Computer Networks, Cyber Security and Preventing Cyber Security Threats

Types of Network

  • A network is two or more devices connected together for sharing resources.

  • Three main types of networks:

    • Local Area Network (LAN)

    • Wide Area Network (WAN)

    • Personal Area Network (PAN)

Advantages of having a network:

  • Users can share resources like printers and internet connections.

  • Users can access files from any computer on the network.

  • Communication is easier via email and social networks.

  • Users can easily share files and folders, such as central databases and spreadsheets.

  • Servers can provide centralized backups, updates, and security.

Disadvantages of having a network:

  • Increased security risk to data.

  • Malicious software can infiltrate the network.

  • Servers and switches can be central points of failure.

  • Factors can impact network performance, such as the number of users and data.

Local Area Network (LAN)

  • Small geographical area (under 1 mile).

  • All hardware is owned by the company/organization/household.

  • Uses unshielded twisted pair (UTP) cable, fiber optic cable, or wireless connections (Wi-Fi).

Wide Area Network (WAN)

  • Large geographical area (over 1 mile).

  • A collection of LANs joined together.

  • Computers are connected via routers.

  • Hardware used to connect the networks may not be owned by the company/organization/household.

  • Uses fiber optic cable, telephone lines, and satellite to connect the LANs together.

Personal Area Network (PAN)

  • Used for data transmission between devices in close proximity.

  • Very short range (10 meters).

  • Bluetooth is the most widely used PAN.

  • Examples: wireless headphones, mobile phones, tablets, laptops.

Worked Example

  • (a) Wireless method for PAN: Bluetooth

  • (b) Differences between LAN and WAN:

    • LANs cover smaller geographical areas; WANs cover larger areas.

    • LANs are often owned by a single entity; WANs often have distributed ownership.

    • WANs are usually several LANs connected together.

    • WANs usually have more devices/users than LANs.

    • LAN has lower latency; WAN has higher latency.

    • WANs are usually slower than LANs.

    • The cost-per-byte for transmission is higher on a WAN.

    • LANs and WANs use different protocols.

Wired & Wireless Networks

Wired Networks

  • Use physical cables to join devices together.

  • Common types of cables:

    • Ethernet

    • Fiber optic

    • Copper

Ethernet

  • Wired networking standard for carrying electrical signals between devices on a LAN.

  • Common in offices and homes.

  • Uses twisted pair cables for duplex communication.

Fiber Optic

  • Uses light to transmit data on a WAN.

  • Higher speed and bandwidth compared to copper cables.

  • Not susceptible to interference, making it secure.

  • Can cover long distances without degradation.

Copper Cable

  • Originally used in telecommunication for voice signals.

  • Can deliver network traffic on a WAN.

  • Degrades over time, limiting range.

  • Susceptible to interference.

  • Slower data transfer rate and lower bandwidth compared to fiber optic.

Advantages & Disadvantages of Wired Networks

  • Advantages:

    • Speed: Fast data transfer.

    • Security: Better physical security.

    • Range: High (up to 100m), less susceptible to interference.

  • Disadvantages:

    • Portability: Limited by physical cable.

    • Cost: More cables are needed to add a new device.

    • Safety: Cables can be trip hazards.

Wireless Networks

  • Use radio waves to transmit data through the air.

  • Common types of wireless connections:

    • Wi-Fi

    • Bluetooth

Wi-Fi

  • Wireless fidelity.

  • Common in homes and offices.

  • Devices communicate with a wireless access point (WAP).

Bluetooth

  • Used for direct connections between two devices.

  • Common for headphones, controllers, keyboards, and mice.

Advantages and Disadvantages of Wireless Networks

  • Advantages:

    • Portability: Easy to move around, limited only by range.

    • Cost: Less expensive to set up and add new devices.

    • Compatibility: Most devices are manufactured with a built-in wireless adapter.

  • Disadvantages:

    • Speed: Slower data transfer than wired networks.

    • Security: Less secure than wired networks.

    • Range: Relies on signal strength to the WAP, signals can be obstructed (up to 90m).

Worked Example

  • Advantages of using a wireless network instead of a wired network:

    • Flexibility to expand the network/add users.

    • No need to drill holes or install cabling.

    • Mobility of users/devices.

    • Modern devices are more likely to connect wirelessly.

    • Guest access.

    • No trip hazards.

LAN Topologies

Network Topology

  • The physical structure of the network.

  • Defines how network hardware will be arranged.

  • Two popular topologies:

    • Star Topology

    • Bus Topology

Star Network Topology

  • Has a central switch to which all other devices connect.

  • The switch ensures traffic goes only to the intended device.

  • Common in homes, businesses, organizations, and schools.

Advantages of a Star Topology

  • If a single cable stops working, the rest of the network continues to work.

Disadvantages of a Star Topology

  • The central switch is a single point of failure.

    • If the switch fails, all connected devices lose network connectivity.

Bus Network Topology

  • All devices are connected to a single 'bus' cable, terminated at each end.

  • Terminators prevent signal bouncing and errors.

  • Devices 'listen' to electrical signals, check data packets for their address, and ignore unrecognized packets.

  • Largely replaced by more efficient topologies like the star topology.

Advantages of a Bus Topology

  • Easy and cheap to set up as only one cable is required.

  • Does not rely on other network hardware such as a central server/switch.

Disadvantages of a Bus Topology

  • Low security as data is seen by all devices on the network.

  • Slow data transfer and prone to data collisions.

  • If the cable breaks, the whole network is affected (central point of failure).

Network Protocols

Protocol Definition

  • A set of rules that govern communication on a network.

  • Different protocols for different purposes.

Examples of Protocols

  • Ethernet & Wi-Fi

  • TCP/IP & UDP

  • HTTP & HTTPS

  • FTP

  • IMAP & SMTP

Ethernet & Wi-Fi

Ethernet

  • A family of related protocols used in data communication/transfer on a wired local area network (LAN).

Wi-Fi

  • A family of related protocols used in data communication/transfer on a wireless local area network (LAN).

  • Wi-Fi is a trademark; the generic term is wireless local area network (WLAN).

TCP/IP & UDP

TCP/IP

  • Transmission Control Protocol (TCP) and Internet Protocol (IP).

  • Allows communication over the internet (WAN).

  • TCP ensures error-free communication between routers.

  • IP ensures data is delivered to the right device on a wide area network (WAN).

UDP

  • User Datagram Protocol.

  • An alternative to TCP to send data across a wide area network (WAN).

  • Faster than TCP but less secure and does not guarantee error-free transmission.

  • Used in activities where some data loss is acceptable (e.g., online gaming).

HTTP & HTTPS

HTTP

  • Hypertext Transfer Protocol.

  • Allows communication between clients and servers for website viewing.

  • Clients receive data from the server (fetching a webpage) and send data to the server (submitting a form, uploading a file).

HTTPS

  • Works the same way as HTTP but with an added layer of security.

  • All data sent and received is encrypted.

  • Used to protect sensitive information such as passwords, financial information, and personal data.

FTP

FTP

  • File Transfer Protocol.

  • Allows sending and receiving files between computers.

  • Uploading and downloading files to/from a web server.

  • Offers greater efficiency and support for bulk transfers and large files, such as resuming interrupted transfers.

  • FTP clients are software applications that use the FTP protocol to make the process easier for users.

IMAP & SMTP

  • A family of protocols that handle sending and receiving email across the internet (WAN).

SMTP

  • Simple Mail Transfer Protocol.

  • Allows communication between an email sender and the email server, and between different email servers using the internet.

IMAP

  • Internet Message Access Protocol.

  • A protocol for downloading emails to a device from an email server.

  • Once the email has been retrieved, a copy is retained on the mail server.

Worked Example

  • Purpose of HTTPS protocol:

    • Sending/receiving web pages using an encrypted connection.

    • Provides an encrypted version of HTTP.

    • Secure web transactions.

    • Authentication of the website being visited.

    • Encryption of the data between the server and the client.

    • Reduces the likelihood of man-in-the-middle attacks.

Network Security

The Need for Network Security

  • Sensitive data is increasingly stored on networks, making it a target for hackers.

  • Computer networks face a variety of threats.

Main Methods of Securing Networks

  • Authentication

  • Encryption

  • Firewalls

  • MAC address filtering

Authentication

Authentication Definition

  • The process of using credentials to check if a user is who they say they are.

  • Credentials typically include:

    • Usernames & passwords

    • ID badges

    • Access/security codes

    • Biometrics (fingerprints, retina, voice etc.)

  • Credentials are verified to see if they match what is stored by the system.

When Authentication is Used

  • Computer systems when data or services require approved access.

  • Examples:

    • Logging into networked computers (i.e., school, office etc.)

    • Accessing online services (i.e., banking, social media, entertainment streaming platforms etc.)

Encryption

Encryption Definition

  • A method of converting plaintext into ciphertext.

  • Uses complex mathematical algorithms to scramble the text.

  • Asymmetric encryption (private key, public key) is often used for web pages and other communication.

When Encryption is Used

  • Any situation where sensitive data is being transmitted across a network.

  • Examples:

    • Passwords

    • Bank details

    • Personal information

Firewalls

Firewall Definition

  • A barrier between a network and the internet.

  • Prevents unwanted traffic from entering a network by filtering requests.

  • Can be hardware and software, often used together to provide stronger security.

When Firewalls are Used

  • Hardware firewalls: protect a whole network.

  • Software firewalls: protect an individual device on the network.

MAC Address Filtering

MAC Address Filtering Definition

  • Using a device's MAC address to determine if it can connect to a network.

  • Devices with allowed MAC addresses are placed on a 'whitelist'; those not allowed are on a 'blacklist'.

  • If a device tries to connect and the MAC address is not on the list, the connection is refused.

  • A MAC address is a unique identifier embedded into a device during manufacturing.

When MAC Address Filtering is Used

  • Predominantly used on Wi-Fi networks to limit access to only devices on the 'whitelist'.

  • Only approved physical devices can connect to the network.

Worked Example

  • Security measure in addition to a password:

    • A code can be sent to your phone as a text message/email/pop-up for verification.

    • An authenticator app on a mobile phone can generate a code.

    • Use two-factor authentication (2FA)/multi-factor authentication requiring a second form of identification.

    • Biometrics: comparing reference data to individual biometric data.

    • Smart cards/fobs requiring insertion into a reader and PIN entry.

    • Security/memorable questions.

The Concept of Layers

Layer Concept

  • Networks rely on many complex parts working together.

  • Dividing network tasks into layers reduces complexity and makes each layer more manageable.

  • The TCP/IP protocol uses a 4-layer model known as a 'stack'.

Advantages of Layers

  • Layers are self-contained, making managing, repairing, and upgrading easier.

  • Layers allow focus on specific parts of a protocol without affecting other layers.

  • Promotes data exchange (interoperability) between hardware and software.

TCP/IP Model

TCP/IP Model Definition

  • Made up of two protocols (TCP & IP), containing 4 layers.

  • Works together to package, address, transmit, and receive data on a wide area network (Internet).

TCP/IP Layers

  • Application

  • Transport

  • Internet

  • Link

Layer Functions and Protocols

  • Application Layer:

    • Function: Application software operates here.

    • Protocols: HTTP, HTTPS, FTP, SMTP, IMAP

  • Transport Layer:

    • Function: Enables communication between two hosts to agree on settings.

    • Protocols: TCP, UDP

  • Internet Layer:

    • Function: Addresses and packages data for transmission; routes packets.

    • Protocol: IP

  • Link Layer:

    • Function: Physical network hardware is located here; OS device drivers.

Worked Example

  • Definition of a 'layer':

    • Breaking up a complex task into more manageable subtasks.

  • Advantage of using layers:

    • Self-contained.

    • Allows developers to concentrate on one aspect of the network.

    • A layer can be edited without affecting other layers.

    • Promotes interoperability between vendors and systems.

Cyber Security & Threats

Cyber Security Definition

  • Processes, practices, and technologies designed to protect networks, computers, programs, and data from attack, damage, or unauthorized access.

Main Cyber Security Threats

  • Social engineering techniques

  • Malicious code (malware)

  • Pharming

  • Weak and default passwords

  • Misconfigured access rights

  • Removable media

  • Unpatched and/or outdated software

Social Engineering

Social Engineering Definition

  • Exploiting weaknesses in a computer system by targeting the people that use or have access to them.

  • Manipulating people to give up confidential information.

Types of Social Engineering

  • Blagging (pretexting): Creating and using an invented scenario to engage a victim to divulge information.

  • Phishing: Sending fraudulent emails/SMS to gain access to details.

  • Shouldering: Observing a person's private information over their shoulder.

How to Protect Against Social Engineering

  • Proper training/education

    • What questions to ask to determine authenticity (blagging)

    • What to look for in an email/SMS (phishing)

    • Being aware of surroundings/location (shouldering)

Malware

Malware Definition

  • Malicious software created to cause harm to a computer system.

Issues Caused by Malware

  • Files being deleted, corrupted, or encrypted

  • Internet connection becoming slow or unusable

  • Computer crashing or shutting down

Types of Malware

  • Computer virus: replicates itself on a user's computer, causing unwanted events.

  • Trojan: disguises itself as legitimate software but contains malicious code.

  • Spyware: allows a person to spy on users' activities on their devices.

How to Protect Against Malware

  • Ensure code is written correctly

  • Keep anti-malware software up to date

  • Install a firewall

  • Educate users

Pharming

Pharming Definition

  • Redirecting a website address to a 'fake' website to trick users into entering sensitive information.

  • Altering DNS settings or changing the user's browser settings.

How to Protect Against Pharming

  • Keep anti-malware software up to date

  • Check URLs regularly

  • Make sure the padlock icon is visible

Weak Passwords

Weak Passwords Definition

  • Passwords with less than 8-12 characters and without a combination of uppercase, lowercase, numbers, and special characters.

How To Protect Against Weak Passwords

  • Use a 'strong' password regularly

  • Regularly change passwords

Access Rights

Access Rights Definition

  • Pre-determined levels of access for how a user can interact with resources on a computer system.

How to Protect Against Misuse of Access Rights

  • Grant minimum access rights unless proven to need more

Removable Media

Removable Media Definition

  • Secondary storage devices that are portable and allow the movement of data between computer systems.

How to Protect Against Removable Media

  • Restrict/block the use

  • Encryption

  • Training

Unpatched/Outdated Data

Unpatched/Outdated Definition

  • Software released in a less than perfect state with flaws/vulnerabilities that can provide an opportunity for hackers.

How to Protect Against Unpatched/Outdated Data

  • Ensure all software is kept up to date

Worked Example

  • Dangers of using a USB memory stick:

    • The USB memory stick could contain malware/virus/trojan/spyware, leading to:

      • The spread of malware to other networked devices

      • Files being deleted/corrupted/encrypted

      • Internet connection becoming slow or unusable

      • Computer crashing or shutting down

Methods of Preventing Cyber Security Threats

Penetration Testing

Penetration Testing Definition

  • Attempting to gain access to resources without knowledge of usernames, passwords, and other normal means of access.

  • Used to test network security and fix any issues found.

Types of Penetration Testing

  • Malicious insider (white-box): testing with knowledge of the system.

  • External attack: testing without knowledge of the system.

Biometric Measures

Biometric Measures Definition

  • Using an individual's personal characteristics to identify them.

Examples of Biometric Measures

  • Fingerprints

  • Iris/retina scans

  • Voice recognition

CAPTCHA

CAPTCHA Definition

  • A method of testing if a website request originates from a human or a machine (bot).

Examples of CAPTCHA

  • Text: Entering characters from a distorted text box

  • Image: Selecting images containing a specific object

  • Checkbox: Confirming they are not a robot

Confirming Identity

Confirming Identity Definiton

  • One method of confirming the identity of a user is to email a link to check that they are using a valid and working email address. A user does not get access to a service/website until the check is complete. This type of check can be carried out using SMS in the same way.

Automatic Software Updates

Automatic Software Updates Definition

  • Reduce the risk of software flaws/vulnerabilities being targeted in out of date software. Automatic updates ensure fast deployment of updates as they release.

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  • Worked Example
    Give three examples of when it would be suitable to use a CAPTCHA system [3]

  • Answer
    accountregistration

  • account access
    online voting systems

  • ticket purchasing / transaction completion on pages where comments / reviews can be posted

  • on parts of the website where fraudulent click-throughs may be possible