• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.1
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• pp.13-24
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• 2009

CLEFIA is a 128-bit block cipher which is proposed by SONY corporation and ARIA is a 128-bit block cipher which is selected as a standard cryptographic primitive. In this paper, we introduce new multiple impossible differential cryptanalysis and apply it to CLEFIA using 9-round impossible differentials proposed in [7], and apply it to ARIA using 4-round impossible differentials proposed in [11]. Our cryptanalytic results on CLEFIA and ARIA are better than previous impossible differential attacks.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.2
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• pp.3-9
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• 2009

In this paper we introduce a new side-channel attack using block cipher cryptanalysis named meet-in-the middle attack. Using our new side-channel technique we introduce side-channel attacks on AES with reduced masked rounds. That is, we show that AES with reduced 10 masked rounds is vulnerable to side channel attacks based on an existing 4-round function. This shows that one has to mask the entire rounds of the 12-round 192-bit key AES to prevent our attacks. Our results are the first ones to analyze AES with reduced 10 masked rounds.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.16 no.1
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• pp.23-33
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• 2006

Key Agreement protocols are among the most basic and widely used cryptographic protocols. In this paper we present an efficient O-based authenticated key agreement (AKA) protocol by using bilinear maps, especially well suited to unbalanced computing environments : an ID-based AKA protocol for Server and Client. Particularly, considering low-power clients' devices, we remove expensive operations such as bilinear maps from a client side. Our protocol uses signcryption and provide security in random oracle model.

• Physical Therapy Rehabilitation Science
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• v.11 no.2
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• pp.154-164
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• 2022

Objective: The purpose of this study is to select a cognitive training game that can evaluate five cognitive domains and to study their validity with existing cognitive evaluation tools. Design: Methods: Delphi survey was conducted through the 2nd questionnaire for 30 experts to select games suitable for training 5 cognitive domains. Five cognitive training games and Mini Mental State Examination - Korea(MMSE-K), and cognitive impairment screening test(CIST) were conducted for 82 elderly in the community. Pearson correlation analysis was performed to find out the correlation of the three tests. The ROC curve was used to calculate the selection criteria for the game results for the screening evaluation of the presence or absence of mild cognitive impairment. Results: The coefficient of variation to evaluate the stability of the Delphi survey was less than 0.50 in most game items. The 'correct answers' and 'level' of the five final selected game items showed a statistically significant positive correlation with the CIST and MMSE-K scores. CIST score and 'time' of all game items except 'number making_time' showed a statistically significant negative correlation. Conclusions: The validity of the cognitive training program using smart devices was evaluated, and the criteria for classifying the cognitive domain and distinguishing the presence or absence of cognitive impairment were confirmed.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.6
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• pp.59-69
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• 2002

Many Linear attacks have introduced after M. Matsui suggested Linear Cryptanalysis in 1993. The one of them is the method suggested by B. Kaliski and M. Robshaw. It was a new method using multiple linear approximations to attack for block ciphers. It requires less known plaintexts than that of Linear Cryptanalysis(LC) by Matsui, but it has a problem. In this paper, we will introduce the new method using multiple linear approximation that can solve the problem. Using the new method, the requirements of the known plaintexts is 5(1.25) times as small as the requirements in LC on 8(16) round DES with a success rate of 95%(86%) respectively. We can also adopt A Chosen Plaintext Linear Attack suggested by L. R. Knudsen and J. E. Mathiassen and then our attack requires about $2^{40.6}$ chosen plaintexts to recover 15 key bits with 86% success rate. We believe that the results in this paper contain the fastest attack on the DES full round reported so far in the open literature.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.1
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• pp.47-57
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• 2003

In this paper, we firstly evaluate the resistance of the reduced 5-round version of the block cipher CIKS-1 against linear cryptanalysis(LC) and show that we can attack full-round CIKS-1 with \ulcorner56-bit key through the canonical extension of our attack. A feature of the CIKS-1 is the use of both Data-Dependent permutations(DDP) and internal key scheduling which consist in data dependent transformation of the round subkeys. Taking into accout the structure of CIKS-1 we investigate linear approximation. That is, we consider 16 linear approximations with p=3/4 for 16 parallel modulo $2^2$ additions to construct one-round linear approximation and derive one-round linear approximation with the probability P=1/2+$2^{-17}$ by Piling-up lemma. Then we present 3-round linear approximation with 1/2+$2^{-17}$ using this one-round approximation and attack the reduced 5-round CIKS-1 with 64-bit block by LC. In conclusion we present that our attack requires $2^{38}$chosen plaintexts with a probability of success of 99.9% and about $2^{67-7}$encryption times to recover the last round key.(But, for the full-round CIKS-1, our attack requires about $2^{166}$encryption times)

• Journal of the Korea Institute of Information Security & Cryptology
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• v.24 no.1
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• pp.135-144
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• 2014

Since anti-forensics have been developed in order to avoid digital forensic investigation, the forensic methods for analyzing anti-forensic behaviors have been studied in various aspects. Among the factors for user activity analysis, "Iconcache.db" files, which have the icon information of applications, provides meaningful information for digital forensic investigation. This paper illustrates the features of IconCache.db files and suggests the countermeasures against anti-forensics utilizing them.

• ETRI Journal
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• v.31 no.5
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• pp.625-627
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• 2009

This letter describes an improved side-channel attack on DES with the first four rounds masked. Our improvement is based on truncated differentials and power traces which provide knowledge of Hamming weights for the intermediate data computed during the enciphering of plaintexts. Our results support the claim that masking several outer rounds rather than all rounds is not sufficient for the ciphers to be resistant to side-channel attacks.

• ETRI Journal
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• v.30 no.1
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• pp.68-80
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• 2008

Since many efficient algorithms for implementing pairings have been proposed such as ${\eta}_T$ pairing and the Ate pairing, pairings could be used in constraint devices such as smart cards. However, the secure implementation of pairings has not been thoroughly investigated. In this paper, we investigate the security of ${\eta}_T$ pairing over binary fields in the context of side-channel attacks. We propose efficient and secure ${\eta}_T$ pairing algorithms using randomized projective coordinate systems for computing the pairing.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2007.02a
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• pp.105-107
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• 2007

최근에 제안되고 있는 원격 서버에 로그인하기 위한 방법은E와 패스워드뿐만 아니라 스마트카드를 함께 사용한다. 기존의 ID 와 패스워드를 사용한 인증은 공격자에 의해 추측이 가능하므로 사용자 가장 공격이 가능하다는 약점을 가지고 있다. 하지만 스마트카드와 ID, 패스워드를 사용하면 ID와 패스워드가 추측가능할지라도 스마트카드를 소지하고 있지 않다면 사용자 가장 공격 (impersonate attack)을 할 수 없다. 이 논문에서는 스마트카드와 ID, 패스워드를 함께 사용하여 원격 서버에 인증과 더불어 안전한 키 교환을 하며, 기존에 다른 논문들에서 언급한 조건들을 모두 만족하면서 안전한 키 교환까지 제안하였다. 기존의 스킴은 해쉬 기반으로 제안 되었으나 이 논문에서 제안한 스킴은 페어링 (pairing) 연산을 기반으로 제안 되었다. 또한, Computational Diffie-Hellman문제를 기반으로 스킴을 제안하여 안전성에 대한 증명이 가능하다 최근에 스마트카드를 사용한 인증에서 요구 되는 성질의 모든 조건을 만족한다는 장점을 가지고 있다.