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

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.

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.