The key difference between a code and a cipher
(also spelled cypher
)is that a code has no physical relationship to the message. A code can be a word, a symbol
, a sequence of events
, or an arrangement of objects.
For example, Paul Revere used a lantern code to know what his observer saw of British troop movements. "One if by land, and two if by sea, and I on the opposite shore shall be." Other examples include color codes, codewords, and international traffic symbols.
A cipher is a straight one-for-one letter substitution using letters, numbers, or symbols that replace each letter in the encoded message.