International Journal of Electrical and Computer Engineering (IJECE) Vol. 8, No. 4, August 2018, pp. 2468~2476 ISSN: 2088-8708, DOI: 10.11591/ijece.v8i4.pp2468-2476  2468 Journal homepage: http://iaescore.com/journals/index.php/IJECE Protecting Data by Improving Quality of Stego Image based on Enhanced Reduced difference Expansion Maurice Ntahobari 1 , Tohari Ahmad 2 1,2 Department of Informatics, Institut Teknologi Sepuluh Nopember, Indonesia 2 Groupe Scolaire de Gishubi, Gisagara District, Southern Province, Rwanda Article Info ABSTRACT Article history: Received Jan 31, 2018 Revised Apr 2, 2018 Accepted Apr 20, 2018 In this era of internet development, security of information sharing is the main problem faced by human being. Data hiding technique is one of the solutions. However, hiding credential information within a multimedia file such as image reduces its visual quality. Therefore, unauthorized users may suspect the existance of secret data within that image. In the past years, various data hiding algorithms have been developed by researchers to overcome the problem of high distortion of image after data embedding process. Achieving a high quality stego image, however, is still a challenging problem. In this paper, we proposed a new data hiding algorithm based on different expansion. It aims to enhance the quality of stego image for a given payload size. The new algorithm is evaluated on various medical images. Thereafter, the experimental results show that the visual quality is improved; and increasing the embedding capacity leads to more noises. Therefore, a better choice of base point and a reduced difference expansion affect the quality of stego image. Keyword: Data hiding Data protection Information security Secret data Visual quality Copyright © 2018 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Maurice Ntahobari, Department of Informatics, Institut Teknologi Sepuluh Nopember, Surabaya, Sukolilo, 6011, Jawa Timur, Indonesia. Email: mntahobari@gmail.com 1. INTRODUCTION In this information technology age, transferring files between users has been a need for everyone, anytime and anywhere. Public network that is normally used for such communication is however insecure. This means that everything being transferred through the internet can be intercepted and changed. If the modified message is forwarded to the receiver, the message integrity and confidentiality are violated. Hence, data should be protected during the transmission process. As one of the methods to protect data, data hiding technique hides secret information within a multimedia file such as image, video, audio or text [1]. In the simplest form, it was implemented thousands years ago before the information technology was developed [2]. Furthermore, this technique was also used in the Second World War [3]. Watermarking technique is a kind of spatial domain-based data hiding approach that uses the same technique as data hiding. In the spatial domain, secret data are hidden within the redundancy information in a cover media. This is different from transformed domain where secret information are hidden in coefficients obtained by transforming spatial values to frequency coefficients by using dimensional transform methods such as discrete cosine transform (DCT), discrete wavelet transform (DWT) or integer wavelet transform (IWT). These coefficients are then utilized for hiding secret data in transformed domain data hiding [4]. Nevertheless, in watermarking-based method the hidden secret data are related to the cover media for its copyright identification [5]. In this research field, high visual quality for high embedding capacity is a challenging problem.