How to Generate an SSH Key Pair with ssh-keygen and Upload It to a Server

Step 1: Generating Your SSH Key Pair

To generate your SSH key pair, you will use the ssh-keygen command. This command creates both a public and private key.

Instructions:

• Open a terminal window.
• Run the following command to generate an RSA key pair with a passphrase for added security:

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

• You will be prompted to enter a file in which to save the keys (default is ~/.ssh/id_rsa). Press Enter to accept the default.
• Next, you'll be asked for a passphrase. A strong passphrase adds an extra layer of security, so choose one carefully.

Step 2: Understanding id_rsa.pub

After generating your SSH key pair, the public key (idrsa.pub) is stored in ~/.ssh/idrsa.pub. This file contains the unique identifier that allows remote servers to authenticate you when you connect. The private key (id_rsa) should remain on your local machine and must never be shared.

Step 3: Copying the Public Key to Your Server

To copy the public key to the server, use ssh-copy-id. This tool securely copies the contents of ~/.ssh/idrsa.pub to the remote server's .ssh/authorizedkeys file.

Instructions:

• On your local machine, run:

ssh-copy-id -i ~/.ssh/id_rsa.pub root@a.b.c.d

Replace root@a.b.c.d with the appropriate username and IP address of your server.

Step 4: Verifying SSH Connection

After copying the key to your server, you should be able to log in without a password using SSH. To verify this:

1. Log out from the current session.
2. Attempt to log back into the server:

ssh root@a.b.c.d

If everything was set up correctly, you should now be logged in with no password prompt.

Summary of File Locations:

• Local Machine:
• ~/.ssh/id_rsa (private key)
• ~/.ssh/id_rsa.pub (public key)

• Server:
• /root/.ssh/authorized_keys (where the public key is added after using ssh-copy-id)

By following these steps, you ensure a secure method of logging into your server without needing to enter a password every time.