lecture 7 access control modified from slides of lawrie brown
TRANSCRIPT
Lecture 7Access Control
modified from slides of Lawrie Brown
Access Control
• ITU-T Recommendation X.800 definition: – “The prevention of unauthorized use of a resource,
including the prevention of use of a resource in an unauthorized manner.”
• RFC 2828 defines computer security as:– “Measures that implement and assure security
services in a computer system, particularly those that assure access control service”.
Access Control Principles
Verification that the credentials of a user or an entity are valid.
Granting of a right or permission to an entity to access a system resource.
An independent review and examination of system records and activities
Access Control Policies• dictates
– what types of access are permitted, – under what circumstances, – by whom.
based on the identity of the requestor and on access rules
based on comparingsecurity labels with clearances
based on the roles and their accesses
Attribute-based access controlbased on attributes of the user, the resource to be accessed, and current environmental conditions
Access Control Requirements
• reliable input• support for fine and coarse specifications• least privilege• separation of duty• open and closed policies• policy combinations and conflict resolution• administrative policies• dual control
Access Control Basic Elementssubject entity
capable of accessing objects
•concept equates with that of process•typically held accountable for the actions they initiate
•often have three classes: owner, group, world
object resource to
which access is controlled
•entity used to contain and/or receive information
•protection depends on the environment in which access control operates
access right: the way in
which a subject may access an
object
•e.g. read, write, execute, delete, create, search
Discretionary Access Control
• scheme in which an entity may enable another entity to access some resource– often provided using an access matrix
• one dimension consists of identified subjects that may attempt data access to the resources
• the other dimension lists the objects that may be accessed
– each entry in the matrix indicates the access rights of a particular subject for a particular object
Access Matrix
Example of Access Control Structures
Authorization Table
Extended Access Control Matrix
Access Control
Function
Access Control System
Commands
Protection Domains
• set of objects together with access rights to those objects
• more flexibility when associating capabilities with protection domains
• in terms of the access matrix, a row defines a protection domain
• user can spawn processes with a subset of the access rights of the user
Protection Domains
• association between a process and a domain can be static or dynamic
• in user mode certain areas of memory are protected from use and certain instructions may not be executed
• in kernel mode privileged instructions may be executed and protected areas of memory may be accessed
UNIX File Access Control
• control structures with key information needed for a particular file
• several file names may be associated with a single inode• an active inode is associated with exactly one file• file attributes, permissions and control information are
sorted in the inode• on the disk there is an inode table, or inode list, that
contains the inodes of all the files in the file system• when a file is opened its inode is brought into main memory
and stored in a memory resident inode table
UNIX files are administered using inodes (index nodes)
• may contain files and/or other directories• contains file names plus pointers to associated inodes
directories are structured in a hierarchical tree
UNIX File Access Control• unique user identification
number (user ID)• member of a primary group
identified by a group ID– belongs to a specific group– 12 protection bits
• specify read, write, and execute permission for owner of file, members of group, and all other users
– owner ID, group ID, and protection bits are part of file’s inode
Traditional UNIX File Access Control
• “set user ID”(SetUID)
• “set group ID”(SetGID)– system temporarily uses rights of the file owner /
group in addition to the real user’s rights when making access control decisions
– enables privileged programs to access files / resources not generally accessible
Traditional UNIX File Access Control
• sticky bit – when applied to a directory it specifies that only
the owner of any file in the directory can rename, move, or delete that file
• superuser – is exempt from usual access control restrictions– has system-wide access
Access Control Lists (ACLs) in UNIX
• modern UNIX systems support ACLs– FreeBSD, OpenBSD, Linux, Solaris
• FreeBSD– Setfacl assigns a list of UNIX user IDs and groups– any number of users and groups can be associated
with a file– read, write, execute protection bits– a file does not need to have an ACL– includes an additional protection bit that indicates
whether the file has an extended ACL
Access Control Lists (ACLs) in UNIX
• when a process requests access to a file system object two steps are performed:– step 1: selects the most appropriate ACL
• owner, named users, owning / named groups, others
– step 2: checks if the matching entry contains sufficient permissions
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Mandatory Access Control (MAC)
Unclassified
Confidential
Secret
Top Secret
can-flowdominance
Labeling Mechanism is used
Military Security
Require a strict classification of subjects and objects in security levels
Drawback of being too rigid
Applicable only to very few environments
Prevent any illegal flow of information through the enforcement of multilevel security
Adopted from : Role-Based Access Control by Prof.Ravi Sandhu
Compartments and Sensitivity Levels
Unclassified
Restricted
Confidential
Secret
Top SecretCompartment 1
Compartment 3Compartment 2
• Information access is limited by the need-to-know• Compartment: Each piece of classified information
may be associated with one or more projects called compartments
Classification & Clearance
• <rank; compartments>– class of a piece of information
• Clearance: an indication that a person is trusted to access information up to a certain level of sensitivity
• <rank; compartments>– clearance of a subject
Dominance Relation
• We say that s dominates o (or o is dominated by s) if o <= s
For a subject s and an object o,o <= s if and only if
rank(o) <= rank(s) andcompartments(o) is subset of
compartments(s)
• A subject can read an object if the subject dominates the object.
Example
• Information classified as <secret; {Sweden}>
• Which of the following subject clearances can read the above information?– <top secret; {Sweden}>– <secret; {Sweden, crypto}>– <top secret; {crypto}>– <confidential; {Sweden}>– <secret; {France}>
Role-Based Access Control
(RBAC)
AccessControlMatrix
Role-Based Access Control
ROLES
Usrer-RoleAssignment
Permission-RoleAssignment
USERS PERMISSIONS
...Sessions
Role Hierarchies
• Users are human beings or other active agents• Business function the user perform is role• A user can be a member of many roles• Each role can have many users as members• A user can invoke multiple sessions• In each session a user can invoke any subset
of roles that the user is a member of
• A permission can be assigned to many roles
• Each role can have many permissions‐ read, write, append, execute
Health-Care Provider
Physician
Primary-CarePhysician
SpecialistPhysician
Adopted from : Role-Based Access Control by Prof.Ravi Sandhu
Role-Based Access Control
Scope RBAC Models
Example of Role Hierarchy
Constraints - RBAC
• provide a means of adapting RBAC to the specifics of administrative and security policies of an organization
• a defined relationship among roles or a condition related to roles
mutually exclusive roles
• a user can only be assigned to one role in the set (during a session or statically)
• any permission can be granted to only one role in the set
cardinality
• setting a maximum number with respect to roles
prerequisite roles
• dictates that a user can only be assigned to a particular role if it is already assigned to some other specified role
RBAC System
administrative functions
• provide the capability to create, delete, and maintain RBAC elements and relations
supporting system
functions
• provide functions for session management and for making access control decisions
review functions
• provide the capability to perform query operations on RBAC elements and relations
NIST RBAC Basic Definitions
• object– any system resource subject to access control,
such as a file, printer, terminal, database record• operation
– an executable image of a program, which upon invocation executes some function for the user
• permission– an approval to perform an operation on one or
more RBAC protected objects
NIST RBAC Model
Core RBACadministrative
functions• add and delete
users from the set of users
• add and delete roles from the set of roles
• create and delete instances of user-to-role assignment
• create and delete instances of permission-to-role assignment
supporting system functions• create a user
session with a default set of active roles
• add an active role to a session
• delete a role from a session
• check if the session subject has permission to perform a request operation on an object
review functions
• enable an administrator to view but not modify all the elements of the model and their relations
Hierarchical RBAC
general role hierarchies
allow an arbitrary partial ordering of the role hierarchy
supports multiple inheritance, in which a role may inherit permissions from multiple
subordinate roles and more than one role can inherit from
the same subordinate role
limited role hierarchies
impose restrictions resulting in a simpler tree structure
role may have one or more immediate ascendants
but is restricted to a single immediate descendant
Static Separation of Duty• enables the definition of a set of mutually exclusive
roles, – if a user is assigned to one role in the set, the user may not be
assigned to any other role in the set
• can place a cardinality constraint on a set of roles– defined as a pair (role set, n) where no user is assigned to n or
more roles from the role set
• includes administrative functions for creating and deleting role sets and adding and deleting role members
• includes review functions for viewing the properties of existing SSD sets
Dynamic Separation of Duty• limit the permissions available to a user
– places constraints on the roles that can be activated within or across a user’s sessions
• define constraints as a pair (role set, n) with the property that no user session may activate n or more roles from the role set– where n is a natural number n ≤ 2
• enables the administrator to specify certain capabilities for a user at different, time spans
• includes administrative and review functions for defining and viewing DSD relations
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Task Based Access Control
P – PermissionS – SubjectO – ObjectA – ActionsU – Usage and Validity CountsAS – Authorization step
• Active Security Model• Dynamic authorization gives flexibility• No Roles Involved• Constraints for this model is still under
study
• For each authorization step consumes permission, usage count is incremented
• Usage Count reaches its limit, the associated permission is deactivated
Adopted from Source: Task based authorization controls by R.S.Sandhu and R.K.Thomas
Classical subject-object access control P S x O x A
TBAC view of access control P S x O x A x U x AS
TBAC extensions
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Constraints
Users are not given more permission than is necessary to perform their duties
Constraints
User Instance
Tasks Permissions
Task constraints – Least Privilege
Achieved through task instances
Alice Check Patient Josh
Access Permissions starts when the instance is initiated
Access Permissions end when the instance is completed or revoked
Fine Grained Access Control
Initiated
Active
Completed Revoked
status
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WorkflowUsers
Alice
Bob
Tasks
Check Patient
Do Physical Exam
Non-Workflow
Workflow
Start
Do Physical Exam (T1)
Check Patient (T2)
Perform Lab Test (T3)
View Lab Results (T4)
Write Prescription (T5)
Refer another specialist (T6)
End
Out Patient Workflow
Non-WorkflowView Current Patient List
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Passive and Active Access Control
Start
Do Physical Exam (T1)
Check Patient (T2)
Perform Lab Test (T3)
View Lab Results (T4)
Write Prescription (T5)
Refer another specialist (T6)
End
Workflow
Physician Write Prescription
View Current Patient List
File 2
File 1Read
Write
Passive Access
Active Access
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Spatial and Temporal Constraints
• Accessed from anywhere and at anytime– User’s location and time is taken into
consideration for granting access to a task
Family Practice
Physician
Nurse
Location Constraint
(Reno Office)
Time Constraint
(8 - 5)
Tasks
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Static and Dynamic Separation of Duty
No single individual can execute all tasks within the workflowDo Physical Exam (T1)
Check Patient (T2)
Perform Lab Test (T3)
View Lab Results (T4)
Write Prescription (T5) End
Start
Alice Check Patient JoshTask Instance 1
Protects against fraudulent activities of users
Static SOD - Defining the tasks in workflow or non workflow govern the administration or design-time associations between users and permissions.Dynamic SOD - permissions or task instances are granted at run-time.
Nurse Physician Technician Physician
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Delegation of TasksInitially assigned user is not available to complete the task
Supervisor can delegate task to another junior user in the same hierarchy
Access rights revoked once the task is completed
Alice Check Patient JoshTask Instance
Physician (Alice)
Physician (Bob)
Senior Physician
(Jan)
Bob Check Patient JoshTask Instance
Jan can delegate task to Bob
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Classification of TasksNon-Inheritable Inheritable
Passive Access Control Private Supervision
Active Access control Workflow Approval
Class Private
Class Supervision
Start
Do Physical Exam (T1)
Check Patient (T2)
Perform Lab Test (T3)
View Lab Results (T4)
Write Prescription (T5)
Refer another specialist (T6)
End
View Current Patient List
Family Practice
Physician (Alice)
Senior Physician
(Jan)
Workflow
Diagnosis Details
Non-Inheritable InheritablePassive Access Control Private SupervisionActive Access control Workflow Approval
Class WorkflowClass Approval
Classification of Tasks
Start
Do Physical Exam (T1)
Check Patient (T2)
Perform Lab Test (T3)
View Lab Results (T4)
Write Prescription (T5)
Refer another specialist (T6)
End
Workflow
Check Patient
Family Practice
Physician (Alice)
Senior Physician
(Jan)
Physician (Alice)
Physician (Bob)
Senior Physician
(Jan) Same Hierarchy
Attribute Based Access Control
Subject attributes
• A subject is an active entity that causes information to flow among objects or changes the system state
• Attributes define the identity and characteristics of the subject
Object attributes
• An object (or resource) is a passive information system-related entity containing or receiving information
• Objects have attributes that can be leverages to make access control decisions
Environment attributes
• Describe the operational, technical, and even situational environment or context in which the information access occurs
• These attributes have so far been largely ignored in most access control policies
ABACDistinguishable because it
controls access to objects by evaluating rules against the
attributes of entities, operations, and the
environment relevant to a request
Relies upon the evaluation of attributes of the subject,
attributes of the object, and a formal relationship or
access control rule defining the allowable operations for
subject-object attribute combinations in a given
environment
Systems are capable of enforcing DAC, RBAC, and
MAC concepts
Allows an unlimited number of attributes to be combined to satisfy any access control
rule
ABAC Scenario
ACL Trust Chain (NIST)
ABAC Trust Chain (NIST)
ABAC Policies• A policy is a set of rules and relationships that govern
allowable behavior within an organization, – based on the privileges of subjects and how resources or
objects are to be protected under which environment conditions
– Typically written from the perspective of the object that needs protecting and the privileges available to subjects
• Privileges represent the authorized behavior of a subject and are defined by an authority and embodied in a policy– rights, authorizations, and entitlements
Identity, Credential, and Access Management
• A comprehensive approach to manage and implement digital identities, credentials, and access control– Developed by the U.S. government
• Designed to:– Create trusted digital identity representations of individuals
and nonperson entities (NPEs)– Bind those identities to credentials that may serve as a proxy
for the individual of NPE in access transactions• A credential is an object or data structure that authoritatively binds
an identity to a token possessed and controlled by a subscriber
– Use the credentials to provide authorized access to an agency’s resources
Identity Management• Concerned with assigning attributes to a digital identity and
connecting that digital identity to an individual or NPE– Goal is to establish a trustworthy digital identity that is independent of a
specific application or context
• Most common approach to access control for applications and programs is to create a digital representation of an identity for the specific use of the application or program– Maintenance and protection of the identity itself is treated as secondary to
the mission associated with the application– Final element is lifecycle management which includes:
• Mechanisms, policies, and procedures for protecting personal identity info• Controlling access to identity data• Techniques for sharing authoritative identity data with applications that need it• Revocation of an enterprise identity
Credential Management• The management of the life cycle of the credential
– E.g. smart cards, private/public cryptographic keys, digital certificates• Encompasses five logical components:
– An authorized individual sponsors an individual or entity for a credential to establish the need for the credential
– The sponsored individual enrolls for the credential• Process typically consists of identity proofing and the capture of biographic and
biometric data• This step may also involve incorporating authoritative attribute data, maintained by
the identity management component– A credential is produced
• Depending on the credential type, production may involve encryption, the use of a digital signature, the production of a smart card or other functions
– The credential is issued to the individual or NPE– A credential must be maintained over its life cycle
• Might include revocation, reissuance/replacement, reenrollment, expiration, personal identification number (PIN) reset, suspension, or reinstatement
Access Management• Deals with the management and control of the ways
entities are granted access to resources
• Covers both logical and physical access
• May be internal to a system or an external element
• Purpose is to ensure that the proper identity verification is made when an individual attempts to access a security sensitive building, computer systems, or data
Support elements for an enterprise-wide access control
• Concerned with defining rules for a resource that requires access control• Rules would include credential requirements and what user attributes, resource
attributes, and environmental conditions are required for access of a given resource for a given function
Resource management
• Concerned with establishing and maintaining the entitlement or privilege attributes that comprise an individual’s access profile
• These attributes represent features of an individual that can be used as the basis for determining access decisions to both physical and logical resources
• Privileges are considered attributes that can be linked to a digital identity
Privilege management
• Governs what is allowable and unallowable in an access transaction
Policy management
Identity Federation• Term used to describe the technology, standards,
policies, and processes that allow an organization to trust digital identities, identity attributes, and credentials created and issued by another organization
• Addresses two questions:– How do you trust identities of individuals from external
organizations who need access to your systems– How do you vouch for identities of individuals in your
organization when they need to collaborate with external organizations
Open Identity Trust FrameworkOpenID•An open standard that allows users to be authenticated by certain cooperating sites using a third party service
OIDF•OpenID Foundation is an international nonprofit organization of individuals and companies committed to enabling, promoting, and protecting OpenID technologies
ICF•Information Card Foundation is a nonprofit community of companies and individuals working together to evolve the Information Card ecosystem
OITF•Open Identity Trust Framework is a standardized, open specification of a trust framework for identity and attribute exchange, developed jointly by OIDF and ICF
OIX•Open Identity Exchange Corporation is an independent, neutral, international provider of certification trust frameworks conforming to the OITF model
AXN•Attribute Exchange Network is an online Internet-scale gateway for identity service providers and relying parties to efficiently access user asserted, permissioned, and verified online identity attributes in high volumes at affordable costs
Summary• access control
– prevent unauthorized users from gaining access to resources– prevent legitimate users from accessing resources in an unauthorized manner– enable legitimate users to access resources – subjects, objects, access rights– authentication, authorization, audit
• discretionary access controls (DAC)– controls access based on identity
• mandatory access control (MAC)– controls access based on security labels
• role-based access control (RBAC)– controls access based on roles
• task-based access control (TBAC)– controls based on task at hand
• attribute-based access control (ABEC)– Controls based on attributes