Po-Yen Huang

Investigation of 4-ASK modulation with digital filtering to increase 20 times of direct modulation speed of white-light LED visible light communication system

In this demonstration, we propose and experimentally investigate the quaternary-amplitude-shift-keying (4-ASK) modulation with digital filtering to enhance the direct modulation speed of white-light light-emitting-diode (LED) in visible light communication (VLC) system. Here, an ordinary LED commercially available for lighting application with a direct modulation speed of 1 MHz is used. Data rate of 20 Mbit/s can be achieved in a 1 m free space transmission without using optical blue filter. In the previous studies, the transmission rate of LED VLC could only be increased by 2 to 10 times of the direct modulation speed of the white-light LED if using electrical equalization only. Moreover, the adaptive-controlled FIR filter makes the system closer to the matched filtering condition for reducing the inter-symbol-interference (ISI) for the LED VLC. A recorded 20 times enhancement of the direct modulation speed of white-light LED VLC system is demonstrated by using digital filter only and without using optical blue filter.

Mitigation of Optical Background Noise in Light-Emitting Diode (LED) Optical Wireless Communication Systems

One challenge faced by the in-home light-emitting diode (LED) optical wireless communication is the optical noises. Here, we first experimentally characterize the effect of optical background noise to the performance of the LED optical wireless communication channel. We demonstrate using Manchester coding for the LED to mitigate the optical noise. No adaptive monitoring, feedback, or optical filtering is required. The theoretical and numerical analysis of Manchester decoding process to mitigate the optical background noise is provided. Our experimental result shows that Manchester coding can significantly eliminate optical noise generated by the AC-LED operated at <; 500 kHz and fluorescent light.

Background Optical Noises Circumvention in LED Optical Wireless Systems Using OFDM

Background optical noises generated by the conventional fluorescent light sources or AC-power light-emitting diode (LED) can significantly affect the performance of the LED optical wireless communication and produce challenges to implementation. We demonstrate using orthogonal frequency division multiplexing (OFDM) to effectively circumvent the optical background noises. Besides, by using simple equalization at the receiver side, the transmission capacity can be extended from 1 Mb/s to 12 Mb/s. The theory and analysis of the equalization are presented. Experiments at different data rates and different OFDM subcarriers are preformed, and results show that, by adjusting the number of OFDM subcarriers, the influence of the background optical noises can be significantly circumvented.

CRAX: Software Crash Analysis for Automatic Exploit Generation by Modeling Attacks as Symbolic Continuations

We present a simple framework capable of automatically generating attacks that exploit control flow hijacking vulnerabilities. We analyze given software crashes and perform symbolic execution in concolic mode, using a whole system environment model. The framework uses an end-to-end approach to generate exploits for various applications, including 16 medium scale benchmark programs, and several large scale applications, such as Mplayer (a media player), Unrar (an archiver) and Foxit(a pdf reader), with stack/heap overflow, off-by-one overflow, use of uninitialized variable, format string vulnerabilities. Notably, these applications have been typically regarded as fuzzing preys, but still require a manual process with security knowledge to produce mitigation-hardened exploits. Using our system to produce exploits is a fully automated and straightforward process for crashed software without source. We produce the exploits within six minutes for medium scale of programs, and as long as 80 minutes for mplayer (about 500,000 LOC), after constraint reductions. Our results demonstrate that the link between software bugs and security vulnerabilities can be automatically bridged.

Software Crash Analysis for Automatic Exploit Generation on Binary Programs

This paper presents a new method, capable of automatically generating attacks on binary programs from software crashes. We analyze software crashes with a symbolic failure model by performing concolic executions following the failure directed paths, using a whole system environment model and concrete address mapped symbolic memory in S2 E. We propose a new selective symbolic input method and lazy evaluation on pseudo symbolic variables to handle symbolic pointers and speed up the process. This is an end-to-end approach able to create exploits from crash inputs or existing exploits for various applications, including most of the existing benchmark programs, and several large scale applications, such as a word processor (Microsoft office word), a media player (mpalyer), an archiver (unrar), or a pdf reader (foxit). We can deal with vulnerability types including stack and heap overflows, format string, and the use of uninitialized variables. Notably, these applications have become software fuzz testing targets, but still require a manual process with security knowledge to produce mitigation-hardened exploits. Using this method to generate exploits is an automated process for software failures without source code. The proposed method is simpler, more general, faster, and can be scaled to larger programs than existing systems. We produce the exploits within one minute for most of the benchmark programs, including mplayer. We also transform existing exploits of Microsoft office word into new exploits within four minutes. The best speedup is 7,211 times faster than the initial attempt. For heap overflow vulnerability, we can automatically exploit the unlink() macro of glibc, which formerly requires sophisticated hacking efforts.

Demonstration of using digital FIR filter and matched filter to increase data rate in visible light communication

Using digital-filters in time domain are demonstrated to enhance the modulation-speed of 1 MHz bandwidth white LED communication. Digital FIR filter and matched filtering are used to reduce the inter-symbol-interference (ISI). Hence, 20-Mbps is achieved by using 4-ASK modulation.