Blockchain Papers

Xin Li, Chong Wang, Qi Wang

No abstract is available for this record.

Jens Groth, Markulf Kohlweiss

Abstract. We construct a 3-move public coin special honest verifier zero-knowledge proof, a so-called Sigma-protocol, for a list of commitments having at least one commit-ment that opens to 0. It is not required for the prover to know openings of the other commitments. The proof system is efficient, in particular in terms of communication requiring only the transmission of a logarithmic number of commitments. We use our proof system to instantiate both ring signatures and zerocoin, a novel mech-anism for bitcoin privacy. We use our Sigma-protocol as a (linkable) ad-hoc group identi-fication scheme where the users have public keys that are commitments and demonstrate knowledge of an opening for one of the commitments to unlinkably identify themselves (once) as belonging to the group. Applying the Fiat-Shamir transform on the group identification scheme gives rise to ring signatures, applying it to the linkable group iden-tification scheme gives rise to zerocoin. Our ring signatures are very small compared to other ring signature schemes and we only assume the users ’ secret keys to be the discrete logarithms of single group elements so the setup is quite realistic. Similarly, compared with the original zerocoin protocol we rely on a weak cryptographic assumption and do not require a trusted setup. A third application of our Sigma protocol is an efficient proof of membership of a secret committed value u belonging to a public list L = {λ1,..., λN}.

Joseph Chen-Yu Wang

This working paper presents a simple model for the macroeconomic behavior of bitcoin based on the economic equation of exchange. According to this model, the value of bitcoin is determined largely by the willingness of bitcoin holders to save bitcoin and not by its transactional use. This model therefore predicts that increased use of bitcoin will not cause its value to rise, but that the value of bitcoin in terms of fiat currency will be almost solely determined by the willingness of bitcoin holders to pull bitcoin out of circulation. This model suggests that bitcoin will not fall victim to a liquidity trap as suggested by some economists.

Franziska Boehm, Paulina Jo Pesch

No abstract is available for this record.

Garrick Hileman

No abstract is available for this record.

Eli Ben‐Sasson, Alessandro Chiesa, Christina Garman, Matthew Green · 7 authors

Bitcoin is the rst digital currency to see widespread adoption. Although payments are conducted between pseudonyms, Bitcoin cannot oer strong privacy guarantees: payment transactions are recorded in a public decentralized ledger, from which much information can be deduced. Zerocoin (Miers et al., IEEE S&P 2013) tackles some of these privacy issues by unlinking transactions from the payment’s origin. Yet it still reveals payment destinations and amounts, and is limited in functionality. In this paper, we construct a full-edged ledger-based digital currency with strong privacy guarantees. Our results leverage recent advances in zero-knowledge Succinct Non-interactive ARguments of Knowledge (zk-SNARKs). We formulate and construct decentralized anonymous payment schemes (DAP schemes). A DAP scheme lets users pay each other directly and privately: the corresponding transaction hides the payment’s origin, destination, and amount. We provide formal denitions and proofs of the construction’s security. We then build Zerocash, a practical instantiation of our DAP scheme construction. In Zerocash, transactions are less than 1 kB and take under 6 ms to verify | orders of magnitude more ecient than the less-anonymous Zerocoin and competitive with plain Bitcoin.

Akash Malhotra, Mayank Maloo

No abstract is available for this record.

George M. Giaglis, Kalliopi N. Kypriotaki

No abstract is available for this record.

Samuel Ranellucci, Alain Tapp, Rasmus Winther Zakarias

Abstract. Even though Zero-knowledge has existed for more than 30 years, few generic constructions for Zero-knowledge exist. In this paper we present a new kind of commitment scheme on which we build a novel and efficient Zero-knowledge protocol for circuit satisfiability. 1

Dongdai Lin, Yu-Juan Quan, Jian Weng, Jun Yan

Watrous (STOC 2006) proved that plugging classical bit commitment scheme that is secure against quantum attack into the GMW-type construction of zero-knowledge gives a classical zero-knowledge proof that is secure against quantum attack. In this paper, we showed that plugging quantum bit commitment scheme (allowing quantum computation and communication) into the GMW-type construction also gives a quantum zero-knowledge proof, as one expects. However, since the binding condition of quantum bit commitment scheme is inherently different from its classical counterpart, compared with Watrous ’ security proof, here we encounter new difficulty in soundness analysis. To overcome the difficulty, we take a geometric approach, managing to reduce quantum soundness analysis to classical soundness analysis. We also propose a formalization of non-interactive quantum bit commitment scheme, which may come in handy in other places. Moreover, inspired by our formalization, we generalize Naor’s construction of bit commitment scheme to the quantum setting, achieving non-interactive commit stage. We hope quantum bit commitment scheme can find more applications in quantum cryptog-raphy. 1

Eli Ben‐Sasson, Alessandro Chiesa, Eran Tromer, Madars Virza

No abstract is available for this record.

Salvador Lucas, José Meseguer

No abstract is available for this record.

Clément Méda Ziemlé, Chung‐Chien Huang, Issiaka Sombié, Lassina Konaté · 7 authors

INTRODUCTION: This article reports the results and the lessons learned from implementing the decentralized approach to tuberculosis (TB) detection and treatment, embedded with Human Immunodeficiency Virus (HIV) co-infection in health district. The objective was to increase the TB screening indicators in the district using the common ways for offering care to patients in health district. METHODS: Conducted from August 2006 to July 2007, this large-scale intervention using Non-experimental study Designs has implemented a decentralized approach for fighting against TB in Orodara Health District (OHD), Burkina Faso. Pretest-posttest design has been used for quantitative part using indicators in one hand, and postests-only design for the qualitative part in other hand. In the pretest-posttest design, the TB indicators from years before 2006 (from 2002 to 2005) were used as earlier measurement observations allowing examining changes over time. The decentralized approach was incorporated into the annual planning of the OHD. For the quantitative study design, indicators used were those from National TB Program in Burkina Faso: TB detection rate, incidence density of TB per 100,000 inhabitants per year, and HIV prevalence in incident TB cases with positive smears. Data entry and analysis employed Microsoft Access and Excel software. For the qualitative, in-depth interview was used in which a total of 16 persons have been interviewed. Discussions were tape-recorded and transcribed verbatim for analysis using the computer-based qualitative software program named QSR NVIVO. RESULTS: There were a total of 99,259 outpatient visits during the study period: the7,345 patients (7.43%) presented with cough. Of the 7,345 patient having cough, 503 cases (6.8%) were declared chronic coughing. These 503 patients were screened for TB, including 35.59% whose coughing had lasted 10 to 15 days. We observed an increase in a measured variable was observed. The TB detection rate and incidence-density rate based on positive smears were 16.11% (11.00% in 2005) and 10.42 per 100,000 inhabitants per year (6.88 per 100,000 inhabitants in 2005), respectively. There were 29 patients positive for TB: 41.37% of these had cough lasting 10 to 15 days, 10.34% were also positive for HIV, and 68.97% were from rural areas. Health workers and patients reported satisfaction with the intervention. It was found that implementing a decentralized approach to TB prevention in rural areas is plausible and effective under some conditions: considering that health district system is functional; carefully designing the intervention for TB case management; setting up and implementing of decentralized approach including strong monitoring; and taking into account the all financing, community and volunteer involvement, evaluation of the cost savings from integrating specific donor funding, and being supported by regional and central levels including National TB program. CONCLUSION: The study has shown that TB detection rate can be increased by implementing a decentralized approach to primary care. When carefully implemented, a decentralized approach is a suitable approach to TB and HIV prevention in rural and inaccessible settings.

Nicolas Houy

When processing transactions in a block, a miner increases his reward but also decreases his probability to earn any reward because the time needed for his block to reach consensus depends on its size. We show that this leads to a game situation between miners. We analytically solve this game for two miners. Then, we show that miners do not play a Nash equilibrium in the current Bitcoin mining environment, instead, they should not process any transaction. Finally, we show that the situation where no transaction is ever processed would stop being a Nash equilibrium if the transaction fee was multiplied or, equivalently, the fixed reward divided by a factor of about 12.

Sergii Shcherbak

Published online: 28 July 2014

Loredana Maftei

The proliferation of technology emphasized new forms of payment. During the last years, current literature highlighted the role of virtual currency, the channels of payment through digital coins and the importance of assimilation of such platforms. Bitcoin or BTC is known as a digital coin, issued for the first time in 2009 and based on a peer to peer system. The difference from other forms of payment is that BTC is not controlled by any institution or central authority. BTC transactions have grown rapidly, ”asking" for regulation measures or legal approval of governments. Although BTC has become very popular, the market is poor and unfortunately of no confidence. There is a lack of regulation which can determine a number of risks associated with criminal financing activities. However, the legal status of Bitcoin is present in many European countries like Belgium, Bulgaria, Denmark, Finland, Germany, Lithuania, Norway, Poland, Slovenia, Switzerland or Turkey. Also, this type of currency has experienced a rapid evolution among coffee shops and restaurants.

Alexandre Mallard, Cécile Méadel, Francesca Musiani

International audience

Peter Šurda

No abstract is available for this record.

Sébastien Canard, David Pointcheval, Olivier Sanders

International audience

Yuval Ishai, Mor Weiss

A probabilistically Checkable Proof (PCP) allows a randomized verifier, with oracle access to a purported proof, to probabilistically verify an input statement of the form “x ∈ L” by querying only few bits of the proof. A PCP of proximity (PCPP) has the additional feature of allowing the verifier to query only few bits of the input x, where if the input is accepted then the verifier is guaranteed that (with high probability) the input is close to some x′ ∈ L.

Sarah Jane Hughes, Stephen T. Middlebrook

This article explores the state of virtual currencies and their regulation in and by the United States and the States. It offers thoughts on which models of regulation might suit virtual currencies best. It also surveys recent enforcement actions brought by the Departments of Treasury, Justice and Homeland Security against providers of virtual currencies or comparable electronic stored value. It concludes that issuers and users of virtual currencies are not being realistic if they think that the United States will not regulate virtual currencies for some purposes.

Marc Gronwald

No abstract is available for this record.

David Vandervort

No abstract is available for this record.

Robleh Ali, John Barrdear, Roger Clews, James Southgate

Modern electronic payment systems rely on trusted, central third parties to process payments securely. Recent developments have seen the creation of digital currencies like Bitcoin, which combine new currencies with decentralised payment systems. Although the monetary aspects of digital currencies have attracted considerable attention, the distributed ledger underlying their payment systems is a significant innovation. As with money held as bank deposits, most financial assets today exist as purely digital records. This opens up the possibility for distributed ledgers to transform the financial system more generally.