A K MOHAN et al: SEPARABLE REVERSIBLE DATA HIDING USING CHAOTIC ENCRYPTION AND . . . DOI 10.5013/IJSSST.a.15.04.6 48 ISSN: 1473-804x online, 1473-8031 print Separable Reversible Data Hiding using Chaotic Encryption and Histogram Shifting Arun K Mohan, Saranya M R, K Anusudha Department of Electronics Engineering School of Engineering & Technology Pondicherry University Puducherry, India. arun.k.mohan@ieee.org, saranyamr.pu@gmail.com, anusudhak@yahoo.co.in Abstract — In recent years, the chaotic system based cryptographic algorithms have suggested some new and efficient ways to develop secure image encryption techniques. Likewise, a new technology called Reversible Data Hiding (RDH) has been gaining popularity since its inception in the beginning of twenty first century. Here we propose a new approach by clubbing the two different techniques for achieving an algorithm for secure image transfer while concealing some data in the communication and discloses only upon the verification of the authenticity of the destination node. Beauty of the proposed system is that at the content owner side, sequential processing of the two algorithms is mandatory whereas at receiver the reverse process can be done in any succession. Content owner first encrypts the image by using user defined key derived chaotic sequence with the help of standard logistic map function. Then the data hider embeds the data by histogram modification method. By exploiting the advantage of histogram shifting, this method can provide minimum bound of Peak Signal to Ratio (PSNR) value as 48.13 dB, which is much higher than the existing methods. Zero error in the retrieved information, higher quality of recovered cover image and directly decrypted marked stego-image, better embedding capacity and etc. are achieved with the proposed method. Keywords— Reversible Data Hiding (RDH); Image Encryption; Key derivation; Chaos; Logistic map; Decryption; Histogram shifting. I. INTRODUCTION In the last decades, globe have witnessed an explosive growth in the frequent flow of digital images through the transmission Medias, now its security is very vital. Many applications like military images, confidential video conferencing, medical imaging system, cable TV, online personal photograph album, etc. require reliable, fast and robust security system to store and transmit digital images. To prevent all the privacy threats and fulfil all the security needs researchers in the cryptography branch of study have developed efficient set of encryption schemes. Cryptography basically does the scrambling of data for ensuring secrecy, as well as authenticity of the information. It enables us to transmit data across insecure networks so that it cannot be interpreted partially or completely by malicious end, or other than the authorized recipient. Two main branches of cryptography are cryptology and cryptanalysis, Cryptology is to keep plaintext secret from intruder while cryptanalysis deals with the defeating techniques from forging information in between. In cryptography, we usually employ encryption schemes to prevent any data from unauthorized access. In last few years, numerous encryption algorithms [1] have been proposed in the literature by utilizing different techniques. Among them, chaotic system based encryption techniques are practically used as these techniques provide a good amalgamation of high security, reasonable computational overheads, speed, computational power and complexity. Strong correlation among adjacent pixels, redundancy of data, being less sensitive as compared to the text data are the desirable characteristics of a digital image. Since traditional data encryption algorithms require large computational time and high computing power, IDEA, AES, DES, RSA etc. are not suitable for real time image encryption. Only those ciphers which take a lesser amount of time and at the same time without compromising security are only preferred for real time image encryption schemes. Systems with higher degree of security aspect and lower computational speed are obsolete in practical. In the very beginning of twenty first century researchers are attracted towards a new scheme called reversible data hiding (RDH) in encrypted images. RDH is a technique to embed a secret message into some distortion unacceptable cover media like military images, medical images, and etc. in such a way that the cover image can be perfectly restored after extracting the secret message. There are a number of schemes which perform data hiding and encryption jointly. In some of them, a part of the cover is used to carry additional data and the rest of the cover is encrypted. For example, in [2], watermark is added to the amplitude of DCT coefficients, and motion vector difference, intra-prediction mode and signs of DCT coefficients are encrypted. A reversible data hiding technique in the encrypted image is described in [3], which hides data into completely encrypted image. But in this method, image decryption and data extraction are not separable. The method in [4] hides data into an encrypted image in a separable manner. A variety of schemes have been proposed since the inception of RDH to perform data hiding techniques in encrypted image, [5] has adopted difference expansion technique. In this method, one bit can be embedded into two consecutive pixels. Maximum embedding capacity is 0.5 bpp (bits per pixel). Later this method was generalized and the embedding capacity has been improved to (n-1)/n bpp. A different scheme of reversible data hiding, called reserving room before encryption is discussed in [6]-[7]. Another domain of RDH is histogram based method. [8]- [10] cover different methods under this technique. A new technique for RDH is implemented in [11] by estimating the errors. Methods of [5], [6], [7], [11] deal with RDH in separable Manner.