Sangchul Han

Efficient and anonymous two-factor user authentication in wireless sensor networks: achieving user anonymity with lightweight sensor computation.

A smart-card-based user authentication scheme for wireless sensor networks (hereafter referred to as a SCA-WSN scheme) is designed to ensure that only users who possess both a smart card and the corresponding password are allowed to gain access to sensor data and their transmissions. Despite many research efforts in recent years, it remains a challenging task to design an efficient SCA-WSN scheme that achieves user anonymity. The majority of published SCA-WSN schemes use only lightweight cryptographic techniques (rather than public-key cryptographic techniques) for the sake of efficiency, and have been demonstrated to suffer from the inability to provide user anonymity. Some schemes employ elliptic curve cryptography for better security but require sensors with strict resource constraints to perform computationally expensive scalar-point multiplications; despite the increased computational requirements, these schemes do not provide user anonymity. In this paper, we present a new SCA-WSN scheme that not only achieves user anonymity but also is efficient in terms of the computation loads for sensors. Our scheme employs elliptic curve cryptography but restricts its use only to anonymous user-to-gateway authentication, thereby allowing sensors to perform only lightweight cryptographic operations. Our scheme also enjoys provable security in a formal model extended from the widely accepted Bellare-Pointcheval-Rogaway (2000) model to capture the user anonymity property and various SCA-WSN specific attacks (e.g., stolen smart card attacks, node capture attacks, privileged insider attacks, and stolen verifier attacks).

Predictability of earliest deadline zero laxity algorithm for multiprocessor real-time systems

Validation methods for hard real-time jobs are usually performed based on the maximum execution time. The actual execution time of jobs are assumed to be known only when the jobs arrive or not known until they finish. A predictable algorithm must guarantee that it can generate a schedule for any set of jobs such that the finish time for the actual execution time is no later than the finish time for the maximum execution time. It is known that any job-level fixed priority algorithm (such as earliest deadline first) is predictable. However, job-level dynamic priority algorithms (such as least laxity first) may or may not. In this paper, we investigate the predictability of a job-level dynamic priority algorithm EDZL (earliest deadline zero laxity). We show that EDZL is predictable on the domain of integers regardless of the knowledge of the actual execution times. Based on this result, furthermore, we also show that EDZL can successfully schedule any periodic task set if the total utilization is not greater than (m + 1)/2, where m is the number of processors

Predictability of least laxity first scheduling algorithm on multiprocessor real-time systems

A priority-driven scheduling algorithm is said to be start time (finish time) predictable if the start time (finish time) of jobs in the schedule where each job executes for its actual execution time is bounded by the start times (finish times) of jobs in the schedules where each job executes for its maximum/minimum execution time. In this paper, we study the predictability of a job-level dynamic priority algorithm, LLF (Least Laxity First), on multiprocessor real-time systems. We present a necessary and sufficient condition for a priority-driven algorithm to be start time (finish time) predictable. Then, in LLF scheduling, we show that both the start time and the finish time are predictable if the actual execution times cannot be known. However, solely the finish time is predictable if the actual execution times can be known.

A kernel-based monitoring approach for analyzing malicious behavior on Android

This paper proposes a new technique that monitors important events at the kernel level of Android and analyzes malicious behavior systematically. The proposed technique is designed in two ways. First, in order to analyze malicious behavior that might happen inside one application, it monitors file operations by hooking the system calls to create, read from, and write to a file. Secondly, in order to analyze malicious behavior that might happen in the communication between colluding applications, it monitors IPC messages (Intents) by hooking the binder driver. Our technique can detect even the behavior of obfuscated malware using a run-time monitoring method. In addition, it can reduce the possibility of false detection by providing more specific analysis results compared to the existing methods on Android. Experimental results show that our technique is effective to analyze malicious behavior on Android and helpful to detect malware.

Measuring similarity of android applications via reversing and K-gram birthmarking

By measuring similarity of programs, we can determine whether someone illegally copies a program from another program or not. If the similarity is significantly high, it means that a program is a copy of the other. This paper proposes three techniques to measure similarity of the Dalvik executable codes (DEXs) in the Android application Packages (APKs). Firstly, we decompile the DEXs of candidate applications into Java sources and compute the similarity between the decompiled sources. Secondly, candidate DEXs are disassembled and the similarities between disassembled codes are measured. Finally, we extract k-gram based software birthmark form the dissembled codes and calculate the similarity of sample DEXs by comparing the extracted birthmarks. We perform several experiments to identify effects of the three techniques. With the analysis of the experimental results, the advantages and disadvantages of each technique are discussed.

Power-Aware EDZL Scheduling upon Identical Multiprocessor Platforms

Upon multiprocessor platforms, global EDZL is known to be at least as effective as global EDF in scheduling task sets to meet deadlines, but there has been no research on power-aware EDZL scheduling. In this paper, we firstly address the problem of reducing energy consumption of real-time tasks on EDZL scheduling by lowering processor speed. An off-line algorithm and an on-line algorithm are proposed to reduce energy consumption while guaranteeing a hard real-time constraint. Then we show the effectiveness of our algorithms through extensive simulation.

Two-Round Password-Only Authenticated Key Exchange in the Three-Party Setting

We present the first provably-secure three-party password-only authenticated key exchange (PAKE) protocol that can run in only two communication rounds. Our protocol is generic in the sense that it can be constructed from any two-party PAKE protocol. The protocol is proven secure in a variant of the widely-accepted model of Bellare, Pointcheval and Rogaway (2000) without any idealized assumptions on the cryptographic primitives used. We also investigate the security of the two-round, three-party PAKE protocol of Wang, Hu and Li (2010) and demonstrate that this protocol cannot achieve implicit key authentication in the presence of an active adversary.

Scalable Group Key Exchange for Securing Distributed Operating Systems

Distributed operating systems are designed to run over a collection of computing nodes that are spatially disseminated and communicate through a computer network. The computing nodes interact collaboratively with each other in order to pursue a common purpose. Protecting group communication between the collaborating nodes against potential attacks is one of the major challenges faced by the designers of distributed operating systems. This challenge can be effectively addressed by a group key exchange (GKE) protocol which allows a group of communicating parties to build a secure multicast channel over an insecure network. In this work, we propose a scalable GKE protocol that achieves both constant round complexity and logarithmic computation complexity. Our GKE protocol achieves its scalability by employing a complete binary tree structure combined with a so-called ”nonce-chained authentication technique”. Besides the scalability, our protocol features provable security against active adversaries in a well-defined communication model.

Enhancing Security of a Group Key Exchange Protocol for Users with Individual Passwords

Group key exchange protocols allow a group of parties communicating over a public network to come up with a common secret key called a session key . Due to their critical role in building secure multicast channels, a number of group key exchange protocols have been suggested over the years for a variety of settings. Among these is the so-called EKE-M protocol proposed by Byun and Lee for password-based group key exchange in the different password authentication model , where group members are assumed to hold an individual password rather than a common password. While the announcement of the EKE-M protocol was essential in the light of the practical significance of the different password authentication model, Tang and Chen showed that the EKE-M protocol itself suffers from an undetectable on-line dictionary attack. Given Tang and Chens attack, Byun et al. have recently suggested a modification to the EKE-M protocol and claimed that their modification makes EKE-M resistant to the attack. However, the claim turned out to be untrue. In the current paper, we demonstrate this by showing that Byun et al.s modified EKE-M is still vulnerable to an undetectable on-line dictionary attack. Besides reporting our attack, we also figure out what has gone wrong with Byun et al.s modification and how to fix it.

An effective and intelligent Windows application filtering system using software similarity

As licensed programs are pirated and illegally spread over the Internet, it is necessary to filter illegally distributed or cracked programs. The conventional software filtering systems can prevent unauthorized dissemination of the programs maintained by their databases using an exact matching method where the feature of a suspicious program is the same as that of any program stored in the database. However, the conventional filtering systems have some limitations to deal with cracked or new programs which are not maintained by their database. To address the limitations, we design and implement an efficient and intelligent software filtering system based on software similarity. Our system measures the similarity of the characteristics extracted from an original program and a suspicious one (or, a cracked one) and then determines whether the suspicious program is a cracked version of the copyrighted original program based on the similarity measure. In addition, the proposed system can handle a new program by categorizing it using a machine learning scheme. This scheme helps an unknown program to be identified by narrowing the search space. To demonstrate the effectiveness of the proposed system, we perform a series of experiments on a number of executable programs under Microsoft Windows. The experimental results show that our system has achieved comparable performance.