Step-By-Step RSA Authentication Setup

This guide will demonstrate how to set up RSA-based authentication on a remote machine. RSA authentication allows ssh access without entering a password each time. Be aware that RSA doesn't do Kerberos authentication, so RSA won't work if your target machine expects to speak Kerberos.

1. Select machine you will be logging in from.

RSA authentication is machine-specific, so repeat these steps for each machine that you wish use. This example uses a machine called farfo as our host and wonderdog as our target.

2. Change to your ~/.ssh directory.

farfo(1)% cd ~/.ssh

3. Generate RSA Keys

The command is ssh-keygen. Specify the key type (with the -t option) as rsa. Enter a hostname-specific name for the keyfile (id_farfo in this example), and when prompted, enter your password for the target machine.

farfo(2)% ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/u/j/o/joeuser/.ssh/id_rsa): id_farfo
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in id_farfo.
Your public key has been saved in id_farfo.pub.
The key fingerprint is:
ff:bb:cc:bb:aa:99:88:77:66:55:44:33:22:11:00:00 joeuser@farfo.cs.wisc.edu

4. SSH to the Target Machine

farfo(3)% ssh wonderdog
Last login: Sat Jul 7 1:49:01 2006 from farfo Sun Microsystems Inc. SunOS 5.11 snv_33 October 2007 wonderdog(1)%

5. Copy the Public Key to the Target

Copy the public keyfile to the ~/.ssh/ directory on the target with the scp utility. Enter passwords as necessary.

wonderdog(1)% scp farfo:.ssh/id_farfo.pub ~/.ssh/
Password:
id_farfo.pub 100% |***********************************| 240 00:00

6. Append the Key to the Authentication File

If the file ~/.ssh/authorized_keys does not exist, copy your public key to this file. Otherwise, append your public key to the file.

7. Log out and test RSA Authentication

You should not be promted for a password when you log into the target from the host.