Bitcoin is the most widely known distributed, peer-to-peer payment network without existence of a central authority. In Bitcoin, users do not use real names; instead, pseudonyms are used. Managing and verifying transactions and issuing of bitcoins are performed collectively by peers in the network. Since pseudonyms are used without providing any identity, it is perceived that Bitcoin provides anonymity. However, it is one of the most transparent payment networks since all transactions are publicly announced. Blockchain, which is the public ledger of Bitcoin, includes all transactions to prevent double-spending and to provide integrity. By using data in the blockchain, flow of bitcoins between transactions can be observed and activities of the users can be traced. When the implications obtained from the blockchain are combined with external data, identity and profile of a user can be revealed. This possibility has undesirable effects such as spending history of a user becomes accessible to other people, or cash flow of a merchant becomes exposed to competitors. There are several proposals as extensions or alternatives to Bitcoin, which improve anonymity and privacy. This survey presents an overview and detailed investigation of anonymity and privacy in Bitcoin-like digital cash systems. We examine the studies in the literature/Web in two major categories: 1) analyses of anonymity and privacy in Bitcoin and 2) extensions and alternatives to Bitcoin, which improve anonymity and privacy. We list and describe methods and outcomes for both categories and group studies according to these methods and outcomes. We also present relationships between outcomes of analyses and the improvement methods. We compare performances of the methods and show relationships between the proposals. Moreover, we present guidelines for designing an anonymity/privacy improvement and discuss future research directions.
The blockchain is a technology designed to verify whether online financial transaction data has been tampered with or not. It has been proven to be reliable as it has been introduced into various fields requiring reliability as well as financial institutions around the world. As the introduction of blockchain technology is expected to bring about a lot of changes in the public service sector, technology adoption is also being reviewed in many countries around the world. In particular, the introduction of blockchain technology in the online voting sector has the advantage of enhancing the reliability, transparency and efficiency of voting. Therefore, in this paper, we analyze the institutional and technical problems that may occur when applying the blockchain technology to online voting system, and suggest ways of using it.
As in 2009 the first encrypted electronic currency Bitcoin is introduced, the block chain technology has received attention. Bitcoin is a currency issued without a trusted third party, in peer-to-peer (Peer-to-Peer) network and gives a guarantee of the reliability of money transactions, ensures the integrity of transactions. There is a back end-technique called block-chain that guarantees these without trusted third party. Block chain is a public ledger that all nodes to verify transactions and maintain integrity with the same ledger. Block chain technology applies not only electronic currency but also in various industries such as contract document integrity, cloud storage service, internet of thigns, supply chain for transaction integrity. However, there are problems to be solved if the bitcoin block chain consensus rule is applied to these industry. First, there is problem of low transaction throughput and block generation rate by an inefficient consensus rule. Second, There is problem of tampered block broadcast with non-dependency (internet of things data, food history data) transactions when applying the block chain consensus rule, which is proof-of-work of bitcoin's competitive system.
Bitcoin is promoted as decentralized cryptocurrency by using pseudonym to achieve anonymity. Unfortunately, numerous seminal works have demonstrated that Bitcoin only offers weak anonymity in practice. Indeed, the practical technologies of clustering and flow analysis are much effective for tracing Bitcoin transaction and thereby revealing the owner involved. Otherwise said, user's privacy in Bitcoin has been sadly degenerated to be linkable. In this paper, we propose a completely decentralized scheme that can provide full anonymity in Bitcoin. The idea behind the output is to exploit a secure escrow address, which is consensual by all the involved users. The escrow address is generated from the trick of cryptographically secure distributed key generation and can then be used for mixing transactions in Bitcoin. Our protocol is secure against malicious adversaries. The users can jointly perform the protocol and successfully accomplish the transaction without the help of any (trusted) third party and no extra fees. Besides, our proposal is completely compatible with the current Bitcoin architecture.
Open access
Blockchain Technology Applications and Security
Internet Traffic Analysis and Secure E-voting
Advanced Steganography and Watermarking Techniques
As a recently proposed public key primitive, attribute-base encryption(ABE) divided into Ciphertext-policy ABE (CP-ABE) and Key-policy ABE (KP-ABE) is a highly promising tool for the management and protection of data. And Blockchain, as one of the core technologies of Bitcoin that is the most representative cryptocurrency, has received extensive attentions recently. Supervision and privacy protection are two difficulties in blockchain. In this paper, a new scheme combining blockchain and accountable CP-ABE is proposed. In this scheme, each change of the data is recorded on the blockchain. And the different permissions of access are realized through ABE. If a malicious user shares a decryption key illegally, it will be considered illegal. Similarly, if the authority generates a decryption key for any unauthorized user, it also will be considered illegal. This scheme allows any third party to publicly verify the identity of a decryption key. And it is achievable for an auditor to publicly audit whether a malicious user or the authority should be responsible for an exposed decryption key, and the key abuser cannot deny it. At last this scheme is applied to the management of electronic documents.
The purpose of this paper is to explore applications of blockchain technology related to demand side management of smart grid and to present an example that blockchain is used to facilitate machine-to-machine (M2M) interaction and frame an electricity market in the context of demand request. We use blockchain technology to record data derived from power flow calculation model and electricity price customization, and use smart contract to store transaction data and transfer assets automatically. Firstly, we establish a power flow calculation for microgrid operation system of 34 node master-slave control island, and the power flow is calculated and an optimal generator work adjustment is used. Then, according to the price customization, the participation mode of priced demand response is acquired. The presented scenario includes that a power management system and a generator which can actively adjust the power generation trading with each other over a blockchain. According to flow calculation and price customization, power management system generate smart contracts automatically. The final is that two sides complete the transaction and the load state of grid has been adjusted. This work contributes a proof-of-concept implementation of the scenario. This example verifies the feasibility of the method.
Safdar Hussain Shaheen, Muhammad Yousaf, Mudassar Jalil
In this article, a secure and verifiable electronic voting scheme is proposed. Encrypted votes are accumulated and prepared in the form of block on each electronic polling booth at the end of polling time. The resultant block from each electronic polling booth is distributed to the authorized nodes of group for temper proof block chaining that assures the internal verifiability. The external verifiability is attained through the redistribution of temper proof Blockchain ledger to the validated and authorized nodes of auditing group. The temper proof property of electoral data is achieved using an emerging Blockchain Technology. Whereas the secure data distribution in the form of temper proof blocks and ledger amongst the authenticated group members is accomplished through the cryptographically secure group oriented scenario. The individual and universal verifiability features in our proposed scheme make the electoral process transparent, reliable and verifiable.
Blockchain is one of the hottest topics in the discussion of technologies lately. As the enabling technology for Bitcoin, the pioneering cryptocurrency, blockchain is an append-only distributed ledger that is virtually impossible to attack given sufficient scale of participants. Hence, blockchain holds great promises as the fundamental technology to enable Internet-based electronic voting. However, Internet-based voting has additional requirements than monetary transactions. In this paper, we analyze these requirements, review existing proposed solutions, and outline possible improvements. Specifically, we propose to use live biometrics of the voter to perform secure and highly reliable remote authentication. We also propose a scheme to protect the secrecy of the ballots and eliminate the influence of votes already cast. Finally, we propose to impose a hierarchy to the voting infrastructure that aligns naturally with traditional voting, which enables parallel processing of multiple blockchains, to overcome the intrinsic scalability limitation of the blockchain technology.
Yi Liu, Ruilin Li, Xingtong Liu, Jian Wang · 6 authors
Bitcoin is a decentralized digital currency, widely used for its perceived anonymity property, and has surged in popularity in recent years. Bitcoin publishes the complete transaction history in a public ledger, under pseudonyms of users. This is an alternative way to prevent double-spending attack instead of central authority. Therefore, if pseudonyms of users are attached to their identities in real world, the anonymity of Bitcoin will be a serious vulnerability. It is necessary to enhance anonymity of Bitcoin by a coin mixing service or other modifications in Bitcoin protocol. But in a coin mixing service, the relationship among input and output addresses is not hidden from the mixing service provider. So the mixing server still has the ability to track the transaction records of Bitcoin users. To solve this problem, We present a new coin mixing scheme to ensure that the relationship between input and output addresses of any users is invisible for the mixing server. We make use of a ring signature algorithm to ensure that the mixing server can't distinguish specific transaction from all these addresses. The ring signature ensures that a signature is signed by one of its users in the ring and doesn't leak any information about who signed it. Furthermore, the scheme is fully compatible with existing Bitcoin protocol and easily to scale for large amount of users.
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Kentaroh Toyoda, Tomoaki Ohtsuki, P. Takis Mathiopoulos
Although Bitcoin is one of the most successful decentralized cryptocurrency, recent research has revealed that it can be used as fraudulent activities such as HYIP (High Yield Investment Program). To identify such undesired activities, it is important to obtain Bitcoin addresses related with fraud. So far, the identification of such activities is based upon relating Bitcoin addresses with graph mining procedures. In this paper, we follow a different approach for identifying Bitcoin addresses related with HYIP by analyzing transactions patterns. In particular, based on the individual inspection of HYIP activity in Bitcoin, we propose a number of features that can be extracted from transactions. In particular, a signed integer called pattern is assigned to each transaction and the frequency of each pattern is calculated as key features. By evaluating the classification performance with more than 1,500 labeled Bitcoin addresses, it is shown that about 83% of HYIP addresses are correctly classified while maintaining false positive rate less than 4.4%.
Cryptocurrency platforms such as Bitcoin and Ethereum have become more popular due to decentralized control and the promise of anonymity. Ethereum is particularly powerful due to its support for smart contracts which are implemented through Turing complete scripting languages and digital tokens that represent fungible tradable goods. It is necessary to understand whether de-anonymization is feasible to quantify the promise of anonymity. Cryptocurrencies are increasingly being used in online black markets like Silk Road and ransomware like CryptoLocker and WannaCry. In this paper, we propose a model for persisting transactions from Ethereum into a graph database, Neo4j. We propose leveraging graph compute or analytics against the transactions persisted into a graph database.
Bitcoin is digital assets infrastructure powering the first worldwide decentralized cryptocurrency of the same name. All history of Bitcoins owning and transferring (addresses and transactions) is available as a public ledger called blockchain. But real-world owners of addresses are not known in general. That's why Bitcoin is called pseudo-anonymous. However, some addresses can be grouped by their ownership using behavior patterns and publicly available information from off-chain sources. Blockchain-based common behavior pattern analysis (common spending and one-time change heuristics) is widely used for Bitcoin clustering as votes for addresses association, while offchain information (tags) is mostly used to verify results. In this paper, we propose to use off-chain information as votes for address separation and to consider it together with blockchain information during the clustering model construction step. Both blockchain and off-chain information are not reliable, and our approach aims to filter out errors in input data. The results of the study show the feasibility of a proposed approached for Bitcoin address clustering. It can be useful for the users to avoid insecure Bitcoin usage patterns and for the investigators to conduct a more advanced de-anonymizing analysis.
The wisdom of the crowd is a valuable asset in today’s society. It is not only important in predicting elections but also plays an essential role in marketing and the financial industry. Having a trustworthy source of opinion can make forecasts more accurate and markets predictable. Until now, a fundamental problem of surveys is the lack of incentives for participants to provide accurate information. Classical solutions like small monetary rewards or the chance of winning a prize are often not very attractive for participants. More attractive solutions, such as prediction markets, face the issue of illegality and are often unavailable. In this work, we present a solution that unites the advantages from classical polling and prediction markets via a customizable incentivization framework. Apart from predicting events, this framework can also be used to govern decentralized autonomous organizations.
Bitcoin owes its success to the fact that transactions are transparently recorded in the blockchain, a global public ledger that removes the need for trusted parties. Unfortunately, recording every transaction in the blockchain causes privacy, latency, and scalability issues. Building on recent proposals for "micropayment channels" --- two party associations that use the ledger only for dispute resolution --- we introduce techniques for constructing anonymous payment channels. Our proposals allow for secure, instantaneous and private payments that substantially reduce the storage burden on the payment network. Specifically, we introduce three channel proposals, including a technique that allows payments via untrusted intermediaries. We build a concrete implementation of our scheme and show that it can be deployed via a soft fork to existing anonymous currencies such as ZCash.
Bitcoin is a cryptocurrency attracting a lot of interest both from the general public and researchers. There is an ongoing debate on the question of users' anonymity: while the Bitcoin protocol has been designed to ensure that the activity of individual users could not be tracked, some methods have been proposed to partially bypass this limitation. In this article, we show how the Bitcoin transaction network can be studied using complex networks analysis techniques, and in particular how community detection can be efficiently used to re-identify multiple addresses belonging to a same user.
Daniel Augot, Hervé Chabanne, Olivier Clémot, William R. George
The most fundamental purpose of blockchain technology is to enable\npersistent, consistent, distributed storage of information. Increasingly common\nare authentication systems that leverage this property to allow users to carry\ntheir personal data on a device while a hash of this data is signed by a\ntrusted authority and then put on a blockchain to be compared against. For\ninstance, in 2015, MIT introduced a schema for the publication of their\nacademic certificates based on this principle. In this work, we propose a way\nfor users to obtain assured identities based on face-to-face proofing that can\nthen be validated against a record on a blockchain. Moreover, in order to\nprovide anonymity, instead of storing a hash, we make use of a scheme of Brands\nto store a commitment against which one can perform zero-knowledge proofs of\nidentity. We also enforce the confidentiality of the underlying data by letting\nusers control a secret of their own. We show how our schema can be implemented\non Bitcoin's blockchain and how to save bandwidth by grouping commitments using\nMerkle trees to minimize the number of Bitcoin transactions that need to be\nsent. Finally, we describe a system in which users can gain access to services\nthanks to the identity records of our proposal.\n
A mix-net is an important cryptographic tool in schemes requiring anonymity of messages, such as in secure e-voting and e-auction schemes. In this paper, we present a novel mix-net protocol which achieves stronger security and satisfies both public verifiability and sender verifiability. Our mix-net is constructed based on Wikström's scheme and strengthens its se-curity by introducing an improved key generation procedure and proposing a new method for constructing zero knowledge proof of secret shuffle. It is proved to be CCA-secure under the assumption of random oracle. Compared with previous mix-net schemes which are CCA-secure, the proposed protocol does not require any trusted center, and incurs fewer inter-actions between servers which resulting in a lower computation and communication complexity.
Bitcoin is a decentralized currency system that does not need any central authorities. All transactions issued by users have been recorded in the common ledger, called blockchain, which is shared by all users. In Bitcoin, an SPV (Simplified Payment Verification) client, which is a lightweight client that does not possess the entire blockchain, are developed for storage constrained devices such as a mobile phone. For an SPV client to check if there are transactions related to it, a Bloom filter where their Bitcoin addresses are involved is sent to a full client that possesses the entire blockchain. The full client only transfers transactions of which Bitcoin addresses are positive on the received Bloom filter. However, it is necessary to preserve the privacy of SPV clients when designing a Bloom filter because SPV clients' Bitcoin addresses will be identified by a full client with high probability. In this paper, we propose a privacy-preserving Bloom filter design for SPV clients based on γ-Deniability. γ-Deniability is a privacy metric that shows how much true positive Bitcoin addresses are hidden by the false positives in a Bloom filter. Furthermore, in order to design a Bloom Filter that satisfies a certain γ-Deniability, it is necessary to know the number of unique Bitcoin addresses that appear for the first time since the queried time. Based on our manual inspection, we propose to estimate it based on the linear regression. We show that our scheme achieves good estimation accuracy and γ through the simulation with a real Bitcoin blockchain.
Yukun Niu, Lingbo Wei, Chi Zhang, Jianqing Liu · 5 authors
Anonymous authentication can protect users' privacy and security when they access public Wi-Fi hotspots. However, most of the existing privacy-enhanced authentication schemes either do not consider users' accountability or they are inherently dependent on trusted third parties, and therefore are undeployable in practical settings. In this paper, we design and implement an access authentication scheme to simultaneously and efficiently provide anonymity and accountability without relying on any trusted third party. Our scheme is inspired by the recent progress of Bitcoin techniques such as Colored Coins and CoinShuffle protocol. We utilize the unmodified Bitcoin blockchain as the powerful platform to manage and determine ownership of access credentials in a peer-to-peer fashion and introduce a completely decentralized Bitcoin mixing protocol that allows users to anonymously exchange their access credentials offline. The verification path of access credentials is designed to support blacklisting and punishing misbehaving anonymous users. Our proposed scheme is compatible with the current Bitcoin system, and its effectiveness and feasibility in Wi-Fi hotspot access scenario are also demonstrated by security analysis and performance evaluation.
Transactive microgrids are emerging as a transformative solution for the problems faced by distribution system operators due to an increase in the use of distributed energy resources and a rapid acceleration in renewable energy generation, such as wind and solar power. Distributed ledgers have recently found widespread interest in this domain due to their ability to provide transactional integrity across decentralized computing nodes. However, the existing state of the art has not focused on the privacy preservation requirement of these energy systems -- the transaction level data can provide much greater insights into a prosumer's behavior compared to smart meter data. There are specific safety requirements in transactive microgrids to ensure the stability of the grid and to control the load. To fulfil these requirements, the distribution system operator needs transaction information from the grid, which poses a further challenge to the privacy-goals. This problem is made worse by requirement for off-blockchain communication in these networks. In this paper, we extend a recently developed trading workflow called PETra and describe our solution for communication and transactional anonymity.
Recently, blockchains have been gathering a lot of interest. Many applications can benefit from the advantages of blockchains. Nevertheless, applications with more restricted privacy or participation requirements cannot rely on public blockchains. First, the whole blockchain can be downloaded at any time, thus making the data available to the public. Second, anyone can deploy a node, join the blockchain network and take part in the consensus building process. Private and consortium blockchains promise to combine the advantages of blockchains with stricter requirements on the participating entities. This is also the reason for the comparably small number of nodes that store and extend those blockchains. However, by targeting specific nodes, an attacker can influence how consensuses are reached and possibly even halt the blockchain operation. To provide additional security to the blockchain nodes, ChainGuard utilizes SDN functionalities to filter network traffic, thus implementing a firewall for blockchain applications. ChainGuard communicates with the blockchain nodes it guards to determine which origin of the traffic is legitimate. Packets from illegitimate sources are intercepted and thus cannot have an effect on the blockchain. As is shown with experiments, ChainGuard provides access control functionality and can effectively mitigate flooding attacks from several sources at once.