Building a Secure VPN Server on Android Using OpenVPN and Firewalld

Introduction

The increasing demand for online security has led to the growing popularity of Virtual Private Networks (VPNs). A VPN allows users to create a secure and encrypted connection between their device and a remote server, protecting them from cyber threats and surveillance. While most people think of VPNs as being used on desktop computers or laptops, mobile devices can also benefit greatly from this technology. In this blog post, we will explore the process of building a secure VPN server on Android using OpenVPN and Firewalld.

Prerequisites

Before starting the process, it’s essential to have the following prerequisites installed on your Android device:

  • Root access: You need to have root access on your Android device. This can be achieved by installing a custom ROM or using a rooting app like Magisk.
  • Termux: Termux is a terminal emulator for Android that allows you to run Linux commands and install packages. It’s available for download from the Google Play Store.
  • OpenVPN: OpenVPN is an open-source VPN protocol that provides strong encryption and secure connections. You can install it on your device using the following command: pkg install openvpn

Step 1: Setting Up Firewalld

Firewalld is a firewall management system for Linux operating systems. It’s used to configure and manage network traffic rules. To set up Firewalld on your Android device, follow these steps:

  • Install Firewalld: Install Firewalld using the following command: pkg install firewalld
  • Start Firewalld: Start Firewalld by running the following command: systemctl start firewalld
  • Enable Firewalld on Boot: Enable Firewalld to start automatically on boot by running the following command: systemctl enable firewalld

Step 2: Generating OpenVPN Configuration Files

To set up a VPN server using OpenVPN, you need to generate configuration files. These files contain the necessary settings for the VPN connection.

  • Generate CA Certificate: Generate a Certificate Authority (CA) certificate using the following command: openssl req -x509 -newkey rsa:4096 -nodes -keyout ca.key -subj "/C=US/ST=State/L=Locality/O=Organization/CN=ca" -days 3650 -out ca.crt
  • Generate Server Certificate: Generate a server certificate using the following command: openssl req -newkey rsa:4096 -nodes -keyout server.key -subj "/C=US/ST=State/L=Locality/O=Organization/CN=server" -days 3650 -out server.csr
  • Generate Server Key: Generate a server key using the following command: openssl rsa -in server.key -pubout -out server.pub

Step 3: Creating OpenVPN Configuration Files

Create the necessary configuration files for OpenVPN:

  • server.conf: Create a new file called server.conf with the following content:
port 1194
proto udp
dev tun
ca ca.crt
cert server.crt
key server.key
dh dh2048.pem
topology subnet
  • client.ovpn: Create a new file called client.ovpn with the following content:
client
dev tun
proto udp
remote <server_ip> 1194
resolv-retry infinite
nobind
persist-key
persist-tun
ca ca.crt
cert client.crt
key client.key

Step 4: Starting OpenVPN Server

To start the OpenVPN server, follow these steps:

  • Start OpenVPN: Start OpenVPN using the following command: openvpn --daemon --config server.conf

Step 5: Configuring Firewalld for OpenVPN

Configure Firewalld to allow incoming traffic on port 1194 (the default OpenVPN port):

  • Allow Incoming Traffic: Allow incoming traffic on port 1194 by running the following command: firewall-cmd --zone=public --add-port=1194/udp

Conclusion

In this blog post, we covered the process of building a secure VPN server on Android using OpenVPN and Firewalld. We installed the necessary packages, generated CA certificates, created configuration files for OpenVPN, started the OpenVPN server, and configured Firewalld to allow incoming traffic on port 1194.

By following these steps, you can create a secure VPN connection between your Android device and a remote server, protecting yourself from cyber threats and surveillance. Remember that building a VPN server requires technical expertise and careful planning to ensure security and stability.