CDL-BOT is looking for a PhD student to join the team at TU Wien. For details, please see the job description. The application deadline is November 15th, but applications are accepted until the position is filled.


Our paper "Blockchain-based Result Verification for Computation Offloading" (Authors: Benjamin Körbel, Marten Sigwart, Philip Frauenthaler, Michael Sober, Stefan Schulte) has been accepted for publication as a full paper at the 19th International Conference on Service Oriented Computing. In this paper, the authors propose an innovative approach to apply zero-knowledge proofs to verify computation offloading via the blockchain.

The paper is available as a preprint.

Abstract: Offloading of computation, e.g., to the cloud, is today a major task in distributed systems. Usually, consumers which apply offloading have to trust that a particular functionality offered by a service provider is delivering correct results. While redundancy (i.e., offloading a task to more than one service provider) or (partial) reprocessing help to identify correct results, they also lead to significantly higher cost.
Hence, within this paper, we present an approach to verify the results of offchain computations via the blockchain. For this, we apply zero-knowledge proofs to provide evidence that results are correct. Using our approach, it is possible to establish trust between a service consumer and arbitrary service providers. We evaluate our approach using a very well-known example task, i.e., the Traveling Salesman Problem.


We are pleased to announce that our paper "A Voting-Based Blockchain Interoperability Oracle" by Michael Sober, Giulia Scaffino, Christof Spanning, and Stefan Schulte has been accepted as a "Regular Paper" at the 4th IEEE International Conference on Blockchain (Blockchain 2021). In this work, the authors present a blockchain oracle that enables cross-blockchain communication.
The paper is available as a preprint.
Abstract: Today's blockchain landscape is severely fragmented as more and more heterogeneous blockchain platforms have been developed in recent years. These blockchain platforms are not able to interact with each other or with the outside world since only little emphasis is placed on the interoperability between them. Already proposed solutions for blockchain interoperability such as naive relay or oracle solutions are usually not broadly applicable since they are either too expensive to operate or very resource-intensive.

For that reason, we propose a blockchain interoperability oracle that follows a voting-based approach based on threshold signatures. The oracle nodes generate a distributed private key to execute an off-chain aggregation mechanism to collectively respond to requests. Compared to state-of-the-art relay schemes, our approach does not incur any ongoing costs and since the on-chain component only needs to verify a single signature, we can achieve remarkable cost savings compared to conventional oracle solutions.


We are pleased to inform you that our paper "Decentralized Cross-Blockchain Asset Transfers" by Marten Sigwart, Philipp Frauenthaler, Christof Spanring, Michael Sober, and Stefan Schulte has been accepted for presentation at the 3rd International Conference on Blockchain Computing and Applications (BCCA2021). In this work, the authors provide the requirements, a specification, and a prototypical implementation of a cross-blockchain asset transfer protocol.
The paper is available as a preprint.
Abstract: Today, several solutions for cross-blockchain asset transfers exist. However, these solutions are either tailored to specific assets or neglect finality guarantees that prevent assets from getting lost in transit.
In this paper, we present a cross-blockchain asset transfer protocol that supports arbitrary assets and adheres to finality requirements. The ability to freely transfer assets between blockchains may increase transaction throughput and provide developers with more flexibility by allowing them to design digital assets that leverage the capacities and capabilities of multiple blockchains.


We congratulate Stefan Schulte on his new position as full professor at TU Hamburg. In the course of this, the CD-Laboratory was transferred to TU Hamburg and an additional external module was set up at TU Wien.

The Cross-Blockchain Transactions module, which is based at TU Hamburg, is headed by Dr.-Ing. Stefan Schulte and focuses on cross-blockchain aspects, such as cross-blockchain communication. Fundamental research is also done in the area of ​​developer support.

The Lightweight Blockchain Protocols module is located at TU Wien and led by Dr. Matteo Maffei. The focus here is on investigating lightweight interoperability solutions, verification of smart contracts, and sharding of DLTs.

While the structure of CDL-Bot has changed, the underlying research questions remain unchanged, but the new structure allows us to consider other aspects of the research. We look forward to the new possibilities and the future steps that can be taken through them.


We are happy to announce that the paper "Towards Cross-Blockchain Smart Contracts" by Markus Nissl, Emanuel Sallinger, Stefan Schulte, and Michael Borkowski has been accepted as a full paper at the 3rd IEEE International Conference on Decentralized Applications and Infrastructures. Within this paper, we present a first approach to provide interoperability between smart contracts running in different Ethereum Virtual Machines.

The paper is available as a preprint.


In recent years, manifold blockchain protocols have been proposed by researchers and industrial companies alike. This has led to a very heterogeneous blockchain landscape. Accordingly, it would be desirable if blockchains could interact with each other. However, current blockchain technologies offer only limited support for interoperability, thus preventing tokens or smart contracts from leaving the scope of a particular blockchain.

As a first step towards a solution for cross-chain smart contract interactions, we introduce a framework which allows to invoke a smart contract from another blockchain. We offer support for continuing a smart contract after receiving a result from a different blockchain, and for calling smart contracts recursively across blockchains. We provide a reference implementation for Ethereum-based blockchains using Solidity and evaluate the performance regarding time and cost overheads.


Stefan Schulte gave a presentation on DLT Interoperability: Relays and Other Solutions at the IOTA Research Symposium 2021. During his presentation, he presented some general information about CDL-BOT, and then introduced the different ways how to "tear down the walls" between closed-world DLTs. A recording of the presentation can be found at Youtube.


The Christian Doppler Laboratory for Blockchain Technologies for the Internet of Things (CDL-BOT) offers Postdoc and PhD positions at Hamburg University of Technology (TUHH).

The selected researchers will work at the newly established Institute of Data Engineering at TUHH under the supervision of Prof. Stefan Schulte. The main goal of these positions is to research and develop the next generation of blockchain interoperability concepts and solutions, e.g., in the areas of token transfer, data access, and smart contracts. The research aims at providing fundamental research results in the area of blockchain interoperability, which can also be applied in practical settings.

The positions are employed full-time by TU Hamburg, with an initial term of one year. An extension of the contracts to four years is foreseen.

For the PhD student position, a very good Diploma or Master university degree in computer science, informatics, business informatics, mathematics, or a related discipline is expected. For the Postdoc position, a very good PhD in computer science, informatics, business informatics, or a related discipline is expected.

We offer

  • The chance to pursue your research (theoretical and experimental) within a young and international team, which is delivering very important contributions to blockchain and Internet of Things research.
  • Continuing personal and professional education.
  • The possibility to present your research results at international top conferences.
  • The opportunity for stays abroad at international partner universities.
  • To become part of a creative team at an aspiring university and in one of the most livable cities in the world.
  • A highly competitive salary. Entry level salaries as a PhD student are at a minimum of 4050 € per month (gross; 12 times per year), for a Postdoc at a minimum of 4600 € per month (gross; 12 times per year; depending on the previous experience). The salaries are following the German TV-L 13 scheme.

We expect

  • In-depth interest in scientific problems and the motivation for independent and goal-oriented research.
  • The ability to develop methods, concepts, and models, as well as their realization and evaluation and the willingness to contribute to scientific projects.
  • The willingness to contribute to an industry-oriented scientific project aiming at fundamental research results.
  • Very good programming skills.
  • Very good knowledge about and passion for distributed systems.
  • Knowledge in blockchain technology or cryptography is a plus.
  • Very good scientific communication and writing skills.
  • Very good knowledge in English communication and writing.

Please direct your complete application pack - including a motivation letter, a current CV, academic transcripts and certificates, and a digital copy of your latest thesis (either Master or PhD) - to Applications from female candidates are highly encouraged. The preferred starting date is October 2021, but a later start is also possible.

Deadline for applications: August 15th, 2021. For further information please contact Prof. Stefan Schulte ( and see


The head of CDL-BOT, Stefan Schulte, has been interviewed for the latest issue of "Wien Wissen", talking about the usage of blockchains in the Internet of Things. Please find the resulting article on blockchain research at TU Wien at Unfortunately, the article is only available in German.


On May 4th, 2021, Stefan Schulte, head of CDL-BOT, participated in the Panel Discussion on Cross Chain Operations at the IEEE International Conference on Blockchain and Cryptocurrency. Within the panel, Stefan discussed with Peter Robinson (ConsenSys & The University of Queensland), Ying Xue (Brown University), and Raghvendra Ramesh (ConsenSys) current trends and future developments in the field of blockchain interoperability. The panel was moderated by David Hyland-Wood (Bits-Core).


Talk at the Austrian Blockchain Center

On 29.04.2021, Stefan Schulte (CDL-BOT), Christof Spanring, and Philip Gahler (both from Pantos GmbH) gave a presentation at the Austrian Blockchain Center Talk series to an audience of roundabout 300 listeners. Within the presentation, a general overview of interoperability issues and solution approaches in the realm of Distributed Ledger Technologies were presented. Also, the application of interoperability solutions was discussed. A video from the talk can be found at Youtube.


Inauguration of the Christian Doppler Laboratory

The Christian Doppler Laboratory Blockchain Technologies for the Internet of Things has been inaugurated today. Because of the ongoing Corona pandemic, the opening had to take place online. An audience of more than 650 people watched speeches by Austria's Minister of Digital and Economic Affairs, Dr. Margarete Schramböck, the rector of TU Wien, Dr. Sabine Seidler, the head of the Christian Doppler Laboratory, Dr.-Ing. Stefan Schulte, as well as Dominik Schiener (Co-Founder IOTA) and Eric Demuth (CEO Bitpanda and Pantos).


Best Paper Award at IEEE Blockchain 2020

Congratulations to Tamara Brandstätter, Stefan Schulte, Jürgen Cito and Michael Borkowski for winning the Best Paper Award for their paper "Characterizing Efficiency Optimizations in Solidity Smart Contracts" at the 3rd IEEE International Conference on Blockchain.

Paper Download

Presentation of 2 Research Papers at IEEE Blockchain 2020

The papers "Characterizing Efficiency Optimizations in Solidity Smart Contracts" and "ETH Relay: A Cost-Efficient Relay for Ethereum-Based Blockchains" have been presented by Dr.-Ing. Stefan Schulte at the 3rd IEEE International Conference on Blockchain. This conference is the top conference in the blockchain research field, with an acceptance rate of 16% in 2020.


Official start of CDL-BOT

We are very happy to announce that today, the Christian Doppler Laboratory Blockchain Technologies for the Internet of Things (CDL-BOT) has started. We want to thank our partners Pantos and IOTA as well as the Christian Doppler Research Association for their support. We are looking forward to do groundbreaking research in the field of blockchains and other Distributed Ledger Technologies (DLTs) for the IoT.