• Journal of the Korea Institute of Information Security & Cryptology
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• v.33 no.5
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• pp.753-760
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• 2023

KakaoTalk has the highest market share among domestic messengers. As such, KakaoTalk's conversation content is an important evidence in digital forensics, and the conversation is stored in the form of an encrypted database on a user's device. In addition, macOS has the characteristic that it is difficult to access because the disk encryption function is basically activated. The decryption method of the KakaoTalk database for Windows has been studied, but the decryption method has not been studied for KakaoTalk for macOS. In this paper, research the decryption method of the KakaoTalk database for macOS and a way to Brute-Force plan using the characteristics of KakaoTalk's UserID and compare it with KakaoTalk for Windows to examine the commonalities and differences. The results of this paper are expected to be used to analyze users' actions and events when investigating crimes using macOS.

• Journal of Internet Computing and Services
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• v.16 no.2
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• pp.27-40
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• 2015

Inferring firewall policy is to discover firewall policy by analyzing response packets as results of active probing without any prior information. However, a brute-force approach for generating probing packets is unavailable because the probing packets may be regarded as attack traffic and blocked by attack detection threshold of a firewall. In this paper, we propose a firewall policy inference method using an efficient probing algorithm which considers the number of source IP addresses, maximum probing packets per second and interval size of adjacent sweep lines as inference parameters to avoid detection. We then verify whether the generated probing packets are classified as network attack patterns by a firewall, and present the result of evaluation of the correctness by comparing original firewall policy with inferred firewall policy.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.6
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• pp.2074-2093
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• 2022

RSA is known as one of the best techniques for securing secret information across an unsecured network. The private key which is one of private parameters is the aim for attackers. However, it is exceedingly impossible to derive this value without disclosing all unknown parameters. In fact, many methods to recover the private key were proposed, the performance of each algorithm is acceptable for the different cases. For example, Wiener's attack is extremely efficient when the private key is very small. On the other hand, Fermat's factoring can quickly break RSA when the difference between two large prime factors of the modulus is relatively small. In general, if all private parameters are not disclosed, attackers will be able to confirm that the private key is unquestionably inside the scope [3, n - 2], where n is the modulus. However, this scope has already been reduced by increasing the greatest lower bound to [d_il, n - 2], where d_il ≥ 3. The aim of this paper is to decrease the least upper bound to narrow the scope that the private key will remain within this boundary. After finishing the proposed method, the new scope of the private key can be allocated as [d_il, d_ir], where d_ir ≤ n - 2. In fact, if the private key is extremely close to the new greatest lower bound, it can be retrieved quickly by performing a brute force attack, in which d_ir is decreased until it is equal to the private key. The experimental results indicate that the proposed method is extremely effective when the difference between prime factors is close to each other and one of two following requirement holds: the first condition is that the multiplier of Euler totient function is very close to the public key's small value whereas the second condition is that the public key should be large whenever the multiplier is far enough.

• KIPS Transactions on Computer and Communication Systems
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• v.13 no.1
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• pp.31-37
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• 2024

Conventional secret sharing techniques often derive shares from randomly generated polynomials or planes, resulting in lengthy and complex shares that are challenging to memorize and/or manage without the aid of a separate computer or specialized device. Modifying existing secret sharing methods to use a predetermined value, such as a memorizable password or bio-metric information, offers a solution. However, this approach raises concerns about security, especially when the predetermined value lacks randomness or has low entropy. In such cases, adversaries may deduce a secret S with just (t - 1) shares by guessing the predetermined value or employing brute force attacks. In this paper, we introduce a share hardening method designed to ensure the security of secret sharing while enabling the use of memorizable passwords or biometric information as predetermined shares.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.2
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• pp.109-121
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• 2020

Depth calculation of objects in a scene from images is one of the most studied processes in the fields of image processing, computer vision, and photogrammetry. Conventionally, depth is calculated using a pair of overlapped images captured at different view points. However, there have been studies to calculate depths from a single image. Theoretically, it is known to be possible to calculate depth using the diameter of CoC (Circle of Confusion) caused by defocus under the assumption of a thin lens model. Thus, this study aims to verify the validity of the thin lens model to calculate depth from edge blur amount which corresponds to the radius of CoC. For this study, a commercially available DSLR (Digital Single Lens Reflex) camera was used to capture a set of target sheets which had different edge contrasts. In order to find out the pattern of the variations of edge blur against varying combination of FD (Focusing Distance) and OD (Object Distance), the camera was set to varying FD and target sheet images were captured at varying OD under each FD. Then, the edge blur and edge displacement were estimated from edge slope profiles using a brute-force method. The experimental results show that the pattern of the variations of edge blur observed in the target images was apart from their corresponding theoretical amounts derived under the thin lens assumption but can still be utilized to calculate depth from a single image for the cases similar to the limited conditions experimented under which the tendency between FD and OD is manifest.

• Journal of Internet Computing and Services
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• v.6 no.5
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• pp.11-25
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• 2005

In MIPv6 environment, an important design consideration for public key based binding update protocols is to minimize asymmetric cryptographic operations in mobile nodes with constraint computational power, such as PDAs and cellular phones, For that, public key based protocols such as CAM-DH. SUCV and Deng-Zhou-Bao's approach provides an optimization to offload asymmetric cryptographic operations of a mobile node to its home agent. However, such protocols have some problems in providing the optimization. Especially, CAM-DH with this optimization does not unload all asymmetric cryptographic operations from the mobile node, while resulting in the home agent's vulnerability to denial of service attacks. In this paper, we improve the drawbacks of CAM-DH. Furthermore, we adopt Aura's two hash-based CGA scheme to increase the cost of brute-force attacks searching for hash collisions in the CGA method. The comparison of our protocol with other public key based protocols shows that our protocol can minimize the MN's computation overhead, in addition to providing better manageability and stronger security than other protocols.

• Journal of Korean Society for Atmospheric Environment
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• v.34 no.2
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• pp.294-305
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• 2018

Quantitative assessment on the impact from North Korean emissions to surface particulate matter(PM) concentration in the Seoul Metropolitan Area (SMA), South Korea is conducted using a 3-dimensional chemistry transport model. Transboundary transport of air pollutants and their precursors are important to understand regional air quality in East Asian countries. As North Korea locates in the middle of main transport pathways of Chinese pollutants, quantifiable estimation of its impact is essential for policy making in South Korean air quality management. In this study, the Community Multiscale Air Quality Modeling System is utilized to simulate regional air quality and its sensitivity, using the Comprehensive Regional Emissions inventory for Atmospheric Transport Experiment 2015 and the Clean Air Policy Support System 2013 emissions inventories for North and South Korea, respectively. Contributions were estimated by a brute force method, perturbing 50% of North and South Korean emissions. Simulations demonstrate that North Korean emissions contribute $3.89{\mu}g/m^3$ of annual surface PM concentrations in the SMA, which accounts 14.7% of the region's average. Impacts are dominant in nitrate and organic carbon (OC) concentrations, attributing almost 40% of SMA OC concentration during January and February. Clear seasonal variations are also found in North Korean emissions contribution to South Korea (and vice versa) due to seasonal characteristics of synoptic weather, especially by the change of seasonal flow patterns.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.1
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• pp.123-129
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• 2017

New mobile phones with high tech-camera and a large size memory have been recently launched and people upload pictures of beautiful scenes or unknown flowers in SNS. This paper develops a flower recognition system that can get information on flowers in the place where mobile communication is not even available. It consists of a registration part for reference flowers and a recognition part based on OpenCV for Android platform. A new color classification method using RGB color channel and K-means clustering is proposed to reduce the recognition processing time. And ORB for feature extraction and Brute-Force Hamming algorithm for matching are used. We use 12 kinds of flowers with four color groups, and 60 images are applied for reference DB design and 60 images for test. Simulation results show that the success rate is 83.3% and the average recognition time is 2.58 s on Huawei ALEUL00 and the proposed system is suitable for a mobile phone without a network.

• Journal of Korean Society for Atmospheric Environment
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• v.33 no.2
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• pp.139-158
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• 2017

CMAQ (Community Multiscale Air Quality Model) simulations were carried out to estimate the potential range of contributions on surface $PM_{2.5}$ concentrations over the Seoul Metropolitan Area (SMA) with the gaseous precursors and Primary Particulate Matters(PPM) available from a recent national emissions inventory. In detail, on top of a base simulation utilizing the 2013 Clean Air Policy Supporting System (CAPSS) emission inventory, a set of Brute Force Method (BFM) simulations after reducing anthropogenic $NO_x$, $SO_2$, $NH_3$, VOCs, and PPM emissions released from area, mobile, and point sources in SMA by 50% were performed in turn. Modeling results show that zero-out contributions(ZOC) of $NH_3$ and PPM emissions from SMA are as high as $4{\sim}5{\mu}g/m^3$ over the region during the modeling period. On the contrary, ZOC of local $NO_x$ and $SO_2$ emissions to SMA $PM_{2.5}$ are less than $1{\mu}g/m^3$. Moreover, model analyses indicate that a wintertime $NO_x$ reduction at least up to 50% increases SMA $PM_{2.5}$ concentrations, probably due to increased HNO3 formation and conversion to aerosols under more abundant ozone and radical conditions after the $NO_x$ reduction. However, a nation-wide $NO_x$ reduction decreased SMA $PM_{2.5}$ concentrations even during winter, which implies that nation-wide reductions would be more effective to curtail SMA $PM_{2.5}$ concentrations than localized efforts.

• Journal of KIISE
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• v.43 no.10
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• pp.1165-1172
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• 2016

In cloud storage environment, deduplication enables efficient use of the storage. Also, in order to save network bandwidth, cloud storage service provider has introduced client-side deduplication. Cloud storage service users want to upload encrypted data to ensure confidentiality. However, common encryption method cannot be combined with deduplication, because each user uses a different private key. Also, client-side deduplication can be vulnerable to security threats because file tag replaces the entire file. Recently, proof of ownership schemes have suggested to remedy the vulnerabilities of client-side deduplication. Nevertheless, client-side deduplication over encrypted data still causes problems in efficiency and security. In this paper, we propose a secure and practical client-side encrypted data deduplication scheme that has resilience to brute force attack and performs proof of ownership over encrypted data.