There has been a wide-ranging discussion on the issue of content copyright protection in digital content distribution systems. Fiat and Tassa proposed the framework of dynamic traitor tracing. Their framework requires dynamic computation transactions according to the real-time responses of the pirate, and it presumes real-time observation of content redistribution. Therefore, it cannot be simply utilized in an application where such an assumption is not valid. In this paper, we propose a new scheme that provides the advantages of dynamic traitor tracing schemes and also overcomes their problems.

The superconducting band-pass filter has small insertion loss and excellent out-of-band rejection properties. It has been put to practical use in a number of applications. However, in order to expand its range of application, a tuning technique that can restore the filter characteristics is needed. We propose an automatic tuning system using a trimming library and checked the feasibility of the system by tuning a forward-coupled filter with three resonators. The results show that the trimming library method is an effective way of automatically improving the filter characteristics.

Today, users themselves are becoming subjects of content creation. The fact that blog, wiki, and UCC have become very popular shows that users want to participate to create and modify digital content. Users who participate in composing content also want to have their copyrights on their modification parts. Thus, a copyright protection system for the content which can be modified by multiple users is required. However, the conventional DRM (Digital Rights Management) systems like OMA DRM are not suitable for the modifiable content because they do not support the content created and modified by different users. Therefore in this paper, we propose a new copyright protection system which allows each modifier of the content created and modified by multiple users to have one's own copyright. We propose data formats and protocols, and analyze the proposed system in terms of the correctness and security. Performance evaluation in the view of response time shows that the proposed system is 2 to 18 times shorter than other comparative schemes.

We developed a content delivery system using a partially reconfigurable FPGA to securely distribute digital content on the Internet. With partial reconfigurability of a Xilinx Virtex-II Pro FPGA, the system provides an innovative single-chip solution for protecting digital content. In the system, a partial circuit must be downloaded from a server to the client terminal to play content. Content will be played only when the downloaded circuit is correctly combined (=interlocked) with the circuit built in the terminal. Since each circuit has a unique I/O configuration, the downloaded circuit interlocks with the corresponding built-in circuit designed for a particular terminal. Thus, the interface of the circuit itself provides a novel authentication mechanism. This paper describes the detailed architecture of the system and clarify the feasibility and effectiveness of the system. In addition, we discuss a fail-safe mechanism and future work necessary for the practical application of the system.

We report on suppressing adjacent-frequency interference (AFI) by using a RF receive bandpass-filter (BPF) with high-selectivity. By considering a high temperature superconducting (HTS) multi-pole BPF as a high selective BPF, the effect was estimated by numerical simulations. The simulations of the RF signals with an OFDM modulation transmitted to the demodulator via the BPF were carried out using the HTS BPF for 5 GHz band. The results confirmed the improvement of the bit error rate (BER) characteristic with the assumed HTS BPF with the high multi-poles under a strong AFI.

This paper reviews our progress on the high-Tc superconducting (HTS) sampler development, covering from the circuit design to the latest experimental data in the sinusoidal and pulse waveform measurements. A computer simulation has revealed that our sampler circuit with an improved design enables waveform measurement with the bandwidth over 100 GHz even with the thermal noise at around 40 K. Using the HTS sampler circuits fabricated employing an improved layout, we demonstrated waveform measurements for sinusoidal signals with frequencies of up to 50 GHz, the upper limit of the signal generator we used, both in the voltage-input-type system with a high-frequency input line and in the current-input-type one with a superconducting pickup coil. In the pulse measurement using an on-chip sampler, we succeeded in observing pico-second-order-wide single flux quantum (SFQ) current pulses, suggesting the potential bandwidth of our HTS sampler of more than 125 GHz.

Effective and simply realizable rate compatible low-density parity-check (LDPC) codes are proposed. A parity check matrix is constructed with the progressively increased column weights (PICW) order and adopted to achieve a punctured LDPC coding scheme for a wide range of the code rates of the rate compatible systems. Using the proposed rate compatible punctured LDPC codes, low complex adaptive communication systems, such as wireless communication systems, can be achieved with the reliable transmissions.

We present a novel precomputed radiance transfer method for efficient relighting under all-frequency environment illumination. Environment illumination is represented as a set of environment lights. Each environment light comprises a direction and an intensity. In a preprocessing step, the environment lights are clustered into several clusters, taking into account only the light directions. By experiment, we confirmed that the environment lights can be clustered into a much smaller number of clusters than their original number. Given any environment illumination, sampled as an environment map, an efficient relighting is then achieved by computing the radiance using the precomputed clusters. The proposed method enables relighting under very high-resolution environment illumination. In addition, unlike previous approaches, the proposed method can efficiently perform relighting when some regions of the given environment illumination change.

We propose a new receiving method for an information-providing system that uses LED-based traffic lights as the transmitter. We analyzed the improvements obtained when 2-dimentional image sensor replaced the conventional single-element photodiode. First, we discuss the maximum receiver's field of view (FOV) when using the 2-dimentional image sensor at a particular focal length. We analyzed the best vertical inclination for both lanes and quantified the improvements in terms of the enhancement of received signal-noise ratio (SNR) when different numbers of pixels were applied. Our results indicate that using more pixels increases the received SNR and the service area becomes wider compared to the conventional single-element system. Consequently, receivable information within the service area also increased. We also found that the optimum number of pixels to accomplish a reliable communication system is 5050 because performance degradation occured with a larger number of pixels.

We have examined the improvement of filter properties using sapphire and nickel rod trimmers. We measured the resonance frequency of the hairpin resonator in the filter, and examined the difference between the simulated and measured values. When the measured resonance frequency was lower than the simulated frequency, we used a nickel trimmer to increase the resonance frequency, and when high, a sapphire trimmer to decrease the frequency. Our results showed that the use of sapphire and nickel rod trimmers is effective in improving the frequency response of HTS bandpass filters.

We propose a design theory of the miniaturized high temperature superconducting (HTS) coplanar waveguide (CPW) bandpass filter (BPF), which is composed of meanderline quarter-wavelength resonator, J- and K-inverters. The J- and K-inverters are realized by using interdigital gap and meander-shape inductor. To evaluate the kinetic inductance of the K-inverter, we fabricate the YBCO resonator connected with K-inverters and redesigned the YBCO filter parameters. Finally, we designed and fabricated the YBCO CPW quarter-wavelength resonator BPF by taking account of the kinetic inductance of the K-inverter. The experimental results are in agreement with the design parameters.

The optimal antenna weighting scheme that minimizes the average bit error rate in a closed-loop transmit antenna diversity system is investigated under the assumption that channel state information is provided at both the transmitter and the receiver. A closed-form expression for the optimal transmitter weights is derived with a fixed average transmit power constraint. Also, the effect of limited peak transmit power on the performance of the optimal weighting method is analyzed. Base on this analysis, it is shown that the proposed transmitter weights yield significant performance improvements over the conventional weights on the wide range of practical system parameters.

We propose a new class of binary nonlinear codes of constant weights derived from a permutation representation of a group that is given by a combinatorial definition such as Cayley graphs of a group. These codes are constructed by the following direct interpretation method from a group: (1) take one discrete group whose elements are defined by generators and their relations, such as those in the form of Cayley graphs; and (2) embedding the group into a binary space using some of their permutation representations by providing the generators with realization of permutations of some terms. The proposed codes are endowed with some good characteristics as follows: (a) we can easily learn information about the distances of the obtained codes, and moreover, (b) we can establish a decoding method for them that can correct random errors whose distances from code words are less than half of the minimum distances achieved using only parity checking procedures.

In this paper, we propose an MPEG-2 TS encryption and decryption scheme which can support MPEG-2 TS streaming, and a key management scheme which can provide secure delivery of the key used to encrypt MPEG-2 TS from the package server to DRM clients in a secure manner. The key management scheme protects the key not only from purchasers but also among the other principals who manage the distribution servers and license servers. The proposed scheme can protect from attacks over a network since a pre-encrypted MPEG-2 TS is sent by a streaming server and only DRM clients can decrypt the streamed MPEG-2 TS. An MPEG-2 TS streaming server can send the encrypted stream without modifying it and degrading its performance because MPEG-2 TS is encrypted but compliant to the MPEG-2 TS format. The processing time to decrypt a streamed MPEG-2 TS in client systems is minimized to guarantee the quality of streaming.

Evaluation of cyclic transitions in the discrete-time neural networks with antisymmetric and circular interconnection weights has been derived in an asymptotic mathematical form. The type and the number of limit cycles generated by circular networks, in which each neuron is connected only to its nearest neurons, have been investigated through analytical method. The results show that the estimated numbers of state vectors generating n- or 2n-periodic limit cycles are an exponential function of (1.6)n for a large number of neuron, n. The sufficient conditions for state vectors to generate limit cycles of period n or 2n are also given.

Secure distribution of digital goods is now a significantly important issue for protecting publishers' copyrights. In this paper, we study a useful primitive for constructing a secure and efficient digital rights management system (DRM) where a server which encrypts digital content and one which issues the corresponding decryption key works independently, and existing schemes lack this property. We first argue the desired property necessary of an encryption scheme for constructing an efficient DRM, and formally define an encryption scheme as split encryption scheme containing such property. Also, we show that an efficient split encryption scheme can be constructed from any identity-based scheme. More precisely, we show an equivalence result implying that a split encryption scheme for some system parameter setting and an identity-based encryption scheme have the same primitives but for different uses. Since currently there is no identity-based encryption scheme which is based on well-known computational assumption and/or provably secure in the standard model (i.e. without the random oracle model), by reasonably tuning the system parameter, we show another construction of split encryption which is secure against chosen ciphertext attacks in the standard model assuming that decision Diffie-Hellman problem is hard to solve.

Digital rights management in client-server environments requires the establishment of client integrity, in order to protect sensitive (secret) information from loss or misuse. Clients are vulnerable to powerful man-in-the-middle attacks through malicious software (viruses, etc.), which is undetectable by conventional anti-virus technology. We present such powerful viruses and demonstrate their ability to compromise clients. Furthermore, we introduce a defense against all viruses, which is based on simple hardware devices that execute specialized protocols to establish client integrity and protect against sensitive data loss.

As an RF high Tc superconducting (HTS) front end for a microwave receiver, we propose a new design method for the broadband matching circuit composed of coplanar waveguide (CPW) meanderline resonators connecting a slot antenna with CMOS low noise amplifier (LNA). The parameters of the antenna sections with matching circuit are calculated and simulated with the circuit simulator and electromagnetic field simulator. CMOS LNA was designed and its input and output impedances and noise figure were obtained by SPICE simulation.

We propose the new and highly accurate design theory of the high Tc superconducting (HTS) miniaturized coplanar waveguide (CPW) bandpass filters (BPFs) with highly packed meanderlines. BPFs are designed using the external quality factor (Qe) and coupling constant (k) (Q-k method). These parameters are estimated from the transmission coefficient obtained by the 2.5-dimensional electromagnetic field simulator. Moreover, the Q-k method is compared with the J-b method (designed using admittance inverter and susceptance slope parameter) presented previously; in this way we confirmed that the Q-k method has higher accuracy than the J-b method. We realized the design of a the highly packed meanderline CPW BPF (5 pole, center frequency = 2 GHz, fractional band width = 15 MHz, ripple = 0.1 dB) in a 3.5 mm 8 mm substrate.

The measurement sensitivity of microwave surface resistance, Rs, of high temperature superconducting (HTS) thin films using half-wavelength microstrip resonator with copper and HTS ground plane is analyzed for fundamental and higher order modes of the resonator. The estimated sensitivity of Rs-measurement is at least an order of magnitude greater at fundamental resonant frequency compared to when measured using higher order harmonic modes.