Muhammad Saad, Aziz Mohaisen, Charles Kamhoua, Kevin Kwait · 5 authors
In this paper, we look at the use of hash-based, one-time signatures in the context of the Blockchain systems and demonstrate how the replacement of currently utilized schemes into a one-time signature can help deter double-spending. Towards this goal, we make the following contributions. 1) We introduce a notion of double- spending deterrence, a form of malleability that does not require pre-authorization from the signer to create a signature on an arbitrary message using two previously signed messages. It is used as a penalty to deter double-spending and disincentivize forgery. 2) We study features of various one-time signature schemes, and we demonstrate their effectiveness in thwarting double-spending. 3) We explore the design space of applying our methodology to the Blockchain system with a clear example and design options to deter double-spending. The results reported in this paper are promising, and open several new directions.
Ahmed E. Kosba, Charalampos Papamanthou, Elaine Shi
Many cloud and cryptocurrency applications rely on verifying the integrity of outsourced computations, in which a verifier can efficiently verify the correctness of a computation made by an untrusted prover. State-of-the-art protocols for verifiable computation require that the computation task be expressed as arithmetic circuits, and the number of multiplication gates in the circuit is the primary metric that determines performance. At the present, a programmer could rely on two approaches for expressing the computation task, either by composing the circuits directly through low-level development tools; or by expressing the computation in a high-level program and rely on compilers to perform the program-to-circuit transformation. The former approach is difficult to use but on the other hand allows an expert programmer to perform custom optimizations that minimize the resulting circuit. In comparison, the latter approach is much more friendly to non-specialist users, but existing compilers often emit suboptimal circuits. We present xJsnark, a programming framework for verifiable computation that aims to achieve the best of both worlds: offering programmability to non-specialist users, and meanwhile automating the task of circuit size minimization through a combination of techniques. Specifically, we present new circuit-friendly algorithms for frequent operations that achieve constant to asymptotic savings over existing ones; various globally aware optimizations for short- and long- integer arithmetic; as well as circuit minimization techniques that allow us to reduce redundant computation over multiple expressions. We illustrate the savings in different applications, and show the framework's applicability in developing large application circuits, such as ZeroCash, while minimizing the circuit size as in low-level implementations.
Jack Doerner, Yashvanth Kondi, Eysa Lee, Abhi Shelat
The Elliptic Curve Digital Signature Algorithm (ECDSA) is one of the most widely used schemes in deployed cryptography. Through its applications in code and binary authentication, web security, and cryptocurrency, it is likely one of the few cryptographic algorithms encountered on a daily basis by the average person. However, its design is such that executing multi-party or threshold signatures in a secure manner is challenging: unlike other, less widespread signature schemes, secure multi-party ECDSA requires custom protocols, which has heretofore implied reliance upon additional cryptographic assumptions such as the Paillier encryption scheme. We propose new protocols for multi-party ECDSA key-generation and signing with a threshold of two, which we prove secure against malicious adversaries in the random oracle model using only the Computational Diffie-Hellman Assumption and the assumptions already implied by ECDSA itself. Our scheme requires only two messages, and via implementation we find that it outperforms the best prior results in practice by a factor of 55 for key generation and 16 for signing, coming to within a factor of 12 of local signatures. Concretely, two parties can jointly sign a message in just over two milliseconds.
Wireless Sensor Networks (WSN) interconnects thousands of sensor nodes to support the services of Internet of Things (loT). However, data collected from sensor nodes may be tempered, forged and divulged. Traditional WSN data process platform handle the data centralized in terminal devices which is vulnerable to attacks and reduce the security of the system. Blockchain is a kind of distributed databases. It has been successfully applied in finance, securities, digital currency and other fields. We first propose a blockchain-based distributed collocation storage architecture for data security process platform of WSN with consensus protocol and asymmetric signature scheme. The security and efficiency are verified on the simulation to enable blockchain as a good solution.
Sushmita Ruj, Mohammad Shahriar Rahman, Anirban Basu, Shinsaku Kiyomoto
In order to ensure faster audits, higher transparency and security, many applications are being designed using blockchains. We propose BlockStore, a secure decentralized storage framework using blockchain technology. The primary motivation is efficient utilization of storage resources of users. Users often have un-utilized or underutilized storage in their devices. They can choose to host their storage resources when they are not in use. Users rent storage from the host for a fee for a fixed period of time and release back after the time expires. BlockStore keeps track of un-utilized storage of hosts in Space Wallet, a structure that helps in assigning storage to renters on request. The ownership of storage can be proved by logging all storage transactions in a public ledger (the blockchain), which can be verified by any user. A host cannot host the same storage to two users at the same time, nor can it tamper with the data of the renter. Renters cannot frame a host of cheating. BlockStore uses proofs of storage and data possession to verify that the hosts do not tamper with data and penalizes parties for misbehavior. Users can encrypt data for privacy. Payment and penalty are handled using smart contracts. BlockStore differs from existing solutions, by providing stronger audit that detects and penalizes misbehaving parties earlier than existing schemes.
In this paper, we propose an architecture for Blockchain-based Electronic Medical Records (EMRs) called GAA-FQ (Granular Access Authorisation supporting Flexible Queries) that comprises an access model and an access authorisation scheme. Unlike existing Blockchain schemes, our access model can authorise different levels of granularity of authorisation, whilst maintaining compatibility with the underlying Blockchain data structure. Furthermore, the authorisation, encryption, and decryption algorithms proposed in the GAA-FQ scheme dispense with the need to use a public key infrastructure (PKI) and hence improve the computation performance needed to support more granular and distributed, yet authorised, EMR data queries. We validated the computation performance and transmission efficiency for GAA-FQ using a simulation of GAA-FQ against an access control scheme for EMRs called ESPAC as our baseline that was not designed using a Blockchain. To the best of our knowledge, GAA- FQ is the first Blockchain-oriented access authorisation scheme with granular access control, supporting flexible data queries, that has been proposed for secure EMR information management.
Fabio Massacci, Chan Nam Ngo, Jing Nie, Daniele Venturi · 5 authors
In a Futures-Exchange, such as the Chicago Mercantile Exchange, traders buy and sell contractual promises (futures) to acquire or deliver, at some future pre-specified date, assets ranging from wheat to crude oil and from bacon to cash in a desired currency. The interactions between economic and security properties and the exchange's essentially non-monotonic security behavior; a valid trader's valid action can invalidate other traders' previously valid positions, are a challenge for security research. We show the security properties that guarantee an Exchange's economic viability (availability of trading information, liquidity, confidentiality of positions, absence of price discrimination, risk-management) and an attack when traders' anonymity is broken. We describe all key operations for a secure, fully distributed Futures-Exchange, hereafter referred to as simply the 'Exchange'. Our distributed, asynchronous protocol simulates the centralized functionality under the assumptions of anonymity of the physical layer and availability of a distributed ledger. We consider security with abort (in absence of honest majority) and extend it to penalties. Our proof of concept implementation and its optimization (based on zk-SNARKs and SPDZ) demonstrate that the computation of actual trading days (along Thomson-Reuters Tick History DB) is feasible for low-frequency markets; however, more research is needed for high-frequency ones.
Motivated by the great success and adoption of Bitcoin, a number of cryptocurrencies such as Litecoin, Dogecoin, and Ethereum are becoming increasingly popular. Although existing blockchain-based cryptocurrency schemes can ensure reasonable security for transactions, they do not consider any notion of fairness. Fair exchange allows two players to exchange digital “items,” such as digital signatures, over insecure networks fairly, so that either each player gets the other's item, or neither player does. Given that blockchain participants typically do not trust each other, enabling fairness in existing cryptocurrencies is an essential but insufficiently explored problem. In this article, we explore the solution space for enabling the fair exchange of a cryptocurrency payment for a receipt. We identify the timeliness of an exchange as an important property especially when one of the parties involved in the exchange is resource-constrained. We introduce the notion of strong timeliness for a fair exchange protocol and propose two fair payment-for-receipt protocol instantiations that leverage functionality of the blockchain to achieve strong timeliness. We implement both and compare their security and efficiency.
Distributed Ledger technology and its most notable implementation, the Blockchain, is disrupting today's industry in extremely fast pace with a potential to change the world. The security posture of Blockchain remains one of a key topics in today's industry and distributed services. On and on, we can embrace the attempts to implement the Blockchain technology in sensitive areas of our daily life like finance [1], insurance services [2], health care [3] etc. It is therefore crucial raise awareness of its limitations, possible improvements, as well as embedded compensations. In this paper, we provide a holistic view on the security aspects of the Blockchain technology. We identify the most notable security threats applicable in the above context and reveal technology-specific challenges, that need to be taken into account. Our analysis lists the security features already embedded in the Blockchain and sample uses in nowadays industry. Our results lead to several observations, recommendations, and open points that could be considered in ongoing development of the technology.
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.
Cryptocurrencies have seen a massive surge in popularity and behind these new virtual currencies is an innovative technology called the blockchain: a distributed digital ledger in which cryptocurrency transactions are recorded after having been verified. The transactions within a ledger are verified by multiple clients or “validators,” within the cryptocurrency's peer-to-peer network using one of many varied consensus algorithms for resolving the problem of reliability in a network involving multiple unreliable nodes. The most widely used consensus algorithms are the Proof of Work (PoW) algorithm and the Proof of Stake (PoS) algorithm; however, there are also other consensus algorithms which utilize alternative implementations of PoW and PoS, as well as other hybrid implementations and some altogether new consensus strategies. In this paper, we perform a comparative analysis of typical consensus algorithms and some of their contemporaries that are currently in use in modern blockchains. Our analysis focuses on the algorithmic steps taken by each consensus algorithm, the scalability of the algorithm, the method the algorithm rewards validators for their time spent verifying blocks, and the security risks present within the algorithm. Finally, we present our conclusion and some possible future trends for consensus algorithms used in blockchains.
Subasri Mathiyalahan, Shobana Manivannan, Mahalakshmi Nagasundaram, R. Ezhilarasie
Data integrity of outsourced data is main problem in CSP (cloud service provider). Space overhead and computation complexity are very high issue in recent PDP(Provable Data Possession) verification schemes. To overcome such issues MPDP (Mobile Provable Data Possession) schemes using hash tree data structure and Boneh-Lynn-Snacham short signature scheme have been used over decade. Data dynamics is well supported in MPDP scheme via block less verification, dynamic data operations, stateless verification, and verification out sourcing. But still there are some operations which can be performed much more efficiently in some other way than that of the two methods prescribed above. Operations in particular, data modification operations like insertion and deletion operations is somewhat difficult or in other words time consuming in hash tree data structure. In this paper, we have deployed an improved hash tree structure called MPT (Merkle Patricia Tree) for integrity checking.MPT is combination of MHT (Merkle Hash Tree) and patricia tree where each node consists of key-value pairs. As of now, MPT has been used only in block chain technology for providing authentication of transactions through Ethereum.
The prevalence of Internet of Things (IoT) allows heterogeneous embedded smart devices to collaboratively provide smart services with or without human intervention. While leveraging the large-scale IoT-based applications like Smart Gird or Smart Cities, IoT also incurs more concerns on privacy and security. Among the top security challenges that IoT face, access authorization is critical in resource sharing and information protection. One of the weaknesses of today's access control (AC) is the centralized authorization server, which can be the performance bottleneck or the single point of failure. In this paper, BlendCAC, a blockchain-enabled decentralized capability-based AC is proposed for the security of IoTs. The BlendCAC aims at an effective access control processes to devices, services and information in large scale IoT systems. Based on the blockchain network, a capability delegation mechanism is suggested for access permission propagation. A robust identity-based capability token management strategy is proposed, which takes advantage of a smart contract for registration, propagation and revocation of the access authorization. In the proposed BlendCAC scheme, IoT devices are their own master to control their resources instead of being supervised by a centralized authority. Implemented and tested on a Raspberry Pi device and on a local private blockchain network, the experimental results demonstrate the feasibility of the proposed BlendCAC approach to offer a decentralized, scalable, lightweight and fine-grained AC solution to IoT systems.
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.
Summary Fog computing is a new computing paradigm that can provide flexible resources and services at the edge of network. It is an extension of cloud computing and usually cooperated with cloud computing. Therefore, end users, fog nodes, and cloud servers can form a three‐layer service model in practical application. In this model, they should have an agreement on a service contract, which contains every party's rights and obligations before the beginning of the service. However, due to lack of trust, it will suffer from some fairness problems during signing a service contract. Contract signing protocol allows two or more mutual distrust entities to sign a predefined digital contract in a fair and effective way. In this paper, we propose a fair three‐party contract signing protocol based on the primitive of blockchain, which can be applied to the scenario of fog computing. Our proposed construction allows the participants to sign a contract in a fair way without the involvement of an arbitrator. Moreover, the privacy of the contract content can be preserved on the public chain. Finally, we realize the proposed protocol through the private blockchain and provide the experimental simulation that analyzes the efficiency and effectiveness.
Raymond Cheng, Fan Zhang, Jernej Kos, Warren He · 9 authors
Smart contracts are applications that execute on blockchains. Today they manage billions of dollars in value and motivate visionary plans for pervasive blockchain deployment. While smart contracts inherit the availability and other security assurances of blockchains, however, they are impeded by blockchains' lack of confidentiality and poor performance. We present Ekiden, a system that addresses these critical gaps by combining blockchains with Trusted Execution Environments (TEEs). Ekiden leverages a novel architecture that separates consensus from execution, enabling efficient TEE-backed confidentiality-preserving smart-contracts and high scalability. Our prototype (with Tendermint as the consensus layer) achieves example performance of 600× more throughput and 400× less latency at 1000× less cost than the Ethereum mainnet. Another contribution of this paper is that we systematically identify and treat the pitfalls arising from harmonizing TEEs and blockchains. Treated separately, both TEEs and blockchains provide powerful guarantees, but hybridized, though, they engender new attacks. For example, in naïve designs, privacy in TEE-backed contracts can be jeopardized by forgery of blocks, a seemingly unrelated attack vector. We believe the insights learned from Ekiden will prove to be of broad importance in hybridized TEE-blockchain systems.
Franklin Schrans, Susan Eisenbach, Sophia Drossopoulou
Blockchain-based platforms such as Ethereum support the execution of versatile decentralized applications, known as smart contracts. These typically hold and transfer digital currency (e.g., Ether) to other parties on the platform. Contracts have been subject to numerous attacks, losing hundreds of millions of dollars (in Ether). We propose Flint, a new type-safe, capabilities-secure, contract-oriented programming language specifically designed for writing robust smart contracts. To help programmers reason about access control of functions, Flint programmers use caller capabilities. To prevent vulnerabilities relating to the unintentional loss of currency, transfers of assets in Flint are performed through safe atomic operations, inspired by linear type theory.
Incorporating accountability mechanisms in online services requires effective trust management and immutable, traceable source of truth for transaction evidence. The emergence of the blockchain technology brings in high hopes for fulfilling most of those requirements. However, a major challenge is to find a proper consensus protocol that is applicable to the crowdsourcing services in particular and online services in general. Building upon the idea of using blockchain as the underlying technology to enable tracing transactions for service contracts and dispute arbitration, this paper proposes a novel consensus protocol that is suitable for the crowdsourcing as well as the general online service industry. The new consensus protocol is called “Proof-of-Trust” (PoT) consensus; it selects transaction validators based on the service participants' trust values while leveraging RAFT leader election and Shamir's secret sharing algorithms. The PoT protocol avoids the low throughput and resource intensive pitfalls associated with Bitcoin' s “Proof-of-Work” (PoW) mining, while addressing the scalability issue associated with the traditional Paxos-based and Byzantine Fault Tolerance (BFT)-based algorithms. In addition, it addresses the unfaithful behaviors that cannot be dealt with in the traditional BFT algorithms. The paper demonstrates that our approach can provide a viable accountability solution for the online service industry.
Bitcoin has attracted everyone's attention and interest recently. Ethereum (ETH), a second generation cryptocurrency, extends Bitcoin's design by offering a Turing-complete programming language called Solidity to develop smart contracts. Smart contracts allow creditable execution of contracts on EVM (Ethereum Virtual Machine) without third parties. Developing correct smart contracts is challenging due to its decentralized computation nature. Buggy smart contracts may lead to huge financial loss. Furthermore, smart contracts are very hard, if not impossible, to patch once they are deployed. Thus, there is a recent surge of interest on analyzing/verifying smart contracts. While existing work focuses on EVM opcode, we argue that it is equally important to understand and define the semantics of Solidity since programmers program and reason about smart contracts at the level of source code. In this work, we develop the structural operational semantics for Solidity, which allows us to identify multiple design issues which underlines many problematic smart contracts. Furthermore, our semantics is executable in the K framework, which allows us to verify/falsify contracts automatically.
Hung Dang, Tien Tuan Anh Dinh, Dumitrel Loghin, Ee‐Chien Chang · 6 authors
Existing blockchain systems scale poorly because of their distributed consensus protocols. Current attempts at improving blockchain scalability are limited to cryptocurrency. Scaling blockchain systems under general workloads (i.e., non-cryptocurrency applications) remains an open question. In this work, we take a principled approach to apply sharding, which is a well-studied and proven technique to scale out databases, to blockchain systems in order to improve their transaction throughput at scale. This is challenging, however, due to the fundamental difference in failure models between databases and blockchain. To achieve our goal, we first enhance the performance of Byzantine consensus protocols, by doing so we improve individual shards' throughput. Next, we design an efficient shard formation protocol that leverages a trusted random beacon to securely assign nodes into shards. We rely on trusted hardware, namely Intel SGX, to achieve high performance for both consensus and shard formation protocol. Third, we design a general distributed transaction protocol that ensures safety and liveness even when transaction coordinators are malicious. Finally, we conduct an extensive evaluation of our design both on a local cluster and on Google Cloud Platform. The results show that our consensus and shard formation protocols outperform state-of-the-art solutions at scale. More importantly, our sharded blockchain reaches a high throughput that can handle Visa-level workloads, and is the largest ever reported in a realistic environment.
While the cyber insurance market has been growing significantly in recent years, its insurance providers face several challenges: first, there is a lack of standardized frameworks to rate ""cyber""; second, there's a shortage of relevant data to calculate premiums; and third, security postures of insured organizations constantly change. Unlike other types of insurance, cyber insurance requires creating a continuous feedback loop between customers and insurers. In this article, we introduce BlockCIS, a blockchain-based continuous monitoring and processing system for cyber insurance. BlockCIS aims to realize an automated, real-time, and immutable feedback loop between the insurer, its customer, third parties and potential auditors. As an example instantiation, we prototype BlockCIS using the open source Hyperledger Composer blockchain framework.