Citation: Kamil Khudhair, S.; Sahu, M.; K. R., R.; Sahu, A.K. Secure Reversible Data Hiding Using Block-Wise Histogram Shifting. Electronics 2023, 12, 1222. https:// doi.org/10.3390/electronics12051222 Academic Editors: Ruifan Li and Xin Ning Received: 1 February 2023 Revised: 18 February 2023 Accepted: 22 February 2023 Published: 3 March 2023 Copyright: © 2023 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). electronics Article Secure Reversible Data Hiding Using Block-Wise Histogram Shifting Samar Kamil Khudhair 1 , Monalisa Sahu 2 , Raghunandan K. R. 3 and Aditya Kumar Sahu 4, * 1 Department of Business Administration Techniques, Technical College Management, Middle Technical University, Bab Al Moatham, Baghdad 10047, Iraq 2 Department of CSE, School of Engineering and Technology, GIET University, Gunupur 765022, Odisha, India 3 Department of Computer Science and Engineering, NMAM Institute of Technology, NITTE (Deemed to be University), Nitte 574110, Karnataka, India 4 Amrita School of Computing, Amrita Vishwa Vidyapeetham, Amaravati 522502, Andhra Pradesh, India * Correspondence: s_adityakumar@av.amrita.edu or adityasahu.cse@gmail.com Abstract: Reversible data hiding (RDH) techniques recover the original cover image after data ex- traction. Thus, they have gained popularity in e-healthcare, law forensics, and military applications. However, histogram shifting using a reversible data embedding technique suffers from low em- bedding capacity and high variability. This work proposes a technique in which the distribution obtained from the cover image determines the pixels that attain a peak or zero distribution. Af- terward, adjacent histogram bins of the peak point are shifted, and data embedding is performed using the least significant bit (LSB) technique in the peak pixels. Furthermore, the robustness and embedding capacity are improved using the proposed dynamic block-wise reversible embedding strategy. Besides, the secret data are encrypted before embedding to further strengthen security. The experimental evaluation suggests that the proposed work attains superior stego images with a peak signal-to-noise ratio (PSNR) of more than 58 dB for 0.9 bits per pixel (BPP). Additionally, the results of the two-sample t-test and the Kolmogorov–Smirnov test reveal that the proposed work is resistant to attacks. Keywords: reversible data hiding; histogram shifting; imperceptibility; embedding capacity 1. Introduction Reversible data hiding (RDH) techniques can restore the original cover media and the embedded information on the receiver end [1]. The least significant bit (LSB) strategy is a highly preferred data hiding technique [2]. This technique replaces the LSBs of the cover image pixels with data bits [3]. The stego image is processed to extract the secret data bits on the receiver side without recovering the original cover image [4]. Interestingly, there are several application areas, such as e-healthcare, law forensics, and military im- agery, where original secret data and cover image recovery are crucial on the receiving end [5]. In [6], cover image pixels are processed to recover the cover image after secret data extraction. Various reversible data embedding techniques have been proposed, including difference expansion and its variants [7–10], histogram shifting [11–15], prediction-based technique [16], and vector quantized-based technique [17]. Of these, the histogram-based shifting technique has gained popularity due to its simplicity and ability to offer higher security. However, a significant setback for the histogram-based shifting technique is that secret data are embedded without taking care of the contrast of the cover image, which pro- vides distortion in a large number of pixels and, thus, negatively impacts the visual quality. To overcome this challenge, a dynamic histogram shifting RDH technique is proposed based on the contrast of the cover image. In the peak value of the cover image histogram, left-side or right-side data embedding is done. Furthermore, to improve the embedding capacity, the image is divided into fixed blocks, and for each block, the histogram bins’ Electronics 2023, 12, 1222. https://doi.org/10.3390/electronics12051222 https://www.mdpi.com/journal/electronics