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Private Key Recovery on Bitcoin with Duplicated Signatures
( Ju-seong Ko ),( Jin Kwak ) 한국인터넷정보학회 2020 KSII Transactions on Internet and Information Syst Vol.14 No.3
In the modern financial sector, interest in providing financial services that employ blockchain technology has increased. Blockchain technology is efficient and can operate without a trusted party to store all transaction information; additionally, it provides transparency and prevents the tampering of transaction information. However, new security threats can occur because blockchain technology shares all the transaction information. Furthermore, studies have reported that the private keys of users who use the same signature value two or more times can be recovered. Because private keys of blockchain identify users, private key leaks can result in attackers stealing the ownership rights to users’ property. Therefore, as more financial services use blockchain technology, actions to counteract the threat of private key recovery must be continually investigated. Private key recovery studies are presented here. Based on these studies, duplicated signatures generated by blockchain users are defined. Additionally, scenarios that generate and use duplicated signatures are applied in an actual bitcoin environment to demonstrate that actual bitcoin users’ private keys can be recovered.
조영제와 생리식염수 혼합물을 이용한 표면선량 감소에 관한연구
고주성(Ju seong Ko),임상묵(Sang muk Yim),강화원(Hwawon Gang),김대현(Dae hyeon Kim) 대한전산화단층기술학회 2015 대한CT영상기술학회지 Vol.17 No.2
목적 : 조영제와 생리식염수를 섞어서 조영제 농도를 달리해 차폐물을 제작하여 조영제 농도에 따른 표면선량 차폐효과에 대해 알아보고자 하였다. 대상 및 방법 : CT장비는 SOMATOM Definition(Siemens, Germany)를 사용하였고, 선량의 측정을 위해 Atom Phantom(CIRS)과 형광유리소자(GD-352M:Chiyoda Technol Japan)을 사용하으며, 선량판독기(FDG-1000;AGC, Techno Glass, Shizuoka, Japan)를 이용하였다. 화질평가를 위해 AAPM Phanrom(Model 76-410, Nuclear Associates LTD)을 사용하였다. 기존의 차폐물질인 BISMUTH(F&L Medical Products co, 0.060mmpb equivalent, USA)와조영제와 생리식염수를 혼합하여 제작한 조영제 200 cc+생리식염수 200 cc, 조영제 100 cc+생리식염수 300cc, 조영제 50 cc+ 생리식염수 350cc, 조영제 25 cc+생리식염수 375 cc, 조영제 10cc+생리식염수 390 cc을 비교하였.다 조영제 혼합차폐물을 Atom 팬텀의 흉부위에올려놓고 형광유리선랑계를 양측 유두부 위치와 폐야에 위치시켜서 각각 선량을 측정하였으며, 비교를 위해 BISMUTH 사용했을 때와 차폐체 없을때 와의 선량을 비교 측정하였다. 피사체와차폐물과의 거리를 0 cm, 0.7 cm, 1.4 cm, 2.1 cm으로 변화시켜 거리에 따른 선량변화를 측정하였고 Image Quality를 측정하기 위해 AAPM Phantom을 이용하여 위 실험과 같은 방법으로 노이즈와 균일도를 측정하였다. 결과 : bone plus algorithm을 대조군으로 환자데이터를 분석하였다. soft tissue에서 SD값이 ultra algorithm은 FBP와 ASIR30% 모두 bone plus algorithm과 차이가 없었다. edge algorithm은 SD값이 FBP와 ASIR30% 각각 28.78%, 34.63% 증가했다. bone어|서 SD값이 ultra algorithm은 FBP와 ASIR30% 가각 18.88%, 19.78% 증가했고, edge algorithm은 FBP와 ASIR30% 각각 10%, 9.1% 감소했다. 공간분해능과 선예도 측정결과 bone plus, edge, ultra algorithm의 MTF50% 값은 FBP에서 각각 4.28, 0.62, 5.64였고, ASIR30%는 4.39, -3.77, 6.17이었다. MTF10%값은 FBP에서 6.50, 5.85, 10.01 이었고, ASIR30%는 6.91, 5.74, 21.98이었다. 측정결과 ultra algorithm의 공간분해능과 선예도가 가장 좋았다. 결론 : Ultra algorithm은 기존의 bone plus, edge algorithm과 비교했을 때 저주파영역의 노이즈 증가없이 고주파영역만 강조하면서 영상의 화질 또한 우수하다는 것을 알 수 있었다. 임상 Temporal bone CT검사에서 ultra algorithm은 bone plus algorithm과 비교하여 적절히 사용한다면 매우 유용할 것이라 사료된다. Purpose : The purpose of this study lies in examining the screening effect of surface absorbed dose based on concentration of contrast media by manufacturing a screen with different contrast media concentration by mixing contrast media and physiological saline solution. Materials & Methods : SOMATOM Definition (Siemens, Germany) was used for CT device and Atom Phantom (CIRS) and fluorescent glass element (GD-352M;Chiyoda Technol Japan) were used for measurement of dose. Also, dosimeter (FDG-1000;AGC, Techno Glass, Shizuoka, Japan) was used to measure absorbed dose and AAPM Phantom(Model 76-410, Nuclear Associates LTD) was used for image quality assessment. The comparison was conducted with mixture of previous screen BISMUTH (F&L Medical Products co, 0.060mmpb equivalent, USA) and contrast media 200 cc + normal saline solution 200 cc, contrast media 100 cc + normal saline solution 300cc. contrast media 50 cc + normal saline solution 350 cc. contrast media 25 cc + normal saline solution 375 cc, and contrast media 10 cc + normal saline solution 390 cc manufactured with mixture of contrast media and normal saline solution. The absorbed dose was measured by fluorescent glass dosimeter after placing contrast media mixed screen to the thorax of atom phantom and fluorescent glass dosimeter to the location of both nipples and lung field. Comparative measurement was conducted in order to compare the dose with the use of BISMUTH and without use of screen. The changes in doses accordingly with distance were measured by changing distance between the subject and screen into 0cm. 0.7cm, 1.4cm, and 2.1 cm and noise and uniformity were measured with same method as above experiment using AAPM Phantom for the measurement of image quality. Result : Although reduction effect of surface absorbed dose was greatest with the use of contrast media 200 cc + normal saline solution 200 cc presenting 4.2 mGy, it has exceeded allowable range when measuring the uniformity. Although there was two-fold increase in surface absorbed dose for screen manufactured with made of contrast media 25cc + normal saline solution 375 cc in comparison with contrast media 200 cc+ normal saline solution 200 cc, the uniformity was measured within allowable range presenting the surface absorbed dose of 8.1 mGy. Also, there was surface absorbed dose reduction of 27% compared to surface absorbed dose 11.0 mGy scanned without screen. There were little changes in surface absorbed doses based on changes in distance between contrast media mixed screen and subject. In regards to noise assessment, it was measured to be the lowest presenting 11.7 without screen and the highest presenting 29.3 with the use of contrast media 200 cc+ normal saline solution 200 cc. With the screen, it was measured to be the lowest presenting 14.7 for contrast media 10 cc + normal saline solution 390 cc. Conclusion : Surface absorbed dose reduction effect of 27% could be acquired compared to previous screen BISMUTH and uniform CT number could be obtained with the use of contrast media mixed screen 25 cc + 375 cc. It is believed that contrast media mixed screen wⅢ be of great assistance to surface absorbed dose reduction in case there is no previous screen.
고석주 ( Seok Ju Ko ),홍석진 ( Suk Jin Hong ),윤혜정 ( Hye Jeong Youn ),정성숙 ( Seong Soog Jeong ),정은주 ( Eun Ju Jung ),최충호 ( Choong Ho Choi ) 대한예방치과·구강보건학회 2010 大韓口腔保健學會誌 Vol.34 No.1
Objectives. To evaluate the results of a dental service program operated for foreign workers by a dental team in Gwangju. Methods. Data was collected and analyzed from the dental charts of 312 foreign workers treated at a single dental center from September, 2005 to August, 2007. The general condition of the dental service program was also surveyed. Chi-square test was used for comparison among groups. Results. Most patients were East Asian men 20~39-years-of-age, likely due to the location of the health center in an industrial area and its treatment-only purpose. They received oral medicine treatment (50 patients, 53 cases), periodontal treatment (130 patients, 163 cases), operative and root canal treatment (228 patients, 422 cases), surgical treatment (87 patients, 99 cases), and prosthetic treatment (16 patients, 16 cases). No differences were evident in patients receiving oral medicine and surgical treatments in terms of gender, nationality, and age (p>0.05). Significant difference were evident in patients receiving. operative and root canal treatments in terms of amalgam filling (nationality), zinc oxide eugenol filling (nationality and age) and glass ionomer filling (gender and age)(p<0.05). Significant differences were evident in patients receiving periodontal treatment in terms of gender and nationality (p<0.05). Conclusions. In order to improve the dental service program for foreign workers, practitioners should be encouraged to establish relationships with dental association, have access to interpreters to ease language-related difficulties, focus on preventive treatments through available oral health education resources, and use prosthetic treatments. In addition, systemic government and private sector financial and infrastructure support would be fruitful to enable maximum provision of services and hiring of more practitioners.
Development of high capacity stirling cryocooler
Ko, Junseok,Yeom, Hankil,Kim, Hyobong,Hong, Yong-Ju,In, Sehwan,Park, Seong-Je The Korea Institute of Applied Superconductivity a 2015 한국초전도저온공학회논문지 Vol.17 No.3
Cryogenic cooling system for HTS electric power devices requires a reliable and efficient high-capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has gamma-type configuration. Piston and displacer are supported with flexure spring. A slit-type heat exchanger is adopted for cold and warm-end, and the generated heat is rejected by cooling water. In cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. Moreover, temperatures of cooling water, housing and linear motor are recorded and electric power parameters of driving circuit are also obtained. The developed Stirling cryocooler reaches to 47.8 K within 23.4 min. with no-load. From heat load tests, it shows cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.
Ko, Sang-won,Park, Sang-Hyun,Gwon, Hui-Jeong,Lee, Jun-seong,Kim, Min-Jeong,Kwak, Yeon-ju,Do, Young-kyu,Churchill, David G. Korean Chemical Society 2006 Bulletin of the Korean Chemical Society Vol.27 No.2
Three novel potential metal ion chelating units have been synthesized and characterized: 5-hexylcarbamoyl-3,4-dihydroxythiophene-2-carboxylic acid methyl ester (5), 3-benzyloxy-4-hydroxythiophene-2,5-dicarboxylic acid bis-hexylamide (6), and 3,4-dihydroxythiophene-2,5-dicarboxylic acid bis-hexylamide (7). The crystal structure of 6 was obtained and suggests the presence of three distinct intramolecular hydrogen bonds, namely $[N_{amide}-H{\cdot}{\cdot}{\cdot}O]$ $[O-H{\cdot}{\cdot}{\cdot}O_{amide}]$ and $[N_{amide}-H{\cdot}{\cdot}{\cdot}S]$. Boron chelation with 5, 6 and 7 through the use of $BF_3, \;B(OH)_3 \;or \;B(OMe)_3$ was probed by $^1H$, $^{11}B$, and $^{13}C$ NMR spectroscopy. Technetium (I) chelation with 5, 6 and 7 was also studied via HPLC elutions using $[^{99m}Tc(CO)_3(OH_2)_3]^+$.