Tubitak UEKAE

Gebze, Turkey

Tubitak UEKAE

Gebze, Turkey
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Sezgin M.,Tubitak UEKAE
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

In this paper hand-held dual sensor detector development requirements are considered dedicated to buried object detection. Design characteristics of such a system are categorized and listed. Hardware and software structures, ergonomics, user interface, environmental and EMC/EMI tests to be applied and performance test issues are studied. Main properties of the developed system (SEZER) are presented, which contains Metal Detector (MD) and Ground Penetrating Radar (GPR). The realized system has ergonomic structure and can detect both metallic and non-metallic buried objects. Moreover classification of target is possible if it was defined to the signal processing software in learning phase. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Kahraman S.,Tubitak Uekae | Celebi M.E.,Technical University of Istanbul
IEEE International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC | Year: 2010

In this paper, we propose a technique which is efficient in reducing the required computational complexity of the maximum-likelihood decoding for BLAST system. Our technique is based on the determination of reducible computational complexity for any given BLAST system. In this fashion a specialized decoding can be defined. Our idea is based on the determination of zero entries of the upper-triangular matrix R which occurs in QR-decomposition step of the sphere decoding algorithm. Through the determined zero at kth row of the matrix R, at least 8 arithmetic operations can be canceled for every time of node visiting in the search tree at level k. Furthermore, properties of the matrix structure can be exploited in sphere decoding in order to reduce complexity of the metric computations for each branch. For this case, considerable saving in the computational complexity can be obtained. ©2010 IEEE.


Akgun M.,Tubitak UEKAE | Caglayan M.U.,Istanbul University
Proceedings of the 2011 6th International Conference on Availability, Reliability and Security, ARES 2011 | Year: 2011

In this paper, we propose a privacy-preserving authentication scheme for RFID systems with fast lookup time. Our solution is based on the use of Physically Unclonable Functions (PUFs). Although there are many proposals that addresses the security and privacy issues of RFID, the search efficiency still remains as a challenging issue. A first treebased mutual authentication scheme for RFID systems has been proposed by Molnar and Wagner to solve the search efficiency problem. The large communication overhead of this scheme has been reduced by Dimitriou performing the authentication with one message from the tag to the reader. However, tree-based schemes are vulnerable to tag compromising attack due to lack key-updating mechanism. Therefore, tree-based schemes are weak private in the Vaudenay-Model. In this paper, we present a tree-based authentication protocol for RFID systems that is destructive-private in the Vaudenay-Model. Our proposed scheme provides resistance against tag compromising attack by using PUFs as a secure storage to keep secrets of the tag. © 2011 IEEE.


Akgun M.,Tubitak UEKAE | Caglayan M.U.,Istanbul University
Proceedings - International Conference on Network Protocols, ICNP | Year: 2014

Many RFID authentication protocols have been proposed to provide desired security and privacy level for RFID systems. Almost all of these protocols are based on symmetric cryptography because of the limited resources of RFID tags. Recently Cheng et. Al have proposed an RFID security protocol based on chaotic maps. In this paper, we analyse the security of this protocol and discover its vulnerabilities. We firstly present a de-synchronization attack in which a passive adversary makes the shared secrets out-of-synchronization by eavesdropping just one protocol session. We secondly present a secret disclosure attack in which a passive adversary extracts secrets of a tag by eavesdropping just one protocol session. An adversary having the secrets of the tag can launch some other attacks. Finally, we propose modifications to Cheng et. Al's protocol to eliminate its vulnerabilities. © 2014 IEEE.


Yoldemir A.B.,Tubitak UEKAE | Sezgin M.,Tubitak UEKAE
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

In the underground inspection problem, signature of a big target at a certain depth may give equivalent information to the signature of a smaller target at shallower depth, unless depth information is not used. This results in a difficulty in the identification process. Therefore, depth information is coming into prominence in the classification step to increase the identification performance. In this study, we propose a burial depth estimation method on GPR data. In our work, discrete wavelet transform is used in the preprocessing step. After this stage, statistical hypothesis tests are utilized to detect the statistical discrepancies in the returning signals at different depth levels. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Akgun M.,Tubitak UEKAE | Caglayan M.U.,Istanbul University
IWCMC 2015 - 11th International Wireless Communications and Mobile Computing Conference | Year: 2015

Radio Frequency Identification (RFID) protocols should have a secret updating phase in order to protect the privacy of RFID tags against tag tracing attacks. In the literature, there are many lightweight RFID authentication protocols that try to provide key updating with lightweight cryptographic primitives. In this paper, we analyze the security of two recently proposed lightweight RFID authentication protocol against desynchronization attacks. We show that secret values shared between the back-end server and any given tag can be easily desynchronized. This weakness stems from the insufficient design of these protocols. © 2015 IEEE.


Eksim A.,Tubitak UEKAE | Celebi M.E.,Technical University of Istanbul
IETE Technical Review (Institution of Electronics and Telecommunication Engineers, India) | Year: 2010

The statistical cooperative diversity, based on space-time block codes (statistical STBC cooperative -diversity) is proposed for binary sensors by several authors. Since Alamouti's code is the only orthogonal code which achieves full diversity and full rate for two sensors, it is used in their works, and their achievable diversity order is 2. Instead of using Alamouti's code, we use extended cooperative space-time block coding (ECBSTBC) which achieves full diversity which is shown analytically and full rate for an arbitrary number of sensors if a limited feedback is available at the active sensors. Another method to increase diversity in cooperative communications is sensor (relay) selection. However, the sensor selection method may lead to the selection of the same (near) sensor for transmission over a long period causing the energy hole problem in sensor networks. The ECBSTBC which utilizes every sensor in sight thus distributes the energy consumption among active sensors and alleviates the energy hole problem. In addition, it can be shown with detailed simulations that the ECBSTBC outperforms both the statistical STBC cooperative diversity and the sensor selection schemes. Copyright © 2009 by the IETE.


Yetginer E.,Tubitak UEKAE | Liu Z.,North Carolina State University | Rouskas G.N.,North Carolina State University
Journal of Optical Communications and Networking | Year: 2011

Wavelength division multiplexing rings are now capable of supporting more than 100 wavelengths over a single fiber. Conventional link and path formulations for the routing and wavelength assignment problem are inefficient due to the inherent symmetry in wavelength assignment and the fact that the problem size increases fast with the number of wavelengths. Although a formulation based on maximal independent sets (MIS) does not have these drawbacks, it suffers from exponential growth in the number of variables with increasing network size. We develop a new ILP (integer linear program) formulation based on the key idea of partitioning the path set and representing the MIS in the original network using the independent sets calculated in each of these partitions. This exact decomposition trades off the number of variables with the number of constraints and, as a result, achieves a much better scalability in terms of network dimension. Numerical results on ring networks of various sizes demonstrate that this new ILP decomposition achieves a decrease of several orders of magnitude in running time compared to existing formulations. Our main contribution is a novel and extremely fast technique for obtaining, in a few seconds using commodity CPUs, optimal solutions to instances of maximum size SONET rings with any number of wavelengths; such instances cannot be tackled with classical formulations without vast investments in computational resources and time. © 2011 Optical Society of America.


Akgun M.,Tubitak UEKAE | Akgun M.,Bogazici University | Caglayan M.U.,Bogazici University
Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) | Year: 2011

There are numerous works on the privacy and the security problems for RFID systems. However, many of them have failed due to the lack of formal security proof. In the literature, there are a few formal models that consider forward untraceability. In ASIACRYPT 2007, Vaudenay presented an new security and privacy model for RFID that combines early models to more understandable one. In this paper, we revisit Vaudenay's model and modify it by considering the notion of forward untraceability. Our modification considers all message flows between RFID reader and tags before and after compromising secrets of tag. We analyze some RFID schemes claiming to provide forward untraceability and resistance to server impersonation. For each scheme, we exhibit attacks in which a strong adversary can trace the future interactions of the tag and impersonate the valid server to the tag. Further, we show that a previously proposed attack claiming to violate forward untraceability of an existing RFID scheme does not violate forward untraceability. © 2011 Springer-Verlag.


Eksim A.,Tubitak UEKAE | Celebi M.E.,Technical University of Istanbul
SIU 2010 - IEEE 18th Signal Processing and Communications Applications Conference | Year: 2010

Code selection and transmit antenna selection are widely used in limited feedback wireless systems. When one of the antenna channel gains is much higher than the other antenna channel gains; using antenna selection method increases received SNR at the receiver. However, when antenna channel gains are close to each other; using code selection method increases the received SNR at the receiver. In this paper, we propose an adaptive code and antenna selection scheme to increase the received SNR at the destination. In this technique, using one additional bit feedback yields improved SNR at the destination compared to using solely code or transmit antenna selection method. Detailed simulations show that adaptive code and antenna selection with four bit feedback yields a performance of the extended balanced space-time block coding with ideal feedback which requires exact channel state information at the transmitter. ©2010 IEEE.

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