Naoki Shibata’s research while affiliated with Nara Institute of Science and Technology and other places

Mobile payment system in a disaster area have the potential to provide electronic transactions for people purchasing recovery goods like foodstuffs, clothes, and medicine. Conversely, to enable transactions in a disaster area, current payment systems need communication infrastructures (such as wired networks and cellular networks) which may be ruined during such disasters as large-scale earthquakes and flooding and thus cannot be depended on in a disaster area. In this paper, we introduce a new mobile payment system utilizing infrastructureless MANETs to enable transactions that permit users to shop in disaster areas. Specifically, we introduce an endorsement-based mechanism to provide payment guarantees for a customer-to-merchant transaction and a multilevel endorsement mechanism with a lightweight scheme based on Bloom filter and Merkle tree to reduce communication overheads. Our mobile payment system achieves secure transaction by adopting various schemes such as location-based mutual monitoring scheme and blind signature, while our newly introduce event chain mechanism prevents double spending attacks. As validated by simulations, the proposed mobile payment system is useful in a disaster area, achieving high transaction completion ratio, 65% - 90% for all scenario tested, and is storage-efficient for mobile devices with an overall average of 7MB merchant message size.

To address the large amount of energy wasted by blockchains, we propose a decentralized consensus protocol for blockchains in which the computation can be used to search for good approximate solutions to any optimization problem. Our protocol allows the wasted energy to be used for finding approximate solutions to problems submitted by any nodes (called clients). Our protocol works in a similar way to proof-of-work, and it makes nodes evaluate a large number of solution candidates to add a new block to the chain. A client provides a search program that implements any search algorithm that finds a good solution by evaluating a large number of solution candidates. The node that finds the best approximate solution is rewarded by the client. Our analysis shows that the probability of a fork and the variance in the block time with our protocol are lower than those in proof-of-work.

To support various practical applications that are expected to work over vehicular networks, it is important to develop a network infrastructure that provides quality communications on which applications can rely. However, since a vehicular network is essentially a delay tolerant network (DTN) in which connected paths to the destinations do not always exist, providing reliable communications on such a network is a challenging research goal. In this paper, we propose a new table-driven distance-vector routing protocol called RDV (Reliable Distance-Vector routing) for static-node-assisted vehicular networks. RDV provides the guarantee that the expected packet delivery ratio exceeds the preconfigured value by creating the necessary number of packet copies sent on the shortest path. Evaluation results show that RDV provides a stably high packet delivery ratio and outperforms other conventional routing schemes in both packet delivery ratio and overhead of packet copies.

Secure communications is essential in many areas such as disaster management and battlefield communications. To detect and prevent attacks in such applications, most existing protocols adopt a cryptography-based approach, trust-based approach (reputation of nodes), or incentive-based approach. However, such protocols still have drawbacks, such as expensive overhead, difficulty in maintaining secure key and session management, or leaving routes unsecured against Byzantine attacks. In this paper, we introduce a monitoring-based method in the link state routing protocol to secure the packets’ route against Byzantine attacks. The goal of our proposed scheme is to guarantee communication among connected benign nodes in the network. Specifically, each node monitors the action of neighboring nodes and compares the optimal packet route against the packet route history. Nodes in the network create a packet history field which is used to record all activities of an intermediate node when receiving and forwarding packets. Our scheme provides mutual monitoring in which nodes in the network can validate the packet history field of other nodes and report malicious activities. Also, our scheme uses a statistical method to know if a node is dropping packets intentionally by analyzing the packet dropping behavior of each node. The proposed scheme provides protection against colluding attacks and other Byzantine attacks. The proposed monitoring-based method achieves an average of 89% to 96% packet delivery ratio when 11% to 21% active malicious links are excluded from the network.

Mobile payment system in a disaster area have the potential to provide electronic transactions for people purchasing recovery goods like foodstuffs, clothes, and medicine. Conversely, to enable transactions in a disaster area, current payment systems need communication infrastructures (such as wired networks and cellular networks) which may be ruined during such disasters as large-scale earthquakes and flooding and thus cannot be depended on in a disaster area. In this paper, we introduce a new mobile payment system utilizing infrastructureless mobile adhoc networks to enable transactions that permit users to shop in disaster areas. Specifically, we introduce an endorsement-based mechanism to provide payment guarantees for a customer-to-merchant transaction and a multilevel endorsement (MLE) mechanism with a lightweight scheme based on Bloom filter and Merkle tree to reduce communication overheads. Our mobile payment system achieves secure transaction by adopting various schemes such as location-based mutual monitoring scheme and blind signature, while our newly introduced event chain mechanism prevents double spending attacks. As validated by simulations, the proposed mobile payment system is useful in a disaster area, achieving high transaction completion ratio, 65%-90% for all scenario tested, and is storage-efficient for mobile devices with an overall average of 7 MB merchant message size.

We propose a new static-node-assisted routing scheme RDV (Reliable Distance Vector routing) for vehicular networks. In RDV, static nodes located at intersections behave as distance-vector routers to assist packet forwarding, i.e., they exchange messages, compute paths, and help packets travel along the computed forwarding paths to their destinations. To support various practical applications over vehicular networks, RDV provides reliable communications such that the average packet delivery ratio exceeds the preconfigured delivery ratio by creating the necessary number of packet copies sent on the shortest path. Evaluation results show that the proposed scheme provides stably high packet delivery ratio, and outperforms other existing routing schemes in both packet delivery ratio and the number of generated packet copies.

In this paper, we focus on multilevel parking facilities and propose a navigation system that minimizes the time required for cars to find vacant parking spaces. Parking zones at large parking facilities provide drivers conditions to drivers due to differences in distances from the entrance of the parking facility or to the entrances of the shopping areas. This leads to many cars concentrating at some parking zones while other zones are not occupied. It is not easy for car drivers entering a large parking facility to know which parking zones are vacant. It is fairly common that parking facilities have indicators that show occupancy information to the drivers. However, since these indicators deliver the same information to all drivers, this method tends to make a new congested zone by sending many drivers to that zone. In this paper, we propose a system that provides each driver with a recommended route in the parking facility that minimizes the expected parking time. Our method estimates the occupancy of each zone from the information sensed by the cars that implement the proposed method. This information is collected to a server installed in the facility, and then the server disseminates the processed information to the cars. The cars then calculates the recommended route from this information. We conducted a simulation-based evaluation of the proposed method using a realistic model simulating a real parking facility in Nara. As a result, we confirmed that the proposed method reduced parking waiting time by 20%-70% even with low penetration ratio.

A payment system in a disaster area is essential for people to buy necessities such as groceries, clothing, and medical supplies. However, existing payment systems require the needed communication infrastructures (like wired networks and cellular networks) to enable transactions, so that these systems cannot be relied on in disaster areas, where these communication infrastructures may be destroyed. In this paper, we propose a mobile payment system, adopting infrastructureless mobile ad-hoc networks (MANETs), which allow users to shop in disaster areas while providing secure transactions. Specifically, we propose an endorsement-based scheme to guarantee each transaction and a scheme to provide monitoring based on location information, and thus achieve transaction validity and reliability. Our mobile payment system can also prevent collusion between two parties and reset and recover attacks by any user. Security is ensured by using location-based mutual monitoring by nearby users, avoiding thereby double spending in the system.