Various state actors around the world deploy some degree of censorship. To prevent users from accessing specific websites, they alter, drop, and redirect connection attempts to websites and services they deem malicious. Countries facilitate censorship by inspecting protocols like IP, TPC, HTTP, DNS, TLS, and VPNs. The sophistication of censors varies as much as the techniques they use. Overall, this leads to a diverse landscape of censorship around the world. In recent years, the analysis of censorship has increased greatly. Automated tools for global censorship analysis and circumvention have been introduced together with country-specific in-depth analyses.
To aid in this acquisition of knowledge, we want to ascertain censorship techniques and the circumventability of censorship around the globe. This includes both country-specific analyses and new circumvention or analysis techniques. Below, we gather potential thesis topics:
DPYProxy Extension [BA]. Our censorship circumvention tool, DPYProxy, currently implements circumventions for TLS . In the TLS module, the main circumvention method is to use TLS record fragmentation to bypass the censor. TCP segmentation and encrypted DNS are also supported. Your first task will be to enhance the currently implemented circumvention methods. For instance, being able to vary the fragmentation size over subsequent messages. Your second task is to implement additional circumvention methods for other protocols such as HTTP. For HTTP, circumvention methods like the already implemented TCP segmentation can be implemented as well as HTTP-specific circumventions that change the censored HTTP Host header. Your task will be to implement an HTTP module while implementing some circumvention strategies (e.g., alternating casing of the hostname in the Host header) from related work. This new module should also be evaluated against the censor in China.
Comparing Circumvention Tool Latency[BA/MA] To aid affected people in censorship circumvention, a plathora of different tool as been developed. While we roughly understand their different features and capabilities, their usability aspect is only analyzed sparsely. An important aspect of the usability of these censorship circumvention tools is their added latency. As most of these tools operate as some kind of proxy they naturally require time to reroute (and potentially) change the original message. Similarly, servers might require more time to interpret the messages altered by a circumvention tool. In this thesis, you will analyze the latency induced by different tools in different settings. In the end, you can compare the results for different tools and make statements about their usability and possible improvements.
QUIC Client Censorship Robustness [MA]. Many censors perform censorship by injecting additional packets (like TCP Reset packets), rather than dropping packets. Because TCP Reset packets are not authenticated, censors can forge them and tear down connections. For QUIC, this method is not applicable: Instead of using TCP, QUIC uses UDP, where there is no TCP Reset packet, and QUIC's mechanism of closing connections (sending a Connection Close frame) is authenticated after the handshake—so, once the handshake is complete, it cannot be forged by a censor. Prior work conjectures that this makes QUIC more robust against injection-based censorship. This assumption has, however, not yet been validated in depth. In particular, censors are not limited to injecting authenticated Connection Close frames. Instead, they may attempt to inject Connection Close frames early in the handshake, early Server Hello messages impersonating the server, malformed packets, or other packets that may cause clients to give up on a connection. Your goal would be to evaluate different QUIC clients (and possibly servers) for robustness against packet injection, and to determine whether such attacks pose a practical threat.
Testing New Circumvention Methods [BA]. There are many circumvention tools available to people in censored regions, but censors continually attempt to block successful tools. Therefore, when popular circumvention tools are blocked, additional methods are necessary to keep people in censored regions connected. One candidate protocol for censorship circumvention is TURN, which is normally used for NAT traversal in video conferencing applications. In normal use, TURN acts as a proxy for conference participants behind restrictive NATs (unrelated to censorship), and allows them to directly connect to other participants. When used for censorship circumvention, the proxy it provides could be used to circumvent IP blocking and other forms of censorship. Your goal would be to analyze the TURN servers provided by conferencing systems, integrate STUN+TURN as a circumvention strategy into our tool DPYProxy, and to test its applicability in censored regions.
None of these topics interest you, but you still want to analyze censorship in your thesis? Feel free to contact us with your own ideas. We can try to find a topic together!
Requirements (usually):
- Programming: Java, Kotlin, Python
- Knowledge of protocols: TLS, QUIC, DNS, HTTP, Network Stack (TCP/IP), depending on the topic
- Interest in censorship (circumvention)
