• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.12
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• pp.2318-2324
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• 2017

Quantum cryptography, which is emerging as a next generation password, is being studied by quantum cryptographic transfer protocols and quantum secret communication. Quantum key transfer protocol can be used in combination with the modern password because of the inefficiency of the use of the password, or the use of OTP(one time password). In this paper an algorithm for direct communication by means of direct cryptographic communications rather than quantum keys. The method of implementing quantum secure direct community was adopted using 2-channel methods using Einstein gravity field. Two channels were designed to adopt a quantum secret communication protocol that applies time delay between 2-channels of channel to apply time difference between 2-channels. The proposed time delay effect reflects the time delay by reflecting the gravitational lensing phenomenon. Gravity generator with centrifugal acceleration is incorporated in the viscometer, and the time delay using this implies the correlation between the variance of the metametry.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.21 no.2
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• pp.91-100
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• 2011

The Triple Data Encryption Algorithm (Triple DES) is an international standard of block cipher, which composed of two encryption processes and one decryption process of DES to increase security level. In this paper, we proposed a Differential Fault Analysis (DFA) attack to retrieve secret keys using reduction of last round execution for each DES process in the Triple DES by fault injections. From the simulation result for the proposed attack method, we could extract three 56-bit secret keys using exhaustive search attack for $2^{24}$ candidate keys which are refined from about 9 faulty-correct cipher text pairs. Using laser fault injection experiment, we also verified that the proposed DFA attack could be applied to a pure microprocessor ATmega 128 chip in which the Triple DES algorithm was implemented.

• Proceedings of the KAIS Fall Conference
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• 2010.05a
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• pp.77-80
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• 2010

일반적인 메일 시스템은 제 3자의 악의적인 목적으로 메일의 내용을 열람했을 경우 모든 내용이 그대로 노출 된다는 위험성을 내포하고 있다. 이러한 문제점을 해결하기 위해서, 본 논문에서는 ARIA를 이용한 메일 암호시스템을 제안한다. 제안한 암호시스템은 메일 내용을 송 수신 하는 쌍방 간의 합의된 비밀 키로 암 복호화하여 악의적인 의도로 메일에 접근했을 경우에도 비밀 키가 노출되지 않는 한메일 내용을 알 수 없도록 설계하였다.

• Proceedings of the Korea Institutes of Information Security and Cryptology Conference
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• 1997.11a
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• pp.91-100
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• 1997

암호학적으로 안전한 해쉬 함수는 디지털 서명, 메시지 인증, 키 유도와 같은 분야에서 중요한 암호 도구이다 현재까지 제안된 소프트웨어로 고속 수행이 가능한 해쉬 함수들의 대부분은 Rivest가 제안한 MD4의 설계 원리에 기반을 두고 있다. 이들 MD 계열 해쉬 함수 중에서 현재 안전하다고 알려진 전용 해쉬 함수는 SHA-1, RIPEMD-160, HAVAL 등이다. 본 논문에서는 이들 세 가지 해쉬 함수들의 장점에 기반하여 이들 함수들이 가지는 안전성을 최대한 유지하면서 보다 효율적인 새로운 해쉬 함수를 제안한다. 제안된 해쉬 함수는 임의 길이 메시지를 512비트 단위로 처리하여 160비트의 출력을 가지며, 입력 데이터에 의존한 순환이동(data-dependent rotation)의 특징을 가짐으로써 기존에 알려진 공격에 강인함을 보장한다. 또한 제안된 해쉬 함수를 이용한 메시지 인증 코드(Message Authentication Code:MAC) 구성 알고리즘을 제안한다 MAC은 두 번째 입력, 즉 비밀키를 가진 해쉬 함수로 keyed 해쉬 함수라고 하며, 메시지 출처 인증과 무결성 확인을 제공한다. 제안된 MAC은 최대 160-비트의 키를 사용하며 해쉬 결과보다 같거나 적은 MAC 결과를 가지며, 성능 면에서 사용되는 해쉬 함수에 비해 약 10% 정도의 저하를 초래한다.

• Proceedings of the Korea Information Processing Society Conference
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• 2006.05a
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• pp.873-876
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• 2006

POP는 공개키 인증서의 발급과정에서 인증기관(CA)이 신청자가 제출한 공개키에 대응하는 비밀키를 가지고 있는가와 선택한 암호 알고리즘 및 용도에 적합한 연산을 수행할 능력이 있는 가를 확인하는 절차를 의미한다. WAP PKI에서는 POP 확인을 위해 암호화용 인증서는 WTLS 프로토콜을 수행하고, 전자서명용은 signText()함수를 이용하여 전자서명을 생성하도록 정의하고 있다. 이런 방식은 WTLS 프로토콜의 수행과 전자서명의 생성과정에서 많은 연산과 통신 부담이 발생한다. 본 논문에서는 ECDSA에 기반한 Signcryption 방식을 이용하여 효율적으로 POP를 검증하는 방식을 제안한다.

• Journal of KIISE
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• v.43 no.8
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• pp.933-945
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• 2016

Sharing data by multiple users on the public storage, e.g., the cloud, is considered to be efficient because the cloud provides on-demand computing service at anytime and anywhere. Secure data sharing is achieved by fine-grained access control. Existing symmetric and public key encryption schemes are not suitable for secure data sharing because they support 1-to-1 relationship between a ciphertext and a secret key. Attribute based encryption supports fine-grained access control, however it incurs linearly increasing ciphertexts as the number of attributes increases. Additionally, the decryption process has high computational cost so that it is not applicable in case of resource-constrained environments. In this study, we propose an efficient attribute-based secure data sharing scheme with outsourceable decryption. The proposed scheme guarantees constant-size ciphertexts irrespective of the number of attributes. In case of static attributes, the computation cost to the user is reduced by delegating approximately 95.3% of decryption operations to the more powerful storage systems, whereas 72.3% of decryption operations are outsourced in terms of dynamic attributes.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2008.02a
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• pp.85-87
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• 2008

Kumar 등은 interlacing과 decomposition을 적용한 112-비트 블록 암호를 제안하였다. 본 논문에서는 이 블록 암호에 대한 첫 번째 분석 결과를 소개한다. 이 블록 암호를 구성하는 연산들은 모두 선형성만을 가지고 있다. 따라서 112개의 독립인 평문/암호문 쌍이 주어졌을 경우, 비밀키를 복구하지 않더라도 임의의 암호문을 복호화할 수 있다. 본 논문의 분석 결과를 통하여 이 블록 암호는 매우 취약함을 알 수 있다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.5 no.1
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• pp.25-36
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• 1995

Differential Cryptanalysis(DC) and Linear Cryptanalysis(LC) are considered to be efficient attack methods which could be applied to DES and other DES-like private key Cryptosystems. This paper analyzes the DC and LC attack to DES and design a 80-bit block Cipher (80-DES) which could be strong against DC and LC Attack.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.6
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• pp.17-22
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• 2009

Certificateless cryptography eliminates the need of certificacates in the public key crytosystems and solves the inherent key escrow problem in identity-based cryptosystems. This paper demonstrates that two certificateless signature schemes proposed by Guo et al. and Wang et al. respectively are insecure against key replacement attacks by a type I adversary. We show that the adversary who can replace a signer's public key can forge signatures under the replaced public key. We then make a suggestion to prevent the attacks.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.5
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• pp.1035-1045
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• 2018

Recently, with the development of IT technology, authentication methods of users using cloud services have been diversified. However, research on providing authentication information of a user using a cloud service securely according to authority has not been make until now. In this paper, we propose a key establishment protocol which can perform split authentication using secret key and access control key according to the role authority of user in Intra cloud environment. The proposed protocol generates the access control key and secret key of the user by using the attributes of the user and the generated random number($t_1$, $t_2$), and classifies the roles according to the user's authority after generating the key. Unnecessary operation processes can be reduced. As a result of the performance evaluation, the proposed protocol guarantees the security against various type of attacks that may occur in the cloud environment because the user is authenticated by dividing the access control key and secret key. The size of the ciphertext used to establish the key could be reduced by ${\sum}+1$ more than the existing protocol.