Hasso-Plattner-Institut25 Jahre HPI
Hasso-Plattner-Institut25 Jahre HPI

Current Topics in Group Messaging (Wintersemester 2022/2023)

Dozent: Prof. Dr. Anja Lehmann (Cyber Security - Identity Management) , Dennis Dayanikli (Cyber Security - Identity Management) , Tarek Galal Abdelsalam (Cyber Security - Identity Management)

Allgemeine Information

  • Semesterwochenstunden: 4
  • ECTS: 6
  • Benotet: Ja
  • Einschreibefrist: 01.10.2022 - 31.10.2022
  • Prüfungszeitpunkt §9 (4) BAMA-O: 01.12.2022
  • Lehrform: Seminar
  • Belegungsart: Wahlpflichtmodul
  • Lehrsprache: Englisch
  • Maximale Teilnehmerzahl: 6

Studiengänge, Modulgruppen & Module

Cybersecurity MA
  • IDMG: Identity Management
    • HPI-IDMG-K Konzepte und Methoden
  • IDMG: Identity Management
    • HDI-IDMG-T Techniken und Werkzeuge
  • IDMG: Identity Management
    • HPI-IDMG-S Spezialisierung
IT-Systems Engineering MA
Digital Health MA
Data Engineering MA
Software Systems Engineering MA


Centralized messaging services such as Signal and WhatsApp have become the dominant form of asynchronous digital messaging in recent years. To reduce trust in messaging service providers and state actors, many of such services employ End-to-end encryption (E2EE) to restrict the capability of decrypting messages to the intended recipients. While E2EE guarantees certain security and privacy properties for the communicating participants, other requirements arise when conversations contain more than two communicating parties (a group) such as hiding the list of group members from the server.

This seminar consists of two parts. In part 1, the Signal Private Group System will be broken down into its cryptographic building blocks where a group of 1-2 students will select one of those topics, prepare a technical presentation (~45-60min), and lead a discussion (~30-45min) for it. By the end of part 1, we will have collected an understanding of how group messaging in Signal works and how the different components fall in together. In the second part of the seminar, each of the groups will implement the part they presented using the Python programming language. The goal of part 2 is to integrate the pieces implemented by the participants together to produce a Python library providing a working signal groups implementation for use by other developers.

Topics covered include:

  • Elliptic Curve Cryptography
  • Anonymous Credential Systems
  • Zero-Knowledge Proofs
  • Algebraic MACs
  • Verifiable Encryption
  • Keyed-verification Anonymous Credentials

At the end of the seminar, participants also hand in a brief written report summarizing their topics, what they have implemented, and any encountered challenges.



To participate in the seminar, you must enroll in Moodle in addition to your registration with the Studienreferat. The first (introductory) session takes place on 20.10  and its attendance is mandatory for participation. As the seminar capacity is limited to 6 students, we will describe a selection procedure during the introductory session if more students show interest. A final decision regarding the participants list will be made on 24.10.


Successful completion of the (Introduction to) Cryptography lecture at HPI or a similar course at another university is required and attendance of the Advanced Cryptography lecture (every summer term) is recommended.

For the practical part, participants should be motivated to carry it out using python, are comfortable using git, and are willing to put in the effort to deliver a high quality output.


The final grade is based on the presentation (25%), the implementation work (50%) and the final report (25%).


The seminar takes place on Thursdays 13:30-15:00 in G3.E15/16. First session is on 20.10 with mandatory attendance.