The Bitcoin cryptocurrency records its transactions in a public log called the blockchain. Its security rests critically on the distributed protocol that maintains the blockchain, run by participants called miners. Conventional wisdom asserts that the mining protocol is incentive-compatible and secure against colluding minority groups, that is, it incentivizes miners to follow the protocol as prescribed. We show that the Bitcoin mining protocol is not incentive-compatible. We present an attack with which colluding miners' revenue is larger than their fair share. The attack can have significant consequences for Bitcoin: Rational miners will prefer to join the attackers, and the colluding group will increase in size until it becomes a majority. At this point, the Bitcoin system ceases to be a decentralized currency. Unless certain assumptions are made, selfish mining may be feasible for any coalition size of colluding miners. We propose a practical modification to the Bitcoin protocol that protects Bitcoin in the general case. It prohibits selfish mining by a coalition that command less than 1/4 of the resources. This threshold is lower than the wrongly assumed 1/2 bound, but better than the current reality where a coalition of any size can compromise the system.
Tooba Faisal, Nicolas T. Courtois, Antoaneta Serguieva
The use of blockchains is growing every day, and their utility has greatly expanded from sending and receiving crypto-coins to smart-contracts and decentralized autonomous organizations. Modern blockchains underpin a variety of applications: from designing a global identity to improving satellite connectivity. In our research we look at the ability of blockchains to store metadata in an increasing volume of transactions and with evolving focus of utilization. We further show that basic approaches to improving blockchain privacy also rely on embedding metadata. This paper identifies and classifies real-life blockchain transactions embedding metadata of a number of major protocols running essentially over the bitcoin blockchain. The empirical analysis here presents the evolution of metadata utilization in the recent years, and the discussion suggests steps towards preventing criminal use. Metadata are relevant to any blockchain, and our analysis considers primarily bitcoin as a case study. The paper concludes that simultaneously with both expanding legitimate utilization of embedded metadata and expanding blockchain functionality, the applied research on improving anonymity and security must also attempt to protect against blockchain abuse.
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cs.CR
Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
By comparing cryptocurrencies with other existing payment methods, including banknotes and bank cards, it is clear that the use of Bitcoin and its competitors (Ethereum, \dots) is almost insignificant in world trade. We may also note that these cryptocurrencies have become tools of speculation, which is the antithesis of their primary purpose. Based essentially on the security of electronic signatures, the Ecash introduced here will put the users back to the center of the game and exclude miners and their enormous waste of power energy. Thus, the purpose of this paper is to show that even a piece of paper can be recycled into a secure Ecash, while remaining environmentally friendly. Hence, we create here a cryptocurrency that would use a slight modification of the current banknotes to set up anonymous electronic transactions. By trading with banknotes, we mechanically transfer ownership of the paper money from one owner to another, hence, in this scheme, we introduce the notion of ownership transfer. It implies that at each transaction the elements allowing to authenticate the Ecash does not change, while the ownership certificate will change since the Ecash is transfer towards someone else.
Devices to support pervasive computing and the Internet of Things (IoT) are becoming present in almost every aspect of our lives. Due to their limited power and computation, these devices often need to rely on some more powerful outsourced cloud services, which raises a security and privacy concern as IoT data is often sensitive. On the other hand, blockchain technology has recently gained much attention due to its decentralized, trustless and immutable design. We propose CapChain - an access control framework based on blockchain that allows users to share and delegate their access rights easily to IoT devices in public but still maintain privacy. To protect privacy, we adapt multiple techniques from anonymous crypto-currency blockchain systems to hide sensitive information, including users' identities and related information about the capabilities. We also build a testbed as a proof of concept.
As a distributed database mapping the domain name and IP address, DNS makes it easier to access the Internet However, DNS relies on the resolution of the root server, which is a hierarchical network topology centered on the root. It is vulnerable to single points of failure and domain name resolution data tampered, affects the normal service of Internet domain name resolution seriously. To solve this problem, we proposed a new blockchain-based decentralization DNS data storage method by studying the principle and characteristics of blockchain. And implement a decentralization system DecDNS to establish multiple parallel DNS nodes, store the key information of the zone file resolution data. In the experiment, we proactively invalidated multiple nodes in the parallel resolution node and tampered the domain name resolution data. The experimental results show that, the DecDNS can provide normal resolution services, solve the problem of single point failure and the falsification of domain name resolution data. While compatible with the original domain name system, it is also enhances the stability and security of DNS framework, so it is an effective and feasible solution.
Stefano Bistarelli, Ivan Mercanti, Francesco Santini
In Bitcoin, the most common kind of transactions is in the form "Bob pays Alice", and it is based on the Pay to-Public Key Hash (P2PKH) script. P2PKH transactions are just one among many standard classes: a transaction is standard if it passes BitcoinCore's IsStandard() and IsStandardTx() tests. However, the creation of ad-hoc scripts to lock (and unlock) transactions allows for also generating non-standard transactions, which can be nevertheless broadcast and mined as well. In this work, we explore the Bitcoin block-chain with the purpose to analyse and classify standard and non-standard transactions, understanding how much the standard behaviour is respected.
Bitcoin is a decentralized transaction platform and the largest cryptocurrency system. Bitcoin represents a chain of blocks containing its entire legal transaction history, thereby providing convenience for tracking money. However, mixing services are used as an effective means to hide the identity of a transaction address by combining several transfers from different users. Detecting the original user of a Bitcoin address and the money flow is essential in some special circumstances such as anomaly detection. Recognizing Bitcoin mixing services and de-mixing user accounts have only rarely been studied. Here we demonstrate that Bitcoin transaction graphs possess community properties and that a mixing service can be regarded as a cluster outlier. Motivated by the success of graph embedding in social network analysis, we propose a feature-based method to identify mixing services, testing our method on the real Bitcoin ledger.
Bitcoin is a cryptocurrency based on blockchain technology that enables peer-to-peer transactions without a central authority. Bitcoin is known for resolving double-spending problems. When two or more miners generate a block that includes transaction information at nearly the same time, an accidental fork occurs. In this case, the longest chain of blocks is selected to avoid the double-spending problem. However, if there is an attacker node whose hash power is greater than half of the total hash power, that node can perform a double-spending attack, i.e., a 51% or majority attack. We propose a random mining group selection technique to reduce the probability of successful double-spending attacks. The analysis results demonstrate that if the number of groups is greater than or equal to two, the probability that the attacker will find the next block is less than 50%.
Seong Seok Choi, Jin Wook Burm, Wonjin Sung, Ju Wook Jang · 5 authors
We implement a scheme to securely control IoT devices using smart contracts which resides on blockchain. Our implementation provides guaranteed authentication, nonrepudiation and integrity without any central administration. We illustrate how a smart contract works in conjunction with a blockchain to prevent any tempering from possible intruders. We implement ethereum nodes on Raspberry Pi using node.js and web3 library.
Yao‐Chieh Hu, Ting‐Ting Lee, Dimitris Chatzopoulos, Pan Hui
Although the primary role of decentralized ledgers, such as blockchains in cryptocurrencies, is to store data related to interactions between users to establish trust within incognizant parties, their capabilities allow them to offer more sophisticated functionalities. Smart contracts are decentralized rules that are stored on the blockchain and are executed on demand. Furthermore, smart contracts can interact with each other via message exchange to access data that are stored on them and to call each others' methods. In this paper, we propose a two-level hierarchical architecture that is composed of two types of smart contracts: custodian and client. A custodian contract can deploy on-demand client contract, access their data and call their methods to perform specific updates. Moreover, we develop a framework to allow client contracts to share common variables among all or partial group of the contracts, which may only be mutated by its creator, custodian contracts. We measure the performance of our proposal by developing the proposed contracts and deploying them on three popular testnets.
Recent work has demonstrated significant anonymity vulnerabilities in\nBitcoin's networking stack. In particular, the current mechanism for\nbroadcasting Bitcoin transactions allows third-party observers to link\ntransactions to the IP addresses that originated them. This lays the groundwork\nfor low-cost, large-scale deanonymization attacks. In this work, we present\nDandelion++, a first-principles defense against large-scale deanonymization\nattacks with near-optimal information-theoretic guarantees. Dandelion++ builds\nupon a recent proposal called Dandelion that exhibited similar goals. However,\nin this paper, we highlight simplifying assumptions made in Dandelion, and show\nhow they can lead to serious deanonymization attacks when violated. In\ncontrast, Dandelion++ defends against stronger adversaries that are allowed to\ndisobey protocol. Dandelion++ is lightweight, scalable, and completely\ninteroperable with the existing Bitcoin network. We evaluate it through\nexperiments on Bitcoin's mainnet (i.e., the live Bitcoin network) to\ndemonstrate its interoperability and low broadcast latency overhead.\n
James Tapsell, Raja Naeem Akram, Konstantinos Markantonakis
Bitcoin is a decentralised digital currency that relies on cryptography rather than trusted third parties such as central banks for its security. Underpinning the operation of the currency is a peer-to-peer (P2P) network that facilitates the execution of transactions by end users, as well as the transaction confirmation process known as bitcoin mining. The security of this P2P network is vital for the currency to function and subversion of the underlying network can lead to attacks on bitcoin users including theft of bitcoins, manipulation of the mining process and denial of service (DoS). As part of this paper the network protocol and bitcoin core software are analysed, with three bitcoin message exchanges (the connection handshake, GETHEADERS/HEADERS and MEMPOOL/INV) found to be potentially vulnerable to spoofing and use in distributed denial of service (DDoS) attacks. Possible solutions to the identified weaknesses and vulnerabilities are evaluated, such as the introduction of random nonces into network messages exchanges.
Freya Sheer Hardwick, Apostolos Gioulis, Raja Naeem Akram, Konstantinos Markantonakis
Technology has positive impacts on many aspects of our social life. Designing a 24hour globally connected architecture enables ease of access to a variety of resources and services. Furthermore, technology like Internet has been a fertile ground for innovation and creativity. One of such disruptive innovation is blockchain -- a keystone of cryptocurrencies. The blockchain technology is presented as a game changer for many of the existing and emerging technologies/services. With its immutability property and decentralised architecture, it is taking centre stage in many services as an equalisation factor to the current parity between consumers and large corporations/governments. One of such potential applications of the blockchain is in e-voting schemes. The objective of such a scheme would be to provide a decentralised architecture to run and support a voting scheme that is open, fair and independently verifiable. In this paper, we propose potentially a new e-voting protocol that utilises the blockchain as a transparent ballot box. The protocol has been designed with adhering to the fundamental e-voting properties in mind as well as offering a degree of decentralisation and allowing for the voter to change/update their vote (within the permissible voting period). The paper highlights the pros and cons of using blockchain for such a proposal from practical point view in both development/deployment and usage contexts. Concluding the paper with a potential roadmap for blockchain technology to be able to support complex applications.
Younggee Hong, Hyunsoo Kwon, Jihwan Lee, Junbeom Hur
Bitcoin mixing services improve anonymity by breaking the connection between Bitcoin addresses. In the darkweb environment, many illegal trades, such as in drugs or child pornography, avoid their transactions being traced by exploiting mixing services. Therefore, de-mixing algorithms are needed to identify illegal financial flows and to reduce criminal activity. Unfortunately, to the best of our knowledge, few studies on analyzing mixing services and de-anonymizing transactions have been proposed. In this paper, we conduct an in-depth analysis of real-world mixing services, and propose a de-mixing algorithm for Helix, one of the most widely used Bitcoin mixing services. The proposed algorithm de-anonymizes the relationship between the input and output addresses of mixing services by exploiting the static and dynamic parameters of mixing services. Our experiment showed that, we could identify the relationships between the input and output addresses of the Helix mixing service with a 99.14% accuracy rate.
Freya Sheer Hardwick, Raja Naeem Akram, Konstantinos Markantonakis
At a time when society is in constant transition to keep up with technological advancement, we are seeing traditional paradigms being increasingly challenged. The fundamentals of governance are one such paradigm. As society's values have shifted, so have expectations of government shifted from the traditional model to something commonly referred to as `open governance'. Though a disputed term, we take open governance to mean a concept, which encourages and facilitates openness, accountability, and responsiveness to citizens. For the success of open governance initiatives, there are some technologies, such as the internet, that are crucial. These technologies enable access to both the data and to engagement activities between citizens and government. There are also other technologies, like blockchain and smart contacts, which could be utilised to assist open governance. A sound starting point would be moving from a system where information is tediously released by a government, on an `as they please' basis, to an infrastructure where critical actions are captured with strong integrity, non-repudiation and evidential guarantees. With an added dimension that facilitates these actions record be accessible to public scrutiny in near real-time. One candidate technology for capturing such actions is blockchain. Initially, blockchains were mainly used to facilitate cryptocurrencies as a record of transactions. The notable example being bitcoin. However, in recent years, blockchains utility is being recognised through smart contracts - potentially a vital building block to realising open and transparent government activities. In this paper, we employ the concept of smart contracts to government tendering activities. The proposed scheme is based on smart contracts, enabling a fair, transparent and independently verifiable (auditable) government tendering scheme. The scheme is then implemented on the Ethereum platform to evaluate the performance and financial cost implications, along with an evaluation of the potential security and auditability challenges.
We present IPchain, a blockchain to store the allocations and delegations of IP addresses, with the aim of easing the deployment of secure interdomain routing systems. Interdomain routing security is of vital importance to the Internet since it prevents unwanted traffic redirections. IPchain makes use of blockchains' properties to provide flexible trust models and simplified management when compared to existing systems. In this paper we argue that Proof of Stake is a suitable consensus algorithm for IPchain due to the unique incentive structure of this use-case. We have implemented and evaluated IPchain's performance and scalability storing around 150k IP prefixes in a 1GB chain.
In this work, we present a low-latency partition tolerant distributed ledger using a novel directed acyclic graph (DAG) structure. By forcing information to be published at specific deterministic locations, we avoid complex consensus algorithms and eliminate confirmation periods. We implement our DAG over a fully decentralized overlay network, leveraging BitTorrent concepts for peer-to-peer (P2P) rendezvous and block propagation. We compute overall expected latency using Erd¨os-R´enyi random graph models and present initial proof-of-concept software. The resulting work will allow anyone to create fully decentralized services (records, databases, etc.) resistant to attack, manipulation, and censorship.
George Kappos, Haaroon Yousaf, Mary Maller, Sarah Meiklejohn
Among the now numerous alternative cryptocurrencies derived from Bitcoin, Zcash is often touted as the one with the strongest anonymity guarantees, due to its basis in well-regarded cryptographic research. In this paper, we examine the extent to which anonymity is achieved in the deployed version of Zcash. We investigate all facets of anonymity in Zcash's transactions, ranging from its transparent transactions to the interactions with and within its main privacy feature, a shielded pool that acts as the anonymity set for users wishing to spend coins privately. We conclude that while it is possible to use Zcash in a private way, it is also possible to shrink its anonymity set considerably by developing simple heuristics based on identifiable patterns of usage.
The use of technology has become important at this point in helping to meet human needs.Due to the increasing use of technology, new challenges are brought in the process of democracy as most people today don’t trust their governments, making elections is very important in modern democracy . Elections have a great importance in determining who will rule a nation or an organization or it can be said as it is an event that decides the fate of any nation. In modern democracy, elections are very important but large sections of society around the world do not trust their election system which is a major concern for democracy. Even the world’s largest democracies like India, United States, still suffer from a flawed electoral system. Vote rigging, hacking of EVM (Electronic voting machine), election manipulation, and polling booth capturing are the major issues in the current voting system The blockchain is said as emerging, decentralized, and distributed technology that promises to enhance different aspects of many industries. Expanding e-voting into blockchain technology could be the solution to eliminate the present concerns in e-voting system There is no doubt that the ever changing concept of the blockchain, which is the backbone of the famous cryptocurrency Bitcoin has triggered the start of a new era in the Internet and the online services. While most people focus only on bitcoin and other cryptocurrencies; there are in fact, many operations, both administrative and fintech that can only be done online/offline can now safely be moved to the Internet as online services because of immutability of blockchain. What makes blockchain a powerful tool is its smarts contracts and many features which overcomes traditional systems. Smart contracts are meaningful pieces of codes, to be integrated in the blockchain and executed as scheduled in every step of blockchain updates. E-votin, is another trending, yet critical, topic related to the online services. The blockchain with the smart contracts, emerges as a good candidate to use in developments of safer, cheaper, more secure, more transparent, and easier-to-use e-voting systems.Due to its consistency, widespread use, and provision of smart contracts logic, Ethereum and its network is one of the most suitable ones. An e-voting system must be secure, as it should not allow duplicated votes and be fully transparent, while protecting the privacy of the attendees. In this project, we have implemented and tested an e-voting application as a smart contract for the Ethereum network using the Ethereum and the Solidity language.
Immigrants usually are pro-social towards their hometowns and try to improve them. However, the lack of trust in their government can drive immigrants to work individually. As a result, their pro-social activities are usually limited in impact and scope. This paper studies the interface factors that ease collaborations between immigrants and their home governments. We specifically focus on Mexican immigrants in the US who want to improve their rural communities. We identify that for Mexican immigrants having clear workflows of how their money flows and a sense of control over this workflow is important for collaborating with their government. Based on these findings, we create a blockchain based system for building trust between governments and immigrants. We finish by discussing design implications of our work and future directions.
A trusted electronic election system requires that all the involved information must go public, that is, it focuses not only on transparency but also privacy issues. In other words, each ballot should be counted anonymously, correctly, and efficiently. In this work, a lightweight E-voting system is proposed for voters to minimize their trust in the authority or government. We ensure the transparency of election by putting all message on the Ethereum blockchain, in the meantime, the privacy of individual voter is protected via an efficient and effective ring signature mechanism. Besides, the attractive self-tallying feature is also built in our system, which guarantees that everyone who can access the blockchain network is able to tally the result on his own, no third party is required after voting phase. More importantly, we ensure the correctness of voting results and keep the Ethereum gas cost of individual participant as low as possible, at the same time. Clearly, the pre-described characteristics make our system more suitable for large-scale election.
The Transport Layer Security (TLS) protocol is a de facto standard of secure client-server communication on the Internet. Its security can be diminished by a variety of attacks that leverage on weaknesses in its design and implementations. An example of a major weakness is the public-key infrastructure (PKI) that TLS deploys, which is a weakest-link system and introduces hundreds of links (i.e., trusted entities). Consequently, an adversary compromising a single trusted entity can impersonate any website. Notary systems, based on multi-path probing, were early and promising proposals to detect and prevent such attacks. Unfortunately, despite their benefits, they are not widely deployed, mainly due to their long-standing unresolved problems. In this paper, we present Persistent and Accountable Domain Validation (PADVA), which is a next-generation TLS notary service. PADVA combines the advantages of previous proposals, enhancing them, introducing novel mechanisms, and leveraging a blockchain platform which provides new features. PADVA keeps notaries auditable and accountable, introduces service-level agreements and mechanisms to enforce them, relaxes availability requirements for notaries, and works with the legacy TLS ecosystem. We implemented and evaluated PADVA, and our experiments indicate its efficiency and deployability.
Among various network attacks, botnet led attacks are considered as the most serious threats. A botnet, i.e., the network of compromised computers is able to perform large scale illegal activities such as Distributed Denial of Service attacks, click fraud, bitcoin mining etc. These attacks are considered as the major concern now-a-days. In this paper, we present a comprehensive review of botnets, their lifecycle and types. We also discuss the peer-to-peer botnet detection techniques' behaviors using various latest detection techniques.