# An Efficient Steganographic Protocol for WebP Files
###### Abstract
In such strategic applications, third parties should not even be aware that communication is taking place. One of the possible solutions of this problem is steganography, a branch of security focused on information hiding. In steganography, the secret message is embedded in an insignificant container which is used as a carrier for the payload. The container is provided to the receiver, who extracts the message out of it. The main goal of this scheme is to conceal from external observers that secret data are hidden inside the cover medium. Over the years, steganographic methods evolved from physical messages on paper to modern digital algorithms. Due to increasing computing power, new complex solutions were established (for example, the combination of steganography and cryptography [2]) and also a lot of potential carriers were used, such as texts [3; 4], images [5; 6; 7; 8], videos [9; 10], binary executables [11], network packets [12; 13; 14; 15], documents [16; 17; 18], or even DNA [19]. On the other hand, a number of counter-techniques were developed, called steganalysis. Their objective is to detect the possible presence of secret data in a container. The perpetual struggle between two sides results in the development of more and more creative algorithms. Of all carriers, the most popular are digital images, for two reasons. First, they are omnipresent (not suspicious), and second, they offer great capacity (a large amount of data may be hidden inside). Image steganography algorithms from the literature may be divided into a few categories, depending on the adopted methodology. Popular methods with low computational cost include spatial domain methods, which conceal secret data directly into pixel values. The best known is the least significant bit (LSB) technique, belonging to the container modification branch of steganography. In this method, bits of the secret message are placed as least significant bits of subsequent bytes of the container [20]. The invention of LSB replacement was a big achievement and researchers have created multiple variants of this algorithm. For instance, to increase capacity, it is possible to hide more than one bit per pixel [21; 22; 23; 24] in various planes. The other modifications use a key to scatter secret data evenly throughout various regions of the carrier [25; 26]. There is also the idea of choosing the embedding area without a key, but by considering only the most frequent pixel values, ignoring their least significant bit [27]. Then the capacity and payload placement are dependent on the contents of the image. Overall, the LSB technique has good sensory undetectability even when more than one bit per pixel is used [28; 29]. However, with specialized software, the adversary is able to detect statistical anomalies introduced by the embedding process. They are manifested by a similar number of even and odd values in the histogram [30]. Some papers try to combat it and invent mechanisms of preserving the histogram during data hiding [5]. Another approach to spatial steganography is based on the fact that edges have better hiding potential than smooth areas. In this technique, called pixel value differentiation (PVD), embedding regions are selected by analyzing differences between consecutive pixels [31]. PVD is characterized by good stego image quality and has its own modifications [32; 33; 34]. Spatial methods of image steganography, while useful, also have disadvantages. They are limited to lossless formats and vulnerable to filtration or compression attacks. For this reason, another category of algorithm has emerged, namely transform domain. Such techniques convert picture data into the frequency domain and then conduct the hiding process. There are various possible transforms, including discrete cosine transform (DCT), discrete (DFT) or fast Fourier transform (FFT), and discrete wavelet transform (DWT). Usually they find application in JPEG files to compress data. DCT divides the image into frequency bands and hides the secret message in quantized coefficients [35].