Cryptography Reference
In-Depth Information
legally acceptable records of those transactions. Because
of this broadened interpretation of cryptography, the field
of cryptanalysis has also been enlarged.
The fundamenTals of codes,
ciphers, and auThenTicaTion
Security is obtained from legitimate users being able to
transform information by virtue of a secret key or keys—
i.e., information known only to them. The resulting
cipher, although generally inscrutable and not forgeable
without the secret key, can be decrypted by anyone know-
ing the key either to recover the hidden information or
to authenticate the source. Secrecy, though still an impor-
tant function in cryptology, is often no longer the main
purpose of using a transformation, and the resulting trans-
formation may be only loosely considered a cipher.
Because much of the terminology of cryptology dates
to a time when written messages were the only things
being secured, the source information, even if it is an
apparently incomprehensible binary stream of 1s and 0s,
as in computer output, is referred to as the plaintext. As
noted above, the secret information known only to the
legitimate users is the key, and the transformation of
the plaintext under the control of the key into a cipher
(also called ciphertext) is referred to as encryption. The
inverse operation, by which a legitimate receiver recovers
the concealed information from the cipher using the key,
is known as decryption.
The most frequently confused, and misused, terms in
the lexicon of cryptology are
code
and
cipher
. Even experts
occasionally employ these terms as though they were
synonymous.
