Angelos Fylakis

A data hiding approach for sensitive smartphone data

We develop and evaluate a data hiding method that enables smartphones to encrypt and embed sensitive information into carrier streams of sensor data. Our evaluation considers multiple handsets and a variety of data types, and we demonstrate that our method has a computational cost that allows real-time data hiding on smartphones with negligible distortion of the carrier stream. These characteristics make it suitable for smartphone applications involving privacy-sensitive data such as medical monitoring systems and digital forensics tools.

Reversible blind data hiding for verifying integrity and authenticating MRI and X-Ray images

We present a reversible data hiding technique for digital medical images. The idea is to embed the header of the image or other data in the image itself, pursuing tamper-proofing capabilities and inseparability. In particular, the proposed data hiding technique using Least Significant Bits (LSBs) hides information into the Region of Interest (ROI) and preserves lost information in the Region of Non Interest (RONI) for reversibility purposes. ROI pixels are accessed consecutively or in accordance to a Just Noticeable Distortion (JND) model, while RONI pixels are accessed in a consecutive or pseudo-random order. In the experiments with MRI and X-Ray images, we prove excellent fidelity and 100% reversibility of the ROI.

Reversible Data Hiding in FTIR Microspectroscopy Images with Tamper Indication and Payload Error Correction

Fourier transform infrared (FTIR) microspectroscopy images contain information from the whole infrared spectrum used for microspectroscopic analyses. In combination with the FTIR image, visible light images are used to depict the area from which the FTIR spectral image was sampled. These two images are traditionally acquired as separate files. This paper proposes a histogram shifting-based data hiding technique to embed visible light images in FTIR spectral images producing single entities. The primary objective is to improve data management efficiency. Secondary objectives are confidentiality, availability, and reliability. Since the integrity of biomedical data is vital, the proposed method applies reversible data hiding. After extraction of the embedded data, the FTIR image is reversed to its original state. Furthermore, the proposed method applies authentication tags generated with keyed Hash-Based Message Authentication Codes (HMAC) to detect tampered or corrupted areas of FTIR images. The experimental results show that the FTIR spectral images carrying the payload maintain good perceptual fidelity and the payload can be reliably recovered even after bit flipping or cropping attacks. It has been also shown that extraction successfully removes all modifications caused by the payload. Finally, authentication tags successfully indicated tampered FTIR image areas.

Improving Robustness of Biometric Identity Determination with Digital Watermarking

The determination of an identity from noisy biometric measurements is a continuing challenge. In many applications, such as identity-based encryption, the identity needs to be known with virtually 100% certainty. The determination of identities with such precision from face images taken under a wide range of natural situations is still an unsolved problem. We propose a digital watermarking based method to aid face recognizers to tackle this problem in applications. In particular, we suggest embedding multiple face dependent watermarks into an image to serve as expert knowledge on the corresponding identities to identity-based schemes. This knowledge could originate, for example, from the tagging of those people on a social network. In our proposal, a single payload consists of a correction vector that can be added to the extracted biometric template to compile a nearly noiseless identity. It also supports the removal of a person from the image. If a particular face is censored, the corresponding identity is also removed. Based on our experiments, our method is robust against JPEG compression, image filtering, and occlusion and enables a reliable determination of an identity without side information.

Watermarking Digital Images in the Frequency Domain: Performance and Attack Issues

In this work we propose an efficient model for watermarking images that are intended for uploading on the web under intellectual property protection. Headed to this direction, we recently suggested a way in which an integer number \(w\) which being transformed into a self-inverting permutation, can be represented in a two dimensional (2D) object and thus, since images are 2D structures, we propose a watermarking algorithm that embeds marks on them using the 2D representation of \(w\) in the frequency domain. In particular, we propose a watermarking technique that uses the 2D representation of self-inverting permutations and utilizes marking at specific areas thanks to partial modifications of the image’s Discrete Fourier Transform (DFT). Those modifications are made on the magnitude of specific frequency bands and they are the least possible additive information ensuring robustness and imperceptiveness. We have experimentally evaluated our algorithms using various images of different characteristics under JPEG compression, Gaussian noise addition, and geometric transformations. The experimental results show an improvement in comparison to the previously obtained results and they also depict the validity of our proposed codec algorithms.

A watermarking system for teaching intellectual property rights: Implementation and performance

In this paper we propose a watermarking system, which we call WaterIP, that can be efficiently used in support of teaching students to respect intellectual property rights. Our system uses an efficient technique for watermarking images by exploiting certain properties of a specific 2D representation of permutations, it has a friendly graphical user interface, and shows interesting performance figures. We demonstrate the educational effectiveness of our WaterIP system by presenting ways of how it can be applied in class and show that WaterIP helps to understand what intellectual property rights really stand for. We have implemented our system and evaluated it in an simulated environment; the experimental results show that WaterIP has optimal time and space performance. Apart from that the figures show that the system provides watermarked images of high quality and everything is accessed through a user interface leading to the desired educational efficiency.