Cryptography Reference
In-Depth Information
The system can be made much more secure by using a key to
create a pseudo-random bit stream that is added into the data
as it is mixed into the mix. Only the person with the key can
remove this extra encryption.
How to Use It
In the most abstract sense, just choose a number of
locations in the file with a pseudo-random bit stream, break
the data into little parts, and add these parts into all of the
locations. Recover the message by finding the correct parts and
adding them together.
This process is very efficient if it is done with a fast Fourier
transform. In these cases, the data can be hidden by tweaking
the coefficients after the transform. This can add or subtract
different frequency data.
Further Reading
Using wavelets, cosines or other functions to model sound and
image data is one of the most common strategies for water-
marking images today. There are too many good papers and
books to list all of them. Some suggestions are:
•
Digital Watermarking
by Ingemar Cox, Matthew L. Miller
and Jeffrey A. Bloom is a great introduction to using wavelet
techniques to embed watermarks and hide information.
The 2007 edition is broader and it includes a good treat-
ment of steganography and steganalysis. [CMB02, CMB07]
•
The proceedings of the International Workshop on Digital
Watermarking are invaluable sources that track the devel-
opment of steganography using wavelets and other func-
tional decomposition. [PK03, KCR04, CKL05, SJ06]
•
A good conference focused on watermarking digital con-
tent is the Security, Steganography, and Watermarking of
Multimedia Contents. [DW04, DW05]
•
Jessica J. Fridrich, Miroslav Goljan, Petr Lisonek and David
Soukal discuss the use of Michael Luby's LT Codes as
a foundation for building better versions of perturbed
quantization. These graph-based codes can be faster to
compute than thematrix-based solutions.[Lub02, FGLS05]
