Reputation and Reward : Two Sides of the Same Bitcoin

In Mobile Crowd Sensing (MCS), the power of the crowd, jointly with the sensing capabilities of the smartphones they wear, provides a new paradigm for data sensing. Scenarios involving user behavior or those that rely on user mobility are examples where standard sensor networks may not be suitable, and MCS provides an interesting solution. However, including human participation in sensing tasks presents numerous and unique research challenges. In this paper, we analyze three of the most important: user participation, data sensing quality and user anonymity. We tackle the three as a whole, since all of them are strongly correlated. As a result, we present PaySense, a general framework that incentivizes user participation and provides a mechanism to validate the quality of collected data based on the users' reputation. All such features are performed in a privacy-preserving way by using the Bitcoin cryptocurrency. Rather than a theoretical one, our framework has been implemented, and it is ready to be deployed and complement any existint MCS system

An Empirical Analysis of Privacy in the Lightning Network

Payment channel networks, and the Lightning Network in particular, seem to offer a solution to the lack of scalability and privacy offered by Bitcoin and other blockchain-based cryptocurrencies. Previous research has focused on the scalability, availability, and crypto-economics of the Lightning Network, but relatively little attention has been paid to exploring the level of privacy it achieves in practice. This paper presents a thorough analysis of the privacy offered by the Lightning Network, by presenting several attacks that exploit publicly available information about the network in order to learn information that is designed to be kept secret, such as how many coins a node has available or who the sender and recipient are in a payment routed through the network.Comment: 26 pages, 5 figure

Analysis of the Bitcoin UTXO set

Bitcoin relies on the Unspent Transaction Outputs (UTXO) set to efficiently verify new generated transactions. Every unspent out- put, no matter its type, age, value or length is stored in every full node. In this paper we introduce a tool to study and analyze the UTXO set, along with a detailed description of the set format and functionality. Our analysis includes a general view of the set and quantifies the difference between the two existing formats up to the date. We also provide an ac- curate analysis of the volume of dust and unprofitable outputs included in the set, the distribution of the block height in which the outputs where included, and the use of non-standard outputs

Bitcoin Private Key Locked Transactions

Bitcoin smart contracts allow the development of new protocols on top of Bitcoin itself. This usually involves the definition of complex scripts, far beyond the requirement of a single signature. In this paper we introduce the concept of private key locked transactions, a novel type of transactions that allows the atomic verification of a given private key (belonging to an asymmetric key pair) during the script execution

Towards a better understanding of Bitcoin: from system analyses to new protocol designs

Bitcoin ha donat peu a un dels majors canvis de paradigma de l’últim segle respecte a com entenem i utilitzem els diners. El naixement de les criptomonedes ha obert la porta a un sistema econòmic distribuït on la necessitat de terceres parts de confiança, o d’entitats centrals, ha estat substituïda per la criptografia i el flux obert d’informació entre tots els actors del sistema, construint d’aquesta forma un registre de transaccions comú conegut com a blockchain. Aquest canvi de paradigma, però, comporta certes implicacions que, de no ser tractades adientment, poden comprometre la seguretat del sistema. En aquesta tesis ens hem centrat en analitzar dos dels grans components de Bitcoin: la seva xarxa P2P i el conjunt de monedes en circulació. Amb aquest anàlisis es pretén identificar els punts forts i les febleses de Bitcoin, amb l’objectiu de proposar solucions i/o millores per aquestes. Aquests anàlisis ens han permès, per una banda, caracteritzar les xarxes P2P de criptomonedes, i, per altra banda, identificar un dels actuals problemes d’escalabilitat de Bitcoin: les monedes no rentables. D’altra banda, i un cop assolit un coneixement suficient del sistema, la tesis s’ha centrat en el disseny de protocols per estendre la funcionalitat de Bitcoin en diferents escenaris de pagament. A més a més, s’ha proposat una solució per reduir la probabilitat de ser estafat a l’utilitzar transaccions sense confirmar. I finalment, s’ha dissenyat un protocol de compra-venta de dades utilitzant Bitcoin, eliminant la necessitat inherent de confiança per part del comprador.Bitcoin has kicked off one of the biggest paradigm shifts of the last century regarding how we understand and use money. The birth of criptocurrencies lays the foundations of a new financial system, where the need of trusted third parties, or central authorities, has been replaced by cryptography and an open flow of information between all the actors of the system. By sharing all the information regarding the operations of the system, all users can eventually agree in a distributed ledger, known as blockchain. Such a paradigm shift, however, poses some threads that, if not properly handled, may compromise the security of the system. In this thesis we have studied two of the core components of Bitcoin: its P2P network, and the set of unspent Bitcoins. Such analysis aimed to spot the strengths and weaknesses of the system in order to design solutions for them. The outcomes of our analyses have been, on the one side, characterizing the cryptocurrency P2P networks and, on the other side, spotting one of the current Bitcoin scalability problems: the unprofitable coins. Moreover, after analysing the system and obtaining a deep understanding of it, the thesis has focused on designing protocols to extend Bitcoin’s functionality in different payment scenarios. First, we have designed a solution to reduce the likelihood of a merchant of being deceived when accepting zero-confirmation transactions. Finally, we have designed a fair protocol for data trading using Bitcoin, where the exchange between data and coins is performed atomically

Reputation and Reward: Two Sides of the Same Bitcoin

In Mobile Crowd Sensing (MCS), the power of the crowd, jointly with the sensing capabilities of the smartphones they wear, provides a new paradigm for data sensing. Scenarios involving user behavior or those that rely on user mobility are examples where standard sensor networks may not be suitable, and MCS provides an interesting solution. However, including human participation in sensing tasks presents numerous and unique research challenges. In this paper, we analyze three of the most important: user participation, data sensing quality and user anonymity. We tackle the three as a whole, since all of them are strongly correlated. As a result, we present PaySense, a general framework that incentivizes user participation and provides a mechanism to validate the quality of collected data based on the users’ reputation. All such features are performed in a privacy-preserving way by using the Bitcoin cryptocurrency. Rather than a theoretical one, our framework has been implemented, and it is ready to be deployed and complement any existing MCS system

Towards a better understanding of Bitcoin: from system analyses to new protocol designs

Bitcoin ha donat peu a un dels majors canvis de paradigma de l’últim segle respecte a com entenem i utilitzem els diners. El naixement de les criptomonedes ha obert la porta a un sistema econòmic distribuït on la necessitat de terceres parts de confiança, o d’entitats centrals, ha estat substituïda per la criptografia i el flux obert d’informació entre tots els actors del sistema, construint d’aquesta forma un registre de transaccions comú conegut com a blockchain. Aquest canvi de paradigma, però, comporta certes implicacions que, de no ser tractades adientment, poden comprometre la seguretat del sistema. En aquesta tesis ens hem centrat en analitzar dos dels grans components de Bitcoin: la seva xarxa P2P i el conjunt de monedes en circulació. Amb aquest anàlisis es pretén identificar els punts forts i les febleses de Bitcoin, amb l’objectiu de proposar solucions i/o millores per aquestes. Aquests anàlisis ens han permès, per una banda, caracteritzar les xarxes P2P de criptomonedes, i, per altra banda, identificar un dels actuals problemes d’escalabilitat de Bitcoin: les monedes no rentables. D’altra banda, i un cop assolit un coneixement suficient del sistema, la tesis s’ha centrat en el disseny de protocols per estendre la funcionalitat de Bitcoin en diferents escenaris de pagament. A més a més, s’ha proposat una solució per reduir la probabilitat de ser estafat a l’utilitzar transaccions sense confirmar. I finalment, s’ha dissenyat un protocol de compra-venta de dades utilitzant Bitcoin, eliminant la necessitat inherent de confiança per part del comprador.Bitcoin has kicked off one of the biggest paradigm shifts of the last century regarding how we understand and use money. The birth of criptocurrencies lays the foundations of a new financial system, where the need of trusted third parties, or central authorities, has been replaced by cryptography and an open flow of information between all the actors of the system. By sharing all the information regarding the operations of the system, all users can eventually agree in a distributed ledger, known as blockchain. Such a paradigm shift, however, poses some threads that, if not properly handled, may compromise the security of the system. In this thesis we have studied two of the core components of Bitcoin: its P2P network, and the set of unspent Bitcoins. Such analysis aimed to spot the strengths and weaknesses of the system in order to design solutions for them. The outcomes of our analyses have been, on the one side, characterizing the cryptocurrency P2P networks and, on the other side, spotting one of the current Bitcoin scalability problems: the unprofitable coins. Moreover, after analysing the system and obtaining a deep understanding of it, the thesis has focused on designing protocols to extend Bitcoin’s functionality in different payment scenarios. First, we have designed a solution to reduce the likelihood of a merchant of being deceived when accepting zero-confirmation transactions. Finally, we have designed a fair protocol for data trading using Bitcoin, where the exchange between data and coins is performed atomically

Towards a better understanding of Bitcoin : from system analyses to new protocol designs

Bitcoin ha donat peu a un dels majors canvis de paradigma de l'últim segle respecte a com entenem i utilitzem els diners. El naixement de les criptomonedes ha obert la porta a un sistema econòmic distribuït on la necessitat de terceres parts de confiança, o d'entitats centrals, ha estat substituïda per la criptografia i el flux obert d'informació entre tots els actors del sistema, construint d'aquesta forma un registre de transaccions comú conegut com a blockchain. Aquest canvi de paradigma, però, comporta certes implicacions que, de no ser tractades adientment, poden comprometre la seguretat del sistema. En aquesta tesis ens hem centrat en analitzar dos dels grans components de Bitcoin: la seva xarxa P2P i el conjunt de monedes en circulació. Amb aquest anàlisis es pretén identificar els punts forts i les febleses de Bitcoin, amb l'objectiu de proposar solucions i/o millores per aquestes. Aquests anàlisis ens han permès, per una banda, caracteritzar les xarxes P2P de criptomonedes, i, per altra banda, identificar un dels actuals problemes d'escalabilitat de Bitcoin: les monedes no rentables. D'altra banda, i un cop assolit un coneixement suficient del sistema, la tesis s'ha centrat en el disseny de protocols per estendre la funcionalitat de Bitcoin en diferents escenaris de pagament. A més a més, s'ha proposat una solució per reduir la probabilitat de ser estafat a l'utilitzar transaccions sense confirmar. I finalment, s'ha dissenyat un protocol de compra-venta de dades utilitzant Bitcoin, eliminant la necessitat inherent de confiança per part del comprador.Bitcoin has kicked off one of the biggest paradigm shifts of the last century regarding how we understand and use money. The birth of criptocurrencies lays the foundations of a new financial system, where the need of trusted third parties, or central authorities, has been replaced by cryptography and an open flow of information between all the actors of the system. By sharing all the information regarding the operations of the system, all users can eventually agree in a distributed ledger, known as blockchain. Such a paradigm shift, however, poses some threads that, if not properly handled, may compromise the security of the system. In this thesis we have studied two of the core components of Bitcoin: its P2P network, and the set of unspent Bitcoins. Such analysis aimed to spot the strengths and weaknesses of the system in order to design solutions for them. The outcomes of our analyses have been, on the one side, characterizing the cryptocurrency P2P networks and, on the other side, spotting one of the current Bitcoin scalability problems: the unprofitable coins. Moreover, after analysing the system and obtaining a deep understanding of it, the thesis has focused on designing protocols to extend Bitcoin's functionality in different payment scenarios. First, we have designed a solution to reduce the likelihood of a merchant of being deceived when accepting zero-confirmation transactions. Finally, we have designed a fair protocol for data trading using Bitcoin, where the exchange between data and coins is performed atomically