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Security
Security refers to providing a protection system to computer system resources such as
CPU, memory, disk, software programs and most importantly data/information stored in
the computer system. If a computer program is run by an unauthorized user, then
he/she may cause severe damage to computer or data stored in it. So a computer
system must be protected against unauthorized access, malicious access to system
memory, viruses, worms etc. We're going to discuss following topics in this chapter.
Authentication
One Time passwords
Program Threats
System Threats
Computer Security Classifications
Authentication
Authentication refers to identifying each user of the system and associating the
executing programs with those users. It is the responsibility of the Operating System to
create a protection system which ensures that a user who is running a particular
program is authentic. Operating Systems generally identifies/authenticates users using
following three ways −
Username / Password − User need to enter a registered username and password with
Operating system to login into the system.
User card/key − User need to punch card in card slot, or enter key generated by key
generator in option provided by operating system to login into the system.
User attribute - fingerprint/ eye retina pattern/ signature − User need to pass his/her
attribute via designated input device used by operating system to login into the system.
One Time passwords
One-time passwords provide additional security along with normal authentication. In
One-Time Password system, a unique password is required every time user tries to
login into the system. Once a one-time password is used, then it cannot be used again.
One-time password are implemented in various ways.
Random numbers − Users are provided cards having numbers printed along with
corresponding alphabets. System asks for numbers corresponding to few alphabets
randomly chosen.
Secret key − User are provided a hardware device which can create a secret id mapped
with user id. System asks for such secret id which is to be generated every time prior to
login.
Network password − Some commercial applications send one-time passwords to user on
registered mobile/ email which is required to be entered prior to login.
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Program Threats
Operating system's processes and kernel do the designated task as instructed. If a
user program made these process do malicious tasks, then it is known as Program
Threats. One of the common example of program threat is a program installed in a
computer which can store and send user credentials via network to some hacker.
Following is the list of some well-known program threats.
Trojan Horse − Such program traps user login credentials and stores them to send to
malicious user who can later on login to computer and can access system resources.
Trap Door − If a program which is designed to work as required, have a security hole in its
code and perform illegal action without knowledge of user then it is called to have a trap
door.
Logic Bomb − Logic bomb is a situation when a program misbehaves only when certain
conditions met otherwise it works as a genuine program. It is harder to detect.
Virus − Virus as name suggest can replicate themselves on computer system. They are
highly dangerous and can modify/delete user files, crash systems. A virus is generatlly a
small code embedded in a program. As user accesses the program, the virus starts getting
embedded in other files/ programs and can make system unusable for user
System Threats
System threats refers to misuse of system services and network connections to put
user in trouble. System threats can be used to launch program threats on a complete
network called as program attack. System threats creates such an environment that
operating system resources/ user files are misused. Following is the list of some well-
known system threats.
Worm − Worm is a process which can choked down a system performance by using system
resources to extreme levels. A Worm process generates its multiple copies where each
copy uses system resources, prevents all other processes to get required resources.
Worms processes can even shut down an entire network.
Port Scanning − Port scanning is a mechanism or means by which a hacker can detects
system vulnerabilities to make an attack on the system.
Denial of Service − Denial of service attacks normally prevents user to make legitimate use
of the system. For example, a user may not be able to use internet if denial of service
attacks browser's content settings.
Computer Security Classifications
As per the U.S. Department of Defense Trusted Computer System's Evaluation Criteria
there are four security classifications in computer systems: A, B, C, and D. This is
widely used specifications to determine and model the security of systems and of
security solutions. Following is the brief description of each classification.
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S.N. Classification Type & Description
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Type A
Highest Level. Uses formal design specifications and verification techniques. Grants
a high degree of assurance of process security.
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Type B
Provides mandatory protection system. Have all the properties of a class C2 system.
Attaches a sensitivity label to each object. It is of three types.
B1 − Maintains the security label of each object in the system. Label is used
for making decisions to access control.
B2 − Extends the sensitivity labels to each system resource, such as storage
objects, supports covert channels and auditing of events.
B3 − Allows creating lists or user groups for access-control to grant access or
revoke access to a given named object.
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Type C
Provides protection and user accountability using audit capabilities. It is of two types.
C1 − Incorporates controls so that users can protect their private information
and keep other users from accidentally reading / deleting their data. UNIX
versions are mostly Cl class.
C2 − Adds an individual-level access control to the capabilities of a Cl level
system.
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Type D
Lowest level. Minimum protection. MS-DOS, Window 3.1 fall in this category.
