What is the SSH Protocol?

What is the SSH Protocol?

In this article, we will discuss what is meant by ssh? The ssh protocol, known as Secure Shell or Secure Socket Shell, provides users, especially system administrators, with a secure way to access computers through an insecure network.

In addition to providing secure network services, ssh refers to a set of other services that implement the ssh protocol. Secure shell provides strong password authentication, public key authentication, and encrypted data communication between two computers connected over an open network such as the Internet. In addition to providing strong encryption, the ssh protocol is widely used by network administrators to manage computers and programs remotely, allowing them to connect to another computer over a network, execute commands and transfer files from one computer to another.

It should be noted that ssh refers to both the encrypted protocol and the set of applications that implement it. Ssh uses a client-server model and connects a Secure Shell server program, which is at the end of the session view, to an ssh server, and this end is where the session is executed. Implementations of its protocol often include support for application protocols used for terminal emulation and file transfer. Ssh can also be used to create secure tunnels for other application protocols, such as for securely running remote X Window System graphical sessions.

How does the ssh protocol work?

Secure Shell was created to replace insecure terminal emulation programs such as Telnet, rlogin (remote login), and rsh or remote shell. Ssh enables similar functionality (login and running terminal sessions on remote systems). Also, the ssh protocol replaces file transfer programs such as File Transfer Protocol (FTP) and RCP (remote copy).

The most basic use of the ssh protocol is to connect to a remote host for a terminal session, whose command is as follows:

ssh UserName@SSHserver.example.com

This command causes the client to connect to the server named server.example.com using the username ID UserName. Suppose this is the first time localhost and server are being negotiated. In that case, the user will prompt you with the remote host’s public key fingerprint and be prompted to connect despite the lack of a previous connection:

The authenticity of host ‘sample.ssh.com’ cannot be established.
DSA key fingerprint is 01:23:45:67:89:ab:cd:ef:ff:fe:dc:ba:98:76:54:32:10.
Are you sure you want to continue connecting (yes/no)?

A timely yes answer causes the session to continue, and the host key is saved in the well-known local_hosts file of the local system, which is a hidden file and is stored by default in a hidden cover directory called /.ssh/known_hosts in the user’s home directory. After the host keys are stored in the Known_Host files, the client system can connect directly to that server again without needing approvals, and the host keys confirm the connection.

Applications of using the ssh protocol

The ssh protocol in all data centers is shipped by default with every Unix, Linux, and Mac server. Ssh protocol connections provide security for many different types of communication between a device and a remote host, including secure remote access to resources, remote execution of commands, delivery of software patches and updates, and others. Administrative or managerial work is used. In addition to creating a secure channel between local and remote computers, the ssh protocol is used to manage routers, server hardware, virtualization platforms, operating systems (OS), internal management systems, and file transfer programs.

Secure Shell is used to connect to servers, make changes, perform uploads, and exit through the tool or directly through the terminal. SSH keys can automate server access and are often used in backup systems scripts and configuration management tools. For easy access and working across organizational boundaries, SSH keys provide single sign-on (SSO) so users can move between accounts without typing a password each time.

While SSH plays important roles in identity and access management, it does more than an encrypted connection. All SSH traffic is encrypted. Members where users are transferring a file, browsing the web, or executing a command, their actions are private.

While the ssh protocol can be used with a regular id and password for authentication, the ssh protocol relies more on public key pairs to authenticate hosts to each other. Users still have to use their user ID and password – or other authentication methods – to connect to the remote hosts. Still, the local machine and the remote machine are authenticated separately. This is done by generating a unique public key pair for each host in the communication. Each session requires two public key pairs: one to authenticate the remote device to the local device and another to authenticate the remote device to the local device. Authentication of the local device to the remote device.


The functions that the ssh protocol enables include the following:

  • It provides remote access to systems or network devices with ssh capability for users and security for automated processes.
  • Secure and interactive file transfer sessions
  • Transfer files automatically and safely
  • Issuing commands on remote devices or systems
  • Secure management of network infrastructure components

The ssh protocol can enable terminal sessions interactively and should be used instead of the less secure Telnet program. Also, the ssh protocol is usually used in scripts and other software so that programs and systems can access data and other resources remotely and securely.


The first version of the ssh protocol was published and designed by Tatu Ylönen in 1995, who was then a researcher at the Helsinki University of Technology and later started SSH Communications Security, a cybersecurity vendor based in Finland. Over time, various flaws have been found in ssh-1, and now this version is no longer used and is not safe to use. ssh-2 The current version of the Secure Shell protocols was adopted in 2006 as a Standards Track specification by the Internet Engineering Task Force (IETF).

SSH-2 is incompatible with SSH-1 and uses Diffie-Hellman key exchange and stronger integrated authentication that uses message authentication verification codes to improve security. SSH clients and servers can use several encryption methods, the most common being Advanced Encryption Standard (AES) and Blowfish. However, there are no known exploitable vulnerabilities in SSH-2, although leaks by Edward Snowden in 2013 suggested that the National Security Agency (NSA) might be able to decrypt some SSH traffic.

Protocol security

To use the ssh protocol, companies must use methods to manage host keys stored on client systems that can accumulate over time, especially for information technology (IT) staff who need to be able to access them for management purposes. Remote hosts have access. Because data stored in a known ssh file from the host can be used to authenticate access to remote systems, organizations should be aware of the existence of these files, and even after logging out should be a standard procedure. Maintain control over files because hard drives may store this data in plain text. While it is possible to issue an ssh command that includes an id and password to authenticate the user’s local machine to a user account on a remote host, doing so may provide an attacker with access to the source code…

The main difference between ssh and Telnet protocol

Telnet protocol was one of the first application protocols of the Internet – the other is FTP – which is used to start and maintain a terminal simulation session on a remote host. It is worth noting that the ssh protocol and Telnet are functionally similar, with the main difference being that the ssh protocol uses public key encryption to authenticate endpoints when setting up a terminal session and encrypt session commands and output. At the same time, Telnet is primarily used for terminal emulation.

It is noteworthy that the ssh protocol can be used for terminal emulation similar to the login command, as well as for issuing remote commands such as rsh, transferring files using ssh file transfer protocol (SFTP), and tunneling to other programs. Another application should be used.

The main difference between ssh and SSL/TLS protocol

The Transport Layer Security (TSL) protocol, which updates the Secure Sockets Layer (SSL) protocol, is designed to secure network traffic at the transport layer. Also, the SSH protocol works on top of the transport layer, but there are differences between these two protocols.

While both depend on public or private key pairs to authenticate hosts, the TLS protocol is authenticated with only one key pair. Still, the ssh protocol uses a separate key pair to authenticate each connection, one for each connection, from a local device to a remote device and another to confirm the connection from the remote device to the local device. Another difference between the ssh protocol and TLS is that TLS encrypts or does not authenticates connections, but ssh encrypts and authenticates all connections.

SSH provides IT and information security (infosec) professionals with a secure mechanism to manage SSH clients remotely. Ssh protocol authenticates devices instead of requiring password confirmation to communicate between client and server. This enables IT staff to connect to remote systems and change ssh settings, including adding or removing host key pairs in known_host files.


The ssh protocol has been implemented as an open protocol for most computing operating systems. The open-source OpenSSH implementation is the most commonly found on Linux, Unix, and other Berkeley Software Distribution or BSD-based operating systems, including Apple’s macOS. . OpenSSH was first introduced in Windows PowerShell in 2015, and in 2018 OpenSSH support was added to Windows 10. While the ssh protocol is available on most UNIX-like operating systems, Microsoft’s ported version of OpenSSH must be explicitly enabled in the Windows Settings program.

PuTTY is another open source implementation of the ssh protocol. While it is currently available for Windows, macOS, and Unix/BSD, PuTTY was originally written to run on the Windows operating system and has long been one of The best options to use ssh protocol in Wind the own system. Most implementations of the ssh protocol suite, such as three utilities – slogan (secure login), ssh, and SCP (secure copy) – are secure versions of earlier insecure Unix services: login, rsh, and RCP.

The ssh protocol uses public key encryption to authenticate the remote computer and enables the remote computer to authenticate the user if necessary. Under various open source and proprietary licenses, dozens of ssh protocol implementations are currently available for operating systems. While there are graphical implementations of the ssh protocol, this program is usually invoked on the command line or executed as part of a script. Running the ssh protocol command alone without arguments such as destination host or user ID returns a list of ssh protocol command parameters and options.

The most basic form of the ssh command is calling the program and the destination hostname or Internet Protocol (IP) address:

ssh server.example.org

This will connect you to server.example.org. The destination host will respond by sending a password for the user ID of the user account the client is running under. In other words, if the user ID is smith, the remote host will ask for a password associated with the smith account on the remote host. In many cases, the user ID for the remote host will be different, in which case the command must be issued with the user ID of the remote host. Like the following command:

ssh remote_host_userID@server.example.org The ssh protocol can also use the command line to issue a single command on the remote host and then exit – for example, ssh example.org ls

This command executes the Unix ls command, which displays the contents of all directories on the remote host. While this example is trivial, it demonstrates that the ssh protocol can be used to execute commands on a remote host. For example, one could construct a command that provides an initial server that gives a remote device access to a single file—or another resource—and after the file is accessed by the specified remote host. Done, terminates the server.

In addition to the executable ssh protocol, SSH has other executable commands that are used on the command line for additional functions, including the following:

  • She starts an ssh server that waits for ssh connection requests and enables authorized systems to connect to localhost.
  • Ssh-keygen is a program to create a new pair of authentication keys for the ssh protocol, which can be used for automatic login, SSO implementation, and host authentication.
  • Ssh-copy-id is a program used to copy, install and configure an SSH key on a server for automatic passwordless logins and SSO.
  • Ssh-agent is a helper program that tracks identity keys and their passphrases—from which SSH encryption keys are derived—and enables users to log in without re-entering passwords or passphrases. Use identification keys.
  • Ssh-add is used to add a key to the SSH authentication agent, and ssh-agent is used to implement SSO using SSH.
  • Scp is a program that copies files from one computer to another and is a version of RCP with SSH security.
  • sftp is a program that copies files from one computer to another and is an SSH-version of FTP, the main file transfer protocol. SFTP has become a mechanism for sharing files over the Internet, and
  • FTP replaces FTP/S (FTP Secure), a protocol for using FTP over an SSL/TLS tunnel.

Frequently Asked Questions

What are the most common uses of the ssh protocol?

Among the most common uses of the ssh protocol the following can be mentioned:

  • Remote access to network systems or devices
  • Secure and interactive file transfer sessions
  • Transfer files automatically and safely
  • Secure management of network infrastructure components
  • Issuing commands on remote devices or systems

What is the difference between ssh protocol and SSL/TLS?

Both ssh and SSL/TLS protocols are in the transport layer.

What operating systems can the ssh protocol be implemented on?

The ssh protocol can be implemented on most computing operating systems but is most commonly found on Linux, Unix. And other Berkeley Software Distribution or BSD-based operating systems, including Apple’s macOS.