Difference between revisions of "OPS235 Lab 7 - Fedora17"
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+ | * 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_dsa</code> and your public key will be saved as <code>id_dsa.pub</code> | ||
+ | {{Admon/tip | Tip: | 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.}} | ||
+ | * 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. | ||
+ | * Use the following commands to secure them: | ||
+ | ** <code>chmod 700 ~/.ssh</code> | ||
+ | ** <code>chmod 600 ~/.ssh/id_dsa*</code> | ||
+ | * The next step is to copy your public key to the remote host. You can use the scp command to do it. | ||
+ | * <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. | ||
+ | * Issue the command: | ||
+ | ** <code>scp ~/.ssh/id_dsa.pub ops235@fedora3:</code> | ||
+ | * This will copy your public key to your home directory on the remote host. | ||
+ | * The ''':''' is important as it separates the hostname from the path where it is copied to. | ||
+ | * The default location is your home directory on the remote host but you can also use an absolute or relative path after the ''':''' |
Revision as of 19:07, 15 March 2010
Contents
Setup and Configure Secure Shell Services (ssh) Using Virtual Machines
Objectives
- To set up, configure Secure Shell Services (ssh/sshd)
- To use the ssh, scp, and sftp clients to access another host securely
- Use ssh to tunnel X applications
- Use ssh to tunnel other traffic
- To customize sshd to create a more private, secure system
Reference
- man pages for ssh, ssh-keygen, sshd_config, ssh_config, scp, netstat, sftp, ifconfig, ping, arp, netstat, service
- A good ssh tutorial
- A good HOW-TO to make ssh more secure
Required materials
- Fedora 12 Live CD or a classmate on the same pod
- One SATA hard disk in a removable drive tray with Fedora host and 3 Fedora Virtual Machines installed
- Completion of Lab 6
Lab Preparation
Lab Investigations
Investigation 1: How do you enable the sshd service.
- OpenSSH should have been installed by default. Lets confirm this by issuing the command:
-
rpm -qa | grep ssh
-
- You should see a number of packages installed including
openssh-clients
andopenssh-server
-
openssh-server<code> installs a service called <code>sshd
, confirm this service is running by issuing the command:-
service sshd status
-
- Now check that the sshd service is configured to start for runlevels 2, 3, 4, & 5, by issuing the command:
-
chkconfig --list sshd
-
- If the service is not configured correctly fix it by issuing the command:
-
chkconfig --level 2345 sshd on
-
- Now that you know the service is running investigate what port number and protocol sshd uses by issuing the command:
-
netstat -atunp
-
- 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
netstat
command without then
option. - What is the difference?
- The
n
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/etc/hosts
and/etc/services
-
netstat
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
sshd
service is running on all 3 of your VM's - Answer the Investigation 1 question in your lab log book.
Investigation 2: How do you establish an ssh connection.
- As your learn account establish an ssh connection to your fedora3 VM using the command:
-
ssh ops235@fedora3
-
- 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:
The authenticity of host 'fedora3 (192.168.235.13)' can't be established. 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 Warning: Permanently added 'fedora3' (RSA) to the list of known hosts.
- Answer yes to add to the list of known hosts.
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: POSSIBLE DNS SPOOFING DETECTED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ The RSA host key for fedora3 has changed, and the key for the according IP address 192.168.235.13 is unchanged. This could either mean that DNS SPOOFING is happening or the IP address for the host and its host key have changed at the same time. Offending key for IP in /home/user1/.ssh/known_hosts:10 @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that the RSA host key has just been changed. The fingerprint for the RSA key sent by the remote host is 96:92:62:15:90:ec:40:12:47:08:00:b8:f8:4b:df:5b. Please contact your system administrator. 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 RSA host key for fedora3 has changed and you have requested strict checking. Host key verification failed.
- When prompted enter your password for your ops235 account on fedora3.
- Establish an ssh connection using your learn account from fedora3 to fedora2.
- Logout of your ssh connection by typing
exit
. - Check the state of the connection after logging out. Wait a few minutes and then check again. Record your observations.
- Use the Internet to search for "TCP 3 way handshake" to see how TCP connections are established and closed.
- Answer the Investigation 2 question in your lab log book.
Investigation 3: How do you establish an ssh connection using Public Key Authentication.
- Start by generating a keypair as your learn account on fedora2 using the command:
-
ssh-keygen -t dsa
-
- That should generate output similar to the following:
Generating public/private dsa key pair. Enter file in which to save the key (/home/user1/.ssh/id_dsa): Enter passphrase (empty for no passphrase): Enter same passphrase again: Your identification has been saved in /home/user1/.ssh/id_dsa. Your public key has been saved in /home/user1/.ssh/id_dsa.pub. The key fingerprint is: 93:58:20:56:72:d7:bd:14:86:9f:42:aa:82:3d:f8:e5 user1@fedora2
- After generating the keys it prompts you for the location to save the keys. The default is
~/.ssh
Your private key will be saved asid_dsa
and your public key will be saved asid_dsa.pub
- Once your keys have been saved you should check to make sure the permissions of the
.ssh
directory and your key files are secure. - Use the following commands to secure them:
-
chmod 700 ~/.ssh
-
chmod 600 ~/.ssh/id_dsa*
-
- The next step is to copy your public key to the remote host. You can use the scp command to do it.
-
scp
(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. - Issue the command:
-
scp ~/.ssh/id_dsa.pub ops235@fedora3:
-
- This will copy your public key to your home directory on the remote host.
- The : is important as it separates the hostname from the path where it is copied to.
- The default location is your home directory on the remote host but you can also use an absolute or relative path after the :