To improve the efficiency for the threshold schemes, the major problem is that the secret shadows cannot be reused after renewing or recovering the shared secret. However, if the secret shadows cannot be reused, the established threshold scheme is limited to be used only once. It is inefficient to reconstruct the whole secret sharing system. Therefore, we introduce an efficient dynamic threshold scheme. In the new scheme, the shadowholders can reuse the secret shadows no matter that the shared secret is renewed or recovered. In addition, the new scheme provides a way by which the dealer can renew the shared secret or reconstruct the secret sharing system, efficiently. Therefore, this scheme is good for maintaining the important secrets.

Access control has been an important security issue in information systems. Multilevel hierarchical information access widely exists in present-day government, military, and business applications. Extending access control design to work in a hierarchical environment is natural and necessary but rarely addressed so far in the literature. In this paper, a dynamic group-oriented cryptographic scheme to access a multilevel data hierarchy is proposed. In the proposed scheme, a trusted central authority is in charge of the administrative activities among the organization hierarchy. At the beginning, each user class submits its associated information and a cryptographic key of its preference to the central authority. Next the central authority generates a public information for each class according to their location in the organization hierarchy. The cryptographic key held by each class can be used directly as an encryption key to encipher data. These keys need not be modified when adding/deleting a class to/from the system. Compare with other existing schemes, ours has the advantages of flexibility in choosing user preferred cryptographic keys, cryptographic keys not exceeding a fixed length, reduced storage space in publishing pubic information, and protection from conspiracy attack.

RDES cryptosystem is an n-round DES in which an probabilistic swapping is added onto the right half of the input in each round. It is more effective than a simple increase of DES rounds for a countermeasure against differential attack. In this paper, we show that the RDES is also effective against linear cryptanalysis. We applied Matsui's search algorithm to find the best expression for RDES-1 and RDES-2. The results are as follows: (a) The 16-round RDES-1 is approximately as strong as a 22-round DES, and the 16-round RDES-2 is approximately as strong as a 29-round DES. (b) Linear cryptanalysis for a 16-round RDES-1 and a 16-round RDES-2 requires more than 264 known-plaintexts.

This paper proposes a dynamically randomized version of DES (called RDES) in which a input-dependent swapping Sk(X) is added onto the right half of the input in each round of DES. This new scheme decreases the probability of success in differential cryptanalysis because it decreases the characteristic probability. Each "best" two-round characteristic probability is analyzed for typical schemes of the RDES: (i) RDES-1 with a simple one-level swapping, (ii) RDES-1' with an optimal one-level swapping, (iii) RDES-2 with a simple two-level swapping, and (iv) RDES-2' with an optimal two-level swapping. The main results are as follows. (a) The differential attacks on the 16-round RDES-1' and the 16-round RDES-2 require more computational time than the exhaustive search. (b) A differential attack is substantially inapplicable to the 16-round RDES-2' because more than 263 chosen plaintext pairs are required. (c) The encryption/decryption speed of the n-round RDES is almost the same as that of the n-round DES.

An extension of the notion of cryptographically strong pseudo-random generator to a distributed setting is proposed in this paper. Instead of a deterministic function to generate a pseudo-random bit string from a truly random shorter string, we have a deterministic secure protocol for a group of separate entities to compute a secretly shared pseudo-random string from a secretly shared and truly random shorter string. We propose a precise definition of this notion in terms of Yao's computational entropy and describe a concrete construction using Shamir's pseudo-random number generator. Several practical applications are also discussed.

Directional dry etching of Tantalum is described X-ray lithography absorber patterns. Experiments are carried out using both reactive ion etching in CBrF3-based plasma and electron-cyclotron-resonance ion-stream etching in Cl2-based plasma. Ta absorber patterns with perpendicular sidewalls cannot be obtained by RIE when only CBrF3 gas is used as the etchant. While adding CH4 to CBrF3 effectively improves the undercutting of Ta patterns, it deteriorates etching stability because of the intensive deposition effect of CH4 fractions. By adding an Ar/CH4 mixture gas to CBrF3, it is possible to use RIE to fabricate 0.2-µm Ta absorber patterns with perpendicular sidewalls. ECR ion-stream etching is investigated to obtain high etching selectivity between Ta and SiO2 (etching mask)/SiN (membrane). Adding O2 to the Cl2 etchant improves undercutting without remarkably decreasing etching selectivity. Furthermore, an ECR ion-stream etching method is developed to stably etch Ta absorber patterns finer than 0.2µm. This is successfully applied to X-ray lithography mask fabrication for LSI test devices.

The interface between laser-recrystallized Si and SiO2 is investigated by means of capacitance-voltage curve measurements. The recrystallization is performed by scanning cw Ar+ laser. The change in the C-V curves shows that the laser-recrystallization generates positive charge and the fast interface states at the Si-SiO2 interface, and creates n-type defects in recrystallized bulk silicon. Nominal interface charge increases linearly with a laser power. The increase in the charge is enhanced by fast laser-beam scanning velocity. The change in the C-V curve is suppressed, if a substrate is heated up to 450 during recrystallization. Complete recovery of the induced change in the C-V curves requires a subsequent furnace annealing at a temperature as high as 1100. These phenomena are explained by the generation of oxygen vacancy at the Si-SiO2 interface and quenched-in point defects in the recrystallized Si. The oxygen vacancy is produced by a reaction between the melted Si and SiO2. The quenched-in defects are produced during fast cooling of the melted Si.

This paper investigates a two-class priority queue with decrementing service of a parameter (k1=, k2=k,1k) which operates as follows: Starting once a class-1 message service, a single server serves all messages in queue 1 until it becomes empty. After service completion in queue 1, the server switches over to queue 2 and continues serving messages in queue 2 until either queue 2 becomes empty, or the number of messages decreases to k less than that found upon the server's arrival at queue 2, whichever occurs first. It is assumed that arrival streams are Poissonian, message service times are generally distributed, and switch-over times are zero. We derive queue-length generating functions and LSTs of message waiting time distributions.

We fabricated a 4 GHz thin-base (120 nm) lateral bipolar transistor on bonded SOI by applying our sidewall self-aligning base process. By applying this device to BiCMOS circuits, bipolar transistor base junction capacitance, and MOSFET source and drain capacitance were very small. Furthermore, MOSFET and bipolar transistors are completely isolated from each other. Thus, it is easy to optimize MOS and bipolar processes, and provide protection from latch-up problems and soft errors caused by α-particles. In this paper, we describe device characteristics and discuss the crystal quality degradation introduced by ion implantation, and two dimensional effects of base diffusion capacitance.

Modeling and numerical simulation of crystal growth of Si film and heat transport in 3D structure were made for optimization of physical and geometrical parameters used during laser recrystallization. Based on simulations a new concept called micro-absorber was introduced for obtaining defect-free Si films.