CS 483 – SD SECTION (8) AUTHORIZATION

INTRODUCTION The authorization (or access control) process is used to decide if person, program or device X is allowed to have access to data, functionality or service Y. The authorization is usually after a successful authentication. In this chapter, we will describe:  additional forms of Access Control  CAPTCHAs, which are designed to restrict access to humans  Firewalls, which view as a form of access control for networks  Intrusion Detection systems, which come into play when firewalls fail to keep the bad guys out

ACCESS CONTROL MATRIX The fundamental concepts in authorization are derived from Lampson’s access control matrix, which has a row for every subject and a column for every object Payroll Data Insurance Data Accounting Data Accounting Program OS --rrx Bob rw rrx Alice rw rrwx Sam rrw rx acct. program

ACCESS CONTROL MATRIX Problem: dealing with a large matrix Solution: spilt it into manageable pieces using one of the two fundamental concepts in authorization : 2. Capabilities (C-lists) Split the matrix into its rows and store each row with it corresponding subject 1. Access Control Lists (ACLs) Split the matrix into its columns and store each column with it corresponding object Payroll Data Insur. Data Ac. Data Ac. Prog. OS --rrx Bob rw rrx Alice rw rrwx Sam rrw rx acct. Payroll Data Insur. Data Ac. Data Ac. Prog. OS --rrx Bob rw rrx Alice rw rrwx Sam rrw rx acct.

CONFUSED DEPUTY Problem:  Alice and Bob has the same privilege to invoke the compiler.  The complier has a privileges (rw) to access Bill when Alice invokes the compiler, while the complier has a privileges (r only) to access Bill when Bob invokes the compiler. Solution:  Use C-lists

ACL’s vs. C-List

MULTILEVEL SECURITY MODELS (MLS) These models tell us what to be protected. MLS systems are designed to restrict legitimate channels of communication. In MLS subjects are the users and the object are the data. Classification apply to object while clearances apply to subjects.  For example US. DoD separate their employs into four levels: (TOP SECRET > SECRET > CONFIDENTIAL > UNCLASSIFIED) MLS is needed when subjects and objects at different levels and use the same system resources.

CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart). CAPTCHA is a test that a human can pass, but a computer can’t pass with a probability better than guessing. This test is the “gold standard” in artificial intelligence. If attackers are able to break such CAPTCHAs, they have solved a hard AI problem.

FIREWALLS The firewall examines requests to access the network, and it decides whether they pass a reasonableness test. A firewall acts like a lot like a secretary for your network. There is no standard firewall terminology. The classification of firewalls:  A packet filter is a firewall that lives at the network layer.  A stateful packet filter is a firewall that operates at the transport layer.  An application proxy is a firewall that operates at the application layer where it functions as a proxy.

INTRUSION DETECTION Authentication can be viewed as a way to prevent intrusions, and firewalls are certainly a form of intrusion prevention, as are most types of virus protection The primary focus of computer security is intrusion prevention, where the goal is to keep bad guys out of your system or network There are essentially only two methods of intrusion detection:  Signature-based IDSs attempt to detect attacks based on known “signatures” or patterns. This is analogous to signature-based virus detection.  Anomaly-based IDSs attempt to define a baseline, or normal, behavior of a system and provide a warning whenever the system strays too far from this baseline.