• Journal of the Korea Society of Computer and Information
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• v.13 no.1
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• pp.161-167
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• 2008

As the authentication and the integrity methods based on the hash chain are popular, several certificate status validation methods based on the same function are proposd at the moment. In NOVOMODO, a CA generates and releases the hash value to each user. In Jianying Zhou's framework and Jong-Phil Yang's framework, a user generates and releases the hash value to verifier. Therefore, the CA loads are distributed to each user. However, these frameworks are based on the assumption that the CA's secret key is not lost or compromised and the certificates issued by the CA are error-free. Therefore, these frameworks are not suitable in real PKI environments. In this paper, as one hash value generated by CA is included in the user's certificate in addition, the certificate revocation published by CA using that value can be managed. The hash value included in user's certificate is the same for all users. The computation costs, the storage amounts and the release costs are small in the CA. And we modify the procedure for the signature and its validation in Jong-Phil Yang's framework. Our solution is more suitable than those frameworks in real PKI environments.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.8C
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• pp.633-641
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• 2008

Since WSNs encounter attacks, such as jamming or eavesdropping without physical access occurs, security is one of the important requirements for WSNs. The key pre-distribution scheme that was recently researched for advance of security in WSNs distributes the keys and probability with the use of q-composite random key pre-distribution method, but there is a high probability that no key shared between sensor nodes, and it takes a lot of time and energy to find out the shared key. Therefore, it is not suitable for WSNs. In order to enhance stability of a node that plays a role of gateway without depending on probabilistic key, this paper proposesa key pre-distribution scheme combined with random key pre-distribution scheme and double hash chain. Since the proposed scheme can maintain a small storage place and strong security strengths, it is more efficient than the existing schemes with the same security strengths. In addition, since it uses a small size of key generation key set, it can reduce a great deal of storage overhead.

• The Journal of the Korea institute of electronic communication sciences
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• v.8 no.4
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• pp.605-610
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• 2013

A cryptography for enforcing hierarchic groups in a system where hierarchy is represented by a partially ordered set was introduced by Akl et al. But the key generation algorithm of Akl et al. is infeasible when there is a large number of users. To overcome this shortage, in 1985, MacKinnon et al. proposed a paper containing a condition which prevents cooperative attacks and optimizes the assignment. In 2005, Kim et al. proposed the key management systems for using one-way hash function, RSA algorithm, poset dimension and Clifford semigroup in the context of modern cryptography, the key management system using Clifford semigroup of imaginary quadratic non-maximal orders. We, in this paper, show that Kim et al. cryptosystem is insecure in some reasons and propose a revised cryptosystem.

• Journal of the Korea Society of Computer and Information
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• v.21 no.9
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• pp.73-78
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• 2016

In 2014, Wuu et al. proposed a group key management scheme based on (2,2) secret sharing. They asserted that their scheme satisfies security requirements and mutual authentication. But this paper pointed out that their scheme does not satisfy mutual authentication and impersonating attack. In this paper, we describe the reasons and processes that a malicious group member can impersonate the Group Key Distributor. To fill the gaps, we discuss the problems, and propose an improved protocol.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.5
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• pp.1693-1701
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• 2010

In this paper, requirements of efficient group key creation in multiple hierarchy structure environment with clear distinction of hierarchical roles within organizations are explained and the method of creating a group key that satisfies such requirements is proposed. The proposed method creates the group key through logical sum operation of hierarchy identifier created using uni-directional hash chain and group identifier randomly created according to the access right. The problem of excessive possession of key information by upper group users in the existing static group key creation technique was resolved. At the same time, lower group users were prevented from deducing key information of upper group users. In addition, as a result of comparative analysis performed with an experiment on existing super group key creation technique and multiple hierarchy group key method, the proposed method was found to be equivalent or superior to existing method in terms of various items including the total number of keys created, the number of keys possessed by users, the number of keys used for encoding and decoding of information, and expandability of keys.

• Phonetics and Speech Sciences
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• v.4 no.1
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• pp.77-87
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• 2012

Interest in music recognition has been growing dramatically after NHN and Daum released their mobile applications for music recognition in 2010. Methods in music recognition based on audio analysis fall into two categories: music recognition using audio fingerprint and Query-by-Singing/Humming (QBSH). While music recognition using audio fingerprint receives music as its input, QBSH involves taking a user-hummed melody. In this paper, research trends are described for music recognition using audio fingerprint, focusing on two methods: one based on fingerprint generation using energy difference between consecutive bands and the other based on hash key generation between peak points. Details presented in the representative papers of each method are introduced.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.12
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• pp.6161-6176
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• 2018

Pseudorandom numbers are useful in cryptographic operations for using as nonce, initial vector, secret key, etc. Security of the cryptosystem relies on the secret key parameters, so a good pseudorandom number is needed. In this paper, we have proposed a new approach for generation of pseudorandom number. This method uses the three dimensional combinational puzzle Rubik Cube for generation of random numbers. The number of possible combinations of the cube approximates to 43 quintillion. The large possible combination of the cube increases the complexity of brute force attack on the generator. The generator uses cryptographic hash function. Chaotic map is being employed for increasing random behavior. The pseudorandom sequence generated can be used for cryptographic applications. The generated sequences are tested for randomness using NIST Statistical Test Suite and other testing methods. The result of the tests and analysis proves that the generated sequences are random.

• Proceedings of the Korea Information Processing Society Conference
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• 2013.11a
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• pp.277-279
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• 2013

스크램블링(Scrambling)은 네트워크에서 영상을 전송할 때 보안을 위해 데이터를 특정한 키에 의해 암호화 하여 전송함으로써, 수신자만이 원본 영상으로 복원할 수 있도록 하는 기술이다. 스크램블링은 전송에서 TDES, AES 뿐만아닌 SEED, AIRA의 암호화 알고리즘을 사용한다. 이 경우 암복호화에 많은 시간이 소요되어 실시간 전송환경에서는 전송속도 저하에 따른 QoS 문제가 발생한다. 이와 같은 문제를 해결하기 위해 기존 연구에서는 속도가 빠른 해쉬 함수를 이용하여 스크램블링 암호화 하는 기법을 제안하였다. 하지만 원본 이미지의 일부가 노출될 경우 이후 원본프레임이 노출될 수 있는 문제점을 가지고 있다. 본 논문에서는 이러한 문제점을 방지하기 위해 다중 해쉬 키 프레임을 이용한 Multi Hash key Frame based Scrambling Encryption 알고리즘을 제안한다. 성능평가에서는 제안하는 스크램블링 기법에 대한 암복호화 비용과 성능을 측정하였으며, 기존기법과 비교하였을 때 원본 노출로 인한 대입공격 취약성 부분을 기존 해쉬 함수의 보안 안전성만큼 향상시켰다.

• Proceedings of the Korea Information Processing Society Conference
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• 2003.11c
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• pp.1367-1370
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• 2003

본 논문에서는 인덱스가 존재하지 않는 두 개의 입력 릴레이션에 대해서도 최적의 조인 연산을 수행할 수 있는 공간 해쉬 조인 알고리즘을 제안한다. 인덱스가 존재하지 않는 릴레이션의 처리에 사용하는 기존의 공간 해쉬 조인(SHJ: Spatial Hash Join)과 Scalable Sweeping-Rased Spatial Join(SSSJ) 알고리즘을 결합하여 SHJ 알고리즘의 단점으로 지적되고 있는 편향된(skewed) 데이터에 대한 조인 연산의 성능저하 문제를 개선한 수 있는 Spatial Hash Strip Join(SHSJ) 알고리즘을 제안한다. SHJ에서 편향된 데이터의 경우 해쉬 버킷의 오버플로우 처리를 위해 버킷 재분할 방법을 사용하고 있는데 반하여 본 논문에서 제안한 SHSJ 알괴리즘에서는 버킷의 재분할 처리 대신에 버킷에 데이터를 삽입하고, 조인 연산과정에서 오버플로우가 발생한 버킷에 대하여 SSSJ 알고리즘을 사용함으로써 편향된 입력 릴레이션의 처리 성능을 제고시킬 수 있도록 한다.

• Journal of KIISE
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• v.42 no.9
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• pp.1100-1108
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• 2015

Classes.dex, which is the executable file for android operation system, has Java bite code format, so that anyone can analyze and modify its source codes by using reverse engineering. Due to this characteristic, many android applications using classes.dex as executable file have been illegally copied and distributed, causing damage to the developers and software industry. To tackle such ill-intended behavior, this paper proposes a technique to encrypt classes.dex file using an AES(Advanced Encryption Standard) encryption algorithm and decrypts the applications encrypted in such a manner in order to prevent reverse engineering of the applications. To reinforce the file against reverse engineering attack, hash values that are obtained from substituting a hash equation through the combination of salt values, are used for the keys for encrypting and decrypting classes.dex. The experiments demonstrated that the proposed technique is effective in preventing the illegal duplication of classes.dex-based android applications and reverse engineering attack. As a result, the proposed technique can protect the source of an application and also prevent the spreading of malicious codes due to repackaging attack.