A simple guide to connect to a server using SSH key-based authentication with a custom .ssh/config file.

Prerequisites

You should have:

• A server with SSH enabled (e.g., cloud instance, VPS, dedicated server).
• Access to an account on the server (e.g., admin, or user).
• A local machine with OpenSSH installed (Linux, macOS, or Windows with WSL/PowerShell).
• Permission to add your SSH public key to the server.

1. SSH Authentication Types

SSH supports multiple authentication methods:

• Password-based
  Enter a username and password when connecting. Simple, but less secure.

• Key-based (recommended)
  Use a cryptographic key pair for authentication. No password sent over the network.

• Other methods
  Includes GSSAPI/Kerberos, certificate-based, and hardware tokens.

This guide focuses on key-based authentication.

2. Generate an SSH Key Pair

Run this command on your local machine:

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

• -t ed25519 — modern, secure key type.
• -C — optional comment (usually your email).
• Press Enter to accept default location (~/.ssh/id_ed25519).
• You can set a passphrase for extra protection (optional).

If you prefer RSA (for compatibility with older systems):

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

3. Add Your Public Key to the Server

Option A — You have server access and can edit authorized_keys directly:

1. Copy your public key to the server:

   ssh-copy-id user@example.com
   

   (Replace user@example.com with your server username and address.)

2. Or manually append your public key to:

   ~/.ssh/authorized_keys
   

Option B — You send your public key to the server administrator:

• Provide the contents of your public key file (e.g., ~/.ssh/id_ed25519.pub).
• The admin will add it to ~/.ssh/authorized_keys for your account.

4. Configure .ssh/config for Easier Connections

Instead of typing a long SSH command with username, hostname, and key path each time, create a shortcut.

Edit (or create) your SSH config file:

nano ~/.ssh/config

or for vim users:

vi ~/.ssh/config

Example:

Host myserver
  HostName server.example.com
  User myuser
  IdentityFile ~/.ssh/myserver-key.pem

• Host — nickname for the connection.
• HostName — server’s public IP or domain.
• User — username on the server.
• IdentityFile — path to your private key.

Save the file, then:

chmod 600 ~/.ssh/config

5. Connect to the Server

Now you can connect with just:

ssh myserver

Instead of:

ssh -i ~/.ssh/myserver-key.pem myuser@server.example.com

6. Troubleshooting

• Permission denied (publickey)

  • Check that the public key is in the correct ~/.ssh/authorized_keys file.
  • Ensure ~/.ssh (700) and authorized_keys (600) permissions are correct.

• .ssh/config not applied

  • Ensure file permissions are chmod 600.
  • Confirm that Host name matches the shortcut you’re using.

Best Practices

• Use ed25519 keys for stronger security and faster authentication.
• Never share your private key.
• Keep a backup of your private key in a safe location.
• Disable password authentication on the server for better security (optional).