Feistel Cipher
 
For the singular step, with a broader view:

The most important parts of this approach:
- number of rounds
- more rounds = harder cryptanalysis
 
- design of the function \(F\)
- best if nonlinear
- should have good avalanche properties
- strict avalanche criterion - SAC
- bit independence criterion - BIC
 
- strict avalanche criterion - 
 
- key schedule algorithm