Steganography: The Science of Hidden Information

In 2013, I published a steganography application named Köker GizliBilgi. It concealed entered text inside an image. My first experiment hid the phrase “Ne Mutlu Türküm Diyene” in an image of the Turkish flag.

The initial method caused visible degradation in the image. By applying digital image-processing techniques and optimizing the algorithm, I was able to conceal information without visibly damaging the image and without making the modification perceptible to the human eye. I then adapted the algorithm to audio files and added encryption of the concealed data.

At the time of writing, I was also working on a more unusual file-within-file hiding algorithm. The planned release was intended to include three different concealment techniques.

Information Hiding in Popular Culture

Steganography was mentioned in the television series Kanıt and the film A Beautiful Mind.

In an episode of Kanıt, Prof. Sevil Atasoy described information-hiding methods used by photocopier manufacturers. These machines print very small marks on each document. The marks can contain information such as the machine serial number and printing date, helping investigators address document forgery.

The word steganography comes from Ancient Greek and means “concealed writing.” It has an important place in digital forensics. Its greatest advantage is that the existence of the hidden information may not be noticed.

Steganography from the Past to the Present

Steganography was used both before and after the development of modern cryptology. In Ancient Greece, messages were written on wooden tablets and covered with wax. The object appeared to be an unused writing tablet, while melting the wax revealed the concealed message.

According to a story recounted by Herodotus, before a Persian attack a warning was written on the shaved scalp of an enslaved messenger. The message was concealed after the hair grew back, allowing it to reach its destination without attracting attention. The hair was then shaved again so the warning could be read.

During the Second World War, an agent named Velvalee Dickinson operated in New York under the cover of a doll dealer. Information about the United States military was hidden in letters that appeared to contain doll orders.

A simple steganography technique can also be implemented with inks and pens that are visible only under ultraviolet light.