The book of science

Tom Sharp

Johannes Trithemius cryptography


Early forms of hidden writing

As for why

Steganography is a form of cryptography that can be combined with ciphers, codes, and encryption. These terms are often used loosely; however, it can be useful to give them distinct meanings. Steganography is a means of hiding a message; a cipher is a one-to-one alphabetic substution; a code is a one-to-many substitution such as binary or Morse code; encryption uses a mathematical scheme to disguise any digital message.

See also in The book of science:

Readings in wikipedia: