• Journal of Broadcast Engineering
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• v.13 no.1
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• pp.53-61
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• 2008

Public Key Broadcast Encryption (PKBE) allows a sender to distribute a message to a changing set of users over an insecure channel. PKBE schemes should be able to dynamically exclude (i.e., revoke) a certain subset of users from decrypting a ciphertext, so that only remaining users can decrypt the ciphertext. Another important requirement is for the scheme to be forward-secrecy. A forward-secure PKBE (fs-PKBE) enables each user to update his private key periodically. This updated private key prevents an adversary from obtain the private key for certain past period, which property is particularly needed for pay-TV systems. In this paper, we present a fs-PKBE scheme where both ciphertexts and private keys are of $O(\sqrt{n})$ size. Our PKBE construction is based on Boneh-Boyen-Goh's hierarchical identity-based encryption scheme. To provide the forward-secrecy with our PKBE scheme, we again use the delegation mechanism for lower level identities, introduced in the BBG scheme. We prove chosen ciphertext security of the proposed scheme under the Bilinear Diffie-Hellman Exponent assumption without random oracles.

• Journal of the Korea Society of Computer and Information
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• v.22 no.9
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• pp.49-55
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• 2017

Despite the Openflow's switch migration occurs after the channel was established in secure manner (optional), the current cryptography protocol cannot prevent the insider attack as the attacker possesses a valid public/private key pair. There are methods such as the certificate revocation list (CRL) or the online certificate status protocol (OCSP) that tries to revoke the compromised certificate. However, these methods require a management system or server that introduce additional overhead for the communication. Furthermore, these methods are not able to mitigate power abuse of an insider. In this paper, we propose a role-based identity-based cryptography (RB-IBC) that integrate the identity of the node along with its role so the nodes within the network can easily mitigate any role abuse of the nodes. Besides that, by combining with IBC, it will eliminate the need of exchanging certificates and hence improve the performance in a secure channel.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.14 no.4
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• pp.25-37
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• 2004

A certificate is expected to use for its entire validity period. However, a false information record of user and compromise of private key may cause a certificate to become invalid prior to the expiration of the validity period. The CA needs to revoke the certificate. The CA periodically updates a signed data structure called a certificate revocation list(CRL) at directory server. but as CA updates a new CRL at directory server. the user can use a revoked certificate. Not only does this paper analyzes a structure of CRL and a characteristic of certificate status conviction, OCSP method but also it proposes a new certificate status verification method adding an observer information in handshake process between user and server.

• Journal of Korea Multimedia Society
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• v.8 no.7
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• pp.974-987
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• 2005

As the ad hoc networks have been received a great deal of attention to not only the military but also the industry applications, some security mechanisms are required for implementing a practical ad hoc application. In this paper, we propose a security architecture in ad hoc networks for the purpose of supporting ID-based public key cryptosystems because of the advantage that ID-based schemes require less complex infrastructure compared with the traditional public key cryptosystems. We assume a trusted key generation center which only issues a private key derived from IDs of every nodes in the system setup phase, and use NIL(Node ID List) and NRL(Node Revocation List) in order to distribute the information about IDs used as public keys in our system. Furthermore, we propose a collaborative status checking mechanism that is performed by nodes themselves not by a central server in ad-hoc network to check the validity of the IDs.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7C
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• pp.653-663
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• 2002

The signature-then-encryption based on RSA scheme provides forward secrecy, but requires 4 modulo exponentiation operations in total, and the signcryption scheme proposed by Zheng simultaneously fulfills both the functions of digital signature and symmetric key encryption in a logically single step, and with a computational cost significantly smaller than that required by the current standard signature-then-encryption, but it can not provide forward secrecy. In this paper, we propose an enhanced signcryption scheme which can provide forward secrecy with lower computational cost and lower communication overhead comparing with those of the signature-then-encryption based on RSA, and with a similar communication overhead of Zheng's scheme. The proposed scheme can be also easily modified to the direct signature verification scheme by the recipient without using the recipient's private key. Additionally, we suggest a new design protocol with server-supported signatures which solves the CRLs(Certificate Revocation Lists) burden and provides non-repudiation of origin. This protocol with server-supported signatures also can be applied to the original signcryption scheme proposed by Zheng in order to improve security.