Tzeng (2002) proposed a time-bound cryptographic key assignment scheme for access control in a partial-order hierarchy. In this paper, we show that Tzeng's scheme is insecure against the collusion attack whereby three users conspire to access some secret class keys that they should not know according to Tzeng's scheme.

A well-designed cooperation strategy for a task oriented multiagent team is important as it can improve performance. A challenging research issue in cooperation concerns the extent to which an agent should pay attention to the actions and effects of other agents. In this paper, we address this issue in the context of an object search team. We first propose the concept of an activity window which captures an agent's view of the activities and effects of the team. Then we pinpoint some criteria that can be used to determine whether it is beneficial for an agent to put an action of the team into its window. Finally, we present experimental results to test these criteria.

A growing application area in mobile communications is mobile teleconference in which a group of mobile users collaborate in an interactive procedure, such as a board meeting, a task force, a scientific discussion, or even a virtual classroom. Wireless communications transmit conversations via radio, making them more susceptible to eavesdropping and unauthorized access than are conversations carried via wires. Therefore, it is crucial to ensure confidentiality and authenticity in a mobile teleconference. The authors design a new secure conference scheme for mobile communications. Based on a modular square root technique, this scheme is secure against eavesdropping, impersonating, and tracking attacks and allows a participant to join or quit a mobile teleconference dynamically.

Object search is the task of searching for a given 3D object in a given 3D environment by a controllable camera. Sensor planning for object search refers to the task of how to select the sensing parameters of the camera so as to bring the target into the field of view of the camera and to make the image of the target to be easily recognized by the available recognition algorithms. In this paper, we study the task of sensor planning for object search from the theoretical point of view. We formulate the task and point out many of its important properties. We then analyze this task from the complexity level and prove that this task is NP‐Complete.

In this paper we introduce the concept of knowledge granularity and study the relationship between different knowledge representation schemes and the scaling problem. By scale to a task, we mean that an agent's planning system and knowledge representation scheme are able to generate the range of behaviors required by the task in a timely fashion. Action selection is critical to an agent performing a task in a dynamic, unpredictable environment. Knowledge representation is central to the agent's action selection process. It is important to study how an agent should adapt its methods of representation such that its performance can scale to different task requirements. Here we study the following issues. One is the knowledge granularity problem: to what detail should an agent represent a certain kind of knowledge if a single granularity of representation is to be used. Another is the representation scheme problem: to scale to a given task, should an agent represent its knowledge using a single granularity or a set of hierarchical granularities.

We study how agents can facilitate and mediate interaction, communication, and cooperation among people. We propose the concepts of a smart distance and an awareness network in a distributed collaborative environment. We illustrate the architecture of an agent-mediated collaborative system - the agent-buddy system that can create a sense of group presence and, at the same time, preserve the privacy of each user. Virtual springs systems are used to model the awareness degrees among team members. Each agent makes decisions by considering multiple factors. The goal of the multi-agent team is to minimize the global awareness frustrations with respect to different kinds of tasks. Empirical studies were conducted to analyze the influence of individual behavior on global performance for various kinds of tasks.