Informatica

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.

Matrix transpose in parallel systems typically involves costly all-to-all communications. In this paper, we provide a comparative characterization of various efficient algorithms for transposing small and large matrices using the popular symmetric multiprocessors (SMP) architecture, which carries a relatively low communication cost due to its large aggregate bandwidth and low-latency inter-process communication. We conduct analysis on the cost of data sending / receiving and the memory requirement of these matrix-transpose algorithms. We then propose an adaptive algorithm that can minimize the overhead of the matrix transpose operations given the parameters such as the data size, number of processors, start-up time, and the effective communication bandwidth.

This paper proposes a threshold key escrow scheme from pairing. It tolerates the passive adversary to access any internal data of corrupted key escrow agents and the active adversary that can make corrupted servers to deviate from the protocol. The scheme is secure against threshold adaptive chosen-ciphertext attack. The formal proof of security is presented in the random oracle model, assuming the decision Bilinear Diffie-Hellman problem is computationally hard.

The quality of software engineering projects often suffers due to the large gap between the way stakeholders present their requirements and the way analysts capture and express those requirements. With this problem in mind the new method for business rules driven IS requirements specification has been developed. In this paper the architecture of the requirements repository, which is at the core of the proposed method, is presented. The repository model supports the storage and management of all components of the captured requirements, including functions, business decisions, data sources, conceptual data model elements, business rules and their templates. The important aspects of the specialised requirements specification tool implementation are also overviewed.

In this paper optimization of DSR is achieved using New Link Cache structure and Source Transparent Route Maintenance Method. The new link cache effectively utilizes the memory by caching the routes in adjacent list type of data structures. It selects the shortest hop and least congested path, which in turn reduce the control packets, route request packets, route reply packets and increase the data packets forwarded by the nodes. To solve the DSR route maintenance problem during high mobility, source transparent route maintenance method is introduced in this paper. This method has two schemes namely cache validation and local route repair. These schemes reduce the packet loss, end-to-end delay and increase the throughput.

We revisit the password-based group key exchange protocol due to Lee et al. (2004), which carries a claimed proof of security in the Bresson et al. model under the intractability of the Decisional Diffie–Hellman problem (DDH) and Computational Diffie–Hellman (CDH) problem. We reveal a previously unpublished flaw in the protocol and its proof, whereby we demonstrate that the protocol violates the definition of security in the model. To provide a better insight into the protocol and proof failures, we present a fixed protocol. We hope our analysis will enable similar mistakes to be avoided in the future. We also revisit protocol 4 of Song and Kim (2000), and reveal a previously unpublished flaw in the protocol (i.e., a reflection attack).

We know the necessity for information security becomes more widespread in these days, especially for hardware-based implementations such as smart cards chips for wireless applications and cryptographic accelerators. Fast modular exponentiation algorithms are often considered of practical significance in public-key cryptosystems. The RSA cryptosystem is one of the most widely used technologies for achieving information security. The main task of the encryption and decryption engine of RSA cryptosystem is to compute M^E mod N. Because the bit-length of the numbers M, E, and N would be about 512 to 1024 bits now, the computations for RSA cryptosystem are time-consuming. In this paper, an efficient technique for parallel computation of the modular exponentiation is proposed and our algorithm can reduce time complexity. We can have the speedup ratio as 1.06 or even 2.75 if the proposed technique is used. In Savas–Tenca–Koc algorithm, they design a multiplier with an insignificant increase in chip area (about 2.8%) and no increase in time delay. Our proposed technique is faster than Savas–Tenca–Koc algorithm in time complexity and improves efficiency for RSA cryptosystem.

Most of the Takagi–Sugeno Fuzzy (TSF) systems found in the literature have only used linear functions of input variables as rule consequent and can be called as TSF Models with Fixed Coefficient (TSFMFC). This paper presents TSF model with variable coefficient (TSFMVC) which can more closely approximate a class of nonlinear systems, nonlinear dynamic systems, and nonlinear control systems. It is also shown that TSFMFC is a special case of TSFMVC. Moreover Variable Gain TSF Controller (VGTSFC) is defined and it performs better, as shown by the simulation results, when compared with Fixed Gain TSF Controller (FGTSFC).