Minkyu Kim

Forward Secure Dynamic Searchable Symmetric Encryption with Efficient Updates

The recently proposed file-injection type attacks are highlighting the importance of forward security in dynamic searchable symmetric encryption (DSSE). Forward security enables to thwart those attacks by hiding the information about the newly added files matching a previous search query. However, there are still only a few DSSE schemes that provide forward security, and they have factors that hinder efficiency. In particular, all of these schemes do not support actual data deletion, which increments both storage space and computational complexity. In this paper, we design and implement a forward secure DSSE scheme with optimal search and update complexity, for both computation and communication point of view. As a starting point, we propose a new, simple, theoretical data structure, called dual dictionary that can take advantage of both the inverted and the forward indexes at the same time. This data structure allows to delete data explicitly and in real time, which greatly improves efficiency compared to previous works. In addition, our scheme provides forward security by encrypting the newly added data with fresh keys not related with the previous search tokens. We implemented our scheme for Enron email and Wikipedia datasets and measured its performance. The comparison with Sophos shows that our scheme is very efficient in practice, for both searches and updates in dynamic environments.

Analysis on a generalized algorithm for the strong discrete logarithm problem with auxiliary inputs

We investigate a recently proposed algorithm solving the strong discrete logarithm problem with auxiliary inputs, and show that this algorithm in general is not more efficient than ordinary discrete-logarithm-solving algorithms such as Pollard’s rho method, by analyzing a lower bound on the sum of digits of integers.

Estimating the Number of Clusters with Database for Texture Segmentation Using Gabor Filter

This paper addresses a novel solution of the problem of image segmentation by its texture using Gabor filter. Texture segmentation has been worked well by using Gabor filter, but there still is a problem; the number of clusters. There are several studies about estimating number of clusters with statistical approaches such as gap statistic. However, there are some problems to apply those methods to texture segmentation in terms of accuracy and time complexity. To overcome these limits, this paper proposes novel method to estimate optimal number of clusters for texture segmentation by using training dataset and several assumptions which are appropriate for image segmentation. We evaluate the proposed method on dataset consists of texture image and limit possible number of clusters from 2 to 5. And we also evaluate the proposed method by real image contains various texture such as rock stratum.

Computing prime divisors in an interval

We address the problem of finding a nontrivial divisor of a composite integer when it has a prime divisor in an interval. We show that this problem can be solved in time of the square root of the interval length with a similar amount of storage, by presenting two algorithms; one is probabilistic and the other is its derandomized version.

Security of Stateful Order-Preserving Encryption

Most of the proposed order-preserving encryption (OPE) schemes in the early stage of development including the first provably secure one are stateless and work efficiently, but guarantee only weak security. Additionally, subsequent works have shown that an ideal security notion IND-OCPA can be achieved using statefulness, ciphertexts mutability, and interactivity between client and server. Though such properties hinder availability of IND-OCPA secure OPE schemes, the only definitively known result is the impossibility of constructing a feasible IND-OCPA secure OPE scheme without ciphertext mutability. In this work, we study the security that can be fulfilled by only statefulness, from a viewpoint different from the existing research. We first consider a new security notion, called (delta )-IND-OCPA, which is a natural relaxation of IND-OCPA. In comparison to IND-OCPA in which ciphertexts reveal no additional information beyond the order of the plaintexts, our notion can quantify the rate of plaintext bits that are leaked. To show achievability of our notion, we construct a new (delta )-IND-OCPA secure OPE scheme. The proposed scheme is stateful and non-interactive, but does not require ciphertext mutation. Through several experiments, we show that our construction is also feasible and that has an advantage in the correlation analysis compared with the IND-OCPA secure scheme.

Performance comparison of tap gestures on small-screen touch devices

This paper describes a new type of tapping touch gesture called different-finger tap. We classified four tapping gestures as expanding tap gestures and performed a user experiment to investigate their tapping speed and error count during button touch interaction together with the different-finger tap gesture. The results showed that the different-finger tap gesture led to faster tapping time than the long-tap gesture and a lower error count than that seen with the double-tap gesture, although users were required to perform complex mental activities to use the different-finger tap gesture because it was unfamiliar. Participants reported that the different-finger tap gesture was the most suitable for tasks that require the tapping of small buttons correctly and quickly, such as text entry, when it was used together with the single-tap gesture.

Development of multimodal surface interface for audio and tactile feedback

This paper deals with the development of a surface multimodal interface system for audio and tactile feedback. The multimodal interface system consists of a PVDF film and an ITO glass. We have controlled the applied voltage between the PVDF film and ITO glass for the tactile feedback. Similarly, we have controlled the applied voltage between the transparent electrodes on both sides of PVDF film for audio feedback. This paper shows the performance of the developed surface multimodal interface system.

Hand Gesture Segmentation Method using a Wrist-Worn Wearable Device

Objective: We introduce a hand gesture segmentation method using a wrist-worn wearable device which can recognize simple gestures of clenching and unclenching ones fist. Background: There are many types of smart watches and fitness bands in the markets. And most of them already adopt a gesture interaction to provide ease of use. However, there are many cases in which the malfunction is difficult to distinguish between the users gesture commands and users daily life motion. It is needed to develop a simple and clear gesture segmentation method to improve the gesture interaction performance. Method: At first, we defined the gestures of making a fist (start of gesture command) and opening ones fist (end of gesture command) as segmentation gestures to distinguish a gesture. The gestures of clenching and unclenching ones fist are simple and intuitive. And we also designed a single gesture consisting of a set of making a fist, a command gesture, and opening ones fist in order. To detect segmentation gestures at the bottom of the wrist, we used a wrist strap on which an array of infrared sensors (emitters and receivers) were mounted. When a user takes gestures of making a fist and opening ones a fist, this changes the shape of the bottom of the wrist, and simultaneously changes the reflected amount of the infrared light detected by the receiver sensor. Results: An experiment was conducted in order to evaluate gesture segmentation performance. 12 participants took part in the experiment: 10 males, and 2 females with an average age of 38. The recognition rates of the segmentation gestures, clenching and unclenching ones fist, are 99.58% and 100%, respectively. Conclusion: Through the experiment, we have evaluated gesture segmentation performance and its usability. The experimental results show a potential for our suggested segmentation method in the future. Application: This can be adopted to user interface for fashion apparel such as a smart watch and wrist band.