49 research outputs found
Front-running Attack in Sharded Blockchains and Fair Cross-shard Consensus
Sharding is a prominent technique for scaling blockchains. By dividing the
network into smaller components known as shards, a sharded blockchain can
process transactions in parallel without introducing inconsistencies through
the coordination of intra-shard and cross-shard consensus protocols. However,
we observe a critical security issue with sharded systems: transaction ordering
manipulations can occur when coordinating intra-shard and cross-shard consensus
protocols, leaving the system vulnerable to attack. Specifically, we identify a
novel security issue known as finalization fairness, which can be exploited
through a front-running attack. This attack allows an attacker to manipulate
the execution order of transactions, even if the victim's transaction has
already been processed and added to the blockchain by a fair intra-shard
consensus.
To address the issue, we offer Haechi, a novel cross-shard protocol that is
immune to front-running attacks. Haechi introduces an ordering phase between
transaction processing and execution, ensuring that the execution order of
transactions is the same as the processing order and achieving finalization
fairness. To accommodate different consensus speeds among shards, Haechi
incorporates a finalization fairness algorithm to achieve a globally fair order
with minimal performance loss. By providing a global order, Haechi ensures
strong consistency among shards, enabling better parallelism in handling
conflicting transactions across shards. These features make Haechi a promising
solution for supporting popular smart contracts in the real world. To evaluate
Haechi's performance, we implemented the protocol using Tendermint and
conducted extensive experiments on a geo-distributed AWS environment. Our
results demonstrate that Haechi achieves finalization fairness with little
performance sacrifice compared to existing cross-shard consensus protocols
Prophet: Conflict-Free Sharding Blockchain via Byzantine-Tolerant Deterministic Ordering
Sharding scales throughput by splitting blockchain nodes into parallel
groups. However, different shards' independent and random scheduling for
cross-shard transactions results in numerous conflicts and aborts, since
cross-shard transactions from different shards may access the same account. A
deterministic ordering can eliminate conflicts by determining a global order
for transactions before processing, as proved in the database field.
Unfortunately, due to the intertwining of the Byzantine environment and
information isolation among shards, there is no trusted party able to
predetermine such an order for cross-shard transactions. To tackle this
challenge, this paper proposes Prophet, a conflict-free sharding blockchain
based on Byzantine-tolerant deterministic ordering. It first depends on
untrusted self-organizing coalitions of nodes from different shards to
pre-execute cross-shard transactions for prerequisite information about
ordering. It then determines a trusted global order based on stateless ordering
and post-verification for pre-executed results, through shard cooperation.
Following the order, the shards thus orderly execute and commit transactions
without conflicts. Prophet orchestrates the pre-execution, ordering, and
execution processes in the sharding consensus for minimal overhead. We
rigorously prove the determinism and serializability of transactions under the
Byzantine and sharded environment. An evaluation of our prototype shows that
Prophet improves the throughput by and achieves nearly no aborts
on 1 million Ethereum transactions compared with state-of-the-art sharding
Functional mapping of B-cell linear epitopes of SARS-CoV-2 in COVID-19 convalescent population
The Sterility of Allotriploid Fish and Fertility of Female Autotriploid Fish
Based on the formation of an autotetraploid fish line (4nAUT, 4n = 200; F2–F11) derived from the distant hybridization of female Carassius auratus red var. (RCC, 2n = 100) × male Megalobrama amblycephala (BSB, 2n = 48), we produced autotriploid hybrids (3nAUT) by crossing females of RCC with males of 4nAUT and allotriploid hybrids (3nALT) by crossing females of Cyprinus carpio (CC, 2n = 100) with males of 4nAUT. The aim of this study was to comparatively investigate the reproductive characteristics of 3nALT and 3nAUT. We investigated morphological traits, chromosomal numbers, DNA content and gonadal development in 3nAUT and 3nALT. The results indicated both 3nAUT and 3nALT possessed 150 chromosomes and were triploid hybrids. The females and males of 3nALT and males of 3nAUT had abnormal gonadal development and could not generate mature eggs or sperm, but the females of 3nAUT had normal gonadal development and generated mature eggs at 2 years old. The females of 3nAUT generated different sizes of eggs, which fertilized with haploid sperm from RCC and formed viable diploid, triploid, and tetraploid offspring. The formation of these two kinds of triploid hybrids provides an ideal model for studying the reproductive traits of triploid hybrids, which is of great value in animal genetics and reproductive biology
Determination of dosage compensation and comparison of gene expression in a triploid hybrid fish
Small-Signal Performance of Type 4 Wind Turbine Generator-Based Clusters in Power Systems
The impact of Type 4 wind turbine generator (WTG)-based 10 million megawatt clusters (TMMC) on small-signal dynamics of power systems was investigated using the second-generation generic models (GM) of Western Electricity Coordinating Council (WECC). A WTG participation index (WTG PI) was defined to investigate the impact of Type 4 WTGs on the traditional interarea electromechanical modes. To identify the new electromechanical modes dominated by Type 4 WTGs, an identification factor (IF) was also defined using participation factors. Given the increasing penetration of Type 4 WTGs replacing synchronous generators, the changed law of damping and frequencies of the traditional interarea modes was also investigated using the WTG PI. One new type of electromechanical mode dominated by Type 4 WTGs was identified by using the defined IF. These new modes can be divided into two categories: strong-interaction modes and weak-interaction modes, depending on the number of participating WTGs. The strong-interaction modes dominated by Type 4 WTGs can result in widely spread power oscillations in power systems. The results of small-signal analysis were validated by time domain simulation and mode detection
The Method for Risk Assessment of SSR Caused by Doubly-Fed Wind Farms
The existing method for investigating the subsynchronous resonance (SSR) caused by wind powergeneration is mainly aimed at a deterministic condition. In order to analyse the impact of uncertain factors onSSR in wind farms, this paper defines the risk matrix and risk index, and develops a SSR-oriented riskassessment method of using probabilistic collocation method (PCM). Considering the uncertain of windspeeds, the proposed method is used to assess the SSR risk of a wind farm. The results show that under thesame wind speed distribution, the higher the series compensation level in the system is, the greater the SSRrisk of the system could be; under the same series compensation level, the SSR risks caused by different windspeed distribution are different, and the system in the areas with lower average wind speed obtains greater
SSR risk
Small-Signal Performance of Type 4 Wind Turbine Generator-Based Clusters in Power Systems
The impact of Type 4 wind turbine generator (WTG)-based 10 million megawatt clusters (TMMC) on small-signal dynamics of power systems was investigated using the second-generation generic models (GM) of Western Electricity Coordinating Council (WECC). A WTG participation index (WTG PI) was defined to investigate the impact of Type 4 WTGs on the traditional interarea electromechanical modes. To identify the new electromechanical modes dominated by Type 4 WTGs, an identification factor (IF) was also defined using participation factors. Given the increasing penetration of Type 4 WTGs replacing synchronous generators, the changed law of damping and frequencies of the traditional interarea modes was also investigated using the WTG PI. One new type of electromechanical mode dominated by Type 4 WTGs was identified by using the defined IF. These new modes can be divided into two categories: strong-interaction modes and weak-interaction modes, depending on the number of participating WTGs. The strong-interaction modes dominated by Type 4 WTGs can result in widely spread power oscillations in power systems. The results of small-signal analysis were validated by time domain simulation and mode detection