Computer Security

Computer Security

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.

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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.

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Availability: prevents resources from being deleted or becoming inaccessible.

Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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Security Threats 

Error and omissions

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Fraud and theft

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Loss of physical and infrastructure support

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Hacker and cracker

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Malicious code and software

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Foreign government espionage Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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Malicious Programs  Virus

 Other

destructive programs

 Affecting

computer system

 Protecting

computer system Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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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

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File infecting virus

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Polymorphic virus

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Stealth virus

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Multipartite virus

Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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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.

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Trojan horse: it activates sometimes after a long time, can be in the emails or free downloaded software.

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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

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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 email.

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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

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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

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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

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Cryptography 

Secret key cryptography

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Public key cryptography

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Hash function

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Digital signature

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Firewall

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Users identification and authentication

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Security awareness and policies

Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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Cryptography Techniques 

Secret key cryptography

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Public key cryptography

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Hash functions

Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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Secret Key Cryptography •

Single key used to encrypt and decrypt.

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Key must be known by both parties.

Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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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

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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

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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

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Digital Signature • Public key cryptography is also used to provide digital signatures. plaintext

signing

signed message

private key signed message

verification

plaintext

public key

Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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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

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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

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How does a software firewall work? 

Inspects each individual “packet” of data as it arrives at either side of the firewall

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Inbound to or outbound from your computer

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Determines whether it should be allowed to pass through or if it should be blocked

Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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Firewall Rules 

Allow – traffic that flows automatically because it has been deemed as “safe” (Ex. Meeting Maker, Eudora, etc.)

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Block – traffic that is blocked because it has been deemed dangerous to your computer

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Ask – asks the user whether or not the traffic is allowed to pass through Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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What a personal firewall can do 

Stop hackers from accessing your computer

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Protects your personal information

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Blocks “pop up” ads and certain cookies

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Determines which programs can access the Internet Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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What a personal firewall cannot do 

Cannot prevent e-mail viruses  Only

an antivirus product with updated definitions can prevent e-mail viruses

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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

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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

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Application-Level Gateway

pplication 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

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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

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Users Identification and Authentication There are three ways of authenticating users identity: 

Users requirement (Pin, Password, cryptographic key)

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Users possessions (ATM card or smart card)

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Users Biometric (Voice pattern, handwriting dynamics, fingerprints)

Nidhi Gautam Prabhakar, Assistant Professor, UIAMS, Panjab University Chandigarh

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Security Awareness and Policies   

Awareness 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

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