分散管理型システムに対する主な攻撃対象は，暗号技術ではなくコンセンサスであり，その攻撃に対する防御の安全性は暗号通貨で計量されるコストとして評価される．DAOの運営には出資金による金融機関としての機能が必須だが，参加者のアイデンティティ管理を基本とするガバナンスの適正化に失敗すると保有資産や収益を失う．そしてガバナンスへの攻撃も本質はコンセンサスへの攻撃である．

Cryptocurrencies based on UTXO (Unspent Transaction Output) model keep the deposit's total amount to meet withdraws' one for preventing double spend, in other words, they audit "the conservation of currency value" in every transaction. In order to use the cryptocurrencies in financial business, it is necessary to express the increase or decrease of debt amount by interest, however, it is incompatible with the safety of cryptocurrency operation. We propose a management method which can express interests or repayments with keeping the conservation of currency value. In the proposed method, an issuer simultaneously issues the same amount of positive and negative cryptocurrencies, where the former means the lending amount considering interest and the latter means the debt. Following these issues, the two currencies are offset only by the issuer.

The potential of blockchain technology has received attention in the area of FinTech the combination of finance and technology. Blockchain technology was first introduced as the technology behind the Bitcoin decentralized virtual currency, but there is the expectation that its characteristics of accurate and irreversible data transfer in a decentralized P2P network could make other applications possible. Although a precise definition of blockchain technology has not yet been given, it is important to consider how to classify different blockchain systems in order to better understand their potential and limitations. The goal of this paper is to add to the discussion on blockchain technology by proposing a classification based on two dimensions external to the system: (1) existence of an authority (without an authority and under an authority) and (2) incentive to participate in the blockchain (market-based and non-market-based). The combination of these elements results in four types of blockchains. We define these dimensions and describe the characteristics of the blockchain systems belonging to each classification.

本稿の目的は，仮想通貨以外の用途への「ブロックチェーン」技術の利用可能性について，要件の整理を試みることである．我々の立脚点は，「ブロックチェーン」という用語の唯一の実像であるビットコインのブロックチェーンである．我々は，これが（1）「対称的な非集中型の監査」を継続的に実施しているシステムであってかつ（2）「絶対中立的な記録」を実現しているシステムである，という2つの特性を持つことに注目する．そしてこの2つの性質を備えた「ブロックチェーン」が従来のデータベース技術で実現されている電子投票システムよりも優れていることを明らかにする．

In this paper, we propose a trust rating method for information providers using the structure of human relationships and meta-level communication protocol over the social web service. In our first approach, we proposed a trust rating method based on the number of followers on Twitter and the similarity of activity of active Twitter users. However, the results of our experimentation showed that this approach does not provide an effective trust rating system because shrewd software robots get very high trust ratings under this method. As a reflection of the first approach, our second approach is that a trust rating method requires more explicit and precise evidence of trust. We consider that a trust rating system should meet the following conditions. (1) The system provides some methods to prove the person who is trusted has the ability to perform the trusted task. (2) The system provides some motivation for the people to maintain trusted behavior. (3) The system provides explicit meta-level communications such as 'I will trust you', and 'All right' and the results cause a change of the state and reputation of the parties involved. As an example of this method, we put forward a trust rating system for a job-hunting system for IT-engineers. We also discuss how to avoid the phenomenon of information cascading, which is a typical problem of collective intelligence systems over the social web. © 2011 IEEE.

In this paper, we propose a trust estimation method for a parson by the rating of his or her active audience of social web such as Twitter. We call this method 'trust by the rating of a persona's active audience.' A 'persona', such as 'Display Name' of Twitter (with additional authentication) or 'Claimed ID' of OpenID, denotes an artificial identity to represent one's social position in the user-centric authorization. We utilize the 'persona' to be an object to accumulate the rating of trust for IT services for our trust estimation method. The most significant difference of our trust model and traditional one like PKI is that the trustworthiness of persona is not stable. Therefore, we focused on the implement methods for the sensitivity of the temporal change of a persona's trustworthiness. The basic idea of our 'trust by the rating of a persona's active audience' is similar to the Google Page Rank method. We also try to show that this kind of social web based trust has a possibility to be a global infrastructure for trust. © 2010 IEEE.

We propose a service model and system functions for service promotion in business oriented NPOs using e-community currency. We propose a currency distribution model such that service users and providers save the community currency through the exchange of services, and they can use the community currency for receiving other services. Then we describe the system functions to securely implement the model on the Internet.

Mobile devices will have enough power to provide various kinds of services on themselves in the Internet. In these services, users buy and sell products by peer-to-peer contact on streets and shops. In order to realize the peer-to-peer services, we need a platform that satisfies the following requirements: describing a service independent of its location, and providing a service under dynamically changing network environment. This paper proposes a new framework, called Virtual Private Community (VPC), for such services. VPC provides flexible collaboration and a new computation framework for the flexible collaboration, in order to realize such services.

This paper proposes a new framework called Virtual Private Community (VPC) for the next generation e-commerce, in which users buy and sell products by peer-to-peer contact. VPC enables e-commerce to be carried out by employing simple definitions called policy packages. VPC offers an extended e-commerce transactions that enable flexible e-commerce services by transferring policy packages together with copyright protection information on users' products. VPC provides a new method in which users can start their businesses by using the simple definitions.

ワンストップサービスとは, 申請や届出などの一連の行政手続を一つの電子的窓口で統合的に完結できるようにする情報サービスのことである.ワンストップサービスは低コストで利便性の高い「電子政府」を実現する上で中核となるサービスであるが, 様々な利点の反面, 使い方次第では深刻なプライバシー危機を引き起しかねない影の部分をも含んでいる.本稿では, このワンストップサービスの光と影の部分を公平に記述した上で, 影の部分の回避に暗号技術が重要な手段になることについて述べる.

福岡市早良区の"シーサイドももち地区"に無線を利用した地域ネットワークを構築し，都市のインフラとしてのインターネットの利用の実証実験を行った．本稿では高層建築物を利用した都市部に適した無線LAN装置によるネットワークの構築方法，地域ネットワークのコンテンツとサービス，そして地域コミュニティによる地域ネットワーク利用について報告する．

The validity of a digital signature for a digital certificate is insufficient to trust it because berification of earranty and assigned use policy of the digital certificate is indispensable. In this paper, we propose a cross authentication infrastructure that integrates a variety of services that require different use policies and warranties. We describe design and implementation of a prototype system for this model. The significant feature of our model is to separate the function of a certificate authority into "issuing authority, " "registration authority" and "use policy approval authority". We call this model "the separation of three authority models for digital certification system." We utilize trustable certificate repository for cross authentication. The warranty information is not embedded into a digital certificate in our model. Warranty information of a digital certificate is provided by the certificate repository. Our prototype system can provide an integrated service of servers that requires different use policies and warranties by only one certificate. Our certification system also endure practical use through our experimentation.

We built wireless LAN based network over Momochi area in Fukuoka city. Our purpose to build this network is to propose usage of internet as a new infrastructure for city. We realize the 24-hours connectivity for house of monitors of this experimentation and public facilities of Fukuoka city like a library and a museum over this network. In this paper, we describe the construction of this network, and propose the suitable usage of wireless LAN for urban area and report the construction of our network and some features of this network.

This research focuses on the three layers structure of Blockchain economy. It consists of code layer, economics layer, and regulation layer. In order to prove the three layers hypothesis, we implemented the local virtual currency system as a test to visualize the peoples' purchasing behavior, as well as the electronic voting system as a test to visualize the factors that affects on the peoples' voting behavior. Throughout these experiment we have found that the distribution of virtual currency may strengthen the social relation of participants and three layers structure of Blockchain economy is efficient to visualize the social relationship.

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