Cryptography Reference
In-Depth Information
Chapter 11
Information Theory and
Coding
That was a little more information than I needed to know.
Quentin Tarentino
(1963-), American film director
— from the movie
Pulp Fiction
(1994), spoken byUma Thurman
11.1 Shannon
“Information theory” is a term derived from the seminal work of C.E. Shan-
non,
The Mathematical Theory of Communication
, published in 1948 (see [249]).
In Section 11.2, we will define what “information” means, and see that it is not
to be confused with the everyday understanding of the word. We will also see
that the Internet would not exist without information theory. Since Shannon is
the prime mover and prover of the concepts of perfect secrecyand information
theory, we begin with a brief biographical sketch of his life.
Claude Elwood Shannon (see Figure 11.1) was born on April 30, 1916, in
Gaylord, Michigan, where he stayed and graduated from the University of Michi-
gan in 1936. He left to do his graduate work at MIT. His supervisor, Vannevar
Bush, had Shannon take care of a computing device called the
Differential An-
alyzer
, which was a concoction of rods and gears that needed manual alignment
before a problem could be “input” to the machine. These problems involved
finding numerical solutions to ordinarydifferential equations. It was Shannon's
experience with this machine that got him thinking along the lines of replac-
ing the unwieldymechanical device with electrical circuits. Then he realized
that Boolean algebra was similar to the electrical circuit, and from this derived
the notion of circuit design according to Boolean algebra to analyze, test, and
optimize relayswitching circuits. These ideas were expounded in his master's
thesis entitled,
A Symbolic Analysis of Relay and Switching Circuits
, for which
he earned his master's degree in 1937. His Ph.D., on population genetics, was
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