Cipher Texts

Cipher Texts


Encryption and Cipher Texts


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 operations.

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 1891Étienne 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.



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