Input:
 

1

0

1

0

0

1

0

1

Key:
 

0

0

1

0

0

1

0

1

1

1

Original key :
 

0

0

1

0

0

1

0

1

1

1

After applying (A):
 

1

0

0

0

0

1

0

1

1

1

After applying (B):
 

0

0

0

0

1

0

1

1

1

1

After applying (C):
 

Original key :
 

0

0

1

0

0

1

0

1

1

1

After applying (A):
 

1

0

0

0

0

1

0

1

1

1

After applying (B):
 

0

0

0

0

1

0

1

1

1

1

After applying (D):
 

0

0

1

0

0

1

1

1

0

1

After applying (C):

Original input:
 

1

0

1

0

0

1

0

1

(1)  Apply IP:
 

0

1

1

1

0

1

0

0

(2)  Apply  F_Key1:
 

 F_Key1(0 1 1 1 0 1 0 0) = ((0 1 1 1) XOR  f(0 1 0 0, Key1), (0 1 0 0))

 To compute  f(0 1 0 0 , Key1):
 

(A)  Apply E/P:
 

0

0

1

0

1

0

0

0

(B)  Add  Key1:
 

0

0

0

0

0

1

1

1

(C)  Pass left 4 bits through S0 and right four bits through S1:
 

0

1

1

1

(D)  Apply P4:
 

1

1

1

0

F_Key1(0 1 1 1 0 1 0 0) = ((0 1 1 1)  XOR  (1 1 1 0) , (0 1 0 0)) =
 

1

0

0

1

0

1

0

0

(3)  Apply SW:
 

0

1

0

0

1

0

0

1

(4)  Apply  F_Key2:
 

 F_Key2(0 1 0 0 1 0 0 1) = ((0 1 0 0) XOR  f(1 0 0 1 , Key2), (1 0 0 1))

To compute  f(1 0 0 1 , Key2):
 

(A)  Apply E/P:
 

1

1

0

0

0

0

1

1

(B)  Add  Key2:
 

0

0

1

0

1

0

0

1

(C)  Pass left 4 bits through S0 and right four bits through S1:
 

0

0

1

0

(D)  Apply P4:
 

0

0

1

0

F_Key2(0 1 0 0 1 0 0 1) = ((0 1 0 0)  XOR  (0 0 1 0) , (1 0 0 1)) =
 

0

1

1

0

1

0

0

1

(5)  Apply IP^-1:
 

0

0

1

1

0

1

1

0

*Example by Laura Sanchis, Colgate University.