Abstract
This contribution proposes a novel steganographic method based on the compression standard according to the Joint Photographic Expert Group and an Entropy Thresholding technique. The steganographic algorithm uses one public key and one private key to generate a binary sequence of pseudorandom numbers that indicate where the elements of the binary sequence of a secret message will be inserted. The insertion takes eventually place at the first seven AC coefficients in the transformed DCT domain. Before the insertion of the message the image undergoes several transformations. After the insertion the inverse transformations are applied in reverse order to the original transformations. The insertion itself takes only place if an entropy threshold of the corresponding block is satisfied and if the pseudorandom number indicates to do so. The experimental work on the validation of the algorithm consists of the calculation of the peak signal-to-noise ratio (PSNR), the difference and correlation distortion metrics, the histogram analysis, and the relative entropy, comparing the same characteristics for the cover and stego image. The proposed algorithm improves the level of imperceptibility analyzed through the PSNR values. A steganalysis experiment shows that the proposed algorithm is highly resistant against the Chi-square attack.
Highlights
First, we describe the generation of 15 subkeys, and how the subkeys are used to determine a pseudorandom sequence of locations where the secret bits are inserted
The Inverse Discrete Cosine Transform (IDCT) is applied, and to each byte of the resultant image the value 128 is added in order to reconstruct the image, obtaining the expected stego image
The experimental results show that the proposed algorithm produces high quality stego images with appropriate peak signal-to-noise ratio (PSNR) values; see Figures 4–8, which is in correspondence with the heuristic values of PSNR (30 to 50 db) found in literature [42]
Summary
In [31], Chang et al presented a new steganography method based upon Joint Photographic Expert-Group (JPEG) and a quantization table modification In this case, the secret message is first encrypted and embedded in the 26 coefficients located in the middle-frequency area of the cover image. Mali et al propose a novel image steganographic method using a block level Entropy Thresholding technique where the secret message is embedded in the 26 coefficients located in the middlefrequency area of the cover image [16]. The JPEG method divides the cover image into nonoverlapping blocks of 8 × 8 bytes and applies the discrete cosine transform with the purpose of hiding the secret message in the DCT domain by modifying certain coefficients located in the low-frequency area of the cover image. The Entropy Thresholding method decides whether or not to embed the secret message in a certain matrix of order 8 of transformed coefficients, depending on the entropy within that matrix
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