Blockchain Papers

Alex Kibet

No abstract is available for this record.

Şerif Dilek, Yunus Furuncu

Bitcoin, with its market value among cryptocurrenciesand being the biggest in terms of its processing volume, carries greatpotential in terms of low cost, speedy processing and low-level risk while alsobringing with it important global-level change and transformation. On the otherhand, the fact that cryptocurrencies and Bitcoin specifically are new, ofunclear legal status, and carry the risk of being involved in illegal activity,there is the potential for their use as an extremely volatile and speculativeinvestment tool and have environmental effects. This study examines Bitcoinmining and blockchain technology and investigates the high amounts of energyconsumed by Bitcoin and its environmental effects. It is argued that the energyconsumed as a result of increased Bitcoin mining will have environmental andsocial consequences, such as global warming and climate change.

Antônio Unias de Lucena, Marco Aurélio Amaral Henriques

Um computador quântico com alta capacidade de processamento quebrará as assinaturas digitais utilizadas nos principais blockchains. Este trabalho traz um estudo preliminar sobre a adoção de assinaturas baseadas em hash no blockchain do Bitcoin para torná-lo resistente ao computador quântico. O estudo mostra os pontos a serem modificados e seus impactos. O maior deles refere-se ao tamanho da assinatura digital, que influencia no tamanho de uma transação e diminui o número de transações por bloco. Soluções para este problema incluem o aumento do tamanho do bloco, a diminuição do tamanho das assinaturas baseadas em hash e/ou a adoção de algoritmos pós-quânticos que produzam assinaturas digitais menores.

Tom Billitteri

Bitcoin may not last, but blockchain could be the real dealEconomist Nouriel Roubini, aka Dr. Doom since he predicted the 2008 financial crisis, called it "the mother of all bubbles."The head of the Royal Bank of Scotland, Sir Howard Davies, invoked Dante's Inferno to warn investors off it.JPMorgan Chase CEO Jamie Dimon flat-out called

Letra, Ivo José Santos

No abstract is available for this record.

NAM, Yonghyeon

No abstract is available for this record.

Quentin Alamélou, Olivier Blazy, Stéphane Cauchie, Philippe Gaborit

No abstract is available for this record.

William J. Buchanan

Imagine being told that your wage was going to be cut in half. Well, that’s what’s soon going to happen to those who make money from Bitcoin mining, the process of earning the online currency Bitcoin.The current expected date for this change is 11 July 2016. Many see this as the day when Bitcoin prices will rocket and when Bitcoin owners could make a great deal of money. Others see it as the start of a Bitcoin crash. At present no one quite knows which way it will go.Bitcoin was created in 2009 by someone known as Satoshi Nakamoto, borrowing from a whole lot of research methods. It is a cryptocurrency, meaning it uses digital encryption techniques to create bitcoins and secure financial transactions. It doesn’t need a central government or organisation to regulate it, nor a broker to manage payments.Conventional currencies usually have a central bank that creates money and controls its supply. Bitcoin is instead created when individuals “mine” for it by using their computers to perform complex calculations through special software. The algorithm behind Bitcoin is designed to limit the number of bitcoins that can ever be created.All Bitcoin transactions are recorded on a public database known as a blockchain. Every time someone mines for Bitcoin, it is recorded with a new block that is transmitted to every Bitcoin app across the network, like a bank updating its online records.

Peter, Kimberley, Schaus, Michael

No abstract is available for this record.

Jason S. Seligman

No abstract is available for this record.

Jorge F. Chávez, Roberto F. Iunes, Hector Conroy, Johanna Ramos · 7 authors

This evaluation examines the IDB's Country Program with Colombia for the 2007-2011 period. The evaluation found social investment and decentralization as two areas in which the IDB maintained presence and relevance during this period. In social investment, the IDB was consolidated as a stable partner to Colombia in the creation and operation of a long-term social safety net. In regards to decentralization, cooperation was crosscutting, as the IDB worked with subnational institutions in diverse sectors, such as transportation, business development, housing, and modernization of the State. The IDB also continued its long-term work with Colombia to modernize and improve the efficiency of oversight agencies and the judicial branch, helping the country to obtain sizeable savings. To continue to improve the strategy with Colombia, OVE recommends that the IDB should: (i) increase its efforts to lower the transaction costs of IDB's cooperation with the country; (ii) improve the evaluability, monitoring and evaluation of the Country Strategy and the projects financed by the IDB; (iii) identify and strengthen the IDB's capacity in the areas and sectors in which the country will concentrate its demand for financial cooperation; and (iv) identify international development experiences that have been successful and present them to Colombia.

Albert Nowacki

According to a contemporary Pole, Ukraine is a country which, having broken out of the clutches of communism, makes its way towards Europe, the place it has always belonged to. The proof of that are the Ukrainians’ European aspirations—to become a member of the EU or NATO, as well as the events of the Orange Revolution, which proved that Ukrainians are mature enough to break free from Russia for the sake of democratization of the country, following the example of Western European countries. However, Ukrainians themselves are no longer so unanimous. A careful look at the country of our neighbours makes it evident that both in the sphere of politics as well as culture the Ukrainian nation is strongly divided. This was demonstrated by the Orange Revolution, which made the West realise that in Ukraine a fight is taking place, where the choice of an eastern or western variant is at stake. Ukrainians are also divided as far as their identity is concerned, both cultural and national, for whose roots they are still searching, both in Russia and Western Europe. We may say that as far as the matter of their place on earth is concerned, Ukrainians are almost in exactly the same place as they were eighty years ago.

Kaoru Kurosawa, Swee‐Huay Heng

Abstract. In undeniable signature schemes, zero-knowledgeness and non-transferability have been identified so far. In this paper, by separating these two notions, we show the first 3-move confirmation and disavowal protocols for Chaum’s undeniable signature scheme which is secure against active and concurrent attacks. Our main observation is that while the signer has one public key and one secret key, there exist two witnesses in the confirmation and disavowal proofs of Chaum’s scheme.

Craig Gentry, Dávid Molnár, Zulfikar Ramzan

Abstract. Most prior designated confirmer signature schemes either prove security in the random oracle model (ROM) or use general zeroknowledge proofs for NP statements (making them impractical). By slightly modifying the definition of designated confirmer signatures, Goldwasser and Waisbard presented an approach in which the Confirm and ConfirmedSign protocols could be implemented without appealing to general zero-knowledge proofs for NP statements (their Disavow protocol still requires them). The Goldwasser-Waisbard approach could be instantiated using Cramer-Shoup, GMR, or Gennaro-Halevi-Rabin signatures. In this paper, we provide an alternate generic transformation to convert any signature scheme into a designated confirmer signature scheme, without adding random oracles. Our key technique involves the use of a signature on a commitment and a separate encryption of the random string used for commitment. By adding this “layer of indirection, ” the underlying protocols in our schemes admit efficient instantiations (i.e., we can avoid appealing to general zero-knowledge proofs for NP statements) and furthermore the performance of these protocols is not tied to the choice of underlying signature scheme. We illustrate this using the Camenisch-Shoup variation on Paillier’s cryptosystem and Pedersen commitments. The confirm protocol in our resulting scheme requires 10 modular exponentiations (compared to 320 for Goldwasser-Waisbard) and our disavow protocol requires 41 modular exponentiations (compared to using a general zero-knowledge proof for Goldwasser-Waisbard). Previous schemes use the encryption of a signature paradigm, and thus run into problems when trying to implement the confirm and disavow protocols efficiently. 1

Olivier Saint‐Jean

The French health-care system is almost totally under the supervision of the government, which defines the general orientation of health policy. For example, a health-care policy for cancer treatment will be developed in France within the next 5 years. The government organizes the initial formation of all categories of health professionals and so controls the number of professionals in each category. In France, 4500 medical students graduate each year. Demographic problems at the present time are caused by the quota for all medical professions. The government also ensures that the number and location of hospitals are adequate for the needs of the French population. It supervises public hospitals and the management of private clinics, with the objective of providing a consistent standard of care in all health-care structures. The government also proposes the health budget for parliament's approval. In 1996, in line with the concept of decentralization, which means ‘to think globally but act locally’, regional agencies for hospital care were created in each administrative region. They are responsible for the strategic and economic supervision of hospitals, and for the organization of regional health care. However, they have no authority with regard to ambulatory care, thus creating a gap between hospital and ambulatory care in France, which represents a great obstacle to the coordination of care for disabled and elderly people. The French health-care system is a mixed system, being both etatic and liberal. There is a collective health insurance program in place based on incomes; the premium payments are automatically deducted from salaries. The rate is determined each year by the government for an equilibrated budget. Patients have completely free access to all medical care, including hospitals and choice of practitioners. They can have as many consultations and hospitalizations as they want. Furthermore, public and private health structures coexist. Sixty-five percent of hospitals are public and 35% are private. Ambulatory care structures are mainly private (95%). Therefore, although the French system is complex, comprising etatic and private organizations, it functions well. Furthermore, freedom and heterogeneity are probably the main guarantees of quality of health care in France, even if the cost is high and constantly increasing. In France, the number of available hospital beds for acute care (short-stay units), rehabilitation, long-term care and psychiatry is high (Table 1). The rates per 1000 people are the highest in Europe. However, the number of beds for disabled geriatric patients is low: 400 000 beds in retirement homes and 68 000 beds in long-term care units. There is a very long queue to get into such establishments. For psychiatric institutions, there are a total of 6430 beds. The number of health professionals is quite high (Table 2), but they are growing older and demographic problems will arise in the next 10 years. To finance the health-care system, including ambulatory and hospital care, a budget is approved by parliament annually. Ten percent of the gross domestic product (GDP) is devoted to the health-care system (130bn euros), including public hospitals, private hospitals, ambulatory care organizations and pharmacies (Table 3). The budget is being constantly increased. Patients can get a refund of the total cost of health care. For example, refunds for hospitalization costs are between 80% and 100%. For ambulatory care, refunds are between 70% and 100% and for drugs, between 35% and 100%. Health care is free for the homeless and poor people (100% refund). There is a list of 30 severe diseases, including Alzheimer's disease (AD), for which patients are entitled to a 100% refund. Last year, the treatment of AD was listed as a national priority and the government established a care program for the disease. Two main initiatives were proposed. The first one is diagnosis, particularly early diagnosis, as only half of the patients are diagnosed in France. In regard to this, the program proposed the development of memory clinics and regional expert centers. The second initiative is to provide better care for people with AD. This covers ethical issues, the possibility of family caregivers benefiting from some help, financial aid, and the creation of social day-care centers. Hospital care for people with AD is totally paid for by the social security system. Various options are available: short-stay units, rehabilitation units, and day hospitals (of which there are too few) for diagnosis and rehabilitation. Furthermore, people with AD are generally not very welcome in traditional short-stay and rehabilitation units, and it is very difficult to get them a place in such units. Memory clinics are being developed and regional expert centers will be created next year to assist in the early diagnosis of the disease. An expert center must meet specific defined criteria. It must have a multidisciplinary team (neurologists, geriatricians, psychiatrists, and neuropsychologists) and a day hospital for disease diagnosis (capable of handling at least 100 new patients a year). It must also be a source of expertise in research, possess postgraduate knowledge about dementia, and be the centre of a network including general practitioners, ambulatory neurologists and memory clinics of the first degree. Ambulatory care for people with AD is provided by neurologists and psychiatrists (both in insufficient numbers), and by general practitioners, who are not accurately trained for dementia care. Very few geriatricians are included in ambulatory care. Nurses, orthophonists, and physiotherapists are also involved, but again, they are insufficient in number. In other words, social day-care centers should be developed. Social support for patients is financed by a new prestation, the ‘APA’ (personalized prestation for the promotion of autonomy). This prestation was defined in 2002. The amount of the prestation is calculated according to the loss of autonomy. Patients are classified into six groups upon evaluation of their autonomy. It is possible for patients to buy the time of professional social workers and caregivers. The highest level of financial aid they can obtain is 1200 euros per month. Today, 50% of patients are being looked after only by family caregivers. Nursing homes are currently evolving in France. Retirement homes and long-term care units now belong to a single category. The total living expenses comprise three parts: food and housing costs are borne by the patients (through family or social aid); nursing costs are covered by the APA prestation and patients (or their families); and the total cost of medical care is covered by social security (100%). In conclusion, the French health-care system is quite unique since it involves both etatic and liberal organizations. It is an excellent system for patients because of low medical costs, but it requires a high cost of maintenance.

Masayuki Abe, Serge Fehr

Abstract. We propose the first distributed discrete-log key generation (DLKG) protocol from scratch which is adaptively-secure in the nonerasure model, and at the same time completely avoids the use of interactive zero-knowledge proofs. As a consequence, the protocol can be proven secure in a universally-composable (UC) like framework which prohibits rewinding. We prove the security in what we call the singleinconsistent-player UC model, which guarantees arbitrary composition as long as all protocols are executed by the same players. As an application, we propose a fully UC threshold Schnorr signature scheme. Our results are based on a new adaptively-secure Feldman VSS scheme. Although adaptive security was already addressed by Feldman in the original paper, the scheme requires secure communication, secure erasure, and either a linear number of rounds or digital signatures to resolve disputes. Our scheme overcomes all of these shortcomings, but on the other hand requires some restriction on the corruption behavior of the adversary, which however disappears in some applications including our new DLKG protocol. We also propose several new adaptively-secure protocols, which may find other applications, like a sender non-committing encryption scheme, a distributed trapdoor-key generation protocol for Pedersen’s commitment scheme, or distributed-verifier proofs for proving relations among commitments or even any NP relations in general. 1

Ivan Damgård, Serge Fehr, Louis Salvail

The concept of zero-knowledge (ZK) has become of fundamental importance in cryptography. However, in a setting where entities are modeled by quantum computers, classical arguments for proving ZK fail to hold since, in the quantum setting, the concept of rewinding is not generally applicable. Moreover, known classical techniques that avoid rewinding have various shortcomings in the quantum setting.<br /> <br />We propose new techniques for building <em>quantum</em> zero-knowledge (QZK) protocols, which remain secure even under (active) quantum attacks. We obtain computational QZK proofs and perfect QZK arguments for any NP language in the common reference string model. This is based on a general method converting an important class of classical honest-verifier ZK (HVZK) proofs into QZK proofs. This leads to quite practical protocols if the underlying HVZK proof is efficient. These are the first proof protocols enjoying these properties, in particular the first to achieve perfect QZK.<br /> <br />As part of our construction, we propose a general framework for building unconditionally hiding (trapdoor) string commitment schemes, secure against quantum attacks, as well as concrete instantiations based on specific (believed to be) hard problems. This is of independent interest, as these are the first unconditionally hiding string commitment schemes withstanding quantum attacks.<br /> <br />Finally, we give a partial answer to the question whether QZK is possible in the plain model. We propose a new notion of QZK, <em>non-oblivious verifier</em> QZK, which is strictly stronger than honest-verifier QZK but weaker than full QZK, and we show that this notion can be achieved by means of efficient (quantum) protocols.

Mario Di Raimondo, Rosario Gennaro

No abstract is available for this record.

Carlos Centeno, S. Hernansanz, Luis Alberto Flores, Álvaro Sanz Rubiales · 5 authors

Abstract This chapter offers an in-depth look at health politics and the tax-financed, universal health system in Spain. It traces the development of the Spanish healthcare system, focusing in particular on its double transition in the 1980s and 1990s from a centralized social insurance system, mostly funded through workers’ and employers’ contributions, to a decentralized universal model financed by general taxation. The new national health system aimed at covering all residents and transferred healthcare competences to the regions, i.e. the seventeen Autonomous Communities, a process completed in 2001. Key issues include rationalization, harmonization, and territorial equity-building of the decentralized healthcare system; efficiency improvement through the introduction of private management elements; and cost containment to bolster the system’s financial sustainability in the context of growing demand and scarce resources. As the chapter argues, these challenges along with the remarkable changes in the political party system have increased the political salience of healthcare in public debate in the 2010s, but the prospects for developing consensual healthcare policies have worsened, such that structural problems are likely to persist.

Masayuki Abe, Ronald Cramer, Serge Fehr

Abstract. A commitment multiplication proof, CMP for short, allows a player who is committed to secrets s, s ′ and s ′ ′ = s · s ′ , to prove, without revealing s, s ′ or s ′ ′ , that indeed s ′ ′ = ss ′. CMP is an important building block for secure general multi-party computation as well as threshold cryptography. In the standard cryptographic model, a CMP is typically done interactively using zero-knowledge protocols. In the random oracle model it can be done non-interactively by removing interaction using the Fiat-Shamir heuristic. An alternative non-interactive solution in the distributed setting, where at most a certain fraction of the verifiers are malicious, was presented in [1] for Pedersen’s discrete log based commitment scheme. This CMP essentially consists ofa few invocations ofPedersen’s verifiable secret sharing scheme (VSS) and is secure in the standard model. In the first part ofthis paper, we improve that CMP by arguing that a building block used in its construction in fact already constitutes a CMP. This not only leads to a simplified exposition, but also saves on the required number ofinvocations ofPedersen’s VSS. Next we show how to construct non-interactive proofs of partial knowledge [8] in this distributed setting. This allows for instance to prove non-interactively the knowledge of ℓ out of m given secrets, without revealing which ones. We also show how to construct efficient non-interactive zero-knowledge proofs for circuit satisfiability in the distributed setting. In the second part, we investigate generalizations to other homomorphic commitment schemes, and show that on the negative side, Pedersen’s VSS cannot be generalized to arbitrary (black-box) homomorphic commitment schemes, while on the positive side, commitment schemes based on q-one-way-group-homomorphism [7], which cover wide range ofcurrently used schemes, suffice. 1

Christian Cachin, Jan Camenisch

No abstract is available for this record.

Giovanni Di Crescenzo, Rafail Ostrovsky

No abstract is available for this record.

Ronald Cramer, Ivan Damgård

We present zero-knowledge proofs and arguments for arithmetic circuits over finite prime fields, namely given a circuit, show in zero-knowledge that inputs can be selected leading to a given output. For a field GF(q), where q is an n-bit prime, a<br />circuit of size O(n), and error probability 2^−n, our protocols require communication of O(n^2) bits. This is the same worst-cast complexity as the trivial (non zero-knowledge)<br />interactive proof where the prover just reveals the input values. If the circuit involves n multiplications, the best previously known methods would in general require communication<br />of Omega(n^3 log n) bits.<br />Variations of the technique behind these protocols lead to other interesting applications.<br />We first look at the Boolean Circuit Satisfiability problem and give zero-knowledge proofs and arguments for a circuit of size n and error probability 2^−n in which there is an interactive preprocessing phase requiring communication of O(n^2)<br />bits. In this phase, the statement to be proved later need not be known. Later the prover can non-interactively prove any circuit he wants, i.e. by sending only one message, of size O(n) bits.<br />As a second application, we show that Shamirs (Shens) interactive proof system for the (IP-complete) QBF problem can be transformed to a zero-knowledge proof<br />system with the same asymptotic communication complexity and number of rounds. The security of our protocols can be based on any one-way group homomorphism with a particular set of properties. We give examples of special assumptions sufficient for this, including: the RSA assumption, hardness of discrete log in a prime order group, and polynomial security of Die-Hellman encryption. We note that the constants involved in our asymptotic complexities are small enough for our protocols to be practical with realistic choices of parameters.