Cryptography Reference
In-Depth Information
program
10
to prevent sensitive information from leaking through electromagnetic
emanation. More recently, people have tried to exploit and employ diffuse visible
light from cathode-ray tube (CRT) displays
11
and acoustic emanation
12
for cryptan-
alytical purposes. From a practical point of view, all of the earlier mentioned types of
attacks (and many others that will be developed in the future) are relevant and must
be considered with care (e.g., [20]). For the purpose of this topic, however, we only
mention some of the more important attacks, but we do not address them in detail.
You may refer to the referenced literature to get more information about them.
1.3
HISTORICAL BACKGROUND INFORMATION
Cryptography has a long and thrilling history that is addressed in many topics (e.g.,
[21-23]). Since the very beginning of the spoken and—even more important—
written word, people have tried to transform “data to render its meaning unintelli-
gible (i.e., to hide its semantic content), prevent its undetected alteration, or prevent
its unauthorized use” [1]. According to this definition, these people have always em-
ployed cryptography and cryptographic techniques. The mathematics behind these
early systems may not have been very sophisticated, but they still employed cryp-
tography and cryptographic techniques. For example, Gaius Julius Caesar
13
used
an encryption system in which every letter in the Latin alphabet was substituted
with the letter that is found three positions afterwards in the lexical order (i.e.,
“A” is substituted with “D,” “B” is substituted with “E,” and so on). This simple
additive cipher is known as
Caesar cipher
(see Section 10.1.1). Later on, people
employed encryption systems that use more involved mathematical transformations.
Many topics on cryptography contain numerous examples of historically relevant
encryption systems—they are not repeated in this topic.
Until World War II, cryptography was considered to be an art (rather than a
science) and was primarily used in the military and diplomacy. The following two
developments and scientific achievements turned cryptography from an art into a
science:
•
During World War II, Claude E. Shannon
14
developed a mathematical the-
ory of communication [24] and a related communication theory of secrecy
10
http://www.eskimo.com/
∼
joelm/tempest.html
11
http://www.cl.cam.ac.uk/TechReports/UCAM-CL-TR-577.pdf
12
http://www.wisdom.weizmann.ac.il/
∼
tromer/acoustic
13
Gaius Julius Caesar was a Roman emperor who lived from 102 BC to 44 BC.
14
Claude E. Shannon was a mathematician who lived from 1916 to 2001.
