The complete subtree (CS) method is one of the most well-known broadcast encryptions which do not enforce the receivers to keep "online." This paper is to reduce the size of secret information which must be stored in a terminal of the method. In the original CS method, the size of the secret information increases as the number of terminals increases. It is shown in this paper that, by making use of a one-way trapdoor permutation, we can make the size constant regardless of the number of terminals. The security of the proposed scheme is investigated, and detailed comparison with other similar schemes is presented. The proposed scheme is suitable for practical implementations of the CS method.

Cutoff rate of m-ary PPM is derived for an avalanche photodiode (APD) based receiver. The cutoff rate is compared among m=8-256 under the condition of the same total signal energy in 256 slots, where the effects of the timing jitter and atmospheric turbulence are included. Numerical results are shown for the illustrative examples of the cutoff rate.

We have recently developed a programmable composite noise generator (P-CNG) which can easily control noise parameters such as average power, time-based amplitude probability distribution (APD), crossing rate distribution, occurrence frequency distribution and burst duration. Two applications of the P-CNG are demonstrated to show its usefulness. For the first application, Middleton's Class A noise is simulated. A method of setting parameters for Class A noise is demonstrated. The APD of P-CNG output is in good agreement with that of true Class A noise. In the second application, the P-CNG is used for subjective evaluation test (opinion test) of TV picture degradation. Five simple composite noise models with two kinds of APD are used. Other parameters such as average power are kept constant. Experimental results show that the envelope and APD of composite noises do not greatly influence the subjective evaluation. Finally the capabilities of the P-CNG are shown.

This is a study on a certain group theoretic property of the set of encryption functions of a block cipher. We have shown how to construct a subset which has this property in a given symmetric group by a computer algebra software GAP4.2 (Groups, Algorithms, and Programming, Version 4.2). These observations on group structures of block ciphers suggest us that we may be able to set a trapdoor based on meet-in-the-middle attack on block ciphers.

A trapdoor one-way function is an extended version of a zero-way permutation. A zero-way permutation was first introduced by Niemi-Renvall in Asiacrypt'94. In this paper we define the class of functions called no-way functions. This is an extended version of a zero-way permutation. Intuitively, a function f is no-way if, without trapdoor, both computing f and computing f-1 are hard. Li-Chida-Shizuya defined the notion of a no-way function, which is a provable-security version of a zero-way permutation. They also gave an example of a no-way function such that computing f and f-1 is proven to be as hard as breaking the Diffie-Hellman key exchange scheme. We redefine the notion of a trapdoor no-way function more preciously, classify no-way functions by the property of the trapdoor: common, separated and semi-separated trapdoor no-way, give a method for constructing trapdoor no-way functions from trapdoor one-way functions, and also give an example of trapdoor no-way functions.

Initial leveling of strapdown inertial navigation system is a prerequisite work for distinguishing between gravity and acceleration effects in the accelerometer sensing's. This study presents an on-line methodology to resolve the initial leveling problem of a vehicle, which is subject to a large, long duration, and abrupt disturbance input with a deterministic nature under noisy circumstances. The developed method herein is the Kalman filter based scheme with a robust input estimator, generalized M estimator, and a testing criterion. The generalized M estimator identifies the unexpected disturbance inputs in real time. In addition, hypothetical testing based on the least-squares estimator is devised to detect the input's onset and presence. A required regression equation between the observed value of the residual sequence with an unknown input and theoretical residual sequence of the Kalman filter with no input is formulated. Input estimation and detection are then provided on the basis of the derived regression equation. Moreover, Monte Carlo simulations are performed to assess the superior capabilities of the proposed method in term of rapid responses, accuracy, and robustness. The efficient initial leveling can facilitate the entire alignment of the inertial system.

Performance of optical asynchronous code-division multiple-access (CDMA) systems with double optical hard-limiters is analyzed in the presence of avalanche photodiode (APD) noise and thermal noise. Optical orthogonal codes (OOC's) are employed as signature sequence codes. In the analysis, chips are assumed to be synchronous among users: the chip synchronous case. Thus, the performance results in the upper bound on the performance of the asynchronous system. The results show that the optical asynchronous CDMA systems with double optical hard-limiters have good performance in the presence of the APD noise and the thermal noise even when the number of simultaneous users is large.

The bit error rate (BER) performance of Multi-pulse pulse position modulation (MPPM) using an avalanche photodiode (APD) is evaluated in optical intersatellite links (ISL's) . We derive theoretical expression of BER of MPPM consisting of M slots and P pulses, referred to as (M, P) MPPM with output statistics of the APD which is approximated by Gaussian distribution. The BER performance of (7, 2) MPPM and (9, 2) MPPM is compared with that of 4-ary PPM under the conditions that bit rate is constant (200 Mbits/s) and that bandwidth is limited (slot time period is 2.5 ns) . It is shown that (9, 2) MPPM using the APD can achieve better BER performance than 4-ary PPM using the APD with broadening slot time period by about 10% under the condition that bit rate is constant or with improving bit rate by about 10% under the condition that bandwidth is constant when average photons/nat is somewhat large in achieving BER of 10-9.

A random pulse stream (RPS) generator was developed for the noise immunity test of various digital system including communication system. By using this RPS generator along with the composite noise generator (CNG) developed formerly, the Middleton's "Class A" noise could be generated, and the total system (RPS+CNG) became more general noise simulator. In this paper, the configuration of CNG with newly developed RPS generator, and a typical example of Class A noise generated by this system are shown.