• Journal of the Korea Institute of Information Security & Cryptology
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• v.13 no.4
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• pp.139-149
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• 2003

In this paper a hardware design of area-efficient hash processor which implements MD5 algorithm using hardware sharing and carry-save addition schemes is described. To reduce area, the processor adopts hardware sharing scheme in which 1 step operation is divided into 2 substeps and then each substep is executed using the same hardware. Also to increase clock frequency, three serial additions of substep operation are transformed into two carry-save additions and one carry propagation addition. The MD5 hash processor is designed using 0.25 $\mu\textrm{m}$CMOS technology and consists of about 13,000 gates. From timing simulation results, the designed MD5 hash processor has 465 Mbps hash rates for 512-bit input message data under 120 MHz operating frequency.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.19 no.6
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• pp.71-82
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• 2009

There have been a lot of researches on providing privacy in MANET (Mobile Ad hoc NETwork) using trapdoor, onion, and anonymous authentication. Privacy protection in MANET can be divided into satisfying ID privacy, location privacy, route privacy, and unlinkability between sessions. Most of the previous works, however, were unsatisfactory with respect to location privacy or route privacy. Moreover, in previous schemes, cryptographic operation cost needed to meet the privacy requirements was relatively high. In this paper, we propose a new efficient anonymous routing protocol that satisfies all the privacy requirements and reduces operation costs. The proposed scheme does not use onion or anonymous authentication techniques in providing privacy. We also provide a more accurate analysis of our scheme's efficiency by considering all the nodes involved in the route establishment.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.5
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• pp.1209-1223
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• 2018

Android apps are made up of bytecode, so they are vulnerable to reverse engineering, and protection services are emerging that robustly repackage the app to compensate. Unlike cryptographic algorithms, the robustness of these protection services depends heavily on hiding the protection scheme. Therefore, there are few systematic discussions about the protection method even if destruction techniques of the protection service are various. And it is implemented according to the intuition of the developer. There is a need to discuss systematic protection schemes for robust security chains, rather than simple deployment of techniques disrupting static or dynamic analysis. In this paper, we analyze bangcle, a typical commercial Android app protection service, to examine the protection structure and vulnerable elements. We propose the requirements for robust structure and principles of protection structure.

• Journal of Information Technology Services
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• v.3 no.2
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• pp.119-127
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• 2004

A mobile ad hoc network(MANET) is a network where a set of mobile devices communicate among themselves using wireless transmission without the support of a fixed network infrastructure. The use of wireless links makes MANET susceptible to attack. Eavesdroppers can access secret information, violating network confidentiality, and compromised nodes can launch attack from within a network. Therefore, the security for MANET depends on using the cryptographic key, which can make the network reliable. In addition, because MANET has a lot of mobile devices, the authentication scheme utilizing only the symmetric key cryptography can not support a wide range of device authentication. Thereby, PKI based device authentication technique in the Ad Hoc network is essential and the paper will utilize the concept of PKI. Especially, this paper is focused on the key management technique of PKI technologies that can offer the advantage of the key distribution, authentication, and non-reputation, and the issuing and managing technique of certificates based on clustering using Threshold Cryptography for secure communication in MANET.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.10
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• pp.1783-1798
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• 2011

Recently, a cryptographic construct, called fuzzy vault, has been proposed for crypto-biometric systems, and some implementations for fingerprint have been reported to protect the stored fingerprint template by hiding the fingerprint features. In this paper, we implement the fuzzy fingerprint vault, combining fingerprint verification and fuzzy vault scheme to protect fingerprint templates. To implement the fuzzy fingerprint vault as a complete system, we have to consider several practical issues such as automatic fingerprint alignment, verification accuracy, execution time, error correcting code, etc. In addition, to protect the fuzzy fingerprint vault from the correlation attack, we propose an approach to insert chaffs in a structured way such that distinguishing the fingerprint minutiae and the chaff points obtained from two applications is computationally hard. Based on the experimental results, we confirm that the proposed approach provides higher security than inserting chaffs randomly without a significant degradation of the verification accuracy, and our implementation can be used for real applications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.11
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• pp.4028-4049
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• 2014

Attribute-based encryption (ABE) is a promising cryptographic primitive for implementing fine-grained data sharing in cloud computing. However, before ABE can be widely deployed in practical cloud storage systems, a challenging issue with regard to attributes and user revocation has to be addressed. To our knowledge, most of the existing ABE schemes fail to support flexible and direct revocation owing to the burdensome update of attribute secret keys and all the ciphertexts. Aiming at tackling the challenge above, we formalize the notion of ciphertext-policy ABE supporting flexible and direct revocation (FDR-CP-ABE), and present a concrete construction. The proposed scheme supports direct attribute and user revocation. To achieve this goal, we introduce an auxiliary function to determine the ciphertexts involved in revocation events, and then only update these involved ciphertexts by adopting the technique of broadcast encryption. Furthermore, our construction is proven secure in the standard model. Theoretical analysis and experimental results indicate that FDR-CP-ABE outperforms the previous revocation-related methods.

• Journal of the Korea Society of Computer and Information
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• v.18 no.10
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• pp.81-88
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• 2013

Since nowadays mobile phone messages are flourishing, the application of electronic coupon (e-coupon) will become a trend for mobile users. E-coupon for mobile commerce can provide mobility for users and distribution flexibility for issuers. In this paper, we propose a mobile e-coupon system that just applies some simple cryptographic techniques, such as one-way hash function and XOR operation. In our system, the customer can control the number of issued e-coupons and the issuer can prevent them from double-redeeming. The customer does not need to perform any exponential computation in redeeming and transferring the coupons. Our scheme uses one-way hash chains for preventing from double-spending.

• Journal of the Optical Society of Korea
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• v.17 no.5
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• pp.362-370
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• 2013

In this paper, we propose a novel optical implementation of a 3DES algorithm based on dual XOR logic operations for a cryptographic system. In the schematic architecture, the optical 3DES system consists of dual XOR logic operations, where XOR logic operation is implemented by using a free-space interconnected optical logic gate method. The main point in the proposed 3DES method is to make a higher secure cryptosystem, which is acquired by encrypting an individual private key separately, and this encrypted private key is used to decrypt the plain text from the cipher text. Schematically, the proposed optical configuration of this cryptosystem can be used for the decryption process as well. The major advantage of this optical method is that vast 2-D data can be processed in parallel very quickly regardless of data size. The proposed scheme can be applied to watermark authentication and can also be applied to the OTP encryption if every different private key is created and used for encryption only once. When a security key has data of $512{\times}256$ pixels in size, our proposed method performs 2,048 DES blocks or 1,024 3DES blocks cipher in this paper. Besides, because the key length is equal to $512{\times}256$ bits, $2^{512{\times}256}$ attempts are required to find the correct key. Numerical simulations show the results to be carried out encryption and decryption successfully with the proposed 3DES algorithm.

• Journal of Communications and Networks
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• v.14 no.1
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• pp.104-110
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• 2012

Group key agreement protocols allow a group of users, communicating over a public network, to establish a shared secret key to achieve a cryptographic goal. Protocols based on certificateless public key cryptography (CL-PKC) are preferred since CL-PKC does not need certificates to guarantee the authenticity of public keys and does not suffer from key escrow of identity-based cryptography. Most previous certificateless group key agreement protocols deploy signature schemes to achieve authentication and do not have constant rounds. No security model has been presented for group key agreement protocols based on CL-PKC. This paper presents a security model for a certificateless group key agreement protocol and proposes a constant-round group key agreement protocol based on CL-PKC. The proposed protocol does not involve any signature scheme, which increases the efficiency of the protocol. It is formally proven that the proposed protocol provides strong AKE-security and tolerates up to $n$-2 malicious insiders for weak MA-security. The protocol also resists key control attack under a weak corruption model.

• Journal of KIISE:Computer Systems and Theory
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• v.36 no.5
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• pp.396-403
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• 2009

An anonymous asymmetric fingerprinting protocol combined with watermarking techniques, is one of the copyright protection technologies keeping both right of a seller and that of a buyer, where a seller and an anonymous buyer perform such a protocol that employs various cryptographic tools in order that the seller does not know the exact watermarked copy that the buyer receives, while inserting an invisible non-removable fingerprint i.e., each different unique watermark, into each copy of the digital content to be sold. In such a protocol innocent buyers are kept anonymous during transactions, however, the unlawful reseller is unambiguously identified with a real identity as a copyright violator. In 2007, Yong and Lee proposed an anonymous asymmetric fingerprinting scheme with trusted third party. In this paper we point out the weakness of their scheme such as: the buyer with intention can remove the fingerprint in the watermarked content, because he/she can decrypt the encrypted fingerprint with a symmetric key using man-in-the-middle-attack; a real identity of a buyer can be revealed to the seller through the identification process even though he/she is honest. Furthermore, we propose an improved secure and efficient anonymous asymmetric fingerprinting scheme which enables to reduce the number of communication between the participants.