Everything you need to know about the Secure Shell protocol

An ultimate guide to Secure Shell, what it is, how it works and what it is used for in computer networks!

Secure Shell is a common term often used when discussing computer networks. Simply put, SSH secure shell refers to a secure network protocol that allows secure access to remote computers in a network. However, it is much more complicated than it seems.

So, in this blog, we will study all about secure shell protocol. We will also explore how it works, its concepts, and the mechanisms it leverages for secure remote access. Let’s start!

What is a secure shell?

SSH in computer networks refers to a remote administration protocol that allows users, especially system administrators, to access, manage, and modify remote servers over an unsecured network.

SSH makes it easy Public key authentication and strong password authentication for servers. It is also used to communicate between two computers that use encrypted data over an open network or the Internet.

Additionally, system administrators widely use secure shells to log into a different computer system over a network. They use it to execute commands and transfer files from one system to another.

SSH is a common term used for both the cryptonet protocol and the suite of utilities that implement the protocol. Secure shell generally operates a client-server model that connects an SSH secure shell client application to an SSH server.

SSH is a very versatile protocol and can also be used to create secure tunnels for other application protocols.

Why do we need SSH in computer networks?

The need for the secure shell protocol dates back to its beginnings in 1995, when it was designed to address the security issues faced by insecure remote access protocols such as Telnet, rlogin, and rsh.

Telnet was the most widely used protocol at the time for transmitting and receiving messages over a network. However, the biggest challenge with Telnet was that it was very insecure.

As the data was transmitted to multiple networks, there was a risk that the data would be intercepted and manipulated before reaching the target machine. At that time, communication was in clear text without encryption.

Therefore, intercepting the network and stealing the information was extremely simple. Thus, the SSH secure shell protocol was designed with an encryption mechanism that could prevent data from being tampered with.

Another reason why SSH is important these days is the evolution of technology. Today, the market is cloud servers. Most companies prefer to use cloud servers for their websites. SSH allows network administrators to perform multiple tasks on cloud servers.

SSH is typically used for:

  • Setting up a web server for the client’s website.
  • Deployment of source code on a production server.

How does Secure Shell work?

The Secure Shell protocol uses a client-server architecture to establish secure network communication. It connects an SSH secure shell client to a secure ssh server. The SSH server is programmed by default to listen on the standard TCP port 22. Therefore, SSH uses this port to initiate communication with other remote systems.

To authenticate the client and the server, SSH uses the technique of public key cryptography. The protocol uses hash and solid algorithms symmetric encryption to exchange messages between client and server. It provides a great way to ensure confidentiality and data integrity.

Generally, Linux is used to run the SSH protocol due to its durability and security. However, if you are using a Windows based system, you will need an SSH secure shell client to access SSH connections.

How SSH works

SSH sessions generally have only two operations:

1. Authentication

SSH servers must authenticate clients before they can access the network. To authenticate clients, two methods are typically used:

  • Password-based: In this method, the SSH server uses a password to authenticate clients. It is one of the most basic methods used for authentication purposes. However, this method is not very secure and can be circumvented using brute force attacks.
  • Key-based: This is a more reliable and secure way to authenticate clients. This method generates and maps SSH key pairs to authenticate users and establish a secure connection.

2. Execution of the order

The next task of the Secure Shell protocol is to access the remote server using various commands. Mac and Linux users have the advantage of using the terminal directly to run SSH commands.

However, a third-party terminal emulator client must be installed for Windows users to run commands. The most popular and widely used SSH secure shell client is PuTTY.

How to login?

To connect to a remote server via SSH, you need the following information:

The basic SSH command is:

$ssh @ -p


  • The username is the remote machine you are trying to connect to.
  • The host is either a domain name or an IP address.

Once these credentials are successfully entered, you will connect to the remote system server. There you can use the terminal of this system to execute commands and perform necessary operations.

SSH features at a glance

The SSH secure shell has multiple features that make it essential in computer networks. Some of its features are:

Secure remote connections

The fundamental feature of the SSH secure shell protocol is to provide secure login access to a remote system over open networks. Your username and password are encrypted on the local machine before establishing a connection.

The client then uses this encrypted connection to authenticate you to the remote system’s SSH server. The entire login session remains encrypted in this mechanism.

Secure file transfer

Another cool feature that SSH is loved and used by thousands of network administrators is its ability to securely transfer a file at a fast speed. You literally have to type a single copy command with the name of the file and its source, and the file is ready to be transferred. The file is encrypted before transfer and automatically decrypts after transfer.

Here is the command to transfer a file from one system to another remote system:

$ scp myfile [email protected]

Secure execution of remote commands

System administrators often need to run the same command on different computers. However, to save itself from this monotonous task, the secure shell provides a way to safely run the command for different computers in one go.

Here is the command used to do so:


for machine in 1 2 3 4 (1,2,3,4 are machine names)


ssh $machine /usr/bin/w


Keys and Agents

Remembering multiple passwords for different networks and computer systems is a difficult task. This is why the SSH secure shell uses keys for its authentication mechanisms. Leveraging keys and a program known as an authentication agent, the secure shell protocol authenticates you to all of your computer accounts securely at once.

You only need to enter all key files once in your remote system accounts. Then, whenever you need to access a system, you can invoke the ssh-agent program using the command line which helps you access the remote system without asking for authentication.

Access control

SSH also allows its users to authorize another person to use their personal account to access remote computers. However, the other person may only have limited access to certain features.

Also, your password or keys are not exposed to the user to whom you lend your system. This is a very beneficial feature that eases the workflow of network and system administrators.

Port forwarding

This is a technique in which a TCP/IP connection can be transmitted over a secure shell connection to secure data transmission. This process is also known as tunneling in computer networks. It is mainly used when a network firewall is blocking incoming connections to system ports.

This mostly happens while using your desktop systems. To bypass the firewall, the SSH protocol can establish a secure tunnel on an arbitrary local TCP port and offer data transmission.

How secure is SSH?

In general, SSH secure shell is considered one of the most secure protocols for remote network communication. However, SSH also has its drawbacks. Brute force attacks can be performed when using passwords to establish a connection using SSH. The brute force attack involves using common usernames and passwords to access SSH servers and the root account.

Conversely, SSH keys are a more secure way to authenticate. Unfortunately, if your SSH key management routine is poor, hackers can still manage to gain access to your system keys.

Moreover, their misuse can be very disastrous as it can lead to access to privileged information such as databases, routers, payment systems, etc.

Other than that, another potential security weakness of SSH is exposed SSH ports. Some malicious programs can attack exposed ports and use them to breach the local network.

However, not all of these scenarios are so common and easy to implement. But you still need to take the right steps and be aware of your networks to ensure the best security for your system.


SSH Secure Shell is a remarkable protocol that has been used for over twenty-seven years to facilitate transparent communication between remote computers. Now that you have a better understanding of SSH, you can leverage it in your projects to develop unique and secure applications. Good luck!

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