Friedemann Lipphardt after successfully defending his thesis. Photo: MPI-INF/Bertram Somieski
On 18 December 2025, Friedemann Lipphardt successfully defended his PhD thesis with the title "Towards a better understanding of under-explored facets of Internet censorship". He joined MPI for Informatics and Saarland University as a doctoral candidate in June 2020. The thesis was supervised by Prof. Dr. Anja Feldmann, Scientific Director of the Internet Architecture Department, and , head of the Sampling and Rendering group. The doctoral degree is awarded by Saarland University.
Abstract of the thesis:
The Internet has transformed how information is accessed and controlled, enabling both free expression and increasingly fine-grained systems of censorship and moderation. This dissertation examines two major forms of information control: network-level Internet censorship and content moderation in large language models (LLMs). It shows that LLM safety filters do not act uniformly but vary significantly by users’ location and language. Studying 15 LLMs from 12 global vantage points in 13 languages, the work finds moderation rate differences of up to 60% and clear behavioral gaps between Chinese and Western models, especially on political and religious topics, raising concerns about unequal and opaque access to information.
Beyond LLMs, the dissertation analyzes sophisticated censorship of voice communication services in Saudi Arabia and the UAE, uncovering middlebox systems that selectively block VoIP calls while leaving other app features intact through protocol fingerprinting and targeted interference. To study such practices at scale, it integrates over 36 million monthly censorship measurements into a knowledge graph that links events to network infrastructure and geopolitical context. Together, these findings show that modern information control operates across multiple technical layers with growing precision but limited transparency, with important implications for digital rights, fairness, and the design of more equitable information systems.