on an
object
 objects – represent the resources that are being protected by the
system
 operations – represent all the actions that the subjects can perform
on the objects
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Access Control (III)
Access Control Models/Technologies

- Access Control Matrix or Access Matrix (AM)
- Access Control List (ACL)
- Role-Based Access Control (RBAC)
- Attribute-Based Access Control (ABAC)
- Context-Aware Access Control (CAAC)
- Extended RBAC Models: TMAC (team), OrBAC (organization), …
- ABAC Models: XACML, …
- …
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Access Control (IV)
Traditional forms of Access Control

 AM, ACL, RBAC, …
 file systems, operating systems, database systems, …
Access Control on the Web

 XACML (OASIS standard Web-based AC), XACML for RBAC, …
 Domain-specific inputs converted to the XACML Request
Context.xml (PEP)
 XACML core policy framework or XACML RBAC implementation
using (J2SE, CORBA, etc.), resources are exposed as Web services
(PDP, PIP, PAP)
 XACML Response Context.xml is converted to the domain-specific
7
outputs (PEP)
© Swinburne University of Technology
Outline

What is Access Control?

Access Control Matrix and Access Control List

Role-Based Access Control
 User-Role Assignment
 Role-Permission Assignment

Attribute-Based Access Control

Context-Aware Access Control
 Context-Aware User-Role Assignment
 Context-Aware Role-Permission Assignment
8
© Swinburne University of Technology
Access Control Matrix (I)
Access Control Matrix or Access Matrix (AM)

 access control technology has a long history that started in the late
60s
 it was first introduced by Lampson in 1971, who introduced a formal,
mathematical description of a basic access control model named
Access Control Matrix
<Lampson, Butler W. (1971), Protection, Proceedings of the 5th Princeton
Conference on Information Sciences and Systems>
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Access Control Matrix (II)

Access Control Matrix or Access Matrix (AM)
 the first basic model of access control is the AM
 a formal security model in computer systems
 characterizes the rights of the subjects with respect to the objects
 describes the relationships between subjects and objects in a system
<Lampson, Butler W. (1971), Protection, Proceedings of the 5th Princeton
Conference on Information Sciences and Systems>
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Access Control Matrix (III)

Access Control Matrix: It has three components
 a set of Objects O, a set of Subjects S, and an Access function A
 an Object is an entity in the system which has to be protected
 a Subject is an entity that has access to the Object
 which Subjects can access which Objects is determined by the
Access function
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Access Control Matrix (IV)

Access Control Matrix
 the rows of the Access function are labelled with the Subject names
and its columns by the Object names.
 element Ai,j specifies the access which Subject i has to Object j
 each element or cell of the matrix consists of a set of strings called
access attributes, such as read and write, which are typical access
attributes
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Access Control Matrix (V)

AM Implementations
 operating systems
 database systems
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Access Control Matrix (VI)

AM Implementations
 a rectangular array of cells, with one row per subject and one column
per object
Table: A rectangular array
user1
user2
user3
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file1
file2
read, write
read, write, execute
read
execute
write
read
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Access Control List (I)

Access control list (ACL)
- each column in an Access Control Matrix (AM) is translated to an
Access Control List (ACL)
- the ACL contains entries for each subject defining the operations that
the subject can execute on the given object
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Access Control List (II)

Access control list (ACL): it specifies
- which users or system processes are granted access to objects
- what operations are allowed on given objects
<Access Control List: Google patents,
http://www.google.com/patents/US20130145028>
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Access Control List (III)

ACL Implementations
 File System ACL: A file system ACL is
 a data structure (table) containing entries that specify individual
user or group rights to specific system resources.
 resources - programs, files, etc.
 entries – access control entries (ACEs).
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Access Control List (IV)

ACL Implementations
 File System ACL - used to administrate file permissions
 for example, a file has an ACL that contains (Bob, delete)
 this gives Bob permission to delete the file.
<MS Windows, Unix/Linux Operating Systems>
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Access Control List (V)

ACL Implementations
 File System ACL – access ACL and default ACL (Red Hat Linux)
 an access ACL is the access control list for a specific file or
directory.
 a default ACL can only be associated with a directory; if a file
within the directory does not have an access ACL.
 default ACL uses the rules of the default ACL for the directory.
 ACLs can be configured per user or per group.
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<https://access.redhat.com/site/documentation/enUS/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/chacls.html>
© Swinburne University of Technology
Access Control List (VI)

ACL Implementations
 File System ACL – access ACL and default ACL (Red Hat Linux)
 the setfacl utility sets ACLs for files and directories.
# setfacl -m rules files
 use the -m option to add/modify the ACL of a file/directory
 rule formats u:uid:perms, g:gid:perms
# setfacl -m u:bob:rw /cos80011/waa
<https://access.redhat.com/site/documentation/enUS/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/chacls.html>
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Access Control List (VII)

ACL Implementations
 SQL-based systems
 relational database systems
 networking ACLs
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AM and ACL (VIII)

Advantages
 easy to implement, simplicity and flexibility are the keys
 effective in closed and relatively unchangeable systems

Disadvantages
 do not allow modelling the global policy rules by which permissions
can change in any particular system
 they do not have adequate functionalities to maintain the users and
objects in the large-scale systems, where more than one user need
same object
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Outline

What is Access Control?

Access Control Matrix and Access Control List

Role-Based Access Control
 User-Role Assignment
 Role-Permission Assignment

Attribute-Based Access Control

Context-Aware Access Control
 Context-Aware User-Role Assignment
 Context-Aware Role-Permission Assignment
23
© Swinburne University of Technology
Role-Based Access Control (I)

Role-Based Access Control (RBAC)
- a well accepted access control model based on the role of the user
is Role-based Access Control (RBAC) was introduced to tackle the
problems: global policy rules, large-scale systems
- first RBAC, Ferraiolo et al (RBAC92)
- the RBAC92 model has been subsequently extended by Sandhu et
al (RBAC96)
<Sandhu et al (RBAC96): http://dl.acm.org/citation.cfm?id=226710>
<Ferraiolo et al (RBAC92): http://csrc.nist.gov/rbac/ferraiolo-kuhn-92.pdf>
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Role-Based Access Control (II)

Role-Based Access Control (RBAC)
- in RBAC, it is not important to identify the individual who makes the
access request, but to know his position in the structure of an
organization
- this concept is known as a role in RBAC
- the authorizations are not assigned directly to a particular user, but to
the user’s role
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Role-Based Access Control (III)

Role-Based Access Control (RBAC)
- user group and user role – roles are closely related to the concept of
user groups in access control
- however, a role brings together a set of users on one side and a set
of permissions on the other
- whereas user groups are typically defined as a set of users only
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Role-Based Access Control (IV)

Role-Based Access Control (RBAC): three main concepts
- RBAC ensures that only an authorized user is given access to a
certain resource, and is based on a user’s role in an organization
- users, roles, and permissions in a simple/basic RBAC model
- users – subjects are typically represented by users, who are
assigned to roles and are granted membership into the roles based
on their credentials and responsibilities in an organization
- roles – roles represent a job function, describing the authority and
responsibility conferred on a user assigned to that role, within an
organization
- permissions – permissions are assigned to roles, permissions
27
contain resources and operations (the operations are allowed on the
objects/resources)
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Role-Based Access Control (V)

Role-Based Access Control (RBAC) Model
U
User
User
Assignment
UA
R
Role
Permission
Assignment
PA
P
Permission
Figure: Basic RBAC Model
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Role-Based Access Control (VI)

Role-Based Access Control (RBAC) Model
- U, R and P are the users, roles and permissions respectively
- UA is a many-to-many user to role assignment relation
U𝑨 ⊆ 𝑼 × 𝑹
- PA is a many-to-many permission to role assignment relation
P𝑨 ⊆ 𝑷 × 𝑹
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Role-Based Access Control (VII)

Role-Based Access Control (RBAC): ESP Submissions (Assignments)
- user-role and role-permission assignments (policies)
Table: Relationships among users, roles and permissions
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User
Role
Permission
<s7021046, ******>
Student
<Assignment2, submit>
<akayes, ******>
Tutor/Marker
<Assignment2, marking>
<acolman, ******>
Lecturer/Convenor <Assignment2, marks release>
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Role-Based Access Control (VIII)

Role-Based Access Control (RBAC): Role Hierarchy
- also called role inheritance
- for structuring roles to reflect an organization’s lines of authority and
responsibility
- the senior roles can inherit all permissions from the junior roles
- the senior roles can have permissions in addition to those inherited
from the junior roles
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Role-Based Access Control (IX)

Role-Based Access Control (RBAC): Role Hierarchy Example
- The lecturer role (senior role) can inherits all permissions from the
staff role (junior role)
- The lecturer role can have own permissions also
University
User
Student
UGS
Staff
PGS
Tutor
Lecturer
Figure: Role Hierarchy
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Role-Based Access Control (X)

Role-Based Access Control (RBAC): Other RBAC Concepts
- RBAC Session (users can create and terminate sessions, to
activate/deactivate roles)
- RBAC Constraints (predicates that can apply to the UA and PA
relations)
<Sandhu et al (RBAC96): http://dl.acm.org/citation.cfm?id=226710>
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© Swinburne University of Technology
Role-Based Access Control (XI)

Role-Based Access Control (RBAC): Patient Medical Records
Management
- user-role assignments
User
userID
Role
Jane
Jane00X
Registered Nurse RN00X
Mary
Mary00X
PP00X
Bob
Bob00X
Primary-care
Physician
Emergency
Doctor
ED00X
Specialist
Physician
SP00X
Physician
P00X
User-Role Assignments (UA)
<Jane00X, PP00X>
<Jane00X, ED00X>
<Mary00X, PP00X>
roleID
<Bob00X, RN00X>
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<Jane00X, SP00X>
© Swinburne University of Technology
Role-Based Access Control (XII)

Role-Based Access Control (RBAC): Patient Medical Records
Management
- role-permission assignments
Role -Permission Assignments (PA)
Permission <resource, operation>
<ED00X, <EHR, write>>
<Electronic Health Records (EHR), write>
<RN00X, <DMR, read>>
<daily medical records (DMR), read>
<P00X, <DMR, write>>
<Past Medical History (PMH), write>
<P00X, <PMH, write>>
<SP00X, <EHR, read>>
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Role-Based Access Control (XIII)

Role-Based Access Control (RBAC): Patient Medical Records
Management
- The specialist physician role (senior role) can inherits all permissions
from the physician role (junior role)
Healthcare
User
Nurse
Registered
Nurse
36
Physician
Nurse
Manager
Emergency
Doctor
Figure: An Excerpt of Healthcare Role Hierarchy
Specialist
Physician
Primary-care
Physician
© Swinburne University of Technology
Role-Based Access Control (XIV)
Role-Based Access Control (RBAC): Patient Medical Records
Management
UA
PA
Role
roleID
<Jane00X, PP00X>

Registered Nurse RN00X
Primary-care
Physician
PP00X
Emergency
Doctor
ED00X
Specialist
Physician
SP00X
Physician
P00X
<ED00X, <EHR, write>>
<RN00X, <DMR, read>>
<Jane00X, ED00X>
<P00X, <DMR, write>>
<Mary00X, PP00X>
<P00X, <PMH, write>>
<Bob00X, RN00X>
<SP00X, <EHR, read>>
<Jane00X, SP00X>
Physician
Emergency
Doctor
37
Primary-care
Physician
Specialist
Physician
© Swinburne University of Technology
Role-Based Access Control (XV)

Role-Based Access Control (RBAC): main part
Organization
Resource
Role
Operation
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Role-Based Access Control (XVI)

Advantages
 simplifies management of permissions
 effective/useful model in large-scale systems/domains

Disadvantages
 the user-role and role-permission assignments are static without
taking into account the dynamic attributes, such as the location of
users
 this makes a less effective solution in today’s open and dynamic
environments
39
© Swinburne University of Technology
Outline

What is Access Control?

Access Control Matrix and Access Control List

Role-Based Access Control
 User-Role Assignment
 Role-Permission Assignment

Attribute-Based Access Control

Context-Aware Access Control
 Context-Aware User-Role Assignment
 Context-Aware Role-Permission Assignment
40
© Swinburne University of Technology
Attribute-Based Access Control (I)
 Attribute-Based Access Control (ABAC)
- a new access control paradigm where access rights are granted to
users through the use of policies which combine attributes together
- the policies can use any type of attributes (user attributes, resource
attribute, etc.)
- it is a rule-based approach to access control, it does not use the
concept of a role
- the building blocks in the ABAC model are the attributes
- an ABAC policy specifies which constraints need to be satisfied
based on the attributes (e.g., user age is greater than 20) in order to
grant access to an object
41
© Swinburne University of Technology
Attribute-Based Access Control (II)
 Attribute-Based Access Control (ABAC)
- the formal definition of basic ABAC is composed of four parts: access
control related entities, attributes of entities, policy representation,
and policy evaluation
- entities – requestor (Req), resource (Res), action (Act), environment
(Env)
- attributes of entities (e.g., attributes of environment (Attr(Env)) – the
current date or time)
- policy specification – the definition of access control policies
- policy evaluation – the process of making an access decision based
on the security policy
<ABAC, http://www.mcs.anl.gov/uploads/cels/papers/P1367.pdf>
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Attribute-Based Access Control (III)
 Attribute-Based Access Control (ABAC): policy evaluation
- an access control decision is made by the evaluation function
(𝑃𝑖_𝑎𝑑𝑓() ), access control decision function, ADF
- it takes the attributes of the requestor, the resource, the action, the
environment as parameters
𝑷𝒊_𝒂𝒅𝒇() 𝐴𝑡𝑡𝑟 𝑅𝑒𝑞 , 𝐴𝑡𝑡𝑟 𝑅𝑒𝑠 , 𝐴𝑡𝑡𝑟 𝐴𝑐𝑡 , 𝐴𝑡𝑡𝑟 𝐸𝑛𝑣
= 𝒑𝒆𝒓𝒎𝒊𝒕 𝑜𝑟 𝒅𝒆𝒏𝒚
43
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Attribute-Based Access Control (IV)

eXtensible Access Control Markup Language (XACML)
- is the standard that implements attribute-based access control
- a standard XML-based protocol for access control policies
- suitable for a variety of application environments (e.g., Web-based)
- uses the attributes of subject, resource, action, and environment
- this framework contains PEP, PDP, PIP, and PAP
<OASIS XACML 3.0 (2013), http://docs.oasis-open.org/xacml/3.0/xacml-3.0core-spec-os-en.pdf>
44
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Attribute-Based Access Control (V)

eXtensible Access Control Markup Language (XACML): four main
components
- Policy Enforcement Point (PEP)
- Policy Decision Point (PDP)
- Policy Administration Point (PAP)
- Policy Information Point (PIP)
<OASIS XACML 3.0 (2013), http://docs.oasis-open.org/xacml/3.0/xacml-3.0core-spec-os-en.pdf>
45
© Swinburne University of Technology
Attribute-Based Access Control (VI)

XACML Data Authorization Framework
46
Figure: XACML Data Flow Diagram
<OASIS XACML 3.0 (2013), http://docs.oasisopen.org/xacml/3.0/xacml-3.0-core-spec-os-en.pdf> © Swinburne University of Technology
Attribute-Based Access Control (VII)

XACML Data Authorization Framework: when access request comes
from the access requesters (users)
- the PEP intercepts the access requests from users and sends the
requests to the PDP (through the context handler)
- the PDP makes access decisions according to the security policy
(policy set) written by the PAP
- the PDP uses the attributes of the subjects, the resources, and the
environment obtained by querying the PIP (via the context handler)
- the access decision given by the PDP is sent to the PEP(through the
context handler)
- the PEP sends either permitted or denied request to the users
according to the decision of PDP
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Attribute-Based Access Control (VIII)
 XACML
Implementation
 Domain-specific Inputs (from the requesters)
converted to
 XACML Request Context (.xml)
 XACML Policy (.xml)
 XACML Response Context (.xml)
converted to
 Domain-specific Outputs (back to the requesters)
48
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Attribute-Based Access Control (IX)

Language Model of XACML
Figure: XACML Context and Policy
49
<OASIS XACML 3.0 (2013), http://docs.oasis-open.org/xacml/3.0/xacml-3.0-core-spec-os-en.pdf>
© Swinburne University of Technology
Attribute-Based Access Control (X)

Advantages
 easy to implement/setup
 very useful model in small-scale systems/domains

Disadvantages
 when the number of users is high, the number of authorizations can
become extremely large, which complicates the administration tasks
 this brings high complexity of security administration and significant
cost of management of growing large-scale systems
 it does not provide adequate functionalities for dynamic access
permissions
50
© Swinburne University of Technology
Outline

What is Access Control?

Access Control Matrix and Access Control List

Role-Based Access Control
 User-Role Assignment
 Role-Permission Assignment

Attribute-Based Access Control

Context-Aware Access Control
 Context-Aware User-Role Assignment
 Context-Aware Role-Permission Assignment
51
© Swinburne University of Technology
Context-Aware Access Control (I)

Static Access Permissions
 AM
 ACL
 RBAC
 ABAC
 XACML
Dynamic access permissions (to dynamically make access control decisions)
The dynamic user-role and role-permission assignments
Access to medical records of patients should be dynamically controlled
depending on the location and request time of users. Normally, a
nurse that is not located in the hospital should not have access to
medical records of patients. Moreover, this access is allowed only
during her ward duty time, and knowing the relationship between
© Swinburne University of Technology
52 patient and nurse.
Context-Aware Access Control (II)
 RBAC
has become the most widely used access control model
 The
CAAC model adopts RBAC concepts and extends its
user-role and role-permission assignments
 CAAC
incorporates the dynamic attributes (context
information) into both user-role and role-permission
assignments
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© Swinburne University of Technology
Context-Aware Access Control (III)

CAAC Policy Framework
<A. S. M. Kayes, Jun Han, and Alan Colman, A Semantic Policy Framework for Context-Aware Access
Control Applications, TrustCom 2013, http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6680911&tag=1>
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Context-Aware Access Control (IV)

Dynamic Context-Aware Environments
 Shift from desktop environments to dynamic environments described
by Mark Weiser, where users need seamless access to various
resources at anytime from anywhere even when they are on the
move
 Pervasive/Ubiquitous environments
 Privacy and security of accessing resources/services is of greater
concern
 Context information
<Mark Weiser, Some computer science issues in ubiquitous computing, Comm. ACM
1993, http://dl.acm.org/citation.cfm?id=159617>
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© Swinburne University of Technology
Context-Aware Access Control (V)

Context Information and Context Awareness
 Dey, Context information is defined as any information that can be
used to characterize the situation of an entity and Context awareness
is the ability to use context information to provide relevant
information and/or services to the user
Our focus is “CAAC Model”
 Context-aware access control (CAAC), decision making based on the
context information, reauthorization of access if context changes
<Dey et al, A Conceptual Framework for Context-Aware Applications, PUC 2001,
http://www.tandfonline.com/doi/abs/10.1207/S15327051HCI16234_02#.U29vNfmSzzg>
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© Swinburne University of Technology
Context-Aware Access Control (VI)
 Application Scenario
Users from different locations
Organization
User
Resources
A Patient in
an Emergency
Health
Condition
Users from
different
devices
Users at
different times
57
Figure: User-to-Resource Access Scenario in Context-Aware Environments
© Swinburne University of Technology
Context-Aware Access Control (VII)

Application Scenario
A patient Bob who is in the emergency room due to a heart
attack. While not being Bob's usual treating physician, Jane, a
medical practitioner at the hospital, is required to treat Bob and
needs to access Bob's electronic health records from the
emergency room.
Resources
User
Patients’
Medical
Records
Healthcare
Figure: Healthcare Scenario
58
© Swinburne University of Technology
Context-Aware Access Control (VIII)

Application Scenario
After getting emergency treatment, Bob is shifted and has been
assigned a registered nurse Mary, who has regular follow-up
visits to monitor his health condition. Mary needs to access
several types of Bob's records (daily medical records and private
health records) from the general ward.
Resources
User
Patients’
Medical
Records
Healthcare
Figure: Healthcare Scenario
59
© Swinburne University of Technology
Context-Aware Access Control (IX)
 Application Scenario
Different users with
different roles from
different
environments for
different intentions
Privacy and
security
Resources
User
Patients’
Medical
Records
Healthcare
Figure: Healthcare Scenario
60
© Swinburne University of Technology
Context-Aware Access Control (X)

Main Challenges/Requirements
 (Req1) - representation of context entities and context information
relevant to access control (context model)
 (Req2) - inferring high-level context information from the available
information (reasoning model)
 (Req3) - incorporating dynamic contextual information into access
control policies (policy model)
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Context-Aware Access Control (XI)
62
Figure: CAAC Model
© Swinburne University of Technology
Context-Aware Access Control (XII)

CAAC Model Concepts (elements)
 Users(U) – a user is a human-being (who is a service requester)
interacting with a computing system, whose access request is being
controlled (e.g., Jane, Mary)
 Roles(R) – a role reflect user's job function within the organization
(e.g., healthcare domain)
 Resources(Res) – a resource is an object protected by access
control that represents the data/information container (e.g., patient’s
electronic health records)
 Operations(Op) - an operation is an action that can be executed on
the resources (e.g., read, write)
 Permissions(P) - permissions are the approvals to perform certain
operations on resources, by the users who initiate access requests
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Context-Aware Access Control (XIII)

CAAC Model Concepts (elements)
 Context Information(CI) – context Information used in an access
control decision is defined as any relevant information about the
state of an entity or the state of a relevant relationships between
entities (e.g., location of the patient, social or interpersonal
relationship between doctor and patient)
 Policies(Pol) – two sets of policies: the context-aware user-role
assignment policies and context-aware role-permission assignment
policies
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Context-Aware Access Control (XIV)
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Figure: CAAC Model
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Context-Aware Access Control (XV)

CAAC Model Concepts (relationships)
 Role Hierarchy(RH) – it supports the concept of role inheritance (like
RBAC). The role is considered in a hierarchical manner in that if a
permission assigned to a junior role, then it is also assigned to all the
senior roles of that role
 Resource Hierarchy(ResH) – the resource is also considered in a
hierarchical manner in that if a user has the right to access a
resource with the highest granularity level, then he also has the right
to access the lower granularity levels of that resource
 Operation Assignment(OpA) – each operation could be associated
with many resources, and for each resource could be granted to
many operations
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Context-Aware Access Control (XVI)

CAAC Model Concepts (relationships)
 Context-Aware User-Role Assignment(CAURA) – a many-to-many
mapping between a set of users and roles, when a set of dynamic
contextual conditions are satisfied
CAUR𝑨 ⊆ 𝑼 × 𝑹 × 𝑪𝑰
 Context-Aware Role-Permission Assignment(CARPA) – a many-
to-many mapping between a set of roles and permissions, when a
set of dynamic contextual conditions are satisfied
CARP𝑨 ⊆ 𝑹 × 𝑷 × 𝑪𝑰
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Context-Aware Access Control (XVII)
Context
Ontology
Policy
Ontology
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Figure: CAAC Model
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Context-Aware Access Control (XVIII)

Advantages
 dynamic access permissions (dynamic access control decision
making)
 dynamic user-role and role-permission assignments
 efficient model in today’s dynamic and context-aware environments

Disadvantages
 implementation efforts
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Review
 Access
Control
 AM
 ACL
 RBAC
 ABAC
 XACML
 CAAC
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Next
 Semantic
Web
 Semantic
Technology
 Ontology
Concept
 OWL,
DL and SWRL
 Ontology-Based Framework
 XACML-Based
 XACML
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for Access Control
Framework for Access Control
for RBAC
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Questions?
 ABAC, Core XACML – attribute-based
 RBAC – role-based
 CAAC –
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?
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Questions?
 ABAC, Core XACML – attribute-based
 RBAC – role-based
 CAAC – role-
and attribute-based
akayes@swin.edu.au
(dblp: A. S. M. Kayes)
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