5211158
Finding Frequent Items in Data Streams
We present a 1-pass algorithm for estimating the most frequent items in a data stream using limited storage space. Our method relies on a data structure called a COUNT SKETCH, which allows us to reliably estimate the frequencies of frequent items in the stream. Our algorithm achieves better space bounds than the previously known best algorithms for this problem for several natural distributions on the item frequencies. In addition, our algorithm leads directly to a 2-pass algorithm for the problem of estimating the items with the largest (absolute) change in frequency between two data streams. To our knowledge, this latter problem has not been previously studied in the literature. c © 2003 Elsevier B.V. All rights reserved.
35381627
Finding frequent items in data streams
We present a 1-pass algorithm for estimating the most frequent items in a data stream using limited storage space. Our method relies on a data structure called a COUNT SKETCH, which allows us to reliably estimate the frequencies of frequent items in the stream. Our algorithm achieves better space bounds than the previously known best algorithms for this problem for several natural distributions on the item frequencies. In addition, our algorithm leads directly to a 2-pass algorithm for the problem of estimating the items with the largest (absolute) change in frequency between two data streams. To our knowledge, this latter problem has not been previously studied in the literature.
8321087
Improvements on the WTLS protocol to avoid denial of service attacks
The current WTLS protocol is closely modeled after the well-studied SSL protocol. However, since some differences exist between these two protocols, even if the SSL protocol is secure, the WTLS protocol may not. We propose three kinds of possible Denial of Service (DoS) attacks on the existing WTLS protocol, which can be categorized into two types: memory exhaustion attacks and CPU exhaustion attacks. The first and the second kinds of attacks belong to memory exhaustion attacks, and the third kind of attack is a CPU exhaustion attack. Not only wireless network clients but also Internet clients can launch these three kinds of attacks, which are very simple and effective. Since Internet clients are more powerful in network bandwidth and CPU resources, damages made by these attackers are more serious, which can even make the WTLS server stop providing services for legitimate clients. Client cookies, client puzzles and an application timer is used to improve the current protocol, and our improvements are secure against such attacks.
207789246
Electronic Payment in Mobile Environment
11647155
Methods of Combining Multiple Classifiers with Different Features and Their Applications to Text-Independent Speaker Identification
In practical applications of pattern recognition, there are often different features extracted from raw data which needs recognizing. Methods of combining multiple classifiers with different features are viewed as a general problem in various application areas of pattern recognition. In this paper, a systematic investigation has been made and possible solutions are classified into three frameworks, i.e. linear opinion pools, winner-take-all and evidential reasoning. For combining multiple classifiers with different features, a novel method is presented in the framework of linear opinion pools and a modified training algorithm for associative switch is also proposed in the framework of winner-take-all. In the framework of evidential reasoning, several typical methods are briefly reviewed for use. All aforementioned methods have already been applied to text-independent speaker identification. The simulations show that results yielded by the methods described in this paper are better than not only the individual classifiers' but also ones obtained by combining multiple classifiers with the same feature. It indicates that the use of combining multiple classifiers with different features is an effective way to attack the problem of text-independent speaker identification.
44251234
Efficient and Proactive Threshold Signcryption
To make the system more secure and robust, threshold schemes are proposed to avoid single point failure. At the same time, there are more and more applications which utilize the two basic blocks encryption and digital signature to secure message delivery (such as SSL, SSH). Combining the three tools organically leads to an interesting security tool termed as threshold signcryption which can be used in distributed systems especially the mobile networks. In this paper, we present an efficient threshold signcryption scheme. The scheme is designed for an asynchronous network model which may better present practical distributed systems, especially Internet or mobile ad hoc networks. In order to resist mobile attacks, we add proactive property to our scheme. To the best of our knowledge, the proposed scheme is the first threshold signcryption scheme which is noninteractive, proactive and provably secure and works on asynchronous network models.
32873189
A Typed Theory for Access Control and Information Flow Control in Mobile Systems
We propose a novel security type system for the π-calculus in which a fine-grained access control mechanism is guaranteed by static type checking and secure information flow can be characterized by a new form of non-interference property based on typed behavioral equivalence. In this paper, we present the syntax, subtyping rules, and typing rules of the type system, and explain how the secure data access can be controlled by typing. And then we elaborate a framework of typed level bisimulation to construct the secure information flow property named as non-interference at level. Moreover, some results are presented to indicate that our theory is an efficient enforceable model to support the specification and analysis of secure mobile systems.