Defense Notices

Coupled line couplers are used as directional couplers to enable measurement of forward and reverse power in RF transmitters. These measurements provide valuable feedback to the control loops regulating transmitter power output levels. This project seeks to synthesize, simulate, build, and test a broadband, five-stage coupled line coupler with a 20 dB coupling factor. The coupler synthesis is evaluated against ideal coupler components in Keysight ADS.  Fabrication of coupled line couplers is typically accomplished with a stripline topology, but a microstrip topology is additionally evaluated. Measurements from the fabricated coupled line couplers are then compared to the Keysight ADS EM simulations, and some explanations for the differences are provided. Additionally, measurements from a commercially available broadband directional coupler are provided to show what can be accomplished with the right budget.

Survival analysis plays a crucial role in many healthcare decisions, where the risk prediction for the events of interest can support an informative outlook for a patient's medical journey. Given the existence of data censoring, an effective way of survival analysis is to enforce the pairwise temporal concordance between censored and observed data, aiming to utilize the time interval before censoring as partially observed time-to-event labels for supervised learning. Although existing studies mostly employed ranking methods to pursue an ordering objective, contrastive methods which learn a discriminative embedding by having data contrast against each other, have not been explored thoroughly for survival analysis. Therefore, we propose a novel Ontology-aware Temporality-based Contrastive Survival (OTCSurv) analysis framework that utilizes survival durations from both censored and observed data to define temporal distinctiveness and construct negative sample pairs with adjustable hardness for contrastive learning. Specifically, we first use an ontological encoder and a sequential self-attention encoder to represent the longitudinal EHR data with rich contexts. Second, we design a temporal contrastive loss to capture varying survival durations in a supervised setting through a hardness-aware negative sampling mechanism. Last, we incorporate the contrastive task into the time-to-event predictive task with multiple loss components. We conduct extensive experiments using a large EHR dataset to forecast the risk of hospitalized patients who are in danger of developing acute kidney injury (AKI), a critical and urgent medical condition. The effectiveness and explainability of the proposed model are validated through comprehensive quantitative and qualitative studies.

Significant developments in communication methods to help support at-risk populations have increased over the last 10 years. We view at-risk populations as a group of people present in environments where the use of infrastructure or electricity, including telecommunications, is censored and/or dangerous. Security features that accompany these communication mechanisms are essential to protect the confidentiality of its user base and the integrity and availability of the communication network.

In this work, we look at the feasibility of using Bluetooth Mesh as a communication network and analyze the security features that are inherent to the protocol. Through this analysis we determine the strengths and weaknesses of Bluetooth Mesh security features when used as a messaging medium for at risk populations and provide improvements to current shortcomings. Our analysis includes looking at the Bluetooth Mesh Networking Security Fundamentals as described by the Bluetooth Sig: Encryption and Authentication, Separation of Concerns, Area isolation, Key Refresh, Message Obfuscation, Replay Attack Protection, Trashcan Attack Protection, and Secure Device Provisioning.  We look at how each security feature is implemented and determine if these implementations are sufficient in protecting the users from various attack vectors. For example, we examined the Blue Mirror attack, a reflection attack during the provisioning process which leads to the compromise of network keys, while also assessing the under-researched key refresh mechanism. We propose a mechanism to address Blue-Mirror-oriented attacks with the goal of creating a more secure provisioning process.  To analyze the key refresh mechanism, we implemented our own full-fledged Bluetooth Mesh network and implemented a key refresh mechanism. Through this we form an assessment of the throughput, range, and impacts of a key refresh in both lab and field environments that demonstrate the suitability of our solution as a secure communication method.

With the increasing scale of high-performance computing (HPC) systems, transient bit-flip errors are now more likely than ever, posing a threat to long-running scientific applications. A substantial portion of these applications involve the simulation of partial differential equations (PDEs) modeling physical processes over discretized spatial and temporal domains, with some requiring the solving of sparse linear systems. While these applications are often paired with system-level application-agnostic resilience techniques such as checkpointing and replication, the utilization of these techniques imposes significant overhead. In this work, we present a probability-aware framework that produces low-overhead selective protection schemes for the widely used Preconditioned Conjugate Gradient (PCG) method, whose performance can heavily degrade due to error propagation through the sparse matrix-vector multiplication (SpMV) operation. Through the use of a straightforward mathematical model and an optimized machine learning model, our selective protection schemes incorporate error probability to protect only certain crucial operations. An experimental evaluation using 15 matrices from the SuiteSparse Matrix Collection demonstrates that our protection schemes effectively reduce resilience overheads, often outperforming or matching both baseline and established protection schemes across all error probabilities.

The growth of IoT and voice assistant (VA) apps poses increasing concerns about sensitive data leaks. While privacy policies are required to describe how these apps use private user data (i.e., data practice), problems such as missing, inaccurate, and inconsistent policies have been repeatedly reported. Therefore, it is important to assess the actual data practice in apps and identify the potential gaps between the actual and declared data usage. We find that app stores lack in regulating the compliance between the app practices and their declaration, so we use AI to discover the compliance issues in these apps to assist the regulators and developers. For VA apps, we also develop a mechanism to enforce the compliance using AI. In this work, we conduct a measurement study using our framework called IoTPrivComp, which applies an automated analysis of IoT apps’ code and privacy policies to identify compliance gaps. We collect 1,489 IoT apps with English privacy policies from the Play Store. IoTPrivComp detects 532 apps with sensitive external data flows, among which 408 (76.7%) apps have undisclosed data leaks. Moreover, 63.4% of the data flows that involve health and wellness data are inconsistent with the practices disclosed in the apps’ privacy policies. Next, we focus on the compliance issues in skills. VAs, such as Amazon Alexa, are integrated with numerous devices in homes and cars to process user requests using apps called skills. With their growing popularity, VAs also pose serious privacy concerns. Sensitive user data captured by VAs may be transmitted to third-party skills without users’ consent or knowledge about how their data is processed. Privacy policies are a standard medium to inform the users of the data practices performed by the skills. However, privacy policy compliance verification of such skills is challenging, since the source code is controlled by the skill developers, who can make arbitrary changes to the behaviors of the skill without being audited; hence, conventional defense mechanisms using static/dynamic code analysis can be easily escaped. We present Eunomia, the first real-time privacy compliance firewall for Alexa Skills. As the skills interact with the users, Eunomia monitors their actions by hijacking and examining the communications from the skills to the users, and validates them against the published privacy policies that are parsed using a BERT-based policy analysis module. When non-compliant skill behaviors are detected, Eunomia stops the interaction and warns the user. We evaluate Eunomia with 55,898 skills on Amazon skills store to demonstrate its effectiveness and to provide a privacy compliance landscape of Alexa skills.

Deep learning leads the performance in many areas of computer vision. However, after a decade of research, it tends to require larger datasets and more complex models, leading to heightened resource consumption across all fronts. Regrettably, meeting these requirements proves challenging in many real-life scenarios. First, both data collection and labeling processes entail substantial labor and time investments. This challenge becomes especially pronounced in domains such as medicine, where identifying rare diseases demands meticulous data curation. Secondly, the large size of state-of-the-art models, such as ViT, Stable Diffusion, and ConvNext, hinders their deployment on resource-constrained platforms like mobile devices. Research indicates pervasive redundancies within current neural network structures, exacerbating the issue. Lastly, even with ample datasets and optimized models, the time required for training and inference remains prohibitive in certain contexts. Consequently, there is a burgeoning interest among researchers in exploring avenues for efficient artificial intelligence.

This study endeavors to delve into various facets of efficiency within computer vision, including data efficiency, model efficiency, as well as training and inference efficiency. The data efficiency is improved from the perspective of increasing information brought by given image inputs and reducing redundancies of RGB image formats. To achieve this, we propose to integrate both spatial and frequency representations to finetune the classifier. Additionally, we propose explicitly increasing the input information density in the frequency domain by deleting unimportant frequency channels. For model efficiency, we scrutinize the redundancies present in widely used vision transformers. Our investigation reveals that trivial attention in their attention modules covers useful non-trivial attention due to its large amount. We propose mitigating the impact of accumulated trivial attention weights. To increase training efficiency, we propose SuperLoRA, a generation of LoRA adapter, to fine-tune pretrained models with few iterations and extremely-low parameters. Finally, a model simplification pipeline is proposed to further reduce inference time on mobile devices. By addressing these challenges, we aim to advance the practicality and performance of computer vision systems in real-world applications.

Convolutional Neural Networks (CNNs) have significantly enhanced performance across various computer vision tasks such as image recognition and segmentation, owing to their robust representation capabilities. To further boost CNN performance, a self-attention module is integrated after each network layer. Transformer-based models, which leverage a multi-head self-attention module as their core component, have recently demonstrated outstanding performance. However, several challenges persist, including the limitation to class-specific channels in CNNs, the constrained receptive field in local transformers, and the incorporation of redundant features and the absence of multi-scale features in U-Net type segmentation architectures.

In our study, we propose new strategies to tackle these challenges. (1) We propose a novel channel-based self-attention module to diversify the focus more on the discriminative and significant channels, and the module can be embedded at the end of any backbone network for image classification. (2) To mitigate noise introduced by shallow encoder layers in U-Net architectures, we substitute skip connections with an Adaptive Global Context Module (AGCM). Additionally, we introduce the Semantic Feature Enhancement Module (SFEM) to enhance multi-scale features in polyp segmentation. (3) We introduce a Multi-scaled Overlapped Attention (MOA) mechanism within local transformer-based networks for image classification, facilitating the establishment of long-range dependencies and initiation of neighborhood window communication. (4) We propose a pioneering Fuzzy Attention Module designed to prioritize challenging pixels, thereby augmenting polyp segmentation performance. (5) We develop a novel dense attention gate module that aggregates features from all preceding layers to compute attention scores, refining global features in polyp segmentation tasks. Moreover, we design a new multi-layer horizontally extended decoder architecture to enhance local feature refinement in polyp segmentation.

Radar systems perform 3 basic tasks: search/detection, tracking, and imaging. Traditionally, varied operational and hardware requirements have compartmentalized these functions to separate and specialized radars, which may communicate actionable information between them. Expedited by the growth in computational capabilities modeled by Moore’s law, next-generation radars will be sophisticated, multi-function systems comprising generalized and reprogrammable subsystems. The advance of fully Digital Array Radars (DAR) has enabled the implementation of highly directive phased arrays that can scan, detect, and track scatterers through a volume-of-interest. As a strategical converse, DAR technology has also enabled Multiple-Input Multiple-Output (MIMO) radar systems that seek to illuminate all space on transmit, while forming separate but simultaneous, directive beams on receive.

Waveform diversity has been repeatedly proven to enhance radar operation through added Degrees-of-Freedom (DoF) that can be leveraged to expand dynamic range, provide ambiguity resolution, and improve parameter estimation.  In particular, diversity among the DAR’s transmitting elements provides flexibility to the emission, allowing simultaneous multi-function capability. By precise design of the emission, the DAR can utilize the operationally-continuous trade-space between a fully coherent phased array and a fully incoherent MIMO system. This flexibility could enable the optimal management of the radar’s resources, where Signal-to-Noise Ratio (SNR) would be traded for robustness in detection, measurement capability, and tracking.

Waveform diversity is herein leveraged as the predominant enabling technology for multi-function radar emission design. Three methods of emission optimization are considered to design distinct beams in space and frequency, according to classical error minimization techniques. First, a gradient-based optimization of Space-Frequency Template Error (SFTE) is implemented on a high-fidelity model for a wideband array’s far-field emission. Second, a more efficient optimization is considered, based on SFTE for narrowband arrays. Finally, optimization via alternating projections is shown to provide rapidly reconfigurable transmit patterns. To improve the dynamic range observed for MIMO radars using pulse-agile quasi-orthogonal waveforms, a pulse-compression model is derived, and experimentally validated, that manages to suppress both autocorrelation sidelobes and multi-transmitter-induced cross-correlation. Several modifications to the demonstrated algorithms are proposed to refine implementation, enhance performance, and reflect real-world application to the degree that numerical simulations can.

Semantic remote attestation is the process of gathering and appraising evidence to establish trust in a remote system. Remote attestation occurs at the request of an appraiser or relying party and proceeds with a target system executing an attestation protocol that invokes attestation services in a specific order to generate and bundle evidence. An appraiser may then evaluate the generated evidence to establish trust in the target's state.  In this current framework, requested measurement operations must be provisioned by a knowledgeable system user who may fail to consider situational demands which potentially impact the desired measurement operation. To solve this problem, we introduce Attestation Protocol Negotiation or the process of establishing a mutually agreed upon protocol that satisfies the relying party's desire for comprehensive information and the target's desire for constrained disclosure.

    This research explores the formal modeling and verification of negotiation, introducing refinement and selection procedures to enable communicating peers to achieve their goals. First, we explore the formalization of refinement or the process by which a target generates executable protocols. Here we focus on a definition of system specifications through manifests, protocol sufficiency and soundness, policy representation, and the negotiation structure. By using our formal models to represent and verify negotiation's properties we can statically determine that a provably sound, sufficient, and executable protocol is produced. Next, we present a formalized model for protocol selection, introducing and proving a preorder over Copland remote attestation protocols to facilitate selection of the most adversary-constrained protocol. With this modeling, we prove selected protocols increase the difficulty of an active adversary. By addressing the target's capability to generate provably executable protocols and the ability to order these protocols, this methodology has the potential to revolutionize the attestation protocol provisioning process.

 The advent of deep learning has enabled the development of powerful AI models that are being used in fields such as medicine, surveillance monitoring, optimizing manufacturing processes, allowing robots to navigate their environment, chatbots, and much more. These applications are only made possible because of the enormous research in the fields of Neural networks and deep learning. In this paper, I’ll be discussing a branch of Neural Networks called Convolution Neural Network (CNN), and how they are used for object detection tasks for detecting and classifying objects in an image. I’ll also discuss a popular object detection framework called Single Shot Multibox Detector (SSD) and implement it in my web application project which allows users to detect objects in images and search for images based on the presence of objects. The main aim of the project was to allow easy access to perform detections with a few clicks.