Thomas L. Martin

Denial-of-service attacks on battery-powered mobile computers

Sleep deprivation attacks are a form of denial of service attack whereby an attacker renders a pervasive computing device inoperable by draining the battery more quickly than it would be drained under normal usage. We describe three main methods for an attacker to drain the battery: (1) service request power attacks, where repeated requests are made to the victim for services, typically over a network - even if the service is not provided the victim must expend energy deciding whether or not to honor the request; (2) benign power attacks, where the victim is made to execute a valid but energy-hungry task repeatedly, and (3) malignant power attacks, where the attacker modifies or creates an executable to make the system consume more energy than it would otherwise. Our initial results demonstrate the increased power consumption due to these attacks, which we believe are the first real examples of these attacks to appear in the literature. We also propose a power-secure architecture to thwart these power attacks by employing multi-level authentication and energy signatures.

Using piezoelectric materials for wearable electronic textiles

An open issue for electronic textiles (e-textiles) used for wearable computing is the choice of materials. This paper describes the desirable characteristics of piezoelectric materials for wearable e-textiles, including shape sensing, sound detection, and sound emission. The paper then describes an initial prototype of a glove for user input that employs piezoelectrics to sense the movement of the hands to illustrate the design issues involved in using piezoelectrics.

Medical Monitoring Applications for Wearable Computing

Medical monitors have benefited from technological advances in the field of wireless communication, processing and power sources. These advances have made possible miniaturization and prolonged operating times of medical monitors, as well as their global integration into telemedical systems. This allows patients to have real-time feedback about medical conditions while going about their normal daily activities. System designers are facing specific issues related to monitor acceptability, application requirements, power consumption and system connectivity. In this paper we discuss system design issues, present a survey of existing systems and sensors, and introduce two taxonomies of medical monitoring applications for wearable computing.

Towards an intrusion detection system for battery exhaustion attacks on mobile computing devices

Mobile computers are subject to a unique form of denial of service attack known as a battery exhaustion attack, in which an attacker attempts to rapidly drain the battery of the device. In this paper we present our first steps in the design of an intrusion detection system for these attacks, a system that takes into account the performance, energy, and memory constraints of mobile computing devices. This intrusion detection system uses several parameters, such as CPU load and disk accesses, to estimate the power consumption using a linear regression model, allowing us to find the energy used on a per process basis, and thus identifying processes that are potentially battery exhaustion attacks.

Towards a design framework for wearable electronic textiles

This paper presents a design framework for wearableelectronic textiles. The focus is on the design andsimulation issues that arise from the interaction of theelectronic textile, the human body, and the environment.To assist in design choices within this framework, asimulation environment is described that uses Ptolemy IIto integrate models of the physical environment, humanlocomotion, sensor behavior, network communication,power consumption, and software execution. We describeresults for two e-textile design case studies, a shape-sensinggarment and a wearable phased array ofmicrophones, demonstrating how the design frameworkencompasses the effects of design variables for wearableelectronic textiles.

A power metric for mobile systems

The advent of mobile computing has made power consumption a critical design factor. There has been little systematic consideration of the power sources for mobile computing systems. This paper presents a class of system-level metrics intended to make a systematic study more feasible and to more accurately reflect the trade-off between battery life and performance. An example involving the clock frequency of a CPU shows the possible impact of the nonlinearity, an impact not predicted by existing metrics. Results of an initial attempt to verify the example are presented and explained. The paper concludes with drawbacks of the metric and possible extensions to overcome these drawbacks.

Local Dynamic Stability Assessment of Motion Impaired Elderly Using Electronic Textile Pants

A clear association has been demonstrated between gait stability and falls in the elderly. Integration of wearable computing and human dynamic stability measures into home automation systems may help differentiate fall-prone individuals in a residential environment. The objective of the current study was to evaluate the capability of a pair of electronic textile (e-textile) pants system to assess local dynamic stability and to differentiate motion-impaired elderly from their healthy counterparts. A pair of e-textile pants comprised of numerous e-TAGs at locations corresponding to lower extremity joints was developed to collect acceleration, angular velocity and piezoelectric data. Four motion-impaired elderly together with nine healthy individuals (both young and old) participated in treadmill walking with a motion capture system simultaneously collecting kinematic data. Local dynamic stability, characterized by maximum Lyapunov exponent, was computed based on vertical acceleration and angular velocity at lower extremity joints for the measurements from both e-textile and motion capture systems. Results indicated that the motion-impaired elderly had significantly higher maximum Lyapunov exponents (computed from vertical acceleration data) than healthy individuals at the right ankle and hip joints. In addition, maximum Lyapunov exponents assessed by the motion capture system were found to be significantly higher than those assessed by the e-textile system. Despite the difference between these measurement techniques, attaching accelerometers at the ankle and hip joints was shown to be an effective sensor configuration. It was concluded that the e-textile pants system, via dynamic stability assessment, has the potential to identify motion-impaired elderly.

The impact of battery capacity and memory bandwidth on CPU speed-setting: a case study

The purpose of this paper is to report the power and performance of an application on a real system as the CPU frequency varies. Previous work in CPU speed-setting considered only the power of the CPU and only CPUs that vary supply voltage with frequency. This work takes a broader approach, considering total system power, battery capacity and main memory bandwidth. The results, which are up to a factor of four less than ideal, show that all three must be considered when setting the CPU speed, whether the speed is fixed at a single value or varied dynamically during operation.

Performance and energy efficiency of block ciphers in personal digital assistants

Encryption algorithms can be used to help secure wireless communications, but securing data also consumes resources. The goal of this research is to provide users or system developers of personal digital assistants and applications with the associated time and energy costs of using specific encryption algorithms. Fouriblock ciphers (RC2, Blowfish, XTEA, and AES) were considered. The experiments included encryption and decryption tasks with different cipher and file size combinations. The resource impact of the block ciphers were evaluated using the latency, throughput, energy-latency product, and throughput/energy ratio metrics. We found that RC2 encrypts faster and uses less energyithan XTEA, followed by AES. The Blowfish cipher is a fast encryption algorithm, but the size of the plaintext affects its encryption speed and energy consumption. Faster algorithms seem to be more energy efficient because of differences in speed rather than differences in power consumption levels while encrypting.

E-textile based automatic activity diary for medical annotation and analysis

Health monitoring applications often require that the patient maintain a diary of activities so that the physiological data can be correlated to what the user was doing. However, patients are notoriously bad at self-reporting. Consequently, it would be beneficial to automatically generate an activity diary. This paper presents a proof-of-concept prototype electronic textile system for recording both physiological data and context information. It also presents some of the issues that arise in the design and use of a health monitoring and activity annotation system