# Enhanced Joint and Separable Reversible Data Hiding in Encrypted Images with High Payload
## 1 Introduction  
With the rapid growth of internet technology, it has become very easy to download media such as pictures, images, and audio or video files. This makes media data not only easy to transmit but also easy to copy and distribute. Therefore, pirates can easily record and distribute copyright-protected material without paying the appropriate compensation to the owner. Thus, a legal issue arises such that some media need to be protected against unauthorized use or operations. Data hiding and encryption are two effective and prevalent means of privacy protection and secret communication. Data hiding has attracted considerable research interest in recent years [1; 2; 3]. By this technique, secret data can be embedded into a cover medium, and later the embedded data can be extracted from the marked medium for various purposes. [PERSON] et al. [1] proposed a novel data-embedding method using adaptive pixel pair matching. [PERSON] et al. [2] introduced a hybrid data hiding method combining the right-most digit replacement (RMDR) with an adaptive least significant bit (ALSB) for digital images. [PERSON] et al. [3] proposed a new data hiding technique for absolute moment block truncation coding (AMBTC) compressed image based on quantization level modification. However, for most data hiding systems, during the data hiding operation the cover medium has been distorted and hence, after data extraction, the cover medium cannot be recovered to its original state. Such permanent distortion is unacceptable and the exact recovery of the original cover medium is prerequisite in some sensitive applications like medical, defense, legal matters, artwork, and so on. To solve this problem, reversible data hiding (RDH), also known as lossless or invertible data hiding, is proposed to exactly recover both the hidden data and the cover medium. Explicitly, with the RDH, not only the hidden data but also the cover medium can be exactly recovered from the marked medium. Several RDH techniques have been introduced [4; 5; 6; 7; 8; 9; 10]. In 2003, [PERSON] [4] proposed a reversible data hiding method using the difference expansion technique, where one bit is embedded into the difference of two successive pixels. In 2006, [PERSON] et al. [5] introduced a novel RDH system based on histogram shifting by utilizing the minimum and maximum points of the image histogram; data are concealed by shifting the histogram. In 2007, [PERSON] and [PERSON] [6] proposed a different technique by expanding the prediction errors. In 2010, [PERSON] et al. [7] presented a new reversible data hiding process by adopting an additive interpolation error expansion technique, which provides very small falsification and a comparatively high capability. Moreover, to improve performance, many techniques have been proposed for typical reversible data hiding approaches [8; 9; 10]. In some applications of data hiding, the embedded carriers are further encrypted to prevent the carrier from being analyzed to expose the existence of the embedding [11; 12]. In 2007, [PERSON] et al. [11] proposed a video encryption and watermarking scheme based on H.264, the advanced video coding (AVC) codec, where media data are encrypted and partially watermarked. In 2010, [PERSON] et al. [12] presented a commutative watermarking and ciphering scheme where a watermarked image is further encrypted to increase the security of the system. Most of the existing reversible data-hiding systems are only suitable for unencrypted covers. However, for maintaining confidentiality or protecting privacy, in many fields--like medicine, the military, and the law--a content owner may demand to encrypt the original images. Meanwhile, without knowing the encryption key and the plaintext content, a channel administrator or an inferior assistant may need to insert some additional information within the encrypted images.