SSH Public Key Based Authentication — Howto

The SSH protocol is recommended for remote login and remote file transfer which provides confidentiality and security for data exchanged between two computer systems, through the use of public key cryptography. The OpenSSH server provides this kind of setup under Linux. It is installed by default. This how-to covers generating and using ssh keys for automated usage such as:

  1. Automated Login using the shell scripts.
  2. Making backups.
  3. Run commands from the shell prompt etc.


Task: Generating SSH Keys

First, log on to your workstation ( for example log on to workstation called as vivek user). Please refer the following sample setup – You will be log in, on your local system, AS THE USER you wish to make passwordless ssh connections.

Fig.01 ssh key based authentication

Create the cryptographic Key on FreeBSD / Linux / UNIX workstation, enter:
ssh-keygen -t rsa
Assign the pass phrase (press [enter] key twice if you don’t want a passphrase). It will create 2 files in ~/.ssh directory as follows:

#~/.ssh/id_rsa : identification (private) key

#~/.ssh/ : public key

Use scp to copy the (public key) to server as authorized_keys2 file, this is know as Installing the public key to server.
<pre>scp .ssh/</pre>
From FreeBSD workstation login to server:


Changing the pass-phrase on workstation (if needed):

ssh-keygen -p

Use of ssh-agent to avoid continues pass-phrase typing
At freebsd workstation type:

ssh-agent $BASH

Type your pass-phrase

Now ssh server will not use prompt for the password. Above two commands can be added to your ~/.bash_profile file so that as soon as you login into workstation you can set the agent.

Deleting the keys hold by ssh-agent

To list keys, enter:

ssh-add -l

To delete all keys, enter:

ssh-add -D

To delete specific key, enter:

ssh-add -d key