📡 P2P Offline Group Messaging App

An offline P2P group messaging application designed for small community groups, where the app is independent of central servers.

🎓 This project was part of my MSc Thesis at the University of Basel, CH.

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🧭 Overview

The goal of this project is to build a fully offline P2P group chat system that operates without:

• Centralized servers
• Persistent internet connectivity
• Dedicated infrastructure running 24/7

Key Characteristics

• Fully decentralized peer-to-peer architecture
• Offline-first design
• No central coordination or server dependency
• CRDTs
• Command-line interface (CLI)
• Designed for small, local community groups

📁 Repository Structure

The repository is organized as follows:

• implementations/ Contains the core application source code.
  Implementations are provided in:

  • Bash
  • Rust

• evaluation-scripts/ Contains testing scripts for the evaluation of this project. There are two sub-folders:

  • Exp 1
  • Exp 2

  More files are added related to data cleaning, and plot functions in the sub-folders of the evaluation-scripts folder.

• my-report/

  • My MSc report.

Illustration

The idea is to build a consensus-free P2P Group Chat using CRDTs [1.]. Our core focus was on group membership model, designing group operations APIs like add/remove member etc. can be found in implementations/ README file. And, how do the group state converges without needing a consensus. Therefore, we used CRDTs [2., 3.].

Implementation Design

We embedded our CRDTs in the Git objects. Our idea of implmentation is similar to Merkle-CRDTs [4.], but we don't build our own Merkle-DAG from scratch, instead we use Git.

• Above is the structural representation of mapping CRDTs to Git objects.
• Each commit is like a message exchanged between group users that points to a tree object.
• The tree object pointed by the commit stores group information like group name, and description. This tree object itself points to another tree object.
• The second tree object stores the members, and each member value is like a tuple(size=2) which is our grow-only counters. The first tuple value indicates the presence of a member where as the second tuple value denotes the admin presence.
• Each commit object is pointed by git reference. If a group has N members, then each group will have N references.

The above design is just a high level design and we won't go much into detail explanation.

My report can be found here my-report/

References

1. Marc Shapiro, Nuno Preguiça, Carlos Baquero, and Marek Zawirski, Conflict-free replicated data types. URL: https://arxiv.org/abs/1805.06358, 2011.
2. Weihai Yu and Sigbjørn Rosta, A Low-Cost Set CRDT Based on Causal Lengths. URL: https://nva.sikt.no/registration/0198cc5de8b2-ae7d8d7f-4359-4729-a7c0-46e59e059714, 2020.
3. Erick Lavoie, State-based ∞p-set conflict-free replicated data type. URL: https://arxiv.org/abs/2304.01929, 2023.
4. Hector Sanjuan, Samuli Poyhtari, Pedro Teixeira, Ioannis Psaras, Merkle-CRDTs: Merkle-DAGs meet CRDTs. URL: https://arxiv.org/abs/2004.00107, 2020.

📌 Repository Notice

• This repository is a continuation of the following archived repository:

  • Thesis-crdt-bash
  • Thesis-CRDT-Scripts

• Moreover, this repository contains additional codes which were not pushed in the archived repositories.

• Additional code and improvements that were not included in the archived repositories are available here.

• ✅ All future development and updates will take place in this repository.

• ❌ Please do not use or reference the archived repositories..

🚫 Issues & Contributions

• Please do not open issues or submit pull requests.
• This repository is not actively maintained for public collaboration.
• It exists solely for personal development and documentation related to my MSc thesis.

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📜 License

This project is licensed under the BSD 3-Clause License © 2026, Abhilash.