• Journal of Korea Multimedia Society
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• v.3 no.6
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• pp.617-624
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• 2000

We introduce the concept of a Identity Escrow Scheme, an application of key escrow ideas to solve the problem of authentication. In the Identity Escrow Scheme, the User escrows a own real identity to the Issuer and receives a Authentication Information. In authentication step, between the User to the Service Provider, the User only gives a Authentication Information to the Service Provider. Therefore, the Service Provider don't know a real identity of user's. However, when the User does unlawful actions, the Lawful Agent is called by the Service Provider, and his anonymity is revoked by cooperation of the Issuer and the Lawful Agent. We propose new Identity Escrow Schemes and analyze these.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.12
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• pp.3352-3365
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• 2012

Group key agreement (GKA) is a cryptographic primitive allowing two or more users to negotiate a shared session key over public networks. Wu et al. recently introduced the concept of asymmetric GKA that allows a group of users to negotiate a common public key, while each user only needs to hold his/her respective private key. However, Wu et al.'s protocol can not resist active attacks, such as fabrication. To solve this problem, Zhang et al. proposed an authenticated asymmetric GKA protocol, where each user is authenticated during the negotiation process, so it can resist active attacks. Whereas, Zhang et al.'s protocol needs a partially trusted certificate authority to issue certificates, which brings a heavy certificate management burden. To eliminate such cost, Zhang et al. constructed another protocol in identity-based setting. Unfortunately, it suffers from the so-called key escrow problem. In this paper, we propose the certificateless authenticated asymmetric group key agreement protocol which does not have certificate management burden and key escrow problem. Besides, our protocol achieves known-key security, unknown key-share security, key-compromise impersonation security, and key control security. Our simulation based on the pairing-based cryptography (PBC) library shows that this protocol is efficient and practical.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.12
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• pp.1863-1871
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• 2022

In the era of Fourth Industrial Revolution, secure networking technology is playing an essential role in the defense weapon systems. Encryption technology is used for information security. The safety of cryptographic technology, according to Kerchoff's principles, is based on secure key management of cryptographic technology, not on cryptographic algorithms. However, traditional centralized key management is one of the problematic issues in battlefield environments since the frequent movement of the forces and the time-varying quality of tactical networks. Alternatively, the system resources of each node used in the IoBT(Internet of Battlefield Things) environment are limited in size, capacity, and performance, so a lightweight key management system with less computation and complexity is needed than a conventional key management algorithm. This paper proposes a novel key escrow scheme in a lightweight manner for the IoBT environment. The safety and performance of the proposed technique are verified through numerical analysis and simulations.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38C no.7
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• pp.595-604
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• 2013

Devising a secure authenticated key agreement (AKA) protocol for two entities communicating over an open network is a matter of current research. McCullagh et al. proposed a new two-party identity-based AKA protocol supporting both key escrow and key escrow-less property instantiated by either in a single domain or over two distinct domains. In this paper, we show that their protocol over two distinct domains suffers from masquerading attack and therefore does not satisfy the claimed security. The attack is made possible due to the lack of sufficient authentication of entity and integrity assurance in the protocol. We then propose an efficient verifiable key agreement protocol by including signature primitive in the authentication procedure to solve the problem of McCullagh et al.'s protocol.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.5
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• pp.165-176
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• 2004

Al-Riyami and Paterson$^{[1]}$ suggested the new public key paradigm which is called the certificateless public key system. This system takes the advantages of both traditional PKC and ID-based PKC. It does not require the use of certificates of the public key and does not have the key escrow problem caused from the ID-based cryptosystem. In this paper, we propose an efficient certificateless public key encryption scheme which satisfies mutual authentication. The security of our protocol is based on the hardness of two problems; the computational Diffie-Hellman problem(CDHP) and the bilinear Diffie-Hellman problem(BDHP). We also give a formal security model for both confidentiality and unforgeability, and then show that our scheme is probably secure in the random oracle model.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.10 no.1
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• pp.99-110
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• 2000

암호 시스템에서 가장 중요한 정보는 키 정보이다. 키가 손상되거나 유실되면 모든정보가 유실되기 때문이다. 키 위탁 시스템이란 유사시의 상황에 대비해서 키를 특정한 위탁기관에 위탁함으로써 정보를 암호의 오용이나 키의 분실로부터 보호 할 수 있는 시스템이다. 키 위탁 시스템은 유사시에 확실하게 키를 복원할 수 있어야 하며, 동시에 복구 정보의 안전한 보관이 이루어져야 한다. 그리고 위탁 시스템으로 인해 사생활이 침해되지 않는 것 또한 중요하다. 이러한 요구사항들은 서로 상충되는 점이 있기 때문에 모든 요구사항을 만족시키는 키 위탁 시스템을 설계하기는 매우 어렵다. 본 논문에서는 키 위탁 시스템 설계시에 고려해야 할 요소를 도출하고, 키 위탁 시스템 설계 및 분석을 위한 모델을 제안한다. 이 모델은 정의된 요구사항을 만족시키는 키 복구 시스템을 설계할 때 유용하게 사용될 수 있으며, 이미 제안된 키 복구 시스템을 분석하는 도구로 활용될 수 있다.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.12 no.1
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• pp.11-20
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• 2002

In 1998, A. Young and M. Yung proposed the auto-recovery auto-certificate cryptosystem in public key infrastructure. We propose the new recoverable cryptosystem in public key infrastructure which is designed with the concept of A. Young et al's auto-recovery auto-certificate cryptosystem. It has the private/public key pairs of the user and the master private/public key pairs of the escrow authority. It is based on RSA cryptosystem and has efficiency and security.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.4
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• pp.1832-1853
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• 2018

The personal health record (PHR) system is a promising application that provides precise information and customized services for health care. To flexibly protect sensitive data, attribute-based encryption has been widely applied for PHR access control. However, escrow, exposure and abuse of private keys still hinder its practical application in the PHR system. In this paper, we propose a coordinated ciphertext policy attribute-based access control with user accountability (CCP-ABAC-UA) for the PHR system. Its coordinated mechanism not only effectively prevents the escrow and exposure of private keys but also accurately detects whether key abuse is taking place and identifies the traitor. We claim that CCP-ABAC-UA is a user-side lightweight scheme. Especially for PHR receivers, no bilinear pairing computation is needed to access health records, so the practical mobile PHR system can be realized. By introducing a novel provably secure construction, we prove that it is secure against selectively chosen plaintext attacks. The analysis indicates that CCP-ABAC-UA achieves better performance in terms of security and user-side computational efficiency for a PHR system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.6
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• pp.1109-1122
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• 2016

Certificateless public key cryptography is a technique that can solve the certificate management problem of a public key cryptosystem and clear the key escrow issue of ID-based cryptography using the public key in user ID. Although the studies were actively in progress, many existing schemes have been designed without taking into account the safety of the secret value with the decryption key exposure attacks. If previous secret values and decryption keys are exposed after replacing public key, a valid private key can be calculated by obtaining the partial private key corresponding to user's ID. In this paper, we propose a new security model which ensures the security against the key exposure attacks and show that several certificateless public key encryption schemes are insecure in the proposed security model. In addition, we design a certificateless public key encryption scheme to be secure in the proposed security model and prove it based on the DBDH(Decisional Bilinear Diffie-Hellman) assumption.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.46 no.1
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• pp.20-34
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• 2009

We newly propose a multiple and unlinkable identity-based public key encryption scheme which allows the use of a various number of identity-based public keys in different groups or applications while keeping a single decryption key so that the decryption key can decrypt every ciphertexts encrypted with those public keys. Also our scheme removes the use of certificates as well as the key escrow problem so it is functional and practical. Since our public keys are unlinkable, the user's privacy can be protected from attackers who collect and trace the user information and behavior using the known public keys. Furthermore, we suggest a decryption key renewal protocol to strengthen the security of the single decryption key. Finally, we prove the security of our scheme against the adaptive chosen-ciphertext attack under the random oracle model.