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Virtual Private Network (VPN) is a private network that uses public network to tunnel the connection from the users’ end to the VPN server. VPN allows users to create a secure connection to another network over the public Internet. VPNs can be used to shield users’ browsing activity and encrypts data transmitted over the network to prevent sniffing attack. Nowadays, users can either pay a premium price for a good VPN service or risk their privacy using free browser-based VPN. Thus, SafeSearch is developed to address these issues in mind. With SafeSearch, users will not need to fork out a lot of money for premium VPN subscription services or expose themselves to targeted advertising when utilising free browser-based VPN. In this study, open VPN protocol was used to create the VPN server on a microcomputer called Raspberry Pi. The software used was mostly open-source except for the VPN client. Obfuscation technique was used to hide VPN traffic by disguising it as just another normal Internet traffic against Deep Packet Inspection when passing through firewall. After the VPN server was established, tests were carried out to evaluate the functionality and reliability of the VPN server in “real-world” environment. The tests conducted were network restriction penetration assessment, network performance and user acceptance test. Penetration assessment result showed that SafeSearch is capable of bypassing web filtering and deep packet inspection. Network performance during SafeSearch connection has slight latency and bandwidth decline, although it is not overly affected. The outcome of the user acceptance test was positive as the majority of participants of the study were confident that SafeSearch can secure their connection and protect their privacy when browsing the web. To conclude, both objectives of this project were fully achieved and the scope of study was followed thoroughly.

Blockchain-based Internet of Things (BIoT) is an emerging paradigm of Internet of Things (IoT) which utilizes the blockchain technology to provide security services to the IoT applications. In essence, the blockchain built-in security mechanism can provide services such as availability, authentication, authorization, confidentiality, and integrity to the IoT applications. While most of the IoT devices are inherently resource-constrained in terms of computational power and storage capacity, the downside for blockchain is a requirement of massive amount of energy and computational resources for its operation, which poses challenges to the realization of BIoT. This paper strives to explore the challenges associated with the integration of blockchain and IoT and review their solutions. First, a brief introduction of blockchain technology is presented, followed by characterization of blockchain-based IoT applications as per their heterogeneous traffic demand and Quality of Service (QoS) requirements. Next, challenges that limit the design, development, and deployment of BIoT applications are explained in detail such as energy efficiency, privacy, throughput, latency, fork problem, security, legal issues, smart contracts, storage, and network broadcast mechanism and their proposed solutions are discussed. Finally, future research directions of blockchain and IoT integration are indicated. This investigation will benefit the researchers and developers to identify and solve blockchain and IoT integration challenges in order to realize efficient BIoT applications.

A universal response to replication stress is replication fork reversal, where the nascent complementary DNA strands are annealed to form a protective four-way junction allowing forks to avert DNA damage while replication stress is resolved. However, reversed forks are in turn susceptible to nucleolytic digestion of the regressed nascent DNA arms and rely on dedicated mechanisms to protect their integrity. The most well studied fork protection mechanism involves the BRCA pathway and its ability to catalyze RAD51 nucleofilament formation on the reversed arms of stalled replication forks. Importantly, the inability to prevent the degradation of reversed forks has emerged as a hallmark of BRCA deficiency and underlies genome instability and chemosensitivity in BRCA-deficient cells. In the past decade, multiple factors underlying fork stability have been discovered. These factors either cooperate with the BRCA pathway, operate independently from it to augment fork stability in its absence, or act as enablers of fork degradation. In this review, we examine these novel determinants of fork stability, explore the emergent conceptual underpinnings underlying fork protection, as well as the impact of fork protection on cellular viability and cancer therapy.

Blockchain technology, which would be the underlying technology, has recently become very popular with the increase in cryptocurrencies and is being used in IoT and other fields. There have been shortfalls, however, which impede its implementation, including the volume of space. Transactions will be produced at a significant level due to the huge amount of Connected systems that often work in many networks as data processors. In IoT, the storage issue will become more intense. Current storing data platforms have a wide range of features to respond to an extensive variety spectrum of uses. Nevertheless, new groups of systems have arisen, e.g., blockchain with data version control, fork semantics, tamper-evidence or some variation thereof, and distributed analysis. They're showing new challenges for storage solutions to effectively serve such energy storage Systems by integrating the criteria mentioned in the processing. This paper discusses the potential security and privacy concerns of IoT applications and also it is shown that in first step the storage is enhanced by 50% and further in the next step, it is improved and it takes only 256 bytes irrespective of the input data size.

The current blockchain deployment solutions rely on a continuous connectivity network. Unfortunately, the delay tolerant network does not meet this condition. Therefore, we construct a novel blockchain transaction framework with discrete token negotiation called DTNB, which can be deployed on the delay tolerant network to provide transaction services. Specifically, we present the structure of add-chains by modifying the existing block structure. Then, we design a mining qualification determining scheme to achieve fair transactions, including discrete token generation algorithm and mining qualification attribution algorithm, and this scheme avoids the problem that nodes with more stakes in the PoS and DPoS algorithms can obtain mining qualifications with a higher probability. Furthermore, we present two mining schemes and also design a fork processing algorithm, which ensures that blocks on the add-chain generated by the local network can be appended to the main chain with the equal probability. Finally, we design the second consensus algorithm to avoid the problem of false and repeated transactions of the blocks on the add-chains in the local network. Theoretical analysis shows three properties of DTNB, including safety, reliability and activeness, and the experimental simulations demonstrate DTNB has advantages in throughput, block generation time and fork rate.

Card-based cryptography, introduced by den Boer aims to realize multiparty computation (MPC) by using physical cards. We propose several efficient card-based protocols for the millionaires’ problem by introducing a new operation called Private Permutation (PP) instead of the shuffle used in most of existing card-based cryptography. Shuffle is a useful randomization technique by exploiting the property of card shuffling, but it requires a strong assumption from the viewpoint of arithmetic MPC because shuffle assumes that public randomization is possible. On the other hand, private randomness can be used in PPs, which enables us to design card-based protocols taking ideas of arithmetic MPCs into account. Actually, we show that Yao’s millionaires’ protocol can be easily transformed into a card-based protocol by using PPs, which is not straightforward by using shuffles because Yao’s protocol uses private randomness. Furthermore, we propose entirely novel and efficient card-based millionaire protocols based on PPs by securely updating bitwise comparisons between two numbers, which unveil a power of PPs. As another interest of these protocols, we point out they have a deep connection to the well-known logical puzzle known as “The fork in the road.”

The food sector is driven by a large number of actors, including primary producers, manufacturers, logistics providers, retailers, and consumers. At each phase of the food value chain, a significant amount of data is generated that provides important information to the agents involved in processing and flow of food products from farm to fork. Proper handling of food data has a crucial role in providing safe, quality and affordable products to the increasing world population. The independent production of food data, without following any specific guidelines and procedures, often results in inconsistent and incomparable datasets that cannot be directly utilised by multiple users. Data harmonisation means reconciling various types, levels and sources of data in formats that are compatible and comparable, and thus useful for better decision making. In the food sector, one way of performing data harmonisation is to represent food data according to reliable classification and description systems. Another approach towards harmonisation is to match various food concepts to the existing and widely used ontologies. Furthermore, harmonisation is facilitated by following specific guidelines and procedures during data collection processes. This study explores some of the most important tools, frameworks and methodologies for data harmonisation in the food sector.

The work aims at the problem of multi-tag collision in RFID system, then analysis the binary tree algorithm and ALOHA and points out their shortcomings, we proposed a Hybrid of ALOHA and Tree (HAMT) Algorithm. The algorithm first uses the DFSA algorithm for tag identification, and dynamically selects the multi-fork tree algorithm for tag identification based on the number of unidentified tags secondly, thus ensuring that the tag is 100% identified, and improves recognition efficiency and shortens recognition time. The results of the simulation show that when the number of tags is about 1000, the recognition efficiency of the HAMT algorithm can reach around 0.72. So the HAMT algorithm can solve the multi-tag collision problem.

The integration of SERS-active enhanced agents with the functional supporting substrate of paper to expand the application of SERS technology has attracted much attention. However, it is still highly desired to improve the detection ability of paper-based SERS substrates for complex mixtures to extend the application of SERS further in real-word scenarios. Herein, we assemble raspberry-like bimetallic Au@AgNP nanostructures with multiple hotspots on an arrow-shaped paper strip to detect complex samples sensitively. Raspberry-like bimetallic nanoparticles show more sensitive and stable SERS performance than spherical AgNPs, which improves the practicability of SERS-based paper substrates in realistic situations. The intervention of charge gradients as well as designing of arrow-shaped non-interference tips yields the substrate-integrated shunt and preconcentration abilities for mixture samples. Thus, this SERS-based paper substrate may provide a promising way for the determination of complex samples in food security and environmental protection. Our work will have a positive impact in pushing forward the application process of SERS technology in real-word scenarios.

Unikernel, specializing a minimalistic libOS with an application, is an attractive design for cloud computing. However, the Achilles’ heel of unikernel is the lack of multi-process support, which makes it less flexible and applicable. Many applications rely on the process abstraction to isolate different components. For example, Apache with the multi-processing module isolates a request handler in a process to guarantee security. Prior art tackles the problem by simulating multi-process with multiple unikernels, which is incompatible with existing cloud providers and also introduces high overhead. This paper proposes Iso-UniK, a new unikernel design enabling multi-task applications with the support of both functionality and isolation. Iso-UniK leverages a recent hardware feature, named Intel Memory Protection Key (Intel MPK), to provide lightweight and efficient isolation for multi-process in unikernel. Our design has three benefits compared with previous approaches. First, Iso-UniK does not need hypervisor support and is thus compatible with existing cloud computing platforms; second, Iso-UniK promises fast system calls with only 45 cycles; last, a process can be isolated with a flexible configuration. We have implemented a prototype based on OSv, a unikernel system supporting unmodified applications. Iso-UniK can achieve fast fork operation with only 66 μs for multi-process applications. Our evaluation shows that the isolation and multi-process support in Iso-UniK will not damage the applications’ performance.

Data sharing and content offloading among vehicles is an imperative part of the Internet of Vehicles (IoV). A peer-to-peer connection among vehicles in a distributed manner is a highly promising solution for fast communication among vehicles. To ensure security and data tracking, existing studies use blockchain as a solution. The Blockchain-enabled Internet of Vehicles (BIoV) requires high computation power for the miners to mine the blocks and let the chain grow. Over and above, the blockchain consensus is probabilistic and the block generated today can be eventually declared as a fork and can be pruned from the chain. This reduces the overall efficiency of the protocol because the correct work done initially is eventually not used if it becomes a fork. To address these challenges, in this paper, we propose a Directed Acyclic Graph enabled IoV (DAGIoV) framework. We make use of a tangle data structure where each node acts as a miner and eventually the network achieves consensus among the nodes. A game-theoretic approach is used to model the interactions between the vehicles providing and consuming offloading services. The proposed model is proven to be highly scalable and well suited for microtransactions or frequent data transfer among the nodes in the vehicular network. This work was supported in part by the National Key Research and Development Program under Grant 2017YFE0125300, in part by the National Natural Science Foundation of China-Guangdong Joint Fund under Grant U1801264, in part by the JiangsuKey Research andDevelopment Program under Grant BE2019648, in part by FCT/MCTES through national funds and when applicable cofunded EU funds under Project UIDB/EEA/50008/2020, and in part by Brazilian NationalCouncil for Scientific andTechnologicalDevelopment (CNPq) under Grant 309335/2017-5.

The blockchain technology emerged in 2008 as a distributed peer to peer network structure, capable of ensuring security for transactions made using the Bitcoin digital currency, without the need for third party intermediaries to validate them. Although its beginning was linked to cryptocurrencies, its use has diversified over the recent years. There are various projects using the blockchain technology to perform document validation, electronic voting, tokenization of non-perishable goods, and many others. With its increasing use, concern arises with possible attacks that could threaten the integrity of the consensus of the chain. One of the well-known attacks to the blockchain consensus mechanism is the selfish mining attack, in which malicious nodes can deflect their behavior from the standard pattern by not immediately disclosing their newly mined blocks. This malicious behavior can result in a disproportionate share of rewards for those nodes, especially if they have a significant processing power. The goal of this paper is to present a simple heuristic to detect the presence of selfish mining attack (and variants) in blockchain networks that use the proof-of-work (PoW) consensus algorithm. The proposal is to signal when the blockchain fork height deviates from the standard, indicating when the network is under the influence of such attacks.

I just counted how many files are currently sitting on my C: drive, where Windows 10 is installed on my PC. This doesn’t count my documents, pictures, music, and video, which I store elsewhere to ensure file security, but there are still almost half a million files in more than seventy thousand folders sitting on the drive.

We propose supporting hybrid conference experiences using the Augmented Reality Edge Network Architecture (ARENA). ARENA is a platform based on web technologies that simplifies the creation of collaborative mixed reality for standard Web Browsers (Chrome, Firefox) in VR, Headset AR/VR Browsers (Magic Leap, Hololens, Oculus Quest 2), and mobile AR (WebXR Viewer for iOS, Chrome with experimental flags for Android, and our own custom WebXR fork for iOS). We use a 3D scan of the conference venue as the backdrop environment for remote users and a model to stage various AR interactions for in-person users. Remote participants can use VR in a browser or a VR headset to navigate the scene. In-person participants can use AR headsets or mobile AR through WebXR browsers to see and hear remote users. ARENA can scale up to hundreds of users in the same scene and provides audio and video with spatial sound that can more closely capture real-world interactions.

Bitcoin Cash, created in 2017, is a "hard fork" from Bitcoin responding to the need for allowing a higher transaction volume. This is achieved by a larger block size, as well as a new difficulty adjustment (target recalculation) function that acts more frequently (as opposed to Bitcoin's difficulty adjustment happening about every two weeks), resulting in a potentially different target for each block. While seemingly achieving its goal in practice, to our knowledge there is no formal analysis to back this proposal up. In this paper we provide the first formal cryptographic analysis of Bitcoin Cash's target recalculation functions---both ASERT and SMA (current and former recalculation functions, respectively)---against all possible adversaries. The main distinction with respect to Bitcoin's is that they are no longer epoch-based, and as such previous analyses fail to hold. We overcome this technical obstacle by introducing a new set of analytical tools focusing on the "calibration" of blocks' timestamps in sliding windows, which yield a measure of closeness to the initial block generation rate. With that measure, we then follow the analytical approach developed in the Bitcoin backbone protocol [Eurocrypt 2015 and follow-ups] to first establish the basic properties of the blockchain data structure, from which the properties of a robust transaction ledger (namely, Consistency and Liveness) can be derived. We compare our analytical results with data from the Bitcoin Cash network, and conclude that in order to satisfy security (namely, properties satisfied except with negligible probability in the security parameter) considerably larger parameter values should be used with respect to the ones used in practice.

Superlight blockchain clients learn facts about the blockchain state while requiring merely polylogarithmic communication in the total number of blocks. For proof-of-work blockchains, two known constructions exist: Superblock and FlyClient. Unfortunately, none of them can be easily deployed to existing blockchains, as they require consensus changes and at least a soft fork to implement. In this paper, we investigate how a blockchain can be upgraded to support superblock clients without a soft fork. We show that it is possible to implement the needed changes without modifying the consensus protocol and by requiring only a minority of miners to upgrade, a process termed a “velvet fork” in the literature. While previous work conjectured that superblock clients can be safely deployed using velvet forks as-is, we show that previous constructions are insecure, and that using velvet techniques to interlink a blockchain can pose insidious security risks. We describe a novel class of attacks, called “chain-sewing”, which arise in the velvet fork setting: an adversary can cut-and-paste portions of various chains from independent temporary forks, sewing them together to fool a superlight client into accepting a false claim. We show how previous velvet fork constructions can be attacked via chain-sewing. Next, we put forth the first provably secure velvet superblock client construction which we show secure against adversaries that are bounded by 1/3 of the upgraded honest miner population. Like non-velvet superlight clients, our approach allows proving generic predicates about chains using infix proofs and as such can be adopted in practice for fast synchronization of transactions and accounts.

Antimicrobial resistance (AMR) of foodborne pathogens is a global crisis in public health and economic growth. A real-time surveillance system is key to track the emergence of AMR bacteria and provides a comprehensive AMR trend from farm to fork. However, current AMR surveillance systems, which integrate results from multiple laboratories using the conventional broth microdilution method, are labor-intensive and time-consuming. To address these challenges, we present the internet of things (IoT), including colorimetric-based microfluidic sensors, a custom-built portable incubator, and machine learning algorithms, to monitor AMR trends in real time. As a top priority microbe that poses risks to human health, Campylobacter was selected as a bacterial model to demonstrate and validate the IoT-assisted AMR surveillance. Image classification with convolution neural network ResNet50 on the colorimetric sensors achieved an accuracy of 99.5% in classifying bacterial growth/inhibition patterns. The IoT was used to carry out a small-scale survey study, identifying eight Campylobacter isolates out of 35 chicken samples. A 96% agreement on Campylobacter AMR profiles was achieved between the results from the IoT and the conventional broth microdilution method. The data collected from the intelligent sensors were transmitted from local computers to a cloud server, facilitating real-time data collection and integration. A web browser was developed to demonstrate the spatial and temporal AMR trends to end-users. This rapid, cost-effective, and portable approach is able to monitor, assess, and mitigate the burden of bacterial AMR in the agri-food chain.

Replication fork stalling occurs when the replisome encounters a barrier to normal fork progression. Replisome stalling events are common during scheduled DNA synthesis, but vary in their severity. At one extreme, a lesion may induce only temporary pausing of a DNA polymerase; at the other, it may present a near-absolute barrier to the replicative helicase and effectively block fork progression. Many alternative pathways have evolved to respond to these different types of replication stress. Among these, the homologous recombination (HR) pathway plays an important role, protecting the stalled fork and processing it for repair. Here, we review recent advances in our understanding of how blocked replication forks in vertebrate cells can be processed for recombination and for replication restart.

Forklifts are necessary to carry pallets in agricultural work; however, a high level of skill is required to steer and control forks. Inserting the forks into a hole of the pallet is difficult for operators to control both the height and angle of the forks to avoid damaging the pallets because the size of the hole is small. The slight inclination of the ground could lead to the collision of the pallet and the forks. We describe an approach to automatically insert forks into a hole of a pallet on a truck under a tilted ground. Our approach for the safe fork insertion of an autonomous forklift uses an RGB-D (RGB, Depth) camera. The pallet is detected by semantic segmentation with the RGB image during insertion. The system calculates the position and orientation of the pallet with the result of semantic segmentation and depth. We verify the effectiveness of the approach with an experiment with the forklift in an outdoor environment assuming the real task.

Symbiotic is a bug-finding and verification tool that integrates light-weight static analyses and instrumentation with program slicing and symbolic execution. The techniques are suitably combined according to a given goal. The paper describes a particular configuration competing in Test-Comp 2019. We also provide a brief analysis of Symbiotic ’s results achieved in the competition. As our tool uses a fork of the open-source symbolic executor Klee, we focus on comparison with mainstream Klee that also participated in the competition this year.

Maintaining stability of replication forks is important for genomic integrity. However, it is not clear how replisome proteins contribute to fork stability under replication stress. Here, we report that ATAD5, a PCNA unloader, plays multiple functions at stalled forks including promoting its restart. ATAD5 depletion increases genomic instability upon hydroxyurea treatment in cultured cells and mice. ATAD5 recruits RAD51 to stalled forks in an ATR kinase-dependent manner by hydroxyurea-enhanced protein-protein interactions and timely removes PCNA from stalled forks for RAD51 recruitment. Consistent with the role of RAD51 in fork regression, ATAD5 depletion inhibits slowdown of fork progression and native 5-bromo-2ʹ-deoxyuridine signal induced by hydroxyurea. Single-molecule FRET showed that PCNA itself acts as a mechanical barrier to fork regression. Consequently, DNA breaks required for fork restart are reduced by ATAD5 depletion. Collectively, our results suggest an important role of ATAD5 in maintaining genome integrity during replication stress., How the replisome machinery contributes to fork stability under replication stress is currently not clear. Here the authors reveal a role for ATAD5 in maintaining genome integrity during replication stress by promoting replication restart through RAD51/PCNA regulation.

The central recombination enzyme RAD51 has been implicated in replication fork processing and restart in response to replication stress. Here, we use a separation-of-function allele of RAD51 that retains DNA binding, but not D-loop activity, to reveal mechanistic aspects of RAD51’s roles in the response to replication stress. Here, we find that cells lacking RAD51’s enzymatic activity protect replication forks from MRE11-dependent degradation, as expected from previous studies. Unexpectedly, we find that RAD51’s strand exchange activity is not required to convert stalled forks to a form that can be degraded by DNA2. Such conversion was shown previously to require replication fork regression, supporting a model in which fork regression depends on a non-enzymatic function of RAD51. We also show RAD51 promotes replication restart by both strand exchange-dependent and strand exchange-independent mechanisms., RAD51 has been implicated in replication fork processing and restart in response to replication stress. Here, authors reveal mechanistic aspects of non-enzymatic roles of RAD51 for fork reversal and cooperation with FBH1.

Introducing intelligent safety devices in the roads would lead to enhance both the time of reaction and the traffic safety. Nevertheless, these intelligent devices are expensive, so choosing their location should be done carefully. This research is focused a decision support system to decide the placement of a specific safety device designed in a research project. This approach includes a feature selection stage, a model learning stage and the deployment stage. Decision models learn from real datasets with information related with accidents, classifying the samples as Fatal, Severe or Slight injury. Also, a case based risk index is proposed, so samples within the same label can be sorted. Therefore, in the deployment stage, each possible location is ranked and the user gets a feedback of the suitability of each of them to be considered for placing the intelligent safety device. The experimentation shows the proposal is valid provided the dataset for training includes enough granularity. However, it is shown that specific risk index should be designed for each road type and fork.

Mobile Crowdsourcing (MCS) is an effective and novel method of data collection and processing. Current MCS generally adopts a centralized architecture by depending on an assumed trusted party. This design easily suffers from single-point failure and cannot be realized in practice since a trusted service provider does not really exist. More dangerously, the centralized party may perform dishonestly and thus harms the benefit and privacy of MCS users. To tackle these problems, we propose a novel blockchain-based MCS system, named MCS-Chain, to realize fully distributed and decentralized trust management in MCS. Aiming at improving the poor efficiency of traditional blockchain technology, we propose a novel consensus mechanism for block generation, which greatly reduces computational overhead. The proposed MCS-Chain system also solves the fork issue and centralization problem suffered by most existing blockchain-based systems. Serious security analysis and experimental evaluation further illustrate the security and efficiency of our system.

To address the large amount of energy wasted by blockchains, we propose a decentralized consensus protocol for blockchains in which the computation can be used to search for good approximate solutions to any optimization problem. Our protocol allows the wasted energy to be used for finding approximate solutions to problems submitted by any nodes~(called clients). Our protocol works in a similar way to proof-of-work, and it makes nodes evaluate a large number of solution candidates to add a new block to the chain. A client provides a search program that implements any search algorithm that finds a good solution by evaluating a large number of solution candidates. The node that finds the best approximate solution is rewarded by the client. Our analysis shows that the probability of a fork and the variance in the block time with our protocol are lower than those in proof-of-work., in IEEE Access

Replication stress (RS) is a hallmark of cancer cells that is associated with increased genomic instability. RS occurs when replication forks encounter obstacles along the DNA. Stalled forks are signaled by checkpoint kinases that prevent fork collapse and coordinate fork repair pathways. Fork restart also depends on chromatin remodelers to increase the accessibility of nascent chromatin to recombination and repair factors. In this review, we discuss recent findings on the causes and consequences of RS, with a focus on endogenous replication impediments and their impact on fork velocity. We also discuss recent studies on the interplay between stalled forks and innate immunity, which extends the RS response beyond cell boundaries and opens new avenues for cancer therapy.

As large graph processing emerges, we observe a costly fork-processing pattern (FPP) that is common in many graph algorithms. The unique feature of the FPP is that it launches many independent queries from different source vertices on the same graph. For example, an algorithm in analyzing the network community profile can execute Personalized PageRanks that start from tens of thousands of source vertices at the same time. We study the efficiency of handling FPPs in state-of-the-art graph processing systems on multi-core architectures. We find that those systems suffer from severe cache miss penalty because of the irregular and uncoordinated memory accesses in processing FPPs. In this paper, we propose ForkGraph, a cache-efficient FPP processing system on multi-core architectures. To improve the cache reuse, we divide the graph into partitions each sized of LLC capacity, and the queries in an FPP are buffered and executed on the partition basis. We further develop efficient intra- and inter-partition execution strategies for efficiency. For intra-partition processing, since the graph partition fits into LLC, we propose to execute each graph query with efficient sequential algorithms (in contrast with parallel algorithms in existing parallel graph processing systems) and present an atomic-free query processing by consolidating contending operations to cache-resident graph partition. For inter-partition processing, we propose yielding and priority-based scheduling, to reduce redundant work in processing. Besides, we theoretically prove that ForkGraph performs the same amount of work, to within a constant factor, as the fastest known sequential algorithms in FPP queries processing, which is work efficient. Our evaluations on real-world graphs show that ForkGraph significantly outperforms state-of-the-art graph processing systems with two orders of magnitude speedups., in SIGMOD 2021

Blockchains promise to provide a tamper-proof medium for transactions, and thus enable many applications including cryptocurrency. As a system built on consensus, the correctness of a blockchain heavily relies on the consistency of states between its nodes. But consensus protocols of blockchains only guarantee the consistency in the transaction sequence rather than nodes’ internal states. Instead, nodes must replay and exe-cute all transactions to maintain their local states independently. When executing transactions, any different execution result could cause a node out-of-sync and thus gets isolated from other nodes.After systematically modeling the transaction execution process in blockchains, we present a new attack INCITE, which can lead different nodes to different states. Specifically, attackers could invoke an ambiguous transaction of a vulnerable smart contract, utilize software bugs in smart contracts to lead nodes that execute this transaction into different states. Unlike attacks that bring short-term inconsistencies, such as fork attacks, INCITE can cause nodes in the blockchain to fall into a long-term inconsistent state, which further leads to great damages to the chain (e.g., double-spending attacks and expelling mining power). We have discovered 7 0day vulnerabilities in 5 popular blockchains which can enable this attack. We also proposed a defense solution to mitigate this threat. Experiments showed that it is effective and lightweight.

Enclave applications that rely on blockchains for integrity and availability are vulnerable to eclipse attacks. In this paper, we present an approach for reliably detecting extended eclipse attacks, even when the adversary controls all network connectivity. By monitoring changes to the difficulty parameter in Proof-of-Work (PoW) protocols, our algorithm detects suppression of new blocks, as well as difficulty-lowering attacks that attempt to force an enclave client onto a malicious fork mined solely by an attacker. We present analysis that attackers have negligible probability of evading our block monitoring algorithm, and demonstrate its robustness to most historical fluctuations in difficulty on the Ethereum blockchain, resulting in a very low false-positive rate.

Using blockchain technology to build a trusted transaction foundation has become a hot topic of current research and practice. The double-spending phenomenon refers to the bifurcation of the blockchain structure. In the process of trusted transactions, the fork caused by malicious attacks will destroy the correctness, integrity, and consistency of the entire ledger, and causes serious economic losses to users. Therefore, eliminating double-spending attacks is an important issue to ensure the security of the blockchain. The current method of defending against double-spending attacks in trusted transactions mainly revolves around the Bitcoin blockchain system. In the process of researching the Nano blockchain grid project, a high-throughput trusted transaction system, we proposed a double-spending elimination solution for the system: the occupying mechanism. By using Java to reconstruct the Nano project and implement the occupying mechanism, the experimental results verify the effectiveness of the occupying mechanism, and it is superior to the Nano project's double-spending solution based on the traditional voting mechanism in terms of time performance.

Blockchain technologies have been rapidly enhanced in recent years. However, its scalability still has limitations in terms of throughput and broadcast delay as the network and the amount of transaction data increase. To improve scalability of blockchain networks, we propose a novel approach named PiChu that accelerates block propagation in blockchain networks by pipelining and verifying chunks of a block in parallel. Accelerating block propagation reduces the mining interval and chance of fork occurring, which in turn increases throughput. Our approach can be applied to the blockchain networks either directly or with a minor modification to the consensus. Through an extensive and large scale simulations, we validate that the proposed PiChu scheme significantly enhances the scalability of blockchain networks. For instance, a 64 MB block can be broadcasted in just 80 seconds in a blockchain network with a million nodes. The efficiency of PiChu broadcasting increases with bigger block sizes and a larger number of nodes in the network., Comment: 2020 IEEE International Conference on Blockchain

Decentralized Finance (DeFi) is a blockchain-asset-enabled finance ecosystem with millions of daily USD transaction volume, billions of locked up USD, as well as a plethora of newly emerging protocols (for lending, staking, and exchanges). Because all transactions, user balances, and total value locked in DeFi are publicly readable, a natural question that arises is: how can we automatically craft profitable transactions across the intertwined DeFi platforms?In this paper, we investigate two methods that allow us to automatically create profitable DeFi trades, one well-suited to arbitrage and the other applicable to more complicated settings. We first adopt the Bellman-Ford-Moore algorithm with DeFiPoser-ARB and then create logical DeFi protocol models for a theorem prover in DeFiPoser-SMT. While DeFiPoser-ARB focuses on DeFi transactions that form a cycle and performs very well for arbitrage, DeFiPoser-SMT can detect more complicated profitable transactions. We estimate that DeFiPoser-ARB and DeFiPoser-SMT can generate an average weekly revenue of 191.48 ETH (76,592 USD) and 72.44 ETH (28,976 USD) respectively, with the highest transaction revenue being 81.31 ETH (32,524 USD) and 22.40 ETH (8,960 USD) respectively. We further show that DeFiPoser-SMT finds the known economic bZx attack from February 2020, which yields 0.48M USD. Our forensic investigations show that this opportunity existed for 69 days and could have yielded more revenue if exploited one day earlier. Our evaluation spans 150 days, given 96 DeFi protocol actions, and 25 assets.Looking beyond the financial gains mentioned above, forks deteriorate the blockchain consensus security, as they increase the risks of double-spending and selfish mining. We explore the implications of DeFiPoser-ARB and DeFiPoser-SMT on blockchain consensus. Specifically, we show that the trades identified by our tools exceed the Ethereum block reward by up to 874×. Given optimal adversarial strategies provided by a Markov Decision Process (MDP), we quantify the value threshold at which a profitable transaction qualifies as Miner Extractable Value (MEV) and would incentivize MEV-aware miners to fork the blockchain. For instance, we find that on Ethereum, a miner with a hash rate of 10% would fork the blockchain if an MEV opportunity exceeds 4× the block reward.

Blockchain technology originates from the Bitcoin system, and due to its great success it can draw awareness to other fields because of its global acceptable features like decentralization, anonymity, and audibility. Other than finance, blockchain technology has evolved in various applications like legal, supply chain, health care, etc. Though blockchain technology is a bit difficult to maintain and monitor, still a blockchain network is more secure than other technologies. In this work, we want to give some avenues of the blockchain security system and also highlight some specific security threats. The issues related to mining or fork problems have also been discussed. It is found that several unexpected fields contribute to security concerns rather than decentralized computing and any cryptographic issues.

A blockchain distributed ledger is an actively developed technology that goes beyond its original cryptocurrency application and integrates to IoT, smart manufacturing, smart cities, logistics and more. Therefore, the blockchain security is of the current interest. The article considers a blockchain security issue caused by imbalanced hashing power distribution between nodes: the majority attack. The majority attack (the 51% attack) is a technique which intends to fork the blockchain in order to cancel confirmed transactions and violate data integrity. Despite the attack cost, it has become frequent in current blockchains. The existing security mechanisms against the majority attack have significant weaknesses and limitations. This paper proposes a novel criterion of the blockchain vulnerability to the majority attack. The criterion allows to detect vulnerable states of the distributed ledger based on hashing power distribution assessment. The blockchain hashing power time series are constructed and analyzed in order to evaluate the portion of total hashing power that is controlled by attacker. This estimate is used as a foundation of the proposed criterion. The criterion may be used to in conjunction with other security mechanisms to enhance protection of distributed ledgers in vulnerable states.

The setup of Symbiotic 8 for Test-Comp 2021 brings radical changes in the test generation for property. Similarly as in Symbiotic 7, we generate tests by running our fork of symbolic executor Klee on the analyzed program. Symbiotic 8, however, runs several instances of Klee in parallel. We run one instance of Klee on the original program and, simultaneously, we create one (intentionally unsound) program slice for every program-terminating instruction in the program and run Klee on these slices. Apart from this principal change, we also improved other components of the tool, mainly the program slicer. Further, our fork of Klee now supports symbolic pointer arithmetics and comparison of symbolic addresses.

We investigate the degree to which neurons are fractal, the origin of this fractality, and its impact on functionality. By analyzing three-dimensional images of rat neurons, we show the way their dendrites fork and weave through space is unexpectedly important for generating fractal-like behavior well-described by an ‘effective’ fractal dimension D. This discovery motivated us to create distorted neuron models by modifying the dendritic patterns, so generating neurons across wide ranges of D extending beyond their natural values. By charting the D-dependent variations in inter-neuron connectivity along with the associated costs, we propose that their D values reflect a network cooperation that optimizes these constraints. We discuss the implications for healthy and pathological neurons, and for connecting neurons to medical implants. Our automated approach also facilitates insights relating form and function, applicable to individual neurons and their networks, providing a crucial tool for addressing massive data collection projects (e.g. connectomes).

Symbiotic 8 extends the traditional combination of static analyses, instrumentation, program slicing, and symbolic execution with one substantial novelty, namely a technique mixing symbolic execution with k-induction. This technique can prove the correctness of programs with possibly unbounded loops, which cannot be done by classic symbolic execution.Symbiotic 8 delivers also several other improvements. In particular, we have modified our fork of the symbolic executorKleeto support the comparison of symbolic pointers. Further, we have tuned the shape analysis toolPredator(integrated already inSymbiotic 7) to perform better onllvmbitcode. We have also developed a light-weight analysis of relations between variables that can prove the absence of out-of-bound accesses to arrays.

Despite the tremendous interest in cryptocurrencies like Bitcoin and Ethereum today, many aspects of the underlying consensus protocols are poorly understood. Therefore, the search for protocols that improve either throughput or security (or both) continues. Bitcoin always selects the longest chain (i.e., the one with most work). Forks may occur when two miners extend the same block simultaneously, and the frequency of forks depends on how fast blocks are propagated in the network. In the GHOST protocol, used by Ethereum, all blocks involved in the fork contribute to the security. However, the greedy chain selection rule of GHOST does not consider the full information available in the block tree, which has led to some concerns about its security. This paper introduces a new family of protocols, called Medium, which takes the structure of the whole block tree into account, by weighting blocks differently according to their depths. Bitcoin and GHOST result as special cases. This protocol leads to new insights about the security of Bitcoin and GHOST and paves the way for developing network- and application-specific protocols, in which the influence of forks on the chain-selection process can be controlled. It is shown that almost all protocols in this family achieve strictly greater throughput than Bitcoin (at the same security level) and resist attacks that can be mounted against GHOST.

International audience; Replication stress (RS) is intrinsic to normal cell growth, is enhanced by exogenous factors and elevated in many cancer cells due to oncogene expression. Most genetic changes are a result of RS and the mechanisms by which cells tolerate RS has received considerable attention because of the link to cancer evolution and opportunities for cancer cell-specific therapeutic intervention. Site-specific replication fork barriers have provided unique insights into how cells respond to RS and their recent use has allowed a deeper understanding of the mechanistic and spatial mechanism that restart arrested forks and how these correlate with RS-dependent mutagenesis. Here we review recent data from site-specific fork arrest systems used in yeast and highlight their strengths and limitations.

As the world’s leading software development platform, GitHub has become a social networking site for programmers and recruiters who leverage its social features, such as star and fork, for career and business development. However, in this paper, we found a group of GitHub accounts that conducted promotion services in GitHub, called “promoters”, by performing paid star and fork operations on specified repositories. We also uncovered a stealthy way of tampering with historical commits, through which these promoters are able to fake commits retroactively. By exploiting such a promotion service, any GitHub user can pretend to be a skillful developer with high influence. To understand promotion services in GitHub, we first investigated the underground promotion market of GitHub and identified 1,023 suspected promotion accounts from the market. Then, we developed an SVM (Support Vector Machine) classifier to detect promotion accounts from all active users extracted from GH Archive ranging from 2015 to 2019. In total, we detected 63,872 suspected promotion accounts. We further analyzed these suspected promotion accounts, showing that (1) a hidden functionality in GitHub is abused to boost the reputation of an account by forging historical commits and (2) a group of small businesses exploit GitHub promotion services to promote their products. We estimated that suspicious promoters could have made a profit of $3.41 million and $4.37 million in 2018 and 2019, respectively.

A recent CSCML'2020 paper by Dolev and Liber presents a low cost blockchain based on cryptographic mechanism. Its main feature is a mechanism discouraging a user to fork a blockchain - if this happens, then a user's secret is leaked and thereby a proof of his misbehavior emerges. This approach is very attractive as long as we can guarantee that breaking the underlying cryptographic problem is infeasible for all parties. The situation changes dramatically in case of a partial compromise of a cryptographic scheme: when a powerful adversary can break the underlying scheme, while for the regular users the scheme is still resistant to attacks. In this case the blockchain techniques proposed becomes a dangerous trap allowing discrediting the users by powerful parties hiding own cryptanalytic power. To address this problem we introduce a David and Goliath adversary model, where a powerful adversary (Goliath) can break the underlying cryptographic assumption, but for a regular user (David) this is infeasible. For almost all cryptographic schemes, the situation of David is hopeless in this model: e.g., Goliath can forge standard signatures of David. Such an advantage of Goliath in case of a blockchain would be disastrous. We show that one can create a blockchain such that the advantage of Goliath is limited: if he creates a fork in a blockchain mimicking a double-spending attempt by David, then David can prove to be innocent.

PriA is a member of the SuperFamily 2 helicase family. Its rolein vivois to reload the primosome onto stalled replication forks resulting in the restart of the previously stalled DNA replication process. SSB is known to play key roles in mediating activities at replication forks and it is known to bind to PriA. To gain mechanistic insight into the PriA-SSB interaction, a coupled spectrophotometric assay was utilized to characterize the ATPase activity of PriAin vitroin the presence of fork substrates. The results demonstrate that SSB enhances the ability of PriA to discriminate between fork substrates 140-fold. This is due to a significant increase in the catalytic efficiency of the helicase induced by DNA-bound SSB. This interaction is species-specific as bacteriophage gene 32 protein cannot substitute for theE.coliprotein. SSB, while enhancing the activity of PriA on its preferred fork, both decreases the affinity of the helicase for other forks and decreases catalytic efficiency. Central to the stimulation afforded by SSB is the unique ability of PriA to bind with high affinity to the 3’-OH placed at the end of the nascent leading strand at the fork. When both the 3’-OH and SSB are present, the maximum effect is observed. This ensures that PriA will only load onto the correct fork, in the right orientation, thereby ensuring that replication restart is directed to only the template lagging strand.

Several software projects start from an existing project. This practice, in the VCS ecosystem, is called fork. For instance, the Bootstrap project, initially developed on Twitter, today has more than 68,000 forks, which indicates that several projects started from the Bootstrap source code at a certain moment and are being customized. The problem occurs when customized projects want to obtain updates from the original project, i.e., new features, bug fixes, etc. The merge of the source code between the original and the customized projects usually generates conflicts that need human resolution. More important, the resolution of those conflicts might not be trivial and poses an arduous task for developers. This article, therefore, proposes an approach for updating forks against the original project where features are modularized, documented, traceable, and can be reused. We claim that the such task can no longer be carried out on an ad hoc basis. In a nutshell, instead of modify the method foo from the original project, the developer implements it locally and specifies, using one of the nine instructions of the proposed DSL, something like "replace the foo method with local implementation". We have developed a tool that automates our approach and conducted an evaluation on a large-scale real-world project that is regularly updated against your original project.

Protecting replication fork integrity during DNA replication is essential for maintaining genome stability. Here, we report that SDE2, a PCNA-associated protein, plays a key role in maintaining active replication and counteracting replication stress by regulating the replication fork protection complex (FPC). SDE2 directly interacts with the FPC component TIMELESS (TIM) and enhances its stability, thereby aiding TIM localization to replication forks and the coordination of replisome progression. Like TIM deficiency, knockdown of SDE2 leads to impaired fork progression and stalled fork recovery, along with a failure to activate CHK1 phosphorylation. Moreover, loss of SDE2 or TIM results in an excessive MRE11-dependent degradation of reversed forks. Together, our study uncovers an essential role for SDE2 in maintaining genomic integrity by stabilizing the FPC and describes a new role for TIM in protecting stalled replication forks. We propose that TIM-mediated fork protection may represent a way to cooperate with BRCA-dependent fork stabilization., The fork protection complex (FPC), including the proteins TIMELESS and TIPIN, stabilizes the replisome to ensure unperturbed fork progression during DNA replication. Here the authors reveal that that SDE2, a PCNA-associated protein, plays an important role in maintaining active replication and protecting stalled forks by regulating the replication fork protection complex (FPC).

The CAP theorem says that no blockchain can be live under dynamic participation and safe under temporary network partitions. To resolve this availability-finality dilemma, we formulate a new class of flexible consensus protocols, ebb-and-flow protocols, which support a full dynamically available ledger in conjunction with a finalized prefix ledger. The finalized ledger falls behind the full ledger when the network partitions but catches up when the network heals. Gasper, the current candidate protocol for Ethereum 2.0's beacon chain, combines the finality gadget Casper FFG with the LMD GHOST fork choice rule and aims to achieve this property. However, we discovered an attack in the standard synchronous network model, highlighting a general difficulty with existing finality-gadget-based designs. We present a construction of provably secure ebb-and-flow protocols with optimal resilience. Nodes run an off-the-shelf dynamically available protocol, take snapshots of the growing available ledger, and input them into a separate off-the-shelf BFT protocol to finalize a prefix. We explore connections with flexible BFT and improve upon the state-of-the-art for that problem., Forthcoming in IEEE Symposium on Security and Privacy 2021

In programming, concurrency allows threads to share processing units interleaving and seemingly simultaneous to improve resource utilization and performance. Previous research has found that concurrency faults are hard to avoid, hard to find, often leading to undesired and unpredictable behavior. Further, with the growing availability of multi-core devices and adaptation of concurrency features in high-level languages, concurrency faults occur reportedly often, which is why countermeasures must be investigated to limit harm. Reactive programming provides an abstraction to simplify complex concurrent and asynchronous tasks through reactive language extensions such as the RxJava and Project Reactor libraries for Java. Still, blocking violations are possibly resulting in concurrency faults with no Java compiler warnings. BlockHound is a tool that detects incorrect blocking by wrapping the original code and intercepting blocking calls to provide appropriate runtime errors. In this study, we seek an understanding of how common blocking violations are and whether a tool such as BlockHound can give us insight into the root-causes to highlight them as pitfalls to developers. The investigated Softwares are Java-based open-source projects using reactive frameworks selected based on high star ratings and large fork quantities that indicate high adoption. We activated BlockHound in the project’s test-suites and analyzed log files for common patterns to reveal blocking violations in 7/29 investigated open-source projects with 5024 stars and 1437 forks. A small number of system calls could be identified as root-causes. We here present countermeasures that successfully removed the uncertainty of blocking violations. The code’s intentional logic was retained in all validated projects through passing unit-tests.

SUMMARY Replication stress response ensures impediments to DNA replication do not compromise replication fork stability and genome integrity. In a process termed replication fork protection, newly synthesized DNA at stalled replication forks is stabilized and protected from nuclease-mediated degradation. We report the identification of DDB1- and CUL4-associated factor 14 (DCAF14), a substrate receptor for Cullin4-RING E3 ligase (CRL4) complex, integral in stabilizing stalled replication forks. DCAF14 localizes rapidly to stalled forks and promotes genome integrity by preventing fork collapse into double-strand breaks (DSBs). Importantly, CRL4DCAF14 mediates stalled fork protection in a RAD51-dependent manner to protect nascent DNA from MRE11 and DNA2 nucleases. Thus, our study shows replication stress response functions of DCAF14 in genome maintenance., In Brief Townsend et al. find that DDB1- and CUL4-associated factor DCAF14 is recruited to stalled replication forks. DCAF14 prevents replication fork collapse in a CRL4-dependent manner to promote genome stability and cell survival. DCAF14 depletion triggers nascent strand degradation that is reversible by enhancing RAD51 levels at forks., Graphical Abstract

In this paper, we present the design and development of a game-assisted stroke rehabilitation system RehabFork that allows a user to train their upper-limb to perform certain functions related to the task of eating. The task of eating is divided into several components: (i) grasping the eating utensils such as a fork and knife; (ii) lifting the eating utensils; (iii) using the eating utensils to cut a piece of food; (iv) transferring the food to the mouth; and (v) chewing the food. The RehabFork supports the user through sub-tasks (i)-(iii). The hardware components of RehabFork consist of an instrumented fork and knife, and a 3D printed pressure pad, that measure and communicate information on user performance to a gaming environment to render an integrated rehabilitation system. The gaming environment consists of an interactive game that utilizes sensory data as well as user information about the severity of their disability and current level of progress to adjust the difficulty levels of the game to maintain user motivation. Information pertaining to the user, including performance data, is stored and can be shared with care providers for ongoing oversight.

In Bitcoin and Ethereum, nodes require large storage capacity to maintain all the blockchain data, such as transactions, UTXOs, and account states. As of May 2020, the storage size of the Bitcoin blockchain has expanded to 270 GB, and it will continue to increase. This storage requirement is a major hurdle to becoming a block proposer or validator. Although many studies have attempted to reduce the storage size, in the proposed methods, a node cannot keep all blocks or cannot generate a block. We propose an architecture called Trail that allows nodes to hold all blocks in a small storage and to generate and validate blocks and transactions. Trail does not depend on a consensus algorithm or fork choice rule. In this architecture, a client who issues transactions has the data to prove its own balances and can generate a transaction containing the proof of balances. The nodes in Trail do not store transactions, UTXOs and account balances: they keep only blocks. The blocksize is approximately 8 KB, which is 100 times smaller than that of Bitcoin. Further, the block size is constant regardless of the number of accounts and the number of transactions. Compared to traditional blockchains, clients who issue transactions must store additional data. However, we show that proper data archiving can keep the account device storage size small. Trail allows more users to be block proposers and validators and improves the decentralization of the blockchain., Proc. 25th IEEE Symposium on Computers and Communications (IEEE ISCC 2020)

Blockchain, the technology behind the popular Bitcoin, is considered a "security by design" system as it is meant to create security among a group of distrustful parties yet without a central trusted authority. The security of blockchain relies on the premise of honest-majority, namely, the blockchain system is assumed to be secure as long as the majority of consensus voting power is honest. And in the case of proof-of-work (PoW) blockchain, adversaries cannot control more than 50% of the network's gross computing power. However, this 50% threshold is based on the analysis of computing power only, with implicit and idealistic assumptions on the network and node behavior. Recent researches have alluded that factors such as network connectivity, presence of blockchain forks, and mining strategy could undermine the consensus security assured by the honest-majority, but neither concrete analysis nor quantitative evaluation is provided. In this paper we fill the gap by proposing an analytical model to assess the impact of network connectivity on the consensus security of PoW blockchain under different adversary models. We apply our analytical model to two adversarial scenarios: 1) honest-but-potentially-colluding, 2) selfish mining. For each scenario, we quantify the communication capability of nodes involved in a fork race and estimate the adversary's mining revenue and its impact on security properties of the consensus protocol. Simulation results validated our analysis. Our modeling and analysis provide a paradigm for assessing the security impact of various factors in a distributed consensus system., Comment: In proceedings of 2020 IEEE International Conference on Computer Communications (INFOCOM 2020)