Hide in Plain Sight

In the Histories, written by the ancient Greek Herodotus, there’s a wonderful story about Histiaeus: Histiaeus was being held prisoner by King Darius and wanted to give his son-in-law Aristagoras a message to lead a revolt. After much thought, he shaved the head of his most trusted slave and tattooed a message upon the man’s scalp. Once the slave’s hair grew back, he sent the slave to Aristagoras, who shaved the slave’s head and beheld the message. As a result, the revolt began, and Histiaeus was released (see http://classics.mit.edu/Herodotus/history.5.v.html).

Histiaeus’ story is one of the earliest examples of steganography, which literally means “hidden writing.” Histiaeus used the flesh of his slave to hide his message, but nowadays we hide data inside pictures, digital music, or even text documents. You’ll find that steganographic tools are some of the easiest, yet coolest, things you can use with Linux.

There are several software choices for creating steganograph messages, but let’s focus on the command-line program Outguess. At this time, Outguess can hide data inside PPM, PNM, and JPEG files, which means that you could post an innocent-looking JPEG file on your web site that contains a wealth of secret information and no one would be the wiser.

To try Outguess, head over to http://www.outguess.org, grab the source code, and compile it. You can also try finding binaries for your distribution. Debian users, for instance, can just type apt-get install outguess.