Prehistory of Cryptography - A Classical Introduction to Cryptography: Applications for Communications Security - page 2

Most of these stories, however, used cryptography in a pedestrian way. This was the
prehistory of cryptography. Most of the secret codes had a security based on obscurity:
secret codes were dedicated to applications, and people who wanted to communicate
securely had to choose their own secret code. Thus, all communication users had to
be cryptographers. Modern cryptography history began with electrical communication
technology to which this model was clearly not well suited.
Knowledge and science used to be limited to a small category of privileged peo-
ple in ancient civilizations until education became accessible to everyone. Hopefully,
education brings communication to people: most people in developed countries know
(more or less) how to read and write in a common language (or even several ones) and
most people have access to communication systems. It is furthermore impractical to
invent a new language, or a new communication system, in order to provide secrecy.
So we cannot use common communication systems in order to provide secrecy.
Language makes it feasible to encode any information into a standard message
which consists of a character stream. Following the Shannon Separation Principle
paradigm, we should definitely use an additional code in order to encode the standard
message into a secret code. This process, called encryption, must be invertible, and the
inversion should require a secret information.
1.1.2 Key Words
We list here a few key words. The reader may also use the Internet Security Glossary
which was published by the Internet Society as the RFC 2828 informational standard
(Ref. [168]).
Confidentiality, secrecy : insurance that a given information cannot be accessed
by unauthorized parties.
Privacy : ability for a person to control how his personal information spreads in
a community. This is often (improperly) used as a synonym of “secrecy.”
Code : a system of symbols (formally, a set of “words” called codewords) which
represent information. Note that codes are not related to secrecy from this defi-
nition.
Coding theory : science of code transformation which enables to send informa-
tion through a communication channel in a reliable way. Usually, this theory
focuses on noisy channels and tries to make the information recovery feasible
to anyone (as opposed to cryptography which tries to make the information
recovery feasible for authorized parties only).
Encode, Decode : basic processes of coding theory: action to transform an infor-
mation into a codeword, or to recover the information from a codeword.
Cryptography : (originally) the science of secret codes, enabling the confidential-
ity of communication through an insecure channel. As opposed to coding the-
ory which faces random noises, cryptography faces malicious adversaries. Now