The primary purpose of encryption in protecting data transmitted over the internet is to ensure confidentiality, integrity, and authentication. Confidentiality means preventing unauthorized access to the data. Integrity ensures the data hasn't been altered during transmission. Authentication verifies the identity of the sender.

Symmetric encryption uses the same key for encryption and decryption. It's generally faster than asymmetric encryption. A real-world example is encrypting a file on a local computer using AES. It's efficient for encrypting large amounts of data when a secure channel already exists.

Asymmetric encryption uses a pair of keys – a public key for encryption and a private key for decryption. It's slower than symmetric encryption but provides stronger security. A real-world example is using HTTPS on a website. The website's public key is used to encrypt the session key, which is then used for symmetric encryption of the data transmitted between the browser and the server. This allows secure communication even if the private key isn't known.

Answer:

Role of Firewalls: Firewalls act as a barrier between a network and external networks (like the internet). They examine network traffic and block unauthorized access, protecting the internal network from threats. They are a fundamental component of network security.

Packet Filter Firewall:

• Description: Examines individual network packets based on source and destination IP addresses, port numbers, and protocols. It allows or blocks packets based on pre-defined rules.
• Example: A packet filter firewall would be effective in blocking access to specific ports (e.g., port 25 for SMTP) to prevent spam or unauthorized email communication. It's a basic level of protection.

Stateful Inspection Firewall:

• Description: Examines the state of network connections (e.g., TCP handshakes) to determine whether a packet is part of an established, legitimate connection. It keeps track of the connection state and allows packets only if they belong to an existing connection.
• Example: A stateful inspection firewall would be more effective in preventing unauthorized access to a web server. It can track the entire conversation between a client and the server, ensuring that only legitimate requests are allowed. It provides a higher level of security than a packet filter.

A digital certificate is an electronic document that verifies the identity of an individual or organisation. It's essentially a digital version of a physical certificate, providing assurance that the certificate is genuine and hasn't been tampered with. It contains information such as the certificate holder's name, a public key, and the issuing authority's digital signature.

Here are three different purposes for which digital certificates are used:

• Secure Website Communication (HTTPS): Digital certificates are crucial for establishing secure connections between a web browser and a web server using HTTPS. They verify the website's identity, ensuring that data transmitted between the user and the website is encrypted and protected from eavesdropping.
• Email Security (S/MIME): Digital certificates can be used to digitally sign emails, proving the sender's identity and ensuring the email hasn't been altered in transit. This helps prevent phishing and other email-based attacks.
• Software Authentication: Software developers use digital certificates to sign their software. This allows users to verify that the software is authentic and hasn't been modified by malicious actors before installation.