Offline electronic cash is a new and well-acknowledged type of e-cash scheme that can release the bank from participating in every spending protocol. However, it is still an unsolved problem to design a secure and efficient fair offline e-cash scheme. Considering this problem, in this paper, we have proposed a fair offline electronic cash scheme with multiple banks in pairing-based instantiation. We adopt Groth–Sahai non-interactive zero-knowledge proof technology in our scheme, to design non-interactive e-cash transactions. Additionally, inspired by Water’s group signature, our solution supports not only multiple users, but also users with accounts in different banks. Moreover, our scheme has efficient double-spending checking and a fair control mechanism. We have formally defined the security properties of the scheme in a standard model, and provided the detailed security proofs of the security properties concerning chosen ciphertext attack (CCA) anonymity, unforgeability and traceability. Analysis and comparison show that our scheme has advantages both in security and in efficiency.
Tobias Korb, David Michel, Oliver Riedel, Armin Lechler
For several years, blockchain technology have been used and tested in various prototypes for production environments. The main focus of these approaches is the feasibility of different applications. It is usually simply assumed that data in a blockchain is stored immutably. However, the path from data generation to entry into a blockchain is usually neglected. Exactly this topic is discussed in this paper and a solution proposal for a secure data flow from the machine to the blockchain is presented. For this, the hardware and software architecture of the solution is shown, followed by measurements of the operational capability of the solution.
Huge storage volume is one of the main bottlenecks for the development of blockchain, so how to release the burden by optimizing the storage mechanism has become an important problem. Most of the current solutions would modify the architecture of blockchain, which weakens the characteristics of the decentralization, such as cloud storage. In this paper, a storage optimization mechanism based on residual number system is proposed to reduce the storage volume on each node. In addition, the recovery procedure of CRT-II (The new Chinese Remainder Theorem) is used to detect garbled data from devil nodes, which enable the proposed storage mechanism with strong fault tolerance capability. Both theoretical analysis and simulation results prove the effectiveness and reliability of the proposed scheme.
The architecture of integrating blockchain with Industry 4.0 IoT network has emerged in recent years. Industry 4.0 refers to the new concept of intelligent manufacturing paradigm, including Internet of Things (IoT), Cloud computing and Cyber-Physical System (CPS). Blockchain is a decentralized, distributed ledger system used to record transactions across multiple participants. Blockchain offers a way of recording data that is designed to be secure, reliable and auditable, which makes it a preferred solution for securing IoT network. However, traditional blockchain suffers from storage scalability issue because each blockchain node stores the entire blockchain. The storage scalability problem can be even worse when blockchain is used in IoT network due to the high volume of data generated by massive number of IoT sensors. In this thesis, we propose a distributed storage architecture for blockchain based on erasure coding. The property of erasure coding makes it possible to greatly reduce storage overhead for each node without affecting the overall data integrity. Furthermore, to minimize the latency of rebuilding data in this distributed storage architecture, we formulate a latency-cost trade-off optimization problem and propose an efficient and scalable algorithm. Simulation results show that our architecture can achieve up to 80% latency reduction compared with other widely used distributed storage architectures. In addition, our architecture can save up to 90% storage space for each node, which removes the largest obstacle for integrating blockchain into IoT network.
We focus on securely computing the ranks of sealed integers distributed among n parties. For example, we securely compute the largest or smallest integer, the median, or in general the kth-ranked integer. Such computations are a useful building block to securely implement a variety of sealed-bid auctions. Our objective is efficiency, specifically low interactivity between parties to support blockchains or other scenarios where multiple rounds are time-consuming. Hence, we dismiss powerful, yet highly-interactive MPC frameworks and propose BOREALIS, a special-purpose protocol for secure computation of ranks among integers. BOREALIS uses additively homomorphic encryption to implement core comparisons, but computes under distinct keys, chosen by each party to optimize the number of rounds. By carefully combining cryptographic primitives, such as ECC Elgamal encryption, encrypted comparisons, ciphertext blinding, secret sharing, and shuffling, BOREALIS sets up systems of multi-scalar equations which we efficiently prove with Groth-Sahai ZK proofs. Therewith, BOREALIS implements a multi-party computation of pairwise comparisons and rank zero-knowledge proofs secure against malicious adversaries. BOREALIS completes in at most 4 rounds which is constant in both bit length l of integers and the number of parties n. This is not only asymptotically optimal, but surpasses generic constant-round secure multi-party computation protocols, even those based on shared-key fully homomorphic encryption. Furthermore, our implementation shows that BOREALIS is very practical. Its main bottleneck, ZK proof computations, is small in practice. Even for a large number of parties (n=200) and high-precision integers (l=32), computation time of all proofs is less than a single Bitcoin block interval.
Cryptocurrencies, like Bitcoin, present challenges to plaintiffs seeking to recover these digital assets. No third-party intermediaries are involved in cryptocurrency transactions, and there is no controlling authority that can revoke or avoid a transaction once completed. The possessor of a cryptocurrency's private key-its password-has total and exclusive control over the account's assets. These digital assets cross jurisdictional boundaries without impediment. The features of cryptocurrencies make it easy for defendants to judgment-proof themselves and make these assets difficult to recover after a court has entered judgment. This comment explains cryptocurrency features relevant to asset recovery, explores pre-and postjudgment procedures as applied to cryptocurrencies, and suggests ways to mitigate the risks of this potentially difficult-to-recover asset.
The future of distributed ledger technology such as blockchain is dependent on its ability to interact and integrate with other systems. Therefore, interoperability has become a fundamental issue that needs to be addressed. The emerging category of crypto-assets are managed and understood using different frameworks. There is, therefore, a need for a unified classification of crypto-assets. This work aims to bring some clarity to and understanding on interoperable crypto-assets and their characteristics. This paper categorizes digital crypto-assets for the purpose of implementing interoperability. The categorization of crypto-assets is based on their functionalities and their purpose. An interoperability scenario has been given for the defined crypto-asset classes.
Smart contracts on blockchain systems implement business logic and directly handle important assets. Although smart contracts play these critical roles, it is hard for users interacting with the system to understand the real behavior of the deployed bytecodes of smart contracts. The quirks of smart contracts, such as code reuse and limited unique datasets, make it challenging to recognize the functional details of smart contracts. In this paper, we propose a new method for characterizing bytecode-only smart contracts by automatically assigning multiple attribute tags. Using a deep learning approach, our system, the ScanAT, extracts attribute tags from the source code and metadata of known smart contracts and trains their bytecode with the attribute tags. The ScanAT then infers attribute tags from the bytecode of smart contracts alone. Our experiments show that ScanAT can achieve 81% accuracy in predicting attribute tags, using convolutional neural networks and a customized autoencoder.
Decentralised ledgers are a prime application case for consensus protocols. Changing sets of validators have to agree on a set of transactions in an asynchronous network and in the presence of Byzantine behaviour. Major research efforts focus on creating consensus protocols under such conditions, with proof-of-stake (PoS) representing a promising candidate. PoS aims to reduce the waste of energy inherent to proof-of-work (PoW) consensus protocols. However, a significant challenge is to get PoS protocols "right", i.e. ensure that they are secure w.r.t. safety and liveness. The "Correct-by-Construction" (CBC) Casper approach by the Ethereum project employs pen-and-paper proofs to ensure its security. CBC Casper is a framework to define consensus protocols and aims to prove safety without loss of abstractness. Each member of the CBC Casper family of protocols is defined by five parameters. CBC Casper models the protocol by a state of each validator and messages sent by validators. Each validator can transition its state using messages by other validators that include their current consensus value and a justification (i.e. their previous messages). We extend CBC Casper in three ways. First, we summarise the research of CBC Casper and extend the definitions of safety and liveness properties. To this end, we discuss an instance of CBC Casper called Casper The Friendly GHOST (TFG), a consensus protocol using a variant of the GHOST fork-choice rule. Second, we refine the properties of messages and states in CBC Casper and give a definition of blockchain safety for Casper TFG. Third, we formally verify the CBC Casper framework together with our refined message and state properties as well as our blockchain safety definition in the Isabelle/HOL proof assistant.
Zhiyi Zhang, Vishrant Vasavada, Randy King, Lixia Zhang
Over the last few years, blockchain-based technologies have flourished in many application areas. One of them is the creation of distributed ledgers where records of immutable objects are widely replicated for both transparency and availability. However, the Proof-of-Work (PoW) approach, a popular gating control that determines who can add new records into a ledger, is deemed infeasible for IoT devices with resource constraints.
Zsolt István, Alessandro Sorniotti, Marko Vukolić
Processing at block granularity and blockchains seem inseparable. The original role of blocks is to amortize the cost of cryptography (e.g., solving proof-of-work) and to make data transfers more efficient in a geo-distributed setting. While blocks are a simple and powerful tool for amortizing these costs, today in permissioned distributed ledgers, that are often neither geo-distributed, nor require proof-of-work, the benefits of operating on blocks are overshadowed by the large latencies they introduce.
Blockchains yield to new workloads in database management systems and K/V-Stores. Distributed Ledger Technology (DLT) is a technique for managing transactions in 'trustless' distributed systems. Yet, clients of nodes in blockchain networks are backed by 'trustworthy' K/V-Stores, like LevelDB or RocksDB in Ethereum, which are based on Log-Structured Merge Trees (LSM-Trees). However, LSM-Trees do not fully match the properties of blockchains and enterprise workloads.
Yonggen Gu, Dingding Hou, Xiaohong Wu, Jie Tao · 5 authors
Distributed data storage has received more attention due to its advantages in reliability, availability and scalability, and it brings both opportunities and challenges for distributed data storage transaction. The traditional transaction system of storage resources, which generally runs in a centralized mode, results in high cost, vendor lock-in and single point failure risk. To overcome the above shortcomings, considering the storage policy with erasure coding, in this paper we propose a decentralized transaction method for cloud storage based on a smart contract, which takes into account the resource cost for distributed data storage. First, to guarantee the availability and decrease the storing cost, a reverse Vickrey-Clarke-Groves (VCG) based auction mechanism is proposed for storage resource selection and transaction. Then we deploy and implement the proposed mechanism by designing a corresponding smart contract. Especially, we address the problem of how to implement a VCG-like mechanism in a blockchain environment. Based on the private chain of Ethereum, we make the simulation for the proposed storage transaction method. The results of simulation show that the proposed transaction model can realize competitive trading of storage resources and ensure the safe and economic operation of resource trading.
In this paper, we consider blockchain technology that enabledthe existence of digital currency and we investigate Bitcoin cryptocurrency application. This technology nowadays represents a new feature that replaces existing client-server core system on top of some distributed systems with many additional features such as high availability, resistance to alteration, fault tolerance and cost reduction. After overviewing how such technology is working, we highlightthe requirements and benefits related to the security, database and network. We mainly focus on answering the most Bitcoin queries including privacy and double spending. Furthermore, as blockchain has potential applications far beyond bitcoin, we draw future insights where applications based blockchain are provisioned in the market in order to be totally or partially independent of the centralized systems and we provide a questionnaire helping organizations for better using the blockchain feasibilities.
We investigate a family of bugs in blockchain-based smart contracts, which we call event-ordering (or EO) bugs. These bugs are intimately related to the dynamic ordering of contract events, i.e., calls of its functions on the blockchain, and enable potential exploits of millions of USD worth of Ether. Known examples of such bugs and prior techniques to detect them have been restricted to a small number of event orderings, typicall 1 or 2. Our work provides a new formulation of this general class of EO bugs as finding concurrency properties arising in long permutations of such events. The technical challenge in detecting our formulation of EO bugs is the inherent combinatorial blowup in path and state space analysis, even for simple contracts. We propose the first use of partial-order reduction techniques, using happen-before relations extracted automatically for contracts, along with several other optimizations built on a dynamic symbolic execution technique. We build an automatic tool called ETHRACER that requires no hints from users and runs directly on Ethereum bytecode. It flags 7-11% of over ten thousand contracts analyzed in roughly 18.5 minutes per contract, providing compact event traces that human analysts can run as witnesses. These witnesses are so compact that confirmations require only a few minutes of human effort. Half of the flagged contracts have subtle EO bugs, including in ERC-20 contracts that carry hundreds of millions of dollars worth of Ether. Thus, ETHRACER is effective at detecting a subtle yet dangerous class of bugs which existing tools miss.
This paper explains how the distributed ledger technology that has successfully decentralized currencies can be used to enable a decentralized marketplace for digital content rights. Today, multiple centralized rights lockers from companies and consortiums offer similar but incompatible systems to register a consumer's video purchases and manage content rights. Each is representing a monopoly that centrally governs the content rights and is motivated to do so only for as long as it remains profitable. — Blockchain technology can be used to establish a permanent, secure, decentralized and distributed registry for content registration, assignment and archival of rights. The benefits of leveraging blockchain for video content distribution and content rights management provide longevity that is independent of a single standard, company or governance body as well as security of transactions with cryptographic guarantee of entitlements and grants of content licenses that cannot be changed and verified permanently. Lastly, the distributed and replicated nature of the peer-to-peer (P2P) network provides resiliency, eliminating a single point of failure as well as the need to rely on just one single standard, company or governance body. This paper will provide a novel system design that explains how a blockchain can be applied to not only manage content rights but to also secure content by including digital rights management (DRM) and playback control as an integral part of the decentralized network. It also details how to improve common ledger technology to overcome concerns of performance and abuse that are relevant to this application.
Traditionally, the Net Present Value method has been used to compare diverging investment strategies. However, valuating crypto-projects with fiat-based currency is confusing due to extreme coin appreciation rates as compared to fiat interest rates. Here, we provide a net present value method based on using crypto-coin as the underlying asset. Using this method, we compare buy-and-hold versus mine-and-hold; we also provide a sensitivity analysis of profitability.