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Lab 2: Secure Access with SSH

In this lab you will customize SSH for secure and convenient access to class computers. 

In this lab you will create a public/private key pair for use with SSH. The key will allow you to login to Opus and your VMs without using a password. Using keys this way is more secure than passwords because keys are much harder to guess and when you use keys you can disable password logins. This is especially useful for the root account which is a very high value target. 

Part 1: Complete Your Network Setup
Last week you setup the network on Ubuntu. In this lab you'll get Fedora connected too. The first step is to bring up the internal interface (eth1) on Ubuntu. Add the following lines to your /etc/network/interfaces file. 

auto eth1 
iface eth1 inet static

This will give your internal network interface the address Because this is an internal interface all of your VMs can share it. Now you will need to configure Ubuntu to act as a router for Fedora. Do that by editing the file /etc/rc.local file. Add the following lines (above the exit line):

sysctl -w net.ipv4.ip_forward=1
iptables -t nat -A POSTROUTING -s -o eth0 -j MASQUERADE

Now use the GUI on Fedora to set the following network settings: 
    IPv4 address: 

See the picture below:

Part 2: Create an SSH Key Pair
It's simple to create an SSH key. You run the command on Opus:


That command will (by default) place your keys in the following files:


The *.pub key is your public key. You can do what you want with that, make it your email signature or post it on the Internet. The other one must be kept secret in order to stay secure. If your private key is on a shared computer (like Opus) you must encrypt it with a password. Be sure to encrypt the key you create with a password

Part 3: Install Your Public Key
Now that you have a public key you must install it on any machine you want to be able to login to. To do this simply copy the contents of your id_dsa.pub into the file:


The authorized_keys file MUST be on the host you intend to login to. In other words if you want to login to your VM from Opus the private key must be on Opus and the public key must be in the authorized_keys file on your VM. You can have as many keys in your authorized_keys as you like. Once you have completed this step test that you can login as student without supplying student's password. 

Part 4: Start SSH Agent
After the last part of the lab you were able to login to your VM without typing in the user's password. Yet, you still had to type in the password for your private key. If you login again you'll have to type the password in again. That's because, by default, SSH agent is not started for you on Opus. 

Turn In
  1. Submit your public key with the IP address of your Ubuntu VM. 
Submit your homework on blackboard.

  • 20 points for a public key that is installed on your VM