• Journal of KIISE:Computing Practices and Letters
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• v.15 no.9
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• pp.617-625
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• 2009

NAND flash memory is widely used in embedded systems because of many attractive features, such as small size, light weight, low power consumption and fast access speed. However, it requires garbage collection, which includes erase operations. Erase operation is very slow. Besides, the number of the erase operations allowed to be carried out for each block is limited. The proposed garbage collection method focuses on minimizing the total number of erase operations, the deviation value of each block and the garbage collection time. NAND flash memory consists of pages of three types, such as valid pages, invalid pages and free pages. In order to achieve above goals, we use a page rate to decide when to do garbage collection and to select the target victim block. Additionally, We implement allocating method and group management method. Simulation results show that the proposed policy performs better than Greedy or CAT with the maximum rate at 82% of reduction in the deviation value of erase operation and 75% reduction in garbage collection time.

• Proceedings of the Korea Information Processing Society Conference
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• 2017.04a
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• pp.32-35
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• 2017

직접 통로(Direct Pass-through) 기반 GPU(Graphic Processing Unit) 가상화 기법은 클라우드 환경에서 가상머신에게 GPU 장치의 기능을 지원하기 위한 일반적인 방법 중 하나이다. GPU 장치는 GPGPU 기술을 통해 연산을 가속화 할 수 있기 때문에 클라우드 환경에서도 가상머신에 고성능 연산을 지원하기 위해 많이 사용되고 있다. 하지만 기존 가상머신 스케줄링 기법은 가상머신의 CPU 사용 시간을 기반으로 스케줄링 되며, GPU 자원 사용을 고려하지 않는다. 본 논문에서는 GPU와 CPU 연산을 수행하는 가상머신들이 동시에 실행되는 환경에서 성능 실험을 통해 가상머신의 GPU 연산이 다른 가상머신에게 미치는 성능 영향과 GPU 작업 길이가 다른 가상머신에게 미치는 영향을 분석한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2011.04a
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• pp.785-788
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• 2011

급속한 기술의 발전과 더불어 스마트카드 하나만으로도 서비스 제공에 필요한 인증이 가능한 기술이 제시되고 있다. 우리는 편리함과 간편함을 제공받는 대신에 보안취약성이라는 위험에 노출되게 된다. 스마트카드는 사용자의 정보와 같은 민감한 정보를 포함하기 때문에 이를 보호하기 위한 다양한 연산(사칙연산, 지수연산, 해시연산 그리고 암호화연산)들을 통해 메시지 인증 및 암호화를 수행하게 된다. 현재 산학연을 중심으로 다양한 암호화 프로토콜들이 제시되고 있다. 그 중에서도 2008년 Rhee. et. al에 의해 제시된 속성기반 스마트카드 인증기법은 사용자의 특성에 따라 다양한 서비스 제공이 가능하다는 장점을 가진다. 하지만 이동성을 제공하지 못하는 단점이 있어 자신의 스마트카드를 통한 인증범위가 제한되는 단점을 가진다. 본 논문에서는 이동성을 보장하는 개선된 속성기반 암호화 기법을 제시한다.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.43 no.5 s.311
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• pp.44-59
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• 2006

This paper describes the efficient implementation of DNA sequence generate system with genetic algorithm for reducing computation time of NACST. The proposed processor is based on genetic algerian with fitness functions which would suit the point of reference for generated sequences. In order to implement efficient hardware structure, we used the pipelined structure. In addition our design was applied the parallelism to achieve even better simulation time than the sequence generator system which is designed on software. In this paper, our hardware is implemented on the FPGA board with xc2v6000 devices. Through experiment, the proposed hardware achieves 467 times speed-up over software on a PC and sequence generate performance of hardware is same with software.

• The KIPS Transactions:PartC
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• v.17C no.3
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• pp.233-242
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• 2010

In the recent years, power attacks were widely investigated, and so various countermeasures have been proposed. In the case of block ciphers, masking methods that blind the intermediate results in the algorithm computations(encryption, decryption) are well-known. In case of SEED block cipher, it uses 32 bit arithmetic addition and S-box operations as non-linear operations. Therefore the masking type conversion operations, which require some operating time and memory, are required to satisfy the masking method of all non-linear operations. In this paper, we propose a new masked S-boxes that can minimize the number of the masking type conversion operation. Moreover we construct just one masked S-box table and propose a new formula that can compute the other masked S-box's output by using this S-box table. Therefore the memory requirements for masked S-boxes are reduced to half of the existing masking method's one.

• Proceedings of the Korean Information Science Society Conference
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• 2000.10c
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• pp.6-8
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• 2000

본 연구에서는 자원제약이 존재할 때의 스케듈링 문제인 자원제약에서 리스트 스케듈링 방법을 이용했으며, 기존의 리스트 스케듈링 기법이 모든 우선순위 함수를 산출한 후, 이에 근거에 스케듈링을 하는 반면, Forward 스케듈링 기법은 스케듈링 과정 내에서 필요한 경우에만 연산의 우선순위 함수를 산출하여 이를 이용하는 방식을 택했다.

• Journal of KIISE:Computer Systems and Theory
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• v.30 no.7_8
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• pp.417-425
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• 2003

We propose an efficient one-time signature scheme for stream authentication by improving HORS. When one-time signatures are used for authenticating live streams, one of the most serious drawbacks is that its large signature size yields high communication overhead. Compared with the previous one-time signature schemes, proposed scheme has the smallest signature size. Moreover, verification overhead is very low. Compared with the previous schemes for stream authentication, signing overhead of our scheme is larger than that of HORS but much lower than those of BiBa or Powerball. Moreover, signing operation can be trivially parallelized without any additional risk because it does not require sharing of the secret key between distributed servers.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.20 no.3
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• pp.135-140
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• 2010

The computation using Chinese Remainder Theorem in RSA cryptosystem is well suited in the digital signature or decryption processing due to its low computational load compared to the case of general RSA without CRT. Since the RSA-CRT algorithm is vulnerable to many fault insertion attacks, some countermeasures against them were proposed. Among several countermeasures, Yen et al. proposed two schemes based on fault propagation method. Unfortunately, a new vulnerability was founded in FDTC 2006 conference. To improve the original schemes, Kim et al. recently proposed a new countermeasure in which they adopt the AND operation for fault propagation. In this paper, we show that the proposed scheme using AND operation without checking procedure is also vulnerable to fault insertion attack with chosen messages.

• Journal of KIISE:Databases
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• v.28 no.3
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• pp.494-511
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• 2001

In the environment that database management systems manage disk spaces for storing databases directly, this paper proposes a correct and efficient scheme of performing pending actions for the removal of database files. As for performing pending actions, upon performing recovery, the recovery process must identify unperformed pending actions of not-yet-terminated transactions and then perform those actions completely. Making the recovery process identify those actions through the analysis of log records in the log file is the basic idea of this paper. This scheme, as an extension of the execution of transactions, fuzzy checkpoint, and recovery of ARIES, uses the following methods: First, to identify not-yet-terminated transactions during recovery, transactions perform pending actions after writing 'pa_start'log records that signify both the commit of transactions and the start of executing pending actions, and then write 'eng'log records. Second, to restore pending-actions-lists of not-yet-terminated transactions during recovery, each transaction records its pending-actions-list in 'pa_start'log record and the checkpoint process records pending-actions-lists of transactions that are decided to be committed in 'end_chkpt'log record. Third, to identify the next pending action to perform during recovery, whenever a page is updated during the execution of pending actions, transactions record the information that identifies the next pending action to perform in the log record that has the redo information against the page.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.21 no.7
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• pp.805-814
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• 2010

The Crank-Nicolson isotropic-dispersion finite difference time domain(CN ID-FDTD) scheme is proposed based on isotropic-dispersion finite difference(ID-FD) $equation^{[1],[2]}$. The dispersion relation of CN ID-FDTD is derived for lossy media by solving the eigenvalue problem of iteration matrix in spatial spectral domain, in addition, the weighting factors and scaling factors of the CN ID-FDTD scheme are presented for low dispersion error. The CN ID-FDTD scheme makes the dispersion error drastically reduced and shows accurate numerical results compared to the conventional Crank-Nicolson FDTD method.