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Secure your connection

brlbr edited this page Mar 20, 2022 · 20 revisions

What is a X.509 certificate?

"X.509" is a standard type of certificate commonly used for websites. However, they are also useful for securing TigerVNC.

Certificates allow two important security functions.

  • Certificates prove the identity of the computer you are viewing (the one with the TigerVNC server).
  • Certificates keep private the contents of the communication between you and the remote computer.

When it comes to obtaining a certificate, you can use an External Certificate Authority if you own a domain name, or create a self-signed certificate.

Certificate from an External Certificate Authority

External Certificate Authorities issue certificates for public domain names but not local network IP addresses. As a result you need to own a domain name (like example.com). The basic setup would be something like the following.

  1. If your public website is example.com, rename your local network to something like local.example.com
  2. Obtain a certificate for computer1.local.example.com. Assuming computer1 is not available to the public internet, you need to use a DNS-01 challenge. (If you are using Let's Encrypt, see https://letsencrypt.org/docs/challenge-types/#dns-01-challenge)
  3. When you want to connect to computer1 on your network, type the hostname as computer1.local.example.com

Note: External Certificate Authorities have certificate transparency requirements that post the details of every certificate publicly. So don't name your computers after any secret company projects.

Once you obtain your certificate, see Use the certificate with TigerVNC

Create a self-signed certificate

If you do not own a domain name, or prefer not to use an external certificate authority, you can create a self-signed certificate.

Creating a certificate differs a little depending on whether you are on Windows or Linux. Jump to the heading that matches your system.

Windows

Unfortunately TigerVNC doesn't understand Windows-style certificates saved in the Windows certificate store or that end with the file extension .pfx. However, you can download OpenSSL to do the job.

On the computer with the TigerVNC server:

  1. Find out the local IP address of the computer running the TigerVNC server. See LifeHacker's instructions.
  2. Visit http://wiki.overbyte.eu/wiki/index.php/ICS_Download#Download_OpenSSL_Binaries_.28required_for_SSL-enabled_components.29 (Of the binaries suggested by OpenSSL, this is the simplest to run.)
  3. Choose the latest .zip download that matches your computer system (probably the first one labeled "Win-64")
  4. Uncompress the zip file.
  5. Go to the uncompress folder and double click openssl.exe.
  6. If you have Windows Defender SmartScreen, you may have to choose More info > Run anyway.
  7. Type the following (replace both instances of "192.168.1.5" with the local IP address you found in step 1 above) req -x509 -newkey rsa -days 365 -nodes -config openssl.cnf -keyout vnc-server-private.pem -out vnc-server.pem -subj '/CN=192.168.1.5' -addext "subjectAltName=IP:192.168.1.5"

Linux

  1. Find out the local IP address of the computer running the TigerVNC server. See Stackoverflow instructions.
  2. Open Terminal (if you haven't already)
  3. Install OpenSSL
    • On RedHat/CentOS/Fedora, type: sudo yum install openssl
    • On Debian/Ubuntu, type: sudo apt-get install openssl
  4. Create a self-signed certificate. Type the following (replace both instances of "192.168.1.5" with the local IP address you found in step 1 above) openssl req -x509 -newkey rsa -days 365 -nodes -config openssl.cnf -keyout vnc-server-private.pem -out vnc-server.pem -subj '/CN=192.168.1.5' -addext "subjectAltName=IP:192.168.1.5"

On Ubuntu (and related distros), you may also need to change the path to openssl.cnf to /usr/lib/ssl/openssl.cnf

Manage the certificates

The private key should remain private to your computer. If you have syncing services (such as OneDrive, Dropbox, etc.), consider moving "vnc-server-private.pem" to a location that isn't synced or backed up. If you ever loose the private key, just create a new certificate and private key.

The certificate you created expires in 365 days. A year from now, you will need to go through these steps again and create a new certificate.

Use the certificate with TigerVNC

On the computer with TigerVNC server:

  1. Right click the TigerVNC icon in the system tray (bottom right in Windows) and choose Options
  2. Under "Session encryption" choose TLS with X.509 certificates, and uncheck None and Anonymous TLS.
  3. Choose Load X.509 Certificate. Browse to the public key file you saved above ("vnc-server.pem").
  4. Choose Load X.509 Certificate key. Browse to the private key file you saved above ("vnc-server-private.pem").
  5. Choose Apply
  6. Copy the public key file ("vnc-server.pem") to your remote computer. Save it in the same folder as the TigerVNC viewer. This avoids some problems with the TigerVNC viewer on Windows.

On the remote (client) computer:

  1. Open the TigerVNC viewer
  2. Type in the name or IP address of the computer you want to connect to.
  3. Choose Options...
  4. Choose the Security tab
  5. Under Path to X509 CA certificate type the name of the your public key file you just copied (e.g. "vnc-server.pem"). If you are on Windows, this file needs to be located in the same folder as the viewer. Note: If you really want it in a different folder, you can use Linux-style path names, except the path name can't include spaces (and quotes around the path name don't work either).
  6. Type the password and choose OK. If you get any error messages at this point, read them carefully. If you skip over any error messages, you may bypass all the security guarantees of using certificates.
  7. On the computer with TigerVNC server you may have to choose Accept within 10 seconds. You can change this setting if needed.