Εκπαίδευση - Σπουδές

  • Δίπλωμα Μηχανικού Ηλεκτρονικών Υπολογιστών και Πληροφορικής, Πανεπιστήμιο Πατρών
  • Μεταπτυχιακό Δίπλωμα Ειδίκευσης στα Συστήματα Επεξεργασίας Σημάτων και Εικόνων, Τμήμα Μηχανικών Ηλεκτρονικών Υπολογιστών και Πληροφορικής, Πανεπιστήμιο Πατρών
  • Διδακτορικό Δίπλωμα, Τμήμα Μηχανικών Ηλεκτρονικών Υπολογιστών και Πληροφορικής, Πανεπιστήμιο Πατρών

Ερευνητικά Ενδιαφέροντα

  • Information forensics and security
  • Digital image watermarking
  • Efficient schemes for image registration
  • Optimization of digital image processing algorithms for efficient hardware implementation
  • Hardware Security

Διδασκαλία

  • Σήματα και Συστήματα
  • Πολυμέσα
  • Αρχιτεκτονική Υπολογιστών - Εργαστήριο
  • Ψηφιακή Επεξεργασία Εικόνας
  • Λειτουργικά Συστήματα

 

Δημοσιεύσεις σε Διεθνή Περιοδικά (Journals)


Copyright Notice: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted or mass reproduced without the explicit permission of the copyright holder.


K. Pexaras, I. G. Karybali, E. Kalligeros, "Optimization and Hardware Implementation of Image and Video Watermarking for Low Cost Applications", IEEE Transactions on Circuits and Systems I: Regular Papers, Vol. 66, No. 6, pp. 2088-2101, 2019, https://ieeexplore.ieee.org/stamp/s..., IF = 3.934
 

Abstract
The prevalence of wireless networks has made the long-term need for communications security more imperative. In various wireless applications, images and/or video constitute critical data for transmission. For their copyright protection and authentication, watermarking can be used. In many cases, the cost of wireless nodes must be kept low, which means that their processing and/or power capabilities are very limited. In such cases, low-cost hardware implementations of digital image/video watermarking techniques are necessary. However, to end up with such implementations, proper selection of watermarking techniques is not enough. For this reason, in this paper, we introduce computation optimizations of the implemented algorithm to keep the integer part of arithmetic operations at optimal size, and, hence, arithmetic units as small as possible. In addition, further analysis is performed to reduce quantization error. Three different hardware-architecture variants, two for image watermarking and one for video (pipelined), are proposed, which reutilize the already small arithmetic units in different computation steps, to further reduce implementation cost. The proposed designs compare favorably to already existing implementations in terms of area, power, and performance. Moreover, the watermarked images'/frames' errors, compared to their floating point counterparts, are very small, while robustness to various attacks is high.

I. G. Karybali, E. Z. Psarakis, K. Berberidis , G. D. Evangelidis, An Efficient Spatial Domain Technique for Subpixel Image Registration, Signal Processing: Image Communication, Vol. 23, pp. 711-724, 2008, Elsevier, http://www.sciencedirect.com/scienc..., IF = 2.814
 

Abstract
In this paper a new technique for performing image registration with subpixel accuracy is presented. The proposed technique, which is based on the maximization of the correlation coefficient function, does not require the reconstruction of the intensity values and provides a closed-form solution to the subpixel translation estimation problem. Moreover, an efficient iterative scheme is proposed, which reduces considerably the overall computational cost of the image registration problem. This scheme properly combined with the proposed similarity measure results in a fast spatial domain technique for subpixel image registration.

I. G. Karybali, K. Berberidis , Efficient Spatial Image Watermarking via New Perceptual Masking and Blind Detection Schemes, IEEE Transactions on Information Forensics and Security, Vol. 1, No. 2, pp. 256-274, 2006, http://ieeexplore.ieee.org/stamp/st..., IF = 6.211
 

Abstract
The aim of this paper is to improve the performance of spatial domain watermarking. To this end, a new perceptual mask and a new detection scheme are proposed. The proposed spatial perceptual mask is based on the cover image prediction error sequence and matches very well with the properties of the human visual system. It exhibits superior performance compared to existing spatial masking schemes. Moreover, it allows for a significantly increased strength of the watermark while, at the same time, the watermark visibility is decreased. The new blind detection scheme comprises an efficient prewhitening process and a correlation-based detector. The prewhitening process is based on the least-squares prediction error filter and substantially improves the detector’s performance. The correlation-based detector that was selected is shown to be the most suitable for the problem at hand. The improved performance of the proposed detection scheme has been justified theoretically for the case of linear filtering plus noise attack and through extensive simulations. The theoretical analysis is independent of the proposed mask and the derived expressions can be used for any watermarking technique based on spatial masking. It is shown though that in most cases the detector performs better if the proposed mask is employed.

Επιστημονικά Συνέδρια (Conferences)


Copyright Notice: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted or mass reproduced without the explicit permission of the copyright holder.


E. Kalligeros, N. Karousos, I. G. Karybali, "Oracle-based Logic Locking Attacks: Protect the Oracle Not Only the Netlist", Design Automation and Test in Europe (DATE) Conference, (to_appear), Mar, 2020,
 

Abstract
Logic locking has received a lot of attention in the literature due to its very attractive hardware-security characteristics: it can protect against IP piracy and overproduction throughout the whole IC supply chain. However, a large class of logic-locking attacks, the oracle-based ones, take advantage of a functional copy of the chip, the oracle, to extract the key that protects the chip. So far, the techniques dealing with oracle-based attacks focus on the netlist that the attacker possesses, assuming that the oracle is always available. For this reason, they are usually overcome by new attacks. In this paper, we propose a hardware security scheme that targets the protection of the oracle circuit, by locking the circuit when the, necessary for setting the inputs and observing the outputs, scan in/out process begins. Hence, no correct input/output pairs can be acquired to perform the attacks. The proposed scheme is not based on controlling global signals like test_enable or scan_enable, whose values can be easily suppressed by the attacker. Security threats are identified, discussed and addressed. The developed scheme is combined with a traditional logic locking technique with high output corruptibility, to achieve increased levels of protection.

K. Pexaras, C. Tsiourakis, I. G. Karybali, E. Kalligeros, "Optimization and Hardware Implementation of Image Watermarking for Low Cost Applications", IEEE International Conference on Electronics, Circuits and Systems (ICECS), pp. 347-350, Dec, 2017, http://ieeexplore.ieee.org/stamp/st...
 

Abstract
In many resource/ power constrained applications (e.g., in wireless-network nodes) there is a need for low cost hardware implementations of digital image watermarking techniques. However, to end up with such an implementation, a proper selection of a watermarking technique, based on performance and cost criteria, is not enough. For that reason, in this paper we introduce computation optimizations of the implemented algorithm to keep the integer portion of arithmetic operations at optimal size, and, hence, arithmetic units as small as possible. Additionally, the proposed architecture reutilizes those units in different computation steps, to further reduce implementation cost. The proposed design compares favorably with the already existing implementations, in terms of area, power and performance.

N. Karousos, K. Pexaras, I. G. Karybali, E. Kalligeros, "Weighted Logic Locking: A New Approach for IC Piracy Protection", IEEE International Symposium on On-Line Testing and Robust System Design (IOLTS), pp. 221-226, Jul, 2017, http://ieeexplore.ieee.org/stamp/st...
 

Abstract
Logic locking has been successfully used for protecting digital circuits against IC piracy. Modern logic locking techniques offer significant security advantages, like high corruptibility of the locked circuit's outputs when applying random keys (= 50% Hamming Distance -HD- compared to the correct outputs), or resilience to the key-sensitization attack. However, there are no techniques to combine both advantages. To solve this problem, weighted logic locking is proposed in this paper. Instead of the conventional single key-input control, the proposed technique uses multiple key-inputs to control every key-gate. This new, weighted key-gate control is by construction immune to the key-sensitization attack, while by employing a new key-gate insertion metric, 50% HD is obtained even for circuits with many outputs. Additionally, weighted key-gate control increases dramatically the probability of any key-gate to corrupt the circuit’s values, which means that fewer key-gates are needed to achieve 50% HD. This way, execution time for locking the circuits is drastically reduced. Apart from these advantages, weighted logic locking is fairly "generic" and can be combined with other techniques to improve security (e.g., to thwart the SAT attack).

I. G. Karybali, E. Z. Psarakis, K. Berberidis , G. D. Evangelidis, Efficient image registration with subpixel accuracy, 14th European Signal Processing Conference (EUSIPCO 2006), Sep, 2006, http://www.eurasip.org/Proceedings/...
 

Abstract
The contribution of this paper is twofold. First, a new spatial domain image registration technique with subpixel accuracy is presented. This technique is based on a double maximization of the correlation coefficient and provides a closed-form solution to the subpixel translation estimation problem. Second, an efficient iterative scheme for integer registration is proposed, which reduces significantly the number of searches, as compared to the exhaustive search. This scheme can be used as a pre-processing step in the sub-pixel accuracy technique, leading to lower computational complexity. Extensive simulation results have shown that the performance of the proposed technique compares very favorably with respect to existing ones.

I. G. Karybali, K. Berberidis , Improved Embedding Of Multiplicative Watermarks Via Space-Time Block Coding, 13th European Signal Processing Conference (EUSIPCO 2005), Sep, 2005, http://www.eurasip.org/Proceedings/...
 

Abstract
In this paper, a new scheme for image watermarking in spatial domain based on space-time block coding is proposed. Specifically, a 4x4 real orthogonal design is employed for embedding a multiplicative watermark in the image. The image is divided into four blocks, which, after some simple operations, can be viewed as four different flat fading channels. At the receiver’s end, a low cost maximum likelihood decoding is performed based only on linear processing. This scheme turns out to perform much better than repetitive watermarking, taking advantage of the well-known merits of space-time block coding, i.e., it achieves full diversity offering at the same time the maximum possible transmission rate for real constellations.

I. G. Karybali, K. Berberidis , A New Blind Image-Adaptive Watermarking Scheme: Theoretical and Experimental Results, 12th European Signal Processing Conference (EUSIPCO 2004), pp. 1489-1492, Sep, 2004, http://www.eurasip.org/Proceedings/...
 

Abstract
In this paper a new blind image-adaptive watermarking scheme is proposed. The scheme employs a new spatial mask whose construction is based on the HVS’s (Human Visual System) properties. Specifically, the mask is a function of the local variance of the cover image prediction error sequence. An improved blind detection scheme has also been developed, based on a proper pre-whitening process. Due to the above modifications the proposed technique exhibits superior performance as compared to conventional HVS-based blind adaptive watermarking. The proposed detector’s performance improvement has been justified theoretically for the cases of no attack, noise attack and linear filtering attack, and is also verified through extensive simulations. The theoretical analysis is independent of the proposed mask and the derived expressions can be used for any watermarking technique based on spatial masking. Moreover, proper expressions have been derived that enable the computation of detection thresholds adaptable to the attacking conditions.

I. G. Karybali, K. Berberidis , Blind Image-Adaptive Watermarking, 10th IEEE International Conference on Electronics, Circuits and Systems (ICECS 2003), pp. 894-897, Dec, 2003, http://ieeexplore.ieee.org/iel5/912...
 

Abstract
In this paper a new blind image-adaptive watermarking technique is proposed. The main contributions in this work are the following. First, a new spatial mask taking into account the Human Visual System (HVS) properties, is proposed. The mask is constructed based on the local variance of the cover image prediction ermr sequence. Second, an improved detection scheme has heen developed, which is blind, in the sense that no knowledge concerning the cover image is required. The similarity measure used in the detector is the normalized correlation between the reproduced watermark and the prediction error of the watermarked and possibly attacked image (instead of the image itself). Due to the above modifications the proposed technique exhibits superior performance as compared to the conventional HVS-based blind adaptive watermarking. This performance improvement has been justified theoretically and verified through extensive simulations. In particular, the proposed technique is robust to additive white noise, JPEG and Wavelet compression, filtering etc.

K. Berberidis , I. G. Karybali, A New Efficient Cross-Correlation Based Image Registration Technique with Improved Performance, 11th European Signal Processing Conference (EUSIPCO 2002), pp. 13-16, Sep, 2002, http://www.eurasip.org/Proceedings/...
 

Abstract
In many applications the image registration task turns out to be a fundamental prerequisite for any further processing and analysis. In the proposed paper a new eÆcient technique is presented, appropriate for registering images which are translated and rotated versions of a reference image. The technique consists of two main parts: an efficiently implemented prewhitening part, and an iterative part which yields the unknown displacements after a few iterations. The cross-correlation operations involved in the iterative part are performed efficiently via a new scheme based on a proper partitioning of the images and the use of the FFT. Note that this efficient scheme is also applicable to the conventional spatial cross-correlation method. The new registration technique exhibits a superior performance as compared to the conventional cross-correlation method.

I. G. Karybali, K. Berberidis , C. Balas, A High-Performance Image Registration Technique and Application to Multispectral Imaging for Medical Diagnosis, 16th International Eurasip Conference BIOSIGNAL, pp. 255-258, Jun, 2002, http://www.icsd.aegean.gr/karybali/...
 

Abstract
In many applications the image registration task is a fundamental prerequisite for any further processing and analysis. In the proposed paper a new efficient technique is presented, appropriate for registering images, which are translated and rotated versions of a reference image. The technique consists of two main parts: an efficiently implemented prewhitening part and an iterative part, which yields the unknown displacements after a few iterations. The most costly part of the algorithm (i.e. cross-correlation computations) is performed efficiently via a new scheme based on a proper partitioning of the images and the use of the FFT. The new registration technique exhibits a superior performance compared to the conventional cross-correlation method. The new technique has been successfully applied in a visual diagnostic method for detecting, in vivo, epithelial dysplasias and malignancies.

Βιβλία


Copyright Notice: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted or mass reproduced without the explicit permission of the copyright holder.


Κεφάλαια σε Βιβλία


Copyright Notice: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted or mass reproduced without the explicit permission of the copyright holder.


Επιμέλεια Πρακτικών Διεθνών Συνεδρίων


Copyright Notice: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted or mass reproduced without the explicit permission of the copyright holder.