There are generally two broad classification of classical cryptographic methods:
Classic Cryptography
The oldest, simplest and the most primitive of all of the methods, the 'translation
table', has been used long since, before the first computer was invented.
Each 'chunk' of data (usually 1 byte) is used as an offset within a 'translation table',
and the resulting 'translated' value from within the table is then written into the output
stream. The encryption and decryption programs would each use a table that translates to
and from the encrypted data.
While this method is very simple and fast, the down side is that once the translation
table is known, the code is broken. Further, such a method is relatively straightforward
for code breakers to decipher. Still, for general "unreadability" of encoded
data, without adverse effects on performance, the 'translation table' method lends itself
well.
Classic Cryptography