• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.1
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• pp.139-146
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• 2003

In this paper we demonstrate a cryptanalysis of the stream cipher LILI-128. Our approach to analysis on LILI-128 is to solve an overdefined system of multivariate equations. The LILI-128 keystream generato $r^{[8]}$ is a LFSR-based synchronous stream cipher with 128 bit key. This cipher consists of two parts, “CLOCK CONTROL”, pan and “DATA GENERATION”, part. We focus on the “DATA GENERATION”part. This part uses the function $f_d$. that satisfies the third order of correlation immunity, high nonlinearity and balancedness. But, this function does not have highly nonlinear order(i.e. high degree in its algebraic normal form). We use this property of the function $f_d$. We reduced the problem of recovering the secret key of LILI-128 to the problem of solving a largely overdefined system of multivariate equations of degree K=6. In our best version of the XL-based cryptanalysis we have the parameter D=7. Our fastest cryptanalysis of LILI-128 requires $2^{110.7}$ CPU clocks. This complexity can be achieved using only $2^{26.3}$ keystream bits.

• Review of KIISC
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• v.5 no.2
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• pp.90-96
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• 1995

Gollmann이 제안한 Cascade 생성기는 비선형성, 발생되는 수열의 난수특성, 주기성등 암호 알고리즘으로서 필요한 제반 특성을 보장하기 때문에 그동안 스트림 암호의 핵심 논리로 널리 사용되어 왔다. 그러나 최근 생성기 내부의 각 단계별로 시각 제어 수열과 출력 수열 사이에 암호 알고리즘으로는 부적당한 상관관계 특성이 존재함이 입증되었다. 본 고에서는 이러한 상관관계 특성을 이용하여,. 단순 순환 쉬프트 래지스터로 구성된 Cascade 생성기에 대한 기지 평문 공격 방식을 제안한다. 기존의 Lock-in effect 공격방식에 대하여 $10^{21}$ 정도의 안전성을 보장하는 8단계 11-cycle Cascade 생성기에 본 방식을 적용한 결과 불과 88,000 출력 비트만을 사용하여 공격이 성공함을 실험적으로 입증하였다.

• Annual Conference of KIPS
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• 2022.11a
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• pp.222-224
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• 2022

미국 국립표준기술연구소는 사물 인터넷 환경 상에서 원활하게 구동할 수 있는 경량암호의 표준화 공모전을 개최하였다. 경량암호 표준화 공모전은 2019년 Round 1 결과가 발표되었고, 2021년에는 최종 라운드 후보를 발표하였다. 최종 선정된 알고리즘은 총 10종이다. 선정된 알고리즘은 동작 방식에 따라서 순열 기반, 블록암호 기반, 트위커블 블록암호 기반, 그리고 스트림 암호 기반으로 분류된다. 또한 필수적으로 AEAD 기능을 제공할 것을 요구하며, 추가적으로 해시 기능을 제공하기도 한다. 본 논문에서는 국립표준기술연구소에서 진행한 경량암호 표준화 공모전의 최종 라운드에 대해서 확인해본다.

• The KIPS Transactions:PartD
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• v.13D no.3 s.106
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• pp.437-444
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• 2006

A chaos cipher system that focuses on the stream cipher system has a demerit that the longer the text is, the slower the speed of the encryption and description and the transmission and reception. On this study, we designed the cipher web mail system showing much better capabilities than the existing web mail system as the text is longer. In the embodiment of the cipher web mail system, we developed the key stream, the encryption and description of the text and the inside and outside mail viewer and so on. After the efficiency test, it was valued high in the respect of the speed of the encryption and description and the transmission and reception. And it made up for the defect of the stream cipher system. We expect that we can use it through the persistent applied study in the server system security, the file security, the security of the internet information, the protection of the e-commerce system information and other fields based on the cipher technique as the wide use cipher system that can replace the block cipher system.

• The Journal of the Korea Contents Association
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• v.4 no.1
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• pp.55-66
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• 2004

Recently, as the personal computers are supplied rapidly, they formed the nucleus of the computer system. But, because of the easiness that anyone uses them to go near easily, it is the fact that the security of personal computer is weakness. So, in the paper, 1 propose the technical method that minimizes the loss and leakage of important data. This paper implemented a crypto system for security of data file on personal computer and assistance storage medium. The way of encryption/decryption is applied by complexity method which mixed Diffie-Hellman key exchange protocol, a typical RC4(Rivest Cipher version 4) algorithm of stream cipher and a typical MD5(Message Digest version 5) of Hash Function. For valuation implemented crypto system, three criteria is presented, which are crypto complexity, processing time and pattern matching. And according to analysis the three criteria the crypto system is verified the security, efficiency and usefulness. The crypto system is programmed with Visual C++ language of Microsoft. And so, as this is software system, we shall have a technical security system at a minimum cost for all personal computer.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.18 no.5
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• pp.3-16
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• 2008

A Wireless Sensor Network (WSN for short) is a wireless network consisting of distributed small devices which are called sensor nodes or motes. Recently, there has been an extensive research on WSN and also on its security. For secure storage and secure transmission of the sensed information, sensor nodes should be equipped with cryptographic algorithms. Moreover, these algorithms should be efficiently implemented since sensor nodes are highly resource-constrained devices. There are already some existing algorithms applicable to sensor nodes, including public key ciphers such as TinyECC and standard block ciphers such as AES. Stream ciphers, however, are still to be analyzed, since they were only recently standardized in the eSTREAM project. In this paper, we implement over the MicaZ platform nine software-based stream ciphers out of the ten in the second and final phases of the eSTREAM project, and we evaluate their performance. Especially, we apply several optimization techniques to six ciphers including SOSEMANUK, Salsa20 and Rabbit, which have survived after the final phase of the eSTREAM project. We also present the implementation results of hardware-oriented stream ciphers and AES-CFB fur reference. According to our experiment, the encryption speeds of these software-based stream ciphers are in the range of 31-406Kbps, thus most of these ciphers are fairly acceptable fur sensor nodes. In particular, the survivors, SOSEMANUK, Salsa20 and Rabbit, show the throughputs of 406Kbps, 176Kbps and 121Kbps using 70KB, 14KB and 22KB of ROM and 2811B, 799B and 755B of RAM, respectively. From the viewpoint of encryption speed, the performances of these ciphers are much better than that of the software-based AES, which shows the speed of 106Kbps.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.10
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• pp.2164-2170
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• 2011

Rapid surge in date quantity lead to increase in storage demand from corporate. The existing SAN with fiber channel is being changed to IP-based SAN environment due to installment and maintenance cost. But the IP-based network still have some similar security problems as existing TCP/IP network. Also, for the security reasons of storage traffic, data are encrypted, but with the existing system, data larger than 10G can't be handled. To address security and speed issue, this paper proposes to a structure applied to IP SAN environment with Parallel Structure Word-based FSR (PS-WFSR) as hardware.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2009.10a
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• pp.383-386
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• 2009

In this paper, we propose some parallel structures of the word-based nonlinear combine functions in word-based stream cipher, high-speed versions of general (bit-based) nonlinear combine functions. Especially, we propose the high-speed structures of popular three kinds in word-based nonlinear combiners using by PS-WFSR (Parallel-Shifting or Parallel-Structured Word-based FSR): m-parallel word-based nonlinear combiner without memory, m-parallel word-based nonlinear combiner with memories, and m-parallel word-based nonlinear filter function. Finally, we analyze its cryptographic security and performance.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.1
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• pp.97-104
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• 2011

Pseudo-random sequences with high linear complexity and low correlation function values are widely used in communication and cryptology. In this paper, we study the properties of interleaved sequences generated by shrinking generator. And we give a method for obtaining the shrunken sequence from a partial description of the shrunken sequence by using the phase shifting of PN sequences generated by shrinking generator.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.6
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• pp.604-610
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• 1989

As the volume of communication data and information exchange, the protection of data which we want to keep secret from invalid users would be a main topic nowadays. This paper describes the use of an arbitrary bit-sequence generating algorithm as the cryptographic key for a stream cipher. Emphasis is places on methods for combining stream generators into more complex ones, with and without randomization.