Changes

{{Admon/caution | Important/warning! | This ==Overview== * In this lab is heavily under construction, It you will learn how to use the ssh, scp, sftp commands to work between computer systems via a network.* In addition, you will undergo major changes until this warning is removedlearn various methods of how to communicate between computer networks using SSH tunneling, and simplify secure network communication by using Public Key Authentication.}}

 ==Required Materials (Bring to All Labs)== * Fedora 17 LIVE CD* Fedora 17 x86_64 Installation DVD* SATA Hard Disk (in removable disk tray)* USB Memory Stick* Lab Logbook == Prerequisites== * Completion and Instructor "Sign-off" of Lab 6: [[OPS235 Lab 6]]  ==Linux Command Online Reference ==Each Link below displays online manpages for each command (via [http://linuxmanpages.com/ http://linuxmanpages.com]): {|width="100%" cellpadding="5" width="50%"|'''Networking Utilities '''|'''Additional Utilities:'''|'''Configuration Files:'''|- valign="top"|* [http://linuxmanpages.com/ man pagesman1/ssh.1.php ssh] for *[http://linuxmanpages.com/man1/ssh, -keygen.1.php ssh-keygen, sshd_config, ssh_config, ]*[http://linuxmanpages.com/man1/scp.1.php scp, ]*[http://linuxmanpages.com/man1/sftp.1.php sftp]*[http://linuxmanpages.com/man8/netstat.8.php netstat, sftp, ]*[http://linuxmanpages.com/man8/ifconfig.8.php ifconfig, ]*[http://linuxmanpages.com/man8/ping, .8.php ping]*[http://linuxmanpages.com/man8/arp, netstat, service.8.php arp]*[http://linux.die.net/man/1/ssh-copy-id ssh-copy-id]|*[http://www.linuxcertif.com/man/1/systemctl/ systemctl]*[http://linuxmanpages.com/man1/hostname.1.php hostname]*[http://linuxmanpages.com/man8/restorecon.8.php restorecon]|*[http://linux.about.com/library/cmd/blcmdl5_ssh_config.htm ssh_config]*[http://linux.about.com/od/commands/l/blcmdl5_sshdcon.htm sshd_config]|}  ==Resources on the web==Additional links to tutorials and HOWTOs:* [[IPTables]] Reference

== Configuring & Establishing an SSH Connection == === Lab Preparation ===

{{Admon/note | Note! Use your f17host computer system | Complete the following steps on your fedora host.}}

* # OpenSSH should have been installed by default. Lets confirm this by issuing the command: ** <br /> <code>rpm -qa | grep ssh</code>* # You should see a number of packages installed including <code>openssh-clients</code> and <code>openssh-server</code> * # <code>openssh-server</code> installs a service called <code>sshd</code>, confirm this service is running by issuing the command:** <br /><code>systemctl status sshd.service sshd status</code>* # Now check that the sshd service is configured to start for runlevels 2, 3, 4, & 5, by issuing the commandautomatically:** <code>chkconfig -systemctl is-list enabled sshd</code> * If the .service is not configured correctly fix it by issuing the command:** <code>chkconfig --level 2345 sshd on</code>* # Now that you know the service is running investigate what port number and protocol sshd uses by issuing the command:** <br /><code>netstat -atunp</code>* # What protocol and port is the sshd process using?* # What is the state of the port?* # Why do UDP ports not have a state?* # Reissue the <code>netstat</code> command without the <code>n</code> option. * # What is the difference? * # The <code>n</code> option tells netstat to list everything with numerical values, without it netstat resolves IP addresses and port numbers to host names and protocol names using the files <code>/etc/hosts</code> and <code>/etc/services</code> * # <code>netstat</code> is a very useful command for anything to do with networking. Read its man page and make sure you understand its output.* # Make sure your <code>sshd</code> service is running on all 3 of your VM's* '''Answer the Investigation 1 question observations / questions in your lab log book.'''

{{Admon/note | Note! Use your fedora2 VM | Complete this investigation on your fedora2 VM.}}

* As your learn account establish # Establish an ssh connection to your fedora3 VM using the command:** <br /><code>ssh ops235@fedora3</code>* <br />(Where 'ops235' is the account on fedora3 and 'fedora3' is the hostname of the fedora3 VM.)* # You should receive a message similar to the following:

{{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> .}}* Answer yes to add to the list of known hosts.{{Admon<br /><br /note | | >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:}}<ol><li value="3"> Answer '''yes''' to add to the list of known hosts.</li></ol> 

{{Admon/note | POSSIBLE DNS SPOOFING DETECTED | If you receive a message like this 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="4">When prompted enter your password for your ops235 account on fedora3.</li><li>Establish an ssh connection using your learn account from fedora3 to fedora2.</li></ol>{{Admon/note |Proof of Established SSH Connection | When you have both ssh connections established between fedora2 and fedora3 check your network connections using the netstat command. You should now see at least 2 TCP connections with a state of ESTABLISHED. One connection represents the connection from fedora2 to fedora3 and the other represents the connection from fedora3 to fedora2. You should also see that you still have ssh listening to TCP port 22. Notice that the client side of each connection uses a random port number in the upper ranges. This common behaviour for client side applications.}}<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>Make certain to exit all connections, and that your shell is located in your <u>Fedora2</u> server. You can verify this by entering the command: <code>hostname</code><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.'''

{{Admon/note | Note! Use your fedora2 VM | Complete this investigation on your fedora2 VM.}}

{{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.}}* # Start by generating a keypair as your learn account on fedora2 using the command:** <br /><code>ssh-keygen -t dsa</code>* # That should generate output similar to the following:

Generating public/private dsa rsa key pair.Enter file in which to save the key (/home/user1/.ssh/id_dsaid_rsa):

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

* <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_dsaid_rsa</code> and your public key will be saved as <code>id_dsaid_rsa.pub</code></li></ol>{{Admon/tip | 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><li value="4"> Once your keys have been saved you should check to make sure the permissions of the <code>.ssh</code> directory and your key files are secure. </li>* <li> Use the following commands to secure them:** <br /><code>chmod 700 ~/.ssh</code>** <br /><code>chmod 600 ~/.ssh/id_dsaid_rsa*</code><br /></li>* <li>The next step is to copy your public key to fedora3 (the remote host). You can use the scp command to do it.</li>* <li><code>scp</code> (secure copy) is used to copy files between hosts over the ssh protocol. The files are sent over an encrypted channel as is all ssh traffic. </li>* <li>Issue the command:** <br /><code>scp ~/.ssh/id_dsaid_rsa.pub ops235@fedora3:</code></li>* <li>This will copy your public key to your ops235 home directory on fedora3.</li>* <li>The ''':''' is important as it separates the hostname from the path where it is copied to. </li>* <li>The default location is the users home directory on the remote host but you can also use an absolute or relative path after the ''':'''</li>* <li>Enter your password to complete the copy.</li>* <li>Now ssh to fedora3 using a password to authenticate.</li>* <li>Once logged in to fedora3 we need to add the public key to your list of authorized_keys</li>* The <li>he safest way to do this is to append the contents of <code>id_dsaid_rsa.pub</code> to the <code>.ssh/authorized_keys</code> file. To do this use the command:** <br /><code>cat ~/id_dsaid_rsa.pub >> ~/.ssh/authorized_keys</code></li></ol>

* <ol><li value="16"> Once again you should secure the <code>.ssh</code> directory and the <code>authorized_keys</code> file using the following commands:** <br /><code>chmod 700 ~/.ssh</code>** <br /><code>chmod 600 ~/.ssh/authorized_keys</code></li>* <li>Logout of fedora3 and log back in again.</li>* <li>You should be prompted to enter your passphrase to unlock your private key.</li></ol>

* --><ol><li value="3">Now issue the command <code>ssh-copy-id -i ~/.ssh/id_rsa.pub fedora3</code></li> <li>Now we can ssh into fedora3 from fedora2 using 2 different authentication methods.</li>* <li>Make certain to logout of your Fedora3 system. Use the <code>hostname</code> command to verify you are back in your Fedora2 server.</li></ol> '''Answer the Investigation 3 question observations / questions in your lab log book.''' == Using SSH &amp; Other Secure Shell Utilities ==

{{Admon/note | Note! Use your fedora2 VM | Complete this investigation on your fedora2 VM.}}

{{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. }}

* # To connect to a remote host type the command:** <br /><code>sftp ops235@fedora3</code>* # This will establish an interactive session after authentication. * # Type <code>help</code> to see the list of sftp commands at any time.* # The 2 main commands are <code>put</code> to copy a file from the local host to the remote host (upload) and <code>get</code> to copy a file from the remote host to the local host (download).* # 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.# Use <code>scp</code> to copy your services file to the fedora3 host into the /tmp directory. (The path on a remote host follows the ''':''') using the command: <br /><code>scp /etc/services ops235@fedora3:/tmp</code># Experiment with <code>scp</code> to copy a file from fedora3 directly to fedora1.{{Admon/tip| SELinux | SELinux may prevent ssh from accessing your home directories on Fedora 1 because you created a new filesystem there. You can reset the security context of the /home directory with this command: <code>restorecon -Rv /home</code>}}  '''Answer the Investigation 4 observations / questions in your lab log book.'''

{{Admon/note | Note! Use your fedora2 and fedora1 VMs | Complete this investigation on your fedora2 and fedora1 VM's.}}

{{Admon/note tip | fedora1 VM iptables and ssh service | You may need to adjust the firewall on your fedora1 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 <code>gedit</code> or <code>firefox</code> and the application will run on the remote host but be displayed on the local host. }}

<!-- * In order to allow remote users to tunnel your XWindows X window (GUI) applications you must configure <code>sshd</code> to forward this type of data.* # Edit the sshd configuration file on fedora1. <code>/etc/ssh/sshd_config</code> and edit or uncomment the following:

* <ol><li value="2"> Restart the <code>sshd</code> service on fedora1 using the command:** <br /><code>service sshd restart</code> -->* # From fedora2 <code>ssh</code> to fedora1 using the following command:** <br /><code>ssh -X -C user@fedora1</code> (Where 'user' is your learn account on fedora1). The <code>-X</code> enables the forwarding of X window information, and the <code>-C</code> enables compression for better performance.* # Once connected run the <code>gedit</code> application. (Gnome Text Editor)* # The gedit window will display on fedora2 but it is running fedora1.* # 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 question observations / questions in your lab log book.'''  == Further Securing your Secure Shell Connection ==

{{Admon/note | | You can also 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 an ssh connection 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 tunnel "guess" the password.}} {{Admon/tip | Tip! | Making your root password (and all other types accounts!) both quite complex but easy to remember is not hard. Passwords should be a minimum of 8 characters long, preferably longer, contain upper and lower case letters, numbers, and special characters. A good example of traffica strong password might be "LotR3--RotK." This is not that hard to remember as it corresponds to a book title. "Lord of the Rings 3 Return of the King." The password "P@ssw0rd!" is not as good because it is quite obvious and common.}} # Think of a good quality password and change your root passwords on all 3 VM's to be more secure. There could (It would be different reasons a good idea to do this for doing thisnon-root accounts also)# The next change you can make is to prevent the root account from logging in to sshd altogether. For example tunneling traffic # Edit the file <code>/etc/ssh/sshd_config</code> and look for an unencrypted applicationthe option <code>PermitRootLogin</code>. Uncomment the option (or add the option if it does not appear) and change the option value to <code>"no"</code>.# Even better, it is possible to restrict access to just specific users that require it. # Edit the file <code>/etc/protocol through ssh can increase /sshd_config</code> and add a new option of <code>"AllowUsers account"</code> using your login account for account.# In order for these changes to be effective, issue the following command to restart the sshd service:<br /><code>service sshd restart</code># Now any hacking attempt also has to guess an account name as well as the security of that applicationpassword. Alternatively If you could need to ssh with root access, ssh as a regular user and use <code>su -</code> to become root.# Next change the default port number that sshd uses (TCP:22). # Edit the sshd configuration file again and change the port number it uses to circumvent 2200. # Restart the service. # 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># To test the new port connect to fedora1 from fedora2 using the following command:<br /><code>ssh -p 2200 user@fedora1</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>On Fedora systems the log file that is blocking traffic you wish used is <code>/var/log/secure</code> </li><li>It also logs all uses of the <code>su</code> and <code>sudo</code> commands.</li><li>Attempt to connect to use but allows ssh traffic 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><li>Inspect the log to pass throughsee what kind of information is logged.</li></ol> '''Answer the Investigation 7 observations / questions in your lab log book.'''  == Completing the lab == {{Admon/important|Time for a new backup!|If you have successfully completed this lab, make a new backup of your virtual machines.}} Arrange proof of the following on the screen:# have configured sshd to allow connections over a non default port.# have logged in to a VM using public key authentication# have scp'd and sftp'd files to a VM.# have tunneled Xwindows applications through ssh# have tunneled http through firewall using ssh# have secured ssh against root access == Preparing for Quizzes ==

* You will be working with the 2nd scenario of bypassing a firewall that blocks http traffic.* In this investigation fedora1 will be your http server and fedora2 will be your client.# What port does sshd use by defaults? * On the HTTP server (fedora1), make sure the Apache web server # What file is installed by typing the command:used to configure sshd?** <code>rpm -q httpd<# What sftp commands are used to upload/code>download files?* If it is installed check the configuration # What kind of files are stored in the service to see if it is automatically started at any runlevels by issuing the command:** <code>chkconfig --list httpd<"~/.ssh/code>" directory?* If it has not been started automatically start # How do you determine whether the sshd service using the command:** <code>service httpd start</code>is running on your system or not?* Confirm that httpd # What is listening to TCP/80 using the command:** <code>netstat -atnp</code>* Create a small html document called <code>/var/www/htmlpurpose of the ~/index.html<ssh/code> that displays a short message.* known_hosts file?* On # What is the fedora1 (purpose of the http server) confirm everything is working locally by using a browser to connect to http:~/.ssh/localhostauthorized_keys file?* The default firewall configuration on fedora1 is to REJECT incoming requests to http (TCP/80)# Which system log file records each use of the sudo command?* Confirm that # How do you can't connect by using firefox on fedora2 to connect to fedora1 http://fedora1/* On fedora2 confirm that stop the httpd sshd service is stopped so it cannot interfere with your observations.?* The next step is to establish a tunnel. When # How do you establish a tunnel you make an ssh connection to a remote host and open a new XWindows applications?# What port on is the local host. That local host default scp port is then connected to a ?# What port on the remote host through the established tunnel. When you send requests to the local port it (s) is forwarded through the tunnel to the remote port./are used by httpd service?