Navigating Internet Censorship: An In-Depth Look at Tor, VPNs, and Circumvention Strategies

It’s an unfortunate reality that governments and nation-states around the world employ sophisticated methods to control and restrict their citizens' access to the Internet. I recently received an email from a student asking about using VPNs, Tor, etc., to bypass these restrictions. I replied to their question but thought the topic may interest other people, so I decided to turn it into a blog post as well.

This blog post will examine the ongoing battle between censorship authorities and those using tools like Tor and VPNs to bypass these restrictions. We'll look at the various techniques used by nation-states to block or throttle VPN usage, dive into the technical details of how these methods work, and discuss strategies for circumventing censorship. Furthermore, we'll discuss the role of proxies, the effectiveness of the Tor network, and the importance of staying informed in the face of ever-evolving censorship tactics.

Understanding VPN Blocking Techniques:

To effectively combat VPN blocking, it's essential to understand the methods employed by nation-states and ISPs. Let's take a closer look at some of the most common techniques:

1. Deep Packet Inspection (DPI):

DPI is a powerful tool used by network administrators and censorship authorities to analyze the contents of data packets transmitted over a network. Unlike traditional packet filtering, which only examines header information, DPI inspects the actual payload of the packets.

When a data packet passes through a DPI system, the system compares the packet's contents against a predefined set of rules or patterns. These rules can be based on keywords, protocols, or other specific characteristics. If a packet matches a rule, the DPI system can take various actions, such as blocking, redirecting, or logging the packet.

In the context of VPN blocking, DPI is used to identify patterns unique to VPN protocols. For example, OpenVPN traffic has a distinctive signature that can be detected using DPI. The censorship authority can then block or throttle the detected VPN traffic based on these signatures.

2. IP Blocking:

IP blocking is a straightforward method used by censorship authorities to restrict access to known VPN servers. By maintaining lists of IP addresses associated with VPN providers, ISPs can easily block traffic to and from these servers.

To illustrate this, let's use the popular VPN provider, Private Internet Access (PIA). By searching for "Private Internet Access" on a platform like search.censys.io, you can quickly fingerprint their entire infrastructure, revealing the IP addresses of their servers. Censorship authorities can use this information to add these IP addresses to their blocklists, effectively preventing users from connecting to the VPN service.

3. Port Blocking:

VPN protocols rely on specific ports to establish connections between the client and the server. By monitoring and blocking traffic on these ports, ISPs can disrupt VPN services and make it difficult for users to connect.

For example, OpenVPN typically uses port 1194 (UDP), 1196 (UDP) or port 443 (TCP) for its connections. If a censorship authority identifies and blocks traffic on these ports (tough to do with 443 since that’s what legitimate HTTPS traffic uses), users will be unable to establish a connection to their VPN server using the standard OpenVPN configuration.

4. Protocol Fingerprinting:

Different VPN protocols have unique characteristics that can be used to identify and block VPN traffic. This technique, known as protocol fingerprinting, involves analyzing the patterns and behaviors of network traffic to determine whether it belongs to a specific VPN protocol.

For instance, the OpenVPN protocol has a distinctive handshake process that can be recognized by censorship systems. By identifying this handshake, authorities can block or throttle the VPN connection without needing to decrypt the actual content of the traffic.

Advanced Strategies for Bypassing VPN Blocking:

Now that we've explored the various methods used to block VPNs let's dive into some advanced strategies for circumventing these restrictions.

1. Obfuscation Techniques:

Obfuscation techniques aim to disguise VPN traffic as regular internet traffic, making it harder for DPI systems to detect and block the VPN connection. One common approach is to make VPN traffic resemble HTTPS traffic.

HTTPS (HTTP Secure) is an encrypted protocol widely used for secure communication on the web. It's essential for online activities like banking and e-commerce. Due to its prevalence, censorship systems cannot easily block HTTPS traffic outright without causing significant collateral damage.

VPN providers offering "stealth" modes or obfuscation features often employ techniques such as:

a. Wrapping VPN packets inside an additional layer of encryption, obscuring the underlying VPN protocol.

b. Disguising VPN traffic as regular HTTPS traffic by using common HTTPS ports (443) and mimicking HTTPS packet characteristics.

c. Randomizing packet sizes and timing to avoid creating recognizable patterns that could be detected by DPI.

By implementing these obfuscation techniques, VPN providers can help users bypass VPN blocking and maintain access to uncensored content.

2. Using Less Common VPN Protocols:

Another strategy to evade detection is to use less common VPN protocols that are not as easily recognizable by censorship systems. While protocols like OpenVPN and IKEv2 are widely used and well-known, newer protocols such as WireGuard and custom-developed protocols can be more difficult to identify and block.

WireGuard, for example, is a modern VPN protocol that focuses on simplicity, speed, and security. Its lean codebase and unique cryptographic design make it less susceptible to protocol fingerprinting compared to more established protocols.

Some VPN providers also develop their own custom protocols to further enhance obfuscation and bypass censorship. These proprietary protocols often incorporate additional layers of encryption and obfuscation techniques to make the VPN traffic harder to detect and block.

3. Shadowsocks:

Shadowsocks is an open-source proxy project that has gained popularity for its effectiveness in bypassing internet censorship, particularly in countries like China. It was developed to address the limitations of traditional VPN protocols in the face of advanced censorship systems.

Unlike VPNs, which typically operate at the network layer, Shadowsocks works at the application layer. It encrypts the user's traffic and routes it through a proxy server, which then forwards the traffic to its intended destination. Shadowsocks uses a lightweight encryption protocol and can disguise traffic as regular HTTPS traffic, making it harder to detect and block.

When a user connects to a Shadowsocks server, their traffic is encrypted using a pre-shared key. The encrypted traffic is then sent to the Shadowsocks server, which decrypts the traffic and forwards it to the destination. The response from the destination follows the same path back to the user, being encrypted by the Shadowsocks server before being sent back.

One of the advantages of Shadowsocks is its flexibility. It can be configured to work with multiple proxies, allowing users to distribute their traffic across different servers and making it harder for censorship systems to block all the traffic.

 The Limitation of Proxies:

While proxies are often mentioned as a potential solution for bypassing internet censorship, they have significant limitations compared to VPNs. Proxies work by routing traffic through an intermediary server, hiding the user's IP address and allowing them to access blocked content. However, proxies do not typically encrypt the traffic between the user and the proxy server, leaving the data vulnerable to interception and analysis by censorship authorities.

The lack of encryption in proxy connections is a major drawback when dealing with deep packet inspection techniques. Censorship systems can easily identify and block unencrypted proxy traffic, rendering the proxy ineffective. Moreover, proxies do not provide the same level of privacy and security as VPNs, which encrypt the entire internet connection and protect against various online threats.

For these reasons, VPNs with strong encryption and obfuscation features are generally recommended over proxies for bypassing internet censorship and maintaining online privacy.

The Role of the Tor Network:

The Tor network is a powerful tool for circumventing internet censorship and protecting online anonymity. Tor, short for "The Onion Router," is a free, open-source software, and network that routes user traffic through multiple nodes (relays) before reaching its destination. This multi-layered encryption process makes it extremely difficult to trace the traffic back to its origin.

However, in countries with strict internet censorship, the IP addresses of Tor nodes can be identified and blocked, preventing users from accessing the Tor network altogether. To combat this, Tor introduced the concept of bridges.

Tor bridges are nodes that are not publicly listed in the Tor directory, making it harder for censorship authorities to discover and block them. When a user enables the use of bridges in their Tor configuration, their Tor client connects to a bridge first before joining the main Tor network. This adds an extra layer of obfuscation, as the censorship system only sees the user connecting to an unknown IP address (the bridge) rather than a known Tor node.

Tor bridges can employ various techniques to disguise their traffic, such as:

1. obfs4: This is a type of obfuscation protocol that scrambles the Tor traffic, making it look like random data. obfs4 uses a custom encryption protocol and hides the Tor fingerprint, making it difficult for censorship systems to identify and block the traffic.

2. meek: Meek is a pluggable transport that disguises Tor traffic as HTTPS traffic to popular cloud services like Google App Engine or Amazon CloudFront. By making the Tor traffic appear as if it's coming from these widely-used services, meek helps circumvent censorship systems that block direct connections to Tor nodes.

To obtain bridge addresses, users can visit the Tor Bridges website (https://bridges.torproject.org/) and request a bridge. The website employs CAPTCHAs to prevent automated bridge discovery and blocking by censorship systems.

It's important to note that while Tor bridges provide an additional layer of protection, they are not foolproof. Censorship authorities are constantly developing new techniques to identify and block Tor traffic, including the use of deep packet inspection and machine learning algorithms to detect patterns associated with Tor usage.

Staying Informed and Adapting:

The landscape of internet censorship is continuously evolving, with nation-states and censorship authorities constantly developing new methods to control and restrict access to information. To stay ahead of these efforts, it's crucial for users, privacy advocates, and developers to stay informed about the latest trends and adapt their strategies accordingly.

One of the challenges in staying informed is the lack of a centralized resource for monitoring censorship circumvention techniques. While platforms like Twitter can be helpful for general privacy and security news, the specific nature of this topic makes it difficult to curate a comprehensive list of reliable sources.

Websites like PrivacyTools.io (https://www.privacytools.io/) offer a good starting point, providing information and recommendations on various privacy-enhancing tools, including VPNs and Tor. However, it's important to be aware that some links on such sites may be affiliate links, which could slightly impact the objectivity of the recommendations.

To stay informed, it's essential to engage with the communities and forums dedicated to internet censorship and circumvention techniques. These platforms allow users to share their experiences, discuss new challenges, and collaborate on developing solutions. These can be difficult to locate, but the forums at https://forum.torproject.org/ are a good place to start.

The fight against internet censorship is an ongoing battle, with nation-states and censorship authorities continuously developing new methods to control and restrict access to information. Strategies like those discussed in this post can help users circumvent censorship efforts; however, it's crucial to recognize that there is no one-size-fits-all solution, and the effectiveness of these methods can vary depending on the specific censorship environment and the resources available to the censorship authorities.