.Write short notes on (Any Two): [2.5+2.5]a) DNSb) Public Key Cryptographyc) VPN

a) DNS (Domain Name System): DNS is a system used for translating human-friendly domain names, such as www.google.com, into numerical IP addresses, such as 192.0.2.1, that are used by computers to identify each other on the network. It functions as the internet's phone book, allowing users to connect to websites by typing in easy-to-remember domain names instead of a string of numbers.

The process of DNS resolution involves converting a hostname (such as www.example.com) into a computer-friendly IP address (such as 192.168.1.1). An IP address is given to each device on the Internet, and that address is necessary to find the appropriate Internet device - like a street address is used to find a particular home. When a user wants to load a webpage, a translation must occur between what a user types into their web browser (example.com) and the machine-friendly address necessary to locate the example.com webpage.

b) Public Key Cryptography: Public key cryptography, also known as asymmetric cryptography, is a method of encrypting data that uses two mathematically linked, but not identical, keys - a public key and a private key. It is a complex form of cryptography that uses a pair of keys for encryption: a public key, which encrypts data, and a corresponding private, or secret key for decryption.

In this system, any person can encrypt a message using the receiver's public key, but that encrypted message can only be decrypted with the receiver's private key. This method of encryption is used in many modern security systems and is the basis for such things as secure email, digital signatures, and SSL (Secure Sockets Layer), which is the security technology for establishing an encrypted link between a web server and a browser.

c) VPN (Virtual Private Network): A VPN is a technology that creates a safe and encrypted connection over a less secure network, such as the internet. VPN technology was developed as a way to allow remote users and branch offices to securely access corporate applications and other resources.

When you connect your computer (or another device, such as a smartphone or tablet) to a VPN, the computer acts as if it’s on the same local network as the VPN. All your network traffic is sent over a secure connection to the VPN. Because your computer behaves as if it’s on the network, this allows you to securely access local network resources even when you’re on the other side of the world.

VPNs essentially forward all your network traffic to the network, which is where the benefits – like accessing local network resources remotely and bypassing Internet censorship – all come from. Most operating systems have integrated VPN support.