Now we can implement simple Feistel cipher. You can see algorithm on picture

First of all we should define Rounds Count. Let's say Rounds Count is equal to 5.

For each plaint block we should split the plaintext block into two equal pieces and on each round apply round function F to one half.

Output of f is exclusive-ored with the other half. The two halves are then swapped.

Each round follows the same pattern except for the last round where there is no swap.