What Is SSH and How Does It Work?

Data moves constantly in modern IT environments. Administrators access remote systems, applications exchange information, and business partners transfer files every day. Behind many of these interactions is a common requirement: establishing a secure connection that protects sensitive information from unauthorized access.

That requirement creates an important challenge. How do you protect credentials, commands, and data as they travel across networks while still providing the access and functionality users need?

The answer for many organizations is SSH.  

If you have ever logged into a remote system, transferred files using SFTP, or automated communication between systems, you have likely relied on SSH behind the scenes. It is one of the most widely used protocols for secure communication, helping IT teams, developers, system administrators, and security professionals protect remote access and data exchange.

So, what is SSH and how does it work? Below, we'll go over what SSH is, how an SSH connection is established, and how organizations use it to support secure file transfer, remote administration, and automated data movement.

What Is SSH?

SSH stands for Secure Shell. More specifically, SSH is a cryptographic network protocol that creates an encrypted connection between a client and server for secure remote access, authentication, command execution, and file transfer without exposing sensitive information in plain text.

SSH was created to replace older, less secure remote access protocols such as Telnet and rlogin. Those earlier tools allowed users to connect to remote systems, but they transmitted credentials and session data without the level of protection modern organizations require. If traffic was intercepted, usernames, passwords, commands, and other sensitive information could be exposed.

The SSH protocol addressed this challenge by introducing encrypted sessions between systems. Instead of sending information in clear text, SSH protects the connection so that credentials, commands, files, and responses are shielded from unauthorized viewing.

Today, SSH is commonly used to administer servers, access cloud environments, authenticate automated systems, and support secure file transfer methods such as SFTP and SCP. For many organizations, it serves as a basis for secure infrastructure management, remote administration, and enterprise file exchange.

What Is SSH Used For?

SSH is used anywhere organizations need secure access to systems or protected data movement between environments. It is especially important for organizations managing distributed infrastructure, cloud platforms, development environments, and file transfer workflows.

Common SSH use cases include:

• Remote system administration
• Secure login to servers
• Running commands on remote machines
• Transferring files through SFTP or SCP
• Creating encrypted tunnels
• Supporting automated communication between systems

IT administrators often use SSH to manage Linux or Unix servers without being physically present. Developers may use it to connect to repositories, cloud instances, or test environments. Security teams rely on SSH to reduce exposure when privileged users access infrastructure. Operations teams may use SSH-based file transfers to exchange data with partners, customers, vendors, or internal applications.

SSH is also heavily used in DevOps and infrastructure management. Automated scripts, deployment tools, monitoring systems, and application workflows may depend on SSH to connect securely between systems. When properly configured, SSH helps organizations maintain speed and flexibility without sacrificing control over access and data movement.

How Does SSH Work?

SSH may feel simple from the user’s perspective. You enter an SSH command, authenticate, and gain access to the remote server. Behind the scenes, however, several important steps occur before that secure session begins.

The SSH connection lifecycle generally follows four stages:

• First, the client initiates the connection and the server identifies itself
• Second, an encryption key is negotiated so both systems can communicate securely
• Third, the user or system is authenticated
• Fourth, the encrypted session begins.

SSH relies on three core security functions: encryption, authentication, and integrity checks. Encryption prevents outsiders from reading session data. Authentication confirms that users, systems, and servers are who they claim to be. Integrity protections help verify that data is not altered while in transit.

Together, these controls make SSH one of the most trusted methods for secure remote access and file transfer.

Step 1: The Client Connects to the SSH Server

Every SSH session begins with a client and a server.

The SSH client is the system initiating the connection. This might be a user’s workstation, an automated application, a managed file transfer platform, or another system requesting access.

The SSH server is the system being accessed. This may be a remote server, cloud instance, file transfer endpoint, development environment, or business application.

SSH usually operates over port 22, although organizations may change this default port as part of their SSH configuration. When the client sends a request, the server responds with identifying information, including details needed to begin the secure connection process.

This first step may seem basic, but it is important. The client needs to know which server it is communicating with before sensitive activity begins. If the server cannot be identified or trusted, the connection should not proceed.

Step 2: SSH Negotiates Encryption

Once the client and server begin communicating, they negotiate how the session will be encrypted. This process is part of the SSH handshake.

During the SSH handshake, both systems agree on supported cryptographic algorithms and establish a session key used to protect communication. This session key is temporary and specific to that connection. Once generated, it is used to encrypt commands, credentials, file transfers, responses, and other session data. If an attacker intercepts the traffic, the encrypted data should not be readable without the session key.

This negotiation matters because security depends on strong cryptographic choices. Outdated algorithms or weak configurations can create unnecessary exposure. That’s why organizations should regularly review SSH implementations, approved algorithms, key lengths, and configuration standards.

Step 3: SSH Authenticates the User or System

After encryption is negotiated, SSH verifies identity. This authentication step determines if the user or system should be allowed to access the server.

Common SSH authentication methods include password authentication, public key authentication, and multi-factor authentication when layered with additional access controls. Password-based authentication is familiar, but it can introduce risk if passwords are weak, reused, shared, or exposed. For that reason, many organizations prefer SSH keys.

An SSH key is a cryptographic credential used to authenticate access. SSH keys work as a pair: both the server and client have private keys. The administrator for the server may share their  public key with clients in order for clients to validate that the key they encounter in this “handshake” from the server is the expected key.

If it is not shared, trust can be done upon initial connection for many clients. This is common to see in Linux CLIs or a GUI client, like FileZilla.  

When a connection is attempted, the client proves possession of the private key by cryptographically signing data, and the server verifies that signature using the stored public key. If verification succeeds, access can be granted.

SSH keys are generally stronger than passwords, but they still require governance. Forgotten keys, shared keys, excessive permissions, and unmonitored access can create long-term security gaps.

Step 4: The Secure Session Begins

Once authentication succeeds, the secure session begins.

During the session, users can run commands, manage systems, transfer files, or perform authorized administrative tasks. All communication remains encrypted while the session is active.

SSH can also support port forwarding and SSH tunnels. These capabilities allow organizations to route traffic securely between systems, access internal services, or protect communication across less trusted networks. SSH tunneling can be useful, but it should be controlled carefully. Unmanaged tunnels may bypass security monitoring or create paths that are difficult to audit.

The session ends when the user logs out, the process finishes, or the connection closes. For automated workflows, the same general process occurs without a person manually typing commands. A system initiates the connection, authenticates, completes the required task, and closes the session.

SSH Encryption, Authentication, and Integrity Explained

SSH protects communication through three primary security controls: encryption, authentication, and integrity.

Encryption protects confidentiality. It prevents outsiders from reading commands, credentials, files, and responses while they move between the client and server.

Authentication protects access. It verifies that the identities of the client and server participating in the connection. Without strong authentication, attackers may attempt to impersonate users or systems.

Authentication protects access. It verifies the identities of the client and server participating in the connection.

Integrity protections help confirm that data has not been changed in transit. This matters because secure communication is not only about hiding data from view. It is also about confirming that the data received is the same data that was sent.

Together, these controls help protect against eavesdropping, credential theft, man-in-the-middle attacks, and unauthorized access. However, SSH is only as secure as its implementation and management practices. Weak passwords, unmanaged keys, outdated algorithms, overly broad permissions, and limited logging can still undermine security.

That’s why enterprise SSH usage should be governed through defined policies, access controls, monitoring, and audit-ready processes.

What Are SSH Keys?

SSH keys are cryptographic credentials used to authenticate users, systems, and automated processes. They are one of the most common ways organizations secure SSH access.

Each key pair includes a public key and a private key. The public key can be shared and stored on servers. The private key must remain protected. When the two match, SSH can authenticate the connection without requiring a traditional password.

This model offers significant security advantages because the private key never needs to be transmitted across the network. As a result, organizations can reduce the risk of credential exposure while supporting stronger access controls. Keys can also be protected with passphrases, restricted to specific users or systems, and tied to defined security policies.

As SSH usage grows across an organization, managing those keys becomes increasingly important. Over time, organizations may accumulate hundreds or thousands of keys across users, applications, servers, scripts, and partners. If those keys are not tracked, rotated, or removed when no longer needed, they can become hidden access paths.

Poor SSH key management can create security risks. Organizations should rotate keys, remove unused keys, monitor key-based access, document ownership, and enforce policies around creation, storage, and permissions.

SSH keys are secure when managed well. They become risky when treated as “set it and forget it” credentials.

How GoAnywhere MFT Supports SSH-Based File Transfers

For many organizations, SSH is not just about remote login. It is also a foundation for secure file movement.

GoAnywhere MFT supports SFTP and SCP for SSH-based secure file transfers, helping organizations exchange data with employees, customers, trading partners, applications, and systems. SFTP, also known as SSH File Transfer Protocol, uses SSH to protect file transfer sessions. It is often preferred for business-critical data exchange because it supports encrypted transfer, strong authentication, and controlled access.

Basic SSH and SFTP tools can move files securely, but enterprise environments usually need more than command-line transfers. They need automation, scheduling, visibility, permissions, logging, error handling, reporting, and partner management.

That’s where managed file transfer provides additional value.

GoAnywhere helps operationalize SSH-based file transfers at scale by adding workflow automation, file encryption, centralized logging, audit reports, key management, user permissions, and partner connections. Instead of relying on scattered scripts or manual processes, teams can manage file transfer activity through a centralized platform.

This helps reduce operational friction while supporting security and compliance goals. It also gives IT and security teams better visibility into who is exchanging data, when transfers occur, which workflows succeed or fail, and where sensitive information is moving.

For organizations that depend on SFTP, SCP, and other secure transfer methods, GoAnywhere helps turn SSH-based connectivity into a controlled, auditable, and repeatable business process.

Why SSH Matters for Secure Data Exchange

SSH is foundational for secure remote access, command execution, system-to-system authentication, and encrypted file transfer. It solves a problem that every connected organization faces: how to communicate across networks without exposing credentials, commands, and sensitive data.

When properly configured, SSH protects sessions through encryption, authentication, and integrity checks. It supports administrators managing remote infrastructure, developers working across environments, automated systems exchanging information, and enterprises moving files between business partners.

But SSH should not be managed casually. Keys, permissions, configurations, tunnels, and transfer activity all need oversight. Without centralized controls, SSH usage can become fragmented, difficult to audit, and harder to secure.

For enterprises, SSH becomes more powerful when paired with managed file transfer. GoAnywhere helps organizations use SSH-based transfers securely, reliably, and at scale by combining secure protocols with automation, centralized visibility, audit trails, and policy-driven control.

SSH makes secure connections possible. GoAnywhere helps make those connections manageable.