SlowFuzz: Automated Domain-Independent Detection of Algorithmic Complexity Vulnerabilities

Algorithmic complexity vulnerabilities occur when the worst-case time/space complexity of an application is significantly higher than the respective average case for particular user-controlled inputs. When such conditions are met, an attacker can launch Denial-of-Service attacks against a vulnerable application by providing inputs that trigger the worst-case behavior. Such attacks have been known to have serious effects on production systems, take down entire websites, or lead to bypasses of Web Application Firewalls. Unfortunately, existing detection mechanisms for algorithmic complexity vulnerabilities are domain-specific and often require significant manual effort. In this paper, we design, implement, and evaluate SlowFuzz, a domain-independent framework for automatically finding algorithmic complexity vulnerabilities. SlowFuzz automatically finds inputs that trigger worst-case algorithmic behavior in the tested binary. SlowFuzz uses resource-usage-guided evolutionary search techniques to automatically find inputs that maximize computational resource utilization for a given application.Comment: ACM CCS '17, October 30-November 3, 2017, Dallas, TX, US

Persistence and internalization of Listeria monocytogenes in romaine lettuce, Lactuca sativa var. longifolia

Listeria monocytogenes, has been implicated in a number of outbreaks involving fresh produce. While no L. monocytogenes outbreaks have been linked to romaine lettuce, the number of lettuce recalls specific to L. monocytogenes is increasing. Understanding the potential of persistence and internalization of L. monocytogenes on and within romaine lettuce will aid in determining food safety risk. Persistence of three L. monocytogenes strains on three romaine lettuce cultivars was assessed independently by inoculating seeds in 25 ml of 8 log CFU/ml for 30 minutes. Seeds were grown on two soil types (i.e. standard potting mix, Indiana top soil) or sterile soft-top agar for up to 60 days. Average CFU/g of L. monocytogenesretained on seeds or persisting on growing plants was calculated from a total of 5 replicates per harvest day. Plants grown on sterile soft-top agar maintained between 4.4 to 7.8 log CFU/g L. monocytogenes after a 60 day period, while pathogen levels dropped below the limit of detection (2 log CFU/g) by Day 18 in 75% Indiana top soil, and by Day 45 in commercial potting mix. This suggests that soil microflora may impede pathogen persistence. L. monocytogenes strain differences and the presence of a clay coating on seeds were not factors that affected persistence. Cultivar differences, however, potentially influenced L. monocytogenes growth and survival. For internalization studies, seeds were inoculated with a L. monocytogenes strain constitutively expressing green fluorescent protein (GFP). Three plants were fixed, paraffin embedded, and sectioned; localization was studied using standard immunohistochemistry techniques. A total of 539 L. monocytogenes cells were internalized in all major tissue types of the hypocotyl with the majority localizing in the pith followed by cortex, xylem, phloem and epidermis. The presence of the bacterium in the plant vasculature indicates its potential to be transported throughout the plant system and reside within edible tissue. The significance of these findings is that romaine lettuce can support growth and internalization of L. monocytogenes, which could serve as a vehicle for L. monocytogenestransmission to consumers. Additionally, seeds from 16 cultivars of romaine lettuce and one cultivar of radicchio were examined as a potential source of contamination in a 2014 commercial recall of bagged salad products. Only a single seed, out of 1,700 tested, was found to be contaminated using PCR based methods on isolates recovered. These data indicate that while it is possible that the seed could be a source of potential L. monocytogenescontamination, it is unlikely that the seeds of the tested cultivars were the source of bagged salad recalls

Optical properties of photonic crystals

The ability to confine light in three dimensions has important implications for quantum optics and quantum-optical devices. Photonic crystals, the optical analog of electronic crystals, provide us a means of achieving this goal. This analogy has motivated a whole new series of experimental and theoretical searches for elusive photonic band-gap structures. Combinations of metallic and dielectric materials can be used to obtain the required three-dimensional (3D) periodic variation in the dielectric constant. This could pave the way for photonic crystal structures that have widespread applications. The working of 3D photonic crystals into the wavelength regimes where most optoelectronic devices operate, i.e., 1.3 to 1.5µm was explored in the course of the thesis work. Simulations were run simultaneously on samples that were considered using Multirad. A one to one correspondence was sought between the two, i.e., experimental and simulated results. The basis for the conclusions was drawn from the known and present experimental results and simulations. The need for research on photonic crystal structures in particular areas was evaluated. Inferences drawn from this were then deployed to identify areas of modem science that would benefit from discoveries in photonic crystals

X - Ray Flares and Their Connection With Prompt Emission in GRBs

We use a wavelet technique to investigate the time variations in the light curves from a sample of GRBs detected by Fermi and Swift. We focus primarily on the behavior of the flaring region of Swift-XRT light curves in order to explore connections between variability time scales and pulse parameters (such as rise and decay times, widths, strengths, and separation distributions) and spectral lags. Tight correlations between some of these temporal features suggest a common origin for the production of X-ray flares and the prompt emission.Comment: 7th Huntsville Gamma-Ray Burst Symposium, GRB 2013: paper 15 in eConf Proceedings C130414

Numerical Investigation and Optimization of a Flushwall Injector for Scramjet Applications at Hypervelocity Flow Conditions

An investigation utilizing Reynolds-averaged simulations (RAS) was performed in order to demonstrate the use of design and analysis of computer experiments (DACE) methods in Sandias DAKOTA software package for surrogate modeling and optimization. These methods were applied to a flow- path fueled with an interdigitated flushwall injector suitable for scramjet applications at hyper- velocity conditions and ascending along a constant dynamic pressure flight trajectory. The flight Mach number, duct height, spanwise width, and injection angle were the design variables selected to maximize two objective functions: the thrust potential and combustion efficiency. Because the RAS of this case are computationally expensive, surrogate models are used for optimization. To build a surrogate model a RAS database is created. The sequence of the design variables comprising the database were generated using a Latin hypercube sampling (LHS) method. A methodology was also developed to automatically build geometries and generate structured grids for each design point. The ensuing RAS analysis generated the simulation database from which the two objective functions were computed using a one-dimensionalization (1D) of the three-dimensional simulation data. The data were fitted using four surrogate models: an artificial neural network (ANN), a cubic polynomial, a quadratic polynomial, and a Kriging model. Variance-based decomposition showed that both objective functions were primarily driven by changes in the duct height. Multiobjective design optimization was performed for all four surrogate models via a genetic algorithm method. Optimal solutions were obtained at the upper and lower bounds of the flight Mach number range. The Kriging model predicted an optimal solution set that exhibited high values for both objective functions. Additionally, three challenge points were selected to assess the designs on the Pareto fronts. Further sampling among the designs of the Pareto fronts may be required to lower the surrogate model errors and perform more accurate surrogate-model-based optimization

Gamma-Ray Bursts: Temporal Scales and the Bulk Lorentz Factor

For a sample of Swift and Fermi GRBs, we show that the minimum variability timescale and the spectral lag of the prompt emission is related to the bulk Lorentz factor in a complex manner: For small $\Gamma$'s, the variability timescale exhibits a shallow (plateau) region. For large $\Gamma$'s, the variability timescale declines steeply as a function of $\Gamma$ ($\delta T\propto\Gamma^{-4.05\pm0.64}$). Evidence is also presented for an intriguing correlation between the peak times, t$_p$, of the afterglow emission and the prompt emission variability timescale.Comment: Accepted for publication in Ap