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On the Security of a Digital Signature with Message Recovery Using Selfcertified Public Key. Informatica 29:343–346
 Public Key, Soft Computing in Multimedia Processing Special Issue of the Informatica Journal
, 2005
"... Selfcertified public keys are proposed to eliminate the burden of verifying the public key before using. To alleviate reliance on system authority and strengthen the security of system, Chang et al propose a new digital signature schemes, no redundancy is needed to be embedded in the signed message ..."
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Selfcertified public keys are proposed to eliminate the burden of verifying the public key before using. To alleviate reliance on system authority and strengthen the security of system, Chang et al propose a new digital signature schemes, no redundancy is needed to be embedded in the signed messages in this scheme. Moreover, Chang et al claimed that the schemes are still secure even without the trustworthy system authority, and only the specified recipient can recover the message in his authentication encryption schemes. Unfortunately, In this work, we analyze the security of Chang et al scheme and show that if the system authority is trustless, the scheme is insecure, namely, the system authority can recover the message without the private key of the recipient in Chang ’ authentication encryption schemes. Finally, we propose an improved scheme to overcome the weakness of Chang et al scheme. Povzetek: Predstavljena je tehnika digitalnega certifikata z javnim ključem. 1
Delayed Information and Action in OnLine Algorithms
 39th IEEE symposium on Foundations of Computer Science
, 1998
"... Most online analysis assumes that, at each time step, all relevant information up to that time step is available and a decision has an immediate effect. In many online problems, however, the time relevant information is available and the time a decision has an effect may be decoupled. For example, ..."
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Most online analysis assumes that, at each time step, all relevant information up to that time step is available and a decision has an immediate effect. In many online problems, however, the time relevant information is available and the time a decision has an effect may be decoupled. For example, when making an investment, one might not have completely uptodate information on market prices. Similarly, a buy or sell order might only be executed some time later in the future. We introduce and explore natural delayed models for several wellknown online problems. Our analyses demonstrate the importance of considering timeliness in determining the competitive ratio of an online algorithm. For many problems, we demonstrate that there exist algorithms with small competitive ratios even when large delays affect the timeliness of information and the effect of decisions.
Page migration in dynamic networks
, 2005
"... In the last couple of decades, network connected systems have gradually replaced centralized parallel computing machines. To provide smooth operation of network applications, the underlying system has to provide socalled basic services. One of the most crucial services is to provide a transparent a ..."
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In the last couple of decades, network connected systems have gradually replaced centralized parallel computing machines. To provide smooth operation of network applications, the underlying system has to provide socalled basic services. One of the most crucial services is to provide a transparent access to data like
Reconfigurable resource scheduling
 In Proceedings of 18th ACM Symposium on Parallelism in Algorithms and Architectures
, 2006
"... To my parents ..."
Online Algorithms: A Study of GraphTheoretic Concepts
"... . In this paper we survey results on the design and analysis of online algorithms, focusing on problems where graphs and graphtheoretic concepts have proven particularly useful in the formulation or in the solution of the problem. For each of the problems addressed, we also present important ope ..."
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. In this paper we survey results on the design and analysis of online algorithms, focusing on problems where graphs and graphtheoretic concepts have proven particularly useful in the formulation or in the solution of the problem. For each of the problems addressed, we also present important open questions. 1 Introduction The traditional design and analysis of algorithms assumes that an algorithm, which generates output, has complete knowledge of the entire input. However, this assumption is often unrealistic in practical applications. Many of the algorithmic problems that arise in practice are online. In these problems the input is only partially available because some relevant input arrives only in the future and is not accessible at present. An online algorithm must generate output without knowledge of the entire input. Online problems arise in areas such as resource allocation in operating systems, data structuring, robotics, distributed computing and scheduling. We give some...
Object Grouping and Replication Algorithms for Word Wide Web. Informatica 29:347–356
"... This paper presents an algorithm to group correlated objects that are most likely to be requested by a client in a single session. Based on these groups, a centralized algorithm that determines the placements of objects to a cluster of webservers is proposed to minimize latency. Due to the dynamic ..."
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This paper presents an algorithm to group correlated objects that are most likely to be requested by a client in a single session. Based on these groups, a centralized algorithm that determines the placements of objects to a cluster of webservers is proposed to minimize latency. Due to the dynamic nature of the Internet traffic and the rapid changes in the access pattern of the WorldWide Web, we also propose a distributed algorithm where each site relies on some collected information to decide what object should be replicated at that site. The performance of the proposed algorithms is evaluated through a simulation study. Povzetek: Grupiranje objektov na spletu. 1
Aspects of Network Design
, 2007
"... In this dissertation we study two problems from the area of network design. The first part discusses the multicommodity buyatbulk network design problem, a problem that occurs naturally in the design of telecommunication and transportation networks. We are given an underlying graph and associated ..."
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In this dissertation we study two problems from the area of network design. The first part discusses the multicommodity buyatbulk network design problem, a problem that occurs naturally in the design of telecommunication and transportation networks. We are given an underlying graph and associated with each edge of the graph, a cost function that represents the price of routing demand along this edge. We are also given a set of demands between pairs of vertices each of which needs to be satisfied by paying for sufficient capacity along a path connecting the vertices of the pair. In the multicommodity network design problem the objective is to minimize the cost of satisfying all demands. There are often situations where there is an initial fixed cost of utilizing an edge, or there is discounting or economies of scale that give rise to concave cost functions. We have an instance of the buyatbulk network design problem when the cost functions along all edges are concave. Unlike the case of linear cost functions, for which polynomial time algorithms exist, the buyatbulk network design problem is NPhard. We give the first nontrivial approx
Kpage Migration Problem
"... k servers located in some k points of the metric space. There is a sequence of requests oe = oe 1 oe 2 : : :, where oe i is a point in the metric space. For each request oe i , the online algorithm should serve the request by moving one of the k servers at a cost of the distance travelled. The pro ..."
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k servers located in some k points of the metric space. There is a sequence of requests oe = oe 1 oe 2 : : :, where oe i is a point in the metric space. For each request oe i , the online algorithm should serve the request by moving one of the k servers at a cost of the distance travelled. The problem is to minimize the total service cost. We can formulate the problem in the following way. Let a configuration of be the positions of the k servers and define dist(C; C 0 ) as the cost of changing configuration from C to C 0 , where C and C 0 are two configurations. To serve a request r in configuration C, the online algorithm: ffl move a server to t
.1 Page Migration
"... distributed paging have been defined by Bartal, Fiat and Rabani [BFR92]. 10.1.1 A 3competitive Randomized Algorithm The intuitive idea here is that we need about D requests in a region before we can decide that it is worthwhile to move the page to that region. Hence, for any one request, we move ..."
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distributed paging have been defined by Bartal, Fiat and Rabani [BFR92]. 10.1.1 A 3competitive Randomized Algorithm The intuitive idea here is that we need about D requests in a region before we can decide that it is worthwhile to move the page to that region. Hence, for any one request, we move the page with probability about 1=D. More precisely, when the page is at s and the request is at r, the FLIP algorithm first serves the request, and then moves the page from s to r with probability 1 2D . This algorithm is due to Westbrook [West91]. Claim 10.1 FLIP is 3competitive against adaptive online adversaries. Proof: We define the potential function \Phi = 3D \Delta d(t; s); 101 102 Lecture 10: February 20 whe