Eder J. Scheid, Timo Hegnauer, Bruno Rodrigues, Burkhard Stiller
The blockchain (BC) world is rapidly becoming a universe of several ledgers designed for a specific purpose, holding data previously stored (i.e., siloed) in centralized databases. The use of different BCs for the same purpose could hamper the frictionless exchange of data or value. On one hand, it is natural that there are competing implementations exploring the benefits of BC. On the other hand, the problem of siloed data re-emerges, with respect to isolated chains. In this regard, BC interoperability is necessary to connect different BCs, exchanging information and assets. Moreover, to foster BC employment, developers must be able to interact with such different BCs without knowing the details of each implementation. This paper presents a novel solution, called Bifröst, to store and retrieve data on different BCs. Bifröst employs a notary scheme, which allows for connectivity to different BCs. The presented prototype is highly modular and currently implements seven adapters to popular BC implementations, including Bitcoin, Ethereum, and Stellar. The developed prototype was evaluated concerning performance, security, and data size to verify the feasibility of such an implementation and assess design decisions taken during its development.
I Gusti Bagus Baskara Nugraha, Yoanes Bandung, Ahmad Zaky
In general, the electronic official documents system is designed with a centralized system and managed by each government agency, so that data and records of official documents process activities are stored in a centralized database and managed by a single organizational unit. However, there are some disadvantages of this centralized system, especially in the workflow of official documents that involve more than one organizational unit. i.e. dependence on third parties which is the sole authority of the official documents data management. If there is a system failure there is a certain period of time, it will increase the activity cycle time and decrease activity time efficiency in the official documents business process. The blockchain-based solution described in this paper is to avoid the occurrence of delay times during the activity cycle time in business processes when a system failure occurs which can cause a decrease in activity time efficiency. Blockchain makes the official documents system become “Trusless Operation” with each participant of different organizational unit having a copy of transaction data through a consensus mechanism. The simulation results show that our system can reduce time delay in activity cycle time during a system failure as long as the number of faulty peers within the tolerance limit so that it can increase the activity time efficiency.
Léonard Lys, Arthur Micoulet, Maria Potop-Butucaru
Blockchains interoperability is one of the hardest problems to be solved in the nowadays blockchain ecosystem that contains thousands of different blockchains. This paper focuses on swapping assets from a blockchain to another without a trusted third party. One recent scheme for atomically swapping assets, Atomic Cross Chain Swap (ACCS), has been formally analyzed in [2]. This paper proposes an implementation of an ACCS between the two most valued crypto-currencies today: Bitcoin and Ether.
Block-chain is rapidly evolving. There are continuous enhancements. In order to validate transactions algorithm is used. The traditional approach of Proof of Work (POW) is where miners are incentivized to compete with each other to complete transactions. Alternate system is proof of stake (POS) where in the validators lock up some of their tokens and thus replace the role of miners. Generation three block chain, which are the latest and fastest ones are mostly Proof of Stake (POS). Hence the POW systems seek to leverage the POS properties in order to attain higher speed and scalability. The paper discusses the approach with Ethereum has taken to migrate from the current POW protocol to POS protocol. The concept of Caster is focused as implementation. Casper further has two subtypes of approaches know as Friendly Finality Gadget (FFG) and Correct by Construction (CBC). The paper discusses on safety guard over these algorithms.
Blockchain is a distributed system with decentralized, tamper-proof, traceability and other characteristics. The primary function of a distributed system is to enable consensus among nodes without trust. It is especially important to choose the appropriate consensus mechanism to improve the performance of the blockchain. Based on the original Proof of Stake (PoS), this paper introduces behavioral credits, establishes credit ratings, and interacts with the currency age in the PoS mechanism. By this way, it makes the revenue distribution of the nodes participating in the generation of the PoS mechanism more fair and reasonable, improves social stratification and resists the trend of system centralization.
Designing a secure permission distributed ledger that has the same performance a centralized counterpart, such as Visa, is a challenging task. The majority of available distributed ledgers are unable to scale to that degree. To increase the number of transactions per second, we can either compromise on security or partition the Blockchain. Here, we present Apex, a novel hierarchical distributed ledger that increases the overall performance by 1) partitioning groups of nodes into smaller concurrent distributed ledgers 2) limiting how transactions can flow to the system while guaranteeing the security and 3) combining blocks of each partition into a separate aggregated distributed ledger. Apex is designed for use-cases that require public and transparent accounting such as intellectual property rights in the music industry. An evaluation of our experimental prototype shows that Apex's throughput scales linearly with the number of active nodes while transaction confirmation is less than two seconds. By applying these tree constructs we achieve almost linear speedup in terms of transactions per second simultaneously lowering latency and verification computation-cost per node.
Public blockchains like Ethereum use Merkle trees to verify transactions received from untrusted servers before applying them to the blockchain. We empirically show that the low throughput of such blockchains is due to the I/O bottleneck associated with using Merkle trees for processing transactions. We present RAINBLOCK, a new architecture for public blockchains that increases throughput without affecting security. RAINBLOCK achieves this by tackling the I/O bottleneck on two fronts: first, decoupling transaction processing from I/O, and removing I/O from the critical path; second, reducing I/O amplification by customizing storage for blockchains. RAINBLOCK uses a novel variant of the Merkle tree, the Distributed Sharded Merkle tree (DSM-TREE) to store system state. We evaluate RAINBLOCK using workloads based on public Ethereum traces (including smart contracts) and show that RAINBLOCK processes 20K transactions per second in a geo-distributed setting with four regions spread across three continents.
Bitcoin is the first fully-decentralized permissionless blockchain protocol to achieve a high level of security, but at the expense of poor throughput and latency. Scaling the performance of Bitcoin has a been a major recent direction of research. One successful direction of work has involved replacing proof of work (PoW) by proof of stake (PoS). Proposals to scale the performance in the PoW setting itself have focused mostly on parallelizing the mining process, scaling throughput; the few proposals to improve latency have either sacrificed throughput or the latency guarantees involve large constants rendering it practically useless. Our first contribution is to design a new PoW blockchain Prism++ that has provably low latency and high throughput; the design retains the parallel-chain approach espoused in Prism but invents a new confirmation rule to infer the permanency of a block by combining information across the parallel chains. We show security at the level of Bitcoin with very small confirmation latency (a small constant factor of block interarrival time). A key aspect to scaling the performance is to use a large number of parallel chains, which puts significant strain on the system. Our second contribution is the design and evaluation of a practical system to efficiently manage the memory, computation, and I/O imperatives of a large number of parallel chains. Our implementation of Prism++ achieves a throughput of over 80,000 transactions per second and confirmation latency of tens of seconds on networks of up to 900 EC2 Virtual Machines.
Distributed Ledger Technology (DLT) is a shared, synchronized and replicated data spread spatially and temporally with no centralized administration and/or storage. Each node has a complete and identical set of records. All participants contribute to building and maintaining the distributed ledger. Current DLT technologies fall into two broad categories. Those that use block-chains such as in Bitcoin or Ethereum, and newer approaches which reduce computational loads for verification. All current approaches though difficult to crack can be vulnerable to quantum algorithms using Quantum Information Technologies (QIT). This effort joins the 2 technologies, constructing a Quantum Distributed Ledger (QDL) which provides a higher level of security using QIT and a decentralized data depository using DLT. This enhanced security prevents middleman attacks with quantum computers yet retains the advantages of a decentralized ledger of data.
There is a preconception that a blockchain needs consensus. But consensus is a powerful distributed property with a remarkably high price tag. So one may wonder whether consensus is at all needed.
We introduce a new blockchain architecture called ABC that functions despite not establishing consensus, and comes with an array of advantages: ABC is permissionless, deterministic, and resilient to complete asynchrony. ABC features finality and does not rely on costly proof-of-work.
Without establishing consensus, ABC cannot support certain applications, in particular smart contracts that are open for interaction with unknown agents. However, our system is an advantageous solution for many important use cases, such as cryptocurrencies like Bitcoin.
We introduce a new permissionless blockchain architecture called ABC. ABC is completely asynchronous, and does rely on neither randomness nor proof-of-work. ABC can be parallelized, and transactions have finality within one round trip of communication. However, ABC satisfies only a relaxed form of consensus by introducing a weaker termination property. Without full consensus, ABC cannot support certain applications, in particular ABC cannot support general smart contracts. However, many important applications do not need general smart contracts, and ABC is a better solution for these applications. In particular, ABC can implement the functionality of a cryptocurrency like Bitcoin, replacing Bitcoin's energy-hungry proof-of-work with a proof-of-stake validation.
A blockchain and smart contract enabled security mechanism for IoT applications has been reported recently for urban, financial, and network services. However, due to the power-intensive and a low-throughput consensus mechanism in existing blockchain, like Bitcoin and Ethereum, there are still challenges in integrating blockchain technology into resource-constrained IoT platforms. In this paper, Microchain, based on a hybrid Proof-of-Credit (PoC)-Voting-based Chain Finality (VCF) consensus protocol, is proposed to provide a secure, scalable and lightweight distributed ledger for IoT systems. By using a bias-resistant randomness protocol and a cryptographic sortition algorithm, a random subset of nodes are selected as a final committee to perform the consensus protocol. The hybrid consensus mechanism relies on PoC, a pure Proof of stake (PoS) protocol, to determine whether or not a participant is qualified to propose a block, given a fair initial distribution of the credit assignment. The voting-based chain finality protocol is responsible for finalizing a history of blocks by resolving conflicting checkpoint and selecting a unique chain. A proof-of-conception prototype is implemented and tested on a physical network environment. The experimental results verify that the Micorchain is able to offer a partially decentralized, scalable and lightweight distributed ledger protocol for IoT applications.
In this work, we present IBFT 2.0 (Istanbul BFT 2.0), which is a Proof-of-Authority (PoA) Byzantine-fault-tolerant (BFT) blockchain consensus protocols that (i) ensures immediate finality, (ii) is robust in an eventually synchronous network model and (iii) features a dynamic validator set. IBFT 2.0, as the name suggests, builds upon the IBFT blockchain consensus protocol retaining all of the original features while addressing the safety and liveness limitations described in one of our previous works. In this paper, we present a high-level description of the IBFT 2.0 protocol and related robustness proof. Formal specification of the protocol and related formal proofs will be subject of a separate body of work. We also envision a separate work that will provide detailed implementation specifications for IBFT 2.0.
A blockchain is a database of sequential events that is maintained by a distributed group of nodes. A key consensus problem in blockchains is that of determining the next block (data element) in the sequence. Many blockchains address this by electing a new node to propose each new block. The new block is (typically) appended to the tip of the proposer's local blockchain, and subsequently broadcast to the rest of the network. Without network delay (or adversarial behavior), this procedure would give a perfect chain, since each proposer would have the same view of the blockchain. A major challenge in practice is forking. Due to network delays, a proposer may not yet have the most recent block, and may, therefore, create a side chain that branches from the middle of the main chain. Forking reduces throughput, since only one a single main chain can survive, and all other blocks are discarded. We propose a new P2P protocol for blockchains called Barracuda, in which each proposer, prior to proposing a block, polls $\ell$ other nodes for their local blocktree information. Under a stochastic network model, we prove that this lightweight primitive improves throughput as if the entire network were a factor of $\ell$ faster. We provide guidelines on how to implement Barracuda in practice, guaranteeing robustness against several real-world factors.
In this paper, we propose a scheme that implements a Distributed Ledger Technology (DLT) based on Directed Acyclic Graph (DAG) to generate, validate, and confirm the electricity transaction in Smart Grid. The convergence of the Smart Grid and distributed ledger concept has recently been introduced. Since Smart Grids require a distributed network architecture for power distribution and trading, the Distributed Ledger-based Smart Grid design is a spotlighted research domain. However, only the Blockchain-based methods, which are a type of the distributed ledger scheme, are currently either being considered or adopted in the Smart Grid. Due to computation-intensive consensus schemes such as Proof-of-Work and discrete block generation, Blockchain-based distributed ledger systems suffer from efficiency and latency issues. We propose a DAG-based distributed ledger for Smart Grids, called PowerGraph, to resolve this problem. Since a DAG-based distributed ledger does not need to generate blocks for confirmation, each transaction of the PowerGraph undergoes the validation and confirmation process individually. In addition, transactions in PowerGraph are used to keep track of the energy trade and include various types of transactions so that they can fully encompass the events in the Smart Grid network. Finally, to ensure that PowerGraph maintains a high performance, we modeled the PowerGraph performance and proposed a novel consensus algorithm that would result in the rapid confirmation of transactions. We use numerical evaluations to show that PowerGraph can accelerate the transaction processing speed by over 5 times compared to existing DAG-based DLT system.
To implement a blockchain, the trend is now to integrate a non-trivial Byzantine fault tolerant consensus algorithm instead of the seminal idea of waiting to receive blocks to decide upon the longest branch. After a decade of existence, blockchains trade now large amounts of valuable assets and a simple disagreement could lead to disastrous losses. Unfortunately, Byzantine consensus solutions used in blockchains are at best proved correct "by hand" as we are not aware of any of them having been formally verified. In this paper, we propose two contributions: (i) we illustrate the severity of the problem by listing six vulnerabilities of blockchain consensus including two new counter-examples; (ii) we then formally verify two Byzantine fault tolerant components of Red Belly Blockchain using the ByMC model checker. First, we specify a simple broadcast primitive in 116 lines of code that is verified in 40 seconds on a 2-core Intel machine. Then, we specify a blockchain consensus algorithm in 276 lines of code that is verified in 17 minutes on a 64-core AMD machine using MPI. To conclude, we argue that it has now become both relatively simple and crucial to formally verify the correctness of blockchain consensus protocols.
Jun Zhao, Jing Tang, Zengxiang Li, Huaxiong Wang · 6 authors
Formal analyses of blockchain protocols have received much attention recently. Consistency results of Nakamoto's blockchain protocol are often expressed in a quantity $c$, which denotes the expected number of network delays before some block is mined. With $μ$ (resp., $ν$) denoting the fraction of computational power controlled by benign miners (resp., the adversary), where $μ+ ν= 1$, we prove for the first time that to ensure the consistency property of Nakamoto's blockchain protocol in an asynchronous network, it suffices to have $c$ to be just slightly greater than $\frac{2μ}{\ln (μ/ν)}$. Such a result is both neater and stronger than existing ones. In the proof, we formulate novel Markov chains which characterize the numbers of mined blocks in different rounds.
Zhimin Gao, Lei Xu, Keshav Kasichainula, Lin Chen · 6 authors
Bitcoin brings a new type of digital currency that does not rely on a central\nsystem to maintain transactions. By benefiting from the concept of\ndecentralized ledger, users who do not know or trust each other can still\nconduct transactions in a peer-to-peer manner. Inspired by Bitcoin, other\ncryptocurrencies were invented in recent years such as Ethereum, Dash, Zcash,\nMonero, Grin, etc. Some of these focus on enhancing privacy for instance crypto\nnote or systems that apply the similar concept of encrypted notes used for\ntransactions to enhance privacy (e.g., Zcash, Monero). However, there are few\nmechanisms to support the exchange of privacy-enhanced notes or assets on the\nchain, and at the same time preserving the privacy of the exchange operations.\nExisting approaches for fair exchanges of assets with privacy mostly rely on\noff-chain/side-chain, escrow or centralized services. Thus, we propose a\nsolution that supports oblivious and privacy-protected fair exchange of crypto\nnotes or privacy enhanced crypto assets. The technology is demonstrated by\nextending zero-knowledge based crypto notes. To address "privacy" and\n"multi-currency", we build a new zero-knowledge proving system and extend note\nformat with new property to represent various types of tokenized assets or\ncryptocurrencies. By extending the payment protocol, exchange operations are\nrealized through privacy enhanced transactions (e.g., shielded transactions).\nBased on the possible scenarios during the exchange operation, we add new\nconstraints and conditions to the zero-knowledge proving system used for\nvalidating transactions publicly.\n
Maximilian Schiedermeier, Omar M. Hassan, Lionel Brunie, Tobias Mayer · 5 authors
High voter turnout in elections and referendums is very desirable in order to ensure a robust democracy. Secure electronic voting is a vision for the future of elections and referendums. Such a system can counteract factors that hinder strong voter turnout such as the requirement of physical presence during limited hours at polling stations. However, this vision brings transparency and confidentiality requirements that render the design of such solutions challenging. Specifically, the counting must be implemented in a reproducible way and the ballots of individual voters must remain concealed. In this paper, we propose and evaluate a referendum protocol that ensures transparency, confidentiality, and integrity, in trustless networks. The protocol is built by combining Secure Multi-Party Computation (SMPC) and Distributed Ledger or Blockchain technology. The persistence and immutability of the protocol communication allows verifiability of the referendum outcome on the client side. Voters therefore do not need to trust in third parties. We provide a formal description and conduct a thorough security evaluation of our proposal.
In his talk, Bela Gipp, Professor for Data & Knowledge Engineering at the University of Wuppertal, presented the blockchain-based trusted timestamping service Origin-Stamp. Bela developed OriginStamp as a Ph.D. student in 2012, as no convenient and tamper-proof method existed to create timestamps. Since then, OriginStamp has been used over 6 million times by researchers, journalists in war regions, pharmaceutical companies, and individuals. Use cases are the timestamping of ideas for patent applications, timestamping of digital archives or timestamping of pre-existing damage, e.g., when hiring a rental car. The service can be used via a website, mobile phone apps, or an API, which allows developers to easily make use of trusted timestamping in their own applications. Trusted timestamping is the process of securely tracing the creation and modification time of any digital file. In contrast to conventional commercial timestamping authorities, OriginStamp uses the blockchain of the cryptocurrency Bitcoin as a decentralized, tamper-proof, and cost-efficient timestamping authority. To try it yourself, visit www.originstamp.org.
Blockchain platforms are coming into broad use for processing critical transactions among participants who have not established mutual trust. Many blockchains are programmable, supporting smart contracts, which maintain persistent state and support transactions that transform the state. Unfortunately, bugs in many smart contracts have been exploited by hackers. Obsidian is a novel programming language with a type system that enables static detection of bugs that are common in smart contracts today. Obsidian is based on a core calculus, Silica, for which we proved type soundness. Obsidian uses typestate to detect improper state manipulation and uses linear types to detect abuse of assets. We describe two case studies that evaluate Obsidian's applicability to the domains of parametric insurance and supply chain management, finding that Obsidian's type system facilitates reasoning about high-level states and ownership of resources. We compared our Obsidian implementation to a Solidity implementation, observing that the Solidity implementation requires much boilerplate checking and tracking of state, whereas Obsidian does this work statically.
This paper applies biomimetic engineering to the problem of permissionless Byzantine consensus and achieves results that surpass the prior state of the art by four orders of magnitude. It introduces a biologically inspired asymmetric Sybil-resistance mechanism, Proof-of-Balance, which can replace symmetric Proof-of-Work and Proof-of-Stake weighting schemes.
The biomimetic mechanism is incorporated into a permissionless blockchain protocol, Key Retroactivity Network Consensus (KRNC), which delivers ~40,000 times the security and speed of today's decentralized ledgers. KRNC allows the fiat money that the public already owns to be upgraded with cryptographic inflation protection, eliminating the problems inherent in bootstrapping new currencies like Bitcoin and Ethereum.
The paper includes two independently significant contributions to the literature. First, it replaces the non-structural axioms invoked in prior work with a new formal method for reasoning about trust, liveness, and safety from first principles. Second, it demonstrates how two previously overlooked exploits, book-prize attacks and pseudo-transfer attacks, collectively undermine the security guarantees of all prior permissionless ledgers.
Bitcoin is a peer-to-peer payment system proposed by Nakamoto in 2008. The bitcoin backbone protocol has been analyzed in some depth: the blockchain growth property quantifies the number of blocks added to the blockchain during any time intervals; the blockchain quality property ensures the honest miners always contribute at least a certain fraction of the blockchain; the common prefix property ensures if a block is deep enough, it must be adopted by all honest miners with high probability. The Prism protocol was recently proposed to dramatically improve the blockchain throughput while maintaining the same level of security. Prior analyses of the bitcoin and Prism backbone protocols assume the lifespan of blockchain is finite. This paper presents a streamlined and strengthened analysis in synchronous networks without the finite lifespan assumption. Specifically, the results include a blockchain growth property, a blockchain quality property, and a common prefix property of the bitcoin backbone protocol, as well as the liveness and persistence of the Prism backbone protocol regardless of whether the blockchains have finite lifespan. The properties take the form of explicit expressions in lieu of order optimal results.