1. Computer Security

2. Computer Security
Computer Security refers to the protection given to computers and the information contained in them from unauthorised access. It involves the measures and controls that ensures confidentiality, integrity and availability of the information, processed and stored by a computer.
Confidentiality: ensures that information is available only to those persons who are authorised to access it.
Integrity: ensures that information cannot be modified in unexpected ways, as loss of integrity could result from human error, intentional tampering, or even catastrophic events.
Availability: prevents resources from being deleted or becoming inaccessible.
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

3. Security Threats Error and omissions Fraud and theft
Loss of physical and infrastructure support
Hacker and cracker
Malicious code and software
Foreign government espionage
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

4. Malicious Programs Virus Other destructive programs
Affecting computer system
Protecting computer system
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

5. Virus
Viruses are programs, which are designed to replicate, attach to other programs, and perform unsolicited and malicious actions. It executes when an infected program is executed. On MS-DOS systems, these files usually have the extensions .exe, .com, or .bat.
Boot sector virus
File infecting virus
Polymorphic virus
Stealth virus
Multipartite virus
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

6. Other destructive programs
Worms: use n/w connections to spread from one computer system, thus worms attack systems that are linked through communication lines. To reproduce itself it uses n/w links like: n/w mail facility, remote execution capability, and remote log in capability.
Trojan horse: it activates sometimes after a long time, can be in the s or free downloaded software.
Logic bomb: it’s a program which gets activated when a certain piece of code is executed i.e. date.
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

7. Affecting Computer System
How virus spreads: viruses come through many sources and because it is a software code, it can be transmitted with any other software, for example, on a disk, through network, or using .
System components affected by virus: two conditions can cause a virus to attack on the computer system i.e. executable file on the storage disk, write-enabled disk (floppy disk, hard disk).
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

8. Protecting Computer System
Using antivirus software:
antivirus software has normally built-in scanner, which scans all files in the computer’s hard disk. It looks for changes and activity in computers that are typical in case of a virus attack.
Scanners look for particular types of code within programs. The s/w generally relies on having prior knowledge of the virus. As a result, frequent updates to the tool are necessary.
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

9. Cryptography
The art of protecting information by transforming it (encrypting it) into an unreadable format, called cipher text.
Only those who possess a secret key can decipher (or decrypt) the message into plain text.
Encrypted messages can sometimes be broken by cryptanalysis, also called code breaking, although modern cryptography techniques are virtually unbreakable.
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 9 9

10. Cryptography Secret key cryptography Public key cryptography
Hash function
Digital signature
Firewall
Users identification and authentication
Security awareness and policies
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

11. Cryptography Techniques
Secret key cryptography
Public key cryptography
Hash functions
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 11

12. Secret Key Cryptography
Single key used to encrypt and decrypt.
Key must be known by both parties.
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 12 12

13. Public Key Cryptography (a.k.a. asymmetric cryptography)
Each entity has 2 keys:
private key (a secret)
public key (well known).
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 13 13

14. Hash Functions
A hash function H is a transformation that takes a variable-size input m and returns a fixed-size string, which is called the hash value h (that is, h = H(m)).
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 14

15. Digital Signature
Hash value of a message when encrypted with the private key of a person is his digital signature on that e-Document
Digital Signature of a person therefore varies from document to document thus ensuring authenticity of each word of that document.
As the public key of the signer is known, anybody can verify the message and the digital signature
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 15

16. plaintext signed message
Digital Signature
Public key cryptography is also used to provide digital signatures.
signing
plaintext signed message
private key
verification
signed message plaintext
public key
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 16 16

17. Firewall
A firewall is hardware, software, or a combination of both that is used to prevent unauthorized programs or Internet users from accessing a private network and/or a single computer
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 17

18. Hardware vs. Software Firewalls
Hardware Firewalls
Protect an entire network
Implemented on the router level
Usually more expensive, harder to configure
Software Firewalls
Protect a single computer
Usually less expensive, easier to configure
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

19. How does a software firewall work?
Inspects each individual “packet” of data as it arrives at either side of the firewall
Inbound to or outbound from your computer
Determines whether it should be allowed to pass through or if it should be blocked
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

20. Firewall Rules
Allow – traffic that flows automatically because it has been deemed as “safe” (Ex. Meeting Maker, Eudora, etc.)
Block – traffic that is blocked because it has been deemed dangerous to your computer
Ask – asks the user whether or not the traffic is allowed to pass through
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

21. What a personal firewall can do
Stop hackers from accessing your computer
Protects your personal information
Blocks “pop up” ads and certain cookies
Determines which programs can access the Internet
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

22. What a personal firewall cannot do
Cannot prevent viruses
Only an antivirus product with updated definitions can prevent viruses
After setting it initially, you can forget about it
The firewall will require periodic updates to the rule sets and the software itself
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

23. Packet Filters
It operates at the n/w layer to examine incoming and outgoing packets. A border router configured to pass or reject packets based on information in the header of each individual packet
can theoretically be configured to pass/reject based on any field
but usually done based on:
protocol type
IP address
TCP/UDP port
Fragment number
Source routing information
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

24. Application-Level Gateway
Application level gateway is an approach to firewall where the application specific proxies filter the incoming and outgoing information packets before copying and forwarding information across the gateway at the level of the application layer of the OSI Model. The application specific proxy means that, for instance, only a Telnet proxy can copy, forward, and filter Telnet traffic. An application gateway is generally implemented on a separate computer on the network whose primary function is to provide proxy service.
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 24

25. Circuit-Level Gateway
This type of proxy server provides a controlled network connection between internal and external systems (i.e., there is no "air-gap"). A virtual "circuit" exists between the internal client and the proxy server. Internet requests go through this circuit to the proxy server, and the proxy server delivers those requests to the Internet after changing the IP address. External users only see the IP address of the proxy server. Responses are then received by the proxy server and sent back through the circuit to the client. While traffic is allowed through, external systems never see the internal systems. This type of connection is often used to connect "trusted" internal users to the Internet
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 25

26. Users Identification and Authentication
There are three ways of authenticating users identity:
Users requirement (Pin, Password, cryptographic key)
Users possessions (ATM card or smart card)
Users Biometric (Voice pattern, handwriting dynamics, fingerprints)
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 26

27. Security Awareness and Policies
Security Policy
Components of security policy:
1. computer technology purchasing guidelines
2. privacy policy
3. access policy
4. accountability policy
5. authentication policy
6. information technology system and network maintenance policy
7. violations reporting policies
Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh 27