As privacy‐enhancing authentications without any TTP (Trusted Third Party), blacklistable anonymous credential systems with reputation have been proposed. However, the previous systems have the efficiency problem: The authentication data size is or , where L is the reputation list, and K is the size of a window indicating the most recent K authentications of the user. Therefore, the previous systems suffer from or ‐size data in each authentication. In addition, the authentication needs the computation of or exponentiations. In this paper, an efficient blacklistable anonymous credential system with reputation is proposed. In our system, the data size of the authentication is . Furthermore, although the computational costs in the authentication depend on some parameters, the parameter‐related costs are only multiplications instead of exponentiations. Compared to the previously proposed blacklistable system FARB with the constant computational and communication costs, our system has the advantage that the clear/redeem protocol only has to be executed every interval instead of every session. For constructing our system, we newly introduce the concept of an accumulator for reputation, and propose an efficient construction.

In group signature schemes, one of the important issues is the member revocation, and lots of revocable schemes have been proposed. Recently, a Group Signature scheme with Probabilistic Revocation (GSPR) is proposed. In GSPR, by employing a novel notion of probabilistic revocation, the computation cost of the revocation check is drastically reduced, although the correctness of the check is with a certain probability. However, in the GSPR scheme, there is another problem: m alias tokens are embedded into the certificate of a member. Then, in signing, each token is used, and O(m) exponentiations are needed to prove that the used token is embedded in the certificate. When m is large, this signing cost including O(m) exponentiations becomes a big problem for powerless mobile devices. In this paper, we propose an extended GSPR scheme where the signing cost is reduced, but the revocation mechanism is exactly the same as the original GSPR scheme. Our main idea is to utilize an efficient pairing-based accumulator with multiplications to embed lots of alias tokens in a certificate. Thus, in the proposed scheme, the signing cost is reduced to only O(m) multiplications instead of O(m) exponentiations.

In conventional ID-based user authentications, privacy issues may occur, since users' behavior histories are collected in Service Providers (SPs). Although anonymous authentications such as group signatures have been proposed, these schemes rely on a Trusted Third Party (TTP) capable of tracing misbehaving users. Thus, the privacy is not high, because TTP can always trace users. Therefore, the anonymous credential system using a blacklist without TTP has been proposed, where blacklisted anonymous users can be blocked. Recently, an RSA-based blacklistable anonymous credential system with efficiency improvement has been proposed. However, this system still has an efficiency problem: The data size in the authentication is O(K'), where K' is the maximum number of sessions in which the user can conduct. Furthermore, the O(K')-size data causes the user the computational cost of (K') exponentiations. In this paper, a blacklistable anonymous credential system using a pairing-based accumulator is proposed. In the proposed system, the data size in the authentication is constant for parameters. Although the user's computational cost depends on parameters, the dependent cost is (δBL·K) multiplications, instead of exponentiations, where δBLis the number of sessions added to the blacklist after the last authentication of the user, and is the number of past sessions of the user. The demerit of the proposed system is O(n)-size public key, where corresponds to the total number of all sessions of all users in the system. But, the user only has to download the public key once.

As an inexpensive, scalable Internet-access wireless network, we have studied the architecture, protocols, and design optimizations of the wireless Internet-access mesh network (WIMNET) that uses multiple access-points (APs) connected by wireless links. WIMNET can improve the dependability to failures of links and/or APs by allocating APs redundantly in the network field. Because redundant APs can increase the operational cost and degrade the performance due to increasing radio interferences, only the necessary APs for connections between the hosts and the Internet gateway should be activated at communications. Previously, we have defined the active AP selection problem of selecting the minimum number of active APs, and proposed its heuristic algorithm, assuming that every link has the same constant speed for simplicity. However, our preliminary experiments found that the link speed is greatly affected by the distance in the high-speed IEEE802.11n protocol that has recently become popular. In this paper, we propose a modification of the active AP selection algorithm to consider the link speed change, where we introduce a new design parameter for WIMNET to select links that have sufficient throughputs. We verify the effectiveness of our modified algorithm through simulations in four instances using the WIMNET simulator.

With the advancement of communication technologies, multiple wireless local area networks (WLANs) have been often deployed in the same building for the Internet access services. Usually, their wireless access-points (APs) have been independently managed and operated by different groups such as departments or laboratories in a university or a company. Then, a WLAN user host can detect signals from multiple APs, which may increase the interference and the operation cost, and degrade the communication performance. As a result, the number of active APs should be minimized by aggregating the physical APs allocated in the field into limited ones by introducing virtual APs. In this paper, we define this AP aggregation problem for WLANs that aggregates the APs into the minimum number of active APs, and prove the NP-completeness of its decision problem. Then, we propose the heuristic algorithm that is composed of five phases. The effectiveness of our proposal has been verified through simulations in two instances.

For busy persons such as working people, students, and nurturing parents, it is very hard to spend a long time in cooking foods by themselves at home after working for long hours on weekdays. As one solution, the cooking process can be divided into two phases, where the preparation steps for foods that they will eat on the following weekdays are performed on a weekend, and the final steps for some foods are finished on the eating day in a short time. Then, the task of generating a menu planning with this two-phase cooking becomes a complex problem to satisfy the limited cooking time. In this paper, we formulate this time-constrained menu planning problem with the two-phase cooking, and prove the NP-completeness of its decision problem through the reduction from the NP-complete knapsack problem. Then, we present its heuristic algorithm based on a simple greedy method for the knapsack problem, where foods are sequentially selected into the menu in descending order of food priorities. We apply the algorithm to the generation of one week menu plan from 53 food candidates, where the result verifies the effectiveness of our approach.

The Web-based lecture-scene playback system using the digital picture-card show has been studied to improve the educational quality of lectures with computer-aided slide presentations in universities. In this system, fine still images of lecture scenes, containing the lecturer, the blackboard, and the presentation screen, are periodically taken by a commercial digital photo camera, and the lecturer voice is recorded into a digital file by a personal computer during a class. Then, the digital picture-card show to play back the lecture scenes is edited by selecting one image and the voice file section corresponding to one lecture scene that is defined as the time span of teaching one slide page by the lecturer. The picture-card show is delivered to students through the World-Wide Web system on demand. In this paper, we propose the structured learning assistance function for this lecture-scene playback system, so that students can study important technical concepts in the lecture structurally. This function classifies the lecture scenes corresponding to one concept into five structures, and generates the links between them automatically. Through applications to one course for freshmen in our department, we show the effectiveness of our proposal.

In group signature schemes, a signature is anonymous for a verifier, while only a designated Privacy Manager (PM) can identify the signer. This identification is used for tracing a dishonest anonymous signer in case of an illegal act using the signature. However, PM can violate signers' anonymity. Recently, Brickell and Li propose a novel countermeasure for the anonymous dishonest signer without PM in the setting of the direct anonymous attestation. Here, we call the generalized group signature version anonymously revocable group signature scheme. In this scheme, after an illegal act using a group signature was found, the membership of the dishonest signer can be anonymously revoked for excluding the signer without the help of any PM. However, since the Brickell-Li scheme is based on the RSA assumption and the DDH assumption, the signature is long. In this paper, we propose a short anonymously revocable group signature scheme from supersingular curves, where we adopt the decision linear (DLIN) assumption. Compared to the simple adoption of the Brickell-Li DDH-based revoking approach to supersingular curves, the length of our signature is reduced to about from 30% to 60%.

This paper presents a formulation of the optical-drop wavelength assignment problem (ODWAP) and its heuristic algorithm for WDM ring networks. The wavelength-division multiplexing (WDM) technology has been popular in communication societies for providing very large communication bands by multiple lightpaths with different wavelengths on a single optical fiber. Particularly, a double-ring optical network architecture based on the packet-over-WDM technology such as the HORNET architecture has been studied as a next generation platform for metropolitan area networks (MANs). Each node in this architecture is equipped with a wavelength-fixed optical-drop and a tunable transmitter so that a lightpath can be established between any pair of nodes without wavelength conversions. In this paper, we formulate ODWAP for efficient wavelength reuse under heterogeneous traffic in this network. Then, we propose a simple heuristic algorithm for ODWAP. Through extensive simulations, we demonstrate the effectiveness of our approach in reducing waiting times for packet transmissions when a small number of wavelengths are available to retain the network cost for MANs.