= Setup and Configure Secure Shell Services (ssh) Using Virtual Machines =

=== Investigation 2: How do you establish an ssh connection. ===

# You should receive a message similar to the following:

<pre>

RSA key fingerprint is 53:b4:ad:c8:51:17:99:4b:c9:08:ac:c1:b6:05:71:9b.

Are you sure you want to continue connecting (yes/no)? yes

</pre>

{{Admon/note |Storing Fingerprints | When a user connects to a host using ssh, the host sends a fingerprint or digital signature to the client to establish its identity. The first time a connection is established the identity must be stored for subsequent connections. The fingerprints are stored separately for each user in a file called <code>~/.ssh/known_hosts</code> . <br /><br />From now on when you connect to that host the client will compare the received fingerprint against the list of known hosts before connecting. If the fingerprint does not match it could indicate somebody had setup a system to impersonate the computer you wish to connect to and you would receive a message like this}}

@ WARNING: POSSIBLE DNS SPOOFING DETECTED! @

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@

and the key for the according IP address 192.168.235.13

is unchanged. This could either mean that

Add correct host key in /home/user1/.ssh/known_hosts to get rid of this message.

Offending key in /home/user1/.ssh/known_hosts:53

checking.

Host key verification failed.

{{Admon/note |POSSIBLE DNS SPOOFING DETECTED | If you receive a message like the one displayed above, you should investigate why it is happening as it could indicate a serious security issue, or it could just mean that something on the host has changed, i.e. the OS was reinstalled.}}

<ol><li value="6">Logout of your ssh connection by typing <code>exit</code>.

<li>Check the state of the connection after logging out. Wait a few minutes and then check again. Record your observations.</li>

<li>Use the Internet to search for "TCP 3 way handshake" to see how TCP connections are established and closed.</li></ol>

{{Admon/tip | Methods of Authenticating User Identity | In this part of the lab you established an ssh connection to another host using a password to establish your identity. But passwords are not the only or even the best way of authenticating your identity. We can also use Public/Private key encryption. We will be looking at Public Key Authentication in the next investigation}}

'''Answer the Investigation 2 observations / questions in your lab log book.'''

=== Investigation 3: How do you establish an ssh connection using Public Key Authentication. ===

{{Admon/note | | '''Public Key authentication''' is a method of establishing identity using a pair of encryption keys that are designed to work together. One key is known as your private key (which as the name suggests should remain private and protected) and the other is known as the public key. (which as the name suggests can be freely distributed) The keys are designed to work together to encrypt data asymmetrically, that is to say that when we encrypt data with one of the keys it can only be decrypted with the other key from the pair. This means that when we connect, ssh can use the private key that only exists on my system in my account, to encrypt a message. That message can be decrypted by anybody with the corresponding public key. While it doesn't mean the message is secure as anybody could decrypt it with the public key, it does establish my identity, if the host can successfully decrypt the message then it must have come from the one person in possession of the private key. This basic method of authentication is used extensively in many network communications protocols that require the ability to authenticate identity.}}

# That should generate output similar to the following:

<pre>

Your public key has been saved in /home/user1/.ssh/id_rsa.pub.

The key fingerprint is:

<ol><li value="3"> After generating the keys it prompts you for the location to save the keys. The default is <code>~/.ssh</code> Your private key will be saved as <code>id_rsa</code> and your public key will be saved as <code>id_rsa.pub</code></li></ol>

{{Admon/tip | Lengthy Passphrases | You will then be prompted for a passphrase. The passphrase must be entered in order to use your private key. Passphrases are more secure than passwords and should be lengthy, hard to guess and easy to remember. For example one passphrase that meets this criteria might be "seneca students like fish at 4:00am". Avoid famous phrases such as "to be or not to be" as they are easy to guess. It is possible to leave the passphrase blank but this is dangerous. It means that if a hacker were able to get into your account they could then use your private key to access other systems you use.}}

</ol>

=== Investigation 4: How do you use scp and sftp. ===

{{Admon/note | | There are 2 common command line tools for transferring files between hosts over an encrypted ssh connection, <code>scp</code> and <code>sftp</code>.<br /> <code>sftp</code> is an interactive file transfer program that functions much like an ftp client. }}

# This will establish an interactive session after authentication.

# Type <code>help</code> to see the list of sftp commands at any time.

# Try using <code>sftp</code> to transfer files back and forth between hosts.

# As you did previously you can also use the <code>scp</code> command to copy files to and from remote hosts and even from one remote host to another.

=== Investigation 5: How do you use ssh to tunnel X. ===

You can also use ssh to tunnel window and bitmap information. Allowing us to login to a remote desktop host and run a Xwindows application such as <code>gedit</code> or <code>firefox</code> and the application will run on the remote host but be displayed on the local host.

# Once connected run the <code>gedit</code> application. (Gnome Text Editor)

# Enter some text and save a file with <code>gedit</code>.

# Exit <code>gedit</code>.

# Where was the file saved?

# Experiment with running other GUI applications through <code>ssh</code>.

'''Answer the Investigation 5 observations / questions in your lab log book.'''

== Further Securing your Secure Shell Connection ==

=== Investigation 6: How do you use ssh to tunnel other traffic. ===

{{Admon/note | | You can also use an ssh connection to tunnel other types of traffic. There could be different reasons for doing this. For example tunneling traffic for an unencrypted application/protocol through ssh can increase the security of that application. Alternatively you could use it to circumvent a firewall that is blocking traffic you wish to use but allows ssh traffic to pass through.}}

# You will be working with the 2nd scenario of bypassing a firewall that blocks http traffic.

# Create a small html document called <code>/var/www/html/index.html</code> that displays a short message.*

# The next step is to establish a tunnel. When you establish a tunnel you make an ssh connection to a remote host and open a new port on the local host. That local host port is then connected to a port on the remote host through the established tunnel. When you send requests to the local port it is forwarded through the tunnel to the remote port.

:::: [[Image:Tunnel.png]]

<li>Close the ssh connection and verify that the port 20808 is no longer listening.</li>

</ol>

=== Investigation 7: How do you make sshd more secure ===

{{Admon/note | | Anytime you configure your computer to allow logins from the network you are leaving yourself vulnerable to potential unauthorized access by so called "hackers". Running the sshd service is a fairly common practice but care must be taken to make things more difficult for those hackers that attempt to use "brute force" attacks to gain access to your system. Hackers use their knowledge of your system and many password guesses to gain access. They know which port is likely open to attack (TCP:22), the administrative account name (root), all they need to do is to "guess" the password.}}

# Confirm the new port is being used with a <code>netstat</code> command.

# Before we can use this new port we must change our firewall to allow traffic through the new port number and block access to port 22:<br /><code>iptables -I INPUT -p tcp -s0/0 --dport 22 -j DROP</code><br /><code>iptables -I INPUT -p tcp -s0/0 --dport 2200 -j ACCEPT</code>

{{Admon/important|Cannot connect via SSH?|To fix issues with the ability to ssh, on both machines:<ul><li>Ensure ssh is running. Systemctl status sshd.service.</li><li>Disable selinux by going into /etc/selinux/config and change "enforcing" to "disabled"; "targeted" to "minimum".</li><li>If your are still encountering problems flush iptables.</li></ul>}}

{{Admon/tip | Tip! | For scp access the option to be used is: <code>scp -P 2200</code>}}

{{Admon/tip | Tip! | For more ideas on making sshd more secure consult the HOW-TO link above.}}

<ol><li value="14">Finally as a system administrator you should periodically monitor your system logs for unauthorized login attempts.</li>

<li>It also logs all uses of the <code>su</code> and <code>sudo</code> commands.</li>

<li>Attempt to connect to all of your VM's as root and other users using both public key and password authentication. Use some su and sudo commands also. </li>

'''Answer the Investigation 7 observations / questions in your lab log book.'''

== Completing the lab ==