The anonymity of the Bitcoin system has some shortcomings. Analysis of Transaction Chain (ATC) and Analysis of Bitcoin Protocol and Network (ABPN) are two important methods of deanonymizing bitcoin transactions. Nowadays, there are some anonymization methods to combat ATC but there has been little research into ways to counter ABPN. This paper proposes a new anonymization technology called Transaction Remote Release (TRR). Inspired by The Onion Router (TOR), TRR is able to render several typical attacking methods of ABPN ineffective. Furthermore, the performance of encryption and decryption of TRR is good and the growth rate of the cipher is very limited. Hence, TRR is suited for practical applications.
Open access
2 source records
cs.CR
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Enormous amounts of data are collected by hospitals, social networking systems, government agencies, and other organizations. There are huge social benefits in analyzing this data, but we must protect the privacy of the individuals in the data. The current standard definition of data privacy is differential privacy [22, 19]. In this thesis, we introduce new definitions of data privacy that can be better than differential privacy in certain ways. We first argue that differential privacy might not be strong enough in social network settings. We then introduce a zero-knowledge based definition of privacy called zero-knowledge privacy, which is strictly stronger than differential privacy and is particularly attractive when modeling privacy in social networks. Both differential privacy and zero-knowledge privacy provide strong privacy guarantees. However, for certain tasks, mechanisms satisfying these privacy definitions have to add a lot of "noise", thus lowering the utility of the released data. Thus, we introduce a new definition of privacy called crowd-blending privacy that strictly relaxes the notion of differential privacy. We demonstrate crowd-blending private mechanisms for histograms and for releasing synthetic data points, achieving strictly better utility than what is possible using differentially private mechanisms. Differential privacy guarantees the same level of privacy protection for all individuals. However, we demonstrate that some individuals may need more privacy than others. Thus, we introduce a generalization of differential privacy called tai- lored differential privacy, where an individual's privacy parameter is "tailored" for the individual based on the individual's data and the data set. We focus on a natural instance of tailored differential privacy, which we call outlier privacy: an individual's privacy parameter is determined by how much of an "outlier " the individual is. In this thesis, we also study the problem of strategy-proof voting, which is plagued by impossibility results. We take a bounded-rationality approach to this problem and consider a setting where voters have "coarse" beliefs (a notion that has gained popularity in the behavioral economics literature). In particular, we construct good voting rules that satisfy a notion of strategy-proofness with respect to coarse i.i.d. beliefs, thus circumventing the existing impossibility results.
Gurchetan S. Grewal, Mark Ryan, Liqun Chen, Michael R. Clarkson
Du-Vote is a new remote electronic voting protocol that eliminates the often-required assumption that voters trust general-purpose computers. Trust is distributed in Du-Vote between a simple hardware token issued to the voter, the voter's computer, and a server run by election authorities. Verifiability is guaranteed with high probability even if all these machines are controlled by the adversary, and privacy is guaranteed as long as at least either the voter's computer, or the server and the hardware token, are not controlled by the adversary. The design of the Du-Vote protocol is presented in this paper. A new non-interactive zero-knowledge proof is employed to verify the server's computations. Du-Vote is a step towards tackling the problem of internet voting on user machines that are likely to have malware. We anticipate that the methods of Du-Vote can be used in other applications to find ways of achieving malware tolerance, that is, ways of securely using platforms that are known or suspected to have malware.
This thesis is devoted to low-resource off-path deanonymisation techniques for two popular systems, Tor and Bitcoin. Tor is a software and an anonymity network which in order to confuse an observer encrypts and re-routes traffic over random pathways through several relays before it reaches the destination. Bitcoin is a distributed payment system in which payers and payees can hide their identities behind pseudonyms (public keys) of their choice. The estimated number of daily Tor users is 2,000,000 which makes it arguable the most used anonymity network. Bitcoin is the most popular cryptocurrency with market capitalization about 3.5 billion USD. In the first part of the thesis we study the Tor network. At the beginning we show how to remotely find out which Tor relays are connected. This effectively allows for an attacker to reduce Tor users' anonymity by ruling out impossible paths in the network. Later we analyze the security of Tor Hidden Services. We look at them from different attack perspectives and provide a systematic picture of what information can be obtained with very inexpensive means. We expose flaws both in the design and implementation of Tor Hidden Services that allow an attacker to measure the popularity of arbitrary hidden services, efficiently collect hidden service descriptors (and thus get a global picture of all hidden services in Tor), take down hidden services and deanonymize hidden services. In the second part we study Bitcoin anonymity. We describe a generic method to deanonymize a significant fraction of Bitcoin users and correlate their pseudonyms with their public IP addresses. We discover that using Bitcoin through Tor not only provides limited level of anonymity but also exposes the user to man-in-the middle attacks in which an attacker controls which Bitcoin blocks and transactions the user is aware of. We show how to fingerprint Bitcoin users by setting an "address cookie" on their computers. This can be used to correlate the same user across different sessions, even if he uses Tor, hidden-services or multiple proxies. Finally, we describe a new anonymous decentralized micropayments scheme in which clients do not pay services with electronic cash directly but submit proof of work shares which the services can resubmit to a crypto-currency mining pool. Services credit users with tickets that can later be used to purchases enhanced services.
Jun 1, 2015·2015 IEEE/ACIS 16th International Conference on Software Engineering, Artificial Intelligence, Networking and Parallel/Distributed Computing (SNPD)
Bitcoin, a distributed, peer to peer crypto currency, has gained a significant popularity among different users around the world by promising users a fully decentralized network with an inherently independence from governments and without the influence of any central authorities and organizations. Mining is the fundamental concept in Bitcoin which must be done in checking all monetary transactions and verifying them which in return generates Bitcoin as a reward to encourage this work. While the qualitative nature of this unique system is clearly accepted and understood, there are some issues regarding to its decentralized network environment. Based on our analysis due to the high variance of solo mining, the number of users joining top most famous Bitcoin mining pools are increasing due to the fact that users together under a Bitcoin pool will have a higher chance of generating next block in the Bitcoin's blockchain by reducing the variance and earning the mining reward. Furthermore, emerging huge mining farms with strong mining resources and fast processing power is another trend toward centralization. Although some might argue that, the protocol itself is purely decentralized and these are marketbased centralization, this trend clearly illustrates that the pure, decentralized protocol of Bitcoin is going toward centralization in its distributed network, where any kind of centralization should be considered carefully due to the 51% attack. By analysing all the created blocks from 2009 to 2014 we proposed a centralization factor which shows how centralized is the state of Bitcoin's network in different years. Centralization, due its simplicity, is a phenomenon that happens to any disciplined and organized system automatically, which in case of Bitcoin is against the pure initial decentralized nature of it and might arise some concerns and threats to the Bitcoin's unforeseeable future.
Ghassan Karame, Elli Androulaki, Marc Roeschlin, Arthur Gervais · 5 authors
Bitcoin is a decentralized payment system that relies on Proof-of-Work (PoW) to resist double-spending through a distributed timestamping service. To ensure the operation and security of Bitcoin, it is essential that all transactions and their order of execution are available to all Bitcoin users. Unavoidably, in such a setting, the security of transactions comes at odds with transaction privacy. Motivated by the fact that transaction confirmation in Bitcoin requires tens of minutes, we analyze the conditions for performing successful double-spending attacks against fast payments in Bitcoin, where the time between the exchange of currency and goods is short (in the order of a minute). We show that unless new detection techniques are integrated in the Bitcoin implementation, double-spending attacks on fast payments succeed with considerable probability and can be mounted at low cost. We propose a new and lightweight countermeasure that enables the detection of double-spending attacks in fast transactions. In light of such misbehavior, accountability becomes crucial. We show that in the specific case of Bitcoin, accountability complements privacy. To illustrate this tension, we provide accountability and privacy definition for Bitcoin, and we investigate analytically and empirically the privacy and accountability provisions in Bitcoin.
Till Neudecker, Philipp Andelfinger, Hannes Hartenstein
We present a simulation model of the Bitcoin peer-to-peer network, a widely deployed distributed electronic currency system. The model enables evaluations of the feasibility and cost of attacks on the Bitcoin network at full scale of 6,000 nodes. The simulation model is based on unmodified code from core segments of the Bitcoin reference implementation used by 99% of nodes. Parametrization of the model is performed based on large-scale measurements of the real-world network. We present preliminary validation results showing a reasonable correspondence of the propagation of messages in the Bitcoin network compared with simulation results. We apply the model to study the feasibility of a partitioning attack on the network and show that the attack is sensitive to the churn of the attacking nodes.
Joseph Bonneau, Andrew Miller, Jeremy Clark, Arvind Narayanan · 6 authors
Bit coin has emerged as the most successful cryptographic currency in history. Within two years of its quiet launch in 2009, Bit coin grew to comprise billions of dollars of economic value despite only cursory analysis of the system's design. Since then a growing literature has identified hidden-but-important properties of the system, discovered attacks, proposed promising alternatives, and singled out difficult future challenges. Meanwhile a large and vibrant open-source community has proposed and deployed numerous modifications and extensions. We provide the first systematic exposition Bit coin and the many related crypto currencies or 'altcoins.' Drawing from a scattered body of knowledge, we identify three key components of Bit coin's design that can be decoupled. This enables a more insightful analysis of Bit coin's properties and future stability. We map the design space for numerous proposed modifications, providing comparative analyses for alternative consensus mechanisms, currency allocation mechanisms, computational puzzles, and key management tools. We survey anonymity issues in Bit coin and provide an evaluation framework for analyzing a variety of privacy-enhancing proposals. Finally we provide new insights on what we term disinter mediation protocols, which absolve the need for trusted intermediaries in an interesting set of applications. We identify three general disinter mediation strategies and provide a detailed comparison.
Trusted timestamping is a process for proving that certain information existed at a given point in time. This paper presents a trusted timestamping concept and its implementation in form of a web-based service that uses the decentralized Bitcoin block chain to store anonymous, tamper-proof timestamps for digital content. The service allows users to hash files, such as text, photos or videos, and store the created hashes in the Bitcoin block chain. Users can then retrieve and verify the timestamps that have been committed to the block chain. The non-commercial service enables anyone, e.g., researchers, authors, journalists, students, or artists, to prove that they were in possession of certain information at a given point in time. Common use cases include proving that a contract has been signed, a photo taken, a video recorded, or a task completed prior to a certain date. All procedures maintain complete privacy of the user's data.
Jan Henrik Ziegeldorf, Fred Grossmann, Martin Henze, Nicolas Inden · 5 authors
Bitcoin is a digital currency that uses anonymous cryptographic identities to achieve financial privacy. However, Bitcoin's promise of anonymity is broken as recent work shows how Bitcoin's blockchain exposes users to reidentification and linking attacks. In consequence, different mixing services have emerged which promise to randomly mix a user's Bitcoins with other users' coins to provide anonymity based on the unlinkability of the mixing. However, proposed approaches suffer either from weak security guarantees and single points of failure, or small anonymity sets and missing deniability. In this paper, we propose CoinParty a novel, decentralized mixing service for Bitcoin based on a combination of decryption mixnets with threshold signatures. CoinParty is secure against malicious adversaries and the evaluation of our prototype shows that it scales easily to a large number of participants in real-world network settings. By the application of threshold signatures to Bitcoin mixing, CoinParty achieves anonymity by orders of magnitude higher than related work as we quantify by analyzing transactions in the actual Bitcoin blockchain and is first among related approaches to provide plausible deniability.
The Bitcoin system (https://bitcoin.org) is a pseudo-anonymous currency that can dissociate a user from any real-world identity. In that context, a successful breach of the virtual and physical divide represents a signficant aw in the Bit-coin system [1]. In this project we demonstrate how to glean information about the real-world users behind Bitcoin transactions. We analyze publicly available data about the cryptocurrency. In particular, we focus on determining information about a Bitcoin user's physical location by examining that user's spending habits.
Bitcoins have recently become an increasingly popular cryptocurrency through which users trade electronically and more anonymously than via traditional electronic transfers. Bitcoin's design keeps all transactions in a public ledger. The sender and receiver for each transaction are identified only by cryptographic public-key ids. This leads to a common misconception that it inherently provides anonymous use. While Bitcoin's presumed anonymity offers new avenues for commerce, several recent studies raise user-privacy concerns. We explore the level of anonymity in the Bitcoin system. Our approach is two-fold: (i) We annotate the public transaction graph by linking bitcoin public keys to "real" people - either definitively or statistically. (ii) We run the annotated graph through our graph-analysis framework to find and summarize activity of both known and unknown users.
Bitcoin and other cryptocurrencies are getting into common usage more and more frequently. Unfortunately this spread is connected with attempts to misuse their principles for personal benefit. The goal of this thesis is to explain the main principles of using bitcoin in relation to the internet identity. This connection is represented by two sources in the thesis: the first is a bitcoin blockchain, the second is the sum of various user profiles used in discussion forums and similar websites. The aim is to create and explain the process how to, by using the combination of this two sources, reveal the identity of a human using cryptocurrencies for payment (from a private person point of view). First, methods used for extraction of correct and useful data from the blockchain and internet profiles must be developed to be able to mine data from the joint database, merging into a full user profile containing personal data. Results of this investigation are extended by the rules of preserving anonymity on the internet, containing both technological and behavioural measures avoiding a share of personal data. The end of this thesis explains possible attack vectors that might be used for compromising cryptocurrencies. The methods of searching of the internet identity are a useful tool for facing these attacks.
The English version of this paper can be found at: http://ssrn.com/abstract=2709713 Italian Abstract: La tecnologia fondamentale del protocollo Bitcoin, conosciuta come blockchain, è emersa recentemente in tutta la sua straordinaria portata innovativa, teoricamente in grado di riconfigurare le nostre attuali interazioni economiche, politiche e sociali. Sebbene l'interesse accademico per questa tecnologia sia ormai crescente, finora non è stata ancora divulgata un'analisi esaustiva delle sue applicazioni dal punto di vista politologico. Questa ricerca si propone di discutere i punti essenziali di una governance decentralizzata fondata sulla blockchain, che sfida in varia misura i meccanismi tradizionali della autorità statale, della cittadinanza e della democrazia. In particolare, la ricerca si pone l'obiettivo di verificare la performance della blockchain e delle piattaforme decentralizzate come strumenti iperpolitici, in grado cioè di gestire interazioni sociali su ampia scala e di destituire eventualmente le autorità centrali tradizionali. L'analisi evidenzia i rischi relativi a posizioni dominanti di natura privatistica negli ecosistemi distribuiti, che potrebbero spogliare i cittadini dei loro diritti e permettere l'insorgere di una società globale senza stato. Se gli utopisti tecnologici sollecitano la destituzione di qualsiasi autorità centrale, questa ricerca difende invece il ruolo dello Stato come necessario punto di coordinazione nella società civile e dimostra come la decentralizzazione attuata attraverso algoritmi e sistemi di consenso distribuito costituisca una teoria organizzativa, non una teoria politica autonoma. English Abstract: The core technology of Bitcoin, the blockchain, has recently emerged as a disruptive innovation with a wide range of applications, potentially able to redesign our interactions in business, politics and society at large. Although scholarly interest in this subject is growing, a comprehensive analysis of blockchain applications from a political perspective is severely lacking to date. This paper aims to fill this gap and it discusses the key points of blockchain-based decentralized governance, which challenges to varying degrees the traditional mechanisms of State authority, citizenship and democracy. In particular, the paper verifies to which extent blockchain and decentralized platforms can be considered as hyper-political tools, capable to manage social interactions on large scale and dismiss traditional central authorities. The analysis highlights risks related to a dominant position of private powers in distributed ecosystems, which may lead to a general disempowerment of citizens and to the emergence of a stateless global society. While technological utopians urge the demise of any centralized institution, this paper advocates the role of the State as a necessary central point of coordination in society, showing that decentralization through algorithm-based consensus is an organizational theory, not a stand-alone political theory.
Il saggio propone alcune considerazioni sulla natura giuridica delle 'criptovalute' e dei Bitcoin in particolare, in assenza di specifica legislazione che ne definisca i caratteri e che individui la disciplina loro applicabile.
Artykuł porusza problem identyfikacji (w oparciu o rozkład Benforda) nietypowych transakcji w sieci Bitcoin. Dla przykładowo wybranych adresów portfeli Bitcoin porównano rozkład Benforda z rozkładem częstotliwości występowania poszczególnych cyfr na pierwszej najbardziej znaczącej pozycji w kwotach transakcji związanych z tymi adresami. Rozkłady te nie były zgodne z rozkładem Benforda. Zwrócono uwagę na konieczność zachowania dużej ostrożności przy analizowaniu transakcji za pomocą narzędzi statystycznych takich jak rozkład Benforda. Brak zgodności z rozkładem Benforda w żadnym wypadku nie jest równoznaczny z prowadzeniem działalności niezgodnej z prawem. Z drugiej strony, zgodność z rozkładem Benforda nie stanowi gwarancji tego, że nie występują nieprawidłowości.
We present a new, decentralized, efficient, and secure digital cryptocurrency, in which the ordinary users themselves keep turns to ensure that the systems works well. ∗sergeyg@mit.edu †silvio@csail.mit.edu
David Derler, Henrich C. Pöhls, Kai Samelin, Daniel Slamanig
Abstract. A redactable signature scheme (RSS) allows removing parts of a signed message by any party without invalidating the respective signa-ture. State-of-the-art constructions thereby focus on messages represented by one specific data-structure, e.g., lists, sets or trees, and adjust the secu-rity model accordingly. To overcome the necessity for this myriad of models, we present a general framework covering arbitrary data-structures and even more sophisticated possibilities. For example, we cover fixed elements which must not be redactable and dependencies between elements. Moreover, we introduce the notion of designated redactors, i.e., the signer can give some extra information to selected entities which become redactors. In practice, this often allows to obtain more efficient schemes. We then present two RSSs; one for sets and one for lists, both constructed from any EUF-CMA secure signature scheme and indistinguishable cryptographic accumulators in a black-box way and show how the concept of designated redactors can be used to increase the efficiency of these schemes. Finally, we present a black-box construction of a designated redactor RSS by combining an RSS for sets with non-interactive zero-knowledge proof systems. All the three constructions presented in this paper provide transparency, which is an im-portant property, but quite hard to achieve, as we also conceal the length of the original message and the positions of the redactions. 1