Part II: Applications

For a long time, cryptography was strictly a military application.
2000 BC - 1900 AD: Manual cipher systems
1900: Mechanical cipher machines
1950: Computers
At first, designed to break the cipher machines
Now, they are the cipher machines

Good reading:
"The Puzzle Palace" (Bamford)
"The Codebreakers" (Kahn)

Now: many commercial and personal applications.