Remote access to the desktop Linux with SSL encryption: x11vnc + SSVNC client
In the latest versions of the GNOME desktop software is available that allows for remote access to the desktop with a simple client VNC from any other operating system. I'm talking about WINE. Although it is easy to set up, it does not guarantee a sufficiently strong encryption of data. In fact, we may be subject (for technical reasons that I'm not here to explain) to bouts of man-in-the-middle. For this reason I decided to show the configuration of another VNC server and a VNC client slightly more advanced: x11vnc (server) and SSVNC (client). All seasoned with a SSL tunnel that provides us shelter from prying eyes!
First, an introduction. The guide covers the installation of the server (x11vnc) on a Debian Sid (unstable release), but the process is identical for Ubuntu and other Debian-based distribution with the appropriate changes to the commands of installing packages of interest. Moreover, it is very important to remember that after installing the server, you must open TCP port of VNC (default 5900) on the firewall eventually installed on the server. Still, to be able to conveniently access from the outside (ie the Internet) should evaluate to a free subscription with a service like Dyndns or no-ip that allow you to have a host name in network with our ADSL. At this point I would say that we are ready to start.
- Installing and configuring the server x11vnc + openssl
x11vnc and openssl are present in the repositories of debian and ubuntu, so you can type usually apt-get command in a terminal and logged in as root:
# Apt-get install openssl x11vnc
The openssl package is needed to create encryption certificates to use for remote connections protected by SSL. The next step will be to create the certificates to be used for subsequent connections. I chose to use the safest method, namely the use of a Certification Authority (hereafter CA) to sign the various certificates. In this way we will be sure to use the client side of the original and not a counterfeit. Proceed with the creation of the certificate and the key to our CA (attention, you have to type these commands from simple user and not as root!):
$ X11vnc -sslGenCA
When you ran the command shown above, you will see that you will create all the necessary say in your user's home directory and then you will be asked to enter a passphrase. It 'a good idea to choose a password long and difficult, and if you are anxious to forget, will you start using some soft of password management such as those of which I have spoken on other occasions. After you type the passphrase, you will be asked for all the information regarding our CA. We carry a small sample of what you'll see on the terminal and what I've typed:
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:
You are about to be asked to enter information That will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', The field will be left blank.
Country Name (2 letter code) [AU]: IT
State or Province Name (full name) [mystate]: Italy
Locality Name (eg, city) : Power
Organization Name (eg, company) [x11vnc server CA]:
Organizational Unit Name (eg, section) :
Common Name (eg, YOUR name) [zeno x11vnc server CA]:
Email Address [x11vnc@CA.nowhere]:
Your public x11vnc CA cert is:
It may be copied to other applications, eg Web browser, Java
Applet keystore, or stunnel cfg, to use to verify signed server
or client certs, etc.
Your private key is x11vnc CA:
It will be used to sign the server or client certs, keep it secret.
Now we are ready to proceed to the next step, namely the creation of Chavi and the certificate for the VNC server. So, always from the terminal and simple user, launch the following command:
$ X11vnc -sslGenCert server
You'll find yourself having to answer some questions in a manner very similar to what happened with the previous command. It 'important to you to insert a PEM passphrase for the certificate and that, when asked, to insert also the passphrase used previously for the certificate of the CA. Here is a small sample of what you will see on the terminal and where you have to act by inserting the passphrase:
Do you want to protect the generated private key with a passphrase?
Doing so will Significantly decrease the chances someone could steal
the key and pretend to be your x11vnc server. The downside is it is
inconvenient Because You will have to supply the passphrase every
time you start x11vnc using this key.
Protect key with a passphrase? [Y] / n
writing RSA key
Enter PEM pass phrase:
Verifying - Enter PEM pass phrase:
Now signing the new key with the CA private key. You will need to supply
the CA key passphrase and reply "y" to sign and commit the key.
Using configuration from /home/zeno/.vnc/certs/tmp/cnf.11234
Enter pass phrase for ./CA/private/cakey.pem:
Check That the request matches the signature
Until now we have created the keys and certificates to encrypt the connection and, therefore, there rirtoveremo with the following files in our home directory:
~ / .vnc / Certs / CA / cacert.pem -> public certificate of our CA
~ / .vnc / Certs / CA / private / cakey.pem -> the private key of our CA
~ / .vnc / Certs / server.crt -> the public certificate of the VNC server
~ / .vnc / Certs / server.pem -> the private key + certificate of our server VNC
At this point we need to copy the file cacert.pem with a secure method on the PC on which we will use the VNC client. Obviously I leave to you to decide how to do, but it is really essential that this step is done in the safest way possible. Personally I transfer it via a USB stick or through the use of scp. If you need to use the VNC client on another Linux machine you can copy the files in the home directory of the user who will launch the client itself (~ / .vnc / certs / CA / cacert.pem). Moreover, we must ensure that the certificate of our CA is then used by the VNC client that we will use and in our case we will see how to proceed with the client SSVNC.
We have not yet finished with the configuration of the server, we miss the last step which is to create the password to access the server. In fact, the current state of the configuration, the server is running, but is not required the use of a password from the client to access and, therefore, it is sufficient to obtain the certificate. Obviously this is not very safe, and for this reason we insert a password to access the server:
$ X11vnc -storepasswd
The command you typed earlier will return the following prompt:
Enter the VNC password:
Write to /home/zeno/.vnc/passwd password? [Y] / ny
Password written to: /home/zeno/.vnc/passwd
Now the server is ready to be started. To do that we can type the following command:
$ X11vnc -usepw -ssl SAVE -display: 0
You will be prompted to enter the pass phrase choice when creating server certificates (server not the AC!) And then the VNC server will be started and listening on port 5900. If you want we can choose to start the server on a different port from the standard by adding the command to start the following parameter:
We finished with the server. We proceed with the installation of the client.
- Installation and use of the client SSVNC
In fact the client to our server must not be installed E 'can directly download the binaries available for Windows, MAC OS and Unix / Linux. We can grab the file from here . If you want you can get the files containing the tracks of the only operating system of our interest or those containing the source code of the client by going to this page . I decided to use SSVNC also because downloading a USB stick all the binaries for different operating systems can access our desktop with any computer available in the world without having to install anything! ... Also for example in an Internet café in London ... Obviously forewarned how preserved encryption certificates and do not miss the USB stick!
After downloading the files of our interest, we have to unpack and inside, having downloaded the file with the tracks I have pointed out in the first link, we will find various folders for different operating systems. We identify what interests us and we start "ssvnc". We will be facing this screen (the client was started on Win XP):
First click on the button "Certs ..." that allows us to open the window to enter the SSL certificate from our server to the client. Obviously, this certificate must be previously copied to the computer where the client is started, exactly as explained earlier when we talked about the server configuration. Here is shielded attraction
In the row for "ServerCert" we load our certificate "cacert.pem". When we will have done we can click the "Done" and return to the previous screen. Here we must first enter the IP address or hostname of the server into our line. You'll have to find yourself qulcosa like this:
Click if you want (not mandatory!) On the file "Fetch Cert":
And the client will connect to the server and acquire the certificate from the server:
When you finish viewing the certificate, click the "Dismiss". This last step is used to maintain control of congruity between the server certificate and the certificate that we have just loaded manually to prevent the server certificate or what is loaded manually on the client have been compromised. This manual control can be avoided leave unchecked the option of SSVNC "Verify all certs". Now I would say that it is time to start the VNC session itself. So, click on the "Connect" button and it will start trying to connect to the server:
If everything went well, in a few moments we will see the screen that asks for the password:
We type the password you chose earlier and finally we will be ready to use our remote desktop protected by an encrypted connection with SSL tunnel!
If you have questions, especially on how to access the Internet and how to configure NAT on your router, ask!
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