Deep Packet Inspection (DPI) is an advanced method for analyzing network traffic. Many governments and organizations deploy DPI systems to monitor and filter internet traffic, which can compromise the privacy of VPN users. One effective way to circumvent this threat is by using obfs4, a pluggable transport protocol that obfuscates VPN traffic, making it difficult to detect as VPN traffic. In this article, we’ll go through the setup and usage of obfs4 to hide VPN traffic from DPI.
What is obfs4?
obfs4 is a pluggable transport that uses various obfuscation techniques to disguise VPN traffic. It’s primarily used to avoid detection by DPI mechanisms and prevent VPN blocking. obfs4 operates by transforming the VPN traffic into seemingly innocuous data patterns, making it appear as if the traffic is something else entirely, such as regular HTTPS traffic.
Installing obfs4 on Your System
Before you can use obfs4, you need to install the necessary components. Below are the steps for installing obfs4 on a Linux-based system.
After installing obfs4proxy, you can start using it to obfuscate your VPN traffic.
Step 2: Verify Installation
obfs4proxy --version
This will display the installed version of obfs4proxy, ensuring the installation was successful.
Configuring obfs4 with OpenVPN
Next, you need to configure OpenVPN to work with obfs4. OpenVPN is the most commonly used VPN protocol, and it is compatible with pluggable transports like obfs4.
Step 1: Set up the obfs4 bridge
The first step in configuring obfs4 with OpenVPN is to set up an obfs4 bridge. This is a server-side configuration that allows your VPN traffic to be obfuscated. The bridge configuration can be obtained from various public sources, or you can set up your own obfs4 bridge. For example, Tor provides public obfs4 bridges:
https://bridges.torproject.org/
Once you have the bridge address, you’ll need to configure OpenVPN to use it.
Step 2: Edit the OpenVPN configuration file
You will need to modify your OpenVPN configuration file (typically located in /etc/openvpn/). Add the following lines to connect to the obfs4 bridge:
client
dev tun
proto udp
remote 443
resolv-retry infinite
nobind
persist-key
persist-tun
ca /etc/openvpn/ca.crt
cert /etc/openvpn/client.crt
key /etc/openvpn/client.key
remote-cert-tls server
cipher AES-256-CBC
auth SHA256
verb 3
Here, replace with the address of the obfs4 bridge you obtained earlier.
Step 3: Running obfs4proxy
Next, you’ll need to run the obfs4proxy service. This service will handle the obfuscation of your VPN traffic.
Replace the certificate and key paths with the actual locations of your obfs4 certificate and private key. These keys are used to encrypt and obfuscate the traffic.
Verifying obfs4 Traffic Obfuscation
To verify that obfs4 is working and successfully obfuscating your VPN traffic, you can use network monitoring tools. One common tool is Wireshark, which allows you to analyze network traffic.
Step 1: Capture Network Traffic
Open Wireshark and start capturing traffic. Look for the VPN connection traffic. If obfs4 is successfully obfuscating the traffic, you should see patterns that are indistinguishable from regular HTTPS traffic, with no clear signs of VPN usage.
Step 2: Analyze the Obfuscated Traffic
Examine the packets closely. The data should be scrambled and not recognizable as VPN data, ensuring that it’s being effectively hidden from DPI systems.
Advanced Configuration for obfs4
If you need more control over the obfuscation process, you can tweak some advanced settings. For example, obfs4 allows you to specify the use of additional encryption methods or configure the timeout and retry behavior for the obfuscation process.
Timeout and Retries
You can modify the timeout and retry settings for obfs4 to improve reliability in unstable network conditions. For example:
obfs4proxy -server -timeout 30 -retry 5
Here, the timeout is set to 30 seconds, and obfs4 will attempt to reconnect up to 5 times if the connection is lost.
Encryption Settings
While the default encryption method is sufficient for most use cases, you may also change the encryption strength for additional privacy. However, note that increasing encryption strength may impact performance.
obfs4proxy -server -cipher aes-128-gcm
This will use AES-128-GCM for encryption, which is slightly faster than the default AES-256-CBC, but still provides strong security.
