• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.4
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• pp.999-1007
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• 2018

To implement crowdsensing system in reality, trustiness between service provider server and user is necessary. Service provider server could manipulate the evaluation of sensing data to reduce incentive. Moreover, user could send a fake sensing data to get unjust incentive. In this paper, we adopt private blockchain on crowdsensing system, and thus paid incentives and sent data are unmodifiablely recorded. It makes server and users act as watcher of each others. Through adopting smart contract, our system automates sensing data evaluation and opens to users how it works. Finally, we show the feasibility of proposing system with performance evaluation and comparison with other systems.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.31 no.5
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• pp.863-874
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• 2021

Distributed key generation (DKG) with trustless setup is a cryptographic protocol that distributes Shamir secret shares of a private key to participants while keeping the actual private key hidden to the participants. Also, by extending it to a threshold signature protocol, digital signatures can be generated without construction of private keys. This paper proposes a recovery protocol maintaining trustless setup assumptions, in particular to the useful (1,3) share structure. The proposed protocol meets same levels of security requirements with DKG in terms of correctness and secrecy. The protocol can also enable delegation and revocation of digital sign rights for blockchain-based asset management.

• Journal of the Korea Society of Computer and Information
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• v.25 no.4
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• pp.71-77
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• 2020

Through the consensus algorithm, which is the core technology of the blockchain, the same data is accurately shared between connected nodes. The use of an appropriate consensus algorithm that considers the user and the usage environment ensures efficient maintenance of data integrity and accuracy. In this paper, we proposed a performance evaluation method for efficient selection of a consensus algorithm among authorized nodes considering the characteristics of a private blockchain platform, and applied the modified item to the existing published formula considering the number of authoritative connected nodes. Through this process, it was possible to simplify the consensus process considering the stability between nodes. The stability of the consensus process can be improved by selecting an appropriate consensus algorithm based on the proposed research.

• Asia pacific journal of information systems
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• v.30 no.1
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• pp.21-30
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• 2020

Bitcoin (BTC) is a type of cryptocurrency that supports transaction/payment of virtual money between BTC users without the presence of a central authority or any third party like bank. It uses some cryptographic techniques namely public- and private-keys, digital signature and cryptographic-hash functions, and they are used for making secure transactions and maintaining distributed public ledger called blockchain. In BTC system, each transaction signed by sender is broadcasted over the P2P (Peer-to-Peer) Bitcoin network and a set of such transactions collected over a period is hashed together with the previous block/other values to form a block known as candidate block, where the first block known as genesis-block was created independently. Before a candidate block to be the part of existing blockchain (chaining of blocks), a computation-intensive hard problem needs to be solved. A number of miners try to solve it and a winner earns some BTCs as inspiration. The miners have high computing and hardware resources, and they play key roles in BTC for blockchain formation. This paper mainly analyses the underlying cryptographic techniques, identifies some weaknesses and proposes their enhancements. For these, two modifications of BTC are suggested ― (i) All BTC users must use digital certificates for their authentication and (ii) Winning miner must give signature on the compressed data of a block for authentication of public blocks/blockchain.

• KIPS Transactions on Computer and Communication Systems
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• v.12 no.8
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• pp.253-262
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• 2023

E-voting is a concept that includes actions such as kiosk voting at a designated place and internet voting at an unspecified place, and has emerged to alleviate the problem of consuming a lot of resources and costs when conducting offline voting. Using E-voting has many advantages over existing voting systems, such as increased efficiency in voting and ballot counting, reduced costs, increased voting rate, and reduced errors. However, centralized E-voting has not received attention in public elections and voting on corporate agendas because the results of voting cannot be trusted due to concerns about data forgery and modulation and hacking by others. In order to solve this problem, recently, by designing an E-voting system using blockchain, research has been actively conducted to supplement concepts lacking in existing E-voting, such as increasing the reliability of voting information and securing transparency. In this paper, we proposed an electronic voting system that introduced hybrid blockchain that uses public and private blockchains in convergence. A hybrid blockchain can solve the problem of slow transaction processing speed, expensive fee by using a private blockchain, and can supplement for the lack of transparency and data integrity of transactions through a public blockchain. In addition, the proposed system is implemented as BaaS to ensure the ease of type conversion and scalability of blockchain and to provide powerful computing power. BaaS is an abbreviation of Blockchain as a Service, which is one of the cloud computing technologies and means a service that provides a blockchain platform ans software through the internet. In this paper, in order to evaluate the feasibility, the proposed system and domestic and foreign electronic voting-related studies are compared and analyzed in terms of blockchain type, anonymity, verification process, smart contract, performance, and scalability.

• Journal of Information Processing Systems
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• v.16 no.2
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• pp.421-434
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• 2020

The development of digital technology has changed the lives of many people in terms of the velocity and convenience of completing tasks. This technology has also been applied to the process of voting, yet electronic voting is seldom used. The existing electronic voting scheme operates by applying various encryption algorithms. This type of electronic voting can be problematic since the administrator is given full authority. The administrator cannot always be trusted, and the contents of the ballot could be forged or tampered by a single point of failure. To resolve these problems, researchers continue to apply blockchain technology to electronic voting. Blockchain technology provides reliability and data integrity because all untrusted network participants have the same data. In this paper, we propose an electronic voting system that secures reliability by applying blockchain technology to electronic voting and ensures secret voting.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.12
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• pp.1718-1721
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• 2020

This paper proposes a method to protect the copyright of creators' content shared through an online sharing platform in a legal battle. When creators upload their independent creation content to the online sharing platform, it automatically upload information necessary for copyright effect to this system. The data warehouse of this system is as a private blockchain for to ensure non-repudiation and transparency of the information. We present that the data warehouse is to build as Hyperledger Fabric in this paper. And We present the transaction data structure of the blockchain to prevent orphan works. We also dealt with how to build a website where users can conveniently check the data (copyright related information) of this blockchain.

• Smart Media Journal
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• v.9 no.1
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• pp.9-15
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• 2020

Recently there have been increasing attempts to apply blockchains to businesses and public institutions. Blockchain is a distributed shared ledger with excellent transparency and security of data and through consensus algorithm, the same data can be shared to all nodes in order. In this paper, Modified PBFT which does not modify the PBFT consensus algorithm is proposed. MPBFT is able to tolerate Byzantine faults on a private blockchain on an asynchronous network. Even with the increase of participating nodes, the network communication cost can be effectively maintained. Modified PBFT takes into account the characteristics of an asynchronous network environment where node-to-node trust is guaranteed. In response to the client's request, PBFT performed the entire participation broadcast several times, but Modified PBFT enabled consensus and authentication through the 2 / N leader. By applying the Modified PBFT consensus algorithm, the broadcast process can be simplified to maintain the minimum number of nodes for consensus and to efficiently manage network communication costs.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.19 no.5
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• pp.33-38
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• 2019

In this paper, we propose a new blockchain technology that could comply with GDPR. The proposed model can prevent illegal access by controlling access to the personal information according to a access policy. For example, it can control access to the information on a role-basis and information validation period. The core mechanism of the proposed model is to encrypt the personal information with public key which is associated with users attributes policy, and then decrypt it with a private key and users attributes based on a Attribute-based Encryption scheme. It can reduce a trusted third-part risk by replacing it with a number of nodes selected from the blockchain. And also the private key is generated in the form of one-time token to improve key management efficiency. We proved the feasibility by simulating the proposed model using the chaincode of the Hyperledger Fabric and evaluate the security.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.31 no.3
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• pp.341-351
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• 2021

Recently, user-driven privacy control technology, such as distributed ID management, has been gaining attention. However, the existing blockchain-based access control studies have not provided a sufficient level of privacy control method to users. This paper proposes a method that combines permissioned blockchain technology and a recent privacy control standard. To allow users to participate in privacy control, a token-based user access control service that conforms to the UMA2 standard was applied to the blockchain dApp. By combining the blockchain and UMA2, the proposed method provides a user-centered privacy control function that the existing blockchain could not provide. In addition, we solved the problem of privacy, security, and availability of entities, which are the disadvantages of UMA2.