SANS Institute InfoSec Reading Room

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Abstract
Steganography (a rough Greek translation of the term Steganography is secret writing) has been
used in various forms for 2500 years. It has found use in variously in military, diplomatic,
personal and intellectual property applications. Briefly stated, steganography is the term applied
to any number of processes that will hide a message within an object, where the hidden message
will not be apparent to an observer. This paper will explore steganography from its earliest
instances through potential future application.

Past
Johannes Trithemius (1462-1516) was a German Abbot. His writing, “Steganographia:hoe est
ars per occultam scripturam animi sui voluntatem absentibus aperiendi certa” is ostensibly a
work describing methods to communicate with spirits(1). A very rough translation (with
apologies to my Latin instructors) of this Latin title is: “Steganography: the art through which
writing is hidden requiring recovery by the minds of men.” Published as a trilogy in Latin, the
first two parts of his works are apparently some of the first books on cryptology describing
methods to hide messages in writing. The third part of the trilogy is outwardly a book on occult
astrology. The third book contains a number of tables containing numbers.



On viewing the ASCII text file (converted to .jpg here for convenience), it is apparent that while
the text file itself might not have a hidden file, an industrious individual could arrange certain
letters in the visible text file itself to have certain meanings.
Another digital format that may escape notice is the venerable animated GIF format. Normal
steganalysis of GIF formats wouldn’t necessarily indicate any hidden messages while it would be
trivial to hide a message using this format.
Without going into detail, other areas that could conceivably be employed to hide messages are:
· Holography technology
· Infrared (e.g. programmable IR hand controls for computers (27)
· Pagers
· Colored glasses that filter all but intended wavelengths to make hidden messages
visible
· Ink, magnetic, thermochromic, photochromic
· DNA message hiding (28)
· Jargon speak
· “Blank” areas on hard drives, floppies, etc.
· HTML code
This list should not be considered exhaustive, there are numerous other possibilities.
One last bit of steganotrivia before we return to “serious steganography.” If one viewed the
following image at an art gallery, it might not be obvious that this is another work of
steganography.