Zisang Xu, Feng Li, Han Deng, Minfu Tan · 6 authors
With the rapid development of mobile networks, there are more and more application scenarios that require group communication. For example, in mobile edge computing, group communication can be used to transmit messages to all group members with minimal resources. The group key directly affects the security of the group communication. Most existing group key agreement protocols are often flawed in performance, scalability, forward or backward secrecy, or single node failure. Therefore, this paper proposes a blockchain-based authentication and dynamic group key agreement protocol. With our protocol, each group member only needs to authenticate its left neighbor once to complete the authentication, which improved authentication efficiency. In addition, our protocol guarantees the forward secrecy of group members after joining the group and the backward secrecy of group members after leaving the group. Based on blockchain technology, we solve the problem of single node failure. Furthermore, we use mathematics to prove the correctness and security of our protocol, and the comparison to related protocols shows that our protocol reduces computation and communication costs.
In most practical cloud computing applications such as e-voting, auctions, health, and financial applications or cloud services in common, to prove the exactness of outsourced data is one of the major needs today. Most of the time, third party auditing is employed for this task. This auditing work is controlled by assigning the secret inputs to an entity trusted third party, or worker, who is liable for performing computations and hand over the result of the computation to the cloud users or clients. To verify the integrity of computations using traditional cryptographic techniques, the time required to generate and validate the proof is a major computation issue. This paper proposes an improved public auditing technique for multi-party computation to check the integrity of outsourced data using a cryptographic solution. Many researchers have given auditing protocols that generate and verify proof using a cryptographic solution. Most of these scheme uses Non-Interactive Zero-Knowledge Proof (NIZK) which are basically built on bilinear map technology. The verification time using these existing technique is computationally expensive which affect the performance of the auditing system. We propose an efficient protocol that verifies the result correctness using modern cryptographic technique Indistinguishability Obfuscation. The proposed system works in two phases, (i) auction and (ii) audit. During the auction phase, multiple clients share their encrypted bid value to the worker. The worker generates auction result and proof using Pedersen Commitment Scheme. The audit phase starts only after the completion of the auction phase which results in reduced verification time. During the Audit phase, clients can verify the integrity of results using NIZK with the IO technique. The results for reduced verification time in auction system have been presented. It is found that the performance of the proposed system has improved compared to the pertinent NIZK Proof technique. In our setting, we assumed that a worker is one of the trusted entity. By this notion, our protocol also guarantees privacy to the clients during the audit phase.
We propose a smart contract that allows two mutually distrusting parties to transact any non-digital good or service by deploying a smart contract on a blockchain to act as escrow. The contract settles disputes by letting parties wager that they can convince an arbiter that they were the honest party. We analyse the contract as an extensive-form game and prove that the honest strategy is secure in a strong game-theoretic sense if and only if the arbiter is biased in favor of honest parties. By relaxing the security notion, we can replace the arbiter by a random coin toss. Finally, we show how to generalize the contract to multiparty transactions in a way that amortizes the transaction fees.
Christian Killer, Lucas Thorbecke, Bruno Rodrigues, Eder J. Scheid · 6 authors
Trust in electoral processes is fundamental for democracies. Further, the identity management of citizen data is crucial, because final tallies cannot be guaranteed without the assurance that every final vote was cast by an eligible voter. In order to establish a basis for a hybrid public verifiability of voting, this work (1) introduces Proverum, an approach combining a private environment based on private permissioned Distributed Ledgers with a public environment based on public Blockchains, (2) describes the application of the Proverum architecture to the Swiss Remote Postal Voting system, mitigating threats present in the current system, and (3) addresses successfully the decentralized identity management in a federalistic state.
In this paper, we present Zecale, a general purpose SNARK proof aggregator that uses recursive composition of SNARKs. We start by introducing the notion of recursive composition of SNARKs, before introducing Zecale as a privacy preserving scalability solution. Then, we list application types that can emerge and be built with Zecale. Finally, we argue that such scalability solutions for privacy preserving state transitions are paramount to emulate "cash" on blockchain systems.
In a distributed system, cross-domain access control is an important mechanism to realize secure data sharing among multiple domains. Most of the existing cross-domain access control mechanisms are generally based on a single-server architecture, which has limitations in terms of security and reliability (the access decision may be incorrect) and completeness and confidentiality (the access records can be modified). Blockchain technology with decentralization, verifiability, and immutability properties can solve these problems. Motivated by these facts, in this article, we construct a trusted and efficient cross-domain access control system based on blockchain. Consequently, we integrate blockchain and role mapping technology to provide reliable and verifiable cross-domain access process. We use blockchain to record user roles, role mapping rules, access policies, and audit records, realizing user self-validation, and access nonreputation. Considering the low throughput of the blockchain, we design an efficient smart contract to make the access decision based on the access history of users. Finally, a performance evaluation of the system is presented to demonstrate the feasibility of the proposed system.
Matteo Nardini, Sven Helmer, Nabil El Ioini, Claus Pahl
Abstract We propose a framework for building a decentralized electronic marketplace for computing resources. The idea is that anyone with spare capacities can offer them on this marketplace, opening up the cloud computing market to smaller players, thus creating a more competitive environment compared to today’s market consisting of a few large providers. Trust is a crucial component in making an anonymized decentralized marketplace a reality. We develop protocols that enable participants to interact with each other in a fair way and show how these protocols can be implemented using smart contracts and blockchains. We discuss and evaluate our framework not only from a technical point of view, but also look at the wider context in terms of fair interactions and legal implications.
Palina Tolmach, Yi Li, Shang‐Wei Lin, Yang Liu · 5 authors
A smart contract is a computer program which allows users to automate their actions on the blockchain platform. Given the significance of smart contracts in supporting important activities across industry sectors including supply chain, finance, legal and medical services, there is a strong demand for verification and validation techniques. Yet, the vast majority of smart contracts lack any kind of formal specification, which is essential for establishing their correctness. In this survey, we investigate formal models and specifications of smart contracts presented in the literature and present a systematic overview in order to understand the common trends. We also discuss the current approaches used in verifying such property specifications and identify gaps with the hope to recognize promising directions for future work.
Abstract Currently, attribute-based authentication provides a feasible solution for fine-grained access control in cloud environment. However, the existing schemes can not solve the following problems at the same time, that is, how to ensure that the computation cost of the client does not depend on the size of underlying access structure, and how to introduce distributed authorities to manage and maintain the attribute universe. To solve the above problems, an efficient multi-authority attribute-based authentication scheme is proposed. The new scheme uses the technique of distributed attribute-based encryption to realize the access control of anonymous users, and reduces users’ computation burden by optimizing the standard implementation zero-knowledge proof and outsourcing users’ computing tasks in the authentication stage. Under the new definition of security, it can be proved that the new scheme is secure and satisfies many attractive properties, such as introducing distributed authorities, supporting outsourcing computation, satisfying attribute anonymity.
Given that Proof-of-Work (PoW) and Proof-of-Stake (PoS) are plutocratic, and other common consensus protocols are mostly permission-based, we look for a consensus protocol that will suit the needs of e-Democracy. In particular, what we need is a distributed ledger that will record and, to the possible extent, execute the public will. We propose a combination of any given permission-based protocol together with a trust graph between the nodes, which supplies the required permission for new nodes. As a result, the consensus protocol reaches consensus at every iteration between a known list of agents and then updates this list between iterations. This paper is based on prior work that shows the conditions under which a community can grow while maintaining a bounded number of byzantines. It combines a permission-based consensus protocol (such as pBFT) with a community expansion algorithm (such as the one in the prior work) to arrive at a consensus protocol in which the set of agents can change in time, while being sybil-resilient.
This article integrates existing theory from distributed computing and cryptology with anecdotal material from the cryptocurrency industry, to provide a comprehensive description of the minimum requirements of the hypothetical academic blockchain. The paper argues that such a community could significantly reduce the biases and misconduct that now exist in the academic peer review process. Theory suggests such a system could operate effectively as a distributed encrypted telecommunications network where nodes are anonymous, do not trust each other, and there is minimal central authority. To incentivize the academic community to join such a proposed community, the paper proposes a pseudo-cryptocurrency called litcoin (literature coin). This litcoin-based system would create economic scarcity based on proof of knowledge (POK), which is a synthesis of the proof of work (POW) mechanism used in bitcoin, and the proof of stake (POS) mechanism used in various altcoin communities. The paper argues that the proposed POK system would enable the academic community to more effectively develop the research it finds valuable.
Artificial intelligence (AI) has demonstrated huge potential in a variety of real-world applications. However, some significant considerations like fairness, transparency and trustworthiness are still challenging when applying AI to trust-oriented applications such as E-voting. E-voting plays a significant role in democratic societies, which requires voters and initiators have strong mutual trust. In this paper, we aim to facilitate the consolidation of AI ecosystems by developing a blockchain-based traceable self-tallying e-voting system. We take advantage of an event-oriented linkable group signature and a homomorphic time-lock puzzle to balance the anonymity and accountability, and the voting scale and efficiency of an e-voting system. The proposed e-voting protocol supports additional functions like multi-choice and self-tallying. We prove that the proposed protocol satisfies anonymity, time-bounded privacy, linkability and full-traceability. We also evaluate the time cost of off-chain operations and the gas cost of on-chain operations, which show the proposed e-voting protocol is practical and can be adopted in real-world applications.
Riccardo Longo, Alessandro Sebastian Podda, Roberto Saia
Currently, an increasing number of third-party applications exploit the Bitcoin blockchain to store tamper-proof records of their executions, immutably. For this purpose, they leverage the few extra bytes available for encoding custom metadata in Bitcoin transactions. A sequence of records of the same application can thus be abstracted as a stand-alone subchain inside the Bitcoin blockchain. However, several existing approaches do not make any assumptions about the consistency of their subchains, either (i) neglecting the possibility that this sequence of messages can be altered, mainly due to unhandled concurrency, network malfunctions, application bugs, or malicious users, or (ii) giving weak guarantees about their security. To tackle this issue, in this paper, we propose an improved version of a consensus protocol formalized in our previous work, built on top of the Bitcoin protocol, to incentivize third-party nodes to consistently extend their subchains. Besides, we perform an extensive analysis of this protocol, both defining its properties and presenting some real-world attack scenarios, to show how its specific design choices and parameter configurations can be crucial to prevent malicious practices.
As the core of blockchain technology, the consensus algorithm plays an important role in determining the security, data consistency, and efficiency of blockchain systems. The existing mainstream consensus algorithm is experiencing difficulties satisfying the needs of efficiency, security, and decentralization in real-world scenarios. This paper proposes a hybrid consensus algorithm based on modified Proof-of-Probability and Delegated Proof-of-Stake. In this method, the work of block generation and validation is, respectively, completed by the nodes using the modified Proof-of-Probability consensus algorithm and Delegated Proof-of-Stake consensus algorithm. When a transaction occurs, the system sends several target hash values to the whole network. Each modified Proof-of-Probability node has a different sorting algorithm, so they have different mining priorities. Every time a hash is decrypted by a modified Proof-of-Probability node, the modulo operation is done to the value of nonce, which is then compared with the expected value given by the supernode selected by the Delegated Proof-of-Stake nodes. If they are not the same, the Proof-of-Probability node enters the waiting time and the other Proof-of-Probability nodes continue to mine. By adopting two consensus algorithms, the malicious nodes must control more than 51% of the nodes that adopt the two consensus algorithms, at the same time, to effectively attack the system, that is, they must have more than 51% of the computing power and more than 51% of the tokens. This not only increases the cost of malicious attacks, but also reduces waste of computing power. In addition, the efficiency of the DPoS algorithm makes up for the deficiency of the PoP algorithm in system efficiency, and the mining behavior based on probability in the PoP algorithm also significantly weakens the ability of supernodes in the DPoS algorithm to conduct monopoly behavior or other malicious behaviors. In a word, the combination of the two algorithms makes the system perform better in terms of security, system efficiency, and decentralization.
Fault-tolerant distributed systems move the trust in a single party to a majority of parties participating in the protocol. This makes blockchain based crypto-currencies possible: they allow parties to agree on a total order of transactions without a trusted third party. To trust a distributed system, the security of the protocol and the correctness of the implementation must be indisputable. We present the first machine checked proof that guarantees both safety and liveness for a consensus algorithm. We verify a Proof of Stake (PoS) Nakamoto-style blockchain (NSB) protocol, using the foundational proof assistant Coq. In particular, we consider a PoS NSB in a synchronous network with a static set of corrupted parties. We define execution semantics for this setting and prove chain growth, chain quality, and common prefix which together imply both safety and liveness.
The long-standing impossibility of reaching agreement restricts the lifespan of blockchains. In fact, the consensus on a block to be appended to any blockchain succeeds either with some probability or at the condition that two thirds of the $n$ replicas are not Byzantine. In the former case, the probability that the blockchain fails grows exponentially with the number of newly appended blocks. In the latter case, the blockchain fails as soon as a coalition bribes $f=n/3$ replicas. As a result, one may wonder whether blockchains are doomed to fail.
In this paper, we answer this question in the negative by proposing the first Longlasting Blockchain system, \emph{LLB}. LLB builds upon the observation that blockchains are rarely subject to benign faults. As opposed to probabilistic blockchains, LLB solves consensus deterministically when $f<n/3$. As opposed to Byzantine fault tolerant blockchains, it resolves a series of disagreements by reducing eventually the number of deceitful replicas from $n/3\leq f<2n/3$ to $f'<n'/3$ among a new set of $n'$ replicas. To demonstrate its effectiveness, we implement two coalition attacks and a zero loss payment application that forces replicas that misbehave to reimburse conflicting transactions. Finally, LLB outperforms the raw state machine replication at the heart of Facebook's Libra and achieves performance comparable to a scalable blockchain that cannot tolerate $n/3$ failures.
Alberto García-Martínez, Stefano Angieri, Bingyang Liu, Fei Yang · 5 authors
The current mechanism to secure Border Gateway Protocol relies on the resource public key infrastructure (RPKI) for route origin authorization. The RPKI implements a hierarchical model that intrinsically makes lower layers in the hierarchy susceptible to errors and abuses from entities placed in higher layers. In this article, we present InBlock, a distributed autonomous organization that provides decentralized management of IP addresses based on blockchain, embedding an alternative trust model to the hierarchical one currently implemented by the RPKI. By leveraging on blockchain technology, InBlock requires consensus among the involved parties to change existent prefix allocation information. InBlock also fulfills the same objectives as the current IP address allocation system, i.e., uniqueness, fairness, conservation, aggregation, registration, and minimized overhead. InBlock is implemented as a set of blockchain smart contracts in Ethereum, performing all the functions needed for the management of a global pool of addresses without human intervention. Any entity may request an allocation of addresses to the InBlock registry by solely performing a (crypto) currency transfer to the InBlock. We describe our InBlock implementation and we perform several experiments to show that it enables fast address registering and incurs in very low management costs.
Max DiGiacomo-Castillo, Yiyun Liang, Advay Pal, John C. Mitchell
The Bitcoin Backbone Protocol [GKL15] is an abstraction of the bitcoin proof-of-work consensus protocol. We use a model-checking tool (UPPAALSMC) to examine the concrete security of proof-ofwork consensus by varying protocol parameters and using an adversary that leverages the selfish mining strategy introduced in [GKL15]. We provide insights into modeling proof-of-work protocols and demonstrate tradeoffs between operating parameters. Applying this methodology to protocol design options, we show that the uniform tie-breaking rule from [ES18] decreases the failure rate of the chain quality property, but increases the failure rate of the common prefix property. This tradeoff illustrates how design decisions affect protocol properties, within a range of concrete operating conditions, in a manner that is not evident from prior asymptotic analysis.
Smart contracting protocols promise to regulate the transfer of cryptocurrency amongst participants in a trustless manner. A safe smart contract implementation should ensure that each participant can always append a contract transaction to the blockchain in order move the contract towards secure completion. To this goal, we propose Bitcoin Trace-Net, a contract verification framework which generates an executable symbolic model from the underlying contract implementation. A Trace-Net model consists of a Petri Net formalism enriched with a Dolev-Yao-like actor knowledge model. The explicit symbolic actor knowledge model supports the verification of contracts featuring cryptographic sub-protocols, which may not be observable on the blockchain. Trace-Net is sufficiently expressive to accurately model blockchain semantics such as the delay between a transaction broadcast and its subsequent confirmation, as well as adversarial blockchain reorganizations of finite depths, both of which can break smart contract safety. As an implementation level framework, Trace-Net can be instantiated at run-time to monitor and verify smart contract protocol executions.
The need for data trading promotes the emergence of data market. However, in conventional data markets, both data buyers and data sellers have to use a centralized trading platform which might be dishonest. A dishonest centralized trading platform may steal and resell the data seller's data, or may refuse to send data after receiving payment from the data buyer. It seriously affects the fair data transaction and harm the interests of both parties to the transaction. To address this issue, we propose a novel blockchain-based data trading framework with Trusted Execution Environment (TEE) to provide a trusted decentralized platform for fair data trading. In our design, a blockchain network is proposed to realize the payments from data buyers to data sellers, and a trusted exchange is built by using a TEE for the first time to achieve fair data transmission. With these help, data buyers and data sellers can conduct transactions directly. We implement our proposed framework on Ethereum and Intel SGX, security analysis and experimental results have demonstrated that the framework proposed can effectively guarantee the fair completion of data tradings.
Suyash Gupta, Jelle Hellings, Sajjad Rahnama, Mohammad Sadoghi
Since the introduction of Bitcoin---the first wide-spread application driven by blockchains---the interest of the public and private sector in blockchains has skyrocketed. At the core of this interest are the ways in which blockchains can be used to improve data management, e.g., by enabling federated data management via decentralization, resilience against failure and malicious actors via replication and consensus, and strong data provenance via a secured immutable ledger.
Jiaqi Wang, Ning Lu, Qingfeng Cheng, Lu Zhou · 5 authors
With the development of communication 5G networks and technologies, spectrum resources are increasingly scarce. The scarcity of the spectrum resource makes market-driven spectrum auction become an important means of spectrum allocation, and due to the complexity of the network environment, the security of spectrum auctions can not be ignored. Most existing secure spectrum auction schemes introduce a semi-honest agent to complete spectrum auction. However, the hypothetical semi-honest model does not guarantee the security of spectrum auction in the actual application scenario, which may lead to potential security threats: the agent may reveal the privacy of bidders, agent or auctioneer may collude with the bidder to manipulate the spectrum auction, and so on. In this paper, a secure spectrum auction scheme without a trusted party is proposed based on the smart contract technology, and the smart contract written into the blockchain replaces the traditional semi-honest agent to cooperate with the auctioneer server to complete the auction. In order to ensure the security of our scheme, a secure spectrum auction protocol is designed, in which the Software Guard Extensions (SGX) technology and Paillier cryptosystem are used to protect the privacy of bidders. Public verification is provided in our protocol by using extensive Pedersen commitment, which prevents the auctioneer server and the bidder from colluding with each other and verifies group bid sum values. Finally, the security analysis is given to propose several types of attacks that can be defended. Besides, theoretical analysis and simulation experiments of our protocol are also provided.
Digital identity is one of the biggest challenges in cyberspace. This field has been evolving for many decades with a number of Identity Management (IDM) models being proposed and employed; however, few were able to solve the issue of sovereignty of an identity and storage-control of its associated personal and confidential data. Self-Sovereign Identity (SSI) was introduced to solve this crucial issue offering a user full sovereignty of their identity and storage-control of their associated personal and confidential data. Alongside ownership of an identity, it maintains all private information in a Digital Wallet which is owned and controlled by the user. However, SSI is an emerging IDM, therefore it requires careful evaluation of various aspects of SSI for it to become an operative IDM. This paper proposes several specifications to evaluate any SSI solution. Subsequently, it analyses two emerging SSI solutions uPort and Sovrin. Finally, an evaluation of uPort and Sovrin SSI is performed utilising the proposed specifications, highlighting their strengths and limitations.