shadow

shadow is a tool, fully written in Java, that allows a user to hide and expose a message within and from a bitmap (.bmp) image. It works by reading a secret message - whether it is text, a photo, ...-, and replacing the n (1 through 8, and a power of 2) least-significant bits of every data byte in the image with n bits from the message.

The maximum number of bytes that can be hidden within a bitmap image can be easily estimated using the following formula: (size of image file) / 8 * (bits per byte). For example, a 36MB image will hold 18MB of data if 4 bits per each byte are replaced with the secret message.

Please note the emphasis on the estimated, as this calculation would require looking at the actual pixel array length. However, the estimation is good enough to give you a rough idea of how much data an image can hold.

This tool is the result of a group practical work for the DAI (Internet App Development) course, which is part of the bachelor's degree I'm currently enrolled in. Initially, it was supposed to allow us to exercise what we'd learned so far in class, which was mostly around Java I/O.Groups were free to choose their application's functions, so we turned our app into an interesting project.

The project was initially written with JDK 21. It might, however, work on previous and / or later versions.