How To Find IP Address Applying S-DES With Help Of Cipher Text and plain Text

Let’s:

Plain text: X= 1 1 0 0 1 1 0 0

                 X= 1 1 0 0 1 1 0 0

 

Give No:          1 2 3 4 5 6 7 8

IP formula:       2 6 3 1 4 8 5 7

 

IP (X):                1 1 0 1 0 0 1 0

Output IP(X):   1101 0010

Complex function: Fk(L,F(L F(R,SK1),R)

Putting values in formula

Dividing IP (x) into two parts right and lift side

IP (x)=1101 0010

Right side=1101   lift side=0010

Fk(1101,0010)=(1101⊕f(0010, 10100),0010)

1^ST SOLVE F: 

F given in formula

F: E/P

E/P Formula: 4 1 2 3 2 3 4 1

Right side:      0010

Give No:         1234

Applying E/P: 4 1 2 3 2 3 4 1

Output (E/P):  0 0 0 1 0 1 0 0

Taking XOR BETWEEN E/P and sk 1

E/P:           0 0 0 1 0 1 0 0

SK-1:       1 0 1 0 0 1 0 0

OUTPUT: 1 0 1 1 0 0 0 0

S 0= 1011

S 1= 0000

 S1=1101

11= 3 (Define row)

01= 1(Define Colum)

Inter section decimal 1= 01 in binary 

S0=0000

00= 0 (Define row)

00= 0(Define Colum)

Inter section decimal 0= 00 in binary

Output = 0100

 

Find P 4?

P 4=          2431

(x)=          0100

Give No=1234

Output= 1000

TAKING XOR b/t P 4 and 1101

Lift side=               1101

P 4=                        1000

Output XOR=        0101

F k= 0101

Right side 4 bit =0010

IP SW= 0101 0010

Output SW= 0010 0101