Blockchain Papers

Adegboyega Ojo, Samuel Adebayo

No abstract is available for this record.

Ben Fisch, Rafael Pass, Abhi Shelat

Mining for Bitcoins is a high-risk high-reward activity. Miners, seeking to reduce their variance and earn steadier rewards, collaborate in pooling strategies where they jointly mine for Bitcoins. Whenever some pool participant is successful, the earned rewards are appropriately split among all pool participants. Currently a dozen of different pooling strategies (i.e., methods for distributing the rewards) are in use for Bitcoin mining. We here propose a formal model of utility and social welfare for Bitcoin mining (and analogous mining systems) based on the theory of discounted expected utility, and next study pooling strategies that maximize the social welfare of miners. Our main result shows that one of the pooling strategies actually employed in practice--the so-called geometric pay pool--achieves the optimal steady-state utility for miners when its parameters are set appropriately. Our results apply not only to Bitcoin mining pools, but any other form of pooled mining or crowdsourcing computations where the participants engage in repeated random trials towards a common goal, and where "partial" solutions can be efficiently verified.

Carla Reyes

No abstract is available for this record.

Vadim Lyubashevsky, Gregor Seiler

No abstract is available for this record.

Mary E. Hicks

Between 1500 and 1840, ships under Portuguese colors embarked more than 5 million enslaved men, women and children from the coasts of Africa. Despite its position as the preeminent slave trading empire in the Atlantic World, no studies have systematically traced the evolution in maritime investment practices in Portugal and its American colonies which propelled this massive forced transportation of captive Africans. Beginning with Portuguese merchants’ earliest forays into Atlantic trade, on the West African island of Cabo Verde in the fifteenth century, maritime cargoes were collectively owned through the distribution of small shares. Drawing on medieval Mediterranean precedents, these collective, legally constructed partnerships opened early transoceanic trading opportunities to a diverse group of traders, colonists, and mariners, creating a decentralized mercantile trade which diffused profits throughout slave trading communities. Slaving merchants in Salvador da Bahia adopted this collectivist model of investment by the early eighteenth century, converting commercial disadvantages into a prosperous and durable trade which wove together the economic interests of a heterogeneous cross-section of Salvador’s inhabitants—including merchants, their families and slaves, and mariners—within the business of slaving. This article traces the persistence of this financial strategy, and argues that it enabled the longevity of the transatlantic slave trade in Salvador.

Rajesh Kumar

No abstract is available for this record.

Peter Mell, John Kelsey, James M. Shook

Most modern electronic devices can produce a random number. However, it is difficult to see how a group of mutually distrusting entities can have confidence in any such hardware-produced stream of random numbers, since the producer could control the output to their gain. In this work, we use public and immutable cryptocurrency smart contracts, along with a set of potentially malicious randomness providers, to produce a trustworthy stream of timestamped public random numbers. Our contract eliminates the ability of a producer to predict or control the generated random numbers, including the stored history of random numbers. We consider and mitigate the threat of collusion between the randomness providers and miners in a second, more complex contract.

Lin Chen, Lei Xu, Nolan Shah, Zhimin Gao · 6 authors

No abstract is available for this record.

Iddo Bentov, Yan Ji, Fan Zhang, Yunqi Li · 8 authors

No abstract is available for this record.

Iddo Bentov, Pavel Hubáček, Tal Moran, Asaf Nadler

We propose Meshcash, a protocol for implementing a permissionless ledger (blockchain) via proofs of work, suitable for use as the underlying consensus mechanism of a cryptocurrency. Unlike most existing proof-of-work based consensus protocols, Meshcash does not rely on leader-election (e.g., the single miner who managed to extend the longest chain). Rather, we use ideas from traditional (permissioned) Byzantine agreement protocols in a novel way to guarantee convergence to a consensus from any starting state. Our construction combines a local “hare” protocol that guarantees fast consensus on recent blocks (but doesn’t, by itself, imply irreversibility) with a global “tortoise” protocol that guarantees irreversibility. Our global protocol also allows the ledger to “self-heal” from arbitrary violations of the security assumptions, reconverging to consensus after the assumptions hold again.

Leonid Reyzin, Dmitry Meshkov, Alexander Chepurnoy, Sasha Ivanov

No abstract is available for this record.

Marco Bianchetti, Camilla Ricci, Marco Scaringi

The growth of peer-to-peer exchanges and the blockchain technology has led to a proliferation of cryptocurrencies and to a massive increase in the number of investors who actually negotiate digital money. Cryptocurrencies trade at prices mainly driven by investor sentiment, becoming a potential source of financial bubbles and instabilities. In this work, we apply quantitative models to the study of Bitcoin and Ether, two of the most famous cryptocurrencies. Our bubble detection methodology combines the Log Periodic Power Law (LPPL) model, originally created by Johansen, Ledoit and Sornette (JLS), and the statistical model developed by Phillips, Shi, and Yu (PSY). In particular, we employ three different versions of JLS model, i.e. Ordinary Least Square (OLS), Generalised Least Squares (GLS) and Maximum Likelihood Estimation (MLE), and two PSY statistical tests (BSADF and BSADF*). We find that, during the sample period 1st December 2016 - 16th January 2018, Bitcoin shows typical hallmarks of a bubble phase in mid December 2017 and in the first half of January 2018, anticipating the large crashes observed thereafter. Also the Ether price dynamics reveals bubble evidence in mid June 2017, anticipating the crash observed on 12th June, and a weaker signal around 12th January 2018, anticipating the crash observed in the same days. This paper confirms the high risk of speculative bubbles associated with cryptocurrencies, related to investor exuberance pumping market prices far away from their fundamental values, thus creating critical situations subject to possible crashes. Our methodology is general and can be applied to virtually any financial time series, and may support investing and risk management strategies.

Nancy Nakamoto

No abstract is available for this record.

Jonathan Chiu, Thorsten V. Koeppl, Chiu, Jonathan, Koeppl, Thorsten

How well can a cryptocurrency serve as a means of payment? We study the optimal design of cryptocurrencies and assess quantitatively how well such currencies can support bilateral trade. The challenge for cryptocurrencies is to overcome double-spending by relying on competition to update the blockchain (costly mining) and by delaying settlement. We estimate that the current Bitcoin scheme generates a large welfare loss of 1.4% of consumption. This welfare loss can be lowered substantially to 0.08% by adopting an optimal design that reduces mining and relies exclusively on money growth rather than transaction fees to finance mining rewards. We also point out that cryptocurrencies can potentially challenge retail payment systems provided scaling limitations can be addressed.

Dietmar Peetz, Gregory Mall

No abstract is available for this record.

Siamak Solat, Maria Potop-Butucaru

No abstract is available for this record.

Emmanuelle Anceaume, Romaric Ludinard, Maria Potop-Butucaru, Frédéric Tronel

No abstract is available for this record.

Louise Axon, Michael Goldsmith

Conventional public-key infrastructure (PKI) designs using certificate authorities and web-of-trust are not optimal and have security flaws. The properties afforded by the Bitcoin blockchain are a natural solution to some of the problems with PKI - in particular, certificate transparency and elimination of single points-offailure. Proposed blockchain-based PKI designs are built as public ledgers linking identity with public key, providing no privacy. We consider cases requiring privacy-aware PKIs, which do not link identity with public key. We show that blockchain technology can be used to construct a privacy-aware PKI while eliminating some of the problems of conventional PKI, and present PB-PKI, a privacy-aware blockchain-based PKI.

Svein Ølnes, Arild Jansen

No abstract is available for this record.

L Er-Rajy, El Kiram My A, El Ghazouani M, Omar Achbarou

Bitcoin has experienced rapid growth in the transactions number and in their value since its appearance in 2008. Its success is mainly due to the innovative use of a peer-to-peer network to implement all aspects of the currency life cycle, from creation to transfer between users. Bitcoin offers cash transactions that are almost instant and non-refundable, while allowing truly global transactions processed at the same speed as local ones. It offers a public transactions history, which allows untrusted audibility, and introduces many new and innovative use cases such as smart property, micropayments, contracts and escrow transactions for disputes mediation. However, the same features that make Bitcoin attractive to its end users are also its main limitations. Its decentralized nature limits the number of transactions and the speed at which transactions can be carried out and confirmed. The problem with slow confirmations is combined with the semantics of the confirmations which are not definitive, requiring several confirmations and further delaying the transaction acceptance. In this paper, we described the operating principles of peer-to-peer cryptographic currencies and especially security of bitcoin system. Moreover, For Bitcoin enhancements and additional mitigations we provide ideas for node auditing users in the network in aim to keep clients from the trusted transaction branch database generated by the attackers.

Erwin Filtz, Axel Polleres, Roman Karl, Bernhard Haslhofer

No abstract is available for this record.

Haoyan Wu

Affordable and reliable supply chain visibility is becoming increasingly important as the complexity of the network underlying supply chains is becoming orders of magnitudes higher compared to a decade ago. Moreover, this increase in complexity is starting to reflect on the cost of goods and their availability to the consumers. Optimizing the physical distribution phase in supply chain by providing increased visibility to trading partners can directly reduce product cost. Current supply chain information systems often lack the ability to cost-effectively relay ground truth information in near real time to all stakeholders and most importantly to the supplier and the customer during the transport of the shipment. This thesis presents a solution that addresses this gap through a distributed architecture. The solution enables small, medium and large businesses to interact in a dynamic and shipment-centric manner through a private blockchain sub-ledger that digitizes the transfer of custody for each shipment. Information in this private ledger is augmented by a public event ledger that reflects the movement of the shipment in real time. Third party monitors are engaged in the validation of the geolocation of the shipments by posting their physical proximity in the form of events to the public ledger.

Jennifer Hongbo Jiang

Thesis: S.M. in Management of Technology, Massachusetts Institute of Technology, Sloan School of Management, 2017.

Aissam Outchakoucht, Hamza Es-Samaali, Jean Philippe

The Internet of Things (IoT) is now destroying the barriers between the real and digital worlds. However, one of the huge problems that can slow down the development of this global wave, or even stop it, concerns security and privacy requirements. The criticality of these latter comes especially from the fact that the smart objects may contain very intimate information or even may be responsible for protecting people’s lives. In this paper, the focus is on access control in the IoT context by proposing a dynamic and fully distributed security policy. Our proposal will be based, on one hand, on the concept of the blockchain to ensure the distributed aspect strongly recommended in the IoT; and on the other hand on machine learning algorithms, particularly on reinforcement learning category, in order to provide a dynamic, optimized and self-adjusted security policy.