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Generating SSH RSA/DSA keys locally – on devices running Junos

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This article describes the procedure to generate SSH RSA/DSA keys on a device running Junos and configure the device to use password-less public key based encrypted SSH authentication.

The goal of this article is to show a reader how to generate SSH RSA/DSA keys locally and configure the device to use password-less public key based encrypted SSH authentication.

In some case, users may need to generate SSH RSA/DSA keys locally to allow remote login using SSH RSA/DSA keys instead of using passwords stored locally.

We have to enable SSH service on the switch using the following command:

root@Juniper# set system services ssh

We can generate the SSH key on a device running Junos by logging into the shell prompt as a root user:

root@Juniper>start shell
root@Juniper% ssh-keygen -t rsa

Generating public/private rsa key pair.

Enter file in which to save the key (/root/.ssh/id_rsa): 
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 

Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.

The key fingerprint is:

91:6e:b9:52:fd:14:85:1e:8c:40:9a:7c:2d:c7:d4:0d root@SW_Jaffa_Monitor_104
% ssh-keygen -t rsa/dsa

Once the keys are generated we can associate the key with the “userid” using the following command.

root@Juniper#set system login user <userid> uid 2000
root@Juniper#set system login user <userid> class super-user
root@Juniper#set system login user <userid> authentication load-key-file /root/.ssh/id_rsa.pub

After running the above configuration commands, it will create a directory with <userid> in /var/home and the authorized_key for SSH will be created.

When an upgrade/downgrade is performed, the files – id_rsa and id_rsa.pub, which are locally created and are not part of configuration, will not be restored.
Hence we will have to copy the contents of the /root/.ssh directory and put them back after the upgrade/downgrade is complete.
We also will have to associate the user with the key using the following CLI command:

root@Juniper#set system login user <userid> authentication load-key-file /root/.ssh/id_rsa.pub