3 SSH intro

SSH (Secure Shell) is a cryptographic network protocol used for securely connecting to remote servers over an unsecured network. It allows users to execute commands, transfer files, and manage systems remotely in a secure manner.

Key Features of SSH:

Encrypted Communication – SSH uses encryption (typically RSA, ECDSA, or Ed25519 keys) to prevent eavesdropping and unauthorized access.
Authentication – Users authenticate via passwords or SSH key pairs (more secure).
Remote Command Execution – You can run commands on the remote machine as if you were physically present.
File Transfer – With scp (Secure Copy) or sftp (SSH File Transfer Protocol), you can securely transfer files.
Port Forwarding (Tunneling) – SSH can forward ports securely (e.g., accessing a database behind a firewall).

3.0.1 Basic SSH Usage

3.0.1.1 Connect to a Remote Server

ssh username@remote_server_ip

Example:
```
ssh user@192.168.1.100
```

3.0.1.2 Using SSH Key Authentication (Recommended)

Generate an SSH key on your local machine:

ssh-keygen -t ed25519 -C "your_email@example.com"

Copy the key to the remote server:

ssh-copy-id username@remote_server_ip

Then, connect without a password:

ssh username@remote_server_ip

3.0.1.3 Securely Transfer Files

Copy a file to the remote server:

scp file.txt username@remote_server_ip:/remote/path/

Copy a file from the remote server:

scp username@remote_server_ip:/remote/path/file.txt .

3.0.1.4 Running a Command on a Remote Server

Execute a command without logging in:

ssh username@remote_server_ip "ls -lah /var/log"

3.0.2 Common SSH Configurations

3.0.2.1 Editing SSH Config File (`~/.ssh/config`)

You can simplify SSH connections by adding configurations:

Host myserver
    HostName 192.168.1.100
    User myuser
    IdentityFile ~/.ssh/id_ed25519

Now, connect using:

ssh myserver

3.0.3 Security Best Practices

Use SSH Keys Instead of Passwords – Keys are harder to brute-force.
Disable Root Login – Set PermitRootLogin no in /etc/ssh/sshd_config.
Change Default SSH Port – Using a non-standard port (e.g., 2222) helps reduce bot attacks.
Use a Firewall – Allow SSH access only to trusted IPs.
Enable Fail2Ban – Prevent brute-force attacks by banning repeated failed attempts.