Leander Jehl

University of Stavanger · Department of Electrical engineering and Computer science

Decentralized storage networks offer services with intriguing possibilities to reduce inequalities in an extremely centralized market. Fair distribution of rewards, however, is still a persistent problem in the current generation of decentralized applications using token-based incentives. They are often dispro-portionally concentrated with small nu...

Decentralized storage networks offer services with intriguing possibilities to reduce inequalities in an extremely centralized market. The challenge is to conceive incentives that are fair in regard to the income distribution among peers. Despite many systems using tokens to incentivize forwarding data, like Swarm, little is known about the interpl...

With the advancement of blockchain systems, many recent research works have proposed distributed ledger technology~(DLT) that employs Byzantine fault-tolerant~(BFT) consensus protocols to decide which block to append next to the ledger. Notably, BFT consensus can offer high performance, energy efficiency, and provable correctness properties, and it...

Blockchains based on proof-of-work suffer from serious drawbacks, such as high computational overhead, long confirmation time, and forks. Committee-based blockchains provide an alternative that tackles these problems. These blockchains use a committee to approve a block at each height. However, rewarding the committee for their work is challenging....

Peer-to-peer (p2p) networks are not independent of their peers, and the network efficiency depends on peers contributing resources. Because shared resources are not free, this contribution must be rewarded. Peers across the network may share computation power, storage capacity, and bandwidth. This paper looks at how bandwidth incentive encourages p...

Byzantine fault-tolerant agreement (BFT) in a partially synchronous system usually requires 3f + 1 nodes to tolerate f faulty replicas. Due to their high throughput and finality property BFT algorithms build the core of recent permissioned blockchains. As a complex and resource-demanding infrastructure, multiple cloud providers have started offerin...

Researchers develop software to process or generate data to test their scientific hypotheses. Especially researchers from STEM disciplines (Science, Technology, Engineering, and Mathematics) validate their models through self-developed software prototypes. However, they do not necessarily have a programming or software engineering background. Moreo...

Still to this day, academic credentials are primarily paper-based, and the process to verify the authenticity of such documents is costly, time-consuming, and prone to human error and fraud. Digitally signed documents facilitate a cost-effective verification process. However, vulnerability to fraud remains due to reliance on centralized authorities...

HotStuff is a recent algorithm for repeated distributed consensus used in permissioned blockchains. We present a simplified version of the HotStuff algorithm and verify its safety using both Ivy and the TLA Proof Systems tools.

Blockchain is the driving force behind a myriad of decentralized applications (dapps) that promise to transform the Internet. The next generation Internet, or web3, introduces a "universal state layer" to store data in p2p networks. Swarm, a native layer of the Ethereum web3 stack, aims at providing redundant storage for dapp code, data, as well as...

Readily available blockchain technologies allow to improve reliability and availability of existing cloud applications. This paper presents a blockchain based distributed storage system for permissioned settings. We use a blockchain to form verifiable contracts between clients and storage providers, specifying what should be stored, and when stored...

Gorums is a novel RPC framework aimed at simplifying development of fault tolerant distributed systems. In this paper, we want to assess whether Gorums can simplify the implementation of a practical fault tolerant service that supports reconfiguration. To this end, we implemented the Raft consensus algorithm using Gorums, and show that Gorums's abs...

This paper studies reliability of probabilistic neighbor-aware gossip algorithms over three well- known large-scale random topologies, namely Bernoulli (or Erd\H{o}s-R\'enyi) graph, the random geometric graph, and the scale-free graph. We propose a new and simple algorithm which ensures higher reliability at lower message complexity than the three...

In this paper, we study reconfiguration mechanisms for atomic storage systems. We observe that the state of the art approach for reconfiguration in an asynchronous environment has several disadvantages compared to the classical consensus-based approach, which requires eventual synchrony. For example, an unfortunate combination of remove operations...

This paper addresses reconfiguration of a Replicated State Machine (RSM) in an asynchronous system. It is well known that consensus cannot be solved in an asynchronous system. Therefore an RSM providing strong consistency, cannot guarantee progress in an asynchronous system. However, we show that reconfiguring the RSM is possible in a purely asynch...

Paxos is a flexible and fault tolerant protocol for solving the consensus problem, where participants in a distributed system need to agree on a common value. However, Paxos is reputed for being difficult to understand. This tutorial aims to address this difficulty by visualizing Paxos in a completely new way. Starting from a naive solution and str...

More than a decade of research has gone into techniques aimed at tolerating arbitrary failures in client/server interaction, using consensus based replication. These works made Byzantine fault tolerance possible [5], competitive [18], robust [7], and feasible to apply [6]. In this paper we establish a connection between the pub/sub interaction mode...

We investigate methods for handling failures in a Paxos State Machine and introduce Live Replacement, which quickly repairs failures at a low cost. Live Replacement enables a failed or disconnected replica to be replaced with a new one, with minimal disruption. Replacement does not rely on a special state machine command, and need not be ordered wi...