Blockchain Papers

Henning Kopp, Christoph Bösch, Frank Kargl

No abstract is available for this record.

Marko Vukolić

No abstract is available for this record.

S.D. Norberhuis

Peer-to-peer networks are often large, collaborative networks where peers can join openly. The essence of a collaborative, distributed system is that every node performs tasks for other nodes. The peers often help in singular interactions and without direct reciprocity. Malicious peers can abuse and freeride the public goods. The network without countermeasures can fall into a tragedy of the commons where no one helps another and everyone takes advantage of the generosity of peers. Only when the reputation of a peer is publicly available at scale and peers trust this reputation can the network escape the problems of freeriding and attain high utility for all participants. This thesis focuses on designing and implementing the first step of a tamper proof reputation system within Tribler. Tribler is a peer-to-peer BitTorrent system developed at the Delft University of Technology. This first step, made by this thesis, is to create MultiChain, a proof-of-concept bookkeeping system. MultiChain tracks the upload and download amounts of peers to eliminate freeriding. Multi-Chain is cryptographically protected and validated. The bookkeeping system has to be scalable to be publicly available and be able to process enough transactions. The system has to work in an asynchronous network. A new design of a distributed data structure that can be used as a ledger is introduced by this thesis. This first step with MultiChain is already more resilient to tampering than previous work, like BarterCast. BarterCast has no security measures against tampering records. The design of MultiChain is to have a chain of blocks for every peer as a ledger. Peers are participants of a peer-to-peer network. A block contains a transaction between two peers. This block is shared and added to both chains. This makes both chains of the peers intertwined and entangled at a shared block. The proposed design abandons the typical global, full ledger. The protocol of creating these blocks between peers is described. The problems faced by MultiChain in an asynchronous network are explained. The thesis proposes how the design can overcome these problems by only allowing atomic operations to be performed on the chain and to introduce unfinished blocks in the chain. The implementation of the design is tested and experimented with within this thesis to validate it to work correctly. Furthermore, a number of weak points are discussed. These weak points have to be addressed in the future to create a tamper proof reputation system.

Matthew D. Sleiman, Adrian P. Lauf, Roman V. Yampolskiy

The Bit coin currency is steadily growing in popularity as an alternative to physical currencies. This paper presents an approach for utilizing the Bit coin system for creating permanent messages that are located on computers worldwide. By manipulating the amount field of Bit coin transactions, messages can be embedded into the Bit coin block chain. This approach was implemented by extending the Bit coin-Qt v0.7.2 application and the source code is freely available.

Krzysztof Rzaḑca, Anwitaman Datta, Gunnar Kreitz, Sonja Buchegger

In a decentralized storage system, agents replicate each other’s data to increase availability. Compared to organizationally centralized solutions, such as cloud storage, a decentralized storage system requires less trust in the provider and may result in smaller monetary costs. Our system is based on reciprocal storage contracts that allow the agents to adopt to changes in their replication partners’ availability (by dropping inefficient contracts and forming new contracts with other partners). The data availability provided by the system is a function of the participating agents’ availability. However, a straightforward system in which agents’ matching is decentralized uses the given agent availability inefficiently. As agents are autonomous, the highly available agents form cliques replicating data between each other, which makes the system too hostile for the weakly available newcomers. In contrast, a centralized, equitable matching is not incentive compatible: it does not reward users for keeping their software running. We solve this dilemma by a mixed solution: an “adoption” mechanism in which highly available agents donate some replication space, which in turn is used to help the worst-off agents. We show that the adoption motivates agents to increase their availability (is incentive-compatible), but also that it is sufficient for acceptable data availability for weakly-available agents.

Rodrigue Carlos Nana Mbinkeu, Bernabé Batchakui

For the past five years, the bitcoin network constantly experience a growth in its size as more communities turn to accept the currency for payment exchanges. Using Flat File and a LevelDB of indices to save blocks on disk, bitcoin users require more memory to save the history of transaction. We focus on issues of memory management and access time in the bitcoin protocol using SQLite DataBase. With all the advantages of SQLite DataBase, it would be efficient if it is fitted in this architecture. The SQLite comes with many flavors one of which is its ability to support sql queries. Thus, instead of parsing indices to search a block from the database, a more powerful query can do the job.

K. Down, Martin Hutchinson

Bitcoin is most radical innovation in monetary space for a very long time. It is an entirely private monetary system that runs itself and does not depend on trust in any central authority to honor its promises. Instead, it relies on trust in Bitcoin community or network that verifies transactions and maintains integrity of system. This system of distributed trust creates bitcoins and produces an automatic, tamper-proof bitcoin money supply process. (1) As such, it avoids dangers of discretionary monetary policy--namely, quantitative easing, manipulated interest rates, and need to rely on wise men or women to withstand political pressure or successfully forecast future. Indeed, under Bitcoin there is no monetary policy at all. There is just an automatic monetary rule dictated by Bitcoin protocol designed in 2009 by an anonymous programmer using alias Satoshi Nakamoto. Bitcoin has been widely hailed as a success and has won a substantial following. Unfortunately, underlying economics of Bitcoin mean that it is unsustainable and in all likelihood will be remembered as a failed experiment--at best a pointer to some superior successor. A first-pass intuition into Bitcoin can be obtained from a comparison with stone money in Milton Friedman's (1992) case study, Island of Stone Money. In this story, people of island of Yap in Micronesia used as money large round limestone disks transported from nearby island of Palau. These were too heavy to conveniently move around, so they were placed in prominent places. When ownership was to be transferred (e.g., as part of a dowry, inheritance, or ransom payment), current owner would publicly announce change in ownership but stone would typically remain where it was and islanders would maintain a collective memory of ownership history of stones. This collective memory ensured that there was no dispute over who owned which stones. Similarly, in Bitcoin, record of all transactions, blockchain, is also public knowledge and is regarded as die definitive record of who owns which bitcoins. Both stone money and Bitcoin share a critical feature that is highly unusual for a monetary system: both systems operate via a decentralized collective memory. On February 11, 2009, Nakamoto gave an explanation of thinking behind Bitcoin in an e-mail announcing its launch: root problem with conventional currency is all trust that is required to make it work. The central bank must be trusted not to debase currency, but history of fiat currencies is full of breaches of that trust.... With e-currency based on cryptographic proof, without die need to trust a third-party middleman, money can be secure and transactions complete. Cryptocurrencies, however, face problem of As Nakamoto notes, owner could try to re-spend an already spent coin by [digitally] signing it again to another owner. The usual solution is for a trusted company with a central database to check for double-spending, but that just gets back to trust model.... Bitcoin's solution is to use a peer-to-peer network to check for double-spending. Consequently, the result is a distributed system with no single point of failure. (2) Kevin Dowd is Professor of Finance and Economics at Durham University in United Kingdom and a partner at Cobden Partners. Martin Hutchinson is a journalist and author of Bear's Lair column (www.tbwns.com/category/the-bears-lair). The authors thank Ferdinando Ametrano, Gavin Andresen, Raadhiyah Anees, Steve Baker MP, Roger Brown, Dave Campbell, Akin Fernandez, Dominic Frisby, Jim Harper, Doug Jackson, Gordon Kerr, Jim Rapp, Eric Samieski, Lawrence H. White and Basil Zafiriou for much helpful feedback. We note that several of our readers have expressed serious reservations about our analysis and conclusions. Any remaining mistakes are authors' own. …

J.S. Barkatullah, Timo Hanke

There is an intense technological race underway to build the highest-performance and lowest-power custom Bitcoin mining appliances using custom ASIC processors. This article describes the architecture and implementation details of CoinTerra's first-generation Bitcoin mining processor, Goldstrike 1, and how this processor is used to design a complete Bitcoin mining machine called Terraminer IV. Because of high power density in the Bitcoin mining processor, delivering power and cooling the die posed enormous challenges. This article describes some of the solutions adopted to overcome these challenges.

Daniel Folkinshteyn, Mark M. Lennon

Bitcoin is widely represented in the popular press, but far less so in serious academic inquiry. Researchers have analyzed Bitcoin from various discipline-specific perspectives using their own sets of theories and jargon. Yet cross-disciplinary research has been muddled by the inaccurate interpretation of terminology across fields of research. This results in polarized assessments. In an effort to examine the Bitcoin phenomenon in a more holistic and multidisciplinary manner, this paper compares Bitcoin with another innovative technology – the World Wide Web – as first envisioned by Tim Berners-Lee. By exploring the early development of the World Wide Web, we seek to compare and contrast its development with that of Bitcoin and blockchain technology. The goal of this study is to show similarities and differences in their historic development, in order to identify key success factors related to the adoption of these technologies. Through identification of these factors we seek to guide both academics and practitioners towards fruitful avenues of research and development.

Andrew Miller, Rob Jansen

We describe a new methodology that enables the di-rect execution of multi-threaded applications inside of Shadow, an existing parallel discrete-event network sim-ulation framework. Our methodology utilizes function interposition and an application-layer thread library to emulate the ordinary thread interface to the application. Using this methodology, we implement a new Shadow plug-in that directly executes the Bitcoin reference client software. We describe optimizations that enable scalable execution of thousands of Bitcoin nodes on a single ma-chine, and discuss how to model the Bitcoin network for experimental purposes. Finally, we present novel denial-of-service attacks against the Bitcoin software, which exploit low-level implementation artifacts in the Bitcoin reference client. We demonstrate these attacks using our methodology, tools, and models. 1

Kourosh Davarpanah, Dan Kaufman, Ophelie Pubellier

NeuCoin is a decentralized peer-to-peer cryptocurrency derived from Sunny\nKing's Peercoin, which itself was derived from Satoshi Nakamoto's Bitcoin. As\nwith Peercoin, proof-of-stake replaces proof-of-work as NeuCoin's security\nmodel, effectively replacing the operating costs of Bitcoin miners\n(electricity, computers) with the capital costs of holding the currency.\nProof-of-stake also avoids proof-of-work's inherent tendency towards\ncentralization resulting from competition for coinbase rewards among miners\nbased on lowest cost electricity and hash power.\n NeuCoin increases security relative to Peercoin and other existing\nproof-of-stake currencies in numerous ways, including: (1) incentivizing nodes\nto continuously stake coins over time through substantially higher mining\nrewards and lower minimum stake age; (2) abandoning the use of coin age in the\nmining formula; (3) causing the stake modifier parameter to change over time\nfor each stake; and (4) utilizing a client that punishes nodes that attempt to\nmine on multiple branches with duplicate stakes.\n This paper demonstrates how NeuCoin's proof-of-stake implementation addresses\nall commonly raised "nothing at stake" objections to generic proof-of-stake\nsystems. It also reviews many of the flaws of proof-of-work designs to\nhighlight the potential for an alternate cryptocurrency that solves these\nflaws.\n

Florian Tschorsch, Björn Scheuermann

Besides attracting a billion dollar economy, Bitcoin revolutionized the field of digital currencies and influenced many adjacent areas. This also induced significant scientific interest. In this survey, we unroll and structure the manyfold results and research directions. We start by introducing the Bitcoin protocol and its building blocks. From there we continue to explore the design space by discussing existing contributions and results. In the process, we deduce the fundamental structures and insights at the core of the Bitcoin protocol and its applications. As we show and discuss, many key ideas are likewise applicable in various other fields, so that their impact reaches far beyond Bitcoin itself.

Dominic Wörner, Thomas von Bomhard

Bitcoin is an emerging technology which allows two entities to exchange value overt the Internet without trust. Embracing that those entities could well be machines we present a system that allows a sensor to offer its measurement data directly to a world-wide data market. Based on the concept introduced in Noyen et al [1], we describe a prototypical implementation of the process of exchanging data for electronic cash between a sensor and a requester by leveraging the Bitcoin network and discuss its current limitations.

Israa Alqassem, Davor Svetinović

Bit coin is a new protocol with a potential to revolutionize financial system. Bit coin has a complex structure, where several interacting components build a peer-to-peer currency and a payment system without relying on any trusted third party. Bit coin is continually improved by an open source community, and various Bit coin libraries, APIs, and alternative implementations are being developed. Nevertheless, there is no up-to-date protocol specification or architecture description since the official whitepaper was published back in 2008. In this paper, we provide an up-to-date protocol specification and architectural analysis of the Bit coin system. We perform this analysis as the first step towards specification of the crypto currency reference architecture. The future reference architecture will serve as a starting architectural point for the development of new systems that leverage Bit coin protocol in different contexts and for various purposes. We also discuss whether the current architecture satisfies the system's primary purpose, i.e., Providing a pure decentralized version of the crypto currency.

J.S. Barkatullah, Timo Hanke, Ravi Iyengar, Ricky Lewelling · 5 authors

This article consists of a collection of slides from the author's conference presentation on the special features, system design and architectures, processing capabilities, and targeted markets for CoinTerra's Goldstrike, a first generation crypto-currency processor for Bitcoin mining machines.

Saramago, Rodrigo Q., Meling, Hein, Jehl, Leander N.

A certification system is responsible for issuing digital credentials, which attest claims about a subject, e.g., an academic diploma. Such credentials are valuable for individuals and society, and widespread adoption requires a trusted certification system. Trust can be gained by being transparent when issuing and verifying digital credentials. However, there is a fundamental tradeoff between privacy and transparency. For instance, admitting a student to an academic program must preserve the student’s privacy, i.e., the student’s grades must not be revealed to unauthorized parties. At the same time, other applicants may demand transparency to ensure fairness in the admission process. Thus, building a certification system with the right balance between privacy and transparency is challenging. This paper proposes a novel design for a certification system that provides sufficient transparency and preserves privacy through selective disclosure of claims such that authorized parties can verify them. Moreover, unauthorized parties can also verify the correctness of the certification process without compromising privacy. We achieve this using an incremental Merkle tree of cryptographic commitments to users' credentials. The commitments are added to the tree based on verifying zero-knowledge issuance proofs. Users store credentials off-chain and can prove the ownership and authenticity of credentials without revealing their commitments. Further, our approach enables users to prove statements about the credential’s claims in zero-knowledge. Our design offers a cost-efficient solution, reducing the amount of linkable on-chain data by up to 79% per credential compared to prior work, while maintaining transparency.

Nicolas T. Courtois

In this paper we revisit some major orthodoxies which lie at the heart of the bitcoin crypto currency and its numerous clones. In particular we look at The Longest Chain Rule, the monetary supply policies and the exact mechanisms which implement them. We claim that these built-in properties are not as brilliant as they are sometimes claimed. A closer examination reveals that they are closer to being... engineering mistakes which other crypto currencies have copied rather blindly. More precisely we show that the capacity of current crypto currencies to resist double spending attacks is poor and most current crypto currencies are highly vulnerable. Satoshi did not implement a timestamp for bitcoin transactions and the bitcoin software does not attempt to monitor double spending events. As a result major attacks involving hundreds of millions of dollars can occur and would not even be recorded. Hundreds of millions have been invested to pay for ASIC hashing infrastructure yet insufficient attention was paid to network neutrality and to insure that the protection layer it promises is effective and cannot be abused. In this paper we develop a theory of Programmed Self-Destruction of crypto currencies. We observe that most crypto currencies have mandated abrupt and sudden transitions. These affect their hash rate and therefore their protection against double spending attacks which we do not limit the to the notion of 51% attacks which is highly misleading. In addition we show that smaller bitcoin competitors are substantially more vulnerable. In addition to small hash rate, many bitcoin competitors mandate incredibly important adjustments in miner reward. We exhibit examples of 'alt-coins' which validate our theory and for which the process of programmed decline and rapid self-destruction has clearly already started.

Andrew Miller, Ari Juels, Elaine Shi, Bryan Parno · 5 authors

Bit coin is widely regarded as the first broadly successful e-cash system. An oft-cited concern, though, is that mining Bit coins wastes computational resources. Indeed, Bit coin's underlying mining mechanism, which we call a scratch-off puzzle (SOP), involves continuously attempting to solve computational puzzles that have no intrinsic utility. We propose a modification to Bit coin that repurposes its mining resources to achieve a more broadly useful goal: distributed storage of archival data. We call our new scheme Perm coin. Unlike Bit coin and its proposed alternatives, Perm coin requires clients to invest not just computational resources, but also storage. Our scheme involves an alternative scratch-off puzzle for Bit coin based on Proofs-of-Retrievability (PORs). Successfully minting money with this SOP requires local, random access to a copy of a file. Given the competition among mining clients in Bit coin, this modified SOP gives rise to highly decentralized file storage, thus reducing the overall waste of Bit coin. Using a model of rational economic agents we show that our modified SOP preserves the essential properties of the original Bit coin puzzle. We also provide parameterizations and calculations based on realistic hardware constraints to demonstrate the practicality of Perm coin as a whole.

Harald Gjermundrød, Ioanna Dionysiou

No abstract is available for this record.

Michael Taylor

Recently, the Bitcoin cryptocurrency has been an international sensation. This paper tells the story of Bitcoin hard-ware: how a group of early-adopters self-organized and financed the creation of an entire new industry, leading to the development of machines, including ASICs, that had orders of magnitude better performance than what Dell, Intel, NVidia, AMD or Xilinx could provide. We examine this story for clues as to how we can foster greater innovation in the semiconductor industry and enable this phenomenon to occur more broadly for more application areas, spawning a new age of hardware innovation tailored to emerging application domains-an Age of Bespoke Silicon.

Flavio Junqueira, I. W. Kelly, Benjamin Reed

Practical systems must often guarantee that changes to the system state are durable. Examples of such systems are databases, file systems, and messaging middleware with guaranteed delivery. One common way of implementing durability while keeping performance high is to use a log to persist updates to the system state. Such systems use the log to reconstruct the system state in the event of a crash. When implementing such a log, if the log is only stored locally, the system state is permanently lost when the server writing the log experiences a permanent hardware failure. BookKeeper is a system that exposes a log abstraction for building high performance, highly available distributed systems. BookKeeper transparently implements replication for high availability and striping for high performance. A Book- Keeper deployment comprises storage servers called bookies, which are designed to serve a large number of concurrent ledgers. BookKeeper is currently an open-source project and is in production use at Yahoo!

Mark S. Miller, Tom Van Cutsem, Bill Tulloh

Contracts enable mutually suspicious parties to cooperate safely through the exchange of rights. Smart contracts are programs whose behavior enforces the terms of the contract. This paper shows how such contracts can be specified elegantly and executed safely, given an appropriate distributed, secure, persistent, and ubiquitous computational fabric. JavaScript provides the ubiquity but must be significantly extended to deal with the other aspects. The first part of this paper is a progress report on our efforts to turn JavaScript into this fabric. To demonstrate the suitability of this design, we describe an escrow exchange contract implemented in 42 lines of JavaScript code.

Wojciech Nowakowski

No abstract is available for this record.

Simon Barber, Xavier Boyen, Elaine Shi, Ersin Uzun

Abstract. Bitcoin is a distributed digital currency which has attracted a substan-tial number of users. We perform an in-depth investigation to understand what made Bitcoin so successful, while decades of research on cryptographic e-cash has not lead to a large-scale deployment. We ask also how Bitcoin could become a good candidate for a long-lived stable currency. In doing so, we identify several issues and attacks of Bitcoin, and propose suitable techniques to address them. 1