Security refers to providing a protection to computer system. Computer system must be protected against unauthorized access, malicious access to system memory, viruses, worms etc.
A security goals defines the operations that can be executed by a system while still preventing unauthorized access.
Security Requirements
The main security requirements are
Authorization: It allows to access for those users, which are related to the system.
Authentication: It refers to verifying each user of the system. OS generally authenticate users using username/password, user card, finger print, eye retina etc.
Privacy/Confidentiality
Ensure that personal information is not being accessed by unauthorized parties.
Integrity
Ensuring that the data has not been tampered with.
Unix system provides a special login name for the exclusive use of the administrator called as root.
Its password is generally set at the time of installation of the system and has to be used for login.
The root is the user name or account that by default has access to all commands and files on a Linux or other Unix-like operating system.
It is also referred to as the root account, root user, and the superuser. Root user has complete access to all files and commands.
Linux Users
Linux root user If more than one person use a single a system, then everyone may have their own user account.
Who: The who command gives the information about the users logged on to the system.
Who am i: This command displays the information about the current user only.
Su: the su command allows you to run a shell as another user. Any user can acquire superuser status with su command he/she knows the root password.
Su to root: This command is used to change the user to root when you know the root password.
sudo command : in Linux sudo (Super User DO) command in Linux is generally used as a prefix of some command that only superuser are allowed to run.
If you prefix sudo with any command, it will run that command with proper permissions to execute a command as the superuser. This is the equivalent of “run as administrator”.
These users who can use the sudo command need to have an entry in the sudoers file located at “/etc/sudoers”.
By default, sudo requires that users authenticate themselves with a password which is the user’s password, not the root password itself.
Working with Password
Passwd command is used to change the user password Syntax: #passwd Entering just passwd would allow you to change the password.
After entering password you will receive the following three prompt Current password: ******** New Password: ******* Conform New Password: ****** SSH, or Secure Shell, is a remote administration protocol that allows users to control and modify their remote servers over the Internet.
SSH or Secure Shell is a network protocol that provides administrator with a secure way to access a remote computer.
Unerstanding SSH
SSH establishes a cryptographic secure connection between two parties (Client and Server), authenticating each side to the other, and passing commands and output back and forth.
SSH is powerful, software based approach to network security that provides a secure channel for data transmission through a network.
The SSH command consists of 3 distinct parts: ssh {user}@{host} The SSH key command instructs your system that you want to open an encrypted Secure Shell Connection. {user} represents the account you want to access.
{host} refers to the computer you want to access. This can be an IP Address (e.g. 244.235.23.19) or a domain name (e.g. www.xyzdomain.com).
Host refers to the remote server you are trying to access, while the client is the computer you are using to access the host.
Symmetric Encryption
Symmetric encryption is a form of encryption where a secret key(Public key) is used for both encryption and decryption of a message by both the client and the host. Effectively, any one possessing the key can decrypt the message.
What is a Computer Network
Computer Network is a group of computers connected with each other through wires, optical fibres or optical links so that various devices can interact with each other through a network.
The aim of the computer network is the sharing of resources among various devices.
In the case of computer network technology, there are several types of networks that vary from simple to complex level.
Features Of Computer network:
- Communication speed
- File sharing
- Back up and Roll back is easy
- Software and Hardware sharing
- Security
- Scalability
Internet Protocol
A network protocol defines rules and conventions for communication between network devices.
Network protocols include mechanisms for devices to identify and make connections with each other, as well as formatting rules that specify how data is packaged into sent and received Protocol is a set of rules that dictate how data should be delivered over the public network (Internet).
HTTP(Hypertext Transfer Protocol)
Hypertext Transfer Protocol provides a network protocol standard that web browsers and servers use to communicate. You see HTTP every day because when you visit a website the protocol's written right in the URL (e.g. http://www.google.com).
HTTP is a communication protocol. It defines mechanism for communication between browser and the web server. It is also called request and response protocol because the communication between browser and server takes place in request and response pairs.
HTTP is the protocol to exchange or transfer hypertext. A web browser may be the client submits an HTTP request message to the web server.
The server, which provides resources such as HTML files and other content as a response message to the client.
HTTP is stateless protocol. In other word, the current request does not know what has been done in the previous request HTTP defines that how browser communicate with web server HTTP defines methods for the client-server communication
Features of HTTP
Connectionless protocol
HTTP is a connectionless protocol. HTTP client initiates a request and waits for a response from the server. When the server receives the request, the server processes the request and sends back the response to the HTTP client after which the client disconnects the connection.
The connection between client and server exist only during the current request and response time only.
Stateless
HTTP is a stateless protocol as both the client and server know each other only during the current request. Due to this nature of the protocol, both the client and server do not retain the information between various requests of the web pages.
FTP(File Transfer Protocol)
FTP stands for File transfer protocol. FTP is a standard internet protocol provided used for transmitting the files from one host to another.
It is mainly used for transferring the web page files from server to other computers on the internet.
It is also used for downloading the files to computer from other servers. FTP client is a program that implements a file transfer protocol which allows you to transfer files between two hosts on the internet.
It allows a user to connect to a remote host and upload or download the files. FTP allows us to transfer the files back and forth.
TCP/IPProtocol
Transmission control protocol is used for communication over a network In TCP data is broken down into small packets and then sent to the destination Ip is addressing protocol provides a standard set of rules for sending and receiving data over the Internet.
IP is making sure packets are transmitted to the right address.
The Internet Protocol (IP) is a protocol, or set of rules, for routing and addressing packets of data so that they can travel across networks and arrive at the correct destination.
Data traversing the Internet is divided into smaller pieces, called packets. IP information is attached to each packet, and this information helps routers to send packets to the right place.
Every device or domain that connects to the Internet is assigned an IP address, and as packets are directed to the IP address attached to them.
DNS is what lets users connect to websites using domain names instead of IP addresses.
The Domain Name System (DNS) is the phonebook of the Internet.
DNS
Web browsers interact through Internet Protocol (IP) addresses. DNS translates domain names to IP addresses so browsers can load Internet resources.
Each device connected to the Internet has a unique IP address which other machines use to find the device.
DNS servers eliminate the need for humans to memorize IP addresses such as 192.168.1.1 (in IPv4), or more complex newer alphanumeric IP addresses such as 2400:cb00:2048:1::c629:d7a2 (in IPv6).
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