Informatica

A generalized group-oriented cryptosystem (GGOC) based on ElGamal cryptosystem was proposed by Yang et al. in 2003. This study shows that if the authorized decryption sets of users are not properly predetermined in Yang et al.'s GGOC, an unauthorized decryption set of users can recover the encrypted message without difficulty. This study also presents an improved protocol to resist such an attack.

Recently, Chen, Chung, and Huang proposed a traceable proxy multisignature scheme based on the elliptic curve cryptosystem. However, this paper shows that the original signers can produce a valid signature as the proxy signer does in the proxy protected scheme. Therefore, Chen et al.'s proxy-protected scheme cannot protect the proxy signer from being forged by the original signers. We further find that the early work of Chen et al. in 2003 suffers the same attack. To overcome this problem, an improved scheme will be presented.

The paper presents, first, the Structural Blanks (SB) approach, then a method to compose loop programs. SB is an approach for expressing computations based on recurrence relations and focuses on data dependencies in loops. The paper presents language constructs and semantics for expressing programs that have complex data dependency patterns. These constructs are expressed using structural “blanks” for computations based on recurrence relations. In SB the recurrence structure and the functional part of a recurrence relation may be described separately. Therefore declarative representation of data dependencies is examined. SB aims at supporting the transformational development and reuse of program modules. The approach deals with two aspects: pragmatics and semantics. In the paper we aim at: (1) developing a theory and language for functional and structural modules, (2) an algorithm for composition of structural modules. The approach is illustrated by toy problems: the Fibonacci function, heat flow, etc. Hence the reuse and verification are viewed as those of, e.g., stacks, queues, bubble sort, etc.

Recently, there are several articles proposed based on Yang and Shieh's password authentication schemes (YS for short) with the following features: (1) A user can choose password freely. (2) The server does not need to maintain a password table. (3) There is no need to involve a trusted third party. Although there were several variants of the YS-like schemes claimed to address the forgery attacks, this paper analyzes their security and shows that they still suffer from forgery attacks. Furthermore, a new scheme based on the concept of message authentication is proposed to foil the forgery attack.

The aim of this paper is to explore some features of the functional test generation problem, and on the basis of the gained experience, to propose a practical method for functional test generation. In the paper presented analysis of random search methods and adjacent stimuli generation allowed formulating a practical method for generating functional tests. This method incorporates the analyzed termination conditions of generation, exploits the advantages of random and deterministic search, as well as the feature that the sets of the selected input stimuli can be merged easily in order to obtain a better set of test patterns.

The paper analyses the problem of ranking accuracy in multiple criteria decision-making (MCDM) methods. The methodology for measuring the accuracy of determining the relative significance of alternatives as a function of the criteria values is developed. An algorithm of the Technique for the Order Preference by Similarity to Ideal Solution (TOPSIS) that applies criteria values' transformation through a normalization of vectors and the linear transformation is considered. A computational experiment is presented, to compare the results of a multiple criteria analysis and the ranking accuracy in a particular situation.

There is presented a technique of transcribing Lithuanian text into phonemes for speech recognition. Text-phoneme transformation has been made by formal rules and the dictionary. Formal rules were designed to set the relationship between segments of the text and units of formalized speech sounds – phonemes, dictionary – to correct transcription and specify stress mark and position. Proposed the automatic transcription technique was tested by comparing its results with manually obtained ones. The experiment has shown that less than 6% of transcribed words have not matched.

A convertible authenticated encryption scheme allows a specified recipient to recover and verify a message simultaneously. Moreover the recipient can prove the dishonesty of the sender to any third party if the sender repudiates her signature later. Recently, Lv et al. (2005) showed that the Wu et al.'s (1999) and the Huang et al.'s (2003) convertible authenticated encryption schemes cannot provide the semantic security of encrypted messages. Then they proposed a practical convertible authenticated encryption scheme using self-certified public keys, and extended it to one with message linkages when the signed message is large. In this paper, we show that the verifier can recover messages if given many triples of message, signature and ciphertext in the Lv et al.'s basic convertible authenticated encryption scheme. Finally we propose a new improvement to these schemes to overcome this weakness and to improve its efficiency.

Robust stability results for nominally linear hybrid systems are obtained from total stability theorems for purely continuous-time and discrete-time systems. The class of hybrid systems dealt with consists of, in general, coupled continuous-time and digital systems subject to state perturbations whose nominal (i.e., unperturbed) parts are linear and time-varying, in general. The obtained sufficient conditions on robust stability are dependent on the values of the parameters defining the over-bounding functions of the uncertainties and the weakness of the coupling between the analog and digital sub-states provided that the corresponding uncoupled nominal subsystems are both exponentially stable.

One important requirement of electronic cash systems is the anonymity of customers. Unconditional anonymity is also very well suited to support criminals in blackmailing. Maitland and Boyd proposed at ICICS 2001 an offline electronic cash system based on a group signature scheme. Their scheme cannot be used to solve blackmailing and other anonymity problems such as money laundering and illegal purchases. Chen, Zhang and Wang suggested an offline electronic cash scheme to prevent blackmailing by using the group blind signature. In their payment system, they used a group signature scheme of Camenisch and Stadler for large groups which is not secure. In this paper we improve these electronic cash systems to prevent blackmailing, money laundering and illegal purchases by using a secure coalition-resistant group blind signature scheme.