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Abstract: Steganographic systems attempt to hide communication by embedding messages in an innocuous looking cover medium. Current steganographic systems provide relatively secured hidden data with small capacity for steganographic messages. In this paper, a new technique is introduced to hide data in the least significant bits (LSB) of the discrete cosine transform (DCT) coefficients of JPEG images. This technique embeds data in a way that maximizes the ratio between even and odd DCT coefficients so as to preserve the first order statistics of JPEG images. Message bits are divided into segments and each segment is possibly modified by embedding the bitwise complement so as to ensure a high ratio between even and odd coefficients. The embedding process is referred to as the hiding appropriate messages (HAM) algorithm. The HAM algorithm searches for optimum segment length to offer high capacity, approximately 0.36 bits/pixel, with statistically minimal changes compared to existing steganographic algorithms. A comparison between HAM and existing steganographic systems is presented.
Keywords: Steganography, information hiding, steganalysis, LSB embedding, covert communication
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1. Introduction
Steganography is the hiding of information in a medium (such as image, audio, or video). A medium that is used for hiding information is called a cover medium. After embedding data in a cover medium, a stego medium is obtained. The embedding algorithm is assumed to be known to the public according to Kerckhoffs principle (Kerckhoffs, 1883:5-38; Anderson and Petitcolas, 1998:474- 481). Therefore the embedding process may use an embedding key (stego key) so that only the intended user can successfully extract the embedded data by using the extraction key in the extraction process. Steganography can be defined as the art and science of invisible communication. A steganographic system embeds hidden content in an innocuous looking cover medium so as not to arouse an eavesdropper's suspicion. Steganography must not be confused with cryptography, where data are encoded such that an unintended recipient can not determine its contents. Steganography, in contrast, does not modify data to make it unusable to an attacker. Instead, the steganographer attempts to prevent an attacker from suspecting that the cover medium has hidden data (Provos and Honeyman, 2001; Cachin, 2002; Memon and Kharrazi, 2006:4-5). The main goal of modern steganography is to...