Example: 4 bit S-box design with a single permutation
- To increase block size we need (prohibitively) larger tables
- As an example a function 16 -> 16 bits would
require a table of 220 bits (16 * 216).
- A substitution permutation network requires a lot less
- Data has to pass through the network multiple times to add
diffusion and confusion to the plaintext
- Result is called a product cipher