Yasuhiro Ohtaki

UC-Secure Searchable Symmetric Encryption

For searchable symmetric encryption schemes (or symmetric-key encryption with keyword search), the security against passive adversaries (i.e. privacy) has been mainly considered so far. In this paper, we first define its security against active adversaries (i.e. reliability as well as privacy). We next formulate its UC-security. We then prove that the UC-security against non-adaptive adversaries is equivalent to our definition of privacy and reliability. We further present an efficient construction which satisfies our security definition (hence UC-security).

How to Update Documents Verifiably in Searchable Symmetric Encryption

In a searchable symmetric encryption (SSE) scheme, a client can store encrypted documents to a server in such way that he can later retrieve the encrypted documents which contain a specific keyword, keeping the keyword and the documents secret. In this paper, we show how to update (modify, delete and add) documents in a verifiable way. Namely the client can detect any cheating behavior of malicious servers. We then prove that our scheme is UC-secure in the standard model.

Time-stamp service makes real-time gaming cheat-free

Assuming time-stamp servers that we can trust exist everywhere in the Internet, we propose a cheat-proof protocol for real-time gaming that has the minimum latency. The assumptions are: 1) Time-stamp servers are available near each player that issue serially numbered time stamps. 2) There is no communication break down between the player and the nearest time-stamp server. By this protocol, each player sends its own action to the other player and also sends its hash to the nearest time-stamp server. The time-stamp server sends back to the player the signed hash with time and a serial number involved. The signature is an undeniable evidence of the action. The actions are checked if they are compatible with the hashes and the signed hashes are checked if they have the correct time and if the serial numbers are contiguous. This verification can be done as a batch after the game is finished. The latency in this protocol is only the packet traveling time from a player to another.

Partial Disclosure of Searchable Encrypted Data with Support for Boolean Queries

The setting in which Alice wishes to disclose log entries to Bob, only of which contain a keyword specified by him was studied. Suppose that Alice also wishes to keep other entries secret to Bob, even after the disclosure, then how could Alice convince Bob that the undisclosed entries surely do not contain the keyword? Such can be ensured with a variation of searchable encryption scheme; With Alices help, Bob can search through the encrypted log and specify the entries which contain the keyword. It is a common step to extend a simple search to a search with boolean queries, such as AND and OR. However, it is not simple to disclose entries which contain more than a single keyword, without leaking information on the undisclosed entries. In this paper, a scheme to disclose entries which match a boolean query is proposed. By using a Bloom filter as an encoded index, the scheme reduces the frequencies of comparison and the size of matching data, at the sacrifice of faultlessness.

Constructing a searchable encrypted log using encrypted inverted indexes

Searchable encrypted log provides a facility to disclose only records which match some specified conditions. However, searching on an encrypted log takes a long time because checking for the condition usually requires a vast number of public key operations. In the field of plain text search, inverted index is a typical data structure to improve the performance of search speed which turns a bunch of comparison into a simple table lookup. This paper introduces an encrypted version of inverted index which can be used for a searchable encrypted log. Encrypted inverted index enables to determine all records that contain a keyword while contents of other records are kept secret. Statistic information such as frequency of each word is also not revealed. A prototype system is implemented to show the efficiency

A multi-stage algorithm of extracting joint points for generating function-fonts

An automatic function-font generating system for brush-written characters has been proposed. The system extracts sharp corners of boundary lines, (so-called joint points), and approximates the boundary lines between adjacent joint points using a piecewise polynomial. The quality of the generated function-fonts is controlled by the location of joint points. An attempt is made to develop an advanced function-font generating system with an algorithm to extract appropriate joint points. The algorithm consists of three stages: (1) extracting joint points by evaluating digital curvature, (2) extracting additional joint points by evaluating the curvature of approximated boundary line, and (3) removing the redundant joint points. The performance of the method is verified by applying it to brush-written characters, printed characters, and figures.<<ETX>>

On compressing method of EEG data for their digital database

The authors propose a compression method for storing the electroencephalogram (EEG) waveforms into digital storage under the condition of keeping the quality sufficient for diagnosis. The method is designed on the basis of features of the EEG waveforms. The data volume is reduced by storing the coefficients of the functions approximating the EEG waveforms. The waveforms are divided into segments, in each of which the difference velocity is similar, and are decomposed into two wave components for efficient compression. The effectiveness of the method has been evaluated by applying it to several EEG waveforms. The quality of the reconstructed waveforms is bandwidth of 0.5 approximately 120 Hz, dynamic range of 60 dB, and maximum error of 2 mu V/sub p-p/. The compression ratio is 0.648 on the average.<<ETX>>

A Network Game Based on Fair Random Numbers

A compromising technique is proposed for deterring clients from cheating by robot players in skill-based real-time network games. This technique is to inject a fair random noise into the manual input for a real-time game modeled as a chaotic dynamical system. The fair random noise is determined by means of the bit commitment protocol so that neither host nor client can control the noise in their favor. A scenario possibly plotted by a robot player for its victory may be spoiled by slight noise injection because of the sensitivity of chaotic systems to the input. The noise injection brings a luck-based factor into a skill-based game. In this sense, the technique proposed in this paper is not a solution but a compromise for the inherent problem of robot players with the skill-based network games. An example implementation of pinball is presented.

Compressing data volume of left ventricular cineangiograms

A method of compressing data volume for left ventricular cineangiograms is proposed. This method enables digital-optical disks to store the cineangiograms with a recording density equivalent to that of high-density television video tape recorders (HDTV VTRs) while preserving the quality of the original image. The data volume of the cineangiograms is compressed by using an approximating function and storing its coefficients. Each cineangiogram frame is first decomposed into three regions: the inner part, the inner wall, and the background. Each region is then compressed by means of a difference operation and an adaptive approximation with smooth functions. Performance was tested for 20 cases using actual cineangiograms. The specifications were verified for a spatial resolution of 1000 TV lines, a dynamic range of 60 dB, an SNR or 40 dB (p-p/rms), volume compression to 7% of the original volume, and 0.19 (second/frame) for decoding on a 1.7 MFLOPS computer.<<ETX>>

File Manager that Shows off Notes Out of the Files

In the real world, sticky notes are often used to mark important pages in the documents with some notes. Sticky notes sticking out of documents are so visible that we can easily locate where the information is. Existing word-processing software is capable of managing virtual sticky notes inside the files. But we cannot see them until we open the files. In this study, we develop a file manager that enables us to see the virtual sticky notes in the Microsoft Office documents as if they are sticking out of the files. This file manager will improve the productivity of our office work.