• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 1997.11a
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• pp.322-331
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• 1997

DES의 키 길이를 확장 시킴에 있어서 처리 속도의 저하없이 112 비트의 키를 사용할 수 있는 SX-DES 구조를 제안하고 SX-DES애서 DES의 P-Box가 SX-DES에 대한 Differential Crytanalysis 공격에 의해 키 길이가 감소되는 효과를 가지고 있으므로 P-Box를 재구성하여 SX-DES가 확장된 키 효과를 충분히 가질 수 있도록 하였다. 처리시간은 DES보다 2 % 정도 더 소요되었다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.7
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• pp.1495-1500
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• 2011

Dynamic cipher has the property that the key-size, the number of round, and the plain text-size are scalable simultaneously. In this paper we propose the block cipher algorithm which is symmetrical in the dynamic network. We present the method for designing secure Dynamic cipher against meet-in-the-middle attack and linear crytanalysis. Also, we show that the differential cryptanalysis to Dynamic cipher is hard.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.24 no.6
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• pp.1129-1138
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• 2014

CAPTCHA is a technique which distinguishes human and machine using what human can judge easily but machine can't. Though Text-based-CAPTCHA has been widely used and can be implemented easily, it is less security than other CAPTCHAs such as image-based, or audio-based CAPTCHAs. To enhance the security of text-based CAPTCHA, many techniques have been developed. One of them is making CAPTCHA recognized hard using complex background or noise. In this paper, we introduce how to apply convolution filtering effectively to attack CAPTCHA and actually analyze Naver's CAPTCHA which has been used for joining a cafe with this method.