Access Control

Li Xiong

CS573 Data Privacy and Security

What is Access Control?

� Security Engineering by Ross Anderson, 2001

� Its function is to control which principles (persons, processes, machines, )) have access to which resources in the system –access to which resources in the system –which files they can read, which programs they can execute, and how they share data with other principles, and so on.

� Access control is pervasive

� OS (unix, windows), databases, Java

Night Club Example

� Authentication

� ID Check

� Access Control

� Over 18 - allowed in

� Over 21 - allowed to drink

� On VIP List - allowed to access VIP area

� Enforcement Mechanism

� Walls, Doors, Locks, Bouncers

Access control and other security services� Identification and Authentication – establishing and

verifying the identity of the user

� Something you know, such as a password or a personal identification number (PIN).

� Something you have, such as a smart card or � Something you have, such as a smart card or security token.

� Something you are, such as fingerprint, voice, retina, or iris characteristics.

� Where you are, for example on or off campus, inside or outside a company firewall

� Access control determines which subject can access what resources after identification and authentication

Access control and other security services

� Enforcement mechanisms

� Auditing – posteriori analysis of all the requests and activities of users in the system

� Deterrent – users may be discouraged from attempting violationsattempting violations

� Means to analyze users behavior to detect possible violations

Access control and other security services

Access control

� Access control mechanisms – low level software functions that can be used to implement a policy

� Access matrix model

Implementation approaches� Implementation approaches

� Access control policies – high level guidelines that determine how accesses are controlled

� Discretionary access control (DAC)

� Mandatory access control (MAC)

� Role based access control (RBAC)

� Attribute based access control (ABAC)

Access Matrix Model

� A set of subjects S

� A set of objects O

� A set of rights R

� An access control matrix� An access control matrix

� One row for each subject

� One column for each subject/object

� Elements are right of subject on an another subject or object

Access matrix

Implementation approaches

� Access control lists (ACLs)

� Capabilities

� Authorization relation or table

Access control lists (ACLs)

� Each object is associated with an ACL

� Storing the matrix in columns

� Modern OS typically take the ACL approach

Capabilities

� Each subject is associated with a capability list

� Storing the matrix in rows

Authorization relation

� Each row, or tuple, specifies one access right of a subject to an object

� Relational databases typically use it

Access control

� Access control mechanisms – low level software functions that can be used to implement a policy

� Access matrix model

Implementation approaches� Implementation approaches

� Access control policies – high level guidelines that determine how accesses are controlled

� Discretionary access control (DAC)

� Mandatory access control (MAC)

� Role based access control (RBAC)

Discretionary AC

� Restricts access to objects based solely on the identity of users who are trying to access them

� No restrictions on information flow

Name AccessTom YesJohn NoCindy Yes

ApplicationAccess List

Individuals Resources

database 1

database 3

database 2

Mandatory AC

� Governs access based on the classification of subjects and objects

� Assign a security level to all information – sensitivity of information

� Assign a security level to each user – security clearance� Assign a security level to each user – security clearance

� Military and government: Top secret (TS) > secret (S) > confidential (C) > unclassified (U)

� Access principles

� Read Down – a subject’s clearance must dominate the security level of the object being read

� Write Up – a subject’s clearance must be dominated by the security level of the object being written

�

Mandatory AC (cont)

� Information can only flow upwards or within the same class

Individuals Resources/Information

Database 1 DS

Database 3 C

Database 2 S

Write up

Read down

TS

C

S

U

Role-Based AC

� Governs the access based on roles

� Access authorizations on objects are specified for roles

� Users are given authorizations to adopt roles

� A user has access to an object based on the roles

Role-Based AC

Individuals Roles Resources

Role 1Database 1

Role 2

Role 3Database 3

Database 2

User’s change frequently, Roles don’t

Role-based Access Control Benefits� Authorization management – assigning users to roles

and assigning access rights to roles

� Hierarchical roles – Inheritance of privileges based on hierarchy of roles

� Least privilege – allow a user to sign on with least � Least privilege – allow a user to sign on with least privilege required for a particular task

� Separation of duties – no single user should be given enough privileges

� Object classes – objects can be grouped based on classifications

RBAC Reference Model (Sandhu ‘96)

� RBAC0, minimum requirement

� RBAC1, RBAC0 + role hierarchies

� RBAC2, RBAC0 + constraints

� RBAC3, RBAC1 + RBAC2� RBAC3, RBAC1 + RBAC2

Models Hierarchies Constraints

RBAC0 No No

RBAC1 Yes No

RBAC2 No Yes

RBAC3 Yes Yes

user_sessions session_roles

(UA)User Assign-

ment

(PA)PermissionAssignment

USERS OBSOPSROLES

PERMISSIONS

Core RBAC System

SESSIONS

USERS

Process

Person

Intelligent Agent

ROLES

A role is a job function with some associated semantics regarding responsibility and authority (permissions).

DeveloperBudgetManager

Help Desk Representative

Director

MTM relation betweenUSERS & PRMS

Permissions

� A permission is an approval of a particular access to one or more objects

� Database – Update Insert Append Delete

� Locks – Open Close

SQL

� Locks – Open Close

� Reports – Create View Print

� Applications - Read Write Execute

UA (user assignment)

A user can be assigned to one or more roles

USERS set ROLES set

Developer

Help Desk Rep

A role can be assignedto one or more users

PA (permission assignment)

A prms can be assigned to one or more roles

PRMS set ROLES set

Create

Admin.DB1

A role can be assignedto one or more prms

User.DB1

ViewUpdateAppend

CreateDeleteDrop

SESSIONS

Each session is a mapping of one user to possibly many roles

USER SESSION

SQL

DB1.table1

FIN1.report1

APP1.desktop

(RH)Role Hierarchy

(UA)User Assign-

ment

(PA)PermissionAssignment

USERS OBSOPSROLES

Role Hierarchy RBAC

user_sessions session_roles

SESSIONS

PERMISSIONS

Tree Hierarchies

ProductionEngineer 1

Engineer 1

Quality Engineer 1

ProductionEngineer 2

Engineer 2

Quality Engineer 2

Engineering Dept

ProductionEngineer 1

Project Lead 1

Quality Engineer 1

Director

ProductionEngineer 2

Project Lead 2

Quality Engineer 2

Lattice Hierarchy

Project Lead 1

Director

Project Lead 2

ProductionEngineer 1

Engineer 1

Quality Engineer 1

Engineering Dept

ProductionEngineer 2

Engineer 2

Quality Engineer 2

(RH)Role Hierarchy

(UA)User Assign-

ment

(PA)PermissionAssignment

USERS OBSOPSROLES

SSD

Constrained RBAC

user_sessions session_roles

SESSIONS

PERMISSIONS

DSD

Static mutual exclusion constraints

� Two mutually exclusive roles: cannot both have the same user as members

� Two mutually exclusive roles: cannot both have the same permissions

� Two mutually exclusive permissions: one role cannot � Two mutually exclusive permissions: one role cannot have both permissions

Cardinality constraints

� On user-role assignment

� At most k users can belong to the role

� At least k users must belong to the role

� Exactly k users must belong to the role

Dynamic Constraints

� At most k users can activate the same role in one session

� No user is allowed to activate n or more roles in one sessionsession

Constraints with Role Hierarchies

� Two roles can be mutually exclusive only if neither one inherits the other

� If two roles are mutually exclusive, no roles can inherit from both

� If two roles are mutually exclusive, there can be no � If two roles are mutually exclusive, there can be no “root” or “super users”

Separation of Duty

� Constraints is a means rather than an end

� Separation of duty is the goal

� No single user possesses all the permissions needed to accomplish a sensitive taskto accomplish a sensitive task

� Permission assignment problem

Attribute based Access Control (ABAC)� Access control decisions are made based on a set of

characteristics, or attributes, associated with the requestor and/or the resource

� A requester provides a set of attributes, they are checked against permissible attributeschecked against permissible attributes

� E.g. a person in UltraMegaCorp tries to access an administration interface for customer data in Atlanta must present credentials with a division attribute of “customer relations division” and a title of “senior manager” and a location attribute of “Atlanta”

� No need for predefined list of roles or permissions

References

� Access control: principle and practice, Sandhu, 1994

� Role-based Access Control Models, Sandhu, 1996

Coming up

� Hippocratic databases

� Fine-grained access control

� Policy management and enforcement� Policy management and enforcement