Yu‐Jin Kwon, Do-Hyun Kim, Yunmok Son, Eugene Y. Vasserman · 5 authors
In the Bitcoin system, participants are rewarded for solving cryptographic puzzles. In order to receive more consistent rewards over time, some participants organize mining pools and split the rewards from the pool in proportion to each participant's contribution. However, several attacks threaten the ability to participate in pools. The block withholding (BWH) attack makes the pool reward system unfair by letting malicious participants receive unearned wages while only pretending to contribute work. When two pools launch BWH attacks against each other, they encounter the miner's dilemma: in a Nash equilibrium, the revenue of both pools is diminished. In another attack called selfish mining, an attacker can unfairly earn extra rewards by deliberately generating forks. In this paper, we propose a novel attack called a fork after withholding (FAW) attack. FAW is not just another attack. The reward for an FAW attacker is always equal to or greater than that for a BWH attacker, and it is usable up to four times more often per pool than in BWH attack. When considering multiple pools - the current state of the Bitcoin network - the extra reward for an FAW attack is about 56% more than that for a BWH attack. Furthermore, when two pools execute FAW attacks on each other, the miner's dilemma may not hold: under certain circumstances, the larger pool can consistently win. More importantly, an FAW attack, while using intentional forks, does not suffer from practicality issues, unlike selfish mining. We also discuss partial countermeasures against the FAW attack, but finding a cheap and efficient countermeasure remains an open problem. As a result, we expect to see FAW attacks among mining pools.
Steven Goldfeder, Harry Kalodner, Dillon Reisman, Arvind Narayanan
Abstract We show how third-party web trackers can deanonymize users of cryptocurrencies. We present two distinct but complementary attacks. On most shopping websites, third party trackers receive information about user purchases for purposes of advertising and analytics. We show that, if the user pays using a cryptocurrency, trackers typically possess enough information about the purchase to uniquely identify the transaction on the blockchain, link it to the user’s cookie, and further to the user’s real identity. Our second attack shows that if the tracker is able to link two purchases of the same user to the blockchain in this manner, it can identify the user’s cluster of addresses and transactions on the blockchain, even if the user employs blockchain anonymity techniques such as CoinJoin. The attacks are passive and hence can be retroactively applied to past purchases. We discuss several mitigations, but none are perfect.
Steven Goldfeder, Harry Kalodner, Dillon Reisman, Arvind Narayanan
We show how third-party web trackers can deanonymize users of\ncryptocurrencies. We present two distinct but complementary attacks. On most\nshopping websites, third party trackers receive information about user\npurchases for purposes of advertising and analytics. We show that, if the user\npays using a cryptocurrency, trackers typically possess enough information\nabout the purchase to uniquely identify the transaction on the blockchain, link\nit to the user's cookie, and further to the user's real identity. Our second\nattack shows that if the tracker is able to link two purchases of the same user\nto the blockchain in this manner, it can identify the user's entire cluster of\naddresses and transactions on the blockchain, even if the user employs\nblockchain anonymity techniques such as CoinJoin. The attacks are passive and\nhence can be retroactively applied to past purchases. We discuss several\nmitigations, but none are perfect.\n
Credible reputation lies at the core of users and devices communicating and transacting successfully. Identity fraud is becoming increasingly difficult to manage in the face of massive-scale database breaches. In critical infrastructure and public safety applications, as well as day-to-day personal and business transactions, it is imperative to have a significant degree of confidence in whom/what one communicates with - whether to know if the recipient can be entrusted with the sender's data, or if the sender's data is to be considered reliably sourced. Even where possible, lost reputation is substantially more cumbersome, timeconsuming and expensive to replace than are compromised, stolen or defective devices and their embedded cryptographic keys. This paper focuses on two methodologies that have considerable implications relative to addressing the reputation issue: (1) blockchain-enabled anomaly detection and assessment that involves dynamically asserted identity at the network edge effected through end-user targeted release of trusted behavioral data; (2) IoT and human interaction that is securely facilitated through use of an "Inviter-Invitee" protocol to set up dedicated maintainable "communication lines." The judiciously applied combination of the cryptographic protocol suites that enable the two methodologies results in a practicably implementable system for smart city use cases.
Felix Konstantin Maurer, Till Neudecker, Martin Florian
Bitcoin, the arguably most popular cryptocurrency to date, allows users to perform transactions using freely chosen pseudonymous addresses. Previous research, however, suggests that these pseudonyms can easily be linked, implying a lower level of privacy than originally expected. To obfuscate the links between pseudonyms, different mixing methods have been proposed. One of the first approaches is the CoinJoin concept, where multiple users merge their transactions into one larger transaction. In theory, CoinJoin can be used to mix and transact bitcoins simultaneously, in one step. Yet, it is expected that differing bitcoin amounts would allow an attacker to derive the original single transactions. Solutions based on CoinJoin therefore prescribe the use of fixed bitcoin amounts and cannot be used to perform arbitrary transactions.In this paper, we define a model for CoinJoin transactions and metrics that allow conclusions about the provided anonymity. We generate and analyze CoinJoin transactions and show that with differing, representative amounts they generally do not provide any significant anonymity gains. As a solution to this problem, we present an output splitting approach that introduces sufficient ambiguity to effectively prevent linking in CoinJoin transactions. Furthermore, we discuss how this approach could be used in Bitcoin today.
Blockchain Technology Applications and Security
Internet Traffic Analysis and Secure E-voting
Advanced Steganography and Watermarking Techniques
Riham AlTawy, Muhammad ElSheikh, Amr Youssef, Guang Gong
Real world physical shopping offers customers the privilege of maintaining their privacy by giving them the option of using cash, and thus providing no personal information such as their names and home addresses. On the contrary, electronic shopping mandates the use of all sorts of personally identifiable information for both billing and shipping purposes. Cryptocurrencies such as Bitcoin have created a stimulated growth in private billing by enabling pseudonymous payments. However, the anonymous delivery of the purchased physical goods is still an open research problem. In this work, we present a blockchain-based physical delivery system called Lelantos1 that within a realistic threat model, offers customer anonymity, fair exchange and merchant-customer unlinkability. Our system is inspired by the onion routing techniques which are used to achieve anonymous message delivery. Additionally, Lelantos relies on the decentralization and pseudonymity of the blockchain to enable pseudonymity that is hard to compromise, and the distributed consensus mechanisms provided by smart contracts to enforce fair irrefutable transactions between distrustful contractual parties.
In this paper, we propose a decentralized identity management system based on Blockchain. The function of the system mainly includes identity authentication and reputation management. The technical advantages of the Blockchain makes the data in the system safe and credible. In addition, we use smart contracts to write system rules to ensure the reliability of user information. We bind the user's entity information with the public key address and determine the true identity of a virtual user on the Blockchain. We use the token to represent the reputation which is shown to be an effective reputation model, making the participants in the system prefer to maintain and manage their personal reputation. Our system makes it possible for users to securely manage their identity and reputation on the Internet.
Electronic voting presents many challenges due to its multiple security requirements. Some of the challenges are related to guaranteeing voters' privacy and system's transparency, which are hard to satisfy simultaneously. Electronic voting also presents other challenges such as usability, particularly from the voter's side. We study two particular problems of electronic voting. Cast-as-intended verifiability comprises those mechanisms which assure the voter that her cast ballot corresponds to her chosen voting options. Current proposals put the verification burden on the voter, something which is undesirable in real-world elections, where both technically skilled and non-skilled voters participate. In this thesis, we introduce the concept of universal cast-as-intended verifiability, which provides mechanisms which allow any entity to check that any ballot corresponds to the voter's selections - without revealing them. We formally define what universal cast-as-intended verifiability is and we give an electronic voting protocol satisfying this property. The other problem we have studied is the problem of invalid votes in electronic elections. Since a common selling point of electronic voting is that it avoids voters inadvertently spoiling their votes, deliberately spoiled ballots appearing in the tallying phase of an electronic election can cause mistrust on the system. Indeed, election stakeholders might think that the system is flawed or that it was exploited somehow. To avoid this situation, we define the concept of vote validatability, which states the electronic voting system should be able to detect spoiled ballots before they are successfully cast. In addition to formally defining this notion, we design an electronic voting protocol satisfying this property. All these security requirements of electronic voting systems are implemented with cryptographic tools. In addition to encryption and signature schemes, another essential primitive for building electronic voting protocols is zero-knowledge proofs. Zero-knowledge proofs allow a prover to convince a verifier that a statement is true without leaking any other information. These zero-knowledge proofs can be used to, for example, prove that the tally of the election was done properly. Recently, Groth and Sahai constructed efficient non-interactive zero-knowledge proofs for a wide range of statements including, among others, statements appearing in electronic voting. In this thesis we give two contributions on Groth-Sahai proofs. On the one hand, we give a framework for deriving cryptographic assumptions from which to build secure cryptographic protocols. In particular, we build new Groth-Sahai proofs improving the efficiency of currently known constructions. Independently, we show how the original Groth-Sahai proofs can be extended to be compatible with even more statements, how to improve their out-of-the-box efficiency for many of these statements and how to improve their re-usability efficiency among multiple statements. Els sistemes de vot electrònic presenten molts reptes a causa dels seus múltiples requeriments. Alguns d'aquests reptes estan relacionats amb garantir la privacitat del votant i la transparència del sistema, requisits que són difícils de satisfer al mateix temps. D'altra banda, els sistemes de vot electrònic presenten altres reptes com la usabilitat, sobretot de cara als votants. En aquesta tesi estudiem dos problemes del vot electrònic. La verificabilitat "cast-as-intended" tracta d'obtenir mecanismes que garanteixin al votant que el seu vot correspon a les seves preferències. Les propostes actuals posen la càrrega de la verificació en el votant, cosa que no és desitjable en eleccions del món real, on participen votants amb diferents graus de coneixements tècnics. Nosaltres introduïm el concepte de "universal cast-as-intended verifiability", que proporciona mecanismes per a que qualsevol entitat de l'elecció pugui comprovar que qualsevol vot conté les preferències del votant que l'ha emès - sense revelar el contingut del vot. A banda de definir formalment el concepte de "universal cast-as-intended verifiability" també proposem un protocol de vot electrònic que satisfà aquesta propietat. L'altre problema que hem estudiat és el problema dels vots invàlids en eleccions electròniques. Un dels avantatges del vot electrònic és que permet evitar que els votants emetin vots nuls sense voler. Per això, si durant el recompte de l'elecció apareixen vots nuls construïts intencionadament es pot crear desconfiança en el sistema de vot. Els usuaris del sistema de vot poden pensar que el sistema té forats de seguretat o que ha estat atacat. Per evitar aquesta situació, definim el concepte de "vote validatability", una propietat dels sistemes de vot electrònic que garanteix que els vots nuls es poden identificar en el moment que s'emeten. En aquesta tesi hem definit formalment aquesta propietat i hem dissenyat un protocol que la satisfà. Tots aquests requisits de seguretat dels protocols de vot electrònic s'implementen amb eines criptogràfiques. Les principals eines que s'utilitzen són esquemes de xifrat, esquemes de firma i proves de coneixement zero. Una prova de coneixement zero permet a una entitat convèncer una altra entitat que una sentència és certa sense donar cap altra informació que la certesa de la sentència. Aquestes proves de coneixement zero es poden fer servir, per exemple, per demostrar que el recompte de l'elecció s'ha fet correctament. Recentment, Groth i Sahai han construït proves de coneixement zero que es poden fer servir per un ampli ventall de sentències com per exemple sentències que apareixen en protocols de vot electrònic. En aquesta tesi hem fet dos contribucions sobre les proves de Groth i Sahai. Per una banda donem un marc teòric que permet derivar hipòtesis criptogràfiques per construir protocols criptogràfics. En particular, construïm noves proves de Groth i Sahai millorant l'eficiència de les construccions existents. De manera independent, indiquem com les proves de Groth i Sahai es poden estendre per fer-les compatibles amb un ventall més ampli de sentències, millorem l'eficiència de les proves de Groth i Sahai per moltes d'aquestes sentències i, en particular, quan es fan servir per demostrar múltiples sentències.
A. Pinar Ozisik, George Bissias, Brian Neil Levine
We make several contributions that quantify the real-time hash rate and therefore the consensus of a blockchain. We show that by using only the hash value of blocks, we can estimate and measure the hash rate of all miners or individual miners, with quanti able accuracy. We apply our techniques to the Ethereum and Bitcoin blockchains; our solution applies to any proof-of-work-based blockchain that relies on a numeric target for the validation of blocks. We also show that if miners regularly broadcast status reports of their partial proof-of- work, the hash rate estimates are signi cantly more accurate at a cost of slightly higher bandwidth. Whether using only the blockchain, or the additional information in status reports, merchants can use our techniques to quantify in real-time the threat of double-spend attacks.
Governments around the world have been trying to implement secure and reliable e-voting (location-independent, individualized voting over the Internet) for a long time, to no avail: E-voting remains fundamentally insecure.This can change with the blockchain technology, an open, transparent, and distributed digital ledger. However, blockchain-based e-voting will only work if the blockchain-based e-voting infrastructure is truly distributed and no one entity, not even the government, controls a majority of it.
In the cryptographic currency Bitcoin, all transactions are recorded in the blockchain - a public, global, and immutable ledger. Because transactions are public, Bitcoin and its users employ obfuscation to maintain a degree of financial privacy. Critically, and in contrast to typical uses of obfuscation, in Bitcoin obfuscation is not aimed against the system designer but is instead enabled by design. We map sixteen proposed privacy-preserving techniques for Bitcoin on an obfuscation-vs.-cryptography axis, and find that those that are used in practice tend toward obfuscation. We argue that this has led to a balance between privacy and regulatory acceptance.
Bitcoin and other cryptocurrencies have surged in popularity over the last decade. Although Bitcoin does not claim to provide anonymity for its users, it enjoys a public perception of being a privacy preserving financial system. In reality, cryptocurrencies publish users' entire transaction histories in plaintext, albeit under a pseudonym; this is required for transaction validation. Therefore, if a user's pseudonym can be linked to their human identity, the privacy fallout can be significant. Recently, researchers have demonstrated deanonymization attacks that exploit weaknesses in the Bitcoin network's peer-to-peer (P2P) networking protocols. In particular, the P2P network currently forwards content in a structured way that allows observers to deanonymize users. In this work, we redesign the P2P network from first principles with the goal of providing strong, provable anonymity guarantees. We propose a simple networking policy called Dandelion which provides quasi-optimal, network-wide anonymity, with minimal cost to the network's utility. We also discuss practical implementation challenges and propose heuristic solutions.
Mauro Conti, E. Sandeep Kumar, Chhagan Lal, Sushmita Ruj
Bitcoin is a popular cryptocurrency that records all transactions in a distributed append-only public ledger called blockchain. The security of Bitcoin heavily relies on the incentive-compatible proof-of-work (PoW) based distributed consensus protocol, which is run by the network nodes called miners. In exchange for the incentive, the miners are expected to maintain the blockchain honestly. Since its launch in 2009, Bitcoin economy has grown at an enormous rate, and it is now worth about 150 billions of dollars. This exponential growth in the market value of bitcoins motivate adversaries to exploit weaknesses for profit, and researchers to discover new vulnerabilities in the system, propose countermeasures, and predict upcoming trends. In this paper, we present a systematic survey that covers the security and privacy aspects of Bitcoin. We start by giving an overview of the Bitcoin system and its major components along with their functionality and interactions within the system. We review the existing vulnerabilities in Bitcoin and its major underlying technologies such as blockchain and PoW-based consensus protocol. These vulnerabilities lead to the execution of various security threats to the standard functionality of Bitcoin. We then investigate the feasibility and robustness of the state-of-the-art security solutions. Additionally, we discuss the current anonymity considerations in Bitcoin and the privacy-related threats to Bitcoin users along with the analysis of the existing privacy-preserving solutions. Finally, we summarize the critical open challenges, and we suggest directions for future research towards provisioning stringent security and privacy solutions for Bitcoin.
Open access
3 source records
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Distributed financial systems are radically changing the way we do business and spend our money. Ripple, in particular, is unique in its kind. It is built on consensus and trust among its users and it allows to exchange both fiat currencies and goods over its network. It does so by storing the accounts of its users, their balances, and all the transactions in a distributed ledger, publicly accessible. In this paper we perform an in-depth study of the Ripple exchange system and its public distributed ledger. We analyze payments, the structure of payment paths, and the role of the entities in the system such as Gateways (the equivalent of banks) and Market Makers. We also analyze the internal stream of events and show that Ripple relies on a surprisingly small number of active validators, raising concerns on the actual robustness and fairness of the system. Moreover, we consider the degree of anonymity that Ripple is able to guarantee. By examining the first three years of Ripple history (more than 500 GB worth of data), we show that even approximate information on a single payment can uncover, with incredible accuracy, the entire financial life of the user. For example, anyone who overhears our order of a Latte at our favourite bar can easily get complete and unlimited access to our balance, our previous and future payments, our monthly income, as well as critical information about the places where we shop and the people we trust.
Jun 1, 2017·2017 IEEE International Conference on Internet of Things (iThings) and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber, Physical and Social Computing (CPSCom) and IEEE Smart Data (SmartData)
Bitcoin, one major virtual currency, attracts users' attention by its novel mode in recent years. With blockchain as its basic technique, Bitcoin possesses strong security features which anonymizes user's identity to protect their private information. However, some criminals utilize Bitcoin to do several illegal activities bringing in great security threat to the society. Therefore, it is necessary to get knowledge of the current trend of Bitcoin and make effort to de-anonymize. In this paper, we put forward and realize a system to analyze Bitcoin from two aspects: blockchain data and network traffic data. We resolve the blockchain data to analyze Bitcoin from the point of Bitcoin address while simulate Bitcoin P2P protocol to evaluate Bitcoin from the point of IP address. At last, with our system, we finish analyzing its current trends and tracing its transactions by putting some statistics on Bitcoin transactions and addresses, tracing the transaction flow and de-anonymizing some Bitcoin addresses to IPs.
We present the first measurement study of JoinMarket, a growing marketplace for more anonymous transfers in the Bitcoin ecosystem. Our study reveals that this market is funded with multiple thousand bitcoins and generated a turnover of almost 29.5 million USD over the course of 13 months. Assessing the resilience of the market against a well-funded attacker, we discover that in a typical scenario, a selective attack with a 90% success rate requires an investment of 14 000–54 000 USD (which is recoverable after the attack). We present economic arguments to explain the existence of this novel market for anonymity and underpin the hypothesis of heterogeneous time preference with empirical data.
Public elections are one of the basis upon which representative democracy is built. Thus, it is of the utmost importance that governments and organizations are able to successfully hold non-fraudulent representative elections. Several methods are employed in order to allow citizens to cast their votes, such as Ballot-based voting, purely electronic methods, and Electronic Voting Machines, among others. However, we argue that current methods, specially those based on electronic platforms, provide unsatisfactory levels of transparency to voters, thus harming the trust voters have that the vote they cast was the same one counted by election officials, a problem known as voter confidence. Instead of stepping back to traditional and inefficient offline strategies, we suggest the modernization of State structures by the use of emerging technologies. In this research, we explore the possibility of using Blockchain technology to help in solving those transparency and confidence problems. First, we give an overview of Blockchain itself and other uses focused on societal problems and their respective analysis. We then analyze how the adoption of Blockchain into a digital government repertoire can contribute to common e-voting issues and also promote elections transparency, increase auditability, enhance voter confidence and strengthen democracy. By attending to this poster presentation, visitors will have a clear understanding of what is Blockchain and its basic concepts, why are market and researchers so excited about it, how it can help to solve common voting systems issues, who is already using it and the benefits and potential risks of its adoption.
Blockchain is offering new opportunities to develop new types of digital services. While research on the topic is still emerging, it has mostly focused on the technical and legal issues instead of taking advantage of this novel concept and creating advanced digital services. In this paper, we are going to leverage the open source Blockchain technology to propose a design for a new electronic voting system that could be used in local or national elections. The Blockchain-based system will be secure, reliable, and anonymous, and will help increase the number of voters as well as the trust of people in their governments.
Open access
Internet Traffic Analysis and Secure E-voting
Advanced Steganography and Watermarking Techniques
This work show an avaliation about the performance of the application of Group Signature technique in Bitcoin system and a study about the anonymity and auditory. The Bitcoin’ goal is provide a virtual currency and an anonymous online transaction system. However, recent researches show that can be to break the anonymity of transactions through the chronological traceability technique in the Bitcoin transactions and analysis of network addresses. As a result of breaking anonymity of Bitcoin transactions, users’ privacy and all Bitcoin ecosystem are affected negatively. For this reason, in this work, it was proposed to include Group Signatures techniques in the Bitcoin system to increasing of anonymity in Bitcoin transactions but with audity possibility in accept time, more or less 10 minutes. The Group Signature generate a lot of dinstinct groups to dinstinct Bitcoin transactions. After to include the Group Signature technique in a modified version of Bitcoin system, we evaluated this technique in Bitcoin system through experiment in simulations. Through the experiments and statistic analysis, it was found that the approach of including the Group Signature is feasible for implementation in Bitcoin system with small groups, 500 clients. For the all cases analyzed, it was verified that the use of Group Signature in Bitcoin transactions increase the anonymity. Therefore, it was verified that the performance of Bitcoin transactions with Group Signature technique show a delay in nearly 50% less than current Bitcoin system whitout this technique. Nevertheless, in small groups with Group Signature get a better anonymity level and audity, but in big groups with more than 500 clients this technique not is good because the transactions time is over.
Despite a great deal of work to improve the TLS PKI, CA misbehavior continues to occur, resulting in unauthorized certificates that can be used to mount man-in-the-middle attacks against HTTPS sites. CAs lack the incentives to invest in higher security, and the manual effort required to report a rogue certificate deters many from contributing to the security of the TLS PKI. In this paper, we present IKP, a platform that automates responses to unauthorized certificates and provides incentives for CAs to behave correctly and for others to report potentially unauthorized certificates. Domains in IKP specify criteria for their certificates, and CAs specify reactions such as financial penalties that execute in case of unauthorized certificate issuance. By leveraging smart contracts and blockchain-based consensus, we can decentralize IKP while still providing automated incentives. We describe a theoretical model for payment flows and implement IKP in Ethereum to show that decentralizing and automating PKIs with financial incentives is both economically sound and technically viable.
Ethereum represents an important first step in the new vision of a decentralized web. Could this new technology provide tools to invent new forms of democracy?
Stefano Bistarelli, Marco Mantilacci, Paolo Santancini, Francesco Santini
In this work we re-adapt the Bitcoin e-payment system and propose it as a decentralised end-to-end voting platform (from voters to candidates). We describe the main architectural choices behind the implementation, which consists of the pre-voting, voting, and post-voting phases. The resulting implementation is completely decentralised: it is possible to directly cast a vote in the block-chain without any collecting intermediate-level. All the votes can be verified by anyone reading such a public ledger. We also exploit digital asset coins to directly keep track of votes (through the Open Asset Protocol), and we show the election cost for n voters.
This paper contributes a systematic account of transaction anonymization techniques that do not require trust in a single entity and support the existing cryptographic currency Bitcoin. It surveys and compares four known techniques, proposes tailored metrics to identify the use of each technique (but not necessarily its users), and presents longitudinal measurements indicating adoption trends and teething troubles. There is a tradeoff between the choice of users' preferred protection mechanisms and the risk that pertaining transactions can be singled out, which hurts privacy due to smaller anonymity sets unless a critical mass adopts the mechanism.