This article is part of a series.
- SSH Series
- Part 1: Introduction to SSH
- Part 2: Setting Up and Using SSH
- Part 3: SSH Key Based Authentication
- Part 4: SSH Best Practices and Security Hardening
- Part 5: Advanced SSH Techniques
- Part 6: Troubleshooting Common SSH Issues
- Part 7: Automating Tasks With Automation
- Part 8: SSH Alternatives and Enhancements
- Part 9: Recap, Further Resources, and Closing Thoughts
Before I dive into hands-on configurations, let’s step back and understand what SSH is and why it’s crucial. SSH stands for Secure Shell, a protocol that encrypts data so that the commands, usernames, and passwords aren’t exposed in plain text. This was a major leap forward from telnet, an older protocol that sent everything unencrypted, making it a prime target for attackers.
In the following sections, I’ll explore how SSH evolved, the core terminology (like client, server, encryption, and authentication), and walk through the client-server handshake that establishes a secure channel for the data. By grasping these foundational concepts, you’ll gain the confidence to use SSH more effectively—and more securely.
SSH—From Telnet to Encrypted Sessions
In the early days of the internet, system administrators needed a way to manage remote machines without being physically present in data centres or server rooms. Telnet, a once-revolutionary protocol, filled this need by providing remote, text-based access to servers. It was simple, effective, and widely adopted. However, as the internet grew beyond research labs and universities, so did the threat of cyberattacks, and Telnet’s biggest flaw quickly became clear: all data travelled across the network unencrypted. If you are interested to know more about telnet let me know in comments below and I would create a post on the topic.

Imagine logging into a critical server to perform maintenance, only to have your username and password displayed in plain text for any hacker, curious co-worker, or malicious actor running a packet sniffer. This was the harsh reality of the “Wild West” days of internet connectivity. As networks expanded and businesses moved critical operations online, the demand for secure remote access skyrocketed.
This is where SSH (Secure Shell) stepped in, forever changing the landscape of network security. SSH offered something Telnet lacked: encryption. No longer would passwords, commands, or any user data be exposed in raw, human-readable format. Instead, SSH provided a secure “tunnel” through which data could pass safely—shielded from prying eyes.
In this first instalment of SSH series, I’ll explore why SSH came to replace Telnet, how it works under the hood, and the foundational concepts you need to understand before diving into advanced configurations.
A Quick Look Back at Telnet
-
Early Standard
Telnet was originally a breakthrough for remote management. Before Telnet, administrators often had to manage machines via direct console or out-of-band connections. With Telnet, a simple command liketelnet server-ip-address
opened a text-based interface on a remote server—no fancy UI required. -
Security Blind Spot
While Telnet excelled at simplicity, it transmitted data (including usernames and passwords) in clear text. With the meteoric rise of the internet, malicious users soon discovered how easy it was to intercept network traffic and harvest confidential login credentials. Telnet became a risky proposition for any organization handling sensitive information.
Genesis of SSH
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A Catalyst for Change
In the mid-1990s, as security incidents involving sniffed Telnet sessions piled up, Finnish researcher Tatu Ylönen created SSH to combat rampant password theft. His innovation replaced Telnet’s clear-text vulnerabilities with robust cryptographic techniques. -
Cryptographic Shield
SSH introduced the concept of a handshake, where both client and server agree on an encryption method before exchanging any sensitive information. This ensures that even if someone intercepts the data, it remains indecipherable. -
Rapid Adoption SSH’s open-source availability and compatibility with multiple platforms helped it spread quickly. By the late 1990s, SSH had effectively become the new standard for secure remote administration, relegating Telnet to a historical footnote or specialized testing tool in most environments.
Why SSH Triumphs Over Telnet
-
Encryption
- Telnet: Sends everything in the clear, making eavesdropping trivial.
- SSH: Encrypts all data so even if it’s captured, it appears as unreadable gibberish to outsiders.
-
Authentication Methods
- Telnet: Only requires a username and password, both sent unencrypted.
- SSH: Supports password authentication (still encrypted in transit), plus more secure key-based authentication for even stronger protection.
-
Extended Functionality
- Telnet: Primarily designed for interactive text-based sessions.
- SSH: Provides advanced features like port forwarding, tunneling, and agent forwarding, expanding its utility beyond simple remote logins.
-
Broad Ecosystem
- Telnet: Mostly used for legacy equipment or debugging.
- SSH: Ubiquitous in DevOps pipelines, automated deployments, secure file transfers (SCP and SFTP), and more.
The Core Principles of SSH
-
Client-Server Model
- You run an SSH client (like OpenSSH) locally.
- The SSH server (also called
sshd
) listens on a default port (22) for incoming connections. - Once connected, a secure channel is established.
-
Encryption & Key Exchange
- Symmetric Encryption: After a handshake, both client and server generate a session key to encrypt all traffic during the session.
- Public Key Infrastructure: SSH can also validate server and client authenticity using public-key cryptography to thwart man-in-the-middle attacks.
-
Authentication
- Password: Simple but less secure than key-based methods.
- Public Key: You store your public key on the server and use your private key locally; the server recognizes your identity without sending a password over the network.
-
Data Integrity
- Each packet includes checksums or hashes, ensuring that no one tampers with your data during transit.
The Big Takeaway
In the grand narrative of remote communication, Telnet was a pioneer but lacked the security required for a connected world. SSH stepped in to solve that problem, ensuring that your server logins and command executions remain confidential. Understanding this evolution—from Telnet’s plain-text vulnerability to SSH’s encrypted tunnel—lays a solid foundation for everything I’ll explore next, from installing SSH on various platforms to implementing advanced configurations like key-based authentication and port forwarding.
What’s Next?
In my upcoming posts, I’ll dive deeper into:
- Setting Up SSH: Installing an SSH server on different operating systems and making first secure connection.
- Exploring Key-Based Authentication: Generating SSH keys, adding them to the server, and improving overall security posture.
- Hardening SSH: Best practices for preventing unauthorized access and locking down servers.
If you’re curious about the finer details of how SSH shields your data or if you’ve ever encountered Telnet in a legacy environment, stay tuned! I have plenty more insights to share in my SSH Series as I continue our journey through secure remote communication.
If you have questions or want to share your experience with SSH, drop a comment below! I’d love to hear your thoughts as I continue exploring how machines secretly chat across the internet.
This article is part of a series.
- SSH Series
- Part 1: Introduction to SSH
- Part 2: Setting Up and Using SSH
- Part 3: SSH Key Based Authentication
- Part 4: SSH Best Practices and Security Hardening
- Part 5: Advanced SSH Techniques
- Part 6: Troubleshooting Common SSH Issues
- Part 7: Automating Tasks With Automation
- Part 8: SSH Alternatives and Enhancements
- Part 9: Recap, Further Resources, and Closing Thoughts
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