Organizational Unit: Department of Electrical and Electronics Engineering
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Master ThesisPublication Metadata only Validating android permission requests by analyzing APP descriptions(2016-07) Şahin, Mustafa Kaan; Aktemur, Tankut Barış; Aktemur, Tankut Barış; Şensoy, Murat; Çakmak, Ali; Department of Electrical and Electronics Engineering; Şahin, Mustafa KaanAndroid applications can access sensitive user data if they are granted certain permissions. Android security model gives users the responsibility to approve permission requests of applications. For this, a user needs to decide whether an app's functionality justifies the permission request. To aid users in their decision, we propose and evaluate a methodology that analyzes the description of an app and identifies unusual and unjustified permission requests. In contrast to existing techniques, our approach is not limited to a fixed set of permissions and does not need source code or binary app data to operate; yet, it is on par with the current state of the art in terms of accuracy.Master ThesisPublication Restricted Combined aes + aegis architectures for high performance and lightweight security applications(2014-08) Şahin, Furkan; Uğurdağ, H. Fatih; Uğurdağ, H. Fatih; Yalçın, T.; Gören Uğurdağ, S.; Aktemur, Tankut Barış; Ercan, Ali Özer; Department of Electrical and Electronics Engineering; Şahin, FurkanGünümüzde kriptografi banka kartlarından telefonlara, arabalardan haberleşme araçlarına ve bulut hizmetlerine kadar pek çok alana girdi. Digital bilgiyi yetkilendirilmemiş erişimlere karşı korumak için bir çok şifreleme algoritması mevcuttur. Gelişmiş Şifreleme Standardı (AES) Amerikan Ulusal Standartlar ve Teknoloji Enstitüsü (U.S. NIST) tarafından standart şifreleme algoritması olarak onaylandıktan sonra en önemli blok şifreleyici olmuştur. AES'in kanıtlanmış güvenliği ve makul donanım kullanımı onu yeni bilgi güvenliği uygulamaları için mantıklı bir seçim yapmaktadır. Bugüne kadar, yüksek performanstan düşük alan kullanımına kadar pek çok tasarım yaklaşımını hedefleyen AES versiyonları donanımsal ve yazılımsal olarak gerçeklendi. Ancak günümüz bilgi güvenliği uygulamaları hem gizlilik hem de kimlik doğrulama gerektirdiği için, kimlik doğrulamalı şifreleme giderek daha çok önem kazanmaktadır. AES, bir çok kriptografi bilimcisi tarafından kimlik doğrulamalı şifrelemenin gerçeklenmesinde mantıklı bir seçim olarak düşünülmektedir. Son zamanlarda literatürde, AES algoritmasını olduğu gibi kullanan ya da AES'te küçük değişiklikler yaparak kullanan kimlik doğrulamalı şifreleme algoritmları çokça gözükmeye başlamıştır. Bu yeni kimlik doğrulamalı şifreleme algoritmalarının bazılarında daha iyi performans ve daha az kaynak kullanımı başarılabileceği iddia edilmektedir. Ancak bu algoritmalar henüz yeni literatüre girdiği için bu iddiaları destekleyen çok az donanım gerçeklemesi mevcuttur, hatta bazıları donanımsal olarak henüz gerçeklenmemiştir. Bu tezde AES'i, çok yakın zamanda literatüre giren AES tabanlı kimlik doğrulamalı şifreleme algoritması olan AEGIS ile aynı donanımda birleştiren mimariler tasarlanmıştır. Buradaki amacımız iki algoritmanın tek bir devrede gerçeklenmesine örnek teşkil edecek bir mimari sunmak, birleşik performans ve donanım kaynağı kullanımını analiz etmek ve AEGIS'ın tasarımcılarının kaynak kullanımı konusundaki iddialarının tartışılabileceği sentez sonuçları elde etmektir. Ayrıca bilgilerimize göre literatürde AEGIS'ın donanımda gerçeklenmesini sunan bir çalışma henüz yapılmamıştır ve AEGIS ilk kez bu çalışmada donanımsal olarak gerçeklenmiştir. Bu tezde yüksek performans ve az donanım kaynağı kullanan olmak üzere iki değişik, birleşik AES + AEGIS donanım mimarisi sunulmuş ve bu devreler Verilog donanım tanımlama dilinde (Verilog HDL) yazmaç transfer seviyesinde (RTL) kodlanmıştır. Ayrıca sadece AES şifrelemesi yapan devreler de gerçeklenip, her iki birleşik mimarinin kaynak kullanımı bu devreler ile kendi kategorisinde kıyaslanmıştır. Devreler UMC 90nm standart hücre kütüphanesiyle ve Cadence RTL derleyicisi kullanılarak gerçeklenmiştir. Sentez sonuçları raporlanmış ve değerlendirilmiştir.Master ThesisPublication Restricted Analysis of ALTO protocol over P2P networks(2012-10) Kökten, Koray; Sunay, M. Oğuz; Sunay, M. Oğuz; Arı, İsmail; Erdem, Tanju; Tan, A. S.; Ercan, Ali Özer; Department of Electrical and Electronics Engineering; Kökten, KorayCurrently, for distributed applications such as Peer-to-Peer (P2P) and Content Delivery Networks (CDNs), the most important challenge is to determine the optimal peer or node selection process, since it sometimes causes low Quality of Experience and affects the economics of the Internet Service Providers (ISPs) negatively. Therefore, in recent years significant research has been conducted in this area. However, since these protocols operate on Layer 7 (Application Layer) according to the Open Systems Interconnection (OSI) model, they are network-oblivious. Therefore, without a co-operation between service or network providers (i.e. ISPs) and applications, obtaining an optimal solution is not easy or even possible. Since P2P applications are one of the most widely used applications on the Internet, Internet Engineering Task Force (IETF) has started to work on a protocol, commonly referred to as the Application Layer Traffic Optimization (ALTO) Protocol, in order to enable a standartized interface between applications and network providers. With this protocol, both applications and service providers have a chance to interact using a common interface via the ALTO Server and share the necessary information in order to calculate the costs of communication between peers, so that a better-than-random peer or node selection is possible. In this thesis, we implement an ALTO Server for several ISPs, describe several(either novel or from the literature) cost calculation methods and try to improve the performance of the communication network from the perspectives of both applications and service providers. We analyse the implemented ALTO Server using a P2P BitTorrent-Like file sharing application, a P2P real-time scalable video streaming application and a CDN application running on a Software DefinedNetwork (SDN) with an OpenFlow Controller. Simulation results and demos show that, with carefully designed peer selection algorithms used in the ALTO Service, the performance of the applications can be sustained (even can be improved), while the inter-ISP traffic rates can be reduced dramatically.Master ThesisPublication Metadata only Design and quantitative analysis of a pulse wave velocity blood-pressure measurement subsystem with multiple-subject controlled experiments(2018-08) Erkurşun, Burcu; Tekin, Ahmet; Tekin, Ahmet; Demiroğlu, Cenk; Çamlıbel, B. T.; Department of Electrical and Electronics Engineering; Erkurşun, BurcuThe main purpose of this study is to perform the pulse wave velocity (PWV) measurements with a new noninvasive optoelectronic continuous-time wearable sensor design and analyze the quantitative relation between the reference blood pressure (BP) measurement. PWV was measured at baseline 32 normotensive volunteers, including 15 females and 17 males aged between 23 and 41 years old. The day before the measurements, the volunteers were not allowed to drink alcohol, stay up late or use any medicine that would affect BP. Repeated BP measurements were performed with an average follow-up system at certain times of the day. Equivalent constituents were established after questioning age, height, weight, physical activity levels in daily life, genetic predisposition for blood pressure and diabetic from all volunteers participating in the measurements. Systolic BP (SBP), diastolic BP (DBP), heart rate (HR), pulse pressure (PP), mean arterial pressure (MAP), a distance between brachial to radial artery (D), pulse transit time between brachial to radial artery (brPTT) and PWV measurements were taken. Following the experimental results, a linear correlation was found between SBP and PWV when the two groups separated by certain components were examined. Measurements taken with the new non-invasive low-power continuous-time sensor design show that the PWV may in the near future be used as a screening tool to identify continuous SBP values in clinical practice. The new non-invasive design suggests that SBP is the main correlation factor in the relationship with PWV compared to any other BP parameters.Master ThesisPublication Embargo Portable devices for In-Vitro characterization based on ultrasound(2015-08) Nabavi, Seyedfakhreddin; Yaralıoğlu, Göksenin; Yaralıoğlu, Göksenin; Uğurdağ, Hasan Fatih; Bozkurt, A.; Department of Electrical and Electronics Engineering; Nabavi, SeyedfakhreddinBu projede taşınabilir kartuş tabanlı lab-on-a-chip platformu öneriliyor. Ve bu platformun ana algılama mekanizması yüksek frekanslı akustik dalgalar ile çalışmaktadır. Biyolojik ölçümler için iki farklı transdüserin uygulanabilirliği incelenmiştir. Kan pıhtılaşma zamanı ölçümleri için ise çinkooksit (ZnO) tabanlı piezoelektrik transdüserler kullanılmıştır. Yöntem olarak kan ile dolu olan bir mikroakışkan kanaldan akustik yansımaların genliğinin ölçülmesi kullanımıştır. Mikroakışkan kanal hacmi 1 mikro-litre gibi düşük bir değer olabilir. Düşük maliyetli tek kullanımlık cam kartuş ise ölçümlerin yapılması için tasarlanmıştır. Kartuş iki cam alt tabakadan ve kanalın bulunduğu bir çift taraflı şerit tabakadan oluşur. Cam alt tabakalarından biri kartuşun dış yüzeyi üzerinde elektrik bağlantıları da sağlanmışbir şekilde 400 MHz'de çalışan bir mikroişlenmiş ZnO transdüsere sahiptir. Transdüser ise kanalı dolduran sıvı içinde akustik darbeleri üretmek için kanal ile hizalanmıştır. Kanalın üstünden gelen yansımalar sıvı içinden yayılmakta ve bu nedenle onların genlik ve fazları sıvının özelliklerinden dolayı etkilemektedir. Deneylerde tüm kan herhangi bir numune hazırlanmadan kullanılmıştır. Pıhtılaşma sırasında kan akışmazlığı değişir dolayısıyla kanalın üst kısmından gelen yansıma genliği izlenerek pıhtılaşma süresi ölçülebilir. Kanın sadece 1 mikro-litre gerektiren yöntem kalsiyum ile test edilmiş ve parsiyel tromboplastin (aPTT) reaktifler ile aktive edilmiştir. Önerilen yöntem, hastanın kendisini test etmek için kullanabileceği pıhtılaşma zamanını ölçen düşük maliyetli ve taşınabilir bir sistem için potansiyele sahiptir. İkinci transdüser CMUTs olarak yapılmıştır. Bu teknolojiyi akışmazlık ölçümleri için sıvıların içine batırılan bir biyolojik sensör olarak tanıtıyoruz. Membran tipi rezonatörler için sınır koşulları kalite faktörünü arttırmak amacıyla değiştirilmiştir. Bu değişim sensöre yüksek hassasiyet kazandırmıştır. Kalite faktöründeki iyileşme sonlu eleman analizi kullanarak gösterilmiştir.Master ThesisPublication Embargo Performance analysis of multi-relay free space optical communication systems(2015-01) Mostaani, Zohreh; Uysal, Murat; Uysal, Murat; Demiroğlu, Cenk; Odabaşoğlu, N.; Department of Electrical and Electronics Engineering; Mostaani, ZohrehFree space optical (FSO) communication has attracted a great attention in recent years because of their high bandwidth capacity in unregulated spectrum which makes them a cost-effective and easy-to-install alternative to fiber optics. Moreover they provide high immunity to interference and jamming due to directional and narrow beams. FSO systems are appealing for number of applications including last-mile access, fiber back-up, back-haul for wireless cellular networks, and disaster recovery among others. The major degrading factor in these systems is atmospheric turbulence induced fading particularly for long range links. Relay-assisted FSO systems provide significant performance gains by using the advantage of shorter hops and the fact that fading variance is distance dependent in FSO channels. In this thesis, we investigate the performance of multi-relay FSO systems in various settings. In the first part of thesis, we consider an all-optical relaying system to remove the need for optical -electrical- optical conversions. We explore the benefits of relay selection and investigate its outage performance over Gamma-Gamma distributed turbulence channels. In the second part of thesis, we assume that source is equipped with multiple transmit apertures employing the so-called spatial pulse position amplitude modulation (SPPAM). We investigate an upper bound for bit error rate of this system with multiple parallel relays over log-normal distributed channels.Master ThesisPublication Metadata only A compact circularly polarized monopulse slotted waveguide array for airborne applications(2019-10-24) Nawaz, Wasim; Uysal, Murat; Uysal, Murat; Durak, Kadir; Akgiray, Ahmet; Adam, Evşen Yanmaz; Güçlüoğlu, T.; Department of Electrical and Electronics Engineering; Nawaz, WasimIn modern radar and communication systems, high gain, high power capability and low-profile antenna systems are frequently utilized. In airborne and space borne applications, slotted waveguide antenna array is widely used due to its rigid structure, low-loss and high power handling capability. In this thesis, a compact, lightweight, high reection bandwidth, high gain and circularly polarzied slotted waveguide array antenna with monopulse capability operating in Ku-band is presented. Target application of this antenna is radio links on airborne platforms with built-in tracking capability . This thesis is divided into two parts: 1) Design of compact standing wave slotted array; 2) Design of a low-cost linear polarization (LP) to circular polarzition (CP) converter. In the first part of thesis, an antenna system is presented that has two key components: monopulse comparator/feed network and antenna section. The antenna is designed at 15 GHz and simulated using ANSYS HFSS. It is a planar array of 6x8 radiating slots with a gain greater than 22:5 dB at 15 GHz , side-lobe level (SLL) 13 dB , reection bandwidth of 1200 MHz. Monopulse comparator network is Magic Tee based waveguide structure. The antenna has maximum dimension of 10:8 cm * 10:7 cm 4 cm that makes it easy to house on an aircraft. In the second part of thesis, a LP to CP polarizer is presented. The proposed polarizer is a multi-layer metasurface based structure that converts incident linearly polarized wave into circularly polarized wave. The polarizer presented in this thesis is based on meander line and strip line hybrid concept. Each substrate layer is rotated 45 with respect to previous layer and is seperated by low permittivity material called spacer. The unit cell of the polarizer is square in shape with dimensions of 5:1mm 5:1 mm. Its axial ratio bandwidth is 2 GHz i.e: axial ratio is less than 3-dB from 14-16 GHz . It is also low-cost as compared to the available literature because thick substrates are used instead of high cost thin substrate and also one substrate layer is based on FR-4 laminate.Master ThesisPublication Restricted Fall detection for elderly people using depth video data obtained by kinect(2013-08) Davari, Amir Abbas; Erdem, Tanju; Erdem, Tanju; Sunay, M. Oğuz; Ercan, Ali Özer; Department of Electrical and Electronics Engineering; Davari, Amir AbbasAutomatic detection of unusual events such as falls is very important especially for elderly people living alone. Real-time detection of these events can reduce the health risks associated with a fall. There has been a series of ongoing researches in the ?eld of unusual event detection using the Microsoft`s depth sensor Kinect. It has been applied in areas like fall detection using only the depth images and features derived from skeletal data having exaggerated dimensionality. This thesis will propose a novel method for automatic detection of fall event by using depth cameras. Depth images generated by these cameras are used in estimating the skeletal data of a person. The contribution here is to use features extracted from this data to form a strong set of features which can help us achieve an increased precision at low redundancy. The achievements indicate that the calculated features which are derived from skeletal data are moderately powerful for detecting unusual events such as fall.Master ThesisPublication Metadata only Vulnerability of speaker verification system under replay spoofing attack and investigation of synthetic speech detection(2016-05) Özbay, Mustafa Caner; Demiroğlu, Cenk; Güz, Ü.; Gürkan, H.; Demiroğlu, Cenk; Güz, Ü.; Gürkan, H.; Department of Electrical and Electronics Engineering; Özbay, Mustafa CanerSecurity issues have become major subject along with developments in the speaker verification system. Previous studies have shown that performance is still not fully proven for vulnerability. Simple and easy methods may be preferred to attack however the verification system can be attacked with high-tech infrastructure. The first example of this method is "Replay Attack". In this thesis, firstly we downloaded data from the Internet in ways that everyone can easily success. Then the data has enrolled into the system that was previously created as universal background model (UBM). Operability of the system have been proved by tests with same people voice data and then system was exposed to attack again with most similar speech that obtained from other speakers. The results also showed that, even it is not high rated but spoofing attack may cause false acceptance by the verification system. After that, noise added to simulate effect of electronic devices and that added noise was found to increase the system performance. With this work it is aimed to point the open field in the anti-spoofing area against the replay attack. Then the specification of synthetic speech system and the differences according to natural sound is investigated. How it is used as spoofing attack and the results are also represented.Master ThesisPublication Metadata only Automated procedure clustering for reverse engineering PL/SQL programs(2016-05) Altınışık, Metin; Sözer, Hasan; Gürsun, Gonca; Sözer, Hasan; Gürsun, Gonca; Aktemur, Tankut Barış; Aktaş, M.; Alkaya, A. F.; Department of Electrical and Electronics Engineering; Altınışık, MetinLarge software systems have to be decomposed into separate, modular units for providing appropriate abstractions and improving maintainability. There exist clustering techniques that are applied to provide such abstractions by automatically grouping system modules based on dependencies among them. Hereby, dependency is usually measured as the extent to which a module refers to elements of another module. This approach cannot be directly applied for all types of programs. Some programs involve modules that are indirectly coupled. For instance, PL/SQL programs include procedures that are in most cases coupled due to their database operations although they do not make calls to each other. In this thesis, we provide an approach and a tool that supports automated modularization of software systems by considering this type of dependencies We also extend this approach for multiple, different types of dependencies. We construct several dependency matrices each of which captures a different type of dependency among the system modules. First, we perform clustering according to each of these matrices separately. Then, we perform cluster aggregation (meta clustering) on the obtained clustering results to propose a packaging structure to the designer. We performed two industrial case studies on real PL/SQL programs from the telecommunications domain. Many unexisted packages were proposed by our tool and the accuracy of the results were confirmed by domain experts.