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{{Admon/caution|THIS IS AN OLD VERSION OF THE LAB|'''This is an archived version. Do not use this in your OPS235 course.'''}}= Setup and Configure Secure Shell Services (ssh) Using Virtual Machines LAB PREPARATION =
==OverviewPurpose / Objectives of Lab 7==[[Image:shield.png|thumb|right|180px|Protecting a computer network from unauthorized access is one of the many day-to-day operations for a Linux system administrator and/or security specialist]]
==My Toolkit (CLI Reference)==
{|width="100%" cellpadding="5" width="50%"
*[http://man7.org/linux/man-pages/man7/hostname.7.html hostname]
*[http://linux.die.net/man/8/restorecon restorecon]
*[http://linux.die.net/man/8/chkconfig chkconfig]
|
*[http://linux.about.com/library/cmd/blcmdl5_ssh_config.htm ssh_config]
== Configuring & Establishing an INVESTIGATION 1: CONFIGURING AND ESTABLISHING AN SSH Connection =CONNECTION=
=== Investigation 2Part 1: How do you establish an ssh connectionEnabling the sshd service. ==={{Admon/note | Use your centos2 VM | Complete this investigation on your centos2 VM.}}
# Establish an ssh connection Use your '''c7host''' machine to your centos3 VM using 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 ops235@centos3</span></code><br /b>(Where 'ops235' is the account on centos3 and 'centos3' is the hostname of the centos3 VM.)# You should receive see a message similar to the followingnumber of packages installed including <b>openssh-clients</b> and <b>openssh-server</b> # <b><code><span style="color:#3366CC;font-size:1.2em;">openssh-server</span></code><pre/b>The authenticity of host installs a service called '''sshd'centos3 (192.168.235.13)' can't be established.RSA key fingerprint Confirm that this service is 53running by issuing the command:b4<br /><b><code><span style="color:ad#3366CC;font-size:c8:51:17:99:4b:c9:08:ac:c1:b6:05:71:9b1.2em;">service sshd status</span></code></b>Are # Also, you sure you want should confirm that the sshd service is enabled (to continue connecting (yes/nostart automatically upon boot-up)? yesWarning. To do this issuing the following command:<br><b><code><span style="color:#3366CC;font-size: Permanently added 'centos3' (RSA) to the 1.2em;">systemctl list of known hosts.-unit-files | grep sshd</span></precode>{{Admon</note |Storing Fingerprints | When b><br><br>'''NOTE:''' the ''netstat'' is a user connects very useful command for anything to a host using ssh, do with networking. Read the host sends a fingerprint or digital signature to man pages and make sure you understand the client to establish its identitynetstat command's output. The first time a connection <br><br># Now that you know the service is established running, investigate what '''port number''' and '''protocol''' sshd uses by issuing the identity must be stored for subsequent connections. The fingerprints are stored separately for each user in a file called command:<br /><b><code>~/<span style="color:#3366CC;font-size:1.ssh/known_hosts2em;">netstat -atunp</codespan> . <br /code><br /b>From now on when you connect to that host # What protocol and port is the client will compare sshd process using? What is the received fingerprint against the list state of known hosts before connecting. If the fingerprint does not match it could indicate somebody had setup a system to impersonate the computer port? Why would you wish to connect to and you would receive think that UDP ports don't have a message like this}}state?# Reissue the <b><olcode><li valuespan style="3color:#3366CC;font-size:1.2em;"> Answer netstat</span></code></b> command without the '''yes-n''' option. What is the difference?# How is the file '''/etc/services''' related to add to the list difference?# Make sure the '''sshd''' service is running on '''all 3 of known hosts.</li></ol>your VM's'''
|- valign=== Investigation 3: How do you establish an ssh connection using Public Key Authentication. ==={{Admon/note | Use your centos2 VM | Complete this investigation on your centos2 VM.}}"top"
|{{Admon/note | Storing Fingerprints | '''Public Key authentication''' is When a user connects to a method of establishing identity host 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 sends a keypair as your learn account on centos2 using the command:<br /><code>ssh-keygen</code># That should generate output similar fingerprint or digital signature to the following:<pre>Generating public/private rsa key pair.Enter file in which client to save the key (/home/user1/.ssh/id_rsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/user1/.ssh/id_rsa.Your public key has been saved in /home/user1/.ssh/id_rsa.pubestablish its identity.The key fingerprint first time a connection is:93:58:20:56:72:d7:bd:14:86:9f:42:aa:82:3d:f8:e5 user1@centos2</pre><ol><li value="3"> After generating established the keys it prompts you identity must be stored for the location to save the keyssubsequent connections. The default is fingerprints are stored separately for each user in a file called <code>~/.ssh</code> Your private key will be saved as <code>id_rsaknown_hosts</code> and your public key will be saved as <code>id_rsa.pub<br /code><br /li></ol>{{Admon/tip | Lengthy Passphrases | You will then be prompted for a passphrase. The passphrase must be entered in order From now on when you connect 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"host the client will compare the received fingerprint against the list of known hosts before connecting. Avoid famous phrases such as "to be or If the fingerprint does not match it could indicate somebody had setup a system to be" as they are easy to guess. It is possible to leave impersonate the passphrase blank but this is dangerous. It means that if a hacker were able computer you wish to get into your account they could then use your private key connect to access other systems and you use.would receive a message like this}}
|} As a system administrator, you have the ability to generate or create public and private keys to ensure safe and secure ssh connections. The system administer can generate these keys for the first time, of if they suspect that a hacker has compromised the server, can remove the existing keys and generate new keys. A common type of attack, Arp Poisoning (Man in the Middle Attack), can be used to redirect packets to a third party while maintaining the illusion that the connection is secure. Therefore, understanding about the generation and management of public/private keys are important to the security of servers. # Use your '''centos2''' 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 '''centos3''' VM using the command:<olbr /><b><code><li valuespan style="3color:#3366CC;font-size:1.2em;">Now issue ssh ops235@centos3</span></code></b><br>(Where 'ops235' is the account on centos3 and 'centos3' is the hostname of the centos3 VM.)<br><br># You should receive a message similar to the command following:<br><codebr>ssh#::<span style="font-copyfamily:courier">The authenticity of host 'centos3 (192.168.235.13)' can't be established.</span><br>#::<span style="font-id 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-i ~family:courier">Are you sure you want to continue connecting (yes/no)? yes</span><br>#::<span style="font-family:courier">Warning: Permanently added 'centos3' (RSA) to the list of known hosts.ssh</id_rsaspan><br><br># Answer '''yes''' to add to the list of known hosts.pub # Issue the following command to confirm that you connected to your centos3VM: <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><livalue="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>Now we can ssh into centos3 from centos2 using two different authentication methodsRun 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 logout of exit all connections, and remain in your centos3 system'''centos2''' VM. When using ssh to connect to other servers, it is very easy to forget which server you are currently using. Use Verify that you are in your '''centos2''' VM by entering the command: <b><code><span style="color:#3366CC;font-size:1.2em;">hostname</span></code> command </b><li>Use the Internet to search for '''TCP 3 way handshake''' to verify you see how TCP connections are back in your centos2 serverestablished and closed.<br><br></li>
</ol>
::So far, we have learned to establish 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 identit'''y. We can also use '''Public/Private key encryption'''.
::'''Answer 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 Investigation 3 observations / questions in your lab log book.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.
::While it doesn't mean the message is <u>secure</u> as anybody could decrypt it with the public key, it does establish my <u>identity</u>, if the host can successfully decrypt the message then it must have come from the one person in possession of the private key.<br><ol><li value="12">We are now going to generate a new set of public/private keys.</li><li'''>Students run into a lot of trouble when using ssh and generating key-pairs by performing these operations as root user by Mistake! Make <u>certain</u> that you are NOT logged in as root!''' (you have been warned!)</li><li>To generate a keypair (public/private keys), issue the following command:<br /><b><code><span style= Using SSH &"color:#3366CC; Other Secure Shell Utilities ==font-size:1.2em;">ssh-keygen</span></code></b></li><li>That should generate output similar to the following:<br><br></li></ol>
::<span style="font-family:courier">Generating public/private rsa key pair.</span><br>::<span style="font-family:courier">Enter file in which to save the key (/home/user1/.ssh/id_rsa):</span> <br>::<span style= Investigation "font-family:courier">Enter passphrase (empty for no passphrase): </span><br>::<span style="font-family:courier">Enter same passphrase again: </span><br>::<span style="font-family:courier">Your identification has been saved in /home/user1/.ssh/id_rsa.</span><br>::<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@centos2</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: How do 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 scp and sftp. <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@centos3</span></code></b></li>{{Admon <li>Try using ssh to now log into your '''centos3''' VM <u>from</note | Use u> your '''centos2 ''' VM. What happens? Were you required to use your pass-phrase? Issue the hostname command to verify that you are successfully logged into your '''centos3''' VM | Complete this investigation on .</li><li>Make certain to logout of your '''centos3''' system. Use the '''hostname''' command to verify you are back in your centos2 VMserver.</li></ol> '''Answer Part 2 observations / questions in your lab log book.''' =INVESTIGATION 2: USING SSH AND OTHER SECURE SHELL UTILITIES= == Part 1: How do you use scp and sftp.}}== When you have created an SSH server, then users can take advantage of secure shell tools (including the '''scp''' and '''sftp''' utilities)
# Remain in your '''centos2''' 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@centos3</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.# The 2 main commands are <b><code><span style="color:#3366CC;font-size:1.2em;">put</span></code></b> to copy a file from the local host to the remote host (upload) and <b><code><span style="color:#3366CC;font-size:1.2em;">get</span></code></b> 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 Confirm that the files were transfer and then enter the command '''exit''' to quit your sftp session.{|width="40%" align="right"|- valign="top" |{{Admon/tip| SELinux | SELinux may prevent ssh from accessing your home directories on centos1 because you created a new filesystem there. You can also use reset the security context of the /home directory with this command: '''restorecon -Rv /home'''}} |}<codeol>scp</codeli 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># Use <codeli>Use '''scp</code> ''' to copy your services file to the centos3 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@centos3:/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 '''centos2''' VM:<br><b><code><span style="color:# Experiment with 3366CC;font-size:1.2em;">ssh ops235@centos3 ls /tmp</span></code></b></li><li>What happened when you issued that command? Where you able to successfully using scpto copy the '''/etc/services''' file to '''centos3's /tmp''' directory?</codeli><li> Experiment with '''scp''' to copy a file from '''centos3 ''' directly to '''centos1'''.{{Admon</tip| SELinux | SELinux may prevent ssh from accessing your home directories on centos1 because you created a new filesystem there. You can reset the security context of the /home directory with this command: <codeli>restorecon -Rv /home</codeol>}}
'''Answer Part 1 observations / questions in your lab log book.'''
== Part 2: How do you use ssh to tunnel X. ==
{|width="40%" align="right"
|- valign="top"
# For this section, you will be using your '''centos1''' and '''centos2''' VMs.# From your '''centos2'''Answer VM issue the Investigation 5 observations ssh command to connect to your '''centos1''' VM using the following command:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">ssh -X -C username@centos1</span></code></ questions b> (where 'username' is your learn account on centos1)<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 '''centos2''' VM, but in reality, this application is running on your lab log book'''centos1''' VM!# Enter some text and save a file with '''gedit'''.# Exit the '''gedit''' application.# In which VM was the file saved?# Experiment with running other GUI applications through '''ssh'''.
Anytime you configure your computer to allow logins from the network you are leaving yourself '''vulnerable to potential unauthorized access'''Answer by so called "hackers". Running the Investigation 6 observations / questions in 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 lab log booksystem.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.<br><br> Making your root password (and all other accounts!) both quite complex but easy to remember is not hard.
# For this section, you will still be using your '''centos1''' and '''centos2''' 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 '''centos2''' VM and open a terminal. # Edit the file <code>'''/etc/ssh/sshd_config</code> ''' and look for the option <code>'''PermitRootLogin</code>'''. Uncomment Un-comment the option (or add the option if it does not appear) and change the option value to <code>'''"no"'''.</codebr><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 <code>'''/etc/ssh/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 /><b><code><span style="color:#3366CC;font-size:1.2em;">service sshd restart</span></code></b># Now any hacking attempt also has Try sshing from your '''centos1''' VM to guess an account name as well as the passwordyour '''centos2''' VM. If Where you successful? Would it work if you need to ssh with root accesslet "AllowUsers account" without a username, ssh as or a regular user and use <code>su non-</code> to become root.existent username? Do not do this for your machine!
# Next change the default port number that sshd uses (TCP:22).
# Edit the sshd configuration '''/etc/ssh/sshd_config''' file again , un-comment the port option and change the port number it uses from ''22'' to '''2200'''. # <u>Restart </u> the service. # Confirm the new port is being used with a <code>the '''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 22by issuing the command:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">iptables -I INPUT -p tcp -s0/0 --dport 22 2200 -j DROPACCEPT</span></code></b># 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 2200 22 -j ACCEPTDROP</span></code></b># To test We have now possibly mislead a potential "hacker" to the new true port for our ssh server's communication channel (port connect ).# Switch to your '''centos1 from ''' VM.# Issue the commmand: <b><code><span style="color:#3366CC;font-size:1.2em;">ssh username@centos2 </span></code></b>. What happens? What port do you think that command is using by default?# Now issue the following commandto ssh via port "2200":<br /b><code><span style="color:#3366CC;font-size:1.2em;">ssh -p 2200 userusername@centos1centos2</span></code></b>. Where you able to connect? {|width="40%" align="right"|- valign="top" |{{Admon/importanttip |Troubleshooting Tips for SSH|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".'''SELinux'''</li><li>If your are still encountering problems flush '''Flush iptables''' (iptables.-F)</li></ulli>}}{{Admon/tip | Tip! | For '''scp ''', use the access the option to be used is: <code>(eg. '''scp -P 2200''' )</codeli></ul>}}{{Admon/tip | Tip! | For more ideas on making sshd more secure consult the HOW-TO link above.}}<ol><li value="1417">Finally , as a system administrator , you should periodically monitor your system logs for unauthorized login attempts.</li><li>On CentOS systems the log file that is 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 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 see what kind of information is logged.</li>
</ol>
'''Answer the Investigation 7 Part 2 observations / questions in your lab log book.''' = LAB 7 SIGN-OFF (SHOW INSTRUCTOR) ={{Admon/important|Time for a new backup, INCLUDING YOUR VIRTUAL HARD DRIVE!|If you have successfully completed this lab, make a new backup of your virtual machines. <br><br>'''Virtual hard-drives created lab5 are image files and may have data changed as a result of performing this lab. Therefore, you need to be backed up this hard disk image as well!'''.}}
== Preparing for Practice For Quizzes , Tests, Midterm & Final Exam ==
# What port does sshd use by defaults?