🚀 A beginner-friendly guide to what SSH is, why it's important, and how to use it securely with key-based authentication.

🧠 What is SSH?

SSH (Secure Shell) is a secure communication protocol that lets you connect to another computer or server remotely over the internet or network — safely and encrypted.

🔍 Example:

You can log into a remote Linux server from your laptop using SSH to run commands, transfer files, or manage services.

🤔 Why Was SSH Developed?

Before SSH, people used protocols like Telnet or FTP, which sent data in plain text — including passwords!

SSH was developed to:

  • Encrypt communication between devices
  • Protect sensitive information
  • Prevent eavesdropping and hacking

SSH was introduced in 1995 and quickly replaced insecure alternatives.

🔐 How Secure is SSH?

SSH uses:

  • Strong encryption algorithms
  • Public-private key pairs
  • Secure authentication methods

This makes it very secure — used by developers, sysadmins, DevOps, cloud engineers, and even big tech companies to manage infrastructure.

🛠️ Where is SSH Used?

SSH is commonly used to:

  • Access and manage remote servers
  • Deploy code to servers
  • Manage cloud platforms (like AWS, DigitalOcean)
  • Create secure tunnels for data transfers
  • Use Git with services like GitHub, GitLab, Bitbucket securely

📦 How to Install SSH

SSH comes pre-installed on most Linux/macOS systems.

To check if SSH is installed:

ssh -V

If not installed, run:

sudo apt update
sudo apt install openssh-client

For enabling SSH on a server:

sudo apt install openssh-server
sudo systemctl enable ssh
sudo systemctl start ssh

🔑 SSH Keys – Public and Private Key

SSH supports two methods of login:

  1. Password-based login (not recommended)
  2. Key-based login ✅ (recommended)

What are SSH Keys?

SSH keys are like your digital identity for secure login:

  • Private Key: Stays on your device (keep it secret 🔒)
  • Public Key: Shared with the server

They work together — your private key proves your identity without needing a password.

🧰 How to Generate SSH Keys

Run this on your terminal:

ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

It will ask:

  • Where to save the key → Default is ~/.ssh/id_rsa
  • Passphrase (optional but recommended)

Result:

  • id_rsa → Your private key (keep safe)
  • id_rsa.pub → Your public key (share with server)

🧭 What’s Inside These Files?

  • id_rsa: Your private key, in PEM format (should never be shared!)
  • id_rsa.pub: A string starting with ssh-rsa ... — your public key

📂 Where to Place and Use These Keys

On Your Local Machine (Your Laptop):

  • Keep both files in ~/.ssh/
  • Set proper permissions:
chmod 600 ~/.ssh/id_rsa
chmod 644 ~/.ssh/id_rsa.pub

On the Remote Server:

  • Add the public key to:
~/.ssh/authorized_keys

You can copy it using:

ssh-copy-id username@remote_host

💡 Connecting Using SSH Key

Once the keys are in place:

ssh username@remote_host

If a passphrase is set, it will ask once and grant access without needing a password.

🛡️ Bonus Tips for Security

  • Use key-based authentication only
  • Disable password login on the server (/etc/ssh/sshd_config)
  • Use strong passphrase on your private key
  • Keep private key backed up securely, but never shared