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== Part 1: Enabling the sshd service. ==
# Use your '''c7hostcentos1''' machine to complete this section
# OpenSSH should have been installed by default. Let's confirm this by issuing the command:<br /> <b><code><span style="color:#3366CC;font-size:1.2em;">rpm -qa | grep ssh</span></code></b>
# You should see a number of packages installed including <b>openssh-clients</b> and <b>openssh-server</b>
# Use your '''centos2centos3''' VM to complete this section.
# Open a terminal and run the '''netstat''' command (pipe to "grep sshd") to check the state of the connection. What is the state (i.e. LISTENING or ESTABLISHED)?
# Open another terminal and establish an ssh connection to your '''centos3centos4''' VM using the command:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">ssh ops235@centos3centos4</span></code></b><br>(Where 'ops235' is the account on centos3 centos4 and 'centos3centos4' is the hostname of the centos3 centos4 VM.)<br><br>
# You should receive a message similar to the following:<br><br>
#::<span style="font-family:courier">The authenticity of host 'centos3 centos4 (192.168.235.13)' can't be established.</span><br>
#::<span style="font-family:courier">RSA key fingerprint is 53:b4:ad:c8:51:17:99:4b:c9:08:ac:c1:b6:05:71:9b.</span><br>
#::<span style="font-family:courier">Are you sure you want to continue connecting (yes/no)? yes</span><br>
#::<span style="font-family:courier">Warning: Permanently added 'centos3centos4' (RSA) to the list of known hosts.</span><br><br>
# Answer '''yes''' to add to the list of known hosts.
# Issue the following command to confirm that you connected to your centos3 centos4 VM: <b><code><span style="color:#3366CC;font-size:1.2em;">hostname</span></code></b>
[[Image:spoof.png|thumb|right|485px|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 <u>reinstalled</u>)]]
<ol><li value="7">Switch back to the original terminal and re-run the netstat pipeline command again. Any change to the connection status?</li><li>Return to the second terminal, and logout of your ssh connection by typing <b><code><span style="color:#3366CC;font-size:1.2em;">exit</span></code></b>.
<li>Run the netstat command in the original terminal and check the state of the connection after logging out. Wait a few minutes and then check again. Record your observations.</li>
<li>Make certain to exit all connections, and remain in your '''centos2centos3''' VM. When using ssh to connect to other servers, it is very easy to forget which server you are currently using. Verify that you are in your '''centos2centos3''' VM by entering the command: <b><code><span style="color:#3366CC;font-size:1.2em;">hostname</span></code></b>
<li>Use the Internet to search for '''TCP 3 way handshake''' to see how TCP connections are established and closed.<br><br></li>
</ol>
::<span style="font-family:courier">Your public key has been saved in /home/user1/.ssh/id_rsa.pub.</span><br>
::<span style="font-family:courier">The key fingerprint is:</span><br>
::<span style="font-family:courier">93:58:20:56:72:d7:bd:14:86:9f:42:aa:82:3d:f8:e5 user1@centos2centos3</span><br><br>
<ol><li value="16"> After generating the keys it prompts you for the location to save the keys. The default is '''~/.ssh''' Your private key will be saved as <b>id_rsa</b> and your public key will be saved as '''id_rsa.pub'''</li>
<li>You will then be prompted for a pass-phrase. The pass-phrase must be entered in order to use your private key. Pass-phrases are more secure than passwords and should be lengthy, hard to guess and easy to remember. For example one pass-phrase 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 pass-phrase 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.<br><br></li>
<li>Now issue the command <b><code><span style="color:#3366CC;font-size:1.2em;">ssh-copy-id -i ~/.ssh/id_rsa.pub ops235@centos3centos4</span></code></b></li> <li>Try using ssh to now log into your '''centos3centos4''' VM <u>from</u> your '''centos2centos3''' VM. What happens? Were you required to use your pass-phrase? Issue the hostname command to verify that you are successfully logged into your '''centos3centos4''' VM.</li><li>Make certain to logout of your '''centos3centos4''' system. Use the '''hostname''' command to verify you are back in your centos2 centos3 server.</li>
</ol>
# Remain in your '''centos2centos3''' VM for this section.# To connect to a remote host type the command:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">sftp ops235@centos3centos4</span></code></b>
# This will establish an interactive session after authentication.
# Type <b><code><span style="color:#3366CC;font-size:1.2em;">help</span></code></b> to see the list of sftp commands at any time.
|- valign="top"
|{{Admon/tip| SELinux | SELinux may prevent ssh from accessing your home directories on centos1 centos2 because you created a new filesystem there. You can reset the security context of the /home directory with this command: '''restorecon -Rv /home'''}}
|}
<ol>
<li value="8">You can also use the '''scp''' command to copy files to and from remote hosts and even from one remote host to another.</li>
<li>Use '''scp''' to copy your services file to the centos3 centos4 host into the /tmp directory. (The path on a remote host follows the ''':''') using the command: <br /><b><code><span style="color:#3366CC;font-size:1.2em;">scp /etc/services ops235@centos3centos4:/tmp</span></code></b></li><li>Here is a neat trick: You can run commands remotely using ssh by typing the command as an argument after the ssh command. Issue the following command in your '''centos2centos3''' VM:<br><b><code><span style="color:#3366CC;font-size:1.2em;">ssh ops235@centos3 centos4 ls /tmp</span></code></b></li><li>What happened when you issued that command? Where you able to successfully using scp to copy the '''/etc/services''' file to '''centos3centos4's /tmp''' directory?</li><li>Experiment with '''scp''' to copy a file from '''centos3centos4''' directly to '''centos1centos2'''.</li>
</ol>
|- valign="top"
|{{Admon/tip | centos1 centos2 VM iptables and ssh service | You may need to adjust the firewall on your '''centos1centos2''' host to complete this section, and verify that the '''sshd''' service is running on that VM.}}
|}
: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 <b>gedit</b> or <b>firefox</b> and the application will run on the remote host but be displayed on the local host.
# For this section, you will be using your '''centos1centos2''' and '''centos2centos3''' VMs.# From your '''centos2centos3''' VM issue the ssh command to connect to your '''centos1centos2''' VM using the following command:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">ssh -X -C username@centos1centos2</span></code></b> (where 'username' is your learn account on centos1centos2)<br>(The '''-X''' option enables the forwarding of X window information, and the '''-C''' option enables compression for better performance).<br><br>
# Once the connection is properly established, run the '''gedit''' application. (Gnome Text Editor)
# The ''gedit'' window will display on your '''centos2centos3''' VM, but in reality, this application is running on your '''centos1centos2''' VM!
# Enter some text and save a file with '''gedit'''.
# Exit the '''gedit''' application.
# For this section, you will still be using your '''centos1centos2''' and '''centos2centos3''' VMs.
# We will be bypassing a firewall that blocks http traffic.
# In this investigation, '''centos1centos2''' will be your '''http server''' and '''centos2centos3''' will be your <u>client</u>.# Use the '''hostname''' command to verify that you are in your centos1 centos2 VM (as opposed to another VM by mistake via ssh!)
# On the HTTP server, make sure that the Apache web server is installed by typing the command:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">rpm -q httpd</span></code></b>
# If this is not installed, make sure to install '''httpd'''.
# Confirm that httpd is listening to TCP/80 using the '''netstat''' command.
# Create a small html document called '''/var/www/html/index.html''' that displays a short message. If you do not know how to use HTML markup language, just type a simple text message...
# <u>Restart</u> your '''centos1centos2''' VM. # On your '''centos1centos2''' VM (i.e. the http server), confirm everything is working locally by using a browser to connect to '''http://localhost'''# Set the default firewall configuration on centos1 centos2 to '''REJECT''' incoming requests to http (TCP/80)# NOTE: '''centos1centos2''': if '''http://localhost''' stops working locally, add the following iptables rule to centos1centos2, as root <br /><b><code><span style="color:#3366CC;font-size:1.2em;">iptables -I INPUT -i lo -j ACCEPT</span></code></b> # On '''centos2centos3''' confirm that the httpd service is stopped so it cannot interfere with your observations.# On '''centos2centos3''' confirm that you can't connect by using firefox to centos1 centos2 '''http://centos1centos2/'''
# The next step is to establish a <u>tunnel</u>. 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.
# In a terminal in your '''centos2centos3''' VM, '''make certain you are NOT logged in as root!'''# Establish a tunnel using a local port on centos2 centos3 of 20808, that connects to the remote port on '''centos1centos2''' of 80, using the following command on '''centos2centos3''':<br /><b><code><span style="color:#3366CC;font-size:1.2em;">ssh -L 20808:centos1centos2:80 username@centos1centos2</span></code></b><br><br> '''Note:'''<br>The '''-L''' option (which means Local port) takes one argument:<br><span style="courier"><local-port>:<connect-to-host>:<connect-to-port></span><br><br> The command basically connects your local port of 20808 to the remote port of 80 on '''centos1centos2'''.<br>This means all requests to 20808 on the <u>localhost</u> ('''centos2centos3''') are actually tunnelled through your ssh connection<br>to port 22 on '''centos1centos2''' and then delivered to port 80 on '''centos1centos2''', bypassing the firewall.<br><br># Once the tunnel is established use '''netstat''' to verify the port 20808 is listening on '''centos2centos3'''# Now using the browser on '''centos2centos3''' connect to '''http://localhost:20808'''#You should see the '''index.html''' page on '''centos1centos2'''.
# Close the ssh connection and verify that the port 20808 is no longer listening.
# For this section, you will still be using your '''centos1centos2''' and '''centos2centos3''' VMs.
# Think of a good quality password and change your root passwords on all 3 VM's to be more secure. (It would be a good idea to do this for non-root accounts also)
# The next change you can make is to prevent the root account from logging in to sshd altogether.
# Change to your '''centos2centos3''' VM and open a terminal.
# Edit the file '''/etc/ssh/sshd_config''' and look for the option '''PermitRootLogin'''. Un-comment the option (or add the option if it does not appear) and change the option value to '''"no"'''.<br><br>'''NOTE:''' Now any hacking attempt also has to guess an account name as well as the password. If you need to ssh with root access, ssh as a regular user and use '''su -''' to become root.<br><br>
# Even better, it is possible to restrict access to just specific users that require it.
# Edit the file '''/etc/ssh/sshd_config''' and add a new option of '''"AllowUsers account"''' using your login account for account
# In order for these changes to be effective, issue the following command to restart the sshd service:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">service sshd restart</span></code></b>
# Try sshing from your '''centos1centos2''' VM to your '''centos2centos3''' VM. Where you successful? Would it work if you let "AllowUsers account" without a username, or a non-existent username? Do not do this for your machine!
# Next change the default port number that sshd uses (TCP:22).
# Edit the '''/etc/ssh/sshd_config''' file again, un-comment the port option and change the port number it uses from ''22'' to '''2200'''.
# Next, we will drop any incoming traffic to port 22 by issuing the command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">iptables -I INPUT -p tcp -s0/0 --dport 22 -j DROP</span></code></b>
# We have now possibly mislead a potential "hacker" to the true port for our ssh server's communication channel (port).
# Switch to your '''centos1centos2''' VM.# Issue the commmand: <b><code><span style="color:#3366CC;font-size:1.2em;">ssh username@centos2centos3</span></code></b>. What happens? What port do you think that command is using by default?# Now issue the following command to ssh via port "2200": <b><code><span style="color:#3366CC;font-size:1.2em;">ssh -p 2200 username@centos2centos3</span></code></b>. Where you able to connect?
{|width="40%" align="right"
'''Arrange proof of the following on the screen:'''
<ol><li><span style="color:green;font-size:1.5em;">✓</span> '''centos2centos3''' VM:<blockquote><ul><li>have tunneled Xwindows application from '''centos1centos2''' via ssh</li><li>have tunneled http through firewall using ssh (on web-browser</li><li>have secured ssh against root access</li></ul></blockquote><li><span style="color:green;font-size:1.5em;">✓</span> '''centos3centos4''' VM:<blockquote><ul><li>have configured sshd to '''allow connection to centos3 centos4 VM'''</li><li>have logged in centos3 centos4 VM using '''public key authentication'''</li><li>have scp'd and sftp'd files to centos3 centos4 VM</li></ul></blockquote></li><li><span style="color:green;font-size:1.5em;">✓</span> '''c7hostcentos1''' Machine:<blockquote><ul><li>Confirmation that sshd is running on host machine</li></ul></blockquote><li><span style="color:green;font-size:1.5em;">✓</span> '''Lab7''' log-book filled out.</li></ol>
