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Now showing 1 - 10 of 52

Multilevel secure database encryption with subkeys
(1997-04-01)
Hwang, MS
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
In this paper, we propose a multilevel database encryption system with subkeys. This new system is called the record-oriented cryptosystem which encrypts each record with different field-subkeys according to a security class of the data element. Each field is decrypted individually by the field-subkeys of which security class is higher than or equal to that of the encrypted field-subkeys. This system is based on the Chinese Remainder Theorem. Our scheme can protect the finest level of granularity such as relation level, attribute level, tuple level, or data element level in the relational database model.
A new subliminal channel based on Fiat-Shamir's signature scheme
(1995-11-01)
Chen, CY
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Chang, CC
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
This paper constructs a subliminal channel in a RSA-like variant of the Fiat-Shamir signature scheme to transfer any secret information. The proposed subliminal channel, unlike that in El-Gamal signature scheme, can avoid the serious shortcoming that a subliminal receiver can undetectably forge a signer's signature. In addition, our channel also overcomes almost all shortcomings from which the subliminal channel in El-Gamal signature scheme suffer.
Some properties of optimal Cartesian product files for orthogonal range queries
(1996-04-01)
Chou, AYH
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Yang, WP
;
Chang, CC
;
資訊工程學系
;
Department of Computer Science
Cartesian product file (CPF) has bren proposed as a good multi-attribute file structure. Although designing an optimal CPF for partial match queries (PMQs) has been proven to be NP-hard, some useful properties have been studied for PMQs to help the work. However, a good CPF for PMQs may not be beneficial for orthogonal range queries (ORQs). Therefore, in this paper, we intend to study properties that help the design of a good CPF for ORQs. We found that the problem of designing the optimal CPF for ORQs is related to the problem of finding a minimal-f N-tuple. We will also show some theories of minimal-f N-tuples and develop a method for generating a minimal-f N-tuple. Finally, we will present some properties of the optimal CPF for ORQs from the theories of minimal-f N-tuples.
Value-based scheduling for multiprocessor real-time database systems
(1998-01-01)
Tseng, SM
;
Chin, YH
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
We present a new scheduling policy named Value-based Processor Allocation (VPA-k) for scheduling value-based transactions in a multiprocessor real-time database system. The value of a transaction represents the profit the transaction contributes to the system if it is completed before its deadline. Using VPA-k policy, the transactions with higher values are given higher priorities to execute first, while at most k percentage of the total processors are allocated to the urgent transactions dynamically. Through simulation experiments, VPA-k policy is shown to outperform other scheduling policies substantially in both maximizing the totally obtained values and minimizing the number of missed transactions.
Authenticated encryption schemes with message linkage
(1996-05-27)
Hwang, SJ
;
Chang, CC
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
Authenticated encryption schemes need redundancy schemes to link up the message blocks; however, these redundancies increase communication costs. To construct links without increasing communication costs, we propose a general solution for all the authenticated encryption schemes based on the discrete logarithm problem. Because the computation cost to construct links is small, the improved scheme adopting our solution is almost as efficient as the original one, Moreover, by our solution, the recipient can easily determine the missing message blocks, and then acknowledge the sender to send only these blocks again. The communication cost will be also reduced. Adopting our solution, we also propose two new authenticated encryption schemes with message linkage.
An efficient conflict-resolution approach to support read/write operations in a video server
(1997-09-01)
Lee, CI
;
Chang, YI
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
In this paper, we propose an efficient conflict-resolution approach based on the multi-disk architecture for the insertion/deletion operations on continuous media that are split up into blocks and placed in various locations on the disk, without reorganizing the whole data. When a new subobject is inserted after subobject i, it will be assigned with an identification number (i+1) and be inserted into a disk in which the retrieval of the new subobject does not conflict with the retrieval of any other subobject, where a conflict means a pair of two consecutive subobjects that are stored in the same disk have to be retrieved simultaneously However, a new conflict on the same disk may occur since all the identification numbers of subobjects after subobject i are increased by one. Only when such a new conflict occurs, one movement operation is required, so does the case of a deletion operation. Moreover, to reduce those additional movement cost, a deferring approach is proposed at the cost of an additional buffer. In this approach, n data insertions are deferred and stored in a buffer. Then, the system starts to insert those data after an optimal insertion sequence is determined. Based on this approach, two strategies are proposed: the conflict-resolved-first-deferring strategy (the CRFD strategy) and the conflict-resolved-last-deferring strategy (the CRLD strategy). From our performance analysis, we will prove that the CRLD strategy with an insertion sequence according to the ascending order of identification numbers is an optimal strategy based on the proposed deferring approach.
Performance evaluation of a high-value scheduling policy for real-time main memory databases
(1996-09-01)
Tseng, SM
;
Chin, YH
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
With the decrease in hardware prices, storing databases in main memory has become feasible for meeting the high-performance requirements of real-time applications. In this paper, an efficient scheduling policy is proposed for scheduling transactions with values in real- time main memory databases, where the value of a transaction means its worthiness to a real-time application of it is completed before the deadline. Through detailed performance evaluation, the proposed policy is shown to outperform the existing policies in both minimizing the number of missed transactions and maximizing the obtained values under various system environments. A cost formula for evaluating the optimal memory size to store partial databases such as to maximize the net profits is developed from the economic standpoint. Some suggestions are given for scheduling value-based transactions in real-time main memory databases.
Byzantine agreement in the presence of mixed faults on processors and links
(1998-04-01)
Siu, HS
;
Chin, YH
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
In early stage, the Byzantine agreement (BA) problem was studied with single faults on processors in either a fully connected network or a nonfully connected network. Subsequently, the single fault assumption was extended to mixed faults (also referred to as hybrid fault model) on processors. For the case of both processor and link failures, the problem has been examined in a fully connected network with a single faulty type, namely an arbitrary fault. To release the limitations of a fully connected network and a single faulty type, the problem is reconsidered in a general network. The processors and links in such a network can both be subjected to different types of fault simultaneously. The proposed protocol uses the minimum number of message exchanges and can tolerate the maximum number of allowable faulty components to make each fault-free processor reach an agreement.
Reaching strong consensus in the presence of mixed failure types
(1998-07-01)
Siu, HS
;
Chin, YH
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
The Strong Consensus (SC) is a variant of the conventional distributed consensus problem. The protocol designed for the SC problem requires that the agreed value among fault-free processors be one of the fault-free processor's initial value. The SC problem is re-examined with the assumption of mixed failure types (also referred to as the hybrid fault model). Compared with the features of the existing protocols, the underlying network topologies of the proposed protocol do not have to be fully connected, the mixed failure types can be tolerated, and no prior information of the system's faulty status is required. The proposed protocol can tolerate a maximum number of faults to enable each fault-free processor to reach an agreement with a minimum number of message exchanges. (C) 1998 Published by Elsevier Science Inc. All rights reserved.
Integration of relations with conflicting schema structures in heterogeneous database systems
(1998-09-01)
Tseng, FSC
;
Chiang, JJ
;
Yang, WP
;
資訊工程學系
;
Department of Computer Science
Schema integration is an important discipline for constructing a heterogeneous database system, since there exists various semantic discrepancies among local schemas. However, prior works rarely address the problems of integrating local relations with conflicts of different schema structures. In this paper, we propose an approach for the integration of local relations with such conflicts. In our approach, we define some auxiliary data called metadata for local schemas. The relations can be classified into some classes according to the metadata. The local relations with conflicts of different schema structures are respectively transformed to new relations with the same structure. Finally, we integrate these new relations. We also explore the query decomposition process for global queries. A global query is decomposed into many local queries according to the local schemas' structures. The results of the local queries will be sent to the global site. Finally, the global site integrates the local results into a new one and poses the global query on the integrated result again to get the final result. Since this process filters out unnecessary data in each local site, it can also be regarded as an important work for global query optimization.

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