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Permanent URI for this collectionhttps://hdl.handle.net/20.500.14288/3
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Publication Metadata only Coarse-to-fine surface reconstruction from silhouettes and range data using mesh deformation(Academic Press Inc Elsevier Science, 2010) N/A; Department of Computer Engineering; Sahillioğlu, Yusuf; Yemez, Yücel; PhD Student; Faculty Member; Department of Computer Engineering; Graduate School of Sciences and Engineering; College of Engineering; 215195; 107907We present a coarse-to-fine surface reconstruction method based on mesh deformation to build watertight surface models of complex objects from their silhouettes and range data. The deformable mesh, which initially represents the object visual hull, is iteratively displaced towards the triangulated range surface using the line-of-sight information. Each iteration of the deformation algorithm involves smoothing and restructuring operations to regularize the surface evolution process. We define a non-shrinking and easy-to-compute smoothing operator that fairs the surface separately along its tangential and normal directions. The mesh restructuring operator, which is based on edge split, collapse and flip operations, enables the deformable mesh to adapt its shape to the object geometry without suffering from any geometrical distortions. By imposing appropriate minimum and maximum edge length constraints, the deformable mesh, hence the object surface, can be represented at increasing levels of detail. This coarse-to-fine strategy, that allows high resolution reconstructions even with deficient and irregularly sampled range data, not only provides robustness, but also significantly improves the computational efficiency of the deformation process. We demonstrate the performance of the proposed method on several real objects.Publication Metadata only Threshold single password authentication(Springer International Publishing Ag, 2017) N/A; N/A; Department of Computer Engineering; İşler, Devriş; Küpçü, Alptekin; Master Student; Faculty Member; Department of Computer Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 168060Passwords are the most widely used form of online user authentication. In a traditional setup, the user, who has a human-memorable low entropy password, wants to authenticate with a login server. Unfortunately, existing solutions in this setting are either non-portable or insecure against many attacks, including phishing, man-in-the-middle, honeypot, and offline dictionary attacks. Three previous studies (Acar et al. 2013, Bicakci et al. 2011, and Jarecki et al. 2016) provide solutions secure against offline dictionary attacks by additionally employing a storage provider (either a cloud storage or a mobile device for portability). These works provide solutions where offline dictionary attacks are impossible as long as the adversary does not corrupt both the login server and the storage provider. For the first time, improving these previous works, we provide a more secure generalized solution employing multiple storage providers, where our solution is proven secure against offline dictionary attacks as long as the adversary does not corrupt the login server and threshold-many storage providers. We define ideal and real world indistinguishability for threshold single password authentication (Threshold SPA) schemes, and formally prove security of our solution via ideal-real simulation. Our solution provides security against all the above-mentioned attacks, including phishing, man-in-the-middle, honeypot, and offline dictionary attacks, and requires no change on the server side. Thus, our solution can immediately be deployed via a browser extension (or a mobile application) and support from some storage providers. We further argue that our protocol is efficient and scalable, and provide performance numbers where the user and storage load are only a few milliseconds.Publication Metadata only FlexDPDP: flexlist-based optimized dynamic provable data possession(assoc Computing Machinery, 2016) N/A; N/A; N/A; Department of Computer Engineering; Department of Computer Engineering; Department of Computer Engineering; Esiner, Ertem; Kachkeev, Adilet; Küpçü, Alptekin; Özkasap, Öznur; Master Student; Master Student; N/A; Faculty Member; Faculty Member; Department of Computer Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; 168060; 113507With increasing popularity of cloud storage, efficiently proving the integrity of data stored on an untrusted server has become significant. authenticated skip lists and rank-based authenticated skip lists (RBaSL) have been used to provide support for provable data update operations in cloud storage. However, in a dynamic file scenario, An RBaSL based on block indices falls short when updates are not proportional to a fixed block size; such an update to the file, even if small, may result in O(n) updates on the data structure for a file with n blocks. To overcome this problem, we introduce FlexList, A flexible length-based authenticated skip list. FlexList translates variable-size updates to O(inverted right perpendicularu/Binverted left perpendicular) insertions, removals, or modifications, where u is the size of the update and B is the (average) block size. We further present various optimizations on the four types of skip lists (regular, Authenticated, rank-based authenticated, and FlexList). We build such a structure in O(n) time and parallelize this operation for the first time. We compute one single proof to answer multiple (non) membership queries and obtain efficiency gains of 35%, 35%, and 40% in terms of proof time, energy, and size, respectively. We propose a method of handling multiple updates at once, Achieving efficiency gains of up to 60% at the server side and 90% at the client side. We also deployed our implementation of FlexDPDP (dynamic provable data possession (DPDP) with FlexList instead of RBaSL) on PlanetLab, demonstrating that FlexDPDP performs comparable to the most efficient static storage scheme (provable data possession (PDP)) while providing dynamic data support.Publication Metadata only Official arbitration with secure cloud storage application(Oxford University Press (OUP), 2015) Department of Computer Engineering; Küpçü, Alptekin; Faculty Member; Department of Computer Engineering; College of Engineering; 168060In a secure cloud storage setting, a client outsources storage of her data to a server, who may, willingly or not, corrupt the data, or delete infrequently accessed parts to save space. Existing proof of storage schemes only solve part of this problem: The client may obtain a cryptographic proof of integrity. But what happens if this proof fails to verify? We argue that in such a case, both the client and the server should be able to contact an official court, providing cryptographic proofs, to resolve this dispute. We show that, this property is stronger than what is known as public verifiability since we must handle a malicious client as well. We present multiple schemes that work for various static and dynamic storage solutions. We showimplementation results where the overhead for adding the ability to resolve such disputes at a court is only 2 ms and 80 bytes for each update on the stored data, using standard desktop hardware. Finally, we note that disputes may arise in many other situations, such as when two parties exchange items (e.g. e-commerce) or agree on something (e.g. contract-signing). We extend our official arbitration protocols for a general case, including dynamic authenticated data structures.Publication Metadata only Engine compartment UWB channel model for intravehicular wireless sensor networks(IEEE-Inst Electrical Electronics Engineers Inc, 2014) Department of Computer Engineering; N/A; Department of Electrical and Electronics Engineering; Demir, Utku; Baş, Celalettin Ümit; Ergen, Sinem Çöleri; Undergraduate Student; Master Student; Faculty Member; Department of Computer Engineering; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 7211Intravehicular wireless sensor network (IVWSN) is a cutting edge research topic that delivers cost reduction, assembly, and maintenance efficiency by removing the wiring harnesses within the vehicle and enables the integration of new sensors into the locations inside a vehicle where cable connection is not possible. Providing energy efficiency through the low-duty-cycle operation and high reliability by exploiting the large bandwidth, ultrawideband (UWB) has been determined to be the most appropriate technology for IVWSNs. We investigate the UWB channel model for IVWSNs within the engine compartment of a vehicle by collecting an extensive amount of data for 19 x 19 links for different types and conditions of the vehicle. These include a Fiat Linea with engine off, Fiat Linea with engine on, and Peugeot Bipper with engine off. The path-loss exponent is estimated to be around 3.5 without exhibiting much variation when the engine is turned on and for different types of vehicles. The power variation around the expected path loss has lognormal distribution with zero mean and standard deviation in the range of [5.5, 6.3] dB for different types of vehicles with almost no variation when the engine of the same vehicle is turned on. The clustering phenomenon in the power delay profile (PDP) is well represented by a modified Saleh-Valenzuela (SV) model. The interarrival times of the clusters are modeled using a Weibull distribution. The cluster-amplitude and ray-amplitude decay functions are represented with a dual-slope linear model with breakpoint around 26.6 and 5.5 ns, respectively. The parameters of the Weibull distribution and these dual-slope linear models do not vary significantly for different types and conditions of the vehicle. The variations of the observed PDPs around the SV model is well modeled by independent normal random variables with zero mean and with a variance independent of the delay bin, and the type and condition of the vehicle. We propose a simulation model for the UWB channel within the engine compartment based on these findings and validate it by comparing the received energy and root mean square (RMS) delay spread of the generated and observed PDPs.Publication Metadata only Inonymous: anonymous invitation-based system(Springer International Publishing Ag, 2017) N/A; Department of Computer Engineering; Boshrooyeh, Sanaz Taheri; Küpçü, Alptekin; PhD Student; Faculty Member; Department of Computer Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 168060In invitation-based systems, a user is allowed to join upon receipt of a certain number of invitations from the existing members. The system administrator approves the new membership if he authenticates the inviters and the invitations, knowing who is invited by whom. However, the inviter-invitee relationship is privacy-sensitive information and can be exploited for inference attacks: The invitee's profile (e.g., political view or location) might leak through the inviters' profiles. To cope with this problem, we propose Inonymous, an anonymous invitationbased system where the administrator and the existing members do not know who is invited by whom. We formally define and prove the inviter anonymity against honest but curious adversaries and the information theoretic unforgeability of invitations. Inonymous is efficiently scalable in the sense that once a user joins the system, he can immediately act as an inviter, without re-keying and imposing overhead on the existing members. We also present InonymouX, an anonymous cross-network invitation-based system where users join one network (e.g., Twitter) using invitations of members of another network (e.g., Facebook).Publication Metadata only A survey of energy efficiency in SDN: Software-based methods and optimization models(Elsevier, 2019) N/A; N/A; Department of Computer Engineering; Assefa, Beakal Gizachew; Özkasap, Öznur; PhD Student; Faculty Member; Department of Computer Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; 113507Software Defined Networking (SDN) paradigm has the benefits of programmable network elements by separating the control and the forwarding planes, efficiency through optimized routing and flexibility in network management. As the energy costs contribute largely to the overall costs in networks, energy efficiency has become a significant design requirement for modem networking mechanisms. However, designing energy efficient solutions is non-trivial since they need to tackle the trade-off between energy efficiency and network performance. In this article, we address the energy efficiency capabilities that can be utilized in the emerging SDN. We provide a comprehensive and novel classification of software-based energy efficient solutions into subcategories of traffic aware, end system aware and rule placement. We propose general optimization models for each subcategory, and present the objective function, the parameters and constraints to be considered in each model. Detailed information on the characteristics of state-of-the-art methods, their advantages, drawbacks are provided. Hardware-based solutions used to enhance the efficiency of switches are also described. Furthermore, we discuss the open issues and future research directions in the area of energy efficiency in SDN.Publication Metadata only Task allocation in volunteer computing networks under monetary budget constraints(Springer, 2015) Barla Cambazoglu, B.; Department of Computer Engineering; Department of Computer Engineering; Güler, Hüseyin; Özkasap, Öznur; PhD Student; Faculty Member; Department of Computer Engineering; College of Engineering; College of Engineering; N/A; 113507In volunteer computing networks, the peers contribute to the solution of a computationally intensive problem by freely providing their computational resources, i.e., without seeking any immediate financial benefit. In such networks, although the peers can set certain bounds on how much their resources can be exploited by the network, the monetary cost that the network brings to the peers is unclear. In this work, we propose a volunteer computing network where the peers can set monetary budgets, limiting the financial burden incurred on them due the usage of their computational resources. Under the assumption that the price of the electricity consumed by the peers has temporal variation, we show that our approach leads to an interesting task allocation problem, where the goal is to maximize the amount of work done by the peers without violating the monetary budget constraints set by them. We propose various heuristics as solution to the problem, which is NP-hard. Our extensive simulations using realistic data traces and real-life electricity prices demonstrate that the proposed techniques considerably increase the amount of useful work done by the peers, compared to a baseline technique.Publication Metadata only Cutting down the energy cost of geographically distributed cloud data centers(Springer-Verlag Berlin, 2013) Cambazoğlu, Berkant Barla; N/A; Department of Computer Engineering; Güler, Hüseyin; Özkasap, Öznur; PhD Student; Faculty Member; Department of Computer Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 113507The energy costs constitute a significant portion of the total cost of cloud providers. The major cloud data centers are often geographically distributed, and this brings an opportunity to minimize their energy cost. In this work, we model a geographically distributed data center network that is specialized to run batch jobs. Taking into account the spatio-temporal variation in the electricity prices and the outside weather temperature, we model the problem of minimizing the energy cost as a linear programming problem. We propose various heuristic solutions for the problem. Our simulations using real-life workload traces and electricity prices demonstrate that the proposed heuristics can considerably decrease the total energy cost of geographically distributed cloud data centers, compared to a baseline technique.Publication Metadata only Fast optimistically fair cut-and-choose 2PC(Springer International Publishing Ag, 2017) Mohassel, Payman; Department of Computer Engineering; Küpçü, Alptekin; Faculty Member; Department of Computer Engineering; College of Engineering; 168060Secure two party computation (2PC) is a well-studied problem with many real world applications. Due to Cleve's result on general impossibility of fairness, however, the state-of-the-art solutions only provide security with abort. We investigate fairness for 2PC in presence of a trusted Arbiter, in an optimistic setting where the Arbiter is not involved if the parties act fairly. Existing fair solutions in this setting are by far less efficient than the fastest unfair 2PC. We close this efficiency gap by designing protocols for fair 2PC with covert and malicious security that have competitive performance with the state-of-the-art unfair constructions. In particular, our protocols only requires the exchange of a few extra messages with sizes that only depend on the output length; the Arbiter's load is independent of the computation size; and a malicious Arbiter can only break fairness, but not covert/malicious security even if he colludes with a party. Finally, our solutions are designed to work with the state-of-the-art optimizations applicable to garbled circuits and cut-and-choose 2PC such as free-XOR, half-gates, and the cheating-recovery paradigm.