Int. J. Signal and Imaging Systems Engineering, Vol. 10, No. 4, 2017 169 Copyright © 2017 Inderscience Enterprises Ltd. Towards a robust and fully reversible image watermarking framework based on number theoretic transform Lamri Laouamer Department of Management Information Systems, College of Business and Economics, Qassim University, P.O. Box 6633, Buraidah 51452, Kingdom of Saudi Arabia and Lab-STICC (UMR CNRS 6285), University of Western Brittany, 20 Avenue Victor Le Gorgeu, BP 817 - CS 93837, 29238 Brest Cedex, France Email: laoamr@qu.edu.sa Abstract: This paper presents a new watermarking approach in the spectral domain based on the number theoretic transform (NTT) to ensure sharing and transferring medical images in a secure way. Through this approach we ensure also the robustness of the embedded watermarks within the medical image to prove ownership. The NTT’s effectiveness has been proven in the images lossless transmission and in convolution fast calculation. In this new approach, the watermark is embedded into the NTT image based on linear interpolation with a specific factor controlling the visibility/invisibility of the watermark. The extraction process will be performed on the attacked watermarked image in order to extract the attacked watermark. We are particularly interested in the NTT since it is considered as a fully reversible transform without any loss when choosing the suitable parameters. We measured the robustness of the proposed approach by the commonly used metrics against several scenarios of attacks (geometric and non-geometric) such as JPEG compression, adding noise, rotation, median filtering, etc. The tests are performed on several types of medical images. The obtained results are very encouraging and represent a remarkable robustness which will be detailed in this paper. Keywords: attacks; Fermat transform; medical image watermarking; NTT; robustness. Reference to this paper should be made as follows: Laouamer, L. (2017) ‘Towards a robust and fully reversible image watermarking framework based on number theoretic transform’, Int. J. Signal and Imaging Systems Engineering, Vol. 10, No. 4, pp.169–177. Biographical note: Lamri Laouamer is an Assistant Professor at the Department of Management Information Systems, College of Business and Economics at Qassim University, KSA. He is also an Associate Researcher in Laboratoire des Sciences et Techniques de l’Information, de la Communication et de la Connaissance (Lab-STICC), University of Bretagne Occidentale, Brest, France. He received his PhD in 2012 in computer science, field of information security from the University of Bretagne Occidentale, France. His MSc in 2006 in computer science and applied mathematics from the University of Quebec at Trois Rivieres in Canada. His BSc in 1999 in computer science from the University of Setif, Algeria. His research interests include multimedia watermarking, cryptology and information security. Currently, Dr. Lamri Laouamer is an Associate Editor of the Journal of Telecommunication Systems by Springer and Associate Editor of the Journal of Innovation in Digital Ecosystems by Elsevier.