• 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.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.6
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• pp.981-997
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• 2020

Blockchain technology can provide a high level security based on a decentralized distributed ledger and consensus-based structure. In order to increase the utilization of blockchain technology, it is necessary to find a way to use it in fields that require personal data processing such as health care and e-commerce. To achieve this goal, the blockchain based system should be able to comply with data privacy regulations represented by European Union(EU)'s GDPR(General Data Protection Regulation). However, because of the properties of the blockchain like the immutability and decentralized recorded data, it is difficult to technically implement the requirements of the existing privacy regulations on the blockchain. In this paper, we propose a multi-chain based access control system that can guarantee the rights of the personal data subject required by GDPR by utilizing Chameleon Hash and Attribute Based Encryption (ABE). Finally, we will show through security analysis that our system can handle personal data while maintaining confidentiality and integrity.

• Proceedings of the Korea Information Processing Society Conference
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• 2013.05a
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• pp.648-651
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• 2013

클라우드 시스템에서는 데이터 소유자가 아닌 클라우드 서비스 제공자가 각 개인의 데이터에 대한 저장과 관리를 책임진다. 따라서 클라우드 서버 상의 사용자 데이터에 대한 보안을 보장해 주는 것이 가장 중요한 이슈이다. 데이터 보안 문제는 안전하고 효율적인 접근제어 기술을 통해 해결 할 수 있다. 기존 시스템에서 많이 이용되고 있는 RBAC(Role based access control)은 접근제어의 형태가 주로 수직적이고, 데이터 접근가능 여부를 역할이라는 고정적인 값에 따라 결정하기 때문에 동적인 클라우드 환경에 적합하지 않다. 반면 HASBE(Hierarchical attribute set based encryption) 모델은 ABAC(Attribute based access control)를 통해 유연하고 탄력적인 접근제어를 제공한다. 또한 HASBE 는 인가자(Authority)와 사용자의 관계 모델이 계층적인 구조를 갖고 있기 때문에 큰 조직에서 수많은 사용자들의 데이터 관리와 키 분배를 좀더 효율적으로 할 수 있다. 본 논문에서는 위의 계층적인 모델에서 더 나아가서, 실제 클라우드 환경에서 데이터가 가질 수 있는 복잡한 속성과 인가자의 관계를 고려해 다중 인가자의 개념이 더해진 모델을 제안한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.5
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• pp.1634-1652
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• 2022

Due to the increasing need for data sharing in the age of big data, how to achieve data access control and implement user permission revocation in the blockchain environment becomes an urgent problem. To solve the above problems, we propose a novel blockchain-based data sharing scheme (BDSS) with fine-grained access control and permission revocation in this paper, which regards the medical environment as the application scenario. In this scheme, we separate the public part and private part of the electronic medical record (EMR). Then, we use symmetric searchable encryption (SSE) technology to encrypt these two parts separately, and use attribute-based encryption (ABE) technology to encrypt symmetric keys which used in SSE technology separately. This guarantees better fine-grained access control and makes patients to share data at ease. In addition, we design a mechanism for EMR permission grant and revocation so that hospital can verify attribute set to determine whether to grant and revoke access permission through blockchain, so it is no longer necessary for ciphertext re-encryption and key update. Finally, security analysis, security proof and performance evaluation demonstrate that the proposed scheme is safe and effective in practical applications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.4
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• pp.1516-1528
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• 2015

We introduce attribute set based signature (ASBS), a new cryptographic primitive which organizes user attributes into a recursive set based structure such that dynamic constraints can be imposed on how those attributes may be combined to satisfy a signing policy. Compared with attribute based signature (ABS), ASBS is more flexible and efficient in managing user attributes and specifying signing policies. We present a practical construction of ASBS and prove its security in the standard model under three subgroup decision related assumptions. Its efficiency is comparable to that of the most efficient ABS scheme.

• IEMEK Journal of Embedded Systems and Applications
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• v.7 no.1
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• pp.53-59
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• 2012

Recently, LEE et al. proposed an attribute-based authenticated key agreement protocol over home network, which aimed to support authentication and key agreement between user and home server. However, if the home server is attacked in the protocol, the effects are influenced to the overall home network components severly. Thereby, this paper proposes a new ticket-based authentication protocol using user attributes between user and home devices to solve the problem. The proposed protocol supports the various levels of security to user by diversifying the network accessibility depending on user attribute. Thereby, the protocol could support more secure home network services.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.5
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• pp.2768-2780
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• 2019

Ciphertext-policy attribute-based encryption (CP-ABE) is one of the practical technologies to share data over cloud since it can protect data confidentiality and support fine-grained access control on the encrypted data. However, most of the previous schemes only focus on data confidentiality without considering data receiver privacy preserving. Recently, Li et al.(in TIIS, 10(7), 2016.7) proposed a CP-ABE with hidden access policy and testing, where they declare their scheme achieves privacy preserving for the encryptor and decryptor, and also has high decryption efficiency. Unfortunately, in this paper, we show that their scheme fails to achieve hidden access policy at first. It means that any adversary can obtain access policy information by a simple decisional Diffie-Hellman test (DDH-test) attack. Then we give a method to overcome this shortcoming. Security and performance analyses show that the proposed scheme not only achieves the privacy protection for users, but also has higher efficiency than the original one.

• ETRI Journal
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• v.41 no.4
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• pp.465-472
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• 2019

The major challenge in wireless body area networks (WBAN) is setting up a protected communication between data consumers and a body area network controller while meeting the security and privacy requirements. This paper proposes efficient and secure data communication in WBANs using a Twofish symmetric algorithm and ciphertext-policy attribute-based encryption with constant size ciphertext; in addition, the proposed scheme incorporates policy updating to update access policies. To the best of the author's knowledge, policy updating in WBAN has not been studied in earlier works. The proposed scheme is evaluated in terms of message size, energy consumption, and computation cost, and the results are compared with those of existing schemes. The result shows that the proposed method can achieve higher efficiency than conventional methods.

• International Journal of Advanced Culture Technology
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• v.10 no.2
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• pp.225-232
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• 2022

When we drive a vehicle in an IoT environment, there is a problem in that information of car users is collected without permission. The security measures used in the existing wired network environment cannot solve the security problem of cars running in the Internet of Things environment. Information should only be shared with entities that have been given permission to use it. In this paper, we intend to propose a method to prevent the illegal use of vehicle information. The method we propose is to use attribute-based encryption and dynamic threshold encryption. Real-time processing technology and cooperative technology are required to implement our proposed method. That's why we use fog computing's proxy servers to build smart gateways in cars. Proxy servers can collect information in real time and then process large amounts of computation. The performance of our proposed algorithm and system was verified by simulating it using NS2.

• Journal of the Korea Society of Computer and Information
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• v.18 no.9
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• pp.79-89
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• 2013

Recently, the need for outsourcing sensitive data has grown due to the wide spreading of cost-effective and flexible cloud service. However, there is a fundamental concern in using such service since users have to trust external servers. Therefore, searchable encryption can be a very valuable tool to meet the security requirements of data outsourcing. However, most of work on searchable encryption focus only on privacy preserving search function and relatively lacks research on encryption mechanism used to actually encrypt data. Without a suitable latter mechanism, searchable encryption cannot be deployed in real world cloud services. In this paper, we analyze previously used and possible data encryption mechanisms for multi-user searchable encryption system and discuss their pros and cons. Our results show that readily available tools such as broadcast encryption, attribute-based encryption, and proxy re-encryption do not provide suitable solutions. The main problem with existing tools is that they may require separate fully trusted servers and the difficulty in preventing collusion attacks between outsiders and semi-trusted servers.