Cipher
A cipher (pronounced SAI-fuhr) is any method
of encrypting text (concealing its readability and meaning).
It is also sometimes used to refer to the encrypted text
message itself although here the term ciphertext is preferred.
Its origin is the Arabic sifr, meaning empty or zero. In
addition to the cryptographic meaning, cipher also means
(1) someone insignificant, and (2) a combination of symbolic
letters as in an entwined weaving of letters for a monogram.
Some ciphers work by simply realigning the alphabet (for
example, A is represented by F, B is represented by G, and
so forth) or otherwise manipulating the text in some consistent
pattern. However, almost all serious ciphers use both a
key (a variable that is combined in some way with the unencrypted
text) and an algorithm (a formula for combining the key
with the text). A block cipher is one that breaks a message
up into chunks and combines a key with each chunk (for example,
64-bits of text). A stream cipher is one that applies a
key to each bit, one at a time. Most modern ciphers are
block ciphers.
Ciphertext
Ciphertext is encrypted text. plaintext is what you have
before encryption, and ciphertext is the encrypted result.
The term cipher is sometimes used as a synonym for ciphertext,
but it more properly means the method of encryption rather
than the result.
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