• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권8호
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• pp.2010-2026
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• 2013

The combination of biometrics and cryptography gains a lot of attention from both academic and industry community. The noisy biometric measurement makes traditional identity based cryptosystems unusable. Also the extraction of key from biometric information is difficult. In this paper, we propose an efficient biometric identity based signature scheme (Bio-IBS) that makes use of fuzzy extractor to generate the key from a biometric data of user. The component fuzzy extraction is based on error correction code. We also prove that the security of suggested scheme is reduced to computational Diffie-Hellman (CDH) assumption instead of other strong assumptions. Meanwhile, the comparison with existing schemes shows that efficiency of the system is enhanced.

• 정보보호학회논문지
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• 제8권1호
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• pp.65-70
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• 1998

K. Nyberg and L.R. Knudsen showed a prototype of a DES-like cipher$^{[1]}$ which has a provable security against differential cryptanalysis. But in the last year, at FSE'97 T. Jakobsen ane L.R.Knudsen broked it by using higher order differential attack and interpolation attack$^{[2]}$ . Furthermore the cipher was just a theoretically proposed one to demonstrate how to construct a cipher which is procably secure against differential cryptanalysis$^{[3]}$ and it was suspected to have a large complexity for its implementation.Inthis paper the two improved results for the dfficidnt hardware and software implementation.

• 정보보호학회논문지
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• 제11권3호
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• pp.13-22
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• 2001

유사난수성(pseudorandomness)은 진정한 난수성(true randomness)을 대신하여 실제 상황에서 사용되는 개념으로서 현대 암호학의 중요한 한 분야이다. 본 논문은 땋임이론(braid theory)에서의 어려운 문제 중 하나인 공액문제(conjugacy problem)에 기반하여 단순하고 실용적인 유사난수 생성기(pseudorandom generator)를 설계한다. 그리고 그 생성기가 암호 학적으로 공액문제를 변형한 또 하나의 어려운 문제 만큼 안전함을 증명한다.

• 정보처리학회논문지C
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• 제9C권6호
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• pp.809-816
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• 2002

신뢰성 있고 효율적인 정보보호를 위한 정보보호 시스템은 안전성이 입증된 암호기술을 사용하여 기밀성과 인증성을 보장받아야 한다. 기본적으로 정보보호시스템이 갖추어야 할 요소인 난수 발생기는 수학적인 논리에 의하여 안전성과 난수성이 증명 가능하도록 설계되는 것이고, 암호알고리즘의 초기 변수값, 키 등을 생성하는데 이용되며 난수 발생기의 안전성이 전체 정보보호시스템의 안전성에 영향을 준다. 본 논문에서는 블록 암호 알고리즘을 기반으로 하는 의사난수 발생기를 설계하여 제안하고, 그의 안전성에 대해서 연구한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권2호
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• pp.1043-1063
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• 2019

With delegating proxy to process data before outsourcing, data owners in restricted access could enjoy flexible and powerful cloud storage service for productivity, but still confront with data integrity breach. Identity-based data auditing as a critical technology, could address this security concern efficiently and eliminate complicated owners' public key certificates management issue. Recently, Yu et al. proposed an Identity-Based Public Auditing for Dynamic Outsourced Data with Proxy Processing (https://doi.org/10.3837/tiis.2017.10.019). It aims to offer identity-based, privacy-preserving and batch auditing for multiple owners' data on different clouds, while allowing proxy processing. In this article, we first demonstrate this scheme is insecure in the sense that malicious cloud could pass integrity auditing without original data. Additionally, clouds and owners are able to recover proxy's private key and thus impersonate it to forge tags for any data. Secondly, we propose an improved scheme with provable security in the random oracle model, to achieve desirable secure identity based privacy-preserving batch public auditing with proxy processing. Thirdly, based on theoretical analysis and performance simulation, our scheme shows better efficiency over existing identity-based auditing scheme with proxy processing on single owner and single cloud effort, which will benefit secure big data storage if extrapolating in real application.

• 정보보호학회논문지
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• 제13권5호
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• pp.147-157
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• 2003

보통의 공개 열쇠 암호 시스템에서 비밀 열쇠가 노출되면 그 비밀 열쇠로 생성된 암호문이나 서명 등의 해독, 위조가 가능하다. 이런 비밀 열쇠 노출의 위험성은 상대적으로 물리적인 보안이 이루어지지 않은 핸드폰, 스마트카드 등과 같은 열쇠 저장 장치에 가장 큰 위협이 되고 있다. 따라서 현재 비밀 정보가 노출되어도 과거의 비밀 열쇠에 의해 생성된 정보는 안전하게 유지되어야 한다는 전방향 안전성 개념(forward security)은 열쇠교환 프로토콜 및 여러 암호 요소(primitive)들이 필수적으로 만족해야 할 조건이다. 본 논문에서는 Cap Diffie-Hellman 군을 사용하여 전방향 안전성을 만족하는 서명 기법을 제안한다. 제안된 서명 기법은 계산적 Diffie-Hellman 문제의 어려움을 기반으로 선택 메시지 공격 모델에 대한 증명가능한 안전성을 가진다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제8권11호
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• pp.4226-4241
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• 2014

Cloud storage provides an easy, cost-effective and reliable way of data management for users without the burden of local data storage and maintenance. Whereas, this new paradigm poses many challenges on integrity and privacy of users' data, since users losing grip on their data after outsourcing the data to the cloud server. In order to address these problems, recently, Worku et al. have proposed an efficient privacy-preserving public auditing scheme for cloud storage. However, in this paper, we point out the security flaw existing in the scheme. An adversary, who is on-line and active, is capable of modifying the outsourced data arbitrarily and avoiding the detection by exploiting the security flaw. To fix this security flaw, we further propose a secure and efficient privacy-preserving public auditing scheme, which makes up the security flaw of Worku et al.'s scheme while retaining all the features. Finally, we give a formal security proof and the performance analysis, they show the proposed scheme has much more advantages over the Worku et al.'s scheme.

• 정보보호학회논문지
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• 제17권3호
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• pp.35-42
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• 2007

본 논문은 Even-Mansour 암호에 대해 안전성 약화 없이 키 사이즈를 줄이는 방법에 대해 다룬다. Even과 Mansour는 랜덤 순열 모델에서 랜덤 순열 P와 두 개의 키를 이용하여 평문 M을 암호화하는 기법($C=k_2\bigoplus P(M\bigoplus k_1)$)을 제안하였다. ASIACRYPT 2004에서 Gentry와 Ramzen은 4 라운드의 Feistel 구조를 이용하여 Even-Mansour 모델의 랜덤 순열을 랜덤 함수로 대치한 새로운 모델을 제안하고 안전성을 증명하였다. 본 논문에서는 Gentry-Ramzen 모델에 필요한 키 사이를 반으로 줄이는 방법을 살펴보고 제안한 방법에 대한 안전성을 랜덤 함수 모델에서 증명한다.

• Journal of Communications and Networks
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• 제4권2호
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• pp.81-89
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• 2002

In this paper, we design and implement an efficient fair off-line electronic cash system based on Elliptic Curve Discrete Logarithm Problem (ECDLP), in which the anonymity of coins is revocable by a trustee in case of dispute. To achieve this, we employ the Petersen and Poupard s electronic cash system [1] and extend it by using an elliptic curve over the finite field GF($2^n$). This naturally reduces message size by 85% compared with the original scheme and makes a smart card to store coins easily. Furthermore, we use the Baek et al. s provably secure public key encryption scheme [2] to improve the security of electronic cash system. As an extension, we propose a method to add atomicity into new electronic cash system. To the best of our knowledge, this is the first result to implement a fair off-line electronic cash system based on ECDLP with provable security.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제7권5호
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• pp.1343-1356
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• 2013

Cloud computing has emerged as perhaps the hottest development in information technology at present. This new computing technology requires that the users ensure that their infrastructure is safety and that their data and applications are protected. In addition, the customer must ensure that the provider has taken the proper security measures to protect their information. In order to achieve fine-grained and flexible access control for cloud computing, a new construction of hierarchical attribute-based encryption(HABE) with Ciphertext-Policy is proposed in this paper. The proposed scheme inherits flexibility and delegation of hierarchical identity-based cryptography, and achieves scalability due to the hierarchical structure. The new scheme has constant size ciphertexts since it consists of two group elements. In addition, the security of the new construction is achieved in the standard model which avoids the potential defects in the existing works. Under the decision bilinear Diffie-Hellman exponent assumption, the proposed scheme is provable security against Chosen-plaintext Attack(CPA). Furthermore, we also show the proposed scheme can be transferred to a CCA(Chosen-ciphertext Attack) secure scheme.