Cryptography Reference
In-Depth Information
Approaches that hide information in
video conferences
or
digitized speech
(audio files) are of particular interest (see [Westf], [Pfitzstego]). Such data are
physically created and superimposed by an independent semi-conductor noise.
This nourishes hopes for secure steganography, in contrast to cryptography,
where we are still searching for a practically
and
provably secure algorithm.
Studies conducted by Westfeld [Westf] look promising and show that a GSM
phone call can be transmitted behind an ISDN video conference.
I should mention a (former) product of Steganos (
www.steganos.com
), a com-
pany based in Frankfurt, Germany, at this point: the product was used to
camouflage information about the choice of synonymous formulations. As a
side effect, the software was able to improve the style (e.g., avoiding repeated
words). This provided an excellent pretense for using the program, and prov-
ing that steganography was involved became really difficult. Currently, the
company offers only a program for embedding messages in images.
We will discuss another approach that's also secure, but not universally usable,
in connection with subliminal channels in digital signatures in Section 6.3.3.
This topic will also turn up again in Section 6.7.
Cryptanalyzing steganographic methods doesn't appear to be in advanced devel-
opment stages in public research (see the next section about digital watermarks).
The two methods mentioned above are uncritically praised over and again as
a panacea. Prohibiting the free use of cryptography would encourage research
and perhaps encourage the discovery of practically usable subliminal channels
in methods other than digital signatures.
Steganography has
one
function in any event: It makes surveillance of data
communications harder. Though thorough statistical studies are possible, they
require sufficient material and considerable computation power. Together with
the innumerable data formats commonly used, this can be a problem for eaves-
droppers, though we should by no means underestimate the power of current
supercomputers. More about this in Section 8.2.1.
Digital Watermarks
Another very young field of research is closely related to steganography. Intel-
lectual property is becoming increasingly available in electronic versions —
think of MP3 players, CDs, and DVDs, just to name the most obvious. As
the use of these formats rises, so does the amount of piracy. If illegal copying
cannot be entirely stopped, then we will at least want to be able to prove fraud.
