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Computer Networks and Telematics
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Oberseminar Rechnernetze und Telematik (Sommer 2026)

Das Oberseminar findet regelmäßig Mittwochs von 14-16 Uhr in 051-02-008 statt. Hier werden aktuelle Forschungsthemen diskutiert, sowie finden Kickoff- und Abschlusspräsentationen von Bachelor/Master-Projekten/Arbeiten statt.

In the oberseminar, talks are held on selected topics, as well as final presentations of master’s & bachelor’s theses, and projects. The seminar takes place hybridly:

Upcoming Oberseminar Talks

02.09.2026 14:00-14:30 Maximilian Herych Bachelor Thesis kickoff presentation

Title: Commitment only shuffle for mental card games – Implementation of the permutation network encoding into arithmetic circuits

Abstract: This thesis is the starting point of an implementation for the commitment only shuffle by M. Bless, which tries to minimize communication by reducing the shuffle to commitments that can then easily be transmitted. The shuffle is based on a permutation network which is converted into arithmetic circuits, the players can then use zero-knowledge proofs on the equations describing these circuits.
The scope of this thesis is limited to the construction of a permutation network that is pruned or expanded to the desired size while limiting bias and the translation into arithmetic circuits. Which is used in the permuting and rerandomization of the deck. The implementation will be in rust to allow integration into existing works in the mental card game repository.

02.09.2026 14:40-15:10 Lorik Hamza Bachelor Thesis final presentation

Title: Analyse kryptographischer Protokolle für die didaktische Aufbereitung in der gymnasialen Oberstufe

Abstract: This thesis explores how the topic of “Mental Card Games” can be used to introduce advanced cryptographic concepts in an educational and accessible way. Mental Card Games are cryptographic protocols that allow players to play card games fairly over a network without relying on a trusted third party. The thesis focuses not only on the underlying cryptographic principles, such as secure shuffling, encryption, and verification, but especially on how these concepts can be simplified and presented to students in an intuitive manner.       

As part of the project, teaching materials for two lessons were developed, implemented, and evaluated in an upper-secondary-school setting. A major goal is to examine which concepts are suitable for classroom use, which difficulties occur, and how the teaching approach can be improved. In this way, the thesis aims to make modern cryptography more understandable, interactive, and engaging for beginners and high school students.
The presentation is the final presentation of my bachelor thesis.

02.09.2026 15:10-15:40 Zeinab Herz

Intermediate presentation of her Bachelor Thesis: Objekterkennung und Distanzbestimmung in Verkehrsszenen auf Basis von Time-of-Flight-Kameras

02.09.2026 15:50-16:15 Regina Qelibari Bachelor thesis kickoff presentation
 
Title : Zero-Knowledge Proofs for RSA Arithmetic in the Exponent of a Composite-Order Subgroup
 
Abstract: 
In this kick-off talk, I outline my bachelor’s thesis plan, which studies RSA-like arithmetic in a cyclic subgroup of composite order. The project considers the construction of subgroups of order n = pq inside Z*_p̂, where p, q, and p̂ = 2kpq + 1 are prime, and empirically investigates how frequently suitable parameters occur. Building on this construction, the thesis aims to study whether classical zero-knowledge techniques for proving exponent and multiplication relations can be adapted to verify the correct evaluation of expressions such as Y = g̃^(m^e mod n) mod p̂. The talk sketches the planned experimental and theoretical methodology and the main evaluation questions concerning composite-order group structure, proof soundness, additional security conditions, and possible cryptographic applications or limitations.

Previous Talks

19.08.2026 14:00-14:30 Regina Qelibari project final presentation

Title: Attack on Third-degree Polynomial Objects in 3D Visual Cryptography System

Abstract: This bachelor project investigates the reconstruction of third-degree implicit polynomial surfaces in a 3D visual cryptography system based on ray tracing. Several polynomial fitting methods are implemented and compared using both monomial and Chebyshev polynomial bases. Their reconstruction accuracy, numerical stability, and robustness are evaluated on representative cubic objects that resemble the polynomial surfaces used in the optical component of the cryptographic scheme. To simulate imperfect surface samples that may occur during a practical reconstruction attack, Gaussian noise and outliers are added to the training data used for polynomial fitting. The performance of the reconstruction methods is evaluated under both ideal and noisy conditions. This work contributes to the analysis of third-degree polynomial surface reconstruction as a building block for future cryptanalysis of the proposed 3D visual cryptography scheme.2.08.2026 14:00-14:30 Alexander Horst Keller Bachelor project final presentation

12.08.2026 14:00-14:30 Alexander Horst Keller Bachelorproject final presenation

Title: An Interpreter for a Card-Game Domain-Specific Language

Abstract: Card games have well-defined rules but complex implementations: turn orders, scoring, and conditional logic typically live in hand-coded state machines that are difficult to rule changes, hard to verify, and coupled to their runtime. This project addresses that separation by building a deterministic interpreter for CGDSL, a domain-specific language that describes a game once and derives execution, testing, replay, and visualization from that description. I implemented the interpreter as the cgdsl-engine crate: a Rust FSM engine in which stages become loops, actions mutate a flat game state, and queries read it. A quantifier preprocessor rewrites all/any/range edges into concrete edges or player prompts at runtime, so the IR itself is never mutated. Every DSL-reachable failure is a typed, recoverable EngineError – no engine panic is reachable from well-formed input. Hosts interact through an InputSource seam, per-transition trace events with typed payloads, and opt-in file or tracing-based logging. The engine is verified by 518 tests across five layers: unit, interpreter, fixtures, deterministic behavioral games, and randomized 40-seed playthroughs over 73 .cgdsl fixtures, including five complete demo games (Blackjack, War, Crazy Eights, Five-Card Draw, Go Fish). The language and parser predate this project; the engine is currently consumed only by its own binaries and tests, with cryptography, networking, and UI integration as the next projects.

12.08.2026 15:00-15:30 Ben de Boer Bachelor Thesis kickoff presentation

Title: Conception, Prototypical Implementation, and Evaluation of Reactive Power Control For Inverters

Abstract:
As the distribution grid is adapted for decentralized, bidirectional power flow, voltage-regulation challenges rise, that reactive power (Q) can address at the point of connection. While German regulation converges on EEBus as the minimum standard, its defined use cases cover only active power, reactive power dispatch is absent. This thesis proposes a new EEBus use Case for continuous Q(t) setpoint dispatch from the Distribution Grid Operator to inverters, with local Q(V) droop as failsafe per standard for emergency power limitation of consumer devices.

07.08.2026 13:00-13:30 Mattis Bless Master Thesis intermediate presentation

Title : Design and Analysis of Communication Protocols for Mental Card Game Shuffle based on the El Gamal Crypto-System

Abstract : In this presentation, we discuss how the zero-knowledge proof of the shuffle’s remasking step can be improved. The remasking step involves creating a ciphertext of the empty message for each card. These ciphertexts are then multiplied to the permuted cards’ existing ciphertexts. The resulting ciphertexts appear random to the other players, and the underlying permutation is hidden from them. The original approach makes use of a large arithmetic circuit to generate the remasking ciphertexts. The circuit’s size results in large vectors, e. g. to represent the edges, as well as many equations to describe the circuit. The number of equations and the vectors’ sizes are reflected in the amount of communication and computation during the zero-knowledge proof. Inspired by a technique used in the shuffle argument by Bayer and Groth in their 2012 paper “Efficient Zero-Knowledge Argument for Correctness of a Shuffle”, we aim at reducing both communication and computation by proving that a single equation holds. The equation shows that the remasking ciphertexts hidden behind a commitment are created using exponents, also hidden behind a commitment, with overwhelming probability. This is achieved by evaluating a polynomial in the exponent of both sides of the equation at a random challenge coming from the honest verifier. In contrast to the former arithmetic citcuit approach, this allows smaller vectors and requires fewer equations to be proven.

07.08.2026 13:45-14:15 Lorik Hamza Bachelor Project final presentation

Title : Mental Card Games Based on Paillier Encryption

Abstract: Mental card games allow several players to play card games over a public network without the need for a trusted dealer. The main challenge is to keep the cards secret while ensuring that all game actions are per- formed correctly and can be verified by every player. This report presents and analyzes a construction of mental card games based on the Paillier cryptosystem. The homomorphic properties of Paillier encryption are used to mask and re-mask cards, while distributed
key generation and zero-knowledge proofs are intended to provide security and public verifiability. In addition, the correctness of the decryption algorithm is explicitly demonstrated when using Euler’s totient function φ(N ) instead of the Carmichael function λ(N ).
Finally, the distributed key construction is analyzed and a critical information leak is identified. The published values g^(φi) , together with the public decryption factor μ^(−1), allow φ(N ) to be recovered. Consequently, the construction does not achieve the intended confidentiality or the n-out-of-n threshold decryption property. The analyzed construction is based on the protocol presented in Mental Poker Revisited.

23.07.2026 11:00-11:30 Nils Steuernagel Bachelor Project final presentation

Title : Scaling of 3D Objects relative to Local Bounding Boxes
Abstract : This bachelor’s project addresses the scaling of three dimensional polynomial surfaces within Local Bounding Boxes (LBBs) in a ray tracing based cryptographic framework. The proposed method uses scale free parameters and scaling rules based on the half extent H of each bounding box to preserve the relative geometry of the surfaces across different box sizes. In addition, the parameter ranges were revised, and the plotting functionality and offset generation were improved.

23.07.2026 11:35-12:05 Tom Pfirsig Bachelor Thesis final presentation

Title: Der Übergang zu Post-Quanten-Ringsignaturen in Blockchain-Systemen- Eine Fallstudie am Beispiel von Privacy-Coins (Monero)

Abstract: Privacy-Coins versprechen Vertrauen auf einer ansonsten transparenten Blockchain. Am Beispiel von Monero (XMR) untersucht diese Arbeit, wie tragfähig dieses Versprechen unter der Annahme eines kryptographisch relevanten Quantencomputers bleibt. Die drei tragenden Datenschutzschichten von Monero, verknüpfbare Ringsignaturen (MLSAG/CLSAG), Ring Confidential Transactions (RingCT) mit Pedersen- Commitments sowie Stealth-Adressen auf Basis des Elliptic-Curve-Di!e-Hellman-Austauschs ruhen sämtlich auf der Härte des Elliptic Curve Discrete Logarithm Problem (ECDLP). Genau dieses Problem löst Shors Algorithmus in polynomieller Zeit.
Die Arbeit ist als systematische Fallstudie angelegt. Sie führt die benötigten Grundlagen ein (Ringsignaturen, elliptische Kurven, Quantencomputing, Gitterkryptographie), analysiert die Monero-Architektur und leitet schichtweise her, welche Datenschutzeigenschaft unter Shor verloren geht. Besondere Aufmerksamkeit gilt dem Harvest-Now-Decrypt-Later -Szenario (HNDL), das Privacy-Coins rückwirkend und unwiderruflich trifft. Anschließend werden publizierte Post-Quanten-Bausteine (RAPTOR, MatRiCT/MatRiCT+, ML-KEM) auf ihre Eignung geprüft, zu einem Integrations- und Migrationskonzept für das Gesamtprotokoll zusammengeführt und abschließend zwei Migrationspfade verglichen: ein vollständig gitterbasierter Pfad
und die vom Monero-Projekt real eingeschlagene FCMP++-Entwicklung.
 
Die Analyse zeigt, dass keiner der beiden Pfade für sich allein alle drei Datenschutzdimensionen quantensicher löst: FCMP++ härtet die Absenderanonymität einschließlich retroaktiver Forward Secrecy mit kompakten Beweisen, lässt aber Beträge und Empfängerableitung ECC-gebunden; der Gitterpfad deckt alle Schichten ab, scheitert jedoch an deutlich größeren Transaktionen, einer Vertauschung der Hiding- und Binding-Eigenschaften der Commitments und der ungelösten Integration quantenresistenter Stealth-Adressen. Ein vollständig quantensicheres Monero
erfordert daher die Kombination beider Ansätze, deren Schnittstellen offene Forschungsfragen bleiben. Aufgrund des HNDL-Drucks auf den bereits heute archivierbaren On-Chain-Datensatz bleibt eine zeitnahe Migration dringlich.
 

23.07.2026 12:10-12:40 Alexander Horst Keller Bachelor Thesis kickoff presentation

Title: A Distributed Protocol for Offline-Verifiable Reaction Tests 

Abstract: I will be presenting my planned bachelor’s thesis, in which I design and analyze a distributed protocol for reaction tests.

22.07.2026 12:00-12:30 Omar Hegab Bachelor Project final presentation

Title : Approximate Data Aggregation on Star Graphs Using Gossip-Based Protocols

Abstract : Distributed systems frequently need to compute global quantities, such as sums or averages, without collecting all data at a central location. This occurs, for example, in sensor networks in which many devices measure local values and communicate through a common
gateway. Gossip-based algorithms are well suited to such settings because they rely only on repeated local exchanges and do not require global coordination. This project studies the Push-Sum protocol, a gossip-based algorithm for distributed averaging, on a star graph. The star topology represents a highly asymmetric communication structure: all communication between the leaves must pass through a single center
node. This asymmetry makes the standard intuition from homogeneous or fully connected networks difficult to apply directly.
We develop a star-specific convergence analysis based on contribution vectors and a potential function measuring the deviation from the correct average. By exploiting the symmetry among the leaves, the evolution of the expected potential is reduced to a two-dimensional recurrence describing the center and leaf contributions separately. We then analyze the mean squared error of the actual ratio estimates and obtain an upper bound of O(n log (1/ε)) rounds for reducing the expected MSE below a threshold ε, assuming a fixed initial scale. The analysis also explains why the individual sum and weight variables need not converge, although their ratio still approaches the correct average. Finally, numerical
simulations support the theoretical results and illustrate the characteristic difference between potential and estimate convergence.

22.07.2026 12:35 – 13:00 Colin Duchilio Bachelor Project final presentation

Title : Node Pairing & Creating a Lobby System for Mental Card Games

Abstract: In his Project, Benjamin Schliebitz created a rust-based codebase for Mental Card Games. Absent from this codebase was a way to play games together with others. This project built upon said codebase in order to remedy that, by utilizing the Iroh crate to implement a peer-to-peer connection and communication system, as well as implementing a lobby system for players to come together and play a game, utilizing QR Codes as easy connection entry points.

16.07.2026 12:00-12:30 Jonathan Schmiederer Bachelor Thesis final presentation

Title: Human Factors of Key Verification in Encrypted Messengers: A System for Field Studies

Abstract : End-to-end encryption is important for securing private communication in mobile messengers, but an active attacker may break it with a Man-in-the-Middle attack. To defend against this, messengers offer features that let users verify their chat
partners’ public keys. Numerous laboratory studies have examined the usability of these features, yet how users perform key verification outside the laboratory has remained unexamined.
For this thesis I developed a privacy-preserving telemetry system that enables what is, to the best of my knowledge, the first field study on key verification, and implemented it in Delta Chat, a messenger whose unusual approach to key verification makes it especially interesting to study. The system is designed to let users see what data is collected, reflecting the constraints of a secure messenger. It was accepted into the official Delta Chat for Android app.
In a pilot study, I demonstrated that the system makes such a field study feasible and produces meaningful data, while also clarifying which research questions can and cannot be answered by instrumenting the messaging application.

15.07.2026 14:00-14:30 Prof. Dr. Sevil Sen Research Seminar presentation

Title: Current Challenges in AI-Driven Cybersecurity
 
Abstract: This interactive research seminar will focus on current research challenges at the intersection of artificial intelligence, cybersecurity, and computer networks. After a short introduction by Professor Sevil Sen on ongoing research at Hacettepe University, participants are invited to present their own research interests and discuss possible collaborations. Topics include explainable AI, malware analysis, IoT security, federated learning, large language models for security applications, and emerging directions in trustworthy AI for cybersecurity.

15.07.2026 16:00-16:30 Shuran Liu Bachelor Thesis final presentation
Title: Investigating RSA Exponentiation and Its Relationship to Subgroups of Order n

Abstract: This presentation studies RSA exponentiation from a group-theoretic perspective. In traditional RSA, the product of two primes is mainly used as the modulus for computation. In this work, it is instead treated as the order of a cyclic subgroup. The main goal is to construct such a subgroup and examine how RSA-like exponentiation behaves inside it.
The construction is based on choosing suitable parameters and generating a cyclic subgroup whose order is equal to the RSA modulus. Experimental tests with different parameter sizes show that suitable parameters can be found for the tested examples. Based on this subgroup, an RSA-like encryption and decryption process is introduced, and its correctness is discussed.
However, because the subgroup has composite order, standard security arguments for prime-order groups cannot be applied directly. Additional conditions are needed, especially when extracting secret values from different protocol transcripts.
Overall, this work provides a framework for connecting RSA-like exponentiation, cyclic subgroups, and zero-knowledge proofs. Future work includes a more detailed implementation of multiplication proofs, the integration of committed primality proofs, and a deeper security analysis of zero-knowledge protocols over composite-order subgroups. Another possible direction is to study whether the hidden-order version of the construction can be developed into a more secure cryptographic scheme.

08.07.2026 14:00–14:45 Luca Diringer Bachelor Thesis kickoff presentation
Title: Characterizing Equal-Distance Point Pairs in Exponential Reflection Trees

Abstract : In a triangular room containing a sender and a receiver, we aim to determine the sender’s position and reconstruct the geometry of the room using only the Time Difference of Arrival (TDoA) and the Angle of Arrival (AoA), without any additional information. To achieve this, we identify pairs of image points whose mutual distance is equal to that of another pair of image points. These equal-distance relationships provide additional constraints that allow the localization and reconstruction problem to be solved using only a small number of image points.
The primary objective of this thesis is to identify as many such equal-distance conditions as possible and to derive a general characterization of their occurrence within the exponential reflection tree. This characterization enables these patterns to be recognized for arbitrary reflection orders.

01.07.2026 14:00–14:45 Lars Schmitt Master Project final presentation
Title : Introducing randomization in the 2D Ray tracing based Cryptographic scheme

Abstract : This project analyzes the IND-CPA security of a two-dimensional ray-tracing-based cryptographic scheme. Since the original construction is deterministic, identical plaintexts always produce identical ciphertexts, making the scheme insecure against chosen-plaintext attacks. To address this, two non-deterministic variants are proposed: one uses pseudorandom masks derived from a synchronized counter and shared key, while the other applies a fresh random mask during encryption. Both approaches prevent deterministic ciphertexts and achieve IND-CPA security under standard cryptographic assumptions. The encryption and decryption procedures, security properties, and practical trade-offs—including synchronization, randomness, communication overhead, and implementation complexity—are analyzed and compared.

01.07.2026 14:40-15:04 Jonathan Altherr Bachelor Thesis kickoff presentation
Title: Achieving IND-CPA Security in a Ray-Tracing-Based Encryption Scheme

Abstract: This presentation outlines the approach to achieving IND-CPA security in a ray-tracing-based encryption scheme. The existing scheme is currently vulnerable to chosen-plaintext attacks because it is deterministic: two identical plaintexts will always result in the same ciphertext for a given key.

This Bachelor’s thesis focuses on the practical realization of a counter-based approach to secure the scheme against chosen-plaintext attacks, with special regard to the following topics:

01.07.2026 15:15–15:45 Zeinab Herz — Bachelor Thesis Kickoff Presentation
Title: Object Detection and Distance Estimation in Traffic Scenes Using Time-of-Flight Cameras

Title:
Close overtaking of cyclists by motor vehicles remains a significant road safety issue.

Abstract:
Das zu enge Überholen von Fahrradfahrern durch Kraftfahrzeuge stellt ein relevantes Problem für die Verkehrssicherheit dar. Um solche Situationen besser untersuchen zu können, beschäftigt sich diese Bachelorarbeit mit der automatisierten Analyse von Überholvorgängen im Straßenverkehr. Ziel ist es, Verkehrsteilnehmer zu erkennen, ihre Positionen zu bestimmen und daraus Informationen über Überholsituationen abzuleiten.
Als Sensortechnologie wird eine Time-of-Flight-Kamera (ToF-Kamera) eingesetzt. Diese ermöglicht die Erfassung der Umgebung durch verschiedene Datenrepräsentationen: Intensitätsbilder, Tiefenkarten sowie dreidimensionale Punktwolken. Diese Informationen bieten die Grundlage für die weitere Auswertung der Verkehrsszene.
Ein Schwerpunkt der Arbeit liegt auf der Objekterkennung. Dabei sollen insbesondere Fahrradfahrer, Kraftfahrzeuge und Passanten zuverlässig erkannt werden. Die Identifikation der beteiligten Verkehrsteilnehmer ist eine wesentliche Voraussetzung, um Überholvorgänge zu erfassen und festzustellen, welches Objekt ein anderes überholt.
Aufbauend auf der Objekterkennung werden erkannte Verkehrsteilnehmer über die Zeit verfolgt und ihre räumlichen Beziehungen analysiert. Abschließend soll die Distanz zwischen Kraftfahrzeugen und Fahrradfahrern während eines Überholvorgangs bestimmt werden. Die gewonnenen Ergebnisse können einen Beitrag zur automatisierten Analyse von Verkehrssituationen leisten.

24.06.2026 14:00–14:30 Mattis Bless — Master Thesis Kickoff Presentation
Title: Efficient Shuffle for Mental Card Games – Revisited

Abstract:
In this thesis, we revisit the problem of a communicationally efficient multiplayer zero-knowledge shuffle argument for mental card games without a trusted third party. The original argument is based on permutation networks, which are then transformed into arithmetic circuits. The circuits are described by efficient zero-knowledge arguments, resulting in the desired zero-knowledge argument for the correctness of the shuffle. Other shuffle arguments typically require each player to know the shuffled ciphertexts in order to check the argument’s correctness, causing a large communication overhead. In comparison, the shuffle argument in this thesis only requires the players to know small commitments to the ciphertexts.

However, this commitment-only shuffle argument still suffers from several limitations that we aim to address. The first goal is to reduce the original argument’s bias towards certain permutations caused by the chosen permutation network. Besides further reducing the communication requirements, for example in the remasking step of the shuffle, we also investigate what we call a provably secure shuffle. In such a shuffle, the applied permutation depends not only on the shuffling player’s choice but also on publicly available input whose value cannot be anticipated or significantly influenced. This ensures that even if all players collude, they cannot intentionally position cards during the shuffle. Such manipulation could not be prevented in the original approach, which assumes that at least one player is honest.

24.06.2026 14:45–15:15 Selin Keles — Master Thesis Kickoff Presentation
Title: Making Flip Networks Secure

Abstract:
Flip networks are dynamic, connected, regular peer-to-peer overlays whose topologies are continuously transformed through distributed random 1-Flipper operations. Although these transformations can improve the expansion and robustness of the network, an adversary may attempt to manipulate the selection, coordination, or execution of flip operations and thereby influence the resulting topology.

This thesis investigates the security of flip networks in the presence of colluding malicious peers, churn, and concurrent topology transformations. It defines fundamental security objectives, including soundness, randomness, generality, and convergence, and identifies flip-network-specific attacks that threaten these properties. Based on this analysis, the thesis aims to design protection mechanisms against selected attack models and formally prove their security guarantees, ensuring that the flip network remains secure against the considered attacks.

24.06.2026 15:25–15:55 Nikita Kroh — Bachelor Thesis Kickoff Presentation
Title: Creating a Hashing Algorithm Based on the 3D Ray-Tracing Cryptographic System

Abstract:
The current 3D ray-tracing-based cryptographic system is well suited for encrypting and decrypting plaintext. In this thesis, our goal is to create a hashing algorithm based on this 3D ray-tracing cryptographic system. To achieve this, we investigate how to derive a valid light ray from a password of arbitrary length, which information should be collected during the ray-tracing process, and how the collected information can be compressed into a fixed-length output. Finally, we evaluate whether the resulting algorithm satisfies the irreversibility requirements of a cryptographic hash function.

24.06.2026 16:00–16:30 Alexander Horst Keller — Research Presentation
Title: The Button Game: A P2P DAG-Based Delayed-Reveal Protocol

Abstract:
In a peer-to-peer reaction game, fair and secure ordering of events while maintaining low latency is a challenging problem. This presentation introduces a DAG-based protocol designed to mitigate frontrunning and censorship by Byzantine participants in a partially synchronous network.

The protocol combines a delayed-reveal mechanism with threshold cryptography to prevent frontrunning and employs a deterministic linearization algorithm to derive a total order of events from a transcript of the game. The resulting design aims to provide fairness and security while preserving responsiveness in distributed reaction games