Short: Hides secret data inside a JPEG file Author: IJG, Derek Upham, Guenther Roehrich Uploader: Guenther studbox uni-stuttgart de (Guenther Roehrich) Type: util/crypt Architecture: m68k-amigaos This version of the Independent JPEG Group's JPEG Software (release 4) has been modifed for 1-bit steganography in JFIF output files. Steganography is the science of hiding data in otherwise plain text or images. Here, we are hiding the data inside images stored in the JFIF format of the JPEG standard. It was believed that this type of steganography was impossible, or at least infeasible, since the JPEG standard uses lossy encoding to compress its data. Any hidden data would be overwhelmed by the noise. The trick used by this steganographic implementation is to recognize that JPEG encoding is split into lossy and non-lossy stages. The lossy stages use a discrete cosine transform and a quantization step to compress the image data; the non-lossy stage then uses Huffmann coding to further compress the image data. As such, we can insert the steganographic data into the image data between those two steps and not risk corruption.