# An Innovative Information Hiding Scheme Based on Block-Wise Pixel Reordering
## 1 Introduction  
In the modern day, iCloud data transmission replaces the physical mail to speed up the time spent on exchanging information. Needless to mention, the Internet is a key element in the transmission process. Digital activities involving both the virtual world and the physical world can be foreseen in the near future, such as if a hospital technician uploads an X-ray image, a CT scan photo, or a patient's information to a data center for a list of specific doctors to download them in order to discuss various treatments over an online meeting. To protect the privacy of the patient, no one should be able to see the information other than the related doctors. Encrypting and decrypting digital information are becoming more and more important in order to increase security. At the same time, there can be diagnostics information to be passed to one or some particular doctors. Data hiding then plays another crucial role in these data transitions [1, 2]. When a content owner wants to send an image to a data receiver, the owner would like to add a secret message in the image before transmitting it to the receiver. Adding the secret message normally needs to go through a data hider, and as it may not be desirable for the data hider to see the image content, the owner encrypts the image before sending it in order to hide the message. A receiver holding the encryption key can recover the image, and a receiver with the data hiding key can extract the secret information. There are various data hiding schemes designed to protect data effectively in different application circumstances that have demonstrated exceptional results. Data hiding has branched out into reversible data hiding (RDH) [3, 4, 5, 6, 7] and non-reversible data hiding depending on whether the image content can be recovered or not. According to the hiding carriers, the hiding schemes can be cataloged into four different domains: spatial, frequency, compression, and encryption. When in the spatial domain, digital cover imagesare modified directly to embed data. As for the frequency domain, images are transformed using wavelet transform methods before embedding data. Images are first compressed with compression techniques prior to embedding information in the compression domain. In the encryption domain, images are encrypted using encryption keys before being sent to the data hider to hide secrets in the encrypted image. Data hiding in encrypted images (DH-EI) combines cryptography and DH technology to achieve higher levels of protection. DH-EI has branched out into reserving room before encryption (RRBE) and vacating room after encryption (VRAE) depending on the timing of room vacating. [PERSON] et al. [8] proposed a reversible method for data hiding in encrypted images by preserving room before encryption in 2013. [PERSON] and [PERSON] proposed a parameter-controlled method to embed data to encrypted images in 2018 [9; 10]. Around the same time, [PERSON] and [PERSON] [11] proposed a method using MSB prediction and gained high embedding capacity by hiding data in encrypted images. [PERSON] et al. [12], in 2020, further improved the method by proposing a multi-MSB compression method. [PERSON] and [PERSON] [13] proposed a fully reversible method by including the MSB error prediction and a reversible adaption in 2020, and [PERSON] et al. [14] proposed an improved version shortly after. Even though RRBE has a higher embedding capacity amount, owners may not have enough knowledge of how to go through the reserving process. Therefore, VRAE schemes still gain popularity among these types of applications to better secure information privacy. In the VRAE scheme, the content owner performs only the operation of encrypting the image and then transmits the encrypted image to the data hider. After obtaining the encrypted image, the data hider vacates the room and embeds the data. [PERSON] et al. [15] proposed a DH-EI method that combined side match and block-wise LSB flipping.