ssh-keygen Command in Ubuntu 20.04 LTS Linux server - Explained with examples

SSH is used for the validation and authenticating the users with the use of key value pairs like private and public keys. Such keys are generated by using the ssh-keygen command. You are able to generate different types of keys like RSA, DSA and so on.

Here at LinuxAPT, we shall look into the process of using the ssh-keygen command to generate different keys which authenticates the public and private keys used by SSH. 

How to use ssh-keygen ?

With ssh-keygen command, you can generate different types of keys like RSA, DSA and so on.

RSA keys;

• $HOME/.ssh/id_rsa: RSA authentication identity file of the user. It is only readable by the user.
• $HOME/.ssh/id_rsa.pub: RSA public key file for the authentication.

DSA keys;

• $HOME/.ssh/id_dsa: DSA authentication identity file of the user. It is only readable by the user.
• $HOME/.ssh/id_dsa.pub: DSA public key file for the authentication.

Using ssh-keygen to create RSA keys

Here, ssh-keygen is used to create RSA keys for authentication. By default, if you just use the ssh-keygen command, it generates the rsa keys. Let’s generate the rsa keys by executing the command:

$ ssh-keygen -t rsa

Or

$ ssh-keygen

Here, both the public key i.e id_rsa.pub and private key i.e id_rsa are saved in the default location that is $HOME/.ssh/.

As the public key needs to be copied to the remote server so the user can login with the SSH authentication. It is copied to the $HOME/.ssh/authorized_keys file of the remote server. Let’s check the public key generated with the above command:

$ cat id_rsa.pub

Simply copy this public key and paste it to this location: $HOME/.ssh/authorized_keys file of the remote server for the authentication.

Using ssh-keygen to create DSA keys

Likewise, DSA keys can also be created with simple change in the command. By default, if you just use the ssh-keygen command, it generates the rsa keys. But to generate DSA keys, simply put -t dsa as an argument in the command. For further details, you can execute the command:

$ ssh-keygen -t dsa

Both the public key i.e id_dsa.pub and private key i.e id_dsa are also saved in the default location that is $HOME/.ssh/.

You can simply copy the public key to the remote server for the user to login with the SSH authentication. It is copied to the $HOME/.ssh/authorized_keys file of the remote server. Let’s check the public key generated with the above command:

$ cat id_dsa.pub

Copy this public key and paste it to this location: $HOME/.ssh/authorized_keys file of the remote server for the authentication.

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