ACCESS CONTROL
William Newton

May 2, 2007
University of Maryland, Baltimore County

What is access control?

“Access control includes authentication,
authorization and audit. It also includes measures
such as physical devices, including biometric scans
and metal locks, hidden paths, digital signatures,
encryption, social barriers, and monitoring by
humans and automated systems.”
Wikipedia

What is access control?

Something you know

Passwords

“Perfect Passwords” by M. Burnett & D.
Kleiman

Something you are

Fingerprint, Iris, Face

Something you have


Token, RFID, Key

Something you know

Passwords

Most passwords can be guessed or cracked

Password policies frustrate users.

Administrators give users a default password

U2n*9kh!

Passwords that follow company procedures are
hard to remember….or are they? Be creative!

Categorize your passwords

Consider a policy that requires a 15 character
password with a character from each character
set:



Something you are

Biometrics


False positives – bad
guy positively
identified as a good
guy

False negatives –
good guy is not
recognized at all

Fingerprint technology
becoming a standard
feature.

Something you have

Physical

Token

Radio Frequency Identification (RFID)

RFID Implants

Problem: Physical security and Replay
Attacks

Shmoocon 2006 – Adam Laurie:
“RFIDiots”

Access Control Approaches


Discretionary Access Control (DAC)

Mandatory Access Control (MAC)

Context-Based Access Control (CBAC)

Role-Based Access Control (RBAC)

Lattice-Based Access Control (LBAC)

Discretionary Access Control

Restrict access to objects based on
the owner of the objects

Bob owner of money.txt

Bob can grant read privileges to Alice to
money.txt.

Security Concern – Buffer Overflow
attack to spawn a shell with root
privileges

Mandatory Access Control

Restrict access to an object based on
the classification of the object.


Policy restricts access

Various levels of control

Disallow programs to open sockets

Render “root” useless

Associate a role to every subject

Buffer Overflow attack for root (or any
other user)

Context-Based Access Control

Filters traffic through a network interface
(Firewall)

Analyze information at the network,
transport, and application layers.

Ex: TCP use multiple channels to handle
connection setup and communications.

Provides: DoS, alerts, auditing, blocking

Role Based Access Control

Roles created for specific functions


Permissions are associated to each
role

Not concerned with object context

Subjects may have access to several
roles [many-to-many relationship]

System management becomes easier

Four RBAC Models

Role Based Access Control

Four models

Core – minimum collection of RBAC elements,
element sets, and relations

Hierarchical – mathematical partial ordering
which defines a hierarchical relationship
between roles

Static Separation of Duty Relations (SSDR) –
Exclusivity relations among roles

Dynamic Separation of Duty Relations (DSDR) –
Multiple roles, but one at a time

RBAC – Core Model


minimum collection of RBAC elements,
element sets, and relations
Image Borrowed From: “Proposal for Fast-Tracking NIST Role-Based Access Control
Standard” by Ferraiolo, Kuhn, and Sandhu

RBAC – Hierarchical Model

mathematical partial ordering which defines a
hierarchical relationship between roles
Image Borrowed From: “Proposal for Fast-Tracking NIST Role-Based Access Control
Standard” by Ferraiolo, Kuhn, and Sandhu

RBAC - SSDR
Static Separation of Duty Relations

Exclusivity relations among roles
Image Borrowed From: “Proposal for Fast-Tracking NIST Role-Based Access Control
Standard” by Ferraiolo, Kuhn, and Sandhu

RBAC - DSDR
Dynamic Separation of Duty Relations
Image Borrowed From: “Proposal for Fast-Tracking NIST Role-Based Access Control
Standard” by Ferraiolo, Kuhn, and Sandhu

Lattice-Based Access Control

Information flow is
controlled from one
security class to

another.

Based around a
security model (Bell
LaPadula Model,
Biba Model)

Lattice-Based Access Control

Partial ordering over a set of element

Notation:

b dominates a

System High – One element dominates all the
elements in the set

System Low – One element that is dominated by all
the elements in the set

Lattice-Based Access Control
Image borrowed from “Computer Security” by Dieter Gollmann

Lattice-Based Access Control
Image borrowed from “Computer Security” by Dieter Gollmann

Bell LaPadula Model

Simple Security property (SS) – (No read up): The

classification of the object must be no higher than
the classification of the subject for reading
operations.

*-property – (No write down): The classification of
the object must be no lower than the classification
of the subject for writing operations.

Discretionary Security property (DS) – An access
matrix is used for DAC

A state is secure if all three properties are satisfied.

Biba (Integrity) Model

Simple integrity property – (No write up):
The classification of the subject must be at
most the classification of the object for
writing operations.

*-property – (No read down): The
classification of the subject must be at least
the classification of the object for read
operations.

Other Security Models

Harrison-Ruzzo-Ullman Model

Authorization system that allows changing of access

rights in a matrix and the creation/deletion of
subjects/objects.

Chinese Wall Model

Used in consulting firms

Restricts information across channels that causes a
conflict of interest

Clark-Wilson Model

Models data integrity and concurrency control in
commercial applications.

Access Control Structures

Definitions:

S  set of subjects

O  set of objects

A  set of access operations

Access Control Matrix (ACM)

M = (M
so
)

s in S, o in O
with M
so

Capabilities

By Subject

Access Control List (ACL)

By Object

Intermediate Controls

Used to implement the ACM in large
complex systems

Groups & Negative Permissions

Protections Rings

Abilities (Partial Ordering)

Data structure that starts with a “.” followed
by a list of integers separated by “.”s.

Ex: .5.4.3, .4.3.2.1, .2.1

Privileges