• Journal of the military operations research society of Korea
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• v.26 no.1
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• pp.115-124
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• 2000

In this paper, we are introduced a certification system for open network environment. The Kerberos which was developed by MIT uses a secret key cryptosystem for authentication. It is secure and efficient for closed network users to authenticate each others. However, the kerberos has a disadvantage of managing a lot of secret keys for In this paper, we are introduced a certification system for open network environment. users in the open network environment. This paper suggests a method that uses X.509 to provide public keys with certification to Kerberos users for authentication in the X.500 directory standard. And we also suggest the smartcard as data storage device to enhance the security and availability.

• The KIPS Transactions:PartC
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• v.10C no.6
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• pp.763-768
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• 2003

In this paper, we propose a S/KEY based authentication protocol using smart cards to address the vulnerebilities of both the S/KEY authentication protocol and the secure one-time password protpcol which YEH, SHEN and HWANG proposed [1]. Because out protpcel is based on public key, it can authenticate the server and distribute a session key without any pre-shared secret. Also, it can prevent off-line dictionary attacks by using the randomly generated user is stored in the users smart card. More importantly, it can truly achieve the strength of the S/KEY scheme that no secret information need be stored on the server.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.4
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• pp.822-839
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• 2011

Group key agreement protocols derive a shared secret key for a group of users to ensure data confidentiality or/and integrity among the users in the subsequent communications. In this paper, we inspect two group key agreement schemes which have been proposed by Shi et al. and Zheng et al. in 2005 and 2007 respectively. Although both schemes were claimed to be secure in a heuristic way, we reveal several flaws using the Bellare-Rogaway security model extended to multi-party setting by Bresson et al. These flaws are found to be originated from inappropriate selection of key derivation function, inadvertent exclusion of partners' identities from the protocol specification and insufficient consideration in preserving known temporary information security and key freshness properties. Furthermore, we suggest and discuss proper countermeasures to address such flaws.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.5
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• pp.1035-1045
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• 2018

Recently, with the development of IT technology, authentication methods of users using cloud services have been diversified. However, research on providing authentication information of a user using a cloud service securely according to authority has not been make until now. In this paper, we propose a key establishment protocol which can perform split authentication using secret key and access control key according to the role authority of user in Intra cloud environment. The proposed protocol generates the access control key and secret key of the user by using the attributes of the user and the generated random number($t_1$, $t_2$), and classifies the roles according to the user's authority after generating the key. Unnecessary operation processes can be reduced. As a result of the performance evaluation, the proposed protocol guarantees the security against various type of attacks that may occur in the cloud environment because the user is authenticated by dividing the access control key and secret key. The size of the ciphertext used to establish the key could be reduced by ${\sum}+1$ more than the existing protocol.

• Korean Journal of Computational Design and Engineering
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• v.12 no.2
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• pp.95-100
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• 2007

Virtual Reality(VR) data in VR environments like Manufacturing industries are often created jointly by many creators. It is then necessary to provide protection of the joint-creatorship and the creatorship of each participating creator. This paper proposes Multiple Digital Watermarking Framework(MDWF) to solve the problem of joint-creatorship. The proposed framework, MDWF, makes use of 3D private watermarking technology and a novel key sharing protocol for joint-creatorship verification. MDWF embeds 3D private multiple watermarks for the creatorship of each participating creators in a non-overlapping manner during the creation process. After key agreement of all private keys, MDWF embeds an additional 3D private watermark for the joint-creatorship. Therefore MDWF successfully handles the creatorship dispute among creators. That is, each participation creator can prove his/her partial creatorship as well as joint-creatorship by MDWF. In addition, MDWF can solve the collusion problems because shared secret key(SSK) can be made by every users.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.2
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• pp.49-55
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• 2004

We propose a new authenticated quantum key distribution protocol. Using Greenberger-Home-Zeilinger(GHZ) state, the users of our protocol can authenticate each other and share a secret key. In our protocol, the shared key is not revealed to the honest arbitrator, which Provides the additional secrecy. Our Protocol not only guarantees secrecy as the other quantum key distribution protocols, but also the users authenticates each other. In practice, our new protocol can be easily implemented because it only uses basic quantum operations.

• Journal of the Korea Society of Computer and Information
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• v.16 no.2
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• pp.173-181
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• 2011

User authentication and key exchange protocols are the most important cryptographic applications. For user authentication, most protocols are based on the users' secret passwords. However, protocols based on the users' secret passwords are vulnerable to the password guessing attack. In 1992, Bellovin and Merritt proposed an EKE(Encrypted Key Exchange) protocol for user authentication and key exchage that is secure against password guessing attack. After that, many enhanced and secure EKE protocols are proposed so far. In 2006, Lo pointed out that Yeh et al.'s password-based authenticated key exchange protocol has a security weakness and proposed an improved protocol. However, Cao and Lin showed that his protocol is also vulnerable to off-line password guessing attack. In this paper, we show his protocol is vulnerable to on-line password guessing attack using new attack method, and propose an improvement of password authenticated key exchange protocol for imbalanced wireless networks secure against password guessing attack.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.15 no.2
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• pp.73-80
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• 2005

We propose a Quantum Authentication and Key distribution protocol based on one-time n using one-way Hash function. The designated users can authenticate each other and the arbitrator using their one-time ID and distribute a quantum secret key using remained GHZ states after authentication procedure. Though the help of the arbitrator is needed in the process of authentication and key distribution, our protocol prevents the arbitrator from finding out the shared secret key even if the arbitrator becomes an active attacker. Unconditional security can be proved in our protocol as the other QKD protocols.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.7
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• pp.3339-3352
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• 2016

In ciphertext-policy attribute-based encryption (CP-ABE) scheme, a user's secret key is associated with a set of attributes, and the ciphertext is associated with an access policy. The user can decrypt the ciphertext if and only if the attribute set of his secret key satisfies the access policy specified in the ciphertext. In the present schemes, access policy is sent to the decryptor along with the ciphertext, which means that the privacy of the encryptor is revealed. In order to solve such problem, we propose a CP-ABE scheme with hidden access policy, which is able to preserve the privacy of the encryptor and decryptor. And what's more in the present schemes, the users need to do excessive calculation for decryption to check whether their attributes match the access policy specified in the ciphertext or not, which makes the users do useless computation if the attributes don't match the hidden access policy. In order to solve efficiency issue, our scheme adds a testing phase to avoid the unnecessary operation above before decryption. The computation cost for the testing phase is much less than the decryption computation so that the efficiency in our scheme is improved. Meanwhile, our new scheme is proved to be selectively secure against chosen-plaintext attack under DDH assumption.

• Journal of Korea Society of Digital Industry and Information Management
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• v.4 no.2
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• pp.21-28
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• 2008

There are some problems on the system that uses a password comprising a digital signature to identify the secret key owner under the public key infrastructure. For example, the password can be difficult to remember or easy to be disclosure, and users should make more complex password to protect it. A number of studies have been proceeded in order to overcome these defects using the fingerprint identification technologies, but they need to change the current standard of public key infrastructure. On the suggested private key escrow system, the private key can be withdrawn only through the enrollment and identification of a fingerprint template after it is saved to a reliable third system. Therefore, this new private key escrow system can remove previous inconveniences of managingthe private key on current public key infrastructure, and it exhibited superior results in terms of the evaluation items when compared with the integrated method of the existing fingerprint identification and public key infrastructure.