Public-key authentication over ssh

To secure access to the OpenSSH, it is recommended to disable the password authentication and use a public-key authentication. It allows user to connect to remote server without sending the password over Internet.

This could be done in three simple steps:

Generate SSH key-par

The below command generates a private key and the public key:

ssh-keygen -t dsa

Two files will be created in the /home/user/.ssh/ directory:
id_dsa – the private dsa key. which must never be made available to anyone
id_dsa.pub – the public dsa key, which can be distributed to other computers

You should get the following output:

Generating public/private dsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_dsa):

Do not forget to enter a passphrase to protect the key.

Transfer public key to the remote server

Copy the key to the remote server:

ssh-copy-id -i ~/.ssh/id_dsa.pub ip.address

This command will add your public key to a remote machine’s authorized_keys2 file, allowing user to login without the password.

Test connection

Now, connect via SSH to your remote server:

ssh -v user@ip.address

You should get output similar to above screenshot.

Related links

SSH Public key based authentication – Howto
O’Reilly Book Excerpts: SSH, The Secure Shell: The Definitive Guide. SSH Public-Key Authentication
Gettin’ Fancy with SSH Keys
HOWTO: set up ssh keys