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Since the inception of Bitcoin in 2009, the market of cryptocurrencies has grown beyond the initial expectations, as witnessed by the thousands of tokenised assets available on the market, whose daily trades exceed dozens of USD billions. The pseudonymity features of cryptocurrencies have attracted the attention of cybercriminals, who exploit them to carry out potentially untraceable scams. The wide range of cryptocurrency-based scams observed over the last ten years has fostered the study on their effects, and the development of techniques to counter them. The research in this field is hampered by various factors. First, there exist only a few public data sources about cryptocurrency scams, and they often contain incomplete or misclassified data. Further, there is no standard taxonomy of scams, which leads to ambiguous and incoherent interpretations of their nature. Indeed, the unavailability of reliable datasets makes it difficult to train effective automatic classifiers that can detect and analyse scams. In this paper, we perform an extensive review of the scientific literature on cryptocurrency scams, which we systematise according to a novel taxonomy. By collecting and homogenising data from different public sources, we build a uniform dataset of thousands of cryptocurrency scams. We build upon this dataset to implement a tool that automatically recognises scams and classifies them according to our taxonomy. We assess the effectiveness of our tool through standard performance metrics. We then analyse the results of the classification, providing key insights about the distribution of scam types, and the correlation between different types. Finally, we propose a set of guidelines that policymakers could follow to improve user protection against cryptocurrency scams. more...

Implementing pseudonymity, key-management, non-repudiation and data minimisation features in isolated procedures is trivial. However, integrating all of them in one consistent architecture has several challenges to tackle. This work proposes data structures to represent Self-Sovereign Identities and to handle those features in a consolidated architecture. Key-management is constructed using secret sharing principles, capable of recovering from a lost or compromised key to a new one without losing track of the original account. Pseudonymity and data minimisation is established using anonymous profiles, showing different views of the same identity. Non-repudiation is contemplated in the profile disclosure process. Profiles are protected against tampering with the use of digital signatures and blockchain cryptographic constructions. All profiles and registries are controlled with a single asymmetric key pair that can be provided by a smart card. Flexible structures are defined that can be used to register claims, attestations, authorisation grants, user consents, or any other activities. All definitions take into consideration the rules of the General Data Protection Regulation (GDPR). more...

Crowdsensing requires scalable privacy-preserving authentication that allows users to send anonymously sensing reports, while enabling eventual anonymity revocation in case of user misbehavior. Previous research efforts already provide efficient mechanisms that enable conditional privacy through pseudonym systems, either based on Public Key Infrastructure (PKI) or Group Signature (GS) schemes. However, previous schemes do not enable users to self-generate an unlimited number of pseudonyms per user to enable users to participate in diverse sensing tasks simultaneously, while preventing the users from participating in the same task under different pseudonyms, which is referred to as sybil attack. This paper addresses this issue by providing a scalable privacy-preserving authentication solution for crowdsensing, based on a novel pseudonym-based signature scheme that enables unlinkable-yet-accountable pseudonymity. The paper provides a detailed description of the proposed scheme, the security analysis, the performance evaluation, and details of how it is implemented and integrated into a real crowdsensing platform. more...

In cryptocurrencies, privacy of users is preserved using pseudonymity. However, it has been shown that pseudonymity does not result in anonymity if a users transactions are linkable. This makes cryptocurrencies vulnerable to deanonymization attacks. The current solutions proposed in the literature suffer from at least one of the following issues: (1) requiring a trusted thirdparty entity, (2) poor performance, and (3) incompatible with the standard structure of cryptocurrencies. In this paper, we propose Unlinkable Coin (UCoin), a secure mixbased approach to address these issues. In UCoin, the link between the input (payer) and output (payee) addresses in a transaction is broken. This is done by mixing the transactions of multiple users into a single aggregated transaction in which the output addresses have been secretly shuffled. In our protocol design, we first develop HDCnet, a secure shuffling protocol that enables a group of users to anonymously publish their data. Then, we deploy the proposed HDCnet protocol in the UCoin architecture (as a mixing unit) to generate the aggregate transactions. We show that UCoin (1) does not rely on a trusted thirdparty, (2) can mix 50 transactions in 6.3 seconds that is 18% faster than the current solutions, and (3) is fully compatible with the architecture of cryptocurrencies. more...

Existing digital identity management systems fail to deliver the desirable properties of control by the users of their own identity data, credibility of disclosed identity data, and network-level anonymity. The recently proposed Self-Sovereign Identity (SSI) approach promises to give users these properties. However, we argue that without addressing privacy at the network level, SSI systems cannot deliver on this promise. In this paper we present the design and analysis of our solution TCID, created in collaboration with the Dutch government. TCID is a system consisting of a set of components that together satisfy seven functional requirements to guarantee the desirable system properties. We show that the latency incurred by network-level anonymization in TCID is significantly larger than that of identity data disclosure protocols but is still low enough for practical situations. We conclude that current research on SSI is too narrowly focused on these data disclosure protocols., Comment: Accepted for publication at the 46th IEEE Conference on Local Computer Networks (LCN), October 4-7, 2021 more...

The Internet of Things (IoT) paves the way for smart applications such as in E-health, E-homes, transportation, or energy production. However, IoT technologies also pose privacy challenges for their users, as they allow the tracking and monitoring of the users' behavior and context. The EU General Data Protection Regulation (GDPR) mandates data controller to follow a data protection by design and default approach by implementing for instance pseudonymity for achieving data minimisation. This paper provides a systematic literature review for answering the question of what types of privacy-preserving identifiers are proposed by the literature in IoT environments for implementing pseudonymity. It contributes with classifications and analyses of IoT environments for which privacy-preserving identifiers have been proposed and of the pseudonym types and underlying identity management architectures used. Moreover, it discusses trends and gaps in regard to addressing privacy trade-offs. more...

Internet of things (IoT), mobile edge computing (MEC), and unmanned aerial vehicle (UAV) have attracted significant attention in both industry and academic research. By consolidating these technologies, IoT can be facilitated with improved connectivity, better data transmission, energy saving, and other advantages. However, the communication between these entities is subject to potential cyber threats. In addition, the integrity of the data must be maintained after storing into local storage. Blockchain is a data structure that supports features like pseudonymity, data integrity etc. This paper represents a blockchain based data acquisition process in which information is gathered from IoTs using UAV as a relay and is securely kept in blockchain at MEC server. In the proposed scheme, data are encrypted prior to transfer to MEC server with the assistance of a UAV. Upon receiving the data, MEC server validates the data and the identity of the sender. Successful validation is followed by stocking of the data into blockchain, subsequent to obtaining consent from the validators. Security analysis is conducted in order to show the feasibility of the proposed secure scheme. Finally, the performance of the proposed scheme is analyzed via simulation and implementation. more...

Privacy is supreme in cryptocurrencies since most users do not want to reveal their identities or the transaction amount in financial transactions. Nevertheless, achieving privacy in blockchain-based cryptocurrencies remains challenging since blockchain is by default a public ledger. For instance, Bitcoin provides builtin pseudonymity rather than true anonymity, which can be compromised by analyzing the transactions. Several solutions have been proposed to enhance the transaction privacy of Bitcoin. Unfortunately, full anonymity is not always desirable, because malicious users are able to conduct illegal transactions, such as money laundering and drug trading, under the cover of anonymity in cryptocurrencies. As a result, regulation in blockchain-based cryptocurrencies is very essential. In this article, we analyze the privacy issues in Bitcoin and investigate some existing privacy-enhancing techniques in blockchain- based cryptocurrencies as well as some privacy-focused altcoins. In addition, we review and compare some works dealing with regulation of cryptocurrencies. Finally, we propose two possible solutions from a top view to balance privacy and regulation of blockchain-based cryptocurrencies. One solution is based on decentralized group signature, in which a group manager is responsible for building a group and tracing the real payer of the group in a transaction. The other solution is based on verifiable encryption, in which a tracing manager is not actively involved in normal transactions but can trace suspicious transactions via an encrypted tag. more...

Data in cloud has always been a point of attraction for the cyber attackers. Nowadays healthcare data in cloud has become their new interest. Attacks on these healthcare data can result in annihilating consequences for the healthcare organizations. Decentralization of these cloud data can minimize the effect of attacks. Storing and running computation on sensitive private healthcare data in cloud are possible by decentralization which is enabled by peer to peer (P2P) network. By leveraging the decentralized or distributed property, blockchain technology ensures the accountability and integrity. Different solutions have been proposed to control the effect of attacks using decentralized approach but these solutions somehow failed to ensure overall privacy of patient centric systems. In this paper, we present a patient centric healthcare data management system using blockchain technology as storage which helps to attain privacy. Cryptographic functions are used to encrypt patient’s data and to ensure pseudonymity. We analyze the data processing procedures and also the cost effectiveness of the smart contracts used in our system. more...

Delay Tolerant Network (DTN) enables communication in opportunistic networks where disruptive links result into intermittent connectivity. Routing protocols in such opportunistic environments mainly rely on broadcast/multicast communication in order to maximize the chances of packet delivery to destination node. Lack of end-to-end path and the essential requirement of store-carry-forward decision of packets by intermediate nodes, pose a serious threat to security and privacy concerns in DTNs. This article proposes a novel approach for secure and private communication in DTNs by hiding the identity of nodes using pseudonyms. The approach is based on Privacy by Architecture (PbA) where minimal identifying information of a user is sent to a certificate authority (CA) while requesting for a certificate. The novel PbA based scheme is composed of a set of protocols to address the aforementioned challenges; the Pseudonym Credential and Pseudonym Identity/Certificate Issuance protocols. The proposed approach is validated using formal modeling in CasperFDR which is the state-of-the art compiler for performance analysis of security protocols. To strengthen our claim, an information theoretic quantification method is employed to measure the Degree of Anonymity (DoA) of the approach. The approach performs efficiently and requires no end-to-end connectivity for messages exchange between the user and the certificate authority, thus making it an ideal choice for ensuring security and privacy in DTNs. Results show that the proposed approach guards against privacy attacks and delivers a high degree of anonymity even in the presence of compromised nodes in the network. more...

Electronic health record (EHR) is a patient’s medical record that can be shared among multiple healthcare facilities, labs, and clinics to diagnose a disease. While sharing the EHR data, security and privacy become a matter of concern as the data are stored centrally. Also, the recent trend of storing EHR data on cloud has gained popularity as the data can be accessed anytime and anywhere. However, centralization of data in the cloud suffers from security and privacy issues. Blockchain technology is a decentralized approach in which blocks are linked together to create a chain of blocks. By design, blockchain is secure as the blocks in the blockchain are practically impossible to tamper with and provides privacy by supporting pseudonymity. Blockchain technology has a huge potential to secure healthcare data and preservation of patient privacy within the cloud environment. Many approaches have been proposed in the last few years to employ the blockchain technology for ensuring security and privacy of data in e-health systems. In this chapter, we present a systematic review of the literature of blockchain-based approaches for e-health systems with focus on e-health system security and privacy of patients’ records. Different research opportunities and practical challenges are identified while using the blockchain technology for ensuring security and privacy in e-health systems. more...

The rapid growth in the number of services invites exponentially increasing malicious traffic which aims to overwhelm a server. This attempt to exhaust the server of its resources is called a Distributed Denial-of-Service (DDoS) attack. The pseudonymity (pseudo-anonymity) of Blockchain can be either desirable or undesirable to society and this unique feature put together with the elimination of trusted intermediaries that smart contracts offer, appeals to the illegal side of the world. This paper sheds light on the “dark side” of smart contracts, i.e., how they are used to stimulate criminal activity, specifically, a contract to allow the terms and execution of a DDoS to take place in a secure community. Though this proposal endeavors to release a DDoS attack, it can be extended to other real-world crimes as well. Apart from this, our work also covers how this framework could be used for Selfish Mining. more...

The problem of maintaining the privacy of sensitive healthcare data is crucial yet the significance of research efforts achieved still need robust development in privacy protection techniques for Wireless Multimedia Sensor Networks (WMSNs). This paper aims to investigate different privacy-preserving methods for WMSNs that can be applied in healthcare, to guarantee a privacy-aware transmission of multimedia data between sensors and base stations. The combination of ant colony optimization-based routing and hierarchical structure of the network have been proposed in the AntSensNet WMSN-based routing protocol to offer QoS and power efficient multipath multimedia packet scheduling. In this paper, the AntSensNet routing protocol was extended by utilizing privacy-preserving mechanisms thus achieving anonymity / pseudonymity, unlinkability, and location privacy. The vulnerability of standard AntSensNet routing protocol to privacy threats have raised the need for the following privacy attacks’ countermeasures: (i) injection of fake traffic, which achieved anonymity, privacy of source and base locations, as well as unlinkability; (ii) encrypting and correlating the size of scalar and multimedia data which is transmitted through a WMSN, along with encrypting and correlating the size of ants, to achieve unlinkability and location privacy; (iii) pseudonyms to achieve unlinkability. The impact of these countermeasures is assessed using quantitative performance analysis conducted through simulation to gauge the overhead of the added privacy countermeasures. It can be concluded that the introduced modifications did enhance the privacy but with a penalty of increased delay and multimedia jitter. The health condition of a patient determines the vitals to be monitored which affects the volumes and sources of fake traffic. Consequently, desired privacy level will dictate incurred overhead due to multimedia transmissions and privacy measures. more...

Attribute-based authentication is considered a cornerstone component to achieve scalable fine-grained access control in the fast growing market of cloud-based services. Unfortunately, it also poses a privacy concern. Users attributes should not be linked to the users identity and spread across different organizations. To tackle this issue, several solutions have been proposed such as Privacy Attribute-Based Credentials (Privacy-ABCs), which support pseudonym-based authentication with embedded attributes. Privacy-ABCs allow users to establish anonymous accounts with service providers while hiding the identity of the user under a pseudonym. However, Privacy-ABCs require the selective disclosure of the attribute values towards service providers. Other schemes such as Attribute Base Signatures (ABS) and mesh signatures do not require the disclosure of attributes; unfortunately, these schemes do not cater for pseudonym generation in their construction, and hence cannot be used to establish anonymous accounts. In this paper, we propose a pseudonym-based signature scheme that enables unlinkable pseudonym self-generation with embedded attributes, similarly to Privacy-ABCs, and integrates a secret sharing scheme in a similar fashion to ABS and mesh signature schemes for attribute verification. Our proposed scheme also provides verifiable collusion, enabling users to share attributes according to the service providers policies. more...

One reason for the popularity of Bitcoin is due to its anonymity. Although several heuristics have been used to break the anonymity, new approaches are proposed to enhance its anonymity at the same time. One of them is the mixing service. Unfortunately, mixing services have been abused to facilitate criminal activities, e.g., money laundering. As such, there is an urgent need to systematically understand Bitcoin mixing services. In this paper, we take the first step to understand state-of-the-art Bitcoin mixing services. Specifically, we propose a generic abstraction model for mixing services and observe that there are two mixing mechanisms in the wild, i.e. {swapping} and {obfuscating}. Based on this model, we conduct a transaction-based analysis and successfully reveal the mixing mechanisms of four representative services. Besides, we propose a method to identify mixing transactions that leverage the obfuscating mechanism. The proposed approach is able to identify over $92$\% of the mixing transactions. Based on identified transactions, we then estimate the profit of mixing services and provide a case study of tracing the money flow of stolen Bitcoins. more...

TheChain is a solution to many problems such as monopoly, heavy state transition, and security vulnerabilities. TheChain solves these problems by introducing the intersection of regions as an incentive before allowing validators to nest a client directory. Intersecting their operating territories forces them to keep a watch over each other. The definition of privacy can take many forms, starting from the right to be forgotten beside being away from public attention. Although the pseudonymity of the user within the network can enhance the user's privacy, several pieces of research have studied the techniques to take advantage of the network structure to identify the users of pseudonyms. Moreover, two models have been used to record the updated exchange of values within the blockchain system, which are the unspent transaction output (UTXO) and the balance model. The UTXO suffers from duplication of information and the balance model suffers from having a single point of entry. This paper introduces TheCoin model that defines the protocol of the exchange of valuable datum within TheChain system. The solution has introduced a novel approach of initiating the transaction from the receiver side by taking advantage of mobile agents empowering a topology hiding to the network. Billing within the platform has been introduced to allow advanced contractual logic to be adopted into the system on the information level. Moreover, traceable fuzziness has been used to eliminate duplication. The paper presents an evaluation of the TheCoin model in terms of system security, block size, and search performance. more...

International audience; Blockchain has been praised for its capacity to hold data in a decentralized and tamper-proof way. It also supports the execution of code through blockchain’s smart contracts, adding automation of actions to the network with high trustability. However, as smart contracts are visible by anybody on the network, the business data and logic may be at risk, thus companies could be reluctant to use such technology. This paper aims to propose a pattern that allows the execution of automatable legal contract clauses, where its execution states are stored in an on-chain smart-contract and the logic needed to enforce it wraps it off-chain. An engine completes this pattern by running a business process that corresponds to the legal contract. We then propose a pattern-based solution based on a real-life use case: transportation of refrigerated goods. We argue that this pattern guarantees companies pseudonymity and data confidentiality while ensuring that an audit trail can be reconstituted through the blockchain smart-contract to identify misbehavior or errors. This paper paves the way for a future possible implementation of the solution described, as well as its evaluation. more...

Vehicular communications disclose rich information about the vehicles and their whereabouts. Pseudonymous authentication secures communication while enhancing user privacy. To enhance location privacy, cryptographic mix-zones were proposed to facilitate vehicles covertly transition to new ephemeral credentials. The resilience to (syntactic and semantic) pseudonym linking (attacks) highly depends on the geometry of the mix-zones, mobility patterns, vehicle density, and arrival rates. We introduce a tracking algorithm for linking pseudonyms before and after a cryptographically protected mix-zone. Our experimental results show that an eavesdropper, leveraging standardized vehicular communication messages and road layout, could successfully link 73% of pseudonyms during non-rush hours and 62% of pseudonyms during rush hours after vehicles change their pseudonyms in a mix-zone. To mitigate such inference attacks, we present a novel cooperative mix-zone scheme that enhances user privacy regardless of the vehicle mobility patterns, vehicle density, and arrival rate to the mix-zone. A subset of vehicles, termed relaying vehicles, are selected to be responsible for emulating non-existing vehicles. Such vehicles cooperatively disseminate decoy traffic without affecting safety-critical operations: with 50% of vehicles as relaying vehicles, the probability of linking pseudonyms (for the entire interval) drops from 68% to 18%. On average, this imposes 28 ms extra computation overhead, per second, on the Roadside Units (RSUs) and 4.67 ms extra computation overhead, per second, on the (relaying) vehicle side; it also introduces 1.46 KB/sec extra communication overhead by (relaying) vehicles and 45 KB/sec by RSUs for the dissemination of decoy traffic. Thus, user privacy is enhanced at the cost of low computation and communication overhead., Comment: 19 pages, 15 Figures, IEEE Internet of Things Journal more...

The evolution of data storage paradigms from centralized systems to hire and use model based cloud computing are the recent transition and developments in business, retail, government and healthcare organizations. The cloud is deceptive and vulnerable to data leakage attacks during transit or at passive state. The recent malware attacks are live examples to describe data breach instances. To protect the privacy and enhance data hiding for sensitive data pertain to healthcare data is at jeopardize. The proposed QABA algorithm enhances privacy and reduces the uniqueness of records to camouflage sensitive data from re-identity disclosure attacks. The experiments conducted on standard dataset and evaluated the privacy. The proposed algorithm exhibit efficiency and robustness in implementing pseudonymity. more...

Vehicular ad hoc networks (VANETs) are becoming the most promising research topic in intelligent transportation systems, because they provide information to deliver comfort and safety to both drivers and passengers. However, unique characteristics of VANETs make security, privacy, and trust management challenging issues in VANETs’ design. This survey article starts with the necessary background of VANETs, followed by a brief treatment of main security services, which have been well studied in other fields. We then focus on an in-depth review of anonymous authentication schemes implemented by five pseudonymity mechanisms. Because of the predictable dynamics of vehicles, anonymity is necessary but not sufficient to thwart tracking an attack that aims at the drivers’ location profiles. Thus, several location privacy protection mechanisms based on pseudonymity are elaborated to further protect the vehicles’ privacy and guarantee the quality of location-based services simultaneously. We also give a comprehensive analysis on various trust management models in VANETs. Finally, considering that current and near-future applications in VANETs are evaluated by simulation, we give a much-needed update on the latest mobility and network simulators as well as the integrated simulation platforms. In sum, this paper is carefully positioned to avoid overlap with existing surveys by filling the gaps and reporting the latest advances in VANETs while keeping it self-explained. more...

The decentralized digital currency Bitcoin presents an anonymous alternative to the centralized banking system and indeed enjoys widespread and increasing adoption. Recent works, however, show how users can be reidentified and their payments linked based on Bitcoins most central element, the blockchain, a public ledger of all transactions. Thus, many regard Bitcoins central promise of financial privacy as broken.In this paper, we propose CoinParty, an efficient decentralized mixing service that allows users to reestablish their financial privacy in Bitcoin and related cryptocurrencies. CoinParty, through a novel combination of decryption mixnets with threshold signatures, takes a unique place in the design space of mixing services, combining the advantages of previously proposed centralized and decentralized mixing services in one system. Our prototype implementation of CoinParty scales to large numbers of users and achieves anonymity sets by orders of magnitude higher than related work as we quantify by analyzing transactions in the actual Bitcoin blockchain. CoinParty can easily be deployed by any individual group of users, i.e.,independent of any third parties, or provided as a commercial or voluntary service, e.g.,as a community service by privacy-aware organizations. We present ideal properties for mixing of digital currencies.We propose a novel efficient decentralized mixing service for Bitcoin.A novel oblivious shuffle protocol improves resilience against malicious attackers.Use of threshold cryptography increases anonymity and enables deniability.The system is usable, scalable and compatible with Bitcoin/other digital currencies. more...

Private set intersection (PSI) allows two parties to compute the intersection of their sets without revealing any information about items that are not in the intersection. It is one of the best studied applications of secure computation and many PSI protocols have been proposed. However, the variety of existing PSI protocols makes it difficult to identify the solution that performs best in a respective scenario, especially since they were not compared in the same setting. In addition, existing PSI protocols are several orders of magnitude slower than an insecure naïve hashing solution, which is used in practice. In this article, we review the progress made on PSI protocols and give an overview of existing protocols in various security models. We then focus on PSI protocols that are secure against semi-honest adversaries and take advantage of the most recent efficiency improvements in Oblivious Transfer (OT) extension, propose significant optimizations to previous PSI protocols, and suggest a new PSI protocol whose runtime is superior to that of existing protocols. We compare the performance of the protocols, both theoretically and experimentally, by implementing all protocols on the same platform, give recommendations on which protocol to use in a particular setting, and evaluate the progress on PSI protocols by comparing them to the currently employed insecure naïve hashing protocol. We demonstrate the feasibility of our new PSI protocol by processing two sets with a billion elements each. more...

Private communication detection (PCD) is a traffic-analysis technique whereby an ordinary user of a communication network exploits side channels in end-point devices to observe the busy/idle activity status of targeted users. Correlations of users’ activity status allows collection of communication records that reveal private relationships. PCD techniques have been demonstrated for a number of communication technologies, such as Wi-Fi and VoIP, and their effectiveness shown even when the communication network is private; i.e., it provides content confidentiality, flow anonymity, and user pseudonymity. In this paper, we present a mathematical model of PCD that captures the activity status of two targets in a private VoIP network, including the probing process of an attacker that aims to breach their communication anonymity. Using this model, we a) develop fundamental bounds on PCD accuracy; b) measure the anonymity leakage in terms of the amount of call record information obtained in an attack; and c) provide performance guarantees and compare the efficacy of different PCD countermeasures, such as resource randomization and use of firewalls. more...

Vehicle-to-everything (V2X) has been regarded as an important enabling technology for future intelligent transportation systems (ITS). Safety-critical applications in V2X require authentication of nodes and messages, and also need to preserve the privacy of vehicles. Pseudonymity plays an important role in V2X communication by satisfying both security and privacy requirements. In this paper, we analyze the weaknesses of a recent relevant work named Issue First Activate Later (IFAL), which is the leading European candidate for V2X. We then propose a novel lightweight, secure and privacy-preserving pseudonym changing scheme. Through the security analysis, we show that the proposed scheme achieves the asynchronous key agreement, and realizes both robust forward secrecy and backward secrecy while keeping security functionalities of IFAL. Furthermore, the performance analysis is conducted on Arduino Mega 2560 to illustrate that the proposed scheme is feasible and practical. © 2014 xxxxxxxx. Hosting by Elsevier B.V. All rights reserved. more...

This article traces the development of Internet communication by examining online names and pseudonyms. I argue that choosing a username, as the first interaction a person has with a platform, sets... more...

With the rapid increase of threats on the Internet, people are continuously seeking privacy and anonymity. Services such as Bitcoin and Tor were introduced to provide anonymity for online transactions and Web browsing. Due to its pseudonymity model, Bitcoin lacks retroactive operational security, which means historical pieces of information could be used to identify a certain user. We investigate the feasibility of deanonymizing users of Tor hidden services who rely on Bitcoin as a payment method by exploiting public information leaked from online social networks, the Blockchain, and onion websites. This, for example, allows an adversary to link a user with @alice Twitter address to a Tor hidden service with private.onion address by finding at least one past transaction in the Blockchain that involves their publicly declared Bitcoin addresses. To demonstrate the feasibility of this deanonymization attack, we carried out a real-world experiment simulating a passive, limited adversary. We crawled 1.5K hidden services and collected 88 unique Bitcoin addresses. We then crawled 5B tweets and 1M BitcoinTalk forum pages and collected 4.2K and 41K unique Bitcoin addresses, respectively. Each user address was associated with an online identity along with its public profile information. By analyzing the transactions in the Blockchain, we were able to link 125 unique users to 20 Tor hidden services, including sensitive ones, such as The Pirate Bay and Silk Road. We also analyzed two case studies in detail to demonstrate the implications of the resulting information leakage on user anonymity. In particular, we confirm that Bitcoin addresses should always be considered exploitable, as they can be used to deanonymize users retroactively. This is especially important for Tor hidden service users who actively seek and expect privacy and anonymity. more...

Cryptocurrencies are defined as anonymous digital currencies. It is widely assumed that the real-world identities of the persons who engage in cryptocurrency transactions are secret and will remain secret. Digital signatures serve as identities of the parties involved in cryptocurrency transactions. They are essentially composed of a pair of keys, the secret key and the public key, which are used for signing transactions. These keys are issued as many times as needed thus creating different identities for the same person. Since transactions are recorded with these pseudo names, it is thought that the real identities may not be linked to the transactions. Unlinkability has to be achieved for complete anonymity. However, recent studies show that real-life identities can be linked to addresses of these cryptocurrencies and transactions which use them. Therefore, it is safe to say that most cryptocurrencies are pseudonymous rather than anonymous. In this chapter, the problem with anonymity and its implications in accounting will be discussed. In addition to this, protocols and services, which make it harder or even impossible to link addresses and transactions to their senders and recipients, will be reviewed. more...

Voting is a very important issue that can be beneficial in terms of choosing the right leader in an election. A good leader can bring prosperity to a country and also can lead the country in the right direction every time. However, elections are surrounded by ballot forgery, coercion, and multiple voting issues. Moreover, while giving votes, a person has to wait in a long queue and it is a very time-consuming process. Blockchain is a distributed database in which data are shared with the participant of the node and each participant holds the same copy of the data. Blockchain has properties like transparency, pseudonymity, and data integrity. In this paper, a fully decentralized e-voting system based on blockchain technology is proposed. This protocol utilizes smart contracts in the e-voting system to deal with security issues, accuracy, and voters’ privacy during the vote. The protocol results in a transparent, non-editable, and independently verifiable procedure. The protocol discards all the intended fraudulent activities occurring during the election process by removing the least participation of the third party. Both transparency and coercion are obtained at the same time. more...

For years now the hype surrounding block-chain as a new and more decentralized architecture to facilitate transactions has led people to search for cases of application for this emerging technology. Before thematizing the hype that has been propelling block-chain on the global stage, it is useful to mention the main novelty that block-chain brings: authentication of uniqueness of data in digital settings or “native authentication,” i.e. without relying on an external/non-digital intermediary. Without this property, it could not be used for digital currency, which, of course, must be unforgeable. Other relevant, and related properties are: decentralization (even if no unique guarantor is often substituted by clusters of miners), immutability (records cannot be deleted), auditability (mathematically provable), and pseudonymity (via key-pair identification). more...

The recent SARS-CoV-2 pandemic gave rise to management approaches using mobile apps for contact tracing. The corresponding apps track individuals and their interactions, to facilitate alerting users of potential infections well before they become infectious themselves. Naive implementation obviously jeopardizes the privacy of health conditions, location, activities, and social interaction of its users. A number of protocol designs for colocation tracking have already been developed, most of which claim to function in a privacy preserving manner. However, despite claims such as “GDPR compliance”, “anonymity”, “pseudonymity” or other forms of “privacy”, the authors of these designs usually neglect to precisely define what they (aim to) protect. We make a first step towards formally defining the privacy notions of proximity tracing services, especially with regards to the health, (co-)location, and social interaction of their users. We also give a high-level intuition of which protection the most prominent proposals likely can and cannot achieve. This initial overview indicates that all proposals include some centralized services, and none protects identity and (co-)locations of infected users perfectly from both other users and the service provider. more...

There are a large number of movies, TV series, novels, short stories, and even plays about cybersecurity and, in particular, about hackers. Some are good, some are so-so, most are frankly quite bad. Some are realistic, most make cybersecurity experts cringe. In this paper, I discuss how a number of basic cybersecurity notions (and even several advanced ones) can be explained with the help of some well-known popular movies and other artworks, and some perhaps less obvious ones. I focus in particular on anonymity, pseudonymity, and authentication, but similar explanations can be given for other security properties, for the algorithms, protocols, and systems that have been developed to achieve such properties, and for the vulnerabilities and attacks that they suffer from. more...

A bitcoin address is required for trading and maintaining pseudonymity for the owner. By exploiting this pseudonymity, various illegal activities are conducted around the world. To detect and deter illegal transactions, this paper proposes a method of identifying the characteristics of bitcoin addresses related to illegal transactions. We extracted 80 features from bitcoin transactions. Using machine-learning techniques, we successfully categorized addresses involved with illegal activities with a \(\sim \)84% accuracy. We also examined the address features most affecting classification performance and compared two machine-learning models. By applying the majority voting to the classification results of bitcoin addresses associated with a particular transaction, it will be possible to determine which category the transaction belongs to. more...

Identity anonymization is believed to be a common mechanism to protect users' privacy in a public review platform, as each user's unique identifier is removed to ensure pseudonymity and unlinkability. However, the usefulness of the mechanism is not explicit, i.e., whether it is possible for an adversary to link anonymous reviews from the same user has not been well studied. In this paper, we attempt to explore this issue by means of machine learning techniques. Specifically, we first extract major features from anonymous reviews and propose some adaptive metrics to measure their effectiveness. Then, we exploit these features and several machine learning methods to link the anonymous reviews created by the same user in a real- world dataset. Considering that different adversaries has different background knowledge, both supervised and unsupervised methods, such as random forest and hierarchical agglomerative clustering, are designed and utilized to perform linkability attacks. The simulation results demonstrate that the supervised methods have a good performance, i.e., almost 40% anonymous reviews can be accurately linked to users if an adversary has the background knowledge. The unsupervised methods, compared with supervised methods, has a bad performance, i.e., it is difficult for an adversary without the background knowledge to link anonymous reviews with a high probability. more...

This chapter considers another claimed benefit of cryptomarkets and the darknet generally, the feature that is seen as most threatening: anonymity. This chapter argues that anonymity is not the dangerous quality it appears to be. Most malicious activities do not take place using a darknet-provided cloak of anonymity. Communities can benefit from anonymity and pseudonymity. In any case, anonymity is neither an inherent quality of the darknet nor the cryptomarkets. Anonymity must be produced by the user. Even then, anonymity is contingent and temporary. It is contingent on the ability of the user to hide in the crowd, and it is temporary because of the growing capacity for various organisations to de-anonymising using blockchain analysis and other kinds of machine-learning and standard investigation techniques. more...

Assuring security and privacy is one of the key issues affecting the Internet of Things (IoT), mostly due to its distributed nature. Therefore, for the IoT to thrive, this problem needs to be tackled and solved. This paper describes a security-oriented architecture for managing IoT deployments. Our main goal was to deal with a fine-grained control in the access to IoT data and devices, to prevent devices from being manipulated by attackers and to avoid information leaking from IoT devices to unauthorized recipients. The access control is split: the management of authentication and access control policies is centered on special components (Authentication, Authorization, and Accounting Controllers), which can be distributed or centralized, and the actual enforcement of access control decisions happens on the entities that stay in the path to the IoT devices (Gateways and Device Drivers). The authentication in the entire system uses asymmetric cryptography and pre-distributed unique identifiers derived from public keys; no Public Key Infrastructure (PKI) is used. A Kerberos-like ticket-based approach is used to establish secure sessions. more...

It is well understood that the huge volumes of data captured in recent years have the potential to underpin significant research developments in many fields. But, to realise these benefits, all relevant parties must be comfortable with how this data is shared. At the heart of this is the notion of privacy — which is recognised as being somewhat difficult to define. Previous authors have shown how privacy notions such as anonymity, unlinkability and pseudonymity might be combined into a single formal framework. We use and extend this work by defining privacy games for individual and group privacy within distributed environments. For each privacy notion, we formulate a game that an adversary has to win in order to break the notion. Via these games, we aim to clarify understanding of, and relationships between, different privacy notions; we also aim to give an unambiguous understanding of adversarial actions. Additionally, we extend previous work via the notion of unobservability. more...

International audience; In the near future, vehicles will communicate with their environment by broadcasting Vehicle to everything (V2x) messages over the vehicular network (IEEE 802.11p). The exchanged messages contain data related to driver's privacy. As the laws in Europe require the privacy protection, the solution is to use pseudonym identities (certificates) in the communication. However, the use of these certificates can create new vulnera-bilities that must be taken into account. In this paper, we do a state of art on the existing vulnerabilities, we applied the TVRA method and propose new vulnerabilities. Finally, we propose new countermeasures that could be implemented. more...

International audience; As the Internet of Things (IoT) starts providing meaningful solutions in multiple domains, users expect to take full advantage of the features and benefits of smart devices, but not at the cost of privacy loss. They want to keep control over their own data, e.g. through consent and authorization management. This paper proposes a lightweight privacy-preserving solution for managing user's consent relative to specific purposes (obligations). The originality of our proposal is manyfold. First, the consent is issued cryptographically by the user over some consented specific purposes, thus it protects both the user and the service provider against possible repudiations. Second, the users' privacy is preserved as the protocol supports untraceability over the channel, and pseudonymity with regard to the service provider. Pseudonyms are fully managed by the users themselves through suitable use of Hierarchical Identity-Based Signature (HIBS). Third, the solution is lightweight in terms of communication and computation, thus making it suitable for IoT resource constrained environments. Fourth, an illustrative car-sharing use case is presented where users are able to personalize their driving experience. Fifth, a formal validation of the protocol is provided with the AVISPA tool, along with an informal security and privacy analysis. Sixth, our approach addresses part of the European General Data Protection Regulation (GDPR), as it supports user consent management and helps providers with handling accountability. more...

Bitcoin ecosystem is supposed to be anonymous and untraceable. Nonetheless, Bitcoin offers weak anonymity in practice. The linkable pseudonymity of Bitcoin system raises privacy concerns for users. There are inputs and outputs of cryptocurrencies that link to Bitcoin public addresses. This is vulnerable to possible linkability and traceability of users’ identity, that can lead to information leakage. Input and output addresses of transactions miss unlinkability in Bitcoin. Several attempts to solve unlinkability and untraceability of users’ transactions found not to satisfy all requirements of a practical anonymity for users to transact business with bitcoins securely and privately. In this paper, the authors focused on preserving identity and transactional behaviour of users in bitcoin cryptocurrency transactions. A secure privacy-preserving scheme is presented. The paper incorporates bilinear pairing, elliptic curve (ECC), ring signature and Zero Knowledge Proof to curb users’ privacy breaches. The authors theoretically analysed, and evaluated proposed scheme, which is proven secure and robust to implement for preserving users’ privacy in bitcoin transactions. The proposal adds a compatible privacy-preserving layer on top of the Bitcoin blockchain, and consistent with the current Bitcoin architecture without offering any modification. more...

Part 3: Selected Papers; International audience; To implement the principle of Privacy by Design mentioned in the European General Data Protection Regulation one important measurement stated there is pseudonymisation. Pseudonymous data is widely used in medical applications and is investigated e.g. for vehicular ad-hoc networks and Smart Grid. The concepts used there address a broad range of important aspects and are therefore often specific and complex. Some privacy patterns are already addressing pseudonymity, but they are mostly abstract or rather very specific. This paper proposes privacy patterns for the development of pseudonymity concepts based on the analysis of pseudonymity solutions in use cases. more...

Since the creation of Bitcoin, transaction tracking is one of the prominent means for following the movement of Bitcoins involved in illegal activities. Although every Bitcoin transaction is recorded in the blockchain ledger, which is transparent for anyone to observe and analyse, Bitcoin's pseudonymity system and transaction obscuring techniques still allow criminals to disguise their transaction trail. While there have been a few attempts to develop tracking methods, there is no accepted evaluation method to measure their accuracy. Therefore, this paper introduces a metrics-based evaluation framework to investigate the performance indicators of a theft transaction tracking. We use this framework to investigate strategies for transaction tracking. This paper also introduces two new tainting methods and an address profiling approach. We run an experiment to compare the accuracy of tainting strategies using data from real Bitcoin theft and a set of controls. more...

A ride-hailing service, where passengers choose the origin and destination of their ride, preserves location privacy if the origin and destination of the ride are not revealed to anyone other than the driver. Pseudonymity means that the driver and the passenger use a pseudonym and do not reveal their true identity to each other. The service is trusted if a dishonest passenger cannot use the service without paying, and a driver must provide the service to get paid. In this paper, we introduce cryptotrasnport---a ride-hailing service powered by cryptocurrency and blockchain---and we show that it can preserve privacy, pseudonymity, and trust, simultaneously. Furthermore, by using blockchain technology, cryptotransport matches riders with vehicles in a decentralized fashion, without relying on any company or organization to manage the system. more...

Anonymity promotes free speech by protecting the identity of people who might otherwise face negative consequences for expressing their ideas. Wrongdoers, however, often abuse this invisibility cloak. Defenders of anonymity online emphasise its value in advancing public debate and safeguarding political dissension. Critics emphasise the need for identifiability in order to achieve accountability for wrongdoers such as trolls. The problematic tension between anonymity and identifiability online lies in the desirability of having low costs (no repercussions) for desirable speech and high costs (appropriate repercussions) for undesirable speech. If we practice either full anonymity or identifiability, we end up having either low or high costs in all online contexts and for all kinds of speech. I argue that free speech is compatible with instituting costs in the form of repercussions and penalties for controversial and unacceptable speech. Costs can minimise the risks of anonymity by providing a reasonable degree of accountability. Pseudonymity is a tool that can help us regulate those costs while furthering free speech. This article argues that, in order to redesign the Internet to better serve free speech, we should shape much of it to resemble an online masquerade. more...

In this paper, we introduce the first geolocation inference approach for reddit, a social media platform where user pseudonymity has thus far made supervised demographic inference difficult to implement and validate. In particular, we design a text-based heuristic schema to generate ground truth location labels for reddit users in the absence of explicitly geotagged data. After evaluating the accuracy of our labeling procedure, we train and test several geolocation inference models across our reddit data set and three benchmark Twitter geolocation data sets. Ultimately, we show that geolocation models trained and applied on the same domain substantially outperform models attempting to transfer training data across domains, even more so on reddit where platform-specific interest-group metadata can be used to improve inferences., Accepted to the EMNLP Workshop on Noisy User-generated Text (W-NUT). Brussels, Belgium. November 1, 2018 more...

Previous contributions have established a framework of privacy games that supports the representation of syntactic privacy notions such as anonymity, unlinkability, pseudonymity and unobservablility in the form of games. The intention is that, via such abstractions, the understanding of, and relationships between, privacy notions can be clarified. Further, an unambiguous understanding of adversarial actions is given. Yet, without any practical context, the potential benefits of these notions and games may be incomprehensible to system designers and software developers. We utilise these games in a case study based on recommender systems. Consequently, we show that the game-based definitions have the potential to interconnect privacy implications and can be utilised to reason about privacy. more...

Blockchain technology though originally designed for keeping financial ledgers, recently has found applications in many different fields including healthcare. Sharing healthcare data for research purposes will boost research innovation in this area. That being said, healthcare data sharing raises many privacy and security issues for the Patients who share their data. In this work, we present the potential of Blockchain technology to facilitate (i) private and auditable healthcare data sharing and (ii) healthcare data access permission handling by proposing a blockchain-based system architecture design. more...

Soon after its introduction in 2009, Bitcoin has been adopted by cyber-criminals, which rely on its pseudonymity to implement virtually untraceable scams. One of the typical scams that operate on Bitcoin are the so-called Ponzi schemes. These are fraudulent investments which repay users with the funds invested by new users that join the scheme, and implode when it is no longer possible to find new investments. Despite being illegal in many countries, Ponzi schemes are now proliferating on Bitcoin, and they keep alluring new victims, who are plundered of millions of dollars. We apply data mining techniques to detect Bitcoin addresses related to Ponzi schemes. Our starting point is a dataset of features of real-world Ponzi schemes, that we construct by analysing, on the Bitcoin blockchain, the transactions used to perform the scams. We use this dataset to experiment with various machine learning algorithms, and we assess their effectiveness through standard validation protocols and performance metrics. The best of the classifiers we have experimented can identify most of the Ponzi schemes in the dataset, with a low number of false positives. more...

Names are important atomic information carriers in unstructured text. Matching names that refer to the same entities is an important issue in text analysis and a key component in many real world applications. Generally referred to as entity linking, it is defined as a task that aligns a name mentioned in free text to its corresponding entry in a Knowledge Base (KB). The difficulty of the task lies in the many-to-many correspondence between names and entities, causing the pseudonymity and polysemy issues. Existing work usually focuses on resolving polysemy by aggregating large numbers of loosely arranged features in supervised learning frameworks, with very few targeting the pseudonymity or both issues with the same depth. In this work, we tackle both issues by comprehensive modeling of an entity's name and context: we tackle the pseudonymity by modeling name variants on the query name and the KB title; and polysemy by modeling heterogeneous aspects of the query and KB context. Specially, we harness entity coreferences within query and KB documents together with the external alias resources for modeling name variants, and further use the name variants to identify focused context. Moreover, we propose a recall-boosted retrieval method for efficient candidate entity generation. Experimental results show that our proposed approach outperforms the state-of-the-art systems on the benchmark data. more...

Inter-vehicle communications disclose rich information about vehicle whereabouts. Pseudonymous authentication secures communication while enhancing user privacy thanks to a set of anonymized certificates, termed pseudonyms. Vehicles switch the pseudonyms (and the corresponding private key) frequently; we term this pseudonym transition process. However, exactly because vehicles can in principle change their pseudonyms asynchronously, an adversary that eavesdrops (pseudonymously) signed messages, could link pseudonyms based on the times of pseudonym transition processes. In this poster, we show how one can link pseudonyms of a given vehicle by simply looking at the timing information of pseudonym transition processes. We also propose "mix-zone everywhere": time-aligned pseudonyms are issued for all vehicles to facilitate synchronous pseudonym update; as a result, all vehicles update their pseudonyms simultaneously, thus achieving higher user privacy protection. QC 20180717 more...

Part 7: Mobility and Privacy; International audience; The potential of digitalisation in healthcare based on mobile health, so-called mHealth applications, is considerable. On the other hand these solutions incorporate huge privacy risks. In the context of goal management training, a neuropsychological training used for the cognitive rehabilitation of executive dysfunction after a brain injury, the use of mHealth applications is considered. Privacy requirements of this scenario are modelled based on methodologies as privacy protection goals and privacy design strategies. Measures to realize the requirements are proposed and discussed in the context of a study. The focus in privacy engineering is on pseudonymity of patients, data minimization and transparency for patients. more...