VTechWorks staff will be away for the winter holidays starting Tuesday, December 24, 2024, through Wednesday, January 1, 2025, and will not be replying to requests during this time. Thank you for your patience, and happy holidays!

Browsing by Author "Xiao, Yang"

Now showing 1 - 11 of 11
  • Thumbnail Image
    Blockchain and Distributed Consensus: From Security Analysis to Novel Applications
    Xiao, Yang (Virginia Tech, 2022-05-13)
    Blockchain, the technology behind cryptocurrency, enables decentralized and distrustful parties to maintain a unique and consistent transaction history through consensus, without involving a central authority. The decentralization, transparency, and consensus-driven security promised by blockchain are unprecedented and can potentially enable a wide range of new applications that prevail in the decentralized zero-trust model. While blockchain represents a secure-by-design approach to building zero-trust applications, there still exist outstanding security bottlenecks that hinder the technology's wider adoption, represented by the following two challenges: (1) blockchain as a distributed networked system is multi-layered in nature which has complex security implications that are not yet fully understood or addressed; (2) when we use blockchain to construct new applications, especially those previously implemented in the centralized manner, there often lack effective paradigms to customize and augment blockchain's security offerings to realize domain-specific security goals. In this work, we provide answers to the above two challenges in two coordinated efforts. In the first effort, we target the fundamental security issues caused by blockchain's multi-layered nature and the consumption of external data. Existing analyses on blockchain consensus security overlooked an important cross-layer factor---the heterogeneity of the P2P network's connectivity. We first provide a comprehensive review on notable blockchain consensus protocols and their security properties. Then we focus one class of consensus protocol---the popular Nakamoto consensus---for which we propose a new analytical model from the networking perspective that quantifies the impact of heterogeneous network connectivity on key consensus security metrics, providing insights on the actual "51% attack" threshold (safety) and mining revenue distribution (fairness). The external data truthfulness challenge is another fundamental challenge concerning the decentralized applications running on top of blockchain. The validity of external data is key to the system's operational security but is out of the jurisdiction of blockchain consensus. We propose DecenTruth, a system that combines a data mining technique called truth discovery and Byzantine fault-tolerant consensus to enable decentralized nodes to collectively extract truthful information from data submitted by untrusted external sources. In the second effort, we harness the security offerings of blockchain's smart contract functionality along with external security tools to enable two domain-specific applications---data usage control and decentralized spectrum access system. First, we use blockchain to tackle a long-standing privacy challenge of data misuse. Individual data owners often lose control on how their data can be used once sharing the data with another party, epitomized by the Facebook-Cambridge Analytica data scandal. We propose PrivacyGuard, a security platform that combines blockchain smart contract and hardware trusted execution environment (TEE) to enable individual data owner's fine-grained control over the usage (e.g., which operation, who can use on what condition/price) of their private data. A core technical innovation of PrivacyGuard is the TEE-based execution and result commitment protocol, which extends blockchain's zero-trust security to the off-chain physical domain. Second, we employ blockchain to address the potential security and performance issues facing dynamic spectrum sharing in the 5G or next-G wireless networks. The current spectrum access system (SAS) designated by the FCC follows a centralized server-client service model which is vulnerable to single-point failures of SAS service providers and also lacks an efficient, automated inter-SAS synchronization mechanism. In response, we propose a blockchain-based decentralized SAS architecture dubbed BD-SAS to provide SAS service efficiently to spectrum users and enable automated inter-SAS synchronization, without assuming trust on individual SAS service providers. We hope this work can provide new insights into blockchain's fundamental security and applicability to new security domains.
  • Thumbnail Image
    Chronic stress and adipose tissue in the anorexic state: endocrine and epigenetic mechanisms
    Xiao, Yang; Liu, Dongmin; Cline, Mark A.; Gilbert, Elizabeth R. (Taylor & Francis, 2020)
    Although adipose tissue metabolism in obesity has been widely studied, there is limited research on the anorexic state, where the endocrine system is disrupted by reduced adipose tissue mass and there are depot-specific changes in adipocyte type and function. Stress exposure at different stages of life can alter the balance between energy intake and expenditure and thereby contribute to the pathogenesis of anorexia nervosa. This review integrates information from human clinical trials to describe endocrine, genetic and epigenetic aspects of adipose tissue physiology in the anorexic condition. Changes in the hypothalamus-pituitary-thyroid, -adrenal, and -gonadal axes and their relationships to appetite regulation and adipocyte function are discussed. Because of the role of stress in triggering or magnifying anorexia, and the dynamic but also persistent nature of environmentally-induced epigenetic modifications, epigenetics is likely the link between stress and long-term changes in the endocrine system that disrupt homoeostatic food intake and adipose tissue metabolism. Herein, we focus on the adipocyte and changes in its function, including alterations reinforced by endocrine disturbance and dysfunctional adipokine regulation. This information is critical because of the poor understanding of anorexic pathophysiology, due to the lack of suitable research models, and the complexity of genetic and environmental interactions.
  • Thumbnail Image
    Chronic stress, epigenetics, and adipose tissue metabolism in the obese state
    Xiao, Yang; Liu, Dongmin; Cline, Mark A.; Gilbert, Elizabeth R. (2020-10-19)
    In obesity, endocrine and metabolic perturbations, including those induced by chronic activation of the hypothalamus–pituitary–adrenal axis, are associated with the accumulation of adipose tissue and inflammation. Such changes are attributable to a combination of genetic and epigenetic factors that are influenced by the environment and exacerbated by chronic activation of the hypothalamus–pituitary–adrenal axis. Stress exposure at different life stages can alter adipose tissue metabolism directly through epigenetic modification or indirectly through the manipulation of hypothalamic appetite regulation, and thereby contribute to endocrine changes that further disrupt whole-body energy balance. This review synthesizes current knowledge, with an emphasis on human clinical trials, to describe metabolic changes in adipose tissue and associated endocrine, genetic and epigenetic changes in the obese state. In particular, we discuss epigenetic changes induced by stress exposure and their contribution to appetite and adipocyte dysfunction, which collectively promote the pathogenesis of obesity. Such knowledge is critical for providing future directions of metabolism research and targets for treating metabolic disorders.
  • Thumbnail Image
    Dietary Supplementation of Baicalein Affects Gene Expression in Broiler Adipose Tissue During the First Week Post-hatch
    Xiao, Yang; Halter, Bailey; Boyer, Casey; Cline, Mark A.; Liu, Dongmin; Gilbert, Elizabeth R. (Frontiers, 2021-06-25)
    Dietary supplementation of baicalein, a flavonoid, has anti-obesity effects in mammals and broiler chickens. The aim of this study was to determine the effect of dietary baicalein supplementation on broiler growth and adipose tissue and breast muscle deposition. Fifty Hubbard Cobb-500 day-of-hatch broiler chicks were assigned to a control starter diet or control diet supplemented with 125, 250, or 500 mg/kg baicalein and diets were fed for the first 6 days post-hatch. Body weight, average daily body weight gain, and average daily food intake were all reduced by 500 mg/kg baicalein. Breast muscle and subcutaneous and abdominal fat weights were also reduced in chicks that consumed the baicalein-supplemented diets. mRNAs for genes encoding factors involved in adipogenesis and fat storage, 1-acylglycerol-3-phosphate-O-acyltransferase 2, CCAAT/enhancer-binding protein b, perilipin-1, and sterol regulatory element-binding transcription factor 1, were more highly expressed in the adipose tissue of broilers supplemented with baicalein than the controls, independent of depot. Diacylglycerol acyltransferase and peroxisome proliferator-activated receptor gamma mRNAs, involved in triacylglycerol synthesis and adipogenesis, respectively, were greater in subcutaneous than abdominal fat, which may contribute to differences in expansion rates of these depots. Results demonstrate effects of dietary supplementation of baicalein on growth performance in broilers during the early post-hatch stage and molecular effects in major adipose tissue depots. The mild reduction in food intake coupled to slowed rate of breast muscle and adipose tissue accumulation may serve as a strategy to modulate broiler growth and body composition to prevent metabolic and skeletal disorders later in life.
  • Thumbnail Image
    Early-Life Stress Induced Epigenetic Changes of Corticotropin-Releasing Factor Gene in Anorexic Low Body Weight–Selected Chicks
    Xiao, Yang; Wang, Jinxin; Siegel, Paul B.; Cline, Mark A.; Gilbert, Elizabeth R. (MDPI, 2020-04-27)
    The expression of neuropeptide Y (NPY) in the arcuate nucleus (ARC) and corticotropin-releasing factor (CRF) in the paraventricular nucleus (PVN) were increased when low body weight–selected (LWS) line chicks, which are predisposed to anorexia, were subjected to a combination of nutritional and thermal stressors at hatch. We hypothesized that such changes resulted from epigenetic modifications. We determined global DNA methylation, DNA methyltransferase (DNMT) activity, and methylation near the promoter regions of NPY and CRF, in the hypothalamus of LWS chicks on day 5 post-hatch. Stress exposure at hatch induced global hypermethylation and increased DNMT activity in the ARC but not PVN. In the PVN of stressed LWS chicks, there was decreased methylation of a CpG site located at the core binding domain of methyl cytosine binding domain protein 2 (MBD2), near the CRF gene promoter. We then demonstrated that this was associated with disrupted binding of MBD2. There was also reduced utilization of yolk reserves and lean and fat masses in chicks that were stress-exposed. These findings provide novel insights on molecular mechanisms through which stressful events induce or intensify anorexia in predisposed individuals and a novel molecular target for further studies.
  • Thumbnail Image
    FLARE: Defending Federated Learning against Model Poisoning Attacks via Latent Space Representations
    Wang, Ning; Xiao, Yang; Chen, Yimin; Hu, Yang; Lou, Wenjing; Hou, Y. Thomas (ACM, 2022-05-30)
    Federated learning (FL) has been shown vulnerable to a new class of adversarial attacks, known as model poisoning attacks (MPA), where one or more malicious clients try to poison the global model by sending carefully crafted local model updates to the central parameter server. Existing defenses that have been fixated on analyzing model parameters show limited effectiveness in detecting such carefully crafted poisonous models. In this work, we propose FLARE, a robust model aggregation mechanism for FL, which is resilient against state-of-the-art MPAs. Instead of solely depending on model parameters, FLARE leverages the penultimate layer representations (PLRs) of the model for characterizing the adversarial influence on each local model update. PLRs demonstrate a better capability to differentiate malicious models from benign ones than model parameter-based solutions. We further propose a trust evaluation method that estimates a trust score for each model update based on pairwise PLR discrepancies among all model updates. Under the assumption that honest clients make up the majority, FLARE assigns a trust score to each model update in a way that those far from the benign cluster are assigned low scores. FLARE then aggregates the model updates weighted by their trust scores and finally updates the global model. Extensive experimental results demonstrate the effectiveness of FLARE in defending FL against various MPAs, including semantic backdoor attacks, trojan backdoor attacks, and untargeted attacks, and safeguarding the accuracy of FL.
  • Thumbnail Image
    The Influence of Behavioral Inhibition and Approach on Affective Modification of the Startle Response
    Xiao, Yang (Virginia Tech, 2013-12-19)
    Startle modification is a robust phenomenon that has been used as a tool in the research of emotion and motivation. In a picture viewing paradigm, valence of affective pictures modulates startle magnitude. There is a debate on whether emotional or attentional processes are the mechanism of startle modification. The present study sought to address this question by investigating the individual differences related to startle modification and explore the relationship of the trait-like physiological variables and startle modification. The study creatively calculated standardized startle scores and treated personality variables as continuous variable. The results showed that specific contents of the affective pictures had different effects of startle modification. Personality variables influence the startle modification in emotion conditions differently. Cardiac activities were related to raw startle magnitude but not to startle modification. The results have suggested that there are the influences of individual differences in attention and effortful control on startle modification and attention and that emotion and attention interact with each other in startle modification. The study filled gaps in the research on startle modification and personality and guided future studies of this topic.
  • Thumbnail Image
    Molecular and cellular mechanisms of energy homeostasis in birds
    Xiao, Yang (Virginia Tech, 2020-04-09)
    Hypothalamus and adipose tissue are essential central and peripheral sites regulating energy homeostasis. Disruption of energy homeostasis can lead to diseases like anorexia and obesity in humans and reduced productivity in animals. Therefore, integrating knowledge in hypothalamic appetite regulation and adipose tissue metabolism is essential to maintain homeostasis. The aim of this dissertation was to elucidate molecular and cellular mechanisms of energy homeostasis in birds. We determined adipose tissue physiological changes during the first two weeks post-hatch in chickens from lines selected for low (LWS) and high (HWS) body weight. LWS was more dependent on yolk and subcutaneous fat mobilization for growth from hatch to day 4 post-hatch, with hyperplasia-predominated replenishment of the reservoir. In contrast, HWS was more dependent on feed for growth and maintained depot mass through hyperplasia and hypertrophy. From day 4 to 14 post-hatch, compared to maintenance of depot weight and adipocyte size in LWS, HWS accumulated clavicular and abdominal fat with minimal lipolysis. There was greater expression of precursor and proliferation markers in LWS with more apoptotic cells in the abdominal stromal vascular fraction on day 14 post-hatch, suggesting that apoptosis contributed to lower adipogenic potential and lack of abdominal fat in LWS. Exposure to thermal and nutritional stressors at hatch impaired growth by reducing yolk utilization and lowering body weight, lean and fat masses in LWS. Stress exposure resulted in increased global DNA methylation and DNA methyltransferase activity in the arcuate nucleus of the hypothalamus in LWS. Moreover, there was decreased binding to methyl-CpG-binding domain protein 2 in the promoter of corticotropin-releasing factor (CRF) because of hypomethylation in one CpG site at its core binding site in stressed LWS, which explains the increased CRF expression in the paraventricular nucleus of the hypothalamus. We next determined effects of nutritional status on adipose tissue physiology in Japanese quail, a less-intensively selected avian species. Six-hour fasting promoted lipolysis and gene expression changes in 7-day old quail with some changes restored to original levels within 1 hour of refeeding. Overall, our results reveal novel cellular and molecular mechanisms regulating appetite and adiposity in birds early post-hatch.
  • Thumbnail Image
    MS-PTP: Protecting Network Timing from Byzantine Attacks
    Shi, Shanghao; Xiao, Yang; Du, Changlai; Shahriar, Md Hasan; Li, Ao; Zhang, Ning; Hou, Y. Thomas; Lou, Wenjing (ACM, 2023-05-29)
    Time-sensitive applications, such as 5G and IoT, are imposing increasingly stringent security and reliability requirements on network time synchronization. Precision time protocol (PTP) is a de facto solution to achieve high precision time synchronization. It is widely adopted by many industries. Existing efforts in securing the PTP focus on the protection of communication channels, but little attention has been given to the threat of malicious insiders. In this paper, we first present the security vulnerabilities of PTP and discuss why the current defense mechanisms are unable to counter Byzantine insiders. We demonstrate how a malicious insider can spoof a time source to arbitrarily shift the system time of a victim node on an IoT testbed.We further demonstrate the harmful consequence of the attack on a real Turtlebot3 robotic platform as the robot fails to locate itself and follows a false trajectory. As a countermeasure, we propose multi-source PTP, in short, MS-PTP, a Byzantine-resilient network time synchronization mechanism that relies on time crowdsourcing. MS-PTP changes the current PTP’s single source hierarchy to a multi-source client-server architecture, in which PTP clients take responses from multiple time servers and apply a novel secure aggregation scheme to eliminate the effect of malicious responses from unreliable sources. MS-PTP is able to counter 𝑓 Byzantine failures when the total number of time sources 𝑛 used by a client satisfies 𝑛 ≥ 3𝑓 + 1. We provide rigorous proof for its non-parametric accuracy guarantee—achieving bounded error regardless of the Byzantine population. We implemented a prototype of MS-PTP on our IoT testbed and the results show its resilience against Byzantine insiders while maintaining high synchronization accuracy.
  • Thumbnail Image
    Squeezing More Utility via Adaptive Clipping on Differentially Private Gradients in Federated Meta-Learning
    Wang, Ning; Xiao, Yang; Chen, Yimin; Zhang, Ning; Lou, Wenjing; Hou, Y. Thomas (ACM, 2022-12-05)
    Federated meta-learning has emerged as a promising AI framework for today’s mobile computing scenes involving distributed clients. It enables collaborative model training using the data located at distributed mobile clients and accommodates clients that need fast model customization with limited new data. However, federated meta-learning solutions are susceptible to inference-based privacy attacks since the global model encoded with clients’ training data is open to all clients and the central server. Meanwhile, differential privacy (DP) has been widely used as a countermeasure against privacy inference attacks in federated learning. The adoption of DP in federated meta-learning is complicated by the model accuracy-privacy trade-off and the model hierarchy attributed to the meta-learning component. In this paper, we introduce DP-FedMeta, a new differentially private federated meta-learning architecture that addresses such data privacy challenges. DP-FedMeta features an adaptive gradient clipping method and a one-pass meta-training process to improve the model utility-privacy trade-off. At the core of DPFedMeta are two DP mechanisms, namely DP-AGR and DP-AGRLR, to provide two notions of privacy protection for the hierarchical models. Extensive experiments in an emulated federated metalearning scenario on well-known datasets (Omniglot, CIFAR-FS, and Mini-ImageNet) demonstrate that DP-FedMeta accomplishes better privacy protection while maintaining comparable model accuracy compared to the state-of-the-art solution that directly applies DP-based meta-learning to the federated setting.
  • Thumbnail Image
    TriSAS: Toward Dependable Inter-SAS Coordination with Auditability
    Shi, Shanghao; Xiao, Yang; Du, Changlai; Shi, Yi; Wang, Chonggang; Gazda, Robert; Hou, Y. Thomas; Burger, Eric W.; Dasilva, Luiz; Lou, Wenjing (ACM, 2024-07-01)
    To facilitate dynamic spectrum sharing, the FCC has designated certified SAS administrators to implement their own spectrum access systems (SASs) that manage the shared spectrum usage in the novel CBRS band. As a premise, different SAS servers must conduct periodic inter-SAS coordination to synchronize service states and avoid allocation conflicts. However, SAS servers may inevitably stop service for regular upgrades, crash down, or even perform maliciously that deviate from the normal routines, posing a fundamental operation security problem — the system shall be robust against these faults to guarantee secure and efficient spectrum sharing service. Unfortunately, the incumbent inter-SAS coordination mechanism, CPAS, is prone to SAS failures and does not support real-time allocation. Recent proposals that rely on blockchain smart contracts or state machine replication mechanisms to realize faulttolerant inter-SAS coordination require all SASs to follow a unified allocation algorithm. They however face performance bottlenecks and cannot accommodate the current fact that different SASs hold their own proprietary allocation algorithms. In this work, we propose TriSAS—a novel inter-SAS coordination mechanism to facilitate secure, efficient, and dependable spectrum allocation that is fully compatible with the existing SAS infrastructure. TriSAS decomposes the coordination process into two phases including input synchronization and decision finalization. The first phase ensures participants share a common input set while the second one fulfills a fair and verifiable spectrum allocation selection, which is generated efficiently via SAS proposers’ proprietary allocation algorithms and evaluated by a customized designed allocation evaluation algorithm (AEA), in the face of no more than one-third of malicious participants. We implemented a prototype of TriSAS on the AWS cloud computing platform and evaluated its throughput and latency performance. The results show that TriSAS achieves high transaction throughput and low latency under various practical settings.