Slide 1

Access Control Intro, DAC and MAC System Security

Slide 2

It is concerned with regulating how entities use resources in a system It consists of two main phases: Authentication: uniquely identifying entities Authorisation: assigning access rights to entities

Slide 3

Authentication Phase It is only concerned with identifying an entity against a known set Assigning a unique identifier to the entity (i.e., user name) Using a secret (supposedly) known only to the specific entity Alternatively, using a unique feature that characterizes the entity

Slide 4

Authorisation Phase Known also as Access Control The prevention of unauthorized use of a resource, including the prevention of use of a resource in an unauthorized manner It assumes users have been authenticated to the system assigned access rights to certain resources on the system (for instance, by an admin)

Slide 5

Access Control Requirements Reliable Input Authenticated entities Genuine information Least Privilege Entities granted minimum set of access rights Administrative Duties Only a special entity should be able to manage access rights for other entities

Slide 6

Access Control Refinements Separation of Duty Fine Vs. Coarse Specifications Open and Closed policies (Automated) Conflict Resolution

Slide 7

Access Control Elements Subject - entity that can access objects a process representing user/application Object - access controlled resource e.g. files, directories, records, programs etc Access right - way in which subject accesses an object e.g. read, write, execute, delete, create, search

Slide 8

Security Modules

Slide 9

Access Control Models Discretionary AC (DAC) Mandatory AC (MAC) Role-based AC (RBAC) Usage Control (UCON) Policy-based Access Control

Slide 10

Discretionary Access Control A means of restricting access to objects based on the identity of subjects and/or groups to which they belong. The controls are discretionary in the sense that a subject with a certain access permission is capable of passing that permission on to any other subject Subjects are able to assign rights to other subjects on the objects they control Model used in operating systems and DB management systems Often provided using an access matrix

Slide 11

Access Control Matrix

Slide 12

Access Control List

Slide 13

Capability List Capability Myths Demolished: http://srl.cs.jhu.edu/pubs/SRL2003-02.pdfhttp://srl.cs.jhu.edu/pubs/SRL2003-02.pdf

Slide 14

Access Matrix Details

Slide 15

UNIX Access Control Lists Modern UNIX systems support ACLs Can specify any number of additional users / groups and associated rwx permissions ACLs are optional extensions to std perms

Slide 16

Mandatory Access Control Entities cannot enable other entities to access their resources It enforces a lattice between labels assigned to subjects and object security labels: how sensitive or critical a system resource is security clearances: which entities are eligible to access certain resources

Slide 17

MAC: The Bell-LaPadula Model The main goal is to control the confidentiality of information

Slide 18

MAC Confidentiality Rules Simple Security Property: No Read-Up Read

Slide 19

MAC Confidentiality Rules *(Star)property: No Write-Down Write

Slide 20

MAC Confidentiality Rules Strong *(Star)-property: No Write-Down & No Write-up Write

Slide 21

MAC: Biba Integrity Model The main goal is to control the integrity of information

Slide 22

MAC Integrity Rules Simple Integrity Axiom: No Read Down Read

Slide 23

MAC Integrity Rules *(Star)-Integrity Axiom: No Write Up Write

Slide 24

Where is MAC used BLP: Implemented the multi-level security policy for US Department of Defense BIBA: Implemented in the FreeBSD MAC policy A combined versions of BLP and BIBA is used in Android

Slide 25

Summary Introduced access control principles subjects, objects, access rights Discretionary Access Control access matrix, access control lists (ACLs), capability tickets UNIX traditional and ACL mechanisms Mandatory Access Control Bell-Lapadula Biba

Slide 26

Resources Chapter 8 in Mark Stamp, Information Security: Principles and Practice, Wiley 2011. Matt Bishop, Computer Security: Art and Science, Addison- Wesley 2003.

Slide 27

Questions?