Cryptography terminology

Plaintext: Everyday language; e.g. "This is plaintext"
Ciphertext: Enciphered language; e.g. "rgua ua xuogwerwzr"

A code is a system of secret communication in which each word in a message is replaced with another word, letter, sentence or symbol. For example:

Plaintext:	British	won (the)	battle (at Alam Halfa)
Ciphertext:	Dog	ate	rabbit

A cipher is a system of secret communication in which each letter in a message is replaced with another letter, word sentence or symbol. For example:

Plaintext:

s

h

i

p

s

s

a

i

l

e

d

t

o

d

a

y

Ciphertext:

r

g

h

o

r

r

z

h

k

d

c

s

n

c

z

x

There are two parts to every cipher, and in order to decipher messages you must know both parts:

Cipher = Algorithm + Key,

where an "algorithm" is a general method of encryption, for example, "swap every letter for a symbol", or "jumble up all the letters in a wird", and a "key" is the particular way a message has been enciphered that time, for example, "replace A by $, B by &", or "move the last letter of every word to the front".

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