Kourosh Davarpanah, Dan Kaufman, Ophelie Pubellier
NeuCoin is a decentralized peer-to-peer cryptocurrency derived from Sunny\nKing's Peercoin, which itself was derived from Satoshi Nakamoto's Bitcoin. As\nwith Peercoin, proof-of-stake replaces proof-of-work as NeuCoin's security\nmodel, effectively replacing the operating costs of Bitcoin miners\n(electricity, computers) with the capital costs of holding the currency.\nProof-of-stake also avoids proof-of-work's inherent tendency towards\ncentralization resulting from competition for coinbase rewards among miners\nbased on lowest cost electricity and hash power.\n NeuCoin increases security relative to Peercoin and other existing\nproof-of-stake currencies in numerous ways, including: (1) incentivizing nodes\nto continuously stake coins over time through substantially higher mining\nrewards and lower minimum stake age; (2) abandoning the use of coin age in the\nmining formula; (3) causing the stake modifier parameter to change over time\nfor each stake; and (4) utilizing a client that punishes nodes that attempt to\nmine on multiple branches with duplicate stakes.\n This paper demonstrates how NeuCoin's proof-of-stake implementation addresses\nall commonly raised "nothing at stake" objections to generic proof-of-stake\nsystems. It also reviews many of the flaws of proof-of-work designs to\nhighlight the potential for an alternate cryptocurrency that solves these\nflaws.\n
Bitcoin is an emerging crypto-currency, which is wrapped in mystery and controversy. The goal is to transform how we transfer payments. The current approach for sending money from one remote party to another is via bank deposit and transfer by check or bank transfer. PayPal and other services were developed to provide faster payments to verified individuals, but each layer in the transaction adds time, cost, and/or risk to the transaction. Users of this new digital currency proclaim the benefits of security, anonymity, and efficiency for making transactions. The functionality and structure of the Bitcoin Network is complex and often attacked for not being a suitable replacement for currency. An independent understanding can be developed of the composite Bitcoin Financial Systems of Systems architecture by considering the challenges any System of System would face. A functional analysis, employing the Systems Modeling Language (SysML), is performed on the Bitcoin System of Systems architecture to help gain an understanding of the structure and functionality, and how that relates to the key actors and use cases, for determining if the usersâ expectations are aligned with the architecture.
The advent of Bitcoin in 2009 has not only introduced Cryptocurrencies and lead to a new digitization movement in the financial, especially payments industry but also made way for a new breed of innovative technologies based on decentralized digital currencies. Generally, decentralized consensus systems could change the very nature of how companies, organizations and individuals are built and interact with each other. Decentralized consensus systems, decentralized applications and smart contracts provide the conceptual framework as well as the technological basis to establish predefined, incorruptible protocols and contracts to organize human behavior and interconnectedness. However, the technical protocols and implementations are quite complex and practitioners as well as interdisciplinary researchers not familiar with cryptography, network protocols or decentralized networks are struggling to find access to these concepts and grasp their potential. To fill this gap, we develop a comprehensive taxonomy of decentralized consensus systems in order to provide a tool for researchers and practitioners alike to facilitate classification and analysis of emerging technologies in the field of "Crypto 2.0", the next level of innovation beyond cryptocurrencies.
Several new services incentivize clients to compete in solving large computation tasks in exchange for financial rewards. This model of competitive distributed computation enables every user connected to the Internet to participate in a game in which he splits his computational power among a set of competing pools â the game is called a computational power splitting game. We formally model this game and show its utility in analyzing the security of pool protocols that dictate how financial rewards are shared among the members of a pool. As a case study, we analyze the Bitcoin cryptocurrency which attracts computing power roughly equivalent to billions of desktop machines, over 70% of which is organized into public pools. We show that existing pool reward sharing protocols are insecure in our game-theoretic analysis under an attack strategy called the âblock withholding attackâ. This attack is a topic of debate, initially thought to be ill-incentivized in todayâs pool protocols: i.e., causing a net loss to the attacker, and later argued to be always profitable. Our analysis shows that the attack is always well-incentivized in the long-run, but may not be so for a short duration. This implies that existing pool protocols are insecure, and if the attack is conducted systematically, Bitcoin pools could lose millions of dollars worth in months. The equilibrium state is a mixed strategyâthat isâin equilibrium all clients are incentivized to probabilistically attack to maximize their payoffs rather than participate honestly. As a result, a part of the Bitcoin network is incentivized to waste resource competing for higher selfish reward.
Feroz Ahmad Ahmad, Prashant Kumar, Gulshan Shrivastava, Med Salim Bouhlel
ON 12 JANUARY 2009 a pseudonymous entity signed a transaction that instructed a distributed network to transfer a small amount of digital currency to Hal Finney, one ofthe key figures of the cypherpunk movement. After a few minutes, the transaction was recorded on a distributed public ledger, permanently updating the balance ofbothparties. This transactionâ the first Bitcoin transactionâmarked the beginning of a new era of decentralized payment systems, ushering in a variety of financial Services that do not depend on any centralized clearinghouse or other financial middleman. Bitcoin is regarded by many as a powerful technological innovation that could disrupt many sectors, in the realm of finance and beyond. But the underlying technology on which the network operates, the Bitcoin blockchain can do much more than that. Just as the internet did in the early-1990s, blockchain technology carries with it a whole new range of promises concerning how decentralization can support and promote individual freedoms and autonomy. Blockchain proponents believe that Bitcoin and other cryptocurrency platforms will revolutionize mechanisms of value exchange in the same way that the internet transformed information sharing, by providing a platform for people to exchange digital resources, in a secure and decentralized manner without the need to rely on any intermediary or trusted authority. But this revolutionary potential also carries with it serious implications for censorship, intellectual property, and the regulated flow of information. A blockchain is a decentralized database of transactions maintained by a distributed network of computers, which all contribute to the verification and the validation of transactions. Once accepted, these transactions are recorded inside a âblockâ of transactions, which incorporates a reference to previous blocks. This creates a long chain of blocksâa âblockchainââthat stores the history of all transactions in a chronological order. Every block contains information about a particular set of transactions, a reference to the preceding block in the blockchain, and the answer to a complex mathematical puzzle that is used to validate the data associated with that block. A copy of the blockchain is stored on every computer in the network, making it virtually impossible for anyone unilaterally to modify the data stored on this decentralized database: if anyone tries to modify any transaction the fraud will be immediately detected by all other network participants.
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Blockchain Technology Applications and Security
Advanced Steganography and Watermarking Techniques
Bitcoin is the first and most popular decentralized cryptocurrency to date. In this work, we extract and analyze the core of the Bitcoin protocol, which we term the Bitcoin backbone , and prove three of its fundamental properties which we call Common Prefix , Chain Quality, and Chain Growth in the static setting where the number of players remains fixed. Our proofs hinge on appropriate and novel assumptions on the âhashing powerâ of the protocol participants and their interplay with the protocol parameters and the time needed for reliable message passing between honest parties in terms of computational steps. A takeaway from our analysis is that, all else being equal, the protocolâs provable tolerance in terms of the number of adversarial parties (or, equivalently, their âhashing powerâ in our model) decreases as the duration of a message passing round increases. Next, we propose and analyze applications that can be built âon topâ of the backbone protocol, specifically focusing on Byzantine agreement (BA) and on the notion of a public transaction ledger. Regarding BA, we observe that a proposal due to Nakamoto falls short of solving it, and present a simple alternative which works assuming that the adversaryâs hashing power is bounded by 1/3. The public transaction ledger captures the essence of Bitcoinâs operation as a cryptocurrency, in the sense that it guarantees the liveness and persistence of committed transactions. Based on this notion, we describe and analyze the Bitcoin system as well as a more elaborate BA protocol and we prove them secure assuming the adversaryâs hashing power is strictly less than 1/2. Instrumental to this latter result is a technique we call 2-for-1 proof-of-work (PoW) that has proven to be useful in the design of other PoW-based protocols.
Christian Decker, Jochen Seidel, Roger Wattenhofer
The Bitcoin system only provides eventual consistency. For everyday life, the time to confirm a Bitcoin transaction is prohibitively slow. In this paper we propose a new system, built on the Bitcoin blockchain, which enables strong consistency. Our system, PeerCensus, acts as a certification authority, manages peer identities in a peer-to-peer network, and ultimately enhances Bitcoin and similar systems with strong consistency. Our extensive analysis shows that PeerCensus is in a secure state with high probability. We also show how Discoin, a Bitcoin variant that decouples block creation and transaction confirmation, can be built on top of PeerCensus, enabling real-time payments. Unlike Bitcoin, once transactions in Discoin are committed, they stay committed.
The growing parallelism and heterogeneity of modern computing infrastructures such as High Performance Computing (HPC) platforms raises new challenges to their programmers and users. Additional requirements have emerged nowadays, such as minimizing the consumed energy, reducing the utilized system resources, or providing built-in reliability mechanisms. Therefore High Performance Computing (HPC) applications require adaptation mechanisms and then must avoid traditional monolithic centralized approaches in favor of novel autonomous, flexible and decentralized decision systems. In this context, we describe here a dynamic and flexible adaptation scheme based on a Multi-Agent System (MAS) to handle parallel or distributed executions in an HPC environment. More precisely, we model and extend the existing HPC middleware Kaapi to offer the power of the ParaMoise multi-agent organizational framework. Our proposed solution, named ParaMASK, relies on the similarities between ParaMoise workflow-based functional specifications and the Direct Acyclic Graph (DAG) representation of the distributed execution within Kaapi. As a result, ParaMASK permits to analyze and reorganize the scheduling of tasks that compose a program in an autonomous and decentralized way, while additionally handling dynamic adaptations (using task migration to fulfill energy consumption goals for example). The proposed solution was implemented on top of the existing Kaapi middleware and includes an optimized algorithm for the agent coordination. ParaMASK has been validated with a series of experiments on a real computational grid. Experimental results show a good scalability and an exceptional low overhead induced by the approach: less than 1.5% execution time increase with periodic coordinations every 15 seconds on 2662 cores.
Enas Al Kawasmi, Edin ArnautoviÄ, Davor SvetinoviÄ
ABSTRACT This paper presents a systemâofâsystems architecture model for a Decentralized Carbon Emissions Trading Infrastructure (DâCETI) with focus on privacy and system security goals. The structure and behavior are implemented as a solution to the problem of trading carbon emissions anonymously among the trading agents. Privacy and security of the trading agents and their carbon credits are the main requirements behind the architecture of DâCETI. The decentralized structure of multiple systems and distributed behavior are the two main features of DâCETI that distinguish it from the traditional carbon trading schemes and protocols. DâCETI is based on Bitcoin, a peerâtoâpeer digital currency with no central authority, and Open Transactions, a system that simplifies the use of cryptography in financial transactions. The architecture of DâCETI is evaluated and compared with the architecture of five other carbon emissions trading platforms.
Jelle van den Hooff, M. Frans Kaashoek, Nickolai Zeldovich
VerSum allows lightweight clients to outsource expensive computations over large and frequently changing data structures, such as the Bitcoin or Namecoin blockchains, or a Certificate Transparency log. VerSum clients ensure that the output is correct by comparing the outputs from multiple servers. VerSum assumes that at least one server is honest, and crucially, when servers disagree, VerSum uses an efficient conflict resolution protocol to determine which server(s) made a mistake and thus obtain the correct output.
Sep 1, 2014·2014 IEEE International Conference on Internet of Things(iThings), and IEEE Green Computing and Communications (GreenCom) and IEEE Cyber, Physical and Social Computing (CPSCom)
Bit coin is a new protocol with a potential to revolutionize financial system. Bit coin has a complex structure, where several interacting components build a peer-to-peer currency and a payment system without relying on any trusted third party. Bit coin is continually improved by an open source community, and various Bit coin libraries, APIs, and alternative implementations are being developed. Nevertheless, there is no up-to-date protocol specification or architecture description since the official whitepaper was published back in 2008. In this paper, we provide an up-to-date protocol specification and architectural analysis of the Bit coin system. We perform this analysis as the first step towards specification of the crypto currency reference architecture. The future reference architecture will serve as a starting architectural point for the development of new systems that leverage Bit coin protocol in different contexts and for various purposes. We also discuss whether the current architecture satisfies the system's primary purpose, i.e., Providing a pure decentralized version of the crypto currency.
With the vast increase in smartphones, there have been an increasing number of opportunities growing in the app industry. One in particular is the way we deal with money. There are huge overheads in the current payment systems around the world particularly in the United States, many of which include large transaction fees. Many new businesses have grown to solve these inefficiencies and create a new platform that provides a new user experience, security, and convenience among many other things. However, many of these platforms are still centralized, making them more susceptible to attacks. This thesis goes over the various methods of payments, starting from their origins and discusses their flaws and ways they are being improved. This study explains where payment platforms are going and how they line up against other platforms in terms of security and usability. We look at the origins of credit cards and why the US is lagging behind other countries in credit card security. Digital wallets like PayPal, Venmo, Square, etc. have done a remarkable job, but still have room for improvement in terms of security and usage. I try to solve these problems with the mobile application AnyCoin by bringing one platform that houses different types of digital wallets. The goal of this application was to grow a large user base and collect data off the transaction for future analysis and advertising. This study goes through an in depth analysis on the application from the iv perspective of merchants and consumers to understand what users are looking for in digital wallets. Decentralized platforms and crypto-currencies like Bitcoin have also created different ways to send money by creating a trustless system that does not depend on any central authority. I discuss what Bitcoin is and exactly how it works and the flaws in the current system. Mining is the process that puts Bitcoin into circulation and secures the network. However, as more customized hardware is released, Bitcoin will fall subject to becoming more centralized, and unfortunately become heavy regulated if it is to be used as a currency. Ethereum is a new technology that takes the concepts of Bitcoin and creates a platform for a developer to create a decentralized application. I create a few contracts that show how we can create a decentralized version of PayPal that works using other crypto- currencies. Ethereum is still in its alpha stage and has yet to
We give an explicit definition of decentralization and show you that\ndecentralization is almost impossible for the current stage and Bitcoin is the\nfirst truly noncentralized currency in the currency history. We propose a new\nframework of noncentralized cryptocurrency system with an assumption of the\nexistence of a weak adversary for a bank alliance. It abandons the mining\nprocess and blockchain, and removes history transactions from data\nsynchronization. We propose a consensus algorithm named Converged Consensus for\na noncentralized cryptocurrency system.\n
The traditional setting for concurrent zero knowledge considers a server that proves a statement in zero-knowledge to multiple clients in multiple concurrent sessions, where the serverâs actions in a session are independent of all other sessions. Persiano and Visconti [ICALP 05] show how keeping a limited amount of global state across sessions allows the server to significantly reduce the overall complexity while retaining the ability to interact concurrently with an unbounded number of clients. Specifically, they show a protocol that has only slightly super-constant number of rounds; however the communication complexity in each session of their protocol depends on the number of other sessions and has no a-priori bound. This has the drawback that the client has no way to know in advance the amount of resources required for completing a session of the protocol up to the moment where the session is completed. We show a protocol that does not have this drawback. Specifically, in our protocol the client obtains a bound on the communication complexity of each session at the start of the session. Additionally the protocol is constant-rounds. Our protocol is fully concurrent, and assumes only collision-resistant hash functions. The proof requires considerably different techniques than those of Persiano and Visconti. Our main technical tool is an adaptation of the âcommitted-simulator â technique of Deng et. al [FOCS 09]. 1
Describing, understanding, and modeling the emergent behavior of self-organizing software systems remains an open challenge. Such systems can solve problems in computing domains where traditional, centralized models are impractical or problematic, including ubiquitous and pervasive computing, peer-to-peer networks, large-scale grids, and Ultra-Large-Scale Systems. Self-organizing approaches have demonstrated great promise in building adaptive behavior into decentralized systems, enabling cooperative, autonomous self-management and the exploitation of the heterogeneity of system components. My investigation of self-organizing software systems has revolved around Myconet, an unstructured overlay protocol for peer-to-peer networks. Myconet takes inspiration from fungal growth patterns in order to build an efficient self-optimizing superpeer topology that can also rapidly self-heal in response to damage orattacks. Myconet has proven to be flexible, and has been used as a platform for the development of other self-organizing applications in large-scale distributed systems, including load-balancing in distributed service networks (Mycoload), and detection and mitigation of attacks against the overlay (Hormone-Inspired Topology Adaptation Protection [HITAP] and Self-Organized Degree Adaptation Protection [SODAP]). Each extension has given additional insights into the self-organizing dynamics of such systems, but has also shown the limitations of ad hoc approaches to the design and analysis of new applications. These experiences have led me to investigate formal tools and models that may provide the designer of a self-organizing system with early and accurate insight through augmented analytical power. This research selects a small set of synergistic modeling techniques, and builds an integrated approach to modeling for the design and validation of self-organizing software systems. These tools are used to model the core Myconet platform and its currently developed extensions, particularly focusing on the SODAP layer which provides self-protection features to a superpeer-based P2P overlay network. Once established, this modeling approach can be applied to the principled design of further Myconet extensions, as well as other self-organizing systems, thus advancing the understanding of how to model and engineer self-organization in software systems.
Antonis Papadimitriou, Mingchen Zhao, Andreas Haeberlen
In this paper, we discuss the problem of detecting general faults in distributed systems that handle confidential information. Detecting non-crash faults is difficult in this setting because, to check the behavior of a given node, we need to know its expected behavior -- but that can depend on the confidential information. Classical zero-knowledge proofs are difficult to apply because they are designed to verify functions with a fixed number of inputs, but in many distributed systems, both the size and the number of a node's "inputs" (the messages it has received from other nodes) are not known.
This paper focuses on future requirements of broadband data transmission of public protection and disaster relief, critical infrastructure protection and military, and presents the concept of redundant and secure data communication network system in the multi-organizational environment. We are proposing a fully decentralized architecture with optimized critical communication channels. Here, network actors and elements identify and authenticate by establishing physical connection. This concept also recommends, group level user-authorization mechanism for each participating organization. Their respective users of command and control centers are identified, authorized and authenticated to various data sources. The decentralized architecture concept is using the Distributed Systems intercommunication Protocol (DSiP). The concept is highly fault-tolerant in routine as well as crises operations. The software-based approach is independent of heterogeneous data communication technologies, IP networks and telecommunication operator services. The solution enables to build an effective and lasting cyber secure data network for multi organizational environment. Being a fully decentralized concept, networks of individual member organizations are virtually autonomous and hard to upset each other. That allows smooth message and information exchange to enable interoperability.
With the constant proliferation of information systems around the globe, the need for decentralized and scalable data sharing mechanisms has become a major factor of integration in a wide range of applications. Literature on information integration across autonomous entities has tacitly assumed that the data of each party can be revealed and shared to other parties. A lot of research, concerning the management of heterogeneous sources and database integration, has been proposed, for example based on centralized or distributed mediators that control access to data managed by different parties. On the other hand, real life data sharing scenarios in many application domains like healthcare, e-commerce market, e-government show that data integration and sharing are often hampered by legitimate and widespread data privacy and security concerns. Thus, protecting the individual data may be a prerequisite for organizations to share their data in open environments such as Internet. Work undertaken in this thesis aims to ensure security and privacy requirements of software systems, which take the form of web services, using query rewriting principles. The user query (SPARQL query) is rewritten in such a way that only authorized data are returned with respect to some confidentiality and privacy preferences policy. Moreover, the rewriting algorithm is instrumented by an access control model (OrBAC) for confidentiality constraints and a privacy-aware model (PrivOrBAC) for privacy constraints. A secure and privacy-preserving execution model for data services is then defined. Our model exploits the servicesÂż semantics to allow service providers to enforce locally their privacy and security policies without changing the implementation of their data services i.e., data services are considered as black boxes. We integrate our model to the architecture of Axis 2.0 and evaluate its efficiency in the healthcare application domain.
Practical systems must often guarantee that changes to the system state are durable. Examples of such systems are databases, file systems, and messaging middleware with guaranteed delivery. One common way of implementing durability while keeping performance high is to use a log to persist updates to the system state. Such systems use the log to reconstruct the system state in the event of a crash. When implementing such a log, if the log is only stored locally, the system state is permanently lost when the server writing the log experiences a permanent hardware failure. BookKeeper is a system that exposes a log abstraction for building high performance, highly available distributed systems. BookKeeper transparently implements replication for high availability and striping for high performance. A Book- Keeper deployment comprises storage servers called bookies, which are designed to serve a large number of concurrent ledgers. BookKeeper is currently an open-source project and is in production use at Yahoo!
Bitcoin is a potentially disruptive new crypto-currency based on a decentralized opensource protocol which is gradually gaining popularity. Perhaps the most important question that will affect Bitcoinâs success, is whether or not it will be able to scale to support the high volume of transactions required from a global currency system. We investigate the restrictions on the rate of transaction processing in Bitcoin as a function of both the bandwidth available to nodes and the network delay, both of which lower the efficiency of Bitcoinâs transaction processing. The security analysis done by Bitcoinâs creator Satoshi Nakamoto [12] assumes that block propagation delays are negligible compared to the time between blocksâan assumption that does not hold when the protocol is required to process transactions at high rates. We improve upon the original analysis and remove this assumption. Using our results, we are able to give bounds on the number of transactions per second the protocol can handle securely. Building on previously published measurements by Decker and Wattenhofer [5], we show these bounds are currently more restrictive by an order of magnitude than the bandwidth needed to stream all transactions. We additionally show how currently planned improvements to the protocol, namely the use of transaction hashes in blocks (instead of complete transaction records), will dramatically alleviate these restrictions. Finally, we present an easily implementable modification to the way Bitcoin constructs its main data structure, the blockchain, that immensely improves security from attackers, especially when the network operates at high rates. This improvement allows for further increases in the number of transactions processed per second. We show that with our proposed modification, significant speedups can be gained in confirmation time of transactions as well. The block generation rate can be securely increased to more than one block per second â a 600 fold speedup compared to todayâs rate, while still allowing the network to processes many transactions per second.