Encryption and Cipher Texts
Edgar Allen Poe was famous for his skill as a cryptographer,
someone skilled at finding the code in which a message is encrypted and
resolving the message into its original natural language. His short story,
Gold Bug„, deals with encryption and deciyption, and Poe wrote several
non-fiction pieces On
Encryption includes any method of transforming a message
to conceal its meaning.
The term is also used synonymously with ciphertext or cryptogram in reference
to the encrypted form of the message. The
term „cipher“ is used to refer to methods of encryption, or often a text
that has been encrypted in a specific manner, using either mathematical
transposition or substitution, or sometimes a combination of these two
In transposition cipher systems, elements of the plaintext
(e.g., a letter, word, or string of symbols)
are rearranged without any change in the identity of the elements. In substitution
systems, such elements are replaced by other objects or groups of objects
without a change in their sequence. In systems involving product ciphers,
transposition and substitution are cascaded; for example, in a system of
this type called a fractionation system, a substitution is first made from
symbols in the plaintext to multiple symbols in the ciphertext, which is
then superencrypted by a transposition.
All operations or steps involved in the transformation
of a message are carried out in accordance to a rule defined by a secret
key known only to the sender of the message and the intended receiver.
Cipher devices or machines have commonly been used
to encipher and decipher messages. The first cipher device appears to have
been employed by the ancient Greeks around 400 BC for secret communications
between military commanders. This device, called the scytale, consisted
of a tapered baton around which was spirally wrapped a piece of parchment
inscribed with the message. When unwrapped the parchment bore an incomprehensible
set of letters, but when wrapped around another baton of identical proportions,
the original text reappeared.
Other simple devices known as cipher disks were
used by European governments for diplomatic communications by the late
1400s. These devices consisted of two rotating concentric circles, both
bearing a sequence of 26 letters. One disk was used to select plaintext
letters, while the other was used for the corresponding cipher component.
In 1891 Étienne Bazeries, a French cryptologist,
invented a more sophisticated cipher device based on principles formulated
by Thomas Jefferson of the United States nearly a century earlier. Bazeries’s
so-called cylindrical cryptograph was made up of 20 numbered rotatable
disks, each with a different alphabet engraved on its periphery. The disks
were arranged in an agreed-upon order on a central shaft and rotated so
that the first 20 letters of the message plaintext appeared in a row; the
ciphertext was then formed by arbitrarily taking off any other row. The
remaining letters of the message were treated in the same way, 20 letters
at a time.
Advances in radio communications and electromechanical
technology in the 1920s brought about a revolution in cryptodevices–the
development of the rotor cipher machine. One common type of rotor system
implemented product ciphers with simple monoalphabetic substitution ciphers
as factors. The rotors in this machine consisted of disks with electrical
contacts on each side that were hardwired to realize an arbitrary set of
one-to-one connections (monoalphabetic substitution) between the contacts
on opposite sides of the rotor.
The rotor cipher machine
was used extensively by both the Allied and the Axis powers during World
War II. The application of electronic components in subsequent years resulted
in significant increases in operation speed though no major changes in
basic design. Since the early 1970s, cryptologists have adapted major developments
in microcircuitry and computer technology to create new, highly sophisticated
forms of cryptodevices and cryptosystems,
as exemplified by the Fibonacci generator and the implementation of the
Data Encryption Standard (DES) through the use of microprocessors.
Reading Four: Cryptographies.