What is SSH; Why we need to use it

What is SSH?

The Secure Shell Protocol (SSH) is a network encryption protocol that secures interactions between a server and a client.

Using SSH enables admins to execute commands and log in remotely through local or remote networks on machines in a secure environment.

Understanding SSH; Why Use SSH on Network Services?

SSH is a powerful tool that helps in sending commands to the target machine/computer through an encrypted connection.

As an administrator, you need to use SSH to manage servers/devices remotely. Knowing What is SSH clarifies why it is necessary to use it.

SSH service was developed as a secure alternative to Telnet unencrypted communication that uses cryptographic techniques.

Using SSH allows data packets to cross networks that they could not cross before, since it comes with tunneling or port forwarding.

What is SSH Protocol used for?

The main purposes of SSH are to provide remote access and secure connections.

To operate network services securely over an unprotected network, SSH is used as a cryptographic network protocol.

SSH encrypts and authenticates device connections using cryptography.

Let’s check the benefits of using SSH in a secure channel:

  • This security protocol enables admins to manage files, transfer or modify them, access control, TCP/IP forwarding, and execute commands directly on the server.
  • SSH mangles the data that travels over the connection using encryption, making it extremely difficult for outsiders to decrypt.
  • SSH is capable of tunneling. It is a technique for sending packets over a network via a path or protocol they wouldn’t normally use.
  • To cover network security flaws, it hides systems from malicious cyber-attacks by creating a secure connection over a network.
  • SSH tunnels transfer packets from one machine to another via a method known as port forwarding.
  • It is designed for Unix-like operating systems, such as Linux, macOS, and BSD. SSH also works on Windows.
  • SSH is used in operating system administration, server hardware management, and a variety of file transfer protocols.
  • Access to servers can be automated by using SSH keys.
  • Network administrators can restrict and manage user access to a network remotely with SSH.

How Does SSH Work?

By linking an SSH client and SSH server, SSH provides secure network communication through a client-server architecture.

When an SSH connection request is sent to the server by the SSH client, the server replies with a random message:

  1. Using the private key, the client encrypts the message before sending it back to the server.
  2. The public key that matches the client’s private key is then used by the server to decrypt that communication.
  3. In this manner, the server confirms that the private key and the public key belong to the same pair.
  4. SSH establishes a cryptographically secure connection between two parties by authenticating one to the other using encryption technology.
  5. A server where a client establishes an SSH connection can be managed just like any other local computer.
  6. The server watches the network over a specified TCP port, waiting for clients to establish a connection.
  7. To protect privacy and data integrity, the protocol also employs hashing algorithms and strong symmetric encryption for message exchanges between the client and server.
  8. A client must complete the authentication procedure before it can connect and begin sending SSH instructions.

Layers of SSH Protocol

  • The Transport Layer
  • The Authentication Layer
  • The Connection Layer

Public-key cryptography is used by SSH to authenticate the client over the channel.

Regardless of the underlying network infrastructure, SSH offers a secure, encrypted means of exchanging information after the connection has been made.

How Does an SSH Session Operate?

Most SSH sessions have Authentication and Command Execution operations.

The SSH servers authenticate clients using two popular methods:

  • Password-based
  • Key-based

For clients that have installed OpenSSH, password-based authentication is the standard mode of authentication.

Although not the most secure, it is the most fundamental kind of SSH authentication.

Passwords are transmitted safely to the server, however, contemporary brute force attacks can get beyond the authentication.

By creating SSH key pairs, key-based authentication significantly strengthens system security and is a dependable and safe substitute.

A secure connection is formed between the client and server upon successful authentication by the server.

SSH Advantages

  • SSH enables data encryption, preventing malicious would-be attackers from accessing your passwords and user details.
  • SSH is capable of bypassing firewall restrictions.
  • With single sign-on enabled by SSH keys, users can switch between accounts without constantly entering their passwords.
  • The traditional remote shell protocols, including Telnet, FTP, rsh, rlogin, and rexec, were superseded by SSH.
  • Administrators can remotely view, remove, move, and manage files, folders, and directories with the help of SSH commands and scripts.
  • The ability to use port tunneling and forwarding, which allows any data to be exchanged over an encrypted secure connection, is built into SSH.
  • Instead of utilizing usernames and passwords, users can rely on SSH keys to authenticate themselves and log in to a system. Systems are shielded against brute-force password attempts by SSH keys.
  • Because cloud-based virtual computers are constantly connected to the internet, SSH shells and tunnels protect them from security flaws.

SSH Disadvantages

  • Slow connections.
  • SSH mismanagement.
  • Private key issues.
  • Poor SSH key management.
  • Tunneling effects.
  • Security vulnerabilities.
  • Encrypted data cannot be monitored.
  • Complex to configure and use.
  • Not supported by all applications.

How to Use/Enable SSH to Access Remote Server?

Enabling SSH to connect to a remote server in Linux requires an SSH client. Both the daemon and the client are preinstalled on the majority of Unix-based and Unix-like operating systems.

The SSH client can be accessed through the terminal on these systems.

The user uses the ssh command, followed by the username and the server address or hostname, to establish a terminal connection to a remote host:

ssh [username]@[server_ip_or_hostname]

As of version 1709, OpenSSH client and server are available for Windows 10. Previous versions of Windows lacked the SSH capability.

Instead, an SSH connection had to be established using programs like PuTTY.

What Port does SSH use?

Port 22 is the default port for SSH. Firewalls can occasionally prevent access to some ports on servers they are protecting while leaving port 22 open.

Because packets destined for port 22 are not banned and can be diverted to any other port, SSH is advantageous for gaining access to servers located on the other side of the firewall.

How to Change SSH Port Number?

To establish a connection to a remote host using a custom SSH port number, you can use the -p switch:

ssh your.server.com -p 3322

In this way, you can change SSH port in Linux.

How to Improve SSH Connection Security?

Use the keygen utility to generate a key pair that will increase the security of SSH connections.

There is a public key and a private key in the pair. While the private key must remain secure, the public key can be shared.

Open a terminal on the host machine and run the command below to create a key pair:

ssh-keygen -t rsa

Is SSH Secure?

As long as keys and credentials are handled correctly, the SSH protocol is thought to be resistant to cryptographic attacks on the network.

The below situations explain why SSH is not completely secure:

  • Brute force attacks:

On SSH servers, brute force attacks are a frequent occurrence. Attackers try to utilize popular usernames and passwords to gain access to many SSH servers.

They employ privilege escalation to get to the root account when they get access to a server.

  • Misuse SSH keys:

Even though SSH keys are secure, misusing them can give nefarious people access to confidential data.

Accounts and resources like databases, routers, payment systems, and more, are included in this data.

  • Exposed SSH ports:

Another potential security flaw is exposed SSH ports. Some malware apps use open ports on IoT devices as a backdoor into the local network, which allows them to attack such devices.

Finally, because there are a lot of SSH clients available, the security of the protocol is also dependent on the security of apps from third parties.


SSH and SSL use different encryption algorithms. Knowing how these two protocols differ from one another will enable you to select the best one for your requirements.

Defenition Secure ShellSecure socket layer
Authentication StatusHas a username/password authentication system.Does not have a username/password authentication system.
Port Number22443
FunctionNetwork TunnelingCertificates
OperationEncrypts the communication between two computers over the internet.Encrypts the communication between the browser and server.
ProtectionAgainst DNS spoofing, data manipulation, IP source routing, data sniffing.Against identity theft and man-in-the-middle (MiTM) attacks.
Security Use caseSecuring file transfers and remote administration.Securing email communication and other non-web-based applications
Authentication MethodsPasswords, public key authentication, and two-factor authenticationDigital certificates to authenticate web servers to client browsers.

A cryptographic protocol is created to enable safe communication in specific situations. SSL is the most well-known cryptographic protocol among internet users.

It secures sensitive data, including credit card numbers, and indicates a secure connection by displaying a lock icon in the address bar of your browser.

Why Using SSH is recommended?

One of the most secure encryption techniques available today is the SSH protocol. It increases security and strengthens credibility.

Using SSH ensures administrators that user authentication, commands, output, and file transfers are encrypted to protect against attacks in the network.

Administrators can safeguard the integrity of data and server modifications by using SSH.

The SSH protocol offers the best protection against hostile activities such as data interception and server intrusions containing sensitive information thanks to its encryption techniques.

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