Seung-Dae Lee

Digital Watermarking for Image Tamper Detection using Block-Wise Technique

Fragile watermarking has the characteristics where the inserted watermark should be easily breakable for a trivial tampering of the image. So, fragile watermarking technique is proposed for the purpose of authentication or tamper detection. In this paper, we propose an efficient image tamper detection method using block-wise technique which is able to detect the tamper locations. In the proposed method, a digital signature is generated from the hash code of the blocks of the final level where the watermark is inserted and the blocks of the upper level where those blocks are included in the image division process and this signature is used as the watermark, which is randomly inserted into selected image blocks. As the result of experiment, the proposed method was confirmed to be able to detect the tampered parts of the image without testing the entire block of the watermarked image.

Design of Security Mechanism for Electronic Document Repository System

The management and deposit of paper document costs are increased gradually. Specially, it is too expensive to safekeeping paper document in the warehouse. Also paper based document system is exposed in several security problems. Therefore, demands of transformation process from paper document into electronic ones are quietly needed. Electronic document repository system is one of the best solutions for solving paper based document system issues. Electronic document repository system can reduce overall costs and provides some advantages in comparison with paper based document system. But, electronic document repository system has no formal methodology for guarantee safeties. Therefore, we suggest a security mechanism for establish electronic document repository system. Suggested security methodology can help for design of more secure electronic document repository system.

Reconfigurable real number field elliptic curve cryptography to improve the security

Elliptic curve cryptography has an advantage of providing stability similar to RSA public key cryptography even when an extremely short key is used, and elliptic curve cryptography studies have been conducted on integer root based on finite field. However, if elliptic curve cryptography can be expanded to real number field, a very effective cryptographic system can be configured by selecting more diverse keys. Accordingly in this paper, a method of configuring cryptographic system using real number field coordinates on an elliptic curve is proposed. In the proposed method, keys can be selected using real number field, as well as finite field. Therefore, as the range of key selection for encryption and decryption can be expanded, there is an advantage of bringing additional improvement on safety from complexity of real number field calculation, while maintaining the advantages of existing elliptic curve cryptographic system.

The Study on Spatial Reuse Efficiency of Network Nodes Using Advanced Power Control Algorithm

An algorithm to minimize power consumption while keeping network throughput such as distributed power control, PCM(power control MAC), and F-PCF(fragmentation based PCM) was suggested to reduce power consumption through power control up to the present. A potential spatial for communication of surrounding nodes was generated as such power control method was planned to make optimal transmit power in order to minimize power consumption. But, potential spatial for communication generated through power control had not yet been utilized appropriately as an algorithm focused on power consumption. This study suggested an algorithm that advanced lots of network throughput by using potential spatial for communication generated by power control.

Tamper Detection of Digital Images using Hash Functions

Abstract Digital watermarking for digital image authentication and integrity schemes are based on fragile watermarking and can detect any modifications in a watermark embedded image by comparing the embedded watermark with the regenerated watermark. Therefore, the digital watermark for image authentication and integrity should be erased easily when the image is changed by digital image processing, such as scaling or filtering etc. This paper proposes an effective tamper detection scheme for digital images. In the proposed scheme, the original imagewas divided into many non-overlapping 2×2 blocks. The digital watermark was divided into two LSB of each block and the image distortion was imperceptible to the human eye. The watermark extraction process can be used to determine if the watermarked image has been tampered. The experimental results successfully revealed the effectiveness of the proposed scheme. Key Words : Fragile Watermarking, Spatial Domain, Tamper Detection 본 논문은 2013년도 서일대학교 학술연구비에 의해 연구되었음.

A Study on the Performance Evaluation of Elliptic Curve Cryptography based on a Real Number Field

Recently, as the use of the applications like online banking and stock trading is increasing by the rapid development of the network, security of data content is becoming more and more important. Accordingly, public key or symmetric key encryption algorithm is widely used in open networks such as the internet for the protection of data. Generally, public key cryptographic systems is based on two famous number theoretic problems namely factoring or discrete logarithm problem. So, public key cryptographic systems is relatively slow compared to symmetric key cryptography systems. Among public key cryptographic systems, the advantage of ECC compared to RSA is that it offers equal security for a far smaller key. For this reason, ECC is faster than RSA. In this paper, we propose a efficient key generation method for elliptic curve cryptography system based on the real number field.

Design and Implementation of Double Down-Converter for Satellite TV

In this paper, the broadband frequency double down-converter based on LC filter technologies has been designed and implemented, and its performances are introduced. The Designed frequency double down-converter is consisted with a low-noise amplifier, mixer, IF amplifier, LC filter, DC-block capacitor and RF-bypass capacitor. Especially, instead of active devices of a typical converter, the suggested converter designed using passive devices to provide both low-power consumption and low-cost model. As results of the measurement, the implemented frequency double down-converter realizes the broadband performance with the bandwidth of  (∼ ) at the center frequency of  , and its gain is approximately  .

A Study on Android-Based Real Number Field Elliptic Curve Key Table Generation

Encryption algorithms are used to protect data, but encrypted data depend on the safety of the key used in the encryption algorithm, so it is very important to generated a key that cannot be easily inferred for a safer protection of data. For this, in order to broaden the choice of keys used in encryption algorithm, this paper proposed the method to generate a key table by expanding the previously proposed elliptic curve algorithm to real number field, and the proposed method was applied to Android-based smartphone cryptosystem for verification.

Design and Implementation of Frequency Down Converter for Satellite Communication

In this paper, design and implementation of frequency down converter based on LC filter technic. Single frequency down converter, designed a low-noise amplifier, mixer, IF amplifier, LC filter was configured. And it is composed of DC block capacitors and RF bypass capacitor. LC filter, replace it with the IC reduced the power and realized low cost. The gain of single down converter is about 10dBm and realized by 18MHz bandwidth at 70MHz band.