The demand for high-capacity satellite communications has continuously increased, owing to the need to enhance the performance of sensors on earth observation satellites. One of the challenges is to realize a high-capacity return link from user satellites to ground stations. The Japan Aerospace Exploration Agency (JAXA) developed an optical intersatellite communication system "LUCAS" in 2020. JAXA aims to demonstrate a 1.8 Gbps data relay between a user satellite in low earth orbit and a ground station. Currently, the realization of a next-generation optical data relay system capable of even higher-speed communications is being studied. However, a detailed performance comparison of channel coding methods for optical data relay systems has not been conducted to enable high-speed communication within the limits of realistic computation power for installation in data relay satellites using optical intersatellite communication. Therefore, in this paper, we conduct numerical simulations to evaluate the characteristics of communication channel coding technologies, such as polar, low-density parity check codes, and Digital Video Broadcasting- Satellite-Second Generation (DVB-S2) channel codes, when applied to optical data relay satellite systems. The results of the simulations indicate that the performance of DVB-S2 codes is relatively good. Furthermore, a simple log-likelihood ratio correction method for DVB-S2 is proposed and shown to be effective.

Interleave division multiple access (IDMA) is a multiple-access scheme and it is expected to improve frequency efficiency. Meanwhile, the damage caused by cyberattacks is increasing yearly. To solve this problem, we propose a method of applying radio-wave encryption to IDMA based on chaos modulation to realize physical layer security and the channel coding effect. We show that the proposed scheme ensures physical layer security and obtains channel coding gain by numerical simulations.

Wireless communication in an intelligent transport system (ITS) requires high quality and low latency vehicle-to-infrastructure (V2I) transmission. However, fading occurs because of vehicle movements and this results in transmission errors, leading to frequent retransmission requests that require long delay times. Furthermore, in suburban areas, the distance between base stations (BSs) and vehicles tends to be long and the quality of wireless transmission degrades. To address this problem, we employ diversity transmission schemes, particularly frequency diversity, because these schemes are effective to increase the throughput. In this paper, we propose a frequency scheduling-based cooperative V2I uplink transmission scheme using vehicle-to-vehicle (V2V) side link (SL) communication in LTE-V2X to achieve improvements in far vehicle transmission from a BS, including efficient frequency use. To verify the proposed scheme, we execute traffic simulation in a suburban road model and apply the proposed transmission scheme to several vehicles. The simulation results demonstrate that the proposed scheme can improve the performance of uplink far-vehicle transmission to the BS compared with conventional schemes.

The non-orthogonal multiple access (NOMA) scheme has been considered as one of the methods for performing large capacity, high-speed communications in fifth-generation mobile communications system (5G). We propose a chaos NOMA scheme that realizes physical layer security and reliable communication. However, in conventional studies, the decoding of chaos NOMA uses joint maximum likelihood sequential estimation (MLSE), which simultaneously estimates the signals of all superposed users, and the decoding complexity increases exponentially with the number of superimposed users. Therefore, in this paper, we propose a low complexity decoding scheme for chaos NOMA using a combination of successive interference cancellation (SIC), which is a typical decoding method for NOMA, and partial MLSE. Through numerical simulations, we show that complexity is significantly reduced with the joint MLSE, and that the transmission performance is still better than that of the conventional NOMA scheme.

Recently, owing to the rapid increase of wireless traffic on smartphones and tablets, higher-capacity wireless communication systems have been developed. The non-orthogonal multiple access (NOMA) scheme has been studied as one of the potential solutions. In addition to the need for higher capacity, the demand for secure wireless transmission has also grown. To meet these requirements, we propose a chaos multiple-input multiple-output (C-MIMO) scheme that realizes both physical layer security and channel coding gain. In this paper, we apply the principle of C-MIMO to the NOMA scheme, and propose a chaos NOMA scheme that achieves higher-capacity, enabling a secure downlink wireless communication system. By performing numerical simulations, we show that compared to conventional power-domain NOMA schemes, we obtain improved performances and the physical layer security effect by introducing the C-MIMO principle into NOMA. In addition, we show that the throughput enhancement is obtained in the proposed scheme compared to previously proposed chaos orthogonal frequency-division multiple access (C-OFDMA) scheme.

In the fifth-generation mobile communications system (5G), wireless connections among numerous Internet of things (IoT) devices will be accommodated in the massive machine-type communications (mMTC) scenario. To realize such massive connectivity, non-orthogonal multiple access (NOMA) technologies have been proposed for 5G. As one of the NOMA schemes, we have proposed a grant-free sparse chaos code multiple access (GF-SCCMA) scheme exploiting the principle of chaos communications for mMTC. It realizes both physical layer security and large-capacity transmission. However, in conventional studies, a message-passing algorithm (MPA) was used in the receiver, which required relatively high calculation complexity, and the maximum number of users in GF-SCCMA was limited to approximately 10. Therefore, we propose an application of the Gaussian belief propagation (GaBP) algorithm for user signal detection to realize a large-scale transmission of more than 50 users with low calculation complexity. The improved transmission performances are shown through numerical simulations, by comparison with a conventional grant-free low-density signature scheme.

The multi-user multiple-input multiple-output (MU-MIMO) scheme is one of the main methods for improving the frequency-efficiency in wireless communication systems. In MU-MIMO systems, a base station equipped with multiple antennas and a large number of receivers with multiple antennas communicate simultaneously. Conventionally, we adopted the principle of chaos communications to MU-MIMO and proposed a multi-user chaos MIMO (MU-C-MIMO) scheme that has physical layer security between each receiver. In the previous study, we utilized block diagonalization (BD) - a liner precoding method - to remove interference components in MU-C-MIMO. On the one hand, channel gain for each user is not maximized in BD. On the other hand, the gain maximization can be realized using nonlinear precoding, and further improvement of transmission quality is expected in MU-C-MIMO. Therefore, in this paper, we propose a MU-C-MIMO scheme using dirty paper coding (DPC), a nonlinear precoding method, in order to realize the most ideal precoding characteristics. The effectiveness of this scheme is evaluated through numerical simulations with comparisons to a conventional MU-C-MIMO system with BD.

In cooperative intelligent transport systems, local dynamic maps (LDMs) are used to achieve safe and efficient transport systems. To transmit LDM data, a reliable, low-latency wireless communication is required. However, the transmission quality between base stations and distant vehicles often degrades, resulting in delays due to retransmission requested by upper-layer protocols. To solve it, in this paper, we propose an uplink cooperative relay transmission scheme using two timeslots in the physical layer, where a vehicle close to a base station relays data from a more distant vehicle. The scheme uses non-orthogonal superposition relaying at the close vehicle and maximum ratio combining at the base station, and improves quality of the data received by the distant vehicle. In addition, high-latency retransmission can be avoided using this scheme. The performance of the proposed scheme is evaluated with link budget calculations and numerical simulations, and it is shown that the proposed scheme greatly enhances a throughput of the distant vehicle.

Wireless communications in intelligent transport systems (ITS) require low-latency high-quality vehicle-to-infrastructure (V2I) transmission. However, fading due to vehicular movement sometimes causes transmission errors, resulting in repeated requests and high latency. A path diversity scheme for data transmission with multiple paths is effective in handling this problem. In addition, it is important that these transmissions should be conducted with a minimum number of resources to avoid signal traffic congestion. In this paper, we propose a novel cooperative V2I uplink transmission scheme that utilizes vehicle-to-vehicle (V2V) network coding, in which the need for additional resources is restricted by using analog network coding (ANC) or digital network coding (DNC). Cooperative communication improves the quality of the V2I transmission. We compare the performances of the required resources and the transmission quality for both schemes. In addition, we propose an iterative decoding scheme for ANC to improve the performance further. Numerical results show that the proposed scheme increases throughput and that the performance of ANC transmission is superior to that of DNC transmission despite that the former requires fewer resources when the average SNR of the link decreases.

As the demand for higher transmission rates and spectral efficiency is steadily increasing, the research and development of novel mobile communication systems has gained momentum. This paper focuses on providing a comprehensive survey of research and development activities on fifth generation mobile communication systems reported in IEICE technical committee on radio communication systems. We try to survey a vast area of wireless communication systems and the developments that led to future 5G systems.

Password-based Authenticated Key Exchange (PAKE) allows a server to authenticate a user and to establish a session key shared between the server and the user just by having memorable passwords. In PAKE, conventionally the server is assumed to have the authentication functionality and also provide on-line services simultaneously. However, in the real-life applications, this may not be the case, and the authentication server may be separate from on-line service providers. In such a case, there is a problem that a malicious service provider with no authentication functionality may be able to guess the passwords by interacting with other participants repeatedly. Abdalla et al. put forward a notion of the server password protection security to deal with this problem. However, their proposed schemes turned out to be vulnerable to Undetectable On-line Dictionary Attack (UDonDA). To cope with this situation, we propose the Gateway Threshold PAKE provably secure against this password guessing attack by also taking the corruption of authentication servers into consideration.

For the next-generation mobile communication system, enlarging the system capacity by allowing the use of non-orthogonal user multiplexing has been suggested. In a downlink multicarrier non-orthogonal multiple access (NOMA) system, single or multiple users are allocated to each subband. In NOMA scheduling, a proportional fair (PF) algorithm, where users with few allocated resources are selected on a priority basis, is generally used. However, to reduce the calculation complexity, only the fairness up to the previous transmitted frames is taken into account. Therefore, to improve the performance, we propose an improved downlink NOMA scheduling scheme that takes the fairness of the target frame into consideration, and orders the allocation subband based on the instantaneous fairness. Through this scheme, a user having little resource allocation may be assigned a good subband. Numerical results show an improved performance in the average user throughput and fairness.

In online services, e.g., Online shopping, a service provider (SP) manages access logs containing customers' buying histories. Therefore, user's personal information, e.g., Their hobbies and diversions, is revealed from the exposed logs if each customer can be linked. In fact, such information exposure has occurred due to the popularization of online services. To cope with this problem, SPs may only have to delete access logs, but then no illegitimate users, who accessed the server illegally, will be traced from the logs. In this paper, we propose a log management mechanism where (1) no user information is revealed even if logs are exposed, but (2) illegitimate users can be traced when necessary. Specifically, we consider single sign on (SSO) systems, since plural access logs might be connected by one account, and this could trigger the above privacy infringement problem. We construct our privacy-enhanced access log management mechanism based on the Wang-Wang-Susilo SSO system (TrustCom 2013) which applies nominative signatures as its building block. Specifically, we realize the system by additionally applying the invisibility property of the Schuldt-Hanaoka nominative signature scheme (ACNS 2011). Finally, we estimate the efficiency of the proposed system by using Pairing-Based Cryptography (PBC) library and confirmed that for each algorithm, computation time is at most just over 80 milliseconds on a PC, which seems sufficiently practical.

We propose generic declarative definitions of individual and collective trust relations between interacting agents and agent collections, and trust domains of trust-related agents in distributed systems. Our definitions yield (1) (in)compatibility, implic

Satellite/terrestrial integrated mobile communication system (STICS) is an advanced system in which the satellite and terrestrial mobile systems share the frequency band and a mobile terminal can connect both of them. STICS is drawing attention as a robust system in terms of disaster and congestion. However, when the satellite link and the terrestrial link use identical frequencies, the interference is caused by each other and the transmission performances are degraded. Therefore, to ease the interference and to raise the capacity, we propose a new weighting scheme taking the interference into account in the frequency allocation at the transmitter and in the frequency-domain equalization at the receiver of STICS. The numerical results show the system throughput performance of multiple-input multiple-output (MIMO)-based STICS is improved by the proposed scheme.

Recently, relay transmission schemes have been much studied according to increasing demands for ad-hoc wireless communication. In bi-directional relay transmission, the transmission efficiency has been decreased due to the waiting time. To tackle this problem, network coding (NC) has been proposed. The orthogonal frequency division multiplexing (OFDM)-based relay transmission applying analog network coding (ANC) can reduce the number of timeslots per one sequence compared to that without NC and it increases the transmission capacity. However, in the bi-directional relay transmission with ANC, the relay node receives the signals of each transmitting nodes simultaneously and the signal detection must be conducted. To do that, the channel state information of each nodes is needed, and the rate-efficient and accurate channel estimation should be applied for the bi-directional relay, which is not much considered so far. Therefore, in this paper, we propose a new channel estimation scheme for bi-directional two-timeslot OFDM relay transmission where the transmitters send sparse Walsh-code pilots and the receiver detects and estimates each channel information by the correlation processing. The proposed scheme can estimate the channels by less pilot symbols sparsely allocated in OFDM frame. In addition, an accurate interpolation scheme with two-dimensional fast Fourier transform (FFT) is utilized. The performances of the proposed scheme are evaluated by computer simulations.

In the present paper, we show that the pairing inversion problem of Ateipairing can be solved under the assumption that we have a generic algorithm for solving “exponentiation inversion” problem. With such an algorithm, the inversion problem of Ateipairing can be solved without solving the Miller inversion. Thus, the pairing inversion problem of Ateipairing is reduced to the exponentiation inversion problem.

In an eHealth peer-to-peer database management system(P2PDBMS), peers exchange data in a pair-wise fashion on-the-fly in response to a query without any centralized control. Generally, the communication link between two peers is insecure and peers create a temporary session while exchanging data. When peers exchange highly confidential data in an eHealth network over an insecure communication link, the data might be tampered with or trapped and disclosed by intruders, which is a serious offence for the clients of an eHealth P2PDBMS. As there is no centralized control for data exchange in eHealth P2PDBMS, it is infeasible to assume a centralized third party security infrastructure to protect confidential data. So far, there is currently no available/existing security protocol for secured data exchange in eHealth P2PDBMS. In this paper we propose three models for secure data exchange in eHealth P2PDBMSs and the corresponding security protocols. The proposed protocol allows the peers to compute their secret session keys dynamically during data exchange based on the policies between them. Our proposed protocol is robust against the man-in-the middle attack, the masquerade attack, and the replay attack.

A secure communication is achieved by upper layer applications such as common key or public key cryptosystems in current transmission systems. However, the security is never exclusive and the multiplexing of security schemes is highly effective, so a secure transmission scheme on physical layer is also important. One of the typical physical-layer schemes is a chaos transmission which produces a secure, safe, wired or wireless communication. However, the main drawback of the chaos scheme is an error-rate performance degradation. We proposed a chaotic convolutional code which improved the performance in the tradeoff with decoding complexity increase. Here, in this paper, we focus on the diversity property of multiple-input multiple output (MIMO) and propose a chaos MIMO transmission scheme to achieve the secure on physical layer, low error-rate, and low complexity transmission. The joint MIMO detection and chaos decoding is done by maximum likelihood decoding (MLD) at the receiver. We will evaluate the performance of the proposed scheme by computer simulations.

This paper is devoted to the design of fast parallel accelerators for the cryptographic \eta_T pairing on supersingular elliptic curves over finite fields of characteristics two and three. We propose here a novel hardware implementation of Miller's algorithm based on a parallel pipelined Karatsuba multiplier. After a short description of the strategies that we considered to design our multiplier, we point out the intrinsic parallelism of Miller's loop and outline the architecture of coprocessors for the \eta_T pairing over {\bf F}_{2^m} and {\bf F}_{3^m}. Thanks to a careful choice of algorithms for the tower field arithmetic associated with the \eta_T pairing, we manage to keep the pipelined multiplier at the heart of each coprocessor busy. A final exponentiation is still required to obtain a unique value, which is desirable in most cryptographic protocols. We supplement our pairing accelerators with a coprocessor responsible for this task. An improved exponentiation algorithm allows us to save hardware resources. According to our place-and-route results on Xilinx FPGAs, our designs improve both the computation time and the area–time trade-off compared to previously published coprocessors.

We propose compact architectures of the SHA-3 candidates BLAKE-32 and BLAKE-64 for several FPGA families. We harness the intrinsic parallelism of the algorithm to interleave the computation of four instances of the Gifunction. This approach allows us to design an Arithmetic and Logic Unit with four pipeline stages, and to achieve high clock frequencies. With careful scheduling, we completely avoid pipeline bubbles. For the time being, the designs presented in this work are the most compact ones for any of the SHA-3 candidates. We show for instance that a fully autonomous implementation of BLAKE-32 on a Xilinx Virtex-5 device requires 56 slices and two memory blocks.

In this paper, we propose a new channel model of optical satellite-to-ground link by analyzing the results of optical transmission experiments between ground station and the Optical Inter-orbit Communications Engineering Test Satellite (OICETS). This will be a practical model on high-capacity optical satellite-to-ground links. In addition, we propose an efficient channel coding scheme using low-density generator matrix (LDGM) codes as a long erasure code over the proposed channel model. Simulation results clarify the required coding rate and the interleaver size for this channel on bare 1 Mbps transmission. The basic idea of the proposed model and the coding system are suitable for higher-speed optical links.

A multimedia surveillance system aims to provide security and safety of people in a monitored space. However, due to the nature of surveillance, privacy-sensitive information, such as face, gait and other physical parameters based on the captured media from multiple sensors, can be revealed without the concern of the people. This is a major concern in recent days. Therefore, it is desirable to have such mechanism that can hide privacy-sensitive information as much as possible, yet supporting effective surveillance tasks. In this paper, we propose a chaos cryptography based data hiding approach that can be applied on selected regions of interest (ROIs) in video camera footage, which contains privacy-sensitive data. Our approach also supports multiple levels of abstraction of data hiding depending on the role of the authorized user. In order to evaluate the suitability of this approach, we applied our algorithm on some video camera footage and observed that our approach is computationally efficient and applicable for real-time video surveillance tasks.

In this paper, we have proposed the signal separation and equalization schemes for MFSK signals using FDE (Frequency Domain equalization) with CP (Cyclic Prefix) and the MLD (Maximum Likelihood Detection) with ZP (Zero Padding) on quasi-static MIMO frequency selective channels. Through computer simulations, we have verified that the MLD with ZP exhibits the better BER characteristics than the conventional FDE with CP. Moreover, we have decreased the computational complexity of MLD using M algorithm.

Maximum Likelihood Detection (MLD) featuring Log-likelihood (LLR) combining technique has been introduced in earlier works to achieve diversity gains in block fading channels for one relay node. In this paper, we extend this strategy to multiple relay systems (MRS) and introduce a new method such that the computational complexity of MLD is further reduced. This method approximates bit LLR values from the symbol LLR, thereby reducing the computational burden at the destination. A cooperative relay scheme of a source node (S), multiple relay nodes (R) and a common destination node (D) is considered. This scheme utilizes a simple relaying protocol which detects the signals (i.e. hard-decision) and forwards (DAF) to the destination node. While LDPC codes do not achieve significant performance gain in Single Input Single Output (SISO) scheme over block fading channel, we suggest that with the proposed scheme, the gain is essentially significant under MRS platform. This improvement is achieved by using a cheap DAF relaying protocol which is well-suited for resource limited conditions, for instance, in wireless sensor networks (WSN). The results are validated through a simulation work and compared with maximum ratio combiner (MRC) and cooperative-MRC (C-MRC).

Recently, much attention has been paid to research on distributed coalitions, as a possible mechanism to embody distributed information flow control which can apply security policies to distributed components over nodes by making the components enforce mandatory access controls for resources based on the policies. Some projects have proposed prototype systems of distributed coalitions, but they assume that each component that participates in a domain has domain management functions. This assumption is reasonable when the components are designed for a distributed coalition, but it has been an obstacle when actually building distributed coalitions in existing environments, because it is difficult for existing components in real environments that were not designed for use in distributed coalitions to update their code and add support for domain management functions while considering the influences of their environments, especially for commercial components. In this paper, we propose a Domain Management Agent (DMA) for building practical distributed coalitions, which performs domain management on behalf of a component and emphasizes minimizing the influence on existing environments. We implement a prototype system on Microsoft Windows platform for broad use by many people, evaluate its performance overhead, and show that our approach is feasible.

Nowadays providing information security (IS) assurance becomes one of key aspects for many organizations worldwide. This is caused not only by desire of management to protect sensitive information fed by growing hackers ' activity but also by recent enforcement of legal requirements and industry regulations. One of the required procedures to manage information security is regular performing of IS risk assessment. Though there already are several approaches proposed to measure IS related risk, they are either inapplicable to real enterprises' IT landscapes or are of qualitative nature (based on subjective decisions of implementation team) and thus could suffer from significant degree of speculation. The purpose of this paper is to present a quantitative approach for effective and efficient assessment of IS related risks which can be easily applied to any enterprise. A key feature of proposed approach is that it does not suffer from subjective considerations and relies on statistical data. Other relevant features are: maintenance cost reduction and possibility to prioritize and compare security initiatives.

Confidentiality and authentication are crucial to wireless sensor networks when sensors are deployed in hostile environments, e.g., battle fields and antiterrorist operations. In this paper, we come up with (1) a group key distribution protocol for a base station to distribute a group key to sensors and (2) a broadcast authentication protocol for sensors to authenticate messages broadcasted by a base station. Security and performance analysis show that both protocols are secure and efficient. In addition, our group key distribution protocol supports dynamic wireless sensor network which allows new sensors to be added in and compromised sensors to be forced to leave.

A restricted universal designated verifier signature scheme proposed by Huang et al., which is a variant of digital signatures, allows a signature holder to convince at most t designated verifiers.The signature will become publicly verifiable when the signature holder uses the signature for t+1 times.The applications of this type of signatures are expected to, for example, trial services or electronic votings on the internet. However, confirming process and universal opening are required in some situations. But both Huang et al.'s scheme as well as Laugullaumie et al.'s scheme do not support universal opening. In this paper, we propose a new restricted undeniable designated verifier signature scheme. Our scheme surpasses both Huang et al.'s scheme and Laugullaumie et al.'s scheme in the sense of universal opening.

The notion of limited verifier signature (LVS) was first introduced by Araki et al. in 1999. It is a useful cryptographic primitive to limit the publicly verifiable property of ordinary digital signatures. In a LVS, the signature can be verified by a limited verifier. When necessary, the signer or the limited verifier can provide a proof to convince a designated verifier (eg., a judge) that the signer has indeed generated the signature. However, the judge cannot transfer this proof to convince any other party. Also, the LVS should be converted into an ordinary one for public verification if required. In this paper, we propose an efficient LVS scheme which is more efficient than previous proposed schemes. Based on the intractability of the Computational Diffie-Hellman (CDH) problem, we give the security proofs of the scheme in the random oracle model.

Abstract The main characteristic of a mobile ad hoc network (MANET) is its infrastructure‐less, highly dynamic topology, which is subject to malicious traffic analysis. Malicious intermediate nodes in MANETs are a threat concerning security as well as anonymity of exchanged information. In this paper, we propose an anonymous on‐demand routing protocol, called RINOMO, to protect anonymity and achieve security of nodes in MANETs. After successful authentication of the legitimate nodes in the network they can use their pseudo IDs for secure communication. Pseudo IDs of the nodes are generated considering pairing‐based cryptography. Nodes can generate their pseudo IDs independently and dynamically without consulting with system administrator. As a result, RINOMO reduces pseudo IDs maintenance costs. Only trust‐worthy nodes are allowed to take part in routing to discover a route. To ensure trustiness each node has to make authentication to its neighbors through the designed anonymous authentication process. Thus, RINOMO safely communicates between nodes without disclosing node identities. It also provides different desirable anonymous properties such as identity privacy, location privacy, route anonymity, and robustness against several attacks. Mathematical analysis of privacy loss is also evaluated and it shows there is no loss of privacy with respect to time. Thus, RINOMO is an anonymous robust protocol in MANETs. Copyright © 2008 John Wiley & Sons, Ltd.

Since their introduction in constructive cryptographic applications, pairings over (hyper)elliptic curves are at the heart of an ever increasing number of protocols. Software implementations being rather slow, the study of hardware architectures became an active research area. In this paper, we discuss several algorithms to compute the ηT pairing in characteristic three and suggest further improvements. These algorithms involve addition, multiplication, cubing, inversion, and sometimes cube root extraction over GF(3m). We propose a hardware accelerator based on a unified arithmetic operator able to perform the operations required by a given algorithm. We describe the implementation of a compact coprocessor for the field GF(397) given by GF(3)[x]/(x97+x12+2), which compares favorably with other solutions described in the open literature.

In order to secure communications for dynamic peer groups in mobile computing environments, key agreement protocols are required. In this paper, we propose a new key agreement protocol based on identities of mobile users, composed of a basic protocol and a dynamic protocol, for dynamic peer groups. With the basic protocol, an initial secret group key can be achieved in a peer group. By the dynamic protocol, a new secret group key can be reached whenever member or mass join, group mergence, group division, member or mass quit occurs. Our protocol has security features, such as implicit group key authentication, key confirmation, forward secrecy, key independence, and etc. Because our protocol runs in parallel, it is more efficient than those running in series.

In this paper, we propose a modified etaTpairing algorithm in characteristic three which does not need any cube root extraction. We also discuss its implementation on a low cost platform which hosts an Altera Cyclone II FPGA device. Our pairing accelerator is ten times faster than previous known FPGA implementations in characteristic three.

In recent years, high speed, high-capacity and reliable transmissions are demanding in wireless communications. To achieve those requests, it is necessary to solve both time and frequency selective fadings caused by multi-path propagation on wireless channels. But up to now, the OFDM technique as the frequency domain equalization has been considered mainly for the frequency selective fading. In this paper, we have proposed some of time domain equalization schemes using block processing on SISO (single input single output) frequency selective channels, i.e., block linear equalizer (BLE), block equalization by QRD and M algorithm (QRD-M) and block equalization by SVD with adaptive modulation (SVD with adapt. mod.). They all have low complexities and excellent performances brought by the effects of path-diversity and zero padding for IBI (inter-block interference) cancellation.

Recently, a chaotic modulation has been proposed and attracts many researchers' attention because of some properties such as noise-like signal, nonlinearity, and pseudo-periodicity. The chaotic modulation is usually treated as a secure transmission scheme rather than an efficient scheme in terms of channel noise. In this paper, to achieve a secure and high-performance transmission, we propose a trellis-based chaotic modulation scheme (called as chaotic-coded modulation: CCM). The coding gain is obtained by the combination of trellis and chaotic convolutions and an adaptive decoding algorithm is used for this coded modulation. Simulation results show that the decoding scheme has a tradeoff between the performance and the decoding complexity.

Two cryptosystems using polynomials on finite fields are introduced; a permutation cipher based on permutation polynomials and a flexible secret sharing scheme. Polynomials are called permutation polynomials if they induce bijective functions. Metric and algebraic properties of permutation polynomials over a finite fields are investigated, especially properties associated with orbits and permutation cycles. Flexible secret sharing schemes have features that they can change a secret, enroll/disenroll members, increase/decrease threshold, without changing shares. A simple scheme using polynomials over finite fields is presented.

This paper presents a multimode block-coded modulation method that enables both multimode transmission and coding gain. In multimode transmission, the property of data is changed for each mode, and the data are adaptively transmitted. In our method, all modes are constructed by separate multilevel block codes, wherein the number of levels, set partition, rate, and distance properties of each mode may differ from those of the other modes. Different modes may also have different signal constellations, that is, different modulation methods. The code length is the same for all modes, and the mode can be switched at each block boundary, if desired. This method uses one-way transmission where the transmitter has no feedback information from the receiver. In decoding, the maximum-likelihood decoding is carried out using the Viterbi (1967) algorithm. The decoding of all modes, including decoding of the mode index, can be accomplished using one trellis diagram. This paper describes the multimode encoding and decoding method, and analyzes the distance properties and upper bounds for inter- and intramodes. It is clarified at which distance the code should be increased to reduce the decoding mode error. Three design examples are presented for unequal error protection/equal error protection, variable rate, and hybrid additive white Gaussian noise/flat-fading codes.

We describe a method of one-way multimode block-coded modulation for mobile communication systems. One-way multimode block-coded modulation is a form of multilevel block-coded modulation (BCM) with multimode characteristics. It also provides large coding gains. The method generates codes with various properties for every mode. The BCM for mobile communications was composed on the basis of a multimode BCM. Different modes of the code have different code distances, so that each mode can adapt to specific transmission environments, such as an additive white Gaussian noise or a flat fading noise environment. We evaluated the method using computer simulation.

Researchers have studied two types of digital multi-carrier modulation, wavelet packet modulation (WPM), and fractal modulation. The advantage of WPM is that it allows signal time and frequency to be divided and multiplexed. Therefore the time and frequency of noise signals, e.g., tone and impulse noise, can be identified and effectively partitioned in packets. Using this advantage, we propose a class-coded modulation method for WPM that has good bit error rate (BER) performance when the length of the code constraint is extended and can select time and frequency noise signals simultaneously. This report describes the proposed method and the computer simulations carried out to test its effectiveness.

We propose a secure auction-like negotiation protocol for agent based Internet trading, which not only retains the agent's mobility and flexibility, but also takes secure measures to prevent attacks from malicious hosts during the negotiation process. The particular features of the proposed protocol are: (1) negotiation for agent based trading is performed through a novel pattern of electronic auction; (2) negotiation results between two hosts are ensured to be valid with their signatures; (3) malicious actions can be detected and the breeder can be dug out by the help of sociological factors; (4) information gathering and negotiation processes are combined together while few communications are needed.

So far tamper-resistance has been considered as a property such as information stored in (I device is hard to read or modify by tampering.Such tamper-resistance is quite important in many situations: superdistribution, electronic commerce systems using IC card, pay television systems with decoders containing secret values for descrambling image and so on.Tamper-resistance ensures proper operation of a program and prevents extraction of secret data and abuse of the program.Moreover, tamper-resistance enables a vendor to enforce his own conditions upon users.A new notion of tamper-resistance is stated as follows.Tamper-resistance means a property such as information stored in a device or software is hard to read or modify by tampering.A tamper-resistant device is usually expensive and not easy to handle compared with its realization in software.It is better to achieve tamperresistance without relying on any physical device.Meanwhile, intellectual property rights for a software program can be easily violated once an attacker analyzes the algorithm of a target program.The attacker can create a distinct program which looks quite different but functions just as the target program does.It is very important for software programs to be protected from any reverse engineering and manipulation.From these observations we study methods to generate a tamper-resistant code and explain an elementary tool, aO/fl/f2/f3.It replaces and shuffles operational codes or inserts reproductive dummy codes in a program so that t,he output becomes hard to read.After

This correspondence proposes an explicit construction of codes achieving capacity for arbitrary discrete memoryless channels. The proposed code is obtained by concatenating variable inner codes and an algebraic geometry code. Further, we clarify that the proposed code achieves the error exponent obtained by Forney for concatenated codes.

In this paper a new type of digital proxy signature is proposed.The proxy signature allows a designated person, called a proxy signer, to sign on behalf of an original signer.Classification of the proxy signatures is shown from the point of view of the degree of delegation, and conditions of a proposed proxy signature for partial delegation are clarified.The proposed proxy signature scheme is based on the discrete logarithm problem.Compared to the consecutive execution of the ordinary digital signature schemes, it has a direct form, and a verifier does not need a public key of a user other than the original signer in the verification stage.Moreover, it requires less amount of computational work than the consecutive execution of the signature schemes.Due to this efficiency together with the delegation property, an organization, e.g. a software company, can very efficiently create many signatures of its own by delegating its signing operations to multiple employees.Another attractive feature of the proposed schemes is their highapplicability to other ordinary signature schemes based on the discrete logarithm problem.For instance, designated confirmer proxy signatures can be constructed.Furthermore, using a proposed on-line proxy updating protocol, the original signer can revoke proxies of dishonest proxy signers.

Pilot symbol assisted modulation (PSAM) has been proposed to overcome Rayleigh fading. However, as the fading rate becomes more rapid, it is difficult to provide an exact interpolation with conventional PSAM. To compensate for fast Rayleigh fading, a PSAM which calculates in the frequency domain rather than the time domain as in conventional PSAM is proposed. This PSAM provides an exact estimate in fast Rayleigh fading environments.

A network information security management system which authenticates and/or encrypts messages is proposed. Both authentication and key distribution are executed in a simple scheme. Once the system is set up, the transactions are done independently by the users involved, yet the amount of information that users must keep is small. The experimental implementation of the system on a personal computer network, using IC cards (smart cards) and digital signal processors, is described. The signal processors shorten calculation time and make the concept practical.>

A key distribution system (KDS) based on identification information (ID-based KDS) is presented. The system is founded on the Diffie-Hellman public key distribution scheme and has an identity authentication function. It uses an individual user's identification information instead of the public file used in the Diffie-Hellman scheme. It does not require any services of a center to distribute work keys or users to keep directories of key-encrypting keys. Therefore, key management in cryptosystems can be simplified by adopting the ID-based KDS. Two kinds of identity-based key distribution system are proposed and applied to actual communication networks. One uses two-way (interactive) communication to distribute work keys, while the other uses one-way communication. Modular exponentiations of large numbers, used in the systems, are implemented with digital signal processors.>