• Journal of Korea Multimedia Society
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• v.17 no.12
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• pp.1402-1411
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• 2014

Buyer-seller watermarking protocol is defined as the practice of imperceptible altering a digital content to embed a message using watermarking in the encryption domain. This protocol is acknowledged as one kind of copyright protection techniques in electronic commerce. Buyer-seller watermarking protocol is fundamentally based on public-key cryptosystem that is operating using the algebraic property of an integer. However, in general usage, digital contents which are handled in watermarking scheme mostly exist as real numbers in frequency domain through DCT, DFT, DWT, etc. Therefore, in order to use the watermarking scheme in a cryptographic protocol, digital contents that exist as real number must be transformed into integer type through preprocessing beforehand. In this paper, we presented a new watermarking scheme in an encrypted domain in an image that is based on the block-DCT framework and homomorphic encryption method for buyer-seller watermarking protocol. We applied integral-processing in order to modify the decimal layer. And we designed a direction-adaptive watermarking scheme by analyzing distribution property of the frequency coefficients in a block using JND threshold. From the experimental results, the proposed scheme was confirmed to have a good robustness and invisibility.

• Journal of Digital Contents Society
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• v.13 no.4
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• pp.531-538
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• 2012

Visual cryptography is a scheme that recovers secret image through human vision by overlapping distributed share images without cryptographic operations. Distribution methods are still being developed for improving quality of shared images keeping size of images invariant and enhancing robustness against resize of images. Since visual cryptography only uses shared images, this fact is exploited to attack. From this fact, a scheme safe for sharing distributed images is needed. In this paper, a new visual cryptographic scheme using cover image is proposed. This scheme reduces the chance of detection against steganalysis and increases security. In addition, this paper shows that the proposed scheme can completely decrypt secret image without creating noise.

• The Transactions of the Korea Information Processing Society
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• v.7 no.10
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• pp.3128-3137
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• 2000

Secret sharing scheme is a cryptographic protocol in which a dealer distribures shares of a secret among a set of participants such that only authorized set of participants can recover the secret at a later. Secret sharing is an important cryptographic primitive in management of secret information, secure multiparty protocol and group-oriented cryptography, etc. In this paper, we propose an efficient, on-line secret sharing scheme based on one-way hash function. This scheme provides the property to share multiple secrets and allows participants to be added/deleted dynamically, without having to redistributo new shares. Proposed scheme has advantage to detect cheating and identify of all cheater, regardless of then number. Frthermore, it is more eficient than previous schemes.

• Journal of Korea Multimedia Society
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• v.10 no.12
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• pp.1663-1670
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• 2007

One-way hash chains are important cryptographic primitives and have been used as building blocks of various cryptographic applications. Advantages of one-way hash chains are their simplicity and efficiency for generation based on low-powered processors with short time. However, a drawback of one-way hash chains is their difficulty of control to compute interval values of one-way hash chains. That is, when hash values in one-way hash chain are used as encryption keys, if one hash value is compromised, then the attacker can compute other encryption keys from the compromised hash value. Therefore, direct use of one-way hash chains as encryption keys is limited to many cryptographic applications, such as pay per view system and DRM system. In this paper, we propose a new concept which is called interval hash chain using a hash function. In particular, proposed hash chains are made for only computing interval hash values by using two different one-way hash chains. The proposed scheme can be applied to contents encryption scheme for grading and partially usable contents in DRM system.

• Journal of the Chungcheong Mathematical Society
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• v.23 no.4
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• pp.885-892
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• 2010

In this paper we study the structures and properties of a single cycle T-finction, whose theory has been lately proposed by Klimov and Shamir. Any cryptographic system based on T-functions may be insecure. Some of the TSC-series stream ciphers have been successfully attacked by some attacks. So it is important to analyze every aspect of a single cycle T-function. We study some properties on a single cycle T-function and we show some examples are single cycle T-functions by these properties, whose proof is easier than existing methods.

• Convergence Security Journal
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• v.22 no.4
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• pp.179-188
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• 2022

Password authentication schemes (PAS) are the most common mechanisms used to ensure secure communication in open networks. Mathematical-based cryptographic authentication schemes such as factorization and discrete logarithms have been proposed and provided strong security features, but they have the disadvantage of high computational and message transmission costs required to construct passwords. Fairuz et al. therefore argued for an improved cryptographic authentication scheme based on two difficult fixed issues related to session key consent using the smart card scheme. However, in this paper, we have made clear through security analysis that Fairuz et al.'s protocol has security holes for Privileged Insider Attack, Lack of Perfect Forward Secrecy, Lack of User Anonymity, DoS Attack, Off-line Password Guessing Attack.

• Proceedings of the KIEE Conference
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• 1999.11c
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• pp.700-702
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• 1999

The protection of data which we want to keep secret from invalid users has become a main topic nowadays. This paper introduces a encryption scheme for protecting speech signals from eavesdropping. The proposed encryption scheme adopts a secure voice cryptographic algorithm based on the scrambling in frequency band. In order to improve the conventional speech signal encryption scheme, we have randomly permuted DCT coefficients of speech signal. Simulation results are included to show the performance of the proposed algorithm for secure transmission of speech signals.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.05a
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• pp.1083-1086
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• 2005

Now these days, many technical concepts and tools have been developed in the cryptographic field. Most digital signature schemes used in practice, such as RSA or DSA, have an important role in information privacy and secure authentication for perfect user. A clearly advantage of such schemes over with security proven relative to such common cryptographic assumptions, is their efficiency: as a result of their relative weak requirements regarding computation, bandwidth and storage, these scheme have so far beaten proven secure schemes in practice. Our aim is to contribute to bridge the gap that exists between the theory and practice of digital signature schemes. In this paper we present a digital signature that ensures information privacy. More precisely, under an appropriate assumption about RSA, the scheme is proven to be existentially forgeable under adaptively chosen message attacks. This mechanism can be applied to smart cards or E-Wallet for maintaining secure authentication for user’s information privacy.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.3
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• pp.71-78
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• 2001

In this paper, we describe the vulnerabilities against mobile agent and analyze existing schemes to cope with them. Also we propose a new scheme which protects the executed information by mobile agent and simultaneously traces the executions of mobile agent. The proposed scheme provides non-repudiation between participations for the executions of mobile agent, forward integrity against modification and protection against code insertion or deletion attack.

• Journal of Digital Contents Society
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• v.8 no.4
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• pp.631-637
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• 2007

In this paper, I propose an adaptive cryptographic protocol which is basic protocol for fair exchange of secrets. For this, I investigate the verifiable oblivious transfer protocol based on discrete logarithm problem proposed by Lein Harn etc. And I propose a new adaptive cryptographic protocol that has the additional funtions on the existing method. This proposed method has the additional functions that enable to authenticate sender and to protect denial of what he/she has sent message to the other. To do this, I make use of bit commitment scheme using pseudo-random sequence generator.